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Booklet of abstracts - European Workshop on Epitaxial Graphene

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June 15th-19th, 2014
Primošten, Croatian Adriatic coast
European workshop
on epitaxial
graphene
and 2D materials
Booklet of
abstracts
Graphisme : CNRS Alpes - service communication - LRF / © Kras99 et berdoulat jerome- Fotolia.co, Roman Klementschitz
European workshop on epitaxial graphene and 2D materials
15-19 June, 2014
Primošten, Croatia
Booklet of abstracts
Organizer: Institut za fiziku, Zagreb, Croatia
Co-organizer: Institut Néel - CNRS/UJF, Grenoble, France
Scientific Committee:
Johann Coraux
Yuriy Dedkov
Roman Fasel
Thomas Greber
Rosana Larciprete
Silvano Lizzit
Thomas Michely
Alexei Preobrajenski
Raoul van Gastel
Institut Néel, Grenoble
Technische Universität Dresden and SPECS GmbH
Empa, Dübendorf
Physik-Institut, Universität Zürich
CNR-ISC, Roma
Sincrotrone Trieste, Trieste
Universität zu Köln, Cologne
MAX-Laboratory, Lund
University of Twente, Enschede
Local organizing Committee:
Hrvoje Buljan
Davor Čapeta
Ida Delač Marion
Marko Kralj
Predrag Lazić
Marin Petrović
Iva Šrut Rakić
Tomislav Vuletić
Prirodoslovno matematički fakultet, University of Zagreb
Prirodoslovno matematički fakultet, University of Zagreb
Institut za fiziku, Zagreb
Institut za fiziku, Zagreb
Institut Ruđer Bošković, Zagreb
Institut za fiziku, Zagreb
Institut za fiziku, Zagreb
Institut za fiziku, Zagreb
Sponsored by: Oxford Instruments | Centre National de la Recherche Scientifique | Ministry
of Science, Education and Sports of the Republic of Croatia | Centre de Compétences en
Nanosciences Grenoble | Nanosciences Foundation Grenoble | Mesa+ Institute | SPECS
Surface Nano Analysis | American Elements (best contributed talk prize) | Mantis deposition |
Nature Communications | Nevac (best poster prize)
Publisher: Institut za fiziku, Zagreb, Croatia
Year: 2014
Editors: Marko Kralj, Johann Coraux, Hrvoje Buljan
ISBN 978-953-7666-10-1
Sunday 15th
9:00 – 9:20
9:20 – 9:40
9:40 – 10:00
10:00 – 10:20
10:20 – 10:40
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11:00 – 11:30
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14:00 – 14:20
14:20 – 14:40
14:40 – 15:00
15:00 – 15:20
15:20 – 15:40
15:40 – 16:00
16:00 – 16:20
16:20 – 16:40
16:40 – 17:00
17:00 – 17:20
17:20 – 17:40
17:40 – 18:00
18:00 – 18:20
18:20 – 18:40
18:40 – 19:00
19:00 – 20:00
20:00 – 22:00
Monday 16th
Tuesday 17th
J. Osterwalder
Wednesday 18th
B. LeRoy
Thursdaty 19th
T. Wehling
J. Knudsen
chair - E. Molinari
chair - M. Kralj
chair - J. Knudsen
chair - P. Liljeroth
V. Vonk
A. J. Martínez-Galera
A. Shikin
Coffee break
I. Gierz
C. Sanchez-Sanchez
P. Jelinek
J. Landers
O. Ourdjini
Coffee break
A. Kis
N. Atodiresei
H. González-Herrero
F. Huttmann
J. A. Martín-Gago
Coffee break
E. Molinari
chair - T. Wehling
chair - B. LeRoy
chair - I. Gierz
F. Calleja
L. Giovanelli
A. Garcia-Lekue
A. Varykhalov
Coffee break
A. Fedorov
M. M. Ugeda
S. Ulstrup
D. Menzel
Lunch
Free time
M. Farmanbar
P. Lacovig
Lunch
Free time
H. Buljan
M. Svec
Lunch
P. Liljeroth
chair - A. Kis
M. Kralj
Arrival
Opening
P. Sutter
chair - T. Michely
Welocme drink
Diner
Y. Liu
chair - R. Larciprete
chair - R. Fasel
M. Sicot
E. Voloshina
Coffee break
C. Busse
S. Vlaic
D. Pacilè
P. Lazić
J. A. Rodriguez-Manzo
J. Wofford
Coffee break
L. Magaud
C. Herbig
Free time
Free time
Diner
Poster Session 1
Diner
Poster Session 2
R. Fasel
W. Jolie
K. Simonov
M. Fonin
Excursion
Roundtable
Gala
chair - S. Lizzit
Concluding remarks
Lunch
Contents
1 Invited talks
3
Sutter- Controlled Synthesis of 2D Alloys and Heterostructures . . . . . . . . . . . . . . .
4
Knudsen- Heterogeneous catalysis on transition metals atop and below graphene
5
. . . . .
Gierz- Non-equilibrium Dirac carrier dynamics in graphene investigated by time- and
angle-resolved photoemission spectroscopy . . . . . . . . . . . . . . . . . . . . . . . .
Kralj- Exploring and exploiting intercalation of epitaxial graphene
. . . . . . . . . . . . .
Osterwalder- Boron nitride and graphene on single-crystal substrates:
6
7
CVD growth of
heterostructures and lm transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
Ki²- Single-Layer MoS2 2D Devices, Circuits and Heterostructures
. . . . . . . . . . . .
Liu- Controllable synthesis of graphene and its electronic properties
. . . . . . . . . . . .
10
. . . . . . . . . . . . . .
11
LeRoy- Imaging and Spectroscopy of Graphene Heterostructures
Molinari- Illuminating graphene nanoribbons
9
. . . . . . . . . . . . . . . . . . . . . . . . .
12
Liljeroth- Scanning probe experiments on atomically well-dened graphene nanostructures
13
Wehling- Adsorbates and many body eects in two dimensional materials
14
. . . . . . . . .
Ugeda- Observation of giant bandgap renormalization and excitonic eects in a monolayer
transition metal dichalcogenide semiconductor
. . . . . . . . . . . . . . . . . . . . .
2 Contributed talks
15
16
Vonk- Atomic Structure of Graphene-Support Interfaces . . . . . . . . . . . . . . . . . . .
17
Martinez Galera- Tailoring Graphene with nanometer accuracy . . . . . . . . . . . . . . .
18
Shikin- Spin current formation at the Graphene/Pt interface for magnetization manipulation in deposited magnetic nanodots
. . . . . . . . . . . . . . . . . . . . . . . . . .
19
Ulstrup- Direct View on the Ultrafast Carrier Dynamics of Massless and Massive Dirac
Fermions in Mono- and Bilayer Graphene
. . . . . . . . . . . . . . . . . . . . . . . .
20
Menzel- Ultrafast charge transfer to graphene monolayers: Substrate coupling, local density of states, nal state dimensionality, and two-step processes. . . . . . . . . . . . .
21
Sicot- Tuning Electronic Properties of Epitaxial Graphene by Copper Intercalation . . . .
22
Voloshina- Crystallographic and electronic structure of graphene on the pseudomorphic
Cu/Ir(111) substrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23
Busse- H2 O on graphene - cluster formation caused by hydrophobicity . . . . . . . . . . .
24
Vlaic- Elementary processes and factors inuencing the intercalation between graphene
and iridium
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
Pacilè- Novel mismatched graphene-ferromagnetic interfaces . . . . . . . . . . . . . . . . .
26
Lazi¢- Graphene spintronics: Spin injection and proximity eects from rst principles
. .
27
Sanchez-Sanchez- On-Surface Synthesis of BN/Graphene Hybrid Structures . . . . . . . .
28
Jelinek- Silicene vs.
ordered 2D silicide: the atomic and electronic structure of the Si-
√
√
19 × 19)R23.4°/Pt(111)
(
surface reconstruction . . . . . . . . . . . . . . . . . . .
29
Landers- Convergent Fabrication of a Perforated Graphene Network with Air-Stability . .
30
Ourdjini- Role of the surface structure in the polymerization of molecular precursor in
graphene nanoribbons: DBBA on the reconstructed 1x2-Au(110) surface . . . . . . .
31
Farmanbar- Tuning the Schottky barrier heights at MoS2 |metal contacts: a rst-principles
study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lacovig- Epitaxial Growth of Single-domain Hexagonal Boron Nitride
. . . . . . . . . . .
32
33
Rodriguez-Manzo- Toward Sensitive Graphene NanoribbonNanopore Devices by Preventing Electron Beam-Induced Damage
. . . . . . . . . . . . . . . . . . . . . . . . . . .
1
34
2
CONTENTS
Woord- Graphene growth by molecular beam epitaxy using high-quality, epitaxial nickel
lms on MgO(111) as substrates
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
35
Magaud- Cleaning graphene: what can be learned from quantum/classical molecular dynamics simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36
Herbig- Ion Irradiation of Metal-Supported Graphene: Exploring the Role of the Substrate
37
Atodiresei- Graphene-surface interfaces from rst-principles simulations
38
. . . . . . . . . .
González-Herrero- Graphene tunable electronic tunneling transparency: A unique tool to
measure the local coupling.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Huttmann- Tuning the van der Waals Interaction of Graphene with Molecules by Doping
39
40
Martin-Gago- Sublattice localized electronic states in atomically resolved Graphene-Pt(111)
edge-boundaries and its relation with the Moiré patterns . . . . . . . . . . . . . . . .
Buljan- Uncovering Damping Mechanisms of Plasmons in Graphene
. . . . . . . . . . . .
41
42
Svec- High-quality single atom N-doping of graphene/SiC(0001) by ion implantation . . .
43
Fasel- Electronic and optical properties of atomically precise graphene nanoribbons . . . .
44
Jolie- Connement of Dirac Electrons on Graphene Quantum Dots . . . . . . . . . . . . .
46
Simonov- Formation and growth dynamics of graphene nanoribbons: inuence of substrate
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47
Fonin- Probing the Electronic Properties of Epitaxial Graphene Flakes on Au(111) . . . .
reactivity
48
Calleja- Adding magnetic functionalities to epitaxial graphene by self assembly on or below
its surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
49
Giovanelli- Magnetic Coupling and Single-Ion Anisotropy in Surface-Supported Mn-based
Metal-Organic Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Garcia-Lekue- Electron scattering and spin polarization at graphene edges on Ni(111)
. .
50
52
Varykhalov- Behavior of Dirac and massive electrons in superlattices of bare and quasifreestanding graphene on Fe(110) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
53
Fedorov- Observation of a universal donor-dependent vibrational mode in graphene: key
to superconductivity in graphene . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 Posters
54
55
Bignardi- Dual character of excited charge carriers in graphene on Ni(111) . . . . . . . . .
56
Dombrowski- Dirac Electron Scattering In Caesium Intercalated Graphene . . . . . . . . .
57
Endlich- Investigations into the dynamical properties of graphene on Ir(111) . . . . . . . .
58
Lisi- Exploring the intercalation process of Cobalt under Graphene . . . . . . . . . . . . .
59
Sipahi- Spin polarization of Co(0001)/graphene junctions from rst principles . . . . . . .
60
Varykhalov- Highly spin-polarized Dirac fermions at the graphene-Co interface
61
. . . . . .
Themlin- Surface umklapp in ARPES : Seeing through 2D overlayers . . . . . . . . . . . .
62
Usachov- Dopant-controlled and substrate-dependent electronic properties of graphene . .
63
Lazi¢- Graphene on Ir(111), adsorption and intercalation of Cs and Eu atoms . . . . . . .
64
Lin- Controllable nitrogen doping of graphene via a versatile plasma-based technique . . .
65
Magaud- Graphene and Moirés
66
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
’rut Raki¢- Eects of uniaxial structural modulation on graphene's electronic structure
.
67
. . . . . . . . .
68
Acun- The instability of silicene on Ag(111) . . . . . . . . . . . . . . . . . . . . . . . . . .
69
Svec- Fulerenes on Graphene Held Together by van der Waals Interaction
Farwick zum Hagen- Graphene Flakes embedding in hexagonal Boron Nitride . . . . . . .
70
Uder- Cold Tip SPM - A new generation of variable temperature SPM for spectroscopy
.
71
. . . . . . . . . . . . . . . . . . . . . .
72
Svec- Buttery Hydrogen Dimers on G/SiC(0001).
ƒapeta- Contacting graphene with liquid metals
. . . . . . . . . . . . . . . . . . . . . . .
73
Shinde- Electronic properties of edge modied zigzag graphene nanoribbons . . . . . . . .
74
Järvinen- Self-assembly and orbital imaging of metal phthalocyanines on graphene model
surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Petrovi¢- Wrinkles of graphene on Ir(111) - internal structure and long-range ordering
Schröder- Etching of Graphene on Ir(111) with Molecular Oxygen
Martin Recio- Unusual Moire Patterns on Graphene on Rh(111)
76
77
. . . . . . . . . . . . .
78
. . . . . . . . . . . . . .
79
Papagno- Hybridization of graphene and a Ag monolayer supported on Re(0001)
Index
. .
. . . . .
80
81
Chapter 1
Invited talks
3
CHAPTER 1.
4
INVITED TALKS
Controlled Synthesis of 2D Alloys and Heterostructures
Invited talk
Sutter, Peter
Contact: [email protected]
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973
(USA)
The ability to tailor materials properties by alloying or in heterostructures with controlled
interfaces has become one of the foundations of modern materials science. Two-dimensional (2D)
crystals, such as graphene, hexagonal boron nitride, and a family of metal dichalcogenides represent
a new class of systems that oer unique opportunities for materials integration.
Mixed phases
(`alloys') and heterostructures of dierent 2D crystals promise tunable electronic structure and
chemical reactivity and raise fundamental questions on interface formation, alloying, strain, and
polarity in a new context at reduced dimensionality. I will discuss recent advances in developing the
synthesis and processing of alloys and heterostructures of 2D materials on metal substrates, derived
primarily from real-time observations by surface electron microscopy, complemented by scanning
probe microscopy and in-situ spectroscopy. Focusing on the integration of graphene with hexagonal
boron nitride, I will highlight progress toward meeting key challenges in the controlled formation of
2D alloys and heterostructures: the continuous blending of immiscible 2D systems; precise thickness
and stacking control in superlattices; and the creation of monolayer heterostructures with nanoscale
characteristic dimensions and atomically sharp line interfaces. Our combined ndings establish a
powerful toolset for the scalable fabrication of 2D alloys and heterostructures for research and
applications.
CHAPTER 1.
INVITED TALKS
5
Heterogeneous catalysis on transition metals atop and below
graphene
Invited talk
Knudsen, Jan (1); Grånäs, Elin (2); Gerber, Timm (3); Andersen, Mie (4); Arman, Mohammad
A. (2); Schulte, Karina (6); Stratmann, Patrick (3), Schnadt, Joachim (2); Feibelman, Peter J. (5);
Hammer, Bjørk (4); Andersen, Jesper N. (1); Michely, Thomas (3)
Contact: [email protected]
(1) Division of Synchrotron Radiation Research and the MAX IV Laboratory, Lund University
(2) Division of Synchrotron Radiation Research, Lund University
(3) Physikalisches Institut, Universität zu Köln
(4) Interdisciplinary Nanoscience Center and Department of Physics and Astronomy, Aarhus
University
(5) Sandia National Laboratories, Albuquerque, United States
(6) MAX IV Laboratory, Lund University
Graphene (Gr) supported arrays of nanoparticles with extremely narrow size distribution and
graphene covered transition metal surfaces are attractive model systems for systematic studies of
gas adsorption and reactivity on nanoparticles and for studying connement eects, respectively.
First, I will discuss how Pt-clusters binds to Gr grown on Ir(111) and how this is visible in X-ray
Photoelectron spectroscopy spectra (XPS). Subsequently, I will discuss molecular adsorption on the
Pt-clusters. Focusing on CO adsorption I will show that small clusters (< 10 atoms) sinter through
Smoluchowski ripening while larger clusters remain stable with respect to sintering [1,2]. Following
adsorption on clusters atop Gr, I will discuss connement eects and show that it is possible to
perform a catalytic reaction under Gr and discuss how Gr aects the chemistry.
I will present
an extensive atomic scale picture of intercalated H2 -, O2 - and CO-structures sequentially formed
under Ir(111) supported Gr when gas is dosed in situ at UHV and ambient conditions based on
XPS, Scanning Tunneling Microscopy, and Density Functional Theory [3, 4]. Finally, I will compare
the water - and CO2 formation reaction on the Gr-Ir(111) system. Without Gr either H2 or CO
react with chemisorbed oxygen and form H2 O or CO2 , which desorb directly. With Gr present the
CO2 formation reaction is unaected while the water formation reaction is signicantly changed
leading to trapped H2 O and OH under Gr.
References
[1] Knudsen et al., Phys. Rev. B, 85, 035407 (2012)
[2] Gerber et al., ACS nano, 7, 2020 (2013)
[3] Grånäs et al., ACS nano, 11, 9951 (2012)
[4] Grånäs et al., Journal of Physcial Chemistry C, 117, 16438 (2013)
CHAPTER 1.
6
INVITED TALKS
Non-equilibrium Dirac carrier dynamics in graphene investigated by time- and angle-resolved photoemission spectroscopy
Invited talk
Gierz, Isabella (1); Mitrano, Matteo (1); Bromberger, Hubertus (1); Petersen, Jesse C. (2);
Cacho, Cephise (3); Chapman, Richard (3); Springate, Emma (3); Stöhr, Alexander (4); Köhler,
Axel (4); Link, Stefan (4); Starke, Ulrich (4); Cavalleri, Andrea (1)
Contact: [email protected]
(1) Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany
(2) Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, United Kingdom
(3) Central Laser Facility, STFC Rutherford Appleton Laboratory, Harwell, United Kingdom
(4) Max Planck Institute for Solid State Research, Stuttgart, Germany
The optical properties of graphene are made unique by the linear band structure and the vanishing density of states at the Dirac point. Even in the absence of a band gap, a relaxation bottleneck
at the Dirac point allows for saturable absorption [1] and even population inversion with potential
applications for lasing at arbitrarily long wavelengths [2]. Furthermore, ecient carrier multiplication by impact ionization has been discussed in the context of light harvesting applications [3].
We have excited epitaxial graphene mono- and bilayers at various wavelengths from the visible to
the mid-infrared range and investigated the response of the electronic structure with time- and
angle-resolved photoemission spectroscopy.
We nd that for excitation at
1.3µm
direct interband transitions occur, resulting in distinct
chemical potentials for valence and conduction band at earliest times. However, there are no indications for carrier multiplication [4]. For excitation below
2µe ,
where
µe
is the chemical potential,
free carrier absorption results in a hot electronic distribution [4]. Finally, when tuning the pump
wavelength resonant to the infrared active in-plane lattice vibration in bilayer graphene at
6.3µm,
we observe a decrease of the fast relaxation time usually associated with electron optical phonon
coupling, demonstrating a control of the electronic properties of graphene on the femtosecond time
scale using tailored light pulses.
References
[1] Q. Bao et al., Adv. Funct. Mater. 19, 3077 (2009).
[2] T. Li et al., Phys. Rev. Lett. 108, 167401 (2012).
[3] T. Winzer et al., Nano Lett.10, 4839 (2010).
[4] I. Gierz et al., Nat. Mater. 12, 1119 (2013).
CHAPTER 1.
INVITED TALKS
7
Exploring and exploiting intercalation of epitaxial graphene
Invited talk
Kralj, Marko
Contact: [email protected]
Institute of Physics, Bijeni£ka cesta 46, 10000 Zagreb
The magic of the electronic, mechanical and optical properties of graphene can be exploited in
applications. In particular, with the zero density of states at the Fermi energy and linear bands
around it, it is easy to change the Fermi surface of graphene by the adsorption either "on top" or
"underneath" graphene where typically charge transfer processes take place. In epitaxial graphene
systems deposition of atoms and molecules often leads to intercalation where species are pushed
between graphene and its support. Besides the common eect of the charge donation, the intercalation can aect the binding interaction and more subtle properties of graphene, e.g. magnetism.
In fact, properties of many layered materials, including copper- and iron-based superconductors,
dichalcogenides, topological insulators, graphite and epitaxial graphene, can be manipulated by
intercalation.
Intercalation involves complex diusion processes along and across the layers but
the microscopic mechanisms and dynamics of these processes are not well understood. To resolve
this issue in great detail, we study the intercalation and entrapment of alkali atoms under epitaxial
graphene on Ir(111) in real and reciprocal space by means of LEEM, STM, ARPES, LEED and
vdW-DFT, and nd that the intercalation is adjusted by the van der Waals interaction, with the
dynamics governed by defects anchored to graphene wrinkles [1]. Moreover, the high uniformity and
quality of strongly n-doped graphene allows us to reveal the quasiparticle properties in graphene,
some of which are still debated.
References
[1] M. Petrovi¢, et al., Nature Commun. 4, 2772 (2013).
CHAPTER 1.
8
INVITED TALKS
Boron nitride and graphene on single-crystal substrates: CVD
growth of heterostructures and lm transfer
Invited talk
Osterwalder, Juerg (1); Roth, Silvan (1); Cun, Huanyao (1); Hemmi, Adrian (1); Bernard, Carlo
(1); Matsui, Fumihiko (2); Kaelin, Thomas (1); Greber, Thomas (1)
Contact: [email protected]
(1) Department of Physics, University of Zurich, Winterthurerstr. 190, CH-8057 Zurich, Switzerland
(2) Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST),
Ikoma, Nara 630-0192, Japan.
Chemical vapor deposition (CVD) performed under ultra-high vacuum conditions on singlecrystal metal surfaces enables the growth of large-area and high-quality graphene and hexagonal
boron nitride (h-BN) single layers.
Aiming towards a platform technology for graphene-based
electronic devices, our group follows two dierent approaches.
On the one hand, we explore the CVD parameter space of precursor pressure and temperature
in order to go beyond the self-saturating single-layer growth, or to grow heterostacks of the two
materials. On Cu(111) a graphene layer could be grown on a pre-deposited single layer of h-BN
when using 3-pentanone as a precursor at a pressure of 2.2 mbar [1]. On Rh(111) the same procedure
leads to an incorporation of carbon into the metal surface layers, while a graphene layer is formed
only upon a second high-pressure dose [2]. In both cases the heterostructures show clear structural
and spectroscopic signatures of graphene on h-BN but are far from defect-free.
The second approach is based entirely on single-layer growth that leads to much lower defect
densities, and subsequent transfer of the layers onto a dierent substrate. First results on h-BN
lms transferred onto oxidized silicon wafers will be presented.
References
[1] S. Roth et al., Nano Lett. 13, 2668 (2013).
[2] S. Roth, PhD Thesis, Department of Physics, University of Zurich (2013).
CHAPTER 1.
INVITED TALKS
9
Single-Layer MoS2 2D Devices, Circuits and Heterostructures
Invited talk
Ki², Andras
Contact: [email protected]
Electrical Engineering, EPFL, Lausanne, Switzerland
After quantum dots, nanotubes and nanowires, two-dimensional materials in the shape of sheets
with atomic-scale thickness represent the newest addition to the family of nanoscale materials.
Monolayer MoS2 , a direct-gap semiconductor is a typical example of new graphene-like materials
that can be produced using the adhesive-tape based cleavage technique. The presence of a band
gap in MoS2 allowed us to fabricate transistors that can be turned o and operate with negligible
leakage currents [1]. Furthermore, our transistors can be used to build simple integrated circuits
capable of performing logic operations and amplifying small signals [2]. We have also successfully
integrated graphene with MoS2 into heterostructures to form ash memory cells [3] that could be
used to extend the scaling of this type of devices. Next, I will show photodetectors based on MoS2
that have a sensitivity surpassing that of similar graphene devices by several orders of magnitude.
Incorporating MoS2 in van der Waals heterostructures can open the way to an extremely diverse
range of materials where dierent layers cam be mixed and matched to dierent functionalities.
This is not only limited to two-dimensional materials: classical 3D semiconductors with saturated
dangling bonds can also be integrated with 2D semiconductors, as I will show on the example of
p-Si/n-MoS2 heterostructures that behave as diodes and can be used to achieve light emission and
energy harvesting in a broad energy range[4].
References
[1] B. Radisavljevic et al., Nat. Nanotechnol. 6, 147 (2011).
[2] B. Radisavljevic, M. B. Whitwick and A. Kis, ACS Nano 5, 9934 (2011).
[3] S. Bertolazzi, D. Krasnozhon and A. Kis, ACS Nano 7, 3246 (2013).
[4] O. Lopez-Sanchez et al., ACS Nano (2014).
CHAPTER 1.
INVITED TALKS
10
Controllable synthesis of graphene and its electronic properties
Invited talk
Liu, Yunqi
Contact: [email protected]
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
Controllable synthesis of graphene is a pre-requirement both for basic research and practical
applications of graphene. In addition to the mechanical cleavage, several ecient methods for the
preparation of graphene have been developed in recent years, including epitaxial technique, chemical
methods (especially, bottom-up chemical synthesis) and chemical vapor deposition (CVD). Among
them, CVD on metal crystals is widely used in the large-scale synthesis of graphene lms, and more
than 5 mm single crystals of monolayer and bilayer graphene have been reported on copper. The
nal goal for the controllable synthesis is to obtain even larger size, monolayer (or layer numbers
are in control) and single-crystal structure.
On the other hand, research on electronic properties of graphene is one of the most important
topics of graphene.
Similar to silicon, which has become a main material for microelectronics,
processes three fundamental electric behaviors: metallic, semiconducting and insulating. Carbon is
another sample to have such a unique property. This might be the physical base why some scientists
proposed that the carbon-based electronics will replace the silicon-based electronics in the future.
However, to realize this, it seems, there is still a long way to go.
In this presentation, I will report a few recent results [1-10] on synthesizing graphene in a
controllable manner, and studies on its electronic properties.
References
[1] Jianyi Chen, et al., Adv. Mater. 26, 1348 (2014).
[2] Lifeng Wang, et al., Adv. Mater. 26, 1559 (2014).
[3] Lili Jiang, et al., Adv. Mater. 25, 250 (2013).
[4] Dacheng Wei, et al., Nature. Commun. 4, 1374 (2013).
[5] Bin Wu, et al., NPG Asia Mater. 5, e36 (2013).
[6] Jianyi Chen, et al., Adv. Mater. 25, 992 (2013).
[7] Liping Huang, et al., Small 9, 1330 (2013).
[8] Dacheng Wei, et al., Acc. Chem. Res. 46, 106 (2013).
[9] Dechao Geng, et al., J. Am. Chem. Soc. 135, 6431 (2013).
[10] Lang Jiang, et al., J. Am. Chem. Soc. 135, 9050 (2013).
CHAPTER 1.
11
INVITED TALKS
Imaging and Spectroscopy of Graphene Heterostructures
Invited talk
LeRoy, Brian
Contact: [email protected]
University of Arizona, 1118 E. 4th St, Tucson AZ 85721 USA
Two-dimensional materials such as graphene and transition metal dichalcogenides are being
extensively studied for potential electronic and optical applications. Recently it has become possible
to create heterostructures of these materials in order to create designer bandstructures. Spatially
resolved information is crucial to understand the properties of these heterostructures.
Using a
combination of scanning probe microscopy and optical spectroscopy, we have probed the local
electronic properties of graphene heterostructures. These systems consist of a monolayer of graphene
in contact with other materials ranging from insulators to two-dimensional semiconductors such as
MoS2 and topological insulators. By using boron nitride, a wide band gap insulator as a substrate,
we observe an improvement in the electronic properties of graphene as well as a moire pattern
due to the misalignment of the graphene and boron nitride lattices [1]. We nd that the periodic
potential due to the boron nitride substrate creates new Dirac points in graphene leading to changes
in its electronic properties [2].
We have recently demonstrated how the stacking conguration
of graphene structures can be modied with an electric eld inducing a metal to semiconductor
transition [3]. Lastly, our latest results on graphene-topological insulator and graphene-transition
metal dichalcogenide heterostructures will be discussed.
References
[1] J. Xue et al., Nature Materials 10, 282 (2011).
[2] M. Yankowitz et al., Nature Physics 8, 382 (2012).
[3] M. Yankowitz et al., Nature Materials advance online publication 28 April 2014, doi:10.1038/nmat3965.
CHAPTER 1.
INVITED TALKS
12
Illuminating graphene nanoribbons
Invited talk
Molinari, Elisa (1,2); Cardoso, Claudia M. (1); Ferretti, Andrea (1), Wang, Shudong (1), Prezzi,
Deborah (1), Ruini, Alice (1,2)
Contact: [email protected]
(1) CNR-Istituto Nanoscienze, S3 Center Modena, Italy
(2) University of Modena and Reggio Emilia, FIM Department, Modena, Italy
Graphene nanostructures have striking properties related to lateral connement, that can open a
band gap in the graphene bands and make them suitable for digital (opto-)electronics. Key features
connected to the tunability of electronic and optical properties were predicted [1], and full atomic
control of GNR geometry was recently demonstrated on gold [2].
We study the electronic and optical excitations of armchair GNRs by ab-initio calculations,
including substrate eects and many-body interactions through the so-called GW-BSE scheme, and
compare them with scanning tunneling (STS), X-ray and reectance dierence spectroscopy (RDS)
experiments [1,3-5]. The results reveal sizable band gaps and parabolic band dispersions near the top
of the valence band, while optical spectra are dominated by strongly anisotropic excitonic features.
We investigate the spectral evolution of the ribbon during its bottom-up fabrication starting from
its molecular precursors through the polymerization phase, thus clarifying the build-up of quasi-1D
excitons in the act of the ribbon formation.
Excellent agreement is found with experimental data [3-5], indicating that this scheme can provide quantitative predictions for GNRs and a powerful tool for characterization. We nally discuss
modulated GNRs and design quantum-dot like conned systems that lead to novel nanostructure
designs with controlled couplings.
References
[1] e.g. D. Prezzi et al, Phys. Rev. B77, 041404 (2008); Phys. Rev. B84, 041401 (2011).
[2] J. Cai et al, Nature 466, 470 (2010).
[3] P. Rueux et al, ACS Nano 6, 6930 (2012).
[4] R. Denk et al, Nature Commun, in press (2014).
[5] A. Batra et al, to be published (2014).
CHAPTER 1.
INVITED TALKS
13
Scanning probe experiments on atomically well-dened graphene
nanostructures
Invited talk
Liljeroth, Peter
Contact: [email protected]
Department of Applied Physics, Aalto University School of Science, PO Box 15100, 00076 Aalto,
Finland
The electronic properties of graphene edges have been predicted to depend on their crystallographic orientation. However, studying them experimentally remains challenging due to the diculty in realizing clean edges without disorder. I will discuss two systems that allow construction of
well-dened graphene edges: graphene nanoribbons (GNRs) obtained through a bottom-up process1
and interfaces between graphene and hexagonal boron nitride (h-BN) in an epitaxial monolayer.
We have synthesized atomically well-dened GNRs through on-surface polymerization [1] that have
armchair edges along the long axis of the ribbon and zigzag (ZZ) ends along the short axis. The
electronic states of the GNRs close to the Dirac point are located at the ZZ ends of the nanoribbons.
In addition to the electronic structure of the GNRs, I will discuss contacting the GNR to a metallic
lead by a single chemical bond by controllably removing individual hydrogen atoms from the ZZ
ends of the GNR [2]. Extended ZZ graphene edges can be passivated and stabilized using hexagonal boron nitride (h-BN). ZZ-terminated, atomically sharp interfaces between graphene and h-BN
is an experimentally realizable, chemically stable model systems for graphene ZZ edges. We have
explored the structure of the graphene- (h-BN) interfaces with both scanning tunnelling microscopy
and numerical methods and show them to host localized electronic states similar to those on the
pristine graphene ZZ edge [3].
References
[1] J. Cai et al., Atomically precise bottom-up fabrication of graphene nanoribbons, Nature 466,
470 (2010).
[2] J. van der Lit et al., Suppression of electron-vibron coupling in graphene nanoribbons contacted via a single atom, Nature Comm. 4, 2023 (2013).
[3] R. Drost et al., Electronic states at the graphene-hexagonal boron nitride zig-zag interface,
submitted.
CHAPTER 1.
INVITED TALKS
14
Adsorbates and many body eects in two dimensional materials
Invited talk
Wehling, Tim
Contact: [email protected]
Institute for Theoretical Physics and Bremen Center for Computational Material Sciences, University of Bremen, 28359 Bremen, Germany
Two dimensional materials combine pronounced surface eects with distinct many body interactions. Both aect material properties decisively, as they determine excitations and boundaries
between dierent electronic as well as structural phases. Here, we discuss three examples of how
interactions aect material properties. First, we consider chemically functionalized graphene and
show how doping triggers adsorbate phase transitions including tendencies towards sublattice symmetry breaking [1].
Regarding the electrons in layered materials, local "Hubbard interactions"
generally compete with large non-local Coulomb interactions. We will discuss the "two-faced" nature of these non-local interactions: while they contribute to strong renormalizations of electronic
excitations, non-local Coulomb terms turn out to weaken ground state electronic correlations frequently [2]. This is helpful in the context of phonon mediated superconductivity in materials like
doped transition metal dichalcogenides [3].
References
[1] T. Wehling, B. Grundkötter-Stock, B. Aradi, T. Niehaus, T. Frauenheim, Charge doping
induced phase transitions in hydrogenated and uorinated graphene, arXiv:1312.2276 (2013).
[2] M. Schüler, M. Rösner, T. O. Wehling, A. I. Lichtenstein, M. I. Katsnelson, Hubbard models
for materials with nonlocal Coulomb interactions: graphene, silicene and benzene, Phys. Rev. Lett.
111, 036601 (2013).
[3] M. Rösner, S. Haas, T. O. Wehling, Phase Diagram of Electron Doped Dichalcogenides,
arXiv:1404.4295 (2014).
CHAPTER 1.
INVITED TALKS
15
Observation of giant bandgap renormalization and excitonic
eects in a monolayer transition metal dichalcogenide semiconductor
Invited talk
Ugeda, Miguel M. (1); Bradley Aaron J. (1); da Jornada, Felipe (1,2); Shi, Sufei (1); Zhang, Yi
(3,4); Qiu, Diana (1,2); Hussain, Zahid (3); Shen, Zhi-Xun (4,5); Wang, Feng (1,2); Louie, Steven
G. (1,2); Crommie, Michael F. (1,2)
Contact: [email protected]
(1) Department of Physics, University of California at Berkeley, Berkeley, California 94720,
USA
(2) Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California
94720, USA
(3) Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley,CA 94720, USA
(4) Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory,
Menlo Park, CA 94025, USA
(5) Geballe Laboratory for Advanced Materials, Departments of Physics and Applied Physics,
Stanford University, Stanford, CA 94305, USA
Atomically-thin transition metal dichalcogenide (TMD) semiconductors have generated great
interest recently due to their remarkable physical properties. For example, reduced screening in 2D
has been predicted to result in dramatically enhanced Coulomb interactions that should cause giant bandgap renormalization and excitonic eects in single-layer TMD semiconductors [1, 2]. Here
we present a direct experimental observation of extraordinarily high exciton binding energy and
bandgap renormalization in a single-layer of semiconducting TMD [3]. We determined the binding
energy of correlated electron-hole excitations in monolayer MoSe2 grown on bilayer graphene (BLG)
using high-resolution scanning tunneling spectroscopy (STS) and photoluminescence spectroscopy.
We have measured both the quasiparticle electronic bandgap and the optical transitions of monolayer MoSe2/BLG, thus enabling us to obtain an exciton binding energy of 0.55 eV for this system,
a value that is orders of magnitude larger than what is seen in conventional 3D semiconductors. We
have corroborated these experimental ndings through ab initio GW and Bethe-Salpeter equation
calculations which show that the large exciton energy arises from enhanced Coulomb interactions
that lead to a dramatic blue-shifting of the quasiparticle bandgap. These results are of fundamental
importance for room-temperature optoelectronic nanodevices involving 2D semiconducting TMDs
as well as more complex layered heterostructures.
References
[1] H. P. Komsa, A. V. Krasheninnikov, Physical Review B. 86, 241201 (2012).
[2] D. Y. Qiu, et al., Physical Review Letters. 111, 216805 (2013).
[3] Miguel M. Ugeda, et al., Submitted. (2014).
Chapter 2
Contributed talks
16
CHAPTER 2.
CONTRIBUTED TALKS
17
Atomic Structure of Graphene-Support Interfaces
Contributed talk
Vonk, Vedran (1); Polman, Krista (3); Franz, Dirk (1); Stierle, Andreas (1); Conrad, Ed (2);
Vlieg, Elias (3)
Contact: [email protected]
(1) DESY Nanolaboratory, Hamburg, Germany
(2) The Georgia Institute of Technology, Atlanta, USA
(3) Radboud University, Nijmegen, The Netherlands
For most applications, graphene is not free-standing but is supported by another material.
This requires to understand the details of the atomic structure and characteristic defects of the
graphene-support interface. We will elucidate two dierent graphene-based structures, both studied
by synchrotron x-rays. Surface x-ray diraction allows it to `see all the way through', which makes it
possible to study the buried interface of graphene and its support. A new scattering scheme, making
use of high-energy x-rays in combination with area detectors, is shown to enable fast non-destructive
characterization in a pressure range up to ambient conditions [1]. Our study of ultrathin furnacegrown epitaxial graphene (EG) on SiC(000-1) shows that the interface consists of approximately
2 layers of atoms, which are partly in registry with the SiC substrate and partly disordered [2].
Furthermore, it is shown that EG has mostly AB-type stacking, see Figure. Two-dimensional arrays
of nearly identical nanoparticles with a very narrow size distribution enable systematic studies of
the catalyst's size-eect on conversion reactions [3]. We will show the results of in-situ investigations
of Pt, Rh and PtRh nanoparticles kept in environments relevant for catalytic CO conversion. A
newly devised high energy scattering scheme enables to record large portions of reciprocal space in
a relatively fast time frame, by which means in-situ measurements during chemical reactions are
possible (see Fig).
References
[1] J. Gustafson, M. Shipilin et al. Science 343, 758-761 (2014).
[2] V. Vonk, K. Polman et al. (in preparation).
[3] D. Franz, S. Runte et al. Phys. Rev. Lett. 110, 065503 (2013).
(left) SXRD data analysis of EG on SiC(000-1) shows that it has mostly AB-type stacking. (right)
High-energy x-ray diraction pattern of Pt nanoparticles grown on graphene-Ir(111) support. The
main diraction rods are indexed corresponding to the substrate, the satellite rods by G.
CHAPTER 2.
18
CONTRIBUTED TALKS
Tailoring Graphene with nanometer accuracy
Contributed talk
Martínez-Galera, Antonio J. (1,2); Brihuega, Iván(1,3); Gutiérrez-Rubio, Ángel (1); Stauber,
Tobias(1,3); Gómez-Rodríguez, José M. (1,3)
Contact: [email protected]
(1) Departamento Física de la Materia Condensada, Universidad Autónoma de Madrid, E-28049
Madrid, Spain
(2) Present address: II. Physikalisches Institut, Universität zu Köln, Zülpicher Straÿe 77, 50937
Köln, Germany
(3) Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049
Madrid, Spain
The selective modication of pristine graphene represents an essential step to fully exploit its
potential.
Two main routes are usually followed to modify graphene properties.
On one hand,
bottom up approaches have demonstrated to be very ecient to change the overall electronic structure of graphene [1-3]. On the other hand, with top down approaches it is possible to induce such
changes on a local scale [4,5]. Here we merge bottom-up and top-down strategies to tailor graphene
with nanometer accuracy. Specically, we have developed a perfectly reproducible nanolithographic
technique that allows, by means of an STM tip, to modify with 2.5 nm accuracy the electronic properties of graphene monolayers epitaxially grown on Ir(111) surfaces. This method can be carried
out also on micrometer sized regions and the structures so created are stable even at room temperature. As a result, we can strategically combine graphene regions presenting large dierences
in their electronic structure to design graphene nanostructures with tailored properties. Therefore,
this novel nanolithography method could open the way to the design of nanometric graphene-based
devices with specic functionalities.
References
[1] R. Balog, B. Jorgensen, et al., Nature Materials 9, 315-319 (2010).
[2] S. Rusponi, M. Papagno, et al., Physical Review Letters 105, 246803 (2010).
[3] T. Ohta, A. Bostwick, et al., Science 313, 951-954 (2006).
[4] M. M. Ugeda, I. Brihuega, et al., Physical Review Letters 104, 096804 (2010).
[5] L. Tapaszto, G. Dobrik, et al., Nature Nanotechnology 3, 397-401 (2008).
Figure 1. Upper panel illustrates the nanopatterning process, with a schematic STM tip drawn on
2
top of a real experimental image. Lower panel shows a 95x35 nm STM image with the nal result
after writing the word graphene.
CHAPTER 2.
CONTRIBUTED TALKS
19
Spin current formation at the Graphene/Pt interface for magnetization manipulation in deposited magnetic nanodots
Contributed talk
Shikin, Alexander
Contact: [email protected]
(1) Ulianovskaya, 1 St-Petrsburg State University Peterhof, St-Petersburg 198504 Russia
Controllable manipulation of magnetization without external magnetic eld only by applied
electrical current attracts enhanced attention due to possibility of creation of new generation memory and quantum logic devices.
Recently, a perspective idea was proposed related to using the
spin torque generated by spin current developed in low-dimensional Rashba system with strong
spin-orbit interaction [1].
Magnetic switching driven by spin-orbit torque is considered more ef-
fective than the switching by external magnetic eld that can allow design of spintronics devices
with greater energy eciency and reduced dimensions. In the talk this idea is applied to analysis of using the spin current developed at the Graphene/Pt interface characterized by enhanced
spin-orbit interaction for induced magnetization of Ni-nanodots arranged atop due to the spin-orbit
torque eect. We report the results of experimental and theoretical investigations of spin electronic
structure of the Graphene/Pt interface and demonstrate a large induced spin-orbit splitting (∼80200meV) of the graphene
π -states
with formation of non-degenerated Dirac cone spin states near
the Fermi level. It makes possible separation of electrons at the Fermi level with opposite oriented
spins. We propose the idea, how this spin structure can be used for the spin current formation and
for creation of spintronics device allowing to switch a magnetization of the attached FM-nanodots
by the induced spin-orbit torque eect [2].
References
[1] I.M. Miron et al., Nature Materials, 9, 230 (2010).
[2] A.M. Shikin et al., ArXiv:1312.6999 (2013).
CHAPTER 2.
20
CONTRIBUTED TALKS
Direct View on the Ultrafast Carrier Dynamics of Massless and
Massive Dirac Fermions in Mono- and Bilayer Graphene
Contributed talk
Ulstrup, Søren, (1); Johannsen, Jens C., (2); Cilento, Federico, (3); Miwa, Jill A., (1); Crepaldi,
Alberto, (3); Zacchigna, Michele, (4); Cacho, Cephise, (5); Chapman, Richard, (5); Springate,
Emma, (5); Mammadov, Samir, (6); Fromm, Felix, (6); Raidel, Christian, (6); Seyller, Thomas,
(6); Parmigiani, Fulvio, (3,7); Grioni, Marco, (2), King, Phil D. C., (8); Hofmann, Philip, (1)
Contact: [email protected]
(1) Aarhus University, 8000 Aarhus C, Denmark
(2) EPFL, 1015 Lausanne, Switzerland
(3) Sincrotrone Trieste, 34149, Trieste, Italy
(4) IOM-CNR Laboratory TASC, 34012 Trieste, Italy
(5) STFC Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom
(6) Technical University of Chemnitz, 09126 Chemnitz, Germany
(7) University of Trieste, 34127 Trieste, Italy
(8) University of St. Andrews, Fife KY16 9SS, United Kingdom
Understanding of the ultrafast carrier dynamics in mono- and bilayer graphene is essential for
exploiting these materials in future electronic and optoelectronic devices [1]. The hallmarks of these
materials are their low energy Dirac spectra consisting of massless and massive Dirac Fermions,
respectively. With the advent of high harmonic laser-based time- and angle-resolved photoemission
(TR-ARPES) it is now possible to record movies that directly capture the momentum-resolved outof-equilibrium properties of these Dirac particles with femtosecond time resolution [2,3]. Here, we
characterize the dynamic processes around the Dirac point in epitaxial mono- and bilayer graphene
using TR-ARPES, addressing the timescales of hot carrier scattering processes in both systems. For
bilayer graphene, we are able to disentangle the dynamics in the two conduction band sub-states
and nd that the gap in the lower sub-state plays a crucially important role, leading to a remarkably
dierent relaxation dynamics compared to monolayer graphene.
References
[1] F. Bonaccorso, Z. Sun et al., Nat. Photonics, 4, 611 (2010).
[2] J. C. Johannsen, S. Ulstrup et al., Phys. Rev. Lett., 111, 027403 (2013).
[3] I. Gierz, J. C. Petersen et al., Nat. Mater. 12, 1119 (2013).
Measuring the ultrafast dynamics of (A) massive, and (B) massless Dirac Fermions using timeand angle-resolved photoemission. Excited electron-hole pairs are induced by an IR pump pulse.
Dynamic processes such as electron-phonon scattering are then probed with a high harmonic XUV
probe pulse.
CHAPTER 2.
21
CONTRIBUTED TALKS
Ultrafast charge transfer to graphene monolayers: Substrate
coupling, local density of states, nal state dimensionality, and
two-step processes.
Contributed talk
Menzel, Dietrich, (1); Lacovig,Paolo, (2); Kostov, Krassimir L., (3); Larciprete, Rosanna, (4);
Lizzit, Silvano, (5)
Contact: [email protected]
(1) Physik-Department E20, Technische Universität München, 85748 München, Germany
(2) Elettra Sincrotrone Trieste, S.S.14 km 163.5, 34149 Trieste, Italy
(3) Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Soa,
Bulgaria
(4) Institute of Complex Systems, 00133 Roma, Italy
(5) Elettra Sincrotrone Trieste, S.S.14 km 163.5, 34149 Trieste, Italy
The ultrafast electron dynamics at graphene monolayers (Gr ML), in particular the charge
exchange with adsorbates and substrates, is of importance for photochemistry and electrochemistry
of Gr.
In order to improve its understanding, we carry out a program to use the so-called core
hole clock (CHC) method [1,2] with adsorbed Ar to determine the charge transfer time constants
(CTT) at Gr ML with strongly varied substrate coupling.
Our rst results, reported at EWEG
2013 and meanwhile published [3], showed strong dependence of the CTT on the dimensionality of
the CT nal state, and on the coupling strength to the substrate. Qualitatively the results follow
expectations, with CT to various decoupled Gr ML being slowest (∼16 fs), and Gr on transition
metals (e.g. Ru) much faster (up to 6x) and depending on the local coupling for corrugated Gr/Ru.
However, CT on physisorbed Gr/Pt(111) is still more than twice as fast than on decoupled Gr,
and new data on strongly coupled Gr/Ni(111) and on (slightly corrugated) Ir(111) are somewhat
puzzling. The following points will be discussed: that the results on transition metals do not simply
follow the coupling strength due to eects of the local density of states at the relevant energy; why
the physisorbed Gr ML on metals show much faster CT than decoupled Gr, and what eects could
slow down the CT into two-dimensional decoupled Gr ML. Further improved understanding will
require detailed calculations which are under way.
References
[1] For an extensive review, see P.A. Brühwiler, O. Karis, and N. Martensson, Rev. Mod. Phys.
74, 703 (2002).
[2] For a recent survey, see D. Menzel, Chem. Soc. Rev. 37, 2212 (2008).
[3] S. Lizzit et al., ACS Nano 5, 4359 (2013), DOI: 10.1021/nn-4008862.
CHAPTER 2.
CONTRIBUTED TALKS
22
Tuning Electronic Properties of Epitaxial Graphene by Copper
Intercalation
Contributed talk
Sicot, Muriel,(1); Fagot-Revurat, Yannick, (1); Vasseur, Guillaume,(1); Kierren, Bertrand,(1);
Malterre, Daniel,(1)
Contact: [email protected]
(1) Université de Lorraine, Institut Jean Lamour, UMR 7198, B.P. 239 F-54506, Vand÷uvre
lès Nancy, France
Structural and electronic properties of epitaxial graphene grown on Ir(111) after intercalation of
about one monolayer of copper has been investigated by low energy electron diraction (LEED), Xray photoemission spectroscopy (XPS), scanning tunneling microscopy/spectroscopy (STM/STS)
and angle-resolved photoemission spectroscopy (ARPES) at 80 K [1]. Studies of structural properties have shown that copper is mostly intercalated at step edges (see area 2 in Figure) and also
forms intercalated nanoislands of about one atomic layer high on terraces (area 1). We show that
graphene-covered Cu layer grows pseudomorphically on Ir surface. Cu penetration under graphene
modies drastically graphene electronic properties i.e. results in electron doping shifting the Dirac
point by more than 500 meV and opening an energy gap at K point as shown by ARPES measurements. Under submonolayer intercalation, we observe strong bias dependency of STM topographs.
It can be explained by the drastic modications of local density of states upon Cu intercalation
such as the attenuation of the Rashba type surface state of Ir as shown by ARPES and STS
measurements.
References
[1] M. Sicot et al., submitted
STM/STS of Gr/Cu (0.3 ML) /Ir(111)
CHAPTER 2.
23
CONTRIBUTED TALKS
Crystallographic and electronic structure of graphene on the
pseudomorphic Cu/Ir(111) substrate
Contributed talk
Voloshina, Elena (1); Vita, Hendrik (2); Böttcher, Stefan (2); Horn, Karsten (2); Ovcharenko,
Roman (1); Kampen, Thorsten (3); Thissen, Andreas (3); Dedkov, Yuriy (3)
Contact: [email protected]
(1) Institut für Chemie, Humboldt-Universität zu Berlin, 10099 Berlin, Germany
(2) Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany
(3) SPECS Surface Nano Analysis GmbH, Voltastraÿe 5, 13355 Berlin, Germany
Understanding the nature of the interaction at the graphene/metal interfaces plays a critical role
for the correct description of graphene-based electron- and spin-transport devices.
Here, several
factors, such as doping level or/and hybridization of the electronic states of graphene and the
metal around the Fermi level dene the properties of such interfaces. Starting from p-doped nearly
free-standing graphene on Ir(111), we tailor its properties via intercalation of one monolayer of
Cu.
The crystallographic and electronic structures of the resulting n-doped nearly free-standing
graphene layer on the lattice mismatched pseudomorphic Cu/Ir(111) substrate were studied by
means of scanning probe microscopy (STM and 3D NC-AFM) and photoelectron spectroscopy
in combination with state-of-the-art density functional theory calculations.
These results allow
understanding the general mechanisms that are responsible for the modication of the electronic
structure of graphene at the Dirac point (doping and the band-gap opening) in such systems.
CHAPTER 2.
CONTRIBUTED TALKS
24
H2 O on graphene - cluster formation caused by hydrophobicity
Contributed talk
Busse, Carsten, (1); Standop, Sebastian, (1); Michely, Thomas (1)
Contact: [email protected]
(1) II. Physikalisches Institut, Universität zu Köln, Zülpicher Straÿe 77, 50937 Köln, Germany
An understanding of the interaction between water and graphene is necessary to assess the
stability of this material under ambient conditions, but also to elucidate basic mechanisms in
graphene-based supercapacitors where the interaction of the carbon sheet with the water based
electrolyte is a key factor for electron transport. Here, we study the adsorption of H2 O on graphene
grown epitaxially on Ir(111) combining the complementary experimental techniques of scanning
tunneling microscopy (STM) and thermal desorption spectroscopy (TDS). Water adsorbed at low
temperatures (20 K) and coverages (< 3 ML) does not wet graphene, but forms a dense packed
lattice of three-dimensional droplets aligned in the gr/Ir(111) moiré. Higher coverage and/or higher
deposition temperature result in coalescence of theses droplets, i.e. a closed water adlayer. The
kinetic parameters (order of desorption process, desorption barrier, exponential prefactor) are determined for the two phases. The formation of the droplet lattice is driven by the low and spatially
varying binding energy between graphene and H2 O.
CHAPTER 2.
25
CONTRIBUTED TALKS
Elementary processes and factors inuencing the intercalation
between graphene and iridium
Contributed talk
Vlaic, Sergio, (1,2); Kimouche, Amina, (1,2); Coraux, Johann, (1,2); Santos, Benito, (3); Locatelli, Andrea, (3); Rougemaille, Nicolas, (1,2)
Contact: [email protected]
(1) Univ. Grenoble Alpes, Inst. NEEL, 25 rue des Martyrs, F-38042 Grenoble, France
(2) CNRS, Inst NEEL, 25 rue des Martyrs, F-38042 Grenoble, France
(3) Elettra Sincrotrone Trieste S.C.p.A., S.S. 14 km 163.5 in Area Science Park, I-34149
Basovizza, Trieste, Italy
Intercalation of foreign species between graphene and its substrate is one of the most used
methods to manipulate graphene's properties and to induce new ones, in a nely controlled manner.
It has allowed one, for instance, to fully decouple graphene from its substrate (H intercalation [1])
and to manipulate the ferromagnetism of an intercalated Co layer [2]. Even though intercalation has
been known since the 1980's, it has only been recent that pathways explaining how intercalation
initiates have been pursued.
To date only a few have been identied:
graphene edges [3] and
pre-existing point defects [4] as well as at the intersection between graphene wrinkles [5].
Real
time monitoring of the intercalation of cobalt between graphene and Ir(111) with the help of lowenergy electron microscopy, has provided us with greater insight.
We discovered unanticipated
intercalation pathways, unveiled the processes energetics and how both depend on the graphenesubstrate interaction.
More specically, we found that intercalation does not require the pre-
existence of point defects inside the graphene lattice to proceed, but can occur at curved regions,
such as those found at graphene wrinkles and on top of substrate step edges (Fig.1 a) and b)).
Curved region intercalation is found to be in competition with edge intercalation (Fig.1 c)). We
show that these two processes and their relative occurrence can be controlled by temperature and
the interaction of graphene with the substrate.
References
[1] C. Riedl, C. Coletti, et al., Phys. Rev. Lett. 103, 246804 (2009).
[2] N. Rougemaille, A.T. N'Diaye, et al., Appl. Phys. Lett. 101, 142403 (2012).
[3] P. Sutter, J. T. Sadowski, et al. J. Am. Chem. Soc. 132, 8175 (2010).
[4] M. Sicot, P. Leicht, et al., ACS Nano 6, 151 (2012).
[5| M. Petrovi¢, I. ’rut Raki¢, et al., Nat. Commun. 4, 2772 (2013).
Schematic representation (left) and LEEM image (right) of Co intercalation between graphene and
Ir(111) at the substrate step edges (a), at graphene wrinkles (b) and at the graphene free edges (c).
Darker areas under the graphene sheet correspond to the intercalation regions.
CHAPTER 2.
26
CONTRIBUTED TALKS
Novel mismatched graphene-ferromagnetic interfaces
Contributed talk
Pacilé, D., (1, 2); Lisi, S., (3); Papagno, M., (1, 2); Ferrari, L., (2, 4); Sheverdyaeva, P.M., (2);
Moras, P., (2); Leicht, P., (5); Krausert, K., (5); Zielke, L., (5); Fonin, M., (5); Dedkov, Yu. S.,(6);
Mittendorfer, F., (7); Doppler, J.,(7); Garhofer, A. (7); Betti, M. G., (3); Mariani, C. (3); Redinger,
J., (7); Carbone, C., (2)
Contact: [email protected]
(1) Dipartimento di Fisica, Università della Calabria, 87036 Arcavacata di Rende (CS), Italy
(2) Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Trieste, Italy
(3) Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale Aldo Moro 5, I-00185
Roma, Italy
(4) Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, Roma, Italy
(5) Fachbereich Physik, Universität Konstanz, 78464 Konstanz, Germany
(6) SPECS Surface Nano Analysis GmbH, Voltastrasse 5, 13355 Berlin, Germany
(7) Institute of Applied Physics and Center for Computational Materials Science, Vienna University of Technology, 1040 Vienna, Austria
The low-energy excitations in graphene depend on the interaction strength with the metal that
serves as support [1, 2].
By varying the support itself or by intercalation of foreign atoms it is
possible, through electron hybridization and structural modications, to tailor graphene electronic
properties [3]. Variable interaction strengths can thus provide an additional control over the properties of graphene and may open new elds of applications.
We will present the structural and
electronic properties of novel mismatched systems obtained by intercalation of one-single ferromagnetic (FM=Ni, Co) layer on graphene/Ir(111).
Upon intercalation the FM lattice is resized to
match the Ir-Ir lattice parameter, resulting in a mismatched graphene/FM/Ir(111) system [4, 5].
By performing scanning tunneling microscopy measurements and density functional theory calculations we prove that the intercalated Ni layer strongly increases the local interaction for specic
adsorption sites and induces a strong rumpling of the graphene lm. Angle-resolved photoemission
spectroscopy studies on graphene/FM/Ir(111) systems show a clear transition from nearly-freestanding to strongly-hybridized character of the graphene lm. The comparison between graphene
grown on bulk Ni and Co and the novel systems allow us to get insight into the graphene-metal
interaction.
References
[1] M. Papagno at al., ACS Nano 6, 199 (2012.
[2] M. Papagno at al., ACS Nano 6, 9299 (2012).
[3] M. Papagno et al., Phys. Rev. B 88, 235430 (2014).
[4] D. Pacilé at al., Phys. Rev. B 87, 035420 (2013).
[5] R. Decker et al., Phys. Rev. B 87, 041403(R)(2013).
a) Constant energy image of G/Ni/Ir taken at binding energy of 3 eV with a photon energy of 70
eV. b) STM overview showing the morphology of graphene with a partially intercalated Ni
submonolayer. The corrugation in the optimized structure of G/Ir and G/Ni/Ir, and C1s core
levels, are superimposed.
CHAPTER 2.
CONTRIBUTED TALKS
27
Graphene spintronics: Spin injection and proximity eects from
rst principles
Contributed talk
Zutic, Igor, (1); Sipahi, Guilherme, (1,2); Lazi¢, Predrag (3); Kawakami, Roland, (4)
Contact: [email protected]
(1) University at Bualo, State University of New York, Bualo, NY 14260, USA
(2) Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Brazil
(3) Rudjer Boskovic Institute, PO Box 180, Bijenicka c. 54, 10 002 Zagreb, Croatia
(4) The Ohio State University, Columbus, Ohio 43210, USA
Ferromagnet/graphene (F/Gr) junctions oer a number of desirable spin-dependent properties.
In such structures graphene can provide eective spin-ltering or replace a tunnel barrier, having
an advantage of low resistance and a small number of defects [1]. F/Gr junctions display magnetic
proximity eects and a robust spin injection, larger than in other materials [2]. Both phenomena
induce a magnetic moment in graphene, which in the rst case already occurs spontaneously in equilibrium, while the second case represents a nonequilibrium process [3]. First-principles methods are
key to assess the properties of F/Gr junctions and relate them to the desired performance, but the
computational cost is often too high. By focusing on magnetologic gates [4] and Ni(111)/graphene
junctions, we include van der Waals interactions from rst principles, crucial for their detailed
understanding.
We formulate a computationally-inexpensive model to study spin injection and
proximity eects [5]. By presenting spin polarization maps, we establish a versatile tool to tailor
the desired spin-dependent properties for graphene spintronics which suggest a wealth of opportunities, not limited to magnetically storing and sensing information, but also including processing
and transferring information [4].
References
[1] O. M. J. van 't Erve et al., Nature Nanotech. 7, 737 (2012).
[2] W. Han, et al., Phys. Rev. Lett. 105, 167202 (2010).
[3] I. Zutic et al., Rev. Mod. Phys. 76, 323 (2004).
[4] H. Dery et al., IEEE Trans. Electron. Dev. 59, 259 (2012).
[5] P. Lazic et al., submitted to Phys. Rev. B, preprint.
Spin polarizations, PN , PN v , PN v 2 for a reference bulk Ni. Inset: Magnetic moment resolved on
each atom in the computational cell (C1,C2,Ni1,..,Ni5) for TOP-FCC Ni/graphene conguration.
Orbital projections of the atomically-resolved DOS spin polarization. Total spin polarizations.
CHAPTER 2.
28
CONTRIBUTED TALKS
On-Surface Synthesis of BN/Graphene Hybrid Structures
Contributed talk
Sanchez-Sanchez, Carlos, (1); Müller, Matthias, (2); Bettinger, Holger F., (2); Brüller, Sebastian, (3); Müllen, Klaus, (3); Talirz, Leopold, (1); Pignedoli, Carlo, (1); Rueux, Pascal, (1); Fasel,
Roman, (1)
Contact: [email protected]
(1) Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse
129, CH-8600 Dübendorf, Switzerland
(2) Institut für Organische Chemie, Universität Tübingen, Auf der Morgenstelle 18, 72076
Tübin-gen, Germany
(3) Max Planck Institute for Polymer Research, 55128 Mainz, Germany.
The absence of an electronic band-gap is a major obstacle to the fabrication of ecient graphenebased switching devices. Dierent strategies, including top-down structuring and chemical modications, have been proposed to transform graphene into a semiconductor [1].
However, most
of these strategies lack accurate atomic control on the nal structures, which can be achieved by
bottom-up strategies based on the surface-assisted colligation and transformation of suitably designed precursor monomers, proved to yield atomically precise surface-supported nanoarchitectures.
Fullerenes, nanodomes and nanographenes have been synthesized via Surface-Assisted Cyclodehydrogenation (SACDH). Furthermore, the combination of SACDH with surface-catalyzed Ullmann
coupling has been used for the synthesis of atomically precise graphene nanoribbons and porous
graphene, where electron connement yields the appearance of a band-gap [2,3]. We will show how
the combination of SACDH and Ullmann coupling on metallic surfaces under ultra-high vacuum
conditions allows for the formation of 2D BN/graphene hybrid networks, which are unavailable
via traditional solution-based chemistry. We nd that scanning tunneling microscopy images and
density functional theory calculations allow the identication of the position and orientation of the
borazine rings.
Our proof-of-concept study opens the door towards the design and synthesis of
atomically precise heterostructures by tailoring of precursor monomers.
References
[1] D. Jariwala, A. Srivastava et al. http://arxiv.org/ftp/arxiv/papers/1108/1108.4141.pdf
[2] J. Mendez, M. F. Lopez, et al., Chem. Soc. Rev., 40, 4578-4590 (2011).
[3] J. Björk and F. Hanke, Chem. Eur. J. 20, 928 934 (2014).
Small-scale STM images of the 1,2:3,4:5,6-Tris(2,2´-biphenylylene)borazole monomer (a) before
(b) and after (c) complete cyclodehydrogenation. b) (100Å x 100Å) I=150pA, U=-1.5V c) (100Å
x 100Å) I=100pA, U=-1.5V.
CHAPTER 2.
29
CONTRIBUTED TALKS
Silicene vs. ordered√2D silicide:
the atomic and electronic
√
structure of the Si-( 19 × 19)R23.4°/Pt(111) surface reconstruction
Contributed talk
Svec, Martin, (1); Hapala, Prokop, (1); Ondracek, Martin, (1); Blanco-Rey, Maria, (2); Merino,
Pablo, (3); Mutombo, Pingo, (1); Chab, Vladimir, (1); Martin Gago, Jose Angel, (3); Jelinek,
Pavel, (1,4)
Contact: [email protected]
(1) Institute of Physics of the AS CR, Cukrovarnická 10, 162 00 Praha, Czech Republic
(2) Donostia International Physics Center, P. Manuel de Lardizabal 4, 20018 Donostia-San
Sebastian, Spain
(3) CSIC-ICMM, C/Sor Juana Ines de la Cruz 3, E-28049 Madrid, Spain
(4) Graduate School of Engineering, Osaka University 2-1, Yamada-Oka, Suita, Osaka 5650871, Japan
Many research groups, encouraged by pioneering works reporting growth of silicene 2D sheets on
Ag surfaces [1], have directed their attention to other noble metal surfaces [2]. On the other hand,
it is well known that Si forms binary alloys with the majority of the transition metals. In order
to resolve the silicene vs. silicide dispute and to understand precisely the atomic structure of the
real surface phases, we provided an extensive comparison of the experimental data with dierent
atomistic models including silicene.
We used a set of complementary experimental techniques
supported by the state-of-the-art theoretical analysis.
√
atomic and electronic structure of Si-(
19 ×
√
We present detailed investigation of the
19)R23.4°/Pt(111)
surface reconstruction by means
of STM, nc-AFM, SRPES, LEED-IV and ARUPS, ; supported by theoretical calculations - DFT,
STM simulation, IV-LEED simulation and k-space electronic band projection.
We proposed an
atomistic model consisting of ordered Si/Pt surface alloy, which ts very well to experimental
evidence. To make our conclusions more relevant, we extended our consideration to similar system
- the Si-(
√ √
7 × 7)R19.1°/Ir(111) [2].
Also here our 2D ordered silicide model made of characteristic
metal/Si tetramers is thermodynamically more favorable than a silicene 2D sheet grown on top of
Ir(111) surface.
These ndings indicate generality of our model and they render unlikely any
formation of silicene or germanene on nobel metal surfaces.
References
[1] A. Kara et al, Surf. Sci. Rep. 68, 1 (2012).
[2] L. Meng et al Nano Lett. 13, 685 (2013).
(a) and (b) Top and side view of predicted model structure. (c) A scheme of the twisted Kagome
structure adopted by the system in the presence of the Si3Pt tetramers. (d) high-resolution STM
topography, a simulated STM image (both at -20mV) and the model.
CHAPTER 2.
30
CONTRIBUTED TALKS
Convergent Fabrication of a Perforated Graphene Network with
Air-Stability
Contributed talk
Landers, John (1); Coraux, Johann (1); Bendiab, Nedjma (1); Lamare, Simon (2); Magaud,
Laurence (1); Chérioux, Frédéric (2)
Contact: [email protected]
(1)University of Grenoble Alpes, Institut NEEL, F-38042 Grenoble, France CNRS
(2)Institut FEMTO-ST, Université de Franche-Comté, CNRS, ENSMM, 32 Avenue de l'Observatoire,
F-25044 Besançon, France
The synthesis of 2D nanostructures on crystalline substrates has emerged in recent years [1] as
one of the most actively pursued topics in nanotechnology [2-3]. 2D porous frameworks synthesized
under ultra high vacuum (UHV) have drawn special attention due to the dierent properties that
they may possess compared to their hermetic counterparts like the ability to open a bandgap, and
the occurrence of magnetic at bands [4]. Of particular interest are eorts towards a fully carbon
backbone, such as porous graphene, through covalent self assembly, where the pore size and shape
can be uniformly controlled. This strategy is a versatile way to produce dierent assemblies, for
instance the long-sought graphene antidot lattice [4], and in applications where size selectivity is
crucial (e.g. catalysis or optical absorption). Nevertheless, their applicability is limited by their
stability at higher temperatures (up to 700K) and atmospheric pressure (exposure to air).
We
report a new convergent synthesis based on a triple aldolisation that we use to create networks of
porous graphene on Au(111) [5]. Using scanning tunneling microscopy (STM), Raman spectroscopy
and density functional theory (DFT), we show that a porous graphene network covers the surface
and identify intermediate states in the growth process. Finally, we have successfully demonstrated
−5
that the network is stable at higher pressures, including argon backed pressures of 10
mbar, and
remains intact after exposure to air.
References
[1] L. Grill, M. Dyer et al. Nat. Nanotechnol. 2, 687 (2007).
[2] M. Bieri, M. Treier et al. Chem. Commun. 46, 6919 (2009).
[3] Y. Q. Zhang, N. Kepcija et al. Nat. Commun. 3, 1286 (2012).
[4] T.G. Pedersen, C. Flindt et al. Phys. Rev. Lett. 100, 136804 (2008).
[5] J. Landers, J. Coraux et al. ACS Nano. (2014). (submitted)
(Left) Scanning tunnel microscopy (STM) topograph of a fully conjugated carbon network
synthesized on Au(111). (Right) Density functional theory (DFT) calculations showing the stable
structure on Au(111). Middle inset shows the reaction based on a novel convergent approach via
triple aldolisation.
CHAPTER 2.
CONTRIBUTED TALKS
31
Role of the surface structure in the polymerization of molecular precursor in graphene nanoribbons: DBBA on the reconstructed 1x2-Au(110) surface
Contributed talk
Ourdjini, Oualid, (1); Massimi, Lorenzo, (1); Betti, Maria Grazia, (1); Mariani, Carlo, (1);
Cavaliere, Emanuele, (2); Gavioli, Luca, (2); Laerentz, Leif (3); Grill, Leonhard, (3)(4)
Contact: [email protected]
(1) LOwtemperature Ultraviolet Spectroscopy laboratory Dipartimento di Fisica, Universita di
Roma La Sapienza Piazzale Aldo Moro 2, I-00185 Roma, Italy
(2) Interdisciplinary Laboratories for Advanced Materials Physics (i-LAMP) Dipartimento di
Matematica e Fisica Università Cattolica del Sacro Cuore via dei Musei 41, 25121 Brescia, Italy
(3) Fritz-Haber-Institute of the Max-Planck-Society, Department of Physical Chemistry, Faradayweg 4-6, 14195 Berlin, Germany
(4) Department of Physical Chemistry, University of Graz, Heinrichstrasse 28, 8010 Graz, Austria
Graphene nanoribbons (GNRs) can be obtained by two-step surface-assisted covalent coupling of
the 10,10'-dibromo-9,9'-bianthryl (DBBA) precursors on metal surfaces [1,2]. The Au(111) metallic
substrate induces the dehalogenation and cyclodehydrogenation reaction steps associated to GNRs
synthesis at elevated substrate temperatures [1] (475K-675K). An appropriate choice of the substrate
could improve the GNRs growth by lowering the polymerization temperature. We have studied the
surface chemistry of the DBBA molecules on the anisotropic 1x2-reconstructed Au(110) surface
by temperature-programmed X-Ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling
Microscopy (STM). The channel geometry of the Au(110) oers an ideal template to investigate the
inuence of the surface structure on the DBBA assembling and to control the GNRs orientation. The
C-Br bond associated to the dehalogenation reaction step is activated at room temperature without
additional activation energy. The cyclodehydrogenation reaction occurs between 425K-515K. The
sequential step process occurs at lower substrate temperatures (315K-510K) than Au(111) while
preserving the hierarchical GNRs growth process. Preliminary STM results show the formation of
GNRs with a reduced length, probably due to the low molecular mobility of DBBA on Au(110).
These results bring new insights into the catalytic eect and the role of anisotropic metallic surfaces
on the GNRs synthesis.
References
[1] J. Cai et al, Nature, 466 (2010).
[2] S. Linden et al, Physical Review Letter, 108, 216801 (2012).
Temperature-programmed HR-XPS of the a) Br 3d core level and b) C1s core level of the
10,10'-dibromo-9,9'-bianthryl (DBBA) precursors on Au(110); c) Schematic model and STM
images of GNRs formation.
CHAPTER 2.
32
CONTRIBUTED TALKS
Tuning the Schottky barrier heights at MoS2 |metal contacts: a
rst-principles study
Contributed talk
Farmanbar, Mojtaba ; Brocks, Geert
Contact: [email protected]
(1) Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of
Twente, P. O. Box 217, 7500 AE Enschede, The Netherlands
Molybdenite consists of layers of covalently bonded MoS2 with weak van der Waals interactions
between the layers, which enable exfoliation of a single layer(SL) of MoS2 through micromechanical
cleavage, similar to graphene.
Indeed experiments on SL-MoS2 have demonstrated a high cur-
rent on/o ratio at room temperature in eld eect transistors(FETs) [1].
in electronic devices requires making contacts with metal electrodes.
Application of MoS2
Such metal-semiconductor
contacts generally lead to Schottky barriers for charge carrier injection, which may hamper the
device performance [2]. In this paper we study the Schottky barriers at SL-MoS2 |metal interfaces
by rst-principles density functional theory (DFT) calculations. For conventional semiconductors
such as Si, the Schottky barrier height (SBH) at the metal-semiconductor interface is often only
weakly dependent on the metal species, and the Fermi level is pinned inside the semiconductor band
gap. We show that Fermi level pinning is absent for clean interfaces with SL-MoS2 . Adsorption of
MoS2 onto a metal substrate gives rise to a potential step across the interface whose size depends
on the metal species. The SBHs can then be tuned by selecting metal with appropriate work functions, and the SBH for electrons can be reduced to zero using metals with moderate work functions
(<4.8), such as Ag or Cu. Only for high work function metals, such as Au, Pd, or Pt, the SBH is
substantial, which is in agreement with experiment [3,4].
References
[1] B. Radisavljevic, A. Radenovic et al. Nature, 6, 147 (2011).
[2] N. R. Pradhan, D. Rhodes et al. Appl. Phys. Lett, 102, 123105 (2013).
[3] W. Chen, E. J.G. Santos et al. Nano Lett, 13, 509 (2013).
[4] S. Das, H. Chen et al. Nano Lett, 13, 100 (2010).
(a) The structure of a SL-MoS2 . (b) The top view of a SL-MoS2 on Au (111) substrate. (c) The
Schottky barrier height (SBH) at SL-MoS2 |metal interfaces as a function of the work function of
the clean metal surface.
CHAPTER 2.
33
CONTRIBUTED TALKS
Epitaxial Growth of Single-domain Hexagonal Boron Nitride
Contributed talk
Lacovig, Paolo, (1); Orlando, Fabrizio, (2,3); Larciprete, Rosanna (4); Baraldi, Alessandro,
(2,3); Lizzit, Silvano (1);
Contact: [email protected]
(1) Elettra-Sincrotrone Trieste S.C.p.A., AREA Science Park, S.S. 14 km 163.5, 34149 Trieste,
Italy
(2) Physics Department and CENMAT, University of Trieste, Via Valerio 2, 34127 Trieste,
Italy
(3) IOM-CNR, Laboratorio TASC, AREA Science Park, S.S. 14 km 163.5, 34149 Trieste, Italy
(4) CNR-Institute for Complex Systems, Via Fosso del Cavaliere 100, 00133 Roma, Italy
The rising interest of the scientic community in graphene (GR), motivated by its fascinating
properties and wide range of potential applications, has triggered substantial interest also on other
two-dimensional (2D) atomic crystals and, in particular, on hexagonal boron nitride (h-BN) [1],
which provides a superior insulating platform for high-performance GR devices [2].
However, a
number of challenges still awaits the scientic community before the full potential of 2D atomic
crystals can be exploited, such as the development of reliable methods for the growth of highquality GR and h-BN single layers. For instance, it is still challenging to obtain large h-BN single
crystalline domains because of the formation of rotated phases that give rise to grain boundaries and
other 1D defects [3,4]. A deeper understanding of the h-BN growth mechanism is therefore highly
desirable in order to nd the optimum approach to grow high-quality lms. Here, we investigate
the structure of h-BN grown on Ir(111) by chemical vapor deposition (CVD) of borazine [5]. Using
synchrotron radiation photoelectron spectroscopy and photoelectron diraction, we show that it is
possible to control the formation of rotated h-BN domains and, under proper conditions, to form
h-BN monolayers with single orientation. Our results provide new insight into the strategies for
producing high-quality h-BN sheets.
References
[1] M. Corso et al., Science 303, 217 (2004).
[2] C. R. Dean et al., Nature Nanotechnology 5, 722 (2010).
[3] W. Auwärter et al., Surface Science 545, L735 (2003).
[4] G. Dong et al., Physical Review Letters 104, 096102 (2010).
[5] F. Orlando et al., The Journal of Physical Chemistry C 115, 157 (2012).
CHAPTER 2.
CONTRIBUTED TALKS
34
Toward Sensitive Graphene NanoribbonNanopore Devices by
Preventing Electron Beam-Induced Damage
Contributed talk
Matthew Puster, Julio Rodriguez-Manzo, Adrian Balan, Marija Drndic
Contact: [email protected]
(1)Department of Physics and Astronomy University of Pennsylvania Philadelphia, PA 19104
United States of America
Graphene-based nanopore devices are promising candidates for next-generation DNA sequencing.
Here we fabricated graphene nanoribbonnanopore (GNR-NP) sensors for DNA detection.
Nanopores with diameters in the range 210 nm were formed at the edge or in the center of
graphene nanoribbons (GNRs), with widths between 20 and 250 nm on silicon nitride membranes.
GNR conductance was monitored in situ during nanopore formation inside a transmission electron
microscope (TEM). GNR resistance increases linearly with electron dose and GNR conductance and
mobility decrease by a factor of 10 or more when GNRs are imaged at relatively high magnication
with a broad beam prior to making a nanopore. By operating the TEM in scanning TEM (STEM)
mode, in which the position of the converged electron beam can be controlled with high spatial
precision via automated feedback, we prevent electron beam-induced damage and make nanopores
in highly conducting GNR sensors.
This method min- imizes the exposure of the GNRs to the
beam resulting in GNRs with unchanged sensitivity after nanopore formation [1].
References
[1] Matthew Puster, Julio A. Rodriguez-Manzo, Adrian Balan, and Marija Drndic "Toward
Sensitive Graphene Nanoribbon-Nanopore Devices by Preventing Electron Beam Induced Damage"
ACS Nano 7 (12), 11283-11289, 2013, DOI: 10.1021/nn405112m.
Illustration of a single DNA molecule passage in solution through a nanopore drilled in a graphene
nanoribbon fabricated on top of a thin silicon nitride membrane.
CHAPTER 2.
CONTRIBUTED TALKS
35
Graphene growth by molecular beam epitaxy using high-quality,
epitaxial nickel lms on MgO(111) as substrates
Contributed talk
Woord, Joseph, (1); Oliveira, Myriano, (1); Schumann, Timo, (1); Jenichen, Bernd, (1); Jahn,
Uwe, (1); Fölsch, Stefan, (1); Lopes, Joao Marcelo, (1); Riechert, Henning, (1)
Contact: [email protected]
(1) Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7 10117 Berlin, Deutschland.
The novel properties of graphene give it many potential applications, all of which will require
improvements in graphene synthesis.
Here we present a study of graphene grown by molecular
beam epitaxy (MBE) on single-crystalline, epitaxial Ni(111) lms on MgO(111) substrates. The
exceptional surface quality of the Ni lms combined with the sub-monolayer precision of MBE
has allowed the observation of growth phenomena which might otherwise have been obscured.
Raman spectroscopy and scanning tunneling microscopy (a) both indicate that the graphene is of
very high crystalline quality, and Raman also reveals the inhomogeneous thickness common in lms
grown on Ni. We examine these variations using scanning electron microscopy (SEM), and discover
that the thicker regions of graphene develop as elongated ribbons, and that these ribbons coincide
with step-edge clusters in the surface of the Ni substrate (b). SEM also shows well-dened angular
features along the perimeter of the thicker regions. The inuence of Ni surface morphology on the
developing graphene lm indicated by these two facts suggests a growth from below mechanism,
where any subsequent graphene layers develop at the interface between the Ni substrate and the
previously deposited graphene [1,2]. Finally, our experiments suggest that the graphene thickness
may be manipulated using a tailored Ni substrate, potentially allowing bi- and multi-layer structures
to be engineered into majority monolayer lms.
References
[1] S. Nie, et al., ACS Nano, 5, 2298 (2011).
[2] S. Nie, et al., New J. Phys., 14, 093028 (2012).
Scanning tunneling microscope (a) and scanning electron microscope (b) images of graphene
grown on Ni-MgO(111) by molecular beam epitaxy. The thicker regions of the graphene lm
coincide with step-clusters in the Ni substrate.
CHAPTER 2.
36
CONTRIBUTED TALKS
Cleaning graphene: what can be learned from quantum/classical
molecular dynamics simulations
Contributed talk
Magaud, Laurence,(1); Delfour, Laure,(1); Davydova, Alessandra,(2); Despiau-Pujo, Emilie,(2);
Cunge, Gilles,(2)
Contact: [email protected]
(1) Institut Néel, CNRS/UJF,Grenoble,France
(2) LTM, CNRS/UJF-Grenoble1, CEA Grenoble, France
During graphene growth or the successive steps needed to create devices, hydrocarbon radicals
often adsorb on graphene samples and alter their transport properties [1].
is then of primary importance.
Cleaning graphene
One promising route for this is the use of a hydrogen plasma.
The goal of the present study is to assist the development of graphene cleaning experiments and
to understand the mechanisms of CH3 groups a rst approximation to resist residues left on
graphene after processing- removal from graphene by a H2 plasma. For this, quantum and classical
molecular dynamics simulations have been performed for varying energies of an incident hydrogen
atom sent on a methyl group adsorbed on graphene. For increasing energies, successive processes
have been found at 0K: reection, etching, sputtering. The eect of temperature on these processes
has then modeled and predictions will be compared to experimental data [2]. Quantum Molecular
dynamics results are obtained at 0K in the NVE ensemble using the code VASP [3]. Classical MD
calculations based on the well tested C-H REBO [4,5] potential have also been performed to enable
longer dynamics and to test the eect of graphene temperature.
References
[1] Y.Ahn, et al. Appl. Phys. Lett. 102, 091602 (2013).
[2] L.Delfour et al. submitted to Phys. Rev B
[3] G.Kresse and J.Hafner, Phys. Rev. B 47, 558 (1993).
[4] E.Despiau-Pujo et al, J. Appl. Phys. 113, 114302 (2013).
[5] D. W. Brenner et al., J. Phys.: Condens. Matter 14, 783 (2002).
Figure 1: molecular dynamics simulation of a H atom sent on a methyl group adsorbed on
graphene. At 1 eV (bottom left) a CH4 molecule is formed and escapes from graphene. At 4 ev
(right) the CH4 molecule forms and then breaks into a H atom and a CH3 group. Both leave
graphene.
CHAPTER 2.
37
CONTRIBUTED TALKS
Ion Irradiation of Metal-Supported Graphene: Exploring the
Role of the Substrate
Contributed talk
Herbig, Charlotte, (1); Åhlgren, Harriet, (2); Simon, Sabina, (1); Kotakoski, Jani, (2, 3);
Krasheninnikov, Arkady V., (2, 4); Michely, Thomas, (1)
Contact: [email protected]
(1) II. Physikalisches Insitut, Universität zu Köln, Zülpicher Straÿe 77, 50937 Köln, Germany
(2) Department of Physics, University of Helsinki, P.O. Box 43, 00014 Helsinki, Finland
(3) Department of Physics, University of Vienna, Boltzmanngasse 5, 1190 Wien, Austria
(4) Department of Applied Physics, Aalto University, P.O. Box 11100, 00076 Aalto, Finland
The investigation of ion irradiation eects on 2D materials is an emerging subject, triggered
by graphene's (Gr) potentials in applications.
Though the eld is still in its infancy, already
new phenomena caused by ion irradiation of 2D layers were discovered [1-3].
For supported Gr
the eect of the substrate on ion beam damage and annealing is important.
We investigate the
behavior of high quality, epitaxially grown Gr, weakly coupled to Ir(111), to low energy noble gas ion
irradiation by scanning tunneling microscopy (STM), molecular dynamics simulations, and density
functional theory (DFT). For a freestanding layer, sputtered atoms leave the layer either in forward
or backward direction. For metal-supported Gr, only C atoms carrying backward momentum are
sputtered while a large fraction of atoms carrying forward momentum are trapped in between the
Gr layer and the substrate. As evident from STM and DFT, trapped C atoms form nm-sized Gr
platelets at the interface upon annealing at 1000K, assisted by substrate defects (see gure). The
incorporation into the Gr layer is suppressed due to high migration barriers, while diusion into
the Ir is energetically unfavorable. By measuring the area fraction of the platelets, we obtain the
trapping yield, i.e., the number of trapped C atoms per incident ion. Interestingly, compared to
the sputtering yield, the trapping yield for Gr on Ir(111) displays a distinctly dierent dependence
on the ion beam angle of incidence.
References
[1] Standop et al., Nano Lett., 13, 1948 (2013).
[2] Akcöltekin et al., Appl. Phys. Lett., 98, 103103 (2011).
[3] Åhlgren et al., Phys. Rev. B, 88, 155419 (2013).
STM topograph of a graphene platelet at the graphene/Ir(111) interface emerging after ion
irradiation at room temperature under normal incidence and subsequent annealing at 1000 K.
Image size is 13 nm x 12 nm.
CHAPTER 2.
CONTRIBUTED TALKS
38
Graphene-surface interfaces from rst-principles simulations
Contributed talk
Atodiresei, Nicolae
Contact: [email protected]
(1) Dr.
Nicolae Atodiresei Peter Grünberg Institut and Institute for Advanced Simulation
Forschungszentrum Jülich Leo-Brandt-Straÿe D-52425 Jülich, Germany
In order to construct a functional graphene-based electronic component it is essential to gain a
fundamental theoretical understanding of the graphene-electrode interface which in turn essentially
controls the transport properties of the graphene-based device. Of course, the geometrical, electronic
and magnetic structure of a graphene-surface interfaces are determined by the adsorbate-substrate
interaction.
Depending on the strength of the graphene-surface interaction, one can distinguish
between the (i) strong (weak) chemisorption implying a direct overlap of the graphene and surface
electronic states, (ii) a physisorption due to the long range van der Waals interactions and (iii) an
electrostatic interaction due to an electron transfer between graphene and its supporting substrate.
We will present a theoretical systematic study that explains how the subtle interplay between
the chemical, electrostatic and the weak van der Waals adsorption mechanisms determines the
geometry, electronic and magnetic structure of graphene adsorbed on substrates with dierent
chemical reactivities.
Such rst-principles calculations are applied to unravel the electronic and
magnetic properties of the adsorbed graphene on surfaces and can provide not only the basic insights
needed to interpret surface-science experiments but are also a key tool to design graphene-substrate
systems with tailored properties that can be integrated in graphene-based devices.
References
[1] K. V. Raman, A. M. Kamerbeek, N. Atodiresei, A. Mukherjee, T. K. Sen, P. Lazic, V.
Caciuc, R. Michel, D. Stalke, S. K. Mandal, S. Blügel, M. Munzenberg, J. S. Moodera, Interface
engineered templates for molecular spin memory and sensor devices, Nature 493, 509 (2013).
[2] S. Schumacher, T. Wehling, P. Lazic, S. Runte, D. Förster, C. Busse, M. Petrovic, M. Kralj,
S. Blügel, N. Atodiresei, V. Caciuc, T. Michely, The backside of graphene: manipulating adsorption
by intercalation, Nano Letters 13, 5013 (2013).
[3] M. Petrovic, I. ’rut, S. Runte, C. Busse, J. T. Sadowski, P. Lazic, I. Pletikosic, Z.-H Pan,
M. Milun, P. Pervan, N. Atodiresei, R. Brako, D. ’okcevic, T. Valla, T. Michely, M. Kralj, The
mechanism of caesium intercalation of graphene, Nature Communications 4, 2772 (2013).
[4] R. Mazzarello, Y. Li, D. Subramaniam, N. Atodiresei, P. Lazic, V. Caciuc, C. Pauly, A.
Georgi, C. Busse, T. Michely, M. Liebmann, S. Blügel, S.; Pratzer, P.; Morgenstern, M., Absence
of magnetic edge states at zigzag edges of graphene on Ir(111), Advanced Materials 25,1967 (2013).
[5] R. Decker, J. Brede, N. Atodiresei, V. Caciuc, S. Blügel, R. Wiesendanger, Atomic-scale
magnetism of cobalt-intercalated graphene, Physical Review B 87, 041403 (2013).
CHAPTER 2.
CONTRIBUTED TALKS
39
Graphene tunable electronic tunneling transparency: A unique
tool to measure the local coupling.
Contributed talk
González Herrero, Héctor, (1); Martínez Galera, Antonio Javier, (2); Moreno Ugeda, Miguel,
(3); Craes, Fabian, (2); Fernández Torre, Delia, (4); Pou, Pablo, (4); Pérez, Rubén, (4); Gómez
Rodríguez, José María, (1); Brihuega, Iván, (1)
Contact: [email protected]
(1) Dept. Física de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid,
Spain
(2) II. Physikalisches Institut, Universität zu Köln, Zülpicher Straÿe 77, 50937 Köln, Germany
(3) Department of Physics, UC Berkeley, Materials Science Division, Lawrence Berkeley National Laboratory,366 Birge Hall,Berkeley, CA 94720, USA
(4) Dept.
de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid,
E-28049 Madrid ,Spain
Graphene grown on metals has proven to be an excellent approach to obtain high quality
graphene lms [1,2].
However, special care has to be taken in order to understand the interac-
tion of graphene with the substrate, since it can strongly modify its properties even in apparently
weakly coupled systems [3].
Here, we have grown one monolayer graphene on Cu (111) by using a new technique consisting
in the thermal decomposition of low energy ethylene ions irradiated on a hot copper surface [4].
By means of low temperature STM/STS experiments, complemented by density functional theory
calculations, we have obtained information about the structural and electronic properties of our
graphene samples with atomic precision and high energy resolution. Our work shows that depending
on the STM tip apex and the tunnel parameters we can get access to either the graphene layer,
the copper surface underneath or even both at the same time, see Figure 1. This fact provides a
unique tool to investigate the local coupling between the graphene layer and the metal underneath.
Moreover, this approach can also be applied to investigate the interaction of point defects in the
graphene layer with the underlying substrate [5].
References
[1] J. Wintterlin and M. L. Bocquet, Surf. Sci., 603, 1841(2009).
[2] X. S. Li et al., Science, 324, 1312 (2009).
[3]I. Brihuega, P. Mallet et al., Phys. Rev. Lett., 109, 196802 (2012).
[4] A.J. Martínez-Galera, I. Brihuega et al., Nano Letters, 11, 3576 (2011).
[5]M. M. Ugeda, D. Fernández-Torre et al., Phys. Rev. Lett., 107, 116803 (2011).
2
Same 60x60 nm terrace measured with dierent tunneling conditions. a) the moire pattern of the
graphene layer is observed. b) the standing-waves patterns associated with the Cu(111) surface
state below the graphene layer are observed. Both images are measured at 6K.
CHAPTER 2.
CONTRIBUTED TALKS
40
Tuning the van der Waals Interaction of Graphene with Molecules
by Doping
Contributed talk
Huttmann, Felix, (1) Martínez-Galera, Antonio J., (1) Atodiresei, Nicolae, (2) Caciuc, Vasile,
(2) Blügel, Stefan, (2) Wehling, Tim O., (3) Michely, Thomas, (1)
Contact: [email protected]
(1) II. Physikalisches Institut, Universität zu Köln, Zülpicher Straÿe 77, 50937 Köln, Germany
(2) Peter Grünberg Institute and Institute for Advanced Simulation, Forschungszentrum Jülich,
52428 Jülich, Germany
(3) Bremen Center for Computational Material Science (BCCMS), Universität Bremen, Am
Fallturm 1a, 28359 Bremen, Germany
Strong n-doping of graphene on its epitaxial substrate can be introduced via intercalation of
highly electropositive elements such as Cs and Eu, and has recently been shown to lead to reduced
binding energy for electropositive, ionic adsorbates [1].
Here, we explore tuning of graphene's van der Waals (vdW) interaction with adsorbates via
doping. Employing an all in-situ surface science approach, we nd by scanning tunneling microscopy
and thermal desorption spectroscopy a signicantly higher binding energy on n-doped as opposed to
undoped graphene for the vdW-bonded molecules benzene and naphthalene. This is just opposite
to the case of electropositive, ionic adsorbates. Based on the model character of these simple piconjugated molecules [2], we propose that the strength of the van der Waals interaction is modied
by doping. The experimental results are compared to density functional calculations, including van
der Waals interactions.
References
[1] S. Schumacher et al., Nano Lett. 13, 5013 (2013).
[2] S. D. Chakarova-Käck et al., Phys. Rev. Lett. 96, 146107 (2006).
CHAPTER 2.
41
CONTRIBUTED TALKS
Sublattice localized electronic states in atomically resolved GraphenePt(111) edge-boundaries and its relation with the Moiré patterns
Contributed talk
Merino, Pablo (1); Rodrigo, Lucia (2); Pinardi, Anna (3); Méndez, Javier (3); López, Maria (3);
Martinez, Ignacio (3); Pou, Pablo (2); Pérez, Ruben (2); Martín-Gago, Jose A. (3)
Contact: [email protected]
(1) Centro de Astrobiología INTA-CSIC, Carretera de Ajalvir, km.4, E-28850, Madrid, Spain
(2)Dpto. de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, E28049, Madrid, Spain
(3)Instituto de Ciencias de Materiales de Madrid CSIC, C. Sor Juana Inés de la Cruz 3, E28049 Madrid, Spain
Understanding the connection of graphene with metal surfaces is a necessary step for developing
atomically-precise graphene-based technology.
Combining high resolution STM experiments and
DFT calculations we have unambiguously unveiled the atomic structure of the boundary between
a graphene zigzag edge and a Pt(111) step. On this surface, the steps are nucleation lines and we
have shown that the graphene edges minimize their strain by inducing a 3-fold edge-reconstruction
on the metal side. DFT calculations and atomically resolved STM images show the existence of
an unoccupied electronic state, which is exclusively localized in the C-edge atoms of a particular
graphene sublattice.
Moreover, we have depicted a model that shows the relation between the
dierent Moiré orientations and the direction of the interface-edage
References
[1] P. Merino et al. ACS nano 5 ,5627-5634 (2011).
STM image showing an atomically resolved Graphene-Pt(111) edge-boundary.
CHAPTER 2.
42
CONTRIBUTED TALKS
Uncovering Damping Mechanisms of Plasmons in Graphene
Contributed talk
Buljan, Hrvoje (1); Jablan, Marinko (2); Solja£ic, Marin (3);
Contact: [email protected]
(1) Department of Physics, Faculty of Science, University of Zagreb, Bijeni£ka c. 32, 10000
Zagreb, Croatia
(2)ICFO - The Institute of Photonic Sciences, Mediterranean Technology Park, Av.
Carl
Friedrich Gauss 3, 08860 Castelldefels (Barcelona), Spain
(3) Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue,
Cambridge MA 02139, USA
The development of nanophotonics depends on our ability to conne and control light at scales
much smaller than the wavelength of light. One, and perhaps the only viable path towards this goal,
is to use surface plasmons - collective excitations of electrons and light at the interface of a conductor
and a dielectric [1]. Plasmon wavelength can be much smaller than the wavelength of light in air at
the same frequency of the wave, which enables smaller diraction limit in the plane of propagation
and exponentially strong connement (at the scale of the plasmon wavelength) perpendicular to
the plane of propagation. However there is a tradeo-o: The strong subwavelength connement of
light is generally accompanied with large losses resulting in small propagation lengths of plasmonic
excitations, imposing a large obstacle to development of nanophotonics. When graphene | a single
sheet of carbon atoms organized in a honeycomb lattice with its extremely interesting electrical
and optical properties was isolated on a dielectric substrate [2], graphene plasmons became a very
hot topic of research in the nanophotonic community due to their strong connement of light,
the possibility of control via gate voltage, and potentially smaller losses than in the previously
used systems [3]. The understanding of plasmon losses in graphene is of key importance for their
potential use in nanophotonics [3]. There are a number of possible damping pathways for plasmons
in graphene, which we discuss in light of the recent experiments [4-6] where plasmon graphene
properties were studied.
First we point out that Landau damping can be eliminated by doping
(e.g., back-gate doping) of graphene.
Second we discuss scattering from phonons and electron-
electron scattering beyond random-phase approximation. Finally we address the role of impurities
and attempt to provide the intrinsic limits on plasmon damping [7].
Some other advantages of
graphene plasmons as the possibility of operation in a broad frequency range (including THz) will
be discussed.
References
[1] W.L. Barnes, A. Dereux, and T. W. Ebbesen, Nature 424, 824, (2003).
[2] K.S. Novoselov et al., Science 306, 666, (2004).
[3] M. Jablan, H. Buljan, and M. Solja£i¢, Phys. Rev. B 80, 245435 (2009).
[4] H. Yan et al., Nature Nanotechnology 7, 330 (2012).
[5] J. Chen et al., Nature 487, 77 (2012).
[6] Z. Fei et al., Nature 487, 82 (2012).
[7] M. Jablan, M. Solja£i¢, and H. Buljan, Phys. Rev. B 89, 085415 (2014).
CHAPTER 2.
CONTRIBUTED TALKS
43
High-quality single atom N-doping of graphene/SiC(0001) by
ion implantation
Contributed talk
Telychko, Mykola, (1); Mutombo, Pingo, (1); Ondracek, Martin, (1); Hapala, Prokop, (1);
Berger, Jan, (1); Spadafora, Evan, (1); Jelinek, Pavel, (1,2); Svec, Martin, (1)
Contact: [email protected]
(1) Institute of Physics of the AS CR, Cukrovarnická 10, 162 00 Praha, Czech Republic
(2) Graduate School of Engineering, Osaka University 2-1, Yamada-Oka, Suita, Osaka 5650871, Japan
Proper functionalization of graphene, in particular substitutional doping, has received enhanced
interest these days. Nitrogen doping [1,2] is probably one of the most extensively studied routes to
tune the electronic properties of pristine graphene. Despite of these advances still there is a lack
of a method, which provides high-quality N-doped graphene with nitrogen exclusively located at
substitutional conguration and without introduction of additional undesired impurities.
Here we report a straightforward method to produce high-quality nitrogen-doped graphene on
SiC(0001) using direct nitrogen ion implantation and subsequent stabilization at temperatures
above 1300K with no additional defects. In addition, we demonstrate that double defects, which
comprise of two nitrogen defects in a second-nearest-neighbor (meta) conguration, can be formed
in a controlled way by adjusting duration of bombardment. We also explain atomic STM contrast
of single N-doped in terms of the quantum interference, which provides more information about
electron transport in N-doped graphene.
References
[1] L. Zhao et al Science 333, 999, (2011).
[2] J.C. Meyer et al Nature materials, 10, 209 (2011).
2
A pair of 9x9nm current maps of graphene with substitutional N-defects, exhibiting the two most
experimentally observed atomically-resolved contrasts: (left) a hollow-triangle contrast and (right)
full-triangle contrast. The insets show registration of the defects with the graphene lattice.
CHAPTER 2.
44
CONTRIBUTED TALKS
Electronic and optical properties of atomically precise graphene
nanoribbons
Contributed talk
Cai, Jinming, (1); Pignedoli, Carlo A., (1); Talirz, Leopold, (1); Söde, Hajo, (1); Denk, Richard,
(2); Hohage, Michael, (2); Zeppenfeld, Peter, (2); Feng, Xinliang, (3); Müllen, Klaus, (3); Wang,
Shudong, (4); Prezzi, Deborah, (4); Ferretti, Andrea, (4); Ruini, Alice, (4,5); Molinari, Elisa, (4,5);
Liang, Liangbo, (6); Meunier, Vincent, (6); Rueux, Pascal, (1); Fasel, Roman, (1)
Contact: [email protected]
(1) Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf,
Switzerland
(2) Institute of Experimental Physics, Johannes Kepler University, 4040 Linz, Austria
(3) Max Planck Institute for Polymer Research, 55128 Mainz, Germany
(4) CNR-Istituto Nanoscienze, S3 Center, 41125 Modena, Italy
(5) Department of Physics, Mathematics, and Informatics, University of Modena and Reggio
Emilia, 41125 Modena, Italy
(6) Department of Physics, Rensselaer Polytechnic Institute, Troy, NY 12180, United States of
America
Graphene nanoribbons (GNRs) narrow stripes of graphene are predicted to be semiconductors with an electronic band gap that sensitively depends on the ribbon width. For armchair
GNRs (AGNRs) the band gap is inversely proportional to the ribbon width, with an additional
quantum connement-related periodic modulation which becomes dominant for AGNRs narrower
than
3 nm.
This allows, in principle, for the design of GNR-based structures with specic and
widely tunable properties, but requires structuring with atomic precision. Recently, we have shown
that a surface-assisted synthetic route using specically designed precursor monomers allows for
the fabrication of ultra-narrow graphene nanoribbons with the needed precision [1].
Here, we will report on detailed experimental investigations of their structural, electronic and
optical properties [1-5].
For the case of AGNRs of width N=7 (7-AGNR), the electronic band
gap and band dispersion have been determined with high precision [2,3]. Optical characterization
has revealed important excitonic eects [4], which are in good agreement with expectations for
quasi-one-dimensional graphene systems. The versatility of the bottom-up approach also allows for
the fabrication of substitutionally doped GNRs and heterostructures [5].
First attempts at eld
eect transistor fabrication and characterization reveal serious challenges in patterning and contact
fabrication that are related to the nanoscale dimensions of individual AGNRs.
References
[1] J. Cai et al., Nature, 466, 470 (2010).
[2] P. Rueux et al., ACS Nano, 6, 6930 (2012).
[3] L. Talirz et al., J. Am. Chem. Soc. 135, 2060 (2013) ; H. Söde et al., submitted.
[4] R. Denk et al., submitted.
[5] J. Cai et al., submitted.
CHAPTER 2.
CONTRIBUTED TALKS
Ultra-narrow armchair graphene nanoribbons investigated in this work.
45
CHAPTER 2.
46
CONTRIBUTED TALKS
Connement of Dirac Electrons on Graphene Quantum Dots
Contributed talk
Jolie, Wouter (1); Craes, Fabian (1); Petrovic, Marin (2); Atodiresei, Nicolae (3); Caciuc, Vasile
(3); Blügel, Stefan (3); Kralj, Marko (2); Michely, Thomas (1); Busse, Carsten (1)
Contact: [email protected]
(1) II. Physikalisches Institut, Universität zu Köln, Zülpicher Straÿe 77, 50937 Köln, Germany
(2) Institut za ziku, Bijenicka 46, 10000 Zagreb, Croatia
(3) Peter Grünberg Institut (PGI) and Institute for Advanced Simulation (IAS), Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
Graphene Quantum Dots (GQD) are a model system to observe quantum size eects due to
the connement of electronic states to their small area. The observation [1-4] of these states on
epitaxial GQDs on Ir(111) has led to a debate: Are the standing wave patterns arising from the
Dirac electrons of graphene or from the free electron-like surface state of Ir(111)?
bands have similar slopes in a wide k-range, no clear identication can be made.
problem by intercalating oxygen between graphene and Ir(111).
Since both
We solve this
We show with angle-resolved
photoemission spectroscopy (ARPES) that the oxygen suppresses the surface state and eectively
decouples graphene. Density functional theory supports this nding, showing an increased distance
between graphene and its substrate while hybridization between the states is absent. We observe
spatial connement on GQDs with scanning tunneling microscopy. We analyze the states with a
relativistic particle-in-a-box model and nd a linear dispersion relation in agreement with ARPES.
This is the rst clear observation of the connement of graphene's Dirac electrons since a dispersive
surface state is ruled out.
We record additional graphene signatures - a dip in the density of
states and standing wave patterns arising from intervalley scattering, underlining the decoupling of
graphene on our substrate.
References
[1] D. Subramaniam et al., Phys. Rev. Lett. 108, 046801 (2012).
[2] S. K. Hämäläinen et al., Phys. Rev. Lett. 107, 236803 (2011).
[3] S.-H. Phark et al., ACS Nano 5, 8162 (2011).
[4] S. J. Altenburg et al., Phys. Rev. Lett. 108, 206805 (2012).
(a) STS-spectra recorded on graphene, revealing the energies of the conned states. (b) STM and
STS images of the GQD, the later measured at the three energies highlighted by three blue vertical
lines in the spectra in (a). The dierently shaded dots indicate where the spectra were detected.
CHAPTER 2.
47
CONTRIBUTED TALKS
Formation and growth dynamics of graphene nanoribbons: inuence of substrate reactivity
Contributed talk
Simonov, Konstantin, (1), (2), (3); Vinogradov, Nikolay, (1), (2), (4); Vinogradov, Alexander,
(3); Generalov, Alexander,(2), (3), (5); Zagrebina, Elena, (3); Mårtensson, Nils, (1),(2); Cafolla,
Attilio (6); Carpy, Tomas, (6); Cunnie, John, (6); Preobrajenski, Alexei, (2)
Contact: [email protected]
(1)Department of Physics, Uppsala University, Box 530, 75121, Uppsala, Sweden
(2)MAX-lab, Lund University, Box 118, 22100, Lund, Sweden
(3)V.A. Fock Institute of Physics, St.
Petersburg State University, 198504, St.
Petersburg,
Russia
(4)European Synchrotron Radiation Facility, 6 Rue Jules Horowitz, B.P. 220, FR-38043, Grenoble Cedex, France
(5)Institute for Solid State Physics, Dresden University of Technology, DE 01062, Dresden,
Germany
(6)School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland
Atomically precise armchair graphene nanoribbons (AGNRs) can be fabricated via thermally
induced polymerization of 10,10'-dibromo-9,9'-biantracene (DBBA) on metal surfaces [1]. Though
the growth mechanism of GNRs on Au(111) is roughly known, the eect of substrate on growth
and structure of the GNRs remains to be established.
In this talk we focus on the process of
AGNRs growth on Au(111), Ag(111) and Cu(111) by means of core-level spectroscopies (Fig.1,a,b)
used in combination with scanning tunnel microscopy (STM) (Fig.1,c). At room temperature (RT)
the DBBA molecules remain intact on Au(111), while on Cu(111) full dehalogenation occurs and
tilted polymer chains start to appear. On Ag(111) the DBBA molecules are partially dehalogenated
at RT, thus leading to distinctive features in GNRs formation. On inert Au(111) dehalogenation
◦
completes at 200 C with the formation of polyantracene chains. Further annealing of the Au(111)
◦
substrate leads to the formation of 7-AGNRs at 400 C, while on the Ag(111) and Cu(111) surfaces
◦
◦
the formation of GNRs takes place at 350 C and 250 C, respectively. On Cu(111) the orientation
of GNRs appears to be governed by a strong ribbon-substrate interaction which is not observed
for weakly-bonded GNRs on Au(111) (Fig.1,c).
Moreover, we demonstrate that on Cu(111) the
presence of atomic Br does not disrupt the growth of GNRs. In general, core-level spectroscopies
are shown to be highly informative for understanding the details of GNR formation.
References
[1] J. Cai et.al., Nature, 466, 470 (2010).
Fig.1 (a)Temperature evolution of Br 3d PE spectrum on Au(111) and Ag(111);(b)Br 3d PE
spectra and corresponding C K-edge NEXAS, recorded after deposition at RT;(c)STM images of
GNRs on Au(111), Ag(111) and Cu(111).
CHAPTER 2.
48
CONTRIBUTED TALKS
Probing the Electronic Properties of Epitaxial Graphene Flakes
on Au(111)
Contributed talk
Fonin, Mikhail (1); Leicht, Philipp (1); Gragnaniello, Luca (1); Tesch, Julia (1); Zielke, Lukas
(1); Bouvron, Samuel (1); Voloshina, Elena (2); Hammerschmidt, Lukas (3); Marsoner Steinkasserer,
Lukas, (3); Paulus, Beate (3); Dedkov, Yuriy S. (4)
Contact: [email protected]
(1) Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany
(2) Institut für Chemie, Humboldt Universität zu Berlin, 12489 Berlin, Germany
(3) Institut für Chemie und Biochemie, Freie Universität Berlin 14195 Berlin, Germany
(4) SPECS Surface Nano Analysis GmbH, 13355 Berlin, Germany
Connement of electrons in graphene quantum dots and nanoribbons represents an exciting eld
of research, owing to predicted peculiar electronic and magnetic properties [1,2]. Recent attempts
with the purpose of measuring the properties of graphene nano dots on Ir(111) have revealed
detrimental edge bonding of graphene to the employed iridium substrate. We have developed an
in-situ fabrication method of graphene nano akes (GNFs) on the Au(111) noble metal surface. We
show that this system is well-suited for scanning tunneling microscopy (STM) investigations of the
electronic properties of epitaxial GNFs.
We show that the prepared GNFs can be easily displaced across terraces at room temperature
by scanning with appropriate tunneling parameters if akes are initially detached from the Au
terraces, underlining negligible graphene-Au bonding.
Furthermore, unreconstructed and single
hydrogen terminated graphene edges are observed by STM as conrmed by the accompanying DFT
calculations.
The electronic properties of the graphene akes can be accessed via quasi-particle
interference mapping at low temperatures (10 K). Owing to the distinctly dierent positions of
graphene scattering processes compared to Au surface state backscattering in the Fourier transforms, we can unambiguously distinguish between graphene and Au electronic contributions. Our
measurements show a linear dispersion for larger graphene akes with Dirac point shifted towards
the unoccupied states.
References
[1] K. Nakada, M. et al.; Phys. Rev. B 54, 17954 (1996).
[2] O. V. Yazyev; Rep. Prog. Phys. 73, 056501 (2010).
3D STM representation of quasi-freestanding graphene ake on Au(111) showing herringbone
reconstruction and moiré as well as quasi-particle interference at edges
CHAPTER 2.
49
CONTRIBUTED TALKS
Adding magnetic functionalities to epitaxial graphene by self
assembly on or below its surface
Contributed talk
Garnica, Manuela (1,2); Calleja, Fabian (1); Vázquez de Parga, Amadeo L. (1,2); Miranda,
Rodolfo (1,2)
Contact: [email protected]
(1)Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco 28049, Madrid, Spain
(2)Dep.
Física de la Materia Condensada, Universidad Autónoma de Madrid, Cantoblanco
28049, Madrid, Spain
By growing epitaxially graphene on Ru(0001)or Ir(111) under Ultra High Vacuum conditions [1]
and adsorbing molecules on it or intercalating heavy atoms below it, we show how to add magnetic
functionalities to graphene.The graphene monolayer on Ru(0001) is spontaneously nanostructured
forming an hexagonal array of nanodomes with a periodicity of 3 nm [2] and localized electronic
states [3].
Cryogenic Scanning Tunnelling Microscopy and Spectroscopy and DFT simulations
show that isolated TCNQ molecules deposited on gr/Ru(0001) acquire charge from the substrate
and develop a sizeable magnetic moment, which is revealed by a prominent Kondo resonance. The
magnetic moment is preserved upon dimer and monolayer formation. The self-assembled molecular
monolayer develops spatially extended spin-split electronic bands with only the majority band
lled, thus becoming a 2D organic magnet whose predicted spin alignment in the ground state is
visualized by spin-polarized STM at 4.6 K [4]. The intercalation of an ordered array of Pb atoms
below graphene grown on Ir(111) results in the appearance a series of equally spaced, sharp peaks
in the dierential conductance, as revealed by laterally resolved Tunnelling Spectroscopy. The Pb
enhances the, usually negligible, spin-orbit interaction of graphene.
The spatial variation of the
spin-orbit coupling when going from graphene intercalated with Pb to the graphene on Ir(111)
creates a pseudo-magnetic eld that originates pseudo-Landau levels [5]
References
[1] A.L. Vázquez de Parga et al, Phys. Rev. Lett. 100, 056807 (2008).
[2] B. Borca et al, Phys. Rev. Lett. 105, 036804 (2010).
[3] D. Stradi et al, Phys. Rev. Lett. 106, 186102 (2011).
[4] M. Garnica et al, Nature Physics 9, 368 (2013).
[5] F. Calleja et al, submitted
CHAPTER 2.
CONTRIBUTED TALKS
50
Magnetic Coupling and Single-Ion Anisotropy in Surface-Supported
Mn-based Metal-Organic Networks
Contributed talk
Giovanelli, Luca, (1); Savoyant, Adrien, (1); Abel, Mathieu, (1); Maccherozzi, Francesco, (2);
Ksari, Younal, (1); Koudia, Mathieu, (1); Hayn, Roland, (1); Choueikani, Fadi, (3); Otero, Edwige,
(3); Ohresser, Philippe, (3); Themlin, Jean-Marc, (1); Dhesi, Sarnjeet, S., (2); and Clair, Sylvain
(1)
Contact: [email protected]
(1) Aix-Marseille Université, CNRS, IM2NP UMR 7334, F-13397 Marseille, France
(2) Diamond Light Source, Didcot, OX11 0DE, United Kingdom
(3) Synchrotron SOLEIL, L'orme des Merisiers, Saint-Aubin - BP48, 91192 Gif-sur-Yvette
CEDEX, France
π -conjugated
macrocycles such as phthalocyanines hosting a single transition metal atom have
shown great versatility in producing 2D magnetic arrays. This includes the possibility to modify
the magnetic state of the central metal atom through ferromagnetic (FM) coupling to the substrate
and by adsorption of smaller molecules [1]. An alternative approach for the synthesis of magnetoorganic nanostructures consists in manipulating the magnetic properties of transition metal atoms
through selective bonding to functional ligands in surface-supported, self-assembled metal organic
networks [2,3].
In the present study the electronic and magnetic properties of Mn coordinated
to 1,2,4,5-tetracyanobenzene (TCNB) have been investigated by combining STM and XMCD performed at low temperature (3 K). When formed on Au(111) and Ag(111) substrates the Mn-TCNB
networks display similar geometric structures. Magnetization curves reveal FM coupling of the Mn
sites with similar single-ion anisotropy energies, but dierent coupling constants. Low-temperature
XMCD spectra show that the local environment of the Mn centers diers appreciably for the two
substrates. Multiplet structure calculations were used to derive the corresponding ligand eld parameters conrming an in-plane uniaxial anisotropy. The observed interatomic coupling is discussed
in terms of superexchange as well as substrate-mediated magnetic interactions.
References
[1] C. Wäckerlin et al., Angew. Chem. Int. Ed. 52, 1 (2013).
[2] T. R. Umbach et al., Phys. Rev. Lett. 109, 267207 (2013).
[3] N. Abdurakhmanova et al., Phys. Rev. Lett. 110, 027202 (2013).
CHAPTER 2.
CONTRIBUTED TALKS
51
Angular dependence of XAS and XMCD over the Mn L2,3 edge for Mn-TCNB/Au(111). T=3 K.
◦
◦
B=6 T. θ = 0 correspond to normal incidence and θ = 70 to grazing incidence. The bottom
curves are obtained by ligand eld multiplet calculations.
CHAPTER 2.
52
CONTRIBUTED TALKS
Electron scattering and spin polarization at graphene edges on
Ni(111)
Contributed talk
Garcia-Lekue, Aran, (1,2); Balashov, Timofey, (3); Olle, Marc, (3); Ceballos, Gustavo, (3);
Arnau, Andres, (1,4,5); Gambardella, Pietro, (3,6,7); Sanchez-Portal, Daniel, (1,4); Mugarza, Aitor,
(3)
Contact: [email protected]
(1) Donostia Internatioal Physics Center (DIPC), San Sebastian, Spain
(2) IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
(3) Catalan Institute for Nanoscience and Nanotechnology (ICN2), Barcelona, Spain
(4) Materials Physics Center CFM-MPC, CSIC-UPV/EHU, San Sebastian, Spain
(5) University of the Basque Country, UPV/EHU, San Sebastian, Spain
(6) Instituciò Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
(7) Swiss Federal Institute of Technology, ETH Zurich, Switzerland
The interaction of graphene with a metal often perturbs its unique electronic properties. However, this interaction can also be positively exploited to engineer graphene-metal hybrid structures
with novel electronic and magnetic properties.
In this work, we investigate graphene nanoislands grown on Ni(111) by local tunneling spectroscopy measurements combined with spin-polarized ab initio electronic structure calculations
[1,2]. We nd that the electron scattering at the graphene edges is spin- and edge-dependent. This
behavior is attributed to the strong distortion of the electronic structure at the interface, which
opens a gap and spin-polarizes the Dirac bands of graphene. Moreover, we demonstrate that edge
scattering is strongly structure dependent, with asymmetries in the reection amplitude of up to
30% for reconstructed and unreconstructed zig-zag edges. These results suggest a lateral 2D spin
ltering for graphene layers, similar to that occurrind across the interface [3].
References
[1] A. Garcia-Lekue et al., Phys. Rev. Lett. (in press)
[2] M. Olle et al. Nano Lett. 12, 4431 (2012).
[3] V. M. Karpan et al. Phys. Rev. Lett. 99, 176602 (2007).
(a) Topographic (Vb = 0.1V) and constant current dI/dV map showing the interference pattern of
the S1 surface state scattered from graphene islands. Setpoint current: I = 0.3 nA. Image size: 30
2
x 37 nm . (b) Dispersion relation obtained from the standing wave periodicity. A parabolic curve
is included.
CHAPTER 2.
53
CONTRIBUTED TALKS
Behavior of Dirac and massive electrons in superlattices of bare
and quasifreestanding graphene on Fe(110)
Contributed talk
Varykhalov, Andrei, (1); Sanchez-Barriga, Jaime, (1); Marchenko, Dmitry, (1); Hlawenka, Peter,
(1); Rader, Oliver, (1);
Contact: [email protected]
(1) Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II,
Albert-Einstein-Strasse 15, 12489 Berlin, Germany
The Dirac electrons forming the
π band in graphene have peculiar properties distinct from other,
massive quasiparticles. A prominent example is Klein tunneling, theoretically predicted [1] as well
as observed in transport experiments on p-n junctions [2]. In the present contribution we address
the band structure of a one-dimensional graphene superlattice on Fe(110) [3] studied by angleresolved photoemission. Unlike the famous case of graphene/Ir(111) which displays intense replica
bands with large and extended minigaps in the Dirac cone [4,5], neither band replicas nor minigaps
are observed for the
π
band of graphene on Fe(110). However, the control experiment consisting of
the measurement of the
σ
bands from the same system reveals intense
σ
band replicas shifted in
momentum space according to the superlattice periodicity. We discuss this surprising result with
the help of theoretical investigations. In the second part of the presentation we report electronic
properties of quasifreestanding graphene on Fe(110) achieved by intercalation of Au. Characterization of its band structure by means of angle- and spin-resolved photoemission shows that interaction
with Au causes remarkable changes of replica bands, charge doping and spin structure of the Dirac
cone.
References
[1] M. I. Katsnelson et al., Nat. Phys. 2, 620 (2006).
[2] A. F. Young, P. Kim, Nature Phys. 5, 222 (2009).
[3] N. A. Vinogradov et al., Phys. Rev. Lett. 109, 026101 (2012).
[4] I. Pletikosi¢ et al., Phys. Rev. Lett. 102, 056808 (2009).
[5] E. Starodub et al., Phys. Rev. B 83, 125428 (2011); J. Sanchez-Barriga et al., Phys. Rev.
B 85, 201413(R)(2012).
ARPES from bare graphene/Fe(110). (a) Dirac cone measured for kk perpendicular to the
σ band sampled at dierent photon
one-dimensional ripples shows no replica bands; (b) and (c)
energies along the ripples displays pronounced replicas (white arrows).
CHAPTER 2.
CONTRIBUTED TALKS
54
Observation of a universal donor-dependent vibrational mode
in graphene: key to superconductivity in graphene
Contributed talk
A., Fedorov (1,2,4); D., Haberer (1); C., Struzzi (2); N., Verbitskiy (3); M., Knupfer (1); B.,
Büchner (1); D., Usachov (4); O., Vilkov (4); L., Pettaccia (2); A., Grüneis (1,2,3)
Contact:
(1) IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany
(2) Köln Universität, Richmodstr. 10, 50667 Köln, Germany
(3) Elettra Sincrotrone Trieste, Strada Statale 14 km 163.5, 34149 Trieste, Italy
(4)Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria
(5) St. Petersburg State University, Ulianovskaya 1 St. Petersburg 198504, Russia
The fundamental interplay of electrons and phonons mediates superconductivity in the conventional superconductors and also plays an important role for many properties of undoped cuprates.
Angle resolved photoemission (ARPES) has become an important tool which allows to probe
electron-phonon coupling (EPC) as a kink in the spectral function of a material. EPC induced superconductivity was found in many other carbon-related materials like intercalated graphite (GIC)
[1], fullerene crystals [2], nanotubes [3] and boron [4] doped diamond, however any report about
superconductivity in graphene is still absent. In order to investigate the possible superconducting
pairing mechanism in doped graphene, we performed a comprehensive study of alkali and earthalkaline doped quasi-free-standing graphene using high resolution ARPES measurements of the
spectral function [5]. Following detail analysis of the experimentally determined self-energies, which
allows us to extract the underlying Eliashberg functions and ascribe the measured ne structure
to peaks in the phonon dispersion relation of graphene. An unexpected low-energy peak appears
for all dopants with an energy and intensity that depend on the dopant atom. We show that this
peak is the result of a dopant-related vibration. The low energy and high intensity of this peak are
crucially important for achieving superconductivity, with Ca being the most promising candidate
for realizing superconductivity in graphene.
References
[1] N.B. Hannay, T.H. Geballe, B.T. Matthias, K. Andres, P. Schmidt, and D. MacNair, Phys.
Rev. Lett. 14, 225 (1965).
[2] S.P. Kelty, C.-C. Chen, and C. M. Lieber, Nature 352, 223 (1991).
[3] Z.K. Tang et al., Science 292, 2462 (2001).
[4] E.A. Ekimov, et al., Nature 428, 542 (2004).
[5] A.V. Fedorov, N.I. Verbitskiy, D. Haberer, C. Struzzi, L. Petaccia, D. Usachov, O.Y. Vilkov,
D.V. Vyalikh, J. Fink, M. Knupfer, B. Buchner & A. Grüneis, Nature Communications, 5, 3257
(2014).
Chapter 3
Posters
55
CHAPTER 3.
56
POSTERS
Dual character of excited charge carriers in graphene on Ni(111)
Poster
Bignardi, Luca, (1); Haarlammert, Thorben, (1); Winter, Carsten, (1); Montagnese, Matteo,
(2); van Loosdrecht, Paul, (2); Voloshina, Elena, (3); Rudolf, Petra, (4); Zacharias, Helmut, (1)
Contact: [email protected]
(1) Physikalisches Institut, University of Münster, Wilhelm-Klemm Str. 10, 48149 Münster,
Germany
(2) II. Physikalisches Institut, University of Köln, Zülpicher Str. 77, 50937 Köln, Germany
(3) Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Str.
2, 12489 Berlin,
Germany
(4) Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747AG
Groningen, The Netherlands
The dynamics of excited charge carriers at the graphene/Ni(111) interface has been investigated
by means of time-resolved, two-photon photoemission spectroscopy, employing fs-XUV pulses with
an energy of 39.2 eV produced by high harmonics generation. Due to the interplay of substrate and
adsorbate band structures, the dependence of the lifetimes on the energy of the excited carriers was
found to be similar to that of Ni 3d electrons measured for clean Ni up to 1 eV above the Fermi
level, while it resembled that of graphite from 1 eV above the Fermi level onwards. This result is
suggested to be the eect of the peculiar electronic structure of the interface, which still possesses
features belonging to the pristine graphene layer, such as a residual saddle point.
CHAPTER 3.
57
POSTERS
Dirac Electron Scattering In Caesium Intercalated Graphene
Poster
Daniela, Dombrowski, (1); Sven, Runte, (1); Fabian, Craes, (1); Jürgen, Klinkhammer, (1);
Marin, Petrovi¢, (2); Marko, Kralj, (2); Thomas, Michely, (1); Carsten, Busse, (1)
Contact: [email protected]
(1) II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
(2) Institut za Fiziku, Bijeni£ka 46, 10000 Zagreb, Croatia
With Fourier-transform scanning tunneling microscopy (FT-STM) one can directly image the
2D Fermi contour of a surface by analysing charge carrier scattering patterns arising at defects [1].
This enables the determination of a dispersion relation
a closed caesium intercalated graphene layer [2].
E(k)
in STM [1]. We apply FT-STM to
The caesium layer electronically decouples the
graphene from the metallic substrate. This allows the detection of long-range scattering patterns
arising, e.g. from intervally-scattering. Defects in the intercalated layer such as domain boundaries
act thereby as the necessary scatterers. The trigonal warping of the Dirac cone is already visible
at the Fermi level, because of the strong n-doping due to the intercalated caesium (see picture).
We analyse the dispersion relation in the range accessible for FT-STM and compare it with
E(k)
determined by angular resolved photoemission spectroscopy (ARPES). With FT-STM we also can
map anisotropies in the scattering patterns to the local symmetry of the scatterers and the structure
of the sample. Finally, we discuss the suppression of specic scattering vectors due to pseudo-spin
conservation [3].
References
[1] L. Petersen et al., Physical Review B, 57, 6858 (1998).
[2] M. Petrovi¢ et. al, Nature Communications, 4, 2772 (2013).
[3] P. Mallet et al., Physical Review B, 86, 045444 (2012).
Scattering patterns arising at defects in a closed caesium intercalated graphene layer. The trigonal
warping of the Dirac cone is clearly visible.
CHAPTER 3.
58
POSTERS
Investigations into the dynamical properties of graphene on
Ir(111)
Poster
Endlich, Michael (1); Miranda, Henrique (2,3); Molina-Sánchez, Alejandro (2,3); Wirtz, Ludger
(2,3); Kröger, Jörg, (1)
Contact: [email protected]
(1) Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany
(2) Physics and Materials Science Research Unit, University of Luxembourg, L-1511 Luxembourg
(3) Institute for Electronics, Microelectronics, and Nanotechnology [IEMN], CNRS UMR 8520,
Dept. ISEN, F-59652 Villeneuve d'Ascq Cedex, France
The phonon dispersion of singly oriented graphene on Ir(111) was determined by angle-resolved
inelastic electron scattering and density functional calculations.
optical phonon branches were observed at the
the Kohn anomaly at
Γ
Γ
and
K
Kohn anomalies of the highest
point of the surface Brillouin zone. While
is virtually identical to the Kohn anomaly observed from graphite and
predicted for pristine graphene (Fig.
a), the Kohn anomaly at
K
is weakened (Fig.
b).
This
observation is rationalized in terms of a decrease of the electron-phonon coupling due to screening
of graphene electron correlations by the metal substrate. The measured dispersion curves further
exhibit replica, which are rationalized in terms of phonon backfolding induced by the graphene
moiré superlattice.
Dispersion of (a) the LO phonon in the vicinity of
Γ
and of (b) the TO phonon close to
K.
CHAPTER 3.
59
POSTERS
Exploring the intercalation process of Cobalt under Graphene
Poster
Lisi, Simone, (1); Di Bernardo, Iolanda, (1); Mariani, Carlo, (1); Pacilé, Daniela, (2); Betti,
Maria Grazia, (1)
Contact: [email protected]
(1) Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale Aldo Moro 5, I-00185
Roma, Italy
(2) Dipartimento di Fisica, Università della Calabria, 87036 Arcavacata di Rende [CS], Italy
The structural and electronic properties of graphene (Gr) can be inuenced by its interaction
with the surrounding environment [1,2] and by modifying the underlying support by adatoms intercalation [3,4]. Graphene shows interesting magnetic properties in contact with a ferromagnetic
metal, as observed when deposited on Ni(111) [5].
The engineering of permanent magnetic mo-
ments in non-magnetic graphene can be achieved by intercalation of magnetic adatoms and it can
open a novel route to design light and exible magnetic materials. We present a photoemission and
absorption spectroscopy study of Co intercalation in high quality graphene sheets grown on Iridium
(111) surface. Core levels photoemission from C1s, Ir4f and Co3p, before and after Co intercalation,
shows a homogeneous diusion of Co adatoms during the intercalation, up to a completion of a
mismatched corrugated Co monolayer. CK and CoL2,3 edges, together with core levels, unravel
a mixing of Co with graphene, with C-Co hybridized character, in contrast to the low interacting
Gr/Ir(111) [2].
Further Co intercalation releases the mismatch of graphene.
CoL2,3 absorption
edges reveal a dierent response, as a function of Co thickness. Graphene can tailor the assembling
of magnetic FePc molecules when deposited on its top [2]. The presence of the Co-intercalated layer
induces interesting electronic response, as deduced by preliminary photoemission results.
References
[1] A. Bostwick et al., Nature Physics, 3, 36 (2007)
[2] M. Scardamaglia et al., The Journal of Physical Chemistry C, 117, 3019 (2013)
[3] D. Pacilé et al., Physical Review B, 87, 035420 (2013).
[4] J. Coraux et al., The Journal of Physical Chemistry Letters 3, 2059 (2012)
[5] M. Weser et al., Applied Physics Letters, 96, 012504 (210)
CHAPTER 3.
POSTERS
60
Spin polarization of Co(0001)/graphene junctions from rst
principles
Poster
Sipahi, Guilherme, (1,2); Zutic, Igor, (1); Atodiresei, Nicolae (3); Kawakami, Roland, (4); Lazic,
Predrag (5)
Contact: [email protected]
(1) University at Bualo, State University of New York, Bualo, NY 14260, USA
(2) Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Brazil
(3) Peter Grünberg Institut and Institute for Advanced Simulation, Jülich, Germany
(4) The Ohio State University, Columbus, Ohio 43210, USA
(5) Rudjer Boskovic Institute, PO Box 180, Bijenicka c. 54, 10 002 Zagreb, Croatia
Junctions comprised of ferromagnets and nonmagnetic materials are one of the key building
blocks in spintronics [1]. With the recent breakthroughs of spin injection in ferromagnet/graphene
junctions it is possible to consider spin-based applications that are not limited to magnetoresistive
eects [2,3]. However, for critical studies of such structures it is crucial to establish accurate predictive methods that would yield atomically resolved information on interfacial properties. By focusing
on Co(0001)/graphene junctions and their electronic structure, we illustrate the inequivalence of
dierent spin polarizations [4]. We show atomically resolved spin polarization maps [4] as a useful
approach to assess the relevance of Co(0001)/graphene for dierent spintronics applications.
References
[1] I. Zutic et al., Rev. Mod. Phys. 76, 323 (2004).
[2] H. Dery et al., IEEE Trans. Electron. Dev. 59, 259 (2012).
[3] O. M. J. van 't Erve et al., Nature Nanotech. 7, 737 (2012).
[4] Sipahi et al., J. Phys. Cond. Matter, in press.
CHAPTER 3.
61
POSTERS
Highly spin-polarized Dirac fermions at the graphene-Co interface
Poster
Marchenko, Dmitry, (1); Varykhalov, Andrei, (1), Sanchez-Barriga, Jaime, (1); Carbone, Carlo
(2); Rader, Oliver (1)
Contact: [email protected]
(1) Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II,
Albert-Einstein-Strasse 15, 12489 Berlin, Germany
(2) Istituto di Struttura della MateriaConsiglio Nazionale delle Ricerche, Basovizza, 34149
Trieste, Italy
The interface of graphene with ferromagnets is most interesting for spintronics.
epitaxially grown p(1x1) on Co(0001) shows an intact Dirac cone [1].
Graphene
A strong hybridization of
the upper Dirac cone with Co3d states is present but it occurs away from the K-point. We show
by spin- and angle-resolved photoemission that these ingredients are balanced to such an extent
that the intact Dirac cone is strongly spin polarized with a spin polarization of
point.
60% of the Dirac
The polarization is of minority spin meaning an antiparallel coupling of graphene and
Co magnetic moments.
Wave-vector dependent measurements exclude a spin-orbit contribution
to the spin polarization, and the ferromagnetic alignment is veried by reversal of the remanent
magnetization. The importance of the spin polarization at the interface for spin ltering is pointed
out since previously a buer layer of noble metals has been required for obtaining spin-ltered
intact Dirac cones. In addition, the use of the present results for possible combination with strong
spin-orbit eects is pointed out.
References
[1] A. Varykhalov et al., Phys. Rev. X 2, 041017 (2012).
Spin-resolved photoemission at the K-point of graphene/Co(0001). (a) and (b) are for opposite
magnetization directions. (c) spin asymmetries from (a) (blue) and (b) (green). Zero asymmetry
level is indicated as dashed line. (d-f ) Same but for 23° away from K. Photon energy is 62 eV.
CHAPTER 3.
62
POSTERS
Surface umklapp in ARPES : Seeing through 2D overlayers
Poster
Giovanelli, Luca, (1); Bocquet, François C., (2); Amsalem, Patrick, (3); Abel, Mathieu, (1);
Salomon, Eric, (4); Koch, Norbert, (3); Petaccia, Luca (5); Goldoni, Andrea (5); Themlin, JeanMarc, (1)
Contact: [email protected]
(1) Aix-Marseille Univ., IM2NP, UMR CNRS 7334, Marseille, France
(2) Peter Grünberg Institut (PGI-3), Functional Nanostructures at Surfaces, Forschungszentrum
Jülich, 52425 Jülich, Germany
(3) Humboldt-Universität zu Berlin, Institut für Physik, D-12489 Berlin, Germany
(4) Aix-Marseille Univ., PIIM, F-13397, Marseille, France
(5) Elettra Sincrotrone Trieste, Strada Statake 14 km 163.5, I-34149 Trieste, Italy
Atomically-thick 2D materials can be synthesized e.g.
from atomic or molecular precursors
on well-dened single-crystal metal surfaces acting both as a catalyst and structural template
[1,2,3]. Angle-resolved photoemission (PE), which provides a direct access to the overlayer 2D band
structure, is a prominent tool to study the electronic properties of these extended 2D nanostructures
and epitaxial 2D crystals. However, the identication of genuine features of the overlayer is often
complicated by the simultaneous contribution of both the adsorbate and the substrate to the overall
PE spectral shape. In particular, electronic states of the substrate may get folded back in k space
through scattering by the ordered overlayer, leading to additional substrate-related features, an
eect also known as surface-umklapp. Going through several examples of 2D overlayers on metal
surfaces, it is shown that, once back-folded, the clean surface contribution of localized and weakly
dispersing d-states is completely washed away: ARPES spectra then mimic that of a substrate
poly-crystal [4].
By employing low photon-energy photoemission and rst-principle calculations,
we show how a 2D ordered overlayer made of ZnPc molecules can be used as a diraction lattice to
eectively probe the Ag band structure (Fig. 1) [5]. In conclusion, the recognition of the ubiquitous
role of surface-umklapp eects should help disentangling genuine adsorbate features from substrate
contributions.
References
[1] M. Corso et al,. Science, 303, 217 (2005).
[2] J. Lobo-Checa et al., Science 325, 300 (2009).
[3] L.Porte et al., Int.J.Nanotechnol., 9, 325 (2012).
[4] L. Giovanelli et al., Phys. Rev B, 87, 035413 (2013).
[5] F. Bocquet et al., 84, 241407(R) (2011).
Fig.1 (a) ARPES image of 1ML ZnPc/Ag(110) around normal emission with hν =9 eV; red and
blue EB(?e) dispersion curves correspond to sp diracted photoelectrons; the dashed lines locate
the HOMO and LUMO of ZnPc. (b) ARPES image of clean Ag(110); the green lines origin from
the sp direct transitions.
CHAPTER 3.
63
POSTERS
Dopant-controlled and substrate-dependent electronic properties of graphene
Poster
Usachov, Dmitry, (1); Fedorov, Alexander, (1); Vilkov, Oleg, (1); Vyalikh, Denis V., (1,2)
Contact: [email protected]
(1) Faculty of Physics, St. Petersburg State University, 198504, St. Petersburg, Russia
(2) Institute of Solid State Physics, Dresden University of Technology, 01062 Dresden, Germany
Many research eorts are focused at elaboration of methods for tuning the graphene properties
for its better performance in electronic applications. One of the promising approaches is doping
with heteroatoms. In particular, nitrogen-doped graphene (N-graphene) is a perspective material
for batteries, supercapacitors, Pt-free fuel cells, electrochemical sensors, etc. However, the impact of
nitrogen on the graphene electronic properties substantially depends on its local chemical bonding.
Thus, the bonding type must be precisely controlled. Recently we have proposed an approach for
the large-scale N-graphene synthesis with the post-synthesis tuning of dopant bonding [1].
Here
we uncover the dependence of the N-graphene electronic structure and charge transfer on the
type and concentration of impurities, and discuss the kinetics and mechanism of interconversion
between dierent nitrogen bonding congurations.
Another successful approach for controlling
the graphene properties is surface alloying of dierent atoms underneath graphene.
It provides
possibility for varying the strength of graphene bonding to substrate and allows tuning of the
substrate composition and properties [2].
Here we demonstrate this approach by several recent
examples, including formation of graphene contacts with dierent metal silicides, widely used in
silicon-based electronics.
This provides a further step towards integration of graphene with the
existing silicon technology.
References
[1] D. Usachov, et al., Nano Lett., 11, 5401 (2011).
[2] O. Vilkov, et al., Sci. Reports, 3, 2168 (2013).
CHAPTER 3.
64
POSTERS
Graphene on Ir(111), adsorption and intercalation of Cs and
Eu atoms
Poster
Lazi¢, Predrag (1); Damir, Sokcevic (1); Radovan, Brako (1); Petrovi¢, Marin (2); ’rut Raki¢,
Iva (2); Kralj, Marko (2); Milun, Milorad (2); Pervan, Petar (2); Pletikosi¢, Ivo (2); Atodiresei,
Nicolae (3); Caciuc, Vasile (3); Bluegel, Stefan (3); Michely, Thomas (4); Runte, Sven (4); Busse,
Carsten (4); F. Foerster, Daniel (4); Schumacher, Stefan (4); Wehling, Tim, O. (5, 6); Valla, Tonica
(7); Pan, Z.-H. (7); Sadowski, J. T. (8)
Contact: [email protected]
(1) Rudjer Boskovic Institute, Zagreb, Croatia
(2) Institut za ziku, Bijeni£ka 46, 10000 Zagreb, Croatia
(3) Peter Grünberg Institut & Institute for Advanced Simulation, Forschungszentrum Jülich and
JARA 52425, Julich, Germany
(4) II. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
(5) Institut für Theoretische Physik, Universität Bremen, Otto-Hahn-Allee 1, 28359 Bremen,
Germany
(6) Bremen Center for Computational Material Science (BCCMS), Universität Bremen, Am
Fallturm 1a, 28359 Bremen, Germany
(7) Department of Condensed Matter Physics & Materials Science, Brookhaven National Lab,
Upton, New York 11973, USA
(8) Center for Functional Nanomaterials, Brookhaven National Lab, Upton, New York 1197
Experimental and theoretical study of Cs and Eu atoms adsorption on graphene on Ir(111) will
be presented. Graphene on Ir(111) surface is an interesting system because graphene has almost
pristine electronic structure in it due to its weak bonding character to iridum surface. The bonding is almost exclusively of the van der Waals type.
However adding Cs or Eu atoms graphene
gets doped and and nature of binding changes - especially in the case when the atoms intercalate.
Density Functional Theory calculations with standard semilocal functionals (GGA) - fail to reproduce experimental ndings even qualitatively. Only when the newly developed nonlocal correlation
functional is used (vdW-DF) which includes van der Waals interactions, are the calculations in
agreement with experiment, revelaing the mechanism of graphene delamination and relamination
which is crucial for intercalation and trapping of atoms under the graphene.
References
[1] M. Petrovic et al., Nature Comm. 4, 2772 (2013).
[2] S.Schumacher et al., Nano Letters 13, 5013 (2013).
CHAPTER 3.
65
POSTERS
Controllable nitrogen doping of graphene via a versatile plasmabased technique
Poster
Lin, Yu-Pu, (1) ; Ksari, Younal, (1) ; Prakash, Jai, (1) ; Giovanelli, Luca, (1) ; Themlin,
Jean-Marc, (1)
Contact: [email protected]
(1) Aix-Marseille Université, CNRS, IM2NP, UMR 7334, 13397 Marseille, France
The eective chemical doping of graphene, able to inuence its electronic and chemical properties, is actively pursued [1]. Indeed, the N-doped graphene has been reported to exhibit superior
performance over the pristine material in several applications (eld-eect transistors, batteries, fuel
cells, and super-capacitors) [2-5].
However, methods to realize a reliable and controlled doping
have still to be mastered. In this work, we present an eective, versatile plasma-based method for
the nitrogen-doping of graphene grown on 6H-SiC(0001). Using a tunable hybrid plasma source,
graphene monolayers are exposed to a stream of N ions and/or to a neutral ow of thermalized N
species. The electronic doping levels of the N-doped graphene (NG) are revealed through the analysis of the pi* states dispersion using angle-resolved inverse photoemission spectroscopy (ARIPES).
It shows that low-energy N ions (5 35 eV) cause an n-type doping (up to 0.4 eV, g.1b) with a
majority of graphitic (substitutional) N (up to 8.7%, g.1a,c), as revealed by XPS (NG-ion spectrum below).
In contrast, neutral N species rather form pyridinic-N in the presence of defects
(NG-atom spectrum).
In brief, we show that the bonding environment of N atoms in graphene
can be easily controlled using a versatile plasma-based technique, which will certainly be of great
interest for the processing of future graphene-based nano-devices using widespread technologies like
plasma-processing.
References
[1] H. Liu, Y. Liu, and D. Zhu, Journal of Materials Chemistry, 21, 3335 (2011).
[2] D. Wei, Y. Liu, Y. Wang, et al. Nano Letters, 9, 1752-1758 (2009).
[3] M. D. Stoller, S. Park, et al. Nano Letters, 8, 3498 (2008).
[4] D. Pan, S. Wang, et al. Chem. Mater., 21, 3136 (2009).
[5] H. M. Jeong, J. W. Lee, et al. Nano Letters, 11, 2472 (2011).
Figure 1. (a) The three major doping congurations of N in graphene: Pyridinic-N, Pyrrolic-N
and Graphitic-N. (b) Linear extrapolation of the
π
states obtained by ARIPES for pristine
graphene (PG), NG-ion and NG-atom with respect to k|| along
studied NG samples.
Γ-K.
(c) N 1s XPS spectra of the
CHAPTER 3.
66
POSTERS
Graphene and Moirés
Poster
Bhatti, Asif Iqbal (1); Ferhat, Karim (1); Lançon, Frédéric (2); Ralko, Arnaud (1); Coraux,
Johann (1); Magaud, Laurence (1)
Contact: [email protected]
(1) Institut Néel, CNRS and UJF, Grenoble, France
(2) LSIM, INAC,CEA Grenoble, Grenoble, France
Graphene outstanding properties are related to its honeycomb lattice and any perturbation to
this sp2 lattice can induce drastic changes [1].
Here we address the case of moiré superperiods
imposed to graphene. Their origins can be multiple: interaction with a substrate such as a metal
surface, h-BN or SiC [2,3], rotated graphene bilayers [4] and defects network. The strength of the
interaction can range from very weak van der Waals interaction to the local formation of strong
covalent bonds. All these cases will be discussed on the basis of ab initio calculations coupled to
an eective potential description.
Superperiods can induce important modications of the elec-
tronic structure of graphene: loss of the linear dispersion and of the Dirac cones in the case of
very strong interaction but also additional Dirac cones, gap opening, van Hove singularities, localization and connement eects for weaker coupling. Graphene morphology also strongly depends
on the strength of the interaction and the lattice mismatch, resulting in corrugations with variable
amplitude and formation of wrinkles [5].
References
[1] Pedersen, T. et al. Phys. Rev. Lett. 100, 136804 (2008).
[2] C.Tonnoir et al, Phys. Rev. Lett.111, 246805 (2013).
[3] F.Varchon et al, Phys. Rev.B 77, 235412 (2008).
[4] G.Trambly de Laissardière et al, Phys.Rev.B86,125413 (2012).
[5] H. Hattab et al, Nano Lett. 12, 678 (2012).
Figure: Graphene on rhenium, side view that shows a strong corrugation (left); Band structure
and density of states of a twisted graphene bilayer with a rotation angle of 7°.
CHAPTER 3.
67
POSTERS
Eects of uniaxial structural modulation on graphene's electronic structure
Poster
’rut Raki¢, Iva, (1); Mik²i¢ Trontl, Vesna, (1); Pervan, Petar, (1); Craes, Fabian, (2); Jolie,
Wouter, (2); Busse, Carsten, (2); Lazi¢, Predrag, (3); Kralj, Marko, (1)
Contact: [email protected]
(1) Institut za ziku, Bijeni?ka cesta 46, 10000 Zagreb, Croatia
(2) II. Physikalisches Institut, Universität zu Köln, Zülpicher Straÿe 77, 50937 Köln, Germany
(3) Institut Ružer Bo²kovi¢, Bijeni£ka cesta 54, 10000 Zagreb, Croatia
Engineering of graphene's electronic structure presents a vital course in graphene research due to
specic requirements in crucial applications such as electronics or optoelectronics. In this work we
utilize the fact that structural modications of graphene, in particular the ones involving strain, lead
to changes of its electronic structure. Our approach, linked to strain engineering, is based on growing
graphene on a stepped surface Ir(332).
Graphene on Ir(332) causes severe surface restructuring
resulting in new mesoscopic features consisting of wide (111) terraces bounded by step bunches
dominantly of (133) orientation. We have studied this system by means of STM, STS, ARPES and
DFT. ARPES averaged on a scale of micrometer, shows an anisotropy of the Fermi velocity as well
as a slight n-doping.
In addition, STS spectra and maps visualize electronic states localized on
at terraces, step bunches or step edges, showing distinction depending on a direction of graphene
bending. More detailed examination of step bunches reveals an additional electronic substructure
likely mediated by local changes in van der Waals interaction with the substrate. Finally, vdW-DFT
results, based on models involving characteristic (111), (133) and (332) structures, are presented.
Our ndings demonstrate a viable route to alter epitaxial graphene's electronic structure by means
of strain and van der Waals interaction.
CHAPTER 3.
68
POSTERS
Fulerenes on Graphene Held Together by van der Waals Interaction
Poster
Svec, Martin, (1); Merino, Pablo, (2), Dappe, Yannick, (3); Gonzalez, Cesar, (1); Jelinek, Pavel,
(1,4); Martin Gago, Jose Angel, (2)
Contact: [email protected]
(1) Institute of Physics of the AS CR, Cukrovarnická 10, 162 00 Praha, Czech Republic
(2) CSIC-ICMM, C/Sor Juana Ines de la Cruz 3, E-28049 Madrid, Spain
(3) Service de Physique de l'Etat Condensé, DSM/IRAMIS/SPEC, CEA Saclay, France
(4) Graduate School of Engineering, Osaka University 2-1, Yamada-Oka, Suita, Osaka 5650871, Japan
In this contribution, we concentrate on the interactions occurring between fullerenes and a
single-layer epitaxial graphene grown on SiC(0001). Using the variable temperature scanning tunneling microscopy (STM) and advanced theoretical simulations, we found the cohesion among the
fullerenes stronger than the binding to the surface despite the presence of a superlattice corrugation.
The fullerenes arrange into planar islands at 40K with a 4x4 periodicity, held together exclusively by
the van der Waals forces, which is manifested by collective movement of the islands upon manipulation with the scanning probe. This has been conrmed by extensive density functional calculations
taking into account the van der Waals contribution. Furthermore, the most energetically favorable
conguration evaluated by the theory corresponds to the experimentally observed internal orientation of the fullerenes in the 4x4 reconstruction. The orientation of the molecule was determined
by matching the experimental to simulated STM images considering a moving fullerene attached
to the probe, that was the origin of a changing intramolecular contrast.
References
[1] M. ’vec et al, Phys. Rev. B. 86, 121407(R) (2012).
2
3D representation of 20x20 nm empty states STM topography of C60 islands on a) SLG taken at
600mV, 100pA and b) (6x6)-SiC(0001) recorded at 1000mV, 100 pA. Both images were obtained
at 40 K.
CHAPTER 3.
69
POSTERS
The instability of silicene on Ag(111)
Poster
Acun, Adil ; Poelsema, Bene ; Zandvliet, Harold ; van Gastel, Raoul
Contact: [email protected]
(1) Physics of Interfaces and Nanomaterials MESA+ Research Institute Faculty of Science and
Technology Carré CR 2.209 University of Twente PO Box 217 7500 AE Enschede The Netherlands
Graphene, a carbon allotrope with a 2D honeycomb structure has opened the door to a new
era in material science. The discovery of graphene has sparked the search to a silicon version of
graphene, referred to as silicene.
Here we have used low energy electron microscopy to directly
visualize the formation and stability of silicene layers on a clean Ag(111) substrate. We have found
that silicene layers are intrinsically unstable against the formation of an sp3-hybridized, bulk-like
silicon structure. The irreversible formation of this bulk-like structure is initiated by thermal Si
adatoms that are produced by the silicene layer itself. The same instability prevents the formation
of a fully closed silicene layer or a thicker bilayer, rendering the future large-scale fabrication of
silicene layers on Ag substrates unlikely.
References
[1] Acun et al., Appl. Phys. Lett., 103, 263119 (2013).
CHAPTER 3.
POSTERS
70
Graphene Flakes embedding in hexagonal Boron Nitride
Poster
Farwick zum Hagen, Ferdinand; Zimmermann, Domenik; Michely, Thomas; Busse, Carsten
Contact: [email protected]
(1) II. Physikalisches Institut, Universität zu Köln, Zülpicher Straÿe 77, 50937 Köln, Germany
Many special properties of graphene, as for example the high carrier mobility and the spinpolarized edge state, are suppressed in any real world sample due to the interaction with the
environment. A possible remedy is embedding graphene in hexagonal boron nitride (hBN) which
provides a promising combination of geometric match and electronic mismatch [1]: It is isostructural
with a small lattice mist of only 1,8% [2], yet at the same time a wide band gap insulator. In this
study we analyse embedding of nm-sized graphene quantum dots in a monolayer of hBN. Using
scanning tunneling microscopy (STM) the morphology of graphene hBN hybrid structures on Ir(111)
is investigated. The materials are synthesised via temperature program growth (TPG) and chemical
vapor deposition (CVD) growth processes using ethylene and borazine as precursor gases. We study
dierent samples in dependence on growth conditions, such as temperature, pressure, gas dose and
method. The analysis of highly resolved STM images focuses on the phase boundaries, following
the question whether heterogeneous or homogeneous nucleation takes place. Finally these hybrid
structures are exposed to oxygen in order to investigate structural coherent junctions between hBN
and graphene.
References
[1] Geim, A. K.; Novoselov, K. S. The rise of graphene. Nature Mater. 6, 183191 (2007).
[2] Liu, L. et al., Structural and electronic properties of h-BN. Phys. Rev. B 68, 104102 (2003).
CHAPTER 3.
71
POSTERS
Cold Tip SPM - A new generation of variable temperature
SPM for spectroscopy
Poster
Troeppner, Carsten (1); Atabak, Mehrdad (1); Koeble, Juergen (1); Uder, Bernd (1)
Contact: [email protected]
(1) Oxford Instruments Omicron NanoScience, 65232 Taunusstein, Germany
We present design and rst results of a new generation of variable temperature scanning probe
microscope (SPM) that has been developed to enhance the performance in tunneling spectroscopy
at lower and variable temperatures.
The new microscope for ultra high vacuum is based on a
new stage design using a ow cryostat compatible for cooling with liquid nitrogen or helium. In
contrast to earlier established designs of variable temperature SPM's [1-3] where only the sample is
cooled, this new SPM also cools the scanner with tip. This is realized by a new developed compact
microscope stage with thermal shields and a cooling management system.
With the new design
we achieve lower temperatures and improve drift by more than an order of magnitude compared
to previous variable temperature stages. Sample temperatures down to 10 K (with helium) and 95
K (with nitrogen) have been achieved. The temperature stability is better than 5mK / min and a
thermal drift of 1 pm/s was achieved. During cooling the mechanical z stability is better than 3
pm. These conditions enhance spectroscopy measurement capability. Loop o times of up to 10 s
per single spectroscopy curve have been measured. The new ow cryostat also allows for changing
between nitrogen cooling and helium cooling in less than 90 min during a running experiment.
Pre-cooling with nitrogen during the starting phase of an experiment also reduces running costs for
liquid helium.
References
[1] Omicron, "VT SPM" (1995)
[2] RHK, "Variable Temp BEETLE"
[3] SPECS, "Aarhus SPM"
CHAPTER 3.
POSTERS
72
Buttery Hydrogen Dimers on G/SiC(0001).
Poster
Merino, Pablo (1), Martinez, Jose Ignacio (1), Svec, Martin (2), Jelinek, Pavel (2,3); Martin
Gago, Jose Angel (1), de Andres, Pedro (1)
Contact: [email protected]
(1) CSIC-ICMM, C/Sor Juana Ines de la Cruz 3, E-28049 Madrid, Spain
(2) Institute of Physics of the AS CR, Cukrovarnická 10, 162 00 Praha, Czech Republic
(3) Graduate School of Engineering, Osaka University 2-1, Yamada-Oka, Suita, Osaka 5650871, Japan
Hydrogen adsorbates on graphene [1] are a prominent model of graphene functionalization and
have important consequences in astrochemistry and material science among others. Here we address
the rst stages of hydrogen deposition on graphene grown on SiC(0001) with a combined exhaustive
theoretical-experimental approach with advanced calculation including for the rst time the full
(6
√
√
3x6 3)R30◦
unit cell of the G/SiC(0001) and high resolution scanning tunneling microscopy
images resolving simultaneously the graphene lattice and the hydrogen adsorbates. The atomic scale
determination of the most stable geometry, the buttery-shaped dimer, will be discussed under this
combined approach and we will unclose the intrinsic diculties in determining the exact atomic
structure for the hydrogen dimers, trimers and small 2D-clusters on graphene.
References
[1] L. Hornekær et al. Phys. Rev. Lett. 96, 156104 (2006).
2
High resolution STM images of hydrogen small dimers on SLG. a) V=-0.3V, I=1nA, 3.8x3.8nm .
b) Image where the atomic graphene grid has been superimposed and a simple interpretation of
where the hydrogen atoms might be chemisorbed have been over imposed.
CHAPTER 3.
POSTERS
73
Contacting graphene with liquid metals
Poster
ƒapeta, Davor (1); Jurdana, Mihovil (1); Plodinec, Milivoj (2); Kralj, Marko (3)
Contact: [email protected]
(1) University of Zagreb, Faculty of Science, Department of Physics, Bijeni£ka 32, 10000 Zagreb,Croatia
(2) Ružer Bo²kovi¢ Institute, Bijeni£ka cesta 54, 10000 Zagreb, Croatia
(3) Institut za ziku, Bijeni£ka 46, 10000 Zagreb, Croatia
Characterization and device fabrication of graphene and related 2D materials requires forming reliable electrical contacts. Standard methods such as e-beam and photolithography are time
consuming, require expensive equipment and usually contaminate samples with resist and process
chemicals residues. "Soldering" with indium is clean, but requires heating so it is not compatible
with heat sensitive substrates. We show that mercury and gallium-indium eutectic, metal and alloy
liquid at the room temperature, form electrical contacts to CVD graphene on common dielectric
substrates. Since mercury doesn't wet graphene, SiC, SiO2 or polymers, mercury contact ("mercury
probe") is temporary and can be removed after measurement without damaging graphene. This enables rapid testing of graphene quality and uniformity during dierent stages of device fabrication.
Gallium-indium alloy forms permanent semi-solid contacts that are highly resistant to stretching
and bending. Glass capillary lled with GaIn can be used as a fountain pen for "drawing" contacts using micromanipulator or by hand. Both methods take only minutes to implement, don't
contaminate graphene with residue and require only basic equipment.
CHAPTER 3.
74
POSTERS
Electronic properties of edge modied zigzag graphene nanoribbons
Poster
Shinde, Prashant (1); Baumgartner, Marion (1); Passerone, Daniele (1); Pignedoli, Carlo (1)
Contact: [email protected]
(1) Swiss Federal Laboratories for Materials Science and Technology, EMPA, Überlandstrasse
129, 8600 Dübendorf, Switzerland
Graphene nanoribbons (GNRs), quasi-one dimensional graphene derivatives, are promising materials for electronic devices [1-2].
geometry of the edges.
The electronic properties of GNRs strongly depend on the
Structural perfection [3-4], during growth and post processing, is of key
importance: occurrence of defects at the edges could be detrimental for the expression of peculiar
properties predicted in theory [5]. On the basis of DFT simulations we discuss here the eect of
edge modications on the electronic and magnetic properties of zigzag GNRs. We explore the characteristics of the electronic band structure with a focus on the nature of localized states. Ribbons
with cove edges (see e.g. Fig. (a)) show partially at bands at the Fermi energy and the frontier
states are localized around the cove defects. The non-magnetic ribbons with even (odd) width, N,
are always metallic (semiconducting). The origin of alternating even/odd behavior is the staggered
cove position. For wide ribbons, N > 9, the ground state is found to be antiferromagnetic. Another
class of ribbons, exhibiting a pentagonal ring at the zigzag backbone (Fig.
(b)), have antiferro-
magnetic ground state with spin polarized states localized at the edges. The HOMO (LUMO) has
maximum intensity in between (on) the pentagons. We discuss eectiveness of edge modied design
of GNRs as an appropriate mechanism to tune electronic and magnetic properties of zigzag GNRs
for potential applications in nanoelectronics.
References
[1] Dutta, S. et. al, J. Mater. Chem. 20, 8207 (2010).
[2] W. Y. Kim, K. S. Kim Nature Nanotech. 3, 408 (2008).
[3] Cai J. et al. Nature, 466, 470 (2010).
[4] Rueux P. et al. ACS Nano, 6, 6930 (2010).
[5] Huang B. et al. Phys. Rev. B, 77, 153411 (2008).
CHAPTER 3.
75
POSTERS
Zigzag graphene nanoribbons: The cove defects in anti-zigzag conguration (top panel, N odd), the
zigzag conguration (middle panel, N even). The bottom panel shows ZGNR with pentagon as a
topological defect at the zigzag backbone.
CHAPTER 3.
76
POSTERS
Self-assembly and orbital imaging of metal phthalocyanines on
graphene model surface
Poster
Järvinen, Päivi; Hämäläinen, Sampsa K; IJäs, Mari; Harju, Ari; Liljeroth, Peter
Contact: [email protected]
(1) Aalto University, Department of Applied Physics
Metal phthalocyanines (MPc) consist of a coordinated metal ion surrounded by an organic
macrocycle of alternating carbon and nitrogen atoms.
As both the central metal ion and the
macrocycle can be modied, the electronic properties and self-assembly of these molecules can be
tuned over a broad range. The use of arrays of MPcs on graphene has been suggested for tuning the
electrical properties of graphene [1]. While the self-assembly of MPcs has been extensively studied
on metal substrates, systematic studies of the symmetry of molecular assemblies and energetic
position of the molecular orbitals on graphene are lacking.
Here, we study the eect of central ion and macrocycle substitution on the self-assembled MPc
structures on epitaxial graphene by low-temperature scanning tunnelling microscopy (STM). We
investigate the energetic positions and symmetries of molecular orbitals by scanning tunneling spectroscopy (STS) experiments and density functional theory (DFT) calculations. We focus on cobalt
phthalocyanine (CoPc), copper phthalocyanine (CuPc) and fully uorinated cobalt phthalocyanine
(F16CoPc) on G/ Ir(111) substrate as model systems.
Our results shed light on the molecular
ordering and the energies of molecular orbitals with respect to the graphene Dirac point for the different MPcs. This information will be crucial for using molecular overlayers to modify the electronic
properties of graphene.
References
[1] P. Järvinen et al. Molecular self-assembly on graphene on hexagonal boron nitride and SiO2
substrates, Nano Letters, 13, 3199-3204, (2013)
STM images show self-assembled structures of CoPc, CuPc, and F16 CoPc.
CHAPTER 3.
POSTERS
77
Wrinkles of graphene on Ir(111) - internal structure and longrange ordering
Poster
Petrovi¢, Marin, (1); Sadowski, Jerzy T. (2); ’iber, Antonio, (2); Kralj, Marko, (1)
Contact: [email protected]
(1) Institut za ziku, Bijeni£ka 46, 10000 Zagreb, Croatia
(2) Center for Functional Nanomaterials, Brookhaven National Lab, Upton, New York 11973,
USA
Wrinkles are an intrinsic feature of many epitaxial graphene systems and transferred graphene
in devices. For graphene/Ir(111), wrinkles have been reported several times up to now [1,2,3], but
a more comprehensive study on their long-range ordering as well as description of their internal
structure are still missing. In this work, STM was used to reveal the structure of individual wrinkles
of graphene/Ir(111) which extends beyond simple half-pipe model. Once graphene is delaminated
from iridium, the van der Waals interaction leads to complex folded structures. By using LEEM, we
were able to characterize the long-range order of graphene's interconnecting wrinkles network. For
the aligned R0 graphene, we found a clear relation between the direction of extension of wrinkles
and high symmetry directions of the iridium substrate. We also show that such network can be
approximated by a Voronoi diagram which greatly facilitates its characterization. In contrast, no
such ordering is observed on R30 rotational domains of graphene/Ir(111), indicating reduced binding
to the substrate.
Most prominent features of wrinkles, including characteristic intra- and inter-
wrinkle length-scales are explained using phenomenological, scaling theoretical arguments based on
the interplay of adsorption and elastic energies of a constrained graphene sheet. Our ndings are
relevant for the control and technological implementation of wrinkled graphene.
References
[1] N'Diaye, A. T. et al. New J. Phys. 11, 113056 (2009).
[2] Hattab, H. et al. Nano Lett. 12, 678 (2012).
[3] Petrovi¢, M. et al. Nat. Commun. 4, 2772 (2013).
CHAPTER 3.
POSTERS
78
Etching of Graphene on Ir(111) with Molecular Oxygen
Poster
Schröder, Ulrike A., (1); Grånäs, Elin, (2); Gerber, Timm, (1); Arman, Mohammad A. (2);
Schulte, Karina (3); Andersen, Jesper N.,(2,3); Knudsen, Jan, (2,3); Michely, Thomas, (1)
Contact: [email protected]
(1) II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77 50937 Köln, Germany
(2) Division of Synchrotron Radiation Research, Lund University, Box 118, 221 00 Lund, Sweden
(3) MAX IV Laboratory, Lund University, Box 118, 221 00 Lund, Sweden
Carbon combustion is important for many applications, but so far, it is not very well understood
on the atomic level. High quality graphene(Gr) on Ir(111) exposed to molecular oxygen provides a
well-dened system, and therefore gives a unique possibility to study the role of defects in etching of
graphitic materials, and develop a detailed understanding of the etching mechanism. Using scanning
tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption
spectroscopy (TDS), we nd that the mechanism governing the onset of etching depends on whether
it is Gr islands or a closed Gr lm that are attacked by oxygen. For Gr islands, etching sets in at
550 K. O2 dissociates on the bare Ir(111). Real time STM measurements reveal that O then attacks
Gr via the edges. Free edges are preferentially etched, compared to Gr edges bound to Ir steps.
From TDS we obtain the ratio of CO2 /CO formed during etching. It depends on the amount of
O present at etching sites. Perfectly closed Gr lms are remarkably stable against oxygen etching,
which rst sets in around 700 K. At this temperature, 5-7 defects stemming from the Gr growth
process act as nucleation points for etching, presumably because O2 dissociation is facilitated there.
At higher etching temperatures, large hexagonal etch holes are visible in the STM: Zigzag edges
are more stable against etching than armchair edges. In contrast to Gr islands, signicantly more
CO than CO2 is produced.
STM images of perfectly closed 1 ML Gr exposed to molecular oxygen at a) 700 K and b) 750 K.
a) Left: 5-7 defect. Right: small etchhole nucleating at a 5-7 defect. Image size 20 nm x 40 nm.
b) Large hexagonal etchholes. Image size 265 nm x 265 nm.
CHAPTER 3.
79
POSTERS
Unusual Moire Patterns on Graphene on Rh(111)
Poster
Martin-Recio, Ana (1); Martinez-Galera, Antonio J. (1,2); Gomez-Rodriguez, Jose M. (1)
Contact: [email protected]
(1) Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid,
Madrid, Spain
(2)Present address: Physikalisches Institut, Universitat zu Koln, Zulpicher Str. 77, Koln, Germany
The growth of graphene on transition metals by means of dierent procedures has been highly
studied in recent years [1] in order to understand the interactions between them. These interactions
do not only change the electronic properties of graphene, but also its geometrical structure which
leads to moire periodic superstructures. It has been found that, if the graphene-metal interaction is
low enough, more than one moire lattice is stable for the same graphene-metal system [2,3]. In the
case of graphene on Rh(111), this interaction is not considered to be low [1]. Therefore, only one
relative orientation of the carbon atom lattice with the Rh(111), leading to only one moire pattern,
has been described [4,5]. It is the (12x12)C aligned with (11x11)Rh(111) moire. In this study, we
report on the growth of graphene on Rh(111) and the formation of several dierent moire structures.
The experiments were performed in ultra-high vacuum (UHV) by means of variable temperature
scanning tunneling microscopy (VT-STM). Graphene monolayers were grown on Rh(111) single
crystals in UHV via chemical vapor deposition (CVD) of low pressure ethylene (C2 H4 ).
In our
STM measurements we observed the usual (12x12)C on (11x11)Rh(111) moire (g.1a) which was
found in previous works [4,5], but also several other rotational graphene domains (g.1b). These
unusual structures, corresponding to smaller periodicities than the normal (12x12)C moire, have
been modeled through atomic resolved data.
References
[1] M. Batzill, Surf. Sci. Reports 67, 83 (2012).
[2] M. M. Ugeda, D. Fernandez-Torre, I. Brihuega, P. Pou, A.J. Martinez-Galera, R. Perez, and
J.M. Gomez-Rodriguez, Phys. Rev. Lett. 107, 116803 (2011).
[3] A. J. Martinez-Galera, I. Brihuega, and J. M. Gomez-Rodriguez, Nano Letters 11, 3576
(2011).
[4] B. Wang, M. Cao, et al., ACS Nano 4, 5773-5782 (2010).
[5] E. N. Voloshina, Yu. S. Dedkov, et al., Appl. Phys. Lett. 100, 241606 (2012).
2
Figure 1. (a) 10x10 nm STM image of the (12x12)C moire with its model. V=-0.4V, I=2nA; (b)
2
15x15 nm image of two dierent moires: the usual moiré on the right-top, and a new one on the
left-bottom. Comparing the angles in both akes, a model for the new structure is obtained.
V=-0.3V, I=19nA.
CHAPTER 3.
80
POSTERS
Hybridization of graphene and a Ag monolayer supported on
Re(0001)
Poster
Papagno, Marco, (1,2); Moras, Paolo (1); Sheverdyaeva, Polina (1); Doppler, Jorg (3); Garhofer,
Andreas, (3); Mittendorfer, Florian (3); Redinger, Josef (3); Carbone, Carlo (1);
Contact: [email protected]
(1) Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Trieste, Italy
(2) Dipartimento di Fisica, Universitá della Calabria, 87036 Arcavacata di Rende (Cs), Italy
(3) Institute of Applied Physics and Center for Computational Material Science, Vienna University of Technology, Gusshausstrasse 25/134, A-1040 Vienna, Austria.
A detailed understanding of the chemical interaction between graphene and a metal substrate
is a major prerequisite for tailoring the electronic properties of graphene, because it allows tuning
the electronic states of graphene by changing the support or via the intercalation of alloy materials
[1].
For instance, for graphene adsorbed on Ni, Rh, Ru and Re the hybridization between the
carbon and metal atoms leads to a loss of the linear dispersion of the graphene bands. In these
cases the electronic properties can be restored by intercalation of noble-metal atoms, as evidenced
by several angle-resolved photoemission spectroscopy (ARPES) studies [2, 3].
The intercalated
noble-metal layers not only act as spacers, but also reduce the hybridization between the metal d
orbitals and graphene
π band.
To shed more light on the role of the intercalated lm we investigated
the electronic structure of graphene supported on Re(0001) before and after the intercalation of
one-monolayer Ag with ARPES experiments and density functional theory (DFT) calculations [4].
In this study, we show that even as the noble-metal lm leads to a decoupling of the substrate,
the electronic states of the intercalated layer still hybridize with the graphene layer and induce
a band gap in the graphene
π
band. The results clearly indicate that the electronic structure of
graphene adsorbed on a noble-metal layer can still deviate signicantly from the structure of an
ideal, unsupported graphene sheet.
References
[1] M. Batzill, Surf. Sci. Rep. 67, 83 (2012).
[2] C. Enderlein, Y. S. Kim, A. Bostwick, E. Rotenberg, and K. Horn, New J. Phys. 12, 033014
(2010).
[3] A. Varykhalov, M. R. Scholz, T. K. Kim, and O. Rader, Phys. Rev. B 82, 121101(R) (2010).
[4] M. Papagno, P. Moras, P. M. Sheverdyaeva, J. Doppler, A. Garhofer, F. Mittendorfer, J.
Redinger, and C. Carbon, Phys. Rev. B 88, 235430 (2013).
Index
Åhlgren, 37
Cavalleri, 6
Ceballos, 52
Abel, 50, 62
Chérioux, 30
Acun, 69
Chab, 29
Amsalem, 62
Chapman, 6, 20
Andersen, 5, 78
Choueikani, 50
Arman, 5, 78
Cilento, 20
Arnau, 52
Clair, 50
Atabak, 71
Conrad, 17
Atodiresei, 38, 40, 46, 60, 64
Coraux, 25, 30, 66
Böttcher, 23
Büchner, 54
Balan, 34
Balashov, 52
Baraldi, 33
Baumgartner, 74
Craes, 39, 46, 57, 67
Crepaldi, 20
Crommie, 15
Cun, 8
Cunge, 36
Cunnie, 47
Bendiab, 30
da Jornada, 15
Berger, 43
Dappe, 68
Bernard, 8
Davydova, 36
Betti, 26, 31, 59
de Andres, 72
Bettinger, 28
Dedkov, 23, 26, 48
Bhatti, 66
Delfour, 36
Bignardi, 56
Denk, 44
Blügel, 40, 46
Despiau-Pujo, 36
Blanco-Rey, 29
Dhesi, 50
Bluegel, 64
Di Bernardo, 59
Bocquet, 62
Dombrowski, 57
Bouvron, 48
Doppler, 26, 80
Brüller, 28
Drndic, 34
Bradley, 15
Brako, 64
Endlich, 58
Brihuega, 18, 39
Brocks, 32
Fölsch, 35
Bromberger, 6
Fagot-Revurat, 22
Buljan, 42
Farmanbar, 32
Busse, 24, 46, 57, 64, 67, 70
Farwick zum Hagen, 70
Fasel, 28, 44
Cacho, 6, 20
Fedorov, 54, 63
Caciuc, 40, 46, 64
Feibelman, 5
Cafolla, 47
Feng, 44
Cai, 44
Ferhat, 66
Calleja, 49
Fernández Torre, 39
Capeta, 73
Ferrari, 26
Carbone, 26, 61, 80
Ferretti, 12, 44
Cardoso, 12
Foerster, 64
Carpy, 47
Fonin, 26, 48
Cavaliere, 31
Franz, 17
81
82
INDEX
Fromm, 20
Kierren, 22
Kimouche, 25
Gómez Rodríguez, 39
King, 20
Gómez-Rodríguez, 18
Kis, 9
Gambardella, 52
Klinkhammer, 57
Garcia-Lekue, 52
Knudsen, 5, 78
Garhofer, 26, 80
Knupfer, 54
Garnica, 49
Koch, 62
Gavioli, 31
Koeble, 71
Generalov, 47
Kostov, 21
Gerber, 5, 78
Kotakoski, 37
Gierz, 6
Koudia, 50
Giovanelli, 50, 62, 65
Kröger, 58
Goldoni, 62
Kralj, 7, 46, 57, 64, 67, 73, 77
Gomez-Rodriguez, 79
Krasheninnikov, 37
González Herrero, 39
Krausert, 26
Gonzalez, 68
Ksari, 50, 65
Grüneis, 54
Grånäs, 5, 78
López, 41
Gragnaniello, 48
Lacovig, 21, 33
Greber, 8
Laerentz, 31
Grill, 31
Lamare, 30
Grioni, 20
Lançon, 66
Gutiérrez, 18
Landers, 30
Larciprete, 21, 33
Hämäläinen, 76
Lazic, 27, 60, 64, 67
Haarlammert, 56
Leicht, 26, 48
Haberer, 54
LeRoy, 11
Hammer, 5
Liang, 44
Hammerschmidt, 48
Liljeroth, 13, 76
Hapala, 29, 43
Lin, 65
Harju, 76
Link, 6
Hayn, 50
Lisi, 26, 59
Hemmi, 8
Liu, 10
Henning, 35
Lizzit, 21, 33
Herbig, 37
Locatelli, 25
Hlawenka, 53
Lopes, 35
Hofmann, 20
Louie, 15
Hohage, 44
Horn, 23
Müllen, 28, 44
Hussain, 15
Müller, 28
Huttmann, 40
Méndez, 41
IJäs, 76
Järvinen, 76
Jablan, 42
Jahn, 35
Jelinek, 29, 43, 68, 72
Jenichen, 35
Johannsen, 20
Jolie, 46, 67
Jurdana, 73
Mårtensson, 47
Maccherozzi, 50
Magaud, 30, 36, 66
Malterre, 22
Mammadov, 20
Marchenko, 53, 61
Mariani, 26, 31, 59
Marsoner Steinkasserer, 48
Martín-Gago, 41
Martínez Galera, 39
Martínez-Galera, 18, 40
Köhler, 6
Martin Gago, 29, 68, 72
Kaelin, 8
Martin-Recio, 79
Kampen, 23
Martinez, 41, 72
Kawakami, 27, 60
Martinez-Galera, 79
83
INDEX
Massimi, 31
Raidel, 20
Matsui, 8
Ralko, 66
Menzel, 21
Redinger, 26, 80
Merino, 29, 41, 68, 72
Rodrigo, 41
Meunier, 44
Rodriguez-Manzo, 34
Michely, 5, 24, 37, 40, 46, 57, 64, 70, 78
Roth, 8
Miksic Trontl, 67
Rudolf, 56
Milun, 64
Rueux, 28, 44
Miranda, 49, 58
Ruini, 12, 44
Mitrano, 6
Runte, 57, 64
Mittendorfer, 26, 80
Miwa, 20
Söde, 44
Molina-Sánchez, 58
Sadowski, 64, 77
Molinari, 12, 44
Salomon, 62
Montagnese, 56
Sanchez-Barriga, 53, 61
Moras, 26, 80
Sanchez-Portal, 52
Moreno Ugeda, 39
Sanchez-Sanchez, 28
Mugarza, 52
Santos, 25
Mutombo, 29, 43
Savoyant, 50
Schnadt, 5
Ohresser, 50
Schröder, 78
Oliveira, 35
Schulte, 5, 78
Olle, 52
Schumacher, 64
Ondracek, 29, 43
Schumann, 35
Orlando, 33
Seyller, 20
Osterwalder, 8
Shen, 15
Otero, 50
Sheverdyaeva, 26, 80
Ourdjini, 31
Shi, 15
Ovcharenko, 23
Shikin, 19
Shinde, 74
Pérez, 39, 41
Siber, 77
Pacilé, 26, 59
Sicot, 22
Pan, 64
Simon, 37
Papagno, 26, 80
Simonov, 47
Parmigiani, 20
Sipahi, 27, 60
Passerone, 74
Sokcevic, 64
Paulus, 48
Solja£ic, 42
Pervan, 64, 67
Spadafora, 43
Petaccia, 62
Springate, 6, 20
Petersen, 6
Srut Rakic, 64, 67
Petrovic, 46, 57, 77
Stöhr, 6
Pettaccia, 54
Standop, 24
Pignedoli, 28, 44, 74
Starke, 6
Pinardi, 41
Stauber, 18
Pletikosic, 64
Stierle, 17
Plodinec, 73
Stratmann, 5
Poelsema, 69
Struzzi, 54
Polman, 17
Sutter, 4
Pou, 39, 41
Svec, 29, 43, 68, 72
Prakash, 65
Preobrajenski, 47
Talirz, 28, 44
Prezzi, 12, 44
Telychko, 43
Puster, 34
Tesch, 48
Themlin, 50, 62, 65
Qiu, 15
Rader, 53, 61
Thissen, 23
Troeppner, 71
INDEX
Uder, 71
Ugeda, 15
Ulstrup, 20
Usachov, 54, 63
Vázquez de Parga, 49
Valla, 64
van Gastel, 69
van Loosdrecht, 56
Varykhalov, 53, 61
Vasseur, 22
Verbitskiy, 54
Vilkov, 54, 63
Vinogradov, A., 47
Vinogradov, N., 47
Vita, 23
Vlaic, 25
Vlieg, 17
Voloshina, 23, 48, 56
Vonk, 17
Vyalikh, 63
Wang, 12, 15, 44
Wehling, 14, 40, 64
Winter, 56
Wirtz, 58
Woord, 35
Zacchigna, 20
Zacharias, 56
Zagrebina, 47
Zandvliet, 69
Zeppenfeld, 44
Zhang, 15
Zielke, 26, 48
Zimmermann, 70
Zutic, 27, 60
84
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