Graphene: The First Studies of its
Formation Structure and Energetics
Formation,
Jack Blakely, MSE, Cornell
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Single crystal surfaces, mainly Ni but also Pt,Pd,Co
Formation of surface carbon layers by near-equilibrium segregation
Characterization of monolayer
y and multilayer
y graphite
g p
by
y electron
spectroscopy and low energy electron diffraction
Monolayer graphite formation as a phase transition
Range of stability of the graphene monolayer before multilayer
formation
Binding energies of carbon in the different surface states
Interplay between surface morphology (steps,facets) and adsorbed
carbon
Step-free substrates for graphene support
SiO2 , Al2O3
Some references to early Cornell work on Carbon layer formation
on Metals
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"Electron Energy Losses in Thin Graphite Layers", H.R. Patil and J.M.Blakely, J.C Shelton, J.
Appl. Phys. 9, 3806 (1974).
"Equilibrium Segregation of Carbon to a Nickel (111) Surface: A Surface Phase Transition",
J.C. Shelton, H.R. Patil and J.M. Blakely, Surface Science 43, 25 (1974).
"Equilibrium Adsorption and Segregation", J.M. Blakely and J.C. Shelton, review article
published in "Surface Physics of Materials", edited by J.M. Blakely, Academic Press (1975).
"Binding Energies of Carbon to Ni (100) from Equilibrium Segregation Studies"
Studies", L
L.C.
C Isett and
J.M. Blakely, Surface Science 47, 645 (1975).
"Binding of Carbon Atoms at a Stepped Nickel Surface", L.C. Isett and J.M. Blakely, J. Vac.
Sci. Tech. 12, 237 (1975).
"Segregation Isosteres for Carbon at the (100) Surface of Nickel", L.C. Isett and J.M.
Blakely,
y, Surface Science 58,
, 397 (1976).
"Structure of the Gas-Solid Interface", J.M. Blakely, in proceedings of the Darken
Conference: Physical Chemistry in Metallurgy (1976).
"Reconstruction of Stepped Nickel Surfaces", H.V. Thapliyal and J.M. Blakely, J. Vac. Sci.
Tech. 15, 600 (1978).
"Carbon Layer Formation on the Pt(111) Surface as a Function of Temperature", J.C. Hamilton
and J.M. Blakely, J. Vac. Sci. Tech. 15, 559 (1978).
"Segregation to Surfaces: Dilute Alloys of the Transition Metals, J.M. Blakely, CRC Critical
Reviews in Solid State Sciences and Materials Sciences, Nov. (1978), p. 333.
"Structure and Phase Transitions of Segregated Surface Layers", J.M. Blakely and H.V.
Thapliyal, in Interfacial Segregation, A.S.M. (1978).
"Carbon Monolayer Phase Condensation on Ni(111)"
Ni(111)", M
M. Eizenberg and J.M.
J M Blakely
Blakely, Surface Sci
Sci.
82, 228 (1979).
"Surface Carbon Segregation in Dilute Alloys of Pt, Pd and Co", J.C. Hamilton and J.M.
Blakely, Surface Science 91, 199 (1980).
"Carbon Interaction with Ni Surfaces: Monolayer Formation and Structural Stability", M.
g and J.M.Blakely,
y J. Chem. Phys.
y
71, 3467 (1979).
Eizenberg
"Morphology and Composition of Crystal Surfaces", Chapter 1, Vol. 1 of Chemical Physics of
Solid Surfaces and Heterogeneous Catalysis, edited by D.P. Woodruff and D.A. King (1981).
"Estimating the Density of Carbon Atoms on a Ni Catalyst Surface in Equilibrium with a Carbonaceous Gas", R. Ramanathan and
J.M. Blakely, Appl. Surf. Sci., 29, 427 (1987).
Various graphite-related forms of carbon.
Figure from Geim & Novoselov 2010
Carbon-carbon
bond energy is
~2.5eV,
spacing~0.12nm
i
0 12
and not very
sensitive to small
displacements
normal to basal
plane
Distance
between (0001)
planes in
graphite is
~0.35nm
Some of the methods to make and characterize graphene
• Cleavage of 3D graphite
• Reduction of graphitic oxide
C8O2(OH)2 (intercalated
graphite)
• Decomposition of SiC
• Segregation from solid or
liquid metals containing
dissolved carbon
• Decomposition of hydocarbon
or other carbon containing gas
• Challenge to identify graphene
or thin graphite layers
• Optical reflection from graphene
on SiO2
• Raman microscopy, graphene
and multilayer graphite have
different characteristic spectra
• Secondary electron
spectroscopy…Auger,
p
py
g , ARUPS
etc
• Electron and X-ray diffraction
Relationship between equilibrium adsorption and
eq ilibri m segregation from solid/liq
equilibrium
solid/liquid
id sol
solution
tion
On Ni(100) the low carbon coverage region shows
Langmuir type of behavior
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Data on Ni
surfaces shown
here is for low
carbon coverages
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Data on Fe(100)
from Grabke et al
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Ni(100)6o[013] is
a stepped surface
vicinal to (100)
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Surfaces near
Ni(111) do not
show this smooth
variation of
carbon
concentration with
temperature
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"Segregation Isosteres for
Carbon at the (100) Surface
of Nickel", L.C. Isett and
J.M. Blakely, Surface
Science 58, 397 (1976).
Segregation Isosteres for low carbon coverage region
on Ni(100)
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The fractional coverage, θ,
is normalized to 1/4
monolayer.
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At carbon coverages on
Ni(100) below ~1/4
monolayers the variation of
coverage with temperature
is gradual
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By using a range of bulk
doping levels to vary the
carbon chemical potential
isosteres can be
constructed and give a heat
of segregation to (100)
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"Segregation Isosteres for Carbon
at the (100) Surface of Nickel",
L.C. Isett and J.M. Blakely, Surface
Science 58, 397 (1976).
Variation of carbon concentration as a function of
temperature on Ni(111) due to segregation
The surface monolayer phase, graphene, has a range of stability of ~ 100K
around ~1100K
"Equilibrium Segregation of Carbon to a Nickel (111) Surface: A Surface Phase Transition", J.C. Shelton, H.R. Patil and J.M. Blakely, Surface
Science 43 25 (1974)
Model of graphene as an epitaxial carbon layer
on the Ni(111) surface.
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From LEED patterns and
quantitative Auger spectroscopy
the overlayer is identified as
p(1x1)C
(1 1)C2
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The lattice mismatch between
(
) and g
graphite
p
((0001)) is <
Ni(111)
1%
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Without extensive analysis of the
variation of diffracted intensities
versus electron energy the exact
lateral and vertical positions of the
carbons is not well defined
defined.
Carbon Binding Energies in and on Ni crystals
Note the small fractional change for different sites
sites.
p(1x1)C2 on Ni(111) is graphene
"Binding Energies of
Carbon to Ni (100) from
Equilibrium Segregation
Studies", L.C. Isett and
J.M. Blakely,
y, Surface
Science 47, 645 (1975).
"Structure and Phase
Transitions of Segregated
Surface Layers",
J M Blakely and
J.M.
H.V. Thapliyal, in
Interfacial Segregation,
A.S.M. (1978).
Dependence of the temperature of formation and range of stability of the
graphene phase on the doping level of the Ni(111) crystal
"Carbon Monolayer Phase Condensation on Ni(111)", M. Eizenberg and J.M. Blakely, Surface Sci. 82, 228 (1979).
Dependence of the graphene formation temperature and
range of stability on the orientation or step structure of the
Ni substrate
The formation of graphene is accompanied by facetting to expose {111} planes
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Data for Ni surfaces along the [110] zone
"Carbon Interaction with Ni Surfaces: Monolayer Formation and Structural Stability", M. Eizenberg and J.M.Blakely, J. Chem. Phys. 71, 3467
(1979).
Carbon Segregation to Ni surfaces of various
orientations
Formation of the graphite monolayer phase seems to be insensitive to
the orientation of the Ni substrate.
"Carbon Interaction with Ni Surfaces: Monolayer Formation and Structural Stability", M. Eizenberg and J.M.Blakely, J. Chem. Phys. 71, 3467 (1979).
Electron diffraction from stepped surfaces
shows splitting of reflections corresponding to the average inter-step
spacing. Segregation of carbon at low coverages causes a pairing or
clustering of the steps.
"Reconstruction
of Stepped
Nickel
Surfaces",
H.V. Thapliyal
and
J.M. Blakely,
J. Vac. Sci.
Tech. 15, 600
(1978).
Segregation of Carbon to surfaces of different
materials
Pt, Pd, Co
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Surfaces studied included Pt(100),
Pd(100), Pd(111)and Co(0001)
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Pd(100), Pd(111) and Co(0001) all
exhibited the formation of a
monolayer graphite (graphene)
phase;
h
similar
i il to Ni(111)
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Pt(100) showed no signification
carbon accumulation before the
onsett off multilayer
ltil
graphite
hit
formation.
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These results are consistent with
th Ni d
the
data
t and
d again
i suggestt th
thatt
the exact orientation of the
substrate has little effect on the
quasi-equilibrium formation of the
graphene phase.
phase
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"Surface Carbon Segregation in Dilute Alloys of Pt,
Pd and Co", J.C. Hamilton and J.M. Blakely, Surface
Science 91, 199 (1980).
Occurrence of the graphene phase of carbon on Ni
surfaces
f
is
i iinsensitive
iti tto th
the exactt Ni orientation
i t ti
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The morphology and transport properties of graphene formed on
Ni surfaces that are atomically rough or have atomic steps or
facets may be different from that formed on flat (111)
Ranges of stability of different carbon states on Ni(111) surfaces in
equilibrium with dissolved C from our data.
The corresponding ranges for coexistence with CO/CO2 and CH4/H2 gas
mixtures are calculated using the data.
Typical Atomic Step Array on a Surface Vicinal to Si(001)
Step
Terrace
2x1
1 x2
2x1
"STM Studies of Phase Separation on Si(100) Surfaces with Periodic Step Arrays", C.C. Umbach, M.E. Keeffe, and J.M.
Blakely,J. Amer Vac. Soc.,B9,721,(1991).
Making Step-free substrates
1
Growth of Si on Mesa Structures using
Energetic Beam of Si2H6
In this work the trench width and depth were
2μm and 0.5μm respectively, with the mesa
edge dimensions being 2
2, 4
4, 8
8,12
12 and 24μm
24μm.
"A Growth Method for Creating
Arrays of Atomically Flat Mesas on
Silicon", Doohan Lee
Silicon
Lee, Jack Blakely
Blakely,
Todd W. Schroeder and J. R.
Engstrom, Applied Physics Letters,
78,1349, (2001).
Formation of arrays of step-free mesas on Si(111)
due to Si deposition in the ‘step-flow’
step flow growth regime
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Doohan Lee, Jack Blakely, Todd Schroeder and Jim Engstrom, Appl. Phys. Lett.,78,1349, (2001)
Patterned Si Surface used as starting structure for producing
large Atomically Flat Areas by the Sublimation Method
L1 = 2-50 microns
L2 = 1 micron
Ridges ~ 1micron high
"Atomic Step Distributions on Annealed Periodic Si(001) Gratings, So Tanaka, C.C. Umbach, Jack Blakely, Ruud Tromp and Marion Mankos, J. Vac. Sci.
Technol. A, 15, p. 1345-1350 (1997).
"Formation and Stability of Large Step-free Areas on Si(001) and Si(111), Doohan Lee and Jack Blakely, Surface Science,445,32,(2000).
Removal of Steps by Flow into the ridges
step
bunch
evaporated
atoms
g
single
step
•Steps flow into ridges and become pinned
p nucleated
•No new steps
Allows surfaces to be prepared with up to 50μm x 50μm step free areas
Capacitor Structures formed both on Step-Free Areas
between the Ridges and on ‘normal’ stepped wafer
surface
Valerian Ignatescu and Jack.M. Blakely, ""Leakage currents through thin silicon oxide grown on atomically flat silicon surfaces"", MRS Proceedings, 849, KK7.11.1(2005).
Comparison of Stepped Surface Morphology
Before/After Oxidation
Upper: before oxidation
Lower: after oxidation
~7nm oxide thickness
5μm
5μm
Steps did not move significantly during oxidation!
"Surface and Interfacial Morphology of Oxides on Si(111) with Ultra-Low Atomic Step Density", Antonio Oliver and Jack
Blakely, JVST B, 18, 2862, (2000)
Formation of step-free mesas on Al2O3(0001) by
g temperature
p
annealing
g only
y
high
• The dynamics of the step motion controlled by a balance of surface
diffusion and evaporation rates
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Kee-Chul Chang, Doohan Lee, Christopher Umbach and Jack Blakely,. "Scanning Probe Microscopy of Atomically
Engineered Silicon and Sapphire Surfaces" in Microscopy of Semiconducting Materials, Inst. Physics Conferences
#180, UK, 637-640, (2004).
Occurrence of the graphene phase of carbon on Ni
surfaces
f
is
i iinsensitive
iti tto th
the exactt Ni orientation
i t ti
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The morphology and transport properties of graphene formed on
Ni surfaces that are atomically rough or have atomic steps or
facets may be different from that formed on flat (111)