pubs.acs.org/JPCL
Structure and Epitaxial Registry on Graphite of a Series of
Nanoporous Self-Assembled Molecular Monolayers
ger,† Ludovic Douillard,§
Claire Arrigoni,§,† Guillaume Schull,§,‡ David Ble
§
C
eline Fiorini-Debuisschert, Fabrice Mathevet,† David Kreher,† Andr
e-Jean Attias,*,† and
Fabrice Charra*,§
§
Nanophotonics Laboratory, Service de Physique et Chimie des Surfaces et Interfaces, IRAMIS, CEA, F-91191 Gif-sur-Yvette
Cedex, France, †Laboratoire de Chimie des Polym
eres;UMR7610, Universit
e Pierre et Marie Curie, 4 place Jussieu, case 185,
75252 Paris Cedex 05, France, and ‡Institut de Physique et de Chimie de Strasbourg, Universit
e Louis Pasteur, CNRS UMR 7504,
23 rue du Loess, 67034 Strasbourg, France
ABSTRACT We have analyzed by STM the detailed structures of a series of
nanoporous honeycomb networks stabilized by alkyl chain interdigitation on
graphite at the liquid-solid interface, that is, clip-like noncovalent bonding. The
variations observed as a function of the length of the peripheral aliphatic chains
show that the assembly is directed not only by lateral intermolecular interactions
but also by the adsorption site on the substrate. We derive an atomically accurate
model for the registry with graphite of our nanoporous model series of systems. In
full agreement with the quantitative model, the pore areas vary step-by-step by
more than one order of magnitude along the whole series while preserving the
detailed features of the graphite-induced alkyl chain interdigitation. The largest
pores observed correspond to a ratio of uncovered substrate area as large as 35%.
SECTION Surfaces, Interfaces, Catalysis
M
exploitation of these properties. From the structure of the
above-mentioned network (Figure 1), one may anticipate that
varying the length of peripheral alkyl chains will result in
changes of pore dimensions. Yet, although the influence of the
substrate is seldom considered in interpreting self-assembled
molecular structures, in the present case, the core role of
HOPG on clip formation requires a more careful account of
the substrate. In the above series of molecules, the step-bystep variation of alkyl chain lengths offers a unique opportunity to analyze the influence of adsorbate-adsorbent interactions.
In this paper, we analyze the evolution of the epitaxial
relationships of nanoporous networks formed on HOPG by
interdigitation of alkyl side-chains with various lengths. We
show that the molecular lattices stay in registry with HOPG
following a common atomically accurate model while pore
areas vary by more than one order-of-magnitude.
Molecules of 1,3,5-tristyrylbenzene substituted by alkoxy
peripheral chains presenting n = 6, 8, 10, 12, or 14 carbon
atoms (TSB3,5-Cn; see Figure 1) were deposited on the HOPG
surface. They have been synthesized and purified by adapting
the procedure described in the literature,26 using the corresponding 3,5-dialkyloxybenzaldehydes. The solvent was 1-phenyloctane (98%, Aldrich), which is well suited for in situ scanning
tunneling microscopy (STM) because it is hydrophobic, highly
olecular self-assembly is a promising route for the
bottom-up manufacturing of nanostructures on
atomically flat surfaces1. The mechanisms of molecular self-organization have been the subject of numerous
investigations aimed at the realization of building blocks
designed so as to spontaneously form 2D monolayers with
specific topologies. Intermolecular interaction may be driven
by various molecular recognition processes, from steric hindrance 2,3 to hydrogen bonding,4-9 metal coordination, 10-13
or interdigitation of alkyl chains, 14-16 The latter may be
strongly favored by adsorption on the surface of highly
oriented pyrolytic graphite (HOPG). As a matter of fact, the
value of the alkyl-chain period allows an adsorption in registry
with HOPG along its Æ1,0,0æ axis according to the Groszek
model.17-20 It has been noticed that the distance which
minimizes the energy of side interaction between alkyl
chains, 4.26 Å, exactly matches a period of Æ1,0,0æ rows.20
Thus, molecular moieties able to “clip” together by interdigitation on HOPG have been designed by finely adjusting the
lateral distance between chains.15
Among the various geometries based on alkyl chain clips
demonstrated so far at the solution-solid interface,15,21 one22
forms a nanoporous matrix, a generic structure which currently attracts strong interest.23 This specific nanoporous
system presents intriguing molecular sieve and dynamic
properties.22,24,25 The structure of its building block molecule
is represented in Figure 1 together with the honeycomb
structure that it forms. The possibility to finely tune the pore
dimensions constitutes a prerequisite toward the control and
r 2009 American Chemical Society
Received Date: October 15, 2009
Accepted Date: November 9, 2009
Published on Web Date: November 13, 2009
190
DOI: 10.1021/jz900146f |J. Phys. Chem. Lett. 2010, 1, 190–194
pubs.acs.org/JPCL
Figure 1. Molecular formula and structure of the self-assembly on HOPG. Left: molecular formula of TSB3,5-Cn. R represents the alkyl
chain -CnH2nþ1. For the studied molecules n = 6, 8, 10, 12, or 14. Middle: example of a self-assembled monolayer as observed by STM at the
solid-liquid interface for n = 10. The scanned area, within a single domain, is 70 nm 70 nm. Right: scheme of alkyl chain interdigitation as
observed for the case of n = 10.22 Two pores are separated by four interdigitated alkyl chains forming the so-called clip structure.15
alkyl chain lengths. In each case, only two kinds of domains
are formed, displaying mirror-symmetric STM images. Specifically, it can be observed that, depending on the orientation
of the domain, two neighboring molecules are tilted either
both clockwise or both counterclockwise with respect to the
axis defined by the pair of molecule centers. The angles
formed by the unit cell axes of two domains of opposite lefthanded and right-handed orientations grown on the same
terrace are shown in Figure 2 for TSB3,5-C6, TSB3,5-C8, and
TSB3,5-C10 and reported below their respective images.
TSB3,5-C12 is a specific case where both types of domains
have the same direction, within experimental uncertainties
(0.8). A thorough observation of STM images of the unit cell
still permits one to discern two distinct mirror-symmetric
variants of domains, their unit cell axes being parallel one to
the other. Thus, the angle θ between the two sets of domains
varies uniformly from 23.6 (TSB3,5-C6) to 0 (TSB3,5-C12). In
the case of TSB3,5-C14, the only operational deposition
procedure, employing the lowest concentration and high
substrate temperature during the self-assembly, yields very
large single domains occupying entire terraces. Then, the
angle can not be reproducibly measured, but the two sets of
mirror-symmetric domains are still observed. The measured
lattice parameters, that is, the unit cell dimensions a and the
angles θ, are reported in Figure 2.
The qualitative features of self-assembled monomolecular
layers can often be explained solely in terms of intermolecular
interactions, the substrate contribution to lateral order being
limited to the interplay between coverage maximization and
steric hindrance. Yet, the existence of fixed lattice orientations, observed even for disjoined domains, can only be
explained by interactions with the underlying HOPG substrate. To understand quantitatively the structure of the
molecular assembly, an important point is whether the
above-described lattice variations with alkyl chain length are
governed only by intermolecular distances or are quantified
by conditions of registry of the molecular lattice with HOPG.
To address this question, let us assume an optimal registry
with the substrate. This means that all molecules are adsorbed
in the same, most stable, geometry relative to the surface of
the HOPG substrate. This hypothesis is consistent with the
high similarity between STM images of different molecules,
insulating, and poorly volatile. The substrate was a freshly
cleaved HOPG (Goodfellow). The self-assembled monolayers
formed from TSB3,5-C6, TSB3,5-C8, and TSB3,5-C10 were
deposited from 10-3 to 10-4 mol 3 L-1 solutions immediately
after cleaving the substrate and were then imaged by STM.
Special care must be taken for the deposition of TSB3,5-C12 and
TSB3,5-C14, which result in large pores and thus low-density
monolayers. Solutions with lower concentration were then used
(10-5 to 10-6 mol 3 L-1) to avoid formation of alternate denser
networks 27. Moreover, those solutions were deposited onto
gently heated substrates (60 C) before the system was progressively cooled down to room temperature for STM observation. In
turn, this method happens to favor the formation of large
domains. As an example, a typical large-area image of a selfassembled monolayer is presented in Figure 1. By applying the
above procedure, domains larger than typically 100 nm were
routinely observed. The tips used for STM imaging were mechanically formed in a 250 μm Pt-Ir wire (Pt80/Ir20, Goodfellow). The STM was a homemade fully digital system. The
images reported here were obtained in the current mode, with
slow height regulation, at a sample bias of ∼-1000 mV and
tunnel current set points in the range of 3-17 pA. The scan angle
was adjusted in such a way as to keep the fast-scan axis nearly
perpendicular to the sample slope. Images acquired simultaneously in forward and backward fast-scan directions were
systematically recorded and compared. All images were corrected by homemade software for the drift of the instrument,
which was evaluated by correlating successively acquired
images with the opposite slow-scan direction. For angle measurements between domains, a hexagonal lattice with 60
angles between the lattice directions was assumed. Then, the
combination of the measurements with the three axes, together
with averaging over all domains present in the image, permitted
accuracies of typically 0.5.
For molecules comprising both aliphatic and conjugated
parts, the conjugated moieties appear much brighter in STM
images. On the basis of the observation of the star-shaped
conjugated cores, it appears that each of the five molecules
self-assembles on HOPG, forming large domains of honeycomb network (see Figure 2). The unit cells appear to have
hexagonal symmetry. Their parameters evolve monotonously
from 3.1 (TSB3,5-C6) to 4.5 nm (TSB3,5-C14) with increasing
r 2009 American Chemical Society
191
DOI: 10.1021/jz900146f |J. Phys. Chem. Lett. 2010, 1, 190–194
pubs.acs.org/JPCL
Figure 2. Analysis of molecular lattice evolution with increasing alkyl chain lengths from -C6H13 to -C14H29. Row 1: alkyl chain formula.
Row 2: selected STM images showing mirror-symmetric domains imaged simultaneously. For easier comparison, the five images have been
clipped to represent the same dimensions, 26 nm 26 nm. The domain boundaries are highlighted by dotted lines. In each case, one lattice
direction on each domain is superimposed to the image, and the angle that they form is represented. Row 3: measured lattice parameters,
distance a, and angle 2θ between domains (in parentheses, theoretical values from the model depicted in Figure 3; see text for discussion).
Row 4: epitaxial relationship with HOPG. The period is represented as a green arrow in STM images of the second row. Last row:
representation of pore dimension and diameter of the largest circle circumscribed to the van-der-Waals spheres of frontier H atoms (see text
for discussion). This circle is also reported in green in the STM images of the second row.
exactly matches the series of possible periods displayed in
Figure 3b. This series of lattice vectors is fully consistent with
the molecular model depicted in Figure 3a extrapolated to the
other chain lengths. Specifically, it allows preservation of both
the Groszek-type adsorption of the alkyl chains and their
“clip”-like interdigitation over the whole series. The lattice
epitaxial relation with HOPG follows the general form [(91 þ
15n þ 3n2)1/2 (91 þ15n þ 3n2)1/2Rθ] and tan θ = 31/2[(n - 6)/
(3n þ 16)], where n is the number methylene pairs in the alkyl
chain (from n = 3 for TSB3,5-C6 to n = 7 for TSB3,5-C14). The
corresponding data are reported in Figure 2 below each STM
image. Notice that the angle between the lattice vectors of
mirror-symmetric domains is 2θ. The agreement between
experimental and theoretical data fully confirms the principles
developed here.
The agreement with the model of epitaxial adsorption
enables a derivation of the pore dimensions as a function of
the chain length. As reported in Figure 2 (last row), the
diameter (respectively area) of the circumcircle of the pores
increases monotonously from 0.62 (0.30 nm2) to 2.31 nm
(4.2 nm2) from TSB3,5-C6 to TSB3,5-C14. The ratio of the
HOPG area not covered by molecules also increases, from
∼5% for TSB3,5-C6 up to ∼35% for TSB3,5-C14. In the latter
case, the energy cost corresponding to the lack of molecule
adsorption on a considerable proportion of the available
substrate surface explains the difficulty in forming the layer
and the necessity of a thorough control of the thermodynamics and kinetics of the self-assembly process.
Finally, the observation that the molecule adsorption
strictly preserves the Groszek model structure for alkyl chain
interaction with HOPG further supports the role of the so-called
including between those having different orientations. As a
matter of fact, it has been predicted28,29 and observed30,31 that
the appearance in STM images of such graphene-like conjugated structures changes considerably with the adsorption
site. This imposes a six-fold rotation invariance around the
center of a pore, for both the molecular layer and the topmost
atomic layer of the HOPG substrate. The molecular pores are
thus necessarily centered over alveoli of HOPG as sketched in
Figure 3a (points labeled C6). Notice however that, if one
accounts for the second underlying atomic layer, the six-fold
symmetry is broken and reduced to a three-fold rotation
invariance. Then, two molecules rotated by 60 cannot be
strictly equivalent. The stability of the adsorption is however
governed mainly by interactions with the substrate surface,
which justifies considering only one atomic layer of HOPG.
Similarly, the centers of the molecules correspond to a
three-fold symmetry axis of the molecular layer (points
labeled C3 in Figure 3) and are thus necessarily aligned on
at least a three-fold symmetry axis of HOPG. There are three
possible such situations, represented below Figure 3a
(referred to as C3-1, C3-10 , and C3-2). Each type corresponds to a different adsorption geometry and stability of the
molecule. If we still assume that the molecules systematically
arrange themselves so as to adopt the most stable one, then
this point must remain of the same type when varying the
length of the alkyl chains. This quantifies and reduces the
possible periods of the lattice structures adopted for the
various lengths, as shown in Figure 3b in the case of a C3-1
type. A detailed examination of the few possibilities thus left
shows that the experimentally observed series of lattice
parameters and angles between mirror-symmetric domains
r 2009 American Chemical Society
192
DOI: 10.1021/jz900146f |J. Phys. Chem. Lett. 2010, 1, 190–194
pubs.acs.org/JPCL
AUTHOR INFORMATION
Corresponding Author:
*To whom correspondence should be addressed. E-mail: andre-jean.
[email protected]. Phone: þ33/144275302. Fax: þ33/144277089
(A.-J.A.); E-mail: [email protected]. Phone: þ33/169089722.
Fax: þ33/169088446 (F.C.).
REFERENCES
(1)
(2)
(3)
(4)
(5)
Figure 3. Epitaxial relationship with HOPG. (a) Close-up showing
the molecular positioning relative to HOPG (superimposed light
gray chicken wire). For clarity, the case of shorter chains, TSB3,5C6, has been represented. One lattice vector connecting two C6
points is represented (solid arrow). Two vectors connecting C6 and
C3 points are also represented (dotted arrow). By symmetry, they
must form a 120 angle and have the same lengths. (b) Variations
of the lattice vector with chain length, from TSB3,5-C6 to TSB3,5C14, constrained by the preservation of the nature of the C3 point
relative to HOPG. (Here a C3-1 type). The mirror-symmetric
lattice is also represented in the upper part, showing the variations
of the angle between simultaneously observed domains. In all
schemes, the centers of molecular pores, forming six-fold symmetry axes, are labeled C6. The centers of the molecules are
analogously labeled C3.
(6)
(7)
(8)
clip structure on the organization of the molecular layer, up the
atomically accurate scale.
In conclusion, we have analyzed the detailed structures of a
series of nanoporous honeycomb networks formed by tristilbene derivatives on HOPG by STM at the liquid-solid interface. The variations observed as a function of the length of the
peripheral aliphatic chains shows that the assembly is directed not only by lateral intermolecular interactions, that is,
steric hindrance and chain interdigitation, but also by the
search for the most stable adsorption site on the substrate. We
have thus been able to derive an atomically accurate model
for the registry with HOPG of our nanoporous model series of
systems. The pore areas vary step-by-step by more than one
order of magnitude along the whole series, while preserving
the detailed features of the HOPG-induced alkyl chain interdigitation. The largest pores observed correspond to a ratio of
uncovered substrate area as large as 35%.
(9)
(10)
(11)
(12)
(13)
SUPPORTING INFORMATION AVAILABLE Direct com(14)
parison of the molecular lattice orientation and the HOPGÆ110æ
axis and derivation of the lattice epitaxial registry formula.
This material is available free of charge via the Internet at http://
pubs.acs.org.
r 2009 American Chemical Society
193
Barth, J. V. Molecular Architectonic on Metal Surfaces. Annu.
Rev. Phys. Chem. 2007, 58, 375–407.
Charra, F.; Cousty, J. Surface-Induced Chirality in a SelfAssembled Monolayer of Discotic Liquid Crystal. Phys. Rev.
Lett. 1998, 80, 1682–1685.
Furukawa, S.; Uji-i, H.; Tahara, K.; Ichikawa, T.; Sonoda, M.;
De Schryver, F. C.; Tobe, Y.; De Feyter, S. Molecular Geometry
Directed Kagome and Honeycomb Networks: Toward TwoDimensional Crystal Engineering. J. Am. Chem. Soc. 2006,
128, 3502–3503.
Lackinger, M.; Griessl, S.; Markert, T.; Jamitzky, F.; Heckl,
W. M. Self-Assembly of Benzene-Dicarboxylic Acid Isomers at
the Liquid Solid Interface: Steric Aspects of Hydrogen Bonding. J. Phys. Chem. B 2004, 108, 13652–13655.
Ciesielski, A.; Schaeffer, G.; Petitjean, A.; Lehn, J. M.; Samori,
P. STM Insight into Hydrogen-Bonded Bicomponent 1D
Supramolecular Polymers with Controlled Geometries at
the Liquid-Solid Interface. Angew. Chem., Int. Ed. 2009, 48,
2039–2043.
Wang, D.; Xu, Q.-M.; Wan, L.-J.; Wang, C.; Bai, C.-L. In Situ
Scanning Tunneling Microscopy Study of Adsorption of Diaza-15-crown-5 on Cu(111). Surf. Sci. 2001, 489, L568–L572.
Theobald, J. A.; Oxtoby, N. S.; Phillips, M. A.; Champness,
N. R.; Beton, P. H. Controlling Molecular Deposition and Layer
Structure with Supramolecular Surface Assemblies. Nature
2003, 424, 1029–1031.
Lackinger, M.; Heckl, W. M. Carboxylic Acids: Versatile Building Blocks and Mediators for Two-Dimensional Supramolecular Self-Assembly. Langmuir 2009, 25, 11307.
Payer, D.; Comisso, A.; Dmitriev, A.; Strunskus, T.; Lin, N.;
Woll, C.; DeVita, A.; Barth, J. V.; Kern, K. Ionic Hydrogen
Bonds Controlling Two-Dimensional Supramolecular Systems at a Metal Surface. Chem.;Eur. J. 2007, 13, 3900–3906.
Surin, M.; Samori, P.; Jouaiti, A.; Kyritsakas, N.; Hosseini,
M. W. Molecular Tectonics on Surfaces: Bottom-up Fabrication of 1D Coordination Networks That Form 1D and 2D
Arrays on Graphite. Angew. Chem., Int. Ed. 2007, 46, 245–249.
Langner, A.; Tait, S. L.; Lin, N.; Rajadurai, C.; Ruben, M.; Kern,
K. Self-Recognition and Self-Selection in Multicomponent
Supramolecular Coordination Networks on Surfaces. Proc.
Natl. Acad. Sci. U.S.A 2007, 104, 17927–17930.
Schlickum, U.; Decker, R.; Klappenberger, F.; Zoppellaro, G.;
Klyatskaya, S.; Ruben, M.; Silanes, I.; Arnau, A.; Kern, K.;
Brune, H..; et al. Metal-Organic Honeycomb Nanomeshes
with Tunable Cavity Size. Nano Lett. 2007, 7, 3813–3817.
Schlickum, U.; Decker, R.; Klappenberger, F.; Zoppellaro, G.;
Klyatskaya, S.; Auwarter, W.; Neppl, S.; Kern, K.; Brune, H.;
Ruben, M..; et al. Chiral Kagome Lattice from Simple Ditopic
Molecular Bricks. J. Am. Chem. Soc. 2008, 130, 11778–11782.
Tahara, K.; Furukawa, S.; Uji-I, H.; Uchino, T.; Ichikawa, T.;
Zhang, J.; Mamdouh, W.; Sonoda, M.; De Schryver, F. C.;
De Feyter, S..; et al. Two-Dimensional Porous Molecular Networks of Dehydrobenzo[12]annulene Derivatives via Alkyl
DOI: 10.1021/jz900146f |J. Phys. Chem. Lett. 2010, 1, 190–194
pubs.acs.org/JPCL
(15)
(16)
(17)
(18)
(19)
(20)
(21)
(22)
(23)
(24)
(25)
(26)
(27)
(28)
(29)
(30)
(31)
Chain Interdigitation. J. Am. Chem. Soc. 2006, 128, 16613–
16625.
Bleger, D.; Kreher, D.; Mathevet, F.; Attias, A. J.; Schull, G.;
Huard, A.; Douillard, L.; Fiorini-Debuischert, C.; Charra, F.
Surface Noncovalent Bonding for Rational Design of Hierarchical Molecular Self-Assemblies. Angew. Chem., Int. Ed.
2007, 46, 7404–7407.
Miyake, K.; Hori, Y.; Ikeda, T.; Asakawa, M.; Shimizu, T.;
Sasaki, S. Alkyl Chain Length Dependence of the Self-Organized Structure of Alkyl-Substituted Phthalocyanines. Langmuir 2008, 24, 4708–4714.
Groszek, A. J. Selective Adsorption at Graphite/Hydrocarbon
Interfaces. Proc. R. Soc. London, Ser. A 1970, 314, 473.
Hentschke, R.; Schurmann, B. L.; Rabe, J. P. MolecularDynamics Simulations of Ordered Alkane Chains Physisorbed on Graphite. J. Chem. Phys. 1992, 96, 6213–6221.
Cyr, D. M.; Venkataraman, B.; Flynn, G. W. STM Investigations
of Organic Molecules Physisorbed at the Liquid-Solid Interface. Chem. Mater. 1996, 8, 1600–1615.
Watel, G.; Thibaudau, F.; Cousty, J. Direct Observation of
Long-Chain Alkane Bilayer Films on Graphite by Scanning
Tunneling Microscopy. Surf. Sci. 1993, 281, L297–L302.
Bleger, D.; Kreher, D.; Mathevet, F.; Attias, A. J.; Arfaoui, I.;
Metge, G.; Douillard, L.; Fiorini-Debuisschert, C.; Charra, F.
Periodic Positioning of Multilayered [2.2]ParacyclophaneBased Nanopillars. Angew. Chem., Int. Ed. 2008, 47, 8412–
8415.
Schull, G.; Douillard, L.; Fiorini-Debuisschert, C.; Charra, F.;
Mathevet, F.; Kreher, D.; Attias, A. J. Single-Molecule Dynamics in a Self-Assembled 2D Molecular Sieve. Nano Lett.
2006, 6, 1360–1363.
Elemans, J. A. A. W.; Feyter, S. D. Structure and Function
Revealed with Submolecular Resolution at the Liquid-Solid
Interface. Soft Matter 2009, 5, 721–735.
Schull, G.; Douillard, L.; Fiorini-Debuisschert, C.; Charra, F.;
Mathevet, F.; Kreher, D.; Attias, A. J. Selectivity of SingleMolecule Dynamics in 2D Molecular Sieves. Adv. Mater. 2006,
18, 2954–2955.
Schull, G.; Ness, H.; Douillard, L.; Fiorini-Debuisschert, C.;
Charra, F.; Mathevet, F.; Kreher, D.; Attiast, A. J. Atom Substitution for Marking and Motion Tracking of Individual
Molecules by Scanning Tunneling Microscopy. J. Phys. Chem.
C 2008, 112, 14058–14063.
Xu, S. D.; Zeng, Q. D.; Lu, J.; Wang, C.; Wan, L. J.; Bai, C. L. The
Two-Dimensional Self-Assembled N-Alkoxy-Substituted Stilbenoid Compounds and Triphenylenes Studied by Scanning
Tunneling Microscopy. Surf. Sci. 2003, 538, L451–L459.
Lei, S. B.; Tahara, K.; De Schryver, F. C.; Van der Auweraer, M.;
Tobe, Y.; De Feyter, S. One Building Block, Two Different
Supramolecular Surface-Confined Patterns: Concentration in
Control at the Solid-Liquid Interface. Angew. Chem., Int. Ed.
2008, 47, 2964–2968.
Sautet, P. Images of Adsorbates with the Scanning Tunneling
Microscope: Theoretical Approaches to the Contrast Mechanism. Chem. Rev. 1997, 97, 1097–1116.
Sautet, P.; Bocquet, M. L. Imaging Molecules with the Scanning Tunneling Microscope: A Theoretical Interpretation of
Benzene on Platinum. Isr. J. Chem. 1996, 36, 63–72.
Eremtchenko, M.; Schaefer, J. A.; Tautz, F. S. Understanding
and Tuning the Epitaxy of Large Aromatic Adsorbates by
Molecular Design. Nature 2003, 425, 602–605.
Umbach, E.; Glockler, K.; Sokolowski, M. Surface “Architecture” with Large Organic Molecules: Interface Order and
Epitaxy. Surf. Sci. 1998, 402-404, 20–31.
r 2009 American Chemical Society
194
DOI: 10.1021/jz900146f |J. Phys. Chem. Lett. 2010, 1, 190–194