Control of intermolecular bonds by deposition rates at room temperature: Hydrogen bonds versus metal coordination in trinitrile monolayers

Article abstract of DOI:10.1021/ja306834a

Self-assembled monolayers of 1,3,5-tris(4′-biphenyl-4″- carbonitrile)benzene, a large functional trinitrile molecule, on the (111) surfaces of copper and silver under ultrahigh vacuum conditions were studied by scanning tunneling microscopy and low-energy electron diffraction. A densely packed hydrogen-bonded polymorph was equally observed on both surfaces. Additionally, deposition onto Cu(111) yielded a well-ordered metal-coordinated porous polymorph that coexisted with the hydrogen-bonded structure. The required coordination centers were supplied by the adatom gas of the Cu(111) surface. On Ag(111), however, the well-ordered metal-coordinated network was not observed. Differences between the adatom reactivities on copper and silver and the resulting bond strengths of the respective coordination bonds are held responsible for this substrate dependence. By utilizing ultralow deposition rates, we demonstrate that on Cu(111) the adatom kinetics plays a decisive role in the expression of intermolecular bonds and hence structure selection.

Full text of DOI:10.1021/ja306834a

Article
pubs.acs.org/JACS
Control of Intermolecular Bonds by Deposition Rates at Room
Temperature: Hydrogen Bonds versus Metal Coordination in
Trinitrile Monolayers
Thomas Sirtl,†,‡ Stefan Schlogl,†,‡ Atena Rastgoo-Lahrood,†,‡ Jelena Jelic,§ Subhadip Neogi,∥
̈
Michael Schmittel,∥ Wolfgang M. Heckl,†,‡,⊥ Karsten Reuter,§ and Markus Lackinger*,‡,⊥
†Department of Physics, Technische Universitat Munchen, James-Franck-Str. 1, 85748 Garching, Germany
̈
̈
‡Center for NanoScience (CeNS), Schellingstr. 4, 80799 Munich, Germany
§Department of Chemistry, Technische Universitat Munchen, Lichtenbergstr. 4, 85747 Garching, Germany
̈
̈
∥Center of Micro- and Nanochemistry and Engineering, Organische Chemie I, Universitat Siegen, Adolf-Reichwein-Str. 2, 57068
̈
Siegen, Germany
⊥Deutsches Museum, Museumsinsel 1, 80538 Munich, Germany
S
* Supporting Information
ABSTRACT: Self-assembled monolayers of 1,3,5-tris(4′-
biphenyl-4″-carbonitrile)benzene, a large functional trinitrile
molecule, on the (111) surfaces of copper and silver under
ultrahigh vacuum conditions were studied by scanning
tunneling microscopy and low-energy electron diffraction. A
densely packed hydrogen-bonded polymorph was equally
observed on both surfaces. Additionally, deposition onto
Cu(111) yielded a well-ordered metal-coordinated porous
polymorph that coexisted with the hydrogen-bonded structure.
The required coordination centers were supplied by the adatom gas of the Cu(111) surface. On Ag(111), however, the well-
ordered metal-coordinated network was not observed. Differences between the adatom reactivities on copper and silver and the
resulting bond strengths of the respective coordination bonds are held responsible for this substrate dependence. By utilizing
ultralow deposition rates, we demonstrate that on Cu(111) the adatom kinetics plays a decisive role in the expression of
intermolecular bonds and hence structure selection.
cycles (e.g., pyridine or other azines) or nitriles are among the
favored neutral ligands.2,5,9,10 In contrast to thiol and carboxyl
groups, where the formation of metal-coordinated networks
requires additional thermal activation,2,6,8 nitrile coordination is
readily observed at room temperature with an onset around
180 K.3
For many correspondingly functionalized molecules, the type
of intermolecular bond can be changed by supplying
coordination centers. A good example therefore are dinitriles
on Ag(111).5,9,11−13 Additional deposition of cobalt atoms
induces a change from hydrogen bonding to metal coordina-
tion, accompanied by structural reorganization.
Besides temperature, the competition between molecular flux
onto the surface and diffusion on the surface can also play a
decisive kinetic role in determining the structure. An
experimental example is given by Li and Lin,14 who observed
structurally different pyridyl−porphyrin monolayers upon
variation of the deposition rate. However, all of these structures
were stabilized by the same type of intermolecular bond (i.e.,
INTRODUCTION
■
Self-assembled organic monolayers are promising candidates
for the development of novel materials with tremendous
options.1 Many of their properties decisively depend on the
type of intermolecular bond that stabilizes the monolayer.2 The
bond type is mostly predetermined by functionalization but
may additionally be influenced by kinetic effects. For instance,
temperature can affect structure formation because of activation
barriers.3,4 Among the different non-covalent intermolecular
bonds that can stabilize monolayers, not only is metal
coordination the strongest,5 but thiolate−copper coordination
bonds, for example, can also offer strong intermolecular
electronic coupling as required for molecular electronic
applications.6
Formation of metal-coordination bonds requires both
electron-donating ligands and metal centers. For surface-
supported systems, the latter can be supplied either by metal
deposition or by the adatom gas of a metal surface. Deposition
of extrinsic metal centers facilitates chemical variability, while
network formation with intrinsic metal centers offers facile
preparation. Carboxylates and thiolates are suitable anionic
ligands for coordinative bonds,2,6−8 while nitrogen in hetero-
Received: July 13, 2012
Published: December 18, 2012
© 2012 American Chemical Society
691
dx.doi.org/10.1021/ja306834a | J. Am. Chem. Soc. 2013, 135, 691−695

Journal of the American Chemical Society
Article
copper coordination), and no change of bond type was
induced.
Here we studied the self-assembly of the large functional
molecule 1,3,5-tris(4′-biphenyl-4″-carbonitrile)benzene
(BCNB) on both Cu(111) and Ag(111). These surfaces were
chosen as substrates because they exhibit two-dimensional
adatom gases that are comparable in mobility15 but differ in
reactivity.4,16 To study the influence of the above-mentioned
kinetic competition on the formation of adatom-coordinated
trinitrile networks, experiments were conducted with variation
of the deposition rate over two orders of magnitude.
Figure 1. STM topograph (+1.61 V, 100 pA) of the densely packed
(√39×√39)R 16° BCNB superstructure on Ag(111). Molecules are
overlaid, and the unit cell is indicated by green lines. The structure of
BCNB is shown in the upper inset. The lower inset shows the LEED
pattern. The two rotational domains are marked by red and turquoise
arrows.18 Dashed lines indicate high-symmetry substrate directions.
EXPERIMENTAL DETAILS
■
BCNB monolayers were characterized by scanning tunneling
microscopy (STM) and low-energy electron diffraction (LEED) in
ultrahigh vacuum (UHV). STM data were acquired with a home-built
beetle-type scanning tunneling microscope driven by an SPM100
controller from RHK. The topographs were processed by a mean value
filter. All of the images were obtained at room temperature at a base
pressure below 3 × 10−10 mbar. The Ag(111) and Cu(111) single-
crystal surfaces were prepared by cycles of Ne+ ion sputtering at 1 keV
and electron-beam annealing at 550 °C for 30 min. Thorough
calibration of the microscope with atomically resolved topographs of
Cu(111) allowed lattice parameters and distances to be derived with
an accuracy of ∼5%.
calculations. The closest N···H distances (260 pm) are
consistent with hydrogen-bond lengths in comparable bulk
crystals (250−260 pm).20,21
BCNB deposition with a rate of ∼2.5 × 10−2 monolayer/min
onto Cu(111) yielded two polymorphs, both with p31m
symmetry. The overview STM image in Figure 2a illustrates the
LEED experiments were performed in a separate UHV chamber at a
base pressure below 1 × 10−10 mbar. The LEED optics (Omicron
NanoTechnology GmbH) were controlled by electronics from SPECS
Surface Nano Analysis GmbH. The Ag(111) and Cu(111) surfaces
were prepared by Ar+ ion sputtering at 2 keV and subsequent electron-
beam annealing at 550 °C for 30 min. The deposition parameters were
similar to those for the STM experiments. LEED patterns were
acquired at a sample temperature of ∼60 K. The software LEEDpat3
was used for geometric simulations.
BCNB (see the Figure 1 inset for its molecular structure and the
Supporting Information for its synthesis) was deposited from a home-
built Knudsen cell17 and thoroughly outgassed prior to deposition.
The substrates were held at room temperature. The crucible
temperature was varied between 280 and 330 °C, resulting in
deposition rates between ∼2.5 × 10−4 and ∼2.5 × 10−2 monolayer/
min, respectively. To determine the BCNB sublimation rate as a
function of crucible temperature and to verify the long-term stability of
the sublimation, a Knudsen cell equipped with a quartz crystal
microbalance was used.18
Figure 2. (a) STM topograph (+2.09 V, 80 pA) of a BCNB monolayer
on Cu(111) deposited at a rate of ∼2.5 × 10−2 monolayer/min. The
inset shows the LEED pattern,18 in which arrows indicate the
reciprocal unit cell vectors of the α phase and dashed lines mark high-
symmetry substrate directions. (b) Tentative binding models of the α
(green) and β (yellow) phases; threefold coordination (red) was also
occasionally observed, but only in isolated arrangements.
RESULTS AND DISCUSSION
■
On Ag(111), BCNB self-assembles into long-range-ordered,
densely packed monolayers with p31m symmetry. Both STM
and LEED consistently revealed a (√39×√39)R 16° super-
structure with a lattice parameter of 1.80 nm (Figure 1). The
existence of two rotational domains is evident in the LEED
pattern depicted in the lower inset.18 The identification of the
molecular arrangement is unambiguous since the threefold
contour of BCNB is clearly recognizable and the STM-derived
size is in excellent agreement with the optimized geometry of
the isolated BCNB molecule.18 On the basis of the dense
packing of BCNB, additional constituents can be excluded.
From the molecular arrangement, it is concluded that the
dominant interactions are CN···H−C hydrogen bonds, as
similarly observed in surface self-assembly3,11,19 and bulk
crystals20,21 of carbonitriles. The nitrile groups are in close
proximity to three phenyl hydrogen atoms. Density functional
theory (DFT) calculations of two isolated molecules gave a
center-to-center distance of 1.81 nm.18 The extremely small
deviation from the experiment (1.80 nm) indicates a minor
substrate influence and justifies the comparison with gas-phase
coexistence of both a densely packed α phase and a porous β
phase. The lattice parameter and molecular arrangement of the
α phase on Cu(111) are comparable to those on Ag(111). The
commensurate (4√3×4√3)R30° superstructure on Cu(111)
(cf. the Figure 2a inset for the LEED pattern)18 exhibits a
slightly smaller lattice parameter of 1.77 nm and only one
rotational domain. According to the similarities with the
structure on Ag(111), it is concluded that the α phase on
Cu(111) is likewise stabilized by similar intermolecular
CN···H−C hydrogen bonds.
The pores of the β phase are arranged on a hexagonal lattice,
and the unit cell contains two molecules. The streaky features
observed within some but not all of the pores arise from
entrapped mobile species, either excess molecules or adatoms.
Similar observations have been reported for various porous
systems.11,22−25 Two different epitaxial relations to the
substrate were found, namely, (11√3×11√3)R 30° and
19×19 superstructures having almost identical lattice parame-
ters (4.87 and 4.86 nm, respectively). Generally, the emergence
of a porous polymorph already hints at stronger intermolecular
692
dx.doi.org/10.1021/ja306834a | J. Am. Chem. Soc. 2013, 135, 691−695

Journal of the American Chemical Society
Article
bonds. From the rather large center-to-center distance of
2.8 nm between adjacent molecules, direct interactions via
intermolecular hydrogen bonds can a priori be excluded. A
detailed view of the β phase furthermore revealed an
arrangement where the molecular lobes are not aligned with
the long diagonal of the unit cell but are slightly tilted by 9°
(Figure 3). In most dimeric binding motifs, the two molecules
DFT calculations were performed to derive optimal bond
lengths for copper−nitrile coordination and to find explan-
ations for the tilt in the intermolecular bonds. For a full account
of surface effects, it is also important to include the copper
substrate. However, because of the large system size, the DFT
calculations had to be restricted to benzonitrile as a
representative model system. As depicted in Figure 4a, energy
Figure 3. β phase of BCNB on Cu(111). (a) Close-up STM
topograph (1.41 V, 80 pA) with overlaid tripods. The colors encode
the different tilts of 9°. (b) Tentative models. C, gray; Cu, orange; H,
white; N, blue.
Figure 4. DFT geometry optimization of two benzonitrile molecules
coordinated to copper adatoms (represented by dark-red spheres).
Left: top views (i.e., parallel to [111]). Right: side views (i.e., parallel
to [112]). Only one copper substrate layer is depicted, but three layers
̅
were considered in the calculation. (a) Coordination to one copper
adatom in a threefold hollow site. (b) Coordination to one copper
adatom in a threefold hollow site with a further copper adatom in an
adjacent site.
tilt in the same direction (i.e., one molecule tilts clockwise and
the other counterclockwise). Tilts can occur in both directions
and occur in segregated domains.18
On the basis of the intermolecular arrangement, we propose
that BCNB molecules are interconnected by coordination
bonds between the nitrile groups and copper adatoms. This
hypothesis is further substantiated by occasionally observed
adatom-related contrast features in the STM images, the results
of DFT calculations, and the good match with an epitaxial
model, as detailed in the following. In accordance with most
other experiments on copper-coordinated networks, the copper
atoms are normally not resolved by STM.26−32 This invisibility
of obviously present coordination centers in STM images has
also been reported for many other metal-coordinated networks,
such as Co-coordinated nitriles5,9,12,33 and is attributed to an
electronic effect.34 Nevertheless, occasionally for peculiar tip
conditions, distinct topographic maxima were observed in the β
phase at the proposed positions of the copper coordination
centers (i.e., midway between two BCNB molecules; see the
Supporting Information). Moreover, in these images, the
BNCB molecules appear with diminished apparent height,
indicating a tip that is sensitive to electronic states in a different
energy range. Because of their positions, these topographic
maxima are unambiguously identified as the coordinating
copper adatoms. Similar signatures of coordinating adatoms in
the STM contrast have been reported for Cu−benzoate
complexes on Cu(110).35
In the β phase, copper adatoms coordinate two nitrile
groups. Threefold coordination, the major binding motif in Co-
coordinated nitrile networks5,9,12 and hitherto-known Cu
coordination,3 was only rarely observed in isolated arrange-
ments (Figure 2). However, for surface-supported metal-
coordinated networks, unusual coordination with lower
coordination numbers seems to be the more general
case.8,27,36 This can be rationalized by the special environment
of these surface-supported systems. On the one hand, there is
the restriction to a planar geometry due to the surface
confinement, and on the other hand, there is an additional
electronic influence of the metal surface due to charge transfer
and screening by free electrons.27,36
minimization of two benzonitrile molecules coordinated to one
copper adatom resulted in a straight bond with the adatom
stably adsorbed in a threefold hollow site. The N−Cu bond
length is 0.192 nm, and the copper adatom resides 0.200 nm
above the topmost copper layer and 0.121 nm below the
benzene rings. The DFT calculations revealed a global energy
minimum for the benzene rings oriented along the ⟨110⟩ high-
̅
symmetry direction of the substrate and a further, only slightly
less stable local minimum for alignment in the bisecting ⟨112⟩
̅
direction.
Since DFT geometry optimization yielded a straight bond,
the experimentally observed tilt cannot be explained by intrinsic
properties of the chosen model system. In an alternative
approach, a second copper adatom was placed adjacent to the
coordinating copper atom, likewise in a threefold hollow site.
The optimized geometry is depicted in Figure 4b. Addition of a
second adatom actually results in a tilt of the bond angle by 6°,
thereby offering a possible explanation.
Although the DFT simulations of the model systems
included direct substrate effects, conceivable registry effects
could arise for the full BCNB molecule that could be relevant
for the β phase. Nevertheless, an optimal N−Cu bond length of
0.192 nm in the adsorbed system was deduced from the DFT
calculations, and there is a clear confirmation that copper
adatoms have a strong preference for threefold hollow sites.
The fairly large unit cell of the β phase contains two BCNB
molecules and three copper adatoms. When the above-stated
requirements are considered, it becomes clear that the substrate
registry does not allow for a straight bond configuration. To
keep CN−Cu coordination bonds within 5% of the
optimized length and guarantee threefold hollow sites for all
adatoms, the β phase has to adapt to the substrate lattice in the
energetically most efficient way, which involves tilting the
BCNB molecules with respect to each other. A tentative model
of the β phase that includes all of the requirements and the
experimental tilt angle into account is presented in Figure 5.
693
dx.doi.org/10.1021/ja306834a | J. Am. Chem. Soc. 2013, 135, 691−695

Journal of the American Chemical Society
Article
Figure 5. Tentative model of the β phase on Cu(111). The dashed
green lines indicate the 19×19 unit cell. For clarity, the BCNB
molecules are represented by tripods. This model considers the
experimental tilt angle and the preference of copper adatoms for
threefold hollow sites. All CN−Cu bonds are within 5% of the
DFT-derived optimal bond length of 0.192 nm. The three
coordinating copper adatoms are located on the same sublattice.18
To obtain insights into the growth kinetics, experiments were
conducted with ultraslow deposition, wherein a surface
coverage of one monolayer was accomplished in 67 h. On
Cu(111), this resulted in the exclusive formation of the β phase,
thereby hinting at a kinetic origin of the polymorphism. A
representative STM image is presented in Figure 6a.
Irrespective of the low deposition rate, a similar tilt angle
between the BCNB molecules was observed, pointing to an
equilibrium effect. Occasionally, the STM images also showed a
parallel side-by-side arrangement of two dimers, an example of
which is highlighted in Figure 6a. However, these uncommon
coordination schemes are grouped along a line and thus are
attributed to an antiphase domain boundary. Interestingly,
similarly slow deposition onto Ag(111) still resulted in the
densely packed polymorph, yet with a notably extended domain
size, as illustrated in Figure 6b.
We thus assign the polymorphism on Cu(111) to a kinetic
effect, namely, the availability of Cu adatoms. Upon deposition
of BCNB, formation of the β phase consumes Cu adatoms and
thus depletes the density of the adatom gas below its
equilibrium value. If the progressive consumption of Cu
adatoms caused by further deposition of BCNB molecules is
faster than adatom replenishment from step edges, the
availability of Cu centers for coordination bonds decreases.
The absence of Cu adatoms leads to the realization of the
second best option in terms of intermolecular bonds, namely,
the hydrogen-bonded α phase.
Figure 6. (a) STM topograph (+2.01 V, 39 pA) of BCNB on
Cu(111). The monolayer was prepared by ultraslow deposition (∼2.5
× 10−4 monolayer/min), which exclusively yielded the porous β phase.
The dashed circle highlights a parallel side-by-side arrangement of
dimers, and the dashed line indicates a domain boundary. (b) STM
topograph (−0.19 V, 40 pA) of BCNB on Ag(111). The monolayer
was similarly prepared by ultraslow deposition (∼8.3 × 10−4
monolayer/min). However, on Ag(111) no change of intermolecular
bond type was induced. The α phase was observed exclusively but with
a notably increased domain size.
This striking difference between Cu(111) and Ag(111) can
be explained by the lower bond dissociation energy (BDE) of
CN−Ag vs CN−Cu coordination bonds. The BDE of two
benzonitrile molecules coordinated either by one Cu atom or
one Ag atom for isolated arrangements was evaluated by DFT
calculations. The BDE for the copper case amounts to 0.90 eV
per benzonitrile molecule, which is substantially higher than the
value of 0.30 eV in the case of silver. Accordingly, Ag-
coordinated BCNB networks might be stable only at lower
temperature, although under those conditions the adatom
density and mobility become the limiting factors for the
formation of metal-coordinated networks.
This picture is supported by the experiments on Cu(111)
with ultraslow deposition, which resulted in the exclusive
formation of the β phase. When the BCNB deposition rate is so
low that the equilibrium density of the adatom gas is not
perturbed, Cu centers are constantly available, and the
preferred formation of Cu coordination bonds is not hampered
by kinetic limitations. In contrast, the insufficient reactivity of
Ag adatoms at room temperature leads to the exclusive
formation of the hydrogen-bonded structure on Ag(111), even
for ultraslow deposition. On this less reactive surface, the slow
deposition affects only the nucleation and growth kinetics,
resulting in extended domains of the densely packed hydrogen-
bonded phase.
CONCLUSION
■
The deposition-rate-dependent self-assembly of BCNB on
Ag(111) and Cu(111) demonstrates the importance of both
substrate and kinetic effects for the expression of a specific type
of intermolecular bond. Two types of intermolecular bonds
dominate in BCNB monolayers, namely, hydrogen bonds and
metal-coordination bonds with adatoms. Their emergence can
be controlled by the choice of substrate, a well-known effect
that is in the case of metal coordination mostly related to the
adatom reactivity and the bond strength of the respective
coordination bonds. Moreover, here we discovered that the
deposition rate is also effective in deliberately selecting the type
694
dx.doi.org/10.1021/ja306834a | J. Am. Chem. Soc. 2013, 135, 691−695

Journal of the American Chemical Society
Article
(19) Yokoyama, T.; Yokoyama, S.; Kamikado, T.; Okuno, Y.;
of intermolecular bond and thus controlling the structure. A
qualitative study of these kinetic effects allows for a basic
understanding of growth kinetics and polymorph selection in
the abundantly employed formation of metal−organic networks
through adatom coordination.
Mashiko, S. Nature 2001, 413, 619−621.
̈
(20) Ozbey, S.; Kaynak, F. B.; Goker, H.; Kus, C. J. Chem. Crystallogr.
̈
2004, 34, 851−858.
(21) Dopp, D.; Kruse, C.; Florke, U.; Henkel, G. Acta Crystallogr.,
Sect. E 2006, 62, O3245−O3246.
(22) Griessl, S.; Lackinger, M.; Edelwirth, M.; Hietschold, M.; Heckl,
W. M. Single Mol. 2002, 3, 25−31.
̈
̈
ASSOCIATED CONTENT
* Supporting Information
■
(23) Ruben, M.; Payer, D.; Landa, A.; Comisso, A.; Gattinoni, C.;
Lin, N.; Collin, J. P.; Sauvage, J. P.; De Vita, A.; Kern, K. J. Am. Chem.
Soc. 2006, 128, 15644−15651.
S
Synthesis details, curves showing the sublimation rate as
functions of temperature and time, additional DFT calculations,
STM and LEED data, and an additional structure model. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(24) Otero, R.; Lukas, M.; Kelly, R. E. A.; Xu, W.; Laegsgaard, E.;
Stensgaard, I.; Kantorovich, L. N.; Besenbacher, F. Science 2008, 319,
312−315.
(25) Stohr, M.; Wahl, M.; Galka, C. H.; Riehm, T.; Jung, T. A.; Gade,
̈
L. H. Angew. Chem., Int. Ed. 2005, 44, 7394−7398.
AUTHOR INFORMATION
Corresponding Author
markus@lackinger.org
(26) Classen, T.; Lingenfelder, M.; Wang, Y.; Chopra, R.;
Virojanadara, C.; Starke, U.; Costantini, G.; Fratesi, G.; Fabris, S.; de
Gironcoli, S.; Baroni, S.; Haq, S.; Raval, R.; Kern, K. J. Phys. Chem. A
2007, 111, 12589−12603.
■
Notes
́
(27) Heim, D.; Ecija, D.; Seufert, K.; Auwarter, W.; Aurisicchio, C.;
̈
The authors declare no competing financial interest.
Fabbro, C.; Bonifazi, D.; Barth, J. V. J. Am. Chem. Soc. 2010, 132,
6783−6790.
(28) Tait, S. L.; Langner, A.; Lin, N.; Stepanow, S.; Rajadurai, C.;
Ruben, M.; Kern, K. J. Phys. Chem. C 2007, 111, 10982−10987.
ACKNOWLEDGMENTS
■
Funding by the Fonds der Chemischen Industrie (T.S.), the
Nanosystems-Initiative-Munich Cluster of Excellence, the
Alexander von Humboldt Foundation (S.N.), and the
Elitenetzwerk Bayern (S.S.) and discussions with Debabrata
Samanta are gratefully acknowledged.
(29) Matena, M.; Stohr, M.; Riehm, T.; Bjork, J.; Martens, S.; Dyer,
̈
̈
M. S.; Persson, M.; Lobo-Checa, J.; Muller, K.; Enache, M.; Wadepohl,
H.; Zegenhagen, J.; Jung, T. A.; Gade, L. H. Chem.Eur. J. 2010, 16,
̈
2079−2091.
(30) Wang, Y.; Fabris, S.; White, T. W.; Pagliuca, F.; Moras, P.;
Papagno, M.; Topwal, D.; Sheverdyaeva, P.; Carbone, C.;
Lingenfelder, M.; Classen, T.; Kern, K.; Costantini, G. Chem. Commun.
2011, 48, 534−536.
REFERENCES
■
(1) Barth, J. V. Annu. Rev. Phys. Chem. 2007, 58, 375−407.
(2) Miyashita, N.; Kurth, D. G. J. Mater. Chem. 2008, 18, 2636−2649.
(3) Pawin, G.; Wong, K. L.; Kim, D.; Sun, D. Z.; Bartels, L.; Hong, S.;
Rahman, T. S.; Carp, R.; Marsella, M. Angew. Chem., Int. Ed. 2008, 47,
8442−8445.
(31) Bjork, J.; Matena, M.; Dyer, M. S.; Enache, M.; Lobo-Checa, J.;
̈
Gade, L. H.; Jung, T. A.; Stohr, M.; Persson, M. Phys. Chem. Chem.
̈
Phys. 2010, 12, 8815−8821.
(32) Matena, M.; Riehm, T.; Stohr, M.; Jung, T. A.; Gade, L. H.
̈
Angew. Chem., Int. Ed. 2008, 47, 2414−2417.
(4) Walch, H.; Gutzler, R.; Sirtl, T.; Eder, G.; Lackinger, M. J. Phys.
Chem. C 2010, 114, 12604−12609.
(33) Schlickum, U.; Decker, R.; Klappenberger, F.; Zoppellaro, G.;
Klyatskaya, S.; Ruben, M.; Silanes, I.; Arnau, A.; Kern, K.; Brune, H.;
Barth, J. V. Nano Lett. 2007, 7, 3813−3817.
(5) Bartels, L. Nat. Chem. 2010, 2, 87−95.
(6) Walch, H.; Dienstmaier, J.; Eder, G.; Gutzler, R.; Schlogl, S.; Sirtl,
̈
(34) Classen, T.; Fratesi, G.; Costantini, G.; Fabris, S.; Stadler, F. L.;
Kim, C.; de Gironcoli, S.; Baroni, S.; Kern, K. Angew. Chem., Int. Ed.
2005, 44, 6142−6145.
T.; Das, K.; Schmittel, M.; Lackinger, M. J. Am. Chem. Soc. 2011, 133,
7909−7915.
(7) Lin, N.; Dmitriev, A.; Weckesser, J.; Barth, J. V.; Kern, K. Angew.
Chem., Int. Ed. 2002, 41, 4779−4783.
(35) Dougherty, D. B.; Maksymovych, P.; Yates, J. T., Jr. Surf. Sci.
2006, 600, 4484−4491.
(36) Stepanow, S.; Lin, N.; Payer, D.; Schlickum, U.; Klappenberger,
F.; Zoppellaro, G.; Ruben, M.; Brune, H.; Barth, J. V.; Kern, K. Angew.
Chem., Int. Ed. 2007, 46, 710−713.
(8) Lin, N.; Stepanow, S.; Vidal, F.; Kern, K.; Alam, M. S.;
Stromsdorfer, S.; Dremov, V.; Muller, P.; Landa, A.; Ruben, M. Dalton
̈
̈
̈
Trans. 2006, 2794−2800.
(9) Schlickum, U.; Klappenberger, F.; Decker, R.; Zoppellaro, G.;
Klyatskaya, S.; Ruben, M.; Kern, K.; Brune, H.; Barth, J. V. J. Phys.
Chem. C 2010, 114, 15602−15606.
(10) Schutte, M.; Kurth, D. G.; Linford, M. R.; Colfen, H.; Mohwald,
̈
̈
̈
H. Angew. Chem., Int. Ed. 1998, 37, 2891−2893.
(11) Kuhne, D.; Klappenberger, F.; Decker, R.; Schlickum, U.; Brune,
H.; Klyatskaya, S.; Ruben, M.; Barth, J. V. J. Phys. Chem. C 2009, 113,
̈
17851−17859.
(12) Klyatskaya, S.; Klappenberger, F.; Schlickum, U.; Kuhne, D.;
Marschall, M.; Reichert, J.; Decker, R.; Krenner, W.; Zoppellaro, G.;
Brune, H.; Barth, J. V.; Ruben, M. Adv. Funct. Mater. 2011, 21, 1230−
1240.
(13) Kuhnle, A. Curr. Opin. Colloid Interface Sci. 2009, 14, 157−168.
̈
(14) Li, Y.; Lin, N. Phys. Rev. B 2011, 84, No. 125418.
(15) Agrawal, P. M.; Rice, B. M.; Thompson, D. L. Surf. Sci. 2002,
515, 21−35.
(16) Lin, N.; Payer, D.; Dmitriev, A.; Strunskus, T.; Woll, C.; Barth, J.
̈
V.; Kern, K. Angew. Chem., Int. Ed. 2005, 44, 1488−1491.
(17) Gutzler, R.; Heckl, W. M.; Lackinger, M. Rev. Sci. Instrum. 2010,
81, No. 015108.
(18) See the Supporting Information.
695
dx.doi.org/10.1021/ja306834a | J. Am. Chem. Soc. 2013, 135, 691−695