I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[17737, 20810, 20855]
Abstract: We report the use of a surfactant molecule during the epitaxy of graphene on SiC(0001) that leads to the growth in an unconventional orientation, namely
R
0
°
rotation with respect to the SiC lattice. It yields a very high-quality single-layer graphene with a uniform orientation with respect to the substrate, on the wafer scale. We find an increased quality and homogeneity compared to the approach based on the use of a preoriented template to induce the unconventional orientation. Using spot profile analysis low-energy electron diffraction, angle-resolved photoelectron spectroscopy, and the normal incidence x-ray standing wave technique, we assess the crystalline quality and coverage of the graphene layer. Combined with the presence of a covalently bound graphene layer in the conventional orientation underneath, our surfactant-mediated growth offers an ideal platform to prepare epitaxial twisted bilayer graphene via intercalation.
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Sep 2020
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I09-Surface and Interface Structural Analysis
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Christine
Bruelke
,
Timo
Heepenstrick
,
Ina
Krieger
,
Beatrice
Wolff
,
Xiaosheng
Yang
,
Ali
Shamsaddinlou
,
Simon
Weiss
,
Francois
Bocquet
,
Stefan
Tautz
,
Serguei
Soubatch
,
Moritz
Sokolowski
Diamond Proposal Number(s):
[14878]
Abstract: The adsorption geometry, the electronic properties, and the adsorption energy of the prototype organic molecule 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on a monolayer of hexagonal boron nitride (hBN) grown on the Cu(111) surface were determined experimentally. The perylene core is at a large height of 3.37
Å
and only a minute downward displacement of the functional anhydride groups (0.07 Å) occurs, yielding adsorption heights that agree with the sum of the involved van der Waals radii. Thus, already a single hBN layer leads to a decoupled (physisorbed) molecule, contrary to the situation on the bare Cu(111) surface.
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Mar 2019
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I09-Surface and Interface Structural Analysis
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Open Access
Abstract: We introduce a software, Torricelli, for the analysis of normal incidence x-ray standing wave data. In particular, given the experimental x-ray reflectivity and photoelectron yield of a data set (photon energy scan), Torricelli provides the corresponding structural parameters. The algorithm and equations on which Torricelli is based are explained here in detail. In particular, the model of the experimental reflectivity takes into account the theoretical reflectivity of the double crystal monochromator as well as the sample crystal, and a Gaussian broadening to account for mosaicity and photon energy spread. If statistical errors are provided together with the photoelectron yield data, these are propagated to produce the statistical errors of the structural parameters. For a more accurate analysis, angle-dependent correction parameters specific to the photoemission process, also beyond the dipole approximation, can be taken into account, especially in the case of non-perfect normal incidence. The obtained structural parameters can be compared, averaged, and displayed in an Argand diagram, along with statistical error bars.
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Dec 2018
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I09-Surface and Interface Structural Analysis
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S.
Weiß
,
D.
Gerbert
,
A.
Stein
,
A. K.
Schenk
,
X.
Yang
,
C.
Brülke
,
R.
Kremring
,
S.
Feldmann
,
F. C.
Bocquet
,
M.
Gille
,
S.
Hecht
,
M.
Sokolowski
,
P.
Tegeder
,
S.
Soubatch
,
F. S.
Tautz
Diamond Proposal Number(s):
[12627, 16056]
Abstract: Comparing the adsorption heights of various graphene nanoribbons on Cu(111) and Au(111) surfaces to those of graphene and π-conjugated planar organic molecules, we observe that two-dimensional graphene adsorbs much further away from the surface than both one-dimensional graphene nanoribbons and π-conjugated planar molecules—which represent zero-dimensional graphene flakes. We show that this is a direct consequence of the adsorbates' dimensionality. Our results provide invaluable insights into the interplay of Pauli repulsion, pushback effect, and chemical interaction for graphenelike adsorbates of any dimensionality on metal surfaces.
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Aug 2018
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I09-Surface and Interface Structural Analysis
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Xiaosheng
Yang
,
Ina
Krieger
,
Daniel
Lüftner
,
Simon
Weiss
,
Timo
Heepenstrick
,
Michael
Hollerer
,
Philipp
Hurdax
,
Georg
Koller
,
Moritz
Sokolowski
,
Peter
Puschnig
,
Michael G.
Ramsey
,
F. Stefan
Tautz
,
Serguei
Soubatch
Diamond Proposal Number(s):
[14878]
Abstract: Properties of organic molecules adsorbed on metal surfaces are usually affected by the interaction with the substrate. There is a widespread belief that a thin dielectric layer between the molecular layer and the metal is sufficient for decoupling the former both physically and electronically. Using the example of perylenetetracarboxylic dianhydride on a bilayer of MgO on Ag(100), we show that this strategy is not always successful, as we observe a substantial charge transfer from the metal into the molecules. To avoid this, we suggest an alternative approach. Specifically, we deposit oxygen atoms on Cu(100) surface resulting in immobilization of the surface electrons in Cu-O bonds. This achieves a true electronic and physical decoupling. This mechanism of electronic surface hardening, proposed and demonstrated here by a combination of photoemission tomography, x-ray standing wave technique, and density functional calculations, is of general applicability as a strategy to decouple molecules from metals.
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Jul 2018
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[10370, 11915, 13837]
Abstract: Molecular monolayer films containing two different types of molecules (so called heteromolecular films) are promising candidates for the controlled functionalization of metal-organic hybrid interfaces. This is particularly true for blends formed by charge donor and acceptor molecules. Here we study heteromolecular monolayer systems containing 3,4,9,10-perylene-tetra-carboxylic-dianhydride (PTCDA) as charge acceptor, and either copper-II- or tin-II-phthalocyanine (CuPc or SnPc) as charge donor, adsorbed on Ag(111). We find that both systems exhibit structural phases with identical lateral ordering (iso-structural phases), which is an important prerequisite for studying the role of the central metal atom without competing effects caused by different lateral structures. Using normal incidence x-ray standing waves and photoemission tomography we find distinct differences in the (vertical) geometric and electronic structure for the heteromolecular systems under study: While the vertical structure of CuPc is essentially unaffected by mixing with PTCDA, the SnPc clearly reacts to the formation of a blend by reducing its adsorption height by approx. 0.2 Å. Also, the vertical structure of the PTCDA anhydride groups changes strongly: While the anhydride oxygen atoms are located below the perylene core for most mixed phases, for one of the PTCDA+CuPc phases it is lying above the perylene core. Regarding the electronic structure we find that while mixing with PTCDA causes a complete depletion of the CuPc former lowest unoccupied molecular orbital (FLUMO), the SnPc FLUMO is pinned to the Fermi level instead, and thus it remains partially filled. We demonstrate that all these differences are driven by the rearrangement of the substrate electron density in the vicinity of the PTCDA molecules, which are caused by the interaction with the metal phthalocyanine molecules.
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Mar 2018
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[11752]
Abstract: The hexagonal boron nitride (hBN) monolayer on the Cu(111) surface has recently been considered an example of an extremely weak hBN/metal interaction, as indicated, e.g., from the presence of an only electronic Moiré-like superstructure that was observed in scanning tunneling microscopy images. From these results a large bonding distance of the hBN sheet to the top most Cu layer can be envisaged, but has not been proven so far. We report a structural analysis of the hBN/Cu(111) interface based on high resolution low energy electron diffraction and normal incidence x-ray standing wave experiments. We find that both the boron and the nitrogen atoms are located at very large vertical distances of dB = 3.25 ± 0.02 Å and dN = 3.22 ± 0.03 Å with respect to the nominal position of the topmost Cu(111) layer. Significant vertical buckling and lateral distortions of the hBN layer can be excluded. These results demonstrate that the hBN monolayer on the Cu(111) surface is indeed well described by a rigid and geometrically well separated sheet.
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Sep 2017
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[9722]
Abstract: The adsorption geometry, namely the height and the site, of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on the Cu(100) surface was determined by the normal incidence x-ray standing wave (NIXSW) technique including triangulation. The two PTCDA molecules in the superstructure unit cell, which have perpendicular azimuthal orientation, are both located at bridge sites, the long molecular axis being parallel to the bridge. Carboxylic oxygen atoms and several atoms of the carbon backbone are located close to on-top positions. The vertical distortion motif of PTCDA on Cu(100) differs from that on the three low-index Ag surfaces, because significant downward displacement of the carboxylic oxygen atoms is lacking. In particular, the carbon backbone of PTCDA adsorbs closer to the surface than extrapolated from Ag data. This suggests a relative increase of the attractive interactions between the carbon backbone of PTCDA and the Cu(100) surface versus the attractive interactions on the carboxylic oxygen atoms.
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Aug 2017
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I09-Surface and Interface Structural Analysis
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J.
Sforzini
,
P.
Hapala
,
M.
Franke
,
G.
Van Straaten
,
A.
Stöhr
,
S.
Link
,
S.
Soubatch
,
P.
Jelínek
,
T.-L.
Lee
,
U.
Starke
,
M.
Švec
,
F.
Bocquet
,
S.
Tautz
Diamond Proposal Number(s):
[10271]
Open Access
Abstract: We investigate the structural and electronic properties of nitrogen-doped epitaxial monolayer graphene
and quasifreestanding monolayer graphene on 6H-SiCð0001Þ by the normal incidence x-ray standing wave
technique and by angle-resolved photoelectron spectroscopy supported by density functional theory
simulations. With the location of various nitrogen species uniquely identified, we observe that for the same
doping procedure, the graphene support, consisting of substrate and interface, strongly influences the
structural as well as the electronic properties of the resulting doped graphene layer. Compared to epitaxial
graphene, quasifreestanding graphene is found to contain fewer nitrogen dopants. However, this lack of
dopants is compensated by the proximity of nitrogen atoms at the interface that yield a similar number of
charge carriers in graphene.
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Mar 2016
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I09-Surface and Interface Structural Analysis
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J.
Sforzini
,
L.
Nemec
,
T.
Denig
,
B.
Stadtmüller
,
T. L
Lee
,
C.
Kumpf
,
S.
Soubatch
,
U.
Starke
,
P.
Rinke
,
V.
Blum
,
F.
Bocquet
,
S.
Tautz
Diamond Proposal Number(s):
[8449, 10271]
Open Access
Abstract: We measure the adsorption height of hydrogen-intercalated quasifreestanding monolayer graphene on the
(0001) face of 6H silicon carbide by the normal incidence x-ray standing wave technique. A density
functional calculation for the full ð6
ffiffiffi
3 p × 6
ffiffiffi
3 p Þ-R30° unit cell, based on a van derWaals corrected exchange
correlation functional, finds a purely physisorptive adsorption height in excellent agreement with experiments,
a very low buckling of the graphene layer, a very homogeneous electron density at the interface, and
the lowest known adsorption energy per atom for graphene on any substrate.Astructural comparison to other
graphenes suggests that hydrogen-intercalated graphene on 6H-SiCð0001Þ approaches ideal graphene.
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Mar 2015
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