I09-Surface and Interface Structural Analysis
|
Séverine
Le Moal
,
Ina
Krieger
,
Roman
Kremring
,
Simon
Weiss
,
Xiaosheng
Yang
,
Serguei
Soubatch
,
F. Stefan
Tautz
,
Mathieu
Silly
,
Andrei G.
Borisov
,
Moritz
Sokolowski
,
Eric
Le Moal
Diamond Proposal Number(s):
[14878]
Abstract: We present an experimental and theoretical analysis of the core-level binding energy shifts in metal-supported ultrathin potassium chloride (KCl) films, i.e., a case from a broader class of few-atom-thick, wide-band gap insulating layers that is increasingly used in nanosciences and nanotechnologies. Using synchrotron-based high-resolution photoemission spectroscopy (HRPES) measurements, we identify the different contributions to the core-level binding energy shifts for the Cl– anions and K+ cations of two to three atomic layer-thick KCl films grown on Ag(100). The distances of the Cl– and K+ ions of the first two atomic layers of the KCl film from the metal substrate are determined from normal incidence X-ray standing wave measurements. We also calculated the core-level binding energy shifts using an analytical electrostatic model and found that the theoretical results are in agreement with the experimental HRPES results only when polarization and substrate-induced image charge effects are taken into account. Finally, our results evidence the effect of the third atomic layer of the KCl film, which partially covers and screens the first two atomic layers of KCl, wetting the metal substrate.
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Dec 2023
|
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I09-Surface and Interface Structural Analysis
|
Philip
Schädlich
,
Chitran
Ghosal
,
Monja
Stettner
,
Bharti
Matta
,
Susanne
Wolff
,
Franziska
Schölzel
,
Peter
Richter
,
Mark
Hutter
,
Anja
Haags
,
Sabine
Wenzel
,
Zamin
Mamiyev
,
Julian
Koch
,
Serguei
Soubatch
,
Philipp
Rosenzweig
,
Craig
Polley
,
Frank Stefan
Tautz
,
Christian
Kumpf
,
Kathrin
Küster
,
Ulrich
Starke
,
Thomas
Seyller
,
Francois C.
Bocquet
,
Christoph
Tegenkamp
Diamond Proposal Number(s):
[26188, 33755]
Open Access
Abstract: The synthesis of new graphene-based quantum materials by intercalation is an auspicious approach. However, an accompanying proximity coupling depends crucially on the structural details of the new heterostructure. It is studied in detail the Pb monolayer structure after intercalation into the graphene buffer layer on the SiC(0001) interface by means of photoelectron spectroscopy, x-ray standing waves, and scanning tunneling microscopy. A coherent fraction close to unity proves the formation of a flat Pb monolayer on the SiC surface. An interlayer distance of 3.67 Å to the suspended graphene underlines the formation of a truly van der Waals heterostructure. The 2D Pb layer reveals a quasi ten-fold periodicity due to the formation of a grain boundary network, ensuring the saturation of the Si surface bonds. Moreover, the densely-packed Pb layer also efficiently minimizes the doping influence by the SiC substrate, both from the surface dangling bonds and the SiC surface polarization, giving rise to charge-neutral monolayer graphene. The observation of a long-ranged (
) reconstruction on the graphene lattice at tunneling conditions close to Fermi energy is most likely a result of a nesting condition to be perfectly fulfilled.
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Jul 2023
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[18398]
Abstract: Using the normal incidence x-ray standing-wave technique as well as low-energy electron microscopy we have investigated the structure of quasifreestanding monolayer graphene (QFMLG) obtained by intercalation of antimony under the
(
6
√
3
×
6
√
3
)
R
30
∘
reconstructed graphitized
6
H
-SiC(0001) surface, also known as zeroth-layer graphene. We found that Sb intercalation decouples the QFMLG well from the substrate. The distance from the QFMLG to the Sb layer almost equals the expected van der Waals bonding distance of C and Sb. The Sb intercalation layer itself is monoatomic, flat, and located much closer to the substrate, at almost the distance of a covalent Sb-Si bond length. All data is consistent with Sb located on top of the uppermost Si atoms of the SiC bulk.
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Oct 2022
|
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I09-Surface and Interface Structural Analysis
|
You-Ron
Lin
,
Markus
Franke
,
Shayan
Parhizkar
,
Miriam
Raths
,
Victor
Wen-Zhe Yu
,
Tien-Lin
Lee
,
Serguei
Soubatch
,
Volker
Blum
,
F. Stefan
Tautz
,
Christian
Kumpf
,
Francois C.
Bocquet
Diamond Proposal Number(s):
[17737]
Abstract: In the field of van der Waals heterostructures, the twist angle between stacked two-dimensional layers has been identified to be of utmost importance for the properties of the heterostructures. In this context, we previously reported the growth of a single layer of unconventionally oriented epitaxial graphene that forms in a surfactant atmosphere [F. C. Bocquet et al., Phys. Rev. Lett. 125, 106102 (2020)]. The resulting G-
R
0
∘
layer is aligned with the SiC lattice, and hence represents an important milestone towards high-quality twisted bilayer graphene, a frequently investigated model system in this field. Here, we focus on the surface structures obtained in the same surfactant atmosphere, but at lower preparation temperatures at which a boron nitride template layer forms on SiC(0001). In a comprehensive study based on complementary experimental and theoretical techniques, we find—in contrast to the literature—that this template layer is a hexagonal
B
x
N
y
layer, but not high-quality hBN. It is aligned with the SiC lattice and gradually replaced by low-quality graphene in the
0
∘
orientation of the
B
x
N
y
template layer upon annealing.
|
Jun 2022
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[23317]
Abstract: The discovery of topological superconductivity in doped
Bi
2
Se
3
made this class of materials highly important for the field of condensed matter physics. However, the structural origin of the superconducting state remained elusive, despite being investigated intensively in recent years. We use scanning tunneling microscopy and the normal incidence x-ray standing wave (NIXSW) technique in order to determine the vertical position of the dopants—one of the key parameters for understanding topological superconductivity in this material— for the case of
Sr
x
Bi
2
Se
3
. In particular, we analyze the NIXSW data in consideration of the inelastic mean free path of the photoemitted electrons, which allows us to distinguish between symmetry-equivalent sites. We find that Sr atoms are not situated inside the van der Waals gap between the
Bi
2
Se
3
quintuple layers but rather in the quintuple layer close to the outer Se planes.
|
Aug 2021
|
|
I09-Surface and Interface Structural Analysis
|
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
|
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
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Dec 2018
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Aug 2018
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Jul 2018
|
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