A5036789746- Graphene research and applications
- Surface and Thin Film Phenomena
- Ion-surface interactions and analysis
- Quantum and electron transport phenomena
- Advanced Chemical Physics Studies
- 2D Materials and Applications
- nanoparticles nucleation surface interactions
- Advanced Materials Characterization Techniques
- Molecular Junctions and Nanostructures
- Diamond and Carbon-based Materials Research
- Theoretical and Computational Physics
- Topological Materials and Phenomena
- Magnetic properties of thin films
- Semiconductor materials and devices
- Force Microscopy Techniques and Applications
- Integrated Circuits and Semiconductor Failure Analysis
- Electron and X-Ray Spectroscopy Techniques
- Electronic and Structural Properties of Oxides
- Surface Chemistry and Catalysis
- Catalytic Processes in Materials Science
- Metal and Thin Film Mechanics
- Physics of Superconductivity and Magnetism
- Chemical and Physical Properties of Materials
- Boron and Carbon Nanomaterials Research
- MXene and MAX Phase Materials
University of Cologne
2016-2025
LVR-Klinik Köln
2017
RWTH Aachen University
1999-2008
Westfälische Hochschule
2001
Forschungszentrum Jülich
1991-2000
Stadtwerke Jülich (Germany)
1997
IBM Research - Thomas J. Watson Research Center
1994-1996
IBM (United States)
1995
Low-pressure chemical vapor deposition allows one to grow high structural quality monolayer graphene on Ir(111). Using scanning tunneling microscopy, we show that prepared this way exhibits remarkably large-scale continuity of its carbon rows over terraces and step edges. The layer contains only a very low density defects. These are zero-dimensional defects, edge dislocation cores consisting heptagon-pentagon pairs atom rings, which relate small-angle in-plane tilt boundaries in the...
Lattices of Ir clusters have been grown by vapor phase deposition on graphene moir\'es Ir(111). The are highly ordered, and spatially thermally stable below 500 K. Their narrow size distribution is tunable from 4 to about 130 atoms. A model for cluster binding the presented based scanning tunneling microscopy density functional theory. proposed mechanism suggests that similar lattices might be materials other than Ir.
Epitaxial graphene on Ir(111) prepared in excellent structural quality is investigated by angle-resolved photoelectron spectroscopy. It clearly displays a Dirac cone with the point shifted only slightly above Fermi level. The moiré resulting from overlaid and surface lattices imposes superperiodic potential giving rise to replicas opening of minigaps band structure.
A graphene monolayer has been prepared on an Ir(111) single crystal via pyrolytic cleavage of ethylene (C2H4). The resulting superstructure examined with scanning tunneling microscopy (STM) and low energy electron diffraction. It identified as a well aligned, incommensurate (9.32×9.32) pattern, which is described moiré. This pattern shows three distinct regions from different local configurations the carbon adlayer respect to Ir-substrate. These are imaged differently by STM differ strongly...
Catalytic decomposition of hydrocarbons on transition metals attracts a renewed interest as route toward high-quality graphene prepared in reproducible manner. Here we employ two growth methods for Ir(111), namely room temperature adsorption and thermal at 870–1470 K (temperature programmed (TPG)) well direct exposure the hot substrate 870–1320 (chemical vapor deposition (CVD)). The temperature- exposure-dependent is investigated detail by scanning tunneling microscopy. TPG found to yield...
We neglected to cite the report by Loginova et al (2008 New J. Phys. 10 093026) of evidence for growth graphene flakes on Ru(0001) attachment small carbon clusters.
The nonlocal van der Waals density functional approach is applied to calculate the binding of graphene Ir(111). precise agreement calculated mean height h = 3.41 Å C atoms with their (3.38±0.04) as measured by x-ray standing wave technique provides a benchmark for applicability functional. We find bonding Ir(111) be due interaction an antibonding average contribution from chemical interaction. Despite its globally repulsive character, in certain areas large moiré unit cell charge...
An inversion of the triangular shape two-dimensional islands observed in a narrow temperature range by scanning tunneling microscopy during growth Pt on Pt(111) is reported. This phenomenon due to speed ratio two types close packed 〈110〉 step edges. It tentatively traced back an hierarchy atom diffusion speeds along edges this range.
A new approach for the determination of activation energy and attempt frequency diffusion single adatoms on a surface is proposed demonstrated Pt adatom Pt(111). The method based combination low temperature scanning tunneling microscopy (STM) measurements kinetic Monte Carlo simulations. involves only minimum assumptions independent classical nucleation theory. This independence allows one to analyze applicability latter. In addition, it found that measurement mean square displacement...
The ${\mathrm{H}}_{2}$O adsorption on Pt(111) at 140 K is investigated by temperature-variable scanning tunneling microscopy. adsorbs preferentially the upper side of step edges. At these low coordination sites adsorbates are bound stable as quasi-one-dimensional chains up to 160 K. In contrast, desorption from two-dimensional islands terrace has already started 145 occupancy edges different two types dense packed steps. This anisotropy correlated with dipole moment
Whereas on the clean (111) surface Pt grows in a multilayer (3D) mode at 300 and 400 K, preadsorption of an ordered p(2\ifmmode\times\else\texttimes\fi{}2) oxygen overlayer leads to high quality layer-by-layer (2D) growth with floating film. In contrast other surfactants can be completely removed from film temperature. It is demonstrated that presence reduces barrier height for motion PT adatoms across step edges. This facilitates interlayer mass transport thus growth.
Using X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM) we resolve the temperature-, time-, flake size-dependent intercalation phases of oxygen underneath graphene on Ir(111) formed upon exposure to molecular oxygen. Through applied pressure atomic created bare Ir terraces is driven flakes. The importance substrate steps unbinding edges from for identified. With use CO titration selectively remove energetics uncovered. Cluster decoration techniques are used as an...
On the graphene moire on Ir(111) a variety of highly perfect cluster superlattices can be grown as shown is for Ir, Pt, W, and Re. Even materials that do not form upon room temperature deposition may into such by low or application seeding through Ir Au, AuIr, FeIr. Criteria suitability material to superlattice are given largely confirmed. It proven at least Pt even epitaxial superlattices. The stability investigated understood basis positional fluctuations clusters around their sites...
Following graphene growth by thermal decomposition of ethylene on Ir(111) at high temperatures we analyzed the strain state and wrinkle formation kinetics as function temperature. Using moiré spot separation in a low energy electron diffraction pattern magnifying mechanism for difference lattice parameters between Ir graphene, achieved an unrivaled relative precision ±0.1 pm parameter. Our data reveals characteristic hysteresis parameter that is explained interplay reversible film strain. We...
Using low-temperature scanning tunneling spectroscopy, we map the local density of states graphene quantum dots supported on Ir(111). Because a band gap in projected Ir structure around $K$ point, electronic properties QDs are dominantly graphenelike. Indeed, compare results favorably with tight binding calculations honeycomb lattice based parameters derived from functional theory. We find that interaction substrate near edge island gradually opens Dirac cone, which implies soft-wall...
Using the X-ray standing wave method, scanning tunneling microscopy, low energy electron diffraction, and density functional theory, we precisely determine lateral vertical structure of hexagonal boron nitride on Ir(111). The moiré superstructure leads to a periodic arrangement strongly chemisorbed valleys in an otherwise rather flat, weakly physisorbed plane. best commensurate approximation unit cell is (12 × 12) cells resting (11 11) substrate cells, which at variance with several earlier...
Using scanning tunneling microscopy and spectroscopy, for a monolayer of transition metal dichalcogenide H-NbS
CO coverages as low ${10}^{\ensuremath{-}3}$ monolayers---which may result from background partial pressures in the ${10}^{\ensuremath{-}11}$ mbar range---are found to affect island shapes, densities, step-edge barriers for adatoms and film roughness during homoepitaxial growth on Pt(111). The effects are traced preferential adsorption of molecules coordinated Pt atoms.
We develop a theory of nucleation on top two-dimensional islands bordered by steps with an additional energy barrier $\ensuremath{\Delta}{E}_{S}$ for descending atoms. The is based the concept residence time adatom island, and yields expression rate which becomes exact in limit strong step-edge barriers. This differs qualitatively quantitatively from that obtained using conventional rate-equation approach to [J. Tersoff et al., Phys. Rev. Lett. $72,$ 266 (1994)]. argue fails because...