A5027389982- Graphene research and applications
- Topological Materials and Phenomena
- Quantum and electron transport phenomena
- Surface and Thin Film Phenomena
- Semiconductor materials and interfaces
- Force Microscopy Techniques and Applications
- Electronic and Structural Properties of Oxides
- Nanopore and Nanochannel Transport Studies
- Nonlinear Optical Materials Studies
- Phase-change materials and chalcogenides
- Molecular Junctions and Nanostructures
- Advancements in Battery Materials
- Electrocatalysts for Energy Conversion
- 2D Materials and Applications
- Advanced Battery Technologies Research
- Advanced Condensed Matter Physics
- Semiconductor materials and devices
- Electron and X-Ray Spectroscopy Techniques
RWTH Aachen University
2013-2021
Leibniz Institute for Solid State and Materials Research
2021
Forschungszentrum Jülich
2015-2020
Jülich Aachen Research Alliance
2017-2020
In scanning tunneling microscopy, we witness in recent years a paradigm shift from "just imaging" to detailed spectroscopic measurements at the nanoscale and multi-tip microscope (STM) is technique following this trend. It capable of performing charge transport like "multimeter nanoscale." Distance-dependent four-point measurements, acquisition potential maps current carrying nanostructures surfaces, as well I - V curves nanoelectronic devices are examples capabilities STM technique. review,...
Four-point measurements using a multitip scanning tunneling microscope are carried out in order to determine surface and step conductivities on Si(111) surfaces. In first step, distance-dependent four-point the linear configuration used combination with an analytical three-layer model for charge transport disentangle 2D conductivity from nonsurface contributions. A termination of either Bi or H results two limiting cases pure 3D conductance, respectively. further step-free contribution due...
Dominating electron-electron scattering enables viscous electron flow exhibiting hydrodynamic current density patterns, such as Poiseuille profiles or vortices. The regime has recently been observed in graphene by nonlocal transport experiments and mapping of the profile. Herein, we probe current-induced surface potential maps field-effect transistors with moderate mobility using scanning microscopy at room temperature. We discover micrometer-sized large areas appearing close to charge...
We present an angle-resolved photoemission study of a ternary phase change material, namely Ge2Sb2Te5, epitaxially grown on Si(111) in the metastable cubic phase. The observed upper bulk valence band shows minimum at Gamma-bar being 0.3 eV below Fermi level E_F and circular contour around with dispersing diameter 0.27-0.36 Anstroms^-1. This is agreement density functional theory calculations Petrov stacking sequence which exhibits topological surface state. topologically trivial KH maximum...
Abstract In the thin film limit, surface state of a three-dimensional topological insulator gives rise to two parallel conduction channels at top and bottom film, which are difficult disentangle in transport experiments. Here, we present gate-dependent multi-tip scanning tunneling microscope measurements combined with photoemission experiments all performed situ on pristine BiSbTe 3 films. To analyze data, develop generic model including quantum capacitance effects. This approach allows us...
An analytical $N$-layer model for charge transport close to a surface is derived from the solution of Poisson's equation and used describe distance-dependent electrical four-point measurements on microscale. As comprises channel, multiple intermediate layers, semi-infinite bulk, it can be applied semiconductors in combination with calculation near-surface band bending very precisely measured resistance specific sample extract value conductivity. For describing geometries mixed 2D-3D...
Monolayer graphene grown by chemical vapor deposition and transferred to ${\mathrm{SiO}}_{2}$ is used introduce vacancies ${\mathrm{Ar}}^{+}$ ion bombardment at a kinetic energy of 50 eV. The density defects visible in scanning tunneling microscopy considerably lower than the fluence, implying that most are single as expected from low energy. characterized spectroscopy on highly oriented pyrolytic graphite (HOPG). A peak close Dirac point found within local states similar previously for...
We present a combined experimental and theoretical analysis of Te rich interface layer which represents template for chalcogenide-based van der Waals epitaxy on Si(111). On clean Si(111)-$(1\ifmmode\times\else\texttimes\fi{}1)$ surface, we find to form Te/Si(111)-$(1\ifmmode\times\else\texttimes\fi{}1)$ reconstruction saturate the substrate bonds. A problem arising is that such an can potentially be highly conductive, undermining applicability on-top grown films in electric devices. perform...
Thin films of topological insulators (TI) usually exhibit multiple parallel conduction channels for the transport electrical current. Aside from topologically protected surface states (TSS), may exist, namely, interior not-ideally insulating TI film, interface layer to substrate, and substrate itself. To be able take advantage auspicious properties TSS, influence parasitic on total current has minimized. Because conductivity (bulk) thin film is difficult access by measurements, we propose...
We review the contributions of surface science methods to discover and improve 3D topological insulator materials, while illustrating with examples from our own work. In particular, we demonstrate that spin-polarized angular-resolved photoelectron spectroscopy is instrumental evidence spin-helical Dirac cone, tune its point energy towards Fermi level, novel types insulators such as dual ones or switchable in phase change materials. Moreover, introduce procedures spatially map potential...