A5018926919- Graphene research and applications
- Quantum and electron transport phenomena
- Topological Materials and Phenomena
- Surface and Thin Film Phenomena
- Force Microscopy Techniques and Applications
- Advanced Condensed Matter Physics
- Physics of Superconductivity and Magnetism
- 2D Materials and Applications
- Phase-change materials and chalcogenides
- Electronic and Structural Properties of Oxides
- Chalcogenide Semiconductor Thin Films
- Molecular Junctions and Nanostructures
- Magnetic and transport properties of perovskites and related materials
- Mechanical and Optical Resonators
- Theoretical and Computational Physics
- Magnetic Properties and Applications
- Iron-based superconductors research
- Quantum Dots Synthesis And Properties
- Magnetic properties of thin films
- Nonlinear Optical Materials Studies
- Nuclear Engineering Thermal-Hydraulics
- Advanced Materials Characterization Techniques
- Carbon Nanotubes in Composites
- High-pressure geophysics and materials
- Nanopore and Nanochannel Transport Studies
RWTH Aachen University
2012-2024
Eindhoven University of Technology
2020
Czech Academy of Sciences, Institute of Physics
2017
Jülich Aachen Research Alliance
2009-2013
Yale University
2008-2009
Interface (United States)
2008-2009
Universität Hamburg
2000-2006
Seoul National University
2004
Using scanning tunneling microscopy in an ultrahigh vacuum and atomic force microscopy, we investigate the corrugation of graphene flakes deposited by exfoliation on a Si/SiO2 (300 nm) surface. While SiO2 is long range with correlation length about 25 nm, some monolayers exhibit additional preferential wavelength 15 nm. A detailed analysis shows that long-range substrate also visible graphene, but reduced amplitude, leading to conclusion partly freely suspended between hills substrate. Thus,...
Photoelectron spectroscopy in combination with piezoforce microscopy reveals that the helicity of Rashba bands is coupled to nonvolatile ferroelectric polarization GeTe(111). A novel surface band found and fingerprints a bulk are identified by comparison density functional theory calculations. As service our authors readers, this journal provides supporting information supplied authors. Such materials peer reviewed may be re-organized for online delivery, but not copy-edited or typeset....
One of the intriguing characteristics honeycomb lattices is appearance a pseudomagnetic field as result mechanical deformation. In case graphene, Landau quantization resulting from this has been measured using scanning tunneling microscopy. Here we show that signature local sublattice symmetry breaking observable redistribution density states. This can be interpreted polarization graphene's pseudospin due to strain induced field, in analogy alignment real spin magnetic field. We reveal by...
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...
Ferromagnetic topological insulators exhibit the quantum anomalous Hall effect that might be used for high precision metrology and edge channel spintronics. In conjunction with superconductors, they could host chiral Majorana zero modes which are among contenders realization of qubits. Recently, it was discovered stable 2+ state Mn enables formation intrinsic magnetic A1B2C4 stoichiometry. However, first representative, MnBi2Te4, is antiferromagnetic 25 K N\'eel temperature strongly n-doped....
The recently found material graphene is a truly two-dimensional crystal and exhibits, in addition, an extreme mechanical strength. This combination with the high electron mobility favours for electromechanical investigations down to quantum limit. Here, we show that monolayer of on SiO2 provides natural, ultra-small membranes diameters 3 nm, which are caused by intrinsic rippling material. Some these nano-membranes can be switched hysteretically between two vertical positions using electric...
Using high resolution spin- and angle-resolved photoemission spectroscopy, we map the electronic structure spin texture of surface states topological insulator Sb2Te3. In combination with density functional calculations (DFT), directly show that Sb2Te3 exhibits a partially occupied, single spin-Dirac cone around Fermi energy, which is topologically protected. DFT obtains polarization occupied Dirac 80-90%, in reasonable agreement experimental data after careful background subtraction....
A comprehensive mapping of the spin polarization electronic bands in ferroelectric a-GeTe(111) films has been performed using a time-of-flight momentum microscope equipped with an imaging filter that enables simultaneous measurement more than 10.000 data points (voxels). Rashba type splitting both surface and bulk opposite helicity inner outer is found revealing complex texture at Fermi energy. The switchable electric field GeTe implies new functionalities for spintronic devices.
By visualization of the Barkhausen effect using magnetic force microscopy we are able to provide detailed information about physical principles that govern magnetization reversal a granular ferromagnetic thin film with perpendicular anisotropy. Individual volumes localized and distinguished as either newly nucleated or grown by domain wall propagation. The Gaussian size distribution indicates an uncorrelated random process, while exhibit inverse power law distribution, which points towards...
We present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both tunneling microscopy (STM) noncontact force (NC-AFM) modes. A tuning-fork-based sensor provides flexibility selecting tip materials, which can be either metallic or nonmetallic. When choosing conducting sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems...
In order to stabilize Majorana excitations within vortices of proximity induced topological superconductors, it is mandatory that the Dirac point matches Fermi level rather exactly, such conventionally confined states vortex are well separated from Majorana-type excitation. Here, we show by angle resolved photoelectron spectroscopy (Bi1−xSbx)2Te3 thin films with x = 0.94 prepared molecular beam epitaxy and transferred in ultrahigh vacuum system photoemission setup match this condition. The...
The zigzag edges of graphene on Ir(111) are studied by ab initio simulations and low-temperature scanning tunneling spectroscopy, providing information about their structural, electronic, magnetic properties. No edge state is found to exist, which explained in terms the interplay between a strong geometrical relaxation at hybridization d orbitals Ir atoms with edge. As service our authors readers, this journal provides supporting supplied authors. Such materials peer reviewed may be...
A plasma source has been developed, which makes use of electron cyclotron microwave resonance conditions without cost-intensive tuning or other active elements. magnetron typical domestic ovens is coupled to a cylindrical resonator fixed dimensions. high density maintained with permanent magnets. Sources have designed for both vacuum and ultrahigh environments. In the latter, microwaves are conducted by coaxial feedthrough from ceramic cup inside chamber. This permits shorter working...
Using the recently developed technique of microsoldering, we perform a systematic transport study influence PMMA on graphene flakes revealing doping effect up to 3.8x10^12 1/cm^2, but negligible mobility and gate voltage induced hysteresis. Moreover, show that microsoldered is free contamination exhibits very similar intrinsic rippling as has been found for lithographically contacted flakes. Finally, demonstrate current closing previously phonon gap appearing in scanning tunneling...
InAs nanowires are grown epitaxially by catalyst-free metal organic vapor phase epitaxy and subsequently positioned with a lateral accuracy of less than 1 μm using simple adhesion forces between the an indium tip. The technique, requiring only optical microscope, is used to place individual onto corner cleaved-edge wafer as well across predefined holes in Si3N4 membranes. precision method limited stability micromanipulators microscope.
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 the design of a scanning force microscope, which is optimized for magnetic microscopy experiments. It can be operated at temperatures down to 5.2 K, in ultrahigh vacuum, and fields up 5 T. Cooling provided by liquid helium bath cryostat, field generated superconducting split-coil magnet. The allows easy access from side through shutter system fast situ tip sample exchange, while microscope stays below 25 K. itself features an all-fiber interferometric detection system, 7.5×7.5 μm2...
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...
Compound Bi14Rh3I9 consists of ionic stacks intermetallic [(Bi4Rh)3I]2+ and insulating [Bi2I8]2– layers has been identified to be a weak topological insulator. Scanning tunneling microscopy revealed the robust edge states at all step edges cationic layer as fingerprint. However, these are found 0.25 eV below Fermi level, which is an obstacle for transport experiments. Here, we address this by comparing results density functional slab calculations with scanning spectroscopy angle-resolved...
Data acquisition and analysis procedures for noncontact atomic force microscopy that allow the recording of dense three-dimensional (3D) surface energy fields with resolution are presented. The main obstacles producing high-quality 3D maps long times lead to data sets being distorted by drift, tip changes. Both problems reduced but not eliminated low-temperature operation.