A5078486757- Quantum and electron transport phenomena
- Semiconductor Quantum Structures and Devices
- Advancements in Semiconductor Devices and Circuit Design
- Graphene research and applications
- Terahertz technology and applications
- Magnetic Field Sensors Techniques
- Surface and Thin Film Phenomena
- Semiconductor materials and devices
- Physics of Superconductivity and Magnetism
- Advanced Semiconductor Detectors and Materials
- Advanced Electrical Measurement Techniques
- Quantum Dots Synthesis And Properties
- Mechanical and Optical Resonators
- Magnetic properties of thin films
- Spectroscopy and Laser Applications
- Semiconductor Lasers and Optical Devices
- Laser-Matter Interactions and Applications
- Atomic and Subatomic Physics Research
- Spectroscopy and Quantum Chemical Studies
- Thin-Film Transistor Technologies
- Silicon Nanostructures and Photoluminescence
- Photonic and Optical Devices
- Molecular Junctions and Nanostructures
- Electronic and Structural Properties of Oxides
- Electron and X-Ray Spectroscopy Techniques
Physikalisch-Technische Bundesanstalt
2016-2025
University of Twente
2021
University of Duisburg-Essen
2021
Iowa State University
2021
Heinrich Heine University Düsseldorf
2015-2021
University of Latvia
2011
Radboud University Nijmegen
2011
Leibniz University Hannover
2009-2010
Universidad Autónoma de Madrid
2010
University of Manchester
2009
Controlled charge pumping in an $\mathrm{Al}\mathrm{Ga}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ gated nanowire by single-parameter modulation is experimentally and theoretically studied. Transfer of integral multiples the elementary per cycle clearly demonstrated. A simple theoretical model shows that such a quantized current can be generated via loading unloading dynamic quasibound state. It demonstrates nonadiabatic blockade unwanted tunnel events obliterate requirement having at least two...
In this letter, we report the room-temperature operation of an electrically controlled THz modulator. The modulation is achieved by reducing electron density in a gated two-dimensional gas structure, which leads to increase transmitted intensity incident beam radiation. By depleting 1012 cm−2, maximum depth 3% for pulse terahertz radiation covering range frequencies from 0.1 2 THz.
We present a new fabrication method for epitaxial graphene on SiC which enables the growth of ultra-smooth defect- and bilayer-free sheets with an unprecedented reproducibility, necessary prerequisite wafer-scale high quality graphene-based electronic devices. The inherent but unfavorable formation surface terrace steps during temperature sublimation is suppressed by rapid buffer layer stabilizes surface. enhanced nucleation enforced decomposition polymer adsorbates act as carbon source....
The first THz imaging spectrometer based on continuous-wave radiation is presented. new setup less expensive and more compact than conventional time-domain systems that comprise femtosecond lasers instead. As an example we investigate a human liver with metastasis.
The first demonstration has been made of the transmission an audio signal via a THz communication channel using recently developed room temperature semiconductor modulator which is based on depletion two-dimensional electron gas. A standard time-domain spectroscopy setup modified to transmit signals up 25 kHz over 75 MHz train broadband pulses.
Abstract We present experimental data on the correlation between defect density and Fermi-level position in hydrogenated amorphous silicon (a-Si: H) films doped substitutionally with phosphorus or boron, interstitially lithium. In particular results obtained by in- out-diffusion of lithium suggest that doping formation a-Si: H are controlled an intrinsic process which both creation annihilation occur. compare our predictions two hydrogen-based models for thermal eauilibrium state a-Si:H....
We report noninvasive single-charge detection of the full probability distribution ${P}_{n}$ initialization a quantum dot with $n$ electrons for rapid decoupling from an electron reservoir. analyze data in context model sequential tunneling pinch-off, which has generic solutions corresponding to two opposing mechanisms. One limit considers ``freeze-out'' adiabatically evolving grand canonical distribution, other one is athermal equivalent solution generalized decay cascade model. identify...
The future redefinition of the international system units in terms natural constants requires a robust, high-precision quantum standard for electrical base unit ampere. However, reliability any single-electron current source generating nominally quantized output I=ef by delivering single electrons with charge e at frequency f is eventually limited stochastic nature underlying mechanical tunneling process. We experimentally explore path to overcome this fundamental limitation serially...
We report on characterizations of single-electron pumps at the highest accuracy level, enabled by improvements small-current measurement technique. With these a new record in measurements is demonstrated: 0.16 µA · A−1 relative combined uncertainty was reached within less than 1 d time. Additionally, robustness tests pump operation sub-ppm level revealed good stability tunable-barrier against variations operating parameters.
We present a THz investigation of histo-pathological samples including the larynx pig and human liver with metastasis. Our measurements show that different types tissue can be clearly distinguished in transmission images, either within single image or by comparison images obtained for frequency windows. This leads to problem frequencies inherently have spatial resolution. An from two such simple mathematical operation may contain artefacts. discuss measures deal this problem. Furthermore, we...
This paper investigates a scheme for quantized charge pumping based on single-parameter modulation. The device was realized in an AlGaAs–GaAs gated nanowire. We find remarkable robustness of the regime against variations driving signal, which increases with applied rf power. feature, together its simple configuration, makes this potential module scalable source current.
We advance spin noise spectroscopy to the ultimate limit of single detection. This technique enables measurement dynamic a heavy hole localized in flat (InGa)As quantum dot. Magnetic field and light intensity dependent studies reveal even at low magnetic fields strong dependence longitudinal relaxation time with an extremely long T1 ≥180 μs 31 mT 5 K. The wavelength power discloses for finite intensities inhomogeneous dot spectrum which is explained by charge fluctuations direct neighborhood...
We report on high-accuracy measurements of quantized current, sourced by a tunable-barrier single-electron pump at frequencies $f$ up to $1$ GHz. The were performed with new picoammeter instrument, traceable the Josephson and quantum Hall effects. Current quantization according $I=ef$ $e$ elementary charge was confirmed $f=545$ MHz total relative uncertainty 0.2 ppm, improving state art about factor 5. For first time, accuracy possible future current standard based transport experimentally...
We report on electronic transport measurements in rotational square probe configuration combination with scanning tunneling potentiometry of epitaxial graphene monolayers which were fabricated by polymer-assisted sublimation growth SiC substrates. The absence bilayer the ultralow step edges below 0.75 nm scrutinized atomic force microscopy and result a not yet observed resistance isotropy 4H- 6H-SiC(0001) substrates as low 2%. combine microscopic properties nanoscale experiments thereby...
Hall field induced resistance oscillations (HIROs) are studied in two-dimensional electron gases with resistivities dominated by scattering at identical but randomly distributed circular obstacles hard walls. For sufficiently high number densities, these dominate the HIROs, even though they remain sparse comparison to intrinsic scatterers. With increasing obstacle density, we observe a monotonous increase of HIRO period up factor 2. The results interpreted terms substantial localization...
We have determined the size, shape, and composition of $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dots (QDs) InAs QDs embedded in an AlAs barrier by cross-sectional scanning tunneling microscopy. The outward relaxation lattice constant cleaved surface their wetting layers were calculated using continuum elasticity theory compared with experimental data order to determine indium concentration dots. Based on structural results we electronic ground states a single band, effective...
We study single-parameter quantized charge pumping via a semiconductor quantum dot in high magnetic fields. The is defined between two top gates an AlGaAs/GaAs heterostructure. Application of oscillating voltage to one the leads pumped current plateaus gate characteristic, corresponding controlled transfer integer multiples electrons per cycle. In perpendicular-to-plane field become more pronounced indicating improved quantization. Current quantization sustained up fields where full spin...
The homogeneous and inhomogeneous linewidths of the heavy-hole exciton resonance in a (110)-oriented GaAs multiple-quantum-well sample are measured using optical two-dimensional Fourier transform spectroscopy. By probing nonlinear response for polarization along in-plane crystal axes [1$\overline{1}$0] [001], we measure different two orthogonal directions. This difference is found to be due anisotropic excitation-induced dephasing, caused by crystal-axis-dependent absorption coefficient....
Graphene, the first true two-dimensional material still reveals most remarkable transport properties among growing class of materials. Although many studies have investigated fundamental scattering processes, surprisingly large variation in experimentally determined resistances associated with a localized defect is an open issue. Here, we quantitatively investigate local graphene prepared by polymer assisted sublimation growth (PASG) using scanning tunneling potentiometry. PASG characterized...
We show that the composition of (segregated) InAs wetting layers (WLs) can be determined by either direct counting indium atoms or analysis outward displacement cleaved surface as measured cross-sectional scanning tunneling microscopy. use this approach to study effects deposited amount indium, growth rate, and host material on formation WLs. conclude WLs is a delicate interplay between migration, strain-driven segregation, dissolution quantum dots during overgrowth.