Drt Zahn | Technische Universität Chemnitz (original) (raw)

Papers by Drt Zahn

Journal of Raman Spectroscopy

Scientific reports, Jan 11, 2015

Ferromagnetism can occur in wide-band gap semiconductors as well as in carbon-based materials whe... more Ferromagnetism can occur in wide-band gap semiconductors as well as in carbon-based materials when specific defects are introduced. It is thus desirable to establish a direct relation between the defects and the resulting ferromagnetism. Here, we contribute to revealing the origin of defect-induced ferromagnetism using SiC as a prototypical example. We show that the long-range ferromagnetic coupling can be attributed to the p electrons of the nearest-neighbor carbon atoms around the VSiVC divacancies. Thus, the ferromagnetism is traced down to its microscopic electronic origin.

Scientific Reports, 2021

The use of an appropriate delivery system capable of protecting, translocating, and selectively r... more The use of an appropriate delivery system capable of protecting, translocating, and selectively releasing therapeutic moieties to desired sites can promote the efficacy of an active compound. In this work, we have developed a nanoformulation which preserves its magnetization to load a model anticancerous drug and to explore the controlled release of the drug in a cancerous environment. For the preparation of the nanoformulation, self-assembled magnetic nanospheres (MNS) made of superparamagnetic iron oxide nanoparticles were grafted with a monolayer of (3-aminopropyl)triethoxysilane (APTES). A direct functionalization strategy was used to avoid the loss of the MNS magnetization. The successful preparation of the nanoformulation was validated by structural, microstructural, and magnetic investigations. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to establish the presence of APTES on the MNS surface. The amine content quantified ...

Applied Surface Science, 2021

Abstract Si hyperdoped with chalcogens via ion implantation and pulsed laser melting is known to ... more Abstract Si hyperdoped with chalcogens via ion implantation and pulsed laser melting is known to exhibit strong room-temperature sub-bandgap photoresponse. As a thermodynamically metastable system, an impairment of the optoelectronic properties in hyperdoped Si materials occurs upon subsequent high-temperature thermal treatment (>500 °C). The substitutional Te atoms that cause the sub-bandgap absorption are removed from the Si matrix to form Te-related complexes, which are electrically and optically inactive. In this work, we explore the formation of defects in Te-hyperdoped Si layers which leads to the electrical deactivation upon furnace annealing through the analysis of optical and microstructural properties as well as positron annihilation lifetime spectroscopy. Particularly, Te-rich clusters are observed in samples thermally annealed at temperature reaching 950 °C and above. Combined with polarized Raman analysis and transmission electron microscopy, the observed crystalline clusters are suggested to be Si2Te3.

Journal of Physics: Condensed Matter, 2020

Index matching of guided modes in birefringent multilayered organic waveguides opens new prospect... more Index matching of guided modes in birefringent multilayered organic waveguides opens new prospects for the design of mode coupling and mode switching devices. We demonstrate index matching of guided modes in two multilayered structures, in (a) a PTCDA-Alq3-PTCDA three-layer and (b) a PTCDA-Alq3 effective medium multilayer waveguide. The optical waveguides were grown on a Pyrex substrate by organic molecular beam deposition. The occurrence of index matching was investigated both experimentally by measuring the effective refractive index dispersion of transverse electric and magnetic modes using the m-line technique and theoretically by modelling the index dispersion with a transfer matrix algorithm.

RSC Advances, 2019

Interaction of forming Au nanocrystals with single-layer carbon nitride nanosheets allows the sur... more Interaction of forming Au nanocrystals with single-layer carbon nitride nanosheets allows the surface plasmon resonance peak position of gold/carbon nitride composites to be tuned in a range of 520–610 nm.

MRS Proceedings, 2002

ABSTRACTVibrational properties of self-assembled InAs quantum dots (QD’s) embedded in AlAs and al... more ABSTRACTVibrational properties of self-assembled InAs quantum dots (QD’s) embedded in AlAs and aluminium oxide were studied by Raman spectroscopy. The InAs/AlAs QD structures were grown by molecular beam epitaxy on GaAs (001) substrates. The following main features of the phonon spectra of InAs/AlAs QD nanostructures were observed: 1) asymmetric lines of QD LO phonons affected by strain, confinement and size inhomogeneity of QD’s; 2) confined phonons of InAs wetting layer (WL); 3) two bands of interface phonons in the AlAs frequency region, attributed to modes associated with the planar interface WL/AlAs matrix and the three-dimensional QD/matrix interface; 4) doublets of folded acoustic phonons caused by periodicity in the multilayer QD structures. The influence of growth temperature, varied from 420 to 550°C, on the morphology of QD’s was investigated. QD’s grown at 420°C are found to have the smallest size. Increasing the temperature up to 480°C leads to the formation of larger I...

MRS Proceedings, 1996

6H silicon carbide (SiC) substrates were implanted with nitrogen and aluminum at different doses ... more 6H silicon carbide (SiC) substrates were implanted with nitrogen and aluminum at different doses and annealed in the temperature range from 1300°C-1700°C. Micro-Raman Spectroscopy (μ-RS) measurements were performed in two sample geometries (conventional plane-view and cross-sectional). Changes of the polytype from 6H- to a cubic (SiC)1-xAIN)x, and influences in the 6H-SiC wafer up to depths of 2μm were detected. The results obtained by crosssectional μ-RS are discussed in comparison to other results from Reflection High Electron Energy Diffraction (RHEED), Rutherford Backscattering (RBS), Auger Electron Spectroscopy (AES), Transmission Electron Microscopy (TEM), and Positron Annihilation Spectroscopy (PAS) measurements.

Physics of the Solid State, 2012

Nanotechnology, 2014

Stable colloidal solutions of zinc oxide in dimethylsulfoxide were synthesized via interaction be... more Stable colloidal solutions of zinc oxide in dimethylsulfoxide were synthesized via interaction between zinc(II) acetate and tetraalkylammonium hydroxides (alkyl-ethyl, propyl, butyl, and pentyl). Colloids of ZnO emit photoluminescence in a broad band with a maximum at 2.3-2.4 eV with quantum yields of up to 9-10% at room temperature and 15-16% at 80 K. The photoluminescence is supposed to originate from the radiative recombination of conduction band electrons with holes captured by deep traps having corresponding states in the band gap 1.0-1.2 eV above the valence band edge. The size of colloidal ZnO nanocrystals depends on the duration and temperature of the post-synthesis treatment and varies in the range of 3-6 nm. Growth of the ZnO nanocrystals can be terminated at any moment of the thermal treatment by freezing the colloidal solution or by addition of tetraethyl orthosilicate which hydrolyses forming core-shell ZnO@SiO2 particles. ZnO nanocrystals introduced into polyethyleneimine films can be used as an active component of an LED emitting at an applied voltage higher than 13 V.

Journal of Applied Physics, 2001

Properties of the buried silicon oxide layer in Si–Si bonded wafers upon annealing were studied u... more Properties of the buried silicon oxide layer in Si–Si bonded wafers upon annealing were studied using Infrared (IR) spectroscopy and high resolution transmission electron microscopy (HRTEM). IR spectra of chemically etched Si–Si bonded wafers allow the thickness of the buried oxide layers to be evaluated. The increasing thickness of the buried oxide layer with annealing temperature is determined via a curve fitting procedure of IR spectra measured in the spectral range of longitudinal optical and transversal optical phonons in silicon oxide. The behavior observed is in very good agreement with that obtained from HRTEM measurements.

IEEE Transactions on Magnetics, 2012

The European Physical Journal B, 2000

: Self-organised Ge dot superlattices grown by molecular beam epitaxy of Ge and Si layers utili... more : Self-organised Ge dot superlattices grown by molecular beam epitaxy of Ge and Si layers utilizing Stranski-Krastanov growth mode were investigated by Raman spectroscopy. An average size of Ge quantum dots was obtained from transmission electron microscopy measurements. The strain and interdiffusion of Ge and Si atoms in Ge quantum dots were estimated from the analysis of frequency positions of

Journal of Physics: Condensed Matter, 2004

Analysis of charge transient spectroscopy data originating from Gaussian densities of electron st... more Analysis of charge transient spectroscopy data originating from Gaussian densities of electron states in organics