TY  - JOUR
A1  - Chenari, Hossein Mahmoudi
A1  - Seibel, Christoph
A1  - Hauschild, Dirk
A1  - Reinert, Friedrich
A1  - Abdollahian, Hossein
T1  - Titanium Dioxide Nanoparticles: Synthesis, X-Ray Line Analysis and Chemical Composition Study
JF  - Materials Research
N2  - TiO2 nanoparticleshave been synthesized by the sol-gel method using titanium alkoxide and isopropanolas a precursor. The structural properties and chemical composition of the TiO2 nanoparticles were studied usingX-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy.The X-ray powder diffraction pattern confirms that the particles are mainly composed of the anatase phase with the preferential orientation along [101] direction. The physical parameters such as strain, stress and energy density were investigated from the Williamson- Hall (W-H) plot assuming a uniform deformation model (UDM), and uniform deformation energy density model (UDEDM). The W-H analysis shows an anisotropic nature of the strain in nanopowders. The scanning electron microscopy image shows clear TiO2 nanoparticles with particle sizes varying from 60 to 80nm. The results of mean particle size of TiO2 nanoparticles show an inter correlation with the W-H analysis and SEM results. Our X-ray photoelectron spectroscopy spectra show that nearly a complete amount of titanium has reacted to TiO2
KW  - TiO\(_2\)
KW  - Nanoparticles
KW  - X-ray analysis
KW  - SEM
KW  - XPS
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-165807
VL  - 19
IS  - 6
ER  - 
TY  - JOUR
A1  - Fiedler, Sebastian
A1  - El-Kareh, Lydia
A1  - Eremeev, Sergey V.
A1  - Tereshchenko, Oleg E.
A1  - Seibel, Christoph
A1  - Lutz, Peter
A1  - Kokh, Konstantin A.
A1  - Chulkov, Evgueni V.
A1  - Kuznetsova, Tatyana V.
A1  - Grebennikov, Vladimir I.
A1  - Bentmann, Hendrik
A1  - Bode, Matthias
A1  - Reinert, Friedrich
T1  - Defect and structural imperfection effects on the electronic properties of BiTeI surfaces
JF  - New Journal of Physics
N2  - The surface electronic structure of the narrow-gap seminconductor BiTeI exhibits a large Rashba-splitting which strongly depends on the surface termination. Here we report on a detailed investigation of the surface morphology and electronic properties of cleaved BiTeI single crystals by scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), electron diffraction (SPA-LEED) and density functional theory calculations. Our measurements confirm a previously reported coexistence of Te- and I-terminated surface areas originating from bulk stacking faults and find a characteristic length scale of ~100 nm for these areas. We show that the two terminations exhibit distinct types of atomic defects in the surface and subsurface layers. For electronic states resided on the I terminations we observe an energy shift depending on the time after cleavage. This aging effect is successfully mimicked by depositon of Cs adatoms found to accumulate on top of the I terminations. As shown theoretically on a microscopic scale, this preferential adsorbing behaviour results from considerably different energetics and surface diffusion lengths at the two terminations. Our investigations provide insight into the importance of structural imperfections as well as intrinsic and extrinsic defects on the electronic properties of BiTeI surfaces and their temporal stability.
KW  - electronic structure
KW  - spin–orbit coupling
KW  - surface morphology
KW  - semiconductor surfaces
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-119467
SN  - 1367-2630
VL  - 16
IS  - 075013
ER  - 
TY  - JOUR
A1  - Lüftner, Daniel
A1  - Milko, Matus
A1  - Huppmann, Sophia
A1  - Scholz, Markus
A1  - Ngyuen, Nam
A1  - Wießner, Michael
A1  - Schöll, Achim
A1  - Reinert, Friedrich
A1  - Puschnig, Peter
T1  - CuPc/Au(1 1 0): Determination of the azimuthal alignment by a combination of angle-resolved photoemission and density functional theory
JF  - Journal of Electron Spectroscopy and Related Phenomena
N2  - Here we report on a combined experimental and theoretical study on the structural and electronic properties of a monolayer of Copper-Phthalocyanine (CuPc) on the Au(1 1 0) surface. Low-energy electron diffraction reveals a commensurate overlayer unit cell containing one adsorbate species. The azimuthal alignment of the CuPc molecule is revealed by comparing experimental constant binding energy (kxky)-maps using angle-resolved photoelectron spectroscopy with theoretical momentum maps of the free molecule's highest occupied molecular orbital (HOMO). This structural information is confirmed by total energy calculations within the framework of van-der-Waals corrected density functional theory. The electronic structure is further analyzed by computing the molecule-projected density of states, using both a semi-local and a hybrid exchange-correlation functional. In agreement with experiment, the HOMO is located about 1.2 eV below the Fermi-level, while there is no significant charge transfer into the molecule and the CuPc LUMO remains unoccupied on the Au(1 1 0) surface.
KW  - density functional theory
KW  - angle-resolved photoemission spectroscopy
KW  - organic molecule
KW  - organic–metal interface
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-120986
SN  - 0368-2048
VL  - 195
ER  - 
TY  - JOUR
A1  - Bentmann, Hendrik
A1  - Reinert, Friedrich
T1  - Enhancing and reducing the Rashba-splitting at surfaces by adsorbates: Na and Xe on Bi/Cu(111)
JF  - New Journal of Physics
N2  - The surface alloy Bi/Cu(111) shows a paradigmatic free-electron-like surface state with a very large Rashba-type spin–orbit splitting. Using angle-resolved photoemission we investigate how adsorbates of different chemical nature influence the size of the spin splitting in this system. We find that the adsorption of small amounts of monovalent Na atoms leads to an enhancement of the spin splitting while an overlayer of the closed-shell rare gas Xe causes a reduction. The latter result is in contrast to the Au(111) surface for which an increased splitting size after Xe-adsorption was observed. We discuss these experimental findings in terms of the characteristic differences of the surface state wave functions and their spatial deformation in the presence of different types of adsorbates. Our results provide insight into the complex interplay of atomic and interface potential gradients governing the Rashba effect.
KW  - Rashba-Splitting
Y1  - 2013
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-129722
VL  - 15
IS  - 115011
ER  - 
TY  - JOUR
A1  - El-Kareh, Lydia
A1  - Bihlmayer, Gustav
A1  - Buchter, Arne
A1  - Bentmann, Hendrik
A1  - Blügel, Stefan
A1  - Reinert, Friedrich
A1  - Bode, Matthias
T1  - A combined experimental and theoretical study of Rashba-split surface states on the ( √3x√3) Pb/Ag (111)R30° surface
N2  - We report on a combined low-temperature scanning tunneling spectroscopy (STS), angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) investigation of the ( √3x√3) Pb/Ag (111)R30° surface alloy which provides a giant Rashba-type spin splitting. With STS we observed spectroscopic features that are assigned to two hole-like Rashba-split bands in the unoccupied energy range. By means of STS and quantum interference mapping we determine the band onsets, splitting strengths, and dispersions for both bands. The unambiguous assignment of scattering vectors is achieved by comparison to ARPES measurements. While intra-band scattering is found for both Rashba bands, inter-band scattering is only observed in the occupied energy range. Spin- and orbitally-resolved band structures were obtained by DFT calculations. Considering the scattering between states of different spin- and orbital character, the apparent deviation between experimentally observed scattering events and the theoretically predicted spin polarization could be resolved.
KW  - Rashba effect
KW  - spin–orbit coupling
KW  - scanning tunneling microscopy
KW  - angle resolved photo emission spectroscopy
KW  - density functional theory
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-112786
ER  - 
TY  - JOUR
A1  - Maaß, Henriette
A1  - Bentmann, Hendrik
A1  - Seibel, Christoph
A1  - Tusche, Christian
A1  - Eremeev, Sergey V.
A1  - Peixoto, Thiago R.F.
A1  - Tereshchenko, Oleg E.
A1  - Kokh, Konstantin A.
A1  - Chulkov, Evgueni V.
A1  - Kirschner, Jürgen
A1  - Reinert, Friedrich
T1  - Spin-texture inversion in the giant Rashba semiconductor BiTeI
JF  - Nature Communications
N2  - Semiconductors with strong spin–orbit interaction as the underlying mechanism for the generation of spin-polarized electrons are showing potential for applications in spintronic devices. Unveiling the full spin texture in momentum space for such materials and its relation to the microscopic structure of the electronic wave functions is experimentally challenging and yet essential for exploiting spin–orbit effects for spin manipulation. Here we employ a state-of-the-art photoelectron momentum microscope with a multichannel spin filter to directly image the spin texture of the layered polar semiconductor BiTeI within the full two-dimensional momentum plane. Our experimental results, supported by relativistic ab initio calculations, demonstrate that the valence and conduction band electrons in BiTeI have spin textures of opposite chirality and of pronounced orbital dependence beyond the standard Rashba model, the latter giving rise to strong optical selection-rule effects on the photoelectron spin polarization. These observations open avenues for spin-texture manipulation by atomic-layer and charge carrier control in polar semiconductors.
KW  - applied physics
KW  - spintronics
KW  - semiconductors
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-173769
VL  - 7
ER  - 
TY  - JOUR
A1  - Peixoto, Thiago R. F.
A1  - Bentmann, Hendrik
A1  - Rüßmann, Philipp
A1  - Tcakaev, Abdul-Vakhab
A1  - Winnerlein, Martin
A1  - Schreyeck, Steffen
A1  - Schatz, Sonja
A1  - Vidal, Raphael Crespo
A1  - Stier, Fabian
A1  - Zabolotnyy, Volodymyr
A1  - Green, Robert J.
A1  - Min, Chul Hee
A1  - Fornari, Celso I.
A1  - Maaß, Henriette
A1  - Vasili, Hari Babu
A1  - Gargiani, Pierluigi
A1  - Valvidares, Manuel
A1  - Barla, Alessandro
A1  - Buck, Jens
A1  - Hoesch, Moritz
A1  - Diekmann, Florian
A1  - Rohlf, Sebastian
A1  - Kalläne, Matthias
A1  - Rossnagel, Kai
A1  - Gould, Charles
A1  - Brunner, Karl
A1  - Blügel, Stefan
A1  - Hinkov, Vladimir
A1  - Molenkamp, Laurens W.
A1  - Friedrich, Reinert
T1  - Non-local effect of impurity states on the exchange coupling mechanism in magnetic topological insulators
JF  - NPJ Quantum Materials
N2  - Since the discovery of the quantum anomalous Hall (QAH) effect in the magnetically doped topological insulators (MTI) Cr:(Bi,Sb)\(_2\)Te\(_3\) and V:(Bi,Sb)\(_2\)Te\(_3\), the search for the magnetic coupling mechanisms underlying the onset of ferromagnetism has been a central issue, and a variety of different scenarios have been put forward. By combining resonant photoemission, X-ray magnetic circular dichroism and density functional theory, we determine the local electronic and magnetic configurations of V and Cr impurities in (Bi,Sb)\(_2\)Te\(_3\). State-of-the-art first-principles calculations find pronounced differences in their 3d densities of states, and show how these impurity states mediate characteristic short-range pd exchange interactions, whose strength sensitively varies with the position of the 3d states relative to the Fermi level. Measurements on films with varying host stoichiometry support this trend. Our results explain, in an unified picture, the origins of the observed magnetic properties, and establish the essential role of impurity-state-mediated exchange interactions in the magnetism of MTI.
KW  - shape-truncation functions
KW  - semiconductors
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-230686
VL  - 5
ER  -