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Gross H.,University Wrzburg | Gross H.,Rutgers University | Bansal N.,Rutgers University | Kim Y.-S.,Rutgers University | Oh S.,Rutgers University
Journal of Applied Physics | Year: 2011

We report how argon bombardment induces metallic states on the surface of insulating SrTiO3 at different temperatures by combining in situ conductance measurements and model calculations. At cryogenic temperatures, ionic bombardment created a thin-but much thicker than the argon-penetration depth-steady-state oxygen-vacant layer, leading to a highly-concentric metallic state. Near room temperatures, however, significant thermal diffusion occurred and the metallic state continuously diffused into the bulk, leaving only low concentration of electron carriers on the surface. Analysis of the discrepancy between the experiments and the models also provided evidence for vacancy clustering, which seems to occur during any vacancy formation process and affects the observed conductance. © 2011 American Institute of Physics. Source


Bar M.,Helmholtz Center Berlin | Bar M.,University of Nevada, Las Vegas | Schubert B.-A.,Helmholtz Center Berlin | Marsen B.,Helmholtz Center Berlin | And 6 more authors.
Applied Physics Letters | Year: 2011

Air-exposed Cu2ZnSnS4 (CZTS) thin-film solar cell absorbers have been investigated by surface-sensitive x-ray photoelectron and x-ray-excited Auger electron spectroscopy, as well as by bulk-sensitive energy dispersive x-ray spectroscopy. We find a native surface oxidation of (mainly) tin, but also (to a lesser extent) of zinc and sulfur as well as evidence for a Cu-poor region at the surface of the absorber, best described by a Cu-free Zn-Sn-S surface layer. © 2011 American Institute of Physics. Source


Gross H.,University Wrzburg | Oh S.,Rutgers University
Applied Physics Letters | Year: 2011

We show that ionic-bombardment leads to noticeable resistive memory effect on pure SrTiO 3 (STO). In an Ar-bombarded STO crystal, two orders of resistance difference was observed between the high and low resistive states. We found that Ar-bombardment is more efficient than thermal-reduction in creating memory-effective oxygen vacancies. One of the advantages of the ionic-bombardment scheme is that it can be easily combined with lithographic processes to create spatially selective memory effect. © 2011 American Institute of Physics. Source


Buhmann H.,University Wrzburg
Journal of Applied Physics | Year: 2011

In a two-dimensional system the quantum spin Hall effect (QSHE) state is characterized by an insulating bulk and two counter-propagating helical edge states. These edge channels are protected by time reversal symmetry and spin currents propagate without dissipation. It was shown that HgTe-based quantum well structures are the most suitable candidates for its experimental realization. Here, the experimental requirements are discussed which lead to the observation of quantized edge channel transport which is one of the main signatures of the QSHE. Experiments will be presented which demonstrate the stability of the quantized conductance and its nonlocal character. Furthermore, evidence for the spin polarization of the QSHE edge channels is shown in an all-electrical measurement which demonstrates the potential of the QSHE for spin injection and detection applications in spintronics. © 2011 American Institute of Physics. Source


Ilchmann A.,TU Ilmenau | Wirth F.,University Wrzburg
At-Automatisierungstechnik | Year: 2013

We discuss the concept of 'minimum phase' for scalar semi Hurwitz transfer functions. The latter are rational functions where the denominator polynomial has its roots in the closed left half complex plane. In the present note, minimum phase is defined in terms of the derivative of the argument function of the transfer function. The main tool to characterize minimum phase is the Hurwitz reflection. The factorization of a weakly stable transfer function into an all-pass and a minimum phase system leads to the result that any semi Hurwitz transfer function is minimum phase if, and only if, its numerator polynomial is semi Hurwitz. To characterize the zero dynamics, we use the Byrnes-Isidori form in the time domain and the internal loop form in the frequency domain. The uniqueness of both forms is shown. This is used to show in particular that asymptotic stable zero dynamics of a minimal realization of a transfer function yields minimum phase, but not vice versa. © Oldenbourg Wissenschaftsverlag. Source

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