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436 results on '"Meyer, B.K."'

204. Identification of Transition Metals in GaN

Author

Pressel, K., primary, Heitz, R., additional, Eckey, L., additional, Loa, I., additional, Thurian, P., additional, Hoffmann, A., additional, Meyer, B.K., additional, Fischer, S., additional, Wetzel, C., additional, and Haller, E.E., additional

Published
1995
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226. Structural properties of defects in Cd1−xZnxTe

Author

Hofmann, D.M., primary, Stadler, W., additional, Oettinger, K., additional, Meyer, B.K., additional, Omling, P., additional, Salk, M., additional, Benz, K.W., additional, Weigel, E., additional, and Müller-Vogt, G., additional

Published
1993
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245. W- and F-doped VO2films studied by photoelectron spectrometry

Author

Burkhardt, W, Christmann, T, Meyer, B.K, Niessner, W, Schalch, D, and Scharmann, A

Abstract

Thermochromic tungsten- and fluorine-doped vanadium dioxide films, which are in discussion as intelligent window coatings, were deposited by reactive sputtering. Results of optical measurements and photoelectron spectrometry (XPS, UPS) at low doping levels (≤2.6%) are presented, and together with structural properties they can be well correlated. By applying antireflective coatings the transmittance of films in the visible spectral range may be enhanced to more than 60% with fairly good switching characteristics at room temperature in the case of tungsten doping.

Published
1999
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246. Electron traps in the scintillator material PbWO4and their correlation to thermally stimulated luminescence

Author

Böhm, M., Henecker, F., Hofstaetter, A., Luh, M., Meyer, B.K., Scharmann, A., Kondratiev, O.V., and Korzhik, M.V.

Abstract

AbstractVarious efforts to improve radiation hardness and scintillation properties of lead tungstate with respect to its application in high energy calorimeters by doping with suitable ions like Nb, La, Gd or Lu have been checked for their success mainly by studying optical absorption and thermally stimulated luminescence (TSL) after irradiation at room temperature, in a few cases at liquid nitrogen temperature. Very shallow traps, which contribute to fast scintillation processes, are not stabilized under such conditions. Extending the temperature range for irradiation as well as for experimental studies down to liquid helium temperature, we found new TSL glow peaks and established a correlation to electrons captured by anionic WO4complexes. Their electron spin resonsnance (ESR) data together with other experimental results like temperature dependence of photoconductivity give distinct hints with respect to the energy level scheme of PbWO4.

Published
1999
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247. Defects in CuIn(Ga)Se2solar cell material characterized by positron annihilation: post-growth annealing effects

Author

Börner, F, Gebauer, J, Eichler, S, Krause-Rehberg, R, Dirnstorfer, I, Meyer, B.K, and Karg, F

Abstract

Thin (∼1μm) CuIn(Ga)Se2layers were grown by the rapid thermal processing technique under In-rich conditions. The as-grown samples were slightly p-type but highly compensated. They showed strong positron trapping in vacancies, indicated by a large valence annihilation parameter S. In order to identify the vacancies, we applied a novel PAS-method. In that, we compare the element-specific high-momentum part of the annihilation momentum distribution f(p) in CuInSe2with f(p) from the pure elements constituting the material (i.e. with Cu, In and Se). The results provide direct evidence that the vacancies in our as-grown CuInSe2layers are related to Cu vacancies. Annealing under Ar atmosphere did not alter the annihilation characteristics, i.e. it did not affect the vacancies. However, after annealing in air the samples become more heavily p-type and less compensated, whereas Sis drastically reduced. PAS measurements as a function of temperature revealed that this effect is not due to a reduction of the vacancy concentration but due to the additional presence of negatively charged ions introduced by the annealing process. According to recent results, these ions are attributed to oxygen acceptors OSe. These new acceptors account for the increase of p-type conductivity after air annealing.

Published
1999
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248. Synthesis and characterization of ZnO:Co2+ nanoparticles.

Author

Volbers, N., Zhou, H., Knies, C., Pfisterer, D., Sann, J., Hofmann, D.M., and Meyer, B.K.

Subjects
ZINC oxide, NANOPARTICLES, COBALT, X-ray diffraction, OPTICAL properties, ABSORPTION spectra, ELECTRON paramagnetic resonance, SPECTRUM analysis
Abstract

This work investigates cobalt doped ZnO nanoparticles prepared by using wet chemical methods. The nanoparticles have a typical size of 3–8 nm. The electronic structure as well as the optical and magnetic properties of Co2+ have been characterized. X-ray diffraction spectra of the powder show wurtzite ZnO with no secondary Co phases. In the energy range below the bandgap, the optical absorption spectra show the internal d–d transitions related to Co2+ incorporated on the Zn lattice site in ZnO. Low temperature photoluminescence measurements confirm these results. Based on the analysis of the g-valuesfor bulk ZnO:Co., electron paramagnetic resonance measurements coincide with the simulation of Co-doped ZnO powder. Thus far, no evidence for ferromagnetism has been obtained. [ABSTRACT FROM AUTHOR]

Published
2007
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