Person: Díaz-Guerra Viejo, Carlos
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First Name
Carlos
Last Name
Díaz-Guerra Viejo
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de Materiales
Area
Física Aplicada
Identifiers
3 results
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Now showing 1 - 3 of 3
Item Luminescence from indented Te-doped GaSb crystals(Semiconductor Science and Technology, 2004) Chioncel, M. F.; Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, JavierCathodoluminescence in the scanning electron microscope has been used to investigate the effect of plastic deformation, produced by indentation, in Te-doped GaSb crystals. Deformation has been found to cause a strong quenching of the luminescence emission as well as spectral changes. In particular, the decrease of the near band edge emission is accompanied by the relative increase of the defect band A and of the 730 meV band related to the VGaGaSbTesb centres. Annealing treatments up to 600 degreesC lead to partial recovery of the deformation induced defects, and reveal the existence of Te out-diffusion processes from the deformed areas.Item Cathodoluminescence study of InxGa1_xSb crystals grown by the Bridgman method(Journal of Crystal Growth, 2004) Chioncel, M. F.; Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier; Vincent, J.; Bermúdez, V.; Diéguez, E.The nature and the spatial distribution of radiative defects in InxGa1-xSb grown by the vertical Bridgman method have been studied by cathodoluminescence (CL) in a scanning electron microscope. The CL results have been complemented by X-ray microanalysis and backscattered electron imaging to relate the local luminescence properties to the chemical composition. Measurements of the band-gap energy from the CL spectra, supported by X-ray compositional mappings, reveal an effective incorporation of In in the matrix, leading to the formation of the ternary alloy in the whole volume of the ingot. A low gradient of the In content along the growth axis has been found. The CL spectra of the ternary alloy exhibit similar general features to those reported for GaSb. An observed red shift of the near band edge luminescence in InxGa1-xSbx relative to that of GaSb, is due to the reduction in the band gap with increasing x. A band often observed in the CL spectra, peaked at about 20 meV below the band-gap energy, is attributed to the presence in the ternary alloy of an acceptor level that would correspond to the V-Ga-Ga-Sb acceptor in GaSb.Item Magnetic transitions in alpha-Fe_2O_3 nanowires(Journal of Applied Physics, 2009) Díaz-Guerra Viejo, Carlos; Pérez García, Lucas; Piqueras de Noriega, Javier; Chioncel, M. F.Magnetic transitions in single-crystal alpha-F_2O_3 (hematite) nanowires, grown by thermal oxidation of iron powder, have been studied in the range of 5-1023 K with a superconducting quantum interference device below room temperature and with a vibrating sample magnetometer at higher temperatures. The broad temperature range covered enables us to compare magnetic transitions in the nanowires with the transitions reported for bulk hematite. Morin temperatures (T-M) of the nanowires and of hematite bulk reference powder were found to be 123 and 263 K, respectively. Also the Neel temperature (T-N) of the nanowires, 852 K, was lower than the bulk T-N value. Measurements of the magnetization as a function of temperature show an enhanced signal in the nanowires, which suggests a decrease in the anti ferromagnetic coupling. A coercive field observed below T-M in the hysteresis loops of the nanowires is tentatively explained by the presence of a magnetic phase.