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
8 results
Search Results
Now showing 1 - 8 of 8
Item Study of charged defects in CdTe and CdHgTe by scanning electron and tunneling microscopy techniques(Izvestiya Akademii Nauk Seriya Fizicheskaya, 1998) Panin, G. N.; Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, JavierItem Cathodoluminescence microscopy and secondary electron emission in mechanically polished and electron irradiated YBa_2Cu_3O_(7-x) ceramics(Physica Status Solidi A-Applied Research, 1996) Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier; Tomashpolsky, Y. Y.; Sadovskaya, N. V.Cathodoluminescence (CL) and secondary electron emission (SEE) in the scanning electron microscope have been used to study the effects of mechanical polishing and electron irradiation on YBa2Cu3O7-x ceramics. CL spectra from the mechanically polished superconductors show an enhanced 2.4 eV luminescence band, which is related to oxygen content redistribution or depletion. Electron irradiation induces strong morphological and compositional changes which are proposed to be connected with melting-resolidification processes and surface phase segregation. SEE yield measurements allow to detect an oxygen depleted area with stoichiometric cationic composition surrounding the irradiated region. CL spectra recorded from this oxygen-deficient area also show an enhanced 2.3 to 2.4 eV emission band in comparison with the spectra recorded from the non-irradiated material. Strongly luminescent non-superconducting phases appear in the irradiated regions, showing intense 3.1 and 0.78 to 0.81 eV emission bands.Item Cathodoluminescence microscopy and spectroscopy of n-type 4H-SiC epilayers(European Physical Journal-Applied Physics, 2004) Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, JavierCathodoluminescence (CL) microscopy and spectroscopy have been used to investigate the nature and spatial distribution of defects and impurities in n-type epitaxial 4H-SiC. CL microscopy reveals the existence of 6H-SiC polytype inclusions, while CL spectra recorded at different excitation conditions show luminescence emission related to deep levels in the SiC epilayer. Deconvolution of the mentioned spectra indicates the complex character of the deep-level CL emission, that is actually composed of four bands centred near 2.72, 2.56, 2.42 and 2.00 eV at 88 K. The origin of these bands is discussed considering previous deep level transient spectroscopy measurements carried out in the same material investigated in the present work.Item Deep-level cathodoluminescence in deformed CdTe crystals(Physica Status Solidi A-Applied Research, 1995) Díaz-Guerra Viejo, Carlos; Pal, U.; Fernández Sánchez, Paloma; Piqueras de Noriega, JavierThe effect of indentation on the cathodoluminescence (CL) of CdTe in the scanning electron microscope is investigated. Deformation produces deep level emission changes, in particular, a relative intensity increase of the 1.4 and 1.1 eV bands, explained by vacancy generation. Deep level centers are not found to be related to the CL image contrast changes caused by annealing.Item Study of defects in In_xGa_(1-x)Sb bulk crystals(Physica Status Solidi C, 2005) Díaz-Guerra Viejo, Carlos; Chioncel, M. F.; Vincent, J; Bermudez, V.; Piqueras de Noriega, Javier; Diéguez, E.The homogeneity and luminescence properties of undoped and Te-doped In_xGa_(1-x)Sb crystals grown by the Bridgman and Vertical Feeding methods have been studied by cathodoluminescence (CL) and X-ray microanalysis in a scanning electron microscope. CL micrographs reveal the presence of non-radiative grain boundaries and dislocations in the investigated samples. Annealing at 650 degrees C for 36 h significantly improves the structural quality and the compositional homogeneity of the Te-doped crystals. CL spectra of the ternary alloy were found to show features similar to those reported for GaSb.Item Cathodoluminescence from nanocrystals in mechanically milled silicon(Beam Injection Assessment of Microestructures in Semiconductors, 20, 2000) Díaz-Guerra Viejo, Carlos; Montone, A.; Piqueras de Noriega, Javier; Cardellini, F.Mechanical milling is a technique extensively used to prepare nanocrystalline metallic materials but it has been less frequently applied to semiconductors. The preparation of nanocrystalline silicon by different methods is a subject of increasing interest due to the luminescent properties of this material and its possible application in optoelectronic devices. In this work high-energy ball milling has been used to prepare nanocrystals from single crystalline silicon wafers. The structure of the milled samples has been assessed by X-ray diffraction, transmission electron microscopy (TEM) and Raman spectroscopy, while their luminescence has been investigated by cathodoluminescence (CL) in the scanning electron microscope (SEM). The samples consist of a powder of particles with sizes of hundreds of nanometers aggregated to form bigger particles of several microns. TEM reveals that the particles consist of nanocrystals with a wide range of sizes including crystallites with dimension of few nanometers. CL spectra of the milled samples show a band at 1.61 eV, attributed to the presence of nanocrystals through a quantum confinement effect. It is suggested that a milling induced infrared emission is related to a high density of extended defects present in the milled samples.Item Assessment of InGaSb crystals by cathodo-luminescence microscopy and spectroscopy(Journal of Optoelectronics and Advanced Materials, 2004) Chioncel, M. F.; Díaz-Guerra Viejo, Carlos; Piqueras de Noriega, Javier; Duhanian, N.; Duffar, T.Low band-gap InGaSb crystals are of interest for the development of thermo-photo-voltaic (TPV) cells and other devices operating in the infrared spectral range. In this work, cathodoluminescence (CL) in the scanning electron microscope (SEM) has been applied to study the homogeneity of InGaSb material grown by the vertical Bridgman technique with regard to effective incorporation of In to the ternary alloy and the nature and distribution of defects influencing the luminescence properties of this semiconductor. Back-scattered electron imaging and wavelength dispersive X-ray mapping were used as complementary techniques to CL for analysis of chemical composition and element distribution. The results show that local CL spectra provide information on the effective formation of the alloy, not revealed by other techniques.Item Cathodoluminescence and photoluminescence spectroscopy of NiO(Physica Status Solidi A-Applications and Materials Science, 1997) Díaz-Guerra Viejo, Carlos; Remon, A.; García, J. A.; Piqueras de Noriega, JavierCathodoluminescence (CL) and photoluminescence (PL) of nickel oxide (NiO) have been investigated. The observed emission bands in the visible and near infrared spectral ranges are attributed to Ni^(2+) intraionic transitions. Some of the features observed in the CL spectra recorded from vacuum annealed samples are tentatively attributed to electronic transitions involving defect-induced states located inside the charge-transfer gap of this transition metal oxide.