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© 1997 Elsevier Science B.V. All rights reserved. International Conference on luminescence and Optical Spectroscopy of Condensed Matter (ICL 96) (1996. Praga). C. Xavier thanks JNICT for a grant BM/6613/95. This work was partially supported by JNICT Project0 no. BIC/C/CTM/1925/95., Mid-band-gap emissions in GaN epilayers grown on 6H-SiC and sapphire are studied by time-resolved spectroscopy (TRS). The yellow luminescence peaking at ca. 1.2 eV at low-temperature shifts to higher energies with increasing temperature. The presence of emission with the same characteristics in samples grown on different substrates and by different processes indicates that the defects responsible for the emission are of intrinsic nature but dependent on the cubic or hexagonal habit of the crystals. TRS are compared with cathodoluminescence (CL) in a scanning electron microscope (SEM) and optically detected magnetic resonance (ODMR) data., JNICT, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

In this work, we present a procedure to grow Cu12Sb4S13 and Cu3SbS4 thin films consisting of the deposition of simultaneously sputtered metal precursors followed by a annealing treatment in a sulphur atmosphere. The selection of the ternary phase is performed by adjusting the sulphur evaporation temperature in the chalcogenization process. It is shown that for a sulphur evaporation temperature of 140 °C the predominant phase is Cu12Sb4S13 while for 180 °C the predominant phase is Cu3SbS4. In order to ensure precursor composition homogeneity, the Cu-Sb metallic precursors are deposited simultaneously by RF magnetron sputtering using adjustable segmented targets. The morphological characterization of the films was made by scanning electron microscopy and the composition was analysed by energy dispersive spectroscopy. The structural analysis and phase identification were performed by X-ray diffraction and Raman scattering. The optical properties were studied on films deposited directly on bare glass and the optical bandgap energies of 1.47 eV and 0.89 eV for Cu12Sb4S13 and Cu3SbS4, respectively, were determined.

Buckminster fullerene (C-60) based hybrid metal oxide materials are receiving considerable attention because of their excellent fundamental and applied aspects, like semiconducting, electron transfer, luminescent behaviors, etc. and this work briefly discusses the successful fabrication of C-60 decorated ZnO tetrapod materials and their detailed structure-property relationships including device sensing applications. The electron microscopy investigations indicate that a quite dense surface coverage of ZnO tetrapods with C-60 clusters is achieved. The spectroscopy studies confirmed the identification of the C-60 vibrational modes and the C-60 induced changes in the absorption and luminescence properties of the ZnO tetrapods. An increased C-60 concentration on ZnO results in steeper ZnO bandgap absorption followed by well-defined free exciton and 3.31 eV line emissions. As expected, higher amounts of C-60 increase the intensity of C-60-related visible absorption bands. Pumping the samples with photons with an energy corresponding to these absorption band maxima leads to additional emission from ZnO showing an effective charge transfer phenomenon from C-60 to the ZnO host. The density of states model obtained from DFT studies for pure and C-60 coated ZnO surfaces confirms the experimental observations. The fabricated C-60-ZnO hybrid tetrapod based micro- and nanodevices showed interesting ethanol gas sensing characteristics.

In this work, we investigate the structural and photoluminescence (PL) properties of (SiGe+Al2O3)/Al2O3 multi-layer films with layer thicknesses in the range of a few nanometres. The films were prepared by magnetron sputtering deposition at room temperature followed by an annealing process to promote the formation of small SiGe nanocrystals (NCs) (∼3 to 5 nm) embedded between ultra-thin (∼6 nm thickness) Al2O3 layers. Our results show that the structural and compositional properties of the films can be tuned by changing the RF-power. It is found that nearly spherical and well confined isolated SiGe NCs (∼5 nm) are obtained for an RF-power value of 80 W. The PL properties of the films were studied and optical emission in the blue visible wavelength region was observed. © 2013 IOP Publishing Ltd.

[EN] We report hot filament thermal CVD (HFTCVD) as a new hybrid of hot filament and thermal CVD and demonstrate its feasibility by producing high quality large area strictly monolayer graphene films on Cu substrates. Gradient in gas composition and flow rate that arises due to smart placement of the substrate inside the Ta filament wound alumina tube accompanied by radical formation on Ta due to precracking coupled with substrate mediated physicochemical processes like diffusion, polymerization etc., led to graphene growth. We further confirmed our mechanistic hypothesis by depositing graphene on Ni and SiO 2/Si substrates. HFTCVD can be further extended to dope graphene with various heteroatoms (H, N, and B, etc.,), combine with functional materials (diamond, carbon nanotubes etc.,) and can be extended to all other materials (Si, SiO 2, SiC etc.,) and processes (initiator polymerization, TFT processing) possible by HFCVD and thermal CVD.

High quality Al1xInxN/GaN bilayers, grown by metal organic chemical vapor deposition (MOCVD), were characterized using structural and optical techniques. Compositional analysis was performed using Rutherford backscattering spectrometry(RBS) and elastic recoil detection analysis (ERDA). The InN molar fraction x decreased approximately linearly with increasing growth temperature and ranged from x¼0.13 to0.24. Up tox¼0.20 the layers grow pseudomorphically to GaN with good crystalline quality. These layers show a smoothsurface with V-shaped pits. Two layers with InN contents around 24% showed partial strain relaxation. However, themechanisms leading to relaxation of compressive strain arevery different in the two samples grown both at similartemperature but with different growth rates. One sample shows a decreased c/a ratio, as expected for relaxation of the compressive strain, while In was shown to be homogeneouslydistributed with depth. The other sample started to grow withx¼0.24 but relaxed mainly by reduction of the incorporated InN content towards the lattice-match composition of x0.17. Both samples have an increased surface roughness. All samples show strong Al1xInxN band edge luminescence with large bowing parameter and Stokes’ shifts.

High quality Al1-xInxN/GaN bilayers, grown by Metal Organic Chemical Vapour Deposition (MOCVD), were characterized using structural and optical techniques. Compositional analysis was performed using Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA). The InN molar fraction x decreased approximately linearly with increasing growth temperature and ranged from x=0.13 to 0.24. Up to x=0.20 the layers grow pseudomorphically to GaN with good crystalline quality. These layers show a smooth surface with V-shaped pits. Two layers with InN contents around 24% showed partial strain relaxation. However, the mechanisms leading to relaxation of compressive strain are very different in the two samples grown both at low temperature but with different growth rate. One sample shows a decreased c/a ratio, as expected for relaxation of the compressive strain, while In was shown to be homogeneously distributed with depth. Another sample started to grow with x=0.24 but relaxed mainly by reduction of the incorporated InN content towards the lattice-match composition of x~0.17. Both samples have an increased surface roughness. All samples show strong Al1-xInxN band edge luminescence with large bowing parameter and Stokes’ shifts.