Abstract: In this work, GaN growth on porous Si(111) will be reported. The porosity of the substrates was 30% or 50%. In the latter case, various thicknesses, from 0.6 mu m to 10 mu m, were investigated. The morphology of the GaN surfaces was analyzed by optical interference microscopy. The crystalline quality of the epitaxial layers was characterized by High Resolution X-Ray Diffraction (HR-XRD) and cross-sectional Transmission Electron Microscopy (TEM). A Full Width at Half Maximum (FWHM) of the X-ray symmetric rocking curve (0002) 2 theta – omega scan of 290 arc see was obtained for a 1 mu m thick GaN layer, which is comparable with that of GaN grown on bulk Si(111) substrates. (c) 2007 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim.

Abstract: We compare the magnetic properties of pure and oxidized Co nanoparticles embedded in an amorphous Al2O3 matrix. Nanoparticles with diameters of 2 or 3 nm were prepared by alternate pulsed laser deposition in high vacuum conditions, and some of them were exposed to O-2 after production and before being embedded. The nanoparticles are organized in layers, the effective edge-to-edge in-depth separation being 5 or 10 nm. The lower saturation magnetizations per Co atom for the samples containing oxidized nanoparticles provide evidence for the formation of antiferromagnetic CoO shells in the nanoparticles. None of the samples with Co/CoO nanoparticles show exchange bias, while vertical hysteresis loop shifts and enhanced coercivities (as compared to samples with pure Co nanoparticles) are observed. This constitutes evidence for the nanoparticles size being in all cases smaller than the critical size for exchange bias. The difference in coercivity versus temperature dependences for the samples with pure and oxidized Co nanoparticles shows that the exchange anisotropy in Co/CoO nanoparticles appears at temperatures lower than 50 K. (c) 2007 American Institute of Physics.

Abstract: It is shown that the infrared absorption spectra of pure type IaB diamonds, namely those that on cursory examination show only a B one-phonon component and neither A nor D, and the complete absence of a B' localized-mode platelet absorption peak, may be divided into two subgroups. The defect content of specimens of one of these subgroups has been studied before and comprises slip dislocations and voidites in random homogeneous distributions unconnected with the transformation of platelets to dislocation loops. Electron microscopy of a specimen of the other subgroup, which may be recognized by the presence of weak additional one-phonon absorption near 1100 cm-1, shows a population of dislocation loops resulting from the complete transformation of a former platelet population, plus accompanying voidites. It is suggested that the extra absorption is caused by the dislocation loops. Observation of the way in which loops and voidites are distributed suggests that voidite production and platelet transformation may not, after all, be interlinked phenomena, but parallel independent processes both promoted by the same unknown conditions.