[en] The validity of effective medium theories (EMTs) for mixtures of dielectric materials in weak absorption regions is studied. Based on the Bergman spectral representation, it is possible to show that for any EMT the absorption properties of a mixture consist basically of scaling of the absorption properties of the material with highest absorption. The real part of the dielectric function remains unaffected by the absorption properties. Thin films consisting of Nb₂O₅-SiO₂ mixtures are characterized using optical measurements and the results are compared with the calculations of EMTs. The large discrepancies between the absorption properties observed experimentally and those calculated using EMTs are justified by the failure of these theories to predict a compositional dependence of relevant structural parameters, such as the band-gap energy or the width of localized states. This failure, however, affects the calculation of the refractive index in the weak absorption regions to a less significant degree.

[en] Interface traps at the Si–SiO₂ interface have been and will be an important performance limit in many (future) semiconductor devices. In this paper, we present a study of fast neutron radiation induced changes in the density of Si–SiO₂ interface-related defects. Interface related defects (P_b centers) are detected before and upon the irradiation. The density of interface-related defects is increasing with the fast neutron fluence.

[en] We report on the structure and arrangement of particles created in the Fe_2O_3/TiO_2 + SiO_2 multilayers. X-ray diffraction and extended X-ray absorption fine structure spectroscopy reveal the presence of crystalline rutile-TiO_2 while the iron oxide remains either amorphous or forms very small clusters of Fe_2O_3. The Fe"3"+ oxidation state of iron atoms has been confirmed by Mössbauer and X-ray spectroscopy. The degree of the particle ordering has been studied by grazing-incidence small-angle X-ray scattering. It was demonstrated that with increasing temperature partially ordered nanoparticles are created and grow up to a critical temperature when the ordering is destroyed. Both particle sizes and inter-particle distances depend strongly on the thickness of the Ti/Fe containing layer. - Highlights: • Titanium oxide forms ordered rutile nanoparticles after annealing. • Iron (Fe"3"+) oxide remains in amorphous-like state up to 1000 °C. • Particle sizes and inter-particle distances depend strongly on the layer thickness

[en] We report on the formation of Ge/Si quantum dots with core/shell structure that are arranged in a three-dimensional body centered tetragonal quantum dot lattice in an amorphous alumina matrix. The material is prepared by magnetron sputtering deposition of Al_2O_3/Ge/Si multilayer. The inversion of Ge and Si in the deposition sequence results in the formation of thin Si/Ge layers instead of the dots. Both materials show an atomically sharp interface between the Ge and Si parts of the dots and layers. They have an amorphous internal structure that can be crystallized by an annealing treatment. The light absorption properties of these complex materials are significantly different compared to films that form quantum dot lattices of the pure Ge, Si or a solid solution of GeSi. They show a strong narrow absorption peak that characterizes a type II confinement in accordance with theoretical predictions. The prepared materials are promising for application in quantum dot solar cells. (paper)