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In this work we report on the structure, morphology, composition, chemical bonding and optical properties of tantalum oxynitride (Ta– O–N) thin films prepared by reactive direct current magnetron sputtering. The films have been investigated by grazing incidence x-ray diffraction, x-ray reflectivity, grazing incidence small angle x-ray scattering, time- of-flight elastic recoil detection analysis, x- ray photoelectron spectroscopy and spectroscopic ellipsometry. The composition and the partial pressure of the reactive atmosphere (N2 + O2) have been varied in order to find conditions suitable for the -TaON phase production. As prepared thin films are amorphous and annealing at °C is necessary to promote crystallization. We discuss the role of N2 gas on the kinetics of sputtered particles and its influence on the oxidation rate and porosity of the growing film. The anion composition in Ta–O–N films strongly depends on the reactive gas condition during the deposition. We found that the O/N ratio in - TaON films increases with more N2 or O2 gas in the chamber, whereas the corresponding absorption onset and valence band maximum show a blue shift of up to 0.5 eV. These results were related to the non-stoichiometry in -TaO x N y crystallites with x > y .

Ge/Si core/shell quantum dots (QDs) recently received extensive attention due to their specific properties induced by the confinement effects of the core and shell structure. They have a type II confinement resulting in spatially separated charge carriers, the electronic structure strongly dependent on the core and shell size. Herein, the experimental realization of Ge/Si core/shell QDs with strongly tunable optical properties is demonstrated. QDs embedded in an amorphous alumina glass matrix are produced by simple magnetron sputtering deposition. In addition, they are regularly arranged within the matrix due to their self-assembled growth regime. QDs with different Ge core and Si shell sizes are made. These core/shell structures have a significantly stronger absorption compared to pure Ge QDs and a highly tunable absorption peak dependent on the size of the core and shell. The optical properties are in agreement with recent theoretical predictions showing the dramatic influence of the shell size on optical gap, resulting in 0.7 eV blue shift for only 0.4 nm decrease at the shell thickness. Therefore, these materials are very promising for light-harvesting applications.

Circuit-theory Interpretation of Optical Multilayer ENZ Metamaterial with Enhanced Bandwidth has been investigated.

26th European Photovoltaic Solar Energy Conference and Exhibition; 388-393, Optical and structural measurements of nanocomposites consisting of TiO2 thin films with Au and Ag nanoparticles, which have been fabricated using a novel method developed in our group, were performed to determine the index of refraction of such films. The observed extinction spectra show the localized surface plasmon resonance typical of the metal nanoparticles, whereas reflectance exhibits a minimum at wavelength below this resonance. Another method to grow Au-NPs at the surface of previous Au-TiO2 nanocomposites thin films is demonstrated, with the advantage to control the filling factor of these free Au nanoparticles.

We study the formation of silver nanoparticles embedded in a glass matrix using a two-step procedure: i) the inclusion of silver ions in a glass matrix by electric field assisted dissolution of Ag film deposited on the glass and ii) the later aggregation of silver by thermal annealing. The optical properties of the sample, dominated by the surface plasmon resonance of metal nanoparticles in the visible spectral range, are studied by optical spectrosocopy. The structural characterization is carried out by grazing-incidence small-angle X-ray scattering measurements performed at Syncroton Elettra and silver depth profiles are characterized using Rutherford backscattering. By modification of the parameters of metal film dissolution (electric field, temperature and treatment time) the depth profile of Ag can be tailored. Variation of thermal annealing parameters (temperature and time) allows control on nanoparticles size. As result, the surface plasmon absorption intensity and line shape is changed, enabling the possibility to tune the sample optical properties.