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SiO x thin films with different stoichiometries from SiO 1.3 to SiO 1.8 have been prepared by evaporation of silicon monoxide in vacuum or under well-controlled partial pressures of oxygen ͑P Ͻ 10 −6 Torr͒. These thin films have been characterized by x-ray photoemission and x-ray-absorption spectroscopies, this latter at the Si K and L 2,3 absorption edges. It has been found that the films prepared in vacuum consists of a mixture of Si 3+ and Si + species that progressively convert into Si 4+ as the partial pressure of oxygen during preparation increases. From this spectroscopic analysis, information has been gained about the energy distribution of both the full and empty states of, respectively, the valence and conduction bands of SiO x as a function of the O / Si ratio. The characterization of these films by reflection electron energy-loss spectroscopy ͑REELS͒ has provided further evidences about their electronic structure ͑band gap and electronic states͒ as a function of the oxygen content. The determination of the plasmon energies by REELS has also shown that the films prepared by evaporation in vacuum consist of a single phase which is characterized by a density ͑1.7 g cm −3 ͒ lower than that of SiO 2 ͑i.e., 2.2 g cm −3 ͒ or Si ͑i.e., 2.4 g cm −3 ͒. The optical properties ͑n and k͒ of the films as a function of the O / Si content have been deduced from the analysis of REELS spectra in the energy range from 4 to 20 eV. It has been also shown that the O / Si ratio in the films and several spectroscopic parameters such as the Auger parameter or the energy of bulk plasmons present a linear relationship and that this linear dependence can be used for a rapid characterization of SiO x materials. By contrast, the band-gap energy changes differently with the O / Si ratio, following a smooth linear increase from about 3.8 eV for SiO 1.3 to ca. 5.0 eV for SiO 1.7 and a jump up to 8.7 eV for SiO 2 . These results indicate that the random-bonding model does not apply to thin films prepared by evaporation under our experimental conditions. Other distributions of Si n+ states can be induced if the films are excited with an external source such as heat or photon irradiation. In this case the electronic properties vary and the previous linear correlations as a function of the oxygen content do not hold any longer.

This letter reports a novel methodology for the synthesis of dye-containing nanocomposite thin films containing fluorescent rhodamine 6G (Rh6G) laser dye molecules. The nanocomposites are deposited in one step at room temperature in a downstream microwave plasma operating at low pressure and power. By controlling the plasma chemistry, it is possible to reduce the formation of dye dimers and higher aggregates that quench the fluorescence of the dye molecules. The films are intensely absorbent and fluorescent, insoluble in water, mechanically stable, and present good adhesion to the substrate. Besides, the method is compatible with the present silicon technology and therefore particularly interesting for the fabrication of integrated optoelectronic devices.