Silicon-rich (SR)/SiO2 multilayered systems were produced by reactive magnetron sputtering, through an approach based on the ability of hydrogen, when alternatively mixed to the argon of the plasma, to reduce the oxygen originated from the SiO2 target. Optimum values of both hydrogen partial pressure (45 mTorr) and deposition temperature (500 °C) have led to the highest incorporation of Si in the SR layer which crystallizes after annealing. The SR/SiO2 superlattices grown with such conditions showed that the size of the Si nanocrystals is limited by the thickness of the SR layer. Considering the difference observed between the photoluminescence peak position and the predicted band gap for Si nanocrystals, the results suggest that we deal with a quantum-size confinement assisted by a Si–O vibration located at the interface.

A spectroscopic ellipsometry technique is used to attempt a quantitative analysis of thin Si/SiO2 nanocomposite films obtained by magnetron co-sputtering. The layers are first fabricated with varying values of deposition temperature and sputtered silicon area, before being annealed at different temperatures. Using an effective medium model, the ellipsometry tool allowed the estimate of the thickness and the volume fraction of silicon agglomerates or grains, in addition to the optical parameters of the layer through a tentative determination of the dielectric function of the Si nanostructures. The Si content obtained by the ellipsometry approach agrees with those previously determined by direct measurements. Besides the obvious increase of incorporated Si with the sputtered area of this material, we noticed a maximum excess of Si for a deposition temperature in the 400–500 °C range. In this respect, the peak position of the photoluminescence (PL) detected only in the annealed samples is found to be closely connected with the amount of excess Si, and in consequence, with the mean size of the thermally grown nanocrystallites. The systematic red shift of maximum PL with the rise of Si content, and implicitly with the increase of the particle size, regardless of the deposition conditions used for the fabrication of the original layer, is liable to allow conclusive argument as for the attribution of the PL in the 1.30–1.65 eV range to the quantum confinement effect. Besides the main contribution of the nanoparticle density, the quality of the Si/SiO2 interface, as examined by infrared absorption spectroscopy, appears determining for the PL efficiency, and is increasingly improved towards stoichiometric SiO2 when the annealing temperature is increased up to 1100 °C.

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