Nano Si superlattices for the next generation solar cells.

We present a study on amorphous SiO/SiO2 superlattice formation on Si substrate held at room temperature and annealed in the temperature range 600-1100 degrees C. Grazing-incidence small-angle X-ray scattering (GISAXS) and X-ray reflectivity were used to study such samples. Amorphous SiO/SiO2 superlattices were prepared by high vacuum physical vapor deposition of 4 nm thin films of SiO and SiO2 (10 layers each) from corresponding targets on silicon substrate. Rotation of the Si substrate during evaporation ensured homogeneity of the films over the whole substrate. We observed that the inhomogeneities introduced into the SiO and SiO2 layers during the deposition (evaporation) give rise to small angle scattering at lower annealing temperatures. After an initial SiO layer thickness reduction for 600 degrees C annealing, these thicknesses remain virtually unchanged up to 1000 degrees C, where they start to decrease again which leads to particle formation. Nevertheless, this compacting at low temperatures may lead to the seed formation in SiO layers that will facilitate later Si nanoparticles growth.

Modeling of vapor sorption in polymeric film studied by surface plasmon resonance spectroscopy.

Sorption process by surface plasmon resonance (SPR) was studied by exposing polymeric film made from anthracene labeled poly(methyl methacrylate) (An-PMMA) chains to various concentrations of saturated chloroform vapor. It was observed that the reflectivity changes were fast and reversible. The changes in reflectivity implied the swelling behavior of polymeric film during adsorbtion and can be explained by capturing of chloroform molecules. When clean air is introduced into gas cell similar behavior is observed but this time in the opposite direction as a result of desorption. Fick's law for diffusion was used to quantify real time SPR data for the swelling and desorption processes. It was observed that diffusion coefficients (D(s)) for swelling obeyed the t(1/2) law and found to be correlated with the amount of chloroform content in the cell. Diffusion coefficients (D(d)) during desorption were also measured and found to be increased as the saturated chloroform vapor content is increased in the cell.