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Web-like aggregates of coalesced Si nanocrystals produced by a laser vaporization-controlled condensation technique show luminescence properties that are similar to those of porous Si. The results are consistent with a quantum confinement mechanism as the source of the red photoluminescence (PL) in this system. The oxidized Si nanoparticles do not exhibit the red PL that is characteristic of the surface-oxidized Si nanocrystals. The nanoparticles are allowed to oxidize slowly, and the PL is measured as a function of the exposure time in air. A significant blue shift in the red PL peak is observed as a result of the slow oxidation process. The dependence of quantum size effects on the bonding structure is established by correlating the PL data with the photon-yield electronic structure measurements made at the Advanced Light Source. The results indicate that as the nanoparticles oxidize, the radius of the crystalline core decreases in size, which gives rise to a larger bandgap and consequently to the observed blue-shift in the PL band. The correlation between the PL, SXF, and NEXAFS results provides further support for the quantum confinement mechanism as the origin of the visible PL in Si nanocrystals.

As-Se-Cu glasses, with Cu content varying between 5 and 25 at. %, were produced by quenching from the melt. The values of resistivity and activation energy for conduction decreased continuously with increasing the copper content. Memory switching phenomena was observed in glasses containing Cu less than 20 at. %. Glasses containing higher Cu concentration showed a reverse switching cycle. Thermally induced changes in the structural properties have been examined using x-ray diffraction, differential thermal analysis, and scanning electron microscopy. The results were discussed on the basis of thermally induced transformations.