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We have performed physical and optical characterization of Si nanocrystals grown by ion implantation of Si+ ions at multiple energies with varying doses into thermally grown SiO2 films. The purpose of multiple implants was to achieve uniform composition of the added Si profile throughout the SiO2 film to produce Si particles with a narrow size distribution upon annealing at 1000 °C in a nitrogen atmosphere. The depth distribution of the composition and sizes of the Si particles in SiO2 films before and after the anneal were determined using Rutherford backscattering (RBS), forward recoil spectroscopy, small-angle x-ray diffraction (SXRD), and high-resolution transmission electron microscopy (HRTEM). From RBS we concluded that the amount of free silicon was reduced by annealing, presumably due to oxidation in the annealing process. The mean cluster sizes of the annealed samples were determined by SXRD. HRTEM was also employed to determine the average size of Si particles. Photoluminescence spectra (PL) from these samples were broad and the peak positions of the PL spectra were blue-shifted with decreasing cluster size. The line shapes of the PL spectra were calculated with a quantum confinement model assuming a log-normal size distribution of Si nanoparticles and (1/D)1.25 dependence of the band gap energy as a function of particle size D. The band gap energy and the average particle size obtained from the calculated line shape spectra agree well with the quantum confinement model.

Thin films of C60, 2.5-μm, have been shocked isentropically to 69 GPa, about 2200 K, and thermally quenched at rates up to 1011 K/s. The recovered specimen is transparent with a crystallographic habit, or ‘‘tilelike’’ structure, but it slowly transforms to a black highly disordered carbon at the ambient condition. The selected area electron diffraction patterns suggest that the transparent carbon phase contains an amorphous cubic diamond and n-diamond crystallites sized 50–350 Å in diameter.

We have used vapor etching of ion tracks to create high aspect ratio (i.e., length much greater than diameter), isolated cylindrical holes through ∼600-nm-thick films of thermally fused silica on silicon. Samples were exposed to the vapor from water-based liquids with various HF and HF+HCl concentrations. Independent control of the temperatures of the vapor and the samples provided the means to vary separately the etching rates for the tracks and the track-free material. The very rapid etching of the small latent track zone can be explained by preferential capillary condensation. Holes with diameters of ∼24 to ∼80 nm have been documented with length/diameter ratios of up to 22. Although we have restricted this study to thin-film silica, we have evidence that such holes are also formed in bulk fused silica.

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