Various metals were deposited on luminescent porous silicon (PS) by immersion in metal ion solutions and by evaporation. The photoluminescence (PL) was quenched upon immersion in ionic solutions of Cu, Ag, and Au but not noticeably quenched in other ionic solutions. Evaporation of 100 Å of Cu or 110 Å of Au was not observed to quench PL. Auger electron spectroscopy performed on samples quenched and then immediately removed from solution showed a metallic concentration in the PS layer of order 10 at.%, but persisting to a depth of order 3000 Å.

Silicon has been anodized such that the porous layer is passivated with a homogeneous stretching phase by incorporating H2O2 in the anodization mixture. Fourier transform infrared spectroscopy measurements show that the Si–H stretching mode oriented perpendicular to the surface at ∼2100 cm−1 dominates the spectrum with negligible contribution from the bending modes in the 600–900 cm−1 region. Material analysis using Auger electron spectroscopy shows that the samples have very little impurities, and that the luminescent layer is very thin (5–10 nm). Scanning electron microscopy shows that the surface is smoother with features smaller than those of conventional samples.

Ultrabright ultrasmall ͑ϳ1 nm͒ blue luminescent Si 29 nanoparticles are chlorinated by reaction with Cl 2 gas. A SiN linkage is formed by the reaction of the chlorinated particles with the functional amine group in butylamine. Fourier transform infrared spectroscopy and x-ray photospectroscopy measurements confirm the N linkage and the presence of the butyl group, while emission, excitation, and autocorrelation femtosecond optical spectroscopy show that, after the linkage formation, the particles with the ultrabright blue luminescent remain, but with a redshift of 40 nm.

A Si 29 H 24 particle, with five atoms constituting a tetrahedral core and 24 atoms constituting a H-terminated reconstructed Si surface was recently proposed as a structural prototype of ultrasmall ultrabright particles prepared by electrochemical dispersion from bulk Si. We replace the H termination with a N linkage ͑in butylamine͒ and O linkage ͑in pentane͒. The emission band for N-termination downshifts by ϳ0.25 eV from that of H termination, whereas it blueshift ϳ0.070 eV for C termination. We use density-functional approaches to calculate the atomic structures and correction from the quantum Monte Carlo method to estimate the highest occupied-lowest unoccupied molecular-orbital band gap. We find a downshift of 0.25 eV for N termination and very little for C termination. These features are discussed in terms of exciton penetration in the capping material.

We examine current-less anodization of Si powder grains which are dispersed in a liquid. The grains are prepared red luminescent using a platinum catalyst from a chloroplatinic acid precursor. We also use the procedure to form dispersions of fluorescent Si nanoparticles in the size range of 3–6 nm across by subsequent sonication of the grains. The results are discussed in terms of the calculated thickness of the depletion layer in the grains due to a light metal doping and compared with recent results for the anodization of wirelike geometry.