Surface oxidation and luminescence properties of weblike agglomeration of silicon nanocrystals produced by a laser vaporization-controlled condensation technique

Weblike aggregates of coalesced Si nanocrystals are produced by a laser vaporization-controlled condensation technique. SEM micrographs show particles with similar to 10 nn diameter but the Raman shift suggests the presence of particles as small as similar to 4 nm. FTIR of the freshly prepared particles shows weak peaks due to the stretching, bending, and rocking vibrations of the Si-O-Si bonds, indicating the presence of a surface oxidized layer, SiOx (x < 2). Further oxidation of the Si core appears to be very slow and inefficient under ambient temperature, but annealing at higher temperatures facilitates the oxidation. The particles show luminescence properties that are similar to those of porous Si and Si nanoparticles produced by other techniques. The nanoparticles do not luminesce unless, by exposure to air, they acquire the SiOx passivated coating. They show a short-lived blue emission characteristic of the SiO2 coating and a biexponential longer-lived red emission. The short Lifetime component of the red emission, about 12 mu s, does not depend on emission wavelength. The longer-lived component has a lifetime that ranges from 80 to over 130 mu s (at 300 K), increasing With emission wavelength. The results are consistent with the quantum confinement mechanism as the source of the red photoluminescence.