Size-selective photoetching of nanocrystalline semiconductor particles

An overview is presented of size-selective photoetching experiments on nanocrystalline semiconductor particles. Four different compounds (CdS, ZnS, PbS, and ZnO) have been prepared by standard colloid-chemical synthetic methods. For CdS, the initial mean radius of 35 Angstrom could be gradually decreased to 7.5 Angstrom by size-selective photoetching. The adjustment of the particle size can be controlled to a high degree by varying the wavelength of the light that is used. It is also shown that the particle size distribution narrows during the photoetching process from about 40% to 10-15%. For ZnS and ZnO, only the feasibility of the technique could be demonstrated. This is due to the fact that these compounds have very large band gaps which limit the range far photoetching experiments. The initial radius of the ZnO particles was approximately 30-35 Angstrom and could be decreased to about 15 Angstrom, again accompanied by a narrowing of the particle size distribution. For PbS, no concrete evidence was obtained for the feasibility of size-selective photoetching.