SIZE-SELECTIVE PHOTOETCHING OF NANOCRYSTALLINE SEMICONDUCTOR PARTICLES

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