SIZE CONTROL OF ULTRASMALL CDS PARTICLES IN AQUEOUS-SOLUTION BY USING VARIOUS THIOLS

Size of ultrasmall CdS particles was controlled by adding four kinds of thiols (mercaptoethylamine, mercaptopropionic acid, mercaptoethanol, and cysteine) to a Cd2+ aqueous solution before mixing with an Na2S aqueous solution. The adsorption of thiols on the CdS surface was verified as the effect of surface charges by measuring the yield of photoinduced electron transfer from CdS to positively charged molecules in solution. Observations of growth process by means of stroboscopic stopped-flow spectroscopy indicate that of the four thiols the thiolate group is mainly responsible for obstructing the growth of ultrasmall CdS particles. The effect of the other ionic groups of thiols on the growth feature is of secondary importance. For mercaptoethanol and cysteine, a transient absorption band attributable to a relatively stable small CdS cluster appeared at an early stage of the growth. © 1993 by Academic Press, Inc.