Effect of I- impurity on the efficiency of silver cluster formation on AgBr microcrystal surfaces

Computer simulation is used to study the effect of iodide impurity on silve r cluster formation on AgBr microcrystals. The simulation is based on a nuc leation-and-growth model of silver cluster formation in competition with re combination of electrons and holes. The efficiency of silver cluster format ion is calculated as a function of microcrystal size and shown to increase with size for the impurity-free control, contrary to experimental data. Thi s behavior is due to a partitioning of the hole between free and trapped st ates which favors the free side as size increases. As a result, recombinati on decreases and efficiency increases at large microcrystal size. Iodide im purity decreases efficiency relatively more at larger sizes because it intr oduces an internal recombination pathway not present in the control simulat ion. Because of their larger volume-to-surface-area ratios, the larger micr ocrystals are affected more by this additional recombination pathway than s maller microcrystals. (C) 1999 American Institute of Physics. [S0021-8979(9 9)02115-5].