On the formation mechanism of gamma-AgI thin films

Programmed iodization of silver foils at ambient temperature and pressure l eads to the formation of gamma-AgI films with zinc-blende structure. Gravim etric experiments show that the AgI film formation follows a parabolic time dependence. X-ray diffraction monitoring of the film formation on unanneal ed, annealed and etched silver foils reveals that the absence of intrinsic stacking faults is a necessary condition for the formation of gamma-AgI thi n films and that the presence of such faults invariably results in the form ation of beta-AgI thin films. Optical absorption studies indicate eventual saturation of the direct optical band gap with increase in iodination time, which corroborates Xray diffraction and gravimetry results. (C) 1999 Elsev ier Science S.A. All rights reserved.