Halide composition profiles in silver halide microcrystals

We investigated the halide composition depth profile in micron-size silver halide microcrystals using x-ray photoelectron spectroscopy in conjunction with ion etching. Using a double-jet technique, intentionally mixed halide microcrystals were precipitated such that the thermodynamic equlibrium of the solution-solid interface was maintained. Microcrystals precipitated using halide-conversion techniques showed a compositional variation. In bromide-converted silver chloride microcrystals, after an initial decrease from the surface value, the chloride ion concentration increased smoothly with depth, leveling off (at about 100 nm below the original surface) to a value about 10% higher than in the surface region. X-ray diffraction patterns from these microcrystals show a skewed line shape for the halide-converted materials. A graded-band-gap model is proposed which may account for the tendency of the halide-converted crystals to form an internal latent image.