Surface analysis of halide distributions in complex AgX microcrystals by imaging time-of-flight SIMS (TOF-SIMS)

The composition of the surface layer of silver halide microcrystals influences the behaviour of photographic materials as the latent image is formed at specific locations on the surface. In this work, an Ion-Tof IV TOF-SIMS instrument, equipped with a Ga+ liquid metal ion source (LMIS) operating at 25 keV, is used to reveal the different elemental distributions in surface layers with a thickness below 4 nm. Superior lateral resolution (ca. 70 nm, calculated with computer generated line profiles) of the LMIS allows the analysis of individual microcrystals with a size well below 1 mu m. The proposed methodology is based on a combination of secondary ion mass spectrometry, imaging and local image depth profiling. After selecting the appropriate measurement conditions, automatic data acquisition is possible. The method is successfully demonstrated for the following array of analytical applications: analysis of increased surface contamination due to storage of emulsions, explanation of sensitometric problems of tabular microcrystals, quick detection of cross contamination of different types of crystals and inhomogeneous halide distributions at microcrystal surfaces.