Exchange of fluorinated cyanine dyes between different types of silver halide microcrystals studied by imaging time-of-flight secondary ion mass spectrometry

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is used to study dye adsorption on silver halide (AgBr or Ag(Br,I)) microcrystals. The dyes are labeled with fluorine to allow their detection at the surface of the microcrystals by means of atomic ions. In this study, particular attention is paid to dye adsorption selectivity as a function of microcrystal morphology and to the possibility of dye exchange between different types of microcrystals. Using a gallium (Ga+) liquid metal ion gun operating at 25 keV as the primary ion source, secondary ion images with a lateral resolution of 65 nm have been collected. This high lateral resolution makes it possible to distinguish between octahedral and cubic AgBr crystals even with an edge length of only 0.4 mum, based on their bromide images. It also enables us to detect and localize the fluorine-labeled dyes at the surface of these microcrystals. When larger cubic crystals with an edge length of 0.8 mum are used, the site selectivity of the fluorine-labeled dye for the edges of these crystals can be studied. Apart from cubic and octahedral crystals, dye adsorption on tabular crystals is also studied.