Compositional and structural characterization of isolated Pb-Bi microcrystals co-vapor deposited onto amorphous carbon

Abstract

Recent interest in heterogeneous nucleation of binary alloys requires a knowledge of the structure and composition of deposits. Analytical electron microscopy and x-ray microanalysis is well suited to obtaining such information and has already been applied to the overall characterization of a collection of isolated microcrystals. The methods for performing this characterization are well documented; however, the application of the technique to the determination of composition of individual microcrystals as a function of crystal size is less well documented. In addition to the fundamental interest such information provides, it is of practical importance in such disciplines as supported alloy catalysts where a size-dependent composition and/or structural behavior may change both the selectivity and reactivity of a catalyst.The specimens in this investigation were prepared by co-vapor deposition of Pb and Bi onto hot amorphous carbon substrates between 150°C and 250°C. The Pb and Bi were co-evaporated from separate filaments of Mo and Ta, respectively, or an alloy of PbBi was evaporated from a single filament of tantalum with no significant difference occurring in the deposits prepared by either method.