Mixing behavior and structural formation of quench-condensed binary mixtures of solid noble gases

Mixtures of two noble gases (neon, argon, krypton, and xenon) with similar molar fractions were quench condensed on a substrate held at constant temperature. Subsequently, the solidified mixtures were annealed and their desorption properties were studied by means of high-frequency surface acoustic waves acting as a microbalance. Depending on the preparation conditions, the binary alloys exhibit significant differences in their desorption behavior, namely continuous desorption over a wide temperature range, or steplike desorption at discrete substrate temperatures. Valuable information on the atomic structure of noble gas alloys can be obtained by systematically varying the condensation temperature and monitoring the desorption. If the atomic sizes of the participating atoms is comparable, e.g., in the case of Ar/Kr mixtures, substitutionally disordered solids are formed. With increasing size differences, e.g., in Ne/Ar mixtures, the properties of the alloys strongly depend on the conditions of film preparation. At low condensation temperatures, mixed phases with a fixed stoichiometry of the components ( AB₂ and A₂B ) are formed, whereas at higher condensation temperatures all neon mixtures show a clear tendency to separate into single-component phases.