COMPARATIVE-STUDY OF THE 1ST ADSORBED LAYER OF XENON AND KRYPTON ON BORON-NITRIDE AND GRAPHITE

The thermodynamic properties of the first adsorbed layer of xenon and krypton on crystalline boron nitride have been studied between 95 and 125°K and between 77 and 93°K, respectively. They are compared to those previously determined for the first layer of the same gases adsorbed on graphite. With both xenon and krypton the final state of the layer is probably the same as on graphite: a self-determined two-dimensional (2D) solid state having approximately the same density and structure as a (111) plane of the 3D crystal which forms at saturation. As on graphite, the xenon layer also undergoes two successive first-order transitions above a definite temperature: a 2D gas → 2D liquid transition and a 2D liquid → 2D solid transition. But with krypton, only one phase transition has been observed whereas three occur on graphite: two first-order transitions (2D gas → 2D liquid and 2D liquid → 2D localized solid) and a localized → delocalized transition which is of higher order. The only transition observed with krypton on boron nitride is first order, but the nature of this transition has not yet been determined. © 1979.