SPECIFIC-HEAT OF DISORDERED AND AMORPHOUS RARE-GAS SOLIDS - QUENCH-CONDENSED PURE AND BINARY FILMS

We report measurements of the low-temperature specific heat C of crystalline pure rare-gas films (Ne, Ar, Kr, Xe) and amorphous rare-gas mixtures (Ne-Xe, Ar-Xe) condensed at low temperatures (T approximately 6 K). For both the crystalline and the amorphous films a large contribution to C linear in T (approximately 0.5 mJ/mol K2) is found at very low temperatures (T < 1 K), which is attributed to tunneling states. Annealing strongly decreases this contribution. At higher temperatures an enhancement of C with respect to bulk samples is observed, which is explained by surface vibrations arising from the porous structure of the films. For the crystalline films, this contribution is reduced upon annealing, while only a slight annealing effect is found for the amorphous mixtures.