Article,

Microcalorimetry study of the monolayer4He ordering transition on single crystal graphite

, and .
Journal of Low Temperature Physics, (1989)
DOI: 10.1007/BF00681585

Abstract

We have developed a low-temperature, ac microcalorimeter for exploring adsorption on a single 2.25 mm2 graphite leaf that is capable of 10 picoJoule/degree resolution. The microcalorimeter was used to determine the phase diagram and heat capacity critical exponents agr of monolayer4He films at the commensurate ordering transition. After in situ baking at 600 K, we reproduced the narrow-ordered phase region (sime1% in coverage) reported by Campbell and Bretz for HOPG, but find quasilogarithmic, rather than power law, heat capacity divergences. We argue that the disappearance of the Potts-like exponent in the heat capacity is attributable to the geometry of nucleation along cleavage edge planes present on single crystal graphite surfaces.

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