Phase Diagram of a Physisorbed Krypton Monolayer on Graphite Using an Ellipsometric Technique

Abstract

Vapor pressure adsorption of krypton on highly-oriented pyrolytic graphite (HOPG) in the monolayer region has been studied using a phase-modulated ellipsometric technique. The two successive phase transitions, gas-liquid (or fluid)-solid, were observed during build-up of a monolayer and from these, a 2D triple point could be determined. We also observed that as the adsorption amount of an initially formed 2D solid layer increased, the commensurate - incommensurate structural phase transition progressed. The phase transition from a 2D fluid to a 2D solid was a first order transition, which means that a 2D super-critical fluid can coexist with commensurate solid, which contradicts Berker's theory.