Phase transitions between 2-and 3-dimensions in rare gas thin films on a surface of a metal single crystal.

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We have developed the new experimental equipment for ellipsometric studies of physisorption system, which can be operated under ultra-high vacuum and low temperature environment. Extremely high vacuum as low as 10^<-9> Pa is achieved without experimental components and the range of 10^<-8> Pa under experimental conditions. A platinum single crystal, on which rare gas is physisorbed, is mounted on a helium gas flow type cryostat that was designed and developed in this project. The ellipsometer system with automatic null method by PID controller was developed.We have found the enough traceability of the automatic null ellipsometer for the change of surface conditions during the cleaning process, ion bombardment and annealing, of the surface. The adsorption isotherm of Xe/Pt (111) at temperatures above the triple-point of Xe was obtained in the wide pressure range between 10^<-7> Pa and 10^<-2> Pa. The above-mentioned properties of our ellipsometer system makes it possible to observe layr … More growth from a submonolayr to thick layr where equilibrium pressure is nearly equal to the bulk saturation vapor pressure.The present experimental problem is temperature measurement. A Pt vs.Pt+Rh thermocouple is attached to the Pt crystal because of its durability at a high temperature during the annealing process. However, the relatively low thermoelectric power of the thermocouple in a low temperature range makes it difficult to measure a precise temperature in the adsorption experiment. We are preparing an alternative method : a combination of a Pt resistance thermometer and thermocouple.We are proceeding the measurement of a phase diagram of several adsorbent-adsorbate systems, Ne, Ar, Kr, Xe, and CH_4 on Pt (111), Ag (111), etc. for example. The obtained adsorption isotherms will be compared in the term of a relative temperature to the triple point or the critical point, a relative pressure to the saturation vapor pressure, a ratio between the lattice parameters, etc. From these results, we will deduce empirical laws of 2d-3d and wetting transition, surface roughening and melting, etc. On the basis of these observations, we will finally discuss the theoretical model of these surface phenomena. Less