Two-dimensional supercritical fluid mercury formed on a sapphire substrate

Abstract Under high temperature and pressure near the critical point of fluid mercury, a thin film of fluid mercury is formed on a sapphire substrate. The coverage of the mercury wetting film jumps discontinuously when a prewetting transition line is crossed. In the present work, we report our recent studies on the properties of the mercury wetting film on sapphire by using optical reflectivity measurements and optical emissivity measurements. In the prewetting supercritical region, we observed two types of anomalies, denoted by ‘EPW1’ and ‘EPW2’. ‘EPW1’ is characterized by a sharp dip in the emissivity, and is attributed to the fluctuations in the wetting film caused by the two-dimensional critical phenomena. ‘EPW2’ is characterized by a steep increase in the reflectivity, and is attributed to the cross-over from the complete wetting to the critical adsorption.