Complete wetting transition at the fluid–vapour interface of Ga–Bi studied by spectroscopic ellipsometry

Abstract

We present ellipsometric spectra of liquid gallium–bismuth alloys in the energy range 0.8 eV⩽ℏω⩽4.65 eV and in the temperature range from 277 °C down to 258 °C. Using a phase modulation ellipsometer, high-precision spectra have been recorded approaching the liquid–liquid miscibility gap of this system with decreasing temperature from the homogeneous liquid phase. The spectra have been modelled using a Ga–Bi effective medium as substrate covered by a film of liquid Bi. In the temperature range 277 °C⩽ T⩽264 °C, the Bi film thickness is of the order of one to two monolayers. At 264 °C, i.e. 6 K above the miscibility gap, the character of the spectra changes noticeably and the Bi film thickness increases continuously. As one reaches the demixing regime the film of our particular sample geometry has a gravitationally thinned thickness of approximately 20 Å. This phenomenon can be interpreted by a complete wetting transition in a metallic system.