Supercooling of liquid-metal droplets for x-ray-absorption-spectroscopy investigations

Abstract

A sample preparation technique, suitable for x-ray-absorption measurements of liquid and supercooled metals is described. The method is based on an application of the emulsion technique, consisting in a dispersion of micrometric droplets in an inert rigid matrix. It has been applied to Hg and Ga resulting in a very fine average droplet size in the submicrometer range. A theoretical probabilistic model, confirmed by experimental data, suggests a log-normal droplet-size distribution. The supercooling capabilities of the samples are studied by means of x-ray-absorption near-edge structure measurements showing exceptional supercooling rates: 153 K for Hg and no crystallization at all for Ga down to 34 K. The problem of a quantitative study of the x-ray-absorption fine structure is addressed and the nonlinearity in the absorption measurements induced by the nonuniform thickness distribution discussed. A method to calculate the sample metal thickness distribution and to derive the actual absorption coefficient is presented.