Validity of RHEED specular intensity measurements for structural studies of liquid metal surfaces: applications to liquid In and Sn

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Abstract
The authors propose a method of analysing the glancing angle dependence of the RHEED (reflection high-energy electron diffraction) specular intensity I( theta ) from liquid metal surfaces and apply it to liquid In and Sn, for which preliminary RHEED experiments have recently been performed. They use two models to derive a scattering potential that is supposed to cause the specular reflection of fast electrons. Calculations of I( theta ) based on these models reveal that the tail behaviour of the scattering potential on the vapour side essentially determines the characteristics of I( theta ) in the range of small glancing angle theta . The comparisons of these calculations with experiments suggest that the scattering potential in the liquid-vapour transition zone of liquid In results from neutral atoms, while the scattering potential due to ions and extended conduction electrons is plausible for liquid Sn even in the surface region. It is concluded from the present analyses that accurate experimental data for I( theta ) in a wider range of theta is needed to determine the full behaviour of the surface density profiles of liquid metals.