A NEW X-RAY-DIFFRACTION METHOD FOR STRUCTURAL INVESTIGATIONS OF SOLID-LIQUID INTERFACES

A synchrotron x-ray diffraction method is presented for structural inv estigations of interfaces between low-Z substrates and heavier liquids . The method, similar to methods used in neutron scattering, is based on illuminating the interface through the solid substrate. The backgro unds arising from bulk scattering and the signal-to-background ratio a re estimated and compared with experimental results. An ultrahigh vacu um (UHV) setup is described in which the atomic arrangement and roughn ess of clean interfaces can be studied in situ. Our first results illu strate the possibilities for both out-of-plane and in-plane diffractio n studies. The specular reflectivity of the Ga/diamond(111)-2 X 1 inte rface was measured for perpendicular momentum transfers up to 2.2 Angs trom(-1). In an in-plane study of Ga/Si(111)-7x7 the in-plane structur e factor of Ga liquid within a depth of similar to 50 Angstrom was com pared to the structure factor of the bulk liquid. (C) 1997 American In stitute of Physics. [S0034-6748(97)03211-5].