X-ray diffraction evidence of ordering in a normal liquid near the solid-liquid interface

We have seen X-ray diffraction peaks establishing that the structure of nor mal liquids at solid-liquid interfaces is significantly different from the bulk structures. Wetting film thicknesses of similar to 5000 Angstrom were formed on silicon (111) surfaces with native oxide by pouring and draining the pure liquids; such films are thin enough for X-rays to penetrate easily , but thick enough to eliminate undesired fringes corresponding to the film thickness. The liquids studied were tetrakis(2-ethylhexoxy)silane (TEHOS) and tetrakis(trimethylsiloxy)silane (TTMSS). The observed diffraction peaks are in the specular direction, showing that the liquid molecules form laye rs parallel to the interface. The layer spacings are comparable to the mole cular dimensions, and the peak widths indicate that there are 3-6 layers.