We report the observation of molecular layering in a liquid at the solid-li
quid interface, using X-ray reflectivity. The liquid was tetrakis (2-ethylh
exoxy) silane (TEHOS), which is nonpolar and insulating, with spherical mol
ecules of about 10 Angstrom diameter. We studied both thin (45-90 Angstrom)
and relatively thick (similar to 5000 Angstrom) films, which are prepared
by dipping in a dilute solution and by pouring and draining the pure materi
al, respectively. For 45-90 Angstrom thick films, three layers of density o
scillations are seen near the solid-liquid interface, with a spacing compar
able to the molecular size. There is an inverse dependence on the substrate
surface roughness. For similar to 5000 Angstrom thick films, we observed a
diffraction peak with a correlation length of similar to 32 Angstrom. (C)
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