Structure of interfacial liquids: X-ray scattering studies - art. no. 021205

We have used synchrotron x rays to study three different liquids near solid -liquid interfaces. For either ultrathin (45-90 Angstrom) or thick (similar to 5000 Angstrom) liquid films on silicon substrates, we find ton the basi s of diffraction peaks or specular reflectivity data) that the molecules fo rm 3-6 layers at the interface, with plane spacings close to the molecular dimensions. Rough surfaces and/or impurities reduce the density oscillation amplitudes. Making the liquid film very thin does not observably enhance t he effect, which implies that layering is present even at an isolated inter face (i.e., in a semi-infinite liquid). On the other hand, predeposited imp urities diffuse away from the interface more easily if the liquid films are thick. The liquids studied are nonconducting, nonpolar, and nonreactive; t he molecules are roughly spherical: and our substrate surface has no latera l structure. Thus our observations should apply to any liquid near a hard w all.