Glancing-angle X-ray scattering studies of the premelting of ice surfaces

Abstract

The onset of surface melting at [lcub]00.1[rcub] (“basal”), [lcub]10.0[rcub] and [lcub]11.0[rcub] (“nonbasal”) surfaces of hexagonal ice is studied experimentally by glancing-angle X-ray scattering. The preparation of mirror-like single crystal ice surfaces and a special in situ X-ray chamber is described in detail. The X-ray scattering experiments using synchrotron radiation give clear evidence that all the investigated high-symmetry surfaces exhibit surface melting with onset temperatures T s ≅ − 13.5°C for the basal and T s ≅ − 12.5°C for the nonbasal surfaces. The temperature dependence of the thickness of the quasiliquid is presented and discussed in view of various theoretical predictions. In addition we found thermal faceting at nonbasal surfaces as well as a diffuse (“rough”) solid-quasiliquid interface. The thermal properties of the observed surface disorder implies that the correlation length within the socalled “surface melt” is much larger than the correlation length in the bulk liquid indicating the presence of significant “substrate” interactions.