Grazing-incidence scattering of coherent X-rays from a liquid surface
When a partially coherent X-ray beam is scattered from disorder, a random diffraction image (‘speckle pattern’) is generated, which contains information about both the incoming radiation and the scattering sample. Here, the X-ray beam is applied under grazing incidence (GISAXS) to study a glycerol surface as it is cooled towards its glass transition. The temporal fluctuations of the speckle pattern are characterized by time-correlation spectroscopy (XPCS), and a slowing down of surface dynamics upon cooling is evident. We show that the appearance of the ‘frozen-in’ speckle pattern (figure) obtained in the glassy phase depends crucially on the scattering geometry, and the differences between SAXS and GISAXS geometries are discussed.
A. Madsen, T. Seydel, M. Tolan and G. Grübel