Grazing small-angle scattering of X-rays for the study of thin surface layers

Studies of a thin layer by small-angle scattering (SAS) of X-rays in the transmission mode gives weak intensities because the X-ray path is short. Grazing-incidence X-ray scattering circumvents this difficulty for the analysis of a thin layer deposited on a substrate or the surface of a bulk sample. Here the X-ray path increases and the background is low enough. The penetration depth can be controlled by controlling the incidence angle of the X-ray beam. The prerequisites of a grazing small-angle X-ray scattering apparatus are a small divergence of the incident beam and a large X-ray flux. The instrument described here consists of a rotating-anode X-ray source, a highly asymmetric monochromator and a position-sensitive detector. The feasibility of grazing-incidence experiments is demonstrated with a polished surface of bulk Al-Ag sample. It was possible to perform quantitative measurements of the scattering due to GP (Guinier-Preston) zones in this alloy.