Scattering of X-rays from crystal surfaces

X-ray measurements performed on a variety of materials demonstrate that it is possible to observe diffuse scattering that originates in the abrupt change of density at a crystal surface. Such a discontinuity gives rise, in general, to rods of scattering in reciprocal space which are most intense close to the Bragg peaks tau and are well defined for sufficiently smooth surfaces. For wave-vector transfer Q= tau +q the q-dependence of the intensity of scattering gives information on the topographic structure of the crystal surface. Experimental results on crystals of GaAs and KTaO 3 , with surfaces prepared in various ways, were obtained using conventional X-ray techniques with a rotating anode source and can be described by a continuum model of the surface. There are discrepancies between the predictions of the models and the experimental results and these suggest that further experiments are needed to achieve a more complete understanding.