“…After the work of Sinha et al several other studies on the development of models and algorithms for calculating the scattering of X-rays at small angles have been published (Andre  and Pardo 1988, Stearns 1989, Bridou and Pardo 1994, Plotz and Lischka 1994, Sinha 1994, Stepanov et al 1995, Lu et al 1996, De Caro et al 1997, De Caro and Tapfer 1997, Voorma et al 1997 including non-specular re¯ectivity. Also the experimental aspects of XRR have been the subject of investigations aimed to develop XRR instrumentation for use at synchrotron radiation sources or combined with ultrahigh-vacuu m chambers (Niggemeier et al 1997, Lee andTseng 1998) .…”