REX - A LEAST-SQUARES FITTING PROGRAM FOR THE SIMULATION AND ANALYSISOF X-RAY REFLECTIVITY DATA

A FORTRAN program REX, which has been developed to facilitate the inte rpretation of X-ray reflectivity data, is described. The program allow s the simulation of reflectivity profiles as a function of either inci dent angle or of energy. Factors such as anomalous dispersion, and sur face and interface roughness are taken into account in the model. In a ddition, experimental data of reflectivity as a function of incident a ngle can be matched to user-supplied theoretical parameters by a least -squares refinement procedure. Experimental reflectivity data recorded at several X-ray wavelengths can be analysed simultaneously, thus eli minating certain experimental errors and increasing the probability of finding the correct physical model when fitting the data.