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The lattice relaxation of strained Si 1-x Ge x layers on Si (001) substrates has been examined. Single layers having a nominal composition of x = 0.14 were grown by Molecular Beam Epitaxy to thicknesses of 0.5, 1.0 and 1.5 μm, all of which are greater than the critical thickness where misfit-dislocation generation commences. Double-crystal and white-radiation topographic methods were used to reveal the misfit dislocation structure and distribution. The misfit dislocations were shown to extend from heterogeneous nucleation sites along the four available directions in the plane of the interface. A symmetric distribution of dislocations between the orthogonal directions was observed. Secondary branching of the misfit dislocations was also observed which accelerates the relaxation process.

X-ray reflectance measurements at grazing incidence provide non-destructively a measure of the thickness of thin layers, the electron density as a function of depth, and interface and surface roughness. We show that the effect of roughness at a buried interface is only to reduce the visibility of the interference fringes, whereas roughness at the top surface leads also to an overall increase in the rate of fall of intensity with angle (or energy). These two contributions can then be readily distinguished.Most work has been performed in monochromatic angular dispersive mode. We present here a preliminary study of the application of the high-energy, fixed-angle, energy dispersive mode for the study of thin epitaxial layers, Langmuir-Blodgett films, surface damage on silicon chemi-sol polished wafers and ion implanted silicon and aluminium. Data has been analysed using the theory of Parratt, which we have adapted for use in the energy dispersive method.