Examination of Si<sub>1-x</sub>Ge<sub>x</sub> Laterally Graded Crystals for Use in High Brilliance Synchrotron Beams

Abstract

We report about the feasibility of employing laterally graded Si 1-x Ge x crystals as x-ray monochromators for synchrotron radiation beams. This type of crystals can be used in a divergent beam with nearly the same energy resolution and spectral flux as a regular crystal in a parallel beam. The effect is achieved due to continous changes in the lattice parameter with varying Ge concentration in the Si crystal. Theoretical calculations for BESSY II dipole radiation show, that the optimum gradient of Ge along the surface should be about 1.0 at. % per cm. The properties of the crystals have been investigated by x-ray diffraction and fluorescence analysis with radiation from a conventional x-ray tube. We found nearly perfect crystal quality for Ge concentrations up to 7.0 at. % and gradients of Ge up to 1.1 at. % Ge per cm which would already be sufficient for applications in the x-ray monochromator.