Potential use of V-channel Ge(220) monochromators in X-ray metrology and imaging

Abstract

While channel-cut crystals, in which the diffracting surfaces in an asymmetric cut are kept parallel, can provide beam collimation and spectral beam shaping, they can in addition provide beam compression or expansion if the cut is V-shaped. The compression/expansion ratio depends in this case on the total asymmetry factor. If the Ge(220) diffraction planes and a total asymmetry factor in excess of 10 are used, the rocking curves of two diffractors will have a sufficient overlap only if the second diffractor is tuned slightly with respect to the first one. This study compares and analyses several ways of overcoming this mismatch, which is due to refraction, when the Cu K 1 beam is compressed 21-fold in a V21 monochromator. A more than sixfold intensity increase was obtained if the matching was improved either by a compositional variation or by a thermal deformation. This provided an intensity gain compared with the use of a simple slit in a symmetrical channel-cut monochromator. The first attempt to overcome the mismatch by introducing different types of X-ray prisms for the required beam deflection is described as well. The performance of the V-shaped monochromators is demonstrated in two applications. A narrow collimated monochromatic beam obtained in the beam compressing mode was used for high-resolution grazing-incidence small-angle X-ray scattering measurements of a silicon sample with corrupted surface. In addition, a two-dimensional Bragg magnifier, based on two crossed V15 channel monochromators in beam expansion mode and tuned by means of unequal asymmetries, was successfully applied to high-resolution imaging of test structures in combination with a Medipix detector.

Calculations and surface quality measurements of high-asymmetry angle x-ray crystal monochromators for advanced x-ray imaging and metrological applications

“…15,16 One disadvantage of such a system is the finite distance between crystals magnifying in the horizontal and vertical directions which causes the effective propagation distances between the horizontal and the vertical directions to be different. 16 This problem can be solved by further development of monolithic V-shaped 17 or Z-shaped 18 monochromators, for which we are able to set the horizontal and the vertical diffractions as close together as possible while preserving the inline configuration. The very important parameter of highly asymmetric monochromators as image magnifiers is the crystal surface quality, because the long-range surface undulations 9 deteriorate the final image quality.…”

A high-throughput assembly of beam-shaping channel-cut monochromators for laboratory high-resolution X-ray diffraction and small-angle X-ray scattering experiments

“…Beam shaping by a single germanium CCM with a V-shaped channel (briefly, a V-shaped CCM) for X-ray imaging has been reported more recently (Korytá r et al, 2013). The V-shaped CCM utilizes two asymmetric diffractions at channel walls with generally different asymmetry angles.…”

Exploiting the potential of beam-compressing channel-cut monochromators for laboratory high-resolution small-angle X-ray scattering experiments

“…Recently, a monolithic X-ray channel-cut monochromator (CCM) based on two successive asymmetric diffractions in a V-shaped channel (Fig. 1) has been introduced, and its potential for X-ray metrology and X-ray imaging has been demonstrated (Korytá r et al, 2013;Jergel et al, 2013). Unlike the grooved crystals with parallel walls in a Bonse-Hart camera, such a monochromator has the additional functionality of beam compression or expansion depending on the sense of beam propagation.…”