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

• Published in: Journal of applied crystallography Vol. 46; no. 4; pp. 945 - 952
• Main Authors: Korytár, D., Vagovič, P., Végsö, K., Šiffalovič, P., Dobročka, E., Jark, W., Áč, V., Zápražný, Z., Ferrari, C., Cecilia, A., Hamann, E., Mikulík, P., Baumbach, T., Fiederle, M., Jergel, M.
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01-08-2013; Blackwell Publishing Ltd
• Subjects: Asymmetry; Beams (radiation); Bragg magnifier; channel-cut crystal; Collimation; Compressing; Crystallography; Diffraction; Imaging; metrology; Monochromators; Montel optics; X-Ray Diffraction and Imaging; X-rays; metrology; Montel optics; channel-cut crystal; Bragg magnifier
• ISSN: 1600-5767; 0021-8898; 1600-5767
• DOI: 10.1107/S0021889813006122

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 Kα1 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.