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

• Published in: Optical engineering 2015-03, Vol.54 (3), p.035101-035101
• Main Authors: Zápražný, Zdenko, Korytár, Dušan, Jergel, Matej, Šiffalovič, Peter, Dobročka, Edmund, Vagovič, Patrik, Ferrari, Claudio, Mikulík, Petr, Demydenko, Maksym, Mikloška, Marek
• Format: Article
• Language: English
• Subjects: Asymmetry; Crystal surfaces; Crystals; Diffraction; Imaging; Mathematical models; Monochromators; Polishing; X-rays
• ISSN: 0091-3286; 1560-2303
• DOI: 10.1117/1.OE.54.3.035101

We present the numerical optimization and the technological development progress of x-ray optics based on asymmetric germanium crystals. We show the results of several basic calculations of diffraction properties of germanium x-ray crystal monochromators and of an analyzer-based imaging method for various asymmetry factors using an x-ray energy range from 8 to 20 keV. The important parameter of highly asymmetric monochromators as image magnifiers or compressors is the crystal surface quality. We have applied several crystal surface finishing methods, including advanced nanomachining using single-point diamond turning (SPDT), conventional mechanical lapping, chemical polishing, and chemomechanical polishing, and we have evaluated these methods by means of atomic force microscopy, diffractometry, reciprocal space mapping, and others. Our goal is to exclude the chemical etching methods as the final processing technique because it causes surface undulations. The aim is to implement very precise deterministic methods with a control of surface roughness down to 0.1 nm. The smallest roughness (∼0.3  nm), best planarity, and absence of the subsurface damage were observed for the sample which was machined using an SPDT with a feed rate of 1  mm/min and was consequently polished using a fine polishing 15-min process with a solution containing SiO2 nanoparticles (20 nm).