Assessing the Quality of X-ray Optic Surfaces of Si Crystals Cut by Diamond-Wire and Rotating-Blade Sawing Techniques

The next generation of X-ray diffraction optics will benefit from crystal surfaces with very high quality (extremely flat and strain-free), but knowledge on how to achieve such surfaces, and how surface imperfections affect the diffraction properties, is sparse in the literature. As a first step toward initializing a systematic study on this topic, we evaluate in this paper the surface quality of two Si (111) wafers cut by a diamond-wire saw and a rotating-blade saw, respectively. We concentrate on revealing lattice strains induced by the two cutting methods and on strain evolution during three rounds of chemical etching (without polishing). The measurements may provide basic guidelines for fabrication of high-quality monochromators, and they reveal some important clues as to how surface roughness affects rocking curve widths and other diffraction properties.