X-ray diffraction imaging with micrometer resolution was performed on type Ib and IIa diamond crystals. Experiments were carried out using 8 keV x-rays and a double-crystal diffractometer equipped with a CCD detector (pixel size 60 μm x 60 μm). Diamond samples were rotated about the horizontal axis collinear with a given reciprocal lattice vector. Local rocking curves (LRCs) were extracted from sequences of topographs taken at various angles along the global rocking curves measured at different azimuth positions of the specimen. Based on the angular positions of these LRCs, maps of local tilt and strain were produced. Results demonstrate that local misorientations play a more important role than do lattice parameter variations in broadening of total crystal rocking curves.
A grinding technique referred to as the McCarter Superfinish, for grinding large-size optical components is discussed and certain surface characterization information about flatness and the relative magnitude of the subsurface damage in silicon substrates is reported. The flatness measurements were obtained with a Wyko surface analyzer, and the substrate damage measurements were made by x-ray diffraction and acid etching. Results indicate excellent control of flatness and fine surface finish. X-ray measurements show that the diamond wheels with small particle sizes used in the final phases of the grinding operation renders surfaces with relatively small subsurface damage.
We describe a tunable multilayer monochromator with an adjustable bandpass to be used for reflectivity and grazing incidence diffraction studies on surfaces at energies near 10 keV. Multilayers have a bandpass typically 100 times larger than the Si(111) reflection, and by using multilayers an experimenter can significantly increase data collection rates over those available with a Si monochromator. The transmission through 1 and 2 laterally graded multilayer (LGML) reflections was recorded versus photon energy. The identical LGMLs were comprised of 60 bilayers of W and C on 100 X 25 X 3 mm float glass with a bilayer spacing varying from 35 to 60 angstrom. The average gradient was 0.27 angstrom/mm along the long dimension. The rms deviation of the data for the bilayer spacing from a linear fit was 0.36 angstrom. Data were obtained for a nondispersive (plus or minus) double-multilayer arrangement. The relative bandpass width (FWHM) when the two multilayers exposed the same bilayer spacing was measured to be 2.2% with a transmission of 78.7 plus or minus 1.6%. This value is consistent with the transmission of 88.9% that we also measured for a single LGML at HASYLAB beamline D4. The bandpass was tunable in the range 1.1% to 2.2%.
Three water-cooled pin-post monochromators, to be used on a wiggler beamline at the Advanced Photon Source (APS), were built with the heat exchanger engineered to provide very high heat transfer. The geometry of the heat exchanger as well as calculated data on the heat transfer will be presented. Before using the monochromators on the beamline, they were checked by x-ray diffraction topography. Reflections (333) and (220) in Bragg case were utilized. In all crystals, similar patterns of strain in the diffracting silicon layers were revealed, which can be attributed to the geometry of the heat exchangers, the bonding technology, and the thickness of the top layer. Conclusions about construction of future pin-post monochromators have been drawn.
X-ray scattering measurements at 10 keV from multilayers having a period of 24.8 Angstrom and consisting of 100 W/C bilayers are reported. Specular scans revealed first order reflectivities in the range 73.5% to 78.0% with bandpasses in the range of 1.5% to 1.7%. Total roughness (or interface grading) values deduced from fitting were in the range 2.5 to 3.0 angstrom for the last-to-grow surface of the W layers. Diffuse scattering measurements were made in a novel geometry that permitted investigation of in-plane momentum transfers up to 0.2 Angstrom-1. This is roughly an order of magnitude larger than is possible in conventional rocking scans. A power law dependence of the diffuse scattering after integration over a 'Brillioun zone' is found. The exponent of this power law, 1.75, when interpreted using a logarithmic correlation function leads to a value of 1.0 angstrom for the correlated roughness.
X-ray optical elements (such as single-crystal silicon monochromators) illuminated with high-power synchrotron- radiation beams produced by insertion devices and, to a lesser extent bending magnets, require cooling. When operating a silicon crystal at room temperature, channels for the coolant are often fabricated directly beneath the diffracting surface. Then a separate silicon distribution manifold/plenum is manufactured, and the components are bonded together using an adhesive or some intermediate material. In many cases, such monochromators suffer from strains induced by the bond. A silicon-to-silicon direct- bonding technique (i.e., without any intermediate material) has been developed that appears to be an attractive method for creating a bond with less strain between two pieces of silicon. This technique is well understood for the case of thin wafers (approximately 0.5 mm thickness) and is used by the semiconductor industry. Recently, bonding of 16-mm-thick 10-cm-diameter silicon crystals has been successfully performed inducing very little strain. A short review of the silicon-to-silicon direct-bonding process will be presented with an emphasis on its application to room temperature high-heat-load x-ray optics along with the present status of direct bonding efforts at the APS.