Characterization of TaSi₂-Si composites for use as wide-bandpass optical elements for synchrotron radiation

The wide rocking curves of matrix reflections of the in situ eutectic composite TaSi₂-Si make wafers of this material attractive for use as wide-bandpass monochromators for synchrotron radiation, and characterization of wafers of TaSi₂-Si for use with energies normally accessible at storage rings (i.e., 5-40 keV) is the focus of the present report. A wafer with [111]_Si orientation and a wafer with [110]_Si orientation are studied. The high degree of preferred orientation of the TaSi₂ rods relative to the Si matrix is examined using synchrotron Laue patterns, and the 100_TaSi2, 003_TaSi2, 101_TaSi2, and 102_TaSi2 reflections are used to establish the orientation relationship and to determine that the spread of rod orientations is at least 5° and probably no greater than 6°. Double-axis diffractometry with Cu Kα radiation reveals matrix reflections with rocking curve widths that are about 20 times broader than those from perfect Si and with peak reflectivities approaching 20%. The rocking curves widths are found to be relatively insensitive to irradiated area, thus indicating that most of the observed width is not due to long-range bending. Triple-axis diffractometry with Cu Kα radiation reveals that considerable compressive strain exists in the matrix and that much of the width of the diffraction peak is due to mosaicity. The performance of the [111]_Si TaSi₂-Si wafer and a perfect [111] Si wafer as monochromators for microradiography are compared, and a gain of an order of magnitude in x-ray intensity delivered to the sample is demonstrated with the composite crystal.