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 characteri zation 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) orienta tion are studied. The high degree of preferred orientation of the TaSi 2 rods relative to the Si matrix is examined using synchrotron Laue pa tterns, and the 100(TaSi2), 003(TaSi2), 101(TaSi2), and 102(TaSi2) ref lections are used to establish the orientation relationship and to det ermine that the spread of rod orientations is at least 5 degrees and p robably no greater than 6 degrees. Double-axis diffractometry with Cu K alpha radiation reveals matrix reflections with rocking curve widths that are about 20 times broader than those from perfect Si and with p eak reflectivities approaching 20%. The rocking curves widths are foun d to be relatively insensitive to irradiated area, thus indicating tha t most of the observed width is not due to long-range bending. Triple- axis diffractometry with Cu K alpha radiation reveals that considerabl e compressive strain exists in the matrix and that much of the width o f the diffraction peak is due to mosaicity. The performance of the [11 1](Si) TaSi2-Si wafer and a perfect [111] Si wafer as monochromators f or microradiography are compared, and a gain of an order of magnitude in x-ray intensity delivered to the sample is demonstrated with the co mposite crystal. (C) 1996 American Institute of Physics.