Walter P. Lowe

Small-displacement monochromator for microdiffraction experiments

We describe the design, construction, and performance of the MHATT-CAT microdiffraction x-ray monochromator. This monochromator is specially engineered for x-ray microdiffraction experiments with a high brilliance undulator source. The monochromator passes a small emittance beam, suitable for focusing to submicron size with submilliradian divergence. Over its energy range of 8–22 keV the absolute energy calibration is better than 2 eV and scans of ± 1 keV show no measurable hysterisis. The monochromator operates with a simple water-cooled first crystal and shows no measurable warm-up time. Horizontal linear bearings allow the monochromator crystals to be rapidly inserted or removed from the beam. Slits before and after the monochromator work to pass broad bandpass or monochromatic x-ray beams at the same vertical height. The monochromatic beam direction is adjusted so the monochromatic and broad bandpass beams are coaxial. The design and performance of the monochromator allows efficient collection of micr...

X-Ray Microbeam Measurement of Local Texture and Strain in Metals

Synchrotron x-ray sources provide high-brilliance beams that can be focused to submicron sizes with Fresnel zone-plate and x-ray mirror optics. With these intense, tunable or broad-bandpass x-ray microbeams, it is now possible to study texture and strain distributions in surfaces, and in buried or encapsulated thin films. The full strain tensor and local texture can be determined by measuring the unit cell parameters of strained material. With monochromatic or tunable radiation, at least three independent reflections are needed to determine the orientation and unit cell parameters of an unknown crystal. With broad-bandpass or white radiation, at least four reflections and one measured energy are required to determine the orientation and the unit cell parameters of an unknown crystal. Routine measurement of local texture and strain is made possible by automatic indexing of the Laue reflections combined with precision calibration of the monochromator-focusing mirrors-CCD detector system. Methods used in implementing these techniques on the MHA-IT-CAT beam line at the Advanced Photon Source will be discussed.

3-D Measurement of Deformation Microstructure of Al(0.2%)Mg Using Submicron Resolution White X-Ray Microbeams

We have used submicron-resolution white x-ray microbeams on the MHATT-CAT beamline 7-ID at the Advanced Photon Source to develop techniques for three-dimensional investigation of the deformation microstructure in a 20% plane strain compressed Al(0.2%)Mg tri-crystal. Kirkpatrick-Baez mirrors were used to focus white radiation from an undulator to a 0.7 x 0.7 {micro}m{sup 2} beam that was scanned over bi- and tri-crystal regions near the triple-junction of the tri-crystal. Depth resolution along the x-ray microbeam of less than 5 microns was achieved by triangulation to the diffractibn source point using images taken at a series of CCD distances from the microbeam. Computer indexing of the deformation cell structure in the bi-crystal region provided orientations of individual subgrains to {approximately}0.01 degrees, making possible detailed measurements of the rotation axes between individual cells.

Transmission electron microscopy study of PtSi/Si (p-type) composites grown on Si(111) substrates

Abstract A transmission electron microscopy (TEM) study was made of PtSi/Si (p-type) composite films grown on Si(111) substrates. The films, 3-μm thick, were prepared by sputtering from a Pt–Si target consisting of 81 at.% Si and 19 at.% Pt. They were subsequently annealed in argon at 575°C for 7.5 h. TEM indicated a dense aggregation of PtSi particles 50 nm and smaller in size, concentrated in a surface region about 500 nm thick. Resistivity measurements on this segregated layer showed that it was p-type with a resistivity of 3×10−3 Ω cm. Below this the structure is constant right down to the Si(111) substrate and consists of PtSi particles 10 nm in size clustered around the Si matrix. The Si is partly crystalline (10 nm particles) and partly amorphous. The resistivity of this layer is on the order of 100 Ω cm. These results are attributed to the movement of the PtSi particles in the bulk composite film toward the surface where they exist in a lower energy configuration. A microprobe analysis of these films showed 78 at.% Si and 22 at.% Pt.

The use of reliability factors in analyzing powder patterns in Pt–Si sputtering targets and subsequent films

X-ray powder diffraction was used to characterize a Pt{endash}Si sputtering target and subsequent films. The powder patterns of each sample indicated lines due to diffraction from different phases. We have initiated a preliminary study through which we have analyzed and characterized these films. The results presented for these samples corroborate with results observed for this system in the planar configuration. {copyright} {ital 1998 Materials Research Society.}