Three-Dimensional Diffraction Phenomenon at a 90° Bragg Reflection

Abstract

The experimental observation of a three‐dimensional diffraction phenomenon at a 90° Bragg reflection is reported and discussed. A refined experimental technique for the direct observation and accurate measurement of scattered intensity profiles in the vicinity of a 90° Bragg reflection was proposed and implemented. The detector arrangement allowed the scintillator detection of back‐reflected beams via fluorescence scattering from an in‐beam copper plate. A small hole in the plate allowed free passage of the incident beam. This detector system has allowed a very high ratio, up to five orders of magnitude, of fluorescence back‐reflection peak to the incident beam air scattering background. Three‐dimensional tracking of the reciprocal lattice point of the Si(800) Bragg reflection around the 90° Bragg position was studied over a range of tilt angles in a plane perpendicular to the diffraction plane.

A new method to detect an X-ray diffracted beam at an angle of 90°

“…The usual methods used for detecting the back-diffracted hbeam at exactly 90 are the use of a semitransparent detector, such as an ionization chamber (Cusatis et al, 1996), or a semitransparent crystal (Shvyd'ko et al, 1998;Stepanov et al, 1991). By using a pinhole detector (Nikulin et al, 1998), the method is limited because the maximum possible diffraction angle that can be measured cannot reach 90 .…”

X-ray multiple diffraction from crystalline multilayers: Application to a 90° Bragg reflection

“…The 90°reflection intensity profiles were measured using a NaI scintillation detector coupled to an in-beam polished copper plate 13 (Fig. 4).…”

“…The plate had a small, approximately 0.3-mm-diam hole, which allowed the direct beam to freely pass the detector system. The scintillation detector collected the scattered fluorescence radiation produced by the back- scattered beams, which were scanned vertically across the copper plate 13 (Fig. 4).…”

“…In this detector arrangement there is a "dead" angle, of about Ϯ0.2°, when the 90°reflected beam goes in exactly the opposite direction to the incident beam and misses the fluorescent target. 13 Figure 5 presents the two-dimensional Si (008) Bragg reflection intensity profile that was collected as a function of the angular deviation of the sample from the 90°position and incident synchrotron x-ray energy. The dips near the angular origin (approximately Ϯ0.2°) are due to the "dead" angle described above.…”

“…1,5,8,9 One of the potentially important features of a 90°Bragg reflection from a crystal is its application to x-ray characterization of crystals as novel analytical-experimental techniques for x-ray characterization of crystals. 10 The extremely high sensitivity of the 90°reflection to the incident radiation energy, crystal orientation (with respect to the incident beam), and crystal-lattice spacing changes [11][12][13][14][15][16] makes this experimental environment very attractive for use as an enhanced analytical technique. Recently, an experimental observation of near backdiffraction of synchrotron x rays from a thin crystalline film deposited on a single-crystal substrate was reported.…”