Experimental Observation of X-Ray Diffraction from a Thin Crystalline Film at a 90� Bragg Reflection

Abstract

The first experimental observation of diffraction from a thin surface layer at a 90 Bragg reflection is reported. A thin (< 1 mm) InGaAs film deposited on a GaAs(800) substrate was studied near the 90 Bragg position. Slight, less than 0.1%, difference in the lattice spacing between the layer and the substrate, has allowed, for the first time, a direct and exclusive observation of the diffraction profile from a thin layer as if it was a ªfree-standingº thin crystal.

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

“…A use of semitransparent crystalline detectors such as p-i-n or avalanche photodiodes would very likely lead to unpredictable parasitic reflections inside such detectors. 15 The two-dimensional (angle-energy) intensity profiles in the vicinity of the exact 90°Bragg reflection position were collected as a function of the angular position of the crystal sample and incident synchrotron x-ray energy. The x-ray energy was selected by the primary beamline monochromator with consecutive realignment of the second monochromator to ensure the optimal mutual position of these two crystals along the optical axis.…”

“…Thus, Eqs. (15) and (20) form a system that can be solved with respect to unknown coefficients c ͑n͒ . Using the recurrence formula (20), the final relation between c ͑1͒ and c ͑N͒ can be written as…”

“…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.…”

“…Recently, an experimental observation of near backdiffraction of synchrotron x rays from a thin crystalline film deposited on a single-crystal substrate was reported. 15 However, the possibility of exploiting the backscattering geometry for advanced studies of materials has not been explored as yet. This is largely due to the lack of an established theoretical formalism to describe a 90°B ragg diffraction from a modulated crystal lattice and the fact that 90°diffraction often occurs as multiple-beam diffraction.…”