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90-deg Bragg reflection from a thin crystalline film

Experimental observations of synchrotron radiation diffraction from a thin surface layer at a 90-degree Bragg reflection are reported and discussed. The synchrotron experiments were performed using a bending magnet source at the European Synchrotron Radiation Facility (ESRF) in France and undulator sources at the Advanced Photon Source (APS) in the U.S. and SPring-8 in Japan. Thin (0.5, 1.0 and 1.5 micron) InGaAs films deposited on a GaAs (100) substrate were studied near the 90- degree using the GaAs (800) reflection. A slight, less than 0.1%, difference in the lattice spacing between the layer and the substrate is sufficient to allow a direct and exclusive observation of the diffraction profile from a thin layer as if it was a 'free-standing' thin crystal. This research opens new possibilities for x-ray optical schemes and the development of novel analytical techniques for surface/interface x-ray diffraction studies.