Experimental observation of X-Ray diffraction from a thin crystalline film at a 90° Bragg reflection

The first experimental observation of diffraction from a thin surface layer at a 90° Bragg reflection is reported. A thin (>1 μm) 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 “free‐standing” thin crystal.