Fig. 1: Illustration of Laue condition in a θ–2θ geometry.

Only (hkl) planes perpendicular to the surface normal of the sample—with their corresponding reciprocal lattice vectors Ghkl pointing out-of-plane— are able to generate a detectable diffracted X-ray in θ–2θ symmetric scans. k and k’ are the wave vectors of the incident and the diffracted X-ray beams, respectively. The Ewald sphere is depicted by the dashed circle.