Two possible real-space orientations of a hexagonal lattice on a gold (001) surface. Depending on the orientation, different diffraction peaks will be seen with x rays.

From the article:

Surface X-Ray Speckles: Coherent Surface Diffraction from Au(001)
M. S. Pierce, K. C. Chang, D. Hennessy, V. Komanicky, M. Sprung, A. Sandy, and H. You
Phys. Rev. Lett. 103, 165501 (2009)

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