X-ray diffraction is a technique that uses X-rays to determine the structure of crystalline materials. When X-rays interact with a crystalline material, they are scattered at specific angles that are dependent on the spacing of atoms in the material. This scattering pattern is unique to each material and can be used to identify unknown compounds. Polycapillary optics can focus X-rays into a small beam and overcome limitations of traditional XRD systems, allowing the analysis of small samples and thin films with lower power X-ray sources. X-ray crystallography is a related technique that uses X-ray diffraction data to determine the three-dimensional atomic structure of crystals.