An epitaxial film is a thin coating, often nm in thickness, which is often applied using ALD (Atomic Layer Deposition) with a single crystal structure related to its substrate.
Epitaxial thin films form the basis of modern semiconductor technology with tiny nuances in processing leading to dramatic changes in device performance. The ability to accurately measure subtle film properties is critical. Reciprocal space mapping (RSM) with XRD is the preferred technique for characterizing structural properties of thin films due to its ability to measure both perpendicular and lateral strain, composition, and domain effects.