X-ray diffraction method for the investigation of contacts between solid surfaces

A coherent X‐ray scattering method for investigating the formation of the contact region between two solid surfaces is presented. Diffraction of X‐rays from two crossed cylindrical quartz surfaces, coated with Cr and TiO2, revealed a total contact area of 90 ± 10 µm. In the so‐called Hertz model for two surfaces in non‐adhesive contact, this value is directly related to the displacement of the surfaces and the applied external force. Values of 40 ± 3 nm for the displacement and 24 ± 3 mN for the force are found. The method is also useful for studying liquids in confinement.