The atom arrangementat the surface of a solid differs from that in the bulk. Precise information on the surface geometry is essential, since the geometric structure determines the chemical and electronic properties of the surface.

Each solid has surfaces. An atom or molecule that is situated directly at the surface has a different atomic surrounding than a particle in the bulk. Molecules from the neighbouring gas or fluid phase can interact and lead to further changes in the surface structure. These processes are the basis of heterogenous catalysis or corrosion processes. In Microelectronics the minimisation of dimensions leads to an increasing imporatnce of surfaces and interfaces. The key for understanding surface and interface properties lies, besides direct imaging with electron microscopy or scanning tunnel microscopy, in crystallographic structure analysis, amongst others with neutron scattering.