MBE (molecular beam epitaxy) is a method of depositing layers of materials with atomic thicknesses on to substrates. A gaseous 'beam' of particles, i.e. molecules or single atoms, of a material is created by means of evaporation sources (effusion cells, sublimation sources, etc.). This beam impinges on to a substrate resulting in layers that take on a lattice structure and orientation identical to those of the substrate ('epitaxial growth' of monocrystalline films). These so called 'superlattices' have a number of technologically important uses including quantum well lasers for semiconducting systems, and giant magneto-resistance for metallic systems