MBE is an accronym for Molecular Beam Epitaxy. Molecular beam epitaxy is the growth of thin films by the extremely slow evaporation of semiconductors or metals in an ultra-clean environment with a deposition rate of only a few nanometres per minute. The term 'epitaxy' signifies the growth of crystalline layers generally termed a 'superlattice' with atoms in atomic register with the layers underneath. The growth of metals requires evaporation sources operating at considerably higher temperatures than for semiconductors.