In situ analysis of lattice relaxation by reflection high-energy electron diffraction

Reflection high-energy electron diffraction (RHEED) is a versatile technique for surface and interface analysis during film growth. Analysis of RHEED patterns during film growth is helpful for the understanding of the properties of both surface and interface. The geometrical arrangement of RHEED patterns can be derived from diffraction theory, and the in-plane and out-of-plane lattice constants are computed from the streaky or spotty patterns. During epitaxial growth of SrTiO3/SrTiO3, MgO/SrTiO3 and MgO/LaAlO3 with lattice mismatch of 0%, 7.8% and 11%, respectively, the changes of lattice constants are recorded as a function of film thickness. The in-plane lattice constant oscillates along with the oscillation of RHEED intensity in the case of SrTiO3 homoepitaxial growth. During the MgO cube-on-cube deposition on SrTiO3, the in-plane lattice constant is relaxed due to positive mismatch, and the MgO lattice is distorted into tetragonal phase at the same time. For the in-plane 45° rotation system of MgO/LaAlO3, relaxation behaviour is observed suffering from negative mismatch. The measured in-plane orientation and lattice relaxation correlate well with a two-dimensional nearly coincident site lattice model, in which the match relation of MgO/LaAlO3 growing with a 5 : 4 lattice ratio can result in negative mismatch.