Effects of anharmonicity of ionic bonds on the lattice distortion at the interface of alkali halide heterostructures

The initial stage of heteroepitaxial growth of alkali halide on other alkali halide was studied using reflection high energy electron diffraction, electron energy loss spectroscopy and Auger electron spectroscopy. The lattice distortion relaxed more rapidly for the system where the lattice constant of the film was larger than that of the substrate (i.e. positive misfit), than for the system where the lattice constant of the film was smaller than that of the substrate (i.e. negative misfit). Classical Monte Carlo calculations were performed for KCl films on various kinds of substrates to clarify the relation between the lattice distortion and the ionic potential. The rapid relaxation of lattice distortion for the positive misfit could be explained qualitatively in terms of anharmonicity in ionic bonds.