Evidence for a low-temperature phase transition on the SrTiO3 (001) surface

A reflection high-energy electron diffraction (RHEED) study of the SrTiO3 (001) surface structure in a temperature region from 300 down to 5 K is reported. The diffraction patterns exhibit extra reflections, which are interpreted as evidence for a surface phase transition of a soft-mode type, promoted by the surface symmetry. The RHEED rocking curves obtained at room and liquid-helium temperatures at an electron energy of 50 keV were analyzed in a quasi-kinematic approximation, based on the main postulates of the dynamical theory of scattering. The mutual in-plane octahedron rotations were found to be similar to those that arise in the vicinity of the well-known bulk phase transition in strontium titanate at 110 K.