Laser Irradiation Induced Atomic Structure Modifications in Strontium Titanate

We studied the surface and subsurface structural modifications induced by pulsed laser irradiation on single-crystalline SrTiO3. Using atomic-resolution scanning transmission electron microscopy investigations, we showed that a laser-irradiated surface in single-crystalline SrTiO3 transforms into an amorphous phase with a subsurface oxygen-deficient disordered crystalline region which is attributed to laser-induced melting followed by unidirectional recrystallization. A computational approach to identify positions of individual atoms in atomic-resolution images was used to determine the bond lengths between Sr-Sr and Ti-Ti atoms, and thus the lattice distortions. We estimate ~4% lattice disorder in the disordered region compared with the pristine. This disorder increases up to ~16% towards the surface and transforms to an amorphous phase. Due to rapid recrystallization, these aforementioned structural transformations were accompanied by oxygen vacancies formation and change in the location coordination. With electron energy-loss spectroscopic analysis, we confirmed the transformation of Ti+4 to Ti+3 in the disordered region due to oxygen vacancy formation.