Femtosecond laser induced surface nanostructures on SrTiO₃

SrTiO3 (STO) is one of the key perovskite oxides with fascinating properties in electronics and optoelectronics. The generation and evolution of surface nanostructures induced by femtosecond lasers on STO surfaces are studied, showing distinct features with a clear fluence and pulse number dependence. Unlike regular ripples, which are either parallel or perpendicular to the laser polarization, the ripples coexist in both directions after irradiated with four pulses, and they cover the whole structured area. When increasing the number of laser pulses, the ripples parallel to the laser polarization dominate at a lower fluence regime, while the ripples perpendicular to the laser polarization are the only surface structures formed at a higher fluence regime. The finite-difference time-domain method and the Drude model have been adopted to analyze energy deposition on the STO surface. The results demonstrate that the combination of energy deposition at different excitation levels and the feedback effect is the origin of the formation and evolution behavior of the surface nanostructures on STO.