Growth mode of la_0.5Sr_0.5CoO₃ thin films with oxygenpressure on stepped SrTiO₃ substrates

We have studied the growth mode of La_0.5Sr_0.5CoO ₃ (LSCO) thin films as a function of oxygen pressure on stepped SrTiO₃ substrate by laser molecular beam epitaxy (Laser MBE). The growth behavior and mode of LSCO thin films are sensitive to oxygen ambient during growth. LSCO thin films grown at low oxygen pressures (<10 ^-3 Torr) exhibited a two-dimensional layer-by-layer growth mode at the initial stage, followed by island growth mode within a few tenths of a unit-cell layer. When the ambient oxygen pressure reached 10 mTorr, the LSCO thin films exhibited a well-defined step-and-terrace structure with atomically flat surface roughness close to the SrTiO₃ substrate, which suggests that two-dimensional layer-by-layer growth is obtained through the deposition. Further increasing the oxygen pressure degraded the growing surface, resulting in a gradual increase in surface roughness. This result indicates that two-dimensional growth was obtained in a certain degree of ambient oxygen pressure in the growth of oxide thin film whose oxygen nonstoichiometry is susceptible to oxygen ambient.