Optimization of atomically smooth and metallic surface of SrTiO$_{3}$ for the growth of ultra-thin manganite films*

Atomically smooth, TiO$_{2}$ terminated SrTiO$_{3}$ substrates can be prepared using a combination of chemical and thermal annealing treatments. Such substrates have been widely used to grow sharp oxide interfaces between SrTiO$_{3}$ and materials such as LaAlO$_{3}$. Insulating SrTiO$_{3}$ can also be made metallic by inducing oxygen vacancies or by doping with metals such as niobium. However, such treatments usually generate a rough surface. Thus, further growth of epitaxial thin films or study of the surface itself has been limited. Here, we report the optimal conditions to fabricate atomically smooth and metallic SrTiO$_{3}$ surfaces which show steps of one unit cell height. We directly confirmed the metallic characteristic of SrTiO$_{3}$ using sheet resistance vs. temperature ($R(T))$ measurements. The $R(T)$ data provides information on the physical origin of metallic behavior in SrTiO$_{3}$, which might also be relevant to the current research interest in 2DEG SrTiO$_{3}$ and oxide interfaces. We will also discuss the thin film growth of strain-induced insulating manganites on top of atomically smooth and metallic SrTiO$_{3}$ using pulsed laser deposition.