Structure and dielectric characteristics of SrTiO$_3$(111)/Al$_2$O$_3$(001) films fabricated by RF sputtering

SrTiO$_3$ thin films were grown on an Al$_2$O$_3$(001) substrate in an oxygen atmosphere using a one-stage method of high-frequency cathode sputtering of a strontium titanate ceramic target. It is shown that the obtained SrTiO$_3$ films with a thickness of $\sim$120 nm are single-phase, pure and single-crystalline (surface roughness $\sim$8.5 nm, lateral size of growth blocks $\sim$100 nm). The magnitude of the unit cell strain in comparison with the bulk single crystal, the mutual orientations between unit cells of the film and the substrate, as well as the band gap for the direct allowed transition and the indirect one have been established. The dielectric characteristics of the films had been measured, the results of which indicating that the films are in the paraelectric phase at room temperature.