Stoichiometric, nonstoichiometric, and locally nonstoichiometric SrTiO3 films grown by molecular beam epitaxy

SrTiO3 films were grown by reactive molecular beam epitaxy to have varying degrees of both global and local cationic nonstoichiometries (with stoichiometry defined as 1:1 ratio of Sr:Ti). Slight global excesses of Sr and Ti -resulted in two-fold reconstructions in the reflection high-energy electron diffraction patterns along the [110] and [100] azimuths, respectively. Larger global nonstoichiometries (2:1 and 1:2 ratios) were also accommodated into the film's crystalline structure and affected the long-range crystalline order as observed in the x-ray diffraction patterns, both of which were related to the parent perovskite pattern. Local nonstoichiometries were introduced by depositing multiple monolayers (MLs) (from 2 to 33) of SrO and TiO2 in an alternating fashion, while maintaining the global SrTiO3 stoichiometry. These layered structures of SrO and TiO2 blocks inter-reacted during growth to form highly crystalline epitaxial SrTiO3. Films grown in this manner with blocks thicker than 8 MLs were fully relaxed and, when the, block thicknesses ranged between 8 and 10 MLs, the full widths at half maxima of 2 theta peaks were narrower than the standard SrTiO3 films having blocks 1 ML thick. (c) 2008 American Institute of Physics.