Surface modeling of SrO(SrTiO3)n Ruddlesden-Popper phases

Strontium titanate (STO) is a preferred substrate material for functional oxide growth, whose surface properties can be adjusted through the presence of Ruddlesden-Popper (RP) phases. In this work, density functional theory (DFT) is used to model the (100) and (001) surfaces of SrO(SrTiO3)n RP phases. Relaxed surface structures, electronic properties and stability relations have been determined. In contrast to pure STO, the near-surface SrO-OSr stacking fault can be employed to control surface roughness by adjusting SrO and TiO2 surface rumpling, to stabilize SrO termination in an SrO-rich surrounding or to increase the band gap in the case of TiO2 termination. RP thin films have been epitaxially grown on (001)STO substrates by chemical solution deposition. In agreement with DFT results, the fraction of particular RP phases n=1-3 changes with varying heating rate and molar ratio Sr:Ti. This is discussed in terms of bulk formation energy.