Oxygen scavenging: Eu on SrTiO₃ (001)

EuO is a promising material for spintronic devices due to its strong magnetism (7 µ_B per Eu 2+) and 100% spin polarization of the conduction band. However, growing stoichiometric, high quality EuO on substrates such as buffered -Si is difficult because of high stability of the competing Eu₂O₃ phase. We grow EuO/SrTiO₃/Si structures by molecular beam deposition of metallic Eu in UHV on SrTiO₃/Si without providing additional oxygen. We analyze the composition by x-ray photoelectron spectroscopy. In direct deposition of Eu on SrTiO₃ (STO), oxygen is scavenged from the substrate to form EuO. This leaves behind a conductive oxygen deficient SrTiO_3-δ layer. We investigate the growth mechanism by varying the STO thicknesses and temperature of Eu deposition. We find that single crystal EuO forms on thick STO leaving a SrTiO_3-δ layer of ~4nm. If the STO layer is comparable to the scavenging depth at a given temperature, a solid state reaction occurs. On the other hand, at low temperature only a 1-2 nm-thick EuO layer forms, on top of which Eu metal is stable.