The local atomic geometries in Ba0.5Sr0.5TiO3 thin films grown onMgO(001) substrates have been determined by Ti 1s near-edge x-ray-absorption fine-structure measurements and density-functional-theory calculations. The accuracy of the atomic geometries predicted by density-functional theory is demonstrated by simulations of the near-edge x-ray-absorption fine-structure spectra using a Bethe-Salpeter treatment of the Ti 1s core-hole interaction in the films. Our results show that films with either c > a or c < a tetragonal lattice distortions have their polarization vectors rotated toward or away from the [001] film-normal or c-axis direction, respectively. Both distortions result locally in the monoclinic r phase of the strain-phase diagram of Pertsev et al. [Phys. Rev. Lett. 80, 1988 (1998)], and the polarizations are rotated significantly larger than the geometry would suggest.

A phase-separation instability, resulting in the dewetting of thin SrTiO(3) films grown on Si(100) is shown by scanning transmission electron microscopy. Plan-view imaging of 1-nm thick, buried SrTiO(3) films was achieved by exploiting electron channeling through the substrate to focus the incident 0.2 nm beam down to a 0.04 nm diameter, revealing a nonuniform coverage by epitaxial SrTiO(3) islands and 2 x 1 Sr-covered regions. Density-functional calculations predict the ground state is a coexistence of 2 x 1 Sr-reconstructed Si and Sr-deficient SrTiO(3), in correspondence with the observed islanding.

A highly conductive channel, a few nanometres wide, can be reversibly created by an AFM tip operating at room temperature at the interface between two oxide insulators. This discovery could provide a powerful method for the design and realization of electronic circuits at the nanoscale. Experimental1,2,3,4,5,6,7 and theoretical8,9 investigations have demonstrated that a quasi-two-dimensional electron gas (q-2DEG) can form at the interface between two insulators: non-polar SrTiO3 and polar LaTiO3 (ref. 2), LaAlO3 (refs 3–5), KTaO3 (ref. 7) or LaVO3 (ref. 6). Electronically, the situation is analogous to the q-2DEGs formed in semiconductor heterostructures by modulation doping. LaAlO3/SrTiO3 heterostructures have recently been shown10 to exhibit a hysteretic electric-field-induced metal–insulator quantum phase transition for LaAlO3 thicknesses of 3 unit cells. Here, we report the creation and erasure of nanoscale conducting regions at the interface between two insulating oxides, LaAlO3 and SrTiO3. Using voltages applied by a conducting atomic force microscope (AFM) probe, the buried LaAlO3/SrTiO3 interface is locally and reversibly switched between insulating and conducting states. Persistent field effects are observed using the AFM probe as a gate. Patterning of conducting lines with widths of ∼3 nm, as well as arrays of conducting islands with densities >1014 inch−2, is demonstrated. The patterned structures are stable for >24 h at room temperature.

Ti K and Ti L-2,L-3 x-ray absorption fine-structure near-edge spectra of SrTiO3 thin films grown coherently on Si(001) reveal the presence of a ferroelectric (FE) distortion at room temperature. This unique phase is a direct consequence of the compressive biaxial strain achieved by coherent epitaxial growth.