Conducting interfaces between band insulating oxides: the LaGaO3/SrTiO3

We show that the growth of the heterostructure LaGaO3/SrTiO3 yields the formation of a highly conductive interface. Our samples were carefully analyzed by high resolution electron microscopy, in order to assess their crystal perfection and to evaluate the abruptness of the interface. Their carrier density and sheet resistance are compared to the case of LaAlO3/SrTiO3 and a superconducting transition is found. The results open the route to widening the field of polar-non polar interfaces, pose some phenomenological constrains to their underlying physics and highlight the chance of tailoring their properties for future applications by adopting suitable polar materials.Comment: in press Appl. Phys. Lett. 97, 1 (2010

Double-cell superstructure and vacancy ordering in tensile-strained metallic thin films of P r0.50 C a0.50Co O3 on LaAl O3

The Pr-based cobaltate Pr0.5Ca0.5CoO3 (PCCO) presents in bulk form a singular simultaneous valence and spin-state transition that turns the metallic state into insulator, and displays a large and ultrafast photoresponse in the insulating phase. Epitaxial thin films of PCCO have been grown by deposition on LaAlO3(001) (LAO) substrate, chosen to minimize the mismatch with the film. The films grow epitaxially with two times the substrate periodicity (2a0×2a0×2a0) and the long perovskite axis perpendicular to the surface. We report a reduction of the structural symmetry from Pnma (bulk) to P212121 (film). The P212121 symmetry revealed by synchrotron x ray remains at low temperatures. These PCCO films are metallic, and ferromagnetic below TC=170K, confirming the stabilization of excited Co3+ spin states and the suppression of the concurrent Co spin-state, valence, and metal-insulator transitions. Z-contrast imaging and electron-energy-loss spectroscopy elemental maps reveal long-range ordered oxygen vacancy planes unexpectedly stacking parallel to the interface, in spite of the tensile character of the PCCO/LAO heterostructure. In contrast to the general tendency reported for strained La0.5Sr0.5CoO3-d (LSCO) films, we show that a nominal tensile strain can be also compatible with the presence of alternating O vacancy planes parallel to the interface, instead of perpendicular to it. That occurs thanks to the double cell of the film and the formation of the (1/2, 1/2, 1/2) superstructure studied in this work. These results expand the possibilities of controlling interfacial physical properties via engineering of ordered oxygen-defect structures in strongly correlated oxides

Integration of functional complex oxide nanomaterials on silicon

The combination of standard wafer-scale semiconductor processing with the properties of functional oxides opens up to innovative and more efficient devices with high value applications which can be produced at large scale. This review uncovers the main strategies that are successfully used to monolithically integrate functional complex oxide thin films and nanostructures on silicon: the chemical solution deposition approach (CSD) and the advanced physical vapor deposition techniques such as oxide molecular beam epitaxy (MBE). Special emphasis will be placed on complex oxide nanostructures epitaxially grown on silicon using the combination of CSD and MBE. Several examples will be presented, with a particular stress on the control of interfaces and crystallization mechanisms on epitaxial perovskite oxide thin films, nanostructured quartz thin films, and octahedral molecular sieve nanowires. This review enlightens on the potential of complex oxide nanostructures and the combination of both chemical and physical elaboration techniques for novel oxide-based integrated devicesAC acknowledges the financial support from 1D-RENOX project (Cellule Energie INSIS-CNRS). J.M.V.-F. also acknowledges MINECO for support with a Ph.D. grant of the FPI program. We thank David Montero and L. Picas for technical support. We also thank P. Regreny, C. Botella, J.B. Goure for technical assistance on the Nanolyon technological platform. We acknowledge MICINN (MAT2008-01022 MAT2011-28874-c02-01 and MAT2012-35324), Consolider NANOSELECT (CSD2007-00041), Generalitat de Catalunya (2009 SGR 770 and Xarmae), and EU (HIPERCHEM, NMP4-CT2005-516858) projects. The HAADF-STEM microscopy work was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. This research was supported by the European Research Council (ERC StG-2DTHERMS), Ministerio de Economía y Competitividad of Spain (MAT2013-44673-R) and EU funding Project “TIPS” Thermally Integrated Smart Photonics Systems Ref: 644453 call H2020-ICT-2014-1S

Vertical (La,Sr)MnO3 Nanorods from Track-Etched Polymers Directly Buffering Substrates

A novel and general methodology for preparing vertical, complex-oxide nanostructures from a sol gel-based polymer-precursor solutions is developed using track-etched polymers directly buffering substrates. This method is able to develop a nanostructure over the entire substrate, the dimensions and localization of the vertical nanostructures being preset by the polymeric nanotemplate. Thereby, nanostructures with lateral sizes in the range of 100 to 300 nm and up to 500 nm in height have been grown. Two examples are presented herein, the latter being the evolution of the initial, metastable nanostructure. Specifically, La0.7Sr0.3MnO3 polycrystalline rods are grown at mild temperatures (800 degrees C); upon strong thermal activation (1000 degrees C) they suffer a profound transformation into vertical, single-crystalline (La,Sr)(x)O-y nanopyramids sitting on a La0.7Sr0.3MnO3 epitaxial wetting layer. The driving force for this outstanding nanostructural evolution is the minimization of the total energy of the system, which is reached by reducing the grain-boundary, total-surface, and strain-relaxation energies. Finally, advanced electron-microscopy techniques are used to highlight the complex phase separation and structural transformations occurring when the metastable state is overcome

Photoinduced Persistent Electron Accumulation and Depletion in LaAlO3/SrTiO3 Quantum Wells

Persistent photoconductance is a phenomenon found in many semiconductors, by which light induces long-lived excitations in electronic states. Commonly, persistent photoexcitation leads to an increase of carriers (accumulation), though occasionally it can be negative (depletion). Here, we present the quantum well at the LaAlO_{3}/SrTiO_{3} interface, where in addition to photoinduced accumulation, a secondary photoexcitation enables carrier depletion. The balance between both processes is wavelength dependent, and allows tunable accumulation or depletion in an asymmetric manner, depending on the relative arrival time of photons of different frequencies. We use Green's function formalism to describe this unconventional photoexcitation, which paves the way to an optical implementation of neurobiologically inspired spike-timing-dependent plasticity.status: publishe

Chemical synthesis of oriented ferromagnetic LaSr-2 × 4 manganese oxide molecular sieve nanowires

We report a chemical solution based method using nanoporous track-etched polymer templates for producing long and oriented LaSr-2 x 4 manganese oxide molecular sieve nanowires. Scanning transmission electron microscopy and electron energy loss spectroscopy analyses show that the nanowires are ferromagnetic at room temperature, single crystalline, epitaxially grown and self-aligned