Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session X09: Vacancies and Defects/Structure of Complex Oxide HeterostructuresFocus
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Sponsoring Units: DMP Chair: Derek Meyers, Brookhaven National Laboratory Room: LACC 301A |
Friday, March 9, 2018 8:00AM - 8:12AM |
X09.00001: Oxygen vacancy transport at Y2O3/CeO2 interfaces: Insights from density functional theory Axiel Yael Birenbaum, Valentino Cooper Oxygen-deficient fluorite oxides have shown fast oxygen transport, ideal for the solid electrolytes in solid oxide fuel cells. Crucial to their design are predictions of atomic-scale transport pathways in materials. For instance, while recent experimental studies of unique nanobrush geometries of Ceria-Ytria superlattices demonstrated that these materials exhibit excellent oxygen transport, little is known about the mechanisms that lead to this optimal behavior. Using first-principles methods, we have examined the oxygen vacancy transport at or near the interface in a Y2O3/CeO2 superlattice model. Our results give insights in both the preference for oxygen vacancy formation as well as dynamics within the superlattice – having significant implications for the aforementioned nanobrushes. |
Friday, March 9, 2018 8:12AM - 8:24AM |
X09.00002: Mechanical and electrical control of oxygen vacancies in strained Nb:SrTiO3 thin films Lucía Iglesias, Andrés Gómez, Marti Gich, Francisco Rivadulla Gaining control over the concentration and distribution of cationic and anionic defects is a novel route to induce new functional properties in transition metal oxides. For the particular case of SrTiO3 (STO), local manipulation of oxygen vacancies (VO) in thin films plays a crucial role on the magnetic and thermoelectric properties of this relevant material. |
Friday, March 9, 2018 8:24AM - 8:36AM |
X09.00003: Reduction of SrTiO3 Substrates by Pulsed Laser Deposition of Oxygen-Deficient Perovskite Films Purnima Balakrishnan, Michael Veit, Urusa Alaan, Matthew Gray, Yuri Suzuki SrTiO3 (STO) is a common substrate material for the growth of many perovskite oxide thin films and heterostructures. Oxygen deficiency in STO induces metallic behavior in bulk and thin film form. In this presentation, we report on the metallicity of STO substrates induced by pulsed laser deposition (PLD) of STO films in various growth conditions. STO substrates annealed in the same growth conditions remain insulating. By varying background gas composition (O2, N2, Ar, 99%N2/1%O2) and pressure at a deposition temperature of 750°C, we find: (1) a strong dependence of the transport on O2 partial pressure, transitioning from metallic to insulating behavior between ~7–10×10-6 Torr; (2) increasing resistivity with increasing total pressure for fixed O2 partial pressure; and (3) that metallic behavior persists to higher deposition pressures for N2 and Ar compared to O2. Samples with higher conductance exhibit a homogenously darker color. These results suggest that, during the PLD process, the deposition kinetics are a dominant factor in the formation of oxygen vacancies which then diffuse into the substrate. Understanding these mechanisms is crucial to prevent STO substrate reduction during PLD of films which require low O2 partial pressures during growth. |
Friday, March 9, 2018 8:36AM - 9:12AM |
X09.00004: Engineering complex oxide properties via interface control Invited Speaker: Albina Borisevich This abstract not available. |
Friday, March 9, 2018 9:12AM - 9:24AM |
X09.00005: The oxygen vacancies in the LaAlO3 layer of the LaAlO3/SrTiO3 interface system Xiaofang Zhai, Zhicheng Wang, Yalin Lu Oxygen vacancies have been rarely studied in the top LaAlO3 layer of the LaAlO3/SrTiO3 quasi-two-dimensional electron gas system. Here we found compelling evidences of oxygen vacancy formation in the top LaAlO3 layer using combined experiments of Layer by layer pulsed laser deposition growth, X-ray photoemission and X-ray diffraction. We found that the amount of oxygen vacancies in the LaAlO3 layer is predominately determined by the deposition rate, instead of the commonly thought oxygen partial pressure. Moreover, sub-atmosphere pressure of oxygen post-annealing is necessary for completely removing the oxygen vacancies in the LaAlO3 layer on top of the SrTiO3 substrate. Our study shines new light on the physical mechanism supporting the formation of the quasi-two-dimensional electron gas. |
Friday, March 9, 2018 9:24AM - 9:36AM |
X09.00006: A route from small sized crystals to gated devices using focused ion beams Evgeny Mikheev, Tino Zimmerling, Philip Moll, David Goldhaber-Gordon Current efforts at material discovery divide between exploratory bulk crystal or powder synthesis and targeted growth of key systems in thin film form. Tuning the Fermi level by electrostatic gating is further reserved to a small number of materials available as thin films or millimeter-sized crystals. Here, we present a route to process a smaller single crystal into a gated Hall bar. A micron-sized lamella is cut with a focused ion beam from a crystal protected by a removable coating to minimize surface damage, and transferred into a resin, which is then crosslinked, allowing thin-film like fabrication of electrical contacts for resistivity measurements. Proof-of-concept processing of commercial SrTiO3 single crystals into ionic liquid gated devices by this method will be presented. The process is expected to enable device fabrication in many emerging material systems available only as small-sized single crystals, such as some heavy fermion compounds. |
Friday, March 9, 2018 9:36AM - 9:48AM |
X09.00007: Structural Analysis of Orthorhombic Distortions in Perovskite Thin Films under Epitaxial Strain
and Their Consequences on the Electronic Properties. Stefano Gariglio, Hugo Meley, Joeri de Bruijckere, Duncan Alexander, Kareen Deep, Philippe Ghosez, Jean-Marc Triscone
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Friday, March 9, 2018 9:48AM - 10:00AM |
X09.00008: Influence of misfit dislocation on dopant segregation at complex oxide heterointerfaces Pratik Dholabhai, Enrique Martinez, Blas Uberuaga Complex oxide heterointerfaces and thin-films have emerged as promising candidates for diverse applications, wherein interfaces formed by joining two different oxides play a central role in novel properties not present in individual components. Lattice mismatch between the two oxides leads to the formation of misfit dislocations, which influence vital properties. In oxides, doping is often used as a strategy to improve properties. However, dopant segregation to misfit dislocations, an outcome not well understood, could be detrimental for e.g. ionic transport. We have used atomistic simulations to study the influence of misfit dislocations on dopant segregation at SrTiO3/MgO heterointerfaces, considering two interfacial chemistries where the misfit dislocation structure differs. For both interfaces, we will examine doping of SrTiO3 with various trivalent dopants. We find that all dopants have a thermodynamic preference to go to the interface, but the tendency to segregate is much stronger at TiO2-terminated interfaces. Our results indicate that different dislocation structures at the interface could impact dopant segregation, thereby influencing ionic transport. Overall, our results offer a fundamental atomic-scale perspective of dopant behavior at complex oxide heterointerfaces. |
Friday, March 9, 2018 10:00AM - 10:12AM |
X09.00009: Young's modulus of freestanding oxide thin films Varun Harbola, Samuel Crossley, Seung Sae Hong, Yorick Birkhölzer, Di Lu, Yasuyuki Hikita, Harold Hwang Recent developments in thin film growth provide a powerful route to free-standing single-crystal films of perovskite oxides by water etching of a sacrificial underlayer (Di Lu et al., Nature Materials 15, 1255 [2016]). We have used Atomic Force Microscopy to systematically probe the elastic properties of suspended SrTiO3 films, in the hitherto unexplored sub-100 nm thickness regime. We evaluate and discuss the variation of Young's modulus with film thickness, and compare our freestanding films to bulk SrTiO3. Our study of the mechanical properties of thin SrTiO3 could provide the basis for precise strain control and manipulation of complex oxides at the nanoscale, thus coupling to spin-charge-orbital degrees of freedom, as well as ferroic order. |
Friday, March 9, 2018 10:12AM - 10:24AM |
X09.00010: Synthesis and Characterization of High-Mobility BaSnO3 Membranes Prastuti Singh, Adrian Swartz, Di Lu, Seung Sae Hong, Kazunori Nishio, Yasuyuki Hikita, Harold Hwang Doped BaSnO3 is a wide band-gap semiconductor that is known to exhibit high electron mobility at room temperature, showing great prospects as an alternative transparent conducting oxide to the industry standard indium-tin-oxide. Flexible transparent conducting oxides are of special interest for future photonics and optoelectronic devices but realizing high-quality films as flexible materials has been a challenge. In this work, we will discuss our efforts to synthesize and characterize freestanding membranes of La-doped BaSnO3 (BLSO) films. The films were deposited using pulsed laser deposition on a hygroscopic pseudo-perovskite buffer layer, which acts as a sacrificial layer that can be selectively etched to produce membranes1. Using this technique, we can transfer complex oxides and heterostructures onto flexible substrates. We find that the electron mobility of the freestanding BLSO films is comparable to the as grown films, paving the way for the exploration of the strain-dependent BLSO transport properties for potential flexible electronics applications. |
Friday, March 9, 2018 10:24AM - 10:36AM |
X09.00011: Development of a Portable Conductive AFM Lithography Workstation Joseph Albro, Yun-Yi Pai, Xinyi Wu, Jianan Li, Jessica Montone, Patrick Irvin, Jeremy Levy Conductive Atomic Force Microscope (c-AFM) Lithography provides the tools needed to create devices from the two-dimensional electron system that lies at the LaAlO3/SrTiO3 (LAO/STO) interface. By using c-AFM lithography, we can create devices such as electron waveguides and single electron transistors that allow us to observe properties of LAO/STO that are only found using those devices. Due to the decaying nature of these devices in the ambient environment, even sealing the devices in a portable vacuum chamber can not ensure the survival of the previously written devices. This causes the transportation of such devices made using c-AFM lithography difficult. To provide a solution to this pressing issue, we decided to create a portable lithography workstation by combining a portable AFM with a transport measurement setup, and as such enabling us to perform lithography at any location. |
Friday, March 9, 2018 10:36AM - 10:48AM |
X09.00012: Direct Imaging of Tilts and Rotations of Ca2RuO4 Octahedra in Thin Films with Epitaxial Strain using ABF-STEM Celesta Chang, Megan Holtz, Hari Nair, Jacob Ruf, Kyle Shen, Darrell Schlom, David Muller Recent studies on thin film Ca2RuO4 grown on LaAlO3, NdAlO3, and NdGaO3 substrates show that tuning epitaxial strain can control the tilt and rotation of the RuO6 octahedra. This leads to change in electronic properties such as the d-band bandwidth, electrical resistivity, and the metal-to-insulator transition temperature. Quantifying the exact structural distortions of RuO6 is therefore crucial in understanding the correlation between structure modification and electronic properties. In this work we use Annular Bright Field imaging (ABF) in Scanning Transmission Electron Microscopy (STEM) to directly locate the atom positions with picometer precision. Average Ru-O-Ru bond angles are mapped layer by layer to characterize the degree of tilt relaxation and decay lengths as we move away from the strained interface. We also compare distortions of the octahedra for different epitaxially strained states. |
Friday, March 9, 2018 10:48AM - 11:00AM |
X09.00013: Study of phenomena induced by interfacial oxygen octahedra coupling in La0.5Sr0.5CoO3-δ/SrTiO3 heterostructures using Cryo-STEM Xue Rui, Jeffery Walter, Chris Leighton, Robert Klie In recent years epitaxial transition metal oxide thin films with broken symmetry have been studied extensively due to their novel magnetization and transport properties. Ferromagnetic La0.5Sr0.5CoO3-δ (LSCO) thin films grown on SrTiO3 exhibit oxygen vacancy ordering which is absent in bulk, while SrTiO3 undergoes antiferrodistortive phase transition at 105 K being triggered by rotations of the TiO6 octahedra. This structural symmetry breaking accommodated by interfacial lattice mismatch modifies the Ti-O-Co bond angle at the interface, and hence distorts both CoO6 octahedral and CoO4 tetrahedral structures in LSCO thin films. Here, we use aberration-corrected scanning transmission electron microscopy combined with an in situ TEM cryo-holder to compare the atomic/electronic structure and magnetic properties of La0.5Sr0.5CoO3-δ thin films grown on SrTiO3, below and above 105 K. Atomic-resolution imaging and electron energy-loss spectroscopy (EELS) are used to examine variations in the local density of states and magnetic moments as a function of sample temperature. |
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