Massive Band Gap Variation in Layered Oxide Heterostructures by Atomic Scale Design
9:00 PM - MD3.3.09
Tunneling Spectroscopy in Electric Dipole Engineered Oxide Heterostructures
Hisashi Inoue 1,Adrian Swartz 1,Tyler Merz 1,Yasuyuki Hikita 2,Harold Hwang 2
1 Geballe Laboratory for Advanced Materials, Department of Applied Physics Stanford University Stanford United States,2 Stanford Institute for Materials and Energy Sciences SLAC National Accelerator Laboratory Menlo Park United States1 Geballe Laboratory for Advanced Materials, Department of Applied Physics Stanford University Stanford United States,2 Stanford Institute for Materials and Energy Sciences SLAC National Accelerator Laboratory Menlo Park United StatesShow Abstract
The origin of superconductivity in SrTiO3 is still under active debate despite 50 years of research. Being a semiconducting superconductor with the lowest known bulk carrier density, it is beyond the limit of conventional theories of superconductivity in metals, with a Fermi energy
9:00 PM - MD3.3.10
Towards Two-Dimensional Oxides for Optoelectronic Applications
Jonathan Rackham 1,Bin Zou 1,Kevin Kahn 3,Sneha Rhode 1,Suman-Lata Sahonta 2,Michelle Moram 2
1 Department of Materials Imperial College London London United Kingdom,1 Department of Materials Imperial College London London United Kingdom,3 Department of Physics National University of Singapore Singapore Singapore2 Department of Materials Science amp; Metallurgy University of Cambridge Cambridge United Kingdom1 Department of Materials Imperial College London London United Kingdom,2 Department of Materials Science amp; Metallurgy University of Cambridge Cambridge United KingdomShow Abstract
Perovskite oxides such as barium titanate have been used very successfully as dielectric materials, but they have indirect band gaps and are therefore not used in optoelectronic applications. However, if such materials could be designed to have a direct band gap then perovskite oxide-based optoelectronic devices could become possible. In that case their wide band gaps would be well suited for use in high efficiency ultraviolet emitters and detectors. Such devices, emitting in the 260-280 nm range (4.4-4.8 eV), are needed for water treatment and sterilisation to replace inefficient and bulky mercury vapour lamps.
The dimensionality of a material is known to affect its band structure, but can this be used to produce a direct band gap? To investigate this, thin films of the oxide alloy barium zirconate titanate (BaZrxTi1-xO3, BZT) have been grown by pulsed laser deposition on magnesium oxide (MgO) substrates. BZT is representative of perovskites, has an appropriate band gap range (3.2 - 5.3 eV) for the end application and its alloys are well lattice matched to MgO substrates.
Characterisation data were obtained from BZT films over the full composition range 0 < x < 1 with thicknesses ranging from 100 nm to 1 monolayer.
X-ray diffraction results show out-of-plane lattice constant sensitivity to oxygen partial pressure under growth, while atomic-resolution transmission electron microscopy (TEM) studies show epitaxial growth under all conditions, with a low crystal defect density. UV-Vis spectroscopy and spectroscopic ellipsometry data show that the band gap varies non-linearly with composition and is dependent on film thickness, while the latter reveals interesting electronic effects at the interface. Aberration corrected scanning TEM using a high-angle annular dark field detector reveals the interface structure. In combination, these data confirm that reducing the dimensionality is an effective method of tailoring the band structure of wide band gap perovskites for device applications.
9:00 PM - MD3.3.11
Quantitative Analysis of the Local Ferroelectric-Paraelectric Phase Transitions Induced by Laser Heating
Anton Ievlev 1,Michael Susner 1,Michael McGuire 1,Petro Maksymovych 1,Sergei Kalinin 1
1 Oak Ridge National Laboratory Oak Ridge United States,Show Abstract
Functional imaging enabled by scanning probe microscopy (SPM) allows investigations of nanoscale material properties under a wide range of external conditions, including temperature. However, a number of shortcomings preclude the use of the most common material heating techniques, thereby limiting precise temperature measurements.
Here we introduced a fast local heating technique based on the focused laser irradiation for functional SPM imaging. The laser induces heating in the region much larger than typical SPM probing volume, which allows mapping in an effectively uniform temperature field. The suggested technique has been applied to the layered ferroelectrics of copper indium thiophosphate (Cu1-xIn1+x/3P2S6) for investigation of the ferroelectric-paraelectric phase transition. The in-situ measurements by Piezoresponse force microscopy and confocal micro-Raman spectroscopy revealed correlated changes in the domain structure and Raman spectra. These data were used as a sign of the transition from ferroelectric to paraelectric phase for further temperature calibration.
However, non-polar inclusions of In4/3P2S6 hampered direct identification of the phase transformation. The problem was resolved using Bayesian linear unmixing and principal component analysis for the separation of the Raman spectra corresponding to different material phases. These results, along with the macroscopically measured Curie temperatures and finite element simulation of the temperature distribution, allowed us to calibrate the temperature in the irradiated region close to the tip.
Results of the current research are important for the development of novel SPM techniques and enable a systematic approach for studying temperature dependent material functionalities in previously inaccessible temperature regimes.
A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.
9:00 PM - MD3.3.12
Polarization Effects on the Interfacial Conductivity in the LaAlO3/SrTiO3 Heterostructure: First-Principles Study
Maziar Behtash 1,Safdar Nazir 1,Yaqin Wang 1,Kesong Yang 1
1 UC San Diego La Jolla United States,Show Abstract
Motivated by the recent experimental findings of Moler et al., (Nat. Mater., 2013, 12, 1091), we investigated the influence of uniaxial  strain (-1% to +1%) on the electron transport properties of two-dimensional electron gas (2DEG) at the n-type (LaO)+1 /(TiO2 )0 interface in the LaAlO3 /SrTiO3 (LAO/STO) heterostructure (HS)-based slab system using first-principles density functional theory calculations. Our results demonstrate that applying a tensile strain on the STO substrate along the -direction causes a significant reduction of the polarization in the LAO film towards the vacuum. This reduction in polarization weakens the driving force against charge transfer from the LAO film to the STO substrate, causing an increase in the interfacial charge carrier density. The uniaxial strain also leads to a decrease of the effective mass of interfacial mobile electrons, resulting in a higher electron mobility. These findings suggest that applying a uniaxial  tensile strain on the STO substrate can significantly enhance the interfacial conductivity of the LAO/STO HS system, which gives a comprehensive explanation for the experimental observations. In contrast, compressively strained LAO/STO systems show stronger LAO film polarization than the unstrained system, which reduces the interfacial charge carrier density and increases the electron effective mass, thus suppressing the interfacial conductivity.
9:00 PM - MD3.3.13
Backscattered Scanning Electron Microscopy Domain Imaging of Ferroelectric Films
David Scrymgeour 1,Joseph Michael 1,Bonnie Mckenzie 1,Elizabeth Paisley 1,Jon Ihlefeld 1
1 Sandia National Labs Albuquerque United States,Show Abstract
The ferroelastic domain structure of ferroelectric lead zirconate titanate (PZT) bilayers and thin films are imaged by backscatter scanning electron microscopy using the differential channeling and backscatter electron (BSE) yield to provide contrast. These images are directly correlated to images taken with piezoresponse force microscopy (PFM) to show the complementary nature of the technique. The data clearly shows that BSE imaging can be used to collect similar domain morphology information as PFM with similar resolution. We will show that this offers an alternative and powerful method of evaluating domain structures as well as being able to combine with electron backscatter diffraction to identify grain orientations in polycrystalline films. Additionally, domain structure changes under applied electric fields under 3 nm thick platinum electrodes are observed using the backscatter imaging technique and enable the imaging of domain structure in actual capacitor structures that would be otherwise difficult to capture.
9:00 PM - MD3.3.15
Two-Dimensional Electron Gas Driven by Strain-Induced Polarization in Nonpolar AHfO3/SrTiO3 (001) (A=Ca, Sr, and Ba) Heterostructure: First-Principles Analysis
Jianli Cheng 1,Safdar Nazir 1,Kesong Yang 1
1 Department of Nanoengineering University of California, San Diego La Jolla United States,Show Abstract
The two-dimensional electron gas (2DEG) at polar/nonpolar LaAlO3/SrTiO3 heterostructure (HS) has stimulated a tremendous amount of research activities because of its promising applications in next-generation nanoelectronics. Here, we investigated the formation of 2DEG in nonpolar/nonpolar AHfO3/SrTiO3 (A = Ca, Sr, and Ba) oxide HS-based slab systems via strain-induced polarization (polarization discontinuity) using first-principles electronic structure calculations. Two types of neutral interfaces are modeled, (AO)0/(TiO2)0 and (HfO2)0/(SrO)0, each with AO and HfO2 surface terminations. Our results suggest that as the AHfO3 film thickness increases, the lattice mismatch-induced compressive strain leads to a strong polarization in the AHfO3 film and results in an insulating-metallic transition (IMT). The critical thickness of the AHfO3 film to form the interfacial metallic states depends on the magnitude of lattice mismatch and also the surface termination of AHfO3 film in both types of interface models. It is found that the critical thickness of CaHfO3 film in CaHfO3/SrTiO3 HS exists in all four types models, while the SrHfO3/SrTiO3 and BaHfO3/SrTiO3 HSs only exhibit the IMT with HfO2 surface termination. Our study provides a new route to create 2DEG in complex oxide HSs and can also stimulate the corresponding experimental studies.
9:00 PM - MD3.3.16
Creating Two-Dimensional Electron Gas in Polar/Polar Perovskite Oxide Heterostructures: First-Principles Characterization of LaAlO3/A+B5+O3
Yaqin Wang 1,Wu Tang 2,Jianli Cheng 1,Maziar Behtash 1,Kesong Yang 1
2 University of Electronic Science and Technology of China Chengdu China,1 University of California, San Diego La Jolla United States,2 University of Electronic Science and Technology of China Chengdu China1 University of California, San Diego La Jolla United StatesShow Abstract
We report high-mobility two-dimensional electron gas (2DEG) at polar/polar (LaO)+/(BO2)+ interface in the LaAlO3/A+B5+O3 (A=Na and K, B=Nb and Ta) heterostructures (HS) using first-principles electronic structure calculations. By employing HS-based slab models in our simulations, we find that there does not exist a critical film thickness for the LaAlO3 to have an insulator-to-metal transition in these polar/polar HS systems, different from the case of polar/nonpolar LaAlO3/SrTiO3 HS system in which four unit cells of LaAlO3 are required to cause such a transition. All these polar/polar systems show much higher interfacial charge carrier densities in the order of 1014 cm-2 than that in the LaAlO3/SrTiO3 system. This is because there are two donor layers, i.e., (LaO)+ and (BO2)+ (B=Nb and Ta), in the polar/polar LaAlO3/A+B5+O3 systems, and only one (LaO)+ donor layer in the LaAlO3/SrTiO3 system. Moreover, due to less localized of Nd 4d and Ta 5d states compared to Ti 3d states, these LaAlO3/A+B5+O3 HS systems have a smaller effective mass than that in the LaAlO3/SrTiO3 system, and thus can exhibit potentially higher electron mobility. This work reveals an alternative way to produce superior 2DEG via electronic reconstruction at polar/polar perovskite-oxide-based interface.
Ariando Ariando, National University of Singapore
Gertjan Koster, University of Twente
Ho-Nyung Lee, Oak Ridge National Laboratory
Yayoi Takamura, University of California, Davis
MD3.4: Interfaces in Oxide Heterostructures
Wednesday AM, March 30, 2016
PCC West, 100 Level, Room 101 C
9:00 AM - *MD3.4.01
Confined d Electrons in (001)-, (110)-, and (111)- Oriented Complex Oxide Heterostructures
Zhicheng Zhong 1
1 Max Planck Solid State Research Stuttgart Germany,Show Abstract
Thanks to recent progress of epitaxial growth techniques, complex oxide heterostructures can now be made and controlled at atomic scales so that d electrons are confined within a region of a few unit cells (∼1 nm) in epitaxial growth. In this talk I will show novel physical behavior of the confined d electrons in (001)-, (110)-, and (111)- oriented complex oxide heterostructures
First, d electrons in oxide heterostructures are much more localized than s,p electrons in semiconductor heterostructures. We find that a tight-binding model will give a much better description than the nearly free electron model for the quantum well states in SrVO3 ultrathin films . We employ density functional theory plus dynamical mean field theory and identify the physical origin of why two layers of SrVO3 on a SrTiO3 substrate are insulating: the thin film geometry lifts the orbital degeneracy, which in turn triggers a first-order Mott-Hubbard transition.
Second, We find that the dimensional electron gas of SrTiO3 confined along (110) is strikingly different from that of the (001) crystal orientation. In particular, the quantized subbands show a surprising “semiheavy” band, in contrast with the analog in the bulk.
Third, we find an intrinsic thickness limitation for metallic ferromagnetism in SrRuO3 thin films (001). We propose two ways to realize room-temperature ferromagnetic SrRuO3 thin films:(i) charge carrier doping as an alternative route to manipulate thin films ; (ii)bilayer SrRuO3 ultrathin films sandwiched by SrTiO3 along (111), where the t2g orbitals symmetry is preserved.
 “Quantum confinement in perovskite oxide heterostructures: Tight binding instead of a nearly free electron picture”, Z. Zhong et.al. PRB 88, 125401 (2013)
 “Electronics with Correlated Oxides: SrVO3/SrTiO3 as a Mott Transistor” Z. Zhong et.al. PRL 114, 246401 (2015)
 “Anisotropic two-dimensional electron gas at SrTiO3(110)”, Z. Wang, Z. Zhong, et.al. PNAS 111, 3933 (2014)
“Route to room-temperature ferromagnetic ultrathin SrRuO3 films” L. Si, Z. Zhong et.al. PRB 92, 041108(R) (2015)
9:30 AM - MD3.4.02
Enhanced Controllability of Two-Dimensional Electron Gas Carrier Density Formed in Monolayer LaTiO3 on SrTiO3
Hyangkeun Yoo 2,Luca Moreschini 1,Aaron Bostwick 1,Andrew Walter 3,Tae Won Noh 4,Young Jun Chang 5,Eli Rotenberg 1
1 Advanced Light Source Lawrence Berkeley National Laboratory Berkeley United States,2 Center for Correlated Electron Systems Institute for Basic Science Seoul Korea (the Republic of),1 Advanced Light Source Lawrence Berkeley National Laboratory Berkeley United States3 Photon Sciences Directorate Brookhaven National Laboratory Upton United States2 Center for Correlated Electron Systems Institute for Basic Science Seoul Korea (the Republic of),4 Department of Physics and Astronomy Seoul National University Seoul Korea (the Republic of)5 Department of Physics University of Seoul Seoul Korea (the Republic of)Show Abstract
Control of two-dimensional electron gases (2DEGs) has attracted lots of attention due to many fascinating applications, including unconventional 2D superconductivity and high-mobility devices. Here, we investigated the tunability of 2DEG properties on a bare SrTiO3 (STO) and a monolayer LaTiO3 (LTO) covered STO. First, the 2DEG carrier density of bare STO increases with synchrotron ultraviolet (UV)-irradiation and decreases with oxygen gas (O2(g))-exposure. However, the tunability of the 2DEG carrier density is significantly enhanced in monolayer LTO/STO. The maximum 2DEG carrier density in LTO/STO is increased by a factor of 4 times under UV-irradiation, compared to that of the bare STO. Additionally, with O2(g)-exposure, it becomes much smaller than that of O2(g)-exposed bare STO. This enhanced tunability is attributed to the drastic surface property change of a polar LTO layer, compared to that of nonpolar STO.
9:45 AM - MD3.4.02.1
Thermodynamic Equilibrium States of 2DEGs at Oxide Interfaces
Felix Gunkel 2,Ronja Heinen 2,Susanne Hoffmann-Eifert 2,Yunzhong Chen 3,Nini Pryds 3,Rainer Waser 2,Regina Dittmann 2
1 RWTH Aachen University Juelich Germany,2 Peter Grünberg Institute 7 FZ Jülich Juelich Germany,2 Peter Grünberg Institute 7 FZ Jülich Juelich Germany3 DTU Energy Technical University of Denmark Roskilde DenmarkShow Abstract
2-dimensional electron gases (2DEGs) in oxide heterostructures have attracted a significant amount of attention in recent years. In particular, the 2DEG at the LaAlO3/SrTiO3 (LAO/STO) interface has been studied extensively. In the meanwhile, various material systems including other epitaxial perovskite/perovskite interfaces (e.g. NdGaO3/STO), amorphous-oxide/perovskite interfaces, and spinel/perovskite interfaces (γ-Al2O3/STO) have been evaluated to show a similar electron gas. Some of these 2DEGs even exhibit properties superior to the standard LAO/STO case – in particular enhanced electron mobility .
One well-debated issue is whether the 2DEG formation in all these systems has a similar nature and how the difference in electrical performance comes about.
In this study, we address these questions in a thermodynamic approach. We compare the thermodynamic equilibrium state of various interface systems probed in high temperature equilibrium conductance (HTEC) measurements . We show that epitaxial perovskite-perovskite interfaces exhibit a fundamentally different equilibrium state than amorphous structures as well as the g-Al2O3/STO system.
For epitaxial perovskite/perovskite systems, we find an equilibrium state based on the formation of a thermodynamically stable space charge layer (SCL), in which electrons as well as ionic cation vacancies accumulate [3,4]. It is argued, that the SCL is stabilized by the electrostatic boundary conditions of the system, as derived from the polar catastrophe, which is absent in amorphous material systems.
It will be shown that the formation of this SCL obeys the general rules of the polar catastrophe picture: Significant evidence for the interface SCL are found only for layer thicknesses above the critical thickness of four unit cells. Moreover, the interfacial carrier density in equilibrium is found to scale with polarity of the capping material, as will be shown by comparison of the 2DEG properties in LAO/STO and (La,Sr)(Al,Ta)O3/STO heterostructures.
For amorphous structures as well as for the γ-Al2O3/STO system, the equilibrium conductance is found to be essentially similar to the one of bare STO, indicating the absence of a significant thermodynamically stable SCL. These systems thus rely on a thermodynamic non-equilibrium state based on the formation of oxygen vacancies, which vanish in thermodynamic equilibrium. The formation process of these 2DEGs thus differs fundamentally from the one in epitaxial LAO/STO. We discuss possible implications for the superior electronic properties observed in these structures.
 Chen et al., Nat. Comm. 4, 1371 (2013)
 Gunkel et al., APL 97, 012103 (2010)
 Gunkel et al., APL 100, 052103 (2012)
 Gunkel et al., Nanoscale 7 (2015)
10:00 AM - MD3.4.03
Beyond GaAs: Room-Temperature Intersubband Absorption in SrTiO3/LaAlO3 Multiple Quantum Wells
John Ortmann 1,Agham Posadas 1,Nish Nookala 1,Qian He 2,Albina Borisevich 2,Mikhail Belkin 1,Alexander Demkov 1
1 University of Texas at Austin Austin United States,2 Oak Ridge National Lab Oak Ridge United StatesShow Abstract
With the recent advancements in oxide thin film fabrication, it is possible to design and grow oxide quantum well heterostructures whose well depths far exceed those of traditional GaAs-based quantum wells. Here, we discuss the design, fabrication, structural quality, and optical properties of MBE-grown SrTiO3/LaAlO3 multiple quantum wells. These oxide quantum wells have a conduction band offset of greater than 2eV, as measured by X-ray photoelectron spectroscopy. We present simulations of the confined states within the wells and demonstrate the feasibility of driving intersubband transitions whose energies exceed 1eV. Furthermore, we demonstrate the excellent crystalline quality of these heterostructures via X-ray diffraction spectra and STEM-HAADF imaging and present evidence of atomic-scale control of the structures. Finally, we present room-temperature FTIR spectra demonstrating the first-reported measurements of intersubband absorption in SrTiO3/LaAlO3 multiple quantum wells and discuss the possibility of oxide quantum well-based devices.
10:15 AM - MD3.4.04
Creating Two-Dimensional Electron Gas in Nonpolar/Nonpolar Oxide Interface via Polarization Discontinuity: First-principles Analysis of CaZrO3/SrTiO3 Heterostructure
Kesong Yang 1,Safdar Nazir 1,Jianli Cheng 1
1 Univ of California-San Diego La Jolla United States,Show Abstract
The perovskite-based oxide heterostructures (HS) are attracting increasing interests because of their novel interfacial properties such as the interfacial superconductivity and ferromagnetism that are drastically different from those of the corresponding bulk materials. One example is the formation of the high-mobility Two-Dimensional Electron Gases (2DEG) at TiO2-terminated interface in the polar/nonpolar LaAlO3 /SrTiO3 (LAO/STO) HS system. Compared to the great success of generating 2DEG in the LAO/STO system via the polar discontinuity, there have been few reports on the possibility to produce the 2DEG in the perovskite oxide HS using the polarization. Herein, I will talk about the strain-induced polarization and resulting conductivity in the nonpolar/nonpolar CaZrO3/SrTiO3 (CZO/STO) heterostructure (HS) system by means of first-principles electronic structure calculations. We found that the lattice-mismatch-induced compressive strain leads to a strong polarization in the CZO film, and as the CZO film thickness increases, there exist an insulator-to-metal transition. The polarization direction and critical thickness of the CZO film for forming interfacial metallic states depend on the surface termination of CZO film in both types of interface models. These findings open a new avenue to achieve 2DEG (2DHG) in perovskite-based HS systems via polarization discontinuity.
11:00 AM - *MD3.4.05
Polar Boundary Conditions at the Anatase TiO2/LaAlO3 Interface
Harold Hwang 2
1 Stanford Univ Stanford United States,2 SLAC Menlo Park United States,Show Abstract
Over the past decade, there has been much exploration of the consequences of the atomic-scale electrostatic boundary conditions imposed at oxide heterointerfaces, primarily in perovskite-derived materials. These studies have been predicated on the use of structural internal degrees of freedom, such as the layer-by-layer subcomponents. Here we demonstrate that the atomic boundary conditions of simple binary oxides can be used to impart dramatic changes of state. By changing the substrate surface termination of LaAlO3 (001) from AlO2 to LaO, the room temperature sheet conductance of deposited anatase TiO2 films are increased by over 3 orders of magnitude, transforming the intrinsic insulating state to a high mobility metallic state, while maintaining excellent optical transparency. The interface-dependent metal-insulator transition is driven by a change in carrier density, not mobility, and we discuss possible origins of this interface charge. Using the metallic interface, we construct metal-semiconductor field effect transistors (MESFETs) using a Pt Schottky gate. Excellent rectifying behavior was observed at room temperature, with a gate leakage as low as 10-3 A/cm2, and conductivity modulation of up to 6 decades in a voltage range of 3 V.
This work was done in collaboration with M. Minohara, B. S. Kim, T. Tachikawa, Y. Nakanishi, Y. Hikita, C. Bell, L. F. Kourkoutis, J.-S. Lee, C.-C. Kao, M. Yoshita, and H. Akiyama.
11:30 AM - MD3.4.06
Strain-Induced Metal-Insulator Transitions in d1 and d2 Perovskite Transition Metal Oxides within DFT+DMFT
Gabriele Sclauzero 1,Krzysztof Dymkowski 1,Claude Ederer 1
1 Materials Theory ETH Zurich Zurich Switzerland,Show Abstract
We investigate the effect of epitaxial strain on the Mott metal-insulator transition in perovskite systems with a d1 and d2 electron configuration of the transition metal cation by combining density functional theory (DFT) calculations with dynamical mean-field theory (DMFT). In particular, we focus on the two representative cases of LaTiO3 and LaVO3, which, in their bulk forms, are both paramagnetic Mott insulators at room temperature.
We demonstrate that LaTiO3 undergoes an insulator-to-metal transition under moderate compressive epitaxial strain , while LaVO3 remains insulating even under very strong compressive (and tensile) strains , consistent with experimental observations . In the case of LaVO3 two different growth orientations of the crystal are considered, one preserving the bulk Pbnm space-group symmetry and another giving rise to a symmetry lowering to P21/m. Our calculations do not show a strong preference for either of the two geometries, which suggests that the actual growth orientation is determined by the specific film/substrate interface and/or growth conditions.
In order to obtain a systematic picture of epitaxial strain effects in d1 and d2 transition metal perovskites, we analyze the importance of octahedral rotations by comparing results for LaTiO3 and SrVO3 as well as for LaVO3 with and without octahedral tilts. We discuss the observed trends in terms of the strain-induced changes in the crystal-field splitting and hopping parameters, and we show that in the d1 systems both hopping and crystal-field splitting result in the same qualitative trends, whereas the corresponding effects are competing in the case of the d2 systems.
Our results are important in the context of oxide thin films and heterostructures, where emerging properties can be due to epitaxial strain, genuine interface effects, defects, or a combination thereof.
 K. Dymkowski and C. Ederer, Phys. Rev. B 89, 161109 (2014).
 G. Sclauzero and C. Ederer, arXiv:1510.01231 (2015).
 He et al., Phys. Rev. B 86, 081401 (2012).
11:45 AM - MD3.4.07
Electronic and Magnetic Properties of Epitaxial Ca1-xSrxMn7O12 Films
Amanda Huon 1,Alexander Grutter 2,Brian Kirby 2,Steven May 1
1 Drexel Univ Philadelphia United States,2 NIST Center For Neutron Research Gaithersburg United StatesShow Abstract
CaMn7O12, a quadruple perovskite with Ca and Mn ordering on the A-site, exemplifies the rich physics of complex oxides, exhibiting four phase transitions that induce charge ordering (below 430 K), orbital ordering (below 250 K), simultaneous helical magnetic and ferroelectric ordering (below 90 K), and a second helical magnetic transition at 43 K. Here, we report the growth of Ca1-xSrxMn7O12 thin films using oxide molecular beam epitaxy and how tuning x alters the properties of the parent compound. In relaxed x = 0 films, we find bulk-like electronic and magnetic properties including an abrupt increase in resistivity at 425 K and a net magnetization below 43 K. The changes to electronic and magnetic properties upon Sr doping, which has never been reported for bulk or thin film samples, will be presented. The results highlight the scientific opportunities in heterostructures based on quadruple perovskites. Work supported by the Army Research Office (W911NF-15-1-0133).
12:00 PM - *MD3.4.08
Magnetic Interactions in Oxide Heterostructures and at Nonmagnetic Oxide Surfaces
Michael Coey 1
1 Trinity College Dublin Dublin Ireland,Show Abstract
An important class of oxide heterostructures are sandwich structures where magnetically-ordered layers are separated by a nonmagnetic insulating spacer layer. Oriented all-oxide heterostructures of this kind can be grown from oxides with the perovskite structure, using a spacer such as LaAlO3 or SrTiO3. Such wide band gap oxides have traditionally been regarded as of little interest magnetically unless they contain paramagnetic cations. Magnetic interactions in solids are normally mediated by dipolar fields or by electronic exchange. The dipole interactions are weak but long-range, falling off as the inverse cube of the separation r between atomic moments. Exchange is a stronger Coulomb interaction that couples electron spins, but is usually short-range falling off as exp (-αr), unless the electrons are itinerant, in a conductor, where the interaction falls off as 1/r3. In magnetic tunnel junctions, α is usually ≈ 1 nm-1. Superexchange is restricted to one or two inter-cation distances and double exchange in inoperative in an insulating oxide. Neverthless we have found a new type of magnetic interaction, which can propagate over long distances (~ 10 nm) across thick insulating oxide spacer layers such as 100 LaAlO3, provided they are polar . The ferromagnetic ‘bread’ in the sandwich may be two layers of La0.67Sr0.33MnO3, or La0.67Sr0.33MnO3 on one side and the two-dimensional electron gas induced at the interface between a sufficiently thick LaAlO3 spacer ( > 1.6 nm, or 4 unit cells) and a SrTiO3 substrate on the other. Remarkably, the modification of the joint hysteresis loop coupling seems to oscillate periodically with spacer thickness, and it includes a field-cooled loop shift. Magnetic scattering is induced in the two-dimensional electron gas by a strip of La0.67Sr0.33MnO3 overlaid on the LaAlO3 spacer. All these effects on the hysteresis loop are absent when the oxide spacer layer is nonpolar. It is suggesteded that the magnitude of the magnetizations of the ferromagnetic layers on either side of the polar spacer are correlated by charge transfer. Strong spin-orbit interaction at the interfaces leads to the loop shift via the Dzyaloshinskii-Moria interaction, and there is evidence that the polar spacer mediates a long-range coupling of orbital moments.
Evidence of orbital magnetic moments persisting to high temperatures is found in the different contexts of SrTiO3 surfaces , and CeO2 nanoparticles . Possible explanations will be discussed.
 Weiming Lv et al Magnetic interactions in a polar insulator (unpublished)
 J. M. D. Coey et al Surface magnetism of SrTiO3 (unpublished)
 J. M. D. Coey et al Collective magnetism of CeO2 nanoparticles (unpublished)
12:30 PM - MD3.4.09
Atomic Scale Control of the Junction Properties in Pt/LaVO3/Nb:SrTiO3 (001) Heterostructures
Rea Kolbl 1,Di Lu 2,Yasuyuki Hikita 3,Yanwu Xie 3,Harold Hwang 3
1 Department of Applied Physics Stanford University Stanford United States,2 Department of Physics Stanford University Stanford United States3 Stanford Institute for Materials and Energy Sciences SLAC National Laboratory Menlo Park United States1 Department of Applied Physics Stanford University Stanford United States,3 Stanford Institute for Materials and Energy Sciences SLAC National Laboratory Menlo Park United StatesShow Abstract
Atomic scale manipulation of complex oxide epitaxial interfaces has led to creation of novel electronic states and device functionalities . Recently, the Schottky barrier height at the (001)-oriented SrRuO3/Nb-doped SrTiO3 (Nb:SrTiO3) junctions was modulated by inserting an ultrathin layer of LaAlO3, in which a large electric field was sustained between the two oppositely charged polar surfaces (LaO)+ and (AlO2)- . While such an electric field is expected to impact oxide device performance, the valence degree of freedom readily found in complex oxides and its relation to the interface electrostatic boundary conditions needs to be assessed for further application of this technique.
Here we investigate the junction properties of Pt/LaVO3/Nb:SrTiO3 (001) heterostructure, which not only contains a multi-valent cation vanadium, but has also been suggested to be a promising photovoltaic cell due to the small optical gap of LaVO3 . In particular, it was proposed that for LaVO3 in heterostructures the internal polar field could enhance charge separation. Using pulsed laser deposition, we systematically varied the LaVO3 thickness from 0 to 9 unit cells for both TiO2- and SrO- terminations to control the interface electrostatic boundary conditions as reported previously . We measured the Schottky barrier height variation with LaVO3 thickness using current-voltage, capacitance-voltage, and internal photoemission spectroscopy. The initially rectifying junction exhibited contrasting behavior depending on the Nb:SrTiO3 (001) termination. While the TiO2-terminated junctions became increasingly Ohmic as LaVO3 thickness increased, transitioning from a rectifying to an Ohmic junction at the LaVO3 thickness of only 3 unit cells, the SrO-terminated junctions remained rectifying with a slightly increased, yet thickness independent Schottky barrier height. These results suggest an absence of an internal polar field. We propose that the relative difference in the work function of the three constituents underlies the observed trend, which will be discussed in the presentation.
 H. Y. Hwang et al., Nat. Mater. 11, 103 (2012).
 T. Yajima et al., Nano Lett. 15, 1622 (2015).
 E. Assmann et al., Phys. Rev. Lett. 110, 078701 (2013).
 Y. Hotta et al., Phys. Rev. Lett. 99, 236805 (2007).
12:45 PM - MD3.4.10
Ferroelectric Modulation of Two-dimensional Electron Gas Conductivity at Oxide Interfaces
Wenxiong Zhou 2,Jun Zhou 2,Shengwei Zeng 2,Zhen Huang 2,Kun Han 2,T. Venkatesan 3,Ariando Ariando 2
1 Department of Physics National University of Singapore Singapore Singapore,2 NUSNNI-Nanocore National University of Singapore Singapore Singapore,2 NUSNNI-Nanocore National University of Singapore Singapore Singapore1 Department of Physics National University of Singapore Singapore Singapore,2 NUSNNI-Nanocore National University of Singapore Singapore Singapore,3 Department of Electrical and Computer Engineering National University of Singapore Singapore SingaporeShow Abstract
In this report, by inserting a ferroelectric Ba0.2Sr0.8TiO3 layer between LaAlO3/SrTiO3 heterostructure, a two-dimensional electron gas (2DEG) was found at LaAlO3/ Ba0.2Sr0.8TiO3 interface. With electrical, optical, piezoresponse force microscopic measurements and first-principle calculations, we studied the impact of this ferroelectric Ba0.2Sr0.8TiO3 layer on the 2DEG. Both carrier density and mobility of the 2DEG can be modulated by changing the thickness of the ferroelectric layer. We also observed that Ba0.2Sr0.8TiO3 layer can suppress oxygen vacancy formation, leading to observation of temperature-independent polarization-induced carrier density. These results indicate that the 2DEG at oxide interfaces can be ferroelectrically modulated.
MD3.5: Oxide Electrocatalysts I
Wednesday PM, March 30, 2016
PCC West, 100 Level, Room 101 C
2:30 PM - *MD3.5.01
Rational Design Strategies for Oxide Oxygen Electrocatalysts
Wesley Hong 1,Yang Shao-Horn 2
1 Department of Materials Science amp; Engineering Massachusetts Institute of Technology Cambridge United States,1 Department of Materials Science amp; Engineering Massachusetts Institute of Technology Cambridge United States,2 Department of Mechanical Engineering Massachusetts Institute of Technology Cambridge United StatesShow Abstract
The development of sustainable energy is one of the most important scientific challenges in the 21st century. A critical element for sustainable energy implementation is to have efficient energy conversion and storage. Oxygen electrocatalysis is central to enable photoelectrochemical and electrolytic water-splitting, fuel cells, and metal-air batteries. Probing a fundamental catalyst design principle that links surface structure and chemistry to the catalytic activity can guide the search for highly active catalysts that are cost effective and abundant in nature. The ability to design oxides expressly tuned for electrochemical applications is rooted in fundamental understanding of the relationships between structure, chemical composition, electronic properties, and electrochemical functionality. Using soft X-ray spectroscopy of perovskites, we show that the charge-transfer energy – a parameter that captures the energy configuration of oxygen and transition-metal valence electrons – is a unifying descriptor for tuning oxide surfaces with enhanced catalytic activities. We discuss how these design strategies can be combined with oxide heterostructures for developing oxide catalysts with high activity and improved stability.
3:00 PM - MD3.5.02
Pulsed Laser Epitaxy of VO2(B) and TiO2(B) Thin Films and Heterostructures
Shinbuhm Lee 1,Xiang Gao 1,Tricia Meyer 1,Ho Nyung Lee 1
1 Oak Ridge National Laboratory Knoxville United States,Show Abstract
Due to the open framework in the B-phase of VO2 and TiO2, both materials have long been regarded as promising electrodes or catalysts to use in energy generation and storage devices. Even though various nanostructures have been extensively studied, there has been a lack of fundamental understanding on their physical properties because of the difficulty in growing phase pure single crystals. Here we present epitaxial synthesis of VO2(B) and TiO2(B) thin films and heterostructures by pulsed laser epitaxy. As both materials have multiple polymorphs, the phase stability of the phases under various redox conditions is studied, and the results will be presented. In addition, we have found that our epitaxial B-phase films offer excellent long-term stability with extremely high capacity of Li-ions. Combined studies of scanning transmission electron microscopy and x-ray diffraction found that the crystallinity of the epitaxial B-phase films is well maintained even after over 150 cycles of charging/discharging. Overall, in this talk, epitaxial synthesis and detailed characterizations on the crystal structure, electronic structure, and electronic conduction by X-ray diffraction, scanning transmission electron microscopy, optical and x-ray spectroscopy, and dc transport measurements will be presented together with insights for potential applications as electrodes in Li- and Na-ion batteries.
*The work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.
3:15 PM - MD3.5.03
Stabilization of Catalytically-active Ultrathin Fe (II) Oxide Films on Perovskites by Heteroepitaxy
Matteo Monti 1,Farid El Gabaly 3,Ethan Crumlin 2,William C. Chueh 1
1 Stanford University Stanford United States,3 Materials Physics Department Sandia National Laboratories Livermore United States2 Advanced Light Source Berkeley United StatesShow Abstract
The growth and properties of iron oxide films have been studied for nearly a century due to their intriguing magnetic and electronic characteristics, and their suitability for a host of applications . In particular, the rich variety of stoichiometries and polymorphs as a function of oxygen activity and temperature makes iron oxides promising candidates for heterogeneous catalysis.
When grown in the form of ultrathin films, different phases often coexist. To tailor the properties of the material, an understanding of the phase stability and growth mechanism is necessary . Moreover the preparation of iron oxides as ultrathin films has been reported to yield interesting surface configurations, in which the local environment of the atoms is very different from the bulk. For example, oxygen and iron exhibit enhanced basicity and acidicity respectively, causing dramatic changes to reactivity .
Motivated by these fundamental aspects, we have grown iron (II) oxide films on SrTiO3 (001) surface by O2-reactive molecular beam epitaxy. We used real-time low-energy electron microscopy in order to study and control the growth mechanism. Additionally, atomic force microscopy and surface electron diffraction confirm that the films are atomically-flat and exhibit long-range crystallographic order. Further insight into the surface electronic properties and redox behavior was obtained using near-ambient-pressure X-ray photoelectron spectroscopy at the Advanced Light Source, Berkeley. The relationship of the electronic, structural and redox properties as a function of oxygen partial pressure, film thickness and temperature will finally be discussed.
 R. Cornell and U. Schwertmann, “The Iron Oxides”, (John Wiley & Sons Ltd, 1997)
 Prog. Surf. Sci. 70 (2002) 1–151
 Rep. Prog. Phys. 71 (2008) 016501
3:30 PM - *MD3.5.04
Electrocatalysis at Complex Oxide Interfaces
Nenad Markovic 1,Vojislav Stamenkovic 1
1 Materials Science Division Argonne National Laboratory Argonne United States,Show Abstract
Functional oxides play a significant role in a number of technologically important areas, including superconductivity, magnetism, and heterogeneous catalysis, as well as in electrochemical technologies and processes that utilize both aqueous electrolytes and organic solvents. Electrocatalysis lies at the heart of the chemical phenomena that take place at electrochemical interfaces. In the feature it will be the key to driving technological innovations that are urgently needed to deliver reliable, affordable and environmentally friendly energy. One class of electrochemical reactions of particular significance is the oxygen electrochemistry on metal oxide materials, specifically the production (evolution) of oxygen in electrolyzers. In this lecture, in exploring the oxygen evolution reaction on well-characterized monometallic (Au, Pt, Ir, Ru and Os) and bimetallic (Ru-Ir and Ir-Os) oxides as well as complex SrRuO3(hkl) single crystals in alkaline environments, we report an intimate relationship between the electronic conductivity, stability and activity of oxide catalysts. We determine that for the same conductance, the degree of stability is inversely proportional to their activity. Although the field is still in its infancy, a great deal has already been learned and trends are beginning to emerge that give some predictive ability with respect to the near-surface structure and nature assumed by electrode materials and double layer components and their activity, stability and selectivity towards simple molecules. We conclude that understanding the complexity (simplicity) of interfacial properties of complex oxides in electrochemical environments would open new avenues for design and deployment of alternative energy systems.
MD3.6: Oxide Electrocatalysts II
Wednesday PM, March 30, 2016
PCC West, 100 Level, Room 101 C
4:30 PM - *MD3.6.01
Improved Chemical and Electrochemical Stability on Perovskite Oxides by Oxidizing Cations at the Surface
Bilge Yildiz 1,Nikolai Tsvetkov 1,Qiyang Lu 1,Lixin Sun 1,Ethan Crumlin 2
1 Massachusetts Institute of Technology Cambridge United States,2 Lawrence Berkeley National Laboratory Berkeley United StatesShow Abstract
Segregation and phase separation of aliovalent dopants on perovskite oxide (ABO3) surfaces is detrimental to the performance of energy conversion systems such as solid oxide fuel/electrolysis cells and catalysts for thermochemical H2O and CO2 splitting. One key reason behind the instability of perovskite oxide surfaces is the electrostatic attraction of the negatively charged A-site dopants by the positively charged oxygen vacancies enriched at the surface. Here we show that reducing the surface concentration significantly improves the oxygen surface exchange kinetics and stability, albeit contrary to the well-established understanding that surface oxygen vacancies facilitate reactions with O2 molecules. We take La0.8Sr0.2CoO3 (LSC) as a model perovskite oxide, and modify its surface with additive cations that are more oxidizing than Co on the B-site of LSC. We utilized ambient pressure X-ray absorption and photoelectron spectroscopy to prove that the dominant role of the oxidizing surface additives is to suppress the enrichment and phase separation of while reducing the concentration of at the surface. Consequently, we found the effect of these oxidizing cations to be significantly improved stability, with up to 30x acceleration of the oxygen exchange kinetics after up to 54 hours in air at 550 oC. This improved oxygen exchange kinetics suggests that there is an optimum concentration of oxygen vacancies at the surface of perovskite oxides; i.e. one that balances the reactivity gained by oxygen vacancies and the detrimental Sr segregation driven by oxygen vacancies. The approach we demonstrated here for stabilizing the surfaces opens up novel and practical routes for designing perovskite oxide electrocatalysts that are both stable and highly reactive to oxygen exchange reactions in various electrochemical applications ranging from energy to information.
5:00 PM - *MD3.6.02
Spontaneous Polarization and Anomalous Photovoltaic Effect Induced in Oxide Heterointerfaces
Masao Nakamura 1,Fumitaka Kagawa 1,Toshiaki Tanigaki 1, Hyun Soon Park 1,Tsuyoshi Matsuda 2,Daisuke Shindo 3,Yoshinori Tokura 4,Masashi Kawasaki 4
1 RIKEN Center for Emergent Matter Science Wako Japan,2 Japan Science and Technology Agency Kawaguchi Japan1 RIKEN Center for Emergent Matter Science Wako Japan,3 Institute of Multidisciplinary Research for Advanced Materials Sendai Japan1 RIKEN Center for Emergent Matter Science Wako Japan,4 Department of Applied Physics and Quantum Phase Electronics Center (QPEC), University of Tokyo Tokyo JapanShow Abstract
Electronic reconstruction triggered by the interfacial polar discontinuity, known as the polar catastrophe, results in the accumulation of high-mobility two-dimensional electrons in LaAlO3/SrTiO3, and the following intensive research has revealed interesting phenomena including emergence of superconductivity and magnetism at the interface . It is theoretically predicted that a spontaneous electric polarization can be also induced as another consequence of polar catastrophe [2, 3, 4]. However, the spontaneous polarization is masked by the existence of mobile charges and hard to be experimentally detected in LaAlO3/SrTiO3 junction. In this study, we show that heterojunctions comprised of LaFeO3 and SrTiO3 is a model system showing such an interface-induced spontaneous polarization that invokes anomalous behavior of photovoltaic action.
We grew LaFeO3 on termination-controlled SrTiO3 and found the opposite polarities in photovoltaic action depending on the termination. The emergence of opposite electric polarization was clearly verified by piezoresponse-force microscopy. However, this is not the whole story. Electron holography was employed to distinguish whether dielectric or spontaneous polarization dominates the electric polarization and revealed that the latter is the case. The expected photo-current direction (drift current) from the electric field in LaFeO3 is found to be opposite to the observed photovoltaic action. We propose that the shift current dominates the photo-current in LaFeO3 because the huge spontaneous polarization drives the photo-excited carriers toward opposite directions against those expected from the drift current. From the thickness dependence of the photocurrent amplitude and their action spectra, we conclude that the spontaneous polarization is indeed induced in LaFeO3 by the polar catastrophe process, driving bulk photovoltaic action. The present results imply that the control of the bulk polarization is possible by engineering the interfacial polar discontinuity, and realizing new polar materials with photovoltaic functions. .
 A. Ohtomo and H. Y. Hwang, Nature 427, 423 (2004).
 N. C. Bristowe, E. Artacho, and P. B. Littlewood, Phys. Rev. B 80, 045425 (2009).
 R. Pentcheva and W. E. Pickett, Phys. Rev. Lett. 102, 107602 (2009).
 M. Stengel and D. Vanderbilt, Phys. Rev. B 80, 241103 (2009).
5:30 PM - MD3.6.03
Crystallographic Orientation Dependent Oxygen Electrocatalysis in Epitaxial La2-xSrxCuO4-δ Thin Films
Dongkyu Lee 2,Lu Jiang 1,Donghwa Lee 3,Yang Shao-Horn 2,Ho Nyung Lee 1
1 Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge United States,2 Electrochemical Energy Laboratory Massachusetts Institute of Technology Cambridge United States,1 Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge United States3 School of Materials Science amp; Engineering Chonnam National University Gwangju Korea (the Republic of)2 Electrochemical Energy Laboratory Massachusetts Institute of Technology Cambridge United StatesShow Abstract
Layered mixed ionic and electronic conductors (MIECs) such as Ruddlesden-Popper (RP) oxides have been highlighted as alternative cathode materials for intermediate temperature operation, but still further improvement is desired. To further enhance the catalytic activity of RP oxides, controlling the crystallographic orientation could be beneficial as the anisotropic nature of RP oxides may offer surface states that can be more catalytically active. However, the influence of crystallographic orientation on the surface exchange kinetics of RP oxides is poorly understood due to difficulties in the growth of single crystalline RP oxides. In this work, we report the influence of crystallographic orientation on the oxygen surface exchange kinetics of epitaxial La1.85Sr0.15CuO4 (LSC214) thin films grown on (001)-, (011)-, and (111)-Y2O3-stabilized ZrO2 (YSZ). Using electrochemical impedance spectroscopy (EIS), we find that the surface exchange coefficient (kq) values of (103)-oriented LSC214 thin films are about two orders of magnitude higher than those of (001)-oriented LSC214 thin films. In addition, the kq values of LSC214 thin films can be enhanced by controlling the crystallographic orientation up to four orders of magnitude compared to conventional ABO3 perovskites oxides. Furthermore, we also demonstrate that the orientation dependent surface exchange kinetics in RP oxides is strongly correlated with our first-principles-based descriptors, the bulk transition metal d-band center, which can allow a prediction of catalytic activity of RP oxides for the design of new SOFCs cathodes.
* This work was supported by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy.
5:45 PM - MD3.6.04
Interfacial Control of Oxygen Vacancy Doping and Electrical Conduction in Thin Film Oxide Heterostructures
Jeffrey Eastman 1,Boyd Veal 1,Peter Zapol 1
1 Argonne National Laboratory Lemont United States,Show Abstract
Oxygen vacancies in proximity to surfaces and heterointerfaces in oxide thin film heterostructures have major effects on properties, resulting for example, in emergent conduction behavior, large changes in metal-insulator transition temperatures, or enhanced catalytic activity. In this presentation, the discovery of a means of reversibly controlling the oxygen vacancy concentration and distribution in oxide heterostructures consisting of electronically conducting In2O3 films grown on ionically conducting Y2O3-stabilized ZrO2 substrates will be described. Oxygen ion redistribution across the heterointerface is induced using an applied electric field oriented in the plane of the interface, resulting in controlled oxygen vacancy (and hence electron) doping of the film and possible orders-of-magnitude enhancement of the film's electrical conduction. The reversible modified behavior is dependent on interface properties and is attained without cation doping or changes in the gas environment in contact with the sample. Insight into the energetics of oxygen vacancies in In2O3 / YSZ heterostructures obtained from first-principles calculations will also be discussed.
MD3.7: Poster Session II
Thursday AM, March 31, 2016
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - MD3.7.01
Strain Control Manuptalation of Charge Transfer Induced Metal Insulator Transition via V-Vdimers in VO2 A-B Composite Films-Evidence for Primary Role of Dimerization
Amar Srivastava 1,Helene Rotella 5,Surajit Saha 1,Banabir Pal 2,S.J. Pennycook 3,D. D. Sarma 4,T. Venkatesan 3
1 Department of Physics National University of Singapore Singapore Singapore,1 Department of Physics National University of Singapore Singapore Singapore,5 Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link Singapore Singapore2 Solid State and Structural Chemistry Unit, Indian Institute of Science Bangalore India3 Materials Science and Engineering Department, National University of Singapore Singapore Singapore2 Solid State and Structural Chemistry Unit, Indian Institute of Science Bangalore India,4 Council of Scientific and Industrial Research - Network of Institutes for Solar Energy (CSIR-NISE) New Delhi India1 Department of Physics National University of Singapore Singapore Singapore,5 Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link Singapore Singapore,3 Materials Science and Engineering Department, National University of Singapore Singapore SingaporeShow Abstract
The origin of the metal insulator transition (MIT) in VO2 is still unknown despite having been studied extensively. Is a structural phase transition necessary for the MIT in VO2? In this report we demonstrate a remarkable spontaneous vertically ordered nanocomposite films produced in a newly established VO2(A and B) polymorphs which contains only isolated islands of VO2(M) phase, but nevertheless exhibits a full-fledged MIT. Vertical strain manuplation is demostrated by selecting films of different composition which affects the dynamical change in resistivity across the MIT. Spectral weight transfer during the transition indicates a charge transfer between various constituents of the film at the surface while the bulk is still insulating. In the composite, the A phase is under compressive stress while the B phase is under tensile stress which leads to the dimer induced MIT in this system via charge transfer despite no out of plane change in lattice parameter in the A and B phases. The work establishes a new avenue in the strain controlled manipulation of charge transfer induced MIT in the VO2 system and also a new form of ordered nanostructures for multifunctional applications.
9:00 PM - MD3.7.02
Thickness Dependence of Exchange Coupling in (111)-Oriented Perovskite Oxide Superlattices
Yue Jia 1,Rajesh Chopdekar 1,Elke Arenholz 2,Zhiqi Liu 3,Michael Biegalski 3,Yayoi Takamura 1
1 Department of Chemical Engineering and Materials Science University of California, Davis Davis United States,2 Advanced Light Source, Lawrence Berkeley National Laboratory Berkeley United States3 Center for Nanophase Materials Science, Oak Ridge National Laboratory Oak Ridge United StatesShow Abstract
The coupling between the charge, spin, orbital, and lattice degrees of freedom in perovskite oxide heterostructures can offer additional parameters to tune the magnetic properties. Intriguing properties possessed by (111)-oriented perovskite thin films with buckled honeycomb structure and stackings of highly polar layers have recently been reported in theoretical and experimental work. Epitaxial La0.7Sr0.3MnO3 (LSMO)/La0.7Sr0.3FeO3 (LSFO) superlattices serve as model systems to explore the competing interfacial reactions and exchange coupling between ferromagnetic (FM) and antiferromagnetic (AF) layers. In our previous studies, comparing (001)- and (111)-oriented LSMO/LSFO superlattices with sublayer thickness around 2 nm, we found that the magnetic structure was sensitive to the crystallographic orientation and that exchange interactions in the form of spin-flop coupling was present in both orientations.[1-3] These observations were contrary to the expectations of a simple model based on bulk magnetic structures. In order to determine the thickness dependence of the magnetic properties and exchange coupling, (111)-oriented LSMO/LSFO superlattices with sublayer thicknesses ranging from 3 to 60 unit cells (u.c.) were synthesized and characterized. Element-specific soft X-ray magnetic spectroscopy was used to reveal the magnetic structure of the FM and AF layers separately. In the ultrathin limit (3 to 6 u.c.), we find that the AF properties of the LSFO sublayers are preserved with an out-of-plane canting of the AF spin axis, while the FM properties of the LSMO sublayers are significantly depressed. For thicker LSFO layers (> 9 u.c.), the out-of-plane canting of the AF spin axis is only present in superlattices with thick LSMO sublayers. As a result, spin-flop coupling exists only in superlattices which display both robust ferromagnetism and out-of-plane canting of the AF spin axis. These results demonstrate the complex magnetic behaviors of perovskite oxide heterostructures determined by exchange coupling and the combined effects of the interfacial reactions which can potentially open pathways for device applications.
 Y. Takamura et al., Phys. Rev. B 80, 180417(R) (2009)
 E. Arenholz et al, Appl. Phys. Lett. 94, 072503 (2009)
 Y. Jia et al, Phys. Rev. B 92, 094407 (2015)
9:00 PM - MD3.7.03
Epitaxial Synthesis of BaBiO3 Heterostructures by Using Buffer Layers
Han Gyeol Lee 2,Gideok Kim 2,Minu Kim 2,Tae Won Noh 2
1 Center for Correlated Electron Systems Seoul Korea (the Republic of),2 Physics and Astronomy Seoul National University Seoul Korea (the Republic of),Show Abstract
Epitaxial growth of thin film is an important technique to enhance material’s functionalities, for example, ferroelectric and superconducting properties [1, 2]. Especially in ABO3 perovskite oxides, epitaxial strain is known to modify physical properties of oxide materials by changing oxygen octahedral structure [3, 4]. BaBiO3, a parent compound of a high-Tc superconductor , can be an intriguing candidate to study such effects; novel interplay between electronic and structural properties is predicted by strong electron-phonon coupling of this material . However, lack of commercial substrates that commensurate with BaBiO3 (apseudo-cubic = 4.34 Å) has hindered synthesis of BaBiO3 epitaxial heterostructures.
Here, we attempt to overcome this obstacle by using a buffer layer, which can accommodate the lattice mismatch between a substrate and a film . First, we synthesized a high-quality buffer layer (BaZrO3 and BaCeO3) on a SrTiO3 substrate by pulsed laser deposition. Subsequently, BaBiO3/BaXO3 (X = Zr, Ce) heterostructures were grown and characterized by atomic force microscopy and x-ray diffraction. We revealed that BaBiO3 is fully strained, as well as shows a good crystallinity and surface morphology. These results can be applied to epitaxial growth of perovskite oxides with large lattice constant (~4.3 Å). In the presentation, we will discuss about the evaluation of the electronic properties in BaBiO3 heterostructures in detail.
 K. J. Choi et al., Science 306, 1005 (2004).
 H. Sato et al., Physica C 274, 221 (1997).
 J. M. Rondinelli et al., MRS Bull. 37, 261 (2012).
 W. Lu et al., Sci. Rep. 5, 10245 (2015).
 A. W. Sleight, Physica C 514, 152 (2015).
 K. Foyevtsova et al., Phys. Rev. B 91, 121114 (2015).
 K. Terai et al., Appl. Phys. Lett. 80, 4437 (2002).
9:00 PM - MD3.7.04
Influence of the Local Oxygen Vacancy Concentration on the Piezoresponse of Strontium Titanate Thin Films
Michael Andrae 2,Felix Gunkel 2,Christoph Baeumer 2,Chencheng Xu 2,Regina Dittmann 2,Rainer Waser 2
2 Peter Grünberg Institute 7 FZ Jülich Juelich Germany,1 RWTH Aachen University Juelich Germany,2 Peter Grünberg Institute 7 FZ Jülich Juelich GermanyShow Abstract
In recent years, ultra thin ferroelectric ternary transition metal oxide films have gained a lot of attention. One important measurement technique to detect ferroelectric properties is piezoresponse force microscopy (PFM). In a typical PFM experiment, the local electrical polarization is measured and switched by locally applying voltages with different amplitudes and polarity.
However, resistive switching of oxides is another effect that occurs when locally applying voltages and/or electric fields. An important measurement technique to characterize this effect is local conductivity atomic force microscopy (LC-AFM) which is used locally to measure and switch the electrical resistivity of oxides in a resistive switching experiment. Typically, the resistive switching effect is related to the motion of oxygen vacancies that is triggered by locally applying a voltage of a few volts. The voltages typically applied in both experiments, PFM and LC-AFM, are of the same order of magnitude. Therefore, it is imperative to consider a change of the local conductivity as well as the motion of oxygen vacancies in oxide thin films while performing piezoelectric characterization.
In this study, we investigate the influence of the local oxygen vacancy concentration on the piezoresponse of ultra-thin, single-crystalline SrTiO3 (STO) thin films.  Non-ferroelectric, homoepitaxial STO thin films were deposited on Nb-doped STO substrates and analyzed using a combination of piezoresponse force microscopy and local conductive atomic force microscopy.
After applying different polarization voltages between +/- 2V and +/- 5 V to the thin films, we simultaneously observed a contrast in the piezoresponse amplitude and phase signal as well as a changed conductivity in the exact same region.
Since classic ferroelectricity in homoepitaxial STO can be excluded as the reason of the observed contrast, we consider the effect of a local accumulation of oxygen vacancies on the piezoresponse.
For this, we additionally measuref the surface potential using Kelvin Probe Force Microscopy (KPFM) revealing a change in surface potential in the regions of applied voltage. The contrast in KPFM is found to decay over time. We use this observation to discuss underlying relaxation process, which is shown to be connected to the oxygen incorporation reaction at the surface of the STO thin film.
Within this model, we explain how a local variation of the oxygen vacancy concentration mimics contrast in a PFM measurement in absence of ferroelectricity.
 M. Andrä, F. Gunkel, C. Bäumer, C. Xu, R. Dittmann, R. Waser, Nanoscale 7, 14351 (2015)
9:00 PM - MD3.7.05
Correlated Metals as Transparent Conductors
Lei Zhang 2,Yuanjun Zhou 3,Karin Rabe 3,Roman Engel-Herbert 2
1 Department of Materials Science and Engineering Pennsylvania State University University Park United States,2 Materials Research Institute Pennsylvania State University State College United States,3 Department of Physics and Astronomy Rutgers University Rutgers United StatesShow Abstract
The design challenge of transparent conductors used in photovoltaics, displays, and solid state lighting industries is to ideally combine mutually exclusive properties: large optical transparency and large electrical conductivity. Satisfying these competing demands is commonly achieved by increasing the conductivity of wide band-gap semiconductors through degenerate doping, i.e. tin-doped indium oxide (ITO). On the other hand, noble metal, such as Ag and Au, are ideal conductors; however, they are much less used due to the high reflectance of metals in the visible spectrum.
In this talk, an alternative design strategy for identifying highly conducting, yet highly transparent thin films is presented. Enhancing the carrier effective mass by utilizing the strong electron-electron interaction in correlated metals shifts the free carrier reflection edge to below the visible spectrum despite their metal-like high carrier concentration and thus high electrical conductivity. Experimental data, i.e. a high carrier concentration (>2.2×1022 cm-3) and low screened plasma energies (
9:00 PM - MD3.7.06
Probing Electronic Structure and Polarization in SrTiO3-LaCrO3 Superlattices Using X-Ray Absorption and X-Ray Photoemission Spectroscopies
Ryan Comes 1,Shih Chieh Lin 2,Cheng-Tai Kuo 3,Steve Heald 4,Steven Spurgeon 1,Despoina Kepaptsoglou 5,Quentin Ramasse 5,Mark Engelhard 1,Julien Rault 6,Slavomir Nemsak 3,Charles Fadley 3,Peter Sushko 1,Scott Chambers 1
1 Pacific Northwest Nat'l Lab Richland United States,2 Physics University of California, Davis Davis United States2 Physics University of California, Davis Davis United States,3 Lawrence Berkeley National Lab Berkeley United States4 Advanced Photon Source Argonne National Laboratory Argonne United States5 SuperSTEM Daresbury United Kingdom6 Synchrotron Soleil Saint-Aubin France7 BESSY-II Peter Grunberg Institute Berlin Germany,3 Lawrence Berkeley National Lab Berkeley United StatesShow Abstract
Ferroelectric oxide superlattices combining ferroelectric and non-ferroelectric materials exhibit an intriguing induced polarization in the non-ferroelectric phase. When a ferroelectric is combined with a non-polar material like SrTiO3 (STO), the STO layer may become ferroelectric. However, there has been no demonstration of a superlattice where two non-ferroelectric materials combine to produce bulk polarization. We present work studying STO-LaCrO3 (LCO) superlattices and show that by controlling interfacial termination between layers we can induce a ferroelectric-type polarization in STO. Density functional theory (DFT) predicts that by alternating terminations between positively charged TiO2-LaO and negative CrO2-SrO interfaces a polarization will be induced in both materials. Using molecular beam epitaxy, we have synthesized superlattices with such alternating interfaces. X-ray absorption fine structure analysis of the Ti K edge of the superlattices shows that the Ti-O bond lengths along the growth direction differ by ~0.2 Å. Scanning transmission electron microscopy measurements confirmed these results and were used to estimate the polarization within the STO layers. Both results are in good agreement with DFT predictions. A built-in electric field is also observed using laboratory-source and synchrotron x-ray photoelectron spectroscopy (XPS). Broadening of core-level and valence-band peaks for the various species in the superlattice in lab-source measurements is used to estimate a built-in potential gradient of ~1 V across each layer, in close agreement with DFT predictions. We also present standing-wave core-level photoemission and angle-resolved photoemission spectroscopy (SWARPES) measurements that permit probing the STO and LCO layers of the superlattice separately, which show dramatic differences in the valence band electronic structure. These measurements provide excellent depth sensitivity, allowing for unprecedented resolution of the electronic structure of the buried layers within the superlattice.
9:00 PM - MD3.7.07
Modulate Resistance State by Controlling the Reentrance of Antiferromagnetic Insulator Phase in Manganite Films
Feng Jin 1,Wenbin Wu 3
1 Department of Physics University of Science and Technology of China Hefei China,1 Department of Physics University of Science and Technology of China Hefei China,2 Hefei National Laboratory for Physical Sciences at Microscale Hefei China,3 High Magnetic Field Laboratory of Chinese Academy of Sciences Hefei ChinaShow Abstract
Manganite is one of the prototype strong correlated systems exhibiting intimate coupling between charge, spin, orbital, and lattice degrees of freedom, resulting in the delicate energy proximity of different phases. Although the ground state of optimal doped bulk La2/3Ca1/3MnO3 (LCMO) is ferromagnetic-metal phase (FMM), LCMO films grown on NdGaO3(001) (NGO(001)) suffering anisotropic strain demonstrate a tunable antiferromagnetic insulator phase (AFM) or phase separation (PS) in a wide temperature range after annealed in O2 atmosphere. PS with the coexistence of AFM and FMM was induced in anisotropically strained LCMO/NGO(001) films due to enhanced orthorhombicity. The reentrance of antiferromagnetic charge-order insulator phase (AFM-COI) from a saturated FMM as functions of magnetic field and temperature was observed. The reentrance is mediated by the cooperative MnO6 octahedral distortions, which is consistent with the Martensitic-like transformation. The quantity of the reentrance of the AFM-COI from the saturated FMM can be controlled by magnetic field and temperature in different processes, however, the resistivity changes a little in a wide range of temperature. Magnetic force microscopy morphologies exhibit anisotropically patterns correlating closely with its magnetic and electrical properties.
9:00 PM - MD3.7.08
Enhanced Conductivity and Metal-Insulator Transitions of Ultrathin CaRuO3 Films in Superlattices
Haoran Xu 1,Wenbin Wu 1
1 Hefei National Laboratory for Physical Sciences at Microscale University of Science and Technology of China Hefei China,Show Abstract
High quality superlattices containing SmFeO3 (SFO) and CaRuO3 (CRO) with thicknesses as small as 0.8 nm were fabricated. We studied the enhanced conductivity and metal-insulator transitions (MITs) of ultrathin CRO films in (SFO/CRO) x superlattices. For x=16, All superlattices with the thickness of CRO (t CRO) more than 0.8 nm are metallic, whereas a 2.4 nm single film is insulating. Even for x=2, with t CRO = 1.2 nm the sample is still conductive. Moreover, the SFO space layer was replaced by CaRu0.8Ti0.2O, which is insulator, the conductivity was further strengthened. Additional “conducting channels” at the interfaces and the relaxation of oxygen octahedral tilts arised from a combination of epitaxial strain and oxygen octahedral connectivity may be the two possible interpretations.
For x=16, a transition temperature (T*) dependent MITs was observed with the decreasing t CRO except for 0.8 nm and the T* was strongly affected by the thickness of SFO. The low temperature insulating behavior can be ascribed to the three-dimensional (3D) weak localization, related to the disorder. Meanwhile the superlattices with t CRO = 0.8 nm manifest an insulator-like behavior which can be explained well by the Mott-type variable range hopping conduction mechanism. The physical properties of MITs could be understood within a combined picture of the disorder and the electron correlation effects. In addition, the signs of magnetoresistance (MR) were changed at a critical thickness of t CRO = 1.6 nm and no matter with the thickness of SFO. We can’t account for this exactly at present, but a felicitous reason could be the relaxation of octahedral tilts at the critical thickness. To wit: 1.6nm is the critical modulated length by octahedral tilts. More research is needed to have an insight into the physical properties.
9:00 PM - MD3.7.09
Controlled Growth and Designed Epitaxial Multiferroic Oxide Heterostructures
Yanxi Li 1,Jiefang Li 1,Dwight Viehland 1
1 Materials Science and Engineering Virginia Tech Blacksburg United States,Show Abstract
Multiferroic materials attract enormous scientific and technological interests due to their ability to exhibit a magnetoelectric (ME) effect which enables the control of the polarization/ magnetization with an applied magnetic/ electric field, respectively. Recently, compared with the bulk multiferroics, the research interest has focused more and more in thin films area with the development of thin film growth techniques, which enable deposition under epitaxial engineering and non-equilibrium conditions. Among the most widely studied two-phase multiferroic composite thin films, the self-assembled epitaxial BiFeO3-CoFe2O4 (BFO-CFO) nanostructured composite thin films, which contain nanopillars of one phase embedded inside the matrix of the other phase, have been found to be able to present different structures and multiferroic properties by depositing on various oriented SrTiO3 (STO) substrates by pulsed laser deposition (PLD) method.
Here, we have utilized self-assembled BFO nanopillars in a BFO-CFO two phase layer on STO as a seed layer on which to deposit a secondary top BiFeO3 layer by PLD. The growth mechanism of this secondary BFO layer has been investigated, and its multiferroic properties studied. It has been found from cross-section images of electron microscopy studies that the top BFO layer preferentially grew from the bottom BFO seeds and its grain size could be controlled by these seeds. The multiferroic properties of this new heterostructures have also been studied.
Moreover, based on that above mentioned heterostructures with controlled growth, we optimized the experimental procedures and designed to grow another BFO layer on the top of that heterostructures. Thus, a novel structure with second phase CFO nanoparticles embedded in a primary BFO matrix phase has been fabricated. Improved multiferroic properties have been confirmed by several kinds of characterization methods for this heterostructures. Furthermore, by focusing on switching characteristics of the piezoresponse, we demonstrated that the newly designed oxide film showed magnetic field dependence of piezoelectricity due to the improved coupling enabled by good connectivity amongst the piezoelectric and magnetostrictive phases. The improved connectivity amongst the constituent phases of the composite heterostructure has been examined by the state-of-the-art electron microscopy. We have also provided statistical study for the characteristics and then absolutely confirmed that the yielding notable ME effects result from a better coupling between the ferromagnetic and ferroelectric phases of this special architecture. Such new epitaxial multiferroic oxide heterostructures may open new avenues to the application of multi-functional applications.
9:00 PM - MD3.7.10
Integration of Multifunctional Epitaxial Oxide Heterostructures with III-V Semiconductors
Md Shafiqur Rahman 1,Javad R. Gatabi 1,Susmita Ghose 1,Juan S Rojas Ramirez 1,R. K. Pandey 1,Ravi Droopad 1
1 Texas State University San Marcos United States,Show Abstract
Integration of functional oxide thin films with semiconductors has attracted considerable attention in recent years due to their potential applications in future system-on-a-chip devices. GaAs, for example, have a higher saturated electron velocity and mobility allowing transistors based on GaAs to operate at a much higher frequency with less noise compared to Si. In addition, because of its direct bandgap a number of efficient optical devices are possible and by integrating with other III-V semiconductors the wavelengths can be made tunable through hetero-engineering of the bandgap. In this study, we report on the use of SrTiO3 (STO) films on GaAs (100) substrates by molecular beam epitaxy (MBE) as an intermediate buffer layer for the hetero-epitaxial growth of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and room temperature multiferroic BiFeO3 (BFO) thin films using pulsed laser deposition (PLD). The properties of the multilayer thin films in terms of growth modes, lattice spacing/strain, interface structures and texture were characterized by the in-situ reflection high energy electron diffraction (RHEED). The crystalline quality and chemical composition of the BFO/LSMO/STO/GaAs heterostructures were investigated by a combination of x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Surface morphology, piezo-response with domain structure, and ferroelectric switching observations were carried out on the thin film samples using piezoresponse force microscopy (PFM) in the contact mode. The out-of-plane (OP-PFM) and in-plane (IP-PFM) amplitude images obtained for the BFO by PFM show ferroelectric switching behavior of domains at the nanoscale level. The optical properties and the physical thickness of the multilayers were investigated using variable angle spectroscopic ellipsometry by determining the ellipsometric parameters Ψ and Δ at room temperature. The electrical properties and ferroelectric P-E hysteresis loop were measured using a semiconductor parameter analyzer and a radiant ferroelectric tester system. Saturated ferroelectric hysteresis loop is obtained with Pr~90.68 µC/cm2 and low leakage current for our BFO film. The ferromagnetic behavior of BFO/LSMO heterostructure was confirmed with vibrating sample magnetometer (VSM) studies and found to have a saturation magnetization of Ms~650emu\cm3 with improved magnetic hysteresis squareness originating from the BFO/LSMO interface. We found the nanostructure and the physical-composition results obtained from the multilayers are correlated with their corresponding dielectric, piezoelectric, and ferroelectric properties. These result provide an understanding of the heteroepitaxial growth of ferroelectric-antiferromagnetic BiFeO3 on ferromagnetic La0.7Sr0.3MnO3, integrated on SrTiO3 buffered GaAs (100) with full control over the interface structure at the atomic-scale. This work also represents the first step toward the realization of magneto-electronic devices integrated with GaAs.
9:00 PM - MD3.7.11
In-Situ X-Ray Studies of LaGaO3 Epitaxial Thin Film Synthesis
Matthew Highland 1,Dillon Fong 1,Carol Thompson 2,Guangxu Ju 1,Anthony Ruth 3,Peter Baldo 1,Hua Zhou 4,Paul Fuoss 1,Peter Zapol 1,Jeffrey Eastman 1
1 Materials Science Division Argonne National Laboratory Lemont United States,2 Department of Physics Northern Illinois University DeKalb United States1 Materials Science Division Argonne National Laboratory Lemont United States,3 Department of Physics University of Notre Dame Notre Dame United States4 X-Ray Science Division Argonne National Laboratory Argonne United StatesShow Abstract
In complex oxide thin films, thickness, charge, and strain all help to define the properties of the material. For example, epitaxial strain can alter the oxygen octahedral tilt structure, which influences the electrical and magnetic properties, and the screening of polar interfaces can give rise to a variety of emergent interfacial phenomena. The overall thickness of a film determines the combination of surface and bulk phenomena that dominate its properties. We have studied the interaction between these factors using in-situ synchrotron x-ray scattering during the off-axis sputter deposition of LaGaO3 from separate La2O3 and Ga2O3 sources. The changes in microstructure and oxygen octahedral rotations that occur in these samples as individual layers of LaO and GaO2 are added to the surface of the film will be described. We will discuss the electrostrictive effect that these nominally charged layers have on the film and will compare these results with predictions from first-principles calculations examining the structure and stability of LaO- and GaO2-containing heterostructures with varying termination and thickness.
9:00 PM - MD3.7.12
Big Data in Materials Science: Physics from Imaging, and Changing Materials Paradigms
Rama Vasudevan 1,Arthur Baddorf 1,Sergei Kalinin 1
1 Oak Ridge National Laboratory Oak Ridge United States,Show Abstract
The age of big-data in materials science has arrived. Big-data provides the crucial link between the functional imaging, which has seen vast improvements over the past decade, and modeling, which has also experienced tremendous gains. Here, I will present specific examples of how functional atomic-scale imaging in real-space can be used, through multivariate statistical analysis, to provide deep insight and reveal underlying physics in complex oxides, and how these can be extended to further the progress spurred by the Materials Genome Initiative. Analysis of local crystallography, in addition to clustering of atomic intensities, allows for identification of ‘dopants’ within atomically-resolved images. The use of a sliding fast Fourier transform routine in conjunction with endmember extraction from the N-FINDR algorithm can be used to automatically determine the types and spatial localization of crystallographic phases present in atomically-resolved data. Quantification of adatoms on meandering oxide surfaces, in conjunction with Monte-Carlo modeling, can be used to infer energies of terminations, as well as heights of diffusion barriers. In parallel, in-situ reciprocal space data can be highly useful in determining growth transitions and quality of the final surface, and extension to include chemical information from parallel information streams, combined with deep learning to unravel connections between deposition control parameters and final functional properties, promise a rich tapestry of knowledge that can be harnessed towards a materials by design approach. These examples highlight the utility of big-data for understanding physics of oxides, and show the route towards a shifting paradigm of materials discovery.
This research was sponsored by the Division of Materials Sciences and Engineering, BES, DOE (RKV, SVK). Research was conducted at the Center for Nanophase Materials Sciences, which also provided support (APB) and which is a DOE Office of Science User Facility.
9:00 PM - MD3.7.13
Origin of Magnetic Correlation between La0.7Sr0.3MnO3 and La0.7Sr0.3CoO3 Layers in Artificial Heterostructures
J. Byers 2,Andrew Stevens 2,Vivek Malik 4,Yayoi Takamura 1,Nigel Browning 5
1 Chemical Engineering and Materials Science Univ of California-Davis Davis United States,2 Pacific Northwest National Laboratory Richland United States,3 Electrical and Computer Engineering Duke University Durham United States,2 Pacific Northwest National Laboratory Richland United States1 Chemical Engineering and Materials Science Univ of California-Davis Davis United States,4 Physics Indian Institute of Technology Roorkee Roorkee India1 Chemical Engineering and Materials Science Univ of California-Davis Davis United States2 Pacific Northwest National Laboratory Richland United States,5 Fundamental and Computational Sciences Pacific Northwest National Laboratory Richland United StatesShow Abstract
Engineering tailored materials by exploiting emergent interfacial properties in perovskite heterostructures requires understanding of the complex atomic scale influences driving behavior. Properties in these materials develop via indirect interactions of B-cation electrons through a network of corner-sharing oxygen octahedra which are extremely sensitive to both atomic shifts that cause changes in bond angle or length, and to modification of electronic character. As such, we must be able to observe and identify, accurately and with high spatial resolution, individual structural or electrical changes that occur as a result of cation substitution, epitaxial misfit strain and coherence, or charge transfer. In this work, we employ several complementary, state-of-the-art characterization techniques, including aberration corrected scanning transmission electron microscope (Cs-corrected STEM) imaging, electron energy loss spectroscopy (EELS-SI), STEM energy-dispersive x-ray spectroscopy (STEM-EDS), and position averaged convergent beam electron diffraction (PACBED) to investigate the structural, chemical, and electrical interactions at interfaces in heterostructures of La0.7Sr0.3MnO3 (LSMO) and La0.7Sr0.3CoO3 (LSCO) grown on La0.30Sr0.70Al0.65Ta0.35O3 (LSAT) substrates, and examine how these interactions mediate functional properties. Imaging allows us to determine that interfaces are abrupt and films are fully strained, and we observe variations in strain accommodation, and measure changes in octahedral distortions, through film thicknesses and layers. In a complementary way, with spectroscopy we analyze the electrical and chemical profile through the film thicknesses and across interfaces. This presentation will discuss the importance of parameters such as layer depth, number of interfaces, or growth order, and their impact on the critical B-O-B bond. In addition, we acknowledge the challenges of data collection and beam-sample interaction by conventional methods in Cs-corrected STEM, and how they can be addressed using compressive sensing. Low dose imaging with high resolution can be realized through the novel application of compressive sensing, which reconstructs under-sampled data into high-resolution images and spectra, thus radically reducing the dose delivered to the sample and the data collection time.
This continues work that was supported by the Swiss National Science Foundation Grant PBFRP2-134402, the Defense Advanced Research Projects Agency Grant N66001-11-1-4135, and is supported in part by the NSF Grant No. DMR 1411250 through UC Davis, LDRD Program: Chemical Imaging Initiative at PNNL, and EMSL, a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at PNNL. PNNL is a multiprogram national laboratory operated by Battelle for the DOE under Contract DE-AC05-76RL01830.
9:00 PM - MD3.7.14
Ferroelectric Control of Interfacial Magnetism Studied by Polarized Neutron Reflectivity
Tricia Meyer 1,Andreas Herlotz 1,Valeria Lauter 1,Michael Fitzsimmons 1,T. Zac Ward 1,Ho Nyung Lee 1
1 Oak Ridge National Laboratory Oak Ridge United States,Show Abstract
One of the most powerful means to tune the interfacial electronic and magnetic ground states of a multilayer system is by the ferroelectric field effect. By using a ferroelectric with a switchable polarization, it becomes possible to either accumulate or deplete holes at the interface of a neighboring film layer. Provided the large sensitivity of the physical properties of magnetic La1-xSrxMnO3 (LSMO) to fluctuations in carrier density by chemical substitution of La3+ with lower valent Sr2+, these families of compounds are model systems for studying the role of electrostatic doping at the interface with a highly polar ferroelectric such as PbZr0.2Ti0.8O3 (PZT). Conventional characterization techniques such as SQUID magnetometry and transport measurements enable one to explore changes in a material’s bulk properties, but they are not in themselves direct probes of the interface. Here, we report recent results on the magnetic structure of pulsed laser deposited PZT/La0.8Sr0.2MnO3 multilayers probed using the powerful technique of polarized neutron reflectivity (PNR). Since PNR can provide atomic scale information on the magnetic structure and chemical composition as a function of thickness, we are able to investigate the changes at the interfaces resulting from the ferroelectric polarization. Through carefully designed heterostructures, we have confirmed the nanoscale control of