Massive Band Gap Variation in Layered Oxide Heterostructures by Atomic Scale Design
8:00 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
8:00 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.
8:00 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.
8:00 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.
8:00 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.
8:00 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.
8:00 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.
8:00 PM -
MD3.3.14 moved to MD3.4.02
8:00 PM -
MD3.3.15 moved to MD3.4.02
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
8:00 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)
8:30 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.
8:45 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)
9:00 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.
9:15 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.
10:00 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.
10:30 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).
10:45 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).
11:00 AM - *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)
11:30 AM - 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).
11:45 AM - 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
1:30 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.
2:00 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.
2:15 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
2:30 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
3:30 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.
4:00 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).
4:30 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.
4:45 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
Wednesday PM, March 30, 2016
Sheraton, Third Level, Phoenix Ballroom
8:00 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.
8:00 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)
8:00 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).
8:00 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)
8:00 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 (
8:00 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.
8:00 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.
8:00 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.
8:00 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.
8:00 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.
8:00 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.
8:00 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.
8:00 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.
8:00 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 interfacial magnetic ground states by ferroelectrics. A clear contrast in PNR results was observed depending on the orientation of the polarization, which can either suppress or enhance the magnetic moment. Specifically, we found that the suppressed magnetization common to the manganite-air interface can enhanced using ferroelectrics. Thus, in this presentation, we will discuss the important role of ferroelectric polarization in modifying interfacial magnetic properties by comparing results from non-ferroelectric/magnetic heterostructures such as LSMO/LaAlO3.
Acknowledgements The work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. The work at ORNL’s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
8:00 PM - MD3.7.15
Direct In Situ Observation of Local Oxygen Migration during Resistance Switching in Tantalum Oxide Memristors
Suhas Kumar 2,Catherine Graves 1,John Paul Strachan 1,Emmanuelle Merced 1,A. L. David Kilcoyne 3,Tolek Tyliszczak 3,Yoshio Nishi 2,R. Stanley Williams 1
1 Hewlett Packard Labs Palo Alto United States,2 Stanford University Stanford United States,1 Hewlett Packard Labs Palo Alto United States3 Lawrence Berkeley National Laboratory Berkeley United States2 Stanford University Stanford United StatesShow Abstract
Tantalum oxide memristors promise long endurance in information storage and are frontrunners for next generation memory technology. Recent efforts to uncover the nanophysics behind resistance switching in tantalum oxide and several related materials suggest local conductive channel formation by oxygen-ion-migration as the mechanism of operation, and is supported by indirect experimental observations and theoretical predictions. A more complete understanding and model is critical in enabling widespread implementation of such technology, and our goal was to directly observe this migration.
Here we employed x-ray absorption spectromicroscopy of the O K-edge and Ta-L edge in a planar geometry on micrometer sized crosspoint tantalum oxide memristors. Using a synchronous in-operando technique developed recently,  we were able to isolate very weak signals corresponding to extremely localized elemental, chemical and electronic changes to the material.
We electrically cycled tantalum oxide crosspoint memristors between bistable resistance states using voltage pulses of varying amplitudes. Upon using low voltages (This is a direct in-situ observation of nanoscale composition evolution and atomic motion of oxygen in a functioning memristor that describes possible material behavior during switching, repeated cycling and failure. This also highlights the potential of O K-edge x-ray absorption spectromicroscopy as a sensitive probe to study inhomogeneous localized phenomena in a wide variety of oxides with in-situ and in-operando operations.
8:00 PM - MD3.7.16
Characterizing Atomic Scale Ordering and Antiphase Domains in Double Perovskite Thin Films Using Scanning Transmission Electron Microscopy and Simulation
Bryan Esser 1,Adam Hauser 2,Robert Williams 1,Fengyuan Yang 3,David McComb 1
1 Materials Science and Engineering The Ohio State University Columbus United States,2 Physics and Astronomy amp; MINT Center The University of Alabama Tuscaloosa United States3 Physics The Ohio State University Columbus United StatesShow Abstract
Next generation solid-state devices may exploit spin degrees of freedom (±½) resulting in large increases in read/write performance and storage capacity. Materials that exhibit high Curie temperatures (above room temperature) and high degrees of spin polarization are good candidates for use in such devices. The family of double perovskites (DPs) with the general formula A2BB′O6, have been shown to exhibit favorable properties. In order to use DPs in spintronic devices, high quality, epitaxial thin films with high ordering parameters must be grown, which has proven difficult. Ordering of the B/B′ atoms is essential to maintain the preferred magnetic and electronic properties because of superexchange couplings across B-O-B′ and B-O-B′-O-B bonds.
In this work, we investigate thin films of Sr2CrReO6 (SCRO) grown on (LaAlO3)0,3(Sr2AlTaO6)0.7 (LSAT) with a buffer layer of SrCr0.5Nb0.5O3 (SCNO). SCRO has been shown to grow epitaxially on SCNO buffer layers and to maintain exceptionally high ordering parameters for the B/B′ sublattice. Because of the high atomic number (Z) contrast, high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) was employed to image thin film interfaces, as well as defects within the films. Fully ordered regions are expected to exhibit clear modulations in intensity from column to column in this imaging mode. To a first approximation, this allows for identification of regions within the film that appear fully ordered versus those that do not for further analysis.
In combination with the experimental STEM images, DP structures were modeled followed by HAADF-STEM image and diffraction simulations. Through careful analysis of the data, it can be shown that regions with the SCRO films that appear highly disordered due to a lack of clear intensity variation are actually a consequence of antiphase domains, which result in a misregistry of the B/B′ sublattice. This implies that the SCRO films are, in fact, highly ordered with some local regions exhibiting wrong nearest-neighbors on the B/B′ sublattice, providing an explanation the favorable magnetic properties.
Image simulation was also used to understand variations in HAADF-STEM image intensities based on the effect of B/B′ ordering. It can be shown that the atomic configurations along the path of the electron beam can have significant effects on the overall intensities seen in the image, demonstrating that HAADF-STEM image contrast alone is not the most reliable way to quantify ordering. Other techniques, such as diffraction or chemical analysis in the microscope are necessary, with simulations, to fully quantify the data.
8:00 PM - MD3.7.17
Electron-Doped Manganite Films as Channels in Ferroelectric Mott Transistors
Anke Sander 1,Vincent Garcia 1,Vladimir Strocov 2,Federico Bisti 2,Marius-Adrian Husanu 2,J Rault 3,Francois Bertran 3,Patrick Lefevre 3,Ashima Arora 4,S. Valencia 4,Hiroyuki Yamada 5,Cecile Carretero 1,Agnes Barthelemy 1,M. Bibes 1
1 Unité Mixte de Physique CNRS/Thales Palaiseau France,2 Swiss Light Source Paul Scherrer Institute Villigen Switzerland3 Synchrotron SOLEIL Gif-sur-Yvette France4 BESSY Helmholtz-Zentrum-Berlin Berlin Germany5 National Institute of Advanced Industrial Science and Technology Tsukuba JapanShow Abstract
One highly promising route for future nanoelectronics considers transistors made of Mott insulators . These Mott transistors take advantage of the electronic correlations, enabling higher ON/OFF ratios and lower power consumption than achievable with conventional MOSFET technology. In Mott-insulating CaMnO3 (CCMO) the chemical substitution of Ca2+ by Ce4+ leads to electron doping, inducing a transition to metallic behavior at much lower doping levels compared to the widely investigated hole-doped manganites. CCMO thus appears as a promising channel material for Mott transistors. In bulk CCMO, this transition occurs at 5% Ce doping and is accompanied by the development of a weak ferromagnetic state with a magnetic moment of ∼0.4 μB/Mn . The resulting rich phase diagram can be further modulated by epitaxial strain in thin films [3, 4].
In this study, high quality thin films of CCMO with different doping levels (0, 2 and 4% Ce content) have been epitaxially grown on YAlO3(001) substrates. We will present a detailed analysis of their electronic properties based on transport and soft X-ray ARPES experiments, and of their magnetic response (from SQUID magnetometry, XMCD and anomalous Hall measurements). Finally, we will show results on heterostructures combining CCMO as channel and BiFeO3 as ferroelectric gate oxide, with the aim of controlling the electronic and magnetic response by ferroelectric field effect .
The authors acknowledge financial support from the European Research Council (ERC Advanced Grant FEMMES, No. 267579 and ERC Consolidator Grant MINT, No. 615759) and the German Research Foundation (HO 5346/1-1).
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 Xiang et al., Adv. Mater. 23, 5822 (2011)
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 H. Yamada et al., Scientific Reports 3, 2834 (2014)
8:00 PM - MD3.7.18
Unit Cell Control of Complex Oxides during Sputtering by in situ Reflection High Energy Electron Diffraction
Jacob Podkaminer 1,Jacob Patzner 1,Daesu Lee 1,Bruce Davidson 2,Chang-Beom Eom 1
1 Univ of Wisconsin-Madison Madison United States,2 Temple University Philadelphia United StatesShow Abstract
As novel phenomena at materials interfaces draws increasing attention, it is vital to gain atomic control of material growth to further understand and engineer their properties. Currently, Reflection High-Energy Electron Diffraction (RHEED) is one of the most commonly used in situ diagnostic tools for both molecular beam epitaxy and pulsed laser deposition growth techniques. RHEED is frequently used to observe layer-by-layer growth and used to control the growth at the unit cell level. Sputtering is a common, inexpensive, and industrially viable growth technique for many complex oxide materials but lacks the powerful in situ analysis techniques used by pulsed laser deposition and molecular beam epitaxy. Here we demonstrate the integration of RHEED into the sputtering environment as an in situ tool during the growth of oxide materials. We will present on the challenges associated with performing RHEED analysis during sputter deposition and provide a practical and effective approach for mitigating these challenges. Experimentally we observe strong RHEED specular spot oscillations during SrRuO3 growth for many tens of unit cells, demonstrating the possibility for precise layer-by-layer control of complex oxides during sputter deposition. We apply our approach to the growth of several novel epitaxial heterostructures to demonstrate precise unit cell and interface control.
Ariando Ariando, National University of Singapore
Gertjan Koster, University of Twente
Ho-Nyung Lee, Oak Ridge National Laboratory
Yayoi Takamura, University of California, Davis
MD3.8: Magnetism in 3D and 5D Heterostructures
Thursday AM, March 31, 2016
PCC West, 100 Level, Room 101 C
8:00 AM - *MD3.8.01
Engineering Correlated Dirac Electrons in SrIrO3/SrTiO3 Superlattice+
Hidenori Takagi 3
1 Max Planck Institute for Solid State Research Stuttgart Germany,2 Department of Physics University of Tokyo Tokyo Japan,3 FMQ University of Stuttgart Stuttgart Germany,Show Abstract
In 5d Iridium oxides, a large spin-orbit coupling of lso~0.7 eV, inherent to heavy 5d elements, is not small as compared with other relevant electronic parameters, including Coulomb U, transfer t and crystal field splitting D, which gives rise to a variety of exotic electronic states. In the layered perovskite Sr2IrO4, a spin-orbital Mott state with Jeff=1/2 is realized due to the interplay of lso and U [1,2]. The three-dimensional analog of Sr2IrO4, SrIrO3, distorted perovskite, is a correlated semimetal with Dirac nodes protected by crystalline symmetry . Using (SrIrO3)m/SrTiO3 (m: number of SrIrO3 layers) super-lattice structure on SrTiO3 (001) substrate, we could have controlled successfully the dimensionality and hence increasing effective Coulomb U . With decreasing the number of SrIrO3 layers, we observe a Dirac semimetal to insulator transition at m=3, accompanied with the onset of canted antiferromagnetism. This can be understood as a gapping of the Dirac nodes by breaking time reversal symmetry with magnetic moments. At m=1, the single layer, the transport remains insulating even above the magnetic ordering temperature, indicative of the increased spin-orbital Mott character as in Sr2IrO4. (111) superlattice (Sr0.5Ca0,5IrO3)m/(SrTiO3)2 was also successfully fabricated . We observed analogous behavior as observed for (001) superlattice. Dirac semimetal-magnetic insulator transition was observed at m=6 with decreasing m. The bilayer m=2 film was insulating all the way up to room temperature and no signature of anticipated topological state  was observed.
1) B. J. Kim et al., Phys. Rev. Lett. 101, 076402 (2008).
2) B. J. Kim et al., Science 323, 1329 (2009).
3) Chen, Y. et al. ,Nat. Commun. 6:6593 doi: 10.1038/ncomms7593 (2015).
4) J. Matsuno et al., Phys. Rev. Lett. 114 240749 (2015).
5) D. Hirai et al, APL mat 3, 041508 (2015).2015)
6) D.Xiao et al., Nature Communications 2:596 (2011).
+ Work done in collaboration with D.Hirai, J.Matsuno, N.Matsui.
8:30 AM - MD3.8.02
Metastable Honeycomb SrTiO3/SrIrO3 Heterostructures
Trevor Anderson 1,Sangwoo Ryu 1,Hua Zhou 2,Lin Xie 4,Jacob Patzner 1,Jacob Podkaminer 1,Julian Irwin 5,Yanjun Ma 1,Xiaoqing Pan 4,Mark Rzchowski 5,Chang-Beom Eom 1
1 Materials Science and Engineering University of Wisconsin-Madison Madison United States,2 Advanced Photon Source Argonne National Laboratory Argonne United States3 Materials Science and Engineering University of Michigan Ann Arbor United States,4 College of Modern Engineering and Applied Science Nanjing University Nanjing China5 Physics University of Wisconsin-Madison Madison United StatesShow Abstract
Recent theory predictions of exotic band topologies in (111) honeycomb perovskite SrIrO3 layers sandwiched between SrTiO3 have garnered much attention in the condensed matter physics and materials communities. However, perovskite SrIrO3 film growth in the (111) direction remains unreported as efforts to synthesize pure SrIrO3 on (111) perovskite substrates have yielded films with monoclinic symmetry rather than the perovskite structure required by theory predictions. In this work, we report the synthesis of ultra-thin metastable perovskite SrIrO3 films capped with SrTiO3 grown on (111) SrTiO3 substrates by pulsed laser deposition (PLD). The atomic structure of the ultra-thin films was examined with scanning transmission electron microscopy (STEM), which suggests a perovskite layering distinct from the bulk SrIrO3 monoclinic phase. In-plane 3-fold symmetry for the entire heterostructure was confirmed using synchrotron surface x-ray diffraction to measure symmetry equivalent crystal truncation rods. Our findings demonstrate the ability to stabilize (111) honeycomb perovskite SrIrO3, which provides an experimental avenue to probe the novel phenomena predicted for this material system.
8:45 AM - MD3.8.03
Emerging Ferromagnetism in (SrMnO3)m/(SrIrO3)n Heterostructures
John Nichols 1,Shinbuhm Lee 1,Jonathan Petrie 1,Tricia Meyer 1,Xiang Gao 1,John Freeland 2,Di Yi 4,Jian Liu 3,Daniel Haskel 2,T. Zac Ward 1,Gyula Eres 1,Valeria Lauter 1,Michael Fitzsimmons 1,Ho Nyung Lee 1
1 Oak Ridge National Laboratory Oak Ridge United States,2 Argonne National Laboratory Agronne United States4 Stanford University Stanford United States3 University of Tennessee Knoxville United StatesShow Abstract
Strong interplay between order parameters such as charge, spin, orbital, and lattice in transition metal oxides has proven to produce novel physical phenomena, while interfacial coupling between dissimilar materials is an effective technique to tune such parameters. While there are numerous references to interfaces between 3d–3d and 4d–3d materials, there has been limited work on 5d–3d compounds and no reported evidence of strong interfacial coupling in such systems. We have synthesized high quality [(SrMnO3)m/(SrIrO3)n]z (MmIn) heterostructure samples on SrTiO3 (001) substrates. Although SMO is an antiferromagnetic insulator (AFI) and SrIrO3 is a paramagnetic metal that becomes an AFI under reduced dimensionality, the M1I1 sample is a ferromagnetic metal (Tc ~ 190 K). This is very remarkable since one would expect both SrMnO3 and single-layered SrIrO3 to be insulating antiferromagnets. The magnetic order predominantly resides within the SrMnO3 layer and is governed by double exchange interactions due to the multivalent Mn ions. The magnitude of the magnetic response is approximately independent of n, while it decreases very strongly as m increases being fully suppressed for m ≥ 4. Although the resistivity of these samples increases systematically with decreasing m, this change is less than an order of magnitude and all samples are semimetallic. In addition, we observed enhanced metallicity for 3 ≤ n ≤ 6. Thus, the ferromagnetic metallic ground state observed in these heterostructure samples is completely absent from either constituent material and provides the first experimental evidence of strong interfacial coupling between 5d and 3d materials. We will present their structural, magnetic, and electronic properties and discuss the origin of this unique behavior.
This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.
9:00 AM - *MD3.8.04
Electric-Field Control Of Magnetic Order Just Above Room Temperature
Lee Phillips 1,Ryan Cherifi 1,Viktoria Ivanovskaya 1,Vincent Garcia 1,Alberto Zobelli 2,Ingrid Infante 3,S. Valencia 4,Stephane Fusil 1,Florian Kronast 4,Nicolas Guiblin 3,Akin Uenal 4,Brahim Dkhil 3,M. Bibes 1,Agnes Barthelemy 1
1 Unite Mixte de Physique CNRS/THALES Palaiseau France,2 Laboratoire de Physique des Solides Université Paris-Sud Orsay France3 Laboratoire SPMS Ecole Centrale Paris Chatenay-Malabry France4 Helmholtz Zentrum Berlin für Materialen und Energie Berlin GermanyShow Abstract
Controlling magnetism by electric fields is a key issue for the future development of low-power spintronics . Progress has been made in the electrical control of magnetic anisotropy , domain structure [3,4], spin polarization [5,6] or critical temperatures [7–9]. However, the ability to turn on and off robust ferromagnetism at room temperature and above has remained elusive.
We will present a new approach for the electrical control of magnetic and spintronic properties based on the combination of ferroelectric materials with magnetic transition-metal alloys. Experimental results based on X-ray diffraction and various magnetometry techniques will be presented, demonstrating a giant, low-voltage control of magnetism, just above room temperature in heterostructures combining FeRh with BaTiO3 substrates. The data will be interpreted in the light of first-principles in terms of both strain and field-effect. Our results correspond to a magnetoelectric coupling larger than previous reports by at least one order of magnitude and open new perspectives for the use of ferroelectrics in magnetic storage and spintronics [10, 11]. We will show additional potential of these heterostructures.
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 T. H. E. Lahtinen et al, Sci. Rep. 2, 258 (2012).
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 L. Phillips et al.; Sci Rep. 5: 10026 (2015)
The authors acknowledge financial support from the European Research Council (ERC
Advanced Grant FEMMES, No. 267579)
9:30 AM - MD3.8.05
Hybridization-Controlled Charge Transfer and Induced Magnetism at Correlated Oxide Interfaces
Mathieu Grisolia 1,Julien Varignon 1,S. Valencia 5,Maria Varela 3,G Sanchez Santolino 2,R. Abrudan 5,E Weschke 5,E Schierle 5,J Rault 6,J-P Rueff 6,Agnes Barthelemy 1,J. Santamaria 2,M. Bibes 1
1 CNRS/Thales Palaiseau France,5 Helmholtz-Zentrum Berlin für Materialen und Energie Berlin Germany2 GFMC Universidad Complutense Madrid Madrid Spain,3 Materials Science amp; Technology Division Oak Ridge National Laboratory Oak Ridge United States2 GFMC Universidad Complutense Madrid Madrid Spain4 Institut für Experimentalphysik/Festkörperphysik Ruhr-Universität Bochum Bochum Germany,5 Helmholtz-Zentrum Berlin für Materialen und Energie Berlin Germany6 Synchrotron soleil Saint-Aubin FranceShow Abstract
At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from correlations between transition metal and oxygen ions. Strong correlations thus offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question.
In this presentation, we will show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalency of the metal-oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption and photoemission spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. The mixed Ni2+/Ni3+ valence results in an induced ferromagnetic-like state, observed by means of XMCD, exemplifying the potential of correlated interfaces to design novel phases. Further, using experiments and theory, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalency.
MD3.9: Symmetry and Interfacial Engineering
Thursday AM, March 31, 2016
PCC West, 100 Level, Room 101 C
10:15 AM - MD3.9.01
Control of Interfacial Magnetism via Structurally Induced Symmetry Mismatch in Complex Oxide Superlattices
Arturas Vailionis 1,Alexander Grutter 2,Charles Flint 1,Chunyong He 4,Elke Arenholz 3,Yuri Suzuki 1
1 Geballe Laboratory for Advanced Materials Stanford University Stanford United States,2 NIST Center for Neutron Research National Institute of Standards and Technology Gaithersburg United States4 Department of Materials Science and Engineering University of California Berkeley United States3 Advanced Light Source Lawrence Berkeley National Lab Berkeley United StatesShow Abstract
Complex landscape of structural and magnetic interactions at oxide interfaces has led to the stabilization of highly tunable emergent magnetic ground states. For example, the ferromagnetism observed in (CaRuO3)m/(CaMnO3)n superlattices is tightly confined within a single unit cell at the interface between antiferromagnetic insulator CaMnO3 and paramagnetic metal CaRuO3. The interfacial ferromagnetism in this system can be explained in terms of the leakage of itinerant electrons from CaRuO3 into CaMnO3 facilitating a carrier-mediated double exchange interaction. The competition between antiferromagnetic superexchange and interfacial double exchange interactions in CaMnO3 leads to a canted ferromagnetic state with net magnetization of ~1 μB/Mn. Surprisingly, the superlattices with even and odd number of pseudocubic CaMnO3 unit cells (n) possess strikingly different interfacial saturation magnetization: 1.0 μB/Mn and 0.5 μB/Mn, respectively. This difference is difficult to explain within the existing theoretical framework. Through synchrotron x-ray diffraction, x-ray magnetic circular dichroism and polarized neutron reflectometry we demonstrate that the observed modulation of the interfacial ferromagnetism is governed by a symmetry mismatch of corner-connected octahedral network across the CaRuO3/CaMnO3 interface. For symmetry matched interfaces, we find the coexistence of interfacial ferromagnetic CaMnO3, antiferromagnetic CaMnO3 and metallic CaRuO3. At the symmetry mismatched interfaces, the interfacial ferromagnetism is completely suppressed in CaMnO3. The results demonstrate how octahedral distortions present in (even/even), (even/odd), (odd/even), and (odd/odd) superlattices manipulate interfacial ferromagnetism and this way affect a delicate balance and competition of exchange interactions.
 S. Takahashi et al., Appl. Phys. Lett. 79, 1324 (2001).
 B.R.K. Nanda et al., Phys. Rev. Lett. 98, 216804 (2007).
 C. He et al., Phys. Rev. Lett. 109, 197202 (2012).
10:30 AM - MD3.9.02
Tuning Magnetic Anisotropy by Interfacially Engineering the Oxygen Coordination Environment in a Transition-Metal Oxide
Daisuke Kan 1,Ryotaro Aso 1,Riko Sato 1,Mitsutaka Haruta 1,Hiroki Kurata 1,Yuichi Shimakawa 1
1 ICR Kyoto Univ Uji Japan,Show Abstract
Oxygen coordination environment in transition-metal oxides play crucial roles in yielding a broad spectrum of functional properties, and precise control of such oxygen environment is a key for developing future oxide-based electronics. Recent advances in atomic-level synthesis techniques have made it possible to fabricate artificial heterostructures with chemically abrupt interfaces consisting of dissimilar oxides. These heterostructures have provided a good platform for engineering novel bonding geometries that could lead to emergent phenomena not seen in bulk oxides. Here we show that the oxygen coordination environment of a perovskite, SrRuO3, can be controlled by heterostructuring SrRuO3 with a thin (0–4 monolayers thick) Ca0.5Sr0.5TiO3 layer grown on a GdScO3 substrate . We found that a Ru-O-Ti bond angle characterizing the SrRuO3/Ca0.5Sr0.5TiO3 interface structure can be engineered by layer-by-layer control of the Ca0.5Sr0.5TiO3 layer thickness, and that the engineered Ru-O-Ti bond angle not only stabilizes a Ru-O-Ru bond angle never seen in bulk SrRuO3 but also tunes the magnetic anisotropy in the entire SrRuO3 layer. The results demonstrate that interface engineering of the oxygen coordination environment is a good way to control additional degrees of freedom in designing functional oxide heterostructures.
 D. Kan, R. Aso, R. Sato, M. Haruta, H. Kurata, and Y. Shimakawa, Submitted (2015)
10:45 AM - MD3.9.03
Structural and Electronic Reconstructions in TiO2(B)/VO2(B) Heterostructures
Xiang Gao 1,Shinbuhm Lee 1,T. Zac Ward 1,Matthew Chisholm 1,Ho Nyung Lee 1
1 Oak Ridge National Laboratory Oak Ridge United States,Show Abstract
Transition metal oxides (TMOs) with strongly correlated d-orbital electrons are promising materials for many information and energy technologies, including sensors, data storage, piezoelectrics, photovoltaics, ionic conductors, and electrochemical energy generation and storage. Recently, TMO heterostructures have shown intriguing structural and electronic interactions at well-defined interfaces, giving rise to useful functionalities and physical properties. In this work, we have studied interfaces between materials with a d0-d1 configuration. Rather than using perovskite heterostructures, such as SrTiO3/LaTiO3, we epitaxially synthesized B-phase TiO2 [TiO2(B), 3d0] and B-phase VO2 [VO2(B), 3d1] thin films and heterostructures by pulsed laser epitaxy. Scanning transmission electron microscopy (STEM) was used to characterize TiO2(B)/VO2(B) heterostructures grown on SrTiO3 substrates, in addition to other structural and physical property measurements. Despite the large lattice and symmetry mismatch, high crystal quality was observed with an interesting interfacial transition layer formed to accommodate the crystal symmetry mismatch between VO2(B) and SrTiO3 substrate. In this presentation, results from a unit-cell-by-unit-cell electron energy loss spectroscopy (EELS) study combined with STEM imaging will be discussed. The observed modifications to the fine structures of Ti-L2,3 and O-K edges in both interface and surface regions as compared to the bulk TiO2(B) film indicate the existence of extra electrons in these regions. Discussions on the possible mechanisms for the observed interfacial structural and electronic reconstructions will be presented and compared with those observed in perovskite based d0-d1 interfaces.
*This work was supported by the U.S. Department of Energy, Office of science, Basic Energy Sciences, Materials Sciences and Engineering Division.
11:00 AM - MD3.9.04
Nanostructured Complex Oxides as a Route towards Thermal Behavior in Artificial Spin Ice Systems
Rajesh Chopdekar 1,Binzhi Li 1,Thomas Wynn 1,Michael Lee 1,Yue Jia 1,Zhiqi Liu 2,Michael Biegalski 2,Scott Retterer 2,Anthony Young 3,Andreas Scholl 3,Yayoi Takamura 1
1 Department of Chemical Engineering and Materials Science University of California, Davis Davis United States,2 Center for Nanophase Materials Science Oak Ridge National Laboratory Oak Ridge United States3 Advanced Light Source Lawrence Berkeley National Laboratory Berkeley United StatesShow Abstract
Frustration in magnetic systems occurs due to the inability to find a configuration that simultaneously minimizes all interactions, and can be found in systems with structural disorder (e.g. spin glasses) or systems with structural order but multiple competing interactions. There has been considerable interest in fabrication of a two-dimensional analogue of a geometrically frustrated system via an ensemble of nanomagnets,1 and the thermodynamics of such systems can be explored if the constituent island material has a magnetic transition near room temperature. Prior experiments aimed at examining these effects in ultrathin polycrystalline metal samples were hampered by significant differences between nominally identical islands and surface oxidation which lead to suppression of magnetization on the timescales of experimental observation (hours). In contrast, the use of a nanostructured epitaxial complex oxide such as La0.7Sr0.3MnO3 permits the study of artificial spin ice geometries with a bulk Curie temperature of 370K. We have used soft X-ray photoemission electron microscopy to image the magnetization of 470x170x40 nm elliptical single domain islands arranged in large scale square and kagome spin ice geometries, as well as hexagonal ring patterns whose degree of magnetic frustration scales with the number of rings in the pattern. Upon thermal randomization, we find that the square ice array falls into a single magnetic ground state in regions which extend over 20 microns in diameter with no domain boundaries. Furthermore, a statistical analysis of a large ensemble of one-, two- and three- hexagon ring structures follows the typical low energy populations seen in metallic artificial spin ice systems. The inter-island coupling strength was experimentally determined to be 6x10-12 A2 m, comparable to coupling in thin metallic artificial spin ice systems. Additionally, we have thermally cycled the sample to 470K with no change in the population of the ground and low energy magnetization configurations. Thus, nanostructured complex oxides are well-suited for the exploration of the thermal evolution of frustration in tailored geometries since their epitaxial nature avoids island-to-island disorder and their magnetic properties remain robust and stable against air exposure and/or thermal cycling.
1. L.J. Heyderman and R.L. Stamps, J. Phys. Condens. Matter 25, 363201 (2013).
11:15 AM - MD3.9.05
Tailoring Spin Textures in Complex Oxide Microstructures
Michael Lee 3,Thomas Wynn 3,Erik Folven 2,Rajesh Chopdekar 3,Andreas Scholl 1,Anthony Young 1,Scott Retterer 4,Jostein Grepstad 2,Yayoi Takamura 3
3 Department of Chemical Engineering and Materials Science University of California, Davis Davis United States,2 Department of Electronics and Telecommunications Norwegian University of Science and Technology Trondheim Norway1 Advanced Light Source Lawrence Berkeley National Laboratory Berkeley United States4 Center for Nanophase Materials Science Oak Ridge National Laboratory Oak Ridge United StatesShow Abstract
Strong correlation between the spin, charge, orbital, and lattice degrees of freedom in complex oxides allows for tuning of the material properties, providing more versatile routes to control magnetic phenomena in nano- and micro-patterned structures. La0.7Sr0.3MnO3 (LSMO) is a promising material for future memory device design due to the confluence of many scientifically interesting functional properties, including ferromagnetism, colossal magnetoresistance, and high spin-polarization. In this work, soft x-ray photoemission electron microscopy (X-PEEM) was used to observe and characterize the evolution of magnetic domain structure as a function of temperature in micromagnets patterned into epitaxial films of LSMO. These images reveal the formation of novel spin textures that are a hybridization of well-described configurations, vortex and Landau, and emerge from the balance between fundamental materials parameters, micromagnet geometries, and epitaxial strain. The results demonstrate how the magnetic domain state can be tailored through careful control of these factors with special interest in the role of magnetocrystalline anisotropy. Additional modulation of the magnetic structure may be achieved by incorporating LSMO layers into LSMO/La0.7Sr0.3FeO3 (LSFO) superlattices – a system known to exhibit interfacial coupling between the ferromagnetic and antiferromagnetic layers . Even the character of the LSMO/LSFO interaction may be converted from collinear alignment to spin-flop by the geometry of the microstructure . Furthermore, we have devised a framework with which fundamental materials parameters (saturation magnetization and magnetocrystalline anisotropy constants) can be determined with sub-100 nm spatial resolution as a function of temperature – a capability essential for efficient design and characterization of functional properties in next generation spintronic devices.
 E. Arenholz et al., Appl. Phys. Lett. 94, 072503 (2009)
 E. Folven et al., Nano Letters 12, 2386 (2012)
11:30 AM - *MD3.9.06
Long Range Symmetry Propagation Initiated at Heterostructure Interfaces
Guus Rijnders 1
1 MESA+ Institute for Nanotechnology University of Twente Enschede Netherlands,Show Abstract
Diverse electronic phases in complex oxide materials such as superconductivity, magnetic phases and ferroelectricity are intimately coupled to the crystal symmetry. Atomic layer controlled growth of oxide heterostructures offers a flexible route to tune the symmetry and this has been shown to give rise to many unusual emergent properties that are absent in the original materials. Using such atomic layered growth, we have fabricated perovskite heterostructures in which the altered symmetry is found to propagate over a long range. The interfacial octahedral coupling induced symmetry can even propagate throughout the total thickness of epitaxial films. Desired symmetries of perovskite heterostructures are furthermore achieved by engineering the substrate symmetry, for example by introducing a buffer layer with different symmetry. Our results demonstrate that the long range symmetry propagation can effectively control metal to insulator transition, as well as magnetic ordering.
In this contribution, I will focus on the fabrication of epitaxial heterostructures, the analysis of the crystal symmetry using x-ray diffraction, and high-resolution STEM, as well as resulting properties of magnetic phases.
MD3.10: Topological Phases in Complex Oxides
Thursday PM, March 31, 2016
PCC West, 100 Level, Room 101 C
1:30 PM - *MD3.10.01
Exotic Mott and Interacting Topological Phases by Lattice Engineering
Jak Chakhalian 1
1 Univ of Arkansas Fayetteville United States,Show Abstract
Deterministic control over the spatial arrangement atoms in a crystal is the backbone of its properties that, along with the interactions, defines its ground state. Following this notion, several theoretical proposals exist to utilize a few unit cells of a correlated oxide heterostructured along the pseudo-cubic (111) direction. This geometrically engineered motif relies on the presence of correlated carriers placed on a graphene-like lattice, or dice lattices for bilayers and trilayers of perovskite materials. The guiding principle is to use strong electronic correlations combined with quantum confinement and symmetry-breaking interfaces to enable access to new electronic band structures that may activate novel or latent quantum phases.
In this talk, the current status of research in this field will be reviewed. The experimental challenges in realization and characterization of such heterostructures will be exemplified by rare earth nickelates heterostructures. Several promising examples of such geometrically engineered artificial Mott materials will be discussed.
2:00 PM - *MD3.10.02
Suppression of Three-Dimensional Charge Density Wave Via Thickness Control
Tae Won Noh 2
1 Center for Correlated Electron Systems, Institute for Basic Science Seoul Korea (the Republic of),2 Department of Physics and Astronomy Seoul National University Seoul Korea (the Republic of),Show Abstract
The perovskite bismuthates have attracted widespread interest since superconductivity was discovered in hole-doped compounds BaPb1-xBixO3 and Ba1-xKxBiO3 with moderately high transition temperature of 13 and 30 K, respectively [1,2]. The parent compound BaBiO3 (BBO) is an insulator, generally believed to exhibit charge disproportionation into the Bi3+ and Bi5+ valence states (6s2 and 6s0 configurations). This disproportionation leads to lattice (breathing) distortion originated from variations in the Bi-O bond length, and the formation of charge density wave which creates a gap at Fermi energy . Whereas versatile phase diagram of the bismuthate compounds was explored via chemical substitution using Pb or K , the complexities associated with chemical doping have so far presented a difficult experimental challenge.
Here, we study epitaxial BBO thin films grown via pulsed laser deposition without any insertion of chemical dopants. Surprisingly, spectroscopic ellipsometry reveals the suppression of the charge density wave as film thickness decreases. X-ray diffraction and Raman spectroscopy confirms that thick films have a tetragonal structure with lattice doubled due to the breathing distortion, while thin films have a cubic without any evidence of lattice doubling. A critical thickness of the concurrent suppression of the charge density wave and the breathing distortion is found to be about 10 unit cells. These results suggest that thickness can be an ideal tuning parameter to study the electronic phase of charge-density-wave materials without dopant substitution.
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 R. J. Cava et al., Nature 328, 814 (1988).
 H. Sato, S. Tajima, H. Takagi, S. Uchida, Nature 338, 241 (1989).
 S. Pei et al., Phys. Rev. B 41, 4126 (1990).
2:30 PM - MD3.10.03
Metastable Pseudocubic BaBiO3 Epitaxial Thin Films
David Harris 1,Chang-Beom Eom 1
1 Univ of Wisconsin-Madison Madison United States,Show Abstract
Topological insulators have recently generated significant research activity, with a particular interest in an oxide topological insulator that is robust to air exposure. BaBiO3 is a charge-density-wave insulator that becomes a superconductor when Pb is substituted for Bi or K is substituted for Ba. Concomitant with the electronic transition is a structural transformation from monoclinic (bulk) to tetragonal (Pb-doped) or cubic (K-doped) and charge-density-wave suppression. Recent first principle studies have predicted emergent electronic properties at the surface of (001) BaBiO3 such as a topological insulating state accessible through electron doping. However these calculations require the stabilization of cubic BaBiO3 instead of the bulk monoclinic Ba2Bi3+Bi5+O6 structure. Here we report on the growth of heteroepitaxial pseudocubic (001) BaBiO3 thin films using RF-magnetron sputtering. Our results demonstrate smooth, single phase films with rocking curve width below 0.03°, enabling study of metastable BaBiO3 and the resulting emergent properties. The growth of high quality single crystal BaBiO3 is an important step towards studying a system predicted to contain novel electronic phenomenon.
 Yan, B., Jansen, M. & Felser, C. A large-energy-gap oxide topological insulator based on the superconductor BaBiO3. Nat. Phys. 9, 709–711 (2013).
MD3.11: Advanced Characterization of Functional Oxides
Thursday PM, March 31, 2016
PCC West, 100 Level, Room 101 C
3:15 PM - *MD3.11.01
Aberration-Corrected TEM Imaging and Spectroscopy as a Tool to Understand the Origin of Emergent Phenomena at Oxide Interfaces
Johan Verbeeck 1,Nicolas Gauquelin 1,Zhaoliang Liao 2,Deba Samal 2,Ricardo Egoavil 1,Mark Huijben 2,Gertjan Koster 2,Guus Rijnders 2,Gustaaf Van Tendeloo 1
1 EMAT, University of Antwerp Antwerp Belgium,2 MESA+, University of Twente Enschede NetherlandsShow Abstract
The study of novel physical properties appearing when two materials are interfaced has become one of the major fields of research in solid state physics over the last decade. For example, in the strive for novel non-Silicon based electronics, the discovery of the formation of a conductive layer right at the interface region between 2 insulators (for example LaAlO3 and SrTiO3); a so-called two-dimensional electron gas (2DEG) or two dimensional electron liquid appears. Another important example of such emergent phenomena is the appearance of interface magnetism or superconductivity.
As the materials involved in those new physical phenomena are often complex oxides, many factors such as strain, oxygen stoichiometry, cation intermixing, confinement effects, electronic reconstructions, band bending, orbital ordering… have to be considered when discussing their origin. The exact understanding of those phenomena is a key factor in order to turn these research ideas into working devices and in order to search for the most optimal materials.
In parallel, advances in electron microscopy instrumentation and techniques such as the appearance of aberration-correctors of the probe-forming lens have made it possible to achieve sub-angstrom spatial resolution allowing the study the material on an atom column by atom column basis. High Angle Annular Dark Field (HAADF) combined with Annular Bright Field (ABF) imaging have made it possible to study and understand respectively the cationic and the oxygen sub-lattices in these materials. Furthermore, improved stability and the appearance of electron monochromators has made an energy resolution of 100 meV readily available in Electron energy loss spectroscopy (EELS) offering the benefits of an X ray absorption (XAS)-like signal at atomic spatial resolution.
Using these advances, we can study structural distortions (strain and reconstruction) and intermixing as well as characterize the quality of the epitaxy of thin films. Using advances in EELS, it is now possible to study, through changes in the fine structure, electronic reconstructions, valence changes, and roughness up to atomic resolution at an interface. We will present recent result aiming at understanding the effect of structural distortions, electronic reconstruction and band bending on the presence of a two-dimensional electron gas in different systems. As a second example, studies of the origin of superconductivity in some hybrid engineered multilayer cuprate systems will be discussed. Finally, the effect of oxygen octahederal coupling and orbital reconstruction on the change of the magnetic easy-axis in some ferromagnetic manganite films will be outlined.
3:45 PM - MD3.11.02
Chiral Polar Vortex Arrays in Titanate Superlattices
Padraic Shafer 1,Anoop Rama Damodaran 2,Ajay Yadav 2,Chris Nelson 2,Zijian Hong 3,Long-Qing Chen 3,Lane Martin 2,Ramamoorthy Ramesh 2,Elke Arenholz 2
1 Advanced Light Source Lawrence Berkeley National Lab Berkeley United States,2 Materials Science amp; Engineering University of California Berkeley United States3 Materials Science amp; Engineering The Pennsylvania State University University Park United States1 Advanced Light Source Lawrence Berkeley National Lab Berkeley United States,2 Materials Science amp; Engineering University of California Berkeley United StatesShow Abstract
In ferroelectric films, the interplay of elastic strain, depolarizing fields, and polarization gradient energy contributions can create a variety of stable textures for the electric polarization. We have recently demonstrated  the existence of polar vortices in PbTiO3-SrTiO3 superlattices, in which the ferroelectric polarization of neighboring unit cells rotate about an in-plane axis to form a vortex-like configuration. The diameter of each vortex matches the thickness of an individual PbTiO3 sublayer, and the vortices form a regular array of alternating vortex/anti-vortex pairs with long-range order. This vortex state is distinguished from closure domains that occur in thicker films  because the polarization rotates continuously, more akin to wide magnetic domain walls than to traditional ferroelectric domains. Phase field modeling indicates that vortex arrays are the preferred state for a range of superlattice thicknesses that balances the polarization gradient energy against electrostatic and epitaxial constraints. The curling of ferroelectric polarization into vortices presents the intriguing possibility of additional symmetry breaking that could be exploited by coupling with other functional materials.
To address whether the polar vortex array possesses chirality, we employed resonant soft x-ray diffraction. Resonant soft x-ray diffraction from the regular array of vortex pairs in PbTiO3-SrTiO3 superlattices allows us to probe the spectroscopic signature of the ferroelectrically distorted local bonding environment of the titanium 3d valence states. X-ray energies near the titanium L3 resonance are sensitive to the anisotropic dielectric susceptibility  of the films, causing rotation in the polarization of the diffracted x-ray beam. This effect helps to explain the x-ray circular difference—the difference in diffracted intensity when reversing the circular polarization of the incoming x-rays—as a result of chirality in the polar vortex arrays. Chirality in polar vortex arrays opens new possibilities for controlling multiferroic materials via electric pathways.
1. A. K. Yadav et al., Nature, doi: 10.1038/nature16463 (in press).
2. Y. L. Tang et al., Science 348, 547 (2015).
3. V. E. Dmitrienko, Acta Cryst. A 39, 29 (1983); M. Gorkunov et al., Ferroelectrics 244, 19 (2000).
4:00 PM - MD3.11.03
Advanced Metrology of Epitaxial Oxide Thin Films on a Laboratory X-Ray Diffraction System
Michael Hawkridge 1
1 PANalytical Westborough United States,Show Abstract
Metal oxides offer in general a broader range of functional properties compared to conventional semiconductor thin film systems and have attracted much interest due to this. However, metal oxides can also be engineered at extremely short length scales to produce properties not observed in bulk material. This requires atomic-scale control of growth and therefore metrological methods that can provide accurate information at these length scales, such as x-ray diffraction (XRD).
Here, we present advanced diffraction techniques that can be used to measure metal oxide heterostructure films on a laboratory diffractometer. Various methods will be shown to improve signal to background ratios for symmetric rocking curves in various metal oxide heterostructures with layers as thin as a few monolayers. Rapid determination of strain, composition and mosaicity by ultrafast (sub-minute) reciprocal space mapping will be demonstrated for thicker (~100nm) films. Other novel methods will be presented for wafer mapping techniques and determination of nanostructure dimensions via low angle scattering methods.
4:15 PM - MD3.11.04
Multiscale Characterization of Chemical Ordering and Extended Defects in the Double Perovskite Oxide La2MnNiO6
Steven Spurgeon 1,Yingge Du 2,Timothy Droubay 1,Arun Devaraj 2,Xiahan Sang 3,Paolo Longo 5,Pengfei Yan 2,Paul Kotula 4,Vaithiyalingam Shutthanandan 2,James LeBeau 3,Chongmin Wang 2,Peter Sushko 1,Scott Chambers 1
1 Physical and Computational Sciences Directorate Pacific Northwest National Laboratory Richland United States,2 Environmental and Molecular Sciences Laboratory Pacific Northwest National Laboratory Richland United States3 Materials Science and Engineering North Carolina State University Raleigh United States5 Gatan Inc. Pleasanton United States4 Sandia National Laboratories Albuquerque United StatesShow Abstract
The development of advanced deposition techniques over the past decades has sparked a renaissance in the synthesis of oxide thin film materials. While it is now possible to fabricate oxides in almost limitless combinations, our ability to characterize these systems has lagged behind. In particular, there is a fundamental disconnect between highly local electron microscopy and macroscale properties measurements, resulting in oversimplified and incomplete structure-property models. Here we describe a multiscale characterization approach that combines aberration-corrected transmission electron microscopy with emerging oxide atom probe tomography to measure chemical ordering and extended defects in the double perovskite La2MnNiO6. We visualize the onset of cation ordering, as well as a three-dimensional network of parasitic secondary phases, which we describe in terms of first-principles calculations. We show that these phases act to disrupt cation superexchange, severely degrading macroscale magnetic properties. This array of experimental and theoretical techniques allows us to better understand the relationship between structure and magnetic properties, illustrating the need for a new approach to oxide thin film characterization.
4:30 PM - *MD3.11.05
Resonant Inelastic X-Ray Scattering on Oxide Heterostructures
Thorsten Schmitt 1
1 Paul Scherrer Institut Villigen PSI Switzerland,Show Abstract
Oxide heterostructures made of layered transition metal oxides are attracting great attention due to their extraordinary interface based materials properties not occurring in either of the constituents alone and their potential application for device design. Since the interfaces between the layers in oxide heterostructures greatly influence their functional behavior, it is of crucial importance to determine the electronic and magnetic properties of each layer as well as of the interfaces. In this talk we illustrate how Resonant Inelastic X-ray Scattering (RIXS) on thin rare-earth nickelate films and YBa2Cu3O7/La2/3Sr1/3MnO3 superlattices probes as a function of momentum transfer and energy excitations within charge-, orbital- and spin-degrees of freedom of these materials with bulk sensitivity.
The metal-insulator transitions (MIT) and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. We utilize x-ray absorption (XAS) and RIXS at the Ni L3-edge to investigate the complex electronic ground state properties of compressive and tensile strained NdNiO3 thin films. We clearly identify the coexistence of strong spectral contributions from both localized bound and delocalized continuum states. The continuum contributions are disentangled into charge transfer and electron-hole excitations. We argue that these distinct spectral signatures originate from the unique dominance of Ni 3d8 ground states along with holes in the formally full oxygen valence band (Ni3d8L), confirming suggestions that these materials do not obey a “conventional” positive charge-transfer picture, but instead exhibit a negative charge-transfer energy, with O 2p states extending across the Fermi level.
Ferromagnetic/superconducting heterostructures have a vast applications range in spintronics devices.
We investigated YBa2Cu3O7/La2/3Sr1/3MnO3 (YBCO/LSMO) superlattices with RIXS at Cu L3-edge in order to probe both orbital and magnetic excitations of the YBCO layers as a function of the LSMO layer thickness. Employing angular and polarization dependence of the Cu L3-edge XAS and RIXS signals we followed the electron charge transfer from LSMO to the YBCO layers. We observed suppression of superconductivity in [YBCO5/LSMOx]4 superlattices as a function of the thickness of the LSMO layers and an isotropic 3d9 orbital occupation of the Cu sites with contributions from both the YBCO planes and the chains for the sample with the thickest LSMO layer of 15 unit cells, [YBCO5/LSMO15]4. This entails that both charge transfer of the electrons from LSMO to YBCO and reconstruction of the holes between the planes and the chains are invoked in the depression of the superconducting Tc. The associated quenching of the paramagnon excitations in the YBCO layers highlights that the ground state of the YBCO layers in these heterostructures is distinctively different from bulk YBCO.
Ariando Ariando, National University of Singapore
Gertjan Koster, University of Twente
Ho-Nyung Lee, Oak Ridge National Laboratory
Yayoi Takamura, University of California, Davis
MD3.12: Expitaxial Design of Oxides
Friday AM, April 01, 2016
PCC West, 100 Level, Room 101 C
8:00 AM - *MD3.12.01
Surface Structures and Epitaxial Growth of SrTiO3(110)
Michele Riva 1,Stefan Gerhold 1,Michael Schmid 1,Ulrike Diebold 1
1 Inst. of Applied Physics, TU Wien Vienna Austria,Show Abstract
The surfaces and interfaces of SrTiO3 are still a mystery – despite their importance in in oxide electronics, catalysis, and energy-related applications, and many attempts to clarify their structural and other properties. The most often investigated SrTiO3(001) surface can be produced with a TiO2-layer and a (1x1) LEED pattern by ex-situ etching, but no satisfactory determination of the atomic-scale structure has been achieved. Typical in-UHV surface preparation procedures result in a bewildering variety of reconstructions that depend sensitively on sample treatment and history.
Our group has investigated the SrTiO3(110) surface. Cutting a SrTiO3 single crystal in this orientation results in a polar surface, with a mixed Sr-Ti-O termination. While this surface also forms a variety of reconstructions, one can reversibly and reproducibly switch back-and-forth between the various surface structures. This is achieved by evaporating Sr or Ti, and annealing in oxygen, i.e., by adjusting the chemical potential of the constituents. The most stable reconstruction has a (4x1) symmetry; it was argued it forms to compensate the polarity . This structure and its homologous (nx1) series consist of corner-sharing units of tetrahedrally-coordinated Ti atoms that form rings with various sizes . By varying the O chemical potential one can adjust defect clusters at domain boundaries . The SrTiO3(110)-(4x1) surface is remarkably inert in ultrahigh vacuum. Water does not adsorb , but the surface can be activated by depositing Ni  or NiO. Normally, oxygen vacancies are not present at the (4x1) surface. When produced via photon or electron irradiation, such vacancies migrate to the interface with the underlying SrTiO3 bulk. This results in the formation of an anisotropic 2DEG .
We have also explored growth phenomena using a PLD chamber interfaced with our UHV surface analysis setup. When using the SrTiO3(110)-(4x1) surface as a starting point we find that the (4x1) reconstruction floats to the top during homoepitaxial growth. When the deposited material is slightly off-stochiometric, formation of reconstructions with a different symmetry results in a deviation from layer-by-layer growth.
Supported by the Austrian Science Fund (Project F45, FOXSI) and the ERC Advanced Grant ‘OxideSurfaces’.
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8:30 AM - MD3.12.02
Synchrotron Studies on the Growth of Complex Oxides by Molecular Beam Epitaxy
Dillon Fong 1,I-Cheng Tung 1,Guangfu Luo 2,Dane Morgan 2,Hawoong Hong 1,John Freeland 1,Say Cook 3,Tassie Andersen 3
1 Argonne National Lab Lemont United States,2 University of Wisconsin Madison United States1 Argonne National Lab Lemont United States,3 Northwestern University Evanston United StatesShow Abstract
Functional materials based on complex oxides in thin film form offer new and exciting strategies for meeting many of our outstanding energy challenges through systematic control of layer sequencing, strain, etc. However, synthesis of such oxide films can be a major challenge even when utilizing reactive molecular-beam epitaxy (MBE), a powerful deposition technique that is often regarded to allow the construction of materials atomic plane by atomic plane. To understand the fundamental physics of oxide growth by reactive MBE, we present in-situ surface x-ray scattering results of the homoepitaxial growth of SrTiO3 thin films on (001)-oriented SrTiO3 substrates. By comparing sequential deposition (alternating Sr and Ti monolayer doses) with that of co-deposition of Sr and Ti, both in a background of oxygen pressure, we find drastically different growth pathways. While the co-deposition is marked by the usual roughening-smoothing transition associated with the completion of each layer, shuttered growth demonstrates strong islanding of the SrO monolayer followed by a smoothing transition during the TiO2 layer deposition. Using in-situ x-ray specular reflectivity and surface diffuse x-ray scattering during growth, an area detector simultaneously recorded both the specular x-ray scattering connected to out-of-plane atomic positions and the diffuse x-ray scattering associated with in-plane correlations. During growth of SrTiO3 by co-deposition, where the fluxes of Sr and Ti are roughly equal, the specular intensity at the half-order position is at a minimum while the diffuse intensity is at a maximum. This is consistent with a 2D island growth mode with unit-cell-high SrTiO3 islands that nucleate/grow on the terraces and coalesce before the next layer starts. For the case of sequential deposition, the scattering indicates that the SrO grows as islands and then restructures into SrTiO3 unit cells during the growth of the TiO2 to form an atomically flat layer. The reasons for this behavior will be discussed.
Work at Argonne, including the Advanced Photon, is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
8:45 AM - MD3.12.03
Polar Vortex Arrays in Ferroelectric/Paraelectric Superlattices
Christopher Nelson 1,Ajay Yadav 1,Shang-Lin Hsu 1,Zijian Hong 2,Anoop Rama Damodaran 1,Julia Mundy 1,Long-Qing Chen 2,Lane Martin 1,Ramamoorthy Ramesh 1
1 Materials Science and Engineering University of California Berkeley Berkeley United States,2 Materials Science and Engineering Pennsylvania State University University Park United StatesShow Abstract
In recent years, much attention has been given to complex spin topologies like skyrmions which emerge as a consequence of the electronic band structure and the interplay between spin and spin-orbit coupling in materials. In this work, we produce and study the formation of similarly complex topologies in the electrical analog: the electrical polarization. Ferroelectric materials exhibit a ground state electrical polarization with multiple degenerate directions. The topology of the ferroelectric polarization vector is highly tunable in response to the electrostatic and elastic boundary conditions. While ferroelectric materials form discrete domains which often orient into closed loops (flux closure), multiple theoretical studies have posited the formation of true nanoscale vortex structures under reduced dimensionality such as nanodots, nanowires, and thin films. Here we realize the formation of three-dimensional polar vortex arrays in a ferroelectric / paraelectric superlattice.
In this work a polar vortex array is produced in PbTiO3 / SrTiO3 superlattices with 10 unit cell layer thickness grown by Pulsed Laser Deposition. The structure consists of alternating vortex – antivortex (clockwise and anticlockwise) rotations with a 10nm periodicity along the film interface and in-phase alignment along the film normal. The atomic-scale structure of the polar vortex array is resolved from high-resolution scanning transmission microscopy measuring the cation non-centrosymmetric displacements and the long-range structure is measured by diffraction contrast TEM and X-Ray reciprocal space mapping. The vortices everywhere exhibit a nearly continuous polarization rotation and are not contained within a surrounding discrete flux closure domain structure. TEM, TEM electron diffraction, and X-Ray RSM all evidence long range in-plane and out-of-plane ordering of the vortices. Phase-field modeling corroborates the vortex-array as the low energy state for a small range of short-period superlattices wherein the large gradient energy from the vortex structure is counterbalanc