Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session E47: Surfaces and Interfaces of Complex Oxides |
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Sponsoring Units: DCMP Room: 312 |
Tuesday, March 15, 2016 8:00AM - 8:12AM |
E47.00001: Controlling the electronic properties of Er$_{\mathrm{2}}$O$_{\mathrm{3}}$ thin film by oxygen vacancies Aaron Wang, Andrew Yost, Vivek Jain, Qilin Dai, Jinke Tang, TeYu Chien With a high dielectric constant and wide bandgap, Er$_{\mathrm{2}}$O$_{\mathrm{3}}$ is suitable for applications in electronic and optical devices. It is known that in many oxide materials, oxygen vacancy concentration plays a decisive role in engineering the properties of the oxides. To address the oxygen vacancy concentration effects on the properties of Er$_{\mathrm{2}}$O$_{\mathrm{3}}$, here we present Scanning Tunneling Microscopy and Spectroscopy (STM/S) and X-Ray Diffraction (XRD) studies of the Er$_{\mathrm{2}}$O$_{\mathrm{3}}$ thin film made by Pulsed Laser Deposition (PLD). XRD shows Er$_{\mathrm{2}}$O$_{\mathrm{3}}$ thin film deposited at 700$^{\mathrm{o}}$C in high vacuum (HV) (sample 1) has broader peaks compared to that of the one deposited at room temperature (RT) in HV followed by 400$^{\mathrm{o}}$C annealing in air (sample 2). This indicates that, for sample 1, the loss of long range periodicity in crystal structure is mainly due to oxygen vacancies. Moreover, a relatively rough surface with 2 to 5 nm nanoclusters were observed in sample 1 by STM; while sample 2 is too resistive for STM measurements. In addition, Scanning Tunneling Spectroscopy (STS) analysis for sample 1 revealed the bandgap as well as features in the conduction band which may be related to the oxygen vacancies. [Preview Abstract] |
Tuesday, March 15, 2016 8:12AM - 8:24AM |
E47.00002: \textbf{Effect of LaInO}$_{\mathbf{3}}$\textbf{ layer thickness on the conductance enhancement at the LaInO}$_{\mathbf{3}}$\textbf{/Ba}$_{\mathbf{1-x}}$\textbf{La}$_{\mathbf{x}}$\textbf{SnO}$_{\mathbf{3}}$\textbf{ polar interface} Chulkwon Park, Useong Kim, Juyeon Shin, Young Mo Kim, Youjung Kim, Kookrin Char We have recently reported on the high performance thin film transistors based on La-doped BaSnO$_{3}$ (BLSO), which has high electron mobility and thermal stability, with LaInO$_{3}$ (LIO) gate dielectric [1, 2]. During the course of this research we have observed 10$^{4}$ times enhancement of the sheet conductance of BLSO channel layer, which implies formation of 2DEG, after the interface formation with LIO. Detailed further study revealed that the La concentration in the BLSO channel layer critically affects the enhancement of sheet conductance on the LIO/BSO interface [3]. We investigated the LIO thickness dependence on the conductance of LIO/BSO interface and will discuss the origin of this phenomenon in terms of the intrinsic interface polarization in the LIO layer. This understanding is the first step towards the device application of the perovskite oxide heterostructures and may potentially lead to new interface states. [1] H. J. Kim, U. Kim \textit{et al.}, Appl. Phys. Express \textbf{5}, 061102 (2012). [2] U. Kim \textit{et al.}, APL Mat. \textbf{3}, 036101 (2015). [3] U. Kim \textit{et al}., preprint. [Preview Abstract] |
Tuesday, March 15, 2016 8:24AM - 8:36AM |
E47.00003: Optical properties of CuFeO$_{2}$ and CuFe$_{1-x}$Ga$_{x}$O$_{2} \quad_{\, }$highly epitaxial thin films A. L. Cabrera, R. A. Wheatley, S. Rojas, T. Joshi, P. Borisov, D. Lederman Delafossite thin films of 20 and 200 nm CuFeO$_{2}$ and 52 nm CuFe$_{1-x}$Ga$_{x}$O$_{2\, }$were grown by Pulsed Laser Deposition (PLD) on Al$_{2}$O$_{3}$ (0001) substrates. High epitaxial quality of the films was verified by the techniques of X-Ray Diffraction and Raman spectroscopy.. Optical transmission and reflection spectroscopies were performed on the films under vacuum and in CO$_{2}$ controlled atmosphere, respectively. Tauc plots based on transmission data yielded direct optical band gap at 2.4 eV, 2.8eV and 3.1eV and indirect band gap at 0.9 eV and 1.3 eV for CuFe$_{1-x}$Ga$_{x}$O$_{2}$ (x$=$0.25) and the direct band gap at 1.9eV, 3.1eV and the indirect band gap at 1.1eV for the CuFeO$_{2\, }$films. [Preview Abstract] |
Tuesday, March 15, 2016 8:36AM - 8:48AM |
E47.00004: Comparative study of water and carbon dioxide adsorption on CuFeO$_{\mathrm{2}}$ and CuFe$_{\mathrm{1-x}}$Ga$_{\mathrm{x}}$O$_{\mathrm{2\thinspace }}$highly epitaxial thin films S. Rojas, T. Joshi, P. Borisov, D. Lederman, A. L. Cabrera Thermal programmed desorption (TPD) of CO$_{\mathrm{2}}$ and H$_{\mathrm{2}}$O from a 200 nm thick CuFeO$_{\mathrm{2}}$ and 52 nm thick CuFe$_{\mathrm{1-x}}$Ga$_{\mathrm{x}}$O$_{\mathrm{2\thinspace }}$delafossite surfaces was performed in a Ultra-high vacuum (UHV) chamber. The thin films with epitaxial quality were grown by Pulsed Laser Deposition (PLD) on Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ (0001) substrates . The adsorption / desorption of CO2 and H2O process was also monitored with X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). Our results revealed that carbon dioxide is preferentially chemisorbed by CuFe$_{\mathrm{1-x}}$Ga$_{\mathrm{x}}$O$_{\mathrm{2}}$ over water and we observed the opposite behavior with regard to chemisorption of CO$_{\mathrm{2}}$ and H$_{\mathrm{2}}$O over CuFeO$_{\mathrm{2}}$. Hydroxyls and metal carbonates were formed on the surface due to the chemisorption of H$_{\mathrm{2}}$O and CO$_{\mathrm{2}}$. Arrhenius plots for CO$_{\mathrm{2}}$ and H$_{\mathrm{2}}$O desorption were done and activation energy for desorption were obtained. [Preview Abstract] |
Tuesday, March 15, 2016 8:48AM - 9:00AM |
E47.00005: Crystallographic orientation dependence of electronic properties at LaAlO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$ interfaces Neil Campbell, Mark Rzchowski, Sangwoo Ryu, Hyungwoo Lee, Chang-Beom Eom The two-dimensional electron liquid (2DEL) formed at the interface between perovskite oxides LaAlO$_{\mathrm{3}}$ and SrTiO$_{\mathrm{3}}$ has been found to show many interesting properties, including ones that depend on the electronic and structural properties of the interface. Most research has investigated the (001) orientation, where the crystal structure is square in the plane. Changing the crystallographic orientation can change the polarization mismatch and shift energies and occupations of the orbitals near the Fermi surface. This affects the 2DEL in many ways, particularly by changing the spatial extent and profile of the charge density. The interplay between interlayer hopping integrals and orbital energy shifts make the 2DELs in different orientations behave differently in response to gating. The interface plane defines a symmetry-breaking direction for the $d$ orbitals and electrostatic potential, causing splitting of Ti $d$ bands, affecting band occupation and mass near the interface. Heterostructures grown on (111) SrTiO$_{\mathrm{3}}$, have similar Ti d orbital energies since they all have lobes crossing the interface, while in (001), the d$_{\mathrm{xy}}$, and d$_{\mathrm{x2-y2}}$ orbitals do not have such lobes lobes. We present temperature-dependent Hall and magnetotransport data probing these orientational differences. [Preview Abstract] |
Tuesday, March 15, 2016 9:00AM - 9:12AM |
E47.00006: Thickness Dependence of Electrical and Structural Properties of Tensile Strained Calcium Manganese Oxide Thin Films Cacie Hart, Zoey Warecki, Adeel Chaudhry, Natalie Ferrone, David Houston, Bridget Lawson, Grace Yong, Rajeswari Kolagani We have investigated the properties of CaMnO$_{3-\delta}$ thin films epitaxially grown by pulsed laser deposition on lattice mismatched substrates, (100)LaAlO$_{3}$ and (100)SrTiO$_{3}$ , leading to a tensile strain of $\sim$4$\%$ and 1.5$\%$ respectively. For our films these substrates, thickness dependence of the properties is characteristically different from what has been previously observed in thin films of hole-doped manganites. We observe that the resistivity decreases significantly as the film thickness decreases. The decrease in resistivity is more pronounced in the films on (100)SrTiO$_{3}$ with the larger lattice mismatch, the resistivity of the thinnest films being about 3 orders of magnitude lower than the of bulk CaMnO$_{3}$. Thickness dependence of the lattice constants also show deviations from the behavior expected from strain relaxation. These results suggest a coupling between tensile strain and oxygen deficiency consistent with predictions from models based on density functional theory calculations. Our results are relevant for potential catalytic applications of CaMnO$_{3-\delta}$ thin films. [Preview Abstract] |
Tuesday, March 15, 2016 9:12AM - 9:24AM |
E47.00007: Role of lanthanum aluminate composition in interface formation with strontium titatnate Abdul Rumaiz, Conan Weiland, George Sterbinsky, C. Stephen Hellberg, Joseph Woicik, Shaobo Zhu, Darrell Schlom While LaAlO$_3$ (LAO) and SrTiO$_3$ (STO) are both insulators, the interface between the two materials is conductive when the LAO is above a critical thickness and the STO is TiO$_2$-terminated; the origin of this conductivity is widely debated. It has also been demonstrated that the conductive interface depends on the composition of the LAO film: conductive interfaces were only found to occur for La:Al $<$ 0.97. Hard x-ray photoelectron spectroscopy has been performed on ten unit cell thick Al-rich (La:Al = 0.9), stoichiometric (La:Al = 1), and La-rich (La:Al = 1.1) LAO films deposited on STO to elucidate the role of LAO composition in the interfacial structure. A small built-in potential was observed in the Al-rich film compared to the stoichiometric and La-rich films, as determined from valence-band broadening. The stoichiometric and La-rich films were also found to have La-enrichment at the interface, while the Al-rich film did not. These results combined with first-principles calculations demonstrate the role that defects in the LAO film play in the LAO/STO interfacial structure. [Preview Abstract] |
Tuesday, March 15, 2016 9:24AM - 9:36AM |
E47.00008: Metallic interface in non-SrTiO$_3$ based titanate superlattice Xiaoran Liu, D. Choudhury, Yanwei Cao, M. Kareev, S. Middey, J. Chakhalian We report on the fabrication of all perovskite Mott insulator/band insulator YTiO$_3$/CaTiO$_3$ superlattices by pulsed laser deposition. The combination of {\it{in-situ}} reflection high energy electron diffraction, X-ray diffraction and X-ray reflectivity confirms the high quality of the films grown in a layer-by-layer mode. Electrical transport measurements reveal that a non-SrTiO$_3$ based two-dimensional electron gas system has formed at the YTiO$_3$/CaTiO$_3$ interface. These studies offer another route in the pursuit of complex oxide two-dimensional electron gas systems which allows to obtain greater insights into the exotic many-body phenomena at such interfaces. [Preview Abstract] |
Tuesday, March 15, 2016 9:36AM - 9:48AM |
E47.00009: The Effect of Polarization on Local Electronic Structure in Ferroelectric Nano-Domains in BaTiO$_{3}$ Erie Morales, Carlos Perez, Dawn Bonnell Novel ferroelectric BaTiO$_{3}$ applications ranging from sensors to nanogenerators require a detailed understanding of atomic interactions at surfaces. Single crystals provide a platform that allows the exploitation of surface physical and chemical properties that can be readily transferred to other ABO$_{3}$ perovskites. The processes that result in the atomic and electronic structures of surfaces in tandem with polarization of domains are necessary steps towards understanding BaTiO$_{3}$. Here we treat BaTiO$_{3}$ surface using sputtering-annealing cycles that yield the (6x1) reconstruction. We demonstrate that it is possible to pole a thin BaTiO$_{3}$ single crystal in ultra high vacuum using scanning tunneling microscopy (STM). We determine that we can prepare BaTiO$_{3}$ using \textit{in-situ} annealing that allows us to control the size of poled region to 40nm. We pole in constant-current mode in STM by applying a bias of less than 10 V between tip and sample for 100ms. STM and scanning tunneling spectroscopy characterization allow us to map topography and local density of states, respectively. For a given unique pulse, the poled domains show a fluctuating electronic occupation of conduction bands and shifting of valence band. We will also discuss the effect of polarization on molecular adsorption. [Preview Abstract] |
Tuesday, March 15, 2016 9:48AM - 10:00AM |
E47.00010: Effect of the undoped BaSnO$_{3}$ space layer on the high mobility LaInO$_{3}$/Ba$_{1-x}$La$_{x}$SnO$_{3}$ polar interface Juyeon Shin, Chulkwon Park, Young Mo Kim, Youjung Kim, Kookrin Char We have recently reported on the sheet conductance enhancement at the interface between two band insulators: LaInO$_{3}$ (LIO) and BaSnO$_{3}$ (BSO) [1, 2]. The advantages of the two-dimensional electron gas-like (2DEG) state at the LIO/Ba$_{1-x}$La$_{x}$SnO$_{3}$ (BLSO) polar interface are its stability, the controllability of the local carrier concentration, and the high electron mobility of BLSO [3]. The origin of enhanced conductance at the interface is still under investigation, but the doping level of BSO is a critical parameter for the polar charge contribution. [2] We have investigated a new structure using an undoped BSO space layer at the LIO/BLSO interface. On one hand, this new structure will improve the mobility of the LIO/BLSO structure by reducing La impurity scattering. On the other hand, through this new structure we can answer the issues related with La diffusion at the LIO/BLSO polar interface and trace the origin of the 2DEG-like charge. This new modified structure of the LIO/BSO polar interface looks promising for higher electron mobility devices. [1] U. Kim \textit{et al}., APL Mat. \textbf{3}, 036101 (2015). [2] U. Kim \textit{et al}., preprint. [3] H. J. Kim, U. Kim \textit{et al.}, Appl. Phys. Express \textbf{5}, 061102 (2012). [Preview Abstract] |
Tuesday, March 15, 2016 10:00AM - 10:12AM |
E47.00011: Electronic Structure of Epitaxial Thin Films of the Transparent Conducting Oxide La:BaSnO$_3$ Measured By In-Situ Angle-Resolved Photoemission Spectroscopy Edward Lochocki, Hanjong Paik, Masaki Uchida, Darrell Schlom, Kyle Shen Lanthanum-doped barium stannate (La:BaSnO$_3$) is a transparent conducting oxide where single crystals have exhibited unusually high mobility and oxygen stability. Here we present in-situ angle-resolved photoemission (ARPES) measurements of La:BaSnO$_3$ epitaxial films that were co-deposited onto lattice-matched rare-earth scandate substrates by molecular-beam epitaxy (MBE). Density functional theory (DFT) calculations agree well with the observed valence bands and predict a parabolic conduction band. However, the features observed near the Fermi energy ($E_F$) are non-dispersive yet localized in momentum space. This unusual appearance may be the result of quasi-localized charge carriers or out-of-plane momentum broadening. Over long measurement periods, we also observe changes to the valence band and near-$E_F$ feature that bear a strong resemblance to the beam-induced two-dimensional electron gases previously reported in SrTiO$_3$ and KTaO$_3$. The origin of these unexpected phenomena and their relationship to the structural and transport properties of these films will be discussed. [Preview Abstract] |
Tuesday, March 15, 2016 10:12AM - 10:24AM |
E47.00012: Band gap formation in La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) thin films measured by reflectivity/absorption and ultrafast spectroscopy Guerau Cabrera, Robbyn Trappen, Ying-Hao Chu, Mikel Holcomb Thin film La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) is a prime candidate for highly spin-polarized magnetic-tunnel-junction memories. Due to its magnetic properties, it is also a good candidate for applications utilizing electrical control of magnetism when grown adjacent to a ferroelectric layer such as Pb(Zr/Ti)O$_{3}$ (PZT). Recently, Wu and others have seen the emergence of a band gap (about 1eV) in LSMO thin films, when grown adjacent to PZT. Currently, it is understood that LSMO is a half-metal, with a pseudo-gap due to a low desity of states (DOS) near the Fermi level. The transition from pseudo-gap to band gap is not yet fully understood. It is therefore our aim to investigate the formation of this band gap through optical reflectivity/absorption and ultrafast carrier dynamics for a variety of thicknesses ranging from a few nanometers to thicker films (about 100 nm). [Preview Abstract] |
Tuesday, March 15, 2016 10:24AM - 10:36AM |
E47.00013: Interfacial stability of ultrathin film magnetite (Fe$_{3}$O$_{4})$ in ozone assisted MBE deposition Hawoong Hong, Jongjin Kim, Xinyue Fang, Seungbum Hong, Tai C. Chiang Iron oxide films were grown on sapphire (0001) surfaces using nominally 100{\%} ozone. Both of monolayer-wise deposition and continuous deposition were tried to find the structures of the films at the start of the film formation. The studies utilized x-ray scattering with synchrotron radiation from the Advanced Photon Source. Consideration of substrate and film structures predicts Fe$_{2}$O$_{3}$(0001) (hematite) film formation. However, in both of the deposition modes, the initial films formed as magnetite Fe$_{3}$O$_{4}$(111). As the film growth progresses, hematite (Fe$_{2}$O$_{3}$(0001)) appears. At the later stage, the magnetite disappears and the whole film turned to hematite. Real time and static x-ray diffraction results show the same result. Possibility of the oxidation limited transformation should be excluded. Other possible cause of this reverse stability will be discussed. [Preview Abstract] |
Tuesday, March 15, 2016 10:36AM - 10:48AM |
E47.00014: Effects of strain, electric field and correlations on the resistance noise in epitaxial NdNiO$_3$ films G. Sambandamurthy, Ali Alsaqqa, Sujay Singh, Srimanta Middey, Michael Kareev, Jak Chakhalian Rare earth nickelates are strongly correlated materials that exhibit metal-insulator and Neel transitions as a function of temperature. The nature of the transport mechanisms in individual phases (paramagnetic metal, paramagnetic insulator and antiferromagnetic insulator) is an active area of research. We use low frequency (1 mHz $<$ f $<$ 10 Hz) resistance noise spectroscopy to probe the phases and the transitions between them in ultrathin epitaxial films of NdNiO$_3$ grown on substrates that introduce different strains. While the transport behavior and the transition temperatures are greatly affected by the strain, the noise behavior across the transitions is found to be similar. In the low temperature antiferromagnetic phase, an intriguing switching between two distinct grounds states is observed pointing to a subtle competition in the energy landscape. The noise magnitude as a function of electric field in submicron devices will also be presented. [Preview Abstract] |
Tuesday, March 15, 2016 10:48AM - 11:00AM |
E47.00015: Quantitative measurements and modeling of electronic and atomic surface structure in epitaxial LaNiO$_{3}$ thin films by ARPES, LEED-I(V), and DFT$+$DMFT Jacob Ruf, Elizabeth Nowadnick, Hyowon Park, Philip King, Andrew Millis, Darrell Schlom, Kyle Shen Careful exploration of the phase space available for artificially engineering emergent electronic properties in epitaxial thin films and superlattices of transition-metal oxides requires close feedback between materials synthesis, experimental characterization of both electronic and atomic structures, and modeling based on advanced computational methods. Here we apply this general strategy to the perovskite rare-earth nickelate LaNiO$_{3}$, using molecular-beam epitaxy to synthesize thin films, performing \textit{in situ }angle-resolved photoemission spectroscopy (ARPES) and low-energy electron diffraction (LEED) measurements, and comparing our results with the predictions of density functional theory plus dynamical mean-field theory (DFT$+$DMFT). Our study establishes LaNiO$_{3}$ as a moderately correlated metal in which the quasiparticle mass enhancement can be modeled with quantitative accuracy by DFT$+$DMFT. Finally, in view of efforts to produce $e_{g}$ orbital polarization in nickelate heterostructures as a means of mimicking single-band cuprate-like physics, we discuss the extent to which our ARPES and LEED results suggest that such effects are intrinsically present at film surfaces due to the existence of polar distortions, as reported by coherent Bragg rod analysis of surface x-ray diffraction. [Preview Abstract] |
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