Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C17: Surfaces and Films of Complex Oxides |
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Sponsoring Units: DCMP Chair: Tiffany Kaspar, Pacific Northwest National Lab Room: LACC 306A |
Monday, March 5, 2018 2:30PM - 2:42PM |
C17.00001: Conductance variation in BaSnO3/LaInxGa1-xO3 polar interface Young Mo Kim, Juyeon Shin, Youjung Kim, Kookrin Char We have reported that polar perovskite oxide LaInO3 (LIO) and nonpolar perovskite oxide BaSnO3 (BSO) forms a interface with high conductance [1, 2]. To identify the role of LIO in the conductance enhancement, we tested another interface between BSO and LaGaO3 (LGO). Since LGO, a polar perovskite oxide like LIO, has its lattice constant of 3.9 Å, which is smaller than that of LIO, we expect to see the effect of the lattice constant change on the conductance enhancement. We first investigated epitaxial growth of LaInxGa1-xO3 (LIGO) on BaSnO3 by x-ray diffraction measurement and transmission electron microscopy. The conductance of the LIGO/BSO interface was also measured before and after LIGO deposition at various Ga ratio. Based on the structure and electronic properties of the interface, we will discuss the influence of strain on the conductance enhancement. |
Monday, March 5, 2018 2:42PM - 2:54PM |
C17.00002: Ferroelectric field effect transistor based on BaSnO3 Hahoon Lee, Kookrin Char In order to integrate the newly discovered high-mobility perovskite semiconductor BaSnO3 [1] with a ferroelectric perovskite, we have grown epitaxial ferroelectric Pb(Zr,Ti)O3 (PZT) on 4 % La-doped BaSnO3 (BLSO) and SrRuO3 (SRO) electrodes by pulsed laser deposition technique. X-ray diffraction measurement confirms that the PZT films were epitaxially grown and shows that the lattice constants of PZT depend on the Zr/(Zr+Ti) ratio in PZT. An all-epitaxial sandwich PZT ferroelectric capacitor structure was fabricated with BLSO and SRO electrodes, and the strain effect on the ferroelectric properties of PZT was investigated. The polarization-electric field (P-E) hysteresis curve is discussed from the viewpoint of the strain effect. Furthermore, a ferroelectric field effect transistor with a BaSnO3 channel layer was successfully fabricated, and carrier modulation of BaSnO3 by the ferroelectric polarization field was observed. The output characteristics, transfer characteristics and breakdown field of the ferroelectric transistor will be presented. |
Monday, March 5, 2018 2:54PM - 3:06PM |
C17.00003: Modulation doping in LaInO3/BaSnO3 polar interface Juyeon Shin, Young Mo Kim, Chulkwon Park, Kookrin Char A transparent perovskite oxide, BaSnO3 (BSO), has started to attract a great deal of attention due to its high room temperature mobility (μ) and oxygen stability. Among various heterostructures based on BaSnO3, the two dimensional electron gas-like state at the LaInO3(LIO)/Ba1-xLaxSnO3(BLSO) polar interface is most interesting because the interface exhibits a sheet conductance enhancement up to several orders of magnitude between two band insulators. Here we investigate the transport property of the modulated polar interface in LIO/BSO/BLSO heterostructures. Both the carrier density (ns) and the Hall mobility (μH) continually decrease while increasing the thickness of the BSO spacer layer (d) at the interface, indicating a changing electron density profile as a function of the thickness, which can be confirmed by self-consistent 1D Poisson-Schrodinger calculation. The sharp decrease of ns makes it difficult to see the effect of spacer layer in modulated structures due to simultaneous decrease of μ caused by Coulomb scattering from ionized donors. Hence we controlled the band bending continuously via field effect with a fixed spacer thickness, leading to the observation of the enhanced mobility (μFE) in the modulated heterostructures. |
Monday, March 5, 2018 3:06PM - 3:18PM |
C17.00004: LaInO3 /BaSnO3 Polar Interface on MgO Substrate Youjung Kim, Young Mo Kim, Juyeon Shin, Kookrin Char LaInO3 (LIO)/La-doped BaSnO3 (BLSO) interface shows two dimensional electron gas(2DEG)-like behavior with conductance enhancement of several orders of magnitude after growth of LIO layer on BLSO layer on STO substrates. [1] We investigated the LIO/BLSO interface on MgO substrates. For this experiment, we first confirmed the structure of interface on nonperovskite MgO substrates. Reciprocal Space Mapping result confirms well-formed LIO/BLSO interface. We measured electrical properties to see the effects of the substrate on the conducting interface. There was clear conductance enhancement after growth of LIO layer on the BLSO layer on MgO substrates. Especially we observed large conductance enhancement at LIO/BSO(undoped) interface. This result is different from the insulating property of such interface on STO substrates. Using this 2DEG-like interface with undoped BSO, we fabricated field effect devices. We will report on such FET performances on MgO substrates. |
Monday, March 5, 2018 3:18PM - 3:30PM |
C17.00005: Study of oxygen diffusion process in BaSnO3 and SrTiO3 films Sungyun Hong, Kookrin Char BaSnO3 has not only been recognized for its superb semiconducting properties, such as its high electron mobility when doped with La, but also for its excellent oxygen stability even at high temperatures. However, previous experiments on the oxygen stability of BaSnO3 films grown on SrTiO3 substrates have been plagued by the increased conductivity of SrTiO3 at high temperatures. In order to remove this problem, we have studied undoped and 1 % La-doped BaSnO3 films grown on MgO substrates, which do not exhibit change in conductivity at high temperatures. The resistance of the films was measured using four-point gold wire contacts, at various temperatures ranging from 500°C to 750°C, while switching the background atmosphere between oxygen and argon to induce oxygen diffusion. The results were used to calculate the oxygen diffusion constant of the BaSnO3 film. As a comparison we have also measured a SrTiO3 film grown on a MgO substrate, which showed quicker change of resistance than the BaSnO3 film. At the same time we observed that the resistance of the SrTiO3 film at high temperatures is higher than that of the BaSnO3 film, which can be attributed to the low mobility of carriers in SrTiO3. |
Monday, March 5, 2018 3:30PM - 3:42PM |
C17.00006: Influence of the ferroelectric quantum critical point on SrTiO3 interfaces Bill Atkinson, Patrick Lafleur, Amany Raslan
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Monday, March 5, 2018 3:42PM - 3:54PM |
C17.00007: Dual gate field effect transistor based on two dimensional electron gases at SrTiO3 surfaces Ludi Miao, Renzhong Du, Yuewei Yin, Qi Li We fabricate dual gate field effect transistors (FETs) based on two dimensional electron gas (2DEG) at SrTiO3 (STO) surfaces with high mobility as high as 20,000cm2V-1s-1. The channel conductivity is controlled by a side gate and a back gate. Both gates apply electric fields across STO crystalline, and are most efficient near ground state due to the quantum ferroelectricity of STO. Based on the dual-gate FET structure we made a performance-tunable logic NOT gate. The ON/OFF of the channel is switch by side gate logic input, whereas the switching performance is tunable by the back gate. The back gate voltage window depends on the power supply voltage of the device. On one hand, the window is wider at a higher power supply voltage. On the other hand, by carefull tuning the back voltage, the device can work with good performance at a lower power supply voltage. Our results provide an general approach to energy saving as well as decreasing Joule heat for cryogenic quantum computing. |
Monday, March 5, 2018 3:54PM - 4:06PM |
C17.00008: Surface Lattice, Orbital and Spin Reconstructions and Couplings in Hexagonal Multiferroics Shiqing Deng, Shaobo Cheng, Changsong Xu, Binghui Ge, Xuefeng Sun, Rong Yu, Duan Wenhui, Jing Zhu Delicate surfaces create an intriguing and challenging research subject because of embedded novel physical phenomena and exotic properties. Broken symmetry when it is introduced to original ferroic orders in multiferroics can pose exciting challenges for understanding the reconstructed couplings. Here, we report a peculiar surface state and reconfigurable functionalities within a representative hexagonal multiferroics, YMnO3. The reconstructed spin, orbital and lattice couplings are achieved by changes in O 2p and Y 4d orbital (p-d) hybridization, which is atomically revealed utilizing state-of-the-art aberration-corrected (S)TEM. DFT calculations further verify the key roles of specific in-plane oxygens in modulating electronic structures and reconstructions, which should be regarded as an atomic multiferroic element. Meanwhile, the controversial origin of improper ferroelectricity can also be clearly understood based on its absence in defective unitcells. Our findings advance understandings of surface science in strongly correlated oxides, and provide new insights into design and implementation of surface devices by simply controlling the oxygen stoichiometry. |
Monday, March 5, 2018 4:06PM - 4:18PM |
C17.00009: MBE Growth of BiFeO3 in Bi-oxides Adsorption Regimes Hawoong Hong, Xinyue Fang, Tassie Andersen, Say Cook, Dillon Fong, Tai-Chang Chiang Growing phase pure BFO films by MBE, larger Bi flux is provided due to its volatility. With oxidizing agents, Fe flux will determine the speed of the deposition and excess in bismuth oxide phases desorbed from the film. The phase purity is supposed to be controlled by this desorption. However, stoichiometric BFO was obtained even at temperature lower than suggested narrow region of phase diagram. We investigated growth of BFO under bismuth oxide adsorption regime. The cumulative deposition was madeup to 40 unit cells. Two separate schemes are used. First, in each deposition step, the sample was pre- and post-soaked with Bi-O for 30 sec. In situ x-ray diffraction measurements along (00L) show good interference fringes which match with the film thickness. As the deposition proceeded to thicker films, additional broad feature appeared around L = 0.5. This may indicate a few layers of β-Bi2O3. In the second scheme, pre- or postsoaking was skipped. Sharp interference fringes develop with time. From 7 u.c. thick films, there is a sign of the second phase. The irregularity of the interference fringes are more visible for 20 and 40 u.c. unit cell. This second phase may be a super-tetragonal phase of BFO with c/a = 1.2. |
Monday, March 5, 2018 4:18PM - 4:30PM |
C17.00010: Ultra-fast carrier dynamics of La0.7Sr0.3MnO3 thin films Saeed Yousefi Sarraf, Guerau Cabrera, Robbyn Trappen, Navid Mottaghi, Shalini Kumari, Alan Bristow, Mikel Holcomb Perovskite oxides (ABO3) are a promising class of transition metal oxides with a diverse range of properties such as multiferroicity and superconductivity. Many studies have been done on their structural and magnetic properties. Though, La0.7Sr0.3MnO3 (LSMO) is a semi-metal perovskite oxide, when grown with nanometer scale thicknesses, a band gap will form which can be close to the visible range. While this gap makes LSMO a potential choice for photovoltaic applications, there has been a limited understanding about the carrier dynamics of this oxide. LSMO thin films were fabricated by pulsed laser deposition on (100) SrTiO3 single crystal substrates. A degenerate pump probe setup with a femtosecond laser at 800nm was used to study the ultra-fast free carrier dynamics of LSMO thin films. Subpicosecond, subnanosecond and nanosecond dynamics are observed, which represent Auger, radiative and SRH recombination respectively. Moreover, in ultra-fast and fast regimes, oscillations were observed which can be due to phonons in the thin film or the substrate. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C17.00011: Temperature Dependence of the Surface Structure of Sr3(Ru1-xMnx)2O7 with x = 0.25 Yifan Yang, Lingyi Xing, Pablo Rivero, William Shelton, Rongying Jin, E Plummer The properties of the surface of Mn-doped Sr3(Ru1-xMnx)2O7 are fundamentally different from the bulk: The surface is conducting (insulating) while the bulk is insulating (conducting). Furthermore, the surface has enhanced rotation and tilt that is removed by x = 0.16 Mn doping. Further studies show a surface structural transition that is driven by the bulk magnetic ordering. Here we report the surface properties of the x = 0.25 sample, where both structural distortion and magnetic ordering no longer exist in bulk. Low Energy Electron Diffraction show that the surface remains as a reconstructed structure due to the octahedral rotation. The temperature dependence of the electronic and structural properties will be discussed and compared to recent theoretical calculations for the ground state. |
Monday, March 5, 2018 4:42PM - 4:54PM |
C17.00012: STM Observations of Lanthanum Vanadate Phase Transition Anna Binion, Riju Banerjee, Lavish Pabbi, Bill Dusch, Matthew Brahlek, Roman Engel-Herbert, Eric Hudson Atomic scale studies of phase transitions can offer interesting insight into the fundamental nature of a material’s properties and structure. Lanthanum Vanadate (LaVO3) undergoes a structural phase transition around 139 K from an orthorhombic to a monoclinic structure. Here we will present results from STM investigations of thin (25 nm) films of lanthanum vanadate on LSAT substrates. Temperature dependent topographic and spectroscopic investigations of the surface of the material as it undergoes this structural transition reveal the onset of nanometer scale surface corrugations, and enable us to study the impact of atomic scale strain variations on the local electronic properties of materials. |
Monday, March 5, 2018 4:54PM - 5:06PM |
C17.00013: High Mobility Two-Dimensional Electron Gases at Non-Polar Interfaces PINGCHUN WU, Ying-Hao Chu The discovery of two-dimensional electron gases (2DEGs) at the interface of LaAlO3/SrTiO3 (LAO/STO) heterostructure has advanced the opportunity for oxide electronics. So far, the creation of 2DEGs at oxide interface still remains a huge debate. There are three main mechanisms that have been proposed: electronic reconstruction due to the polar discontinuity, accumulation of oxygen vacancy, and intermixing at the interface. These theories have earned wide recognition but arguments still remain unsettled. In this work, we create 2DEGs at non-polar interfaces by depositing strontium zirconate (SrZrO3), calcium titante (CaTiO3) and STO on STO substrate. The electron mobilities of the samples are all over 20,000 cm2V-1s-1 at 4 K. X-ray photoemission spectroscopy is adopted to reveal the band structure at the interface. Scanning transmission electron microscopy and electron energy-loss spectroscopy are used to evidence the origin of the 2DEGs. This work has excluded the claim of electronic reconstruction from polar discontinuity by creating 2DEGs at non-polar interface. Further, the notion of intermixing is also inconsistent since 2DEGs have been observed at homoepitaxial STO/STO interface. This work advanced the pathway to explore the origin of 2DEGs at oxide interfaces. |
Monday, March 5, 2018 5:06PM - 5:18PM |
C17.00014: Multiband Conduction at the PrAlO3/SrTiO3 Interface Shirin Mozaffari, Rik Dey, Derrick Morin, Gregorio Ponti, John Markert We have measured a set of magneto-transport data for the interface between a SrTiO3 substrate and 15 monolayers of PrAlO3 synthesized at different oxygen pressures PO2 during growth. For the interfaces grown at low PO2, Hall effect data suggest that the transport is dominated by one type of carrier. For these samples, the out-of-plane and in-plane magnetoresistances are positive and negative, respectively (for the measured temperature range of 2 K < T < 100 K). For interfaces grown at high PO2, at low and high temperatures, T < 5 K and T > 50 K, Hall data could be described by a single channel of electron carriers with a low mobility. At intermediate temperatures 10 K < T < 40 K, the Hall data becomes noticeably nonlinear, with positive out-of-plane and in-plane magnetoresistance. The nonlinear Hall resistance can be described by a two-band model with different electron charge carrier types: one band with low mobility and a high carrier density, and another band with high mobility and a low carrier density. |
Monday, March 5, 2018 5:18PM - 5:30PM |
C17.00015: Direct Imaging of Sketched Conductive Nanostructures at the LaAlO3/SrTiO3 Interface Zhanzhi Jiang, Xiaoyu Wu, Hyungwoo Lee, Jungwoo Lee, Jianan Li, Guanglei Cheng, Chang-Beom Eom, Jeremy Levy, Keji Lai Nanoscale control of the quasi-two-dimensional electron gas at the LaAlO3/SrTiO3(LAO/STO) |
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