Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P45: Complex Oxide Surfaces, Interfaces, and Thin Films II |
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Sponsoring Units: DCMP Chair: Mohammad Saghayezhian, Louisiana State University Room: BCEC 211 |
Wednesday, March 6, 2019 2:30PM - 2:42PM |
P45.00001: Operando bi-modal studies of complex oxides growth with RHEED and surface x-ray diffraction Hawoong Hong, Xinyue Fang, Meng-Kai Lin, Tai-Chang Chiang, Friederike Wrobel, Anand Bhattacharya An oxide MBE chamber was developed for simultaneous use of RHEED and surface x-ray diffraction at the same time. It is mounted and coupled to a 6-circle diffractometer. X-ray reflection intensity measurement at one point in reciprocal space is similar to RHEED intensity oscillation measurement. The relationship between two methods has been reported for homo-epitaxial complex oxide growth [1]. With large photon flux at the Advanced Photon Source, the x-ray intensity measurement could be extended to a real-time collection of data on a large swath of a line scan utilizing multi-angle fly scans [2]. Rapid acquisition in the volume around x-ray diffraction rods and RHEED measurements were obtained simultaneously during the growth. This bimodal study was made during La2CuO4 (001) film growth on SrLaAlO4 (001) substrates with MBE techniques. Discussed will be the relation between two different observations and future impacts from utilizing this bimodal method. |
Wednesday, March 6, 2019 2:42PM - 2:54PM |
P45.00002: Suppression of Bi disproportionation in minimally electron doped BaBiO3 epitaxial thin films Hui Cao BaBiO3 is a semiconductor due to three dimension charge density wave (CDW), and it can become a superconductor, with a maximum Tc of 30K via holes doping. We have studied the three-dimensional charge-density-wave in high quality BaBiO3 and electron doped BaBiO3 single crystal thin films by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, Raman shift and ellipsometry technique.The electron doping is achieved by very small amount of oxygen vacancies purposely induced by vacuum annealing. Our results have found that the electron doping can remove bismuth disproportionation (2Bi4+→Bi3+ + Bi5+) but has less effect to the insulating gap. Different from the hole-doping side, the amount of electron needed to suppress the bismuth disproportionation is extremely small. Our study provides new insights to the intricate correlation between CDW and the hybridization between oxygen 2p and Bi 6s orbitals. |
Wednesday, March 6, 2019 2:54PM - 3:06PM |
P45.00003: Polarization switch on h-LuFeO3 multiferroic Petrucio Barrozo da Silva, Bhagwati Prasad, Vishal Thakare, Sujit Das, Ramamoorthy Ramesh The properties of improper ferroelectrics are knowing to be very different from properties present in the proper ferroelectrics. However, the switching behavior of the electric polarization and the dynamics of the ferroelectric domain walls in the multiferroics with improper ferroelectricity don't have been yet reported. In this work, we study the ferroelectric properties of hexagonal LuFeO3 (h-LFO). This structure was firstly obtained in 2004 [1], but its properties are yet not all understood. The epitaxial thin films of h-LFO on YSZ(111) was produced by pulsed laser deposition. The switch of polarization was studied in the screen of Ishibashi-Orihara model [2]. We have observed that the electrical coercive field in improper ferroelectric (h-LFO) grow very fast with the frequency if compared with proper ferroelectric (e.g. PbTiO3 or BiFeO3). In this presentation, we also will discuss mechanisms to reduce the electrical coercive field as well as how to reduce the dependence of the electrical coercive field with the frequency. |
Wednesday, March 6, 2019 3:06PM - 3:18PM |
P45.00004: Superconductivity in doped SrTiO3 Luca Galletti, Kaveh Ahadi, Yuntian Li, Susanne Stemmer We report on the transport properties of a series of doped 250-nm-thick SrTiO3 films, grown by molecular beam epitaxy on undoped (001) SrTiO3 substrates. In particular, we demonstrate anomalies in the superconducting properties. A systematic study of the critical temperatures and fields as a function of the carrier density and type of doping atom reveal deviations from BCS behavior and points towards the role of the specific doping atom. Moreover, the transport properties of the normal state show peaks in the transverse resistance, which indicates an electron nematic phase above the superconducting transition. We discuss the mechanisms of superconductivity of SrTiO3 thin films. |
Wednesday, March 6, 2019 3:18PM - 3:30PM |
P45.00005: Comparative Study of Surface Structural and Physical Properties of Sr3T2O7 (T = Mn, Ru) Yifan Yang, Lingyi Xing, Mohammad Saghayezhian, Rongying Jin, E Ward Plummer Double-layered Ruddlesden-Popper oxides are known to exhibit a strong correlation between octahedral distortion and physical properties. Using low-energy electron diffraction (LEED) and high-resolution electron energy loss spectroscopy (HREELS), we have investigated the surface structural and physical properties of Sr3T2O7 (T = Mn, Ru). While surface RuO6 octahedron in Sr3Ru2O7 has both rotation (~ 12°) and tilt (~ 3°), our LEED – IV analysis reveals that MnO6 octahedron in Sr3Mn2O7 has a similiar rotation (~ 11°) but no tilt. HREELS data suggest that both the surface of Sr3Mn2O7 and Sr3Ru2O7 are semiconducting but for different reasons. The implication of these findings will be discussed. |
Wednesday, March 6, 2019 3:30PM - 3:42PM |
P45.00006: Electronic and magnetic properties of double perovskite thin film Sr2CrReO6 Jose Flores, Keng-Yuan Meng, Adam Ahmed, Fengyuan Yang Chiral magnetic spin textures, such as skyrmions, have been found in systems that have the Dzyaloshinskii-Moriya interaction and ferromagnetic exchange, e.g., heavy metal/ferromagnet bilayers. However, to make skyrmions relevant for modern applications, skyrmions need to operate at room temperature and be sufficiently small for high information densities. Oxides offer an excellent platform to accomplish this owing to their pristine epitaxy and highly tunable properties. We explore this possibility in high magnetic ordering temperature Sr2CrReO6thin films. Sr2CrReO6 films were grown by off-axis dc magnetron sputtering on SrTiO3(001) and Sr2CrNbO6/LSAT(001) substrates. Films were characterized by X-ray diffraction and atomic force microscopy showing both a high degree of crystalline quality and smooth surface topography, respectively. We will also discuss how choice of substrate for growth of Sr2CrReO6is crucial as strain can significantly change the magnetic anisotropy—a crucial tuning parameter for skyrmion stability. Lastly, we will show magnetic and electrical characterization of these films and the potential for future skyrmion heterostructures. |
Wednesday, March 6, 2019 3:42PM - 3:54PM |
P45.00007: High-k perovskite dielectric BaHf1-xTixO3 Hahoon Lee, Dowon Song, Kookrin Char Interest in high-k materials continues as the semiconductor devices shrink in size and in its operating voltage. BaTiO3 is a well-known perovskite ferroelectric material and BaHfO3 is a perovskite high-k dielectric material with a dielectric value of 38. In this study, we fabricated capacitors with an atomically-mixed BaHf1-xTixO3 (BHT, with x varying from 0 to 0.8) layer as the dielectric insulator with a perovskite semiconductor La-doped BaSnO3 (BLSO) layer as the electrode. All the layers were epitaxially grown on SrTiO3 substrates by pulsed laser deposition. X-Ray diffraction was used to investigate the structural properties, from which we confirmed the epitaxial growth of all the layers and obtained their respective lattice constants. The electrical properties of the capacitors, such as the capacitance and breakdown field, were measured. As the x value increased, the relative permittivity value increased and the dielectric breakdown field decreased. When the x value of BHT was 0.4, the relative permittivity and breakdown field values were 61.7 and 5.85 MV/cm, respectively, yielding the maximum 2D charge density 2x1014 cm-2. We will report on the field effect transistor performances with BHT as the gate dielectric and BLSO as the channel layer. |
Wednesday, March 6, 2019 3:54PM - 4:06PM |
P45.00008: Defect-controlled transport phenomena at complex oxide interfaces Jacqueline Boergers, Marc Rose, Regina Dittmann, Felix Gunkel Electric-field control of 2-dimensional electron systems (2DES) in oxide heterostructures is a key tool for tuning properties such as carrier density, magnetism, and superconductivity. There remain open questions however if in all cases gate-tunable properties can be ascribed to electronic phenomena deriving directly from varying the charge accummulated in the interfacial potential well. Here, we discuss that various gate-tunable properties observed in 2DES can also be mimicked by controlling the ionic defect structure and lattice disorder in the vicinity of the interface. As we will show accumulation of scatter centers at the interface can result in diminished charge transfer, while the magnetic response of the electron system is enhanced and quantum interference phenomena (weak-anti-localization) arise. Additionally, we discuss how a controlled and homogenous defect background in thin film SrTiO3 intrinsically yields a transition from positive to negative magnetoresistance, at comparable carrier concentration. Our results yield an ionic-electronic perspective on electrical gating experiments frequently conducted in the oxide electronics community. We provide a comprehensive discussion of the coupling of electronic gating and gradual defect profiles. |
Wednesday, March 6, 2019 4:06PM - 4:18PM |
P45.00009: Superoxygenation study of cuprate and iridate thin films Hao Zhang, Chao Zhang, Nicolas Gauquelin, Shaobo Cheng, Gianluigi Botton, Christopher McMahon, David G Hawthorn, Patrick Clancy, Sae Hwan Chun, Ambrose Seo, Young-June Kim, John Y.T. Wei High-pressure O2 has been used to hole-dope and to stabilize high-oxidation phases of cuprates. We extend this superoxygenation technique to YBa2Cu3O7-δ thin films, which are more reactive due to their large surface-to-volume ratio, and to the layered iridate Sr2IrO4, which is difficult to hole-dope by cation substitution. First, YBa2Cu3O7-δ thin films grown by PLD are annealed in up to 700 atm O2 and then characterized by TEM, XRD and XAS. The annealed films show phase conversion to Y2Ba4Cu7O15-δ and Y2Ba4Cu8O16, as well as regions of YBa2Cu5O9-δ and YBa2Cu6O10-δ. Second, epitaxial thin films of Sr2IrO4 are subjected to extended high-pressure annealing and similarly characterized. The post-annealed films show up to 3 order-of-magnitude drop in room temperature resistivity and an evolution towards semi-metallic behaviour. Furthermore, as film thickness is reduced, the annealed films show a structural transformation towards a quasi-cubic phase. Our results demonstrate the potential of using superoxygenation to stabilize exotic phases of transition metal oxides not achievable in bulk form. [1] |
Wednesday, March 6, 2019 4:18PM - 4:30PM |
P45.00010: Temperature-induced metal-to-insulator transition in epitaxially grown NbO2 films Toyanath Joshi, Eli Cirino, David Lederman Transition metal oxides demonstrating metal-to-insulator transitions (MIT), such as VO2 and NbO2, are widely studied materials for use as selector elements in resistive random-access memory (RRAM). The MIT transition temperature (TMIT) of VO2 is close to room temperature (~340 K). NbO2, on the other hand, has a much higher transition temperature (TMIT = 1081 K), which complicates the direct observation of the MIT in thin films and has not been reported in an epitaxial film, so far. In this presentation, we will demonstrate temperature dependent electrical resistivity of epitaxially grown NbO2 thin films revealing the actual mechanism of MIT in NbO2. High-quality epitaxial films were grown using pulsed laser deposition and structural characterization was performed using x-ray diffraction and atomic force microscopy. The resistivity of the as-grown films was measured from room temperature to 1100 K under a controlled environment using the four-probe resistivity measurement technique. Also, we will examine the effect of epitaxial strain to MIT of NbO2 was demonstrated by varying thickness of the films from 12 to 45 nm |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P45.00011: Interfacial Mott state in iridate-nickelate superlattices Xiaoran Liu, Michele Kotiuga, Heung Sik Kim, Alpha N'Diaye, Yongseong Choi, Yanwei Cao, Banabir Pal, Fangdi Wen, Mikhail Kareev, John William Freeland, Daniel Haskel, Padraic Shafer, Elke Arenholz, Kristjan Haule, David Vanderbilt, Karin Rabe, Jak Chakhalian In new SrIrO3/LaNiO3 superlattices up to a full electron transfer at the interface from Ir to Ni is experimentally observed, triggering a massive structural and electronic reconstruction. The large crystal eld splitting from the distorted interfacial IrO6 octahedra surprisingly dominates over the spin-orbit coupling, and together with the Hund's coupling results in the high-spin (S = 1) congurations on both Ir and Ni sites. First-principles calculations agree well with the experimental results, supporting the formation of an intricate Mott state in the superlattices. |
Wednesday, March 6, 2019 4:42PM - 4:54PM |
P45.00012: Doping study of ultra-wide bandgap spinel semiconductor ZnGa2O4 films Sungyun Hong, Yeaju Jang, Jihoon Seo ZnGa2O4 is a cubic spinel oxide with a bandgap of about 4.6 eV, almost same as that of monoclinic b-Ga2O3 in which the interest keeps increasing for its potential in high power devices. We will report the effect of various dopants on ZnGa2O4. For this study, we grew ZnGa2O4 films on c-Al2O3 substrates via pulsed laser deposition. XRD analysis confirmed the epitaxial growth of the films. Three elements, Sn, Si, and H were chosen as dopant candidates. The Sn-doped film remained highly insulating, showing no significant decrease in resistivity compared to the undoped film. The resistivity of the Si-doped film decreased to the order of 103 Ω*cm, confirming that some carriers were generated by Si dopants. The H-doped films showed a large decrease in resistivity down to the order of 10-1 Ω*cm. Further annealing of the H-doped films under an O2 environment increased the resistivity up to the order of 100 Ω*cm while the Hall measurements on the post-annealed H-doped films yielded mobility values of up to ~50 cm2*V-1*s-1 with a carrier density of ~1017 cm-3. |
Wednesday, March 6, 2019 4:54PM - 5:06PM |
P45.00013: AFM Study of Temperature Driven Phase Transitions in Vanadates Anna Binion, Riju Banerjee, Lavish Pabbi, Jason M Lapano, Roman Engel-Herbert, Eric Hudson Vanadates have many interesting properties with possible applications ranging from solar energy to transparent electronics. As many applications depend on the variation of structural and electronic properties thru phase transitions, to develop new applications it is important to have a good understanding of these transitions. Here we present results from atomic force microscopy studies of vanadates undergoing temperature driven phase transitions. In particular, we observe changes in a stripe order parameter as the materials pass through their structural transition temperatures. These observations give us insight into the nature of these transitions and how they can be controlled. |
Wednesday, March 6, 2019 5:06PM - 5:18PM |
P45.00014: Inversion symmetry breaking at the heterointerface of SrRuO3 thin films Chang Jae Roh, Jeong Rae Kim, Yong Ryun Jo, Jeong Gi Choi, Jin Kwon Kim, Yeongjae Shin, Bongju Kim, Bong Joong Kim, Tae Won Noh, Jongseok Lee We investigate the structural symmetry of SrRuO3 thin films grown on the SrTiO3 substrate by exploiting optical second harmonic generation (SHG) technique. We observe that SHG responses are strongly dependent on the film thickness and temperature; the azimuth-dependence becomes more anisotropic as the film becomes thicker, and the SHG response diminishes as temperature increases above 400 K. We analyze the azimuth dependences by considering the electric dipole and electric quadrupole contributions, and find that the tetragonal and orthorhombic phases are stabilized in fully strained and strain-relaxed regions, respectively. In particular, we demonstrate that the inversion-symmetry-broken state emerges as a stable phase at the interface between centrosymmetric tetragonal and orthorhombic phases. |
Wednesday, March 6, 2019 5:18PM - 5:30PM |
P45.00015: Effect of perovskite dielectric BaxSr1-xHfO3 on BaSnO3 HYEONGMIN CHO, Young Mo Kim, Kookrin Char La-doped BaSnO3 (BLSO) is a wide bandgap semiconducting perovskite oxide with high electron mobility and excellent oxygen stability at room temperature [1]. In recent reports on the excellent carrier modulation of BLSO channel by field effect on perovskite SrTiO3 (STO) [2] and non-perovskite MgO substrates [3], we found an optimized thickness for undoped BaSnO3 (BSO) buffer layer to be around 150 nm. However, BSO shows persistent and large photoconductivity under the light with wavelength smaller than 400 nm. |
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