Sample records for ba srtio3 thin

  1. Epitaxial Ba2IrO4 thin-films grown on SrTiO3 substrates by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Nichols, J.; Korneta, O. B.; Terzic, J.; Cao, G.; Brill, J. W.; Seo, S. S. A.

    2014-03-01

    We have synthesized epitaxial Ba2IrO4 (BIO) thin-films on SrTiO3 (001) substrates by pulsed laser deposition and studied their electronic structure by dc-transport and optical spectroscopic experiments. We have observed that BIO thin-films are insulating but close to the metal-insulator transition boundary with significantly smaller transport and optical gap energies than its sister compound, Sr2IrO4. Moreover, BIO thin-films have both an enhanced electronic bandwidth and electronic-correlation energy. Our results suggest that BIO thin-films have great potential for realizing the interesting physical properties predicted in layered iridates.

  2. Interdiffusion effect on strained La0.8Ba0.2MnO3 thin films by off-axis sputtering on SrTiO3 (100) substrates

    NASA Astrophysics Data System (ADS)

    Chou, Hsiung; Hsu, S. G.; Lin, C. B.; Wu, C. B.

    2007-02-01

    Strained La0.8Ba0.2MnO3 thin films on SrTiO3 (100) substrate are grown by an off-axis sputtering technique. It is found that the ferromagnetic temperature TC increases for thinner films. Secondary ion mass spectroscopy indicates that Sr diffuses partially into the film, making it structurally nonuniform. The region close to the film/substrate interface acts as La1-x(SryBa1-y)xMnO3 with a near negligible y for the as grown film and a non-negligible amount of y for the high-temperature postannealed film. The enhancement of TC is attributed to the combination of the strain and interdiffusion effects.

  3. High ferroelectric polarization in c-oriented BaTiO 3 epitaxial thin films on SrTiO 3/Si(001)

    DOE PAGES

    Scigaj, M.; Chao, C. H.; Gázquez, J.; ...

    2016-09-21

    The integration of epitaxial BaTiO 3 films on silicon, combining c-orientation, surface flatness, and high ferroelectric polarization is of main interest towards its use in memory devices. This combination of properties has been only achieved so far by using yttria-stabilized zirconia buffer layers. Here, the all-perovskite BaTiO 3/LaNiO 3/SrTiO 3 heterostructure is grown monolithically on Si(001). The BaTiO 3 films are epitaxial and c-oriented and present low surface roughness and high remnant ferroelectric polarization around 6 μC/cm 2. Lastly, this result paves the way towards the fabrication of lead-free BaTiO 3 ferroelectric memories on silicon platforms.

  4. Electrical transport across nanometric SrTiO3 and BaTiO3 barriers in conducting/insulator/conducting junctions

    NASA Astrophysics Data System (ADS)

    Navarro, H.; Sirena, M.; González Sutter, J.; Troiani, H. E.; del Corro, P. G.; Granell, P.; Golmar, F.; Haberkorn, N.

    2018-01-01

    We report the electrical transport properties of conducting/insulator/conducting heterostructures by studying current-voltage IV curves at room temperature. The measurements were obtained on tunnel junctions with different areas (900, 400 and 100 μm2) using a conducting atomic force microscope. Trilayers with GdBa2Cu3O7 (GBCO) as the bottom electrode, SrTiO3 or BaTiO3 (thicknesses between 1.6 and 4 nm) as the insulator barrier, and GBCO or Nb as the top electrode were grown by DC sputtering on (100) SrTiO3 substrates For SrTiO3 and BaTiO3 barriers, asymmetric IV curves at positive and negative polarization can be obtained using electrodes with different work function. In addition, hysteretic IV curves are obtained for BaTiO3 barriers, which can be ascribed to a combined effect of the FE reversal switching polarization and an oxygen vacancy migration. For GBCO/BaTiO3/GBCO heterostructures, the IV curves correspond to that expected for asymmetric interfaces, which indicates that the disorder affects differently the properties at the bottom and top interfaces. Our results show the role of the interface disorder on the electrical transport of conducting/insulator/conduction heterostructures, which is relevant for different applications, going from resistive switching memories (at room temperature) to Josephson junctions (at low temperatures).

  5. Direct observation of oxygen-vacancy-enhanced polarization in a SrTiO 3-buffered ferroelectric BaTiO 3 film on GaAs

    DOE PAGES

    Qiao, Q.; Zhang, Y.; Contreras-Guerrero, Rocio; ...

    2015-11-16

    The integration of functional oxide thin-films on compound semiconductors can lead to a class of reconfigurable spin-based optoelectronic devices if defect-free, fully reversible active layers are stabilized. However, previous first-principles calculations predicted that SrTiO 3 thin filmsgrown on Si exhibit pinned ferroelectric behavior that is not switchable, due to the presence of interfacial vacancies. Meanwhile, piezoresponse force microscopy measurements have demonstrated ferroelectricity in BaTiO 3 grown on semiconductor substrates. The presence of interfacial oxygen vacancies in such complex-oxide/semiconductor systems remains unexplored, and their effect on ferroelectricity is controversial. We also use a combination of aberration-corrected scanning transmission electron microscopy andmore » first-principles density functional theory modeling to examine the role of interfacial oxygen vacancies on the ferroelectricpolarization of a BaTiO 3 thin filmgrown on GaAs. Moreover, we demonstrate that interfacial oxygen vacancies enhance the polar discontinuity (and thus the single domain, out-of-plane polarization pinning in BaTiO 3), and propose that the presence of surface charge screening allows the formation of switchable domains.« less

  6. Domain matching epitaxy of BaBiO3 on SrTiO3 with structurally modified interface

    NASA Astrophysics Data System (ADS)

    Zapf, M.; Stübinger, M.; Jin, L.; Kamp, M.; Pfaff, F.; Lubk, A.; Büchner, B.; Sing, M.; Claessen, R.

    2018-04-01

    The perovskite BaBiO3 (BBO) is a versatile oxide parent material which displays superconductivity upon p-doping, while n-doping has been predicted to establish a wide-bandgap topological insulator phase. Here, we report on a mechanism that allows for epitaxial deposition of high-quality crystalline BBO thin films on SrTiO3 substrates despite a significant lattice mismatch of as large as 12%. It is revealed that the growth takes place through domain matching epitaxy, resulting in domains with alternating lateral sizes of 8 and 9 BBO unit cells. In particular, a structurally modified interface layer is identified which serves as a nucleation layer for the BBO films and gradually relieves the strain by decoupling the film lattice from the substrate. The BBO growth mechanism identified here may be prototypical for prospective thin film deposition of other perovskites with large lattice constants.

  7. Ab initio study of cross-interface electron-phonon couplings in FeSe thin films on SrTiO 3 and BaTiO 3

    DOE PAGES

    Wang, Y.; Linscheid, A.; Berlijn, T.; ...

    2016-04-22

    We study the electron-phonon coupling strength near the interface of monolayer and bilayer FeSe thin films on SrTiO 3 , BaTiO 3 , and oxygen-vacant SrTiO 3 substrates, using ab initio methods. The calculated total electron-phonon coupling strength λ = 0.2 – 0.3 cannot account for the high T c ~ 70 K observed in these systems through the conventional phonon-mediated pairing mechanism. In all of these systems, however, we find that the coupling constant of a polar oxygen branch peaks at q = 0 with negligible coupling elsewhere, while the energy of this mode coincides with the offset energymore » of the replica bands measured recently by angle-resolved photoemission spectroscopy experiments. However, the integrated coupling strength for this mode from our current calculations is still too small to produce the observed high T c , even through the more efficient pairing mechanism provided by the forward scattering. Also, we arrive at the same qualitative conclusion when considering a checkerboard antiferromagnetic configuration in the Fe layer. In light of the experimental observations of the replica band feature and the relatively high T c of FeSe monolayers on polar substrates, our results point towards a cooperative role for the electron-phonon interaction, where the cross-interface interaction acts in conjunction with a purely electronic interaction. Finally, we discuss a few scenarios where the coupling strength obtained here may be enhanced.« less

  8. Scavenging of oxygen from SrTiO3 by metals and its implications for oxide thin film deposition

    NASA Astrophysics Data System (ADS)

    Posadas, Agham; Kormondy, Kristy; Guo, Wei; Ponath, Patrick; Kremer, Jacqueline; Hadamek, Tobias; Demkov, Alexander

    SrTiO3 is a widely used substrate for the growth of other functional oxide thin films. However, SrTiO3 loses oxygen very easily during oxide thin film deposition even under relatively high oxygen pressures. In some cases, there will be an interfacial layer of oxygen-deficient SrTiO3 formed at the interface with the deposited oxide film, depending on the metals present in the film. By depositing a variety of metals layer by layer and measuring the evolution of the core level spectra of both the deposited metal and SrTiO3 using x-ray photoelectron spectroscopy, we show that there are three distinct types of behavior that occur for thin metal films on SrTiO3. We discuss the implications of these types of behavior for the growth of complex oxide thin films on SrTiO3, and which oxide thin films are expected to produce an interfacial oxygen-deficient layer depending on their elemental constituents.

  9. BaFe2As2/Fe Bilayers with [001]-tilt Grain Boundary on MgO and SrTiO3 Bicrystal Substrates

    NASA Astrophysics Data System (ADS)

    Iida, K.; Haindl, S.; Kurth, F.; Hänisch, J.; Schulz, L.; Holzapfel, B.

    Co-doped BaFe2As2 (Ba-122) can be realized on both MgO and SrTiO3 bicrystal substrates with [001]-tilt grain boundary by employing Fe buffer layers. However, an additional spinel (i.e. MgAl2O4) buffer between Fe and SrTiO3 is necessary since an epitaxial, smooth surface of Fe layer can not be grown on bare SrTiO3. Both types of bicrystal films show good crystalline quality.

  10. Sintering of BaCe(sub 0.85)Y(sub 0.15)O(sub 3-delta) with/without SrTiO3 Dopant

    NASA Technical Reports Server (NTRS)

    Dynys, F.; Sayir, A.; Heimann, P. J.

    2004-01-01

    The perovskite composition, BaCe(sub 0.85)Y(sub 0.15)O(sub 3-delta), displays excellent protonic conduction at high temperatures making it a desirable candidate for hydrogen separation membranes. This paper reports on the sintering behavior of BaCe(sub 0.85)Y(sub 0.15)O(sub 3-delta) powders doped with SrTiO3. Two methods were used to synthesize BaCe(sub 0.85)Y(sub 0.15)O(sub 3-delta) powders: (1) solid state reaction and (2) wet chemical co-precipitation. Co-precipitated powder crystallized into the perovskite phase at 1000 C for 4 hrs. Complete reaction and crystallization of the perovskite phase by solid state was achieved by calcining at 1200 C for 24 hrs. Solid state synthesis produced a coarser powder with an average particle size of 1.3 microns and surface area of 0.74 sq m/g. Co-precipitation produced a finer powder with a average particle size of 65 nm and surface area of 14.9 sq m/g. Powders were doped with 1, 2, 5, and 10 mole % SrTiO3. Samples were sintered at 1450 C, 1550 C and 1650 C. SrTiO3 enhances sintering, optimal dopant level is different for powders synthesized by solid state and co-precipitation. Both powders exhibit similar grain growth behavior. Dopant levels of 5 and 10 mole % SrTiO3 significantly enhances the grain size.

  11. Tuning the growth and strain relaxation of ferroelectric BaTiO3 thin films on SrRuO3 electrode: influence on electrical properties

    NASA Astrophysics Data System (ADS)

    Aidoud, Amina; Maroutian, Thomas; Matzen, Sylvia; Agnus, Guillaume; Amrani, Bouhalouane; Driss-Khodja, Kouider; Aubert, Pascal; Lecoeur, Philippe

    2018-01-01

    This study is focused on the link between the structural and electric properties of BaTiO3 thin films grown on SrRuO3-buffered (001) SrTiO3 substrates, SrRuO3 acting as bottom electrode. The growth regime and film structure are here tuned through the growth pressure for pulsed laser deposition in the 1-200 mTorr range. The dielectric, ferroelectric and leakage current properties are systematically measured for the different strain states of the BaTiO3 thin films on SrRuO3. The results are discussed with the help of ab initio calculations on the effects of Ba- and Ti-vacancies on BaTiO3 lattice parameters. A sharp increase of the dielectric constant is evidenced in the high pressure region, where the tetragonality of the BaTiO3 is decreasing rapidly with growth pressure. We interpret this divergence of the dielectric function as the signature of the vicinity of the phase boundary between the out-of-plane and in-plane orientations of the tetragonal BTO films.

  12. Growth and interface engineering in thin-film Ba0.6Sr0.4TiO3 /SrMoO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Radetinac, Aldin; Ziegler, Jürgen; Vafaee, Mehran; Alff, Lambert; Komissinskiy, Philipp

    2017-04-01

    Epitaxial heterostructures of ferroelectric Ba0.6Sr0.4TiO3 and highly conducting SrMoO3 were grown by pulsed laser deposition on SrTiO3 (0 0 1) substrates. Surface oxidation of the SrMoO3 film is suppressed using a thin cap interlayer of Ba0.6Sr0.4TiO3-δ grown in reduced atmosphere. As shown by X-ray photoelectron spectroscopy, the Mo4+ valence state of the SrMoO3 films is stable upon annealing of the sample in oxygen up to 600 °C. The described oxygen interface engineering enables utilization of the highly conducting material SrMoO3 in multilayer oxide ferroelectric varactors.

  13. Growth of Nanoscale BaTiO3/SrTiO3 Superlattices by Molecular-Beam Epitaxy

    DTIC Science & Technology

    2008-05-01

    also of interest for novel acous- tic phonon devices including mirrors, filters, and cavities for coherent acoustic phonon generation and control...phonon “laser”).4 The structure of these devices is de- termined by the acoustic phonon wavelength, which is typically in the range of a few nanometers...nanoscale [(BaTiO3)n /(SrTiO3)m]p superlattices with atomically abrupt interfaces that are vital for the perfor- mance of acoustic phonon devices as

  14. Surface Termination Conversion during SrTiO3 Thin Film Growth Revealed by X-ray Photoelectron Spectroscopy

    PubMed Central

    Baeumer, Christoph; Xu, Chencheng; Gunkel, Felix; Raab, Nicolas; Heinen, Ronja Anika; Koehl, Annemarie; Dittmann, Regina

    2015-01-01

    Emerging electrical and magnetic properties of oxide interfaces are often dominated by the termination and stoichiometry of substrates and thin films, which depend critically on the growth conditions. Currently, these quantities have to be measured separately with different sophisticated techniques. This report will demonstrate that the analysis of angle dependent X-ray photoelectron intensity ratios provides a unique tool to determine both termination and stoichiometry simultaneously in a straightforward experiment. Fitting the experimental angle dependence with a simple analytical model directly yields both values. The model is calibrated through the determination of the termination of SrTiO3 single crystals after systematic pulsed laser deposition of sub-monolayer thin films of SrO. We then use the model to demonstrate that during homoepitaxial SrTiO3 growth, excess Sr cations are consumed in a self-organized surface termination conversion before cation defects are incorporated into the film. We show that this termination conversion results in insulating properties of interfaces between polar perovskites and SrTiO3 thin films. These insights about oxide thin film growth can be utilized for interface engineering of oxide heterostructures. In particular, they suggest a recipe for obtaining two-dimensional electron gases at thin film interfaces: SrTiO3 should be deposited slightly Ti-rich to conserve the TiO2-termination. PMID:26189436

  15. Non-linear second harmonic generation (SHG) studies of BaTiO3/SrTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Vlahos, Eftihia; Lee, Che-Hui; Wu, Pingping; Wung Bark, Chung; Jang, Ho Won; Folkman, Chad; Hyub Baek, Seung; Park, J. W.; Biegalski, Mike; Tenne, Dmitri; Schlom, Darrell; Chen, Long-Qing; Eom, Chang-Beom; Gopalan, Venkatraman

    2010-03-01

    Theoretical phase-field simulations predict that certain types of superlattices consisting of alternating (BaTiO3)n/(SrTiO3)n layers have novel vortex domain wall configurations which give rise to exceptionally high polarization tunability combined with negligible polarization hysteresis. Optical second harmonic generation (SHG) was used to probe the phase and transition temperatures of multilayer (BaTiO3)m/(SrTiO3)n superlattices, as a function of epitaxial strain. In addition, in-plane electro-optic measurements were carried out. The experimental results are in excellent agreement both with theoretical predictions, as well as the temperature-strain phase diagram obtained experimentally from UV Raman studies. The ferroelectric, in-plane SHG signal, from the tensile strained SrTiO3 layers reveals an mm2 point group symmetry, whereas the point group symmetry of the compressively strained BaTiO3 layers, was determined to be 4mm.

  16. Microfabrication of SrRuO3 thin films on various oxide substrates using LaAlO3/BaOx sacrificial bilayers

    NASA Astrophysics Data System (ADS)

    Harada, Takayuki; Tsukazaki, Atsushi

    2018-02-01

    Oxides provide various fascinating physical properties that could find use in future device applications. However, the physical properties of oxides are often affected by formation of oxygen vacancies during device fabrication processes. In this study, to develop a damage-free patterning process for oxides, we focus on a lift-off process using a sacrificial template layer, by which we can pattern oxide thin films without severe chemical treatment or plasma bombardment. As oxides need high thin-film growth temperature, a sacrificial template needs to be made of thermally stable and easily etchable materials. To meet these requirements, we develop a sacrificial template with a carefully designed bilayer structure. Combining a thermally and chemically stable LaAlO3 and a water-soluble BaOx, we fabricated a LaAlO3/BaOx sacrificial bilayer. The patterned LaAlO3/BaOx sacrificial bilayers were prepared on oxide substrates by room-temperature pulsed laser deposition and standard photolithography process. The structure of the sacrificial bilayer can be maintained even in rather tough conditions needed for oxide thin film growth: several hundred degrees Celsius under high oxygen pressure. Indeed, the LaAlO3/BaOx bilayer is easily removable by sonication in water. We applied the lift-off method using the LaAlO3/BaOx sacrificial bilayer to a representative oxide conductor SrRuO3 and fabricated micron-scale Hall-bar devices. The SrRuO3 channels with the narrowest line width of 5 μm exhibit an almost identical transport property to that of the pristine film, evidencing that the developed process is beneficial for patterning oxides. We show that the LaAlO3/BaOx lift-off process is applicable to various oxide substrates: SrTiO3, MgO, and Al2O3. The new versatile patterning process will expand the range of application of oxide thin films in electronic and photonic devices.

  17. First-Principles Prediction of Two-Dimensional Electron Gas Driven by Polarization Discontinuity in Nonpolar/Nonpolar AHfO3/SrTiO3 (A=Ca, Sr, and Ba) Heterostructures

    NASA Astrophysics Data System (ADS)

    Cheng, Jianli; Nazir, Safdar; Yang, Kesong

    By using first-principles electronic structure calculations, we explored the possibility of producing two-dimensional electron gas (2DEG) in nonpolar/nonpolar AHfO3/SrTiO3 (A = Ca, Sr, and Ba) heterostructures (HS). Two types of interfaces, AO/TiO2 and HfO2/SrO, each with AO and HfO2 surface terminations, are modeled, respectively. The polarization domain and resulting interfacial electronic property are found to be more sensitive to the surface termination of the film rather than the interface model. As film thickness increases, an insulator-to-metal transition (IMT) is found in all the HS with HfO2 surface termination: for AO/TiO2 interfaces, predicted critical film thickness for an IMT is about 7, 6, and 3 unit cells for CaHfO3/SrTiO3, SrHfO3/SrTiO3, and BaHfO3/SrTiO3, respectively; for HfO2/SrO interfaces, the critical film thickness is about 7.5, 5.5, and 4.5 unit cells, respectively. In contrast, for the HS with AO surface termination, only CaHfO3/SrTiO3 exhibits an IMT with a much larger critical film thickness about 11 - 12 unit cells. This work is expected to stimulate further experimental investigation to the interfacial conductivity in the nonpolar/nonpolar AHfO3/SrTiO3 HS. National Science Foundation and Department of Defense National Security Science and Engineering Faculty Fellowship.

  18. Improvement of laser molecular beam epitaxy grown SrTiO3 thin film properties by temperature gradient modulation growth

    NASA Astrophysics Data System (ADS)

    Li, Jin Long; Hao, J. H.; Li, Y. R.

    2007-09-01

    Oxygen diffusion at the SrTiO3/Si interface was analyzed. A method called temperature gradient modulation growth was introduced to control oxygen diffusion at the interface of SrTiO3/Si. Nanoscale multilayers were grown at different temperatures at the initial growing stage of films. Continuous growth of SrTiO3 films was followed to deposit on the grown sacrificial layers. The interface and crystallinity of SrTiO3/Si were investigated by in situ reflection high energy electron diffraction and x-ray diffraction measurements. It has been shown that the modulated multilayers may help suppress the interfacial diffusion, and therefore improve SrTiO3 thin film properties.

  19. Thermal conductivity of SrVO3-SrTiO3 thin films: Evidence of intrinsic thermal resistance at the interface between oxide layers

    NASA Astrophysics Data System (ADS)

    Katsufuji, T.; Saiki, T.; Okubo, S.; Katayama, Y.; Ueno, K.

    2018-05-01

    By using a technique of thermoreflectance that can precisely measure the thermal conductivity of thin films, we found that the thermal conductivity of SrVO3-SrTiO3 multilayer thin films normal to the surface was substantially reduced by decreasing the thickness of each layer. This indicates that a large intrinsic thermal resistance exists at the interface between SrVO3 and SrTiO3 in spite of the similar phononic properties for these two compounds.

  20. Thin film processing of photorefractive BaTiO3

    NASA Technical Reports Server (NTRS)

    Schuster, Paul R.

    1993-01-01

    During the period covered by this report, October 11, 1991 through October 10, 1992, the research has progressed in a number of different areas. The sol-gel technique was initially studied and experimentally evaluated for depositing films of BaTiO3. The difficulties with the precursors and the poor quality of the films deposited lead to the investigation of pulsed laser deposition as an alternative approach. The development of the pulsed laser deposition technique has resulted in continuous improvements to the quality of deposited films of BaTiO3. The initial depositions of BaTiO3 resulted in amorphous films, however, as the pulsed laser deposition technique continued to evolve, films were deposited in the polycrystalline state, then the textured polycrystalline state, and most recently heteroepitaxial films have also been successfully deposited on cubic (100) oriented SrTiO3 substrates. A technique for poling samples at room temperature and in air is also undergoing development with some very preliminary but positive results. The analytical techniques, which include x-ray diffraction, ferroelectric analysis, UV-Vis spectrophotometry, scanning electron microscopy with x-ray compositional analysis, optical and polarized light microscopy, and surface profilometry have been enhanced to allow for more detailed evaluation of the samples. In the area of optical characterization, a pulsed Nd:YAG laser has been incorporated into the experimental configuration. Now data can also be acquired within various temporal domains resulting in more detailed information on the optical response of the samples and on their photorefractive sensitivity. The recent establishment of collaborative efforts with two departments at Johns Hopkins University and the Army Research Lab at Fort Belvoir has also produced preliminary results using the metallo-organic decomposition technique as an alternative method for thin film processing of BaTiO3. RF and DC sputtering is another film deposition

  1. Structure and magnetic properties of spinel-perovskite nanocomposite thin films on SrTiO3 (111) substrates

    NASA Astrophysics Data System (ADS)

    Kim, Dong Hun; Yang, Junho; Kim, Min Seok; Kim, Tae Cheol

    2016-09-01

    Epitaxial CoFe2O4-BiFeO3 nanocomposite thin films were synthesized on perovskite structured SrTiO3 (001) and (111) substrates by combinatorial pulsed laser deposition and characterized using scanning electron microscopy, x-ray diffraction, and vibrating sample magnetometer. Triangular BiFeO3 nanopillars were formed in a CoFe2O4 matrix on (111) oriented SrTiO3 substrates, while CoFe2O4 nanopillars with rectangular or square top surfaces grew in a BiFeO3 matrix on (001) substrates. The magnetic hysteresis loops of nanocomposites on (111) oriented SrTiO3 substrates showed isotropic properties due to the strain relaxation while those of films on SrTiO3 (001) substrates exhibited a strong out-of-plane anisotropy originated from shape and strain effects.

  2. Fabrication and chemical composition of RF magnetron sputtered Tl-Ca-Ba-Cu-O high Tc superconducting thin films

    NASA Technical Reports Server (NTRS)

    Subramanyam, G.; Radpour, F.; Kapoor, V. J.; Lemon, G. H.

    1990-01-01

    The preparation of TlCaBaCuO superconducting thin films on (100) SrTiO3 substrates is described, and the results of their characterization are presented. Sintering and annealing the thin films in a Tl-rich ambient yielded superconductivity with a Tc of 107 K. The results of an XPS study support two possible mechanisms for the creation of holes in the TlCaBaCuO compound: (1) partial substitution of Ca(2+) for Tl(3+), resulting in hole creation, and (2) charge transfer from Tl(3+) to the CuO layers, resulting in a Tl valence between +3 and +1.

  3. Surface diffusion in homoepitaxial SrTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Woo, Chang-Su; Chu, Kanghyun; Song, Jong-Hyun; Yang, Chan-Ho; Charm Lab Team; Nano Spintronics Lab Collaboration

    The development of growth techniques such as molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) has facilitated growths of complex oxide thin films at the atomic level .... Systematic studies on surface diffusion process of adatoms using theoretical and experimental methods allow us to understand growth mechanism enabling atomically flat thin film surface. In this presentation, we introduce the synthesis of homoepitaxial SrTiO3 thin films using a PLD equipped with reflection of high energy electron diffraction (RHEED). We determine the surface diffusion time as a function of growth temperature and extract the activation energy of diffusion on the surface by in-situ monitoring the RHEED intensity recovery during the film deposition. From the extracted experimental results, we discuss the microscopic mechanism of the diffusion process

  4. High mobility La-doped BaSnO3 on non-perovskite MgO substrate

    NASA Astrophysics Data System (ADS)

    Kim, Youjung; Shin, Juyeon; Kim, Young Mo; Char, Kookrin

    (Ba,La)SnO3 is a transparent perovskite oxide with high electron mobility and excellent oxygen stability. Field effect device with (Ba,La)SnO3 channel was reported to show good output characteristics on STO substrate. Here, we fabricated (Ba,La)SnO3\\ films and field effect devices with (Ba,La)SnO3 channel on non-perovskite MgO substrates, which are available in large size wafers. X-ray diffraction and transmission electron microscope (TEM) images of (Ba,La)SnO3\\ films on MgO substrates show that the films are epitaxial with many threading dislocations. (Ba,La)SnO3 exhibits the high mobility with 97.2 cm2/Vs at 2 % La doping on top of 150 nm thick BaSnO3 buffer layer. Excellent carrier modulation was observed in field effect devices. FET performances on MgO substrates are slightly better than those on SrTiO3 substrates in spite of the higher dislocation density on MgO than on SrTiO3 substrates. These high mobility BaSnO3 thin films and transistors on MgO substrates will accelerate development for applications in high temperature and high power electronics. Samsung Science and Technology Foundation.

  5. Sequentially evaporated thin Y-Ba-Cu-O superconductor films: Composition and processing effects

    NASA Technical Reports Server (NTRS)

    Valco, George J.; Rohrer, Norman J.; Warner, Joseph D.; Bhasin, Kul B.

    1988-01-01

    Thin films of YBa2Cu3O(7-beta) have been grown by sequential evaporation of Cu, Y, and BaF2 on SrTiO3 and MgO substrates. The onset temperatures were as high as 93 K while T sub c was 85 K. The Ba/Y ratio was varied from 1.9 to 4.0. The Cu/Y ratio was varied from 2.8 to 3.4. The films were then annealed at various times and temperatures. The times ranged from 15 min to 3 hr, while the annealing temperatures used ranged from 850 C to 900 C. A good correlation was found between transition temperature (T sub c) and the annealing conditions; the films annealed at 900 C on SrTiO3 had the best T sub c's. There was a weaker correlation between composition and T sub c. Barium poor films exhibitied semiconducting normal state resistance behavior while barium rich films were metallic. The films were analyzed by resistance versus temperature measurements and scanning electron microscopy. The analysis of the films and the correlations are reported.

  6. Ferromagnetism and Ru-Ru distance in SrRuO3 thin film grown on SrTiO3 (111) substrate

    PubMed Central

    2014-01-01

    Epitaxial SrRuO3 thin films were grown on both (100) and (111) SrTiO3 substrates with atomically flat surfaces that are required to grow high-quality films of materials under debate. The following notable differences were observed in the (111)-oriented SrRuO3 films: (1) slightly different growth mode, (2) approximately 10 K higher ferromagnetic transition temperature, and (3) better conducting behavior with higher relative resistivity ratio, than (100)c-oriented SrRuO3 films. Together with the reported results on SrRuO3 thin films grown on (110) SrTiO3 substrate, the different physical properties were discussed newly in terms of the Ru-Ru nearest neighbor distance instead of the famous tolerance factor. PACS 75.70.Ak; 75.60.Ej; 81.15.Fg PMID:24393495

  7. Protonic Conduction of BaCe0.85YO. 1503 Doped with SrTiO3

    NASA Technical Reports Server (NTRS)

    Dynys, Frederick W.; Sayir, Ali

    2005-01-01

    Reformers based on ceramic membrane technology potentially offer hydrogen production that is comparable to the cost of fossil fuels. Protonic conducting ceramic with the chemical formula AB03 offers the promise of highly selective hydrogen separation at intermediate temperature (400-800 C). Among different perovskite-type oxides, BaCe03 and SrCe03 based compositions show high protonic conductivities but strong resistance to densification. X-ray diffraction studies on sintered specimens of BaCe0.85Y0.1503-6 show multi-phase formation which was found to show dependence upon powder synthesis method. Doping with SrTiO3 suppresses multi-phase formation and enhances grain growth. Conductivity measurements in temperature range of 200 to 1000 C were performed by ac impedance spectroscopy under dry and wet conditions. Sintering behavior, phase formation and conductivity results will be reported.

  8. Properties of dielectric dead layers for SrTiO3 thin films on Pt electrodes

    NASA Astrophysics Data System (ADS)

    Finstrom, Nicholas H.; Cagnon, Joel; Stemmer, Susanne

    2007-02-01

    Dielectric measurements as a function of temperature were used to characterize the properties of the dielectric dead layers in parallel-plate capacitors with differently textured SrTiO3 thin films and Pt electrodes. The apparent thickness dependence of the permittivity was described with low-permittivity passive (dead) layers at the interfaces connected in series with the bulk of the SrTiO3 film. Interfacial capacitance densities changed with the film microstructure and were weakly temperature dependent. Estimates of the dielectric dead layer thickness and permittivity were limited by the film surface roughness (˜5nm ). The consequences for the possible origins of dielectric dead layers that have been proposed in the literature are discussed.

  9. Reactive Coevaporation Synthesis and Characterization of SrTiO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Hiromu; Matsubara, Shogo; Miyasaka, Yoichi

    1991-09-01

    SrTiO3 thin films were prepared by the reactive coevaporation method, where the Ti and Sr metals were evaporated in oxygen ambient with an E-gun and K-cell, respectively. A uniform depth profile in composition was achieved by altering the Ti evaporation rate according to the Sr evaporation rate change. A typical dielectric constant of 170 was measured on films of 75 nm in thickness. The in-situ annealing in oxygen plasma reduced the leakage current.

  10. Interfacial dislocations in (111) oriented (Ba 0.7Sr 0.3)TiO 3 films on SrTiO 3 single crystal

    DOE PAGES

    Shen, Xuan; Yamada, Tomoaki; Lin, Ruoqian; ...

    2015-10-08

    In this study, we have investigated the interfacial structure of epitaxial (Ba,Sr)TiO 3 films grown on (111)-oriented SrTiO 3 single-crystal substrates using transmission electron microscopy (TEM) techniques. Compared with the (100) epitaxial perovskite films, we observe dominant dislocation half-loop with Burgers vectors of a<110> comprised of a misfit dislocation along <112>, and threading dislocations along <110> or <100>. The misfit dislocation with Burgers vector of a <110> can dissociate into two ½ a <110> partial dislocations and one stacking fault. We found the dislocation reactions occur not only between misfit dislocations, but also between threading dislocations. Via three-dimensional electron tomography,more » we retrieved the configurations of the threading dislocation reactions. The reactions between threading dislocations lead to a more efficient strain relaxation than do the misfit dislocations alone in the near-interface region of the (111)-oriented (Ba 0.7Sr 0.3)TiO 3 films.« less

  11. Giant Polarization Rotation in BiFeO3/SrTiO3 Thin Films.

    NASA Astrophysics Data System (ADS)

    Langner, M. C.; Chu, Y. H.; Martin, L. M.; Gajek, M.; Ramesh, R.; Orenstein, J.

    2008-03-01

    We use optical second harmonic generation to probe dynamics of the ferroelectric polarization in (111) oriented BiFeO3 thin films grown on SrTiO3 substrates. The second harmonic response indicates 3m point group symmetry and is consistent with a spontaneous polarization normal to the surface of the film. We measure large changes in amplitude and lowering of symmetry, consistent with polarization rotation, when modest electric fields are applied in the plane of the film. At room temperature the rotation is an order of magnitude larger than expected from reported values of the dielectric constant and increases further (as 1/T) as temperature is lowered. We propose a substrate interaction model to explain these results.

  12. Strain Phase Diagram of SrTiO3 Thin Films

    NASA Astrophysics Data System (ADS)

    He, Feizhou; Shapiro, S. M.

    2005-03-01

    SrTiO3 thin films were used as a model system to study the effects of strain and epitaxial constraint on structural phase transitions of oxide films. The basic phenomena revealed will apply to a variety of important structural transitions including the ferroelectric transition. Highly strained, epitaxial films of SrTiO3 were grown on different substrates. The structural phase transition temperature Tc increases from 105 K in bulk STO to 167 K for films under tensile strain and 330 K for films with compressive strain. The measured temperature-strain phase diagram is qualitatively consistent with theory [1], however the increase in Tc is much larger than predicted in all cases. The symmetry of the phases involved in the transition is different from the corresponding bulk structures largely because of epitaxial constraint, the clamping effect. Thus the shape of the STO unit cell is tetragonal at all temperatures. The possibility exists of a very unique low temperature phase with orthorhombic symmetry (Cmcm) but tetragonal unit cell shape. More generally, we have characterized at least three different manifestations of the clamping effect, showing it is much more subtle than usually recognized. This work is supported through NSF DMR-0239667, DMR-0132918, by the Research Corp, and at BNL by the US DOE DE-AC02-98CH10886. [1] N. A. Pertsev, A. K. Tagantsev and N. Setter, Phys. Rev. B61, R825 (2000).

  13. The processes of formation and epitaxial alignment of SrTiO3 thin films prepared by metallo-organic decomposition

    NASA Astrophysics Data System (ADS)

    Braunstein, G.; Paz-Pujalt, G. R.; Mason, M. G.; Blanton, T.; Barnes, C. L.; Margevich, D.

    1993-01-01

    The processes of formation and crystallization of thin films of SrTiO3 prepared by the method of metallo-organic decomposition have been studied with particular emphasis on the relationship between the thermal decomposition of the metallo-organic precursors and the eventual epitaxial alignment of the crystallized films. The films are deposited by spin coating onto single-crystalline silicon and SrTiO3 substrates, pyrolyzed on a hot plate at temperatures ranging from 200 to 450 °C, and subsequently heat treated in a quartz tube furnace at temperatures ranging from 300 to 1200 °C. Heat treatment at temperatures up to 450-500 °C results in the evaporation of solvents and other organic addenda, thermal decomposition of the metallo-organic (primarily metal-carboxylates) precursors, and formation of a carbonate species. This carbonate appears to be an intermediate phase in the reaction of SrCO3 and TiO2 to form SrTiO3. Relevant to this work is the fact that the carbonate species exhibits diffraction lines, indicating the formation of grains that can serve as seeds for the nucleation and growth of randomly oriented SrTiO3 crystallites, thereby leading to a polycrystalline film. Deposition on silicon substrates indeed results in the formation of polycrystalline SrTiO3. However, when the precursor solution is deposited on single-crystalline SrTiO3 substrates, the crystallization process involves a competition between two mechanisms: the random nucleation and growth of crystallites just described, and layer-by-layer solid phase epitaxy. Epitaxial alignment on SrTiO3 substrates can be achieved when the samples are heat treated at temperatures of 1100-1200 °C or at temperatures as low as 600-650 °C when the substrate is heated to about 1100 °C before spin coating.

  14. Very high commutation quality factor and dielectric tunability in nanocomposite SrTiO 3 thin films with T c enhanced to >300 °C

    DOE PAGES

    Sangle, Abhijeet L.; Lee, Oon Jew; Kursumovic, Ahmed; ...

    2018-02-05

    We report on nanoengineered SrTiO 3–Sm2O 3 nanocomposite thin films with the highest reported values of commutation quality factor (CQF or K-factor) of >2800 in SrTiO 3 at room temperature. The films also had a large tunability of dielectric constant (49%), low tangent loss (tan δ = 0.01) and a Curie temperature for SrTiO 3 > 300 °C, making them very attractive for tunable RF applications. The enhanced properties originate from the unique nanostructure in the films, with <20 nm diameter strain-controlling Sm 2O 3 nanocolumns embedded in a SrTiO 3 matrix. Very large out-of-plane strains (up to 2.6%) andmore » high tetragonality (c/a) (up to 1.013) were induced in the SrTiO 3. Finally, the K-factor was further enhanced by adding 1 at% Sc 3+ (acceptor) dopant in SrTiO 3 to a value of 3300 with the tangent loss being ≤0.01 up to 1000 kV cm -1.« less

  15. Very high commutation quality factor and dielectric tunability in nanocomposite SrTiO 3 thin films with T c enhanced to >300 °C

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sangle, Abhijeet L.; Lee, Oon Jew; Kursumovic, Ahmed

    We report on nanoengineered SrTiO 3–Sm2O 3 nanocomposite thin films with the highest reported values of commutation quality factor (CQF or K-factor) of >2800 in SrTiO 3 at room temperature. The films also had a large tunability of dielectric constant (49%), low tangent loss (tan δ = 0.01) and a Curie temperature for SrTiO 3 > 300 °C, making them very attractive for tunable RF applications. The enhanced properties originate from the unique nanostructure in the films, with <20 nm diameter strain-controlling Sm 2O 3 nanocolumns embedded in a SrTiO 3 matrix. Very large out-of-plane strains (up to 2.6%) andmore » high tetragonality (c/a) (up to 1.013) were induced in the SrTiO 3. Finally, the K-factor was further enhanced by adding 1 at% Sc 3+ (acceptor) dopant in SrTiO 3 to a value of 3300 with the tangent loss being ≤0.01 up to 1000 kV cm -1.« less

  16. Structural and Optical properties of poly-crystalline BaTiO3 and SrTiO3 prepared via solid state route

    NASA Astrophysics Data System (ADS)

    Jarabana, Kanaka M.; Mishra, Ashutosh; Bisen, Supriya

    2016-10-01

    Polycrystalline BaTiO3 (BTO) and SrTiO3 (STO) were synthesized by solid state route method and properties of made polycrystalline were characterized by X-Ray diffraction (XRD), Raman Spectroscopy & FTIR Spectroscopy. XRD analysis shows that samples are crystalline in nature. In Raman Spectroscopy measurement, the experiment has been done with the help of JOBIN-YOVN HORIBA LABRAM HR800 single monochromator, which is coupled with a “peltier cooled” charge coupled device (CCD). Raman Spectroscopy at low temperature measurement shows the phase transition above & below the curie temperature in samples. Fourier transform Infrared spectroscopy was used to determine the Ti-O bond length position.

  17. Fabrication and convergent X-ray nanobeam diffraction characterization of submicron-thickness SrTiO 3 crystalline sheets

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tilka, J. A.; Park, J.; Sampson, K. C.

    The creation of thin SrTiO3 crystals from (001)-oriented SrTiO3 bulk single crystals using focused ion beam milling techniques yields sheets with submicron thickness and arbitrary orientation within the (001) plane. Synchrotron x-ray nanodiffraction rocking curve widths of these SrTiO3 sheets are less than 0.02 degrees, less than a factor of two larger than bulk SrTiO3, making these crystals suitable substrates for epitaxial thin film growth. The change in the rocking curve width is sufficiently small that we deduce that dislocations are not introduced into the SrTiO3 sheets. Observed lattice distortions are consistent with a low concentration of point defects.

  18. Voltage Scaling of Graphene Device on SrTiO3 Epitaxial Thin Film.

    PubMed

    Park, Jeongmin; Kang, Haeyong; Kang, Kyeong Tae; Yun, Yoojoo; Lee, Young Hee; Choi, Woo Seok; Suh, Dongseok

    2016-03-09

    Electrical transport in monolayer graphene on SrTiO3 (STO) thin film is examined in order to promote gate-voltage scaling using a high-k dielectric material. The atomically flat surface of thin STO layer epitaxially grown on Nb-doped STO single-crystal substrate offers good adhesion between the high-k film and graphene, resulting in nonhysteretic conductance as a function of gate voltage at all temperatures down to 2 K. The two-terminal conductance quantization under magnetic fields corresponding to quantum Hall states survives up to 200 K at a magnetic field of 14 T. In addition, the substantial shift of charge neutrality point in graphene seems to correlate with the temperature-dependent dielectric constant of the STO thin film, and its effective dielectric properties could be deduced from the universality of quantum phenomena in graphene. Our experimental data prove that the operating voltage reduction can be successfully realized due to the underlying high-k STO thin film, without any noticeable degradation of graphene device performance.

  19. Sputter Deposition of Yttrium-Barium Superconductor and Strontium Titanium Oxide Barrier Layer Thin Films

    NASA Astrophysics Data System (ADS)

    Truman, James Kelly

    1992-01-01

    The commercial application of superconducting rm YBa_2Cu_3O_{7 -x} thin films requires the development of deposition methods which can be used to reproducibly deposit films with good superconducting properties on insulating and semiconducting substrates. Sputter deposition is the most popular method to fabricate Y-Ba-Cu-O superconductor thin films, but when used in the standard configuration suffers from a deviation between the compositions of the Y-Ba-Cu-O sputter target and deposited films, which is thought to be primarily due to resputtering of the film by negative ions sputtered from the target. In this study, the negative ions were explicitly identified and were found to consist predominantly O^-. The sputter yield of O^- was found to depend on the Ba compound used in the fabrication of Y -Ba-Cu-O targets and was related to the electronegativity difference between the components. An unreacted mixture of rm Y_2O_3, CuO, and BaF_2 was found to have the lowest O^- yield among targets with Y:Ba:Cu = 1:2:3. The high yield of O^- from rm YBa_2Cu_3O _{7-x} was found to depend on the target temperature and be due to the excess oxygen present. The SIMS negative ion data supported the composition data for sputter-deposited Y-Ba-Cu-O films. Targets using BaF _2 were found to improve the Ba deficiency, the run-to-run irreproducibility and the nonuniformity of the film composition typically found in sputtered Y -Ba-Cu-O films. Superconducting Y-Ba-Cu-O films were formed on SrTiO_3 substrates by post-deposition heat treatment of Y-Ba-Cu-O-F films in humid oxygen. The growth of superconducting rm YBa_2Cu_3O_{7-x}, thin films on common substrates such as sapphire or silicon requires the use of a barrier layer to prevent the deleterious interaction which occurs between Y-Ba-Cu-O films and these substrates. Barrier layers of SrTiO_3 were studied and found to exhibit textured growth with a preferred (111) orientation on (100) Si substrates. However, SrTiO_3 was found to be

  20. Synchrotron X-ray studies of epitaxial ferroelectric thin films and nanostructures

    NASA Astrophysics Data System (ADS)

    Klug, Jeffrey A.

    The study of ferroelectric thin films is a field of considerable scientific and technological interest. In this dissertation synchrotron x-ray techniques were applied to examine the effects of lateral confinement and epitaxial strain in ferroelectric thin films and nanostructures. Three materials systems were investigated: laterally confined epitaxial BiFeO3 nanostructures on SrTiO3 (001), ultra-thin commensurate SrTiO 3 films on Si (001), and coherently strained films of BaTiO3 on DyScO3 (110). Epitaxial films of BiFeO3 were deposited by radio frequency magnetron sputtering on SrRuO3 coated SrTiO 3 (001) substrates. Laterally confined nanostructures were fabricated using focused ion-beam processing and subsequently characterized with focused beam x-ray nanodiffraction measurements with unprecedented spatial resolution. Results from a series of rectangular nanostructures with lateral dimensions between 500 nm and 1 mum and a comparably-sized region of the unpatterned BiFeO3 film revealed qualitatively similar distributions of local strain and lattice rotation with a 2-3 times larger magnitude of variation observed in those of the nanostructures compared to the unpatterned film. This indicates that lateral confinement leads to enhanced variation in the local strain and lattice rotation fields in epitaxial BiFeO3 nanostructures. A commensurate 2 nm thick film of SrTiO3 on Si was characterized by the x-ray standing wave (XSW) technique to determine the Sr and Ti cation positions in the strained unit cell in order to verify strain-induced ferroelectricity in SrTiO3/Si. A Si (004) XSW measurement at 10°C indicated that the average Ti displacement from the midpoint between Sr planes was consistent in magnitude to that predicted by a density functional theory (DFT) calculated ferroelectric structure. The Ti displacement determined from a 35°C measurement better matched a DFT-predicted nonpolar structure. The thin film extension of the XSW technique was employed to

  1. Influence of anisotropic strain on the dielectric and ferroelectric properties of SrTiO3 thin films on DyScO3 substrates

    NASA Astrophysics Data System (ADS)

    Biegalski, M. D.; Vlahos, E.; Sheng, G.; Li, Y. L.; Bernhagen, M.; Reiche, P.; Uecker, R.; Streiffer, S. K.; Chen, L. Q.; Gopalan, V.; Schlom, D. G.; Trolier-McKinstry, S.

    2009-06-01

    The in-plane dielectric and ferroelectric properties of coherent anisotropically strained SrTiO3 thin films grown on orthorhombic (101) DyScO3 substrates were examined as a function of the angle between the applied electric field and the principal directions of the substrate. The dielectric permittivity revealed two distinct maxima as a function of temperature along the [100]p and [010]p SrTiO3 pseudocubic directions. These data, in conjunction with optical second-harmonic generation, show that the switchable ferroelectric polarization develops first predominantly along the in-plane axis with the larger tensile strain before developing a polarization component along the perpendicular direction with smaller strain as well, leading to domain twinning at the lower temperature. Finally, weak signatures in the dielectric and second-harmonic generation response were detected at the SrTiO3 tilt transition close to 165 K. These studies indicate that anisotropic biaxial strain can lead to new ferroelectric domain reorientation transitions that are not observed in isotropically strained films.

  2. Effects of crystallization on structural and dielectric properties of thin amorphous films of (1 - x)BaTiO3-xSrTiO3 (x=0-0.5, 1.0)

    NASA Astrophysics Data System (ADS)

    Kawano, H.; Morii, K.; Nakayama, Y.

    1993-05-01

    The possibilities for fabricating solid solutions of (Ba1-x,Srx)TiO3 (x≤0.5,1.0) by crystallization of amorphous films and for improving their dielectric properties by adjusting the Sr content were investigated. Thin amorphous films were prepared from powder targets consisting of mixtures of BaTiO3 and SrTiO3 by sputtering with a neutralized Ar-ion beam. The amorphous films crystallized into (Ba1-x, Srx)TiO3 solid solutions with a cubic perovskite-type structure after annealing in air at 923 K for more than 1 h. The Debye-type dielectric relaxation was observed for the amorphous films, whereas the crystallized films showed paraelectric behavior. The relative dielectric constants were of the order of 20 for the amorphous samples, but increased greatly after crystallization to about 60-200, depending on the composition; a larger increase in the dielectric constant was observed in the higher Sr content films, in the range x≤0.5, which could be correlated with an increase in the grain size of the crystallites. The crystallization processes responsible for the difference in the grain size are discussed based on the microstructural observations.

  3. Evidence for filamentary superconductivity up to 220 K in oriented multiphase Y-Ba-Cu-O thin films

    NASA Astrophysics Data System (ADS)

    Schönberger, R.; Otto, H. H.; Brunner, B.; Renk, K. F.

    1991-02-01

    We report on the observation of filamentary superconductivity up to 220 K in multiphase Y-Ba-Cu-O materials that are deposited as highly oriented thin films on (110)-SrTiO 3 substrates by laser ablation from ceramic targets. The high temperature zero resistivity states are reproducible after temperature cycling down to 80 K for samples treated by a special oxygenation and ozonization process at 340 K and measured in a pure oxygen atmosphere. Our results on thin films confirm former experiments of J.T. Chen and co-workers obtained on ceramic samples with preferred crystallite orientation. A close connection between superconductivity and structural instabilities of most likely ferroic nature, which are observed more often for YBa 2Cu 3O 7 in a narrow temperature range near 220 K, is suggested.

  4. Modulation of ferroelectricity and resistance switching in SrTiO3 films

    NASA Astrophysics Data System (ADS)

    Yang, Fang; Wang, Weihua; Guo, Jiandong

    SrTiO3 has remarkable dielectric property; it also exhibits ferroelectricity in thin films with strain or defects. It is expected that modulation of its ferroelectricity and electricity is potential in oxide electronics. The nonstoichiometry SrTiO3 thin films with different cation concentrations were prepared on Si (001) substrates. Piezoresponse force microscopy measurements show that those films with Sr deficiency display obvious ferroelectricity. The scanning transmission electron microscopy results show that there are interstitial Ti atoms in the unit cells. Polar defect pairs can be formed by the interstitial Ti atoms and Sr vacancies along [100] or [110] direction. Such antisitelike defects observed in SrTiO3 films are considered as the origin of the ferroelectricity. In this way, the SrTiO3 ferroelectricity can be modulated by control the concentration of the antisitelike defects via changing the cation concentration. Further, [(SrTiO3)3 /(LaTiO3)2 ]3 superlattices have been prepared on 0.67[Pb(Mg1/3Nb2/3) O3]-0.33[PbTiO3] (PMN-PT) substrate. The superlattices show resistance switching under the ferroelectric polarization of the PMN-PT substrate. The on/off ratio of the interfacial resistance is about 20% 25%. This can be applied in oxide electronics in potential. This work is supported by Chinese MOST (Grant No. 2014CB921001), Chinese NSFC (Grant No. 11404381 & Grant No. 11225422) and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB07030100).

  5. Crystallographic orientation of epitaxial BaTiO3 films: The role of thermal-expansion mismatch with the substrate

    NASA Astrophysics Data System (ADS)

    Srikant, V.; Tarsa, E. J.; Clarke, D. R.; Speck, J. S.

    1995-02-01

    Expitaxial ferroelectric BaTiO3 thin films have been grown on (001) MgO and MgO-buffered (001) GaAs substrates by pulsed laser deposition to explore the effect of substrate lattice parameter. X-ray-diffraction studies showed that the BaTiO3 films on both MgO single-crystal substrates and MgO-buffered (001) GaAs substrates have a cube-on-cube epitaxy; however, for the BaTiO3 films grown on MgO the spacing of the planes parallel to the substrate was close to the c-axis dimension of the unconstrained tetragonal phase, whereas the BaTiO3 films on MgO/GaAs exhibited a spacing closer to the a-axis dimension of the unconstrained tetragonal phase. The cube-on-cube epitaxy was maintained through the heterostructures even when thin epitaxial intermediate buffer layers of SrTiO3 and La(0.5)Sr(0.5)CoO3 were used. The intermediate layers had no effect on the position of the BaTiO3 peak in theta - 2 theta scans. Together, these observations indicate that, for the materials combinations studied, it is the thermal-expansion mismatch between the film and the underlying substrate that determines the crystallographic orientation of the BaTiO3 film. Preliminary measurements indicate that the BaTiO3 films are 'weakly' ferroelectric.

  6. Epitaxial growth of (111)-oriented BaTiO3/SrTiO3 perovskite superlattices on Pt(111)/Ti/Al2O3(0001) substrates

    NASA Astrophysics Data System (ADS)

    Panomsuwan, Gasidit; Takai, Osamu; Saito, Nagahiro

    2013-09-01

    Symmetric BaTiO3/SrTiO3 (BTO/STO) superlattices (SLs) were epitaxially grown on Pt(111)/Ti/Al2O3(0001) substrates with various modulation periods (Λ = 4.8 - 48 nm) using double ion beam sputter deposition. The BTO/STO SLs exhibit high (111) orientation with two in-plane orientation variants related by a 180° rotation along the [111]Pt axis. The BTO layer is under an in-plane compressive state, whereas the STO layer is under an in-plane tensile state due to the effect of lattice mismatch. A remarkable enhancement of dielectric constant is observed for the SL with relatively small modulation period, which is attributed to both the interlayer biaxial strain effect and the Maxwell-Wagner effect.

  7. Terahertz dielectric response of ferroelectric Ba(x)Sr(1-x)TiO3 thin films.

    PubMed

    Kang, Seung Beom; Kwak, Min Hwan; Choi, Muhan; Kim, Sungil; Kim, Taeyong; Cha, Eun Jong; Kang, Kwang Yong

    2011-11-01

    Terahertz time-domain spectroscopy has been used to investigate the dielectric and optical properties of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films for nominal x-values of 0.4, 0.6, and 0.8 in the frequency range of 0.3 to 2.5 THz. The ferroelectric thin films were deposited at approximately 700 nm thickness on [001] MgO substrate by pulsed laser deposition. The measured complex dielectric and optical constants were compared with the Cole-Cole relaxation model. The results show that the Cole-Cole relaxation model fits well with the data throughout the frequency range and the dielectric relaxation behavior of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films varies with the films compositions. Among the compositions of Ba(x)Sr(1-x)TiO(3) films with different Ba/Sr ratios, Ba(0.6)Sr(0.4)TiO(3) has the highest dielectric constants and the shortest dielectric relaxation time.

  8. Characterization of ZrO2 buffer layers for sequentially evaporated Y-Ba-CuO on Si and Al2O3 substrates

    NASA Technical Reports Server (NTRS)

    Valco, George J.; Rohrer, Norman J.; Pouch, John J.; Warner, Joseph D.; Bhasin, Kul B.

    1988-01-01

    Thin film high temperature superconductors have the potential to change the microwave technology for space communications systems. For such applications it is desirable that the films be formed on substrates such as Al2O3 which have good microwave properties. The use of ZrO2 buffer layers between Y-Ba-Cu-O and the substrate has been investigated. These superconducting films have been formed by multilayer sequential electron beam evaporation of Cu, BaF2 and Y with subsequent annealing. The three layer sequence of Y/BaF2/Cu is repeated four times for a total of twelve layers. Such a multilayer film, approximately 1 micron thick, deposited directly on SrTiO3 and annealed at 900 C for 45 min produces a film with a superconducting onset of 93 K and critical temperature of 85 K. Auger electron spectroscopy in conjunction with argon ion sputtering was used to obtain the distribution of each element as a function of depth for an unannealed film, the annealed film on SrTiO3 and annealed films on ZrO2 buffer layers. The individual layers were apparent. After annealing, the bulk of the film on SrTiO3 is observed to be fairly uniform while films on the substrates with buffer layers are less uniform. The Y-Ba-Cu-O/ZrO2 interface is broad with a long Ba tail into the ZrO2, suggesting interaction between the film and the buffer layer. The underlying ZrO2/Si interface is sharper. The detailed Auger results are presented and compared with samples annealed at different temperatures and durations.

  9. Domain structure of BiFeO3 thin films grown on patterned SrTiO3(001) substrates

    NASA Astrophysics Data System (ADS)

    Nakashima, Seiji; Seto, Shota; Kurokawa, Yuta; Fujisawa, Hironori; Shimizu, Masaru

    2017-10-01

    Recently, new functionalities of ferroelectric domain walls (DWs) have attracted much attention. To realize novel devices using the functionalities of the DWs, techniques to introduce the DWs at arbitrary positions in the ferroelectric thin films are necessary. In this study, we have demonstrated the introduction of the DWs at arbitrary positions in epitaxial BiFeO3 (BFO) thin films using the patterned surface of the SrTiO3 (STO) single-crystal substrate. On the slope pattern of the STO surface, the in-plane orientation of BFO has changed because the in-plane orientation of BFO can be controlled by the step propagation direction of the patterned surface. From the piezoresponse scanning force microscopy and X-ray diffraction reciprocal space mapping results, charged 109° DWs have been introduced into the BFO thin film at the bottom and top of the slope pattern of the STO surface. In addition, the conductivity modulation of the positively charged DW has been observed by current-sensitive atomic force microscopy imaging.

  10. Characterization of Fe-doped SrTiO3/BaTiO3 multilayer films and their ethanol sensing applications

    NASA Astrophysics Data System (ADS)

    Supasai, Thidarat; Wisitsoraat, Anurat; Hodak, Satreerat

    2010-03-01

    Fe-doped SrTiO3/BaTiO3 multilayer films have been deposited on alumina substrate using a sol-gel spin coating technique. The field effect scanning electron microscope photographs revealed a mixture of round and facet-shaped crystals in the undoped films. This microstructure disappeared in Fe-doped films which adopted a more porous sponge-like structure. The grain size of the films decreased from 300 nm for undoped films to 100 nm and 70 nm with Fe doping concentrations of 4 and 8 wt%, respectively. The absorption edge energy for X-rays by Fe was found to be about 7121 eV consistent with Fe^2+ oxidation state. Interdigitated electrodes were applied on these films for ethanol gas sensing application. A sensitivity figure of merit based on the relative change in the resistance of the Fe-doped films 8 wt% film was found to be in the 1-3 range for ethanol doses of 100-1000 ppm when operating at 250 C and in the range of 3-10 when the operating temperature was 350 C.

  11. Electronic Degeneracy and Intrinsic Magnetic Properties of EpitaxialNb : SrTiO3 Thin Films Controlled by Defects

    NASA Astrophysics Data System (ADS)

    Sarantopoulos, A.; Ferreiro-Vila, E.; Pardo, V.; Magén, C.; Aguirre, M. H.; Rivadulla, F.

    2015-10-01

    We report thermoelectric power experiments in e -doped thin films of SrTiO3 (STO) which demonstrate that the electronic band degeneracy can be lifted through defect management during growth. We show that even small amounts of cationic vacancies, combined with epitaxial stress, produce a homogeneous tetragonal distortion of the films, resulting in a Kondo-like resistance upturn at low temperature, large anisotropic magnetoresistance, and nonlinear Hall effect. Ab initio calculations confirm a different occupation of each band depending on the degree of tetragonal distortion. The phenomenology reported in this Letter for tetragonally distorted e -doped STO thin films, is similar to that observed in LaAlO3 /STO interfaces and magnetic STO quantum wells.

  12. Sequentially evaporated thin Y-Ba-Co-O superconducting films on microwave substrates

    NASA Technical Reports Server (NTRS)

    Valco, G. J.; Rohrer, N. J.; Warner, J. D.; Bhasin, K. B.

    1989-01-01

    The development of high T sub c superconducting thin films on various microwave substrates is of major interest in space electronic systems. Thin films of YBa2Cu3O(7-Delta) were formed on SrTiO3, MgO, ZrO2 coated Al2O3, and LaAlO3 substrates by multi-layer sequential evaporation and subsequent annealing in oxygen. The technique allows controlled deposition of Cu, BaF2 and Y layers, as well as the ZrO buffer layers, to achieve reproducibility for microwave circuit fabrication. The three layer structure of Cu/BaF2/Y is repeated a minimum of four times. The films were annealed in an ambient of oxygen bubbled through water at temperatures between 850 C and 900 C followed by slow cooling (-2 C/minute) to 450 C, a low temperature anneal, and slow cooling to room temperature. Annealing times ranged from 15 minutes to 5 hrs. at high temperature and 0 to 6 hr. at 450 C. Silver contacts for four probe electrical measurements were formed by evaporation followed with an anneal at 500 C. The films were characterized by resistance-temperature measurements, energy dispersive X-ray spectroscopy, X-ray diffraction, and scanning electron microscopy. Critical transition temperatures ranged from 30 K to 87 K as a function of the substrate, composition of the film, thicknesses of the layers, and annealing conditions. Microwave ring resonator circuits were also patterned on these MgO and LaAlO3 substrates.

  13. Thin film processing of photorefractive BaTiO3

    NASA Technical Reports Server (NTRS)

    Schuster, Paul R.; Potember, Richard S.

    1991-01-01

    The principle objectives of this ongoing research involve the preparation and characterization of polycrystalline single-domain thin films of BaTiO3 for photorefractive applications. These films must be continuous, free of cracks, and of high optical quality. The two methods proposed are sputtering and sol-gel related processing.

  14. The atomic structure and polarization of strained SrTiO3/Si

    NASA Astrophysics Data System (ADS)

    Kumah, D. P.; Reiner, J. W.; Segal, Y.; Kolpak, A. M.; Zhang, Z.; Su, D.; Zhu, Y.; Sawicki, M. S.; Broadbridge, C. C.; Ahn, C. H.; Walker, F. J.

    2010-12-01

    For thin film devices based on coupling ferroelectric polarization to charge carriers in semiconductors, the role of the interface is critical. To elucidate this role, we use synchrotron x-ray diffraction to determine the interface structure of epitaxial SrTiO3 grown on the (001) surface of Si. The average displacement of the O octahedral sublattice relative to the Sr sublattice determines the film polarization and is measured to be about 0.05 nm toward the Si, with Ti off-center displacements 0.009 nm away from the substrate. Measurements of films with different boundary conditions on the top of the SrTiO3 show that the polarization at the SrTiO3/Si interface is dominated by oxide-Si chemical interactions.

  15. Finite-size versus interface-proximity effects in thin-film epitaxial SrTiO3

    NASA Astrophysics Data System (ADS)

    De Souza, R. A.; Gunkel, F.; Hoffmann-Eifert, S.; Dittmann, R.

    2014-06-01

    The equilibrium electrical conductivity of epitaxial SrTiO3 (STO) thin films was investigated as a function of temperature, 950≤ T/K ≤1100, and oxygen partial pressure, 10-23≤ pO2/bar ≤1. Compared with single-crystal STO, nanoscale thin-film STO exhibited with decreasing film thickness an increasingly enhanced electronic conductivity under highly reducing conditions, with a corresponding decrease in the activation enthalpy of conduction. This implies substantial modification of STO's point-defect thermodynamics for nanoscale film thicknesses. We argue, however, against such a finite-size effect and for an interface-proximity effect. Indeed, assuming trapping of oxygen vacancies at the STO surface and concomitant depletion of oxygen vacancies—and accumulation of electrons—in an equilibrium surface space-charge layer, we are able to predict quantitatively the conductivity as a function of temperature, oxygen partial pressure, and film thickness. Particularly complex behavior is predicted for ultrathin films that are consumed entirely by space charge.

  16. Dielectric and piezoelectric properties of lead-free (Bi,Na)TiO3-based thin films

    NASA Astrophysics Data System (ADS)

    Abazari, M.; Safari, A.; Bharadwaja, S. S. N.; Trolier-McKinstry, S.

    2010-02-01

    Dielectric and piezoelectric properties of morphotropic phase boundary (Bi,Na)TiO3-(Bi,K)TiO3-BaTiO3 epitaxial thin films deposited on SrRuO3 coated SrTiO3 substrates were reported. Thin films of 350 nm thickness exhibited small signal dielectric permittivity and loss tangent values of 750 and 0.15, respectively, at 1 kHz. Ferroelectric hysteresis measurements indicated a remanent polarization value of 30 μC/cm2 with a coercive field of 85-100 kV/cm. The thin film transverse piezoelectric coefficient (e31,f) of these films after poling at 600 kV/cm was found to be -2.2 C/m2. The results indicate that these BNT-based thin films are a potential candidate for lead-free piezoelectric devices.

  17. Ultrafast modification of the polarity at LaAlO3/SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Rubano, A.; Günter, T.; Fiebig, M.; Granozio, F. Miletto; Marrucci, L.; Paparo, D.

    2018-01-01

    Oxide growth with semiconductorlike accuracy has led to atomically precise thin films and interfaces that exhibit a plethora of phases and functionalities not found in the oxide bulk material. This has yielded spectacular discoveries such as the conducting, magnetic, and even superconducting LaAlO3/SrTiO3 interfaces separating two prototypical insulating perovskite materials. All these investigations, however, consider the static state at the interface, although studies on fast oxide interface dynamics would introduce a powerful degree of freedom to understanding the nature of the LaAlO3/SrTiO3 interface state. Here, we show that the polarization state at the LaAlO3/SrTiO3 interface can be optically enhanced or attenuated within picoseconds. Our observations are explained by a model based on charge propagation effects in the interfacial vicinity and transient polarization buildup at the interface.

  18. Transport properties and pinning analysis for Co-doped BaFe2As2 thin films on metal tapes

    NASA Astrophysics Data System (ADS)

    Xu, Zhongtang; Yuan, Pusheng; Fan, Fan; Chen, Yimin; Ma, Yanwei

    2018-05-01

    We report on the transport properties and pinning analysis of BaFe1.84Co0.16As2 (Ba122:Co) thin films on metal tapes by pulsed laser deposition. The thin films exhibit a large in-plane misorientation of 5.6°, close to that of the buffer layer SrTiO3 (5.9°). Activation energy U 0(H) analysis reveals a power law relationship with field, having three different exponents at different field regions, indicative of variation from single-vortex pinning to a collective flux creep regime. The Ba122:Co coated conductors present {{T}{{c}}}{{onset}} = 20.2 K and {{T}{{c}}}{{zero}} = 19.0 K along with a self-field J c of 1.14 MA cm‑2 and an in-field J c as high as 0.98 and 0.86 MA cm‑2 up to 9 T at 4.2 K for both major crystallographic directions of the applied field, promising for high field applications. Pinning force analysis indicates a significant enhancement compared with similar Ba122:Co coated conductors. By using the anisotropic scaling approach, intrinsic pinning associated with coupling between superconducting blocks can be identified as the pinning source in the vicinity of H//ab, while for H//c random point defects are likely to play a role but correlated defects start to be active at high temperatures.

  19. Surface structural reconstruction of SrVO3 thin films on SrTiO3 (001)

    NASA Astrophysics Data System (ADS)

    Wang, Gaomin; Saghayezhian, Mohammad; Chen, Lina; Guo, Hangwen; Zhang, Jiandi

    Paramagnetic metallic oxide SrVO3>(SVO) is an itinerant system known to undergo thickness-induced metal-insulator-transition (MIT) in ultrathin film form, which makes it a prototype system for the study of the mechanism behind metal-insulator-transition like structure distortion, electron correlations and disorder-induced localization. We have grown SrVO3 thin film with atomically flat surface through the layer-by-layer deposition by laser Molecular Beam Epitaxy (laser-MBE) on SrTiO3 (001) surface. Low Energy Electron Diffraction (LEED) measurements reveal that there is a (√2X √2) R45°surface reconstruction independent of film thickness. By using LEED-I(V) structure refinement, we determine the surface structure. In combination with X-ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling Microscopy (STM), we discuss the implication on the MIT in ultrathin films below 2-3 unit cell thickness. This work is supported by the National Science Foundation under the NSF EPSCoR Cooperative Agreement No. EPS-1003897 with additional support from the Louisiana Board of Regents.

  20. Carrier-Controlled Ferromagnetism in SrTiO 3

    DOE PAGES

    Moetakef, Pouya; Williams, James R.; Ouellette, Daniel G.; ...

    2012-06-27

    Magnetotransport and superconducting properties are investigated for uniformly La-doped SrTiO 3 films and GdTiO 3/SrTiO 3 heterostructures, respectively. GdTiO 3/SrTiO 3 interfaces exhibit a high-density 2D electron gas on the SrTiO 3 side of the interface, while, for the SrTiO 3 films, carriers are provided by the dopant atoms. Both types of samples exhibit ferromagnetism at low temperatures, as evidenced by a hysteresis in the magnetoresistance. For the uniformly doped SrTiO 3 films, the Curie temperature is found to increase with doping and to coexist with superconductivity for carrier concentrations on the high-density side of the superconducting dome. The Curiemore » temperature of the GdTiO 3/SrTiO 3 heterostructures scales with the thickness of the SrTiO 3 quantum well. The results are used to construct a stability diagram for the ferromagnetic and superconducting phases of SrTiO 3.« less

  1. Memristive behavior in BaTiO 3 thin films integrated with semiconductors

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Prater, John; Narayan, Jay

    BaTiO3 has been studied for emerging non-volatile memory applications. However, most of the previous work has focused on this material when it was deposited on insulting oxide substrates such as SrTiO3. Unfortunately, this substrate is not suitable for CMOS-based microelectronics applications. This motivated us to carry out the present work. We have studied the resistive switching behavior in BaTiO3/La0.7Sr0.3MnO3 (BTO/LSMO) heterostructures integrated with Si (100) using pulsed laser deposition1,2. I-V measurements were conducted on BTO (500nm)/LSMO (25nm) devices at 200K, with the compliance current of 10mA. Here, Pt was used as a top electrode and LSMO served as bottom electrode. A few important observations are noted: (a) broad hysteresis in forward and reverse voltage sweeps -ideal for memory applications, (b) the ratio of high resistance to low resistance state is ~600 -important for switching devices, (c) the device is stable at least up to 50 cycles. However, we found that hysteretic behavior was collapsed after 36 cycles upon oxygen annealing of the device at 1 atmospheric pressure, 200o C for 1 hour, inferring the important role of oxygen vacancies in the resistive switching behavior of BTO/LSMO device. The comprehensive experimental data will be presented and discussed.1,2.

  2. Formation mechanism of Ruddlesden-Popper-type antiphase boundaries during the kinetically limited growth of Sr rich SrTiO3 thin films

    PubMed Central

    Xu, Chencheng; Du, Hongchu; van der Torren, Alexander J. H.; Aarts, Jan; Jia, Chun-Lin; Dittmann, Regina

    2016-01-01

    We elucidated the formation process for Ruddlesden-Popper-type defects during pulsed laser deposition of Sr rich SrTiO3 thin films by a combined analysis of in-situ atomic force microscopy, low energy electron diffraction and high resolution scanning transmission electron microscopy. At the early growth stage of 1.5 unit cells, the excess Sr results in the formation of SrO on the surface, resulting in a local termination change from TiO2 to SrO, thereby forming a Sr rich (2 × 2) surface reconstruction. With progressive SrTiO3 growth, islands with thermodynamically stable SrO rock-salt structure are formed, coexisting with TiO2 terminated islands. During the overgrowth of these thermodynamically stable islands, both lateral as well as vertical Ruddlesden-Popper-type anti-phase boundaries are formed, accommodating the Sr excess of the SrTiO3 film. We suggest the formation of thermodynamically stable SrO rock-salt structures as origin for the formation of Ruddlesden-Popper-type antiphase boundaries, which are as a result of kinetic limitations confined to certain regions on the surface. PMID:27922069

  3. Formation mechanism of Ruddlesden-Popper-type antiphase boundaries during the kinetically limited growth of Sr rich SrTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Xu, Chencheng; Du, Hongchu; van der Torren, Alexander J. H.; Aarts, Jan; Jia, Chun-Lin; Dittmann, Regina

    2016-12-01

    We elucidated the formation process for Ruddlesden-Popper-type defects during pulsed laser deposition of Sr rich SrTiO3 thin films by a combined analysis of in-situ atomic force microscopy, low energy electron diffraction and high resolution scanning transmission electron microscopy. At the early growth stage of 1.5 unit cells, the excess Sr results in the formation of SrO on the surface, resulting in a local termination change from TiO2 to SrO, thereby forming a Sr rich (2 × 2) surface reconstruction. With progressive SrTiO3 growth, islands with thermodynamically stable SrO rock-salt structure are formed, coexisting with TiO2 terminated islands. During the overgrowth of these thermodynamically stable islands, both lateral as well as vertical Ruddlesden-Popper-type anti-phase boundaries are formed, accommodating the Sr excess of the SrTiO3 film. We suggest the formation of thermodynamically stable SrO rock-salt structures as origin for the formation of Ruddlesden-Popper-type antiphase boundaries, which are as a result of kinetic limitations confined to certain regions on the surface.

  4. Enhanced superconductivity due to forward scattering in FeSe thin films on SrTiO 3 substrates

    DOE PAGES

    Rademaker, Louk; Wang, Yan; Berlijn, Tom; ...

    2016-02-10

    In this paper, we study the consequences of an electron–phonon (e–ph) interaction that is strongly peaked in the forward scattering (more » $${\\bf{q}}=0$$) direction in a two-dimensional superconductor using Migdal–Eliashberg theory. We find that strong forward scattering results in an enhanced T c that is linearly proportional to the strength of the dimensionless e–ph coupling constant $${\\lambda }_{m}$$ in the weak coupling limit. This interaction also produces distinct replica bands in the single-particle spectral function, similar to those observed in recent angle-resolved photoemission experiments on FeSe monolayers on SrTiO 3 and BaTiO 3 substrates. Finally, by comparing our model to photoemission experiments, we infer an e–ph coupling strength that can provide a significant portion of the observed high T c in these systems.« less

  5. Mobility Optimization in LaxBa1-xSnO3 Thin Films Deposited via High Pressure Oxygen Sputtering

    NASA Astrophysics Data System (ADS)

    Postiglione, William Michael

    BaSnO3 (BSO) is one of the most promising semiconducting oxides currently being explored for use in future electronic applications. BSO possesses a unique combination of high room temperature mobility (even at very high carrier concentrations, > 1019 cm-3), wide band gap, and high temperature stability, making it a potentially useful material for myriad applications. Significant challenges remain however in optimizing the properties and processing of epitaxial BSO, a critical step towards industrial applications. In this study we investigate the viability of using high pressure oxygen sputtering to produce high mobility La-doped BSO thin films. In the first part of our investigation we synthesized, using solid state reaction, phase-pure stoichiometric polycrystalline 2% La-doped BaSnO 3 for use as a target material in our sputtering system. We verified the experimental bulk lattice constant, 4.117 A, to be in good agreement with literature values. Next, we set out to optimize the growth conditions for DC sputtering of La doped BaSnO3. We found that mobility for all our films increased monotonically with deposition temperature, suggesting the optimum temperature for deposition is > 900 °C and implicating a likely improvement in transport properties with post-growth thermal anneal. We then preformed systematic studies aimed at probing the effects of varying thickness and deposition rate to optimize the structural and electronic transport properties in unbuffered BSO films. In this report we demonstrate the ability to grow 2% La BSO thin films with an effective dopant activation of essentially 100%. Our films showed fully relaxed (bulk), out-of-plane lattice parameter values when deposited on LaAlO3, MgO, and (LaAlO3)0.3(Sr2 TaAlO6)0.7 substrates, and slightly expanded out-of-plane lattice parameters for films deposited on SrTiO3, GdScO3, and PrScO3 substrates. The surface roughness's of our films were measured via AFM, and determined to be on the nm scale or better

  6. Large Energy Density, Excellent Thermal Stability, and High Cycling Endurance of Lead-Free BaZr0.2Ti0.8O3 Film Capacitors.

    PubMed

    Sun, Zixiong; Ma, Chunrui; Wang, Xi; Liu, Ming; Lu, Lu; Wu, Ming; Lou, Xiaojie; Wang, Hong; Jia, Chun-Lin

    2017-05-24

    A large energy storage density (ESD) of 30.4 J/cm 3 and high energy efficiency of 81.7% under an electrical field of 3 MV/cm was achieved at room temperature by the fabrication of environmentally friendly lead-free BaZr 0.2 Ti 0.8 O 3 epitaxial thin films on Nb-doped SrTiO 3 (001) substrates by using a radio-frequency magnetron sputtering system. Moreover, the BZT film capacitors exhibit great thermal stability of the ESD from 16.8 J/cm 3 to 14.0 J/cm 3 with efficiency of beyond 67.4% and high fatigue endurance (up to 10 6 cycles) in a wide temperature range from room temperature to 125 °C. Compared to other BaTiO 3 -based energy storage capacitor materials and even Pb-based systems, BaZr 0.2 Ti 0.8 O 3 thin film capacitors show either high ESD or great energy efficiency. All of these excellent results revealed that the BaZr 0.2 Ti 0.8 O 3 film capacitors have huge potential in the application of modern electronics, such as locomotive and pulse power, in harsh working environments.

  7. Properties and Degradation of Polarization Reversal of Soft BaTiO3 Ceramics for Ferroelectric Thin-Film Devices

    NASA Astrophysics Data System (ADS)

    Thongrueng, Jirawat; Tsuchiya, Toshio; Masuda, Yoichiro; Fujita, Shigetaka; Nagata, Kunihiro

    1999-09-01

    Soft BaTiO3 ceramics having a very low coercive field of 65 V/mm were prepared by substituting 9 mol% Hf Zr for the Ti-site of BaTiO3, for applications to ferroelectric thin-film devices. Electrical properties of the soft BaTiO3 ceramics were measured and compared with those of normal BaTiO3 ceramics. By substituting Hf Zr for Ti-site, the phase transition temperatures were controlled, and we could select the preferred crystal structure from the tetragonal, orthorhombic and rhombohedral phases at room temperature. In addition, the preparation and characterization of the soft BaTiO3 thin-films using a sol-gel process were carried out.

  8. Impact of Fe doping on the electronic structure of SrTiO3 thin films determined by resonant photoemission

    NASA Astrophysics Data System (ADS)

    Kubacki, J.; Kajewski, D.; Goraus, J.; Szot, K.; Koehl, A.; Lenser, Ch.; Dittmann, R.; Szade, J.

    2018-04-01

    Epitaxial thin films of Fe doped SrTiO3 have been studied by the use of resonant photoemission. This technique allowed us to identify contributions of the Fe and Ti originating electronic states to the valence band. Two valence states of iron Fe2+ and Fe3+, detected on the base of x-ray absorption studies spectra, appeared to form quite different contributions to the valence band of SrTiO3. The electronic states within the in-gap region can be attributed to Fe and Ti ions. The Fe2+ originating states which can be connected to the presence of oxygen vacancies form a broad band reaching binding energies of about 0.5 eV below the conduction band, while Fe3+ states form in the gap a sharp feature localized just above the top of the valence band. These structures were also confirmed by calculations performed with the use of the FP-LAPW/APW+lo method including Coulomb correlations within the d shell. It has been shown that Fe doping induced Ti originating states in the energy gap which can be related to the hybridization of Ti and Fe 3d orbitals.

  9. Modulation-Doped SrTiO3/SrTi1-xZrxO3 Heterostructures

    NASA Astrophysics Data System (ADS)

    Kajdos, Adam Paul

    Two-dimensional electron gases (2DEGs) in SrTiO3 have attracted considerable attention for exhibiting a variety of interesting physical phenomena, such as superconductivity and magnetism. So far, most of the literature has focused on interfaces between nonpolar SrTiO3 and polar perovskite oxides (e.g. LaAlO3 or rare-earth titanates), where high carrier density 2DEGs (˜3 x 1014 cm-2) are generated by polar discontinuity. Modulation doping is an alternative approach to generating a 2DEG that has been explored extensively in III-V semiconductors but has not heretofore been explored in complex oxides. This approach involves interfacing an undoped semiconductor with a doped semiconductor whose conduction band edge lies at a higher energy, which results in electrons diffusing into the undoped semiconductor transport channel, where scattering from ionized dopants is minimized. Realizing a high-mobility modulation-doped structure with a SrTiO3 transport channel therefore requires both the optimization of the transport channel by minimizing native defects as well as the development of a perovskite oxide which has a suitable band offset with SrTiO3 and can be electron-doped. The growth of high electron mobility SrTiO3 as a suitable transport channel material was previously demonstrated using the hybrid molecular beam epitaxy (MBE) approach, where Sr is delivered via a solid source and Ti is delivered using a metal-organic precursor, titanium (IV) tetra-isopropoxide (TTIP). Expanding on this, in-situ reflection high-energy electron diffraction (RHEED) is used to track the surface and resulting film cation stoichiometry of homoepitaxial SrTiO3 (001) thin films grown by hybrid MBE. It is shown that films with lattice parameters identical to bulk single-crystal substrates within the detection limit of high-resolution X-ray diffraction (XRD) measurements exhibit an evolution in surface reconstruction with increasing TTIP beam-equivalent pressure. The change in the observed

  10. Influence of Strain on the Thermoelectric Properties of electron-doped SrTiO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Sarantopoulos, Alexandros; Ferreiro-Vila, Elias; Magen, Cesar; Aguirre, Myriam H.; Pardo, Victor; Rivadulla, Francisco

    2015-03-01

    The discovery of a two dimensional electron gas with high mobility at the interface between insulating LaAlO3 / SrTiO3 (LAO/STO) opened the possibility of fabricating functional devices based on this interfacial effect. Therefore, it is important to study the influence of the growth parameters on the properties of the constituent materials. Here, we demonstrate that the thermoelectric properties of epitaxial thin films of Nb:STO can be finely tuned by adjusting the growth conditions in a PLD system. By growing the sample on different substrates, we demonstrate that the amount of vacancies depends on the degree of epitaxial compressive stress. The vacancies produced lead to impurity scattering at low temperatures. We show that the magnetoresistance response, and non-linear behavior of the Hall effect, characteristic of LAO/STO interfaces, can be reproduced in thin films of Nb:STO with a controlled number of vacancies. Moreover, we show that the Seebeck coefficient is a valid tool to obtain information about the degeneracy of the electronic band structure. We acknowledge support from the ERC 2D Therms project.

  11. Optical properties of epitaxial BiFeO3 thin film grown on SrRuO3-buffered SrTiO3 substrate.

    PubMed

    Xu, Ji-Ping; Zhang, Rong-Jun; Chen, Zhi-Hui; Wang, Zi-Yi; Zhang, Fan; Yu, Xiang; Jiang, An-Quan; Zheng, Yu-Xiang; Wang, Song-You; Chen, Liang-Yao

    2014-01-01

    The BiFeO3 (BFO) thin film was deposited by pulsed-laser deposition on SrRuO3 (SRO)-buffered (111) SrTiO3 (STO) substrate. X-ray diffraction pattern reveals a well-grown epitaxial BFO thin film. Atomic force microscopy study indicates that the BFO film is rather dense with a smooth surface. The ellipsometric spectra of the STO substrate, the SRO buffer layer, and the BFO thin film were measured, respectively, in the photon energy range 1.55 to 5.40 eV. Following the dielectric functions of STO and SRO, the ones of BFO described by the Lorentz model are received by fitting the spectra data to a five-medium optical model consisting of a semi-infinite STO substrate/SRO layer/BFO film/surface roughness/air ambient structure. The thickness and the optical constants of the BFO film are obtained. Then a direct bandgap is calculated at 2.68 eV, which is believed to be influenced by near-bandgap transitions. Compared to BFO films on other substrates, the dependence of the bandgap for the BFO thin film on in-plane compressive strain from epitaxial structure is received. Moreover, the bandgap and the transition revealed by the Lorentz model also provide a ground for the assessment of the bandgap for BFO single crystals.

  12. Atomic and electronic structures of BaHfO3-doped TFA-MOD-derived YBa2Cu3O7-δ thin films

    NASA Astrophysics Data System (ADS)

    Molina-Luna, Leopoldo; Duerrschnabel, Michael; Turner, Stuart; Erbe, Manuela; Martinez, Gerardo T.; Van Aert, Sandra; Holzapfel, Bernhard; Van Tendeloo, Gustaaf

    2015-11-01

    Tailoring the properties of oxide-based nanocomposites is of great importance for a wide range of materials relevant for energy technology. YBa2Cu3O7-δ (YBCO) superconducting thin films containing nanosized BaHfO3 (BHO) particles yield a significant improvement of the magnetic flux pinning properties and a reduced anisotropy of the critical current density. These films were prepared by chemical solution deposition (CSD) on (100) SrTiO3 (STO) substrates yielding critical current densities up to 3.6 MA cm-2 at 77 K and self-field. Transport in-field J c measurements demonstrated a high pinning force maximum of around 6 GN/m3 for a sample annealed at T = 760 °C that has a doping of 12 mol% of BHO. This sample was investigated by scanning transmission electron microscopy (STEM) in combination with electron energy-loss spectroscopy (EELS) yielding strain and spectral maps. Spherical BHO nanoparticles of 15 nm in size were found in the matrix, whereas the particles at the interface were flat. A 2 nm diffusion layer containing Ti was found at the YBCO (BHO)/STO interface. Local lattice deformation mapping at the atomic scale revealed crystal defects induced by the presence of both sorts of BHO nanoparticles, which can act as pinning centers for magnetic flux lines. Two types of local lattice defects were identified and imaged: (i) misfit edge dislocations and (ii) Ba-Cu-Cu-Ba stacking faults (Y-248 intergrowths). The local electronic structure and charge transfer were probed by high energy resolution monochromated electron energy-loss spectroscopy. This technique made it possible to distinguish superconducting from non-superconducting areas in nanocomposite samples with atomic resolution in real space, allowing the identification of local pinning sites on the order of the coherence length of YBCO (˜1.5 nm) and the determination of 0.25 nm dislocation cores.

  13. Optimization of Strontium Titanate (SrTiO3) Thin Films Fabricated by Metal Organic Chemical Vapor Deposition (MOCVD) for Microwave-Tunable Devices

    DTIC Science & Technology

    2015-12-01

    induced (non)stoichiometry on the structure, dielectric response, and thermal conductivity of SrTiO3 thin films. Chemistry of Materials. 2012;24:331...must be below a few percent. The external sources of loss, such as conductor interface losses and various losses that inevitably arise from device...epitaxy • Excellent control of film stoichiometry and thickness • Large area uniformity and potential for complex structure coating • Optimized

  14. Spatially Resolved Nano-Scale Characterization of Electronic States in SrTiO3(001) Surfaces by STM/STS

    NASA Astrophysics Data System (ADS)

    Iwaya, Katsuya; Ohsawa, Takeo; Shimizu, Ryota; Hashizume, Tomihiro; Hitosugi, Taro

    2012-02-01

    We have performed low temperature scanning tunneling microscopy/spectroscopy (STM/STS) measurements on TiO2-terminated SrTiO3(001) thin film surfaces. The conductance map exhibited electronic modulations that were completely different from the surface structure. We also found that the electronic modulations were strongly dependent on temperature and the density of atomic defects associated with oxygen vacancies. These results suggest the existence of strongly correlated two-dimensional electronic states near the SrTiO3 surface, implying the importance of electron correlation at the interfaces of SrTiO3-related heterostructures.

  15. Thermoelectric properties of hole-doped SrTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Ferreiro-Vila, Elias; Sarantopoulos, Alexandros; Leboran, Victor; Bui, Cong-Tinh; Rivadulla, Francisco; Condense matter Chemistry Group Team

    2014-03-01

    Two dimensional conductors are expected to show an improved thermoelectric performance due the positive effect of quantum confinement on the thermoelectric power, and the decrease of thermal conductivity by interface boundary scattering. The recent report of a large increase of the thermoelectric power in quantum wells of Nb-doped SrTiO3 (STO) seems to be in agreement with this hypothesis. However, extrinsic effects like the existence of oxygen vacancies that propagate away from the interface cannot be ruled out, and the results are far from clear. Here we will show the thermoelectric properties (electrical conductivity, Seebeck coefficient, and Hall effect), of epitaxial thin-films of (La,Nb)-doped STO. The films have been deposited by PLD on different substrates (STO, LAO...) to study the effect of tensile/compressive stress on the thermoelectric properties of the system. The oxygen pressure during the deposition was carefully controlled to tune the amount of oxygen vacancies and to compare with the cation doping. We have performed a systematic study of the transport properties as a function of thickness and doping, which along with the effect of stress, allows to understand the effect of charge density and dimensionality in an oxide system with promising thermoelectric properties.

  16. Stress generated modifications of epitaxial ferroelectric SrTiO3 films on sapphire

    NASA Astrophysics Data System (ADS)

    Hollmann, E.; Schubert, J.; Kutzner, R.; Wördenweber, R.

    2009-06-01

    The effect of lattice-mismatch induced stress upon the crystallographic structure, strain, strain relaxation, and the generation of different types of defects in heteroepitaxially grown SrTiO3 films on CeO2 buffered sapphire is examined. Depending on the thickness of the SrTiO3 layer, characteristic changes in the structural perfection of the layers, their crystallographic orientation with respect to the substrate system, and their strain is observed. For thin films misfit dislocations partially compensate the stress in the SrTiO3 layer, whereas cracks develop in thicker SrTiO3 films. The cracks are orientated along two predominant crystallographic orientations of the sapphire. The structural modifications and the formation of misfit defects and cracks are explained in a model based on lattice misfit induced stress, on the one hand, and energy considerations taking into account the stress release due to crack formation and the energy necessary for the formation of new surfaces at the crack, on the other hand. The impact of lattice misfit is discussed in two steps, i.e., intrinsic and thermal induced misfits during heteroepitaxial film growth at a given temperature and the subsequent cooling of the sample, respectively. The comparison of the theoretical predictions and the experimental observations demonstrate that intrinsic mismatch and thermal mismatch have to be considered in order to explain strain dependent effects in complex heteroepitaxial layer systems such as induced ferroelectricity of SrTiO3 on sapphire.

  17. Perpendicular magnetic anisotropy of La0.67Sr0.33MnO3 thin films grown on CaMnO3 buffered SrTiO3

    NASA Astrophysics Data System (ADS)

    Wang, Zhi-Hong; Cristiani, G.; Habermeier, H.-U.; Zhang, Zhen-Rong; Han, Bao-Shan

    2003-10-01

    La0.67Sr0.33MnO3(LSMO) thin films were grown onto CaMnO3(CMO) buffered SrTiO3(100) by pulsed laser deposition. Because of the in-plane compressive strain induced by the lattice mismatch between CMO and LSMO, a perpendicular magnetic anisotropy (PMA) was obtained in the overlayer LSMO. Using the magnetic force microscopy, stripe magnetic domains in association with the PMA were observed at room temperature. Furthermore, the magnetoresistance with in-plane magnetic field parallel and vertical to the measuring current was studied at 5 and 300 K, and its correlation with the magnetic anisotropy has been discussed.

  18. Characterization of SrTiO3 target doped with Co ions, SrCoxTi1-xO3-δ, and their thin films prepared by pulsed laser ablation (PLA) in water for visible light response

    NASA Astrophysics Data System (ADS)

    Ichihara, Fumihiko; Murata, Yuma; Ono, Hiroshi; Choo, Cheow-keong; Tanaka, Katsumi

    2017-10-01

    SrTiO3 (STO) and Co-doped SrTiO3 (Co-STO) sintered targets were synthesized and were Ar+ sputtered to elucidate the charge compensation effect between Sr, Ti and Co cations following the reduction by oxygen desorption. Following exposure of the Ar+-sputtered target to the air, charge transfer reactions occurred among Co2+, Ti3+, O2- and Sr2+ species which were studied by their XPS spectra. Pulsed laser ablation (PLA) of these targets was carried out in water to prepare the nanoparticles which could be supplied to the thin films with much higher surface reactivity expected for photocatalytic reactions. The roles of Co ions were studied for the stoichiometry and crystallinity of the nanoparticles which constituted the thin films. Photo-degradation of methylene blue was carried out on the PLA thin films under very weak visible light at 460 nm. The PLA thin films showed the photocatalytic activities, which were enhanced by the presence of Co ions. Such the effect of Co ions was considered from viewpoint of the d-d transition and the charge-transfer between Co ions and the ligand oxygen.

  19. Photovoltaic properties of ferroelectric BaTiO3 thin films RF sputter deposited on silicon

    NASA Technical Reports Server (NTRS)

    Dharmadhikari, V. S.; Grannemann, W. W.

    1982-01-01

    Ferroelectric thin films of BaTiO3 have been successfully deposited on n-type silicon substrates at temperatures above 500 C by RF sputtering in an O2/Ar atmosphere. Analysis by X-ray diffraction patterns show that films deposited at room temperature are amorphous. At temperatures above 500 C, crystalline BaTiO3 films with a tetragonal structure are obtained. The polarization-electric field (P-E) hysteresis loops and a broad peak in the dielectric constant versus temperature curve at Curie point indicate that the RF sputtered BaTiO3 films are ferroelectric. An anomalous photovoltaic effect is observed in these thin films which is related to the remanent polarization of the material. The results on open-circuit and short-circuit measurements provide an important basis for a better understanding of the role of photovoltaic field, photovoltaic current, and the pyroelectric properties in photoferroelectric domain switching.

  20. Top-seeded solution growth of SrTiO3 single crystals virtually free of mosaicity

    NASA Astrophysics Data System (ADS)

    Guguschev, Christo; Kok, Dirk J.; Juda, Uta; Uecker, Reinhard; Sintonen, Sakari; Galazka, Zbigniew; Bickermann, Matthias

    2017-06-01

    Strontium titanate (SrTiO3), a well-established traditional perovskite substrate as well as a promising substrate crystal for the epitaxy of new advanced perovskite-type thin films, suffers from the unavailability in adequate quality for the latter. To improve the situation attempts have been made to grow SrTiO3 at moderate temperatures (<1535 °C) well below the melting temperature and under low temperature gradients by the top-seeded solution growth method. Based on very special modifications of the growth conditions, virtually mosaicity-free SrTiO3 single crystals in the 1-2 cm range were obtained. High crystalline quality was verified by defect selective etching, rocking curve measurements, energy dispersive Laue mappings and by synchrotron X-Ray diffraction topography. The production of virtually subgrain- and dislocation free substrate crystals is essential to considerably improve characteristics of SrTiO3 based SQUIDs, transistors or memory devices and to allow an in-depth analysis of intrinsic and extrinsic factors influencing the properties of epitaxially grown oxide heterostructures.

  1. Out-of-plane easy-axis in thin films of diluted magnetic semiconductor Ba1-xKx(Zn1-yMny)2As2

    NASA Astrophysics Data System (ADS)

    Wang, R.; Huang, Z. X.; Zhao, G. Q.; Yu, S.; Deng, Z.; Jin, C. Q.; Jia, Q. J.; Chen, Y.; Yang, T. Y.; Jiang, X. M.; Cao, L. X.

    2017-04-01

    Single-phased, single-oriented thin films of Mn-doped ZnAs-based diluted magnetic semiconductor (DMS) Ba1-xKx(Zn1-yMny)2As2 (x = 0.03, 0.08; y = 0.15) have been deposited on Si, SrTiO3, LaAlO3, (La,Sr)(Al,Ta)O3, and MgAl2O4 substrates, respectively. Utilizing a combined synthesis and characterization system excluding the air and further optimizing the deposition parameters, high-quality thin films could be obtained and be measured showing that they can keep inactive-in-air up to more than 90 hours characterized by electrical transport measurements. In comparison with films of x = 0.03 which possess relatively higher resistivity, weaker magnetic performances, and larger energy gap, thin films of x = 0.08 show better electrical and magnetic performances. Strong magnetic anisotropy was found in films of x = 0.08 grown on (La,Sr)(Al,Ta)O3 substrate with their magnetic polarization aligned almost solely on the film growth direction.

  2. Optimized dielectric properties of SrTiO3:Nb /SrTiO3 (001) films for high field effect charge densities

    NASA Astrophysics Data System (ADS)

    Cai, Xiuyu; Frisbie, C. Daniel; Leighton, C.

    2006-12-01

    The authors report the growth, structural and electrical characterizations of SrTiO3 films deposited on conductive SrTiO3:Nb (001) substrates by high pressure reactive rf magnetron sputtering. Optimized deposition parameters yield smooth epitaxial layers of high crystalline perfection with a room temperature dielectric constant ˜200 (for a thickness of 1150Å). The breakdown fields in SrTiO3:Nb /SrTiO3/Ag capacitors are consistent with induced charge densities >1×1014cm-2 for both holes and electrons, making these films ideal for high charge density field effect devices.

  3. Tunable dielectric response, resistive switching, and unconventional transport in SrTiO3

    NASA Astrophysics Data System (ADS)

    Mikheev, Evgeny

    The first section of this thesis discusses integration of SR TiO3 grown by molecular beam epitaxy (MBE) in vertical device structures. One target application is as a tunable dielectric. Parallel plate capacitors based on epitaxial Pt(001) bottom electrodes and (Ba,Sr)TiO 3 dielectric layers grown by MBE are demonstrated. Optimization of structural quality of the vertical stack is shown to produce very low dielectric loss combined with very high tunability of the dielectric constant by DC bias. This results in considerable improvement of common figures of merit for varactor performance in comparison to previous reports. Another target application for transition metals oxides is in resistive switching memories, which are based on the hysteretic current-voltage response observed in many oxide-based Schottky junctions and capacitors. A study on the role of metal/oxide interface quality is presented. In particular, the use of epitaxial Pt(001) as Schottky contacts to Nb:SRTiO 3 is shown to suppress resistive switching hysteresis by eliminating unintentional contributions to interface capacitance. Such uncontrolled factors are discussed as a probable root cause for poor reproducibility in resistive switching memories, currently a ubiquitous challenge in the field. Potential routes towards stabilizing reproducible switching through intentional control of defect densities in high-quality structures are discussed, including a proof of concept demonstration using Schottky junctions incorporating intentionally non-stoichiometric SRTiO3 interlayers grown by MBE. The second section of this thesis is concerned with unconventional electronic transport in SRTiO3. A systematic description of scattering mechanisms will be presented for three related material systems: uniformly-doped SRTiO3, two-dimensional electron liquids (2DEL) at SRTiO3/RTiO 3 interfaces (R = Gd, Sm) and confined 2DELs in RTiO3/SRTiO3/ RTiO3 quantum wells. In particular, the prevalence of a well-defined T2

  4. La-doped SrTiO3 films with large cryogenic thermoelectric power factors

    NASA Astrophysics Data System (ADS)

    Cain, Tyler A.; Kajdos, Adam P.; Stemmer, Susanne

    2013-05-01

    The thermoelectric properties at temperatures between 10 K and 300 K of La-doped SrTiO3 thin films grown by hybrid molecular beam epitaxy (MBE) on undoped SrTiO3 substrates are reported. Below 50 K, the Seebeck coefficients exhibit very large magnitudes due to the influence of phonon drag. Combined with high carrier mobilities, exceeding 50 000 cm2 V-1 s-1 at 2 K for the films with the lowest carrier densities, this leads to thermoelectric power factors as high as 470 μWcm-1 K-2. The results are compared with other promising low temperature thermoelectric materials and discussed in the context of coupling with phonons in the undoped substrate.

  5. Magneto-optical properties of BaTiO3/La0.76Sr0.24MnO3/BaTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Moog, M.; Singamaneni, S. R.; Prater, J. T.; Biegalski, M. D.; Tsui, F.

    2018-05-01

    The magnetic properties of epitaxial BaTiO3/La0.76Sr0.24MnO3/BaTiO3 (BTO/LSMO/BTO) heterostructures have been studied using magneto-optic Kerr effect (MOKE) technique. Both longitudinal and polar MOKE were probed as a function of magnetic field and temperature (in the range between 80 and 320 K) for epitaxial films of BTO/LSMO/BTO and LSMO grown on TiO2-terminated SrTiO3 (001) substrates by pulsed laser deposition technique. The LSMO film without the BTO layers exhibits nearly square field-dependent MOKE hysteresis loops with low saturation fields below a bulk-like Curie temperature (TC) of ˜ 350K. In contrast, the film with the BTO layers exhibits a significantly suppressed TC of 155 K, accompanied by significantly enhanced coercive fields and perpendicular magnetic anisotropy.

  6. Structures, Properties and Defects of SrTiO3/GaAs Hetero-interfaces

    NASA Astrophysics Data System (ADS)

    Hong, Liang; Bhatnagar, Kunal; Droopad, Ravi; Öğüt, Serdar; Klie, Robert

    SrTiO3 thin film can be epitaxially grown on GaAs substrate and used as a platform for growing other oxides to create functional metal-oxide-semiconductor devices, where a high-quality SrTiO3/GaAs interface is essential. We studied the structural and electronic properties of SrTiO3/GaAs hetero-interfaces at atomic level using scanning transmission electron microscopy and first-principles calculations. Our results suggest the preferred termination of GaAs (001) is significantly dependent on the oxygen concentration in the first oxide layer. The favorable interface structure is characterized as oxygen-deficient SrO in contact with arsenic and is observed in both experiment and simulation. The electronic properties are calculated and found to be tunable by interfacial defects such as oxygen, gallium and arsenic vacancies. This work was supported by the National Science Foundation (Grant No. DMR-1408427). This work made use of instruments in the Electron Microscopy Service and the High Performance Computing Clusters at University of Illinois at Chicago.

  7. Processing of La(1.8)Sr(0.2)CuO4 and YBa2Cu3O7 superconducting thin films by dual-ion-beam sputtering

    NASA Astrophysics Data System (ADS)

    Madakson, P.; Cuomo, J. J.; Yee, D. S.; Roy, R. A.; Scilla, G.

    1988-03-01

    High-quality La(1.8)Sr(0.2)CuO4 and YBa2Cu3O7 superconducting thin films, with zero resistance at 88 K, have been made by dual-ion-beam sputtering of metal and oxide targets at elevated temperatures. The films are about 1.0 micron thick and are single phase after annealing. The substrates investigated are Nd-YAP, MgO, SrF2, Si, CaF2, ZrO2-(9 pct)Y2O3, BaF2, Al2O3, and SrTiO3. Characterization of the films was carried out using Rutherford backscattering spectroscopy, resistivity measurements, TEM, X-ray diffraction, and SIMS. Substrate/film interaction was observed in every case. This generally involves diffusion of the substrate into the film, which is accompanied by, for example, the replacement of Ba by Sr in the YBa2Cu2O7 structure, in the case of SrTiO3 substrate. The best substrates were those that did not significantly diffuse into the film and which did not react chemically with the film.

  8. Quantum Oscillations at LaTiO3/SrTiO3 Interfaces

    NASA Astrophysics Data System (ADS)

    Veit, Michael; Suzuki, Yuri

    Emergent metallic behavior at the interface of the Mott insulator LaTiO3 and the band insulator SrTiO3 was observed for the first time more than a decade ago. Since then the metallicity has been explained in terms of charge redistribution at the interface combined with lattice relaxation. However to date, Shubnikov de Haas oscillations have not been reported in this two dimensional metallic system. For ultrathin (3-4 unit cells) LaTiO3 thin films on SrTiO3, we report the observation of Shubnikov-de Haas oscillations whose frequency corresponds to a small Fermi pocket. Surprisingly the oscillation are only observed between 1 and 4 T. Above this range, the quantum limit is reached for this pocket so no more oscillations are observed. A Berry's phase of π is also detected in these oscillations. Additionally a strong in-plane anisotropic magnetoresistance was measured in the heterostructures which, along with the Berry's phase, is attributed to a giant Rashba coupling at the interface. This work is funded by a National Security Science Engineering Faculty Fellowship of the Department of Defense under N00014-15-1-0045.

  9. Electronic properties and surface reactivity of SrO-terminated SrTiO3 and SrO-terminated iron-doped SrTiO3

    PubMed Central

    Staykov, Aleksandar; Tellez, Helena; Druce, John; Wu, Ji; Ishihara, Tatsumi; Kilner, John

    2018-01-01

    Abstract Surface reactivity and near-surface electronic properties of SrO-terminated SrTiO3 and iron doped SrTiO3 were studied with first principle methods. We have investigated the density of states (DOS) of bulk SrTiO3 and compared it to DOS of iron-doped SrTiO3 with different oxidation states of iron corresponding to varying oxygen vacancy content within the bulk material. The obtained bulk DOS was compared to near-surface DOS, i.e. surface states, for both SrO-terminated surface of SrTiO3 and iron-doped SrTiO3. Electron density plots and electron density distribution through the entire slab models were investigated in order to understand the origin of surface electrons that can participate in oxygen reduction reaction. Furthermore, we have compared oxygen reduction reactions at elevated temperatures for SrO surfaces with and without oxygen vacancies. Our calculations demonstrate that the conduction band, which is formed mainly by the d-states of Ti, and Fe-induced states within the band gap of SrTiO3, are accessible only on TiO2 terminated SrTiO3 surface while the SrO-terminated surface introduces a tunneling barrier for the electrons populating the conductance band. First principle molecular dynamics demonstrated that at elevated temperatures the surface oxygen vacancies are essential for the oxygen reduction reaction. PMID:29535797

  10. The synthesis of SrTiO3 nanocubes and the analysis of nearly ideal diode application of Ni/SrTiO3 nanocubes/n-Si heterojunctions

    NASA Astrophysics Data System (ADS)

    Bilal Taşyürek, Lütfi; Sevim, Melike; Çaldıran, Zakir; Aydogan, Sakir; Metin, Önder

    2018-01-01

    A perovskite type of strontium titanate (SrTiO3) nanocubes (NCs) were synthesized by using a hydrothermal process and the thin films of these NCs were deposited on an n-type silicon wafer by spin coating technique. As-synthesized SrTiO3 NCs were characterized by transmission electron microscope, scanning electron microscope, energy dispersive x-ray, x-ray diffraction and Raman spectroscopy. After evaporation of 12 Ni dots on the SrTiO3 NCs thin films deposited on n-Si, the Ni/SrTiO3 NCs/n-Si heterojunction devices were fabricated for the first time. The ideality factors of the twelve fabricated devices were vary from 1.05 to 1.22 and the barrier height values varied from 0.64 to 0.68 eV. Furthermore, since all devices yielded similar characteristics, only the current-voltage and the capacitance-voltage of one selected device (named H1) were investigated in detailed. The series resistance of this device was calculated as 96 Ω.

  11. Single-Crystal Thin Films of Cesium Lead Bromide Perovskite Epitaxially Grown on Metal Oxide Perovskite (SrTiO 3)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chen, Jie; Morrow, Darien J.; Fu, Yongping

    High-quality metal halide perovskite single crystals have low defect densities and excellent photophysical properties, yet thin films are the most sought after material geometry for optoelectronic devices. Perovskite single-crystal thin films (SCTFs) would be highly desirable for high-performance devices, but their growth remains challenging, particularly for inorganic metal halide perovskites. Herein, we report the facile vapor-phase epitaxial growth of cesium lead bromide perovskite (CsPbBr 3) continuous SCTFs with controllable micrometer thickness, as well as nanoplate arrays, on traditional oxide perovskite SrTiO 3(100) substrates. Heteroepitaxial single-crystal growth is enabled by the serendipitous incommensurate lattice match between these two perovskites, and overcomingmore » the limitation of island-forming Volmer–Weber crystal growth is critical for growing large-area continuous thin films. Time-resolved photoluminescence, transient reflection spectroscopy, and electrical transport measurements show that the CsPbBr 3 epitaxial thin film has a slow charge carrier recombination rate, low surface recombination velocity (10 4 cm s –1), and low defect density of 10 12 cm –3, which are comparable to those of CsPbBr 3 single crystals. This work suggests a general approach using oxide perovskites as substrates for heteroepitaxial growth of halide perovskites. Furthermore, the high-quality halide perovskite SCTFs epitaxially integrated with multifunctional oxide perovskites could open up opportunities for a variety of high-performance optoelectronics devices.« less

  12. Single-Crystal Thin Films of Cesium Lead Bromide Perovskite Epitaxially Grown on Metal Oxide Perovskite (SrTiO 3)

    DOE PAGES

    Chen, Jie; Morrow, Darien J.; Fu, Yongping; ...

    2017-09-05

    High-quality metal halide perovskite single crystals have low defect densities and excellent photophysical properties, yet thin films are the most sought after material geometry for optoelectronic devices. Perovskite single-crystal thin films (SCTFs) would be highly desirable for high-performance devices, but their growth remains challenging, particularly for inorganic metal halide perovskites. Herein, we report the facile vapor-phase epitaxial growth of cesium lead bromide perovskite (CsPbBr 3) continuous SCTFs with controllable micrometer thickness, as well as nanoplate arrays, on traditional oxide perovskite SrTiO 3(100) substrates. Heteroepitaxial single-crystal growth is enabled by the serendipitous incommensurate lattice match between these two perovskites, and overcomingmore » the limitation of island-forming Volmer–Weber crystal growth is critical for growing large-area continuous thin films. Time-resolved photoluminescence, transient reflection spectroscopy, and electrical transport measurements show that the CsPbBr 3 epitaxial thin film has a slow charge carrier recombination rate, low surface recombination velocity (10 4 cm s –1), and low defect density of 10 12 cm –3, which are comparable to those of CsPbBr 3 single crystals. This work suggests a general approach using oxide perovskites as substrates for heteroepitaxial growth of halide perovskites. Furthermore, the high-quality halide perovskite SCTFs epitaxially integrated with multifunctional oxide perovskites could open up opportunities for a variety of high-performance optoelectronics devices.« less

  13. AES study on the chemical composition of ferroelectric BaTiO3 thin films RF sputter-deposited on silicon

    NASA Technical Reports Server (NTRS)

    Dharmadhikari, V. S.; Grannemann, W. W.

    1983-01-01

    AES depth profiling data are presented for thin films of BaTiO3 deposited on silicon by RF sputtering. By profiling the sputtered BaTiO3/silicon structures, it was possible to study the chemical composition and the interface characteristics of thin films deposited on silicon at different substrate temperatures. All the films showed that external surface layers were present, up to a few tens of angstroms thick, the chemical composition of which differed from that of the main layer. The main layer had stable composition, whereas the intermediate film-substrate interface consisted of reduced TiO(2-x) oxides. The thickness of this intermediate layer was a function of substrate temperature. All the films showed an excess of barium at the interface. These results are important in the context of ferroelectric phenomena observed in BaTiO3 thin films.

  14. Ion blocking dip shape analysis around a LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Jalabert, D.; Zaid, H.; Berger, M. H.; Fongkaew, I.; Lambrecht, W. R. L.; Sehirlioglu, A.

    2018-05-01

    We present an analysis of the widths of the blocking dips obtained in MEIS ion blocking experiments of two LaAlO3/SrTiO3 heterostructures differing in their LaAlO3 layer thicknesses. In the LaAlO3 layers, the observed blocking dips are larger than expected. This enlargement is the result of the superposition of individual dips at slightly different angular positions revealing a local disorder in the atomic alignment, i.e., layer buckling. By contrast, in the SrTiO3 substrate, just below the interface, the obtained blocking dips are thinner than expected. This thinning indicates that the blocking atoms stand at a larger distance from the scattering center than expected. This is attributed to an accumulation of Sr vacancies at the layer/substrate interface which induces lattice distortions shifting the atoms off the scattering plane.

  15. Unified modelling of the thermoelectric properties in SrTiO3

    NASA Astrophysics Data System (ADS)

    Bouzerar, G.; Thébaud, S.; Adessi, Ch.; Debord, R.; Apreutesei, M.; Bachelet, R.; Pailhès, S.

    2017-06-01

    Thermoelectric materials are opening a promising pathway to address energy conversion issues governed by a competition between thermal and electronic transport. Improving the efficiency is a difficult task, a challenge that requires new strategies to unearth optimized compounds. We present a theory of thermoelectric transport in electron-doped SrTiO3, based on a realistic tight-binding model that includes relevant scattering processes. We compare our calculations against a wide panel of experimental data, both bulk and thin films. We find a qualitative and quantitative agreement over both a wide range of temperatures and carrier concentrations, from light to heavily doped. Moreover, the results appear insensitive to the nature of the dopant La, B, Gd and Nb. Thus, the quantitative success found in the case of SrTiO3, reveals an efficient procedure to explore new routes to improve the thermoelectric properties in oxides.

  16. Chemical vapor deposition of silicon, silicon dioxide, titanium and ferroelectric thin films

    NASA Astrophysics Data System (ADS)

    Chen, Feng

    Depositions (CVD) of many oxide thin films including ferroelectric and high dielectric constant BaTiO3, SrTiO 3 and PbTiO3 films had been carried out under reduced pressure (30 torr--80 torr) using liquid precursors containing beta-diketone ligands. The relative reactivities of Ba(beta-diketonate)2, Sr(beta-diketonate) 2, Pb(beta-diketonate)2, Ti(beta-diketonate)3, TiO(beta-diketonate)2 and Ti(OiPr)2(beta-diketonate) 2 had been studied individually prior to the deposition of BaTiO 3, SrTiO3 and PbTiO3 thin films from the mixtures of corresponding precursors. By using multi-step deposition method, carbon free stoichiometric BaTiO3 thin films uniform in large area have been achieved.

  17. Y1Ba2Cu3O(6+delta) growth on thin Y-enhanced SiO2 buffer layers on silicon

    NASA Technical Reports Server (NTRS)

    Robin, T.; Mesarwi, A.; Wu, N. J.; Fan, W. C.; Espoir, L.; Ignatiev, A.; Sega, R.

    1991-01-01

    SiO2 buffer layers as thin as 2 nm have been developed for use in the growth of Y1Ba2Cu3O(6+delta) thin films on silicon substrates. The SiO2 layers are formed through Y enhancement of silicon oxidation, and are highly stoichiometric. Y1Ba2Cu3O(6+delta) film growth on silicon with thin buffer layers has shown c orientation and Tc0 = 78 K.

  18. Structure and conductivity of epitaxial thin films of barium ferrite and its hydrated form BaFeO2.5-x+δ (OH)2x

    NASA Astrophysics Data System (ADS)

    Anitha Sukkurji, Parvathy; Molinari, Alan; Benes, Alexander; Loho, Christoph; Sai Kiran Chakravadhanula, Venkata; Garlapati, Suresh Kumar; Kruk, Robert; Clemens, Oliver

    2017-03-01

    Barium ferrite and its hydrated form (BaFeO2.5-x+δ (OH)2x , BFO) is an interesting cathode material for protonic ceramic fuel cells (PCFC) due to its potential to be both, conducting for electrons and protons. We report on the fabrication of almost epitaxially grown thin films (22 nm) of barium ferrite BaFeO~2.5 (BFO) on Nb-doped SrTiO3 substrates via pulsed laser deposition (PLD), followed by treatment under inert, and subsequently wet inert atmospheres to induce water (respectively proton) incorporation. Microstructure, chemical composition and conducting properties are investigated for the BFO films and their hydrated forms, highlighting the influence of hydration on the conductivity characteristics between ~200-290 K. We find that water incorporation gives a strong enhancement of the conductivity to ~10-9 S cm-1 compared to argon annealed films, inducing electronic and protonic charge carriers at the same time. In comparison to bulk powders, proton conductivity is found to be strongly suppressed in such thin hydrated BFO films, pointing towards the influence of strain on the conductivity, which is evaluated based on a detailed investigation by high-resolution transmission electron microscopy.

  19. (Ba+Sr)/Ti ratio dependence of the dielectric properties for (Ba0.5Sr0.5)TiO3 thin films prepared by ion beam sputtering

    NASA Astrophysics Data System (ADS)

    Yamamichi, Shintaro; Yabuta, Hisato; Sakuma, Toshiyuki; Miyasaka, Yoichi

    1994-03-01

    (Ba0.5Sr0.5)TiO3 thin films were prepared by ion beam sputtering from powder targets with (Ba+Sr)/Ti ratios ranging from 0.80 to 1.50. All of the perovskite (Ba,Sr)TiO3 films were single phase except for the film with a (Ba+Sr)/Ti ratio of 1.41. The dielectric constant values notably depended on the (Ba+Sr)/Ti ratio for films thicker than 70 nm. The highest dielectric constant of 580 was achieved for the 5% (Ba+Sr) rich film. This (Ba+Sr)/Ti ratio dependence was diminished by the thickness dependence for thinner films. The grain sizes for the 9% (Ba+Sr) rich film and for the 6% (Ba+Sr) poor film ranged from 70 to 100 nm and from 30 to 60 nm, respectively. This grain size difference could explain why slightly A-site rich (Ba,Sr)TiO3 films have a larger dielectric constant than A-site poor films.

  20. Preparation of epitaxial TlBa2Ca2Cu3O9 high Tc thin films on LaAlO3 (100) substrates

    NASA Astrophysics Data System (ADS)

    Piehler, A.; Reschauer, N.; Spreitzer, U.; Ströbel, J. P.; Schönberger, R.; Renk, K. F.; Saemann-Ischenko, G.

    1994-09-01

    Epitaxial TlBa2Ca2Cu3O9 high Tc thin films were prepared on LaAlO3 (100) substrates by a combination of laser ablation and thermal evaporation of thallium oxide. X-ray diffraction patterns of θ-2θ scans showed that the films consisted of highly c axis oriented TlBa2Ca2Cu3O9. φ scan measurements revealed an epitaxial growth of the TlBa2Ca2Cu3O9 thin films on the LaAlO3 (100) substrates. Ac inductive measurements indicated the onset of superconductivity at 110 K. At 6 K, the critical current density was 4×106 A/cm2 in zero magnetic field and 6×105 A/cm2 at a magnetic field of 3 T parallel to the c axis.

  1. Influences of Indium Tin Oxide Layer on the Properties of RF Magnetron-Sputtered (BaSr)TiO3 Thin Films on Indium Tin Oxide-Coated Glass Substrate

    NASA Astrophysics Data System (ADS)

    Kim, Tae Song; Oh, Myung Hwan; Kim, Chong Hee

    1993-06-01

    Nearly stoichiometric ((Ba+Sr)/Ti=1.08-1.09) and optically transparent (BaSr)TiO3 thin films were deposited on an indium tin oxide (ITO)-coated glass substrate by means of rf magnetron sputtering for their application to the insulating layer of an electroluminescent flat panel display. The influence of the ITO layer on the properties of (BaSr)TiO3 thin films deposited on the ITO-coated substrate was investigated. The ITO layer did not affect the crystallographic orientation of (BaSr)TiO3 thin film, but enhanced the grain growth. Another effect of the ITO layer on (BaSr)TiO3 thin films was the interdiffusion phenomenon, which was studied by means of secondary ion mass spectrometry (SIMS). As the substrate temperature increased, interdiffusion intensified at the interface not only between the grown film and ITO layer but also between the ITO layer and base glass substrate. The refractive index (nf) of (BaSr)TiO3 thin film deposited on a bare glass substrate was 2.138-2.286, as a function of substrate temperature.

  2. Atomic structure of (111) SrTiO3/Pt interfaces

    NASA Astrophysics Data System (ADS)

    Schmidt, Steffen; Klenov, Dmitri O.; Keane, Sean P.; Lu, Jiwei; Mates, Thomas E.; Stemmer, Susanne

    2006-03-01

    Atomic resolution high-angle annular dark field (HAADF) imaging in scanning transmission electron microscopy was used to investigate the interface atomic structure of epitaxial, (111) oriented SrTiO3 films on epitaxial Pt electrodes grown on (0001) sapphire. The cube-on-cube orientation relationship of SrTiO3 on Pt was promoted by the use of a Ti adhesion layer underneath the Pt electrode. While a Ti-rich Pt surface was observed before SrTiO3 growth, HAADF images showed an atomically abrupt SrTiO3/Pt interface with no interfacial layers. The SrTiO3 films contained two twin variants that were related by a 180° rotation about the ⟨111⟩ surface normal. HAADF images showed two different interface atomic arrangements for the two twins. The role of Ti in promoting (111) epitaxy and the implications for the dielectric properties are discussed.

  3. Electrospinning Fabrication of SrTiO3 Nanofibers and Their Photocatalytic Activity

    NASA Astrophysics Data System (ADS)

    Xu, Lei; Zhao, Yiping; Wang, Wei; Liu, Hao; Wang, Rui

    2018-06-01

    SrTiO3 nanofibers were fabricated by an electrospinning process. The phase, microstructure and photocatalytic activity of the obtained SrTiO3 nanofibers were investigated. The XRD patterns and the SEM images suggest that SrTiO3 nanofibers with perovskite phase and rough surface have been fabricated in the current work. The SrTiO3 nanofibers show a high efficiency decomposition of RhB under ultraviolet light irradiation. The high photocatalytic activity of SrTiO3 nanofibers results from the large specific surface area. The large specific surface area provides more surface active sits and makes an easier charge carrier transport. On the basis of the photocatalytic performance of SrTiO3 nanofibers, the possible photocatalysis mechanism was proposed.

  4. Strain dependence of the electronic properties of LaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Moon, S. J.; Kim, Y. S.

    2014-11-01

    We report on the transport and the core-level X-ray photoemission spectroscopy data of fully-strained LaTiO3 thin films grown on GdScO3 and SrTiO3 substrates. We observed that LaTiO3 thin film grown on GdScO3 showed insulating behavior but that grown on SrTiO3 exhibited a metallic character. We found that while the La 4 d photoemission spectra of the two films were nearly the same, their Ti 2 p and O 1 s data revealed a difference. Our results suggest that strain-induced changes in the Ti-O bonding play an important role in the electronic properties of LaTiO3 thin films.

  5. Band-offsets at BaTiO3/Cu2O heterojunction and enhanced photoelectrochemical response: theory and experiment(Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Sharma, Dipika; Satsangi, Vibha R.; Dass Kaura, Sahab; Shrivastav, Rohit; Waghmare, Umesh V.

    2016-10-01

    -principles calculations compare well, thus suggesting that such calculations have the potential to be used in screening various metal oxide heterojunction before performing the experiments thereby saving precious chemicals, time and energy. Keywords: Photoelectrochemical, Water splitting, heterojunction, Cu2O, BaTiO3 References: [1] Surbhi Choudhary, et al. Nanostructured bilayered thin films in photoelectrochemical water splitting - A review: International Journal of Hydrogen Energy, (2012). [2] Dipika Sharma, Anuradha Verma, V.R. Satsangi, Rohit shrivastav, Sahab Dass Nanostructured SrTiO3 thin films sensitized by Cu2O for Photoelectrochemical Hydrogen Generation. International journal of Hydrogen Energy;42:,4230-4241, 2014.

  6. Electron Mobility in γ -Al2O3/SrTiO3

    NASA Astrophysics Data System (ADS)

    Christensen, D. V.; Frenkel, Y.; Schütz, P.; Trier, F.; Wissberg, S.; Claessen, R.; Kalisky, B.; Smith, A.; Chen, Y. Z.; Pryds, N.

    2018-05-01

    One of the key issues in engineering oxide interfaces for electronic devices is achieving high electron mobility. SrTiO3 -based interfaces with high electron mobility have gained a lot of interest due to the possibility of combining quantum phenomena with the many functionalities exhibited by SrTiO3 . To date, the highest electron mobility (140 000 cm2/V s at 2 K) is obtained by interfacing perovskite SrTiO3 with spinel γ -Al2O3 . The origin of the high mobility, however, remains poorly understood. Here, we investigate the scattering mechanisms limiting the mobility in γ -Al2O3/SrTiO3 at temperatures between 2 and 300 K and over a wide range of sheet carrier densities. For T >150 K , we find that the mobility is limited by longitudinal optical phonon scattering. For large sheet carrier densities (>8 ×1013 cm-2 ), the screened electron-phonon coupling leads to room-temperature mobilities up to μ ˜12 cm2/V s . For 5 K SrTiO3 . At carrier densities higher than the optimum, the SrTiO3 heterostructure gradually becomes bulk conducting, and the electron mobility decreases to approximately 20 000 cm2/V s . We argue that the high electron mobility observed arises from a spatial separation of donors and electrons with oxygen-vacancy donors preferentially forming at the interface, whereas the itinerant electrons extend deeper into SrTiO3 . Understanding the scattering mechanism in γ -Al2O3/SrTiO3 paves the way for creation of high-mobility nanoscale electronic devices.

  7. Enhancing the electron mobility of SrTiO3 with strain

    NASA Astrophysics Data System (ADS)

    Jalan, Bharat; Allen, S. James; Beltz, Glenn E.; Moetakef, Pouya; Stemmer, Susanne

    2011-03-01

    We demonstrate, using high-mobility SrTiO3 thin films grown by molecular beam epitaxy, that stress has a pronounced influence on the electron mobility in this prototype complex oxide. Moderate strains result in more than 300% increases in the electron mobilities with values exceeding 120 000 cm2/V s and no apparent saturation in the mobility gains. The results point to a range of opportunities to tailor high-mobility oxide heterostructure properties and open up ways to explore oxide physics.

  8. Interplay of point defects, biaxial strain, and thermal conductivity in homoepitaxial SrTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Wiedigen, S.; Kramer, T.; Feuchter, M.; Knorr, I.; Nee, N.; Hoffmann, J.; Kamlah, M.; Volkert, C. A.; Jooss, Ch.

    2012-02-01

    Separating out effects of point defects and lattice strain on thermal conductivity is essential for improvement of thermoelectric properties of SrTiO3. We study relations between defects generated during deposition, induced lattice strain, and their impact on thermal conductivity κ in homoepitaxial SrTiO3 films prepared by ion-beam sputtering. Lowering the deposition temperature gives rise to lattice expansion by enhancement of point defect density which increases the hardness of the films. Due to a fully coherent substrate-film interface, the lattice misfit induces a large biaxial strain. However, we can show that the temperature dependence of κ is mainly sensitive on the defect concentration.

  9. Imaging and tuning polarity at SrTiO3 domain walls

    NASA Astrophysics Data System (ADS)

    Frenkel, Yiftach; Haham, Noam; Shperber, Yishai; Bell, Christopher; Xie, Yanwu; Chen, Zhuoyu; Hikita, Yasuyuki; Hwang, Harold Y.; Salje, Ekhard K. H.; Kalisky, Beena

    2017-12-01

    Electrostatic fields tune the ground state of interfaces between complex oxide materials. Electronic properties, such as conductivity and superconductivity, can be tuned and then used to create and control circuit elements and gate-defined devices. Here we show that naturally occurring twin boundaries, with properties that are different from their surrounding bulk, can tune the LaAlO3/SrTiO3 interface 2DEG at the nanoscale. In particular, SrTiO3 domain boundaries have the unusual distinction of remaining highly mobile down to low temperatures, and were recently suggested to be polar. Here we apply localized pressure to an individual SrTiO3 twin boundary and detect a change in LaAlO3/SrTiO3 interface current distribution. Our data directly confirm the existence of polarity at the twin boundaries, and demonstrate that they can serve as effective tunable gates. As the location of SrTiO3 domain walls can be controlled using external field stimuli, our findings suggest a novel approach to manipulate SrTiO3-based devices on the nanoscale.

  10. Photoemission from buried interfaces in SrTiO3/LaTiO3 superlattices.

    PubMed

    Takizawa, M; Wadati, H; Tanaka, K; Hashimoto, M; Yoshida, T; Fujimori, A; Chikamatsu, A; Kumigashira, H; Oshima, M; Shibuya, K; Mihara, T; Ohnishi, T; Lippmaa, M; Kawasaki, M; Koinuma, H; Okamoto, S; Millis, A J

    2006-08-04

    We have measured photoemission spectra of SrTiO3/LaTiO3 superlattices with a topmost SrTiO3 layer of variable thickness. A finite coherent spectral weight with a clear Fermi cutoff was observed at chemically abrupt SrTiO3/LaTiO3 interfaces, indicating that an "electronic reconstruction" occurs at the interface between the Mott insulator LaTiO3 and the band insulator SrTiO3. For SrTiO3/LaTiO3 interfaces annealed at high temperatures (approximately 1000 degrees C), which leads to Sr/La atomic interdiffusion and hence to the formation of La(1-x)Sr(x)TiO3-like material, the intensity of the incoherent part was found to be dramatically reduced whereas the coherent part with a sharp Fermi cutoff was enhanced due to the spread of charge. These important experimental features are well reproduced by layer dynamical-mean-field-theory calculation.

  11. Modulation of superconducting transition temperature in LaAlO3/SrTiO3 by SrTiO3 structural domains

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Noad, Hilary; Moler, Kathryn

    2018-01-01

    The tetragonal domain structure in SrTiO3 (STO) is known to modulate the normal-state carrier density in LaAlO3/SrTiO3 (LAO/STO) heterostructures, among other electronic properties, but the effect of STO domains on the superconductivity in LAO/STO has not been fully explored. Using a scanning SQUID susceptometer microscope to map the superconducting response as a function of temperature in LAO/STO, we find that the superconducting transition temperature is spatially inhomogeneous and modulated in a pattern that is characteristic of structural domains in the STO.

  12. The Role of Annealing Process in Ag-Based BaSnO3 Multilayer Thin Films.

    PubMed

    Wu, Muying; Yu, Shihui; He, Lin; Yang, Lei; Zhang, Weifeng

    2016-12-01

    The BaSnO3/Ag/BaSnO3 multilayer structure was designed and fabricated on a quartz glass by magnetron sputtering, followed by an annealing process at a temperature from 150 to 750 °C in air. In this paper, we investigated the influence of the annealing temperature on the structural, optical, and electrical properties of the multilayers and proposed the mechanisms of conduction and transmittance. The maximum value of the figure of merit of 31.8 × 10(-3) Ω(-1) was achieved for the BaSnO3/Ag/BaSnO3 multilayer thin films annealed at 150 °C, while the average optical transmittance in the visible ranges was >84 %, the resistivity was 5.71 × 10(-5) Ω cm, and the sheet resistance was 5.57 Ω/sq. When annealed at below 600 °C, the values of resistivity and transmittance of the multilayers were within an acceptable range (resistivity <5.0 × 10(-4) Ω cm, transmittance >80 %). The observed property of the multilayer film is suitable for the application of transparent conductive electrodes.

  13. Polarization Rotation in Ferroelectric Tricolor PbTiO3/SrTiO3/PbZr0.2Ti0.8O3 Superlattices.

    PubMed

    Lemée, Nathalie; Infante, Ingrid C; Hubault, Cécile; Boulle, Alexandre; Blanc, Nils; Boudet, Nathalie; Demange, Valérie; Karkut, Michael G

    2015-09-16

    In ferroelectric thin films, controlling the orientation of the polarization is a key element to controlling their physical properties. We use laboratory and synchrotron X-ray diffraction to investigate ferroelectric bicolor PbTiO3/PbZr0.2Ti0.8O3 and tricolor PbTiO3/SrTiO3/PbZr0.2Ti0.8O3 superlattices and to study the role of the SrTiO3 layers on the domain structure. In the tricolor superlattices, we demonstrate the existence of 180° ferroelectric stripe nanodomains, induced by the depolarization field produced by the SrTiO3 layers. Each ultrathin SrTiO3 layer modifies the electrostatic boundary conditions between the ferroelectric layers compared to the corresponding bicolor structures, leading to the suppression of the a/c polydomain states. Combined with the electrostatic effect, the tensile strain induced by PbZr0.2Ti0.8O3 in the PbTiO3 layers leads to polarization rotation in the system as evidenced by grazing incidence X-ray measurements. This polarization rotation is associated with the monoclinic Mc phase as revealed by the splitting of the (HHL) and (H0L) reciprocal lattice points. This work demonstrates that the tricolor paraelectric/ferroelectric superlattices constitute a tunable system to investigate the concomitant effects of strains and depolarizing fields. Our studies provide a pathway to stabilize a monoclinic symmetry in ferroelectric layers, which is of particular interest for the enhancement of the piezoelectric properties.

  14. Evidence of extended cation solubility in atomic layer deposited nanocrystalline BaTiO3 thin films and its strong impact on the electrical properties.

    PubMed

    Falmbigl, Matthias; Karateev, Igor A; Golovina, Iryna S; Plokhikh, Aleksandr V; Parker, Thomas C; Vasiliev, Alexander L; Spanier, Jonathan E

    2018-06-22

    Thin films of ≈50 nm thickness with Ba/Ti-ratios ranging from 0.8 to 1.06 were prepared by depositing alternating layers of Ba(OH)2 and TiO2. Annealing at 750 °C promoted the solid-solid transformation into polycrystalline BaTiO3 films containing a mixture of the perovskite and the hexagonal polymorphs with average crystallite sizes smaller than 14 nm and without impurity phases. This, together with an increase of the cubic lattice parameters for Ba-rich films, suggests an extended metastable solubility range for the perovskite-phase in these nanocrystalline thin films on both sides of the stoichiometric composition. Mapping of the cation distribution utilizing energy-filtered transmission electron microscopy corroborates defect accommodation within the BaTiO3 grains. While the cation off-stoichiometry in thermodynamic equilibrium is negligible for BaTiO3, the metastable extended solubility range in the thin films can be directly correlated to the low annealing temperature and nanocrystalline nature. The leakage current behavior can be explained by the formation of Schottky defects for nonstoichiometric films, and the cation ratio has a distinct impact on the dielectric properties: while excess-BaO has a marginal detrimental effect on the permittivity, the dielectric constant declines rapidly by more than 50% towards the Ti-rich side. The present findings highlight the importance of compositional control for the synthesis of nanocrystalline BaTiO3 thin films, in particular for low annealing and/or deposition temperatures. Our synthesis approach using alternating layers of Ba(OH)2 and TiO2 provides a route to precisely control the cation stoichiometry.

  15. Preparation, characterization and gas sensing performance of BaTiO3 nanostructured thin films

    NASA Astrophysics Data System (ADS)

    Suryawanshi, Dinesh N.; Pathan, Idris G.; Bari, Anil. R.; Patil, Lalchand A.

    2018-05-01

    Spray pyrolysis techniques was employed to prepare BaTiO3 thin films. AR grade solutions of Barium chloride (0.05 M) and Titanium chloride (0.05 M) were mixed in the proportion of 30:70, 50:50 and 70:30. The solutions were sprayed on quartz substrate heated at 350°C temperature to obtain the films. These thin films were annealed for a two hours at 600°C in air medium respectively. The prepared thin films were characterized using XRD, FESEM, EDAX, TEM. The electrical and gas sensing properties of these films were investigated. 50:50 film showed better response to Liquid Petroleum Gas (LPG) as compare 30:70 and 70:30 films.

  16. Strain induced superconductivity in the parent compound BaFe2As2

    NASA Astrophysics Data System (ADS)

    Engelmann, J.; Grinenko, V.; Chekhonin, P.; Skrotzki, W.; Efremov, D. V.; Oswald, S.; Iida, K.; Hühne, R.; Hänisch, J.; Hoffmann, M.; Kurth, F.; Schultz, L.; Holzapfel, B.

    2013-12-01

    The discovery of superconductivity with a transition temperature, Tc, up to 65 K in single-layer FeSe (bulk Tc=8 K) films grown on SrTiO3 substrates has attracted special attention to Fe-based thin films. The high Tc is a consequence of the combined effect of electron transfer from the oxygen-vacant substrate to the FeSe thin film and lattice tensile strain. Here we demonstrate the realization of superconductivity in the parent compound BaFe2As2 (no bulk Tc) just by tensile lattice strain without charge doping. We investigate the interplay between strain and superconductivity in epitaxial BaFe2As2 thin films on Fe-buffered MgAl2O4 single crystalline substrates. The strong interfacial bonding between Fe and the FeAs sublattice increases the Fe-Fe distance due to the lattice misfit, which leads to a suppression of the antiferromagnetic spin density wave and induces superconductivity with bulk Tc≈10 K. These results highlight the role of structural changes in controlling the phase diagram of Fe-based superconductors.

  17. Structural and electrical characterization of ultra-thin SrTiO3 tunnel barriers grown over YBa2Cu3O7 electrodes for the development of high Tc Josephson junctions.

    PubMed

    Félix, L Avilés; Sirena, M; Guzmán, L A Agüero; Sutter, J González; Vargas, S Pons; Steren, L B; Bernard, R; Trastoy, J; Villegas, J E; Briático, J; Bergeal, N; Lesueur, J; Faini, G

    2012-12-14

    The transport properties of ultra-thin SrTiO(3) (STO) layers grown over YBa(2)Cu(3)O(7) electrodes were studied by conductive atomic force microscopy at the nano-scale. A very good control of the barrier thickness was achieved during the deposition process. A phenomenological approach was used to obtain critical parameters regarding the structural and electrical properties of the system. The STO layers present an energy barrier of 0.9 eV and an attenuation length of 0.23 nm, indicating very good insulating properties for the development of high-quality Josephson junctions.

  18. Local atomic and electronic structure of LaCoO3 /SrTiO3 thin films by HAADF STEM and EELS

    NASA Astrophysics Data System (ADS)

    Borisevich, Albina; Hyuck Jang, Jae; Kim, Young-Min; Qiao, Liang; Biegalski, Michael

    2013-03-01

    For perovskite films with several competing functionalities, magnetic and electronic properties can be affected both by structural order parameters and chemical factors. For example, in LaCoO3 (LCO) thin films, magnetic and transport properties are strongly dependent on strain state and oxygen content. For this study, LCO thin films were deposited by pulsed laser deposition method with different thicknesses (2, 5, 15 unit cell and 20 nm thickness) on SrTiO3 substrate. X-ray photoelectron spectroscopy studies of the grown films have demonstrated that Co 3p edges shift up to 2 eV for 15 u.c. and 20 nm films, indicating possible presence of 2D electron gas. The structure of the 5 u.c and 15 u.c LCO films was examined. Atomic position mapping from STEM HAADF and BF images can reveal lattice parameter and octahedral tilt behavior with atomic resolution. BF STEM imaging showed that octahedral tilts were active in the 15 u.c. film but not in the 5 u.c. film. A complex pattern of O K fine structure evolution at the interface was observed; results of the deconvolution of different contributions to this behavior using advanced simulations, as well as data on oxygen vacancy mapping, will be presented. Research supported by the US DOE-BES, Materials Sciences and Engineering Division, and through a user project supported by ORNL's ShaRE User Program.

  19. Infrared Optical Absorption in Low-spin Fe2+-doped SrTiO3

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Comes, Ryan B.; Kaspar, Tiffany C.; Heald, Steve M.

    2016-01-06

    Band gap engineering in SrTiO3 and related titanate perovskites has long been explored due to the intriguing properties of the materials for photocatalysis and photovoltaic applications. A popular approach in the materials chemistry community is to substitutionally dope aliovalent transition metal ions onto the B site in the lattice to alter the valence band. However, in such a scheme there is limited control over the dopant valence, and compensating defects often form. Here we demonstrate a novel technique to controllably synthesize Fe2+- and Fe3+-doped SrTiO3 thin films without formation of compensating defects by co-doping with La3+ ions on the Amore » site. We stabilize Fe2+-doped films by doping with two La ions for every Fe dopant, and find that the Fe ions exhibit a low-spin electronic configuration, producing optical transitions in the near infrared regime and degenerate doping. The novel electronic states observed here offer a new avenue for band gap engineering in perovskites for photocatalytic and photovoltaic applications.« less

  20. Self-assembled Co-BaZrO 3 nanocomposite thin films with ultra-fine vertically aligned Co nanopillars

    DOE PAGES

    Huang, Jijie; Li, Leigang; Lu, Ping; ...

    2017-05-11

    A simple one-step pulsed laser deposition (PLD) method has been applied to grow self-assembled metal-oxide nanocomposite thin films. The as-deposited Co-BaZrO 3 films show high epitaxial quality with ultra-fine vertically aligned Co nanopillars (diameter <5 nm) embeded in BZO matrix. The diameter of the nanopillars can be further tuned by varying the deposition frequency. The metal and oxide phases grow separately without inter-diffusion or mixing. Taking advantage of this unique structure, a high saturation magnetization of ~1375 emu/cm 3 in the Co- BaZrO 3 nanocomposites has been achieved and further confirmed by Lorentz microscopy imaging in TEM. Furthermore, the coercivitymore » values of this nanocomposite thin films range from 600 Oe (20 Hz) to 1020 Oe (2 Hz), which makes the nanocomposite an ideal candidate for high-density perpendicular recording media.« less

  1. Study of defects in an electroresistive Au/La2/3Sr1/3MnO3/SrTiO3(001) heterostructure by positron annihilation

    NASA Astrophysics Data System (ADS)

    Ferragut, R.; Dupaquier, A.; Brivio, S.; Bertacco, R.; Egger, W.

    2011-09-01

    Defects in an ultrathin Au/La2/3Sr1/3MnO3/SrTiO3 (Au/LSMO/STO) heterostructure displaying electroresistive behavior were studied using variable energy positron annihilation spectroscopy. Vacancy-like defects were found to be the dominant positron traps in the LSMO and STO thin perovskite oxides with a number density >1017 cm-3 and 2 × 1017 cm-3 in the STO substrate. High defect density was revealed by strong positron trapping at the Au/LSMO interface. Oxygen deficiency in LSMO would be the main source of these traps. Besides, a low density of sub-nano voids of ˜6 Å was found in the substrate and in the thin LSMO/STO films.

  2. Microstructure and properties of single crystal BaTiO3 thin films synthesized by ion implantation-induced layer transfer

    NASA Astrophysics Data System (ADS)

    Park, Young-Bae; Ruglovsky, Jennifer L.; Atwater, Harry A.

    2004-07-01

    Single crystal BaTiO3 thin films have been transferred onto Pt-coated and Si3N4-coated substrates by the ion implantation-induced layer transfer method using H + and He+ ion coimplantation and subsequent annealing. The transferred BaTiO3 films are single crystalline with root mean square roughness of 17nm. Polarized optical and piezoresponse force microscopy (PFM) indicate that the BaTiO3 film domain structure closely resembles that of bulk tetragonal BaTiO3 and atomic force microscopy shows a 90° a -c domain structure with a tetragonal angle of 0.5°-0.6°. Micro-Raman spectroscopy indicates that the local mode intensity is degraded in implanted BaTiO3 but recovers during anneals above the Curie temperature. The piezoelectric coefficient, d33, is estimated from PFM to be 80-100pm/V and the coercive electric field (Ec) is 12-20kV/cm, comparable to those in single crystal BaTiO3.

  3. Properties of large area ErBa2Cu3O(7-x) thin films deposited by ionized cluster beams

    NASA Technical Reports Server (NTRS)

    Levenson, L. L.; Stan, Mark A.; Bhasin, Kul B.

    1991-01-01

    ErBa2Cu3O(7-x) films have been produced by simultaneous deposition of Er, Ba, and Cu from three ionized cluster beam (ICB) sources at acceleration voltages of 0.3 to 0.5 kV. Combining ozone oxidation with ICB deposition at 650 C eliminated any need of post annealing processing. The substrates were rotated at 10 rotations per minute during the deposition which took place at a rate of about 3 to 4 nm. Films with areas up to 70 mm in diameter have been made by ICB deposition. These films, 100 nm thick, were deposited on SrTiO3 (100) substrates at 650 C in a mixture of six percent O3 in O2 at a total pressure of 4 x 10(exp -4) Torr. They had T(sub c) ranging from 84.3 K to 86.8 K over a 70 mm diameter and J(sub c) above 10(exp 6) A/sq cm at 77 K. X ray diffraction measurements of the three samples showed preferential c-axis orientation normal to the substrate surface. Scanning electron micrographs (SEM) of the three samples also show some texture dependence on sample position. For the three samples, there is a correlation between SEM texture, full width at half-maximum of rocking curves and J(sub c) versus temperature curves.

  4. Electrochemical fabrication of SrTiO3 nanowires with nanoporous alumina template.

    PubMed

    Kang, Jinwook; Ryu, Jaemin; Ko, Eunseong; Tak, Yongsug

    2007-11-01

    Strontium titanate nanowires were electrochemically synthesized with nanoporous alumina template. Both chemical and electrical variables such as electrolyte pH, temperature, and current waveform were modulated to investigate the synthesis process of SrTiO3 nanowires. Superimposed cathodic pulse and diffusion time accelerated the growth of SrTiO3 nanowires, which suggested that the concentration of H+ and Sr2+ ion inside alumina template had a strong influence on the formation of SrTiO3 nanowires. Morphology and crystallinity of SrTiO3 nanowires were investigated with scanning electron microscope, X-ray diffractometer and energy dispersive X-ray spectroscopy.

  5. Shubnikov-de Haas Oscillations in LaTiO3/SrTiO3 Heterostructures

    NASA Astrophysics Data System (ADS)

    Veit, Michael; Ramshaw, Brad; Chan, Mun; Suzuki, Yuri

    Emergent metallic behavior in heterostructures of the Mott insulator LaTiO3 and the band insulator SrTiO3 was observed for the first time more than a decade ago. It has often been compared to other oxide systems which have a two-dimensional Fermi surface, but there have been few studies probing the dimensionality of the metallicity in this system. We have studied the transport properties of thin films of LaTiO3 on SrTiO3 substrates. Our measurements have indicated that the entirety of the LaTiO3 film is conductive with an additional contribution near the interface. When the film thickness is on the order of 3-4 unit cells, we observe two sets of Shubnikov-de Haas oscillations - low frequency oscillations with a frequency of 2T and high frequency of 36T. We attribute the observation of these two sets of oscillations to a Rashba splitting which creates a smaller inner Fermi pocket and a larger outer Fermi pocket. These results are consistent with our measurements of in plane anisotropic magnetoresistance and a weak antilocalization correction to the magnetoconductance Further measurements on the angular dependence of the oscillations indicate that their frequency does not change, thus indicating that the Fermi surface is more three-dimensional.

  6. Imaging and tuning polarity at SrTiO 3 domain walls

    DOE PAGES

    Frenkel, Yiftach; Haham, Noam; Shperber, Yishai; ...

    2017-09-18

    Electrostatic fields tune the ground state of interfaces between complex oxide materials. Electronic properties, such as conductivity and superconductivity, can be tuned and then used to create and control circuit elements and gate-defined devices. Here in this paper, we show that naturally occurring twin boundaries, with properties that are different from their surrounding bulk, can tune the LaAlO 3/SrTiO 3 interface 2DEG at the nanoscale. In particular, SrTiO 3 domain boundaries have the unusual distinction of remaining highly mobile down to low temperatures, and were recently suggested to be polar. Here we apply localized pressure to an individual SrTiO 3more » twin boundary and detect a change in LaAlO 3/SrTiO 3 interface current distribution. Our data directly confirm the existence of polarity at the twin boundaries, and demonstrate that they can serve as effective tunable gates. As the location of SrTiO 3 domain walls can be controlled using external field stimuli, our findings suggest a novel approach to manipulate SrTiO 3-based devices on the nanoscale.« less

  7. Positron annihilation studies on the behaviour of vacancies in LaAlO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Yuan, Guoliang; Li, Chen; Yin, Jiang; Liu, Zhiguo; Wu, Di; Uedono, Akira

    2012-11-01

    The formation and diffusion of vacancies are studied in LaAlO3/SrTiO3 heterostructures. Oxygen vacancies (VOS) appear easily in the SrTiO3 substrate during LaAlO3 film growth at 700 °C and 10-4 Pa oxygen pressure rather than at 10-3-10-1 Pa, thus the latter two-dimensional electron gas should come from the polarity discontinuity at the (LaO)+/(TiO2)0 interface. For SrTiO3-δ/LaAlO3/SrTiO3, high-density VOS of the SrTiO3-δ film can pass through the LaAlO3 film and then diffuse to 1.7 µm depth in the SrTiO3 substrate, suggesting that LaAlO3 has VOS at its middle-deep energy levels within the band gap. Moreover, high-density VOS may combine with a strontium/titanium vacancy (VSr/Ti) to form VSr/Ti-O complexes in the SrTiO3 substrate at 700 °C.

  8. Nitrided SrTiO3 as charge-trapping layer for nonvolatile memory applications

    NASA Astrophysics Data System (ADS)

    Huang, X. D.; Lai, P. T.; Liu, L.; Xu, J. P.

    2011-06-01

    Charge-trapping characteristics of SrTiO3 with and without nitrogen incorporation were investigated based on Al/Al2O3/SrTiO3/SiO2/Si (MONOS) capacitors. A Ti-silicate interlayer at the SrTiO3/SiO2 interface was confirmed by x-ray photoelectron spectroscopy and transmission electron microscopy. Compared with the MONOS capacitor with SrTiO3 as charge-trapping layer (CTL), the one with nitrided SrTiO3 showed a larger memory window (8.4 V at ±10 V sweeping voltage), higher P/E speeds (1.8 V at 1 ms +8 V) and better retention properties (charge loss of 38% after 104 s), due to the nitrided SrTiO3 film exhibiting higher dielectric constant, higher deep-level traps induced by nitrogen incorporation, and suppressed formation of Ti silicate between the CTL and SiO2 by nitrogen passivation.

  9. BaTiO3-based nanolayers and nanotubes: first-principles calculations.

    PubMed

    Evarestov, Robert A; Bandura, Andrei V; Kuruch, Dmitrii D

    2013-01-30

    The first-principles calculations using hybrid exchange-correlation functional and localized atomic basis set are performed for BaTiO(3) (BTO) nanolayers and nanotubes (NTs) with the structure optimization. Both the cubic and the ferroelectric BTO phases are used for the nanolayers and NTs modeling. It follows from the calculations that nanolayers of the different ferroelectric BTO phases have the practically identical surface energies and are more stable than nanolayers of the cubic phase. Thin nanosheets composed of three or more dense layers of (0 1 0) and (0 1 1[overline]) faces preserve the ferroelectric displacements inherent to the initial bulk phase. The structure and stability of BTO single-wall NTs depends on the original bulk crystal phase and a wall thickness. The majority of the considered NTs with the low formation and strain energies has the mirror plane perpendicular to the tube axis and therefore cannot exhibit ferroelectricity. The NTs folded from (0 1 1[overline]) layers may show antiferroelectric arrangement of Ti-O bonds. Comparison of stability of the BTO-based and SrTiO(3)-based NTs shows that the former are more stable than the latter. Copyright © 2012 Wiley Periodicals, Inc.

  10. Physical and electrical properties of SrTiO3 and SrZrO3

    NASA Astrophysics Data System (ADS)

    Fashren Muhamad, Norhizatol; Aina Maulat Osman, Rozana; Sobri Idris, Mohd; Yasin, Mohd Najib Mohd

    2017-11-01

    Perovskite type oxide strontium titanate (SrTiO3) and strontium zirconate (SrZrO3) ceramic powder has been synthesized using conventional solid state reaction method. The powders were mixed and ground undergone calcinations at 1400°C for 12 h and sintered at 1550°C for 5h. X-ray Diffraction exposes physical properties SrTiO3 which exhibit cubic phase (space group: pm-3m) at room temperature meanwhile SrZrO3 has Orthorhombic phase (space group: pnma). The electrical properties such as dielectric constant (ɛr), dielectric loss (tan δ), and conductivity (σ) were studied in variation temperature and frequency. High dielectric constant of SrTiO3 and SrZrO3 were observed at 10 kHz for both samples about 240 and 21 respectively at room temperature. The dielectric loss of SrTiO3 and SrZrO3 is very low loss value approximately 0.00076 and 0.67512 indicates very good dielectric.

  11. Superconductivity-localization interplay and fluctuation magnetoresistance in epitaxial BaPb1 -xBixO3 thin films

    NASA Astrophysics Data System (ADS)

    Harris, D. T.; Campbell, N.; Uecker, R.; Brützam, M.; Schlom, D. G.; Levchenko, A.; Rzchowski, M. S.; Eom, C.-B.

    2018-04-01

    BaPb1 -xBixO3 is a superconductor, with transition temperature Tc=11 K, whose parent compound BaBiO3 possesses a charge ordering phase and perovskite crystal structure reminiscent of the cuprates. The lack of magnetism simplifies the BaPb1 -xBixO3 phase diagram, making this system an ideal platform for contrasting high-Tc systems with isotropic superconductors. Here we use high-quality epitaxial thin films and magnetotransport to demonstrate superconducting fluctuations that extend well beyond Tc. For the thickest films (thickness above ˜100 nm ) this region extends to ˜27 K , well above the bulk Tc and remarkably close to the higher Tc of Ba1 -xKxBiO3 (Tc=31 K). We drive the system through a superconductor-insulator transition by decreasing thickness and find the observed Tc correlates strongly with disorder. This material manifests strong fluctuations across a wide range of thicknesses, temperatures, and disorder presenting new opportunities for understanding the precursor of superconductivity near the 2D-3D dimensionality crossover.

  12. Growth and giant coercive field of spinel-structured Co3- x Mn x O4 thin films

    NASA Astrophysics Data System (ADS)

    Kwak, Yongsu; Song, Jonghyun; Koo, Taeyeong

    2016-08-01

    We grew epitaxial thin films of CoMn2O4 and Co2MnO4 on Nb-doped SrTiO3(011) and SrTiO3(001) single crystal substrates using pulsed laser deposition. The magnetic Curie temperature ( T c ) of the Co2MnO4 thin films was ~176 K, which is higher than that of the bulk whereas CoMn2O4 thin films exhibited a value of T c (~151 K) lower than that of the bulk. For the Co2MnO4 thin films, the M - H loop showed a coercive field of ~0.7 T at 10 K, similar to the value for the bulk. However, the M -H loop of the CoMn2O4(0 ll) thin film grown on a Nb-doped SrTiO3(011) substrate exhibited a coercive field of ~4.5 T at 30 K, which is significantly higher than those of the Co2MnO4 thin film and bulk. This giant coercive field, only observed for the CoMn2O4(0 ll) thin film, can be attributed to the shape anisotropy and strong spin-orbit coupling.

  13. A novel synthesis of SrCO3-SrTiO3 nanocomposites with high photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Márquez-Herrera, A.; Ovando-Medina, Víctor M.; Castillo-Reyes, Blanca E.; Meléndez-Lira, M.; Zapata-Torres, M.; Saldaña, N.

    2014-12-01

    The results of the production and characterization of SrCO3-SrTiO3 nanocomposites as a promising candidate for efficient photocatalysts are reported. The production is based on a novelty route employing the solvothermal method with strontium chloride and titanium (IV) butoxide as the precursor solutions. The effect on the properties of the nanocomposites due to changes in the content of SrCO3 and SrTiO3 is reported. The as-prepared materials were tested in the photodegradation of methylene blue dye in aqueous solutions under the solar light. The reported route allows the production of SrCO3-SrTiO3 nanocomposites with particle sizes ranging between 18 and 29 nm. The SrCO3-SrTiO3 nanocomposites obtained with 19 % of SrCO3 phase and 81 % of SrTiO3 (M10) can achieve 94 and 97 % of dye photodegradation after 30 and 120 min, respectively.

  14. Thickness dependent charge transport in ferroelectric BaTiO3 heterojunctions

    NASA Astrophysics Data System (ADS)

    Singh, Pooja; Rout, P. K.; Singh, Manju; Rakshit, R. K.; Dogra, Anjana

    2015-09-01

    We have investigated the effect of ferroelectric barium titanate (BaTiO3) film thickness on the charge transport mechanism in pulsed laser deposited epitaxial metal-ferroelectric semiconductor junctions. The current (I)-voltage (V) measurements across the junctions comprising of 20-500 nm thick BaTiO3 and conducting bottom electrode (Nb: SrTiO3 substrate or La2/3Ca1/3MnO3 buffer layer) demonstrate the space charge limited conduction. Further analysis indicates a reduction in the ratio of free to trapped carriers with increasing thickness in spite of decreasing trap density. Such behaviour arises the deepening of the shallow trap levels (<0.65 eV) below conduction band with increasing thickness. Moreover, the observed hysteresis in I-V curves implies a bipolar resistive switching behaviour, which can be explained in terms of charge trapping and de-trapping process.

  15. Single-crystal-like, c-axis oriented BaTiO3 thin films with high-performance on flexible metal templates for ferroelectric applications

    NASA Astrophysics Data System (ADS)

    Shin, Junsoo; Goyal, Amit; Jesse, Stephen; Kim, Dae Ho

    2009-06-01

    Epitaxial, c-axis oriented BaTiO3 thin films were deposited using pulsed laser ablation on flexible, polycrystalline Ni alloy tape with biaxially textured oxide buffer multilayers. The high quality of epitaxial BaTiO3 thin films with P4mm group symmetry was confirmed by x-ray diffraction. The microscopic ferroelectric domain structure and the piezoelectric domain switching in these films were confirmed via spatially resolved piezoresponse mapping and local hysteresis loops. Macroscopic measurements demonstrate that the films have well-saturated hysteresis loops with a high remanent polarization of ˜11.5 μC/cm2. Such high-quality, single-crystal-like BaTiO3 films on low-cost, polycrystalline, flexible Ni alloy substrates are attractive for applications in flexible lead-free ferroelectric devices.

  16. Spin Wave Resonances in La_0.67Ba_0.33MnO_3

    NASA Astrophysics Data System (ADS)

    Lofland, S. E.; Dominguez, M.; Tyagi, S. D.; Bhagat, S. M.; Kwon, C.; Robson, M. C.; Sharma, R. P.; Ramesh, R.; Venkatesan, T.

    1996-03-01

    Thin ( ~ 110 nm thick) films of La_0.67Ba_0.33MnO3 (LBMO) were prepared by pulsed laser deposition on LaAlO3 substrates. Some films were grown directly onto LaAlO3 while other films were made by first creating a ~ 80 nm thick buffer layer of SrTiO3 (STO) and then capped with a 20 nm thick layer of STO. X-ray and RBS measurements showed the films to be of high crystalline quality. Film thickness was determined by RBS. Spin wave resonance (SWR) measurements were performed at both 10 and 36 GHz. In both types of films Portis (equally spaced) modes were observed. This indicated a non-uniform magnetization which has a parabolic spatial distribution. However, certain tri-layer films showed Kittel modes which follow the n^2 dependence of the mode number n on the resonance field. From the mode separation and the thickness, we calculate the spin stiffness D(0) to be 47 ± 10 meVÅWith this value of D and the magnetization M, we estimate a spatial variation of the magnetization of ~ 20% for those films which showed Portis modes.

  17. Effects of doping on ferroelectric properties and leakage current behavior of KNN-LT-LS thin films on SrTiO3 substrate

    NASA Astrophysics Data System (ADS)

    Abazari, M.; Safari, A.

    2009-05-01

    We report the effects of Ba, Ti, and Mn dopants on ferroelectric polarization and leakage current of (K0.44Na0.52Li0.04)(Nb0.84Ta0.1Sb0.06)O3 (KNN-LT-LS) thin films deposited by pulsed laser deposition. It is shown that donor dopants such as Ba2+, which increased the resistivity in bulk KNN-LT-LS, had an opposite effect in the thin film. Ti4+ as an acceptor B-site dopant reduces the leakage current by an order of magnitude, while the polarization values showed a slight degradation. Mn4+, however, was found to effectively suppress the leakage current by over two orders of magnitude while enhancing the polarization, with 15 and 23 μC/cm2 remanent and saturated polarization, whose values are ˜70% and 82% of the reported values for bulk composition. This phenomenon has been associated with the dual effect of Mn4+ in KNN-LT-LS thin film, by substituting both A- and B-site cations. A detailed description on how each dopant affects the concentrations of vacancies in the lattice is presented. Mn-doped KNN-LT-LS thin films are shown to be a promising candidate for lead-free thin films and applications.

  18. Fabrication and characterization of lead-free BaTiO3 thin film for storage device applications

    NASA Astrophysics Data System (ADS)

    Sharma, Hakikat; Negi, N. S.

    2018-05-01

    The lead-free BaTiO3 (BT) thin film solution has been prepared by sol-gel method. The prepared solution spin coated on Pt/TiO2/SiO2/ Si substrate. The fabricated thin film was analyzed by XRD and Raman spectrometer for structural conformation. Uniformity of thin film was examined by Atomic force microscope (AFM). Thickness of the film was measured by cross sectional FESEM. Activation energies for both positive and negative biasing have been calculated from temperature dependent leakage current density as a function of electric field. For ferroelectric memory devices such as FRAM the hysteresis loop plays important role. Electric filed dependent polarization of BT thin film measured at different switching voltages. With increasing voltage maximum polarization increases.

  19. Pinhole mediated electrical transport across LaTiO3/SrTiO3 and LaAlO3/SrTiO3 oxide hetero-structures

    NASA Astrophysics Data System (ADS)

    Kumar, Pramod; Dogra, Anjana; Toutam, Vijaykumar

    2013-11-01

    Metal-insulator-metal configuration of LaTiO3/SrTiO3 and LaAlO3/SrTiO3 hetero-structures between two dimensional electron gas formed at the interface and different area top electrodes is employed for Conductive Atomic force microscopy (CAFM) imaging, Current-Voltage (I-V), and Capacitance-Voltage (C-V) spectroscopy. Electrode area dependent I-V characteristics are observed for these oxide hetero-structures. With small area electrodes, rectifying I-V characteristics are observed, compared to, both tunneling and leakage current characteristics for large area electrodes. CAFM mapping confirmed the presence of pinholes on both surfaces. Resultant I-V characteristics have a contribution from both tunneling and leakage due to pinholes.

  20. Effect of oxygen vacancy distribution on the thermoelectric properties of La-doped SrTiO3 epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Sarath Kumar, S. R.; Abutaha, A. I.; Hedhili, M. N.; Alshareef, H. N.

    2012-12-01

    A detailed study of the role of oxygen vacancies in determining the effective mass and high temperature (300-1000 K) thermoelectric properties of La-doped epitaxial SrTiO3 thin films is presented. It is observed that at intermediate temperatures, a transition from degenerate to non-degenerate behavior is observed in the Seebeck coefficient, but not electrical conductivity, which is attributed to heterogeneous oxygen non-stoichiometry. Heikes formula is found to be invalid for the films with oxygen vacancies. By fitting the spectroscopic ellipsometry (SE) data, obtained in the range 300-2100 nm, using a Drude-Lorentz dispersion relation with two Lorentz oscillators, the electrical and optical properties of the films are extracted. Using the excellent agreement between the transport properties extracted from SE modeling and direct electrical measurements, we demonstrate that an increase in concentration of oxygen vacancies results in a simultaneous increase of both carrier concentration and electron effective mass, resulting in a higher power factor.

  1. Quasistatic antiferromagnetism in the quantum wells of SmTiO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Need, Ryan F.; Marshall, Patrick B.; Kenney, Eric; Suter, Andreas; Prokscha, Thomas; Salman, Zaher; Kirby, Brian J.; Stemmer, Susanne; Graf, Michael J.; Wilson, Stephen D.

    2018-03-01

    High carrier density quantum wells embedded within a Mott insulating matrix present a rich arena for exploring unconventional electronic phase behavior ranging from non-Fermi-liquid transport and signatures of quantum criticality to pseudogap formation. Probing the proposed connection between unconventional magnetotransport and incipient electronic order within these quantum wells has however remained an enduring challenge due to the ultra-thin layer thicknesses required. Here we address this challenge by exploring the magnetic properties of high-density SrTiO3 quantum wells embedded within the antiferromagnetic Mott insulator SmTiO3 via muon spin relaxation and polarized neutron reflectometry measurements. The one electron per planar unit cell acquired by the nominal d0 band insulator SrTiO3 when embedded within a d1 Mott SmTiO3 matrix exhibits slow magnetic fluctuations that begin to freeze into a quasistatic spin state below a critical temperature T*. The appearance of this quasistatic well magnetism coincides with the previously reported opening of a pseudogap in the tunneling spectra of high carrier density wells inside this film architecture. Our data suggest a common origin of the pseudogap phase behavior in this quantum critical oxide heterostructure with those observed in bulk Mott materials close to an antiferromagnetic instability.

  2. Imprint control of BaTiO 3 thin films via chemically induced surface polarization pinning

    DOE PAGES

    Lee, Hyungwoo; Kim, Tae Heon; Patzner, Jacob J.; ...

    2016-02-22

    Surface-adsorbed polar molecules can significantly alter the ferroelectric properties of oxide thin films. Thus, fundamental understanding and controlling the effect of surface adsorbates are crucial for the implementation of ferroelectric thin film devices, such as ferroelectric tunnel junctions. Herein, we report an imprint control of BaTiO 3 (BTO) thin films by chemically induced surface polarization pinning in the top few atomic layers of the water-exposed BTO films. Our studies based on synchrotron X-ray scattering and coherent Bragg rod analysis demonstrate that the chemically induced surface polarization is not switchable but reduces the polarization imprint and improves the bistability of ferroelectricmore » phase in BTO tunnel junctions. Here, we conclude that the chemical treatment of ferroelectric thin films with polar molecules may serve as a simple yet powerful strategy to enhance functional properties of ferroelectric tunnel junctions for their practical applications.« less

  3. Phase separation enhanced magneto-electric coupling in La0.7Ca0.3MnO3/BaTiO3 ultra-thin films

    PubMed Central

    Alberca, A.; Munuera, C.; Azpeitia, J.; Kirby, B.; Nemes, N. M.; Perez-Muñoz, A. M.; Tornos, J.; Mompean, F. J.; Leon, C.; Santamaria, J.; Garcia-Hernandez, M.

    2015-01-01

    We study the origin of the magnetoelectric coupling in manganite films on ferroelectric substrates. We find large magnetoelectric coupling in La0.7Ca0.3MnO3/BaTiO3 ultra-thin films in experiments based on the converse magnetoelectric effect. The magnetization changes by around 30–40% upon applying electric fields on the order of 1 kV/cm to the BaTiO3 substrate, corresponding to magnetoelectric coupling constants on the order of α = (2–5)·10−7 s/m. Magnetic anisotropy is also affected by the electric field induced strain, resulting in a considerable reduction of coercive fields. We compare the magnetoelectric effect in pre-poled and unpoled BaTiO3 substrates. Polarized neutron reflectometry reveals a two-layer behavior with a depressed magnetic layer of around 30 Å at the interface. Magnetic force microscopy (MFM) shows a granular magnetic structure of the La0.7Ca0.3MnO3. The magnetic granularity of the La0.7Ca0.3MnO3 film and the robust magnetoelastic coupling at the La0.7Ca0.3MnO3/BaTiO3 interface are at the origin of the large magnetoelectric coupling, which is enhanced by phase separation in the manganite. PMID:26648002

  4. Diamagnetism to ferromagnetism in Sr-substituted epitaxial BaTiO{sub 3} thin films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Singamaneni, Srinivasa Rao, E-mail: ssingam@ncsu.edu; Prater, John T.; Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695

    2016-04-04

    We report on the ferromagnetic-like behavior in otherwise diamagnetic BaTiO{sub 3} (BTO) thin films upon doping with non-magnetic element Sr having the composition Ba{sub 0.4}Sr{sub 0.6}TiO{sub 3} (BST). The epitaxial integration of BST (∼800 nm) thick films on Si (100) substrate was achieved using MgO (40 nm) and TiN (20 nm) as buffer layers to prepare BST/MgO/TiN/Si (100) heterostructure by pulsed laser deposition. The c-axis oriented and cube-on-cube epitaxial BST is formed on Si (100) as evidenced by the in-plane and out-of-plane X-ray diffraction. All the deposited films are relaxed through domain matching epitaxy paradigm as observed from X-ray diffraction pattern and A{submore » 1}TO{sub 3} mode (at 521.27 cm{sup −1}) of Raman spectra. As-deposited BST thin films reveal ferromagnetic-like properties, which persist up to 400 K. The magnetization decreases two-fold upon oxygen annealing. In contrast, as-deposited un-doped BTO films show diamagnetism. Electron spin resonance measurements reveal no evidence of external magnetic impurities. XRD and X-ray photoelectron spectroscopy spectra show significant changes influenced by Sr doping in BTO. The ferromagnetic-like behavior in BST could be due to the trapped electron donors from oxygen vacancies resulting from Sr-doping.« less

  5. Transport properties of layered Ba(Pb,Bi)O3 thin films

    NASA Astrophysics Data System (ADS)

    Hassink, G. W. J.; Munakata, K.; Hammond, R. H.; Beasley, M. R.

    2012-02-01

    Doped BaBiO3 is a 3D oxide superconductor with a maximum Tc of 30 K for Ba0.6K0.4BiO3. There has been a lot of discussion on whether this high Tc can be explained purely by electron-phonon coupling with a high coupling constant λ. In addition, the presence of real-space paired 6s^2 electrons in the parent compound raise intriguing questions about whether there is an electron-electron coupling interaction as well. This possible negative-U interaction might be used to implement the suggestion by Berg, Orgad and Kivelson [Phys.Rev.B 78, 094509] that for a two-layer system where one layer provides electron pairing interaction and the other layer is conducting, the whole can be superconducting with a high Tc. Here we discuss the transport properties of BaPbO3/BaBiO3 bilayers, where the BaBiO3 layer is thought to act as the pairing layer, while the BaPbO3 acts as the conducting layer. The transport behavior changes to insulating upon decreasing the metallic BaPbO3 layer thickness at values that single films are expected to still be metallic.

  6. Strain-induced nanostructure of Pb(Mg1/3Nb2/3)O3-PbTiO3 on SrTiO3 epitaxial thin films with low PbTiO3 concentration

    NASA Astrophysics Data System (ADS)

    Kiguchi, Takanori; Fan, Cangyu; Shiraishi, Takahisa; Konno, Toyohiko J.

    2017-10-01

    The singularity of the structure in (1 - x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) (x = 0-50 mol %) epitaxial thin films of 100 nm thickness was investigated from the viewpoint of the localized residual strain in the nanoscale. The films were deposited on SrTiO3 (STO) (001) single-crystal substrates by chemical solution deposition (CSD) using metallo-organic decomposition (MOD) solutions. X-ray and electron diffraction patterns revealed that PMN-xPT thin films included a single phase of the perovskite-type structure with the cube-on-cube orientation relationship between PMN-xPT and STO: (001)Film ∥ (001)Sub, [100]Film ∥ [100]Sub. X-ray reciprocal space maps showed an in-plane tensile strain in all the compositional ranges considered. Unit cells in the films were strained from the rhombohedral (pseudocubic) (R) phase to a lower symmetry crystal system, the monoclinic (MB) phase. The morphotropic phase boundary (MPB) that split the R and tetragonal (T) phases was observed at x = 30-35 for bulk crystals of PMN-xPT, whereas the strain suppressed the transformation from the R phase to the T phase in the films up to x = 50. High-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) analysis and its related local strain analysis revealed that all of the films have a bilayer morphology. The nanoscale strained layer formed only above the film/substrate semi-coherent interface. The misfit dislocations generated the localized and periodic strain fields deformed the unit cells between the dislocation cores from the R to an another type of the monoclinic (MA) phase. Thus, the singular and localized residual strains in the PMN-xPT/STO (001) epitaxial thin films affect the phase stability around the MPB composition and result in the MPB shift phenomena.

  7. Processing, electrical and microwave properties of sputtered Tl-Ca-Ba-Cu-O superconducting thin films

    NASA Technical Reports Server (NTRS)

    Subramanyam, G.; Kapoor, V. J.; Chorey, C. M.; Bhasin, K. B.

    1993-01-01

    A reproducible fabrication process has been established for TlCaBaCuO thin films on LaAlO3 substrates by RF magnetron sputtering and post-deposition processing methods. Electrical transport properties of the thin films were measured on patterned four-probe test devices. Microwave properties of the films were obtained from unloaded Q measurements of all-superconducting ring resonators. This paper describes the processing, electrical and microwave properties of Tl2Ca1Ba2Cu2O(x) 2122-plane phase thin films.

  8. Dielectric and ferroelectric properties of strain-relieved epitaxial lead-free KNN-LT-LS ferroelectric thin films on SrTiO3 substrates

    NASA Astrophysics Data System (ADS)

    Abazari, M.; Akdoǧan, E. K.; Safari, A.

    2008-05-01

    We report the growth of single-phase (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrRuO3 coated ⟨001⟩ oriented SrTiO3 substrates by using pulsed laser deposition. Films grown at 600°C under low laser fluence exhibit a ⟨001⟩ textured columnar grained nanostructure, which coalesce with increasing deposition temperature, leading to a uniform fully epitaxial highly stoichiometric film at 750°C. However, films deposited at lower temperatures exhibit compositional fluctuations as verified by Rutherford backscattering spectroscopy. The epitaxial films of 400-600nm thickness have a room temperature relative permittivity of ˜750 and a loss tangent of ˜6% at 1kHz. The room temperature remnant polarization of the films is 4μC /cm2, while the saturation polarization is 7.1μC/cm2 at 24kV/cm and the coercive field is ˜7.3kV/cm. The results indicate that approximately 50% of the bulk permittivity and 20% of bulk spontaneous polarization can be retained in submicron epitaxial KNN-LT-LS thin film, respectively. The conductivity of the films remains to be a challenge as evidenced by the high loss tangent, leakage currents, and broad hysteresis loops.

  9. Understanding the interactions of CO 2 with doped and undoped SrTiO 3

    DOE PAGES

    Wu, Qiyuan; Cen, Jiajie; Goodman, Kenneth R.; ...

    2016-06-17

    SrTiO 3 and doped SrTiO 3 have a wide range of applications in different fields. For example, Rh-doped SrTiO 3 has been shown to have photocatalytic activity for both hydrogen production and CO 2 conversion. In this study, both undoped and Rh-doped SrTiO 3 were synthesized by hydrothermal and polymerizable complex methods. Different characterizations techniques including X-ray photoelectron spectroscopy (XPS), XRD, Raman, and UV/Vis spectroscopy were utilized to establish correlations between the preparation methods and the electronic/structural properties of Rh-doped SrTiO 3. The presence of dopants and oxygen vacancies substantially influenced the CO 2 interactions with the surface, as revealedmore » by the in situ infrared spectroscopic study. As a result, the presence of distinctly different adsorption sites was correlated to oxygen vacancies and oxidation states of Ti and Rh.« less

  10. Resistance change effect in SrTiO3/Si (001) isotype heterojunction

    NASA Astrophysics Data System (ADS)

    Huang, Xiushi; Gao, Zhaomeng; Li, Pei; Wang, Longfei; Liu, Xiansheng; Zhang, Weifeng; Guo, Haizhong

    2018-02-01

    Resistance switching has been observed in double and multi-layer structures of ferroelectric films. The higher switching ratio opens up a vast path for emerging ferroelectric semiconductor devices. An n-n+ isotype heterojunction has been fabricated by depositing an oxide SrTiO3 layer on a conventional n-type Si (001) substrate (SrTiO3/Si) by pulsed laser disposition. Rectification and resistive switching behaviors in the n-n+ SrTiO3/Si heterojunction were observed by a conductive atomic force microscopy, and the n-n+ SrTiO3/Si heterojunction exhibits excellent endurance and retention characteristics. The possible mechanism was proposed based on the band structure of the n-n+ SrTiO3/Si heterojunction, and the observed electrical behaviors could be attributed to the modulation effect of the electric field reversal on the width of accumulation and the depletion region, as well as the height of potential of the n-n+ junction formed at the STO/Si interface. Moreover, oxygen vacancies are also indicated to play a crucial role in causing insulator to semiconductor transition. These results open the way to potential application in future microelectronic devices based on perovskite oxide layers on conventional semiconductors.

  11. Photoreduction of CO2 on TiO2/SrTiO3 Heterojunction Network Film

    NASA Astrophysics Data System (ADS)

    Bi, Yongsheng; Zong, Lanlan; Li, Chen; Li, Qiuye; Yang, Jianjun

    2015-08-01

    Nanotube titanic acid (NTA) network film has a porous structure and large BET surface area, which lead them to possessing high utilization of the incident light and strong adsorption ability. We used NTA as the precursor to fabricate a TiO2/ SrTiO3 heterojunction film by the hydrothermal method. In the process of the reaction, part of NTA reacted with SrCl2 to form SrTiO3 nanocubes, and the remainder dehydrated to transform to the rutile TiO2. The ratio of TiO2 and SrTiO3 varied with the hydrothermal reaction time. SEM and TEM images indicated that SrTiO3 nanocubes dispersed uniformly on TiO2 film, and the particle size and crystallinity of SrTiO3 nanocubes increased with the reaction time prolonging. The TiO2/SrTiO3 heterojunction obtained by 1 h showed the best activity for CO2 photoreduction, where the mole ratio of TiO2 and SrTiO3 was 4:1. And the photo-conversion efficiency of CO2 to CH4 improved remarkably after the foreign electron traps of Pt and Pd nanoparticles were loaded. The highest photocatalytic production rate of CH4 reached 20.83 ppm/h cm2. In addition, the selectivity of photoreduction product of CO2 was also increased apparently when Pd acted as the cocatalyst on TiO2/SrTiO3 heterojunction film.

  12. Dielectric properties of BaMg1/3Nb2/3O3 doped Ba0.45Sr0.55Tio3 thin films for tunable microwave applications

    NASA Astrophysics Data System (ADS)

    Alema, Fikadu; Pokhodnya, Konstantin

    2015-11-01

    Ba(Mg1/3Nb2/3)O3 (BMN) doped and undoped Ba0.45Sr0.55TiO3 (BST) thin films were deposited via radio frequency magnetron sputtering on Pt/TiO2/SiO2/Al2O3 substrates. The surface morphology and chemical state analyses of the films have shown that the BMN doped BST film has a smoother surface with reduced oxygen vacancy, resulting in an improved insulating properties of the BST film. Dielectric tunability, loss, and leakage current (LC) of the undoped and BMN doped BST thin films were studied. The BMN dopant has remarkably reduced the dielectric loss (˜38%) with no significant effect on the tunability of the BST film, leading to an increase in figure of merit (FOM). This is attributed to the opposing behavior of large Mg2+ whose detrimental effect on tunability is partially compensated by small Nb5+ as the two substitute Ti4+ in the BST. The coupling between MgTi″ and VO•• charged defects suppresses the dielectric loss in the film by cutting electrons from hopping between Ti ions. The LC of the films was investigated in the temperature range of 300-450K. A reduced LC measured for the BMN doped BST film was correlated to the formation of defect dipoles from MgTi″, VO•• and NbTi• charged defects. The carrier transport properties of the films were analyzed in light of Schottky thermionic emission (SE) and Poole-Frenkel (PF) emission mechanisms. The result indicated that while the carrier transport mechanism in the undoped film is interface limited (SE), the conduction in the BMN doped film was dominated by bulk processes (PF). The change of the conduction mechanism from SE to PF as a result of BMN doping is attributed to the presence of uncoupled NbTi• sitting as a positive trap center at the shallow donor level of the BST.

  13. Effectiveness of BaTiO 3 dielectric patches on YBa 2Cu 3O 7 thin films for MEM switches

    DOE PAGES

    Vargas, J.; Hijazi, Y.; Noel, J.; ...

    2014-05-12

    A micro-electro-mechanical (MEM) switch built on a superconducting microstrip filter will be utilized to investigate BaTiO 3 dielectric patches for functional switching points of contact. Actuation voltage resulting from the MEM switch provokes static friction between the bridge membrane and BaTiO 3 insulation layer. Furthermore, the dielectric patch crystal structure and roughness affect the ability of repetitively switching cycles and lifetime. We performed a series of experiments using different deposition methods and RF magnetron sputtering was found to be the best deposition process for the BaTiO 3 layer. The effect examination of surface morphology will be presented using characterization techniquesmore » as x-ray diffraction, SEM and AFM for an optimum switching device. The thin film is made of YBa 2Cu 3O 7 deposited on LaAlO 3 substrate by pulsed laser deposition. In our work, the dielectric material sputtering pressure is set at 9.5x10 -6 Torr. The argon gas is released through a mass-flow controller to purge the system prior to deposition. RF power is 85 W at a distance of 9 cm. The behavior of Au membranes built on ultimate BaTiO 3 patches will be shown as part of the results. These novel surface patterns will in turn be used in modelling other RF MEM switch devices such as distributed-satellite communication system operating at cryogenic temperatures.« less

  14. Thermoelectric properties of the yttrium-doped ceramic oxide SrTiO3

    NASA Astrophysics Data System (ADS)

    Khan, Tamal Tahsin; Ur, Soon-Chul

    2017-01-01

    The doping dependence of the thermoelectric figure of merit, ZT, of the ceramic oxide SrTiO3 at high temperature has been studied. In this study, yttrium was used as the doping element. A conventional solid-state reaction method was used for the preparation of Y-doped SrTiO3. The doping level in SrTiO3 was controlled to be in the doping range of 2 - 10 mole%. Almost all the yttrium atoms incorporated into the SrTiO3 provided charge carriers, as was observed by using X-ray diffraction pattern. The relative densities of all the samples varied from 98.53% to 99.45%. The thermoelectric properties, including the electrical conductivity σ, Seebeck coefficient S, thermal conductivity k, and the figure of merit, ZT, were investigated at medium temperatures. The ZT value showed an obvious doping level dependence, in which a value as high as 0.18 is realized at 773 K for a doping of 8 mole%.

  15. A comparative study of photoconductivity in LaTiO3/SrTiO3 and LaAlO3/SrTiO3 2-DEG heterostructures

    NASA Astrophysics Data System (ADS)

    Rastogi, A.; Hossain, Z.; Budhani, R. C.

    2013-02-01

    Here we compare the growth temperature dependence of the response of LaTiO3/SrTiO3 and LaAlO3/SrTiO3 2D-electron gas (2-DEG) field effect structure to the optical radiation of near ultraviolet frequency and electrostatic gate field. For both the films the resistance of the channel increases significantly as growth temperature is lowered from 800 to 700 °C. These heterostructures show the photoconductivity (PC) simulated by UV light of λ ≤ 400 nm. The PC follows the stretched exponential dynamics. It is found that photo-response of the LaTiO3 films is prominent and has larger decay time constant as compare to LaAlO3 films. The effect of electric field on the photo-induced conducting state is also studied.

  16. Critical current density of TlBa 2Ca 2Cu 3O 9 thin films on MgO (100) in magnetic fields

    NASA Astrophysics Data System (ADS)

    Piehler, A.; Ströbel, J. P.; Reschauer, N.; Löw, R.; Schönberger, R.; Renk, K. F.; Kraus, M.; Daniel, J.; Saemann-Ischenko, G.

    1994-04-01

    We report on the critical current density of TlBa 2Ca 2Cu 3O 9 thin films on (100) MgO substrates in magnetic fields. Single- phase and highly c-axis oriented thin films were prepared by laser ablation in combination with thermal evaporation of Tl 2O 3. Scanning electron microscope investigations indicated a flat plate-like microstructure and DC magnetization measurements showed the onset of superconductivity at ∼ 115 K. The critical current density jc was determined from magnetization cycles. Typical values of jc were 9 × 10 5 A/cm 2 at 6 K and 2.5 × 10 5 A/cm 2 at 77 K. In a magnetic field to 1 T applied parallel to the c-axis the critical current densities were 3 × 10 5 A/cm 2 at 6 K and 3 × 10 3 A/cm 2 at 77 K. The decrease of jc at higher magnetic fields is discussed and attributed to the microstructure of the TlBa 2Ca 2Cu 3O 9 thin films.

  17. Photocatalytic CO2 reduction over SrTiO3: Correlation between surface structure and activity

    NASA Astrophysics Data System (ADS)

    Luo, Chao; Zhao, Jie; Li, Yingxuan; Zhao, Wen; Zeng, Yubin; Wang, Chuanyi

    2018-07-01

    Perovskite oxide SrTiO3 is a promising semiconductor photocatalyst for CO2 reduction, which has two possible chemical surfaces-TiO2-terminated and SrO-terminated surfaces. Up to now, the effect of chemical surface and its modification on CO2 adsorption, activation and sequential photocatalytic reduction is not established. In the work, SrTiO3, surface-Ti-rich SrTiO3 and Sr(OH)2-decorated SrTiO3 were prepared and their structural, surface, and optical properties and photocatalytic activity were explored. It is found that the absorption edge of surface-Ti-rich SrTiO3 shifted toward visible-light region as compared with that of the other two photocatalysts, which is attributed to the decreased Ti 3d ground-state level at the surface. Bicarbonate- (HCO3-) and bidentate carbonate-like (b-CO3=) species are the main species for CO2 adsorption on the surface-Ti-rich SrTiO3, whereas, besides HCO3- and b-CO3=, plenty of monodentate carbonate-like species (m-CO3=) that has relatively low reactivity is present on the SrTiO3 and Sr(OH)2-decorated photocatalysts. As a result, the surface-Ti-rich SrTiO3 exhibits the highest activity for CO2 reduction. Furthermore, although Sr(OH)2-decoration and SrO-terminated surfaces facilitate CO2 fixing, the produced surface species are attached to the weakly active Sr ions, giving rise to the lower reactivity. The present work might supply a guide for designing highly active perovskite-type semiconductors for photocatalysis.

  18. Electrical-transport properties and microwave device performance of sputtered TlCaBaCuO superconducting thin films

    NASA Technical Reports Server (NTRS)

    Subramanyam, G.; Kapoor, V. J.; Chorey, C. M.; Bhasin, K. B.

    1992-01-01

    The paper describes the processing and electrical transport measurements for achieving reproducible high-Tc and high-Jc sputtered TlCaBaCuO thin films on LaAlO3 substrates, for microelectronic applications. The microwave properties of TlCaBaCuO thin films were investigated by designing, fabricating, and characterizing microstrip ring resonators with a fundamental resonance frequency of 12 GHz on 10-mil-thick LaAlO3 substrates. Typical unloaded quality factors for a ring resonator with a superconducting ground plane of 0.3 micron-thickness and a gold ground plane of 1-micron-thickness were above 1500 at 65 K. Typical values of penetration depth at 0 K in the TlCaBaCuO thin films were between 7000 and 8000 A.

  19. Band-gap narrowing and magnetic behavior of Ni-doped Ba(Ti0.875Ce0.125)O3 thin films

    NASA Astrophysics Data System (ADS)

    Zhou, Wenliang; Deng, Hongmei; Yu, Lu; Yang, Pingxiong; Chu, Junhao

    2015-11-01

    Band-gap narrowing and magnetic effects have been observed in a Ni-doped Ba(Ti0.875Ce0.125)O3 (BTC) thin film. Structural characterizations and microstructural analysis show that the as-prepared Ba(Ti0.75Ce0.125Ni0.125)O3-δ (BTCN) thin film exhibits a cubic perovskite structure with an average grain size of 25 nm. The Ce doping at the Ti-site results in an increasing perovskite volume to favour an O-vacancy-stabilized Ni2+ substitution. Raman spectroscopy, however, shows the cubic symmetry of crystalline structures is locally lowered by the presence of dopants, significantly deviating from the ideal Pm3m space group. Moreover, BTCN presents a narrowed band-gap, much smaller than that of BaTiO3 and BTC, due to new states of both the highest occupied molecular orbital and the lowest unoccupied molecular orbital in an electronic structure with the presence of Ni. Also, magnetic enhancement driven by co-doping has been confirmed in the films, which mainly stems from the exchange interaction of Ni2+ ions via an electron trapped in a bridging oxygen vacancy. These findings may open an avenue to discover and design optimal perovskite compounds for solar-energy devices and information storage.

  20. Processing And Patterning Of Thin Film Superconductors Formed By Metallo-Organic Deposition

    NASA Astrophysics Data System (ADS)

    Micheli, Adolph L.; Mantese, Joseph V.; Hamdi, Aboud H.

    1990-04-01

    Thin film superconductors of Y-Ba-Cu and Yb-Ba-Cu were formed by the pyrolysis of neodecanoate solutions of Y, Yb, Ba and Cu which had been deposited onto <100> SrTiO3 substrates [1]. Rapid thermal annealing, in oxygen, of the as-deposited films produced high T films having superconducting onset temperatures above 90 K and zero resistance at 8g K. Scanning Electron Microscopy (SEM) revealed enhancements in grain growth, compared to furnace annealed films, by a factor of 4. X-ray diffraction analysis showed preferred epitaxial grain growth with the c-axis of the films oriented both perpendicular and parallel to the substrate surface. Separate Rutherford Backscattering Spectrometry (RBS) channeling experiments confirmed the formation of preferred epitaxial grain growth. Film composition was determined by RBS and Inductively Coupled Plasma Emission Spectrometry (ICPES). Selective patterning was accomplished by focused beam exposure of the metal neodecanoate films [2-4]. The exposure rendered the neodecanoate film locally insoluble in xylene, thus permitting selective area patterning prior to pyrolysis. Electron, ion and laser beams were used to pattern films on <100> SrTiO3. The finest lines, approximately 5 #m in width and 26 nm thick, were patterned using electron beams whose lines had superconducting onsets above 90 K and zero resistance at 69 K after rapid thermal annealing. Both ion beam and laser patterning had similar superconducting onsets and zero resistance. Neodecanoates of Y, Yb, Ba, and Cu were formed, as previously described [5], by reacting the metal acetates of these materials with either ammonium neodecanoate or tetramethyl ammonium neodecanoate. The carboxylates formed from these reactions were then dissolved in a solution of xylene and pyridine. The individual chemical constituents were combined to produce solutions, Ln:Ba:Cu, in the ratio 1:2:4. Here, Ln is a rare-earth element. Details of the preparation of the metal carboxylates may be found

  1. Effect of strain on thermoelectric properties of SrTiO3: First-principles calculations

    NASA Astrophysics Data System (ADS)

    Zou, Daifeng; Liu, Yunya; Xie, Shuhong; Lin, Jianguo; Li, Jiangyu

    2013-10-01

    The electronic structures of strained SrTiO3 were investigated by using first-principles calculations, and the anisotropic thermoelectric properties of n-type SrTiO3 under biaxial strain were calculated on the base of the semi-classical Boltzmann transport theory. It was theoretically found that the in-plane and out-of-plane power factors of n-type SrTiO3 can be increased under compressive and tensile strains, respectively, and such dependence can be explained by the strain-induced redistribution of electrons. To further optimize the thermoelectric performance of n-type SrTiO3, the maximum power factors and the corresponding optimal n-type doping levels were evaluated.

  2. Understanding Methanol Coupling on SrTiO 3 from First Principles

    DOE PAGES

    Huang, Runhong; Fung, Victor; Zhang, Yafen; ...

    2018-03-19

    Perovskites are interesting materials for catalysis due to their great tunability. However, the correlation of many reaction processes to the termination of a perovskite surface is still unclear. In this paper, we use the methanol coupling reaction on the SrTiO 3(100) surface as a probe reaction to investigate direct C–C coupling from a computational perspective. We use density functional theory to assess methanol adsorption, C–H activation, and direct C–C coupling reactions on the SrTiO 3(100) surface of different terminations. We find that, although methanol molecules dissociatively adsorb on both A and B terminations with similar strength, the dehydrogenation and C–Cmore » coupling reactions have significantly lower activation energies on the B termination than on the A termination. The predicted formation of methoxy and acetate on the SrTiO 3(100) B termination can well explain the ambient-pressure XPS data of methanol on the single-crystal SrTiO 3(100) surface at 250 °C. Finally, this work suggests that a choice of B termination of perovskites would be beneficial for the C–C coupling reaction of methanol.« less

  3. Structural characterization of niobium oxide thin films grown on SrTiO3 (111) and (La,Sr)(Al,Ta)O3 (111) substrates

    NASA Astrophysics Data System (ADS)

    Dhamdhere, Ajit R.; Hadamek, Tobias; Posadas, Agham B.; Demkov, Alexander A.; Smith, David J.

    2016-12-01

    Niobium oxide thin films have been grown by molecular beam epitaxy on SrTiO3 (STO) (111) and (La0.18Sr0.82)(Al0.59Ta0.41)O3 (LSAT) (111) substrates. Transmission electron microscopy (TEM) confirmed the formation of high quality films with coherent interfaces. Films grown with higher oxygen pressure on STO (111) resulted in a (110)-oriented NbO2 phase with a distorted rutile structure, which can be described as body-centered tetragonal. The a lattice parameter of NbO2 was determined to be ˜13.8 Å in good agreement with neutron diffraction results published in the literature. Films grown on LSAT (111) at lower oxygen pressure produced the NbO phase with a defective rock salt cubic structure. The NbO lattice parameter was determined to be a ≈ 4.26 Å. The film phase/structure identification from TEM was in good agreement with in situ x-ray photoelectron spectroscopy measurements that confirmed the dioxide and monoxide phases, respectively. The atomic structure of the NbO2/STO and NbO/LSAT interfaces was determined based on comparisons between high-resolution electron micrographs and image simulations.

  4. Fabrication and Photocatalytic Property of Novel SrTiO3/Bi5O7I Nanocomposites

    NASA Astrophysics Data System (ADS)

    Xia, Yongmei; He, Zuming; Su, Jiangbin; Liu, Ya; Tang, Bin

    2018-05-01

    The novel SrTiO3/Bi5O7I nanocomposites were successfully fabricated by a thermal decomposition approach. The as-prepared samples were characterized by XRD, XPS, SEM, EDS, FTIR, DRS and PL spectra. The results show that the SrTiO3/Bi5O7I nanocomposites are composed of perovskite SrTiO3 nanoparticles and tetragonal Bi5O7I nanorods. The SrTiO3/Bi5O7I nanocomposites exhibit an excellent photocatalytic performance for the degradation of RhB solution under simulated solar light irradiation, which is superior to that of pristine Bi5O7I and SrTiO3. In particular, the 30 wt% SrTiO3/Bi5O7I nanocomposite is found as the optimal composites, over which the dye degradation reaches 89.6% for 150 min of photocatalysis. The photocatalytic degradation rate of the 30 wt% SrTiO3/Bi5O7I nanocomposite is found to be 3.97 times and 12.5 times higher than that of bare Bi5O7I and SrTiO3, respectively. The reactive species trapping experiments suggest that \\bullet {O}_2- and holes are the main active species responsible for the RhB degradation. In addition, the PL spectra elucidate the effective separation of photoinduced electron-hole pairs. Further, the possible photocatalytic mechanism of the SrTiO3/Bi5O7I nanocomposites is also elucidated based on the experimental evidences.

  5. Fabrication and Photocatalytic Property of Novel SrTiO3/Bi5O7I Nanocomposites.

    PubMed

    Xia, Yongmei; He, Zuming; Su, Jiangbin; Liu, Ya; Tang, Bin

    2018-05-11

    The novel SrTiO 3 /Bi 5 O 7 I nanocomposites were successfully fabricated by a thermal decomposition approach. The as-prepared samples were characterized by XRD, XPS, SEM, EDS, FTIR, DRS and PL spectra. The results show that the SrTiO 3 /Bi 5 O 7 I nanocomposites are composed of perovskite SrTiO 3 nanoparticles and tetragonal Bi 5 O 7 I nanorods. The SrTiO 3 /Bi 5 O 7 I nanocomposites exhibit an excellent photocatalytic performance for the degradation of RhB solution under simulated solar light irradiation, which is superior to that of pristine Bi 5 O 7 I and SrTiO 3 . In particular, the 30 wt% SrTiO 3 /Bi 5 O 7 I nanocomposite is found as the optimal composites, over which the dye degradation reaches 89.6% for 150 min of photocatalysis. The photocatalytic degradation rate of the 30 wt% SrTiO 3 /Bi 5 O 7 I nanocomposite is found to be 3.97 times and 12.5 times higher than that of bare Bi 5 O 7 I and SrTiO 3 , respectively. The reactive species trapping experiments suggest that [Formula: see text] and holes are the main active species responsible for the RhB degradation. In addition, the PL spectra elucidate the effective separation of photoinduced electron-hole pairs. Further, the possible photocatalytic mechanism of the SrTiO 3 /Bi 5 O 7 I nanocomposites is also elucidated based on the experimental evidences.

  6. Electron Correlation in Oxygen Vacancy in SrTiO3

    NASA Astrophysics Data System (ADS)

    Lin, Chungwei; Demkov, Alexander A.

    2014-03-01

    Oxygen vacancies are an important type of defect in transition metal oxides. In SrTiO3 they are believed to be the main donors in an otherwise intrinsic crystal. At the same time, a relatively deep gap state associated with the vacancy is widely reported. To explain this inconsistency we investigate the effect of electron correlation in an oxygen vacancy (OV) in SrTiO3. When taking correlation into account, we find that the OV-induced localized level can at most trap one electron, while the second electron occupies the conduction band. Our results offer a natural explanation of how the OV in SrTiO3 can produce a deep in-gap level (about 1 eV below the conduction band bottom) in photoemission, and at the same time be an electron donor. Our analysis implies an OV in SrTiO3 should be fundamentally regarded as a magnetic impurity, whose deep level is always partially occupied due to the strong Coulomb repulsion. An OV-based Anderson impurity model is derived, and its implications are discussed. This work was supported by Scientific Discovery through Advanced Computing (SciDAC) program funded by U.S. Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences under award number DESC0008877.

  7. Chemical strain-dependent two-dimensional transport at R AlO 3 / SrTiO 3 interfaces ( R = La , Nd , Sm , and Gd )

    DOE PAGES

    Li, Chen; Shen, Xuan; Yang, Yurong; ...

    2016-12-27

    Perovskite RAlO 3 (R = La, Nd, Sm, and Gd) films have been deposited epitaxially on (001) TiO 2-terminated SrTiO 3 substrates. In this paper, it is observed that the two-dimensional transport characteristics at the RAlO 3/SrTiO 3 interfaces are very sensitive to the species of rare-earth element, that is to chemical strain. Although electron energy loss spectroscopy measurements show that electron transfer occurs in all the four polar/nonpolar heterostructures, the amount of electrons transferred across SmAlO 3/SrTiO 3 and GdAlO 3/SrTiO 3 interfaces are much less than those across LaAlO 3/SrTiO 3 and NdAlO 3/SrTiO 3 interfaces. First-principles calculationsmore » reveal the competition between ionic polarization and electronic polarization in the polar layers in compensating the build-in polarization due to the polar discontinuity at the interface. Finally, in particular, a large ionic polarization is found in SmAlO 3/SrTiO 3 and GdAlO 3/SrTiO 3 systems (which experience the largest tensile epitaxial strain), hence reducing the amount of electrons transferred.« less

  8. Strain relaxation in single crystal SrTiO3 grown on Si (001) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Choi, Miri; Posadas, Agham; Dargis, Rytis; Shih, Chih-Kang; Demkov, Alexander A.; Triyoso, Dina H.; David Theodore, N.; Dubourdieu, Catherine; Bruley, John; Jordan-Sweet, Jean

    2012-03-01

    An epitaxial layer of SrTiO3 grown directly on Si may be used as a pseudo-substrate for the integration of perovskite oxides onto silicon. When SrTiO3 is initially grown on Si (001), it is nominally compressively strained. However, by subsequent annealing in oxygen at elevated temperature, an SiOx interlayer can be formed which alters the strain state of SrTiO3. We report a study of strain relaxation in SrTiO3 films grown on Si by molecular beam epitaxy as a function of annealing time and oxygen partial pressure. Using a combination of x-ray diffraction, reflection high energy electron diffraction, and transmission electron microscopy, we describe the process of interfacial oxidation and strain relaxation of SrTiO3 on Si (001). Understanding the process of strain relaxation of SrTiO3 on silicon will be useful for controlling the SrTiO3 lattice constant for lattice matching with functional oxide overlayers.

  9. Epitaxial structure and transport in LaTiO3+x films on (001) SrTiO3

    NASA Astrophysics Data System (ADS)

    Kim, K. H.; Norton, D. P.; Budai, J. D.; Chisholm, M. F.; Sales, B. C.; Christen, D. K.; Cantoni, C.

    2003-12-01

    The structure and transport properties of LaTiO3+x epitaxial thin films grown on (001) SrTiO3 by pulsed-laser deposition is examined. Four-circle X-ray diffraction indicates that the films possess the defect perovskite LaTiO3 structure when deposited in vacuum, with the higher X compounds forming at moderate oxygen pressures. The crystal structure of the LaTiO3 films is tetragonal in the epitaxial films, in contrast to the orthorhombic structure observed in bulk materials. A domain structure is observed in the films, consisting of LaTiO3 oriented either with the [110] or [001] directions perpendicular to the substrate surface. Z-contrast scanning transmission electron microscopy reveals that this domain structure is not present in the first few unit cells of the film, but emerges approximately 2-3 nm from the SrTiO3/LaTiO3 interface. Upon increasing the oxygen pressure during growth, a shift in the lattice d-spacing parallel to the substrate surface is observed, and is consistent with the growth of the La2Ti2O7 phase. However, van der Pauw measurements show that the films with the larger d-spacing remain conductive, albeit with a resistivity that is significantly higher than that for the perovskite LaTiO3 films. The transport behavior suggests that the films grown at higher oxygen pressures are LaTiO3+x with 0.4 < x < 0.5. (

  10. Studies of local structural distortions in strained ultrathin BaTiO3 films using scanning transmission electron microscopy.

    PubMed

    Park, Daesung; Herpers, Anja; Menke, Tobias; Heidelmann, Markus; Houben, Lothar; Dittmann, Regina; Mayer, Joachim

    2014-06-01

    Ultrathin ferroelectric heterostructures (SrTiO3/BaTiO3/BaRuO3/SrRuO3) were studied by scanning transmission electron microscopy (STEM) in terms of structural distortions and atomic displacements. The TiO2-termination at the top interface of the BaTiO3 layer was changed into a BaO-termination by adding an additional BaRuO3 layer. High-angle annular dark-field (HAADF) imaging by aberration-corrected STEM revealed that an artificially introduced BaO-termination can be achieved by this interface engineering. By using fast sequential imaging and frame-by-frame drift correction, the effect of the specimen drift was significantly reduced and the signal-to-noise ratio of the HAADF images was improved. Thus, a quantitative analysis of the HAADF images was feasible, and an in-plane and out-of-plane lattice spacing of the BaTiO3 layer of 3.90 and 4.22 Å were determined. A 25 pm shift of the Ti columns from the center of the unit cell of BaTiO3 along the c-axis was observed. By spatially resolved electron energy-loss spectroscopy studies, a reduction of the crystal field splitting (CFS, ΔL3=1.93 eV) and an asymmetric broadening of the eg peak were observed in the BaTiO3 film. These results verify the presence of a ferroelectric polarization in the ultrathin BaTiO3 film.

  11. Proximity to a ferroelectric instability in Ba1-xCaxZrO3

    NASA Astrophysics Data System (ADS)

    Kim, H. S.; Christen, H. M.; Biegalski, M. D.; Singh, D. J.

    2010-09-01

    Ferroelectricity in ABO3 perovskites driven by A-site disorder is seen as a powerful approach toward lead-free piezoelectrics and ferroelectrics as well as to forming multiferroic compounds. Here we investigate the Ba1-xCaxZrO3 solid solution by structural and dielectric measurements on pulsed laser deposition grown films and by first principles calculations. Films on SrRuO3-coated SrTiO3 substrates are studied for x between 0 and 0.44. Despite the expectation that the Ca-ions assume off-center positions in the perovskite lattice, dielectric measurements show no evidence for ferroelectricity. This behavior is explained by first principles supercell calculations that show ferroelectricity at expanded volume but a rapid suppression thereof as the volume is reduced, thus indicating that our paraelectric Ba1-xCaxZrO3 films are close to a ferroelectric instability. These results demonstrate the important interplay between unit cell volume and ferroelectricity arising from off-centered ions.

  12. Current Status of Thin Film (Ba,Sr) TiO3 Tunable Microwave Components for RF Communications

    NASA Technical Reports Server (NTRS)

    VanKeuls, F. W.; Romananofsky, R. R.; Mueller, C. H.; Warner, J. D.; Canedy, C. L.; Ramesh, R.; Miranda, F. A.

    2000-01-01

    The performance of proof-of-concept ferroelectric microwave devices has been moving steadily closer to the level needed for satellite and other rf communications applications. This paper will review recent progress at NASA Glenn in developing thin film Ba(x)Sr(1-x)TiO3 tunable microwave components for these applications. Phase shifters for phased array antennas, tunable filters and tunable oscillators employing microstrip and coupled microstrip configurations will be presented. Tunabilities, maximum dielectric constants, and phase shifter parameters will be discussed (e.g., coupled microstrip phase shifters with phase shift over 200 deg. at 18 GHz and a figure of merit of 74.3 deg./dB). Issues of postannealing, Mn-doping and Ba(x)Sr(1-x)TiO3 growth on sapphire and alumina substrates will be covered. The challenges of incorporating these devices into larger systems, such as yield, variability in phase shift and insertion loss, and protective coatings will also be addressed.

  13. Current Status of Thin Film (Ba,Sr)TiO3 Tunable Microwave Components for RF Communications

    NASA Technical Reports Server (NTRS)

    VanKeuls, F. W.; Romanofsky, R. R.; Mueller, C. H.; Warner, J. D.; Canedy, C. L.; Ramesh, R.; Miranda, F. A.

    2000-01-01

    The performance of proof-of-concept ferroelectric microwave devices has been moving steadily closer to the level needed for satellite and other rf communications applications. This paper will review recent progress at NASA Glenn in developing thin film Ba(x)Sr(1-x)TiO3 tunable micro-wave components for these applications. Phase shifters for phased array antennas, tunable filters and tunable oscillators employing microstrip and coupled microstrip configurations will be presented. Tunabilities, maximum dielectric constants, and phase shifter parameters will be discussed (e.g., coupled microstrip phase shifters with phase shift over 200 deg at 18 GHz and a figure of merit of 74.3 deg/dB). Issues of post-annealing, Mn-doping and Ba(x)Sr(1-x) TiO3 growth on sapphire and alumina substrates will be covered. The challenges of incorporating these devices into larger systems, such as yield, variability in phase shift and insertion loss, and protective coatings will also be addressed.

  14. Physics of SrTiO3-based heterostructures and nanostructures: a review.

    PubMed

    Pai, Yun-Yi; Tylan-Tyler, Anthony; Irvin, Patrick; Levy, Jeremy

    2018-02-09

    This review provides a summary of the rich physics expressed within SrTiO 3 -based heterostructures and nanostructures. The intended audience is researchers who are working in the field of oxides, but also those with different backgrounds (e.g., semiconductor nanostructures). After reviewing the relevant properties of SrTiO 3 itself, we will then discuss the basics of SrTiO 3 -based heterostructures, how they can be grown, and how devices are typically fabricated. Next, we will cover the physics of these heterostructures, including their phase diagram and coupling between the various degrees of freedom. Finally, we will review the rich landscape of quantum transport phenomena, as well as the devices that elicit them.

  15. Irreversibility and carriers control in two-dimensional electron gas at LaTiO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Bergeal, N.; Biscaras, J.; Hurand, S.; Feuillet-Palma, C.; Lesueur, J.; Rastogi, A.; Budhani, R. C.; Reyren, N.; Lesne, E.; Leboeuf, D.; Proust, C.

    2013-03-01

    It has been shown recently that a two-dimensional electron gas 2DEG could form at the interface of two insulators such as LaAlO3 and SrTiO3, or LaTiO3 (a Mott insulator) and SrTiO3. We present low temperature transport measurements on LaTiO3/SrTiO3 and LaAlO3/SrTiO3 hetero-structures, whose properties can be modulated by field effect using a metallic gate on the back of the substrate. Here we show that when the carrier density is electrostatically increased beyond a critical value, the added electrons escape into the SrTiO3 leading to an irreversible doping regime where all the electronic properties of the 2DEG saturate (carrier density, resistivity, superconducting transition...). The dynamic of leakage was studied using time resolved measurement. Based on a complete self-consistent description of the confinement well, a thermal model for the carriers escape has been developed, which quantitatively accounts for the data.

  16. Acoustoelastic effect of textured (Ba,Sr)TiO{sub 3} thin films under an initial mechanical stress

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kamel, Marwa; Mseddi, Souhir; Njeh, Anouar

    Acoustoelastic (AE) analysis of initial stresses plays an important role as a nondestructive tool in current engineering. Two textured BST (Ba{sub 0.65}Sr{sub 0.35}TiO{sub 3}) thin films, with different substrate to target distance, were grown on Pt(111)/TiO{sub 2}/SiO{sub 2}/Si(001) substrate by rf-magnetron sputtering deposition techniques. A conventional “sin{sup 2} ψ” method to determine residual stress and strain in BST films by X-ray diffraction is applied. A laser acoustic waves (LA-waves) technique is used to generate surface acoustic waves (SAW) propagating in both samples. Young's modulus E and Poisson ratio ν of BST films in different propagation directions are derived from the measuredmore » dispersion curves. Estimation of effective second-order elastic constants of BST thin films in stressed states is served in SAW study. This paper presents an original investigation of AE effect in prestressed Ba{sub 0.65}Sr{sub 0.35}TiO{sub 3} films, where the effective elastic constants and the effect of texture on second and third order elastic tensor are considered and used. The propagation behavior of Rayleigh and Love waves in BST thin films under residual stress is explored and discussed. The guiding velocities affected by residual stresses, reveal some shifts which do not exceed four percent mainly in the low frequency range.« less

  17. Fabrication of Schottky Junction Between Au and SrTiO3

    NASA Astrophysics Data System (ADS)

    Inoue, Akira; Izumisawa, Kei; Uwe, Hiromoto

    2001-05-01

    A Schottky junction with a high rectification ratio between Au and La-doped SrTiO3 has been fabricated using a simple surface treatment. Highly La-doped (5%) SrTiO3 single crystals are annealed in O2 atmosphere at about 1000°C for 1 h and etched in HNO3 for more than five min. The HNO3 etching is performed in a globe box containing N2 to prevent pollution from the air. After the treatment, Au is deposited on the SrTiO3 surface in a vacuum (˜ 10-7 Torr) with an e-gun evaporator. The current voltage characteristics of the junction have shown excellent rectification properties, although junctions using neither annealed nor etched SrTiO3 exhibit high leak current in reverse voltage. The rectification ratio of the junction at 1 V is more than six orders of magnitude and there is no hysteresis in the current voltage spectra. The logarithm of the current is linear with the forward bias voltage. The ideal factor of the junction is estimated to be about 1.68. These results suggest that, if prevented from being pollution by the air, a good Schottky junction can be obtained by easy processes such as annealing in oxygen atmosphere and surface etching with acid.

  18. Thermoelectric properties of n-type SrTiO 3

    DOE PAGES

    Sun, Jifeng; Singh, David J.

    2016-05-26

    We present an investigation of the thermoelectric properties of cubic perovskite SrTiO 3. The results are derived from a combination of calculated transport functions obtained from Boltzmann transport theory in the constant scattering time approximation based on the electronic structure and existing experimental data for La-doped SrTiO 3. The figure of merit ZT is modeled with respect to carrier concentration and temperature. The model predicts a relatively high ZT at optimized doping and suggests that the ZT value can reach 0.7 at T = 1400 K. Thus ZT can be improved from the current experimental values by carrier concentration optimization.

  19. Structural phase transitions in SrTiO 3 nanoparticles

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang, Han; Liu, Sizhan; Scofield, Megan E.

    2017-07-31

    Pressure dependent structural measurements on monodispersed nanoscale SrTiO3 samples with average diameters of 10 to ~80 nm were conducted to enhance the understanding of the structural phase diagram of nanoscale SrTiO3. A robust pressure independent polar structure was found in the 10 nm sample for pressures up to 13 GPa, while a size dependent cubic to tetragonal transition occurs (at P = Pc) for larger particle sizes. The results suggest that the growth of ~10 nm STO particles on substrates with significant lattice mismatch may maintain a polar state for a large range of strain values, possibly enabling device use.

  20. Thermoelectric properties of n-type SrTiO3

    NASA Astrophysics Data System (ADS)

    Sun, Jifeng; Singh, David J.

    2016-10-01

    We present an investigation of the thermoelectric properties of cubic perovskite SrTiO3. The results are derived from a combination of calculated transport functions obtained from Boltzmann transport theory in the constant scattering time approximation based on the electronic structure and existing experimental data for La-doped SrTiO3. The figure of merit ZT is modeled with respect to carrier concentration and temperature. The model predicts a relatively high ZT at optimized doping and suggests that the ZT value can reach 0.7 at T = 1400 K. Thus ZT can be improved from the current experimental values by carrier concentration optimization.

  1. EPR investigation of the trivalent chromium complexes in SrTiO3

    NASA Astrophysics Data System (ADS)

    Azamat, D. V.; Dejneka, A.; Lančok, J.; Jastrabik, L.; Trepakov, V. A.; Bryknar, Z.; Neverova, E. V.; Badalyan, A. G.

    2014-02-01

    The trivalent chromium centers were investigated by means of electron paramagnetic resonance (EPR) in SrTiO3 single crystals grown using the Verneuil technique. It was shown that the charge compensation of the Cr3+-VO dominant centers in octahedral environment is due to the remote oxygen vacancy located on the axial axis of the center. In order to provide insight into spin-phonon relaxation processes the studies of axial distortion of Cr3+-VO centers have been performed as function of temperature. The analysis of the trigonal Cr3+ centers found in SrTiO3 indicates the presence of the nearest-neighbor strontium vacancy. The next-nearest-neighbor exchange-coupled pairs of Cr3+ in SrTiO3 has been analyzed from the angular variation of the total electron spin of S=2 resonance lines.

  2. Structural studies of zirconium doped Ba{sub 0.70}Sr{sub 0.30}TiO{sub 3} lead free ferroelectric thin films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sharma, Sarita, E-mail: sss.sharmasarita@gmail.com; Ram, Mast; Thakur, Shilpa

    2016-05-06

    Ba{sub 0.7}Sr{sub 0.3}(Zr{sub x}Ti{sub 1-x})O{sub 3}(BSZT, x=0,0.05,0.10,0.15,0.20) thin films were prepared by using sol gel method. Structural and microstructural properties were studied by using XRD, Raman Spectroscopy and atomic force microscopy (AFM) respectively. XRD and Raman Spectroscopy show the presence of tetragonal phase in multilayer BSZT thin film. The experimental results demonstrate that structural and microstructural properties of BSZT thin film were significantly dependent on variation of Zr content.

  3. Effect of residual stress on energy storage property in PbZrO3 antiferroelectric thin films with different orientations

    NASA Astrophysics Data System (ADS)

    Ge, Jun; Remiens, Denis; Costecalde, Jean; Chen, Ying; Dong, Xianlin; Wang, Genshui

    2013-10-01

    The effect of residual stress on energy storage property was investigated for a series of PbZrO3 thin films on SrTiO3 and Si substrates. Compressive or tensile residual stress influences the critical electric field EA for the ferroelectric-to-antiferroelectric phase transition, thus for films with (110)/(101) orientation, energy density W of films on SrTiO3 is 38% larger than films on Si; in contrast, (001)-oriented PbZrO3 films on SrTiO3 show slightly smaller W compared to films on Si. We conclude that the different responses of W to stress are related to the different constrain states in films with different orientations.

  4. Strain evolution of each type of grains in poly-crystalline (Ba,Sr)TiO3 thin films grown by sputtering

    PubMed Central

    Park, Woo Young; Park, Min Hyuk; Lee, Jong Ho; Yoon, Jung Ho; Han, Jeong Hwan; Choi, Jung-Hae; Hwang, Cheol Seong

    2012-01-01

    The strain states of [111]-, [110]-, and [002]-oriented grains in poly-crystalline sputtered (Ba,Sr)TiO3 thin films on highly [111]-oriented Pt electrode/Si substrates were carefully examined by X-ray diffraction techniques. Remarkably, [002]-oriented grains respond more while [110]- and [111]-oriented grains do less than the theoretically estimated responses, which is understandable from the arrangement of the TiO6 octahedra with respect to the stress direction. Furthermore, such mechanical responses are completely independent of the degree of crystallization and film thickness. The transition growth temperature between the positive and negative strains was also different depending on the grain orientation. The unstrained lattice parameter for each type of grain was different suggesting that the oxygen vacancy concentration for each type of grain is different, too. The results reveal that polycrystalline (Ba,Sr)TiO3 thin films are not an aggregation of differently oriented grains which simply follow the mechanical behavior of single crystal with different orientations. PMID:23230505

  5. Preferential growth and enhanced dielectric properties of Ba0.7Sr0.3TiO3 thin films with preannealed Pt bottom electrode

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaohong; Defaÿ, Emmanuel; Aïd, Marc; Ren, Yinjuan; Zhang, Caiyun; Zhu, Jiliang; Zhu, Jianguo; Xiao, Dingquan

    2013-03-01

    Ba0.7Sr0.3TiO3 (BST) thin films, about 100 nm in thickness, were prepared on unannealed and 700 °C-preannealed Pt bottom electrodes by the ion beam sputtering and post-deposition annealing method. It was found that the preannealed Pt layer has a more compact structure, making it not only a bottom electrode but also a good template for high-quality BST thin film growth. The BST films deposited on preannealed Pt bottom electrodes showed (0 0 l)-preferred orientation, dense and uniform microstructure with no intermediate phase formed at the film/electrode interface, and thus enhanced dielectric properties. As a result, the typical relative dielectric constant and tunability (under a dc electric field of 1 MV cm-1) reach 180 and 50.1%, respectively, for the BST thin films with preannealed Pt bottom electrodes, which are significantly higher than those (166 and 41.3%, respectively) for the BST thin films deposited on unannealed Pt bottom electrodes.

  6. Nonenzymatic detection of glucose using BaCuO2 thin layer

    NASA Astrophysics Data System (ADS)

    Ito, Takeshi; Asada, Tsuyoshi; Asai, Naoto; Shimizu, Tomohiro; Shingubara, Shoso

    2017-01-01

    A BaCuO2 thin layer was deposited on a glassy carbon electrode and used for the direct oxidation of glucose. The crystalline, electrochemical, and physicochemical properties that depend on the deposition temperature and deposition time were studied. X-ray diffraction (XRD) analysis showed that the thin layer was amorphous even at 400 °C. The current density of the glucose oxidation using the thin layer deposited at 200 °C was higher than those at other deposition temperatures. Under this condition, the current density increased with the glucose concentration and deposition time. These results indicate that a BaCuO2 thin layer has potential for measuring the blood glucose level without enzymes.

  7. Dielectric collapse at the LaAlO 3/SrTiO 3 (001) heterointerface under applied electric field

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Minohara, M.; Hikita, Y.; Bell, C.

    The fascinating interfacial transport properties at the LaAlO 3/SrTiO 3 heterointerface have led to intense investigations of this oxide system. Exploiting the large dielectric constant of SrTiO 3 at low temperatures, tunability in the interfacial conductivity over a wide range has been demonstrated using a back-gate device geometry. In order to understand the effect of back-gating, it is crucial to assess the interface band structure and its evolution with external bias. In this study, we report measurements of the gate-bias dependent interface band alignment, especially the confining potential profile, at the conducting LaAlO 3/SrTiO 3 (001) heterointerface using soft andmore » hard x-ray photoemission spectroscopy in conjunction with detailed model simulations. Depth-profiling analysis incorporating the electric field dependent dielectric constant in SrTiO 3 reveals that a significant potential drop on the SrTiO 3 side of the interface occurs within ~2 nm of the interface under negative gate-bias. These results demonstrate gate control of the collapse of the dielectric permittivity at the interface, and explain the dramatic loss of electron mobility with back-gate depletion.« less

  8. Dielectric collapse at the LaAlO 3/SrTiO 3 (001) heterointerface under applied electric field

    DOE PAGES

    Minohara, M.; Hikita, Y.; Bell, C.; ...

    2017-08-25

    The fascinating interfacial transport properties at the LaAlO 3/SrTiO 3 heterointerface have led to intense investigations of this oxide system. Exploiting the large dielectric constant of SrTiO 3 at low temperatures, tunability in the interfacial conductivity over a wide range has been demonstrated using a back-gate device geometry. In order to understand the effect of back-gating, it is crucial to assess the interface band structure and its evolution with external bias. In this study, we report measurements of the gate-bias dependent interface band alignment, especially the confining potential profile, at the conducting LaAlO 3/SrTiO 3 (001) heterointerface using soft andmore » hard x-ray photoemission spectroscopy in conjunction with detailed model simulations. Depth-profiling analysis incorporating the electric field dependent dielectric constant in SrTiO 3 reveals that a significant potential drop on the SrTiO 3 side of the interface occurs within ~2 nm of the interface under negative gate-bias. These results demonstrate gate control of the collapse of the dielectric permittivity at the interface, and explain the dramatic loss of electron mobility with back-gate depletion.« less

  9. Plentiful magnetic moments in oxygen deficient SrTiO 3

    DOE PAGES

    Ganesh, Panchapakesan; Lopez-Bezanilla, Alejandro; Littlewood, Peter B.

    2015-10-06

    In this research, correlated band theory is employed to investigate the magnetic and electronic properties of different arrangements of oxygen di- and tri-vacancy clusters in SrTiO 3. Hole and electron doping of oxygen deficient SrTiO 3 yields various degrees of magnetization as a result of the interaction between localized magnetic moments at the defect sites. Different kinds of Ti atomic orbital hybridization are described as a function of the doping level and defect geometry. We find that magnetism in SrTiO 3–δ is sensitive to the arrangement of neighbouring vacancy sites, charge carrier density, and vacancy-vacancy interaction. Permanent magnetic moments inmore » the absence of vacancy doping electrons are observed. Our description of the charged clusters of oxygen vacancies widens the previous descriptions of mono- and multi-vacancies and points out the importance of the controlled formation at the atomic level of defects for the realization of transition metal oxide based devices with a desirable magnetic performance.« less

  10. Fabrication of SrTiO3 nanotubes via an isomorphic conversion strategy

    NASA Astrophysics Data System (ADS)

    Yang, Dong; Zou, Xiaoyan; Tong, Zhenwei; Nan, Yanhu; Ding, Fei; Jiang, Zhongyi

    2018-02-01

    One-dimensional nanotubes have attracted enormous attention due to their specific structure and excellent performance since the carbon nanotube was prepared. In this study, the open-ended SrTiO3 nanotubes (STNTs) have been fabricated for the first time via an isomorphic conversion strategy using the protonated titanate nanotubes (HTNTs) as the precursor and template under the hydrothermal treatment. The as-prepared STNTs consist of uniform and continuous multilayers, having inner and outer diameters about 8.0 and 13 nm. The STNT formation involves the exchange of Sr2+ ions with H+ ions in HTNTs and then in situ growth of cubic SrTiO3 crystals by the templating of HTNT frameworks. It is found that the diffusion process of Sr2+ ions plays a critical role in controlling the nanotube morphology of SrTiO3 crystals. In addition, the SrTiO3 nanotubes exhibit high photocatalytic activity for the Cr(VI) reduction, which can reduce nearly 100% Cr(VI) within 6 h under simulated sunlight irradiation. The current strategy may be broadly applicable for fabricating the nanotubes from raw materials without 2D layered nanostructure. [Figure not available: see fulltext.

  11. Microstructure and ferroelectricity of BaTiO3 thin films on Si for integrated photonics

    NASA Astrophysics Data System (ADS)

    Kormondy, Kristy J.; Popoff, Youri; Sousa, Marilyne; Eltes, Felix; Caimi, Daniele; Rossell, Marta D.; Fiebig, Manfred; Hoffmann, Patrik; Marchiori, Chiara; Reinke, Michael; Trassin, Morgan; Demkov, Alexander A.; Fompeyrine, Jean; Abe, Stefan

    2017-02-01

    Significant progress has been made in integrating novel materials into silicon photonic structures in order to extend the functionality of photonic circuits. One of these promising optical materials is BaTiO3 or barium titanate (BTO) that exhibits a very large Pockels coefficient as required for high-speed light modulators. However, all previous demonstrations show a noticable reduction of the Pockels effect in BTO thin films deposited on silicon substrates compared to BTO bulk crystals. Here, we report on the strong dependence of the Pockels effect in BTO thin films on their microstructure, and provide guidelines on how to engineer thin films with strong electro-optic response. We employ several deposition methods such as molecular beam epitaxy and chemical vapor deposition to realize BTO thin films with different morphology and crystalline structure. While a linear electro-optic response is present even in porous, polycrystalline BTO thin films with an effective Pockels coefficient r eff = 6 pm V-1, it is maximized for dense, tetragonal, epitaxial BTO films (r eff = 140 pm V-1). By identifying the key structural predictors of electro-optic response in BTO/Si, we provide a roadmap to fully exploit the linear electro-optic effect in novel hybrid oxide/semiconductor nanophotonic devices.

  12. Red-ultraviolet photoluminescence tuning by Ni nanocrystals in epitaxial SrTiO3 matrix

    NASA Astrophysics Data System (ADS)

    Xiong, Z. W.; Cao, L. H.

    2018-07-01

    In this work, the self-organized Ni nanocrystals (NCs) were embedded in the epitaxial SrTiO3 matrix using pulsed laser deposition method. With the in-situ monitoring of reflection high-energy electron diffraction, both matrix and NCs could be precisely engineered with desired qualities by regulating the growth conditions according to the full release of stress energy at the interfaces of Ni NCs and SrTiO3. We achieved a controllable strained system according to the transformation of growth modes from three dimensional (3D) islands of Ni NCs to 2D layer-by-layer of SrTiO3, corresponding to the (1 1 1) and (0 0 l) orientation for Ni and SrTiO3, respectively. With the increase of Ni NCs concentration, the absorption intensity is increasing in the regions of 190-300 nm, and the band gap is gradually decreased. Besides, photoluminescence (PL) spectra reveal that the energy levels of Ni 3d bands contribute to the different PL colors, further inducing the enhancement of PL intensity and red-shift of emission peaks. Compared with the pure SrTiO3 published in the literature, much wider ranges of PL emission from red to ultraviolet can be tuned by the Ni NCs.

  13. Internal residual stress studies and enhanced dielectric properties in La0.7Sr0.3CoO3 buffered (Ba,Sr)TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Lu, Shengbo; Xu, Zhengkui

    2009-09-01

    Ba0.6Sr0.4TiO3 (BST) thin films were deposited on La0.7Sr0.3CoO3 (LSCO) buffered and unbuffered Pt (111)/Ti/SiO2/Si substrates by pulsed laser deposition. The former exhibits a (100) preferred orientation and the latter a random orientation, respectively. Grazing incident x-ray diffraction study revealed that the tensile residual stress observed in the latter is markedly reduced in the former. As a result, the dielectric property of the LSCO buffered BST thin film is greatly improved, which shows a larger dielectric constant and tunability, smaller loss tangent, and lower leakage current than those of the unbuffered BST thin film. The relaxation of the larger tensile residual stress is attributed to the larger grain size in the buffered BST thin film and to a closer match of thermal expansion coefficient between the BST and the LSCO buffer layer.

  14. Conducting LaAlO3/SrTiO3 heterointerfaces on atomically-flat substrates prepared by deionized-water

    PubMed Central

    Connell, J. G.; Nichols, J.; Gruenewald, J. H.; Kim, D.-W.; Seo, S. S. A.

    2016-01-01

    We have investigated how the recently-developed water-leaching method for atomically-flat SrTiO3 (STO) substrates affects the transport properties of LaAlO3 (LAO) and STO heterointerfaces. Using pulsed laser deposition at identical growth conditions, we have synthesized epitaxial LAO thin-films on two different STO substrates, which are prepared by water-leaching and buffered hydrofluoric acid (BHF) etching methods. The structural, transport, and optical properties of LAO/STO heterostructures grown on water-leached substrates show the same high-quality as the samples grown on BHF-etched substrates. These results indicate that the water-leaching method can be used to grow complex oxide heterostructures with atomically well-defined heterointerfaces without safety concerns. PMID:27033248

  15. Optical study of the free-carrier response of LaTiO3/SrTiO3 superlattices.

    PubMed

    Seo, S S A; Choi, W S; Lee, H N; Yu, L; Kim, K W; Bernhard, C; Noh, T W

    2007-12-31

    We used infrared spectroscopic ellipsometry to investigate the electronic properties of LaTiO_{3}/SrTiO_{3} superlattices (SLs). Our results indicated that, independent of the SL periodicity and individual layer thickness, the SLs exhibited a Drude metallic response with sheet carrier density per interface approximately 3x10;{14} cm;{-2}. This is probably due to the leakage of d electrons at interfaces from the Mott insulator LaTiO3 to the band insulator SrTiO3. We observed a carrier relaxation time approximately 35 fs and mobility approximately 35 cm;{2} V-1 s;{-1} at 10 K, and an unusual temperature dependence of carrier density that was attributed to the dielectric screening of quantum paraelectric SrTiO3.

  16. Structural phase transitions in SrTiO 3 nanoparticles

    DOE PAGES

    Zhang, Han; Liu, Sizhan; Scofield, Megan E.; ...

    2017-08-04

    We present that pressure dependent structural measurements on monodispersed nanoscale SrTiO 3 samples with average diameters of 10 to ~80 nm were conducted to enhance the understanding of the structural phase diagram of nanoscale SrTiO 3. A robust pressure independent polar structure was found in the 10 nm sample for pressures up to 13 GPa, while a size dependent cubic to tetragonal transition occurs (at P = P c) for larger particle sizes. In conclusion, the results suggest that the growth of ~10 nm STO particles on substrates with significant lattice mismatch may maintain a polar state for a largemore » range of strain values, possibly enabling device use.« less

  17. Temperature-dependence of hypersound dynamics in SrTiO3/SrRuO3 heterostructures studied by ultrafast spectroscopy

    NASA Astrophysics Data System (ADS)

    Yang, Chi-Yuan; Yadav, Ajay K.; Ramesh, Ramamoorthy; Wen, Yu-Chieh; Hsu, Chia-Hao; Wu, Maw-Kuen; Chia, Chih-Ta; Lin, Kung-Hsuan

    Strontium titanate (SrTiO3, STO) and strontium ruthenate (SrRuO3, SRO) are complex oxide with perovskite structure. Their property, such as thermoelectricity and superconductivity, has been widely investigated for scientific and industrial purposes. Recently, complex oxide heterostructures can be grown by pulsed laser deposition. It opens many possibilities f or new properties of materials. With ultrafast pump-probe spectroscopy, we demonstrated that metal-like SRO thin film can be served as a phonon transducer to generate hypersound with frequency of several tens to several hundreads of GHz. This technique can be utilized to study not only the elastic properties of perovskite thin films but also the interfaces. In this study, we used this technique to study the temperature dependence of structural phases in STO. During the crossing over the soft-mode transition in STO around 110 K, the shortening of phonon lifetime were also observed.

  18. Oxygen-vacancy-mediated dielectric property in perovskite Eu0.5Ba0.5TiO3-δ epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Li, Weiwei; Gu, Junxing; He, Qian; Zhang, Kelvin H. L.; Wang, Chunchang; Jin, Kuijuan; Wang, Yongqiang; Acosta, Matias; Wang, Haiyan; Borisevich, Albina Y.; MacManus-Driscoll, Judith L.; Yang, Hao

    2018-04-01

    Dielectric relaxation in ABO3 perovskite oxides can result from many different charge carrier-related phenomena. Despite a strong understanding of dielectric relaxations, a detailed investigation of the relationship between the content of oxygen vacancies (VO) and dielectric relaxation has not been performed in perovskite oxide films. In this work, we report a systematic investigation of the influence of the VO concentration on the dielectric relaxation of Eu0.5Ba0.5TiO3-δ epitaxial thin films. Nuclear resonance backscattering spectrometry was used to directly measure the oxygen concentration in Eu0.5Ba0.5TiO3-δ films. We found that dipolar defects created by VO interact with the off-centered Ti ions, which results in the dielectric relaxation in Eu0.5Ba0.5TiO3-δ films. Activation energy gradually increases with the increasing content of VO. The present work significantly extends our understanding of relaxation properties in oxide films.

  19. Roto-flexoelectric coupling impact on the phase diagrams and pyroelectricity of thin SrTiO 3 films

    DOE PAGES

    Morozovska, Anna N.; Eliseev, Eugene A.; Bravina, Svetlana L.; ...

    2012-09-20

    The influence of the flexoelectric and rotostriction coupling on the phase diagrams of ferroelastic-quantum paraelectric SrTiO 3 films was studied using Landau-Ginzburg-Devonshire (LGD) theory. We calculated the phase diagrams in coordinates temperature - film thickness for different epitaxial misfit strains. Tensile misfit strains stimulate appearance of the spontaneous out-of-plane structural order parameter (displacement vector of an appropriate oxygen atom from its cubic position) in the structural phase. For compressive misfit strains are stimulated because of the spontaneous in-plane structural order parameter. Furthermore, gradients of the structural order parameter components, which inevitably exist in the vicinity of film surfaces due tomore » the termination and symmetry breaking, induce improper polarization and pyroelectric response via the flexoelectric and rotostriction coupling mechanism. Flexoelectric and rotostriction coupling results in the roto-flexoelectric field that is antisymmetric inside the film, small in the central part of the film, where the gradients of the structural parameter are small, and maximal near the surfaces, where the gradients of the structural parameter are highest. The field induces improper polarization and pyroelectric response. Penetration depths of the improper phases (both polar and structural) can reach several nm from the film surfaces. An improper pyroelectric response of thin films is high enough to be registered with planar-type electrode configurations by conventional pyroelectric methods.« less

  20. Epitaxial growth of SrTiO3/YBa2Cu3O7 - x heterostructures by plasma-enhanced metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Liang, S.; Chern, C. S.; Shi, Z. Q.; Lu, P.; Safari, A.; Lu, Y.; Kear, B. H.; Hou, S. Y.

    1994-06-01

    We report heteroepitaxial growth of SrTiO3 on YBa2Cu3O7-x/LaAlO3 substrates by plasma-enhanced metalorganic chemical vapor deposition. X-ray diffraction results indicated that SrTiO3 films were epitaxially grown on a (001) YBa2Cu3O7-x surface with [100] orientation perpendicular to the surface. The film composition, with Sr/Ti molar ratio in the range of 0.9 to 1.1, was determined by Rutherford backscattering spectrometry and energy dispersive spectroscopy. The thickness of the SrTiO3 films is 0.1-0.2 μm. The epitaxial growth was further evidenced by high-resolution transmission electron microscopy and selected area diffraction. Atomically abrupt SrTiO3/YBa2Cu3O7-x interface and epitaxial growth with [100]SrTiO3∥[001]YBa2Cu3O7-x were observed in this study. The superconducting transition temperature of the bottom YBa2Cu3O7-x layer, as measured by ac susceptometer, did not significantly degrade after the growth of overlayer SrTiO3. The capacitance-voltage measurements showed that the dielectric constant of the SrTiO3 films was as high as 315 at a signal frequency of 100 KHz. The leakage current density through the SrTiO3 films is about 1×10-6 A/cm2 at 2-V operation. Data analysis on the current-voltage characteristic indicated that the conduction process is related to bulk-limited Poole-Frenkel emission.

  1. Annealing induced effect on the physical properties of ion-beam sputtered 0.5 Ba(Zr0.2Ti0.8)O3 - 0.5 (Ba0.7Ca0.3)TiO3-δ ferroelectric thin films

    NASA Astrophysics Data System (ADS)

    Oliveira, M. J. S.; Silva, J. P. B.; Veltruská, Kateřina; Matolín, V.; Sekhar, K. C.; Moreira, J. Agostinho; Pereira, M.; Gomes, M. J. M.

    2018-06-01

    This work reports thermal annealing induced effect on the structural, optical, chemical and ferroelectric properties of ion-beam sputtered lead-free ferroelectric 0.5 Ba(Zr0.2Ti0.8)O3 - 0.5 (Ba0.7Ca0.3)TiO3-δ (0.5BZT-0.5BCT) thin films. X-ray diffraction studies reveal that the tetragonality increases with the annealing temperature (Ta), while photoluminescence and X-ray photoelectron spectroscopy studies confirm that this effect is associated with the annihilation of the oxygen vacancies as well as changes in the Ba2+ coordination. The films annealed at 750 °C show a remarkable remnant polarization of Pr = 45.0 μC/cm2, with a coercive field of 32 kV/cm. The temperature dependence of the spontaneous polarization of the 0.5BZT-0.5BCT film reveals a mean field behavior of the polarization and the fatigue study reveals that Pr only decreases 3% after passing 109 cycles. Therefore the high remnant polarization and its high Pr stability make these films as promising candidates for memory applications.

  2. Polarity-driven oxygen vacancy formation in ultrathin LaNiO 3 films on SrTiO 3

    DOE PAGES

    Tung, I-Cheng; Luo, Guangfu; Lee, June Hyuk; ...

    2017-10-18

    Oxide heterostructures offer a pathway to control emergent phases in complex oxides, but their creation often leads to boundaries that have a polar discontinuity. In order to fabricate atomic-scale arrangements of dissimilar materials, we need a clear understanding of the pathways by which materials resolve polarity issues. By examining the real-time lattice structure in-situ during growth for the case of polar LaNiO 3 synthesized on non-polar SrTiO 3 (001), we demonstrate how films in ultra-thin limit form as LaNiO 2.5 and then evolve into LaNiO 3 as the thickness increases. Theory explains how the polar energetics drives the formation ofmore » oxygen vacancies and the stability of these phases with thickness and structure.« less

  3. Synthesis, characterization and optical properties of ATiO{sub 3}–Pr thin films prepared by a photochemical method (where A = Ba and Ca)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Cabello, G., E-mail: gerardocabelloguzman@hotmail.com; Lillo, L.; Caro, C.

    2015-10-15

    Highlights: • A method of photochemical deposition has been used to the preparation of (Ba,Ca)TiO{sub 3} thin films doped Pr(III). • The (Ba,Ca)TiO{sub 3}/Pr(III) films under 375 nm excitation shows emissions attributable to {sup 1}D{sub 2} → {sup 3}H{sub 4} transition of Pr ion. • These PL signals decreased above 10 mol% of Pr(III). • Analysis suggests the presence of intermediate energy levels in the band gap influences in the PL processes. - Abstract: This article reports the characterization and optical properties of (Ba,Ca)TiO{sub 3} thin films doped with Pr at different proportions (0–15 mol%). The films were deposited onmore » Si (1 0 0) and quartz substrates using a photochemical method and post-annealed at 900 °C. The evaluation of photo-reactivity of the precursor complexes was monitored by UV–vis and FT-IR spectroscopy. The obtained films were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The results indicate that Ba, Ca, Ti, O and Pr are present in the form of perovskite. Under UV light excitation (375 nm) the (Ba,Ca)TiO{sub 3}–Pr films show the characteristic emissions ascribed to {sup 1}D{sub 2} → {sup 3}H{sub 4} transition of Pr{sup 3+} ion. The optical measurements show the presence of intermediate energy levels in the band gap which influence the emission processes.« less

  4. Synthesis of high-oxidation Y-Ba-Cu-O phases in superoxygenated thin films

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Gauquelin, N.; McMahon, C.; Hawthorn, D. G.; Botton, G. A.; Wei, J. Y. T.

    2018-03-01

    It is known that solid-state reaction in high-pressure oxygen can stabilize high-oxidation phases of Y-Ba-Cu-O superconductors in powder form. We extend this superoxygenation concept of synthesis to thin films which, due to their large surface-to-volume ratio, are more reactive thermodynamically. Epitaxial thin films of YBa2Cu3O7 -δ grown by pulsed laser deposition are annealed at up to 700 atm O2 and 900 ∘C , in conjunction with Cu enrichment by solid-state diffusion. The films show the clear formation of Y2Ba4Cu7O15 -δ and Y2Ba4Cu8O16 as well as regions of YBa2Cu5O9 -δ and YBa2Cu6O10 -δ phases, according to scanning transmission electron microscopy, x-ray diffraction, and x-ray absorption spectroscopy. Similarly annealed YBa2Cu3O7 -δ powders show no phase conversion. Our results demonstrate a route of synthesis towards discovering more complex phases of cuprates and other superconducting oxides.

  5. Phase-field simulations of thickness-dependent domain stability in PbTiO3 thin films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sheng, Guang; Hu, Jia-Mian; Zhang, Jinxian

    Phase-field approach is used to predict the thickness effect on the domain stability in ferroelectric thin films. The strain relaxation mechanism and critical thickness for dislocation formation from both Matthews-Blakeslee (MB) and People-Bean (PB) models are employed. Thickness - strain domain stability diagrams are obtained for PbTiO3 thin films under different strain relaxation models. The relative domain fractions as a function of film thickness are also calculated and compared with experiment measurements in PbTiO3 thin films grown on SrTiO3 and KTaO3 substrates.

  6. Amphoteric doping of praseodymium Pr 3+ in SrTiO 3 grain boundaries

    DOE PAGES

    Yang, H.; Lee, H. S.; Kotula, P. G.; ...

    2015-03-26

    Charge Compensation in rare-earth Praseodymium (Pr 3+) doped SrTiO 3 plays an important role in determining the overall photoluminescence properties of the system. Here, the Pr 3+ doping behavior in SrTiO 3 grain boundaries (GBs) is analyzed using aberration corrected scanning transmission electron microscopy (STEM). The presence of Pr 3+ induces structure variations and changes the statistical prevalence of GB structures. In contrast to the assumption that Pr 3+ substitutes for A site as expected in the bulk, Pr 3+ is found to substitute both Sr and Ti sites inside GBs with the highest concentration in the Ti sites. Asmore » a result, this amphoteric doping behavior in the boundary plane is further confirmed by first principles theoretical calculations.« less

  7. Amphoteric Doping of Praseodymium Pr3+ in SrTiO3 Grain Boundaries

    DOE PAGES

    Yang, Hao; Lee, H. S.; Kotula, Paul G.; ...

    2015-03-23

    Charge Compensation in rare-earth Praseodymium (Pr 3+) doped SrTiO 3 plays an important role in determining the overall photoluminescence properties of the system. Here, the Pr 3+ doping behavior in SrTiO 3 grain boundaries (GBs) is analyzed using aberration corrected scanning transmission electron microscopy (STEM). The presence of Pr 3+ induces structure variations and changes the statistical prevalence of GB structures. In contrast to the assumption that Pr 3+ substitutes for A site as expected in the bulk, Pr 3+ is found to substitute both Sr and Ti sites inside GBs with the highest concentration in the Ti sites. Asmore » a result, this amphoteric doping behavior in the boundary plane is further confirmed by first principles theoretical calculations.« less

  8. Critical thickness for the two-dimensional electron gas in LaTiO3/SrTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    You, Jeong Ho; Lee, Jun Hee

    2013-10-01

    Transport dimensionality of Ti d electrons in (LaTiO3)1/(SrTiO3)N superlattices has been investigated using density functional theory with local spin-density approximation + U method. Different spatial distribution patterns have been found between Ti t2g orbital electrons. The dxy orbital electrons are highly localized near interfaces due to the potentials by positively charged LaO layers, while the degenerate dyz and dxz orbital electrons are more distributed inside SrTiO3 insulators. For N ≥ 3 unit cells (u.c.), the Ti dxy densities of state exhibit the staircaselike increments, which appear at the same energy levels as the dxy flat bands along the Γ-Z direction in band structures. The kz-independent discrete energy levels indicate that the electrons in dxy flat bands are two-dimensional electron gases (2DEGs) which can transport along interfaces, but they cannot transport perpendicularly to interfaces due to the confinements in the potential wells by LaO layers. Unlike the dxy orbital electrons, the dyz and dxz orbital electrons have three-dimensional (3D) transport characteristics, regardless of SrTiO3 thicknesses. The 2DEG formation by dxy orbital electrons, when N ≥ 3 u.c., indicates the existence of critical SrTiO3 thickness where the electron transport dimensionality starts to change from 3D to 2D in (LaTiO3)1/(SrTiO3)N superlattices.

  9. Ferroelectricity of strained SrTiO3 in lithium tetraborate glass-nanocomposite and glass-ceramic

    NASA Astrophysics Data System (ADS)

    Abdel-Khalek, E. K.; Mohamed, E. A.; Kashif, I.

    2018-02-01

    Glass-nanocomposite (GNCs) sample of the composition [90Li2B4O7-10SrTiO3] (mol %) was prepared by conventional melt quenching technique. The glassy phase and the amorphous nature of the GNCs sample were identified by Differential thermal analysis (DTA) and X-ray diffraction (XRD) studies, respectively. DTA of the GNCs exhibits sharp and broad exothermic peaks which represent the crystallization of Li2B4O7 and SrTiO3, respectively. The tetragonal Li2B4O7 and tetragonal SrTiO3 crystalline phases in glass-ceramic (GC) were identified by XRD and scanning electron microscopic (SEM). The strain tetragonal SrTiO3 phase in GNCs and GC has been confirmed by SEM. The values of crystallization activation energies (Ec1 and Ec2) for the first and second exothermic peaks are equal to 174 and 1452 kJ/mol, respectively. The Ti3+ ions in tetragonal distorted octahedral sites in GNCs were identified by optical transmission spectrum. GNCs and GC samples exhibit broad dielectric anomalies at 303 and 319 K because of strained SrTiO3 ferroelectric, respectively.

  10. A facile in-situ hydrothermal synthesis of SrTiO3/TiO2 microsphere composite

    NASA Astrophysics Data System (ADS)

    Wang, Hongxing; Zhao, Wei; Zhang, Yubo; Zhang, Shimeng; Wang, Zihao; Zhao, Dan

    2016-06-01

    TiO2 was successfully used as sacrificed template to synthesise SrTiO3/TiO2 microsphere composite via an in-situ hydrothermal process. The diameter of SrTiO3/TiO2 microsphere was about 700 nm with the same size of the template, and all of the microspheres were in good dispersity. The optimized reaction parameters for the phase and morphology of the as-synthesized samples were investigated. The results showed the SrTiO3/TiO2 microsphere can be synthesized at 170 °C when the concentration of sodium hydroxide was 0.1 M. Lower hydrothermal temperature hampered the formation of the SrTiO3/TiO2 composite, the higher alkali concentration, however, will destroy the morphology of products. The formation mechanism of SrTiO3/TiO2 microsphere composite was proposed and the photocatalytic properties of the samples were characterized using methylene blue solution as the pollutant under the UV light irradiation. The results indicated the proper OH- concentration will provide a channel for Sr2+ to react with Ti4+ located in the template and form the SrTiO3/TiO2 composite, and those with micro-scaled spherical morphology exhibited good photocatalytic activities.

  11. Temperature controlled evolution of monoclinic to super-tetragonal phase of epitaxial BiFeO3 thin films on La0.67Sr0.33MnO3 buffered SrTiO3 substrate

    NASA Astrophysics Data System (ADS)

    Singh, Anar; Kaifeng, Dong; Chen, Jing-Sheng

    2018-03-01

    Epitaxial BiFeO3 thin films of 130nm were deposited by pulsed laser deposition (PLD) technique on La0.67Sr0.33MnO3 buffered SrTiO3 (001) substrate at various temperatures under different ambient oxygen pressures. Reciprocal space mapping reveals that, with decreasing temperature and oxygen pressure, the broadly reported monoclinic phase (MA) of BiFeO3 thin film initially transforms to a tetragonal phase (T1) with c/a =1.05 (1) in a narrow girth of deposition condition and then to a super-tetragonal phase (T2) with giant c/a = 1.24 (1), as confirmed by reciprocal space mapping using high resolution x-ray diffraction. The surface morphology of the films reveals the island growth of the BiFeO3 films deposited at low temperatures. We propose that the transformation from monoclinic to the super-tetragonal phase is essentially due to the manifestation of excess local strain as a result of the island growth. This study offers a recipe to grow the super-tetragonal phase of BiFeO3, with giant c/a =1.24 (1) which exhibits exceptionally large ferroelectric polarization, on ferromagnetic layer La0.67Sr0.33MnO3. This phase of BiFeO3 can be utilized for the ferroelectric control of magnetism at the interface of BiFeO3 and La0.67Sr0.33MnO3.

  12. Morphology modulation of SrTiO3/TiO2 heterostructures for enhanced photoelectrochemical performance.

    PubMed

    Jiao, Zhengbo; Chen, Tao; Yu, Hongchao; Wang, Teng; Lu, Gongxuan; Bi, Yingpu

    2014-04-01

    Design and fabrication of nanoscale semiconductors with regulatable morphology or structure has attracted tremendous interest due to the dependency relationship between properties and architectures. Two types of SrTiO3/TiO2 nanocomposites with different morphologies and structures have been fabricated by controlling the kinetics of hydrothermal reactions. One is TiO2 nanotube arrays densely wrapped by SrTiO3 film and the other is SrTiO3 nanospheres distributed on the top region of TiO2 nanotube arrays, which has been firstly fabricated. It has been found that the photoelectrochemical performances of these heterostructures are crucially dominated by their architectures. Heterostructured SrTiO3/TiO2 nanotube arrays were fabricated by traditional method in the absence of NaOH and they exhibited higher photoelectrochemical performance than pure TiO2 nanotube arrays. However, the compact SrTiO3 coating film on the sidewalls of TiO2 nanotube arrays could inevitably destroy the tubular structures of TiO2 and thus go against the vectorial transport of electrons. Interestingly, when excess NaOH was added into the growth solution, SrTiO3 nanospheres would be rationally grafted on the top of TiO2 nanotube arrays, which could preserve the tubular structures of TiO2, and thus further improve the photoelectrochemical performance. Copyright © 2013 Elsevier Inc. All rights reserved.

  13. Improvement in temperature dependence and dielectric tunability properties of PbZr0.52Ti0.48O3 thin films using Ba(Mg1/3Ta2/3)O3 buffer layer

    NASA Astrophysics Data System (ADS)

    Wu, Zhi; Zhou, Jing; Chen, Wen; Shen, Jie; Yang, Huimin; Zhang, Shisai; Liu, Yueli

    2016-12-01

    In this paper, Pb(Zr0.52Ti0.48)O3 (PZT) thin films were prepared via sol-gel method. The effects of Ba(Mg1/3Ta2/3)O3 (BMT) buffer layer on the temperature dependence and dielectric tunability properties of PZT thin films were studied. As the thickness of BMT buffer layer increases, the tan δ and tunability of PZT thin films decrease while tunability still maintains above 10%. This result shows that BMT buffer layer can improve the dielectric tunability properties of PZT thin films. Furthermore, the temperature coefficient of the dielectric constant decreases from 2333.4 to 906.9 ppm/°C with the thickness of BMT buffer layer increasing in the range from 25 to 205 °C, indicating that BMT buffer layer can improve the temperature stability of PZT thin films. Therefore, BMT buffer layer plays a critical role in improving temperature dependence and dielectric tunability properties of PbZr0.52Ti0.48O3 thin films.

  14. Upper limit to magnetism in LaAlO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Fitzsimmons, Michael

    2012-02-01

    In 2004 Ohtomo and Hwang reported unusually high conductivity in LaAlO3 and SrTiO3 bilayer samples. Since then, metallic conduction, superconductivity, magnetism, and coexistence of superconductivity and ferromagnetism have been attributed to LaAlO3/SrTiO3 interfaces. Very recently, two studies have reported large magnetic moments attributed to interfaces from measurement techniques that are unable to distinguish between interfacial and bulk magnetism. Consequently, it is imperative to perform magnetic measurements that by being intrinsically sensitive to interface magnetism are impervious to experimental artifacts suffered by bulk measurements. Using polarized neutron reflectometry, we measured the neutron spin dependent reflectivity from four LaAlO3/SrTiO3 superlattices. Our results indicate the upper limit for the magnetization averaged over the lateral dimensions of the sample induced by an 11 T magnetic field at 1.7 K is less than 2 G. SQUID magnetometry of the neutron superlattice samples sporadically finds an enhanced moment (consistent with past reports), possibly due to experimental artifacts. These observations set important restrictions on theories which imply a strongly enhanced magnetism at the interface between LaAlO3 and SrTiO3. Work performed in collaboration with N.W. Hengartner, S. Singh, M. Zhernenkov (LANL), F.Y. Bruno, J. Santamaria (Universidad Complutense de Madrid), A. Brinkman, M.J.A. Huijben, H. Molegraaf (MESA+ Institute for Nanotechnology), J. de la Venta and Ivan K. Schuller (UCSD). [4pt] Work supported by the Office of Basic Energy Science, U.S. Department of Energy, BES-DMS and DMR under grant DE FG03-87ER-45332. Work at UCM is supported by Consolider Ingenio CSD2009-00013 (IMAGINE), CAM S2009-MAT 1756 (PHAMA) and work at Twente is supported by the Foundation for Fundamental Research on Matter (FOM).

  15. Tunable anomalous orbital structure in a spinel-perovskite interface γ-Al2O3/SrTiO3

    NASA Astrophysics Data System (ADS)

    Cao, Yanwei; Liu, Xiaoran; Shafer, Padraic; Middey, Srimanta; Meyers, Derek; Kareev, Mikhail; Zhong, Zhicheng; Kim, Jong-Woo; Ryan, Philip; Arenholz, Elke; Chakhalian, Jak

    In all archetypical reported (001)-oriented perovskite heterostructures, for example LaTiO3/SrTiO3, LaAlO3/SrTiO3,YTiO3/SrTiO3 and so on, it has been deduced that the preferential occupation of two-dimensional electron gases is in-plane dxy state. In sharp contrast to this, the investigated electronic structure of a spinel-perovskite heterostructure γ-Al2O3/SrTiO3 by resonant soft X-ray linear dichroism, demonstrates that the preferential occupation is in out-of-plane dxz/dyz states for interfacial electrons. Moreover, the impact of strain further corroborates that this anomalous orbital structure can be linked to the altered crystal field at the interface and symmetry breaking of the interfacial structural units. Our findings provide another interesting route to engineer emergent quantum states with deterministic orbital symmetry. J.C. and Y.C. was supported by the Gordon and Betty Moore Foundation EPiQS Initiative through Grant No. GBMF4534. S.M. and M.K. were supported by the DOD-ARO under Grant No. 0402-172.

  16. Depth profiling of superconducting thin films using rare gas ion sputtering with laser postionization

    NASA Astrophysics Data System (ADS)

    Pallix, J. B.; Becker, C. H.; Missert, N.; Char, K.; Hammond, R. H.

    1988-02-01

    Surface analysis by laser ionization (SALI) has been used to examine a high-Tc superconducting thin film of nominal composition YBa2Cu3O7 deposited on SrTiO3 (100) by reactive magnetron sputtering. The main focus of this work was to probe the compositional uniformity and the impurity content throughout the 1800 Å thick film having critical current densities of 1 to 2×106 A/cm2. SALI depth profiles show this film to be more uniform than thicker films (˜1 μm, prepared by electron beam codeposition) which were studied previously, yet the data show that some additional (non-superconducting) phases derived from Y, Ba, Cu, and O are still present. These additional phases are studied by monitoring the atomic and diatomic-oxide photoion profiles and also the depth profiles of various clusters (e.g. Y2O2+, Y2O3+, Y3O4+, Ba2O+, Ba2O2+, BaCu+, BaCuO+, YBaO2+, YSrO2+, etc.). A variety of impurities are observed to occur throughout the film including rather large concentrations of Sr. Hydroxides, F, Cl, and COx are evident particularly in the sample's near surface region (the top ˜100 Å).

  17. Transition regime from step-flow to step-bunching in the growth of epitaxial SrRuO3 on (001) SrTiO3

    NASA Astrophysics Data System (ADS)

    Gura, Anna; Bertino, Giulia; Bein, Benjamin; Dawber, Matthew

    2018-04-01

    We present a study of the surface morphology of SrRuO3 thin films grown on TiO2 terminated (001) SrTiO3 substrates using an off-axis RF magnetron sputtering deposition technique. We investigated the step bunching formation and the evolution of the films by varying deposition parameters. The thin films were characterized using atomic force microscopy methods, allowing us to study the various growth regimes of SrRuO3 as a function of the growth parameters. We observe a strong influence of both the miscut angle and growth temperature on the evolution of the SrRuO3 surface morphology. In addition, a thickness dependence is present. Remarkably, the formation of a smooth, regular, and uniform "fish-skin" structure at the step-bunch transition is observed. The fish-skin morphology results from the merging of 2D flat islands predicted by previous models. The direct observation of surface evolution allows us to better understand the different growth regimes of SrRuO3 thin films.

  18. Rapid Synthesis and Formation Mechanism of Core-Shell-Structured La-Doped SrTiO3 with a Nb-Doped Shell

    PubMed Central

    Park, Nam-Hee; Akamatsu, Takafumi; Itoh, Toshio; Izu, Noriya; Shin, Woosuck

    2015-01-01

    To provide a convenient and practical synthesis process for metal ion doping on the surface of nanoparticles in an assembled nanostructure, core-shell-structured La-doped SrTiO3 nanocubes with a Nb-doped surface layer were synthesized via a rapid synthesis combining a rapid sol-precipitation and hydrothermal process. The La-doped SrTiO3 nanocubes were formed at room temperature by a rapid dissolution of NaOH pellets during the rapid sol-precipitation process, and the Nb-doped surface (shell) along with Nb-rich edges formed on the core nanocubes via the hydrothermal process. The formation mechanism of the core-shell-structured nanocubes and their shape evolution as a function of the Nb doping level were investigated. The synthesized core-shell-structured nanocubes could be arranged face-to-face on a SiO2/Si substrate by a slow evaporation process, and this nanostructured 10 μm thick thin film showed a smooth surface. PMID:28793420

  19. Thin films of the Bi2Sr2Ca2Cu3O(x) superconductor

    NASA Technical Reports Server (NTRS)

    Mei, YU; Luo, H. L.; Hu, Roger

    1990-01-01

    Using RF sputtering technique, thin films of near single phase Bi2Sr2Ca2Cu3O(x) were successfully prepared on SrTiO3(100), MgO(100), and LaAlO3(012) substrates. Zero resistance of these films occurred in the range of 90-105 K.

  20. Electronic and optical properties of Cr-, B-doped, and (Cr, B)-codoped SrTiO3

    NASA Astrophysics Data System (ADS)

    Wu, Jiao; Huang, Wei-Qing; Yang, Ke; Wei, Zeng-Xi; Peng, P.; Huang, Gui-Fang

    2017-04-01

    Energy band engineering of semiconductors plays a crucial role in exploring high-efficiency visible-light response photocatalysts. Herein, we systematically study the electronic properties and optical response of Cr-, B-doped SrTiO3, and (Cr, B)-codoped SrTiO3 by using first-principles calculations to explore the mechanism for its superior photocatalytic activities in the visible light region. Special emphasis is placed on uncovering the synergy effects of nonmetal B dopant with metal Cr dopant at different cation sites. It is found that the electronic properties and optical absorption of SrTiO3 can be dramatically engineered by mono- or co-doping. In particular, the intermediate levels lying in the bandgap of the codoped SrTiO3 relay on the Cr impurity doped at Sr or Ti cation sites. Moreover, the (Cr@Sr, B@O)-SrTiO3 retains the charge balancing without the generation of unexpected oxygen vacancies, and is more desirable for solar light harvesting due to its higher absorption than others in the entire visible light. The findings can rationalize the available experimental results and are helpful in designing SrTiO3-based photocatalysts with high-efficiency performance.

  1. Effect of Bi(Mg1/2Ti1/2)O3 addition on the electrical properties of Si-Mn modified on SrTiO3

    NASA Astrophysics Data System (ADS)

    Roh, Yoon-ah; Masaki, Takaki; Yoon, Dae-Ho

    2015-05-01

    Single-Crystalline Strontium titanate (SrTiO3) has been widely used in many fields such as catalyst, semiconductors and dielectrics. SrTiO3 is a typical perovskite-type oxide, the physical properties of which strongly depend on its chemical composition, structure, shape, size, and crystallinity. In this work, the effects of Bi(Mg1/2Ti1/2)O3 addition on the nanostructure and the dielectric properties of Si-Mn modified SrTiO3 were investigated to develop nano-sized particles and low-temperature-fired SrTiO3-based ceramics with stable temperature characteristics. The dielectric constant of SrTiO3-Bi(Mg1/2Ti1/2)O3 was found to range from 900 to 1200 at 1 kHz for samples sintered at 1200°C. This new composition, SrTiO3-Bi(Mg1/2Ti1/2)O3, can be applied as a nano-sized dielectric materials in various fields.

  2. Effect of CaRuO3 interlayer on the dielectric properties of Ba(Zr ,Ti)O3 thin films prepared by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Tang, X. G.; Tian, H. Y.; Wang, J.; Wong, K. H.; Chan, H. L. W.

    2006-10-01

    Ba(Zr0.2Ti0.8)O3 (BZT) thin films on Pt(111)/Ti /SiO2/Si(100) substrates without and with CaRuO3 (CRO) buffer layer were fabricated at 650°C in situ by pulsed laser deposition. The BZT thin films showed a dense morphology, many clusters are found on the surface images of BZT/Pt films, which are composed by nanosized grains of 25-35nm; the average grain size of BZT/CRO films is about 80nm, which lager than that of BZT/Pt thin film. The dielectric constants and dissipation factors of BZT/Pt and BZT/CRO thin films were 392 and 0.019 and 479 and 0.021 at 1MHz, respectively. The dielectric constant of BZT/Pt and BZT/CRO thin films changes significantly with applied dc bias field and has high tunabilities and figures of merit of ˜70% and 37 and 75% and 36, respectively, under an applied field of 400kV /cm. The possible microstructural background responsible for the high dielectric constant and tunability was discussed.

  3. In situ study of emerging metallicity on ion-bombarded SrTiO3 surface

    NASA Astrophysics Data System (ADS)

    Gross, Heiko; Bansal, Namrata; Kim, Yong-Seung; Oh, Seongshik

    2011-10-01

    We report how argon bombardment induces metallic states on the surface of insulating SrTiO3 at different temperatures by combining in situ conductance measurements and model calculations. At cryogenic temperatures, ionic bombardment created a thin-but much thicker than the argon-penetration depth-steady-state oxygen-vacant layer, leading to a highly-concentric metallic state. Near room temperatures, however, significant thermal diffusion occurred and the metallic state continuously diffused into the bulk, leaving only low concentration of electron carriers on the surface. Analysis of the discrepancy between the experiments and the models also provided evidence for vacancy clustering, which seems to occur during any vacancy formation process and affects the observed conductance.

  4. Influence of excess SrO on the thermoelectric properties of heavily doped SrTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Wang, Yifeng; Wan, Chunlei; Zhang, Xiaoyan; Shen, Liming; Koumoto, Kunihito; Gupta, Arunava; Bao, Ningzhong

    2013-05-01

    The effects of excess SrO on the thermoelectric properties of n-type SrTiO3 have been investigated through a comparative study of different polycrystalline ceramic samples. These include Gd-doped SrTiO3 with varying SrO, nominally in the form of Ruddlesden-Popper phase of SrO(SrTiO3)n with n = 5, 10, and 20, and previously reported analogues with n = 1, 2, and ∞ (i.e., stoichiometric SrTiO3). As compared with stoichiometric SrTiO3, with increasing SrO excess (i.e., decreasing n value), the electrical conductivity is found to decrease more substantially than the thermal conductivity, while the Seebeck coefficient remains almost unaffected with n in the range of 5-20.

  5. Ferroelectricity-induced resistive switching in Pb(Zr0.52Ti0.48)O3/Pr0.7Ca0.3MnO3/Nb-doped SrTiO3 epitaxial heterostructure

    NASA Astrophysics Data System (ADS)

    Md. Sadaf, Sharif; Mostafa Bourim, El; Liu, Xinjun; Hasan Choudhury, Sakeb; Kim, Dong-Wook; Hwang, Hyunsang

    2012-03-01

    We investigated the effect of a ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin film on the generation of resistive switching in a stacked Pr0.7Ca0.3MnO3 (PCMO)/Nb-doped SrTiO3 (Nb:STO) heterostructure forming a p-n junction. To promote the ferroelectric effect, the thin PZT active layer was deposited on an epitaxially grown p-type PCMO film on a lattice-matched n-type Nb:STO single crystal. It was concluded that the observed resistive switching behavior in the all-perovskite Pt/PZT/PCMO/Nb:STO heterostructure was related to the modulation of PCMO/Nb:STO p-n junction's depletion width, which was caused either by the PZT ferroelectric polarization field effect, the electrochemical drift of oxygen ions under an electric field, or both simultaneously.

  6. Thickness dependent thermoelectric properties of SrTiO3/SrLaTiO3 and SrZrO3/SrLaTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Ishii, Masatoshi; Baniecki, John; Schafranek, Robert; Kerman, Kian; Kurihara, Kazuaki

    2013-03-01

    Thermoelectric power generators will be required for future sensor network systems. SrTiO3 (STO) is one candidate thermoelectric material due to its non-toxicity and comparable power factor to Bismuth telluride. The energy conversion efficiency of SrTiO3-based thermoelectric energy conversion elements has been reported to be enhanced by quantum size effects, such as the two dimensional (2D) electron gas in SrTiO3/SrTi0.8Nb0.2O3/SrTiO3. Nevertheless, a complete understanding of the mechanisms for the reported increase in efficiency are missing owing to a lack of understanding of the thickness dependence of the transport properties. In the talk, we will present a study of the thickness dependence of the transport properties of SrTiO3/SrLaTiO3 and SrZrO3/SrLaTiO3 heterostructures. The SrZrO3/SrLaTiO3 interface has a large conduction band off-set of 1.9 eV which can be utilized to confine electrons in a 2D quantum well. Characterization of the thermopower, conductivity, and Hall effect will be presented as a function of the SrLaTiO3 thickness down to a few unit cells and the implications of the thickness dependence of the transport properties on carrier confinement and increasing the efficiency STO-based 2DEG quantum well structures will be discussed.

  7. Surface diffusion on SrTiO3 (100): A temperature accelerated dynamics and first principles study

    NASA Astrophysics Data System (ADS)

    Hong, Minki; Wohlwend, Jennifer L.; Behera, Rakesh K.; Phillpot, Simon R.; Sinnott, Susan B.; Uberuaga, Blas P.

    2013-11-01

    Temperature accelerated dynamics (TAD) with an empirical potential is used to predict diffusion mechanisms and energy barriers associated with surface diffusion of adatoms and surface vacancies on (100) SrTiO3 (STO). Specifically, Sr, O, and Ti adatoms and vacancies are investigated on each termination - SrO and TiO2 - of the SrTiO3 surface. We find that the empirical potential predicts different surface mobility of adatoms depending on the surface termination: they are mobile with relatively low diffusion barriers on the SrO-terminated surface, whereas they are largely immobile on the TiO2-terminated surface. One important finding is that, of the two binding sites on the SrO-terminated surface, one is typically very close in energy to the saddle point. Thus, one of the two sites is a good estimator of the migration energy of the adatom, a conclusion supported by select density functional theory (DFT) calculations. Motivated by this result, we calculate the migration energies for a number of metal elements on the SrO-terminated surface: Ti, Ba, La, and Al. The DFT results also reveal that the details of the migration mechanism depend on the charge state of the diffusing species and that the ability of the empirical potential to properly estimate the migration mechanism depends on the magnitude and variability of the charge transfer between the adatom and the surface.

  8. Synthesis and Characterization of BaFeO3, (Ba,Bi)FeO3, and Related Epitaxial Thin Films and Nanostructures

    DTIC Science & Technology

    2009-01-01

    measured magnetizations of Ba-doped bulk BiFeO3 samples65, 68 The coercivity, or resistance of the sample to 72 demagnetization , is about 6000 Oe on...methods for sample analysis are briefly discussed. Investigation of BaFeO3 and its structural and magnetic properties, which differ from that of the bulk ...at the atomic level. The interfaces comprised of a magnetic and ferroelectric material layered on one another has great advantage over bulk

  9. Evidence for charge-vortex duality at the LaAlO3/SrTiO3 interface.

    PubMed

    Mehta, M M; Dikin, D A; Bark, C W; Ryu, S; Folkman, C M; Eom, C B; Chandrasekhar, V

    2012-07-17

    The concept of duality has proved extremely powerful in extending our understanding in many areas of physics. Charge-vortex duality has been proposed as a model to understand the superconductor to insulator transition in disordered thin films and Josephson junction arrays. In this model, on the superconducting side, one has delocalized Cooper pairs but localized vortices; while on the insulating side, one has localized Cooper pairs but mobile vortices. Here we show a new experimental manifestation of this duality in the electron gas that forms at the interface between LaAlO(3) and SrTiO(3). The effect is due to the motion of vortices generated by the magnetization dynamics of the ferromagnet that also forms at the same interface, which results in an increase in resistance on the superconducting side of the transition, but an increase in conductance on the insulating side.

  10. Preparation, characterization and photocatalytic activities of TiO2-SrTiO3 composites

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Zhu, Lianjie; Gao, Fubo; Xie, Hanjie

    2017-01-01

    Series of TiO2-SrTiO3 composites were synthesized by hydrothermal method, using TiO2 nanotube array as a precursor and Sr(OH)2 as a Sr source material. TiO2-SrTiO3 products with various composition were obtained by simply changing the reaction time. The as-synthesized products were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The optical properties were studied by means of UV-Vis absorption spectroscopy and photoluminescence (PL) spectra. Their photocatalytic activities were assessed by photodegradation of rhodamine B (RhB) solution and the photocatalytic reaction mechanism was discussed. The TiO2-SrTiO3 composites obtained at 2 h exhibits the highest activity for photodegradation of RhB.

  11. Mechanisms of charge transfer and redistribution in LaAlO3/SrTiO3 revealed by high-energy optical conductivity.

    PubMed

    Asmara, T C; Annadi, A; Santoso, I; Gogoi, P K; Kotlov, A; Omer, H M; Motapothula, M; Breese, M B H; Rübhausen, M; Venkatesan, T; Ariando; Rusydi, A

    2014-04-14

    In condensed matter physics the quasi two-dimensional electron gas at the interface of two different insulators, polar LaAlO3 on nonpolar SrTiO3 (LaAlO3/SrTiO3) is a spectacular and surprising observation. This phenomenon is LaAlO3 film thickness dependent and may be explained by the polarization catastrophe model, in which a charge transfer of 0.5e(-) from the LaAlO3 film into the LaAlO3/SrTiO3 interface is expected. Here we show that in conducting samples (≥ 4 unit cells of LaAlO3) there is indeed a ~0.5e(-) transfer from LaAlO3 into the LaAlO3/SrTiO3 interface by studying the optical conductivity in a broad energy range (0.5-35 eV). Surprisingly, in insulating samples (≤ 3 unit cells of LaAlO3) a redistribution of charges within the polar LaAlO3 sublayers (from AlO2 to LaO) as large as ~0.5e(-) is observed, with no charge transfer into the interface. Hence, our results reveal the different mechanisms for the polarization catastrophe compensation in insulating and conducting LaAlO3/SrTiO3 interfaces.

  12. A review of molecular beam epitaxy of ferroelectric BaTiO3 films on Si, Ge and GaAs substrates and their applications

    PubMed Central

    Mazet, Lucie; Yang, Sang Mo; Kalinin, Sergei V; Schamm-Chardon, Sylvie; Dubourdieu, Catherine

    2015-01-01

    SrTiO3 epitaxial growth by molecular beam epitaxy (MBE) on silicon has opened up the route to the monolithic integration of various complex oxides on the complementary metal-oxide–semiconductor silicon platform. Among functional oxides, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip. We review the growth by MBE of the ferroelectric compound BaTiO3 on silicon (Si), germanium (Ge) and gallium arsenide (GaAs) and we discuss the film properties in terms of crystalline structure, microstructure and ferroelectricity. Finally, we review the last developments in two areas of interest for the applications of BaTiO3 films on silicon, namely integrated photonics, which benefits from the large Pockels effect of BaTiO3, and low power logic devices, which may benefit from the negative capacitance of the ferroelectric. PMID:27877816

  13. On stoichiometry and intermixing at the spinel/perovskite interface in CoFe2O4/BaTiO3 thin films.

    PubMed

    Tileli, Vasiliki; Duchamp, Martial; Axelsson, Anna-Karin; Valant, Matjaz; Dunin-Borkowski, Rafal E; Alford, Neil McN

    2015-01-07

    The performance of complex oxide heterostructures depends primarily on the interfacial coupling of the two component structures. This interface character inherently varies with the synthesis method and conditions used since even small composition variations can alter the electronic, ferroelectric, or magnetic functional properties of the system. The focus of this article is placed on the interface character of a pulsed laser deposited CoFe2O4/BaTiO3 thin film. Using a range of state-of-the-art transmission electron microscopy methodologies, the roles of substrate morphology, interface stoichiometry, and cation intermixing are determined on the atomic level. The results reveal a surprisingly uneven BaTiO3 substrate surface formed after the film deposition and Fe atom incorporation in the top few monolayers inside the unit cell of the BaTiO3 crystal. Towards the CoFe2O4 side, a disordered region extending several nanometers from the interface was revealed and both Ba and Ti from the substrate were found to diffuse into the spinel layer. The analysis also shows that within this somehow incompatible composite interface, a different phase is formed corresponding to the compound Ba2Fe3Ti5O15, which belongs to the ilmenite crystal structure of FeTiO3 type. The results suggest a chemical activity between these two oxides, which could lead to the synthesis of complex engineered interfaces.

  14. Charge transfer mechanism for the formation of metallic states at the KTaO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Nazir, S.; Singh, N.; Schwingenschlögl, U.

    2011-03-01

    The electronic and optical properties of the KTaO3/SrTiO3 heterointerface are analyzed by the full-potential linearized augmented plane-wave approach of density functional theory. Optimization of the atomic positions points at subordinate changes in the crystal structure and chemical bonding near the interface, which is due to a minimal lattice mismatch. The creation of metallic interface states thus is not affected by structural relaxation but can be explained by charge transfer between transition metal and oxygen atoms. It is to be expected that a charge transfer is likewise important for related interfaces such as LaAlO3/SrTiO3. The KTaO3/SrTiO3 system is ideal for disentangling the complex behavior of metallic interface states, since almost no structural relaxation takes place.

  15. Enhanced self-repairing capability of sol-gel derived SrTiO3/nano Al2O3 composite films

    NASA Astrophysics Data System (ADS)

    Yao, Manwen; Peng, Yong; Xiao, Ruihua; Li, Qiuxia; Yao, Xi

    2016-08-01

    SrTiO3/nano Al2O3 inorganic nanocomposites were prepared by using a conventional sol-gel spin coating process. For comparison, SrTiO3 films doped by equivalent amount of sol-Al2O3 have also been investigated. Aluminum deposited by using vacuum evaporation was used as the top electrode. The nanocomposites exhibited a significantly enhanced dielectric strength of 506.9 MV/m, which was increased by 97.4% as compared with the SrTiO3 films doped with sol-Al2O3. The leakage current maintained of the same order of microampere until the ultimate breakdown of the nanocomposites. The excellent electrical performances are ascribed to the anodic oxidation reaction in origin, which can repair the internal and/or surface defects of the films.

  16. Fabrication and electrochemical performance of a stable, anode supported thin BaCe0.4Zr0.4Y0.2O3-δ electrolyte Protonic Ceramic Fuel Cell

    NASA Astrophysics Data System (ADS)

    Nasani, Narendar; Ramasamy, Devaraj; Mikhalev, Sergey; Kovalevsky, Andrei V.; Fagg, Duncan P.

    2015-03-01

    The present work deals with the fabrication and electrochemical characterisation of a potential protonic ceramic fuel cell based on a Ni-BaZr0.85Y0.15O3-δ anode supported thin film proton conducting BaCe0.4Zr0.4Y0.2O3-δ electrolyte with a Pr2NiO4+δ cathode. Anode and electrolyte materials were prepared by an acetate-H2O2 combustion method. A thin (∼5 μm), dense and crack free BaCe0.4Zr0.4Y0.2O3-δ electrolyte film was successfully obtained on a porous anode support by spin coating and firing at 1450 °C. Maximum power densities of 234, 158, 102 and 63 mW cm-2 at 700, 650, 600 and 550 °C, respectively were achieved for the Ni-BaZr0.85Y0.15O3-δ/BaCe0.4Zr0.4Y0.2O3-δ/Pr2NiO4+δ single cell under fuel cell testing conditions. Electrode polarisation resistance was assessed at open circuit conditions by use of electrochemical impedance spectroscopy (EIS) and is shown to dominate the area specific resistance at low temperatures. Postmortem analysis by scanning electron microscopy (SEM), reveals that no delamination occurs at anode/electrolyte or electrolyte/cathode interfaces upon cell operation.

  17. Epitaxial BiFeO3 thin films fabricated by chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Singh, S. K.; Kim, Y. K.; Funakubo, H.; Ishiwara, H.

    2006-04-01

    Epitaxial BiFeO3 (BFO) thin films were fabricated on (001)-, (110)-, and (111)-oriented single-crystal SrRuO3(SRO )/SrTiO3(STO) structures by chemical solution deposition. X-ray diffraction indicates the formation of an epitaxial single-phase perovskite structure and pole figure measurement confirms the cube-on-cube epitaxial relationship of BFO ‖SRO‖STO. Chemical-solution-deposited BFO films have a rhombohedral structure with lattice parameter of 0.395nm, which is the same structure as that of a bulk single crystal. The remanent polarization of approximately 50μC/cm2 was observed in BFO (001) thin films at 80K.

  18. Voltage-controlled ferromagnetism and magnetoresistance in LaCoO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Hu, Chengqing; Park, Keun Woo; Posadas, Agham; Jordan-Sweet, Jean L.; Demkov, Alexander A.; Yu, Edward T.

    2013-11-01

    A LaCoO3/SrTiO3 heterostructure grown on Si (001) is shown to provide electrically switchable ferromagnetism, a large, electrically tunable magnetoresistance, and a vehicle for achieving and probing electrical control over ferromagnetic behavior at submicron dimensions. Fabrication of devices in a field-effect transistor geometry enables application of a gate bias voltage that modulates strain in the heterostructure via the converse piezoelectric effect in SrTiO3, leading to an artificial inverse magnetoelectric effect arising from the dependence of ferromagnetism in the LaCoO3 layer on strain. Below the Curie temperature of the LaCoO3 layer, this effect leads to modulation of resistance in LaCoO3 as large as 100%, and magnetoresistance as high as 80%, both of which arise from carrier scattering at ferromagnetic-nonmagnetic interfaces in LaCoO3. Finite-element numerical modeling of electric field distributions is used to explain the dependence of carrier transport behavior on gate contact geometry, and a Valet-Fert transport model enables determination of spin polarization in the LaCoO3 layer. Piezoresponse force microscopy is used to confirm the existence of piezoelectric response in SrTiO3 grown on Si (001). It is also shown that this structure offers the possibility of achieving exclusive-NOR logic functionality within a single device.

  19. Carrier Density at LaAlO3/SrTiO3 Interfaces: Evidence of Electronic Reconstruction.

    NASA Astrophysics Data System (ADS)

    Xi, Xiaoxing

    The origin of the 2D electron gas at the LaAlO3/SrTiO3 interface has been a controversial subject ever since its discovery. A serious inconsistency with the most accepted mechanism, an electronic reconstruction in response to a polar discontinuity at the interface, is that the carrier densities reported experimentally are invariably lower than the expected value except under conditions where reduction of SrTiO3 substrate is suspected. We have grown LaAlO3 films of different stoichiometry on TiO2-terminated SrTiO3 substrates using atomic layer-by-layer laser molecular beam epitaxy (ALL-Laser MBE), in which La2O3 and Al2O3 targets were sequentially ablated in 37 mTorr oxygen. The high oxygen pressure during growth prevents the possible oxygen reduction in SrTiO3, ensures that the LaAlO3 films are sufficiently oxygenated, and suppresses the La-Sr intermixing due to the bombardment effect. X-ray linear dichroism (XLD) and x-ray magnetic circular dichroism (XMCD) measurements show characteristics of oxygenated samples. In the electronic reconstruction picture, instead of the charge transfer of half of an electron in the case of a sufficiently thick stoichiometric LaAlO3, a LaAlO3 film thickness dependence is expected as well as a linear dependence on stoichiometry. Our experimental results on carrier densities in 10 nm-thick LaAl1 +yO3(1 +0.5y) films agree quantitatively with the theoretical expectations, lending a strong support for the electronic reconstruction mechanism. This material is based upon work supported by the U.S. Department of Energy, Office of Science, under Grant No. DE-SC0004764.

  20. Domain alignment within ferroelectric/dielectric PbTiO 3 /SrTiO 3 superlattice nanostructures

    DOE PAGES

    Park, Joonkyu; Mangeri, John; Zhang, Qingteng; ...

    2018-01-01

    The ferroelectric domain pattern within lithographically defined PbTiO 3/SrTiO 3ferroelectric/dielectric heteroepitaxial superlattice nanostructures is strongly influenced by the edges of the structures.

  1. Optimization of rotational speed for growing BaFe12O19 thin films using spin coating

    NASA Astrophysics Data System (ADS)

    Budiawanti, S.; Soegijono, B.; Mudzakir, I.; Suharno, Fadillah, L.

    2017-07-01

    Barium ferrite (BaFe12O19, BaM) thin films were fabricated by the spin coating of precursors obtained by using a sol-gel method. The effects of the rotational speed on the spin-coating process for growing a BaM thin film were investigated in this study. Coated films were heat-deposited at different rotational speeds ranging from 2000 to 4000 rpm, while the number of layers was set to nine. Further, the effect of the number of layers on the growth of BaM thin films was discussed. For this purpose, we take the layers number 1 to 12 and take the constant rotational speed of 3000 rpm. All the film were characterized using X-Ray diffraction, Scanning Electron microscope, and Energy-dispersive X-Ray spectroscopy and Vibrating Sample Magnetometer. It was found that by increasing the rotational speed the amount of material deposited on the Si substrate decreased. The measured grain size of the BaM thin film was nearly similar for three three different rotational speeds. However, the grain size was found to increase the number of layers.

  2. Investigation of the multiplet features of SrTiO 3 in X-ray absorption spectra based on configuration interaction calculations

    DOE PAGES

    Wu, M.; Xin, Houlin L.; Wang, J. O.; ...

    2018-04-24

    Synchrotron-based L 2,3-edge absorption spectra show strong sensitivities to the local electronic structure and chemical environment. However, detailed physical information cannot be extracted easily without computational aids. Here in this study using the experimental Ti L 2,3-edges absorption spectrum of SrTiO 3as a fingerprint and considering full multiplet effects, calculations yield different energy parameters characterizing local ground state properties. The peak splitting and intensity ratios of the L 3 and L 2 set of peaks are carefully analyzed quantitatively, giving rise to a small hybridization energy around 1.2 eV, and the different hybridization energy values reported in the literature aremore » further addressed. Finally, absorption spectra with different linearly polarized photons under various tetragonal crystal fields are investigated, revealing a non-linear orbital–lattice interaction, and a theoretical guidance for material engineering of SrTiO 3-based thin films and heterostructures is offered. Finally, detailed analysis of spectrum shifts with different tetragonal crystal fields suggests that the e g crystal field splitting is a necessary parameter for a thorough analysis of the spectra, even though it is not relevant for the ground state properties.« less

  3. Investigation of the multiplet features of SrTiO 3 in X-ray absorption spectra based on configuration interaction calculations

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wu, M.; Xin, Houlin L.; Wang, J. O.

    Synchrotron-based L 2,3-edge absorption spectra show strong sensitivities to the local electronic structure and chemical environment. However, detailed physical information cannot be extracted easily without computational aids. Here in this study using the experimental Ti L 2,3-edges absorption spectrum of SrTiO 3as a fingerprint and considering full multiplet effects, calculations yield different energy parameters characterizing local ground state properties. The peak splitting and intensity ratios of the L 3 and L 2 set of peaks are carefully analyzed quantitatively, giving rise to a small hybridization energy around 1.2 eV, and the different hybridization energy values reported in the literature aremore » further addressed. Finally, absorption spectra with different linearly polarized photons under various tetragonal crystal fields are investigated, revealing a non-linear orbital–lattice interaction, and a theoretical guidance for material engineering of SrTiO 3-based thin films and heterostructures is offered. Finally, detailed analysis of spectrum shifts with different tetragonal crystal fields suggests that the e g crystal field splitting is a necessary parameter for a thorough analysis of the spectra, even though it is not relevant for the ground state properties.« less

  4. The structural behavior of SrTiO3 under 400 keV Ne2+ ion irradiation

    NASA Astrophysics Data System (ADS)

    Su, X.; Liu, C. G.; Yang, D. Y.; Wen, J.; Fu, E. G.; Zhang, J.; Chen, L. J.; Xu, D. P.; Wang, Y. Q.; Li, Y. H.

    2015-11-01

    The structural behavior of polycrystalline perovskite SrTiO3 under 400 keV Ne2+ ion irradiation at both liquid nitrogen (LN2) and room temperature (RT) has been investigated. The grazing incident X-ray diffraction technique was applied to examine the radiation-induced structural evolution. The radiation behavior of SrTiO3 depends strongly on the irradiation temperature. At LN2 temperature, the samples exhibit significant lattice swelling and amorphization, whereas at RT, the lattice swelling is much less conspicuous and no amorphization is detected even at the highest irradiation dose of 5.0 dpa. Nevertheless, Ne2+ irradiation induces peak splitting in XRD patterns at both temperatures. Furthermore, first-principle calculations have been performed with VASP, involving possible defect types, to identify which defect is responsible for the radiation effect of SrTiO3. The results reveal that the oxygen vacancy defect is the most likely to contribute to the radiation behavior of SrTiO3.

  5. Incipient 2D Mott insulators in extreme high electron density, ultra-thin GdTiO3/SrTiO3/GdTiO3 quantum wells

    NASA Astrophysics Data System (ADS)

    Allen, S. James; Ouellette, Daniel G.; Moetakef, Pouya; Cain, Tyler; Chen, Ru; Balents, Leon; Stemmer, Susanne

    2013-03-01

    By reducing the number of SrO planes in a GdTiO3 /SrTiO3/ GdTiO3 quantum well heterostructure, an electron gas with ~ fixed 2D electron density can be driven close to the Mott metal insulator transition - a quantum critical point at ~1 electron per unit cell. A single interface between the Mott insulator GdTiO3 and band insulator SrTiO3 has been shown to introduce ~ 1/2 electron per interface unit cell. Two interfaces produce a quantum well with ~ 7 1014 cm-2 electrons: at the limit of a single SrO layer it may produce a 2D magnetic Mott insulator. We use temperature and frequency dependent (DC - 3eV) conductivity and temperature dependent magneto-transport to understand the relative importance of electron-electron interactions, electron-phonon interactions, and surface roughness scattering as the electron gas is compressed toward the quantum critical point. Terahertz time-domain and FTIR spectroscopies, measure the frequency dependent carrier mass and scattering rate, and the mid-IR polaron absorption as a function of quantum well thickness. At the extreme limit of a single SrO plane, we observe insulating behavior with an optical gap substantially less than that of the surrounding GdTiO3, suggesting a novel 2D Mott insulator. MURI program of the Army Research Office - Grant No. W911-NF-09-1-0398

  6. Growing barium hexaferrite (BaFe{sub 12}O{sub 19}) thin films using chemical solution deposition

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Budiawanti, Sri, E-mail: awanty77@yahoo.com; Faculty of Teacher Training and Education, Sebelas Maret University; Soegijono, Bambang

    Barium hexaferrite (BaFe{sub 12}O{sub 19}, or simply known as BaM) thin films has been recognized as a potential candidate for microwave-based devices, magnetic recording media and data storage. To grow BaM thin films, chemical solution deposition is conducted using the aqueous solution of metal nitrates, which involves spin coatings on Si substrates. Furthermore, Thermal Gravimeter Analysis (TGA), X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and Vibrating Sample Magnetometer (VSM) are applied to evaluate the decomposition behavior, structure, morphology, and magnetic properties of BaM thin films. Additionally, the effects of number of layers variation are also investigated. Finally, magnetic properties analysismore » indicates the isotropic nature of the films.« less

  7. Enhanced thermoelectric properties via oxygen non-stoichiometry in La2NiO4 and SrTiO3

    NASA Astrophysics Data System (ADS)

    Pardo, Victor; Botana, Antia S.; Bach, Paul M.; Leboran, Victor; Rivadulla, Francisco; Baldomir, Daniel

    2013-03-01

    We present the results of transport properties calculations and experiments on various oxides. A large enhancement of the thermoelectric properties is predicted[1] via ab initio calculations for La2NiO4+δ, with electronic-only thermoelectric figure of merit (zT) values exceeding unity for oxygen excess δ <= 0.10. The effects of lattice strain (caused, e.g. by growth of thin films on different substrates) enhance even further the thermoelectric response. A similar result is obtained at very low electron-doping in bulk SrTiO3 via oxygen removal. This is analyzed experimentally via thermal annealing that depletes oxygen (~ 1 oxygen vacancy per 106 unit cells). In both these systems, the increase in conductivity reached in the metallic limit retains a large thermopower, with the corresponding enhancement of zT . In the case of SrTiO3, experiments indicate[2] that such a small oxygen vacancy level reduces drastically the thermal conductivity by introducing random scattering centers. In the talk, we will discuss the electronic structure origin of the enhancement of the thermoelectric response and how this can be tuned. Results are general and applicable to other non-stoichiometric oxides.

  8. Low temperature rf sputtering deposition of (Ba, Sr) TiO3 thin film with crystallization enhancement by rf power supplied to the substrate

    NASA Astrophysics Data System (ADS)

    Yoshimaru, Masaki; Takehiro, Shinobu; Abe, Kazuhide; Onoda, Hiroshi

    2005-05-01

    The (Ba, Sr) TiO3 thin film deposited by radio frequency (rf) sputtering requires a high deposition temperature near 500 °C to realize a high relative dielectric constant over of 300. For example, the film deposited at 330 °C contains an amorphous phase and shows a low relative dielectric constant of less than 100. We found that rf power supplied not only to the (Ba, Sr) TiO3 sputtering target, but also to the substrate during the initial step of film deposition, enhanced the crystallization of the (Ba, Sr) TiO3 film drastically and realized a high dielectric constant of the film even at low deposition temperatures near 300 °C. The 50-nm-thick film with only a 10 nm initial layer deposited with the substrate rf biasing is crystallized completely and shows a high relative dielectric constant of 380 at the deposition temperature of 330 °C. The (Ba, Sr) TiO3 film deposited at higher temperatures (upwards of 400 °C) shows <110> preferred orientation, while the film deposited at 330 °C with the 10 nm initial layer shows a <111> preferred orientation on a <001>-oriented ruthenium electrode. The unit cell of (Ba, Sr) TiO3 (111) plane is similar to that of ruthenium (001) plane. We conclude that the rf power supplied to the substrate causes ion bombardments on the (Ba, Sr) TiO3 film surface, which assists the quasiepitaxial growth of (Ba, Sr) TiO3 film on the ruthenium electrode at low temperatures of less than 400 °C.

  9. A review of molecular beam epitaxy of ferroelectric BaTiO 3 films on Si, Ge and GaAs substrates and their applications

    DOE PAGES

    Mazet, Lucie; Yang, Sang Mo; Kalinin, Sergei V.; ...

    2015-06-30

    SrTiO 3 epitaxial growth by molecular beam epitaxy (MBE) on silicon has opened up the route to the monolithic integration of various complex oxides on the complementary metal-oxide-semiconductor silicon platform. Among functional oxides, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip. We review the growth by MBE of the ferroelectric compound BaTiO 3 on silicon (Si), germanium (Ge) and gallium arsenide (GaAs) and we discuss the film properties in terms of crystalline structure, microstructure and ferroelectricity. Lastly, we review the last developments in two areas of interest for the applications of BaTiO 3 films on silicon,more » namely integrated photonics, which benefits from the large Pockels effect of BaTiO 3, and low power logic devices, which may benefit from the negative capacitance of the ferroelectric.« less

  10. Synthesis of Platelike {100} SrTiO3 Particles by Topochemical Microcrystal Conversion and Fabrication of Grain-Oriented Ceramics

    NASA Astrophysics Data System (ADS)

    Saito, Yasuyoshi; Takao, Hisaaki

    2006-09-01

    Platelike SrTiO3 particles with a cubic perovskite structure were synthesized by topochemical microcrystal conversion (TMC) from platelike precursor particles of layer-structured SrBi4Ti4O15 at 950 °C. SrTiO3 particles preserved the shape of precursor particles, and had a thickness of approximately 0.5 μm and a width of 5-10 μm. X-ray diffraction analysis revealed that in the TMC reaction, the crystallographic {001} plane of SrBi4Ti4O15 is converted into the {100} plane of SrTiO3. Using the platelike SrTiO3 particles as a template in templated grain growth method, dense {100} grain-oriented SrTiO3 ceramics having a {100} orientation degree (Lotgering’s factor) higher than 91% could be fabricated at sintering temperatures between 1350 and 1550 °C. The maximum orientation factor reached 99.3%.

  11. Leakage current behavior in lead-free ferroelectric (K,Na)NbO3-LiTaO3-LiSbO3 thin films

    NASA Astrophysics Data System (ADS)

    Abazari, M.; Safari, A.

    2010-12-01

    Conduction mechanisms in epitaxial (001)-oriented pure and 1 mol % Mn-doped (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.1,Sb0.06)O3 (KNN-LT-LS) thin films on SrTiO3 substrate were investigated. Temperature dependence of leakage current density was measured as a function of applied electric field in the range of 200-380 K. It was shown that the different transport mechanisms dominate in pure and Mn-doped thin films. In pure (KNN-LT-LS) thin films, Poole-Frenkel emission was found to be responsible for the leakage, while Schottky emission was the dominant mechanism in Mn-doped thin films at higher electric fields. This is a remarkable yet clear indication of effect of 1 mol % Mn on the resistive behavior of such thin films.

  12. Nature of weak magnetism in SrTiO3/LaAlO3 multilayers.

    PubMed

    Salman, Z; Ofer, O; Radovic, M; Hao, H; Ben Shalom, M; Chow, K H; Dagan, Y; Hossain, M D; Levy, C D P; Macfarlane, W A; Morris, G M; Patthey, L; Pearson, M R; Saadaoui, H; Schmitt, T; Wang, D; Kiefl, R F

    2012-12-21

    We report the observation of weak magnetism in superlattices of LaAlO(3)/SrTiO(3) using β-detected nuclear magnetic resonance. The spin lattice relaxation rate of ^{8}Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO(3) exhibits a strong peak near ~35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO(3)/SrTiO(3) interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of ~4-6 unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments (~0.002μ(B)) in the two samples with a larger LaAlO(3) spacer thickness.

  13. Method of forming a dielectric thin film having low loss composition of Ba.sub.x Sr.sub.y Ca.sub.1-x-y TiO.sub.3 : Ba.sub.0.12-0.25 Sr.sub.0.35-0.47 Ca.sub.0.32-0.53 TiO.sub.3

    DOEpatents

    Xiang, Xiao-Dong; Chang, Hauyee; Takeuchi, Ichiro

    2000-01-01

    A dielectric thin-film material for microwave applications, including use as a capacitor, the thin-film comprising a composition of barium strontium calcium and titanium of perovskite type (Ba.sub.x Sr.sub.y Ca.sub.1-x-y)TiO.sub.3. Also provided is a method for making a dielectric thin film of that formula over a wide compositional range through a single deposition process.

  14. Unexpected metal-insulator transition in thick Ca1-xSrxVO3 film on SrTiO3 (100) single crystal

    NASA Astrophysics Data System (ADS)

    Takayanagi, Makoto; Tsuchiya, Takashi; Namiki, Wataru; Ueda, Shigenori; Minohara, Makoto; Horiba, Koji; Kumigashira, Hiroshi; Terabe, Kazuya; Higuchi, Tohru

    2018-03-01

    Epitaxial Ca1-xSrxVO3 (0 ≦ x ≦ 1) thin films were grown on (100)-oriented SrTiO3 substrates by using the pulsed laser deposition technique. In contrast to the previous report that metal-insulator transition (MIT) in Ca1-xSrxVO3 (CSVO) was achieved only for extremely thin films (several nm thick), MIT was observed at 39, 72, and 113 K for films with a thickness of 50 nm. The electronic structure was investigated by hard and soft X-ray photoemission spectroscopy (HX-PES and SX-PES). The difference between these PES results was significant due to the variation in an escape depth of photoelectrons of PES. While HX-PES showed that the V 2p3/2 spectra consisted of four peaks (V5+, V4+, V3+, and V2+/1+), SX-PES showed only three peaks (V5+, V4+, and V3+). This difference can be caused by a strain from the substrate, which leads to the chemical disorder (V5+, V4+, V3+, and V2+/1+). The thin film near the substrate is affected by the strain. The positive magnetoresistance is attributed to the effect of electron-electron interactions in the disorder system. Therefore, the emergence of MIT can be explained by the electron-electron interactions from the chemical disorder due to the strain.

  15. Conduction Mechanisms in Multiferroic Multilayer BaTiO3/NiFe2O4/BaTiO3 Memristors

    NASA Astrophysics Data System (ADS)

    Samardzic, N.; Bajac, B.; Srdic, V. V.; Stojanovic, G. M.

    2017-10-01

    Memristive devices and materials are extensively studied as they offer diverse properties and applications in digital, analog and bio-inspired circuits. In this paper, we present an important class of memristors, multiferroic memristors, which are composed of multiferroic multilayer BaTiO3/NiFe2O4/BaTiO3 thin films, fabricated by a spin-coating deposition technique on platinized Si wafers. This cost-effective device shows symmetric and reproducible current-voltage characteristics for the actuating voltage amplitude of ±10 V. The origin of the conduction mechanism was investigated by measuring the electrical response in different voltage and temperature conditions. The results indicate the existence of two mechanisms: thermionic emission and Fowler-Nordheim tunnelling, which alternate with actuating voltage amplitude and operating temperature.

  16. Pyroelectric property of SrTiO3/Si ferroelectric-semiconductor heterojunctions near room temperature

    NASA Astrophysics Data System (ADS)

    Bai, Gang; Wu, Dongmei; Xie, Qiyun; Guo, Yanyan; Li, Wei; Deng, Licheng; Liu, Zhiguo

    2015-12-01

    A nonlinear thermodynamic formalism is developed to calculate the pyroelectric property of epitaxial single domain SrTiO3/Si heterojunctions by taking into account the thermal expansion misfit strain at different temperatures. It has been demonstrated that the crucial role was played by the contribution associated with the structure order parameter arising from the rotations of oxygen octahedral on pyroelectricity. A dramatic decrease in the pyroelectric coefficient due to the strong coupling between the polarization and the structure order parameter is found at ferroelectric TF1-TF2 phase transition. At the same time, the thermal expansion mismatch between film and substrate is also found to provide an additional weak decrease of pyroelectricity. The analytic relationship of the out-of-plane pyroelectric coefficient and dielectric constant of ferroelectric phases by considering the thermal expansion of thin films and substrates has been determined for the first time. Our research provides another avenue for the investigation of the pyroelectric effects of ferroic thin films, especially, such as antiferroelectric and multiferroic materials having two or more order parameters.

  17. Magnetism and metal-insulator transition in oxygen deficient SrTiO3

    NASA Astrophysics Data System (ADS)

    Lopez-Bezanilla, Alejandro; Ganesh, P.; Littlewood, Peter

    2015-03-01

    We report new findings in the electronic structure and magnetism of oxygen vacancies in SrTiO3. By means of first-principles calculations we show that the appearance of magnetism in oxygen-deficient SrTiO3 is not determined solely by the presence of a single oxygen vacancy but by the density of free carriers and the relative proximity of the vacant sites. While an isolated vacancy behaves as a non-magnetic double donor, manipulation of the doping conditions allows the stability of a single donor state with emergent local moments. Strong local lattice distortions enhance the binding of this state. Consequently we find that the free-carrier density and strain are fundamental components to obtaining trapped spin-polarized electrons in oxygen-deficient SrTiO3, which may have important implications in the design of switchable magneto-optic devices. AL-B and PBL were supported by DOE-BES under Contract No. DE-AC02-06CH11357. PG was sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT- Battelle, LLC, for the US Department of Energy.

  18. Nanocrystallized SrHA/SrHA SrTiO3/SrTiO3 TiO2 multilayer coatings formed by micro-arc oxidation for photocatalytic application

    NASA Astrophysics Data System (ADS)

    Han, Y.; Chen, D. H.; Zhang, L.

    2008-08-01

    Novel photocatalytic coatings containing strontium hydroxyapatite (SrHA), strontium titanate (SrTiO3), and TiO2 were formed by micro-arc oxidation (MAO) in an aqueous electrolyte containing strontium acetate and β-glycerophosphate disodium at 530 V for 0.1-5 min. The structure evolution of the coatings was investigated as a function of processing time, and the photocatalytic activity of the coatings was evaluated by measuring the decomposition rate of methyl orange under ultraviolet irradiation. During the MAO processing of the coatings, it was observed that some granules appeared in the electrolyte adjacent to the anode and they increased in amount as the processing time was prolonged. The obtained results show that the granules are amorphous and poorly crystallized SrHA with negative charges. The coating prepared for 5 min presents a microporous structure of SrHA/SrHA-SrTiO3/SrTiO3-TiO2 multilayers, in which the SrHA outermost layer and the SrHA-SrTiO3 intermediate layer are nanocrystallized. It is suggested that formation of the granules, electro-migration of the granules onto the pre-formed layer, and crystallization of the adhered granules are possible mechanisms for the formation of a SrHA/SrHA-SrTiO3/SrTiO3-TiO2 multilayer coating. This coating shows much higher photocatalytic decomposition efficiency relative to the MAO-formed TiO2 coating, and is expected to have an important photocatalytic application.

  19. Structure and magnetism of Fe-doped BaSnO 3 thin films

    DOE PAGES

    Alaan, Urusa S.; N’Diaye, Alpha T.; Shafer, Padraic; ...

    2017-02-28

    BaSnO 3 is an excellent candidate system for developing a new class of perovskite-based dilute magnetic semiconductors. Here in this study, we show that BaSn 0.95Fe 0.05O 3 can be grown from a background pressure of ~2×10-3 mTorr to oxygen pressures of 300 mTorr with high crystallinity and excellent structural quality. When grown in vacuum, the films may be weakly ferromagnetic with a nonzero x-ray magnetic circular dichroism signal on the Fe L 3 edge. Growth with oxygen flow appears to suppress magnetic ordering. Even for very thick films grown in 100 mTorr O 2, the films are paramagnetic. Finally,more » the existence of ferromagnetism in vacuum-grown BaSnO 3 may be attributed to the F-center exchange mechanism, which relies on the presence of oxygen vacancies to facilitate the ferromagnetism. However, other possible extrinsic contributions to the magnetic ordering, such as clusters of Fe 3O 4 and FeO or contamination can also explain the observed behavior.« less

  20. Synthesis and Characterization of BaFe12O19 Thin Films Using Suspension of Nano Powders

    NASA Astrophysics Data System (ADS)

    Salemizadeh, Saman; Seyyed Ebrahimi, S. A.

    BaM thin films have been synthesized by dispersing the dried gel nano powders prepared by Sol-Gel method. The solution was made by dissolving iron nitrate Fe(NO3).9H2O, barium nitrate Ba(NO3)2 and citric acid in deyonized water and methanol. This sol was slowly evaporated until a dried gel was formed. This dried gel was then added to ethylene glycol. The final solution was vigorously shaken and mixed in ultrasonic cleaner for 30 min to disperse particles sufficiently. Then the prepared solution spin coated on Si(110) substrate. The obtained thin films were dried at 120 °C and then calcined at 900 °C for 1 h. The films were characterized using X-ray diffraction (XRD) and vibrating sample magnetometer (VSM).

  1. Ferromagnetism in tetragonally distorted LaCoO3 thin films

    NASA Astrophysics Data System (ADS)

    Mehta, Virat Vasav; Liberati, Marco; Wong, Franklin J.; Chopdekar, Rajesh Vilas; Arenholz, Elke; Suzuki, Yuri

    2009-04-01

    Thin films of epitaxial LaCoO3 were synthesized on SrTiO3 and (La ,Sr)(Al,Ta)O3 substrates, varying the oxygen background pressure in order to evaluate the impact of epitaxial growth as well as oxygen vacancies on the long range magnetic order. The epitaxial constraints from the substrate impose a tetragonal distortion compared to the bulk form. X-ray absorption and x-ray magnetic circular dichroism measurements confirmed that the ferromagnetism arises from the Co ions and persists through the entire thickness of the film. It was found that for the thin films to show ferromagnetic order they have to be grown under the higher oxygen pressures. A correlation of the structure and magnetism suggests that the tetragonal distortions induce the ferromagnetism.

  2. Preparation of Cu-loaded SrTiO3 nanoparticles and their photocatalytic activity for hydrogen evolution from methanol aqueous solution

    NASA Astrophysics Data System (ADS)

    Bui, Duc-Nguyen; Mu, Jin; Wang, Lei; Kang, Shi-Zhao; Li, Xiangqing

    2013-06-01

    Cu-loaded SrTiO3 nanoparticles (Cu-SrTiO3) were prepared using a simple in situ photo-deposition method and their photocatalytic activity for hydrogen evolution from methanol aqueous solution was evaluated. The results characterized with XRD, TEM, XPS and EDX indicated that the as-synthesized sample was composed of metallic Cu and cubic SrTiO3, and the metallic Cu was homogeneously loaded on the surface of SrTiO3 nanoparticles. Under UV light irradiation, Cu-SrTiO3 displayed much higher photocatalytic activity for hydrogen evolution and excellent stability in comparison with pure SrTiO3 nanoparticles. The results further confirmed that the efficient separation of photogenerated electron/hole pairs was critical for the enhanced photocatalytic activity of Cu-SrTiO3. Moreover, the rate of hydrogen evolution of 0.5 wt.% Cu-SrTiO3 is comparable with that of 0.5 wt.% Pt-SrTiO3 photocatalyst under optimum conditions, implying that the metallic Cu is an efficient alternative to Pt as a co-catalyst on SrTiO3. The high photocatalytic activity, low cost and chemical stability mean that the Cu-loaded SrTiO3 is a potential catalyst for the photocatalytic hydrogen evolution from methanol aqueous solution.

  3. Average and local structure of the Pb-free ferroelectric perovskites ( Sr , Sn ) TiO 3 and ( Ba , Ca , Sn ) TiO 3

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Laurita, Geneva; Page, Katharine; Suzuki, Shoichiro

    2015-12-16

    The characteristic structural off -centering of Pb 2+ in oxides, associated with its 6s 2 lone pair, allows it to play a dominant role in polar materials, and makes it a somewhat ubiquitous component of ferroelectrics. In this work, we examine the compounds Sr 0.9Sn 0.1TiO 3 and Ba 0.79Ca 0.16Sn 0.05TiO 3 using neutron total scattering techniques with data acquired at di erent temperatures. In these compounds, previously reported as ferroelectrics, Sn 2+ appears to display some of the characteristics of Pb 2+. We compare the local and long-range structures of the Sn2+-substituted compositions to the unsubstituted parent compoundsmore » SrTiO 3 and BaTiO 3. Lastly, we find that even at these small substitution levels, the Sn 2+ lone pairs drive the local ordering behavior, with the local structure of both compounds more similar to the structure of PbTiO 3 rather than the parent compounds.« less

  4. Characterization of (Ba(0.5)Sr(0.5)) TiO3 Thin Films for Ku-Band Phase Shifters

    NASA Technical Reports Server (NTRS)

    Mueller, Carl H.; VanKeuls, Fredrick W.; Romanofsky, Robert R.; Miranda, Felix A.; Warner, Joseph D.; Canedy, Chadwick L.; Ramesh, Rammamoorthy

    1999-01-01

    The microstructural properties of (Ba(0.5)Sr(0.5)TiO3) (BSTO) thin films (300, 700, and 1400 nm thick) deposited on LaAlO3 (LAO) substrates were characterized using high-resolution x-ray diffractometry. Film crystallinity was the parameter that most directly influenced tunability, and we observed that a) the crystalline quality was highest in the thinnest film and progressively degraded with increasing film thickness; and b) strain at the film/substrate interface was completely relieved via dislocation formation. Paraelectric films such as BSTO offer an attractive means of incorporating low-cost phase shifter circuitry into beam-steerable reflectarray antennas.

  5. Improvement of electron mobility in La:BaSnO{sub 3} thin films by insertion of an atomically flat insulating (Sr,Ba)SnO{sub 3} buffer layer

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Shiogai, Junichi, E-mail: junichi.shiogai@imr.tohoku.ac.jp; Nishihara, Kazuki; Sato, Kazuhisa

    One perovskite oxide, ASnO{sub 3} (A = Sr, Ba), is a candidate for use as a transparent conductive oxide with high electron mobility in single crystalline form. However, the electron mobility of films grown on SrTiO{sub 3} substrates does not reach the bulk value, probably because of dislocation scattering that originates from the large lattice mismatch. This study investigates the effect of insertion of bilayer BaSnO{sub 3} / (Sr,Ba)SnO{sub 3} for buffering this large lattice mismatch between La:BaSnO{sub 3} and SrTiO{sub 3} substrate. The insertion of 200-nm-thick BaSnO{sub 3} on (Sr,Ba)SnO{sub 3} bilayer buffer structures reduces the number of dislocationsmore » and improves surface smoothness of the films after annealing as proved respectively by scanning transmission electron microscopy and atomic force microscopy. A systematic investigation of BaSnO{sub 3} buffer layer thickness dependence on Hall mobility of the electron transport in La:BaSnO{sub 3} shows that the highest obtained value of mobility is 78 cm{sup 2}V{sup −1}s{sup −1} because of its fewer dislocations. High electron mobility films based on perovskite BaSnO{sub 3} can provide a good platform for transparent-conducting-oxide electronic devices and for creation of fascinating perovskite heterostructures.« less

  6. Single-Gap Superconductivity and Dome of Superfluid Density in Nb-Doped SrTiO 3

    NASA Astrophysics Data System (ADS)

    Thiemann, Markus; Beutel, Manfred H.; Dressel, Martin; Lee-Hone, Nicholas R.; Broun, David M.; Fillis-Tsirakis, Evangelos; Boschker, Hans; Mannhart, Jochen; Scheffler, Marc

    2018-06-01

    SrTiO3 exhibits a superconducting dome upon doping with Nb, with a maximum critical temperature Tc≈0.4 K . Using microwave stripline resonators at frequencies from 2 to 23 GHz and temperatures down to 0.02 K, we probe the low-energy optical response of superconducting SrTiO3 with a charge carrier concentration from 0.3 to 2.2 ×1020 cm-3 , covering the majority of the superconducting dome. We find single-gap electrodynamics even though several electronic bands are superconducting. This is explained by a single energy gap 2 Δ due to gap homogenization over the Fermi surface consistent with the low level of defect scattering in Nb-doped SrTiO3 . Furthermore, we determine Tc, 2 Δ , and the superfluid density as a function of charge carrier concentration, and all three quantities exhibit the characteristic dome shape.

  7. Photoinduced Demagnetization and Insulator-to-Metal Transition in Ferromagnetic Insulating BaFeO_{3} Thin Films.

    PubMed

    Tsuyama, T; Chakraverty, S; Macke, S; Pontius, N; Schüßler-Langeheine, C; Hwang, H Y; Tokura, Y; Wadati, H

    2016-06-24

    We studied the electronic and magnetic dynamics of ferromagnetic insulating BaFeO_{3} thin films by using pump-probe time-resolved resonant x-ray reflectivity at the Fe 2p edge. By changing the excitation density, we found two distinctly different types of demagnetization with a clear threshold behavior. We assigned the demagnetization change from slow (∼150  ps) to fast (<70  ps) to a transition into a metallic state induced by laser excitation. These results provide a novel approach for locally tuning magnetic dynamics. In analogy to heat-assisted magnetic recording, metallization can locally tune the susceptibility for magnetic manipulation, allowing one to spatially encode magnetic information.

  8. Strain induced enhancement of magnetization in Ba{sub 2}FeMoO{sub 6} based heterostructure with (Ba{sub x}Sr{sub 1-x})TiO{sub 3}

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kim, Kyeong-Won; Norton, David P.; Ghosh, Siddhartha, E-mail: ghoshsid@gmail.com

    2016-05-14

    High quality epitaxial Ba{sub 2}FeMoO{sub 6} thin films and Ba{sub 2}FeMoO{sub 6}–(Ba{sub x}Sr{sub 1−x})TiO{sub 3} bi-layer (BL) and superlattice (SL) structures were grown via pulsed laser deposition under low oxygen pressure, and their structural, magnetic, and magneto-transport properties were examined. Superlattice and bi-layer structures were confirmed by X-ray diffraction patterns. Low temperature magnetic measurement shows that the saturation magnetization (M{sub S}) is significantly higher for SLs and almost similar or lower for BLs, when compared to phase pure Ba{sub 2}FeMoO{sub 6} thin films. The variation of the coercive field (H{sub C}) follows exact opposite trend, where BL samples have highermore » H{sub C} and SL samples have lower H{sub C} than pure Ba{sub 2}FeMoO{sub 6} thin films. Also, a significant decrease of the Curie temperature is found in both BL and SL structures compared to pure Ba{sub 2}FeMoO{sub 6} thin films. Negative magneto-resistance is seen in all the BL and SL structures as well as in pure Ba{sub 2}FeMoO{sub 6} thin films. In contrast to the magnetic properties, the magneto-transport properties do not show much variation with induced strain.« less

  9. Swift heavy-ions induced sputtering in BaF2 thin films

    NASA Astrophysics Data System (ADS)

    Pandey, Ratnesh K.; Kumar, Manvendra; Singh, Udai B.; Khan, Saif A.; Avasthi, D. K.; Pandey, Avinash C.

    2013-11-01

    In our present experiment a series of barium fluoride thin films of different thicknesses have been deposited by electron beam evaporation technique at room temperature on silicon substrates. The effect of film thickness on the electronic sputter yield of polycrystalline BaF2 thin films has been reported in the present work. Power law for sputtered species collected on catcher grids has also been reported for film of lowest thickness. Sputtering has been performed by 100 MeV Au+28 ions. Atomic force microscopy (AFM) has been done to check the surface morphology of pristine samples. Glancing angle X-ray diffraction (GAXRD) measurements show that the pristine films are polycrystalline in nature and the grain size increases with increase in film thickness. Rutherford backscattering spectrometry (RBS) of pristine as well as irradiated films was done to determine the areal concentration of Ba and F atoms in the films. A reduction in the sputter yield of BaF2 films with the increase in film thickness has been observed from RBS results. The thickness dependence sputtering is explained on the basis of thermal spike and the energy confinement of the ions in the smaller grains. Also transmission electron microscopy (TEM) of the catchers shows a size distribution of sputtered species with values of power law exponent 1/2 and 3/2 for two fluences 5 × 1011 and 1 × 1012 ions/cm2, respectively.

  10. Effect of crystal orientation on the phase diagrams, dielectric and piezoelectric properties of epitaxial BaTiO{sub 3} thin films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wu, Huaping, E-mail: wuhuaping@gmail.com, E-mail: hpwu@zjut.edu.cn; State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024; Ma, Xuefu

    2016-01-15

    The influence of crystal orientations on the phase diagrams, dielectric and piezoelectric properties of epitaxial BaTiO{sub 3} thin films has been investigated using an expanded nonlinear thermodynamic theory. The calculations reveal that crystal orientation has significant influence on the phase stability and phase transitions in the misfit strain-temperature phase diagrams. In particular, the (110) orientation leads to a lower symmetry and more complicated phase transition than the (111) orientation in BaTiO{sub 3} films. The increase of compressive strain will dramatically enhance the Curie temperature T{sub C} of (110)-oriented BaTiO{sub 3} films, which matches well with previous experimental data. The polarizationmore » components experience a great change across the boundaries of different phases at room temperature in both (110)- and (111)-oriented films, which leads to the huge dielectric and piezoelectric responses. A good agreement is found between the present thermodynamics calculation and previous first-principles calculations. Our work provides an insight into how to use crystal orientation, epitaxial strain and temperature to tune the structure and properties of ferroelectrics.« less

  11. Two-dimensional superconductivity at a Mott insulator/band insulator interface LaTiO3/SrTiO3.

    PubMed

    Biscaras, J; Bergeal, N; Kushwaha, A; Wolf, T; Rastogi, A; Budhani, R C; Lesueur, J

    2010-10-05

    Transition metal oxides show a great variety of quantum electronic behaviours where correlations often have an important role. The achievement of high-quality epitaxial interfaces involving such materials gives a unique opportunity to engineer artificial structures where new electronic orders take place. One of the most striking result in this area is the recent observation of a two-dimensional electron gas at the interface between a strongly correlated Mott insulator LaTiO(3) and a band insulator SrTiO(3). The mechanism responsible for such a behaviour is still under debate. In particular, the influence of the nature of the insulator has to be clarified. In this article, we show that despite the expected electronic correlations, LaTiO(3)/SrTiO(3) heterostructures undergo a superconducting transition at a critical temperature T(c)(onset)~300 mK. We have found that the superconducting electron gas is confined over a typical thickness of 12 nm and is located mostly on the SrTiO(3) substrate.

  12. Top gating control of superconductivity at the LaAlO3 /SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Jouan, Alexis; Hurand, Simon; Feuillet-Palma, Cheryl; Singh, Gyanendra; Lesueur, Jerome; Bergeal, Nicolas; Lesne, Edouard; Reyren, Nicolas

    2015-03-01

    Transition metal oxides display a great variety of quantum electronic behaviors. Epitaxial interfaces involving such materials give a unique opportunity to engineer artificial materials where new electronic orders take place. It has been shown that a superconducting two-dimensional electron gas could form at the interface of two insulators such as LaAlO3 and SrTiO3 [1], or LaTiO3 and SrTiO3 [2]. An important feature of these interfaces lies in the possibility to control their electronic properties, including superconductivity and spin-orbit coupling (SOC) with field effect [3-5]. However, experiments have been performed almost exclusively with a metallic gate on the back of the sample. In this presentation, we will report on the realization of a top-gated LaAlO3/SrTiO3 device whose physical properties, including superconductivity and SOC, can be tuned over a wide range of electrostatic doping. In particular, we will present a phase diagram of the interface and compare the effect of the top-gate and back-gate. Finally, we will discuss the field-effect modulation of the Rashba spin-splitting energy extracted from the analysis of magneto-transport measurements. Our result paves the way for the realization of mesoscopic devices where both superconductivity and SOC can be tuned locally.

  13. Effect of manganese doping on remnant polarization and leakage current in (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 epitaxial thin films on SrTiO3

    NASA Astrophysics Data System (ADS)

    Abazari, M.; Akdoǧan, E. K.; Safari, A.

    2008-05-01

    Single phase, epitaxial, ⟨001⟩ oriented, undoped and 1mol% Mn-doped (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films of 400nm thickness were synthesized on SrRuO3 coated SrTiO3. Such films exhibit well saturated hysteresis loops and have a spontaneous polarization (Ps) of 10μC /cm2, which is a 150% higher over the Ps of the undoped composition. The coercive field of 1mol% Mn doped films is 13kV/cm. Mn-doping results in three orders of magnitude decrease in leakage current above 50kV/cm electric field, which we attribute to the suppression of intrinsic p-type conductivity of undoped films by Mn donors.

  14. Influence of rare earth doping on thermoelectric properties of SrTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Liu, J.; Wang, C. L.; Li, Y.; Su, W. B.; Zhu, Y. H.; Li, J. C.; Mei, L. M.

    2013-12-01

    Thermoelectric properties of SrTiO3 ceramics, doped with different rare earth elements, were investigated in this work. It's found that the ionic radius of doping elements plays an important role on thermoelectric properties: SrTiO3 ceramics doped with large rare earth ions (such as La, Nd, and Sm) exhibit large power factors, and those doped with small ions (such as Gd, Dy, Er, and Y) exhibit low thermal conductivities. Therefore, a simple approach for enhancing the thermoelectric performance of SrTiO3 ceramics is proposed: mainly doped with large ions to obtain a large power factor and, simultaneously, slightly co-doped with small ions to obtain a low thermal conductivity. Based on this rule, Sr0.8La0.18Yb0.02TiO3 ceramics were prepared, whose ZT value at 1 023 K reaches 0.31, increasing by a factor of 19% compared with the single-doped counterpart Sr0.8La0.2TiO3 (ZT = 0.26).

  15. Prediction of two-dimensional electron gas mediated magnetoelectric coupling at ferroelectric PbTiO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Wei, Lan-ying; Lian, Chao; Meng, Sheng

    2017-05-01

    First-principles calculations predict the emergence of magnetoelectric coupling mediated by two-dimensional electron gas (2DEG) at the ferroelectric PbTiO3/SrTiO3 heterostructure. Free electrons endowed by naturally existing oxygen vacancies in SrTiO3 are driven to the heterostructure interface under the polarizing field of ferroelectric PbTiO3 to form a 2DEG. The electrons are captured by interfacial Ti atoms, which surprisingly exhibits ferromagnetism even at room temperature with a small critical density of ˜15.5 μ C /cm2 . The ferroelectricity-controlled ferromagnetism mediated by interfacial 2DEG shows strong magnetoelectric coupling strength, enabling convenient control of magnetism by electric field and vice versa. The PbTiO3/SrTiO3 heterostructure is cheap, easily grown, and controllable, promising future applications in low-cost spintronics and information storage at ambient condition.

  16. Thin Film Synthesis of New Complex Titanates.

    NASA Astrophysics Data System (ADS)

    Salvador, Paul

    2008-03-01

    Thin film deposition methods allow for one to synthesize rationally specific compositions in targeted crystal structures. Because most of the thermodynamic and kinetic variables that control the range of materials that can be synthesized are unknown for specific compounds/processes, epitaxial stabilization and design of artificially layered crystals are driven through empirical investigations. Using examples taken primarily from the family of complex titanates, which exhibit a range of interesting physicochemical behaviors, the thermodynamic and kinetic factors that control materials design using thin film deposition are discussed. The phase competition between the pyrochlore and the (110) layered perovskite structure in the RE2Ti2O7 family (RE = rare-earth, Bi) will be explored, using pulsed laser deposition as a synthesis method. For RE = Gd, Sm, Nd, and La, the phase stability over a wide range of conditions is dictated entirely by substrate choice, indicating that the free energies of the phases are similar enough such that by controlling nucleation one controls the phase formation. In a related fashion, the growth of AETi2O5 films (AE = Ba or Sr) will be discussed with respect to the formation of single-phase films or films that phase separate into AETiO3 and TiO2. The entire Ba1-xSrxTi2O5 series was grown and will be discussed with respect to growth technique (using MBE and PLD) and/or substrate choice. In this case, rock-salt substrates, which are not expected to interact strongly with any phase in the system, allow for the formation of single-phase films. Finally, several examples will be discussed with respect to the (SrO)m(TiO2)n system, which includes the perovskite SrTiO3 and the Ruddlesden-Popper phase Sr2TiO4, grown using layer-by-layer molecular beam epitaxy. The solid phase epitaxial formation of the perovskite SrTiO3 from superlattices of rock-salt SrO and anatase TiO2 is discussed from both a kinetic and thermodynamic perspective by exploring the

  17. Crystallization dynamics and interface stability of strontium titanate thin films on silicon.

    PubMed

    Hanzig, Florian; Hanzig, Juliane; Mehner, Erik; Richter, Carsten; Veselý, Jozef; Stöcker, Hartmut; Abendroth, Barbara; Motylenko, Mykhaylo; Klemm, Volker; Novikov, Dmitri; Meyer, Dirk C

    2015-04-01

    Different physical vapor deposition methods have been used to fabricate strontium titanate thin films. Within the binary phase diagram of SrO and TiO 2 the stoichiometry ranges from Ti rich to Sr rich, respectively. The crystallization of these amorphous SrTiO 3 layers is investigated by in situ grazing-incidence X-ray diffraction using synchrotron radiation. The crystallization dynamics and evolution of the lattice constants as well as crystallite sizes of the SrTiO 3 layers were determined for temperatures up to 1223 K under atmospheric conditions applying different heating rates. At approximately 473 K, crystallization of perovskite-type SrTiO 3 is initiated for Sr-rich electron beam evaporated layers, whereas Sr-depleted sputter-deposited thin films crystallize at 739 K. During annealing, a significant diffusion of Si from the substrate into the SrTiO 3 layers occurs in the case of Sr-rich composition. This leads to the formation of secondary silicate phases which are observed by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy.

  18. Atomic-scale structural and electronic properties of SrTiO3/GaAs interfaces: A combined STEM-EELS and first-principles study

    NASA Astrophysics Data System (ADS)

    Hong, Liang; Bhatnagar, Kunal; Droopad, Ravi; Klie, Robert F.; Öǧüt, Serdar

    2017-07-01

    The electronic properties of epitaxial oxide thin films grown on compound semiconductors are largely determined by the interfacial atomic structure, as well as the thermodynamic conditions during synthesis. Ferroelectric polarization and Fermi-level pinning in SrTiO3 films have been attributed to the presence of oxygen vacancies at the oxide/semiconductor interface. Here, we present scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy analyses of GaAs films grown on SrTiO3 combined with first-principles calculations to determine the atomic and electronic structures of the SrTiO3/GaAs interfaces. An atomically abrupt SrO/As interface is observed and the interfacial SrO layer is found to be O-deficient. First-principles density functional theory (DFT) calculations show SrO/Ga and Sr/As interfaces are favorable under O-rich and O-poor conditions, respectively. The SrO/Ga interface is reconstructed via the formation of Ga-Ga dimers while the Sr/As interface is abrupt and consistent with the experiment. DFT calculations further reveal that intrinsic two-dimensional electron gas (2DEG) forms in both SrO/Ga and Sr/As interfaces, and the Fermi level is pinned to the localized 2DEG states. Interfacial O vacancies can enhance the 2DEG density while it is possible for Ga/As vacancies to unpin the Fermi level from the 2DEG states.

  19. Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

    PubMed Central

    Mehdizadeh Dehkordi, Arash; Bhattacharya, Sriparna; Darroudi, Taghi; Zeng, Xiaoyu; Alshareef, Husam N.; Tritt, Terry M.

    2015-01-01

    We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO3. PMID:26327483

  20. Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties.

    PubMed

    Mehdizadeh Dehkordi, Arash; Bhattacharya, Sriparna; Darroudi, Taghi; Zeng, Xiaoyu; Alshareef, Husam N; Tritt, Terry M

    2015-08-15

    We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO3.

  1. Magnetic and electronic properties of SrMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Mandal, Arup Kumar; Panchal, Gyanendra; Choudhary, R. J.; Phase, D. M.

    2018-05-01

    Single phase hexagonal bulk SrMnO3 (SMO) was prepared by solid state route and it was used for depositing thin films by pulsed laser deposition (PLD) technique on single crystalline (100) oriented SrTiO3 (STO) substrate. X-ray diffraction shows that the thin film is deposited in cubic SrMnO3 phase. From X-ray absorption at the Mn L edge we observed the mixed valency of Mn (Mn3+& Mn4+) due to strain induced by the lattice mismatching between SMO and STO. Due to this mixed valency of Mn ion in SMO film, the ferromagnetic nature is observed at lower temperature because of double exchange. After post annealing with very low oxygen partial pressure, magnetic and electronic property of SMO films are effectively modified.

  2. Giant negative electrocaloric effect in PbZrO3/0.88BaTiO3-0.12Bi(Mg1/2,Ti1/2)O3 multilayered composite ferroelectric thin film for solid-state refrigeration

    NASA Astrophysics Data System (ADS)

    Huang, D.; Wang, J. B.; Zhong, X. L.; Li, B.; Zhang, Y.; Jin, C.; Zheng, D. F.; Meng, X. J.

    2017-11-01

    A giant negative electrocaloric (EC) effect in a PbZrO3/(0.88BaTiO3-0.12 Bi(Mg1/2,Ti1/2)O3) (PZ/(BT-BMT)) multilayered composite ferroelectric (MCFE) thin film which is grown on Pt(111)/Ti/SiO2/Si(100) substrates by the sol-gel method is investigated in this work. The negative EC effect in the PZ/(BMT-BT) MCFE thin film is greatly higher than that in the PZ AFE thin film with an adiabatic temperature change (ATC) ΔT = 1.5 K. The ATC ΔT of the PZ/(BMT-BT) MCFE thin film is -32 K under the applied electric field change ΔE = 1151 kV/cm. The result is conducive to enhance the EC refrigeration efficiency greatly.

  3. Fine-grained BaZr0.2Ti0.8O3 thin films for tunable device applications

    NASA Astrophysics Data System (ADS)

    Ying, Z.; Yun, P.; Wang, D. Y.; Zhou, X. Y.; Song, Z. T.; Feng, S. L.; Wang, Y.; Chan, H. L. W.

    2007-04-01

    A study of the structure and in-plane dielectric properties of BaZr0.2Ti0.8O3 thin film epitaxially grown on (LaAlO3)0.3(Sr2AlTaO6)0.35 (001) single-crystal substrates through pulsed-laser deposition has been carried out. X-ray diffraction measurements revealed a good crystallinity and tensile in-plane stress in the film. Fine grains with an average size of ˜20 nm were observed using atomic force microscopy. Curie temperature of the film was found to be ˜120 °C, which is 100 °C higher than that of the ceramic. Butterfly-shaped C-V curve confirmed the in-plane ferroelectric state in the film. A large dielectric tunability of ˜50% was found in the film.

  4. Transport Properties of La- doped SrTiO3 Ceramics Prepared Using Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Mehdizadeh Dehkordi, Arash; Bhattacharya, Sriparna; Tritt, Terry M.; Alshareef, Husam N.

    2012-02-01

    In this work, thermoelectric transport properties of La-doped SrTiO3 ceramics prepared using conventional solid state reaction and spark plasma sintering have been investigated. Room temperature power factor of single crystal strontium titanate (SrTiO3), comparable to that of Bi2Te3, has brought new attention to this perovskite-type transition metal-oxide as a potential n-type thermoelectric for high temperature applications. Electronic properties of this model complex oxide, SrTiO3 (ABO3), can be tuned in a wide range through different doping mechanisms. In addition to A site (La-doped) or B site (Nb-doped) substitutional doping, introducing oxygen vacancies plays an important role in electrical and thermal properties of these structures. Having multiple doping mechanisms makes the transport properties of these perovskites more dependent on preparation parameters. The effect of these synthesis parameters and consolidation conditions on the transport properties of these materials has been studied.

  5. Nickel sulfide/graphitic carbon nitride/strontium titanate (NiS/g-C3N4/SrTiO3) composites with significantly enhanced photocatalytic hydrogen production activity.

    PubMed

    Luo, Xiu-Li; He, Gang-Ling; Fang, Yue-Ping; Xu, Yue-Hua

    2018-05-15

    NiS/g-C 3 N 4 /SrTiO 3 (NS/CN/STO) composites were prepared using a facile hydrothermal method. The synergistic effect of g-C 3 N 4 /SrTiO 3 (CN/STO) heterojunction and NiS cocatalyst enhanced the photocatalytic hydrogen evolution activity of NS/CN/STO. A hydrogen production rate of 1722.7 μmol h -1  g -1 was obtained when the 2%NiS/20%g-C 3 N 4 /SrTiO 3 (2NS/20CN/STO) was used for the photocatalytic hydrogen evolution in the presence of methanol used as a sacrificial agent under UV-vis light irradiation; the photocatalytic hydrogen production rate of 2NS/20CN/STO is 32.8, 8.9 and 4.2 times the value of that obtained with pure g-C 3 N 4 , SrTiO 3 and 20%g-C 3 N 4 /SrTiO 3 (20CN/STO), respectively. Moreover, in photoelectrochemical investigations when compared with 20CN/STO, SrTiO 3 and g-C 3 N 4 , 2NS/20CN/STO exhibited significant photocurrent enhancement. The heterojunction and cocatalyst in NS/CN/STO improved the charge separation efficiency and the lifetime of the charge carriers, leading to the enhanced generation of electrons for photocatalytic hydrogen production. Copyright © 2018 Elsevier Inc. All rights reserved.

  6. Impact of cleaning methods on the structural properties and morphology of SrTiO3 surface

    NASA Astrophysics Data System (ADS)

    Arnay, Iciar; Rubio-Zuazo, Juan; Castro, German R.

    2018-01-01

    SrTiO3 is a widely used substrate for the epitaxial growth of complex systems. Nevertheless, in order to get good quality interface and avoid the formation of defects in the adsorbed layer it is essential to prepare the surface of the substrate prior to the deposition. Thermal and chemical treatments are mostly used to eliminate superficial contamination and improve the surface quality. However, there is a lack of information regarding the impact of these treatments on the formation of structural defects at the SrTiO3 surface. In this work we present a detailed characterization of the SrTiO3 surface for the different cleaning methods paying special attention to the formation of oxygen vacancies, large surface mosaicity and roughness. We prove that thermal treatment induces large surface roughness and that chemical etching produces important structural defects at the surface. Our results show that mechanical polishing provided the best compromise in terms of large surface domains, low roughness, absence of oxygen vacancies and absence of atomic structure modification, although with the presence of low level of contaminants at the SrTiO3 surface.

  7. Field emission of silicon emitter arrays coated with sol-gel (Ba0.65Sr0.35)1-xLaxTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Lu, H.; Pan, J. S.; Chen, X. F.; Zhu, W. G.

    2007-07-01

    (Ba0.65Sr0.35)1-xLaxTiO3 (BSLT) thin films with different La concentrations have been deposited on Si field emitter arrays (FEAs) using sol-gel technology for field electron emission applications. The films exhibit the perovskite structure at low La substitution level (x ≤0.5) and the pyrochlore phase at high La concentration (x ≥0.75). The 30-nm-thick BSLT (x =0.25) thin film has higher crystallinity of perovskite structure in the surface region. An x-ray photoelectron spectroscopy study indicates that the oxygen vacancy concentration decreases with La substitution. With respect to the undoped Ba0.65Sr0.35TiO3 thin film, the Fermi level shifts down for the BSLT sample with x =0.1 ascribed to the decreasing oxygen vacancy concentration, and then shifts up for the BSLT sample with x =0.25 attributed to the increasing La substitution level. In highly doped films with an x value over 0.5, it shifts down again associated with the second pyrochlore phase formation. The best enhancement in field emission is found for the BSLT-coated (x =0.25) Si FEAs due to the improved perovskite structure in the surface region and up-moved Fermi level of the coating.

  8. High-carrier-density phase in LaTiO3/SrTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Park, Se Young; Rabe, Karin; Millis, Andrew

    2015-03-01

    We investigate superlattices composed of alternating layers of Mott insulating LaTiO3 and band insulating SrTiO3 from first principles, using the density functional theory plus U (DFT+U) method. For values of U above a critical threshold, we find that melting of the Mott-insulating phase can extend from the interface into the LaTiO3 layer, resulting in a sheet carrier density exceeding the density of 0.5 electrons per in-plane unit cell found in previous studies. The critical U for the melting transition is larger than the critical Coulomb correlation required for the insulating LaTiO3, suggesting the existence of a high sheet carrier density phase in LaTiO3/SrTiO3 superlattices. The effects of in-plane strain and varying layer thickness on the melting transition are discussed. For insulating superlattices, we study the strain and thickness dependence of the polarization and its relation to near-interface local atomic distortions. Support: DOE ER 046169, ONR N00014-11-0666.

  9. Generation and characterization of point defects in SrTiO3 and Y3Al5O12

    NASA Astrophysics Data System (ADS)

    Selim, F. A.; Winarski, D.; Varney, C. R.; Tarun, M. C.; Ji, Jianfeng; McCluskey, M. D.

    Positron annihilation lifetime spectroscopy (PALS) was applied to characterize point defects in single crystals of Y3Al5O12 and SrTiO3 after populating different types of defects by relevant thermal treatments. In SrTiO3, PALS measurements identified Sr vacancy, Ti vacancy, vacancy complexes of Ti-O (vacancy) and hydrogen complex defects. In Y3Al5O12 single crystals the measurements showed the presence of Al-vacancy, (Al-O) vacancy and Al-vacancy passivated by hydrogen. These defects are shown to play the major role in defining the electronic and optical properties of these complex oxides.

  10. Molecular dynamics simulations of oxygen vacancy diffusion in SrTiO3.

    PubMed

    Schie, Marcel; Marchewka, Astrid; Müller, Thomas; De Souza, Roger A; Waser, Rainer

    2012-12-05

    A classical force-field model with partial ionic charges was applied to study the behaviour of oxygen vacancies in the perovskite oxide strontium titanate (SrTiO(3)). The dynamical behaviour of these point defects was investigated as a function of temperature and defect concentration by means of molecular dynamics (MD) simulations. The interaction between oxygen vacancies and an extended defect, here a Σ3(111) grain boundary, was also examined by means of MD simulations. Analysis of the vacancy distribution revealed considerable accumulation of vacancies in the envelope of the grain boundary. The possible clustering of oxygen vacancies in bulk SrTiO(3) was studied by means of static lattice calculations within the Mott-Littleton approach. All binary vacancy-vacancy configurations were found to be energetically unfavourable.

  11. Strain Dependent Electronic Structure and Band Offset Tuning at Heterointerfaces of ASnO3 (A=Ca, Sr, and Ba) and SrTiO3

    PubMed Central

    Baniecki, John D.; Yamazaki, Takashi; Ricinschi, Dan; Van Overmeere, Quentin; Aso, Hiroyuki; Miyata, Yusuke; Yamada, Hiroaki; Fujimura, Norifumi; Maran, Ronald; Anazawa, Toshihisa; Valanoor, Nagarajan; Imanaka, Yoshihiko

    2017-01-01

    The valence band (VB) electronic structure and VB alignments at heterointerfaces of strained epitaxial stannate ASnO3 (A=Ca, Sr, and Ba) thin films are characterized using in situ X-ray and ultraviolet photoelectron spectroscopies, with band gaps evaluated using spectroscopic ellipsometry. Scanning transmission electron microscopy with geometric phase analysis is used to resolve strain at atomic resolution. The VB electronic structure is strain state dependent in a manner that correlated with a directional change in Sn-O bond lengths with strain. However, VB offsets are found not to vary significantly with strain, which resulted in ascribing most of the difference in band alignment, due to a change in the band gaps with strain, to the conduction band edge. Our results reveal significant strain tuning of conduction band offsets using epitaxial buffer layers, with strain-induced offset differences as large as 0.6 eV possible for SrSnO3. Such large conduction band offset tunability through elastic strain control may provide a pathway to minimize the loss of charge confinement in 2-dimensional electron gases and enhance the performance of photoelectrochemical stannate-based devices. PMID:28195149

  12. Domain matched epitaxial growth of (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} thin films on (0001) Al{sub 2}O{sub 3} with ZnO buffer layer

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Krishnaprasad, P. S., E-mail: pskrishnaprasu@gmail.com, E-mail: mkj@cusat.ac.in; Jayaraj, M. K., E-mail: pskrishnaprasu@gmail.com, E-mail: mkj@cusat.ac.in; Antony, Aldrin

    2015-03-28

    Epitaxial (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} (BST) thin films have been grown by pulsed laser deposition on (0001) Al{sub 2}O{sub 3} substrate with ZnO as buffer layer. The x-ray ω-2θ, Φ-scan and reciprocal space mapping indicate epitaxial nature of BST thin films. The domain matched epitaxial growth of BST thin films over ZnO buffer layer was confirmed using Fourier filtered high resolution transmission electron microscope images of the film-buffer interface. The incorporation of ZnO buffer layer effectively suppressed the lattice mismatch and promoted domain matched epitaxial growth of BST thin films. Coplanar inter digital capacitors fabricated on epitaxial (111) BSTmore » thin films show significantly improved tunable performance over polycrystalline thin films.« less

  13. In situ X-ray diffraction and the evolution of polarization during the growth of ferroelectric superlattices

    DOE PAGES

    Bein, Benjamin; Hsing, Hsiang-Chun; Callori, Sara J.; ...

    2015-12-04

    In the epitaxially strained ferroelectric thin films and superlattices, the ferroelectric transition temperature can lie above the growth temperature. Ferroelectric polarization and domains should then evolve during the growth of a sample, and electrostatic boundary conditions may play an important role. In this work, ferroelectric domains, surface termination, average lattice parameter and bilayer thickness are simultaneously monitored using in situ synchrotron X-ray diffraction during the growth of BaTiO 3/SrTiO 3 superlattices on SrTiO 3 substrates by off-axis radio frequency magnetron sputtering. The technique used allows for scan times substantially faster than the growth of a single layer of material. Effectsmore » of electric boundary conditions are investigated by growing the same superlattice alternatively on SrTiO 3 substrates and 20 nm SrRuO 3 thin films on SrTiO 3 substrates. Our experiments provide important insights into the formation and evolution of ferroelectric domains when the sample is ferroelectric during the growth process.« less

  14. Hysteretic Characteristics of Pulsed Laser Deposited 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3/ZnO Bilayers.

    PubMed

    Silva, J P B; Wang, J; Koster, G; Rijnders, G; Negrea, R F; Ghica, C; Sekhar, K C; Moreira, J Agostinho; Gomes, M J M

    2018-05-02

    In the present work, we study the hysteretic behavior in the electric-field-dependent capacitance and the current characteristics of 0.5Ba(Zr 0.2 Ti 0.8 )O 3 -0.5(Ba 0.7 Ca 0.3 )TiO 3 (BCZT)/ZnO bilayers deposited on 0.7 wt % Nb-doped (001)-SrTiO 3 (Nb:STO) substrates in a metal-ferroelectric-semiconductor (MFS) configuration. The X-ray diffraction measurements show that the BCZT and ZnO layers are highly oriented along the c-axis and have a single perovskite and wurtzite phases, respectively, whereas high-resolution transmission electron microscopy revealed very sharp Nb:STO/BCZT/ZnO interfaces. The capacitance-electric field ( C- E) characteristics of the bilayers exhibit a memory window of 47 kV/cm and a capacitance decrease of 22%, at a negative bias. The later result is explained by the formation of a depletion region in the ZnO layer. Moreover, an unusual resistive switching (RS) behavior is observed in the BCZT films, where the RS ratio can be 500 times enhanced in the BCZT/ZnO bilayers. The RS enhancement can be understood by the barrier potential profile modulation at the depletion region, in the BCZT/ZnO junction, via ferroelectric polarization switching of the BCZT layer. This work builds a bridge between the hysteretic behavior observed either in the C- E and current-electric field characteristics on a MFS structure.

  15. Preparation of TlBa2Ca2Cu3O9±δ high Tc thin films by laser ablation in combination with thermal evaporation of thallium oxide

    NASA Astrophysics Data System (ADS)

    Piehler, A.; Löw, R.; Betz, J.; Schönberger, R.; Renk, K. F.

    1993-11-01

    TlBa2Ca2Cu3O9±δ high Tc thin films were prepared on MgO <100> surfaces by a combination of laser ablation from a stoichiometric Ba2Ca2Cu3Ox target and the thermal evaporation of thallium oxide. X-ray diffraction measurements showed that the films consisted of predominantly c axis oriented TlBa2Ca2Cu3O9±δ, and scanning electron microscopy revealed that the surfaces had a flat, platelike morphology. The ac inductive measurements indicated that the onset of superconductivity occurred at 117 K with a transition width (10%-90%) of ˜3 K. Zero resistivity was reached at 120 K. The critical current density was ˜3×104 A/cm2 at 110 K.

  16. Lead-free epitaxial ferroelectric material integration on semiconducting (100) Nb-doped SrTiO3 for low-power non-volatile memory and efficient ultraviolet ray detection

    PubMed Central

    Kundu, Souvik; Clavel, Michael; Biswas, Pranab; Chen, Bo; Song, Hyun-Cheol; Kumar, Prashant; Halder, Nripendra N.; Hudait, Mantu K.; Banerji, Pallab; Sanghadasa, Mohan; Priya, Shashank

    2015-01-01

    We report lead-free ferroelectric based resistive switching non-volatile memory (NVM) devices with epitaxial (1-x)BaTiO3-xBiFeO3 (x = 0.725) (BT-BFO) film integrated on semiconducting (100) Nb (0.7%) doped SrTiO3 (Nb:STO) substrates. The piezoelectric force microscopy (PFM) measurement at room temperature demonstrated ferroelectricity in the BT-BFO thin film. PFM results also reveal the repeatable polarization inversion by poling, manifesting its potential for read-write operation in NVM devices. The electroforming-free and ferroelectric polarization coupled electrical behaviour demonstrated excellent resistive switching with high retention time, cyclic endurance, and low set/reset voltages. X-ray photoelectron spectroscopy was utilized to determine the band alignment at the BT-BFO and Nb:STO heterojunction, and it exhibited staggered band alignment. This heterojunction is found to behave as an efficient ultraviolet photo-detector with low rise and fall time. The architecture also demonstrates half-wave rectification under low and high input signal frequencies, where the output distortion is minimal. The results provide avenue for an electrical switch that can regulate the pixels in low or high frequency images. Combined this work paves the pathway towards designing future generation low-power ferroelectric based microelectronic devices by merging both electrical and photovoltaic properties of BT-BFO materials. PMID:26202946

  17. Lead-free epitaxial ferroelectric material integration on semiconducting (100) Nb-doped SrTiO3 for low-power non-volatile memory and efficient ultraviolet ray detection.

    PubMed

    Kundu, Souvik; Clavel, Michael; Biswas, Pranab; Chen, Bo; Song, Hyun-Cheol; Kumar, Prashant; Halder, Nripendra N; Hudait, Mantu K; Banerji, Pallab; Sanghadasa, Mohan; Priya, Shashank

    2015-07-23

    We report lead-free ferroelectric based resistive switching non-volatile memory (NVM) devices with epitaxial (1-x)BaTiO3-xBiFeO3 (x = 0.725) (BT-BFO) film integrated on semiconducting (100) Nb (0.7%) doped SrTiO3 (Nb:STO) substrates. The piezoelectric force microscopy (PFM) measurement at room temperature demonstrated ferroelectricity in the BT-BFO thin film. PFM results also reveal the repeatable polarization inversion by poling, manifesting its potential for read-write operation in NVM devices. The electroforming-free and ferroelectric polarization coupled electrical behaviour demonstrated excellent resistive switching with high retention time, cyclic endurance, and low set/reset voltages. X-ray photoelectron spectroscopy was utilized to determine the band alignment at the BT-BFO and Nb:STO heterojunction, and it exhibited staggered band alignment. This heterojunction is found to behave as an efficient ultraviolet photo-detector with low rise and fall time. The architecture also demonstrates half-wave rectification under low and high input signal frequencies, where the output distortion is minimal. The results provide avenue for an electrical switch that can regulate the pixels in low or high frequency images. Combined this work paves the pathway towards designing future generation low-power ferroelectric based microelectronic devices by merging both electrical and photovoltaic properties of BT-BFO materials.

  18. Effects of background oxygen pressure on dielectric and ferroelectric properties of epitaxial (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrTiO3

    NASA Astrophysics Data System (ADS)

    Abazari, M.; Akdoǧan, E. K.; Safari, A.

    2008-11-01

    Oxygen partial pressure (PO_2) in pulsed laser deposition significantly influences the composition, microstructure, and electrical properties of epitaxial misfit strain-relieved 450nm ⟨001⟩ oriented epitaxial (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrRuO3 coated SrTiO3. Films deposited at 400mTorr exhibit high remnant and saturated polarization of 7.5 and 16.5μC /cm2, respectively, which is ˜100% increase over the ones grown at 100mTorr. The dielectric constant linearly increases from 220 to 450 with increasing PO2. The observed changes in surface morphology of the films and their properties are shown to be due to the suppression of volatile A-site cation loss.

  19. Enhanced photoelectrical performance of dye-sensitized solar cells with double-layer TiO2 on perovskite SrTiO3 substrate

    NASA Astrophysics Data System (ADS)

    Liu, Qiuhong; Sun, Qiong; Zhang, Min; Li, Yang; Zhao, Mei; Dong, Lifeng

    2016-04-01

    In this research, perovskite SrTiO3 particles are synthesized by a hydrothermal method, and TiO2 with a double-layer structure is grown on the SrTiO3 surface by a hydrolysis-condensation process. Structural characterizations reveal that TiO2 comprises of two phases: anatase film at the bottom and single-crystal rutile nanorods grown along the [110] direction on top. The TiO2-SrTiO3 composite film is investigated as photoanode material for dye-sensitized solar cells. In comparison with pure TiO2 and SrTiO3, the composite photoanode shows a much better performance in photoelectric conversion efficiency (1.35 %), which is about 2 and 100 times as efficient as pure TiO2 and SrTiO3, respectively. This indicates that the composite structure can facilitate charge carrier transfer and reduce electron-hole recombination to enhance photoelectrical properties of TiO2-based photoanode materials.

  20. Influence of applied electric field annealing on the microwave properties of (Ba0.5Sr0.5)TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Cho, Kwang-Hwan; Lee, Chil-Hyoung; Kang, Chong-Yun; Yoon, Seok-Jin; Lee, Young-Pak

    2007-04-01

    The effect of heat treatment in electric field on the structure and dielectric properties at microwave range of rf magnetron sputtering derived (Ba0.5Sr0.5)TiO3 thin films have been studied. It has been demonstrated that postannealing in the proper electric field can increase the dielectric constant and the tunability. The increased out-of-plane lattice constant in the electric-annealed films indicated the formation of small polar regions with tetragonal structure, which are responsible for the increased dielectric constant and tunability. It was proposed that the segregation of Ti3+ ions caused by electric annealing could induce the formation of BaTiO3-like regions, which are ferroelectric at room temperature. And in dielectric loss, as the Ti-O bonding lengths increase, the energy scattering on the ferroelectric mode also increases. So, the value of dielectric loss is slightly increased.

  1. Enhanced magnetic and thermoelectric properties in epitaxial polycrystalline SrRuO3 thin films.

    PubMed

    Woo, Sungmin; Lee, Sang A; Mun, Hyeona; Choi, Young Gwan; Zhung, Chan June; Shin, Soohyeon; Lacotte, Morgane; David, Adrian; Prellier, Wilfrid; Park, Tuson; Kang, Won Nam; Lee, Jong Seok; Kim, Sung Wng; Choi, Woo Seok

    2018-03-01

    Transition metal oxide thin films show versatile electric, magnetic, and thermal properties which can be tailored by deliberately introducing macroscopic grain boundaries via polycrystalline solids. In this study, we focus on the modification of magnetic and thermal transport properties by fabricating single- and polycrystalline epitaxial SrRuO 3 thin films using pulsed laser epitaxy. Using the epitaxial stabilization technique with an atomically flat polycrystalline SrTiO 3 substrate, an epitaxial polycrystalline SrRuO 3 thin film with the crystalline quality of each grain comparable to that of its single-crystalline counterpart is realized. In particular, alleviated compressive strain near the grain boundaries due to coalescence is evidenced structurally, which induced the enhancement of ferromagnetic ordering of the polycrystalline epitaxial thin film. The structural variations associated with the grain boundaries further reduce the thermal conductivity without deteriorating the electronic transport, and lead to an enhanced thermoelectric efficiency in the epitaxial polycrystalline thin films, compared with their single-crystalline counterpart.

  2. Room temperature magnetoelectric coupling in BaTi{sub 1−x}Cr{sub x}O{sub 3} multiferroic thin films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sundararaj, Anuraj; Chandrasekaran, Gopalakrishnan, E-mail: hod.nano@ktr.srmuniv.ac.in; Therese, Helen Annal

    2016-01-14

    We report on room temperature (RT) magnetoelectric coupling in tetragonal BaTi{sub 1−x}Cr{sub x}O{sub 3} thin film multiferroics (BTCO) sputter deposited on (100) SrTiO{sub 3} (where x = 0.005, 0.01, 0.02, and 0.03). As-deposited thin films are vacuum annealed by electron beam rapid thermal annealing technique. 50 nm thick BTCO with “x = 0.01” shows RT ferromagnetic and ferroelectric response with saturation magnetic moment of 1120 emu/cc and polarization of 14.7 microcoulomb/cm{sup 2}. Piezoresponse/magnetic force microscope images shows RT magnetoelectric coupling in BTCO with “x = 0.01,” which is confirmed using magnetocapacitance measurement where an increase in capacitance from 17.5 pF to 18.4 pF is observed with an applied magneticmore » field.« less

  3. Epitaxial thin films of Dirac semimetal antiperovskite Cu3PdN

    NASA Astrophysics Data System (ADS)

    Quintela, C. X.; Campbell, N.; Shao, D. F.; Irwin, J.; Harris, D. T.; Xie, L.; Anderson, T. J.; Reiser, N.; Pan, X. Q.; Tsymbal, E. Y.; Rzchowski, M. S.; Eom, C. B.

    2017-09-01

    The growth and study of materials showing novel topological states of matter is one of the frontiers in condensed matter physics. Among this class of materials, the nitride antiperovskite Cu3PdN has been proposed as a new three-dimensional Dirac semimetal. However, the experimental realization of Cu3PdN and the consequent study of its electronic properties have been hindered due to the difficulty of synthesizing this material. In this study, we report fabrication and both structural and transport characterization of epitaxial Cu3PdN thin films grown on (001)-oriented SrTiO3 substrates by reactive magnetron sputtering and post-annealed in NH3 atmosphere. The structural properties of the films, investigated by x-ray diffraction and scanning transmission electron microscopy, establish single phase Cu3PdN exhibiting cube-on-cube epitaxy (001)[100]Cu3PdN||(001)[100]SrTiO3. Electrical transport measurements of as-grown samples show metallic conduction with a small temperature coefficient of the resistivity of 1.5 × 10-4 K-1 and a positive Hall coefficient. Post-annealing in NH3 results in the reduction of the electrical resistivity accompanied by the Hall coefficient sign reversal. Using a combination of chemical composition analyses and ab initio band structure calculations, we discuss the interplay between nitrogen stoichiometry and magneto-transport results in the framework of the electronic band structure of Cu3PdN. Our successful growth of thin films of antiperovskite Cu3PdN opens the path to further investigate its physical properties and their dependence on dimensionality, strain engineering, and doping.

  4. Microwave Characterization of Ba-Substituted PZT and ZnO Thin Films.

    PubMed

    Tierno, Davide; Dekkers, Matthijn; Wittendorp, Paul; Sun, Xiao; Bayer, Samuel C; King, Seth T; Van Elshocht, Sven; Heyns, Marc; Radu, Iuliana P; Adelmann, Christoph

    2018-05-01

    The microwave dielectric properties of (Ba 0.1 Pb 0.9 )(Zr 0.52 Ti 0.48 )O 3 (BPZT) and ZnO thin films with thicknesses below were investigated. No significant dielectric relaxation was observed for both BPZT and ZnO up to 30 GHz. The intrinsic dielectric constant of BPZT was as high as 980 at 30 GHz. The absence of strong dielectric dispersion and loss peaks in the studied frequency range can be linked to the small grain diameters in these ultrathin films.

  5. Formation of orbital-selective electron states in LaTiO3/SrTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Lechermann, Frank; Boehnke, Lewin; Grieger, Daniel

    2013-06-01

    The interface electronic structure of correlated LaTiO3/SrTiO3 superlattices is investigated by means of the charge self-consistent combination of the local density approximation (LDA) to density functional theory with dynamical mean-field theory. Utilizing a pseudopotential technique together with a continuous-time quantum Monte Carlo approach, the resulting complex multiorbital electronic states are addressed in a coherent fashion beyond static mean field. General structural relaxations are taken into account on the LDA level and cooperate with the driving forces from strong electronic correlations. This alliance leads to a Ti(3dxy) dominated low-energy quasiparticle peak and a lower Hubbard band in line with photoemission studies. Furthermore correlation effects close to the band-insulating bulk SrTiO3 limit as well as the Mott-insulating bulk LaTiO3 limit are studied via realistic single-layer embeddings.

  6. Optical properties of amorphous Ba0.7Sr0.3TiO3 thin films obtained by metal organic decomposition technique

    NASA Astrophysics Data System (ADS)

    Qiu, Fei; Xu, Zhimou

    2009-08-01

    In this study, the amorphous Ba0.7Sr0.3TiO3 (BST0.7) thin films were grown onto fused quartz and silicon substrates at low temperature by using a metal organic decomposition (MOD)-spin-coating procedure. The optical transmittance spectrum of amorphous BST0.7 thin films on fused quartz substrates has been recorded in the wavelength range 190~900 nm. The films were highly transparent for wavelengths longer than 330 nm; the transmission drops rapidly at 330 nm, and the cutoff wavelength occurs at about 260 nm. In addition, we also report the amorphous BST0.7 thin film groove-buried type waveguides with 90° bent structure fabricated on Si substrates with 1.65 μm thick SiO2 thermal oxide layer. The design, fabrication and optical losses of amorphous BST0.7 optical waveguides were presented. The amorphous BST0.7 thin films were grown onto the SiO2/Si substrates by using a metal organic decomposition (MOD)-spin-coating procedure. The optical propagation losses were about 12.8 and 9.4 dB/cm respectively for the 5 and 10 μm wide waveguides at the wavelength of 632.8 nm. The 90° bent structures with a small curvature of micrometers were designed on the basis of a double corner mirror structure. The bend losses were about 1.2 and 0.9 dB respectively for 5 and 10 μm wide waveguides at the wavelength of 632.8 nm. It is expected for amorphous BST0.7 thin films to be used not only in the passive optical interconnection in monolithic OEICs but also in active waveguide devices on the Si chip.

  7. MOCVD (Ba{sub x}Sr{sub 1-x})Ti{sub 1+y}O{sub 3+z} (BST) thin films for high frequency tunable devices.

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Baumann, P. K.; Kaufman, D. Y.; Im, J.

    2001-01-01

    We have investigated the structural and electrical characteristics of (Ba{sub x}Sr{sub 1-x})Ti{sub 1+y}O{sub 3+z} (BST) thin films synthesized at 650{sup o}C on Pt/SiO{sub 2}/Si substrates using a large area, vertical metalorganic chemical vapor deposition (MOCVD) reactor equipped with a liquid delivery system. Films with a Ba/Sr ratio of 70/30 were studied, as determined using X-ray fluorescence spectroscopy (XRF) and Rutherford backscattering spectrometry (RBS). A substantial reduction of the dielectric loss was achieved when annealing the entire capacitor structure in air at 700{sup o}C. Dielectric tunability as high as 2.3:1 was measured for BST capacitors with the currently optimized processing conditions.

  8. Dynamic interface rearrangement in LaFeO3/n -SrTiO3 heterojunctions

    NASA Astrophysics Data System (ADS)

    Spurgeon, Steven R.; Sushko, Peter V.; Chambers, Scott A.; Comes, Ryan B.

    2017-11-01

    Thin-film synthesis methods that have developed over the past decades have unlocked emergent interface properties ranging from conductivity to ferroelectricity. However, our attempts to exercise precise control over interfaces are constrained by a limited understanding of growth pathways and kinetics. Here we demonstrate that shuttered molecular beam epitaxy induces rearrangements of atomic planes at a polar/nonpolar junction of LaFeO3 (LFO)/n -SrTiO3 (STO) depending on the substrate termination. Surface characterization confirms that substrates with two different (TiO2 and SrO) terminations were prepared prior to LFO deposition; however, local electron-energy-loss spectroscopy measurements of the final heterojunctions show a predominantly LaO/TiO2 interfacial junction in both cases. Ab initio simulations suggest that the interfaces can be stabilized by trapping extra oxygen (in LaO/TiO2) and forming oxygen vacancies (in FeO2/SrO), which points to different growth kinetics in each case and may explain the apparent disappearance of the FeO2/SrO interface. We conclude that judicious control of deposition time scales can be used to modify growth pathways, opening new avenues to control the structure and properties of interfacial systems.

  9. Epitaxial Ferroelectric Ba(0.5)Sr(0.5)TiO3 Thin Films for Room-Temperature High-Frequency Tunable Element Applications

    NASA Technical Reports Server (NTRS)

    Chen, C. L.; Feng, H. H.; Zhang, Z.; Brazdeikis, A.; Miranda, F. A.; VanKeuls, F. W.; Romanofsky, R. R.; Huang, Z. J.; Liou, Y.; Chu, W. K.; hide

    1999-01-01

    Perovskite Ba(0.5)SR(0.5)TiO3 thin films have been synthesized on (001) LaAl03 substrates by pulsed laser ablation. Extensive X-ray diffraction, rocking curve, and pole-figure studies suggest that the films are c-axis oriented and exhibit good in-plane relationship of <100>(sub BSTO)//<100>(sub LAO). Rutherford Backscattering Spectrometry studies indicate that the epitaxial films have excellent crystalline quality with an ion beam minimum yield chi(sub min) Of only 2.6 %. The dielectric property measurements by the interdigital technique at 1 MHz show room temperature values of the relative dielectric constant, epsilon(sub r), and loss tangent, tan(sub delta), of 1430 and 0.007 with no bias, and 960 and 0.001 with 35 V bias, respectively. The obtained data suggest that the as-grown Ba(0.5)SR(0.5)TiO3 films can be used for development of room-temperature high-frequency tunable elements.

  10. Probing the bulk ionic conductivity by thin film hetero-epitaxial engineering

    NASA Astrophysics Data System (ADS)

    Pergolesi, Daniele; Roddatis, Vladimir; Fabbri, Emiliana; Schneider, Christof W.; Lippert, Thomas; Traversa, Enrico; Kilner, John A.

    2015-02-01

    Highly textured thin films with small grain boundary regions can be used as model systems to directly measure the bulk conductivity of oxygen ion conducting oxides. Ionic conducting thin films and epitaxial heterostructures are also widely used to probe the effect of strain on the oxygen ion migration in oxide materials. For the purpose of these investigations a good lattice matching between the film and the substrate is required to promote the ordered film growth. Moreover, the substrate should be a good electrical insulator at high temperature to allow a reliable electrical characterization of the deposited film. Here we report the fabrication of an epitaxial heterostructure made with a double buffer layer of BaZrO3 and SrTiO3 grown on MgO substrates that fulfills both requirements. Based on such template platform, highly ordered (001) epitaxially oriented thin films of 15% Sm-doped CeO2 and 8 mol% Y2O3 stabilized ZrO2 are grown. Bulk conductivities as well as activation energies are measured for both materials, confirming the success of the approach. The reported insulating template platform promises potential application also for the electrical characterization of other novel electrolyte materials that still need a thorough understanding of their ionic conductivity.

  11. Flux pinning enhancement in thin films of Y3 Ba5 Cu8O18.5 + d

    NASA Astrophysics Data System (ADS)

    Aghabagheri, S.; Mohammadizadeh, M. R.; Kameli, P.; Salamati, H.

    2018-06-01

    YBa2Cu3O7 (Y123) and Y3Ba5Cu8O18 (Y358) thin films were deposited by pulsed laser deposition method. XRD analysis shows both films grow in c axis orientation. Resistivity versus temperature analysis shows superconducting transition temperature was about 91.2 K and 91.5 K and transition width for Y358 and Y123 films was about 0.6 K and 1.6 K, respectively. Analysis of the temperature dependence of the AC susceptibility near the transition temperature, employing Bean's critical state model, indicates that intergranular critical current density for Y358 films is more than twice of intergranular critical current density of Y123 films. Thus, flux pining is stronger in Y358 films. Weak links in the both samples is of superconductor-normal-superconductor (SNS) type irrespective of stoichiometry.

  12. Temperature-dependent band structure of SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Raslan, Amany; Lafleur, Patrick; Atkinson, W. A.

    2017-02-01

    We build a theoretical model for the electronic properties of the two-dimensional (2D) electron gas that forms at the interface between insulating SrTiO3 and a number of polar cap layers, including LaTiO3, LaAlO3, and GdTiO3. The model treats conduction electrons within a tight-binding approximation and the dielectric polarization via a Landau-Devonshire free energy that incorporates strontium titanate's strongly nonlinear, nonlocal, and temperature-dependent dielectric response. The self-consistent band structure comprises a mix of quantum 2D states that are tightly bound to the interface and quasi-three-dimensional (3D) states that extend hundreds of unit cells into the SrTiO3 substrate. We find that there is a substantial shift of electrons away from the interface into the 3D tails as temperature is lowered from 300 K to 10 K. This shift is least important at high electron densities (˜1014cm-2 ) but becomes substantial at low densities; for example, the total electron density within 4 nm of the interface changes by a factor of two for 2D electron densities ˜1013cm-2 . We speculate that the quasi-3D tails form the low-density high-mobility component of the interfacial electron gas that is widely inferred from magnetoresistance measurements.

  13. Band gap and mobility of epitaxial perovskite BaSn1 -xHfxO3 thin films

    NASA Astrophysics Data System (ADS)

    Shin, Juyeon; Lim, Jinyoung; Ha, Taewoo; Kim, Young Mo; Park, Chulkwon; Yu, Jaejun; Kim, Jae Hoon; Char, Kookrin

    2018-02-01

    A wide band-gap perovskite oxide BaSn O3 is attracting much attention due to its high electron mobility and oxygen stability. On the other hand, BaHf O3 was recently reported to be an effective high-k gate oxide. Here, we investigate the band gap and mobility of solid solutions of BaS n1 -xH fxO3 (x =0 -1 ) (BSHO) as a basis to build advanced perovskite oxide heterostructures. All the films were epitaxially grown on MgO substrates using pulsed laser deposition. Density functional theory calculations confirmed that Hf substitution does not create midgap states while increasing the band gap. From x-ray diffraction and optical transmittance measurements, the lattice constants and the band-gap values are significantly modified by Hf substitution. We also measured the transport properties of n -type La-doped BSHO films [(Ba ,La ) (Sn ,Hf ) O3 ] , investigating the feasibility of modulation doping in the BaSn O3/BSHO heterostructures. The Hall measurement data revealed that, as the Hf content increases, the activation rate of the La dopant decreases and the scattering rate of the electrons sharply increases. These properties of BSHO films may be useful for applications in various heterostructures based on the BaSn O3 system.

  14. Localized versus itinerant states created by multiple oxygen vacancies in SrTiO3

    NASA Astrophysics Data System (ADS)

    Jeschke, Harald O.; Shen, Juan; Valentí, Roser

    2015-02-01

    Oxygen vacancies in strontium titanate surfaces (SrTiO3) have been linked to the presence of a two-dimensional electron gas with unique behavior. We perform a detailed density functional theory study of the lattice and electronic structure of SrTiO3 slabs with multiple oxygen vacancies, with a main focus on two vacancies near a titanium dioxide terminated SrTiO3 surface. We conclude based on total energies that the two vacancies preferably inhabit the first two layers, i.e. they cluster vertically, while in the direction parallel to the surface, the vacancies show a weak tendency towards equal spacing. Analysis of the nonmagnetic electronic structure indicates that oxygen defects in the surface TiO2 layer lead to population of Ti {{t}2g} states and thus itinerancy of the electrons donated by the oxygen vacancy. In contrast, electrons from subsurface oxygen vacancies populate Ti eg states and remain localized on the two Ti ions neighboring the vacancy. We find that both the formation of a bound oxygen-vacancy state composed of hybridized Ti 3eg and 4p states neighboring the oxygen vacancy as well as the elastic deformation after extracting oxygen contribute to the stabilization of the in-gap state.

  15. First-principles Studies of Ferroelectricity in BiMnO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Wang, Yun-Peng; Cheng, Hai-Ping

    The ferroelectricity in BiMnO3 thin films is a long-standing problem. We employed a first-principles density functional theory with inclusion of the local Hubbard Coulomb (U) and exchange (J) terms. The parameters U and J are optimized to reproduce the atomic structure and the energy gap of bulk C2/c BiMnO3. With these optimal U and J parameters, the calculated ferromagnetic Curie temperature and lattice dynamics properties agree with experiments. We then studied the ferroelectricity in few-layer BiMnO3 thin films on SrTiO3(001) substrates. Our calculations identified ferroelectricity in monolayer, bilayer and trilayer BiMnO3 thin films. We find that the energy barrier for 90° rotation of electric polarization is about 3 - 4 times larger than that of conventional ferroelectric materials. This work was supported by the US Department of Energy (DOE), Office of Basic Energy Sciences (BES), under Contract No. DE-FG02-02ER45995. Computations were done using the utilities of the National Energy Research Scientific Computing Center (NERSC).

  16. Effect of O2 partial pressure on post annealed Ba2YCu3O(7-delta) thin films

    NASA Astrophysics Data System (ADS)

    Phillps, J. M.; Siegal, M. P.; Hou, S. Y.; Tiefel, T. H.; Marshall, J. H.

    1992-04-01

    Epitaxial films of Ba2YCu3O(7-delta) (BYCO) as thin as 250 A and with J(sub c)'s approaching those of the best in situ grown films can be formed by co-evaporating BaF2, Y, and Cu followed by a two-stage anneal. High quality films of these thicknesses become possible if low oxygen partial pressure (p(O2) = 4.3 Torr) is used during the high temperature portion of the anneal (T(sub a)). The BYCO melt line is the upper limit for T(sub a). The use of low p(O2) shifts the window for stable BYCO film growth to lower temperature, which allows the formation of smooth films with greater microstructural disorder than is found in films grown in p(O2) = 740 Torr at higher T(sub a). The best films annealed in p(O2) = 4.3 Torr have J(sub c) values a factor of four higher than do comparable films annealed in p(O2) = 740 Torr. The relationship between the T(sub a) required to grow films with the strongest pinning force and p(O2) is log (p(O2)) proportional to T(sub a) exp(1 exp a) independent of growth method (in situ or ex situ) over a range of five orders of magnitude of p(O2).

  17. Combinatorial studies of (1-x)Na0.5Bi0.5TiO3-xBaTiO3 thin-film chips

    NASA Astrophysics Data System (ADS)

    Cheng, Hong-Wei; Zhang, Xue-Jin; Zhang, Shan-Tao; Feng, Yan; Chen, Yan-Feng; Liu, Zhi-Guo; Cheng, Guang-Xi

    2004-09-01

    Applying a combinatorial methodology, (1-x)Na0.5Bi0.5TiO3-xBaTiO3 (NBT-BT) thin-film chips were fabricated on (001)-LaAlO3 substrates by pulsed laser deposition with a few quaternary masks. A series of NBT-BT library with the composition of BT ranged from 0 to 44% was obtained with uniform composition and well crystallinity. The relation between the concentration of NBT-BT and their structural and dielectric properties were investigated by x-ray diffraction (XRD), evanescent microwave probe, atomic force microscopy, and Raman spectroscopy. An obvious morphotropic phase boundary (MPB) was established to be about 9% BT by XRD, Raman frequency shift, and dielectric anomaly, different from the well-known MPB of the materials. The result shows the high efficiency of combinatorial method in searching new relaxor ferroelectrics.

  18. Effect of double layer thickness on magnetoelectric coupling in multiferroic BaTiO3-Bi0.95Gd0.05FeO3 multilayers

    NASA Astrophysics Data System (ADS)

    Hohenberger, S.; Lazenka, V.; Temst, K.; Selle, S.; Patzig, C.; Höche, T.; Grundmann, M.; Lorenz, M.

    2018-05-01

    The effect of double-layer thickness and partial substitution of Bi3+ by Gd3+ is demonstrated for multiferroic BaTiO3–BiFeO3 2–2 heterostructures. Multilayers of 15 double layers of BaTiO3 and Bi0.95Gd0.05FeO3 were deposited onto (0 0 1) oriented SrTiO3 substrates by pulsed laser deposition with various double layer thicknesses. X-ray diffraction and high resolution transmission electron microscopy investigations revealed a systematic strain tuning with layer thickness via coherently strained interfaces. The multilayers show increasingly enhanced magnetoelectric coupling with reduced double layer thickness. The maximum magnetoelectric coupling coefficient was measured to be as high as 50.8 V cm‑1 Oe‑1 in 0 T DC bias magnetic field at room temperature, and 54.9 V cm‑1 Oe‑1 above 3 T for the sample with the thinnest double layer thickness of 22.5 nm. This enhancement is accompanied by progressively increasing perpendicular magnetic anisotropy and compressive out-of-plane strain. To understand the origin of the enhanced magnetoelectric coupling in such multilayers, the temperature and magnetic field dependency of is discussed. The magnetoelectric performance of the Gd3+ substituted samples is found to be slightly enhanced when compared to unsubstituted BaTiO3–BiFeO3 multilayers of comparable double-layer thickness.

  19. Two-dimensional superconductivity induced by high-mobility carrier doping in LaTiO3/SrTiO3 hetero-structures

    NASA Astrophysics Data System (ADS)

    Biscaras, Johan; Hurand, S.; Palma, C.; Lesueur, J.; Bergeal, N.; Leboeuf, D.; Proust, C.; Rastogi, A.; Budhani, R. C.

    2013-03-01

    Transition metal oxides display a great variety of quantum electronic behaviors where correlations often play an important role. The achievement of high quality epitaxial interfaces involving such materials gives a unique opportunity to engineer artificial materials where new electronic orders take place. It has been shown recently that a two-dimensional electron gas 2DEG could form at the interface of two insulators such as LaAlO3 and SrTiO3, or LaTiO3 (a Mott insulator) and SrTiO3. We show that a superconducting two-dimensional electron gas is formed at the LaTiO3/SrTiO3 interface whose properties can be modulated by field effect using a metallic gate on the back of the substrate. The gas consists of two types of carriers : a majority of low-mobility carriers always present, and a few high-mobility ones that can be injected by electrostatic doping. The calculation of the electrons spatial distribution in the confinement potential shows that the high-mobility electrons responsible for superconductivity set at the edge of the gas whose extension can be tuned by field effect.

  20. Independent Control of the Magnetization in Ferromagnetic La2/3Sr1/3MnO3/SrTiO3/LaCoO3 Heterostructures Achieved by Epitaxial Lattice Mismatch.

    PubMed

    Rivas-Murias, Beatriz; Lucas, Irene; Jiménez-Cavero, Pilar; Magén, César; Morellón, Luis; Rivadulla, Francisco

    2016-03-09

    We report the effect of interface symmetry-mismatch on the magnetic properties of LaCoO3 (LCO) thin films. Growing epitaxial LCO under tensile strain on top of cubic SrTiO3 (STO) produces a contraction along the c axis and a characteristic ferromagnetic response. However, we report here that ferromagnetism in LCO is completely suppressed when grown on top of a buffer layer of rhombohedral La2/3Sr1/3MnO3 (LSMO), in spite of identical in-plane and out-of-plane lattice deformation. This confirms that it is the lattice symmetry mismatch and not just the total strain, which determines the magnetism of LCO. On the basis of this control over the magnetic properties of LCO, we designed a multilayered structure to achieve independent rotation of the magnetization in ferromagnetic insulating LCO and half-metallic ferromagnet LSMO. This is an important step forward for the design of spin-filtering tunnel barriers based on LCO.

  1. Significant role of antiferromagnetic GdFeO3 on multiferroism of bilayer thin films

    NASA Astrophysics Data System (ADS)

    Shah, Jyoti; Bhatt, Priyanka; Dayas, K. Diana Diana; Kotnala, R. K.

    2018-02-01

    Inversion of BaTiO3 and GdFeO3 thin films in bilayer configuration has been deposited by pulsed laser deposition technique. A significant effect of strain on thin film has been observed by X-ray diffraction analysis. Tensile strain of 1.04% and 0.23% has been calculated by X-ray diffraction results. Higher polarization value 70.4 μC cm-2 has been observed by strained BaTiO3 film in GdFeO3/BaTiO3 bilayer film. Strained GdFeO3 film in BaTiO3/GdFeO3 bilayer configuration exhibited ferromagnetic behaviour showed maximum magnetization value of 50 emu gm-1. Magnetoelectric coupling coefficient of bilayer films have been carried out by dynamic method. Room temperature magnetoelectric coupling 2500 mV cm-1-Oe has been obtained for BaTiO3/GdFeO3 bilayer film. The high ME coupling of the BaTiO3/GdFeO3 bilayer film reveals strong interfacial coupling between ferroelectric and ferromagnetic dipoles. On magnetoelectric coupling coefficient effect of ferromagnetic GdFeO3 layer has a significant role. Such high value of ME coupling may be useful in realization of magnetoelectric RAM (MeRAM) application.

  2. Thermal strain-induced dielectric anisotropy in Ba0.7Sr0.3TiO3 thin films grown on silicon-based substrates

    NASA Astrophysics Data System (ADS)

    Zhu, X. H.; Guigues, B.; Defaÿ, E.; Dubarry, C.; Aïd, M.

    2009-07-01

    Dielectric properties of Ba0.7Sr0.3TiO3 (BST) thin films, which were prepared on silicon-based substrates by ion beam sputtering and postdeposition annealing method, were systematically investigated in different electrode configurations of metal-insulator-metal and coplanar interdigital capacitors. It was found that a large dielectric anisotropy exists in the films with better in-plane dielectric properties (higher dielectric permittivity and tunability) than those along the out-of-plane direction. The observed anisotropic dielectric responses are explained qualitatively in terms of a thermal strain effect that is related to dissimilar film strains along the in-plane and out-of-plane directions. Another reason for the dielectric anisotropy is due to different influences of the interfacial low-dielectric layer between the BST film and the substrate (metal electrode).

  3. The effect of temperature cycling typical of low earth orbit satellites on thin films of YBa2Cu3O(7-x)

    NASA Technical Reports Server (NTRS)

    Mogro-Campero, A.; Turner, L. G.; Bogorad, A.; Herschitz, R.

    1990-01-01

    The refrigeration of superconductors in space poses a challenging problem. The problem could be less severe if superconducting materials would not have to be cooled when not in use. Thin films of the YBa2Cu3O(7-x) (YBCO) superconductor were subjected to thermal cycling, which was carried out to simulate a large number of eclipses of a low earth orbit satellite. Electrical measurements were performed to find the effect of the temperature cycling. Thin films of YBCO were formed by coevaporation of Y, BaF2, and Cu and postannealing in wet oxygen at 850 C for 3.5 h. The substrates used were (100) SrTiO3, polycrystalline alumina, and oxidized silicon; the last two have an evaporated zirconia layer. Processing and microstructure studies of these types of films have been published. THe zero resistance transition temperatures of the samples used in this study were 91, 82, and 86 K, respectively. The samples were characterized by four point probe electrical measurements as a function of temperature. The parameters measured were: the zero resistance transition temperature, the 10 to 90 percent transition width, and the room temperature resistance, normalized to that measured before temperature cycling. The results for two samples are presented. Each sample had a cumulative exposure. Cycling in atmospheric pressure nitrogen was performed at a rate of about 60 cycles per day, whereas in vacuum the rate was only about 10 cycles per day. The results indicate only little or no changes in the parameters measured. Degradation of superconducting thin films of YBCO has been reported due to storage in nitrogen. It is believed that the relatively good performance of films after temperature cycling is related to the fact that BaF2 was used as an evaporation source. The latest result on extended temperature cycling indicates significant degradation. Further tests of extended cycling will be carried out to provide additional data and to clarify this preliminary finding.

  4. Single-crystalline BaTiO3 films grown by gas-source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Matsubara, Yuya; Takahashi, Kei S.; Tokura, Yoshinori; Kawasaki, Masashi

    2014-12-01

    Thin BaTiO3 films were grown on GdScO3 (110) substrates by metalorganic gas-source molecular beam epitaxy. Titanium tetra-isopropoxide (TTIP) was used as a volatile precursor that provides a wide growth window of the supplied TTIP/Ba ratio for automatic adjustment of the film composition. Within the growth window, compressively strained films can be grown with excellent crystalline quality, whereas films grown outside of the growth window are relaxed with inferior crystallinity. This growth method will provide a way to study the intrinsic properties of ferroelectric BaTiO3 films and their heterostructures by precise control of the stoichiometry, structure, and purity.

  5. Metal-Insulator Transition of strained SmNiO3 Thin Films: Structural, Electrical and Optical Properties

    PubMed Central

    Torriss, B.; Margot, J.; Chaker, M.

    2017-01-01

    Samarium nickelate (SmNiO3) thin films were successfully synthesized on LaAlO3 and SrTiO3 substrates using pulsed-laser deposition. The Mott metal-insulator (MI) transition of the thin films is sensitive to epitaxial strain and strain relaxation. Once the strain changes from compressive to tensile, the transition temperature of the SmNiO3 samples shifts to slightly higher values. The optical conductivity reveals the strong dependence of the Drude spectral weight on the strain relaxation. Actually, compressive strain broadens the bandwidth. In contrast, tensile strain causes the effective number of free carriers to reduce which is consistent with the d-band narrowing. PMID:28098240

  6. Novel organic semiconductors and a high capacitance gate dielectric for organic thin film transistors

    NASA Astrophysics Data System (ADS)

    Cai, Xiuyu

    2007-12-01

    Organic semiconductors are attracting more and more interest as a promising set of materials in the field of electronics research. This thesis focused on several new organic semiconductors and a novel high-kappa dielectric thin film (SrTiO3), which are two essential parts in Organic Thin Film Transistors (OTFTs). Structure and morphology of thin films of tricyanovinyl capped oligothiophenes were studied using atomic force microscopy and x-ray diffraction. Thin film transistors of one compound exhibited a reasonable electron mobility of 0.02 cm2/Vs. Temperature dependent measurements on the thin film transistor based on this compound revealed shallow trap states that were interpreted in terms of a multiple trap and release model. Moreover, inversion of the majority charge carrier type from electrons to holes was observed when the number of oligothiophene rings increased to six and ambipolar transport behavior was observed for tricyanovinyl sexithiophene. Another interesting organic semiconductor compound is the fluoalkylquarterthiophene, which showed ambipolar transport and large hysteresis in the transfer curve. Due to the bistable state at floating gate, the thin film transistor was exploited to study non-volatile floating gate memory effects. The temperature dependence of the retention time for this memory device revealed that the electron trapping was an activated process. Following the earlier work on hybrid acene-thiophene organic semiconductors, new compounds with similar structure were studied to reveal the mechanism of the air-stability exhibited by some compounds. They all formed highly crystalline thin films and showed reasonable device performances which are well correlated with the molecular structures, thin film microstructures, and solid state packing. The most air-stable compound had no observable degradation with exposure to air for 15 months. SrTiO3 was developed to be employed in OTFTs. Optimization of thin film growth was performed using reactive

  7. Stressor-layer-induced elastic strain sharing in SrTiO 3 complex oxide sheets

    DOE PAGES

    Tilka, J. A.; Park, J.; Ahn, Y.; ...

    2018-02-26

    A precisely selected elastic strain can be introduced in submicron-thick single-crystal SrTiO 3 sheets using a silicon nitride stressor layer. A conformal stressor layer deposited using plasma-enhanced chemical vapor deposition produces an elastic strain in the sheet consistent with the magnitude of the nitride residual stress. Synchrotron x-ray nanodiffraction reveals that the strain introduced in the SrTiO 3 sheets is on the order of 10 -4, matching the predictions of an elastic model. Using this approach to elastic strain sharing in complex oxides allows the strain to be selected within a wide and continuous range of values, an effect notmore » achievable in heteroepitaxy on rigid substrates.« less

  8. Stressor-layer-induced elastic strain sharing in SrTiO 3 complex oxide sheets

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tilka, J. A.; Park, J.; Ahn, Y.

    A precisely selected elastic strain can be introduced in submicron-thick single-crystal SrTiO 3 sheets using a silicon nitride stressor layer. A conformal stressor layer deposited using plasma-enhanced chemical vapor deposition produces an elastic strain in the sheet consistent with the magnitude of the nitride residual stress. Synchrotron x-ray nanodiffraction reveals that the strain introduced in the SrTiO 3 sheets is on the order of 10 -4, matching the predictions of an elastic model. Using this approach to elastic strain sharing in complex oxides allows the strain to be selected within a wide and continuous range of values, an effect notmore » achievable in heteroepitaxy on rigid substrates.« less

  9. Studies on novel BiyXz-TiO2/SrTiO3 composites: Surface properties and visible light-driven photoactivity

    NASA Astrophysics Data System (ADS)

    Marchelek, Martyna; Grabowska, Ewelina; Klimczuk, Tomasz; Lisowski, Wojciech; Giamello, Elio; Zaleska-Medynska, Adriana

    2018-03-01

    A series of novel BiyXz-TiO2/SrTiO3 composites were prepared by multistep synthesis route. The as-prepared photocatalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), Fourier transform infrared (FT-IR), Raman spectra and BET analysis. The photocatalytic activity test was performed in aqueous solution of phenol under the irradiation of visible light range (λ ≥ 420 nm). Obtained results revealed that the BiOI_TiO2/SrTiO3 sample exhibit the highest photocatalytic activity under visible irradiation (0.6 μmol/dm3/min). Thus, it was demonstrated that modification of the TiO2/SrTiO3 microspheres by flowers-like structure made of bismuth oxyiodide resulted in enhancement of photocatalytic activity under visible light. The role of active species during the decomposition process of organic compound was investigated using different types of active species scavengers as well as electron paramagnetic resonance analysis (EPR). The study showed that in the BiOI_TiO2/SrTiO3/Vis system the holes (h+) plays relevant role in phenol decomposition. Furthermore, the stability and recyclable properties of obtained BiOI_TiO2/SrTiO3 sample were confirmed during three consecutive processes.

  10. Micrometer-Scale Ballistic Transport of Electron Pairs in LaAlO_{3}/SrTiO_{3} Nanowires.

    PubMed

    Tomczyk, Michelle; Cheng, Guanglei; Lee, Hyungwoo; Lu, Shicheng; Annadi, Anil; Veazey, Joshua P; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Eom, Chang-Beom; Levy, Jeremy

    2016-08-26

    High-mobility complex-oxide heterostructures and nanostructures offer new opportunities for extending the paradigm of quantum transport beyond the realm of traditional III-V or carbon-based materials. Recent quantum transport investigations with LaAlO_{3}/SrTiO_{3}-based quantum dots reveal the existence of a strongly correlated phase in which electrons form spin-singlet pairs without becoming superconducting. Here, we report evidence for the micrometer-scale ballistic transport of electron pairs in quasi-1D LaAlO_{3}/SrTiO_{3} nanowire cavities. In the paired phase, Fabry-Perot-like quantum interference is observed, in sync with conductance oscillations observed in the superconducting regime (at a zero magnetic field). Above a critical magnetic field B_{p}, the electron pairs unbind and the conductance oscillations shift with the magnetic field. These experimental observations extend the regime of ballistic electronic transport to strongly correlated phases.

  11. Anisotropy of the Irreversibility Field for Zr-doped (Y,Gd)Ba 2<\\sub>Cu3<\\sub>O<7-x<\\sub> Thin Films up to 45 T

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tarantini, C.; Jaroszynski, J.; Kametani, F.

    2011-01-01

    The anisotropic irreversibility fieldBIrr of twoYBa2Cu3O7 x thin films dopedwith additional rare earth (RE)= (Gd, Y) and Zr and containing strong correlated pins (splayed BaZrO3 nanorods and RE2O3 anoprecipitates) has been measured over a very broad range up to 45 T at temperatures 56 K < T < Tc. We found that the experimental angular dependence of BIrr ( ) does not follow the mass anisotropy scaling BIrr ( ) = BIrr (0)(cos2 + 2 sin2 ) 1/2, where = (mc/mab)1/2 = 5 6 for the RE-doped Ba2Cu3O7 x (REBCO) crystals, mab and mc are the effective masses along themore » ab plane and the c-axis, respectively, and is the angle between B and the c-axis. For B parallel to the ab planes and to the c-axis correlated pinning strongly enhances BIrr , while at intermediate angles, BIrr ( ) follows the scaling behavior BIrr ( ) (cos2 + 2 RP sin2 ) 1/2 with the effective anisotropy factor RP 3 significantly smaller than the ass anisotropy would suggest. In spite of the strong effects of c-axis BaZrO3 nanorods, we found even greater enhancements of BIrr for fields along the ab planes than for fields parallel to the c-axis, as well as different temperature dependences of the correlated pinning contributions to BIrr for B//ab and B//c. Our results show that the dense and strong pins, which can now be incorporated into REBCO thin films in a controlled way, exert major and diverse effects on the measured vortex pinning anisotropy and the irreversibility field over wide ranges of B and T . In particular, we show that the relative contribution of correlated pinning to BIrr for B//c increases as the temperature increases due to the suppression of thermal fluctuations of vortices by splayed distribution of BaZrO3 nanorods.« less

  12. Excited configurations of hydrogen in the BaTiO3 -xHx perovskite lattice associated with hydrogen exchange and transport

    NASA Astrophysics Data System (ADS)

    Ito, T. U.; Koda, A.; Shimomura, K.; Higemoto, W.; Matsuzaki, T.; Kobayashi, Y.; Kageyama, H.

    2017-01-01

    Excited configurations of hydrogen in the oxyhydride BaTiO3 -xHx (x =0.1 -0.5 ), which are considered to be involved in its hydrogen transport and exchange processes, were investigated by positive muon spin relaxation spectroscopy using muonium (Mu) as a pseudoisotope of hydrogen. Muons implanted into the BaTiO3 -xHx perovskite lattice were mainly found in two qualitatively different metastable states. One was assigned to a highly mobile interstitial protonic state, which is commonly observed in perovskite oxides. The other was found to form an entangled two spin-1/2 system with the nuclear spin of an H- ion at the anion site. The structure of the (H,Mu) complex agrees well with that of a neutralized center containing two H- ions at a doubly charged oxygen vacancy, which was predicted to form in the SrTiO3 -δ perovskite lattice by a computational study [Y. Iwazaki et al., APL Mater. 2, 012103 (2014), 10.1063/1.4854355]. Above 100 K, interstitial Mu+ diffusion and retrapping to a deep defect were observed, which could be a rate-limiting step of macroscopic Mu/H transport in the BaTiO3 -xHx lattice.

  13. Engineered unique elastic modes at a BaTiO 3/2x1-Ge(001) interface

    DOE PAGES

    Kumah, D. P.; Dogan, M.; Ngai, J. H.; ...

    2016-03-07

    Here, the strong interaction at an interface between a substrate and thin film leads to epitaxy and provides a means of inducing structural changes in the epitaxial film. These induced material phases often exhibit technologically relevant electronic, magnetic, and functional properties. The 2×1 surface of a Ge(001) substrate applies a unique type of epitaxial constraint on thin films of the perovskite oxide BaTiO 3 where a change in bonding and symmetry at the interface leads to a non-bulk-like crystal structure of the BaTiO 3. While the complex crystal structure is predicted using first-principles theory, it is further shown that themore » details of the structure are a consequence of hidden phases found in the bulk elastic response of the BaTiO 3 induced by the symmetry of forces exerted by the germanium substrate.« less

  14. Engineered unique elastic modes at a BaTiO 3/2x1-Ge(001) interface

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kumah, D. P.; Dogan, M.; Ngai, J. H.

    Here, the strong interaction at an interface between a substrate and thin film leads to epitaxy and provides a means of inducing structural changes in the epitaxial film. These induced material phases often exhibit technologically relevant electronic, magnetic, and functional properties. The 2×1 surface of a Ge(001) substrate applies a unique type of epitaxial constraint on thin films of the perovskite oxide BaTiO 3 where a change in bonding and symmetry at the interface leads to a non-bulk-like crystal structure of the BaTiO 3. While the complex crystal structure is predicted using first-principles theory, it is further shown that themore » details of the structure are a consequence of hidden phases found in the bulk elastic response of the BaTiO 3 induced by the symmetry of forces exerted by the germanium substrate.« less

  15. Engineered Unique Elastic Modes at a BaTiO 3 / ( 2 × 1 ) - Ge ( 001 ) Interface

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kumah, D. P.; Dogan, M.; Ngai, J. H.

    The strong interaction at an interface between a substrate and thin film leads to epitaxy and provides a means of inducing structural changes in the epitaxial film. These induced material phases often exhibit technologically relevant electronic, magnetic, and functional properties. The 2×1 surface of a Ge(001) substrate applies a unique type of epitaxial constraint on thin films of the perovskite oxide BaTiO3 where a change in bonding and symmetry at the interface leads to a non-bulk-like crystal structure of the BaTiO3. While the complex crystal structure is predicted using first-principles theory, it is further shown that the details of themore » structure are a consequence of hidden phases found in the bulk elastic response of the BaTiO3 induced by the symmetry of forces exerted by the germanium substrate.« less

  16. Competition between structural instabilities in strained ABO3 nanostructures

    NASA Astrophysics Data System (ADS)

    Bousquet, E.

    2010-03-01

    In spite of their simple structure, the family of ABO3 compounds present a large variety of phase transitions involving polar and non polar distortions as well as magnetic orders. Here we will discuss the microscopic origin of these properties and how they are affected in nanostructures through the concept of structural instabilities. We will from the fact that the ferroelectric (FE) and the antiferrodistortive (AFD) instabilities are in competition at the bulk level and are strongly sensitive to pressure and strain. From these considerations we will describe the possibilities to tune this FE/AFD competition by playing with strain and interface engineering. To that end we will first consider the effect of epitaxial strain on BaTiO3, SrTiO3, PbTiO3 and CaTiO3 thin films. In all of these compounds, the epitaxial strain can strongly modify the phase diagrams giving rise to different pure or mixed FE/AFD ground states. We will also extend the discussion on magnetic perovskites like CaMnO3 and will present the different strategies to induce or tune multiferroic properties. Second we will focus on the interface effects as present in bicolor superlattices. As an example we will examine the case of PbTiO3/SrTiO3 superlattice and will show that it exhibits totally unique properties arising from unexpected FE/AFD couplings at the interface between the layers. We will then investigate to which extent similar types of FE/AFD couplings can be induced in other artificially layered systems. We will consider different bicolor superlattices obtained from the combination of PbTiO3, SrTiO3, CaTiO3 and BaTiO3 and discuss how the intrinsic tendency of these compounds to favor either the FE or the AFD instabilities shifts or even suppresses the FE/AFD coupling.

  17. Dielectric properties and microstructure of nano-MgO dispersed Ba{sub 0.3}Sr{sub 0.7}TiO{sub 3} thin films prepared by sputter deposition

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wang, S.-F.; Chu, Jinn P.; Lin, C.C.

    2005-07-01

    In this study, thin films prepared from the targets of Ba{sub 0.3}Sr{sub 0.7}TiO{sub 3} (BST), BST/5 mol % MgO, BST/10 mol % MgO, and BST/20 mol % MgO composites, using radio frequency magnetron sputtering, have been reported. As-deposited films were found to be amorphous and began to crystallize after annealing at temperatures of 650 deg. C and above. The addition of MgO in the BST films resulted in the hindrance of crystallization and inhibition of grain growth. MgO was substituted into the BST lattices to a certain degree. High-resolution transmission electron microscopy results revealed some MgO dispersed in the BSTmore » matrix. The MgO dispersed in the dense BST matrix was found to be around 25 nm in size. The dielectric constant was estimated to be 90 for the pure BST film annealed at 700 deg. C, and observed to be slightly reduced with the MgO addition. The dielectric losses of the Ba{sub 0.3}Sr{sub 0.7}TiO{sub 3} (0.006) and BST/MgO films (0.002-0.004) were much less than those of the Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}(0.013) and Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} films (0.11-0.13). The leakage current was smaller for the BST/10 mol % MgO film compared to the pure BST film and this low leakage current may be attributed to the substitution of Mg in the B sites of BST lattices which might have behaved as an electron acceptors.« less

  18. Resistance switching behavior of atomic layer deposited SrTiO3 film through possible formation of Sr2Ti6O13 or Sr1Ti11O20 phases

    PubMed Central

    Lee, Woongkyu; Yoo, Sijung; Yoon, Kyung Jean; Yeu, In Won; Chang, Hye Jung; Choi, Jung-Hae; Hoffmann-Eifert, Susanne; Waser, Rainer; Hwang, Cheol Seong

    2016-01-01

    Identification of microstructural evolution of nanoscale conducting phase, such as conducting filament (CF), in many resistance switching (RS) devices is a crucial factor to unambiguously understand the electrical behaviours of the RS-based electronic devices. Among the diverse RS material systems, oxide-based redox system comprises the major category of these intriguing electronic devices, where the local, along both lateral and vertical directions of thin films, changes in oxygen chemistry has been suggested to be the main RS mechanism. However, there are systems which involve distinctive crystallographic phases as CF; the Magnéli phase in TiO2 is one of the very well-known examples. The current research reports the possible presence of distinctive local conducting phase in atomic layer deposited SrTiO3 RS thin film. The conducting phase was identified through extensive transmission electron microscopy studies, which indicated that oxygen-deficient Sr2Ti6O13 or Sr1Ti11O20 phase was presumably present mainly along the grain boundaries of SrTiO3 after the unipolar set switching in Pt/TiN/SrTiO3/Pt structure. A detailed electrical characterization revealed that the samples showed typical bipolar and complementary RS after the memory cell was unipolar reset. PMID:26830978

  19. Crystal orientation dependence of the dielectric properties for epitaxial BaZr0.15Ti0.85O3 thin films

    NASA Astrophysics Data System (ADS)

    Miao, J.; Yuan, J.; Wu, H.; Yang, S. B.; Xu, B.; Cao, L. X.; Zhao, B. R.

    2007-01-01

    Epitaxial Ba0.15Zr0.85TiO3 (BZT) ferroelectric thin films with (001), (011), and (111) orientations were, respectively, grown on La0.67Sr0.33MnO3 (LSMO) buffered LaAlO3 substrates by pulsed laser deposition method. The dc electric-field dependence of permittivity and dielectric loss of (001)-, (011)-, and (111)-oriented BZT/LSMO heterostructures obeys the Johnson formula, and the ac electric-field dependence of that obeys the Rayleigh law under the subswitching field region. The anisotropic dielectric properties are attributed to the higher mobility of the charge carriers, the concentration of mobile interfacial domain walls, and boundaries in the (111)-oriental films than in the (110)- and (100)-oriented films.

  20. Preparation of thin-film (Ba(0.5),Sr(0.5))TiO3 by the laser ablation technique and electrical properties

    NASA Astrophysics Data System (ADS)

    Yoon, Soon-Gil; Lee, Jai-Chan; Safari, A.

    1994-09-01

    The chemical composition and electrical properties were investigated for epitaxially crystallized (Ba(0.5),Sr(0.5))TiO3 (BST) films deposited on Pt/MgO and YBa2Cu3O(7-x) (YBCO)/MgO substrates by the laser ablation technique. Rutherford backscattering spectroscopy analysis shows that thin films on Pt/MgO have almost the same stoichiometric composition as the target material. Films deposited at 600 C exhibited an excellent epitaxial growth, a dielectric constant of 430, and a dissipation factor of 0.02 at 10 kHz frequency. They have a charge storage density of 40 fC/sq micron at an applied electric field of 0.15 MV/cm. Leakage current density of BST thin films on Pt/MgO was smaller than on YBCO/MgO. Their leakage current density is about 0.8 microA/sq cm at an applied electric field of 0.15 MV/cm.

  1. Bottom electrodes dependence of microstructures and dielectric properties of compositionally graded (Ba{sub 1-x}Sr{sub x})TiO{sub 3} thin films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang Tianjin; Wang Jinzhao; Zhang Baishun

    2008-03-04

    Compositionally graded (Ba{sub 1-x}Sr{sub x})TiO{sub 3} (BST) thin films, with x decreasing from 0.3 to 0, were deposited on Pt/Ti/SiO{sub 2}/Si and Ru/SiO{sub 2}/Si substrates by radio frequency magnetron sputtering technology. The microstructure and dielectric properties of the graded BST thin films were investigated. It was found that the films on Ru electrode have better crystallization, and that RuO{sub 2} is present between the Ru bottom electrode and the graded BST thin films by X-ray diffraction and SEM analysis. Dielectric measurement reveals that the graded BST thin films deposited on Ru bottom electrode have higher dielectric constant and tunability. Themore » enhanced dielectric behavior is attributed to better crystallization as well as smaller space charge capacitance width and the formation of RuO{sub 2} that is more compatible with the BST films. The graded BST films on Ru electrode show higher leakage current due to lower barrier height and rougher surface of bottom electrode.« less

  2. A novel theoretical probe of the SrTiO3 surface under water-splitting conditions

    NASA Astrophysics Data System (ADS)

    Letchworth-Weaver, Kendra; Gunceler, Deniz; Arias, Tomás; Plaza, Manuel; Huang, Xin; Brock, Joel; Rodriguez-López, Joaquin; Abruña, Hector

    2014-03-01

    Understanding the reaction mechanisms required to generate hydrogen fuel by photoelectrolysis of water is essential to energy conversion research. These reaction pathways are strongly influenced by the geometry and electronic structure of the electrode surface under water-splitting conditions. Electrochemical microscopy has demonstrated that biasing a SrTiO3 (001) surface can lead to an increase in water-splitting activity. In operando X-ray reflectivity measurements at the Cornell High Energy Synchrotron Source (CHESS) correlate this increase in activity to a significant reorganization in the surface structure but are unable to determine the exact nature of this change. Joint Density-Functional Theory (JDFT), a rigorous yet computationally efficient alternative to molecular dynamics, provides a quantum-mechanical description of an electrode surface in contact with an aqueous environment, and a microscopically detailed description of the interfacial liquid structure. Our JDFT calculations determine the structure of the activated SrTiO3 surface and explore why it is correlated with higher activity for water splitting. With no empirical parameters whatsoever, we predict the X-ray crystal truncation rods for SrTiO3, finding excellent agreement with experiment. Funded by the Energy Materials Center at Cornell (EMC2).

  3. How Correlated is the FeSe /SrTiO3 System?

    NASA Astrophysics Data System (ADS)

    Mandal, Subhasish; Zhang, Peng; Ismail-Beigi, Sohrab; Haule, K.

    2017-08-01

    Recent observation of ˜10 times higher critical temperature in a FeSe monolayer compared with its bulk phase has drawn a great deal of attention because the electronic structure in the monolayer phase appears to be different than bulk FeSe. Using a combination of density functional theory and dynamical mean field theory, we find electronic correlations have important effects on the predicted atomic-scale geometry and the electronic structure of the monolayer FeSe on SrTiO3 . The electronic correlations are dominantly controlled by the Se-Fe-Se angle either in the bulk phase or the monolayer phase. But the angle sensitivity increases and the orbital differentiation decreases in the monolayer phase compared to the bulk phase. The correlations are more dependent on Hund's J than Hubbard U . The observed orbital selective incoherence to coherence crossover with temperature confirms the Hund's metallic nature of the monolayer FeSe. We also find electron doping by oxygen vacancies in SrTiO3 increases the correlation strength, especially in the dx y orbital by reducing the Se-Fe-Se angle.

  4. Temperature-dependent leakage current behavior of epitaxial Bi0.5Na0.5TiO3-based thin films made by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Hejazi, M. M.; Safari, A.

    2011-11-01

    This paper discusses the electrical conduction mechanisms in a 0.88 Bi0.5Na0.5TiO3-0.08 Bi0.5K0.5TiO3-0.04 BaTiO3 thin film in the temperature range of 200-350 K. The film was deposited on a SrRuO3/SrTiO3 substrate by pulsed laser deposition technique. At all measurement temperatures, the leakage current behavior of the film matched well with the Lampert's triangle bounded by three straight lines of different slopes. The relative location of the triangle sides varied with temperature due to its effect on the density of charge carriers and un-filled traps. At low electric fields, the ohmic conduction governed the leakage mechanism. The calculated activation energy of the trap is 0.19 eV implying the presence of shallow traps in the film. With increasing the applied field, an abrupt increase in the leakage current was observed. This was attributed to a trap-filling process by the injected carriers. At sufficiently high electric fields, the leakage current obeyed the Child's trap-free square law suggesting the space charge limited current was the dominant mechanism.

  5. Structural and Magnetic Properties of LaCoO3/SrTiO3 Multilayers.

    PubMed

    Zhang, Hongrui; Zhang, Jing; Yang, Huaiwen; Lan, Qianqian; Hong, Deshun; Wang, Shufang; Shen, Xi; Khan, Tahira; Yu, Richeng; Sun, Jirong; Shen, Baogen

    2016-07-20

    Structural and magnetic properties of the LaCoO3/SrTiO3 (LCO/STO) multilayers (MLs) with a fixed STO layer of 4 nm but varied LCO layer thicknesses have been systematically studied. The MLs grown on Sr0.7La0.3Al0.65Ta0.35O3 (LSAT) and SrTiO3 (STO) exhibit the in-plane lattice constant of the substrates, but those on LaAlO3 (LAO) show the in-plane lattice constant between those of the first two kinds of MLs. Compared with the LCO single layer (SL), the magnetic order of the MLs is significantly enhanced, as demonstrated by a very slow decrease, which is fast for the SL, of the Curie temperature and the saturation magnetization as the LCO layer thickness decreases. For example, clear ferromagnetic order is observed in the ML with the LCO layer of ∼1.5 nm, whereas it vanishes below ∼6 nm for the LCO SL. This result is consistent with the observation that the dark stripes, which are believed to be closely related to the magnetic order, remain clear in the MLs while they are vague in the corresponding LCO SL. The present work suggests a novel route to tune the magnetism of perovskite oxide films.

  6. Electronic structure and optical properties of Ta-doped and (Ta, N)-codoped SrTiO3 from hybrid functional calculations

    NASA Astrophysics Data System (ADS)

    Liu, Yanyu; Zhou, Wei; Wu, Ping

    2017-02-01

    A systematic study has been carried out to research the effect of Ta monodoping and (Ta, N)-codoping on the electronic structure and optical properties of SrTiO3. The results indicate that the incorporation of N into the SrTiO3 lattice is in favor of the substitution of Ta at a Ti site, which is the most favorable structure with respect to both the energetic stability and high photocatalytic activity. Furthermore, the carrier recombination centers induced by Ta monodoping are passivated in the (Ta, N)-codoped SrTiO3 system with Ta at a Ti site. Simultaneous incorporation of N and Ta results in a band gap decreasing about 0.7 eV due to the appearance of the new states hybridized by N-p states with the O-p states above the valence band. The band alignment verifies that the (Ta, N)-codoped SrTiO3 simultaneously meets the criteria of band-edge energetic positions and band gap for the overall water splitting under visible light.

  7. Rational design of mixed ionic and electronic conducting perovskite oxides for solid oxide fuel cell anode materials: A case study for doped SrTiO3

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Suthirakun, Suwit; Xiao, Guoliang; Ammal, Salai Cheettu

    2014-01-01

    The effect of p- and n-type dopants on ionic and electronic conductivity of SrTiO3 based perovskites were investigated both computationally and experimentally. Specifically, we performed density functional theory (DFT) calculations of Na- and La-doped SrTiO3 and Na- and Nb-doped SrTiO3 systems. Constrained ab initio thermodynamic calculations were used to evaluate the phase stability and reducibility of doped SrTiO3 under both oxidizing and reducing synthesis conditions, as well as under anodic solid oxide fuel cell (SOFC) conditions. The density of states (DOS) of these materials was analyzed to study the effects of p- and n-doping on the electronic conductivity. Furthermore, Na-more » and La-doped SrTiO3 and Na- and Nb-doped SrTiO3 samples were experimentally prepared and the conductivity was measured to confirm our computational predictions. The experimental observations are in very good agreement with the theoretical predictions that doping n-doped SrTiO3 with small amounts of p-type dopants promotes both the ionic and electronic conductivity of the material. This doping strategy is valid independent of p- and n-doping site and permits the synthesis of perovskite based mixed ionic/electronic conductors.« less

  8. Ultrafast X-ray diffraction probe of terahertz field-driven soft mode dynamics in SrTiO 3

    DOE PAGES

    Kozina, M.; van Driel, T.; Chollet, M.; ...

    2017-05-03

    We use ultrafast x-ray pulses to characterize the lattice response of SrTiO 3 when driven by strong terahertz (THz) fields. We observe transient changes in the diffraction intensity with a delayed onset with respect to the driving field. Fourier analysis reveals two frequency components corresponding to the two lowest energy zone-center optical modes in SrTiO 3. Lastly, the lower frequency mode exhibits clear softening as the temperature is decreased while the higher frequency mode shows slight temperature dependence.

  9. Ultrafast X-ray diffraction probe of terahertz field-driven soft mode dynamics in SrTiO 3

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kozina, M.; van Driel, T.; Chollet, M.

    We use ultrafast x-ray pulses to characterize the lattice response of SrTiO 3 when driven by strong terahertz (THz) fields. We observe transient changes in the diffraction intensity with a delayed onset with respect to the driving field. Fourier analysis reveals two frequency components corresponding to the two lowest energy zone-center optical modes in SrTiO 3. Lastly, the lower frequency mode exhibits clear softening as the temperature is decreased while the higher frequency mode shows slight temperature dependence.

  10. High-Temperature Thermoelectric Properties of (1 - x) SrTiO3 - ( x) La1/3NbO3 Ceramic Solid Solution

    NASA Astrophysics Data System (ADS)

    Srivastava, Deepanshu; Azough, F.; Molinari, M.; Parker, S. C.; Freer, R.

    2015-06-01

    Ceramics based on SrTiO3 are of growing interest as thermoelectric materials because of their high-temperature stability and non-toxicity. Substitution of La and Nb into the perovskite structure provides opportunities to control both the microstructure and properties. Ceramic solid solutions of (1 - x) SrTiO3 - ( x) La1/3NbO3 were prepared by the mixed oxide route, using compositional steps of x = 0.1. Pressed pellets were sintered at temperatures of 1573 K to 1723 K in air. Addition of aliovalent ions (La3+, Nb5+) on the A/B sites (Sr2+, Ti4+) led to A-Site cation deficiency in the stoichiometric compositions and other defect structures which increased carrier concentration. A maximum ZT of 0.004 was obtained for the x = 0.2 stoichiometric sample, although much higher ZT values are possible by sample reduction.

  11. Crystal structure, stability, and optoelectronic properties of the organic-inorganic wide-band-gap perovskite CH3NH3BaI3 : Candidate for transparent conductor applications

    NASA Astrophysics Data System (ADS)

    Kumar, Akash; Balasubramaniam, K. R.; Kangsabanik, Jiban; Vikram, Alam, Aftab

    2016-11-01

    Structural stability, electronic structure, and optical properties of CH3NH3BaI3 hybrid perovskite are examined from theory as well as experiment. Solution-processed thin films of CH3NH3BaI3 exhibited a high transparency in the wavelength range of 400-825 nm (1.5-3.1 eV for which the photon current density is highest in the solar spectrum) which essentially justifies a high band gap of 4 eV obtained by theoretical estimation. Also, the x-ray diffraction patterns of the thin films match well with the {00 l } peaks of the simulated pattern obtained from the relaxed unit cell of CH3NH3BaI3 , crystallizing in the I 4 /m c m space group, with lattice parameters, a =9.30 Å, c =13.94 Å. Atom projected density of state and band structure calculations reveal the conduction and valence band edges to be comprised primarily of barium d orbitals and iodine p orbitals, respectively. The larger band gap of CH3NH3BaI3 compared to CH3NH3PbI3 can be attributed to the lower electronegativity coupled with the lack of d orbitals in the valence band of Ba2 +. A more detailed analysis reveals the excellent chemical and mechanical stability of CH3NH3BaI3 against humidity, unlike its lead halide counterpart, which degrades under such conditions. We propose La to be a suitable dopant to make this compound a promising candidate for transparent conductor applications, especially for all perovskite solar cells. This claim is supported by our calculated results on charge concentration, effective mass, and vacancy formation energies.

  12. Synthesis, structural, characterization and dielectric spectroscopy of PVDF - BaTiO3 polymer composite

    NASA Astrophysics Data System (ADS)

    Kulkarni, S. S.; Belavi, P. B.; Khadke, U. V.

    2018-05-01

    In this paper we report the method of synthesis of ferroelectric polymer Polyvinyldene fluoride (PVDF) and Barium Titanate (BaTiO3) composite self supporting thin films and its dielectric response. BaTiO3 was synthesized by solid state reaction method. The PVDF - BaTiO3 polymer composites with various concentrations were synthesized by solution mixing method using Dimethylformadide (DMF) as a solvent. The phase transformation and surface methodology of the prepared composites were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) respectively. The XRD pattern confirms the formation of tetragonal pervoskite structure of ferroelectric phase. The XRD pattern shows the proper mixing of BaTiO3 particles intestinally and found to be improving its crystallinity with increase of BaTiO3 composition in the PVDF matrix. The dielectric properties of the composites as a function of frequency were computed using impedance analyzer. The dielectric constant decreases with increase of frequency shows the Maxwell - Wagner type of interfacial polarization in accordance with Koop's phenomenological theory.

  13. High- T c superconductivity at the interface between the CaCuO 2 and SrTiO 3 insulating oxides

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Di Castro, D.; Cantoni, C.; Ridolfi, F.

    2015-09-28

    At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low T c. We report the occurrence of high T c superconductivity in the bilayer CaCuO 2/SrTiO 3, where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO 2/SrTiO 3 interface must be realized between the Ca plane of CaCuO 2 and the TiO 2 plane of SrTiO 3. Only inmore » this case can oxygen ions be incorporated in the interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO 2 planes. In addition, a detailed hole doping spatial profile can be obtained by scanning transmission electron microscopy and electron-energy-loss spectroscopy at the O K edge, clearly showing that the (super)conductivity is confined to about 1–2 CaCuO 2 unit cells close to the interface with SrTiO 3. The results obtained for the CaCuO 2/SrTiO 3 interface can be extended to multilayered high T c cuprates, contributing to explaining the dependence of T c on the number of CuO 2 planes in these systems.« less

  14. Observation of the quantum Hall effect in δ-doped SrTiO3

    PubMed Central

    Matsubara, Y.; Takahashi, K. S.; Bahramy, M. S.; Kozuka, Y.; Maryenko, D.; Falson, J.; Tsukazaki, A.; Tokura, Y.; Kawasaki, M.

    2016-01-01

    The quantum Hall effect is a macroscopic quantum phenomenon in a two-dimensional electron system. The two-dimensional electron system in SrTiO3 has sparked a great deal of interest, mainly because of the strong electron correlation effects expected from the 3d orbitals. Here we report the observation of the quantum Hall effect in a dilute La-doped SrTiO3-two-dimensional electron system, fabricated by metal organic molecular-beam epitaxy. The quantized Hall plateaus are found to be solely stemming from the low Landau levels with even integer-filling factors, ν=4 and 6 without any contribution from odd ν's. For ν=4, the corresponding plateau disappears on decreasing the carrier density. Such peculiar behaviours are proposed to be due to the crossing between the Landau levels originating from the two subbands composed of d orbitals with different effective masses. Our findings pave a way to explore unprecedented quantum phenomena in d-electron systems. PMID:27228903

  15. Magnetic spin structure and magnetoelectric coupling in BiFeO{sub 3}-BaTiO{sub 3} multilayer

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lazenka, Vera, E-mail: Vera.Lazenka@fys.kuleuven.be; Modarresi, Hiwa; Bisht, Manisha

    2015-02-23

    Magnetic spin structures in epitaxial BiFeO{sub 3} single layer and an epitaxial BaTiO{sub 3}/BiFeO{sub 3} multilayer thin film have been studied by means of nuclear resonant scattering of synchrotron radiation. We demonstrate a spin reorientation in the 15 × [BaTiO{sub 3}/BiFeO{sub 3}] multilayer compared to the single BiFeO{sub 3} thin film. Whereas in the BiFeO{sub 3} film, the net magnetic moment m{sup →} lies in the (1–10) plane, identical to the bulk, m{sup →} in the multilayer points to different polar and azimuthal directions. This spin reorientation indicates that strain and interfaces play a significant role in tuning the magnetic spin order.more » Furthermore, large difference in the magnetic field dependence of the magnetoelectric coefficient observed between the BiFeO{sub 3} single layer and multilayer can be associated with this magnetic spin reorientation.« less

  16. Complementary resistive switching in BaTiO3/NiO bilayer with opposite switching polarities

    NASA Astrophysics Data System (ADS)

    Li, Shuo; Wei, Xianhua; Lei, Yao; Yuan, Xincai; Zeng, Huizhong

    2016-12-01

    Resistive switching behaviors have been investigated in the Au/BaTiO3/NiO/Pt structure by stacking the two elements with different switching types. The conducting atomic force microscope measurements on BaTiO3 thin films and NiO thin films suggest that with the same active resistive switching region, the switching polarities in the two semiconductors are opposite to each other. It is in agreement with the bipolar hysteresis I-V curves with opposite switching polarities for single-layer devices. The bilayer devices show complementary resistive switching (CRS) without electroforming and unipolar resistive switching (URS) after electroforming. The coexistence of CRS and URS is mainly ascribed to the co-effect of electric field and Joule heating mechanisms, indicating that changeable of resistance in this device is dominated by the redistribution of oxygen vacancies in BaTiO3 and the formation, disruption, restoration of conducting filaments in NiO. CRS in bilayer with opposite switching polarities is effective to solve the sneak current without the introduction of any selector elements or an additional metal electrode.

  17. Large critical current densities and pinning forces in CSD-grown superconducting GdBa2Cu3O7-x -BaHfO3 nanocomposite films

    NASA Astrophysics Data System (ADS)

    Cayado, Pablo; Erbe, Manuela; Kauffmann-Weiss, Sandra; Bühler, Carl; Jung, Alexandra; Hänisch, Jens; Holzapfel, Bernhard

    2017-09-01

    GdBa2Cu3O7-x -BaHfO3 (GdBCO-BHO) nanocomposite (NC) films containing 12 mol% BHO nanoparticles were prepared by chemical solution deposition (CSD) following the TFA route on SrTiO3 (STO) single crystals and buffered metallic tapes supplied by two different companies: Deutsche Nanoschicht GmbH and SuperOx. We optimized the preparation of our GdBCO-BHO solutions with acetylacetone making the film synthesis very robust and reproducible, and obtained 220 nm films with excellent superconducting properties. We show the structural, morphological and superconducting properties of the films after a careful optimization of the processing parameters (growth temperature, oxygen partial pressure and heating ramp). The films reach critical temperatures (T c) of ˜94 K, self-field critical current densities (J c) of >7 MA cm- 2 and maximum pinning force densities (F p) of ˜16 GN m- 3 at 77 K on STO and T c of ˜94.5 K and J c > 1.5 MA cm- 2 on buffered metallic tapes. The transport properties under applied magnetic fields are significantly improved with respect to the pristine GdBCO films. The GdBCO-BHO NC films on STO present epitaxial c-axis orientation with excellent out-of-plane and in-plane texture. The films are, in general, very dense with a low amount of pores and only superficial indentations. On the other hand, we present, for the first time, a systematic study of CSD-grown GdBCO-BHO NC films on buffered metallic tapes. We have used the optimized growth conditions for STO as a reference and identified some limitations on the film synthesis that should be overcome for further improvement of the films’ superconducting properties.

  18. Superconducting properties of Ba(Fe1-xNix)2As2 thin films in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Richter, Stefan; Kurth, Fritz; Iida, Kazumasa; Pervakov, Kirill; Pukenas, Aurimas; Tarantini, Chiara; Jaroszynski, Jan; Hänisch, Jens; Grinenko, Vadim; Skrotzki, Werner; Nielsch, Kornelius; Hühne, Ruben

    2017-01-01

    We report on the electrical transport properties of epitaxial Ba(Fe1-xNix)2As2 thin films grown by pulsed laser deposition in static magnetic fields up to 35 T. The thin film shows a critical temperature of 17.2 K and a critical current density of 5.7 × 105 A/cm2 in self field at 4.2 K, while the pinning is dominated by elastic pinning at two-dimensional nonmagnetic defects. Compared to the single-crystal data, we find a higher slope of the upper critical field for the thin film at a similar doping level and a small anisotropy. Also, an unusual small vortex liquid phase was observed at low temperatures, which is a striking difference to Co-doped BaFe2As2 thin films.

  19. Surface properties of atomically flat poly-crystalline SrTiO3

    PubMed Central

    Woo, Sungmin; Jeong, Hoidong; Lee, Sang A.; Seo, Hosung; Lacotte, Morgane; David, Adrian; Kim, Hyun You; Prellier, Wilfrid; Kim, Yunseok; Choi, Woo Seok

    2015-01-01

    Comparison between single- and the poly-crystalline structures provides essential information on the role of long-range translational symmetry and grain boundaries. In particular, by comparing single- and poly-crystalline transition metal oxides (TMOs), one can study intriguing physical phenomena such as electronic and ionic conduction at the grain boundaries, phonon propagation, and various domain properties. In order to make an accurate comparison, however, both single- and poly-crystalline samples should have the same quality, e.g., stoichiometry, crystallinity, thickness, etc. Here, by studying the surface properties of atomically flat poly-crystalline SrTiO3 (STO), we propose an approach to simultaneously fabricate both single- and poly-crystalline epitaxial TMO thin films on STO substrates. In order to grow TMOs epitaxially with atomic precision, an atomically flat, single-terminated surface of the substrate is a prerequisite. We first examined (100), (110), and (111) oriented single-crystalline STO surfaces, which required different annealing conditions to achieve atomically flat surfaces, depending on the surface energy. A poly-crystalline STO surface was then prepared at the optimum condition for which all the domains with different crystallographic orientations could be successfully flattened. Based on our atomically flat poly-crystalline STO substrates, we envision expansion of the studies regarding the TMO domains and grain boundaries. PMID:25744275

  20. Performance analysis of resistive switching devices based on BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Samardzic, Natasa; Kojic, Tijana; Vukmirovic, Jelena; Tripkovic, Djordjije; Bajac, Branimir; Srdic, Vladimir; Stojanovic, Goran

    2016-03-01

    Resitive switching devices, memristors, have recenty attracted much attention due to promising performances and potential applications in the field of logic and memory devices. Here, we present thin film BaTiO3 based memristor fabricated using ink-jet printing technique. Active material is a single layer barium titanate film with thickness of ̴100 nm, sandwitched between metal electodes. Printing parameters were optimized aiming to achieve stable drop flow and uniform printed layer. Current-voltage characteristics show typical memristive behavior with pinched hysteresis loop crossed at the origin, with marked differences between High Resistive State (HRS) and Low Resistive State (LRS). Obtained resistive states are stable during numerous switching processes. The device also shows unipolar switching effect for negative voltage impulses. Variable voltage impulse amplitudes leads to the shifting of the energy levels of electode contacts resulting in changing of the overall current through the device. Structural charcterization have been performed using XRD analysis and SEM micrography. High-temperature current-voltage measurements combined with transport parameter analysis using Hall efect measurement system (HMS 3000) and Impedance Analyzer AC measurements allows deeper insigth into conduction mechanism of ferroelectric memristors.

  1. Multiferroic fluoride BaCoF4 Thin Films Grown Via Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Borisov, Pavel; Johnson, Trent; García-Castro, Camilo; Kc, Amit; Schrecongost, Dustin; Cen, Cheng; Romero, Aldo; Lederman, David

    Multiferroic materials exhibit exciting physics related to the simultaneous presence of multiple long-range orders, in many cases consisting of antiferromagnetic (AF) and ferroelectric (FE) orderings. In order to provide a new, promising route for fluoride-based multiferroic material engineering, we grew multiferroic fluoride BaCoF4 in thin film form on Al2O3 (0001) substrates by molecular beam epitaxy. The films grow with the orthorhombic b-axis out-of-plane and with three in-plane structural twin domains along the polar c-axis directions. The FE ordering in thin films was verified by FE remanent hysteresis loops measurements at T = 14 K and by room temperature piezoresponse force microscopy (PFM). An AF behavior was found below Neel temperature TN ~ 80 K, which is in agreement with the bulk properties. At lower temperatures two additional magnetic phase transitions at 19 K and 41 K were found. First-principles calculations demonstrated that the growth strain applied to the bulk BaCoF4 indeed favors two canted spin orders, along the b- and a-axes, respectively, in addition to the main AF spin order along the c-axis. Supported by FAME (Contract 2013-MA-2382), WV Research Challenge Grant (HEPC.dsr.12.29), and DMREF-NSF 1434897.

  2. Effect of concurrent Mg/Nb-doping on dielectric properties of Ba0.45Sr0.55TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Alema, Fikadu; Reich, Michael; Reinholz, Aaron; Pokhodnya, Konstantin

    2013-08-01

    Composition, microstructure, and dielectric properties of undoped and Ba(Mg1/3Nb2/3)O3 (BMN) doped Ba0.45Sr0.55TiO3 (BST) thin films deposited via rf. magnetron sputtering on platinized alumina substrates have been investigated. The analysis of microstructure has shown that despite the sizable effect of doping on the residual stress, the latter is partially compensated by the thermal expansion coefficient mismatch, and its influence on the BST film crystal structure is insignificant. It was revealed that BMN doped film demonstrated an average (over 2000 devices) of 52.5% tunability at 640 kV/cm, which is ˜8% lower than the value for the undoped film. This drop is associated with the presence of Mg ions in BMN; however, the effect of Mg doping is partially compensated by that of Nb ions. The decrease in grain size upon doping may also contribute to the tunability drop. Doping with BMN allows achievement of a compensation concentration yielding no free carriers and resulting in significant leakage current reduction when compared with the undoped film. In addition, the presence of large amounts of empty shallow traps related to NbTi• allows localizing free carriers injected from the contacts thus extending the device control voltage substantially above 10 V.

  3. Anomalously deep polarization in SrTiO3 (001) interfaced with an epitaxial ultrathin manganite film

    DOE PAGES

    Wang, Zhen; Tao, Jing; Yu, Liping; ...

    2016-10-17

    Using atomically-resolved imaging and spectroscopy, we reveal a remarkably deep polarization in non-ferroelectric SrTiO 3 near its interface with an ultrathin nonmetallic film of La 2/3Sr 1/3MnO 3. Electron holography shows an electric field near the interface in SrTiO 3, yielding a surprising spontaneous polarization density of ~ 21 μC/cm 2. Combining the experimental results with first principles calculations, we propose that the observed deep polarization is induced by the electric field originating from oxygen vacancies that extend beyond a dozen unit-cells from the interface, thus providing important evidence of the role of defects in the emergent interface properties ofmore » transition metal oxides.« less

  4. Gate-tunable polarized phase of two-dimensional electrons at the LaAlO3/SrTiO3 interface.

    PubMed

    Joshua, Arjun; Ruhman, Jonathan; Pecker, Sharon; Altman, Ehud; Ilani, Shahal

    2013-06-11

    Controlling the coupling between localized spins and itinerant electrons can lead to exotic magnetic states. A novel system featuring local magnetic moments and extended 2D electrons is the interface between LaAlO3 and SrTiO3. The magnetism of the interface, however, was observed to be insensitive to the presence of these electrons and is believed to arise solely from extrinsic sources like oxygen vacancies and strain. Here we show the existence of unconventional electronic phases in the LaAlO3/SrTiO3 system pointing to an underlying tunable coupling between itinerant electrons and localized moments. Using anisotropic magnetoresistance and anomalous Hall effect measurements in a unique in-plane configuration, we identify two distinct phases in the space of carrier density and magnetic field. At high densities and fields, the electronic system is strongly polarized and shows a response, which is highly anisotropic along the crystalline directions. Surprisingly, below a density-dependent critical field, the polarization and anisotropy vanish whereas the resistivity sharply rises. The unprecedented vanishing of the easy axes below a critical field is in sharp contrast with other coupled magnetic systems and indicates strong coupling with the moments that depends on the symmetry of the itinerant electrons. The observed interplay between the two phases indicates the nature of magnetism at the LaAlO3/SrTiO3 interface as both having an intrinsic origin and being tunable.

  5. Gate-tunable polarized phase of two-dimensional electrons at the LaAlO3/SrTiO3 interface

    PubMed Central

    Joshua, Arjun; Ruhman, Jonathan; Pecker, Sharon; Altman, Ehud; Ilani, Shahal

    2013-01-01

    Controlling the coupling between localized spins and itinerant electrons can lead to exotic magnetic states. A novel system featuring local magnetic moments and extended 2D electrons is the interface between LaAlO3 and SrTiO3. The magnetism of the interface, however, was observed to be insensitive to the presence of these electrons and is believed to arise solely from extrinsic sources like oxygen vacancies and strain. Here we show the existence of unconventional electronic phases in the LaAlO3/SrTiO3 system pointing to an underlying tunable coupling between itinerant electrons and localized moments. Using anisotropic magnetoresistance and anomalous Hall effect measurements in a unique in-plane configuration, we identify two distinct phases in the space of carrier density and magnetic field. At high densities and fields, the electronic system is strongly polarized and shows a response, which is highly anisotropic along the crystalline directions. Surprisingly, below a density-dependent critical field, the polarization and anisotropy vanish whereas the resistivity sharply rises. The unprecedented vanishing of the easy axes below a critical field is in sharp contrast with other coupled magnetic systems and indicates strong coupling with the moments that depends on the symmetry of the itinerant electrons. The observed interplay between the two phases indicates the nature of magnetism at the LaAlO3/SrTiO3 interface as both having an intrinsic origin and being tunable. PMID:23708121

  6. Improved electrical properties after post annealing of Ba0.7Sr0.3TiO3 thin films for MIM capacitor applications

    NASA Astrophysics Data System (ADS)

    Rouahi, A.; Kahouli, A.; Sylvestre, A.; Jomni, F.; Defaÿ, E.; Yangui, B.

    2012-11-01

    Dielectric measurements have been performed on ion beam sputtering (IBS) barium strontium titanate Ba0.7Sr0.3TiO3 thin films at annealing temperatures 470 and 700 °C using impedance spectroscopy. The effect of the annealing temperature upon the electrical properties of the films is also investigated using capacitance-voltage techniques. Increasing annealing temperature suggested the increases of density and grain size, whereas the density of the trapped oxygen vacancy may be decreasing with increasing annealing temperature. The barrier height ( E a) of the oxygen vacancy decreases with increasing annealing temperature. The C- V characteristics were investigated in relation to the annealing temperature to identify the anomalous capacitance in the MIM configuration films. Among all measurement temperatures, it was observed that the data fit well by the "LGD" model. The interfacial effect and its dependence of morphology structure have been studied, and the results are discussed.

  7. Effect of vanadium substitution on the dielectric and electrical conduction properties of SrTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Paramita Mantry, Snigdha; Yadav, Abhinav; Fahad, Mohd; Sarun, P. M.

    2018-03-01

    Vanadium (V) substituted SrTiO3 (SrTi1-x V x O3 and x = 0.00-0.20) ceramic powders were synthesized by conventional solid state reaction method at sintering temperature 1250 ◦C for 2 hr. The structural, surface morphology and elemental valancy of the prepared samples were studied by using X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS). The XRD analysis of SrTi1-x V x O3 confirmed the formation of single phase cubic crystal structure. The average grain size significantly increases from 0.5 μm to 7.2 μm with increasing V concentration. XPS spectrum confirms the partial reduction of Ti4+ to Ti3+ due to the doping of V5 + in SrTiO3 ceramics. The effect of V2O5 on the dielectric properties, impedance spectroscopy, Nyquist analysis and conductivity properties of SrTiO3 ceramics were investigated over a wide range of frequency (100 Hz—5 MHz) at 100 ◦C. The magnitude of dielectric constant and dielectric loss decreases with increase in frequency for all the samples. The maximum value of dielectric constant (ɛ r ˜ 500) is observed for x = 0.05 composition. The complex impedance analysis shows that the electrical conduction mechanism is mainly due to grain effect. The optimal dielectric constant (ɛ r ˜ 500) and effective capacitance (C eff = 35.80 nF) is observed for the sample with x = 0.05. Doping of donor cations lead to a drastic change in the microstructure and electrical behavior of SrTiO3 ceramics.

  8. Tuning the nonlinear optical absorption in Au/BaTiO3 nanocomposites with gold nanoparticle concentration

    NASA Astrophysics Data System (ADS)

    Bijeesh, M. M.; Shakhi, P. K.; Varier, Geetha K.; Nandakumar, P.

    2018-06-01

    We report on the nonlinear optical absorption coefficient of Au/BaTiO3 nanocomposite films and its dependence on gold nanoparticle concentration. Au/BaTiO3 nanocomposite films with different molar ratio of Au/Ba are prepared by sol-gel technique and characterized by X-ray diffraction, UV Visible absorption spectroscopy and high resolution transmission electron microscopy. An open aperture Z-scan technique is employed to study the third order nonlinear optical properties of Au/BaTiO3 thin films. An Nd:YAG laser operating at 532 nm wavelength having a pulse width of 5 ns is used for the measurements. The two-photon absorption coefficient of the films increases linearly with gold nanoparticle concentration and significant enhancement of nonlinear optical absorption is observed. This ability to fine tune the nonlinear optical coefficients of Au/BaTiO3 films would be handy in optical device applications.

  9. High Tc superconducting IR detectors from Y-Ba-Cu-O thin films

    NASA Technical Reports Server (NTRS)

    Lindgren, M.; Ahlberg, H.; Danerud, M.; Larsson, A.; Eng, M.

    1990-01-01

    A thin-film high-Tc superconducting multielement optical detector made of Y-Ba-Cu-O has been designed and evaluated using optical pulses from a diode laser (830 nm) and a Q-switched CO2-laser (10.6 microns). Different thin films have been tested. A laser deposited film showed the strongest response amplitude for short pulses and responded to an ultrafast, 50 ps wide pulse. Comparisons between dR/dT and response as a function of temperature indicated, however, a bolometric response.

  10. Influence of impurities on the high temperature conductivity of SrTiO3

    NASA Astrophysics Data System (ADS)

    Bowes, Preston C.; Baker, Jonathon N.; Harris, Joshua S.; Behrhorst, Brian D.; Irving, Douglas L.

    2018-01-01

    In studies of high temperature electrical conductivity (HiTEC) of dielectrics, the impurity in the highest concentration is assumed to form a single defect that controls HiTEC. However, carrier concentrations are typically at or below the level of background impurities, and all impurities may complex with native defects. Canonical defect models ignore complex formation and lump defects from multiple impurities into a single effective defect to reduce the number of associated reactions. To evaluate the importance of background impurities and defect complexes on HiTEC, a grand canonical defect model was developed with input from density functional theory calculations using hybrid exchange correlation functionals. The influence of common background impurities and first nearest neighbor complexes with oxygen vacancies (vO) was studied for three doping cases: nominally undoped, donor doped, and acceptor doped SrTiO3. In each case, conductivity depended on the ensemble of impurity defects simulated with the extent of the dependence governed by the character of the dominant impurity and its tendency to complex with vO. Agreement between simulated and measured conductivity profiles as a function of temperature and oxygen partial pressure improved significantly when background impurities were included in the nominally undoped case. Effects of the impurities simulated were reduced in the Nb and Al doped cases as both elements did not form complexes and were present in concentrations well exceeding all other active impurities. The influence of individual impurities on HiTEC in SrTiO3 was isolated and discussed and motivates further experiments on singly doped SrTiO3.

  11. Design of n - and p -type oxide thermoelectrics in LaNiO3/SrTiO3(001 ) superlattices exploiting interface polarity

    NASA Astrophysics Data System (ADS)

    Geisler, Benjamin; Blanca-Romero, Ariadna; Pentcheva, Rossitza

    2017-03-01

    We investigate the structural, electronic, transport, and thermoelectric properties of LaNiO3/SrTiO3(001 ) superlattices containing either exclusively n - or p -type interfaces or coupled interfaces of opposite polarity by using density functional theory calculations with an on-site Coulomb repulsion term. The results show that significant octahedral tilts are induced in the SrTiO3 part of the superlattice. Moreover, the La-Sr distances and Ni-O out-of-plane bond lengths at the interfaces exhibit a distinct variation by about 7 % with the sign of the electrostatic doping. In contrast to the much studied LaAlO3/SrTiO3 system, the charge mismatch at the interfaces is exclusively accommodated within the LaNiO3 layers, whereas the interface polarity leads to a band offset and to the formation of an electric field within the coupled superlattice. Features of the electronic structure indicate an orbital-selective quantization of quantum well states. The potential- and confinement-induced multiband splitting results in complex cylindrical Fermi surfaces with a tendency towards nesting that depends on the interface polarity. The analysis of the thermoelectric response reveals a particularly large positive Seebeck coefficient (135 μ V /K) and a high figure of merit (0.35) for room-temperature cross-plane transport in the p -type superlattice that is attributed to the participation of the SrTiO3 valence band. Superlattices with either n - or p -type interfaces show cross-plane Seebeck coefficients of opposite sign and thus emerge as a platform to construct an oxide-based thermoelectric generator with structurally and electronically compatible n - and p -type oxide thermoelectrics.

  12. Microstructures and properties of superconducting Y-ErBaCuO thin films obtained from disordered Y-ErBaF2Cu films

    NASA Technical Reports Server (NTRS)

    Cikmach, P.; Diociaiuti, M.; Fontana, A.; Giovannella, C.; Iannuzzi, M.; Lucchini, C.; Merlo, V.; Messi, R.; Paoluzi, L.; Scopa, L.

    1991-01-01

    The preparation procedure used to obtain superconducting thin films by radio frequency magnetron sputtering of a single mosaic target is described in detail. The single mosaic target is composed of (Y-Er), BaF2, and Cu.

  13. Mechanical writing of n-type conductive layers on the SrTiO3 surface in nanoscale

    PubMed Central

    Wang, Yuhang; Zhao, Kehan; Shi, Xiaolan; Li, Geng; Xie, Guanlin; Lai, Xubo; Ni, Jun; Zhang, Liuwan

    2015-01-01

    The fabrication and control of the conductive surface and interface on insulating SrTiO3 bulk provide a pathway for oxide electronics. The controllable manipulation of local doping concentration in semiconductors is an important step for nano-electronics. Here we show that conductive patterns can be written on bare SrTiO3 surface by controllable doping in nanoscale using the mechanical interactions of atomic force microscopy tip without applying external electric field. The conductivity of the layer is n-type, oxygen sensitive, and can be effectively tuned by the gate voltage. Hence, our findings have potential applications in oxide nano-circuits and oxygen sensors. PMID:26042679

  14. Writing and Reading of Ultrathin Ferroelectric Domains on Commensurate SrTiO3 on Silicon

    NASA Astrophysics Data System (ADS)

    Levy, Jeremy; Cen, Cheng; Sleasman, Charles R.; Warusawithana, Maitri; Schlom, Darrell G.

    2008-03-01

    Ferroelectricity in ultrathin epitaxial SrTiO3 grown commensurately by oxide-molecular beam epitaxy (MBE) on silicon substrates was investigated using piezoforce microscopy (PFM). A series of samples containing n molecular layers (ML) of SrTiO3 (n = 3, 4, 5, 6, 8, 10, 20) was grown on silicon substrates. Room-temperature ferroelectricity was observed for samples containing n = 5, 6, 8, 10 ML. Temperature-dependent measurements indicate that the sample with n = 5 exhibits a ferroelectric phase transition at Tc˜317 K. Sample with n = 6 remains ferroelectric up to at least 393K. Polar domains created on the n = 6 was found to be stable at room temperature for more than 72 hours. The implications of these results for fundamental and device-related applications will be discussed briefly.

  15. Characterization of the insulator barrier and the superconducting transition temperature in GdBa{sub 2}Cu{sub 3}O{sub 7−δ}/BaTiO{sub 3} bilayers for application in tunnel junctions

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Navarro, H., E-mail: henrynavarro@cab.cnea.gov.ar; Sirena, M.; Haberkorn, N.

    2015-07-28

    The optimization of the superconducting properties in a bottom electrode and the quality of an insulator barrier are the first steps in the development of superconductor/insulator/superconductor tunnel junctions. Here, we study the quality of a BaTiO{sub 3} tunnel barrier deposited on a 16 nm thick GdBa{sub 2}Cu{sub 3}O{sub 7−δ} thin film by using conductive atomic force microscopy. We find that the tunnel current is systematically reduced (for equal applied voltage) by increasing the BaTiO{sub 3} barrier thickness between 1.6 and 4 nm. The BaTiO{sub 3} layers present an energy barrier of ≈1.2 eV and an attenuation length of 0.35–0.5 nm (depending on the appliedmore » voltage). The GdBa{sub 2}Cu{sub 3}O{sub 7−δ} electrode is totally covered by a BaTiO{sub 3} thickness above 3 nm. The presence of ferroelectricity was verified by piezoresponse force microscopy for a 4 nm thick BaTiO{sub 3} top layer. The superconducting transition temperature of the bilayers is systematically suppressed by increasing the BaTiO{sub 3} thickness. This fact can be associated with stress at the interface and a reduction of the orthorhombicity of the GdBa{sub 2}Cu{sub 3}O{sub 7−δ}. The reduction in the orthorhombicity is expected by considering the interface mismatch and it can also be affected by reduced oxygen stoichiometry (poor oxygen diffusion across the BaTiO{sub 3} barrier)« less

  16. Optical Modulation of BST/STO Thin Films in the Terahertz Range

    NASA Astrophysics Data System (ADS)

    Zeng, Ying; Shi, Songjie; Zhou, Ling; Ling, Furi; Yao, Jianquan

    2018-04-01

    The {Ba}_{0.7} {Sr}_{0.3} {TiO}3 (BST) thin film (30.3 nm) deposited on a {SrTiO}3 (STO) film/silicon substrate sample was modulated by 532 nm continuous-wave laser in the range of 0.2-1 THz at room temperature. The refractive index variation was observed to linearly increase at the highest 3.48 for 0.5 THz with the pump power increasing to 400 mW. It was also found that the BST/STO sample had a larger refractive index variation and was more sensitive to the external optical field than a BST monolayer due to the epitaxial strain induced by the STO film. The electric displacement-electric field loops results revealed that the increasing spontaneous polarization with the STO film that was induced was responsible for the larger refractive index variation of the BST/STO sample. In addition, the real and imaginary part of the permittivity were observed increasing along with the external field increasing, due to the soft mode hardening.

  17. Optical Modulation of BST/STO Thin Films in the Terahertz Range

    NASA Astrophysics Data System (ADS)

    Zeng, Ying; Shi, Songjie; Zhou, Ling; Ling, Furi; Yao, Jianquan

    2018-07-01

    The {Ba}_{0.7} {Sr}_{0.3} {TiO}3 (BST) thin film (30.3 nm) deposited on a {SrTiO}3 (STO) film/silicon substrate sample was modulated by 532 nm continuous-wave laser in the range of 0.2-1 THz at room temperature. The refractive index variation was observed to linearly increase at the highest 3.48 for 0.5 THz with the pump power increasing to 400 mW. It was also found that the BST/STO sample had a larger refractive index variation and was more sensitive to the external optical field than a BST monolayer due to the epitaxial strain induced by the STO film. The electric displacement-electric field loops results revealed that the increasing spontaneous polarization with the STO film that was induced was responsible for the larger refractive index variation of the BST/STO sample. In addition, the real and imaginary part of the permittivity were observed increasing along with the external field increasing, due to the soft mode hardening.

  18. Revealing ionization-induced dynamic recovery in ion-irradiated SrTiO 3

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Velisa, Gihan; Wendler, Elke; Xue, Haizhou

    The lack of fundamental understanding on the coupled effects of energy deposition to electrons and atomic nuclei on defect processes and irradiation response poses a significant roadblock for the design and control of material properties. In this work, SrTiO 3 has been irradiated with various ion species over a wide range of ion fluences at room temperature with a goal to deposit different amounts of energy to target electrons and atomic nuclei by varying the ratio of electronic to nuclear energy loss. Here, the results unambiguously show a dramatic difference in behavior of SrTiO 3 irradiated with light ions (Ne,more » O) compared to heavy ions (Ar). While the damage accumulation and amorphization under Ar ion irradiation are consistent with previous observations and existing models, the damage accumulation under Ne irradiation reveals a quasi-saturation state at a fractional disorder of 0.54 at the damage peak for an ion fluence corresponding to a dose of 0.5 dpa; this is followed by further increases in disorder with increasing ion fluence. In the case of O ion irradiation, the damage accumulation at the damage peak closely follows that for Ne ion irradiation up to a fluence corresponding to a dose of 0.5 dpa, where a quasi-saturation of fractional disorder level occurs at about 0.48; however, in this case, the disorder at the damage peak decreases slightly with further increases in fluence. This behavior is associated with changes in kinetics due to irradiation-enhanced diffusional processes that are dependent on electronic energy loss and the ratio of electronic to nuclear energy dissipation. Lastly, these findings are critical for advancing the fundamental understanding of ion-solid interactions and for a large number of applications in oxide electronics where SrTiO 3 is a foundational material.« less

  19. Increased Curie Temperature Induced by Orbital Ordering in La0.67Sr0.33MnO3/BaTiO3 Superlattices.

    PubMed

    Zhang, Fei; Wu, Biao; Zhou, Guowei; Quan, Zhi-Yong; Xu, Xiao-Hong

    2018-01-17

    Recent theoretical studies indicated that the Curie temperature of perovskite manganite thin films can be increased by more than an order of magnitude by applying appropriate interfacial strain to control orbital ordering. In this work, we demonstrate that the regular intercalation of BaTiO 3 layers between La 0.67 Sr 0.33 MnO 3 layers effectively enhances ferromagnetic order and increases the Curie temperature of La 0.67 Sr 0.33 MnO 3 /BaTiO 3 superlattices. The preferential orbital occupancy of e g (x 2 -y 2 ) in La 0.67 Sr 0.33 MnO 3 layers induced by the tensile strain of BaTiO 3 layers is identified by X-ray linear dichroism measurements. Our results reveal that controlling orbital ordering can effectively improve the Curie temperature of La 0.67 Sr 0.33 MnO 3 films and that in-plane orbital occupancy is beneficial to the double exchange ferromagnetic coupling of thin-film samples. These findings create new opportunities for the design and control of magnetism in artificial structures and pave the way to a variety of novel magnetoelectronic applications that operate far above room temperature.

  20. Realization of single terminated surface of perovskite oxide single crystals and their band profile: (LaAlO3)0.3(Sr2AlTaO6)0.7, SrTiO3 and KTaO3 case study

    NASA Astrophysics Data System (ADS)

    Tomar, Ruchi; Wadehra, Neha; Budhiraja, Vaishali; Prakash, Bhanu; Chakraverty, S.

    2018-01-01

    To characterize the physical properties of thin films without ambiguity and design interface with new functionalities, it is essential to have detailed knowledge of physical properties and appropriate estimation of the band profile of perovskite oxide substrates. We have developed and demonstrated a chemical free unified framework to realize single terminated surface of KTaO3, (LaAlO3)0.3 (Sr2AlTaO6)0.7 and SrTiO3 (001) oriented single crystals. The electronic band line-up of these single crystal substrates, using a combination of optical spectroscopy and Kelvin Probe Force Microscopy, has been constructed. A polar-polar interface of KTaO3 and LaBO3 (B-Transition metal ion) before and after the possible surface/electronic reconstruction has also been schematically presented.

  1. Orientation effect on microwave dielectric properties of Si-integrated Ba0.6Sr0.4TiO3 thin films for frequency agile devices

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Suk; Hyun, Tae-Seon; Kim, Ho-Gi; Kim, Il-Doo; Yun, Tae-Soon; Lee, Jong-Chul

    2006-07-01

    The effect of texture with (100) and (110) preferred orientations on dielectric properties of Ba0.6Sr0.4TiO3 (BST) thin films grown on SrO (9nm) and CeO2 (70nm ) buffered Si substrates, respectively, was investigated. The coplanar waveguide (CPW) phase shifter using (100) oriented BST films on SrO buffered Si exhibited a much-enhanced figure of merit of 24.7°/dB, as compared to that (10.2°/dB) of a CPW phase shifter using (110) oriented BST films on CeO2 buffered Si at 12GHz. This work demonstrates that the microwave properties of the Si-integrated BST thin films are highly correlated with crystal orientation.

  2. Growth control of oxygen stoichiometry in homoepitaxial SrTiO3 films by pulsed laser epitaxy in high vacuum

    PubMed Central

    Lee, Ho Nyung; Ambrose Seo, Sung S.; Choi, Woo Seok; Rouleau, Christopher M.

    2016-01-01

    In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Therefore, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but expands the utility of pulsed laser epitaxy of other materials as well. PMID:26823119

  3. Large piezoelectricity in electric-field modified single crystals of SrTiO3

    NASA Astrophysics Data System (ADS)

    Khanbabaee, B.; Mehner, E.; Richter, C.; Hanzig, J.; Zschornak, M.; Pietsch, U.; Stöcker, H.; Leisegang, T.; Meyer, D. C.; Gorfman, S.

    2016-11-01

    Defect engineering is an effective and powerful tool to control the existing material properties and produce completely new ones, which are symmetry-forbidden in a defect-free crystal. For example, the application of a static electric field to a single crystal of SrTiO3 forms a strained near-surface layer through the migration of oxygen vacancies out of the area beneath the positively charged electrode. While it was previously shown that this near-surface phase holds pyroelectric properties, which are symmetry-forbidden in centrosymmetric bulk SrTiO3, this paper reports that the same phase is strongly piezoelectric. We demonstrate the piezoelectricity of this phase through stroboscopic time-resolved X-ray diffraction under alternating electric field and show that the effective piezoelectric coefficient d33 ranges between 60 and 100 pC/N. The possible atomistic origins of the piezoelectric activity are discussed as a coupling between the electrostrictive effect and spontaneous polarization of this near-surface phase.

  4. Enhanced and continuous electrostatic carrier doping on the SrTiO3 surface

    PubMed Central

    Eyvazov, A. B.; Inoue, I. H.; Stoliar, P.; Rozenberg, M. J.; Panagopoulos, C.

    2013-01-01

    Paraelectrical tuning of a charge carrier density as high as 1013 cm−2 in the presence of a high electronic carrier mobility on the delicate surfaces of correlated oxides, is a key to the technological breakthrough of a field effect transistor (FET) utilising the metal-nonmetal transition. Here we introduce the Parylene-C/Ta2O5 hybrid gate insulator and fabricate FET devices on single-crystalline SrTiO3, which has been regarded as a bedrock material for oxide electronics. The gate insulator accumulates up to ~1013cm−2 carriers, while the field-effect mobility is kept at 10 cm2/Vs even at room temperature. Further to the exceptional performance of our devices, the enhanced compatibility of high carrier density and high mobility revealed the mechanism for the long standing puzzle of the distribution of electrostatically doped carriers on the surface of SrTiO3. Namely, the formation and continuous evolution of field domains and current filaments.

  5. Enhanced tunability of magnetron sputtered Ba0.5Sr0.5TiO3 thin films on c-plane sapphire substrates

    NASA Astrophysics Data System (ADS)

    Fardin, E. A.; Holland, A. S.; Ghorbani, K.; Reichart, P.

    2006-07-01

    Thin films of Ba0.5Sr0.5TiO3 (BST) were deposited on c-plane (0001) sapphire by rf magnetron sputtering and investigated by complementary materials analysis methods. Microwave properties of the films, including tunability and Q factor were measured from 1to20GHz by patterning interdigital capacitors (IDCs) on the film surface. The tunability is correlated with texture, strain, and grain size in the deposited films. An enhanced capacitance tunability of 56% at a bias field of 200kV/cm and total device Q of more than 15 (up to 20GHz) were achieved following postdeposition annealing at 900°C.

  6. Misfit strain relaxation in (Ba0.60Sr0.40)TiO3 epitaxial thin films on orthorhombic NdGaO3 substrates

    NASA Astrophysics Data System (ADS)

    Simon, W. K.; Akdogan, E. K.; Safari, A.

    2006-07-01

    Strain relaxation in (Ba0.60Sr0.40)TiO3 (BST) thin films on ⟨110⟩ orthorhombic NdGaO3 substrates is investigated by x-ray diffractometry. Pole figure analysis indicates a [010]BST∥[1¯10]NGO and [001]BST∥[001]NGO in-plane and [100]BST∥[100]NGO out-of-plane epitaxial relationship. The residual strains are relaxed at h ˜200nm, and for h >600nm, films are essentially strain free. Two independent dislocations mechanisms operate to relieve the anisotropic misfit strains along the principal directions. The critical thickness for misfit dislocation formation along [001] and [010] are 11 and 15nm, respectively. Stress analysis indicates deviation from linear elasticity for h <200. The films with 10

  7. Evolution of ferromagnetism in two-dimensional electron gas of LaTiO3/SrTiO3

    NASA Astrophysics Data System (ADS)

    Wen, Fangdi; Cao, Yanwei; Liu, Xiaoran; Pal, B.; Middey, S.; Kareev, M.; Chakhalian, J.

    2018-03-01

    Understanding, creating, and manipulating spin polarization of two-dimensional electron gases at complex oxide interfaces present an experimental challenge. For example, despite almost a decade long research effort, the microscopic origin of ferromagnetism in LaAlO3/SrTiO3 heterojunctions is still an open question. Here, by using a prototypical two-dimensional electron gas (2DEG) which emerges at the interface between band insulator SrTiO3 and antiferromagnetic Mott insulator LaTiO3, the experiment reveals the evidence for magnetic phase separation in a hole-doped Ti d1 t2g system, resulting in spin-polarized 2DEG. The details of electronic and magnetic properties of the 2DEG were investigated by temperature-dependent d.c. transport, angle-dependent X-ray photoemission spectroscopy, and temperature-dependent magnetoresistance. The observation of clear hysteresis in magnetotransport at low magnetic fields implies spin-polarization from magnetic islands in the hole rich LaTiO3 near the interface. These findings emphasize the role of magnetic instabilities in doped Mott insulators, thus providing another path for designing all-oxide structures relevant to spintronic applications.

  8. Optical Properties of Nitrogen-Substituted Strontium Titanate Thin Films Prepared by Pulsed Laser Deposition

    PubMed Central

    Marozau, Ivan; Shkabko, Andrey; Döbeli, Max; Lippert, Thomas; Logvinovich, Dimitri; Mallepell, Marc; Schneider, Christof W.; Weidenkaff, Anke; Wokaun, Alexander

    2009-01-01

    Perovskite-type N‑substituted SrTiO3 thin films with a preferential (001) orientation were grown by pulsed laser deposition on (001)-oriented MgO and LaAlO3 substrates. Application of N2 or ammonia using a synchronized reactive gas pulse produces SrTiO3-x:Nx films with a nitrogen content of up to 4.1 at.% if prepared with the NH3 gas pulse at a substrate temperature of 720 °C. Incorporating nitrogen in SrTiO3 results in an optical absorption at 370‑460 nm associated with localized N(2p) orbitals. The estimated energy of these levels is ≈2.7 eV below the conduction band. In addition, the optical absorption increases gradually with increasing nitrogen content.

  9. Observation of a two-dimensional liquid of Fröhlich polarons at the bare SrTiO3 surface

    PubMed Central

    Chen, Chaoyu; Avila, José; Frantzeskakis, Emmanouil; Levy, Anna; Asensio, Maria C.

    2015-01-01

    The polaron is a quasi-particle formed by a conduction electron (or hole) together with its self-induced polarization in a polar semiconductor or an ionic crystal. Among various polarizable examples of complex oxides, strontium titanate (SrTiO3) is one of the most studied. Here we examine the carrier type and the interplay of inner degrees of freedom (for example, charge, lattice, orbital) in SrTiO3. We report the experimental observation of Fröhlich polarons, or large polarons, at the bare SrTiO3 surface prepared by vacuum annealing. Systematic analyses of angle-resolved photoemission spectroscopy and X-ray absorption spectra show that these Fröhlich polarons are two-dimensional and only exist with inversion symmetry breaking by two-dimensional oxygen vacancies. Our discovery provides a rare solvable field theoretical model, and suggests the relevance of large (bi)polarons for superconductivity in perovskite oxides, as well as in high-temperature superconductors. PMID:26489376

  10. Controlling BaZrO3 nanostructure orientation in YBa2Cu3O{}_{7-\\delta } films for a three-dimensional pinning landscape

    NASA Astrophysics Data System (ADS)

    Wu, J. Z.; Shi, J. J.; Baca, F. J.; Emergo, R.; Wilt, J.; Haugan, T. J.

    2015-12-01

    The orientation phase diagram of self-assembled BaZrO3 (BZO) nanostructures in c-oriented YBa2Cu3O{}7-δ (YBCO) films on flat and vicinal SrTiO3 substrates was studied experimentally with different dopant concentrations and vicinal angles and theoretically using a micromechanical model based on the theory of elasticity. The organized BZO nanostructure configuration was found to be tunable, between c-axis to ab-plane alignment, by the dopant concentration in the YBCO film matrix strained via lattice mismatched substrates. The correlation between the local strain caused by the BZO doping and the global strain on the matrix provides a unique approach for controllable growth of dopant nanostructure landscapes. In particular, a mixed phase of the c-axis-aligned nanorods and the ab-plane-aligned planar nanostructures can be obtained, leading to a three-dimensional pinning landscape with single impurity doping and much improved J c in almost all directions of applied magnetic field.

  11. Photovoltaic effect of ferroelectric Pb(Zr0.52,Ti0.48)O3 deposited on SrTiO3 buffered n-GaAs by laser molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zhou, Yunxia; Zhu, Jun; Liu, Xingpeng; Wu, Zhipeng

    Ferroelectric Pb(Zr0.52,Ti0.48)O3(PZT) thin film was grown on n-type GaAs (001) substrate with SrTiO3 (STO) buffer layer by laser molecular beam epitaxy (L-MBE). The epitaxial process of the STO was in situ monitored by reflection high-energy electron diffraction (RHEED). The crystallographical growth orientation relationship was revealed to be (002) 〈100〉 PZT//(002) 〈100〉 STO//(001) 〈110〉 GaAs by RHEED and X-ray diffraction (XRD). It was found that a small lattice mismatch between PZT and GaAs with a 45∘ in-plane rotation relationship can be formed by inserting of a buffer layer STO. Besides, the enhanced electrical properties of the heterostructure were obtained with the short-circuit photocurrent increased to 52mA/cm2 and the better power conversation efficiency increased by 20% under AM1.5G (100mW/cm2) illumination. The work could provide a way for the application of this kind of heterostructure with high photocurrent response in optoelectronic thin film devices.

  12. A-SITE-AND/OR B-SITE-MODIFIED PBZRTIO3 MATERIALS AND (PB, SR, CA, BA, MG) (ZR, TI,NB, TA)O3 FILMS HAVING UTILITY IN FERROELECTRIC RANDOM ACCESS MEMORIES AND HIGH PERFORMANCE THIN FILM MICROACTUATORS

    NASA Technical Reports Server (NTRS)

    Bilodeau, Steven (Inventor); Baum, Thomas H. (Inventor); Roeder, Jeffrey F. (Inventor); Chen, Ing-Shin (Inventor)

    2004-01-01

    A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

  13. Low-Temperature Dielectric Anisotropy Driven by an Antiferroelectric Mode in SrTiO3

    NASA Astrophysics Data System (ADS)

    Casals, Blai; Schiaffino, Andrea; Casiraghi, Arianna; Hämäläinen, Sampo J.; López González, Diego; van Dijken, Sebastiaan; Stengel, Massimiliano; Herranz, Gervasi

    2018-05-01

    Strontium titanate (SrTiO3 ) is the quintessential material for oxide electronics. One of its hallmark features is the transition, driven by antiferrodistortive (AFD) lattice modes, from a cubic to a ferroelastic low-temperature phase. Here we investigate the evolution of the ferroelastic twin walls upon application of an electric field. Remarkably, we find that the dielectric anisotropy of tetragonal SrTiO3 , rather than the intrinsic domain wall polarity, is the main driving force for the motion of the twins. Based on a combined first-principles and Landau-theory analysis, we show that such anisotropy is dominated by a trilinear coupling between the polarization, the AFD lattice tilts, and a previously overlooked antiferroelectric (AFE) mode. We identify the latter AFE phonon with the so-called "R mode" at ˜440 cm-1 , which was previously detected in IR experiments, but whose microscopic nature was unknown.

  14. Lattice relaxation in oxide heterostructures: LaTiO3/SrTiO3 superlattices.

    PubMed

    Okamoto, Satoshi; Millis, Andrew J; Spaldin, Nicola A

    2006-08-04

    Local density approximation + Hubbard U and many-body effective Hamiltonian calculations are used to determine the effects of lattice relaxation in LaTiO3/SrTiO3 superlattices. Large ferroelectric-like distortions of the TiO6 octahedra are found, which substantially affect the Ti d-electron density, bringing the calculated results into good agreement with experimental data. The relaxations also change the many-body physics, leading to a novel symmetry-breaking-induced ordering of the xy orbitals, which does not occur in bulk LaTiO3, or in the hypothetical unrelaxed structure.

  15. Growth and magnetic properties of multiferroic LaxBi1-xMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Gajek, M.; Bibes, M.; Wyczisk, F.; Varela, M.; Fontcuberta, J.; Barthélémy, A.

    2007-05-01

    A comparative study of LaxBi1-xMnO3 thin films grown on SrTiO3 substrates is reported. It is shown that these films grow epitaxially in a narrow pressure-temperature range. A detailed structural and compositional characterization of the films is performed within the growth window. The structure and the magnetization of this system are investigated. We find a clear correlation between the magnetization and the unit-cell volume that we ascribe to Bi deficiency and the resultant introduction of a mixed valence on the Mn ions. On these grounds, we show that the reduced magnetization of LaxBi1-xMnO3 thin films compared to the bulk can be explained quantitatively by a simple model, taking into account the deviation from nominal composition and the Goodenough-Kanamori-Anderson rules of magnetic interactions.

  16. Strain induced atomic structure at the Ir-doped LaAlO3/SrTiO3 interface.

    PubMed

    Lee, M; Arras, R; Warot-Fonrose, B; Hungria, T; Lippmaa, M; Daimon, H; Casanove, M J

    2017-11-01

    The structure of Ir-doped LaAlO 3 /SrTiO 3 (001) interfaces was investigated on the atomic scale using probe-corrected transmission electron microscopy in high-angle annular dark-field scanning mode (HAADF-STEM) and electron energy loss spectroscopy (EELS), combined with first-principles calculations. We report the evolution of the strain state experimentally measured in a 5 unit-cell thick LaAlO 3 film as a function of the Ir concentration in the topmost SrTiO 3 layer. It is shown that the LaAlO 3 layers remain fully elastically strained up to 3% of Ir doping, whereas a higher doping level seems to promote strain relaxation through enhanced cationic interdiffusion. The observed differences between the energy loss near edge structure (ELNES) of Ti-L 2,3 and O-K edges at non-doped and Ir-doped interfaces are consistent with the location of the Ir dopants at the interface, up to 3% of Ir doping. These findings, supported by the results of density functional theory (DFT) calculations, provide strong evidence that the effect of dopant concentrations on the properties of this kind of interface should not be analyzed without obtaining essential information from the fine structural and chemical analysis of the grown structures.

  17. Ba3CuOs2O9 and Ba3ZnOs2O9, a comparative study

    NASA Astrophysics Data System (ADS)

    Feng, Hai L.; Jansen, Martin

    2018-02-01

    Polycrystalline samples of Ba3CuOs2O9 and Ba3ZnOs2O9 were synthesized by solid-state reactions. Ba3CuOs2O9 crystallizes in Cmcm, while Ba3ZnOs2O9 adopts the hexagonal space group P63/mmc. Both the crystal structures consist of face-sharing Os-centered octahedra forming dimer-like Os2O9 units, which are interconnected by corner-sharing CuO6, or ZnO6 octahedra, respectively. In Ba3CuOs2O9, the CuO6 octahedra show a characteristic Jahn-Teller distortion. Both, Ba3CuOs2O9 and Ba3ZnOs2O9, are electrically insulating. Magnetic and specific heat measurements confirm that Ba3CuOs2O9 is antiferromagnetically ordered below 47 K. Analysis of the magnetic data indicated that its magnetic properties are dominated by Cu2+ ions. The magnetic susceptibility of Ba3ZnOs2O9 is weakly temperature-dependent with a broad maximum ≈ 280 K, indicating the presence of strong exchange interactions within the Os2O9 dimer. The residual magnetic susceptibility at low temperatures also suggests the presence of appreciable exchange coupling between the dimers.

  18. Evolution of subband structure with gate-tuning at LaAlO3/SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Tang, Lucas; Smink, Sander; van Heeringen, Linde; Geessinck, Jaap; Rana, Abimanuya; Rastogi, Ankur; Maan, Jan Kees; Brinkman, Alexander; Zeitler, Uli; Hilgenkamp, Hans; McCollam, Alix

    The outstanding characteristic of LaAlO3/SrTiO3 heterostructures is the formation of a high mobility 2D electron gas (2DEG) at the interface. The additional presence of superconductivity, magnetism and large spin-orbit coupling in these systems suggests that strong correlations play an important role in the electronic properties, in contrast to conventional semiconductor-based 2DEGs. Knowledge of the electronic bandstructure, and the interdependence of conduction electron density and properties is therefore essential for our understanding of these materials. We present new results of low temperature transport measurements in a high mobility LaAlO3/SrTiO3-based heterostructure, in magnetic fields up to 33 T. Shubnikov de-Haas oscillations are observed, revealing several subbands with different carrier densities. By application of an electric field in the back gate geometry, the Fermi level is tuned and thus we are able to map the smooth evolution of the subbands and their properties with carrier density. These results are in good agreement with recent theoretical work, such that we can disentangle the complex band structure, and quantify aspects such as Rashba spin-splitting and the mixing of orbital character.

  19. The first-principle study of the electronic, optical and thermoelectric properties of XTiO3 (X = Ca, Sr and Ba) compounds

    NASA Astrophysics Data System (ADS)

    Mubarak, A. A.

    2016-07-01

    The FP-LAPW method is utilized to investigate the elastic, optoelectronic and thermoelectric properties of XTiO3 (X = Ca, Sr and Ba) within the GGA. The calculated lattice constants and bulk modulus are found in agreement with previous studies. The present oxide-perovskite compounds are characterized as elastically stable and anisotropic. CaTiO3 and SrTiO3 are categorized as ductile compounds, whereas the BaTiO3 compound is in the critical region between ductile and brittle. The DOS and the band structure calculations reveal indirect (M-Γ) energy bandgap for the present compounds. The hydrostatic pressure increases the energy bandgap and the width of the valence band. The character of the band structure does not change due to this pressure. The optical parameters are calculated in different radiation regions. Beneficial optics applications are predicted as revealed from the optical spectra. The transport properties are applied as a function of the variable temperatures or carrier concentration. It is found that the compounds under study are classified as a p-type semiconductor. The majority charge carriers responsible for conduction in these calculated compounds are holes rather than electrons.

  20. Insight into synergistically enhanced adsorption and visible light photocatalytic performance of Z-scheme heterojunction of SrTiO3(La,Cr)-decorated WO3 nanosheets

    NASA Astrophysics Data System (ADS)

    Liu, Xin; Jiang, Junzhe; Jia, Yushuai; Qiu, Jinmin; Xia, Tonglin; Zhang, Yuhong; Li, Yuqin; Chen, Xiangshu

    2017-08-01

    The efficient treatment of dye wastewater has been a hot topic of environment field. The integration of adsorption and photocatalytic degradation via fabrication of bi-component heterojunction photocatalyst is considered as a facile and effective strategy to enhance the dye elimination efficiency. In this report, a Z-scheme heterojunction material, SrTiO3(La,Cr)/WO3 with bifunction of adsorption and photocatalysis was successfully synthesized for efficient removal of methylene blue (MB) under visible light irradiation. The morphology and microstructure characterization demonstrates that the SrTiO3(La,Cr) nanoparticles are uniformly decorated on the WO3 nanosheets, forming an intimate heterojunction interface. MB degradation results indicate that the removal efficiency by the synergistic adsorption-photocatalysis process is greatly improved compared to pure WO3 and SrTiO3(La,Cr) with the adsorption and photocatalytic activity closely related to the composition of the material. The possible mechanism for the enhanced photocatalytic activity could be ascribed to the formation of a Z-scheme heterojunction system based on active species trapping experiments. Furthermore, the investigations of adsorption kinetics and isotherm show that the adsorption process follows pseudo-second-order kinetic model and Langmuir isotherm, respectively. Due to the synergistic advantages of negative zeta potential, large surface area and accelerated separation of photogenerated carriers driven by Z-scheme heterojunction, SrTiO3(La,Cr)/WO3 exhibits excellent adsorption-photocatalytic performance and stability on MB removal, which could be potentially used for practical wastewater treatment.

  1. Laser ablated high T(sub c) superconducting thin YBa2Cu3O(7-x) films on substrates suitable for microwave applications

    NASA Astrophysics Data System (ADS)

    Warner, J. D.; Meola, J. E.; Jenkins, K. A.; Bhasin, K. B.

    1990-04-01

    The development of high temperature superconducting YBa2Cu3O(7-x) thin films on substrates suitable for microwave applications is of great interest for evaluating their applications for space radar, communication, and sensor systems. Thin films of YBa2Cu3O(7-x) were formed on SrTiO3, ZrO2, MgO, and LaAlO3 substrates by laser ablation. The wavelength used was 248 nm from a KrF excimer laser. During deposition the films were heated to 600 C in a flowing oxygen environment, and required no post annealing. The low substrate temperature during deposition with no post annealing gave films which were smooth, which had their c-axis aligned to the substrates, and which had grains ranging from 0.2 to 0.5 microns in size. The films being c-axis aligned gave excellent surface resistance at 35 GHz which was lower than that of copper at 77 K. At present, LaAlO3 substrates with a dielectric constant of 22, appears suitable as a substrate for microwave and electronic applications. The films were characterized by resistance-temperature measurements, scanning electron microscopy, and x ray diffraction. The highest critical transition temperatures (T sub c) are above 89 K for films on SrTiO3 and LaAlO3, above 88 K for ZrO2, and above 86 K for MgO. The critical current density (J sub c) of the films on SrTiO3 is above 2 x 10(exp 6) amperes/sq cm at 77 K. The T(sub c) and J(sub c) are reported as a function of laser power, composition of the substrate, and temperature of the substrate during deposition.

  2. New insights on the synthesis and electronic transport in bulk polycrystalline Pr-doped SrTiO3

    NASA Astrophysics Data System (ADS)

    Dehkordi, Arash Mehdizadeh; Bhattacharya, Sriparna; Darroudi, Taghi; Alshareef, Husam N.; Tritt, Terry M.

    2015-02-01

    Recently, we have reported a significant enhancement in the electronic and thermoelectric properties of bulk polycrystalline SrTiO3 ceramics via praseodymium doping. This improvement was originated from the simultaneous enhancement in the thermoelectric power factor and reduction in thermal conductivity, which was contributed to the non-uniform distribution of Pr dopants. In order to further understand the underlying mechanism, we herein investigate the role of praseodymium doping source (Pr2O3 versus Pr6O11) on the synthesis and electronic transport in Pr-doped SrTiO3 ceramics. It was observed that the high-temperature electronic transport properties are independent of the choice of praseodymium doping source for samples prepared following our synthesis strategy. Theoretical calculations were also performed in order to estimate the maximum achievable power factor and the corresponding optimal carrier concentration. The result suggests the possibility of further improvement of the power factor. This study should shed some light on the superior electronic transport in bulk polycrystalline Pr-doped SrTiO3 ceramics and provide new insight on further improvement of the thermoelectric power factor.

  3. High electromechanical strain and enhanced temperature characteristics in lead-free (Na,Bi)TiO3-BaTiO3 thin films on Si substrates.

    PubMed

    Tanaka, Yoshiaki; Okamoto, Shoji; Hashimoto, Kazuya; Takayama, Ryoichi; Harigai, Takakiyo; Adachi, Hideaki; Fujii, Eiji

    2018-05-18

    Here, we demonstrate the high electromechanical strain and enhanced temperature characteristics in the c-axis-oriented lead-free (Na,Bi)TiO 3 -BaTiO 3 (NBT-BT) polycrystalline thin film prepared on Si substrates by rf magnetron sputtering. The effective transverse piezoelectric coefficient, e 31 * , estimated from the electromechanical strain measured under high electric field, reaches a high level of -12.5 C/m 2 , and is comparable to those of conventional Pb(Zr,Ti)O 3 films. In-situ X-ray diffraction measurement and electron diffraction analysis revealed the electromechanical strain of the NBT-BT film to originate predominantly in elongation of the tetragonal (P4bm) crystal lattice in the c-axis direction. In addition to the large e 31 * , the NBT-BT film exhibits enhanced permittivity maximum temperature, T m , of ~400 °C and no depolarization below T m , as compared to bulk NBT-BT having T m ≈ 300 °C and a depolarization temperature of ~100 °C. We conclude that the enhancement of temperature characteristics is associated with the distorted P4bm crystal lattice formed by deposition-induced stress and defects. We believe that the present study paves the way for practical applications of lead-free piezoelectric thin films in electromechanical devices.

  4. Thickness and angular dependent magnetic anisotropy of La0.67Sr0.33MnO3 thin films by Vectorial Magneto Optical Kerr Magnetometry

    NASA Astrophysics Data System (ADS)

    Chaluvadi, S. K.; Perna, P.; Ajejas, F.; Camarero, J.; Pautrat, A.; Flament, S.; Méchin, L.

    2017-10-01

    We investigate the in-plane magnetic anisotropy in La0.67Sr0.33MnO3 thin films grown on SrTiO3 (001) substrate using angular dependent room temperature Vectorial Magneto-Optical Kerr Magnetometry. The experimental data reveals that the magnetic anisotropy symmetry landscape significantly changes depending upon the strain and thickness. At low film thickness (12 and 25 nm) the dominant uniaxial anisotropy is due to interface effects, step edges due to mis-cut angle of SrTiO3 substrate. At intermediate thickness, the magnetic anisotropy presents a competition between magnetocrystalline (biaxial) and substrate step induced (uniaxial) anisotropy. Depending upon their relative strengths, a profound biaxial or uniaxial or mixed anisotropy is favoured. Above the critical thickness, magnetocrystalline anisotropy dominates all other effects and shows a biaxial anisotropy.

  5. Manipulation of Optical Transmittance by Ordered-Oxygen-Vacancy in Epitaxial LaBaCo 2O 5.5+δ Thin Films

    DOE PAGES

    Cheng, Sheng; Lu, Jiangbo; Han, Dong; ...

    2016-11-23

    Giant optical transmittance changes of over 300% in wide wavelength range from 500 nm to 2500 nm were observed in LaBaCo 2O 5.5+δ thin films annealed in air and ethanol ambient, respectively. The reduction process induces high density of ordered oxygen vacancies and the formation of LaBaCo 2O 5.5 (δ = 0) structure evidenced by aberration-corrected transmission electron microscopy. Moreover, the first-principles calculations reveal the origin and mechanism of optical transmittance enhancement in LaBaCo 2O 5.5 (δ = 0), which exhibits quite different energy band structure compared to that of LaBaCo 2O 6 (δ = 0.5). The discrepancy of energymore » band structure was thought to be the direct reason for the enhancement of optical transmission in reducing ambient. Thus, LaBaCo 2O 5.5+δ thin films show great prospect for applications on optical gas sensors in reducing/oxidizing atmosphere.« less

  6. Manipulation of Optical Transmittance by Ordered-Oxygen-Vacancy in Epitaxial LaBaCo2O5.5+δ Thin Films.

    PubMed

    Cheng, Sheng; Lu, Jiangbo; Han, Dong; Liu, Ming; Lu, Xiaoli; Ma, Chunrui; Zhang, Shengbai; Chen, Chonglin

    2016-11-23

    Giant optical transmittance changes of over 300% in wide wavelength range from 500 nm to 2500 nm were observed in LaBaCo 2 O 5.5+δ thin films annealed in air and ethanol ambient, respectively. The reduction process induces high density of ordered oxygen vacancies and the formation of LaBaCo 2 O 5.5 (δ = 0) structure evidenced by aberration-corrected transmission electron microscopy. Moreover, the first-principles calculations reveal the origin and mechanism of optical transmittance enhancement in LaBaCo 2 O 5.5 (δ = 0), which exhibits quite different energy band structure compared to that of LaBaCo 2 O 6 (δ = 0.5). The discrepancy of energy band structure was thought to be the direct reason for the enhancement of optical transmission in reducing ambient. Hence, LaBaCo 2 O 5.5+δ thin films show great prospect for applications on optical gas sensors in reducing/oxidizing atmosphere.

  7. Role of oxygen vacancies on light emission mechanisms in SrTiO3 induced by high-energy particles

    NASA Astrophysics Data System (ADS)

    Crespillo, M. L.; Graham, J. T.; Agulló-López, F.; Zhang, Y.; Weber, W. J.

    2017-04-01

    Light emission under MeV hydrogen and oxygen ions in stoichiometric SrTiO3 are identified at temperatures of 100 K, 170 K and room-temperature. MeV ions predominately deposit their energies to electrons in SrTiO3 with energy densities orders of magnitude higher than from UV or x-ray sources but comparable to femtosecond lasers. The ionoluminescence (IL) spectra can be resolved into three main Gaussian bands at 2.0 eV, 2.5 eV and 2.8 eV, whose relative contributions strongly depend on irradiation temperature, electronic energy loss and irradiation fluence. Two main bands, observed at 2.5 eV and 2.8 eV, are intrinsic and associated with electron-hole recombination in the perfect SrTiO3 lattice. The 2.8 eV band is attributed to recombination of free (conduction) electrons with an in-gap level, possibly related to self-trapped holes. Self-trapped excitons (STEs) are considered suitable candidates for the 2.5 eV emission band, which implies a large energy relaxation in comparison to the intrinsic edge transition. The dynamics of electronic excitation, governs a rapid initial rise of the intensity; whereas, accumulated irradiation damage (competing non-radiative recombination channels) accounts for a subsequent intensity decrease. The previously invoked role of isolated oxygen vacancies for the blue luminescence (2.8 eV) does not appear consistent with the data. An increasing well-resolved band at 2.0 eV dominates at 170 K and below. It has been only previously observed in heavily strained and amorphous SrTiO3, and is, here, attributed to transitions from d(t 2g) conduction band levels to d(e g) levels below the gap. In accordance with ab initio theoretical calculations they are associated to trapped electron states in relaxed Ti3+ centers at an oxygen vacancy within distorted TiO6 octahedra. The mechanism of defect evolution monitored during real-time IL experiments is presented. In conclusion, the light emission data confirm that IL is a useful

  8. Role of oxygen vacancies on light emission mechanisms in SrTiO 3 induced by high-energy particles

    DOE PAGES

    Crespillo, M. L.; Graham, J. T.; Agulló-López, F.; ...

    2017-02-23

    Light emission under MeV hydrogen and oxygen ions in stoichiometric SrTiO 3 are identified at temperatures of 100 K, 170 K and room-temperature. MeV ions predominately deposit their energies to electrons in SrTiO 3 with energy densities orders of magnitude higher than from UV or x-ray sources but comparable to femtosecond lasers. The ionoluminescence (IL) spectra can be resolved into three main Gaussian bands at 2.0 eV, 2.5 eV and 2.8 eV, whose relative contributions strongly depend on irradiation temperature, electronic energy loss and irradiation fluence. Two main bands, observed at 2.5 eV and 2.8 eV, are intrinsic and associatedmore » with electron–hole recombination in the perfect SrTiO 3 lattice. The 2.8 eV band is attributed to recombination of free (conduction) electrons with an in-gap level, possibly related to self-trapped holes. Self-trapped excitons (STEs) are considered suitable candidates for the 2.5 eV emission band, which implies a large energy relaxation in comparison to the intrinsic edge transition. The dynamics of electronic excitation, governs a rapid initial rise of the intensity; whereas, accumulated irradiation damage (competing non-radiative recombination channels) accounts for a subsequent intensity decrease. The previously invoked role of isolated oxygen vacancies for the blue luminescence (2.8 eV) does not appear consistent with the data. An increasing well-resolved band at 2.0 eV dominates at 170 K and below. It has been only previously observed in heavily strained and amorphous SrTiO 3, and is, here, attributed to transitions from d(t 2g) conduction band levels to d(e g) levels below the gap. In accordance with ab initio theoretical calculations they are associated to trapped electron states in relaxed Ti 3+ centers at an oxygen vacancy within distorted TiO 6 octahedra. The mechanism of defect evolution monitored during real-time IL experiments is presented. In conclusion, the light emission data confirm that IL is a useful tool to

  9. Correlation between superconductivity, band filling, and electron confinement at the LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Smink, A. E. M.; Stehno, M. P.; de Boer, J. C.; Brinkman, A.; van der Wiel, W. G.; Hilgenkamp, H.

    2018-06-01

    By combined top- and backgating, we explore the correlation of superconductivity with band filling and electron confinement at the LaAlO3/SrTiO3 interface. We find that the top- and backgate voltages have distinctly different effects on the superconducting critical temperature, implying that the confining potential well has a profound effect on superconductivity. We investigate the origin of this behavior by comparing the gate dependence of Tc to the corresponding evolution of the band filling with gate voltage. For several backgate voltages, we observe maximum Tc to consistently coincide with a kink in tuning the band filling for high topgate voltage. Self-consistent Schrödinger-Poisson calculations relate this kink to a Lifshitz transition of the second dx y subband. These results establish a major role for confinement-induced subbands in the phase diagram of SrTiO3 surface states, and establish gating as a means to control the relative energy of these states.

  10. Atomic and electronic structure of oxygen vacancies and Nb-impurity in SrTiO3

    NASA Astrophysics Data System (ADS)

    Hamid, A. S.

    2009-12-01

    We present the results of a first-principle full-potential linearized augmented plane wave (FLAPW) method to study the effect of defects on the electronic structure of SrTiO3. In addition, the relaxation of nearest neighbor atoms around those defects were calculated self-consistently. The calculations were performed using the local (spin) density approximations (L(S)DA), for the exchange-correlation potential. SrTiO3 was found to experience an insulator-to-metal transition upon the formation of oxygen vacancies or the substitution of Nb at the Ti site. The formation of oxygen divacancy disclosed additional states below the conduction band edge. The crystalline lattice relaxation showed displacements of atoms in rather large defective region. The magnitudes of atomic movements, however, were not large, normally not exceeding 0.15 Å. Our results were compared to the available experimental observations.

  11. Room temperature ferromagnetism in BiFe1-xMnxO3 thin film induced by spin-structure manipulation

    NASA Astrophysics Data System (ADS)

    Shigematsu, Kei; Asakura, Takeshi; Yamamoto, Hajime; Shimizu, Keisuke; Katsumata, Marin; Shimizu, Haruki; Sakai, Yuki; Hojo, Hajime; Mibu, Ko; Azuma, Masaki

    2018-05-01

    The evolution of crystal structure, spin structure, and macroscopic magnetization of manganese-substituted BiFeO3 (BiFe1-xMnxO3), a candidate for multiferroic materials, were investigated on bulk and epitaxial thin-film. Mn substitution for Fe induced collinear antiferromagnetic spin structure around room temperature by destabilizing the cycloidal spin modulation which prohibited the appearance of net magnetization generated by Dzyaloshinskii-Moriya interaction. For the bulk samples, however, no significant signal of ferromagnetism was observed because the direction of the ordered spins was close to parallel to the electric polarization so that spin-canting did not occur. On the contrary, BiFe1-xMnxO3 thin film on SrTiO3 (001) had a collinear spin structure with the spin direction perpendicular to the electric polarization at room temperature, where the appearance of spontaneous magnetization was expected. Indeed, ferromagnetic hysteresis behavior was observed for BiFe0.9Mn0.1O3 thin film.

  12. Suppressed carrier density for the patterned high mobility two-dimensional electron gas at γ-Al2O3/SrTiO3 heterointerfaces

    NASA Astrophysics Data System (ADS)

    Niu, Wei; Gan, Yulin; Zhang, Yu; Valbjørn Christensen, Dennis; von Soosten, Merlin; Wang, Xuefeng; Xu, Yongbing; Zhang, Rong; Pryds, Nini; Chen, Yunzhong

    2017-07-01

    The two-dimensional electron gas (2DEG) at the non-isostructural interface between spinel γ-Al2O3 and perovskite SrTiO3 is featured by a record electron mobility among complex oxide interfaces in addition to a high carrier density up to the order of 1015 cm-2. Herein, we report on the patterning of 2DEG at the γ-Al2O3/SrTiO3 interface grown at 650 °C by pulsed laser deposition using a hard mask of LaMnO3. The patterned 2DEG exhibits a critical thickness of 2 unit cells of γ-Al2O3 for the occurrence of interface conductivity, similar to the unpatterned sample. However, its maximum carrier density is found to be approximately 3 × 1013 cm-2, much lower than that of the unpatterned sample (˜1015 cm-2). Remarkably, a high electron mobility of approximately 3600 cm2 V-1 s-1 was obtained at low temperatures for the patterned 2DEG at a carrier density of ˜7 × 1012 cm-2, which exhibits clear Shubnikov-de Haas quantum oscillations. The patterned high-mobility 2DEG at the γ-Al2O3/SrTiO3 interface paves the way for the design and application of spinel/perovskite interfaces for high-mobility all-oxide electronic devices.

  13. Growth, patterning, and weak-link fabrication of superconducting YBa2Cu3O(7-x) thin films

    NASA Astrophysics Data System (ADS)

    Hilton, G. C.; Harris, E. B.; van Harlingen, D. J.

    1988-09-01

    Thin films of the high-temperature superconducting ceramic oxides have been grown, and techniques for fabricating weak-link structures have been investigated. Films of YBa2Cu3O(7-x) grown on SrTiO3 by a combination of dc magnetron sputtering and thermal evaporation from the three sources have been patterned into microbridges with widths down to 2 microns. Evidence is found that the bridges behave as arrays of Josephson-coupled superconducting islands. Further weak-link behavior is induced by in situ modification of the coupling by ion milling through the bridge.

  14. Growth of Pb(Ti,Zr)O 3 thin films by metal-organic molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Avrutin, V.; Liu, H. Y.; Izyumskaya, N.; Xiao, B.; Özgür, Ü.; Morkoç, H.

    2009-02-01

    Single-crystal Pb(Zr xTi 1-x)O 3 thin films have been grown on (0 0 1) SrTiO 3 and SrTiO 3:Nb substrates by molecular beam epitaxy using metal-organic source of Zr and two different sources of reactive oxygen—RF plasma and hydrogen-peroxide sources. The same growth modes and comparable structural properties were observed for the films grown with both oxygen sources, while the plasma source allowed higher growth rates. The films with x up to 0.4 were single phase, while attempts to increase x beyond gave rise to the ZrO 2 second phase. The effects of growth conditions on growth modes, Zr incorporation, and phase composition of the Pb(Zr xTi 1-x)O 3 films are discussed. Electrical and ferroelectric properties of the Pb(Zr xTi 1-x)O 3 films of ~100 nm in thickness grown on SrTiO 3:Nb were studied using current-voltage, capacitance-voltage, and polarization-field measurements. The single-phase films show low leakage currents and large breakdown fields, while the values of remanent polarization are low (around 5 μC/cm 2). It was found that, at high sweep fields, the contribution of the leakage current to the apparent values of remanent polarization can be large, even for the films with large electrical resistivity (˜10 8-10 9 Ω cm at an electric filed of 1 MV/cm). The measured dielectric constant ranges from 410 to 260 for Pb(Zr 0.33Ti 0.67)O 3 and from 313 to 213 for Pb(Zr 0.2Ti 0.8)O 3 in the frequency range from 100 to 1 MHz.

  15. Impulse voltage control of continuously tunable bipolar resistive switching in Pt/Bi0.9Eu0.1FeO3/Nb-doped SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Wei, Maocai; Liu, Meifeng; Wang, Xiuzhang; Li, Meiya; Zhu, Yongdan; Zhao, Meng; Zhang, Feng; Xie, Shuai; Hu, Zhongqiang; Liu, Jun-Ming

    2017-03-01

    Epitaxial Bi0.9Eu0.1FeO3 (BEFO) thin films are deposited on Nb-doped SrTiO3 (NSTO) substrates by pulsed laser deposition to fabricate the Pt/BEFO/NSTO (001) heterostructures. These heterostructures possess bipolar resistive switching, where the resistances versus writing voltage exhibits a distinct hysteresis loop and a memristive behavior with good retention and anti-fatigue characteristics. The local resistive switching is confirmed by the conductive atomic force microscopy (C-AFM), suggesting the possibility to scale down the memory cell size. The observed memristive behavior could be attributed to the ferroelectric polarization effect, which modulates the height of potential barrier and width of depletion region at the BEFO/NSTO interface. The continuously tunable resistive switching behavior could be useful to achieve non-volatile, high-density, multilevel random access memory with low energy consumption.

  16. Conduction band edge effective mass of La-doped BaSnO{sub 3}

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    James Allen, S., E-mail: allen@itst.ucsb.edu; Law, Ka-Ming; Raghavan, Santosh

    2016-06-20

    BaSnO{sub 3} has attracted attention as a promising material for applications requiring wide band gap, high electron mobility semiconductors, and moreover possesses the same perovskite crystal structure as many functional oxides. A key parameter for these applications and for the interpretation of its properties is the conduction band effective mass. We measure the plasma frequency of La-doped BaSnO{sub 3} thin films by glancing incidence, parallel-polarized resonant reflectivity. Using the known optical dielectric constant and measured electron density, the resonant frequency determines the band edge electron mass to be 0.19 ± 0.01. The results allow for testing band structure calculations and transport models.

  17. Phase transitions and domain structures in multiferroics

    NASA Astrophysics Data System (ADS)

    Vlahos, Eftihia

    2011-12-01

    Thin film ferroelectrics and multiferroics are two important classes of materials interesting both from a scientific and a technological prospective. The volatility of lead and bismuth as well as environmental issues regarding the toxicity of lead are two disadvantages of the most commonly used ferroelectric random access memory (FeRAM) materials such as Pb(Zr,Ti)O3 and SrBi2Ta2O9. Therefore lead-free thin film ferroelectrics are promising substitutes as long as (a) they can be grown on technologically important substrates such as silicon, and (b) their T c and Pr become comparable to that of well established ferroelectrics. On the other hand, the development of functional room temperature ferroelectric ferromagnetic multiferroics could lead to very interesting phenomena such as control of magnetism with electric fields and control of electrical polarization with magnetic fields. This thesis focuses on the understanding of material structure-property relations using nonlinear optical spectroscopy. Nonlinear spectroscopy is an excellent tool for probing the onset of ferroelectricity, and domain dynamics in strained ferroelectrics and multiferroics. Second harmonic generation was used to detect ferroelectricity and the antiferrodistortive phase transition in thin film SrTiO3. Incipient ferroelectric CaTiO3 has been shown to become ferroelectric when strained with a combination of SHG and dielectric measurements. The tensorial nature of the induced nonlinear polarization allows for probing of the BaTiO3 and SrTiO3 polarization contributions in nanoscale BaTiO3/SrTiO3 superlattices. In addition, nonlinear optics was used to demonstrate ferroelectricity in multiferroic EuTiO3. Finally, confocal SHG and Raman microscopy were utilized to visualize polar domains in incipient ferroelectric and ferroelastic CaTiO3.

  18. Conductor-backed coplanar waveguide resonators of Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O on LaAlO3

    NASA Technical Reports Server (NTRS)

    Miranda, F. A.; Bhasin, K. B.; Stan, M. A.; Kong, K. S.; Itoh, T.

    1992-01-01

    Conductor-backed coplanar waveguide (CBCPW) resonators operating at 10.8 GHz have been fabricated from Tl-Ba-Ca-O (TBCCO) and Y-Ba-Cu-O (YBCO) thin films on LaAlO3. The resonators consist of a coplanar waveguide (CPW) patterned on the superconducting film side of the LaAlO3 substrate with a gold ground plane coated on the opposite side. These resonators were tested in the temperature range from 14 to 106 K. At 77 K, the best of our TBCCO and YBCO resonators have an unloaded quality factor (Qo) 7 and 4 times, respectively, larger than that of a similar all-gold resonator. In this study, the Qo's of the TBCCO resonators were larger than those of their YBCO counterparts throughout the aforementioned temperature range.

  19. Electronic Degeneracy and Intrinsic Magnetic Properties of EpitaxialNb: SrTiO3 Thin Films Controlled by Defects.

    PubMed

    Sarantopoulos, A; Ferreiro-Vila, E; Pardo, V; Magén, C; Aguirre, M H; Rivadulla, F

    2015-10-16

    We report thermoelectric power experiments in e-doped thin films of SrTiO3 (STO) which demonstrate that the electronic band degeneracy can be lifted through defect management during growth. We show that even small amounts of cationic vacancies, combined with epitaxial stress, produce a homogeneous tetragonal distortion of the films, resulting in a Kondo-like resistance upturn at low temperature, large anisotropic magnetoresistance, and nonlinear Hall effect. Ab initio calculations confirm a different occupation of each band depending on the degree of tetragonal distortion. The phenomenology reported in this Letter for tetragonally distorted e-doped STO thin films, is similar to that observed in LaAlO3/STO interfaces and magnetic STO quantum wells.

  20. Orientation Control of Interfacial Magnetism at La 0.67Sr 0.33MnO 3/SrTiO 3 Interfaces

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Guo, Er-Jia; Charlton, Timothy; Ambaye, Haile

    Understanding the magnetism at the interface between a ferromagnet and an insulator is essential because the commonly posited magnetic “dead” layer close to an interface can be problematic in magnetic tunnel junctions. Previously, degradation of the magnetic interface was attributed to charge discontinuity across the interface. In this paper, the interfacial magnetism was investigated using three identically prepared La 0.67Sr 0.33MnO 3 (LSMO) thin films grown on different oriented SrTiO 3 (STO) substrates by polarized neutron reflectometry. In all cases the magnetization at the LSMO/STO interface is larger than the film bulk. We show that the interfacial magnetization is largestmore » across the LSMO/STO interfaces with (001) and (111) orientations, which have the largest net charge discontinuities across the interfaces. In contrast, the magnetization of LSMO/STO across the (110) interface, the orientation with no net charge discontinuity, is the smallest of the three orientations. We show that a magnetically degraded interface is not intrinsic to LSMO/STO heterostructures. Finally, the approach to use different crystallographic orientations provides a means to investigate the influence of charge discontinuity on the interfacial magnetization.« less

  1. Orientation Control of Interfacial Magnetism at La 0.67Sr 0.33MnO 3/SrTiO 3 Interfaces

    DOE PAGES

    Guo, Er-Jia; Charlton, Timothy; Ambaye, Haile; ...

    2017-05-16

    Understanding the magnetism at the interface between a ferromagnet and an insulator is essential because the commonly posited magnetic “dead” layer close to an interface can be problematic in magnetic tunnel junctions. Previously, degradation of the magnetic interface was attributed to charge discontinuity across the interface. In this paper, the interfacial magnetism was investigated using three identically prepared La 0.67Sr 0.33MnO 3 (LSMO) thin films grown on different oriented SrTiO 3 (STO) substrates by polarized neutron reflectometry. In all cases the magnetization at the LSMO/STO interface is larger than the film bulk. We show that the interfacial magnetization is largestmore » across the LSMO/STO interfaces with (001) and (111) orientations, which have the largest net charge discontinuities across the interfaces. In contrast, the magnetization of LSMO/STO across the (110) interface, the orientation with no net charge discontinuity, is the smallest of the three orientations. We show that a magnetically degraded interface is not intrinsic to LSMO/STO heterostructures. Finally, the approach to use different crystallographic orientations provides a means to investigate the influence of charge discontinuity on the interfacial magnetization.« less

  2. Photoresponse in La0.9Hf0.1MnO3/0.05wt%Nb-doped SrTiO3 heteroepitaxial junctions

    NASA Astrophysics Data System (ADS)

    Qi, Yaping; Ni, Hao; Zheng, Ming; Zeng, Jiali; Jiang, Yucheng; Gao, Ju

    2018-05-01

    Excellent photo detectors need to have the rapid response and good repeatability from the requirement of industrial applications. In this paper, transport behavior and opto-response of heterostructures made with La0.9Hf0.1MnO3 and 0.05wt%Nb-doped SrTiO3 were investigated. The heterojunctions exhibited an excellent rectifying feature with very low leakage in a broad temperature region (from 40 to 300 K). These thin films presented persistent and stable photovoltages upon light illumination. Rapid shift between small and large voltages corresponding to "light OFF" and "light ON" states, respectively, was observed, demonstrating reliable photo detection behavior. A semiconductor laser with a wavelength of 650 nm was used as the light source. It is also noted that the observed photovoltages are strongly determined by light intensity. The injection of photoexcited charge carriers (electrons) could be responsible for the appearance of the observed opto-response. Such manipulative features by light irradiation exhibit great potential for light detectors for visible light.

  3. Variation in superconducting transition temperature due to tetragonal domains in two-dimensionally doped SrTiO 3

    DOE PAGES

    Noad, Hilary; Spanton, Eric M.; Nowack, Katja C.; ...

    2016-11-28

    Strontium titanate is a low-temperature, non–Bardeen-Cooper-Schrieffer superconductor that superconducts to carrier concentrations lower than in any other system and exhibits avoided ferroelectricity at low temperatures. Neither the mechanism of superconductivity in strontium titanate nor the importance of the structure and dielectric properties for the superconductivity are well understood. We studied the effects of twin structure on superconductivity in a 5.5-nm-thick layer of niobium-doped SrTiO 3 embedded in undoped SrTiO 3. We used a scanning superconducting quantum interference device susceptometer to image the local diamagnetic response of the sample as a function of temperature. We observed regions that exhibited a superconductingmore » transition temperature T c ≳ 10% higher than the temperature at which the sample was fully superconducting. The pattern of these regions varied spatially in a manner characteristic of structural twin domains. Some regions are too wide to originate on twin boundaries; therefore, we propose that the orientation of the tetragonal unit cell with respect to the doped plane affects T c. Finally, our results suggest that the anisotropic dielectric properties of SrTiO 3 are important for its superconductivity and need to be considered in any theory of the mechanism of the superconductivity.« less

  4. Growth control of oxygen stoichiometry in homoepitaxial SrTiO 3 films by pulsed laser epitaxy in high vacuum

    DOE PAGES

    Lee, Ho Nyung; Ambrose Seo, Sung S.; Choi, Woo Seok; ...

    2016-01-29

    In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO 3 (STO) thin films onmore » single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Thus, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but it expands the utility of pulsed laser epitaxy of other materials as well.₃« less

  5. Iso-oriented monolayer α-MoO 3 (010) films epitaxially grown on SrTiO 3 (001)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Du, Yingge; Li, Guoqiang; Peterson, Erik W.

    The ability to synthesis well-ordered two-dimensional materials under ultra-high vacuum and directly characterize them by other techniques in-situ can greatly advance our current understanding on their physical and chemical properties. In this paper, we demonstrate that iso-oriented α-MoO3 films with as low as single monolayer thickness can be reproducibly grown on SrTiO3(001) substrates by molecular beam epitaxy ( (010)MoO3 || (001)STO, [100]MoO3 || [100]STO or [010]STO) through a self-limiting process. While one in-plane lattice parameter of the MoO3 is very close to that of the SrTiO3 (aMoO3 = 3.96 Å, aSTO = 3.905 Å), the lattice mismatch along other directionmore » is large (~5%, cMoO3 = 3.70 Å), which leads to relaxation as clearly observed from the splitting of streaks in reflection high-energy electron diffraction (RHEED) patterns. A narrow range in the growth temperature is found to be optimal for the growth of monolayer α-MoO3 films. Increasing deposition time will not lead to further increase in thickness, which is explained by a balance between deposition and thermal desorption due to the weak van der Waals force between α-MoO3 layers. Lowering growth temperature after the initial iso-oriented α-MoO3 monolayer leads to thicker α-MoO3(010) films with excellent crystallinity.« less

  6. Tailoring the nature and strength of electron-phonon interactions in the SrTiO3(001) 2D electron liquid

    NASA Astrophysics Data System (ADS)

    Wang, Z.; McKeown Walker, S.; Tamai, A.; Wang, Y.; Ristic, Z.; Bruno, F. Y.; de la Torre, A.; Riccò, S.; Plumb, N. C.; Shi, M.; Hlawenka, P.; Sánchez-Barriga, J.; Varykhalov, A.; Kim, T. K.; Hoesch, M.; King, P. D. C.; Meevasana, W.; Diebold, U.; Mesot, J.; Moritz, B.; Devereaux, T. P.; Radovic, M.; Baumberger, F.

    2016-08-01

    Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides. Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO3(001) surface to reveal a remarkably complex evolution of electron-phonon coupling with the tunable carrier density of this system. At low density, where superconductivity is found in the analogous 2DEL at the LaAlO3/SrTiO3 interface, our angle-resolved photoemission data show replica bands separated by 100 meV from the main bands. This is a hallmark of a coherent polaronic liquid and implies long-range coupling to a single longitudinal optical phonon branch. In the overdoped regime the preferential coupling to this branch decreases and the 2DEL undergoes a crossover to a more conventional metallic state with weaker short-range electron-phonon interaction. These results place constraints on the theoretical description of superconductivity and allow a unified understanding of the transport properties in SrTiO3-based 2DELs.

  7. Modification of energy band alignment and electric properties of Pt/Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}/Pt thin-film ferroelectric varactors by Ag impurities at interfaces

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hirsch, S.; Komissinskiy, P., E-mail: komissinskiy@oxide.tu-darmstadt.de; Flege, S.

    2014-06-28

    We report on the effects of Ag impurities at interfaces of parallel-plate Pt/Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}/Pt thin film ferroelectric varactors. Ag impurities occur at the interfaces due to diffusion of Ag from colloidal silver paint used to attach the varactor samples with their back side to the plate heated at 600–750 °C during deposition of Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}. X-ray photoelectron spectroscopy and secondary ion mass spectrometry suggest that amount and distribution of Ag adsorbed at the interfaces depend strongly on the adsorbent surface layer. In particular, Ag preferentially accumulates on top of the Pt bottom electrode. The presence of Agmore » significantly reduces the barrier height between Pt and Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} leading to an increased leakage current density and, thus, to a severe degradation of the varactor performance.« less

  8. Manipulation of Optical Transmittance by Ordered-Oxygen-Vacancy in Epitaxial LaBaCo2O5.5+δ Thin Films

    PubMed Central

    Cheng, Sheng; Lu, Jiangbo; Han, Dong; Liu, Ming; Lu, Xiaoli; Ma, Chunrui; Zhang, Shengbai; Chen, Chonglin

    2016-01-01

    Giant optical transmittance changes of over 300% in wide wavelength range from 500 nm to 2500 nm were observed in LaBaCo2O5.5+δ thin films annealed in air and ethanol ambient, respectively. The reduction process induces high density of ordered oxygen vacancies and the formation of LaBaCo2O5.5 (δ = 0) structure evidenced by aberration-corrected transmission electron microscopy. Moreover, the first-principles calculations reveal the origin and mechanism of optical transmittance enhancement in LaBaCo2O5.5 (δ = 0), which exhibits quite different energy band structure compared to that of LaBaCo2O6 (δ = 0.5). The discrepancy of energy band structure was thought to be the direct reason for the enhancement of optical transmission in reducing ambient. Hence, LaBaCo2O5.5+δ thin films show great prospect for applications on optical gas sensors in reducing/oxidizing atmosphere. PMID:27876830

  9. Magneto-transport in LaTi1-xMnxO3/SrTiO3 oxide heterostructures

    NASA Astrophysics Data System (ADS)

    Kumar, Pramod; Dogra, Anjana; Budhani, R. C.

    2014-04-01

    We report the growth of ultrathin film of Mn doped LaTiO3 on TiO2 terminated SrTiO3 (001) substrate by pulsed laser deposition (PLD) and their electrical transport characteristics including magnetoresistance (MR). Though the replacement of Mn in LaTiO3 at the Ti site in dilute limit does not affect the metallic behaviour of films but variation in resistance is observed. Normalised resistance behaviour is explained on the basis of variation in charge carriers and increased interaction between Mn atoms in the system under investigation.

  10. Appearance and disappearance of ferromagnetism in ultrathin LaMnO3 on SrTiO3 substrate: A viewpoint from first principles

    NASA Astrophysics Data System (ADS)

    An, Ming; Weng, Yakui; Zhang, Huimin; Zhang, Jun-Jie; Zhang, Yang; Dong, Shuai

    2017-12-01

    The intrinsic magnetic state (ferromagnetic or antiferromagnetic) of ultrathin LaMnO3 films on the most commonly used SrTiO3 substrate is a long-existing question under debate. Either strain effect or nonstoichiometry was argued to be responsible for the experimental ferromagnetism. In a recent experiment [X. R. Wang, C. J. Li, W. M. Lü, T. R. Paudel, D. P. Leusink, M. Hoek, N. Poccia, A. Vailionis, T. Venkatesan, J. M. D. Coey, E. Y. Tsymbal, Ariando, and H. Hilgenkamp, Science 349, 716 (2015), 10.1126/science.aaa5198], one more mechanism, namely, the self-doping due to polar discontinuity, was argued to be the driving force of ferromagnetism beyond the critical thickness. Here systematic first-principles calculations have been performed to check these mechanisms in ultrathin LaMnO3 films as well as superlattices. Starting from the very precise descriptions of both LaMnO3 and SrTiO3, it is found that the compressive strain is the dominant force for the appearance of ferromagnetism, while the open surface with oxygen vacancies leads to the suppression of ferromagnetism. Within LaMnO3 layers, the charge reconstructions involve many competitive factors and certainly go beyond the intuitive polar catastrophe model established for LaAlO3/SrTiO3 heterostructures. Our paper not only explains the long-term puzzle regarding the magnetism of ultrathin LaMnO3 films but also sheds light on how to overcome the notorious magnetic dead layer in ultrathin manganites.

  11. Kondo effect with tunable spin-orbit interaction in LaTiO3/CeTiO3/SrTiO3 heterostructure.

    PubMed

    Ghising, Pramod; Das, Debarchan; Das, Shubhankar; Hossain, Z

    2018-07-18

    We have fabricated epitaxial films of CeTiO 3 (CTO) on (0 0 1) oriented SrTiO 3 (STO) substrates, which exhibit highly insulating and diamagnetic properties. X-ray photoelectron spectroscopy was used to establish the 3+  valence state of the Ce and Ti ions. Furthermore, we have also fabricated δ (CTO) doped LaTiO 3 (LTO)/SrTiO 3 thin films which exhibit variety of interesting properties including Kondo effect and spin-orbit interaction (SOI) at low temperatures. The SOI shows a non-monotonic behaviour as the thickness of the CTO layer is increased and is reflected in the value of characteristic SOI field ([Formula: see text]) obtained from weak anti-localization fitting. The maximum value of [Formula: see text] is 1.00 T for δ layer thickness of 6 u.c. This non-monotonic behaviour of SOI is attributed to the strong screening of the confining potential at the interface. The screening effect is enhanced by the CTO layer thickness and the dielectric constant of STO which increases at low temperatures. Due to the strong screening, electrons confined at the interface are spread deeper into the STO bulk where it starts to populate the Ti [Formula: see text] subbands; consequently the Fermi level crosses over from [Formula: see text] to the [Formula: see text] subbands. At the crossover region of [Formula: see text] where there is orbital mixing, SOI goes through a maximum.

  12. Major enhancement of the thermoelectric performance in Pr/Nb-doped SrTiO3 under strain

    NASA Astrophysics Data System (ADS)

    Amin, B.; Singh, N.; Tritt, T. M.; Alshareef, H. N.; Schwingenschlögl, U.

    2013-07-01

    The electronic structure and thermoelectric properties of strained (biaxially and uniaxially) Sr0.95Pr0.05TiO3 and SrTi0.95Nb0.05O3 are investigated in the temperature range from 300 K to 1200 K. Substitutions of Pr at the Sr site and Nb at the Ti site generate n-type doping and thus improve the thermoelectric performance as compared to pristine SrTiO3. Further enhancement is achieved by the application of strain, for example, of the Seebeck coefficient by 21% for Sr0.95Pr0.05TiO3 and 10% for SrTi0.95Nb0.05O3 at room temperature in the case of 5% biaxial strain. At 1200 K, we predict figures of merit of 0.58 and 0.55 for 2.5% biaxially strained Sr0.95Pr0.05TiO3 and SrTi0.95Nb0.05O3, respectively, which are the highest values reported for rare earth doped SrTiO3.

  13. Domain switching kinetics in ferroelectric-resistive BiFeO3 thin film memories

    NASA Astrophysics Data System (ADS)

    Meng, Jianwei; Jiang, Jun; Geng, Wenping; Chen, Zhihui; Zhang, Wei; Jiang, Anquan

    2015-02-01

    We fabricated (00l) BiFeO3 (BFO) thin films in different growth modes on SrRuO3/SrTiO3 substrates using a pulsed laser deposition technique. X-ray diffraction patterns show an out-of-plane lattice constant of 4.03 Å and ferroelectric polarization of 82 µC/cm2 for the BFO thin film in a layer-by-layer growth mode (2D-BFO), larger than 3.96 Å and 51 µC/cm2 for the thin film in the 3D-island formation growth mode (3D-BFO). The 2D-BFO thin film at 300 K shows switchable on/off diode currents upon polarization flipping near a negative coercive voltage, which is nevertheless absent from the above 3D-BFO thin film. From a positive-up-negative-down pulse characterization technique, we measured domain switching current transients as well as polarization-voltage (Pf-Vf) hysteresis loops in both semiconducting thin films. Pf-Vf hysteresis loops after 1 µs-retention time show the preferred domain orientation pointing to bottom electrodes in a 3D-BFO thin film. The poor retention of the domains pointing to top electrodes can be improved considerably in a 2D-BFO thin film. From these measurements, we extracted domain switching time dependence of coercive voltage at temperatures of 78-300 K. From these dependences, we found coercive voltages in semiconducting ferroelectric thin films much higher than those in insulating thin films, disobeying the traditional Merz equation. Finally, an equivalent resistance model in description of free-carrier compensation of the front domain boundary charge is developed to interpret this difference. This equivalent resistance can be coincidently extracted either from domain switching time dependence of coercive voltage or from applied voltage dependence of domain switching current, which drops almost linearly with the temperature until down to 0 in a ferroelectric insulator at 78 K.

  14. Molecular beam epitaxial growth, transmittance and photoluminescence spectra of zinc-blende CdTe thin films with high-quality on perovskite SrTiO3 (1 1 1) substrates

    NASA Astrophysics Data System (ADS)

    Song, Kun; Zhu, Xuanting; Tang, Kai; Bai, W.; Zhu, Liangqing; Yang, Jing; Zhang, Yuanyuan; Tang, Xiaodong; Chu, Junhao

    2018-03-01

    High-crystalline quality CdTe thin films are grown on the largely lattice-mismatched SrTiO3 (STO) (1 1 1) substrates by molecular beam epitaxy. A transformation from a three dimensional regime to a two dimensional one is observed by the reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM). The formation of an elastic deformation CdTe layer on STO (1 1 1), namely a pseudomorphic growth mode with a critical thickness of ∼40 nm, is supported by the RHEED, AFM and X-ray diffraction. Crystal structures and epitaxial relationships of CdTe epitaxial films on STO (1 1 1) are characterized by 2θ-ω scans and reciprocal space mapping. Two strong absorption peaks at the energies of ∼1.621 eV and ∼1.597 eV at 5 K are clearly observed for a ∼120 nm thick CdTe epitaxial film, which are proposed to be ascribed to the strained and unstrained epitaxial CdTe layers, respectively. Moreover, the presence of the exciton band while the absence of deep level defect states for the ∼120 nm thick CdTe film characterized by the temperature dependent photoluminescence spectra further supports the high-crystalline quality.

  15. Influence of the growth parameters on the electronic and magnetic properties of La0.67Sr0.33MnO3 epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Annese, E.; Mori, T. J. A.; Schio, P.; Rache Salles, B.; Cezar, J. C.

    2018-04-01

    The implementation of La0.67Sr0.33MnO3 thin films in multilayered structures in organic and inorganic spintronics devices requires the optimization of their electronic and magnetic properties. In this work we report the structural, morphological, electronic and magnetic characterizations of La0.67Sr0.33MnO3 epitaxial thin films on SrTiO3 substrates, grown by pulsed laser deposition under different growing conditions. We show that the fluence of laser shots and in situ post-annealing conditions are important parameters to control the tetragonality (c/a) of the thin films. The distortion of the structure has a remarkable impact on both surface and bulk magnetism, allowing the tunability of the materials properties for use in different applications.

  16. Physical properties of high performance fluoride ion conductor BaSnF4 thin films by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Patro, L. N.; Ravi Chandra Raju, N.; Meher, S. R.; Kamala Bharathi, K.

    2013-09-01

    This article presents the results on the growth and characterization of BaSnF4 thin films on glass substrates prepared by pulsed laser deposition technique. The structural results of BaSnF4 thin film carried out by glancing angle X-ray diffraction technique indicates the formation of the film with similar structure (tetragonal, P4/nmm) to the bulk target material. The absorption coefficient and band gap of the film is determined by suitable analysis of the transmittance spectra. The transport properties of the thin films are studied using impedance spectroscopy in the temperature range of 323-573 K. The frequency-dependent imaginary part of impedance plot shows that the conductivity relaxation is non-Debye in nature. The scaling behavior of the imaginary part of impedance at various frequencies indicates temperature-independent relaxation behavior.

  17. Hydrogen molecule defect in proton-conductive SrTiO3 Perovskite

    NASA Astrophysics Data System (ADS)

    Onishi, Taku

    2017-11-01

    In proton-conductive SrTiO3 perovskite, no hydrogen molecule defect ideally exists. However, the unforeseen chemical reaction is often observed after the use of fuel cell. From the viewpoint of battery safety, we have investigated the effect of hydrogen molecule defect by molecular orbital analysis. When counter cation vacancy exists, the activation energy for hydrogen molecule migration was 1.39 - 1.50 eV, which is much smaller than the dissociation energy of hydrogen molecule. It implies that hydrogen molecule may migrate without its dissociation.

  18. Grain-Size-Dependent Thermoelectric Properties of SrTiO3 3D Superlattice Ceramics

    NASA Astrophysics Data System (ADS)

    Zhang, Rui-zhi; Koumoto, Kunihito

    2013-07-01

    The thermoelectric (TE) performance of SrTiO3 (STO) 3D superlattice ceramics with 2D electron gas grain boundaries (GBs) was theoretically investigated. The grain size dependence of the power factor, lattice thermal conductivity, and ZT value were calculated by using Boltzmann transport equations. It was found that nanostructured STO ceramics with smaller grain size have larger ZT value. This is because the quantum confinement effect, energy filtering effect, and interfacial phonon scattering at GBs all become stronger with decreasing grain size, resulting in higher power factor and lower lattice thermal conductivity. These findings will aid the design of nanostructured oxide ceramics with high TE performance.

  19. A-site- and/or B-site-modified PbZrTiO3 materials and (Pb, Sr, Ca, Ba, Mg) (Zr, Ti, Nb, Ta)O3 films having utility in ferroelectric random access memories and high performance thin film microactuators

    NASA Technical Reports Server (NTRS)

    Bilodeau, Steven (Inventor); Baum, Thomas H. (Inventor); Roeder, Jeffrey F. (Inventor); Chen, Ing-Shin (Inventor)

    2001-01-01

    A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

  20. P-doped strontium titanate grown using two target pulsed laser deposition for thin film solar cells

    NASA Astrophysics Data System (ADS)

    Man, Hamdi

    Thin-film solar cells made of Mg-doped SrTiO3 p-type absorbers are promising candidates for clean energy generation. This material shows p-type conductivity and also demonstrates reasonable absorption of light. In addition, p-type SrTiO3 can be deposited as thin films so that the cost can be lower than the competing methods. In this work, Mg-doped SrTiO3 (STO) thin-films were synthesized and analyzed in order to observe their potential to be employed as the base semiconductor in photovoltaic applications. Mg-doped STO thin-films were grown by using pulsed laser deposition (PLD) using a frequency quadrupled Yttrium Aluminum Garnet (YAG) laser and with a substrate that was heated by back surface absorption of infrared (IR) laser light. The samples were characterized using X-ray photoelectron spectroscopy (XPS) and it was observed that Mg atoms were doped successfully in the stoichiometry. Reflection high energy electron diffraction (RHEED) spectroscopy proved that the thin films were polycrystalline. Kelvin Probe work function measurements indicated that the work function of the films were 4.167 eV after annealing. UV/Vis Reflection spectroscopy showed that Mg-doped STO thin-films do not reflect significantly except in the ultraviolet region of the spectrum where the reflection percentage increased up to 80%. Self-doped STO thin-films, Indium Tin Oxide (ITO) thin films and stainless steel foil (SSF) were studied in order to observe their characteristics before employing them in Mg-doped STO based solar cells. Self-doped STO thin films were grown using PLD and the results showed that they are capable of serving as the n-type semiconductor in solar cell applications with oxygen vacancies in their structure and low reflectivity. Indium Tin Oxide thin-films grown by PLD system showed low 25-50 ?/square sheet resistance and very low reflection features. Finally, commercially available stainless steel foil substrates were excellent substrates for the inexpensive growth of

  1. Local Structure and Anisotropy in the Amorphous Precursor= to Ba-Hexaferrite Thin Films

    NASA Astrophysics Data System (ADS)

    Snyder, J. E.; Harris, V. G.; Koon, N. C.; Sui, X.; Kryder, M. H.

    1996-03-01

    Ba-hexaferrite thin-films for recording media applications are commonly fabricated by a two-step process: sputter-deposition of an amorphous precursor, followed by annealing to crystallize the BaFe_12O_19 phase. The magnetic anisotropy of the crystalline films can be either in-plane or perpendicular, depending on the sputtering process used in the first step. However, conventional characterization techniques (x-ray diffraction and TEM) have been unable to observe any structure in the amorphous precursor films. In this study, such films are investigated by PD-EXAFS (polarization-dependent extended x-ray absorption fine structure). An anisotropic local ordered structure is observed around both Fe and Ba atoms in the "amorphous" films. This anisotropic local structure appears to determine the orientation of the fast-growing basal plane directions during crystallization, and thus the directions of the c-axes and the magnetic anisotropy. Results suggest that the structure of the amorphous films consists of networks made up of units of Fe atoms surrounded by their O nearest neighbors, that are connected together. Ba atoms appear to fit into in-between spaces as network-modifiers.

  2. Temperature dependence of superfluid density in YBa 2Cu 3O 7- δ and Y 0.7Ca 0.3Ba 2Cu 3O 7- δ thin films: A doping dependence study of the linear slope

    NASA Astrophysics Data System (ADS)

    Lai, L. S.; Juang, J. Y.; Wu, K. H.; Uen, T. M.; Gou, Y. S.

    2005-11-01

    By using a microstrip ring resonator to measure the temperature dependence of the in-plane magnetic penetration depth λ(T) in YBa2Cu3O7-δ (YBCO) and Y0.7Ca0.3Ba2Cu3O7-δ (Ca-YBCO) epitaxially grown thin films, the linear temperature dependence of the superfluid density ρs/m∗ ≡ 1/λ2(T) was observed from the under- to the overdoped regime at the temperatures below T/Tc ≈ 0.3 . For the underdoped regime of YBCO and Ca-YBCO thin films, the magnitude of the slope d(1/λ2(T))/dT is insensitive to doping, and it can be treated in the framework of projected d-density-wave model. Combining these slope values with the thermal conductivity measurements, the Fermi-liquid correction factor α2 from the Fermi-liquid model, suggested by Wen and Lee, was revealed here with various doping levels.

  3. Effect of lattice mismatch on the magnetic properties of nanometer-thick La0.9Ba0.1MnO3 (LBM) films and LBM/BaTiO3/LBM heterostructures

    NASA Astrophysics Data System (ADS)

    Mirzadeh Vaghefi, P.; Baghizadeh, A.; Willinger, M.; Lourenço, A. A. C. S.; Amaral, V. S.

    2017-12-01

    Oxide multiferroic thin films and heterostructures offer a wide range of properties originated from intrinsic coupling between lattice strain and nanoscale magnetic/electronic ordering. La0.9Ba0.1MnO3 (LBM) thin-films and LBM/BaTiO3/LBM (LBMBT) heterostructures were grown on single crystalline [100] silicon and [0001] Al2O3 using RF magnetron sputtering to study the effect of crystallinity and induced lattice mismatch in the film on magnetic properties of deposited films and heterostructures. The thicknesses of the films on Al2O3 and Si are 70 and 145 nm, respectively, and for heterostructures are 40/30/40 nm on both substrates. The microstructure of the films, state of strain and growth orientations was studied by XRD and microscopy techniques. Interplay of microstructure, strain and magnetic properties is further investigated. It is known that the crystal structure of substrates and imposed tensile strain affect the physical properties; i.e. magnetic behavior of the film. The thin layer grown on Al2O3 substrate shows out-of-plane compressive strain, while Si substrate induces tensile strain on the deposited film. The magnetic transition temperatures (Tc) of the LBM film on the Si and Al2O3 substrates are found to be 195 K and 203 K, respectively, slightly higher than the bulk form, 185 K. The LBMBT heterostructure on Si substrate shows drastic decrease in magnetization due to produced defects created by diffusion of Ti ions into magnetic layer. Meanwhile, the Tc in LBMBTs increases in respect to other studied single layers and heterostructure, because of higher tensile strain induced at the interfaces.

  4. Enhanced electron mobility at the two-dimensional metallic surface of BaSnO3 electric-double-layer transistor at low temperatures

    NASA Astrophysics Data System (ADS)

    Fujiwara, Kohei; Nishihara, Kazuki; Shiogai, Junichi; Tsukazaki, Atsushi

    2017-05-01

    Wide-bandgap oxides exhibiting high electron mobility hold promise for the development of useful electronic and optoelectronic devices as well as for basic research on two-dimensional electron transport phenomena. A perovskite-type tin oxide, BaSnO3, is currently one of such targets owing to distinctly high mobility at room temperature. The challenge to overcome towards the use of BaSnO3 thin films in applications is suppression of dislocation scattering, which is one of the dominant scattering origins for electron transport. Here, we show that the mobility of the BaSnO3 electric-double-layer transistor reaches 300 cm2 V-1 s-1 at 50 K. The improved mobility indicates that charged dislocation scattering is effectively screened by electrostatically doped high-density charge carriers. We also observed metallic conduction persisting down to 2 K, which is attributed to the transition to the degenerate semiconductor. The experimental verification of bulk-level mobility at the densely accumulated surface sheds more light on the importance of suppression of dislocation scattering by interface engineering in doped BaSnO3 thin films for transparent electrode applications.

  5. The interface of SrTiO3 and H2O from density functional theory molecular dynamics

    PubMed Central

    Spijker, P.; Foster, A. S.

    2016-01-01

    We use dispersion-corrected density functional theory molecular dynamics simulations to predict the ionic, electronic and vibrational properties of the SrTiO3/H2O solid–liquid interface. Approximately 50% of surface oxygens on the planar SrO termination are hydroxylated at all studied levels of water coverage, the corresponding number being 15% for the planar TiO2 termination and 5% on the stepped TiO2-terminated surface. The lateral ordering of the hydration structure is largely controlled by covalent-like surface cation to H2O bonding and surface corrugation. We find a featureless electronic density of states in and around the band gap energy region at the solid–liquid interface. The vibrational spectrum indicates redshifting of the O–H stretching band due to surface-to-liquid hydrogen bonding and blueshifting due to high-frequency stretching vibrations of OH fragments within the liquid, as well as strong suppression of the OH stretching band on the stepped surface. We find highly varying rates of proton transfer above different SrTiO3 surfaces, owing to differences in hydrogen bond strength and the degree of dissociation of incident water. Trends in proton dynamics and the mode of H2O adsorption among studied surfaces can be explained by the differential ionicity of the Ti–O and Sr–O bonds in the SrTiO3 crystal. PMID:27713660

  6. Shear-strain gradient induced polarization reversal in ferroelectric BaTiO3 thin films: A first-principles total-energy study

    NASA Astrophysics Data System (ADS)

    Li, Guannan; Huang, Xiaokun; Hu, Jingsan; Zhang, Weiyi

    2017-04-01

    Based on the first-principles total-energy calculation, we have studied the shear-strain gradient effect on the polarization reversal of ferroelectric BaTiO3 thin films. By calculating the energies of double-domain supercells for different electric polarization, shear-strain gradients, and domain-wall displacement, we extracted, in addition to the domain-wall energy, the polarization energy, elastic energy, and flexoelectric coefficient of a single domain. The constructed Landau-Devonshire phenomenological theory yields a critical shear-strain gradient of 9.091 ×107/m (or a curvature radius (R ) of 110 Å) for reversing the 180∘ domain at room temperature, which is on the same order of the experimentally estimated value of 3.333 ×107/m (R =300 Å ). In contrast to the commonly used linear response theory, the flexoelectric coefficient derived from fitting the total energy to a Landau-Devonshire energy functional does not depend on the specific pseudopotential. Thus, our method offers an alternative numerical approach to study the flexoelectric effect.

  7. Bond length (Ti-O) dependence of nano ATO3-based (A = Pb, Ba, Sr) perovskite structures: Optical investigation in IR range

    NASA Astrophysics Data System (ADS)

    Ghasemifard, Mahdi; Ghamari, Misagh; Okay, Cengiz

    2018-01-01

    In the current study, ABO3 (A = Pb, Ba, Sr and B = Ti) perovskite structures are produced by the auto-combustion route by using citric acid (CA) and nitric acid (NA) as fuel and oxidizer. The X-ray diffraction (XRD) patterns confirmed the perovskite nanostructure with cubic, tetragonal, and rhombohedral for SrTiO3, PbTiO3, and BaTiO3, respectively. Using Scherrer’s equation and XRD pattern, the average crystallite size of the samples were acquired. The effect of Ti-O bond length on the structure of the samples was evaluated. The type of structures obtained depends on Ti-O bond length which is in turn influenced by A2+ substitutions. Microstructural studies of nanostructures calcined at 850∘C confirmed the formation of polyhedral particles with a narrow size distribution. The values of optical band gaps were measured and the impact of A2+ was discussed. The optical properties such as the complex refractive index and dielectric function were calculated by IR spectroscopy and Kramers-Kronig (K-K) relations. Lead, as the element with the highest density as compared to other elements, changes the optical constants, remarkably due to altering titanium and oxygen distance in TO6 groups.

  8. Tungsten-doped thin film materials

    DOEpatents

    Xiang, Xiao-Dong; Chang, Hauyee; Gao, Chen; Takeuchi, Ichiro; Schultz, Peter G.

    2003-12-09

    A dielectric thin film material for high frequency use, including use as a capacitor, and having a low dielectric loss factor is provided, the film comprising a composition of tungsten-doped barium strontium titanate of the general formula (Ba.sub.x Sr.sub.1-x)TiO.sub.3, where X is between about 0.5 and about 1.0. Also provided is a method for making a dielectric thin film of the general formula (Ba.sub.x Sr.sub.1-x)TiO.sub.3 and doped with W, where X is between about 0.5 and about 1.0, a substrate is provided, TiO.sub.2, the W dopant, Ba, and optionally Sr are deposited on the substrate, and the substrate containing TiO.sub.2, the W dopant, Ba, and optionally Sr is heated to form a low loss dielectric thin film.

  9. Strain-relaxed structure in (001)/(100)-oriented epitaxial PbTiO3 films grown on (100) SrTiO3 substrates by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Nakaki, Hiroshi; Kim, Yong Kwan; Yokoyama, Shintaro; Ikariyama, Rikyu; Funakubo, Hiroshi; Nishida, Ken; Saito, Keisuke

    2007-09-01

    The authors grew (001)- and (001)/(100)-oriented epitaxial PbTiO3 films with various thicknesses on (100)SrTiO3 substrates. They used x-ray diffraction to measure the angles between surface normal [001] of (001)-oriented domains and [100] of (100)-oriented domains. The angles were found to be approximately 3.6° when the film thickness exceeded 1100nm. This value is consistent with the value obtained by a geometric calculation for strain-free PbTiO3. This result suggests that thick epitaxial PbTiO3 films grown on (100)SrTiO3 substrates have a fully strain-relaxed structure.

  10. Structural differences between superconducting and non-superconducting CaCuO2/SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Zarotti, Francesca; Di Castro, Daniele; Felici, Roberto; Balestrino, Giuseppe

    2018-06-01

    A study of the interface structure of superconducting and non-superconducting CaCuO2/SrTiO3 heterostructures grown on NdGaO3(110) substrates is reported. Using the combination of high resolution x-ray reflectivity and surface diffraction, the crystallographic structure of superconducting and non-superconducting samples has been investigated. The analysis has demonstrated the excellent sharpness of the CaCuO2/SrTiO3 interface (roughness smaller than one perovskite unit cell). Furthermore, we were able to discriminate between the superconducting and the non-superconducting phase. In the former case, we found an increase of the spacing between the topmost Ca plane of CaCuO2 block and the first TiO2 plane of the overlaying STO block, relative to the non-superconducting case. These results are in agreement with the model that foresees a strong oxygen incorporation in the interface Ca plane in the superconducting heterostructures.

  11. Microscopic evidence of a strain-enhanced ferromagnetic state in LaCoO3 thin films

    NASA Astrophysics Data System (ADS)

    Park, S.; Ryan, P.; Karapetrova, E.; Kim, J. W.; Ma, J. X.; Shi, J.; Freeland, J. W.; Wu, Weida

    2009-08-01

    Strain-induced modification of magnetic properties of lightly hole doped epitaxial LaCoO3 thin films on different substrates were studied with variable temperature magnetic force microscopy (MFM). Real space observation at 10 K reveals the formation of the local magnetic clusters on a relaxed film grown on LaAlO3 (001). In contrast, a ferromagnetic ground state has been confirmed for tensile-strained film on SrTiO3 (001), indicating that strain is an important factor in creating the ferromagnetic state. Simultaneous atomic force microscopy and MFM measurements reveal nanoscale defect lines for the tensile-strained films, where the structural defects have a large impact on the local magnetic properties.

  12. Mechanism behind the high thermoelectric power factor of SrTiO3 by calculating the transport coefficients

    NASA Astrophysics Data System (ADS)

    Shirai, Koun; Yamanaka, Kazunori

    2013-02-01

    The thermoelectric power factor of SrTiO3 is unusually high with respect to its mobility and band gap. Good thermoelectrics usually have high mobility and a narrow band gap, but such properties are not found in SrTiO3. We have determined the mechanism behind the high power factor by calculating the transport coefficients. The key to understanding the power factor is that different effective masses contribute to different transport phenomena. The discrepancy between the effective mass for the conductivity and the thermoelectric power showed that the conductivity and thermoelectric power are conveyed by electrons with different effective masses in the Brillouin zone. Light electrons were responsible for the high conductivity, whereas heavy electrons were responsible for the high thermoelectric power. The high carrier concentrations of more than 1020 cm-3 did not reduce the thermoelectric power of SrTiO3 above the classical limit. This indicates that the electrons carrying the thermoelectric power were not degenerate. This is achieved by a decrease in the Fermi energy and the contribution of the heavy electrons to the Seebeck coefficient. The strong dielectric screening also contributed to the high power factor. The Coulomb scattering by ionized impurities, which would usually reduce the carrier mobility, was effectively screened. These results clarify the mechanism behind the contribution of different types of electrons, and show that high thermoelectric power does not necessarily reduce conductivity. Our findings provide a new direction for the band engineering of thermoelectric materials.

  13. Correlation Between Material Properties of Ferroelectric Thin Films and Design Parameters for Microwave Device Applications: Modeling Examples and Experimental Verification

    NASA Technical Reports Server (NTRS)

    Miranda, Felix A.; VanKeuls, Fred W.; Subramanyam, Guru; Mueller, Carl H.; Romanofsky, Robert R.; Rosado, Gerardo

    2000-01-01

    The application of thin ferroelectric films for frequency and phase agile components is the topic of interest of many research groups worldwide. Consequently, proof-of-concepts (POC) of different tunable microwave components using either (HTS, metal)/ferroelectric thin film/dielectric heterostructures or (thick, thin) film "flip-chip" technology have been reported. Either as ferroelectric thin film characterization tools or from the point of view of circuit implementation approach, both configurations have their respective advantages and limitations. However, we believe that because of the progress made so far using the heterostructure (i.e., multilayer) approach, and due to its intrinsic features such as planar configuration and monolithic integration, a study on the correlation of circuit geometry aspects and ferroelectric material properties could accelerate the insertion of this technology into working systems. In this paper, we will discuss our study performed on circuits based on microstrip lines at frequencies above 10 GHz, where the multilayer configuration offers greater ease of insertion due to circuit's size reduction. Modeled results of relevant circuit parameters such as the characteristic impedance, effective dielectric constant, and attenuation as a function of ferroelectric film's dielectric constant, tans, and thickness, will be presented for SrTiO3 and Ba(x)Sr(1-x)TiO3 ferroelectric films. A comparison between the modeled and experimental data for some of these parameters will be presented.

  14. Time-resolved study of SrTiO3 homoepitaxial pulsed-laser deposition using surface x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Eres, G.; Tischler, J. Z.; Yoon, M.; Larson, B. C.; Rouleau, C. M.; Lowndes, D. H.; Zschack, P.

    2002-05-01

    Homoepitaxy of SrTiO3 by pulsed-laser deposition has been studied using in situ time-resolved surface x-ray diffraction in the temperature range of 310 °C to 780 °C. Using a two-detector configuration, surface x-ray diffraction intensities were monitored simultaneously at the (0 0 1/2) specular and the (0 1 1/2) off-specular truncation rod positions. Abrupt intensity changes in both the specular and off-specular rods after laser pulses indicated prompt crystallization into SrTiO3 layers followed by slower intra- and interlayer surface rearrangements on time scales of seconds. Specular rod intensity oscillations indicated layer-by-layer growth, while off-specular rod intensity measurements suggested the presence of transient in-plane lattice distortions for depositions above 600 °C.

  15. Cation disorder and gas phase equilibrium in an YBa 2Cu 3O 7- x superconducting thin film

    NASA Astrophysics Data System (ADS)

    Shin, Dong Chan; Ki Park, Yong; Park, Jong-Chul; Kang, Suk-Joong L.; Yong Yoon, Duk

    1997-02-01

    YBa 2Cu 3O 7- x superconducting thin films have been grown by in situ off-axis rf sputtering with varying oxygen pressure, Ba/Y ratio in a target, and deposition temperature. With decreasing oxygen pressure, increasing Ba/Y ratio, increasing deposition temperature, the critical temperature of the thin films decreased and the c-axis length increased. The property change of films with the variation of deposition variables has been explained by a gas phase equilibrium of the oxidation reaction of Ba and Y. Applying Le Chatelier's principle to the oxidation reaction, we were able to predict the relation of deposition variables and the resultant properties of thin films; the prediction was in good agreement with the experimental results. From the relation between the three deposition variables and gas phase equilibrium, a 3-dimensional processing diagram was introduced. This diagram has shown that the optimum deposition condition of YBa 2Cu 3O 7- x thin films is not a fixed point but can be varied. The gas phase equilibrium can also be applied to the explanation of previous results that good quality films were obtained at low deposition temperature using active species, such as O, O 3, and O 2+.

  16. Recent progress in oxide thermoelectric materials: p-type Ca3Co4O9 and n-type SrTiO3(-).

    PubMed

    Ohta, Hiromichi; Sugiura, Kenji; Koumoto, Kunihito

    2008-10-06

    Thermoelectric energy conversion technology to convert waste heat into electricity has received much attention. In addition, metal oxides have recently been considered as thermoelectric power generation materials that can operate at high temperatures on the basis of their potential advantages over heavy metallic alloys in chemical and thermal robustness. We have fabricated high-quality epitaxial films composed of oxide thermoelectric materials that are suitable for clarifying the intrinsic "real" properties. This review focuses on the thermoelectric properties of two representative oxide epitaxial films, p-type Ca 3Co 4O 9 and n-type SrTiO 3, which exhibit the best thermoelectric figures of merit, ZT (= S (2)sigma Tkappa (-1), S = Seebeck coefficient, sigma = electrical conductivity, kappa = thermal conductivity, and T = absolute temperature) among oxide thermoelectric materials reported to date. In addition, we introduce the recently discovered giant S of two-dimensional electrons confined within a unit cell layer thickness ( approximately 0.4 nm) of SrTiO 3.

  17. The enhancement of photovoltaic parameters in dye-sensitized solar cells of nano-crystalline SnO2 by incorporating with large SrTiO3 particles.

    PubMed

    Aponsu, G M L P; Wijayarathna, T R C K; Perera, I K; Perera, V P S; Siriwardhana, A C P K

    2013-05-15

    In this paper, the performance of nano-porous electrodes made of a composite material of SrTiO3 and SnO2 are compared with those made of bare SnO2. When these particular devices are analyzed in a comparative mode the results confirmed the enhancement of photovoltaic parameters in the former device. The performance of respective cells were examined by several methods including I-V characteristic measurements, photocurrent action spectra, dark I-V measurements, Mott-Schottky measurements and X-ray diffraction measurements. Even though such improvements in this particular cell could be explicated by the formation of a potential energy barrier of SrTiO3 particles of comparably large width at the SrTiO3/SnO2 interface, the passivation of voids in the SnO2 film by SrTiO3 particles to a certain extent could not be totally ruled out. Besides, high energetic electrons injected by dye molecules move more credibly through mini-bands formed in the chain of nano-crystalline SnO2 particles to the back contact. The blocking of the recombination path and the shifting up of the uppermost electron occupied level of SnO2 accompanying the conduction band edge in the SrTiO3/SnO2 composite film, may have lead to the observed enhancement of the fill factor and photovoltage, respectively. Copyright © 2013 Elsevier B.V. All rights reserved.

  18. Strain localization in thin films of Bi(Fe,Mn)O 3 due to the formation of stepped Mn 4+-rich antiphase boundaries

    DOE PAGES

    MacLaren, I.; Sala, B.; Andersson, S. M. L.; ...

    2015-10-17

    Here, the atomic structure and chemistry of thin films of Bi(Fe,Mn)O 3 (BFMO) films with a target composition of Bi 2FeMnO 6 on SrTiO 3 are studied using scanning transmission electron microscopy imaging and electron energy loss spectroscopy. It is shown that Mn4+-rich antiphase boundaries are locally nucleated right at the film substrate and then form stepped structures that are approximately pyramidal in three dimensions. These have the effect of confining the material below the pyramids in a highly strained state with an out-of-plane lattice parameter close to 4.1 Å. Outside the area enclosed by the antiphase boundaries, the out-of-planemore » lattice parameter is much closer to bulk values for BFMO. This suggests that to improve the crystallographic perfection of the films whilst retaining the strain state through as much of the film as possible, ways need to be found to prevent nucleation of the antiphase boundaries. Since the antiphase boundaries seem to form from the interaction of Mn with the Ti in the substrate, one route to perform this would be to grow a thin buffer layer of pure BiFeO 3 on the SrTiO 3 substrate to minimise any Mn-Ti interactions.« less

  19. Nonlinearity in the High-Electric-Field Piezoelectricity of Epitaxial BiFeO3 on SrTiO3

    DTIC Science & Technology

    2012-02-10

    Nonlinearity in the high- electric -field piezoelectricity of epitaxial BiFeO3 on SrTiO3 Pice Chen,1 Rebecca J. Sichel-Tissot,1,a) Ji Young Jo,1,b...field linear response in electric fields higher than 150 MV/m. Time-resolved synchrotron x-ray microdiffraction reveals a low-field piezoelectric...decreases throughout the high- electric -field regime, accompanied by increased diffuse scattering, consistent with lattice softening lattice near a field

  20. Large Thermopower of δ-doped LaTiO3/SrTiO3 Interfaces and it's Field Dependence

    NASA Astrophysics Data System (ADS)

    Budhani, R. C.; Das, Shubhankar; Joshi, P. C.; Rastogi, A.; Hossain, Z.

    2015-03-01

    We will present the magneto-thermopower (S(T, H)) of interfacial delta doped LaTiO3/SrTiO3 heterostructure by an iso-structural antiferromagnetic perovskite LaCrO3. The thermoelectric power of 2-dimensional electron gas (2DEG) of pure LaTiO3/SrTiO3 at 300 K is ~ 118 μV/K, but increases dramatically to 337 μV/K on inserting 5 uc LaCrO3 at the interface. The negative sign of the thermoelectric power confirms the electron as major carriers in these interfaces. A linear temperature dependence of S(T) has been observed in the temperature range 100 K to 300 K which is in agreement with the theory of diffusion thermopower of 2DEG. The S(T) shows a distinct enhancement at temperature <100 K, where a Kondo-type minimum has been observed in sheet resistance. We attribute this maximum in S(T) to Kondo scattering of conduction electron by localized impurity spin at the interface. The S in this temperature range is suppressed significantly (<= 20%) by moderate magnetic field (<= 13 T) applied either perpendicular or parallel to the film surface. The isotropic nature of the suppression of S by magnetic field further strengthen the Kondo based interpretation of S(T, H). We acknowledge IIT Kanpur and CSIR India for funding this research work.

  1. Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nano to micrometers.

    PubMed

    Apreutesei, Mihai; Debord, Régis; Bouras, Mohamed; Regreny, Philippe; Botella, Claude; Benamrouche, Aziz; Carretero-Genevrier, Adrian; Gazquez, Jaume; Grenet, Geneviève; Pailhès, Stéphane; Saint-Girons, Guillaume; Bachelet, Romain

    2017-01-01

    High-quality thermoelectric La 0.2 Sr 0.8 TiO 3 (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO 3 (001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 × 10 -4 Ω cm at room temperature), one order of magnitude lower than standard commercial Nb-doped SrTiO 3 single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of approximately -60 μV/K have been recorded for all films. These LSTO films can be integrated on Si for non-volatile memory structures or opto-microelectronic devices, functioning as transparent conductors or thermoelectric elements.

  2. Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nano to micrometers

    NASA Astrophysics Data System (ADS)

    Apreutesei, Mihai; Debord, Régis; Bouras, Mohamed; Regreny, Philippe; Botella, Claude; Benamrouche, Aziz; Carretero-Genevrier, Adrian; Gazquez, Jaume; Grenet, Geneviève; Pailhès, Stéphane; Saint-Girons, Guillaume; Bachelet, Romain

    2017-12-01

    High-quality thermoelectric La0.2Sr0.8TiO3 (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO3(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 × 10-4 Ω cm at room temperature), one order of magnitude lower than standard commercial Nb-doped SrTiO3 single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of approximately -60 μV/K have been recorded for all films. These LSTO films can be integrated on Si for non-volatile memory structures or opto-microelectronic devices, functioning as transparent conductors or thermoelectric elements.

  3. Understanding the Origin of Ferromagnetism in Strained LaCoO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Ma, J. X.; Shi, J.; Freeland, J. W.

    2009-03-01

    Using strain to control the behavior of strongly correlated materials offers new opportunities to control fundamental properties. For the case of magnetism, LaCoO3 offers the ability to use strain through thin film growth to manipulate directly the spin-state of Co in this system. Here we present the results of a detailed polarized x-ray spectroscopy study of LaCoO3 thin films grown on SrTiO3(001) and LaAlO3 (001) substrates. X-ray diffraction from 25 nm thin films confirm the films are fully strained in both cases and, for films under tensile strain, total moment magnetometry shows a clear transition to ferromagnetic state at ˜80K. X-ray absorption shows that the films grown from a LaCoO3 target are slightly hole doped due to non-stoichiometry generated during growth (effective doping ˜ 0.1 holes per unit cell), which in the bulk is sufficient to destroy the low-spin state. However, even though the films are slightly hole doped, the films under tensile strain show long range ferromagnetic order unlike the bulk system. Since the films are insulating, these results are consistent with a ferromagnetic insulating state arising due to superexchange. Work at UCR is supported by ONR/DMEA under award H94003-08-2-0803.

  4. Quantification of flexoelectricity in PbTiO 3/SrTiO 3 superlattice polar vortices using machine learning and phase-field modeling

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Q.; Nelson, C. T.; Hsu, S. -L.

    Flexoelectricity refers to electric polarization generated by heterogeneous mechanical strains, namely strain gradients, in materials of arbitrary crystal symmetries. Despite more than 50 years of work on this effect, an accurate identification of its coupling strength remains an experimental challenge for most materials, which impedes its wide recognition. Here, we show the presence of flexoelectricity in the recently discovered polar vortices in PbTiO 3 /SrTiO 3 superlattices based on a combination of machine-learning analysis of the atomic-scale electron microscopy imaging data and phenomenological phase-field modeling. By scrutinizing the influence of flexocoupling on the global vortex structure, we match theory andmore » experiment using computer vision methodologies to determine the flexoelectric coefficients for PbTiO 3 and SrTiO 3. Here, our findings highlight the inherent, nontrivial role of flexoelectricity in the generation of emergent complex polarization morphologies and demonstrate a viable approach to delineating this effect, conducive to the deeper exploration of both topics.« less

  5. Quantification of flexoelectricity in PbTiO 3/SrTiO 3 superlattice polar vortices using machine learning and phase-field modeling

    DOE PAGES

    Li, Q.; Nelson, C. T.; Hsu, S. -L.; ...

    2017-11-13

    Flexoelectricity refers to electric polarization generated by heterogeneous mechanical strains, namely strain gradients, in materials of arbitrary crystal symmetries. Despite more than 50 years of work on this effect, an accurate identification of its coupling strength remains an experimental challenge for most materials, which impedes its wide recognition. Here, we show the presence of flexoelectricity in the recently discovered polar vortices in PbTiO 3 /SrTiO 3 superlattices based on a combination of machine-learning analysis of the atomic-scale electron microscopy imaging data and phenomenological phase-field modeling. By scrutinizing the influence of flexocoupling on the global vortex structure, we match theory andmore » experiment using computer vision methodologies to determine the flexoelectric coefficients for PbTiO 3 and SrTiO 3. Here, our findings highlight the inherent, nontrivial role of flexoelectricity in the generation of emergent complex polarization morphologies and demonstrate a viable approach to delineating this effect, conducive to the deeper exploration of both topics.« less

  6. Quantification of flexoelectricity in PbTiO3/SrTiO3 superlattice polar vortices using machine learning and phase-field modeling.

    PubMed

    Li, Q; Nelson, C T; Hsu, S-L; Damodaran, A R; Li, L-L; Yadav, A K; McCarter, M; Martin, L W; Ramesh, R; Kalinin, S V

    2017-11-13

    Flexoelectricity refers to electric polarization generated by heterogeneous mechanical strains, namely strain gradients, in materials of arbitrary crystal symmetries. Despite more than 50 years of work on this effect, an accurate identification of its coupling strength remains an experimental challenge for most materials, which impedes its wide recognition. Here, we show the presence of flexoelectricity in the recently discovered polar vortices in PbTiO 3 /SrTiO 3 superlattices based on a combination of machine-learning analysis of the atomic-scale electron microscopy imaging data and phenomenological phase-field modeling. By scrutinizing the influence of flexocoupling on the global vortex structure, we match theory and experiment using computer vision methodologies to determine the flexoelectric coefficients for PbTiO 3 and SrTiO 3 . Our findings highlight the inherent, nontrivial role of flexoelectricity in the generation of emergent complex polarization morphologies and demonstrate a viable approach to delineating this effect, conducive to the deeper exploration of both topics.

  7. Investigations of surface related electronic properties in SmB6 and LaAlO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Adhikari, Sanjay

    This dissertation reports research performed on two types of two-dimensional. systems: SmB6 and LaAlO3/SrTiO3 (LAO/STO). SmB6 has been proposed to be. a topological Kondo insulator at low temperature. In order to understand carriers/. lattice dynamics and their interactions, femtosecond pump-probe spectroscopy. is performed in SmB6 single crystals and thin lms at variable temperatures. The. collective oscillation modes in GHz - THz and the change of carrier relaxations is. observed as a function of temperature. From the temperature dependent results. f 􀀀?d hybridization, opening of the hybridization gap, phonon bottleneck", and th. possible topological surface state formation is revealed. The topological surface state. should support helical Dirac dispersion with momentum-spin lockage. This dissertation. reports on current injection in SmB6 thin lm with circularly polarized light. at oblique incidence. This spin polarized photocurrent is concluded to be a direct. result of spin momentum lockage in SmB6. LAO/STO interface shows 2-dimensional electron gas (2DEG) at the interface. when the thickness of LAO is more than 3 unit cell. Carrier properties at the. LAO/STO interfaces are highly sensitive to the top surface termination of LAO. The spontaneous dissociation of water on LAO surface is systematically studied by. density functional theory and experimental surface characterizations. Extrinsic effects. from surface adsorbates were often ignored in the previous studies of the 2DEG. From the experiments, it is found that the dissociated water molecules, especially the. surface protons, strongly aect the interface density of states, electron distributions. and lattice distortions. The investigations also reveal the importance of additional. molecular water layers. These additional water layers, through hydrogen bonds, provide. an energetically feasible pathway for manipulating the surface-bonded protons. and thus, the interface electrical characteristics.

  8. Oxygen octahedral distortions in LaMO 3/SrTiO 3 superlattices

    DOE PAGES

    Sanchez-Santolino, Gabriel; Cabero, Mariona; Varela, Maria; ...

    2014-04-24

    Here we study the interfaces between the Mott insulator LaMnO 3 (LMO) and the band insulator SrTiO 3 (STO) in epitaxially grown superlattices with different thickness ratios and different transport and magnetic behaviors. Using atomic resolution electron energy-loss spectrum imaging, we analyze simultaneously the structural and chemical properties of these interfaces. We find changes in the oxygen octahedral tilts within the LaMnO 3 layers when the thickness ratio between the manganite and the titanate layers is varied. Superlattices with thick LMO and ultrathin STO layers present unexpected octahedral tilts in the STO, along with a small amount of oxygen vacancies.more » On the other hand, thick STO layers exhibit undistorted octahedra while the LMO layers present reduced O octahedral distortions near the interfaces. In conclusion, these findings will be discussed in view of the transport and magnetic differences found in previous studies.« less

  9. Local Structure of the Amorphous Precursor to Ba-Hexaferrite Thin Films: An Anisotropic Octahedral Fe-O Glass Network

    NASA Astrophysics Data System (ADS)

    Snyder, J. E.; Harris, V. G.; Koon, N. C.; Sui, X.; Kryder, M. H.

    1996-10-01

    Anisotropic local structure has been observed around both the Fe and Ba ions in the amorphous precursor to Ba-hexaferrite thin films, using polarization-dependent extended x-ray-absorption fine structure. This anisotropic local structure, consisting mainly of a network of Fe-O octahedra, determines the orientation of the fast-growing basal planes during crystallization, and thus the directions of the c axes and the resulting magnetic anisotropy.

  10. Magnetic field induced transition in superconducting LaTiO3/SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Biscaras, J.; Bergeal, N.; Hurand, S.; Feuillet-Palma, C.; Rastogi, A.; Budhani, R. C.; Grilli, M.; Caprara, S.; Lesueur, J.

    2013-07-01

    Superconductivity at the LaTiO3/SrTiO3 interface is studied by low temperature and high magnetic field measurements as a function of a back-gate voltage. We show that it is intimately related to the appearance of a low density (a few 1012 cm-2) of high mobility carriers, in addition to low mobility ones always present in the system. These carriers form superconducting puddles coupled by a metallic two-dimensional electron gas, as revealed by the analysis of the phase transition driven by a perpendicular magnetic field. Two critical fields are evidenced, and a quantitative comparison with a recent theoretical model is made.

  11. Transport and thermoelectric properties of the LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Jost, A.; Guduru, V. K.; Wiedmann, S.; Maan, J. C.; Zeitler, U.; Wenderich, S.; Brinkman, A.; Hilgenkamp, H.

    2015-01-01

    The transport and thermoelectric properties of the interface between SrTiO3 and a 26-monolayer-thick LaAlO3 layer grown at high oxygen pressure have been investigated at temperatures from 4.2 to 100 K and in magnetic fields up to 18 T. For T >4.2 K , two different electronlike charge carriers originating from two electron channels which contribute to transport are observed. We probe the contributions of a degenerate and a nondegenerate band to the thermoelectric power and develop a consistent model to describe the temperature dependence of the thermoelectric tensor. Anomalies in the data point to an additional magnetic field dependent scattering.

  12. Interfacial B-site atomic configuration in polar (111) and non-polar (001) SrIrO3/SrTiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Anderson, T. J.; Zhou, H.; Xie, L.; Podkaminer, J. P.; Patzner, J. J.; Ryu, S.; Pan, X. Q.; Eom, C. B.

    2017-09-01

    The precise control of interfacial atomic arrangement in ABO3 perovskite heterostructures is paramount, particularly in cases where the subsequent electronic properties of the material exhibit geometrical preferences along polar crystallographic directions that feature inevitably complex surface reconstructions. Here, we present the B-site interfacial structure in polar (111) and non-polar (001) SrIrO3/SrTiO3 interfaces. The heterostructures were examined using scanning transmission electron microscopy and synchrotron-based coherent Bragg rod analysis. Our results reveal the preference of B-site intermixing across the (111) interface due to the polarity-compensated SrTiO3 substrate surface prior to growth. By comparison, the intermixing at the non-polar (001) interface is negligible. This finding suggests that the intermixing may be necessary to mitigate epitaxy along heavily reconstructed and non-stoichiometric (111) perovskite surfaces. Furthermore, this preferential B-site configuration could allow the geometric design of the interfacial perovskite structure and chemistry to selectively engineer the correlated electronic states of the B-site d-orbital.

  13. Anisotropic strain relaxation in (Ba0.6Sr0.4)TiO3 epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Simon, W. K.; Akdogan, E. K.; Safari, A.

    2005-05-01

    We have studied the evolution of anisotropic epitaxial strains in ⟨110⟩-oriented (Ba0.60Sr0.40)TiO3 paraelectric (m3m) thin films grown on orthorhombic (mm2) ⟨100⟩-oriented NdGaO3 by high-resolution x-ray diffractometry. All the six independent components of the three-dimensional strain tensor were measured in films with 25-1200-nm thickness, from which the principal stresses and strains were obtained. Pole figure analysis indicated that the epitaxial relations are [001]m3m‖[001]mm2 and [1¯10]m3m‖[010]mm2 in the plane of the film, and [110]m3m‖[100]mm2 along the growth direction. The dislocation system responsible for strain relief along [001] has been determined to be ∣b ∣(001)=3/4∣b∣. Strain relief along the [1¯10] direction, on the other hand, has been determined to be due to a coupled mechanism given by ∣b∣(1¯10)=∣b∣ and ∣b∣(1¯10)=√3 /4∣b∣. Critical thicknesses, as determined from nonlinear regression using the Matthews-Blakeslee equation, for misfit dislocation formation along [001] and [1¯10] direction were found to be 5 and 7 nm, respectively. The residual strain energy density was calculated as ˜2.9×106J/m3 at 25 nm, which was found to relax an order of magnitude by 200 nm. At 200 nm, the linear dislocation density along [001] and [1¯10] are ˜6.5×105 and ˜6×105cm-1, respectively. For films thicker than 600 nm, additional strain relief occurred through surface undulations, indicating that this secondary strain-relief mechanism is a volume effect that sets in upon cooling from the growth temperature.

  14. Sulfide and Oxide Heterostructures For the SrTiO3 Thin Film Growth on Si and Their Structural and Interfacial Stabilities

    NASA Astrophysics Data System (ADS)

    Yoo, Young‑Zo; Song, Jeong‑Hwan; Konishi, Yoshinori; Kawasaki, Masashi; Koinuma, Hideomi; Chikyow, Toyohiro

    2006-03-01

    Epitaxial SrTiO3 (STO) thin films with high electrical properties were grown on Si using ZnS single- and SrS/MnS hetero-buffer layers. STO films on both ZnS-buffered and SrS/MnS-buffered Si showed two growth orientations, (100) and (110). The temperature dependence of the growth orientation for STO films was different for the ZnS single-buffer layer in comparison with the SrS/MnS heterobuffer layers. (100) growth of STO films on SrS/MnS-buffered Si became dominant at high temperatures about 700 °C, while (100) growth of STO films on ZnS-buffered Si became dominant at a relatively low growth temperature of 550 °C. STO(100) films on ZnS-buffered and SrS/MnS-buffered Si showed lattice and domain matches for epitaxial relationships with [001]ZnS\\parallel[011]STO and SrS[001]\\parallel[011]STO, respectively via 45° in-plane rotation of STO films relative to both ZnS and SrS layers. The ZnS buffer layer contained many stacking faults because of the mismatch between ZnS and Si, however, those defects were terminated at the ZnS/STO interface. In contrast, the MnS buffer was very stable against stacking defect formation. Transmission electron microscopy measurements revealed the presence of a disordered region at the ZnS/Si and MnS/Si interfaces. Auger electron spectroscopy and transmission electron microscopy results showed that a good MnS/Si interface at the initial growth stage degraded to a SiS2-x-rich phase during MnS deposition and again into a SiO2-x-rich phase during STO deposition at the high growth temperature of 700 °C. It was also observed that STO on SrS/MnS-buffered Si showed a markedly high dielectric constant compared with that of STO on ZnS-buffered Si.

  15. Octahedral tilt independent magnetism in confined GdTiO3 films

    NASA Astrophysics Data System (ADS)

    Need, R. F.; Isaac, B. J.; Kirby, B. J.; Borchers, J. A.; Stemmer, S.; Wilson, Stephen D.

    2018-03-01

    Low temperature polarized neutron reflectometry measurements are presented, exploring the evolution of ferrimagnetism in thin GdTiO3 films embedded within a SrTiO3 matrix. In GdTiO3 films thinner than ˜4 nm, the TiO6 octahedral tilts endemic to GdTiO3 coherently relax toward the undistorted, cubic phase of SrTiO3. Our measurements indicate that the ferrimagnetic state within the GdTiO3 layers survives as these TiO6 octahedral tilts are suppressed. Furthermore, our data suggest that layers of suppressed magnetization (i.e., magnetic dead layers) develop within the GdTiO3 layer at each GdTiO3/SrTiO3 interface and explain the apparent magnetization suppression observed in thin GdTiO3 films when using volume-averaged techniques. Our data show that the low temperature magnetic moment inherent to the core GdTiO3 layers is only weakly impacted as the octahedral tilt angles are suppressed by more than 50% and the t2 g bandwidth is dramatically renormalized.

  16. Crystallinity of tellurium capping and epitaxy of ferromagnetic topological insulator films on SrTiO 3

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Park, Jihwey; Soh, Yeong-Ah; Aeppli, Gabriel

    2015-06-30

    Thin films of topological insulators are often capped with an insulating layer since topological insulators are known to be fragile to degradation. However, capping can hinder the observation of novel transport properties of the surface states. To understand the influence of capping on the surface states, it is crucial to understand the crystal structure and the atomic arrangement at the interfaces. Here, we use x-ray diffraction to establish the crystal structure of magnetic topological insulator Cr-doped (Bi,Sb) 2Te 3 (CBST) films grown on SrTiO 3 (1 1 1) substrates with and without a Te capping layer. We find that bothmore » the film and capping layer are single crystal and that the crystal quality of the film is independent of the presence of the capping layer, but that x-rays cause sublimation of the CBST film, which is prevented by the capping layer. Our findings show that the different transport properties of capped films cannot be attributed to a lower crystal quality but to a more subtle effect such as a different electronic structure at the interface with the capping layer. Our results on the crystal structure and atomic arrangements of the topological heterostructure will enable modelling the electronic structure and design of topological heterostructures.« less

  17. Giant photovoltaic effects driven by residual polar field within unit-cell-scale LaAlO3 films on SrTiO3

    PubMed Central

    Liang, Haixing; Cheng, Long; Zhai, Xiaofang; Pan, Nan; Guo, Hongli; Zhao, Jin; Zhang, Hui; Li, Lin; Zhang, Xiaoqiang; Wang, Xiaoping; Zeng, Changgan; Zhang, Zhenyu; Hou, J. G.

    2013-01-01

    For polar/nonpolar heterostructures, Maxwell's theory dictates that the electric potential in the polar components will increase divergently with the film thickness. For LaAlO3/SrTiO3, a conceptually intriguing route, termed charge reconstruction, has been proposed to avert such “polar catastrophe”. The existence of a polar potential in LaAlO3 is a prerequisite for the validity of the charge reconstruction picture, yet to date, its direct measurement remains a major challenge. Here we establish unambiguously the existence of the residual polar potential in ultrathin LaAlO3 films on SrTiO3, using a novel photovoltaic device design as an effective probe. The measured lower bound of the residual polar potential is 1.0 V. Such a direct observation of the giant residual polar potential within the unit-cell-scale LaAlO3 films amounts to a definitive experimental evidence for the charge reconstruction picture, and also points to new technological significance of oxide heterostructures in photovoltaic and sensing devices with atomic-scale control. PMID:23756918

  18. Effect of the out-of-plane stress on the properties of epitaxial SrTiO3 films with nano-pillar array on Si-substrate

    NASA Astrophysics Data System (ADS)

    Bai, Gang; Xie, Qiyun; Liu, Zhiguo; Wu, Dongmei

    2015-08-01

    A nonlinear thermodynamic formalism has been proposed to calculate the physical properties of the epitaxial SrTiO3 films containing vertical nano-pillar array on Si-substrate. The out-of-plane stress induced by the mismatch between film and nano-pillars provides an effective way to tune the physical properties of ferroelectric SrTiO3 films. Tensile out-of-plane stress raises the phase transition temperature and increases the out-of-plane polarization, but decreases the out-of-plane dielectric constant below Curie temperature, pyroelectric coefficient, and piezoelectric coefficient. These results showed that by properly controlling the out-of-plane stress, the out-of-plane stress induced paraelectric-ferroelectric phase transformation will appear near room temperature. Excellent dielectric, pyroelectric, piezoelectric properties of these SrTiO3 films similar to PZT and other lead-based ferroelectrics can be expected.

  19. Phase transitions and electrical behavior of lead-free (K0.50Na0.50)NbO3 thin film

    NASA Astrophysics Data System (ADS)

    Wu, Jiagang; Wang, John

    2009-09-01

    Lead-free (K0.50Na0.50)NbO3 (KNN) thin films with a high degree of (100) preferred orientation were deposited on the SrRuO3-buffered SrTiO3(100) substrate by off-axis radio frequency magnetron sputtering. They possess lower phase transition temperatures (To-t˜120 °C and Tc˜310 °C), as compared to those of KNN bulk ceramic (To-t˜190 °C and Tc˜400 °C). They also demonstrate enhanced ferroelectric behavior (e.g., 2Pr=24.1 μc/cm2) and fatigue endurance, together with a lower dielectric loss (tan δ ˜0.017) and a lower leakage current, as compared to the bulk ceramic counterpart. Oxygen vacancies are shown to be involved in the conduction of the KNN thin film.

  20. Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nano to micrometers

    PubMed Central

    Apreutesei, Mihai; Debord, Régis; Bouras, Mohamed; Regreny, Philippe; Botella, Claude; Benamrouche, Aziz; Carretero-Genevrier, Adrian; Gazquez, Jaume; Grenet, Geneviève; Pailhès, Stéphane; Saint-Girons, Guillaume; Bachelet, Romain

    2017-01-01

    Abstract High-quality thermoelectric La0.2Sr0.8TiO3 (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO3(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 × 10−4 Ω cm at room temperature), one order of magnitude lower than standard commercial Nb-doped SrTiO3 single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of approximately –60 μV/K have been recorded for all films. These LSTO films can be integrated on Si for non-volatile memory structures or opto-microelectronic devices, functioning as transparent conductors or thermoelectric elements. PMID:28740558

  1. Thermoelectric Properties of Al-Doped ZnO Thin Films

    NASA Astrophysics Data System (ADS)

    Saini, S.; Mele, P.; Honda, H.; Matsumoto, K.; Miyazaki, K.; Ichinose, A.

    2014-06-01

    We have prepared 2 % Al-doped ZnO (AZO) thin films on SrTiO3 substrates by a pulsed laser deposition technique at various deposition temperatures ( T dep = 300-600 °C). The thermoelectric properties of AZO thin films were studied in a low temperature range (300-600 K). Thin film deposited at 300 °C is fully c-axis-oriented and presents electrical conductivity 310 S/cm with Seebeck coefficient -65 μV/K and power factor 0.13 × 10-3 Wm-1 K-2 at 300 K. The performance of thin films increases with temperature. For instance, the power factor is enhanced up to 0.55 × 10-3 Wm-1 K-2 at 600 K, surpassing the best AZO film previously reported in the literature.

  2. Electronic Structure and Band Alignment at the NiO and SrTiO3 p-n Heterojunctions.

    PubMed

    Zhang, Kelvin H L; Wu, Rui; Tang, Fengzai; Li, Weiwei; Oropeza, Freddy E; Qiao, Liang; Lazarov, Vlado K; Du, Yingge; Payne, David J; MacManus-Driscoll, Judith L; Blamire, Mark G

    2017-08-09

    Understanding the energetics at the interface, including the alignment of valence and conduction bands, built-in potentials, and ionic and electronic reconstructions, is an important challenge in designing oxide interfaces that have controllable multifunctionalities for novel (opto-)electronic devices. In this work, we report detailed investigations on the heterointerface of wide-band-gap p-type NiO and n-type SrTiO 3 (STO). We show that despite a large lattice mismatch (∼7%) and dissimilar crystal structure, high-quality NiO and Li-doped NiO (LNO) thin films can be epitaxially grown on STO(001) substrates through a domain-matching epitaxy mechanism. X-ray photoelectron spectroscopy studies indicate that NiO/STO heterojunctions form a type II "staggered" band alignment. In addition, a large built-in potential of up to 0.97 eV was observed at the interface of LNO and Nb-doped STO (NbSTO). The LNO/NbSTO p-n heterojunctions exhibit not only a large rectification ratio of 2 × 10 3 but also a large ideality factor of 4.3. The NiO/STO p-n heterojunctions have important implications for applications in photocatalysis and photodetectors as the interface provides favorable energetics for facile separation and transport of photogenerated electrons and holes.

  3. Optimization of the deposition conditions and structural characterization of Y1Ba2Cu3O(7-x) thin superconducting films

    NASA Technical Reports Server (NTRS)

    Chrzanowski, J.; Meng-Burany, S.; Xing, W. B.; Curzon, A. E.; Heinrich, B.; Irwin, J. C.; Cragg, R. A.; Zhou, H.; Habib, F.; Angus, V.

    1995-01-01

    Two series of Y1Ba2Cu3O(z) thin films deposited on (001) LaAl03 single crystals by excimer laser ablation under two different protocols have been investigated. The research has yielded well defined deposition conditions in terms of oxygen partial pressure p(O2) and substrate temperature of the deposition process Th, for the growth of high quality epitaxial films of YBCO. The films grown under conditions close to optimal for both j(sub c) and T(sub c) exhibited T(sub c) greater than or equal to 91 K and j(sub c) greater than or equal to 4 x 106 A/sq cm, at 77 K. Close correlations between the structural quality of the film, the growth parameters (p(O2), T(sub h)) and j(sub c) and T(sub c) have been found.

  4. Determination of local order in the amorphous precursor to Ba-hexaferrite thin-film recording media

    NASA Astrophysics Data System (ADS)

    Snyder, J. E.; Harris, V. G.; Das, B. N.; Koon, N. C.; Sui, X.; Kryder, M. H.

    1996-04-01

    Ba-hexaferrite thin films for recording media applications are often fabricated by a two-step process: sputter deposition of an amorphous precursor, followed by annealing to crystallize the BaFe12O19 phase. The magnetic anisotropy of the crystalline films can be either in-plane or perpendicular, depending on the sputtering process used in the first step. However, conventional structural characterization techniques have not been able to distinguish between different as-sputtered films. Using polarization-dependent extended x-ray absorption fine structure (PD-EXAFS), we have observed anisotropic local structure around both Ba and Fe atoms in the amorphous precursor films. Comparison of the results suggests that the amorphous films consist of networks of Fe atoms surrounded by their O nearest neighbors, with Ba atoms fitting into in-between spaces as network modifiers (there might also be some minor Fe network modifying contribution). The local structural anisotropy of the amorphous films appears to determine the orientation of the fast-growing basal plane directions during annealing, and thus the directions of the c axes and the magnetic anisotropy.

  5. Direct observation of twin deformation in YBa2Cu3O7-x thin films by in situ nanoindentation in TEM

    NASA Astrophysics Data System (ADS)

    Lee, Joon Hwan; Zhang, Xinghang; Wang, Haiyan

    2011-04-01

    The deformation behaviors of YBa2Cu3O7-x (YBCO) thin films with twinning structures were studied via in situ nanoindentation experiments in a transmission electron microscope. The YBCO films were grown on SrTiO3 (001) substrates by pulsed laser deposition. Both ex situ (conventional) and in situ nanoindentation were conducted to reveal the deformation of the YBCO films from the directions perpendicular and parallel to the twin interfaces. The hardness measured perpendicular to the twin interfaces is ˜50% and 40% higher than that measured parallel to the twin interfaces ex situ and in situ, respectively. Detailed in situ movie analysis reveals that the twin structures play an important role in deformation and strengthening mechanisms in YBCO thin films.

  6. The influence of A-site rare-earth for barium substitution on the chemical structure and ferroelectric properties of BZT thin films

    NASA Astrophysics Data System (ADS)

    Ostos, C.; Martínez-Sarrión, M. L.; Mestres, L.; Delgado, E.; Prieto, P.

    2009-10-01

    Rare-earth ( RE) doped Ba(Zr,Ti)O 3 (BZT) thin films were prepared by rf-magnetron sputtering from a Ba 0.90Ln0.067Zr 0.09Ti 0.91O 3 ( Ln=La, Nd) target. The films were deposited at a substrate temperature of 600 °C in a high oxygen pressure atmosphere. X-ray diffraction (XRD) patterns of RE-BZT films revealed a <001> epitaxial crystal growth on Nb-doped SrTiO 3, <001> and <011> growth on single-crystal Si, and a <111>-preferred orientation on Pt-coated Si substrates. Scanning electron microscopy (SEM) showed uniform growth of the films deposited, along with the presence of crystals of about half-micron size on the film's surface. Transmission electron microscopy (TEM) evidenced high crystalline films with thicknesses of about 100 nm for 30 min of sputtering. Electron-probe microanalysis (EPMA) corroborated the growth rate (3.0-3.5 nm/min) of films deposited on Pt-coated Si substrates. X-ray photoelectron spectroscopy (XPS), in depth profile mode, showed variations in photoelectron Ti 2 p doublet positions at lower energies with spin-orbital distances characteristic of BaTiO 3-based compounds. The XPS analysis revealed that lanthanide ions positioned onto the A-site of the BZT-perovskite structure increasing the MO 6-octahedra distortion ( M=Ti, Zr) and, thereby, modifying the Ti-O binding length. Polarization-electric field hysteresis loops on Ag/ RE-doped BZT/Pt capacitor showed good ferroelectric behavior and higher remanent polarization values than corresponding non-doped system.

  7. Nonzero Berry phase in quantum oscillations from giant Rashba-type spin splitting in LaTiO3/SrTiO3 heterostructures.

    PubMed

    Veit, M J; Arras, R; Ramshaw, B J; Pentcheva, R; Suzuki, Y

    2018-04-13

    The manipulation of the spin degrees of freedom in a solid has been of fundamental and technological interest recently for developing high-speed, low-power computational devices. There has been much work focused on developing highly spin-polarized materials and understanding their behavior when incorporated into so-called spintronic devices. These devices usually require spin splitting with magnetic fields. However, there is another promising strategy to achieve spin splitting using spatial symmetry breaking without the use of a magnetic field, known as Rashba-type splitting. Here we report evidence for a giant Rashba-type splitting at the interface of LaTiO 3 and SrTiO 3 . Analysis of the magnetotransport reveals anisotropic magnetoresistance, weak anti-localization and quantum oscillation behavior consistent with a large Rashba-type splitting. It is surprising to find a large Rashba-type splitting in 3d transition metal oxide-based systems such as the LaTiO 3 /SrTiO 3 interface, but it is promising for the development of a new kind of oxide-based spintronics.

  8. Synergistic effect of Au and Rh on SrTiO3 in significantly promoting visible-light-driven syngas production from CO2 and H2O.

    PubMed

    Li, Dewang; Ouyang, Shuxin; Xu, Hua; Lu, Da; Zhao, Ming; Zhang, Xueliang; Ye, Jinhua

    2016-05-01

    A novel photocatalyst constructed by Rh, Au, and SrTiO3 was developed to realize syngas photosynthesis from low-cost CO2 and H2O feedstock under visible-light irradiation. The synergistic effect of Rh and Au on SrTiO3 contributed to a 22- and 153-fold photoactivity magnification for syngas yield in contrast to Au@SrTiO3 and Rh@SrTiO3 samples, respectively.

  9. Crystallization of Sr0.5Ba0.5Nb2O6 Thin Films on LaNiO3 Electrodes by RF Magnetron Reactive Sputtering

    NASA Astrophysics Data System (ADS)

    Jong, Chao-An; Gan, Jon-Yiew

    2000-02-01

    Strontium barium niobium (Sr0.5Ba0.5Nb2O6) (SBN) thin films are prepared on conductive-oxide LNO (LaNiO3) electrodes by the rf magnetron sputtering system. Instead of conventional furnace annealing, SBN thin films are crystallized by rapid thermal annealing (RTA) above 700°C for 5 min. The textured SBN films are crystallized with two orientations: one is the (001) or (310) direction, and the other is the (002) or (620) direction. Films compositions measured by the electron spectroscopy of chemical analysis (ESCA) quantitative analysis method show nearly the same stoichiometric ratio as the target. The depth profiles of SBN films and the target are examined by secondary ion mass spectrometer (SIMS). The concentrations of the films are quite uniform. After being heat treated at 800°C for 5 min by RTA, La and Ni diffuse into the SBN film. The diffusion coefficient of La in SBN films is also calculated.

  10. Real-time monitoring of the structure of ultrathin Fe3O4 films during growth on Nb-doped SrTiO3(001)

    NASA Astrophysics Data System (ADS)

    Kuschel, O.; Spiess, W.; Schemme, T.; Rubio-Zuazo, J.; Kuepper, K.; Wollschläger, J.

    2017-07-01

    In this work, thin magnetite films were deposited on SrTiO3 via reactive molecular beam epitaxy at different substrate temperatures. The growth process was monitored in-situ during deposition by means of x-ray diffraction. While the magnetite film grown at 400 °C shows a fully relaxed vertical lattice constant already in the early growth stages, the film deposited at 270 °C exhibits a strong vertical compressive strain and relaxes towards the bulk value with increasing film thickness. Furthermore, a lateral tensile strain was observed under these growth conditions although the inverse behavior is expected due to the lattice mismatch of -7.5%. Additionally, the occupancy of the A and B sublattices of magnetite with tetrahedral and octahedral sites was investigated showing a lower occupancy of the A sites compared to an ideal inverse spinel structure. The occupation of A sites decreases for a higher growth temperature. Thus, we assume a relocation of the iron ions from tetrahedral sites to octahedral vacancies forming a deficient rock salt lattice.

  11. Interdiffusion-driven synthesis of tetragonal chromium (III) oxide on BaTi O3

    NASA Astrophysics Data System (ADS)

    Asa, M.; Vinai, G.; Hart, J. L.; Autieri, C.; Rinaldi, C.; Torelli, P.; Panaccione, G.; Taheri, M. L.; Picozzi, S.; Cantoni, M.

    2018-03-01

    Interfaces play a crucial role in the study of novel phenomena emerging at heterostructures comprising metals and functional oxides. For this reason, attention should be paid to the interface chemistry, which can favor the interdiffusion of atomic species and, under certain conditions, lead to the formation of radically different compounds with respect to the original constituents. In this work, we consider Cr/BaTi O3 heterostructures grown on SrTi O3 (100) substrates. Chromium thin films (1-2 nm thickness) are deposited by molecular beam epitaxy on the BaTi O3 layer, and subsequently annealed in vacuum at temperatures ranging from 473 to 773 K. A disordered metallic layer is detected for annealing temperatures up to 573 K, whereas, at higher temperatures, we observe a progressive oxidation of chromium, which we relate to the thermally activated migration of oxygen from the substrate. The chromium oxidation state is +3 and the film shows a defective rocksalt structure, which grows lattice matched on the underlying BaTi O3 layer. One out of every three atoms of chromium is missing, producing an uncommon tetragonal phase with C r2O3 stoichiometry. Despite the structural difference with respect to the ordinary corundum α-C r2O3 phase, we demonstrate both experimentally and theoretically that the electronic properties of the two phases are, to a large extent, equivalent.

  12. Optical Characterization of Tb3+:BaHfO3 Thin Films by Means of Photoacoustic Spectroscopy

    NASA Astrophysics Data System (ADS)

    Jiménez Flores, Yolanda; Nogal, Uriel; Suárez Quezada, Víctor Manuel; Rojas-Trigos, José Bruno

    2018-06-01

    In this work, the synthesis and optical characterization of Al2O3/Tb3+:BaHfO3/Al2O3 heterostructure, grown by ultrasonic spray pyrolysis technique are reported. The X-ray diffraction patterns corroborate that the scintillator layer structure corresponds to perovskite structure, while the elemental chemical composition of it is close to the optimal stoichiometry, but showing barium vacancies. The empirical determination of the optical bandgap energy, achieved by means of the photoacoustic spectroscopy technique, set a principal direct band gap in 3.8 eV, but evidencing the existence of a larger indirect bandgap also. The photoluminescent spectroscopy measurements show that the heterostructure has an intense fluorescent response, congruent to the principal emission lines of trivalent terbium, as was intended to.

  13. Tuning metal-insulator behavior in LaTiO3/SrTiO3 heterostructures integrated directly on Si(100) through control of atomic layer thickness

    NASA Astrophysics Data System (ADS)

    Ahmadi-Majlan, Kamyar; Chen, Tongjie; Lim, Zheng Hui; Conlin, Patrick; Hensley, Ricky; Chrysler, Matthew; Su, Dong; Chen, Hanghui; Kumah, Divine P.; Ngai, Joseph H.

    2018-05-01

    We present electrical and structural characterization of epitaxial LaTiO3/SrTiO3 heterostructures integrated directly on Si(100). By reducing the thicknesses of the heterostructures, an enhancement in carrier-carrier scattering is observed in the Fermi liquid behavior, followed by a metal to insulator transition in the electrical transport. The insulating behavior is described by activated transport, and its onset occurs near an occupation of 1 electron per Ti site within the SrTiO3, providing evidence for a Mott driven transition. We also discuss the role that structure and gradients in strain could play in enhancing the carrier density. The manipulation of Mott metal-insulator behavior in oxides grown directly on Si opens the pathway to harnessing strongly correlated phenomena in device technologies.

  14. Tuning metal-insulator behavior in LaTiO 3/SrTiO 3 heterostructures integrated directly on Si(100) through control of atomic layer thickness

    DOE PAGES

    Ahmadi-Majlan, Kamyar; Chen, Tongjie; Lim, Zheng Hui; ...

    2018-05-07

    Here, we present electrical and structural characterization of epitaxial LaTiO 3/SrTiO 3 heterostructures integrated directly on Si(100). By reducing the thicknesses of the heterostructures, an enhancement in carrier-carrier scattering is observed in the Fermi liquid behavior, followed by a metal to insulator transition in the electrical transport. The insulating behavior is described by activated transport, and its onset occurs near 1 electron per Ti occupation within the SrTiO 3 well, providing evidence for a Mott driven transition. We also discuss the role that structure and gradients in strain could play in enhancing the carrier density. The manipulation of Mott metal-insulatormore » behavior in oxides grown directly on Si opens the pathway to harnessing strongly correlated phenomena in device technologies.« less

  15. Tuning metal-insulator behavior in LaTiO 3/SrTiO 3 heterostructures integrated directly on Si(100) through control of atomic layer thickness

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ahmadi-Majlan, Kamyar; Chen, Tongjie; Lim, Zheng Hui

    Here, we present electrical and structural characterization of epitaxial LaTiO 3/SrTiO 3 heterostructures integrated directly on Si(100). By reducing the thicknesses of the heterostructures, an enhancement in carrier-carrier scattering is observed in the Fermi liquid behavior, followed by a metal to insulator transition in the electrical transport. The insulating behavior is described by activated transport, and its onset occurs near 1 electron per Ti occupation within the SrTiO 3 well, providing evidence for a Mott driven transition. We also discuss the role that structure and gradients in strain could play in enhancing the carrier density. The manipulation of Mott metal-insulatormore » behavior in oxides grown directly on Si opens the pathway to harnessing strongly correlated phenomena in device technologies.« less

  16. Disorder-controlled superconductivity at YBa2Cu3O7/SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Garcia-Barriocanal, J.; Perez-Muñoz, A. M.; Sefrioui, Z.; Arias, D.; Varela, M.; Leon, C.; Pennycook, S. J.; Santamaria, J.

    2013-06-01

    We examine the effect of interface disorder in suppressing superconductivity in coherently grown ultrathin YBa2Cu3O7 (YBCO) layers on SrTiO3 (STO) in YBCO/STO superlattices. The termination plane of the STO is TiO2 and the CuO chains are missing at the interface. Disorder (steps) at the STO interface cause alterations of the stacking sequence of the intracell YBCO atomic layers. Stacking faults give rise to antiphase boundaries which break the continuity of the CuO2 planes and depress superconductivity. We show that superconductivity is directly controlled by interface disorder outlining the importance of pair breaking and localization by disorder in ultrathin layers.

  17. Field-effect control of superconductivity and Rashba spin-orbit coupling in top-gated LaAlO3/SrTiO3 devices

    PubMed Central

    Hurand, S.; Jouan, A.; Feuillet-Palma, C.; Singh, G.; Biscaras, J.; Lesne, E.; Reyren, N.; Barthélémy, A.; Bibes, M.; Villegas, J. E.; Ulysse, C.; Lafosse, X.; Pannetier-Lecoeur, M.; Caprara, S.; Grilli, M.; Lesueur, J.; Bergeal, N.

    2015-01-01

    The recent development in the fabrication of artificial oxide heterostructures opens new avenues in the field of quantum materials by enabling the manipulation of the charge, spin and orbital degrees of freedom. In this context, the discovery of two-dimensional electron gases (2-DEGs) at LaAlO3/SrTiO3 interfaces, which exhibit both superconductivity and strong Rashba spin-orbit coupling (SOC), represents a major breakthrough. Here, we report on the realisation of a field-effect LaAlO3/SrTiO3 device, whose physical properties, including superconductivity and SOC, can be tuned over a wide range by a top-gate voltage. We derive a phase diagram, which emphasises a field-effect-induced superconductor-to-insulator quantum phase transition. Magneto-transport measurements show that the Rashba coupling constant increases linearly with the interfacial electric field. Our results pave the way for the realisation of mesoscopic devices, where these two properties can be manipulated on a local scale by means of top-gates. PMID:26244916

  18. Potential Barrier Lowering and Electrical Transport at the LaAlO3/SrTiO3 Interface

    NASA Astrophysics Data System (ADS)

    Suzuki, Yuri

    2009-03-01

    Interfacial phenomena form the basis for modern-day devices and continue to be an area of fundamental interest in condensed matter research. Advances in oxide thin film fabrication have enabled the synthesis of atomically precise oxide interfaces and hence have allowed for controlled investigation of interfacial phenomena in these materials. With the rich variety of functionalities exhibited by transition-metal oxides, a wide array of novel properties may be achieved at oxide heterointerfaces. An exemplary study is the discovery of metallicity at the interface of two band insulators, LaAlO3 (LAO) and SrTiO3 (STO), which has stimulated many subsequent experimental as well as theoretical studies. However, there is still intense debate on the origin of metallicity, specifically whether it arises from electronic reconstruction or oxygen vacancies. Using a combination of vertical transport measurements across and lateral transport measurements along the LAO/STO heterointerface, we demonstrate that significant potential barrier lowering and band bending are the cause of interfacial metallicity. Transport measurements across the heterointerface, indicate that barrier lowering and enhanced band bending extends over 2.5 nm into LAO as well as STO. We explain the origins of high-temperature carrier saturation, lower carrier concentration, and higher mobility in the sample with the thinnest LAO film on a STO substrate. Lateral transport results suggest that parasitic interface scattering centers limit the low-temperature lateral electron mobility of the metallic channel. [4pt] *In collaboration with Franklin Wong, Miaofang Chi, Rajesh Chopdekar, Brittany Nelson-Cheeseman and Nigel Browning.

  19. Segregation and trapping of oxygen vacancies near the SrTiO 3Σ3 (112) [110] tilt grain boundary

    DOE PAGES

    Liu, Bin; Cooper, Valentino R.; Zhang, Yanwen; ...

    2015-03-21

    In nanocrystalline materials, structural discontinuities at grain boundaries (GBs) and the segregation of point defects to these GBs play a key role in defining the structural stability of a material, as well as its macroscopic electrical/mechanical properties. In this study, the segregation of oxygen vacancies near the Σ3 (1 1 2) [¯110] tilt GB in SrTiO 3 is explored using density functional theory. We find that oxygen vacancies segregate toward the GB, preferring to reside within the next nearest-neighbor layer. This oxygen vacancy segregation is found to be crucial for stabilizing this tilt GB. Furthermore, we find that the migrationmore » barriers of oxygen vacancies diffusing toward the first nearest-neighbor layer of the GB are low, while those away from this layer are very high. Furthermore, the segregation and trapping of the oxygen vacancies in the first nearest-neighbor layer of GBs are attributed to the large local distortions, which can now accommodate the preferred sixfold coordination of Ti. These results suggest that the electronic, transport, and capacitive properties of SrTiO 3 can be engineered through the control of GB structure and grain size or layer thickness.« less

  20. Electrical Transport and Magnetoresistance Properties of Tensile-Strained CaMnO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Ullery, Dustin; Lawson, Bridget; Zimmerman, William; Neubauer, Samuel; Chaudhry, Adeel; Hart, Cacie; Yong, Grace; Smolyaninova, Vera; Kolagani, Rajeswari

    We will present our studies of the electrical transport and magnetoresistance properties of tensile strained CaMnO3 thin films. We observe that the resistivity decreases significantly as the film thickness decreases which is opposite to what is observed in thin films of hole doped manganites. The decrease in resistivity is more pronounced in the films on (100) SrTiO3, with resistivity of the thinnest films being about 3 orders of magnitude lower than that of bulk CaMnO3. Structural changes accompanying resistivity changes cannot be fully explained as due to tensile strain, and indicate the presence of oxygen vacancies. These results also suggest a coupling between tensile strain and oxygen deficiency, consistent with predictions from models based on density functional theory calculations. We observe a change in resistance under the application of moderate magnetic field. Experiments are underway to understand the origin of the magnetoresistance and its possible relation to the tensile strain effects. We acknowledge support from: Towson Office of University Undergraduate Research, Fisher Endowment Grant and Undergraduate Research Grants from the Fisher College of Science and Mathematics, and Seed Funding Grant from the School of Emerging technologies.