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Title: Surface layer of SrRuO{sub 3} epitaxial thin films under oxidizing and reducing conditions

Abstract

Imperfect stoichiometry and heterogeneity of a surface layer of SrRuO{sub 3} epitaxial thin films, grown on SrTiO{sub 3} substrates, are presented with the help of various methods. Rutherford backscattering spectroscopy, x-ray photoemission spectroscopy (XPS), and time of flight secondary ion mass spectrometry are used to obtain information about the stoichiometry and uniformity of the SrRuO{sub 3} structure. The temperature of chemical decomposition is first determined for polycrystalline samples under different conditions using thermogravimetry analysis. Then the determined values are used for thin film annealings in high and low oxygen pressure ambients, namely, air, vacuum, and hydrogen. The surface deterioration of the thin film together with changes in its electronic structure is investigated. O1s and Sr3d core lines measured by XPS for as-made samples obviously consist of multiple components indicating different chemical surroundings of atoms. Thanks to different incident beam angle measurements it is possible to distinguish between interior and surface components. Valence band spectra of the interior of the film are consistent with theoretical calculations. After annealing, the ratio of the different components changes drastically. Stoichiometry near the surface changes, mostly due to ruthenium loss (RuO{sub X}) or a segregation process. The width and position of the Ru3p line formore » as-made samples suggest a mixed oxidation state from metallic to fully oxidized. Long annealing in hydrogen or vacuum ambient leads to a complete reduction of ruthenium to the metallic state. Local conductivity atomic force microscopy scans reveal the presence of nonconductive adsorbates incorporated in the surface region of the film. Charge transport in these measurements shows a tunneling character. Scanning tunneling microscopy scans show some loose and mobile adsorbates on the surface, likely containing hydroxyls. These results suggest that an adequate description of a SrRuO{sub 3} thin film should take into account imperfections and high reactivity of its surface region.« less

Authors:
; ; ; ; ; ;  [1];  [2];  [3]
  1. Institut fuer Festkoerperforschung, Forschungszentrum Juelich, 52425 Juelich (Germany)
  2. (Germany)
  3. (Poland)
Publication Date:
OSTI Identifier:
20982639
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 2; Other Information: DOI: 10.1063/1.2408382; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ANNEALING; ATOMIC FORCE MICROSCOPY; CHARGE TRANSPORT; DECOMPOSITION; ELECTRONIC STRUCTURE; EPITAXY; HYDROXIDES; MASS SPECTRA; MASS SPECTROSCOPY; OXIDATION; RUTHENIUM COMPOUNDS; RUTHERFORD BACKSCATTERING SPECTROSCOPY; SCANNING TUNNELING MICROSCOPY; STOICHIOMETRY; STRONTIUM TITANATES; THERMAL GRAVIMETRIC ANALYSIS; THIN FILMS; TIME-OF-FLIGHT METHOD; TUNNEL EFFECT; X-RAY PHOTOELECTRON SPECTROSCOPY

Citation Formats

Mlynarczyk, M., Szot, K., Petraru, A., Poppe, U., Breuer, U., Waser, R., Tomala, K., Center of Nanoelectronic Systems for Information Technology, Forschungszentrum Juelich, 52425 Juelich, and M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow. Surface layer of SrRuO{sub 3} epitaxial thin films under oxidizing and reducing conditions. United States: N. p., 2007. Web. doi:10.1063/1.2408382.
Mlynarczyk, M., Szot, K., Petraru, A., Poppe, U., Breuer, U., Waser, R., Tomala, K., Center of Nanoelectronic Systems for Information Technology, Forschungszentrum Juelich, 52425 Juelich, & M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow. Surface layer of SrRuO{sub 3} epitaxial thin films under oxidizing and reducing conditions. United States. doi:10.1063/1.2408382.
Mlynarczyk, M., Szot, K., Petraru, A., Poppe, U., Breuer, U., Waser, R., Tomala, K., Center of Nanoelectronic Systems for Information Technology, Forschungszentrum Juelich, 52425 Juelich, and M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow. Mon . "Surface layer of SrRuO{sub 3} epitaxial thin films under oxidizing and reducing conditions". United States. doi:10.1063/1.2408382.
@article{osti_20982639,
title = {Surface layer of SrRuO{sub 3} epitaxial thin films under oxidizing and reducing conditions},
author = {Mlynarczyk, M. and Szot, K. and Petraru, A. and Poppe, U. and Breuer, U. and Waser, R. and Tomala, K. and Center of Nanoelectronic Systems for Information Technology, Forschungszentrum Juelich, 52425 Juelich and M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow},
abstractNote = {Imperfect stoichiometry and heterogeneity of a surface layer of SrRuO{sub 3} epitaxial thin films, grown on SrTiO{sub 3} substrates, are presented with the help of various methods. Rutherford backscattering spectroscopy, x-ray photoemission spectroscopy (XPS), and time of flight secondary ion mass spectrometry are used to obtain information about the stoichiometry and uniformity of the SrRuO{sub 3} structure. The temperature of chemical decomposition is first determined for polycrystalline samples under different conditions using thermogravimetry analysis. Then the determined values are used for thin film annealings in high and low oxygen pressure ambients, namely, air, vacuum, and hydrogen. The surface deterioration of the thin film together with changes in its electronic structure is investigated. O1s and Sr3d core lines measured by XPS for as-made samples obviously consist of multiple components indicating different chemical surroundings of atoms. Thanks to different incident beam angle measurements it is possible to distinguish between interior and surface components. Valence band spectra of the interior of the film are consistent with theoretical calculations. After annealing, the ratio of the different components changes drastically. Stoichiometry near the surface changes, mostly due to ruthenium loss (RuO{sub X}) or a segregation process. The width and position of the Ru3p line for as-made samples suggest a mixed oxidation state from metallic to fully oxidized. Long annealing in hydrogen or vacuum ambient leads to a complete reduction of ruthenium to the metallic state. Local conductivity atomic force microscopy scans reveal the presence of nonconductive adsorbates incorporated in the surface region of the film. Charge transport in these measurements shows a tunneling character. Scanning tunneling microscopy scans show some loose and mobile adsorbates on the surface, likely containing hydroxyls. These results suggest that an adequate description of a SrRuO{sub 3} thin film should take into account imperfections and high reactivity of its surface region.},
doi = {10.1063/1.2408382},
journal = {Journal of Applied Physics},
number = 2,
volume = 101,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • Epitaxial YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]] (YBCO) thin films were deposited on (100) MgO using platinum and SrRuO[sub 3] (SRO) buffer layers by pulsed laser deposition. The films were (001) textured normal to substrate surface with a high degree of in-plane orientation with respect to the substrate's major axes. YBCO films showed superconducting transition temperature ([ital T][sub co]) at 91 K and critical current densities were found to be 2--3[times]10[sup 6] A/cm[sup 2] at 77 K and zero field. An ion beam minimum channeling yield of 16% was obtained for YBCO films, indicating high crystallinity. The orientation relationship for this epitaxialmore » multilayer structure was found to be (100) YBCO[parallel](100) SRO[parallel](100)Pt[parallel](100) MgO. This result showed that high-quality superconducting thin films can be deposited on metal with an appropriate buffer layer.« less
  • Aberration corrected scanning transmission electron microscopy is used to directly observe atom columns in an epitaxial BaTiO{sub 3} thin film deposited on a 3.6 nm-thick SrRuO{sub 3} electrode layer above an SrTiO{sub 3} (001) substrate. Compositional gradients across the heterointerfaces were examined using electron energy-loss spectroscopy techniques. It was found that a small amount of Ba and Ti had diffused into the SrRuO{sub 3} layer, and that this layer contained a non-negligible concentration of oxygen vacancies. Such point defects are expected to degrade the electrode’s electronic conductivity drastically, resulting in a much longer screening length. This may explain the discrepancymore » between experimental measurements and theoretical estimates of the ferroelectric critical thickness of a BaTiO{sub 3} ferroelectric barrier sandwiched between metallic SrRuO{sub 3} electrodes, since theoretical calculations generally assume ideal (stoichiometric) perovskite SrRuO{sub 3}.« less
  • Multiferroic (Bi{sub 0.90}La{sub 0.10})(Fe{sub 0.95}Mn{sub 0.05})O{sub 3} (BLFMO) thin films were deposited on SrRuO{sub 3} (SRO) buffered Pt/TiO{sub 2}/SiO{sub 2}/Si(100) substrates with variable buffer layer thicknesses by using off-axis radio frequency sputtering. The orientation of BLFMO thin films is dependent on the SRO buffer layer thickness, which leads to a change in ferroelectric behavior. Due to the low leakage currents arising from the orientation change in association with the variation in SRO buffer layer thickness and the La and Mn codoping, well saturated P-E hysteresis loops (2P{sub r}approx210.0 muC/cm{sup 2} and 2E{sub c}approx525.5 kV/cm) are shown for the (111)-oriented BLFMOmore » thin film at room temperature and 1 kHz. It also demonstrates little ferroelectric fatigue on 10{sup 9} switching cycles. Moreover, the BLFMO thin film exhibits the enhanced magnetic behavior as compared to pure BFO thin films, due to the canting of antiferromagnetically ordered spins.« less
  • SrRuO{sub 3} thin films deposited on (001) LaAlO{sub 3} substrates by 90{degree} off-axis sputtering at 600{degree}C were studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Both AFM and cross-section TEM investigations show that the films have a rough surface. Plan-view TEM studies demonstrate that the films are composed of all three different types of orientation domains (twins). These domain structures and surface morphology are different from the SrRuO{sub 3} film deposited on the (001) SrTiO{sub 3} substrate which has an atomically flat surface and is composed of only the [110]-type domains. The reason for these differences wasmore » ascribed as the effect of lattice mismatch across the film/substrate interface. It is proposed that a SrRuO{sub 3} thin film grows on a (001) SrTiO{sub 3} substrate through a two-dimensional nucleation process, while a film on LaAlO{sub 3} grows with three steps: the coherent growth of a few monolayers at the initial stage through a two-dimensional nucleation process; the formation of misfit dislocations when the film reaches a critical thickness; and an island-like growth thereafter due to the nonuniform distribution of stress along the film surface. {copyright} 2001 American Institute of Physics.« less
  • We report temperature and magnetic field dependences of the longitudinal and transverse magnetoresistances of high-quality epitaxial SrRuO{sub 3} thin films. We also report Hall effect measurements in the paramagnetic and ferromagnetic states. The magnetic field dependence of the longitudinal magnetoresistivity shows a simple scaling {approximately}{ital H}{sup 2}/({ital T}{minus}{ital T}{sub {ital c}}){sup 2} far above the ferromagnetic transition temperature {ital T}{sub {ital c}}. This observation supports a presence of localized magnetic moments above {ital T}{sub {ital c}}. {copyright} {ital 1996 The American Physical Society.}