Oxidation Kinetics of Yba 2 Cu 3 OT 7-x Thin Films in the Presence of Atomic Oxygen and Molecular Oxygen by In-Situ Resi
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OXIDATION KINETICS OF YBa 2 Cu 3 OT 7 x THIN FILMS IN THE PRESENCE OF ATOMIC OXYGEN AND MOLECULAR OXYGEN BY IN-SITU RESISTIVITY MEASUREMENT K. Yamamoto Central Reserch Laboratories, Kanegafuchi Chemical Industry, Co. Ltd. 2-8-,1-chome, Yoshida-cho, Hyogo-ku, Kobe652, Japan B.M. Lairson, J.C. Bravman and T.H. Geballe Stanford University, Stanford CA94305
ABSTRACT The kinetics of oxidation in YBa2Cu3O7_x thin films in the presence of molecular and atomic oxygen ambients have been studied. The resistivity of c-axis, a-axis, and mixed a+c axis oriented films, deposited in-situ by off-axis magnetron sputtering, was measured as a function of time subsequent to a change in the ambient conditions. The oxidation process is shown to be thermally activated and can be characterized by a diffusion model with an activation energy which varies from approximately 1.2eV in the presence of molecular oxygen to 0.6eV for a flux of 2x10 1 5 oxygen atoms/cm 2sec. In both cases, diffusivity is found to be insensitive to oxygen stoichiometry, but the rate of oxidation is found to be sensitive to the microstructure and orientation of the films. 1 Introduction To study oxygen diffusion in YBa 2Cu 3O7 -x (hereafter referred to as YBaCuO or YBaCuO T., where x is the oxygen deficiency), various relaxation monitoring techniques, 7 such as conductivity(t), thermogravimetry( 2) and SIMS profiles of tracers(3) have been used. From oxygen tracer diffusion studies of both polycrystalline and single crystal YBaCuO(4), it has been proposed that oxygen diffusion is highly anisotropic, as might be expected from the crystal structure, with diffusion in the a-b plane much faster than diffusion parallel to the caxis. In contrast to the case for bulk materials, there are very few reports of oxygenation in thin films, especially in-situ films. Some results for the oxidation of thin films at low temperature using an oxygen plasma have been reported. In these processes, atomic oxygen plays an important role( 5). The importance of atomic oxygen during growth is also reported 6 9 by several workers( )-( ). To investigate the oxygenation process, we report in this paper systematic in-situ conductivity measurements similar to those reported by Tu, et al.(') Several films, including those with a-axis, mixed a+c-axis and c-axis orientations deposited on several substrates (MgO, LaA103, yttria stabilized zirconia (YSZ)), prepared by off-axis magnetron sputtering, were used to study both the orientation dependence and microstructural dependence of the oxygenation process. Both molecular oxygen and atomic oxygen were employed to understand the various processes involved in the oxidation of thin films.
2 Experimental Results and Discussion 2-1 Experimental In-situ YBaCuO films were deposited on several single crystal substrates by off-axis magnetron sputtering(1 0 ). Some properties of films used in this study are listed in Table 1. The general characteristics of YBaCuO films deposited in this manner have been established by many techniques, details of which are publi
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