Microscopical Study of the Structural Evolution of Sol-Gel Derived Buffer Layers for the Integration of YBCO on Biaxiall
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209 Mat. Res. Soc. Symp. Proc. Vol. 619 © 2000 Materials Research Society
In this paper, we use a chelate solution route to fabricate an epitaxial buffer layer of Ho 2 03 on biaxially textured nickel. By applying microscopy techniques, such as scanning electron microscopy (SEM), atomic force microscopy (AFM), scanning tunneling microscopy (STM), electron backscattered diffraction (EBSP), and optical microscopy we want to (1) identify the surface properties of biaxially textured nickel; (2) characterize the microstructural evolution of the Ho 20 3 buffer layer as function of annealing temperature; and (3) investigate the effects of chemical precursor modifications on the microstructure of holmium oxide. EXPERIMENT A 0.15 M holmium acetate precursor solution was prepared by dissolving 0.513 g holmium acetate (Alfa-Aesar, Ward Hill, MA) in 5 ml HPLC glacial acetic acid (Fisher Scientific, Pittsburgh, PA). The temperature was slowly increased to 1 10°C to accelerate the dissolution. After complete dissolution was obtained, the hot plate was switched off and 5 ml of methanol (Fisher Scientific, Pittsburgh, PA) was added to the solution as the solution temperature decreased to 70'C. Finally, the solution was stirred for another 30 minutes. An alternative 0.15 M holmium precursor solution without methanol was also prepared by dissolving the holmium acetate precursor in 10 ml glacial acetic acid to study chemical effects on the structural evolution of holmium oxide thin films deposited on nickel. All solution preparation steps and the film deposition process were carried out under inert atmosphere conditions. Prior to film deposition, the as-received biaxially textured nickel tapes (EURUS Plastronics) were ultrasonically cleaned in acetone, rinsed in methanol, and heat treated in a tube furnace (Lindberg/BlueM TF55030, Asheville, NC) under reducing atmosphere conditions (4%H 2/96%N 2 ) to remove absorbed organics, water and the nickel oxide layer on the nickel surface. After thermal processing, the nickel tapes were transferred and stored in an inert atmosphere glove box to prevent re-oxidation of the nickel. The thin films were deposited by spin-casting (Specialty Coating Systems, Inc.) onto the nickel substrates at 3000 rpm for 30 s. After the deposition of the first layer, the films were pyrolyzed on a hot plate at 300'C for 5 min to remove the organic species. The deposition process was repeated for three more layers. Then, the pyrolyzed films were transferred to the tube furnace and heat treated from 300'C to 1100IC for 60 min, using a heating rate of 50°C/min. Nickel tapes were studied by optical microscopy (BX 60, Olympus, Japan), AFM (Topometrix), and STM (RHK Technology, Inc). Electron backscattered diffraction (EBSD) studies on nickel were performed on a Hitachi S3500 with an EBSD acquisition unit from HKL Technology, Denmark. Holmium oxide film analyses were accomplished using a field emission SEM (Hitachi S4700) and X-ray diffraction (Scintag XDS 2000). RESULTS Biaxially Textured Nickel Because the nickel sub
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