RF Aerosol Mist Plasma Deposition of Oxide Films
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ABSTRACT We report new results on nano-scaled oxide films deposited by an RF aerosol mist plasma technique: including indium tin oxide transparent conductive films; yttria stabilized zirconia, nickel iron oxide/YSZ cermet, and lanthanum strontium manganite for fuel cell applications; Bi2Sr2Ca2Cu3QC superconductor films; gadolinium iron oxide for magnetic heat pumps; silicon oxide for protective coatings, etc. Since this deposition process occurs in an atmospheric environment, it has potential for large scale production. The maximum deposition rate is approximately 1 micrometer per minute per centimeter squared. Substrate temperatures were between 300'C and 900'C. Crystal sizes are analyzed by XRD (Shadow Programs). Some films were also characterized by resistance, optical(IRUV-Vis transmission/reflection and FTIR) and M6ssbauer measurements. Film morphology was found to be strongly dependent on deposition parameters. Controlling the deposition rate by altering solution concentration and mist feed rates, as well as altering plasma torch settings and substrate temperature allowed the formation of different film morphologies. Film density, thickness, and crystallite size could be controlled to obtain films of differing characteristics. This is advantageous to fuel cell depositions where a dense electrolyte as well as porous
electrodes (anode and cathode) are required.
INTRODUCTION Ceramic oxide thin films are deposited to alter the electrical, mechanical and optical properties of the substrate materials. 1 Most deposition techniques involve the use of a vacuum system. 2 The use of vacuum systems limits the size and production rate of the films. 3 We have used an atmospheric, RF aerosol mist plasma deposition technique to deposit a variety of oxide materials. This method shows promising results and allows possible up-scaling to a low cost, large scale industrial 4 coating applications. Film morphology was highly dependent on deposition parameters. Starting solution concentration, mist feed rate, plasma torch settings, and substrate temperature could be adjusted to control film density, thickness, and crystallite size. Film crystallite sizes were analyzed through XRD peak broadening (SHADOW Program). 5 Crystallite sizes in the nanometer range were obtained. Nanoscaled materials are believed to exhibit better thermal and mechanical properties compared to micrometer sized materials. 6 In the case of solid oxide fuel cell (SOFC) applications, a nano- structured material may also be utilized to improve ionic 563 Mat. Res. Soc. Symp. Proc. Vol. 355 01995 Materials Research Society
conductivity and to lower the operating temperature. For example, a ZrO2_x formula unit contains four ZrO2 unit cells. The oxygen vacancy number 'x' was calculated to be 0.305, assuming the YSZ contains 8.27 mol% Y203. 7 In a simplified model, the crystalline size is assumed to be 20nm. For a cubic shaped crystallite, the number of oxygen vacancies is about 14. Considering the significant surface area, approximately 30% of the vacancies are loc
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