Characterization of Porous Pt/Al 2 O 3 Films Produced by Hybrid Gas-to-Particle Conversion and Chemical Vapor Deposition
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Characterization of Porous Pt/Al2O3 Films Produced by Hybrid Gas-to-Particle Conversion and Chemical Vapor Deposition Quynh T. Nguyen and Sheryl H. Ehrman Department of Chemical Engineering, University of Maryland College Park, MD 20742, U.S.A. ABSTRACT A hybrid process, based upon gas-to-particle conversion and chemical vapor deposition, is presented as an alternative technique for producing porous films with the main advantage of solvent-free, low-substrate temperature operation. Starting from precursors of platinum acetylacetonate and aluminum acetylacetonate, nanoparticles were produced by chemical reaction followed by gas-to-particle conversion. Downstream of this reaction zone, these nanoparticles were collected via thermophoresis onto a cooled substrate forming a porous, nanocermet film that may have possible uses in catalytic, sensor, or coating applications. In this study, Pt/Alumina nanocermet films were produced by two routes: either simultaneous precursor injection processing or a layer-by-layer approach. Energydispersive X-ray spectroscopy revealed that this hybrid process results in reasonable control of the amount of Pt within each sample. From transmission electron spectroscopy images taken of films produced by simultaneous processing, Pt nanoparticles appear to be co-agglomerated with alumina. The results may identify changes that can be made to the process to improve properties, such as catalytic activity, in the nanocermet films. INTRODUCTION Differing from their molecular and bulk counterparts, materials consisting of nanoparticles are of interest because of their unique properties. Various routes to nanoparticle synthesis have been developed, including sol-gel based wet chemical methods, and plasma, flame, or furnace based gas-phase syntheses involving either evaporation or condensation of materials or chemical conversion of precursor compounds to the condensable species. Critical to the utility of these materials is the development of processes for the manufacture of functional materials from nanoparticles. Key to the success of these processes is preservation of the small grain size, correspondingly high surface area, and unique properties of the nanoparticles. Porous materials are used as lightweight structural materials, insulators, catalysts and catalyst supports, and sorbents or membranes in separation processes [1]. Films of porous materials have applications including interlayer dielectrics in microelectronics [2], electrocatalysts for polymer electrolytic membrane-based (PEM) fuel cells [3], electrodes for photovoltaic power cells [4], and chemical sensors [5]. Specifically, nanoparticulate Pt/Al2O3 films may be useful in catalytic applications [6] in which the increased surface area may lead to enhanced catalytic activity. Also, these films and their optical properties are useful in coating applications that reduce, absorb, or reflect radiation from the solar spectrum [7,8]. The apparatus for the process has been designed for single-stage operation under
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atmospheric
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