Platinum Nanostructure Growth Using Self-Assembled Fluorocarbon Structure
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Platinum Nanostructure Growth Using Self-Assembled Fluorocarbon Structure Sang Hwui Lee, Zhengchun Liu, J. Jay McMahon, and Jian-Qiang Lu Center for Integrated Electronics, Rensselaer Polytechnic Institute, Troy, NY, 12180 ABSTRACT We report on a novel approach to grow platinum (Pt) nanostructure using a self-assembled fluorocarbon structure as a template. A ring-type structure of fluorocarbon residues forms during the reactive ion etching (RIE) of SiO2 using trifluoromethane (CHF3) and oxygen as etching gases. Typical dimensions of the ring-type fluorocarbon structure are found to be ~50 nm in diameter, ~10 nm in wall thickness, and ~50 nm in height in this study. Platinum nanostructure up to 100 nm in height and 50 nm in diameter are grown on the template using a low-cost thin film sputter coater for 3 minutes. The morphology and growth mechanism of fluorocarbon structure and platinum nanostructure are discussed. This work provides a simple approach to platinum nanostructure growth for a fuel-cell application. INTRODUCTION Miniature proton exchange membrane fuel cells (PEMFCs) are of interest for portable applications such as cell phones, personal digital assistants (PDAs), and laptop computers [1-3]. Silicon-based wafer bonding technology provides potential fabrication advantages for miniature PEMFCs as highly manufacturable batch process can be utilized, integration for heterogeneous materials such as metals, polymers, and ceramics is possible, and high quality sealing can be incorporated (preventing gas or liquid leakages which may damage the mixture system of electronic and fluidic devices) [4]. Other silicon-based batch processes such as photolithographic patterning and deep reactive ion etching (Deep-RIE) can reduce the cost of PEMFC fabrication for high volume applications [3]. One of the key cost drivers in miniature PEMFCs is the platinum-based catalyst. Platinum is an excellent catalyst choice due to its electro-catalytic properties for increasing the oxidation of hydrogen at an anode and reduction of oxygen at a cathode, in spite of its high cost relative to other materials. Typically two approaches have been used to increase platinum catalyst performance and reduce costs: (1) increasing surface area through the use of platinum nanoparticles [5] or porous platinum structure on support materials [1, 6] and (2) forming platinum alloy with a more readily available material [7]. In an effort to develop large surface area in miniature fuel cell applications, we introduce a simply prepared fluorocarbon structure to template nanostructured platinum. Fluorocarbon forms during the plasma-assisted etching process of silicon and silicon dioxide. These residues are generally considered undesirable materials during the RIE of silicon or SiO2 and are often cleaned off in subsequent steps. Previous work [8-10] for fluorocarbon structure explored the properties of fluorocarbon films during SiO2/Si etching process, but did not focus on the morphology of fluorocarbon film formation during SiO2 etching. In t
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