Electrochemical Deposition of Bismuth Micro- and Nanowires Using Electroplate and Lift Lithography
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Electrochemical Deposition of Bismuth Micro- and Nanowires Using Electroplate and Lift Lithography Timea Hohl1, 2, Lori A. Lepak1, Andrew Zimmerman1*, Samuel Hempel1*, Anirudha V. Sumant3, Ralu Divan3, C. Suzanne Miller3, Daniel Rosenmann3, Christopher Verzani1, Endre Takács2, Michael P. Zach1 1
University of Wisconsin – Stevens Point, WI 54481, U.S.A. University of Debrecen, Debrecen, H-4010, Hungary 3 Center for Nanoscale Materials, Argonne National Laboratory, IL 60439, U.S.A. *denotes undergraduate student 2
ABSTRACT Patterned micro- and nanowires of several compositions in the solution series of BixTey were electrochemically deposited using Electroplate and Lift (E&L) Lithography on Ultrananocrystalline Diamond (UNCD) templates. The composition of the deposited BixTey wires was controlled by mixing saturated solutions of bismuth nitrate and tellurium in various ratios in the electroplating bath. All wires were electroplated via pulsed depositions at -1.4V vs. the saturated calomel electrode (SCE). The morphology and composition of all wires were studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). In general, the BixTey wires were fine-grained and brittle, often fracturing during the liftoff process. By contrast, wires containing less than 5% Te are smooth, and strong enough to support their own weight without a supporting medium for a length of over 100 times the wire diameter. INTRODUCTION Thermoelectric materials are expected to play an important role in the quest for novel, renewable energy sources and in increasing the efficiency of current energy generating methods. Temperature differences created by industrial waste heat, heat from the sun, and even from our body have the possibility to be exploited for electrical energy generation. In principle, this can be accomplished via the Seebeck-effect. The Seebeck-effect is a phenomenon where a voltage difference is created due to a temperature gradient in a material. The experimental measurement that determines whether or not a material is a good candidate for thermoelectric use is the material’s non-dimensional figure of merit, or ZT value. The dependency of Seebeck-effect efficiency on the ZT values of materials is described in [1]. As it is presented in [2], theoretical and experimental studies show that the ZT value of nanoscale materials is in general greater than their corresponding bulk value. To increase the efficiency of the Seebeck-effect, materials with high ZT values for temperature ranges of interest need to be investigated. Current thermoelectric devices have ZT values at room temperature of approximately 0.8, with efficiencies of 5% - 6%, whereas ZT values near 3.2 could provide efficiencies of approximately 30% [1]. Bulk bismuth telluride has a room-temperature ZT value of near 1.0[3]. This makes bismuth telluride a good candidate for investigation of its thermoelectric properties in nanostructured forms. In this work, bismuth, tellurium, and bismuth telluride were electrochemically plated using E&L Lithograp
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