UWSP1, Chemistry, Stevens Point, WI 54481 Argonne National Labroratory2, Lemont, IL 60439
Standard silicon-based electronics, produced in multi-million dollar cleanroom facilities by energy-intensive high-vacuum or high-temperature processes, have nearly reached the atomic limits of device performance. Further improvements in the manufacture of electronic devices are most likely to arise through the mass production of components such as micro- and nanowires by new, more economical and less energy-intensive nanomanufacturing techniques than those currently used. In this work, we report the development of an automated, a roll-to-roll process for the rapid mass production of microwires based upon Electroplate-and-Lift (E&L) Lithography1, a technique jointly developed in 2010 by UW-Stevens Point and Argonne National Laboratory’s Center for Nanoscale Materials. E&L Lithography is a fast, simple electrochemical technique which can rapidly synthesize metal and semiconductor nanowires of a variety of sizes, shapes, and chemical compositions, by employing a reusable, non-sacrificial, working electrode. This electrode is a silicon wafer on which a thin film made of ultrananocrystalline diamond (UNCD)TM, has been patterned by photolithography into a template with the desired shape of the wires. A very thin (~ 80 nm), conductive layer of nitrogen-incorporated UNCD (NUNCD) is sandwiched between two insulating layers of UNCD, such that only the exposed edges of the underlying patterned NUNCD layer will nucleate wire growth. This establishes the thickness of the N-UNCD layer as the minimum achievable diameter of the electrodeposited wire, while nano/microwires with larger, controllable diameters may be produced by increasing the deposition time.2 In alloy systems such as bismuth telluride, control over the composition of the electroplating solution leads directly to stoichiometric control of the wire composition.3,4 In early E&L experiments, microwires were manually removed with scotch tape, regenerating the template surface for subsequent depositions. In the roll-to-roll E&L system, the template electrode is attached to a wheel which is slowly rotated through an electrochemical plating bath to deposit the nanowires. Another wheel coated with an adhesive polymer is used to remove and collect the wires, re-exposing the edges of the NUNCD for reuse. This automated process is expected to be capable of producing patterned wires with diameters between 100 nm and 10 microns at a rate of ~ 8 grams per day. If the pattern is a single continuous edge, calculations suggest that this roll-to-roll system should also be capable of producing a single wire less than 1 micron in diameter at a rate of > 1 kilometer per day. A wire with this 109:1 aspect ratio, made of a thermoelectric material such as bismuth telluride, should provide unambiguous experimental evidence related to a theoretical prediction by Dresselhaus5, that thermoelectric materials which are nanoscale in one dimension and macroscopic in another are expected to display an enhanced Seebeck Effect. This Seebeck Effect, in which a temperature gradient generates a voltage difference in the material, may eventually be used to efficiently generate electricity from industrial waste heat, solar heat, and even human body heat -- a clean, sustainable source of energy. References (1) Seley, D.B. et. al., ACS Appl. Mater. Interfaces, 2011, 3 (4), pp 925–930 (April 2011 cover) (2) Jones, D. et. al. Proc. Mater. Res. Soc. 2011, doi: 10.1557/opl.2012.664, 30 March 2012 (3) Grodek, C., et. al. Proc. Mater. Res. Soc. 2011, doi: 10.1557/opl.2012.247, 13 February 2012 (4) Hohl, T., et. al. Proc. Intl. Mater. Res. Cong. 2012, in press (5) Dresselhaus, M. Perspectives on Recent Advances in Thermoelectric Materials Research, Thermoelectrics Applications Workshop, September 30, 2009
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