A simple method for the manufacture of mesoscopic metal wires
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A simple method for the manufacture of mesoscopic metal wires S. Noel, E. Batalla, and P. Rochon Department of Physics, Royal Military College, Kingston, Ontario, Canada, K7K 5L0 (Received 4 October 1995; accepted 4 December 1995)
A process for the manufacture of very thin parallel wires has been developed. A series of parallel silver wires have been written for the study of one-dimensional electron transport. The wires are approximately 200 nm wide and 8 mm long. The method used can produce longer and thinner wires.
Recently, several azo-polymers that deform when illuminated with laser light at specific wavelengths have been developed.1 Once the surface profile of the azopolymer has been altered in this manner, the new shape is stable until the azo-polymer is dissolved, or heated beyond its glass transition temperature (Tg ). At the glass transition temperature, the azo-polymer relaxes into its original (flat) configuration. Simple methods to produce structures in the nanometer scale are being developed using atomicforce microscopy.2 However, the overall extent of these structures is limited by the scanning range of these microscopes, typically 10 mm. Here, by controlling the shape of the polymer surface with a laser beam, and coating that surface using a metal-vapor deposition system, thin metal structures can be formed on the nanometer scale which extend over several millimeters. The azo-polymer poly [40 -(2-methacryloyloxyethyl)ethylamino-3-chloro-4-nitroazobenzene], called PDR13M (structural formula in Ref. 3), is dissolved in tetrahydrofuran (THF) and spin-coated on a glass substrate, producing a thin film. The polymer and substrate are heated beyond the glass transition temperature to remove all remaining THF, and to produce a flat azopolymer surface. Films between 50 nm and 1 mm can be reliably produced in this way. The azo-polymer PDR13M was chosen for these experiments because of its relatively high Tg (97 ±C). The higher the Tg of the polymer, the more stable the surface profile will be during metal vapor deposition, as the deposition process heats the sample slightly. A schematic diagram of the apparatus used to produce a modulated polymer surface, i.e., a grating, is shown in Fig. 1. A laser beam of the correct wavelength for polymer excitation (514 nm for PDR13M) is used. Half the beam impinges directly on the surface of the polymer, while the other half encounters a mirror at an angle to the polymer. The laser beam is an expanded and collimated 5 mW circularly polarized argon laser beam with a diameter of approximately 8 mm. The resulting power density on the azo-polymer is approximately 10 mWycm2 , which is insufficient to cause ablation.4 J. Mater. Res., Vol. 11, No. 4, Apr 1996
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When the laser beam and its reflection meet on the thin polymer film, an interference pattern results. Because of the nature of the azo-polymer, a volumetric migration occurs, causing the surface profile to mirror the inc
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