Materials Science

Thin and Fast

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Science  05 Oct 2007:
Vol. 318, Issue 5847, pp. 19
DOI: 10.1126/science.318.5847.19b

Temperature changes in gas-phase chemical processes such as combustion and explosions can evolve on the submicrosecond time scale, but commercial thermocouples (TCs) are limited to millisecond response times. Thin-film TCs can achieve submicrosecond responses, but extreme film thinness (less than 100 nm) affects sensitivity through decreases in the thermopower. In principle, TCs made from submicrometer- diameter wires (SMTCs) would have a more favorable change in thermal mass and could be thicker (1.0 to 0.5 μm). Bourg et al. fabricated SMTCs by first electrodepositing silver wires 1.0 to 0.5 μm in diameter onto half of a stepped graphite surface. A mask covering the other half of the substrate was removed, the silver wires were coated with a self-assembled alkanethiol monolayer, and nickel wires were deposited. The arrays were then pressed into a cyanoacrylate adhesive, and after hardening, the graphite was removed. Scanning electron microscopy revealed a robust weld at the silver/nickel interface. The success rate for SMTCs ranged up to 80%, and these junctions were functional after months of air exposure. In laser-heating tests, response times varied from tenths of microseconds to several microseconds, with outputs of 20 μV/°C. — PDS

Nano Lett. 7, 10.1021/nl071990q (2007).

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