Chemistry

Gains in Contact

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Science  07 Dec 2007:
Vol. 318, Issue 5856, pp. 1527
DOI: 10.1126/science.318.5856.1527b

Self-assembled monolayers (SAMs) of alkanethiolates on gold or silver substrates have broad applications in surface patterning, but their flexible and thermally sensitive nature complicates efforts to probe properties such as conductivity. Mercury has been applied to SAM surfaces to form contact electrodes, but beyond its toxicity, its tendency to spread through flow can lead to short-circuiting and lack of measurement precision. Chiechi et al. show that a fluid eutectic composed of three parts gallium and one part indium by weight (dubbed “EGaIn”) is a practical alternative. The primary advantage of this material is its capacity to retain its shape below the comparatively high applied surface stress of 0.5 N/m. The authors extruded droplets from a syringe onto a silver surface and then drew back the needle until a sharp micron-scale conical tip formed, the size of which could be tuned by varying the pulling rate. They could then apply these conducting tips to SAM surfaces for robust measurements of current densities as a function of applied voltage. Additional advantages of EGaIn include its stability in air and low toxicity. — JSY

Angew. Chem. Int. Ed. 46, 10.1002/anie.200703642 (2007).

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