In situ self-assembly and photopolymerization for hetero-phase synthesis and patterning of conducting materials using soft oxometalates in thermo-optical tweezers

Subhrokoli Ghosh, Santu Das, Shuvojit Paul, Preethi Thomas, Basudev Roy, Partha Mitra, Soumyajit Roy and Ayan Banerjee

We demonstrate a novel method of simultaneous photoassisted hetero-phase synthesis, doping, and micro-scale patterning of conductive materials. The patterning is performed by controlled self-assembly mediated by a micro-bubble induced in an optical tweezers configuration. The high temperature generated due to the light field of the tweezers also drives diverse chemical reactions that lead to the in situ formation of conducting metal-oxides and polymers due to a charge transfer mechanism with soft oxometalates (SOMs). We synthesize two conducting polymers – polypyrrole and polyaniline – doped by the metal oxides Mo–O2 and Mo–O3, from dispersions of the respective organic compounds with the SOMs, and form permanent patterns out of them by continuous self-assembly arising from manipulation of the micro-bubble using Marangoni flows generated by the tweezers. The electrically conducting patterns of width varying between around 4–50 μm, are written in the form of simple Hall-bar geometries, and a four-probe measurement technique yields conductivities on the order of ∼450–600 Siemens cm−1 – which is much higher than that reported for both polypyrrole and polyaniline in earlier work. This technique can easily be used in patterning complicated electrical circuits in mesoscopic length scales, and can also be extended to solution processed electronic device development by green chemical routes.

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