Controlled patterning of nanostructures at desired positions is of great importance for high-performance M/NEMS devices. Here, we demonstrate a high-resolution, high-speed and cost-effective fabrication method, named coaxial focused electrohydrodynamic jet printing, to print functional nanostructures. A coaxial needle was designed and developed; a functional ink and high viscosity liquid are applied in the inner and outer needle, respectively. Under optimised conditions, a stable coaxial jet is formed; then, the electrical shearing force and electrical field induce viscous shearing force and internal pressure that are jointly applied on the inner functional ink, focusing the inner jet on the nanoscale. Using this stable coaxial jet with a nano-jet inside it, nanostructures with highly aligned nanowire arrays, nano-freebeams and nano-cantilever beams down to the scale of 40 nm were directly printed. The needle size was 130 μm, and the ratio of the sizes of the needle and the printed structure was as high as 3250/1. This technique realizes the controllable printing of nanoscale structures with the use of a one hundred micrometer-sized needle. The printed PZT nanostructures exhibit pure perovskite structures and distinct piezoelectric responses.
Large area and highly aligned polymer semiconductor sub-microwires were fabricated using the coaxial focused electrohydrodynamic jet printing technology. As indicated by the results, the sub-microwire arrays have smooth morphology, well reproducibility and controllable with a width of ~110 nm. Analysis shows that the molecular chains inside the sub-microwires mainly exhibited edge-on arrangement and the π-stacking direction (010) of the majority of crystals is parallel to the long axis of the sub-microwires. Sub-microwires based organic field effect transistors showed high mobility with an average of 1.9 cm2 V−1 s−1, approximately 5 times higher than that of thin film based organic field effect transistors. In addition, the number of sub-microwires can be conveniently controlled by the printing technique, which can subsequently concisely control the performance of organic field effect transistors. This work demonstrates that sub-microwires fabricated by the coaxial focused electrohydrodynamic jet printing technology create an alternative path for the applications of high-performance organic flexible device.
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