Self-regulating pseudo-monolayer printing of percolating networks of ZnO nanostructures for macroelectronics

A patterned dry transfer printing technique that can generate monolayer-like percolating networks of ZnO nanorods (NRs) has been developed. The method relies on the relative adhesion strength between NR-NR and NR-substrate, as well as soft and elastomeric nature of polydimethylsiloxane (PDMS) stamp material. When the NR-substrate adhesion is stronger than the rod-rod interaction, which is the usual case due to a large difference in the contact area, the printing leads to a monolayer-like percolating network of NRs on substrate. The method exploits the contact area difference between NR-NR and NR-substrate, which is inherent in the systems involving high aspect ratio nanostructures on a soft stamp, without considering the complex and elaborate tailoring of the surface chemistry or energetics. When the stamp has multilayer stacks of nanostructures, the monolayer-like printing can be repeated many times, possibly on a large area substrate, due to the self-regulating printing characteristics. The printed percolating network of semiconductor nanostructures have been used as active channels in thin film transistors, where the better gate coupling due to the pseudo-monolayer leads to higher-performance devices compared to other configurations of nanostructures. This self-regulating, patterned dry transfer printing method may enable high-performance macroelectronics with various functional nanostructured materials that have high aspect ratios.