Meniscus-controlled printing of single-crystal interfaces showing extremely sharp switching transistor operation

Meniscus, a curvature of droplet surface around solids, takes critical roles in solution-based thin-film processing. Extension of meniscus shape, and eventual uniform film growth, is strictly limited on highly lyophobic surfaces, although such surface should considerably improve switching characteristics. Here, we demonstrate a technique to control the solution meniscus, allowing to manufacture single-crystalline organic semiconductor (OSC) films on the highest lyophobic amorphous perfluoropolymer, Cytop. We used U-shaped metal film pattern produced on the Cytop surface, to initiate OSC film growth and to keep the meniscus extended on the Cytop surface. The growing edge of the OSC film helped maintain the meniscus extension, leading to a successive film growth. This technique facilitates extremely sharp switching transistors with a subthreshold swing of 63 mV dec^-1 owing to the effective elimination of charge traps at the semiconductor/dielectric interface. The technique should expand the capability of print production of functional films and devices.