Nanoscale Quantized Oscillations in Thin-Film Growth Greatly Enhance Transconductance in Organic Transistors

Abstract

A growth mode of pentacene thin films deposited by high vacuum sublimation where the morphology versus thickness h “rings” back and forth between rough 3D films with pyramid islands and smooth 2D films with ziqqurat islands is discovered. The roughness σ versus h exhibits seamless coherent oscillations whose amplitude and wavelength increase as integer multiples of 1.5 ML thickness. The quantized oscillations are reconducted to dynamic wetting/dewetting transitions involving the upper layers of pentacene film. Importantly, the transconductance of organic field effect transistors, either in solid state or electrolyte-gated, exhibits antiphase oscillations with one-decade swing. Charge mobilities in the wetting regime reach 0.1 cm2 V−1 s−1, in line with high-end values reported for thin-film pentacene transistors. Controlling this growth mode enables the limitations of charge transport imposed by the roughening transition to be overcome, a universal feature of high vacuum growth to date.