Surface-induced orientation of pentacene molecules and transport anisotropy on nanogroove SiO2 dielectric layer by simple scratched method: The study of surface roughness and molecular alignment on the mobility of organic thin film transistors

Abstract

We obtained preferential in-plane molecular orientation and charge-transport anisotropy in pentacene thin-film transistors (TFTs) on conventional SiO2/Si substrates. The nanoscale SiO2 grooves with depths of 1–3 nm were prepared by a simple scratching process with diamond powder to create a new type of alignment template for inducing the aligned growth of pentacene with in-plane anisotropy. Results of atomic force microscopy and grazing-incidence X-ray diffraction showed that the nanogrooved SiO2 structure could control the alignment and growth mode of pentacene, and it remarkably decreased the grain size of the pentacene crystals. The charge-carrier mobility along the parallel axis of the nanogrooved structure (0.392 ± 0.039 cm2/(V·s)) was more than four-fold higher than that perpendicular to the alignment (0.104 ± 0.048 cm2/(V·s)). In addition, we investigated the effect of nanogrooved SiO2's surface roughness on the electrical properties of the pentacene TFT and found out that the surface roughness of SiO2 dielectric layer was more crucial factor on the device performance compared to the preferential alignment of the pentacene molecule.