In electronics such as smartphones and flexible displays, devices such as organic thin-film transistors made of carbon-based organic materials are used. To maximize the performance of these devices, it is extremely important that the organic semiconductor molecules formed on the solid surface are orderly aligned.
A research team led by Professor Go Watanabe of the School of Frontier Engineering, Kitasato University, performed "all-atom molecular dynamics simulation," which tracks and simulates the movement of each atom over time on a supercomputer. With this simulation method, the team visualized the effects of film thickness, molecular type, and presence of solid substrates on the orientation of tripodal triptycene molecules with a propeller-shaped skeleton when they form thin films. They elucidated the "dynamic process" of molecular orientation and ordering on surfaces of self-assembling thin films at the molecular level. The team unraveled the mechanism by which the molecular orientation is preferentially switched to a "parallel orientation" under the influence of the solid surface in the ultrathin film phase while the "antiparallel orientation," where adjacent molecules are oriented in opposite directions, is stably adopted by the molecules in the thickly stacked bulk state. Furthermore, they simulated the annealing process, where a stair-stepped trilayer spontaneously transformed into a highly ordered flat film, and quantitatively verified the underlying mechanism. They also demonstrated the influence of molecular structural differences on film structures.
This approach will play an important role in analyzing how organic semiconductor molecules form crystal thin films and how they achieve structural stability. It is also expected to contribute to the creation of high-performance functional organic thin films and the development of devices.
(Article: Masanori Nakajo)
