Standing Orientation of Pentacene Promoted on Octadecyltrichlorosilane Self-Assembled Monolayers Revealed by pMAIRS

Coating a substrate with a self-assembled monolayer (SAM) is known as an effective surface modification method for improving the quality of organic semiconductor films formed on it. However, there is still a lack of comprehensive understanding regarding the formation of molecular orientation on SAM surfaces. Highly ordered SAMs were prepared on SiO₂ substrates using octadecyltrichlorosilane (OTS). The temperature dependence of the molecular orientation of pentacene films prepared on the OTS substrates was investigated by p-polarized multiple-angle incidence resolution spectrometry (pMAIRS). It was found that pentacene molecules had standing orientations preferentially on the OTS surface regardless of the growth temperature. This indicates that the interaction between the OTS surface and the lying molecules is small, and the self-assembling of the molecules and the formation of standing-oriented crystallites are promoted even when the kinetic energy of depositing molecules is low.