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

Coating a substrate\nwith a self-assembled monolayer (SAM) is known\nas an effective surface modification method for improving the quality\nof organic semiconductor films formed on it. However, there is still\na lack of comprehensive understanding regarding the formation of molecular\norientation on SAM surfaces. Highly ordered SAMs were prepared on\nSiO<sub>2</sub> substrates using octadecyl­trichlorosilane (OTS).\nThe temperature dependence of the molecular orientation of pentacene\nfilms prepared on the OTS substrates was investigated by p-polarized\nmultiple-angle incidence resolution spectrometry (pMAIRS). It was\nfound that pentacene molecules had standing orientations preferentially\non the OTS surface regardless of the growth temperature. This indicates\nthat the interaction between the OTS surface and the lying molecules\nis small, and the self-assembling of the molecules and the formation\nof standing-oriented crystallites are promoted even when the kinetic\nenergy of depositing molecules is low.