Host: The Japan Society of Vacuum and Surface Science
Electronic state of thin film of organic semiconductor molecules can be modified by interaction between molecules and/or molecule and substrate. However, impact of weak interaction such as van der Waals interaction is difficult to be observed in organic molecular system. In this study, therefore, pentacene monolayer on graphite was utilized as well-ordered molecular layer. Low energy electron diffraction measurement revealed that mean distance between adjacent pentacene molecules can be tune by coverage in monolayer regime. In UPS spectra, fine structures of highest occupied molecular orbital of pentacene is observed. On the other hand, upon low photon-energy excitation, intensity of the main peak is observed to decrease with respect to that of the satellite peak. These results suggest that Frank-Condon approximation is not appropriate in this system. The electronic wave function of pentacene monolayer is possibly connecting to that of graphite which is an evidence of a modification of the state by weak interaction.
