Interaction between surface migrating pentacene molecules and chemically modified surfaces of silicon oxides studied by pulsed molecular beam scattering

The interaction between pentacene molecules and organic self-assembling monolayers formed on silicon oxides (SiO2) was studied by measuring the surface scattering time profile of the pulsed molecular beam of pentacene. It was found that the surface residence time (SRT) of pentacene was significantly reduced on a surface treated with hexamethyl silazarane (HMDS) compared with that on a bare SiO2 surface. The activation energies derived from the temperature dependence of the SRT were 24 kJ/mol and 100 kJ/mol for HMDS-SiO2 and the bare SiO2, respectively. A surface treated with octadecyltrichlorosilane (OTS) showed SRT values almost the same as those on the bare SiO2 surface, which was due to exposed SiO2 regions on the thermally-degraded OTS-SiO2. The growth mechanism with improved quality is due to the shallower adsorption potential and enhanced migration of pentacene by the surface alkylation.