Micro-Raman spectroscopy on pentacene thin-film transistors

Molecular orientation in pentacene films and thin-film transistors has been studied by micro-Raman spectroscopy. We have found that the relative intensity of the 1596-cm-1 band (B3g) is sensitive to the molecular orientation. The standing orientation was observed for the films formed on the bare and hexamethyldisilazane (HMDS)-modified SiO2 surfaces and the Au surfaces modified with self-assembled monolayers (SAMs), whereas the lying orientation for the films on the bare Au surface. We have explicitly demonstrated the differences of the molecular orientation in the films on SiO2 dielectric layers and Au electrodes in the devices by mapping measurements.