title: High-resolution core-level photoemission measurements on the pentacene single crystal surface assisted by photoconduction.
abstract: Upon charge carrier transport behaviors of high-mobility organic field effect transistors of pentacene single crystal, effects of ambient gases and resultant probable 'impurities' at the crystal surface have been controversial. Definite knowledge on the surface stoichiometry and chemical composites is indispensable to solve this question. In the present study, high-resolution x-ray photoelectron spectroscopy (XPS) measurements on the pentacene single crystal samples successfully demonstrated a presence of a few atomic-percent of (photo-)oxidized species at the first molecular layer of the crystal surface through accurate analyses of the excitation energy (i.e. probing depth) dependence of the C1s peak profiles. Particular methodologies to conduct XPS on organic single crystal samples, without any charging nor damage of the sample in spite of its electric insulating character and fragility against x-ray irradiation, is also described in detail.
authors.affiliation: Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Nakayama
authors.forename: Yuki
authors.initials: Y
authors.lastname: Uragami
authors.forename: Masayuki
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Keiichirou
authors.initials: K
authors.lastname: Yonezawa
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Mase
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kera
authors.forename: Hisao
authors.initials: H
authors.lastname: Ishii
authors.forename: Nobuo
authors.initials: N
authors.lastname: Ueno