title: Orientation-dependent energy level alignment and film growth of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on HOPG.
abstract: Combining ultraviolet photoemission spectroscopy, X-ray photoemission spectroscopy, atomic force microscopy, and X-ray diffraction measurements, we performed a systematic investigation on the correlation of energy level alignment, film growth, and molecular orientation of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on highly oriented pyrolytic graphite. The molecules lie down in the first layer and then stand up from the second layer. The ionization potential shows a sharp decrease from the lying down region to the standing up region. When C8-BTBT molecules start standing up, unconventional energy level band-bending-like shifts are observed as the film thickness increases. These shifts are ascribed to gradual decreasing of the molecular tilt angle about the substrate normal with the increasing film thickness.
authors.affiliation: Institute of Super-Microstructure and Ultrafast Process in Advanced Materials, School of Physics and Electronics, Central South University, No. 605 Lushan South Road, Changsha, Hunan 410012, People's Republic of China.
authors.forename: Lu
authors.initials: L
authors.lastname: Lyu
authors.affiliation: Institute of Super-Microstructure and Ultrafast Process in Advanced Materials, School of Physics and Electronics, Central South University, No. 605 Lushan South Road, Changsha, Hunan 410012, People's Republic of China.
authors.forename: Dongmei
authors.initials: D
authors.lastname: Niu
authors.affiliation: Institute of Super-Microstructure and Ultrafast Process in Advanced Materials, School of Physics and Electronics, Central South University, No. 605 Lushan South Road, Changsha, Hunan 410012, People's Republic of China.
authors.forename: Haipeng
authors.initials: H
authors.lastname: Xie
authors.affiliation: Institute of Super-Microstructure and Ultrafast Process in Advanced Materials, School of Physics and Electronics, Central South University, No. 605 Lushan South Road, Changsha, Hunan 410012, People's Republic of China.
authors.forename: Ningtong
authors.initials: N
authors.lastname: Cao
authors.affiliation: Institute of Super-Microstructure and Ultrafast Process in Advanced Materials, School of Physics and Electronics, Central South University, No. 605 Lushan South Road, Changsha, Hunan 410012, People's Republic of China.
authors.forename: Hong
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Institute of Super-Microstructure and Ultrafast Process in Advanced Materials, School of Physics and Electronics, Central South University, No. 605 Lushan South Road, Changsha, Hunan 410012, People's Republic of China.
authors.forename: Yuhe
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Institute of Super-Microstructure and Ultrafast Process in Advanced Materials, School of Physics and Electronics, Central South University, No. 605 Lushan South Road, Changsha, Hunan 410012, People's Republic of China.
authors.forename: Peng
authors.initials: P
authors.lastname: Liu
authors.affiliation: Institute of Super-Microstructure and Ultrafast Process in Advanced Materials, School of Physics and Electronics, Central South University, No. 605 Lushan South Road, Changsha, Hunan 410012, People's Republic of China.
authors.forename: Yongli
authors.initials: Y
authors.lastname: Gao