title: The correlations of the electronic structure and film growth of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on SiO2.
abstract: Combining ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM) and small angle X-ray diffraction (SAXD) measurements, we perform a systematic investigation on the correlations of the electronic structure, film growth and molecular orientation of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on silicon oxide (SiO2). AFM analysis reveals a phase transition of disorderedly oriented molecules in clusters in thinner films to highly ordered standing-up molecules in islands in thicker films. SAXD peaks consistently support the standing-up configuration in islands. The increasing ordering of the molecular orientation with film thickness contributes to the changing of the shape and lowering of the leading edge of the highest occupied molecular orbital (HOMO). The end methyl of the highly ordered standing molecules forms an outward pointing dipole layer which makes the work function (WF) decrease with increasing thickness. The downward shift of the HOMO and a decrease of WF result in unconventional downward band bending and decreased ionization potential (IP). The correlations of the orientation ordering of molecules, film growth and interface electronic structures provide a useful design strategy to improve the performance of C8-BTBT thin film based field effect transistors.
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, P. R. China. mayee@csu.edu.cn ygao@csu.edu.cn and Hunan Key Laboratory for Super-microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, Hunan 410012, P. R. China and Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, Erwin-Schrödinger-Straße 46, 67663 Kaiserslautern, Germany.
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, P. R. China. mayee@csu.edu.cn ygao@csu.edu.cn and Hunan Key Laboratory for Super-microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, Hunan 410012, P. R. 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, P. R. China. mayee@csu.edu.cn ygao@csu.edu.cn and Hunan Key Laboratory for Super-microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, Hunan 410012, P. R. 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, P. R. China. mayee@csu.edu.cn ygao@csu.edu.cn and Hunan Key Laboratory for Super-microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, Hunan 410012, P. R. China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Zhao
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, P. R. China. mayee@csu.edu.cn ygao@csu.edu.cn and Hunan Key Laboratory for Super-microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, Hunan 410012, P. R. 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, P. R. China. mayee@csu.edu.cn ygao@csu.edu.cn and Hunan Key Laboratory for Super-microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, Hunan 410012, P. R. 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, P. R. China. mayee@csu.edu.cn ygao@csu.edu.cn and Hunan Key Laboratory for Super-microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, Hunan 410012, P. R. 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, P. R. China. mayee@csu.edu.cn ygao@csu.edu.cn and Hunan Key Laboratory for Super-microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, Hunan 410012, P. R. 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, P. R. China. mayee@csu.edu.cn ygao@csu.edu.cn and Hunan Key Laboratory for Super-microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, Hunan 410012, P. R. China and Department of Physics and Astronomy, University of Rochester, Rochester, NY14627, USA.
authors.forename: Yongli
authors.initials: Y
authors.lastname: Gao