title: Polyphenylsilole multilayers--an insight from X-ray electron spectroscopy and density functional theory.
abstract: We present a combined investigation by means of X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy of condensed multilayers of two polyphenylsiloles, namely hexaphenylsilole (HPS) and tetraphenylsilole (TPS). Both compounds exhibit very similar spectroscopic signatures, whose interpretation is aided by density functional theory (DFT) calculations. High-resolution XPS spectra of the Si 2p and C 1s core levels of these multilayers indicate a positively charged silicon ion flanked by two negatively charged adjacent carbon atoms in the silole core of both molecules. This result is corroborated quantitatively by DFT calculations on isolated HPS (TPS) molecules, which show a natural bond orbital partial charge of +1.67 e (+1.58 e) on the silicon and -0.34 e (-0.58 e) on the two neighbouring carbon atoms in the silole ring. These charges are conserved in direct contact with a Cu(111) substrate for films of submonolayer coverage, as evidenced by the Si 2p XPS data. The C K-edge NEXAFS spectra of HPS and TPS multilayers exhibit distinct and differing features. Their main characteristics reappear in the simulated spectra and are assigned to the different inequivalent carbon species in the molecule. The angle-dependent measurements hardly reveal any dichroism, i.e., the molecular π-systems are not uniformly oriented parallel or perpendicular with respect to the surface. Changes in the growth conditions of TPS, i.e., a reduction of the substrate temperature from 240 K to 80 K during deposition, lead to a broadening of both XPS and NEXAFS signatures, as well as an upward shift of the Si 2p and C 1s binding energies, indicative of a less ordered growth mode at low temperature.
authors.affiliation: Physik-Department, E20, Technische Universität München, 85748 Garching, Germany. katharina.diller@tum.de florian.klappenberger@tum.de.
authors.forename: Katharina
authors.initials: K
authors.lastname: Diller
authors.affiliation: Division of Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, S-106 91 Stockholm, Sweden.
authors.forename: Yong
authors.initials: Y
authors.lastname: Ma
authors.affiliation: Division of Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, S-106 91 Stockholm, Sweden.
authors.forename: Yi
authors.initials: Y
authors.lastname: Luo
authors.affiliation: Physik-Department, E20, Technische Universität München, 85748 Garching, Germany. katharina.diller@tum.de florian.klappenberger@tum.de.
authors.forename: Francesco
authors.initials: F
authors.lastname: Allegretti
authors.affiliation: Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
authors.forename: Jianzhao
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
authors.forename: Ben Zhong
authors.initials: BZ
authors.lastname: Tang
authors.affiliation: Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China. phnlin@ust.hk.
authors.forename: Nian
authors.initials: N
authors.lastname: Lin
authors.affiliation: Physik-Department, E20, Technische Universität München, 85748 Garching, Germany. katharina.diller@tum.de florian.klappenberger@tum.de.
authors.forename: Johannes V
authors.initials: JV
authors.lastname: Barth
authors.affiliation: Physik-Department, E20, Technische Universität München, 85748 Garching, Germany. katharina.diller@tum.de florian.klappenberger@tum.de.
authors.forename: Florian
authors.initials: F
authors.lastname: Klappenberger