title: Polarized near-edge x-ray-absorption fine structure spectroscopy of C60-functionalized 11-amino-1-undecane thiol self-assembled monolayer: molecular orientation and evidence for C60 aggregation.
abstract: Near-edge x-ray-absorption fine structure (NEXAFS) spectroscopy was adopted to probe the unoccupied electronic states of C60 anchored onto an organized assembly of 11-amino-1-undecane thiol on Au(111). The polarization dependence of the intensity of pi* resonance associated with C60 pi network revealed the self-assembled monolayer (SAM) system to be oriented with an average molecular tilt angle of 57 degrees with respect to the surface normal. Invoking the absence of solid-state band dispersion effects and in comparison to solid C60 and /or 1-ML C60/Au(111), the electronic structure of the resulting assembly was found dominated by spectral position shift and linewidth and intensity changes of the lowest unoccupied molecular orbital (LUMO), LUMO+1, and LUMO+2 orbitals. The latter implied hybridization between N Pz of -NH2 group of thiolate SAM and pi levels of C60, resulting in a nucleophilic addition with a change in the symmetry of C60 from Ih to C1 in the SAM. Occurrence of a new feature at 285.3 eV in the NEXAFS spectrum, assigned previously to pi* graphitic LUMO, signified the formation of aggregated clusters, (C60)n of C60 monomer. Low tunneling current scanning tunneling microscopy confirmed them to be spherical and stable aggregates with n approximately 5.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Madras, Chennai-600036, India. archita59@yahoo.com
authors.forename: Archita
authors.initials: A
authors.lastname: Patnaik
authors.forename: Koji K
authors.initials: KK
authors.lastname: Okudaira
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kera
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Setoyama
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Mase
authors.forename: Nobuo
authors.initials: N
authors.lastname: Ueno