title: Surface-segregated monolayers: a new type of ordered monolayer for surface modification of organic semiconductors.
abstract: We report a new type of ordered monolayer for the surface modification of organic semiconductors. Fullerene derivatives with fluorocarbon chains ([6,6]-phenyl-C(61)-buryric acid 1H,1H-perfluoro-1-alkyl ester or FC(n)) spontaneously segregated as a monolayer on the surface of a [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) film during a spin-coating process from the mixture solutions, as confirmed by X-ray photoelectron spectroscopy (XPS). Ultraviolet photoelectron spectroscopy (UPS) showed the shift of ionization potentials (IPs) depending on the fluorocarbon chain length, indicating the formation of surface dipole moments. Surface-sensitive vibrational spectroscopy, sum frequency generation (SFG) revealed the ordered molecular orientations of the C(60) moiety in the surface FC(n) layers. The intensity of the SFG signals from FC(n) on the surface showed a clear odd-even effect when the length of the fluorocarbon chain was changed. This new concept of the surface-segregated monolayer provides a facile and versatile approach to modifying the surface of organic semiconductors and is applicable to various organic optoelectronic devices.
authors.affiliation: Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Qingshuo
authors.initials: Q
authors.lastname: Wei
authors.forename: Keisuke
authors.initials: K
authors.lastname: Tajima
authors.forename: Yujin
authors.initials: Y
authors.lastname: Tong
authors.forename: Shen
authors.initials: S
authors.lastname: Ye
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Hashimoto
mesh_terms: D004583:Electrons; D005466:Fluorocarbons / Q000737:chemistry; D037741:Fullerenes / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D009930:Organic Chemicals / Q000737:chemistry*; D012666:Semiconductors; D013057:Spectrum Analysis; D013499:Surface Properties; D014732:Vibration
chemical_list: C539575:(6,6)-phenyl C61-butyric acid methyl ester; D005466:Fluorocarbons; D037741:Fullerenes; D009930:Organic Chemicals