Effect of Molecule-Substrate Interaction on Thin-Film Structures and Molecular Orientation of Pentacene on Silver and Gold

详细信息    查看全文

• 作者：Yi Zheng ; Dongchen Qi ; N. Chandrasekhar ; Xingyu Gao ; Cedric Troadec ; Andrew T. S. Wee
• 刊名：Langmuir
• 出版年：2007
• 出版时间：July 31, 2007
• 年：2007
• 卷：23
• 期：16
• 页码：8336 - 8342
• 全文大小：325K
• 年卷期：v.23,no.16(July 31, 2007)
• ISSN：1520-5827

文摘

Evaporated pentacene thin films with thicknesses from several nm to 150 nm on gold and silver substrates havebeen studied by ultraviolet photoelectron spectroscopy (UPS), near-edge X-ray absorption fine structure (NEXAFS),scanning tunneling microscopy (STM), and atomic force microscopy (AFM). It was found that pentacene thin-filmstructures, particularly their molecular orientations, are strongly influenced by the metal substrates. UPS measurementsrevealed a distinct change in the valence band structures of pentacene on Au compared to those on Ag, which isattributed to the different packing between adjacent molecules. Using NEXAFS, we observed 74 ± 5 and 46 ± 5molecular tilt angles on Ag and Au, respectively, for all measured thicknesses. We propose that pentacene moleculesstand up on the surface and form the "thin-film phase" structure on Ag. On Au, pentacene films grow in domainswith molecules either lying flat or standing up on the substrate. Such a mixture of two crystalline phases leads to anaverage tilt angle of 46 for the whole film and the change in valence band structures. STM and distance-voltage(z-V) spectroscopy studies confirm the existence of two crystalline phases on Au with different conducting properties.z-V spectra on the low conducting phase clearly indicate its nature as "thin-film phase".