title: Structure of the submonolayer of ethanol adsorption on a vapor/fused silica interface studied with sum frequency vibrational spectroscopy.
abstract: Sum-frequency vibrational spectroscopy in the CH and OH stretch region was used to study ethanol adsorption on fused silica from vapor of different ethanol partial pressures. It was found that the adsorbed ethanol molecules were oriented with their methyl group tilted away from the surface normal by an average angle of ∼45° at low ethanol vapor pressures and ∼39° when approaching saturated vapor pressure. The spectral change with ethanol vapor pressure and the deduced adsorption isotherm show that ethanol molecules have two distinct adsorption sites on silica: One is the silanol group site to which an ethanol molecule can be strongly hydrogen-bonded, and the other is the siloxane (Si-O-Si) group site to which an ethanol molecule can be weakly bonded. The presence of water in vapor significantly reduced the surface coverage of ethanol on silica due to competitive adsorption between ethanol and water.
authors.affiliation: †Department of Physics, State Key Laboratory of Surface Physics, and Key Laboratory of Micro- and Nano-Photonic Structures (MOE), Fudan University, Shanghai 200433, China.
authors.forename: Huijie
authors.initials: H
authors.lastname: Xu
authors.affiliation: ‡Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Donghua
authors.initials: D
authors.lastname: Zhang
authors.affiliation: ‡Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Hu
authors.affiliation: †Department of Physics, State Key Laboratory of Surface Physics, and Key Laboratory of Micro- and Nano-Photonic Structures (MOE), Fudan University, Shanghai 200433, China.|§Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.
authors.forename: Chuanshan
authors.initials: C
authors.lastname: Tian
authors.affiliation: †Department of Physics, State Key Laboratory of Surface Physics, and Key Laboratory of Micro- and Nano-Photonic Structures (MOE), Fudan University, Shanghai 200433, China.|∥Department of Physics, University of California, Berkeley, California 94720, United States.
authors.forename: Y Ron
authors.initials: YR
authors.lastname: Shen