Adsorption of 1H, 1H, 2H, 2H-perfluorodecanethiol monolayer on Cu(111): phase transformation, self-assembly and thermal stability

• Main Authors: Shang-Wei Chou, 周尚威
• Other Authors: Chao-Ming Chiang
• Format: Others
• Language: en_US
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/03398741519958745246

碩士 === 國立中山大學 === 化學系研究所 === 91 === Inspired by Poirier’s mechanism of self-assembled monolayers (SAMs) formation, we realized that observation of the change of molecular orientation relative to the surface using a suitable spectroscopic method might be able to reveal the self – assemblied processes. We mimicked the SAMs formation under UHV conditions, the Reflection Absorption Infrared Spectroscopy (RAIRS) and Temperature-Programmed Desorption / Reaction Spectrometry (TPD/R) were utilized to understand the adsorption, self-assembling and thermal stability after vapor desorption of 1H, 1H, 2H, 2H-perfluorodecanethiol on Cu(111). At 100K, the adsorption of 1H, 1H, 2H, 2H-perfluorodecanethiol was entirely molecular. As the surface was annealed above 220K, the cleavage of the S – H bonds occurred to afford chemisorbed thiolates. By comparisons of spectra to the SAMs / Au(111) and the bulk compound, forming of an orderly and densely packed monolayer on Cu(111) was inferred. Focusing on room temperature deposition experiments, We found that the increase in ratios of Iν(CF2 ∥ chain) (bands in 1300cm-1 ~ 1400 cm-1) to Iν(CF2 ⊥ chain) (bands in 1100cm-1 ~ 1300 cm-1) as a function of exposure implicates a transition from that the lying – down geometry to the more upright orientation relative to the surface as we anticipated, the phase transformation concomitant with the SAMs formation could be identified by RAIRS. By TPD/R measurements, the molecular desorption occurred at 220K and 290K, corresponding to the condensed multilayer and a physisorbed layer on top of the chemisorbed monolayer, respectively. Furthermore, the monolayer would undergo the S – C bond dissociation to sender surface – bound semifluorinated alkyl groups and sulfur atoms. The semifluorinated decene and decane were evolved above 360K as results of β – hydride elimination and hydrogen addition.