Modification of 1H,1H,2H,2H-perfluorooctyltrichlorosilane self-assembled monolayers by atomic hydrogen

作者：Gorham Justin M; Stover Adam K; Fairbrother D Howard^*

来源：Journal of Physical Chemistry C, 2007, 111(50): 18663-18671.

DOI：10.1021/jp075147s

The effect of atomic hydrogen (AH) on the chemical composition and interfacial properties of a semifluorinated self-assembled monolayer (SAM) formed on Si ((CF3)(CF2)(5)(CH2)(2)-Si) has been studied by using a combination of X-ray photoelectron spectroscopy (XPS) and contact angle measurements. XPS results indicate that AH reacts with the SAM in a kinetically controlled process where the rate-determining step involves H atom abstraction from C-H bonds to form carbon-centered radicals tethered to the Si substrate. Subsequent reactions of these carbon-centered radicals with AH lead to desorption of species that contain the fluorocarbon (CF3(CF2)(5)) portion of the adsorbate chain. This proposed mechanism accounts for a number of experimental observations, including the fact that the ratio of CF3 to CF2 groups within the film remains constant during AH exposure and that the loss of fluorine exhibits first-order kinetics with a rate constant proportional to the AH flux. The rate constant for the loss of CF3 + CF2 groups is estimated to be 1.3 x 10(-18) AH(-1) cm(2). Desorption of fluorocarbons from the adsorbate layer is followed by AH-mediated chemical erosion of residual hydrocarbon species. Contact angle measurements conducted on the 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS) monolayer as a function of AH exposure revealed a correlation between wettability and the CF3 (and CF2) group coverage. The ability of AH to control the chemical composition of the monolayer as a route to create patterned surfaces that exhibit different interfacial properties is also demonstrated.

• 出版日期2007-12-20