X-ray induced modification of semifluorinated organic thin film

The X-ray induced modification/defluorination of semifluorinated self-assem bled monolayers (SAMs), based on 1H,1H,2H,2H-perfluorodecanethiol (CF3(CF2) (7)(CH2)(2)SH) has been studied using X-ray photoelectron spectroscopy (XPS ). At short irradiation times X-ray induced defluorination of the semifluor inated SAM exhibits first-order kinetics with respect to the film's fluorin e concentration. The evolution of the C(1s) region during modification is c onsistent with a kinetic model of defluorination involving consecutive C-F bond breaking events (e.g., CF2 --> CF). Relative defluorination rate const ants obtained for the different fluorine-containing functionalities (e.g., CF2, CF) provide support for a stochastic fluorine loss process, where each individual C-F bond is initially equally labile toward dissociative electr on attachment, independent of local chemical environment. Upon atmospheric exposure the modified film's oxygen adsorption characteristics demonstrate that the density of radicals produced within the organic film during X-ray exposure exhibit a non-linear dependence on irradiation time due to the ons et of radical-radical coupling reactions at longer X-ray exposures. The app earance of oxygen within the film is also responsible for further defluorin ation due to the reactivity of peroxy radicals (-CF(OO .)-). Results from t his study support the idea that SAMs can be employed as model systems for d eveloping a detailed understanding of the molecular level events associated with organic surface modification processes.