Temperature-Programmed Desorption (TPD) and Density Functional Theory (DFT) Study Comparing the Adsorption of Ethyl Halides on the Si(100) Surface

The differences between the dissociative adsorption of chloroethane-d(5) (C2D5Cl) and iodoethane-d(5) (C2D5I) on a Si(100)-2 X 1 surface are compared by analyzing the results of density functional theory (DFT) calculations and temperature-programmed desorption (TPD) experiments. The adsorption mechanism for both chloroethane-d(5) and iodoethane-d(5) on a clean Si(100)-2 x 1 surface is based on a dissociative chemisorption following halogen-carbon bond cleavage. Further surface transformations upon heating cause hydrogen elimination by ethyl groups, followed by ethylene and hydrogen desorption. The key difference between iodo- and chloro-derivatives is that the corresponding sticking probabilities of chloroethane-d(5) and iodoethane-d(5) in the same reaction system are extremely different. The experimental study reveals that the exposure for the monolayer saturation of chloroethane-d(5) is 20 times higher than that for iodoethane-d(5). These differences are attributed to the stability of surface-mediated molecular differences in the dissociation barriers based on the DFT investigation.