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

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journal contribution
posted on 17.03.2017, 00:00 by Jing Zhao, Benjamin W. Noffke, Krishnan Raghavachari, Andrew V. Teplyakov
The differences between the dissociative adsorption of chloroethane-d5 (C2D5Cl) and iodoethane-d5 (C2D5I) on a Si(100)-2 × 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-d5 and iodoethane-d5 on a clean Si(100)-2 × 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-d5 and iodoethane-d5 in the same reaction system are extremely different. The experimental study reveals that the exposure for the monolayer saturation of chloroethane-d5 is 20 times higher than that for iodoethane-d5. These differences are attributed to the stability of surface-mediated molecular adsorbates rather than to the differences in the dissociation barriers based on the DFT investigation.