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

Abstract

The differences between the dissociative adsorption of chloroethane-d 5 (C2D5Cl) and iodoethane-d 5 (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-d 5 and iodoethane-d 5 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-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 adsorbates rather than to the differences in the dissociation barriers based on the DFT investigation.

Formation of Germa-ketenimine on the Ge(100) Surface by Adsorption of tert-Butyl Isocyanide

“…With this method, a bond length of 2.72 Å and a vertical separation between the up and the down atom of 0.67 Å were obtained for the central dimer of the cluster, which are close reproductions of the experimental values of 2.5 ± 0.1 Å and 0.86 ± 0.02 Å, respectively . Many similar DFT calculations in the literature using atom-centered basis sets and cluster models to represent the group 14 semiconductor surfaces have been successful in capturing structural, electronic, thermodynamic, and spectroscopic properties of organic adsorbates. − Justification of the current calculation method is provided by benchmark calculations for adsorption energy ( E ads ) of nine organic adsorbates on Ge(100)-2 × 1 whose experimental E ads are available (Table S2, Figure S1, Supporting Information). In our calculations, E ads is systematically overestimated (error = −11.0 ± 5.5 kcal/mol) so that a reasonable correlation ( R 2 = 0.594) between the experimental and calculated E ads is obtained, considering possible errors in previous experimental data.…”

Understanding the Adsorption Energetics of Growth Polymorphs of Ferrocene Derivatives: Microscopic Thermal Desorption Analysis

“…Using the average abundance and an equilibrium desorption–adsorption model, we determined the adsorption energies of different polymorphs. Conventionally temperature-programmed desorption (TPD) has been performed on physisorbed molecules on different surfaces − to understand their adsorption energies and phase transitions. TPD is a bulk measurement, and the averaging effect causes difficulties in differentiating the assemblies with a subtle difference in adsorption energy.…”