Chen-Guang Wang,#,+ Kai Huang,+* and Wei Ji
#Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-nano Devices, Renmin University of China, Beijing, 100872, China
+Lash Miller Chemical Laboratories, Department of Chemistry and Institute of Optical Sciences, University of Toronto, ON, Toronto, M5S 3H6, Canada
DOI:10.1063/1.4899841 Publication Date: Nov. 03, 2014
During the dissociative adsorption on a solid surface, the substrate usually participates in a passive manner to accommodate fragments produced upon the cleavage of the internal bond(s) of a (transient) molecular adsorbate. This simple picture, however, neglects the flexibility of surface atoms. Here, we report a Density Functional Theory (DFT) study to revisit our early studies of the dissociative adsorption of CH3X (X=Br and Cl) on Si(100). We have identified a new reaction pathway, which involves a flip of a silicon dimer; this new pathway agrees better with experiments. For our main exemplar of CH3Br, insights have been gained using a simple model that involves a three-atom reactive center, Br-C-Si. When the silicon dimer flips, the interaction between C and Si in the Br-C-Si center is enhanced, evident in the increased energy-split of the frontier orbitals. We also examine how the dissociation dynamics of CH3Br is altered on a heterodimer (Si-Al, Si-P and Si-Ge) in a Si(100) surface. In all three cases, we conclude, on the basis of computed reaction pathways, that no heterodimer flipping is involved before the system transverses the transition states to dissociative adsorption.