Adsorption and activation pathway of CO on Si(100)
Xiaojie Chen, and W. A. Goddard, III
ab initio Hartree Fock (HF) and density functional methods (DFT) have been used to study the adsorption of CO on Si(100). Different adsorption states are explored. The terminal state is found to be stable with binding energy of 0.63 eV. The bridge state is also stable by 0.36 eV, while the ``side on'' state is unstable. CO is found to bond to Si(100) firstly in terminal state without adsorption barrier. As the CO coverage increases, CO can either transform from terminal state to bridge state with a barrier of 0.37 eV, or can directly adsorbe bonde to Si(100) in the bridge state with energy barrier of 1.1 eV. The desorption of CO from bridge state has also two paths. One through transition to terminal state with barrier of 0.11 eV and subsequent desorption barrier of 0.63 eV, or through direct desorption with barrier of 1.46 eV. The red shift of the electron energy loss spectra associated to the terminal-to-bridge transition is found to be 44.3 meV. The results are consistent with recent experimental results.