Semiempirical molecular orbital calculations were performed to investigate the mechanism of H 2 desorption from dihydride species on Si(001) surfaces. The lowest energy pathways were calculated with respect to three different mechanisms which have been proposed previously. We performed additional calculations under the different H coverage conditions to examine the dependence of activation energy on the varieties of surrounding hydride species. The new transition state structure was obtained by the calculation of the recombinative desorption of two H atoms from adjacent Si dihydrides. We have found that the activation barrier of the recombinative desorption mechanism was the lowest of all and it was hardly influenced no matter what the surrounding hydride species is.
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