Vibrational activation in direct and precursor-mediated chemisorption of SiH4 on Si(100)

The quantum state-resolved reactivity S-0 of SiH4 on Si(100)-2x1 has been measured for the first time for two vibrationally excited Si-H stretch local mode states (vertical bar 2000 > and vertical bar 1100 >) as well the ground state S-0 as a function of translational energy En and surface temperature T-s. We observe evidence for both direct and precursor-mediated chemisorption pathways. As expected, increasing En (or T-s) decreases S-0 for the precursor-mediated reaction and increases S0 for the direct chemisorption. However, vibrational excitation of the incident SiH4 increases S-0 for both the direct and the precursor-mediated pathway with a higher S-0 for the vertical bar 2000 > state than for the vertical bar 1100 > state, indicating a nonstatistical reaction mechanism. (c) 2008 American Institute of Physics.