Vibrational activation in direct and precursor-mediated chemisorption of SiH(4) on Si(100).

The quantum state-resolved reactivity S(0) of SiH(4) on Si(100)-2x1 has been measured for the first time for two vibrationally excited Si-H stretch local mode states (mid R:2000 and mid R:1100) as well the ground state S(0) as a function of translational energy E(n) and surface temperature T(s). We observe evidence for both direct and precursor-mediated chemisorption pathways. As expected, increasing E(n) (or T(s)) decreases S(0) for the precursor-mediated reaction and increases S(0) for the direct chemisorption. However, vibrational excitation of the incident SiH(4) increases S(0) for both the direct and the precursor-mediated pathway with a higher S(0) for the mid R:2000 state than for the mid R:1100 state, indicating a nonstatistical reaction mechanism.