Fragmentation dynamics of silicon cluster anions in collision with a silicon surface: Contrast to aluminum cluster anions

The collision of a size-selected silicon cluster anion, Si^-_N (8 ≤ N ≤ 12), with a silicon surface was investigated by using a tandem time-of-flight mass spectrometer equipped with an ultrahigh-vacuum collision chamber. The size-selected parent cluster anion, Si^-_N, was fragmented dominantly into Si^-_n (n ≈ N/2) in the collision energy range of several electron volts per atom. The measured recoil velocity of the fragment anion from the surface revealed that about 40% of the collision energy is directly converted to the translational kinetic energies of the anion and its counter neutral product scattered from the surface. This conversion efficiency was much higher than that observed for Al^-_N, aluminum cluster anions, reported previously. This marked contrast indicates that Al^-_N interacts for a longer time with the surface and transmits its collision energy more efficiently to the surface than Si^-_N.