Ionization enhancement in silicon clusters and germanium atoms in the presence of zirconium

Molecules/clusters have been shown to undergo an enhancement in ionization under ultrafast laser pulses. This enhancement results in the lowering of the laser intensity required to observe ion signal from higher atomic charge states resulting from Coulomb explosion of clusters. Here, we explore the effect of using an early-group transition metal as an electron source in the formation of small silicon clusters on the observed enhancement in ionization. Intensity selective scanning is used to measure the onset of ion signal for the atomic charge states of silicon, germanium, zirconium, and oxygen. Additionally, the kinetic energy released values for the resulting high charge states of silicon are measured and compared to those previously observed using a copper electron source. A significant increase in ionization enhancement is observed upon using zirconium metal, despite a decrease in cluster size. Germanium metal with zirconium is studied for comparison and shows a larger enhancement in ion signal than silicon, indicating that atomic mass may be significant.