Anomalous enrichment of C2+ ions by laser ablation of graphite in Ar jet

Abstract

The formation mechanisms of C1+, C2+, and C3+ ions by laser ablation of graphite are investigated using time-of-flight (TOF) quadrupole mass spectroscopy. The laser ablation is performed in conjunction with a pulsed Ar expansion to elucidate the third-body effect on the formation of the small carbon cluster ions. Drastic enhancement of the C2+ ion signal is observed by an increase of the local pressure near the target, indicating that C2+ ions are efficiently formed by recombination of carbon atoms and subsequent ionization. The branching ratio of C1+, C2+, and C3+ ions and their mean translational energies are different from those of neutrals. Also, the TOF spectra for Cn+ ions show multiple peak structures, which implies that different mechanisms are involved in the formation of Cn+ ions.