Mass Spectrometric Study of Carbon Cluster Formation in Laser Ablation of Graphite at 355 nm

Abstract

The ablation dynamics and cluster formation of <TEX>$C_n^+$</TEX> ions ejected from 355 nm laser ablation of a graphite target in vacuum are investigated using a reflectron time-of-flight (RTOF) mass spectrometer. At low laser fluence, odd-numbered cluster ions with <TEX>$3{\leq}n{\leq}15$</TEX> are predominantly produced. Increasing the laser fluence shifts the maximum size distribution towards small cluster ions, implying the fragmentation of larger clusters within the hot plume. The temporal evolution of <TEX>$C_n^+$</TEX> ions was measured by varying the delay time of the ion extraction pulse with respect to the laser irradiation, providing significant information on the characteristics of the ablated plume. Above a laser fluence of <TEX>$0.2J/cm^2$</TEX> , large cluster ions (<TEX>$n{\geq}30$</TEX>) are produced at relatively long delay times, indicating that atoms or small carbon clusters aggregate during plume propagation. The dependence of the intensity of ablated <TEX>$C_n^+$</TEX> ions on delay time after laser irradiation shows that the most probable velocity of each cluster ion decreases with cluster size.