In situ monitoring of size distributions and characterization of nanoparticles during W ablation in N2 atmosphere

Abstract

Nanoparticles were generated by pulsed laser ablation of tungsten in a N2 ambient at atmospheric pressure. Size distributions and concentrations were monitored in situ versus laser fluence, repetition rate, and ablated spot size, by a differential mobility analyzer and a particle counter. The multishot ablation threshold was determined to be ∼6 J/cm2 for the laser used (ArF excimer, λ=193 nm). Mostly small, nonlognormally, distributed particles (<20 nm in diameter) were generated below the ablation threshold (φth), and the relative concentration of larger particulates (>20 nm in diameter) increased above φth. Modeling of the temperature and ablated depth dependence on fluence showed that the formation of clusters below φth could not be assigned to a thermal process, but are connected to particle condensation from a photochemically desorbed thin layer. X-ray diffraction and x-ray photoelectron spectroscopy analysis performed on polydisperse nanoparticles revealed an amorphous phase of the particles, and the elemental composition was found to be WN0.3.