Measurements of nanoparticle size distribution produced by laser ablation of tungsten and boron-carbide in N2 ambient

Nanoparticles (NPs) were produced by ablating tungsten and boron-carbide (B4C) target materials in atmospheric pressure nitrogen ambient using ArF excimer laser pulses. The size distributions of the NPs formed during the ablation were monitored—within a 7–133 nm size window—by a condensation particle counter connected to a differential mobility analyzer. The laser repetition rate was varied between 1–50 Hz, and the fluence was systematically changed in the range of 0.5–15 J/cm2, for both materials, allowing a comparative study in an extended laser parameter regime. The multishot ablation threshold (Fth) of B4C was determined to be 1.9 J/cm2 for the laser used (ArF excimer, l = 193 nm). Similarly to earlier studies, it was shown that the size distributions consist of mainly small nanoparticles (< 20 nm) attributed to a non-thermal ablation mechanism below Fth. An additional broad peak appears (between 20 and 40 nm) above Fth as a consequence of the thermally induced macroscopic ablation. Chemical composition of deposited polydisperse nanoparticles was studied by X-ray photoelectron spectroscopy showing nitrogen incorporation into the boron-carbide