SIMS study of plumes generated from laser ablation of polymers

Plumes generated by ablation of polymer targets using a third-harmonic Nd:YAG laser under different atmospheres (air, N₂ and He) were deposited on a H-terminated silicon substrate. The chemical composition and distribution of deposited ablation debris were measured using time-of-flight secondary-ion mass spectrometry. Mass-resolved images show that the size and shape of the plume is dependent on the laser pulse energy and atmosphere in which the plume expanded. In air and nitrogen, plumes are hemispherical with distinct borders. In He they are mushroom-shaped without sharp borders. Since all experiments were carried out at atmospheric pressure, these differences can be related to the reactivity and molecular weight of the gas. Nitrogen-containing compounds (NCCs) and oxygen-containing compounds (OCCs) were found in plumes ablated in air but not in N₂ and He environments. We suggest that the formation of NCCs and OCCs is due to the interaction of the hot plume with air, initiating thermal dissociation of O₂ and oxygen-assisted dissociation of N₂. PACS 52.25.Kn