Negative-ion emission during laser ablation of multicomponent materials

Relevance and formation mechanisms of negative ions upon ablation of Al2O3

“…Interestingly, in spite of the high electron affinities of halogens [14], studies of ablation of alkali halides at power densities below the threshold for optical breakdown and plume formation show no evidence for negative halogen ions [15]. In addition, it is shown that positive and negative alkali ions show a high degree of spatial and temporal overlap similarly to what was reported earlier for YBaCuO [9].…”

“…The existence and importance of negative ions in the ablation process was reported in the 1990s and practically ignored since then. Early studies on ablation of YBaCuO targets reported the thermal emission of O − (1 eV) [8] and a comparable flux of positive and negative ions [9], the energy distribution of the latter overlapping with the high-energy part of the former. Negatively charged oxide species were detected upon ablation of AlN containing oxygen impurities and it was concluded that a bias was needed to obtain stoichiometric films in order to accelerate positive ions and reject the negative oxide ions [10].…”

“…For this study, we have selected an oxide ceramic target (Al 2 O 3 ), i.e. a simple binary oxide formed by a low-mass metal as opposed to earlier studies that involved complex oxides [8,9,12,13]. On the one hand, transparent and high refractive index films and waveguides could be obtained by PLD of ceramic Al 2 O 3 in vacuum [16,17] and thus, any possible contribution of gas species in producing negative ions [12,13] can be ruled out.…”

Modeling of UV pulsed-laser ablation of metallic targets

“…A strong increase of the ion and electron yield as a function of the laser pulse fluence has been observed at moderate laser irradiance and up to ≈ 1.5 GW cm −2 ; then at higher laser intensities (> 1.5 GW cm −2 ) a plateau was reached. A roll-off of the total ion yield was also observed by various authors in laser ablation of different materials, and it was ascribed to plasma shielding of the sample surface [5,7,8,37,38]. The roll-off observed in the theoretical investigations reported here is in quite good agreement with the experimental findings of [22](see Fig.…”

“…For incident laser intensities greater than 10 8 W cm −2 , a large amount of electrons, ions and excited neutrals is present in the vaporized material and absorb the laser light forming plasma above the target surface. Several studies have shown that plasma dynamics plays a crucial role in the laser-ablation process and plasma absorption leads to a significant reduction in the laser coupling with the target [5][6][7][8][9][10].…”