Abstract
Catastrophic ablation of CaF2 crystals is often observed in ultraviolet-laser ablation-inductively coupled plasma-mass spectrometry (UV-LA-ICP-MS) analysis, leading to variations in the volume of ablated material and resulting analytical errors in LA-ICP-MS microanalysis. Therefore, it is essential to understand the ablation behavior and the interaction mechanisms between the laser and CaF2 crystals. In this study, we examined the effects of crystal surface roughness and laser fluence on ablation behavior. The CaF2 crystal polished with 1500 mesh abrasive paper exhibited a stable signal profile, a regular ablation crater, and the formation of nanoparticles, which align with predictions from the thermo-mechanical coupling model. Both higher and lower roughness resulted in either unstable ablation or uncontrolled ejection of fragments; the latter occurred when the thermal stress from accumulated light energy significantly exceeded the compressive strength of CaF2. Consequently, a roughness of 1500 mesh at the bottom of the ablation craters was deduced. We also identified a laser fluence of 14 J·cm−2 as the threshold for effective LA-ICP-MS analysis of CaF2 crystals, based on consistent signal profiles, elemental fractionation index (EFI), and crater morphology as revealed by LA-ICP-MS and scanning electron microscope (SEM) analyses, along with theoretical calculations from the thermo-mechanical coupling model. The optimal roughness (1500 mesh) and fluence (14 J·cm−2), together with the thermo-mechanical coupling model, can serve as guidelines for UV-LA-ICP-MS settings in further quantitative analyses of CaF2 crystals.
Published Version
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