Optimization of nanoparticle-enhanced laser-induced breakdown spectroscopy for the hyperspectral chemical mapping of solid samples.

Background: Nanoparticle-enhanced laser-induced breakdown spectroscopy (NE-LIBS) uses the plasmonic effect of metallic nanoparticles deposited on solid sample surfaces to achieve a significant signal enhancement by lowering the breakdown threshold and elevating plasma temperature. NE-LIBS has been used for localized analysis, but NE-LIBS mapping of solids has rarely been done, due to several challenges. In this study, we scrutinized the performance of NE-LIBS hyperspectral mapping of solid samples, when the controlled deposition of nanoparticles was done using magnetron sputtering.

Results: We performed a detailed optimization of the nanoparticle-related signal enhancement involving the laser wavelength, laser fluence and detector gating. It was confirmed that while the laser wavelength has only a small influence in the studied range (at 266 nm, 532 nm and 1064 nm), but there is an optimum for laser fluence and detection gate delay. The best signal enhancement achieved for a glass sample was 25-30. The applicability of the approach was demonstrated by hyperspectral NE-LIBS mapping of a granite rock sample, which provided an improved sensitivity in the study of the elemental distribution (exemplified for Li and Mg), and by paint linear discriminant analysis, in which NE-LIBS gave rise to a significantly improved accuracy (98 %, as opposed to the LIBS accuracy of only 84 %).

Significance: The analytical benefits of NE-LIBS hyperspectral mapping was demonstrated in two applications involving industrially relevant sample types. For example, the enhanced signals in rock elemental mapping can improve the localization of mineral grains viable for economic mining. The qualitative discrimination application involving paints demonstrates that the NE-LIBS approach can be beneficial in the spatial classification or identification of the local quality of a solid sample surface.