Effect of plasma temperature and electron number density on signal enhancement observed in nanoparticle enhanced LIBS

Abstract

The present work aims to understand the signal enhancement observed in nanoparticle (NP)-enhanced laser induced breakdown spectroscopy (NELIBS) due to changes in the plasma parameters as a result of improved atomization and excitation. A systematic study on signal enhancements during NELIBS using simultaneous spectroscopy and imaging is investigated by varying the experimental parameters like particle size and laser fluence. We have observed similar enhancements in spectroscopy and imaging channels regardless of NP size at different laser fluences. Although the plume size in NELIBS was marginally more prominent than the LIBS at the same laser fluence, the corresponding intensity in NELIBS is significantly higher. This agrees with the hypothesis of efficient atomization and excitation of plasma in the case of NELIBS. Therefore, we performed a sensitivity analysis using simulated LIBS signal to understand changes in experimentally observable plasma parameters (excitation temperature and electron number density) on signal enhancement. We have shown that the enhancements in the emission intensities of typically one order of magnitude can be explained as a result of the change in electron number density and plasma temperature. A comparison of the expected enhancement due to this change with experimental observation for a Cu I line is also presented.