Nanoparticle analysis in low-pressure Radio-Frequency plasma via laserinduced breakdown spectroscopy
Résumé
The emergence of nanotechnology industry is accompanied by new issues in process control and workplace surveillance. Thus new techniques capable of real-time detection of nanoscaled particles are required. Laser-induced breakdown spectroscopy (LIBS) is capable of analyzing particles as small as few hundreds of nanometers but sampling is still not efficient and analyzes require several dozens of minutes to detect nanoparticles in a flow cell. In this context, LIBS can be coupled to new sampling techniques to achieve better analytical performances. To analyze nanoparticles, we coupled LIBS to a low-pressure Radio-Frequency plasma cell. Based on trapping particles using RF plasma generated with an inert gas, the LIBS analysis is performed on particles in levitation. To illustrate the efficiency of this coupling, nanoparticles of zinc oxide (ZnO) with a primary size of 60nm were trapped using RF plasma generated with argon (Ar) at 2mbar. Due to the concentration of particles in a limited volume of the RF plasma, breakdown in these particles is detectable with 100% sampling rate. The LIBS signal corresponding to one laser shot was recorded with an excellent signal to noise ratio with a reduced pressure of 2 mBar. We demonstrate that 60nm diameter nanoparticles can be analyzed by LIBS coupled to RF plasma cell due to the high sampling rate made possible by the trapping of particles. By using this coupling, the signal to noise ratio was enhanced at low-pressure gas even in a singl shot acquisition mode. These preliminary results are very encouraging to use LIBS coupled to RF plasma cell used as particle trap as a new technique to analyze nanoparticles.