Application of the LIBS technique to the detection of nanostructured particles in aerosol form
Résumé
Nanotechnology is often said to be the industry of the 21st century. Nanostructured materials are expected to lead to the emergence of new products with enhanced features and functionalities. Their manufacturing often requires the use of nanoparticles (sizes below 100 nm) or larger particles (with a nanostructure) with varied sizes, shapes and chemical compositions. These nano-objects are the basic building blocks used to design nanostructured materials. The advent of these new objects raises the question of the development of an adapted metrology for their characterization in various contexts. Two examples of need may be underlined, nanosafety and process monitoring. First, little is known yet as to the risks related to nano objects in terms of impact on human health and the environment. There is therefore a need to detect and characterize these particles under various conditions. Second, production processes require tools for on line characterization of the final product. Thus, adapted instruments allowing, on site, on line and even real time characterization of these particles are to be designed. Laser-Induced Breakdown Spectroscopy (LIBS) is deemed as a technique of interest for the detection of nano-objects. Contrary to most particle counters, it allows determining the elemental composition of the particles and the mass concentrations of all the elements they are made of. LIBS tests have been carried out in the field of nanosafety. LIBS was demonstrated as a possible instrument for real-time detection and identification of Carbon Nano Tube (CNT) balls. So far, only random analysis in the particle flow was possible. A prototype allowing targeting particles (sizes > 500nm) prior to LIBS analysis is currently being designed to improve the hit rate. LIBS experiments applied to process monitoring have also been performed. It has been demonstrated that nanopowder stoichiometry could be monitored in real time. More recently, calibration free LIBS has been applied to stoichiometry determination of powders. Nanoparticle analysis using LIBS requires appropriate sampling. Demonstration has been made that nanoparticle analysis by LIBS could be enhanced using a radio frequency plasma as a trap. Applications in the field of nanosafety, process monitoring and life science are envisaged.