On-line Monitoring of Nanoparticle Synthesis by Laser-Induced Breakdown Spectroscopy in Vacuum
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On-line Monitoring of Nanoparticle Synthesis by Laser-Induced Breakdown Spectroscopy in Vacuum Jessica Picard1, Jean-Baptiste Sirven2, Olivier Sublemontier1 1
NIMBE, CEA, CNRS, Université Paris-Saclay, CEA Saclay, F-91191 Gif sur Yvette cedex, France 2 DEN – Service d’Etudes Analytiques et de Réactivité des Surfaces (SEARS), CEA, Université Paris-Saclay, F-91191, Gif sur Yvette cedex, France ABSTRACT We propose a new technique suitable for on-line monitoring of gas phase synthesis of nanoparticles. It is based on aerodynamic focusing of nanoparticles followed by Laser-Induced Breakdown Spectroscopy (LIBS) under vacuum. The laser crosses a beam of particles at low pressure so that the plasma-produced photons to be analyzed are emitted only from the particles. Unlike previous experiments, the background from interaction with the gaseous component is totally eliminated from the collected spectra. Vacuum allows also for easier spectra collection in the UV range. Moreover, as the nanoparticle beam is highly collimated, the optical interface windows are not obstructed by particle deposition and the system can be kept running for hours. INTRODUCTION Laser-Induced Breakdown Spectroscopy (LIBS) is a widely used method in research for elemental analysis. It allows remote specific detection of most of the chemical elements in a sample and at ppm-level concentrations in solid samples [1]. This technique was already used with nanosized aerosols to probe the chemical composition stability of SiC nanoparticles during their production by laser pyrolysis [2]. However, the background from interaction with the ambient gas reduced dramatically the signal-to-noise ratio in the spectra and even hid some of the signal contributions. Furthermore, unavoidable particle deposition on optical windows at atmospheric pressure is a drag to its use as an efficient technique in continuous-wave mode on high-throughput production plants. Here we propose a new experimental setup for eliminating these difficulties by performing the laser-particle interaction in vacuum.
EXPERIMENTAL DETAILS Nanoparticle beam generation The principle of the experiment is to cross a beam of isolated nanoparticles with a highly focused laser beam under vacuum conditions and to analyze the plasma-emitted light in the UV and visible range. The experimental arrangement is shown in Figure 1. An Aerodynamic Lens System (ADLS) produces the collimated nanoparticle beam under vacuum from an aerosol stream at atmospheric pressure. This is achieved by carrying the nano-aerosol flow through a 200
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μm limiting entrance orifice followed by a series of four compartments separated by diaphragms. The geometry of the ADLS used in this study is identical to the design proposed by Jayne et al. [3]. It is part of a dedicated multipurp
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