Influence of Ambient Gas on Laser-Induced Breakdown Spectroscopy of Uranium Metal

Laser-induced breakdown spectroscopy （LIBS） is regarded as a suitable method for the remote analysis of materials in any phase, even in an environment with high radiation levels. In the present work we used the third harmonic pulse of a Nd：YAG laser for ablation of uranium metal and measured the plasma emission with a fiber-optic spectrometer. The LIBS spectra of uranium metal and their features in different ambient gases （i.e., argon, neon, oxygen, and nitrogen） at atmospheric pressure were studied. Strong continuum spectrum and several hundreds of emission lines from UI and UII were observed. It is found that the continuum spectrum observed in uranium not only comes from bremsstrahlung emission but is also due to the complex spectrum of uranium. The influence of ambient gas and the gas flow rate for ablation of uranium metal was investigated. The experimental results indicate that the intensity of the uranium lines was enhanced in argon and nitrogen. However, the intensity of uranium lines was decreased in oxygen due to the generation of UO and other oxides. The results also showed that the highest intensity of uranium lines were obtained in argon gas with a gas flow rate above 2.5 L/min. The enhanced mechanism in ambient gas and the influence of the gas flow rate were analyzed in this work.

Final Status of a Metal Sample Surface after Multipulse Laser Irradiation in an Ambient Gas

We have investigated the role of the ambient gas nature and pressure in the structure and appearance of the laser treated zone. and the influence of the total duration and temporal shape of laser pulse with the laser tight being λ= 10.6μm wavelength incident upon a metallic surface at intermediate taser intensities of 107-108 W / cm2. A plasma is accompanied by the action of the laser pulse, It acts as an active moderator among laser beam and target thus determining the final status of the contact surface

Major elements analysis in bituminous coals under different ambient gases by laser-induced breakdown spectroscopy with PLS modeling

Three major elements, carbon, hydrogen, and nitrogen, in twenty-four bituminous coal samples, were measured by laser-induced breakdown spectroscopy. Argon and helium were applied as ambient gas to enhance the signals and eliminate the interference of nitrogen from surrounding air. The relative standard deviation of the related emission lines and the performance in the partial least squares （PLS） modeling were compared for different ambient environments. The results showed that argon not only improved the intensity, but also reduced signal fluctuation. The PLS model also had the optimal performance in multi-element analysis using argon as ambient gas. The root mean square error of prediction of carbon concentration decreased from 4.25% in air to 3.49% in argon, while the average relative error reduced from 4.96% to 2.98%. Hydrogen line demonstrated similar improvement. Yet, the nitrogen lines were too weak to be detected even in an argon environment which suggested the nitrogen signal measured in air come from the breakdown of nitrogen molecules in the atmosphere.

Fabrication of oxygen-doped MoSe2 hierarchical nanosheets for highly sensitive and selective detection of trace trimethylamine at room temperature in air

Nano Research volume 13,pages1704–1712(2020)Cite this article 191 Accesses Metrics details Abstract Intelligent gas sensors based on the layered transition metal dichalcogenides(TMDs)have attracted great interest in the field of gas sensing due to their multiple active sites,fast electron,mass transfer capability and large surface-to-volume ratio.However,conventional TMDs-based sensors typically work at elevated temperature in inert atmosphere,which would largely limit the corresponding practical applications.Herein,novel oxygen-doped MoSe2 hierarchical nanostructures composed of ultrathin nanosheets with large specific surface area have been designed and generated typically at 200°C in air for fast and facile gas sensing of trimethylamine(TMA),effectively.Benefited from the gas-accessible hierarchical morphology and high surface area with abundant nanochannels,highly sensitive and selective detection of trace TMA has been achieved under ambient condition,and as detected the theoretical limit of detection(LOD)is 8 ppb,which is the lowest for TMA detection under ambient condition among the reported studies.The mechanism of oxygen doping on the improved gas-sensing performance has been investigated,revealing that the oxygen doping could greatly optimize the electronic structure,thus regulate the Fermi level of MoSe2 as well as the affinity between TMA molecule and sensor surface.It is expected that the oxygen doping strategy developed for the highly efficient gas sensors based on TMDs in present work may also be applicable to other types of gas-sensing semiconductors,which could open up a new direction for the rational design of high-performance gas sensors working under ambient condition.