低气压下Au/Ag纳米粒子对LIBS信号增强差异及其真空度检测适用性研究OA

Online vacuum degree detection is important for assessing the operating condition of vacuum switches,while conventional laser-induced breakdown spectroscopy(LIBS)still suffers from weak characteristic spectral lines and insufficient pressure discrimination under low-pressure conditions.Metallic nanoparticles can enhance laser-induced plasma emission,but the enhancement differences between Au and Ag nanoparticles and their applicability to vacuum degree detection remain unclear.This study compares the effects of Au and Ag nanoparticles on Cu-target LIBS signals under low-pressure conditions and evaluates their suitability for characteristic-line-based and radiation-intensity-based vacuum characterization. A low-pressure LIBS experimental platform was established using a Cu target in a vacuum chamber.The pressure range was controlled from 10-4 Pa to 1 Pa.A pulsed Nd:YAG laser was focused on the Cu surface,and the plasma emission was collected by a gated optical detection system.Au and Ag nanoparticle layers with different concentrations and particle sizes were prepared on the Cu surface by spin coating to improve deposition uniformity.The Cu Ⅰ 515.3 nm and 521.8 nm lines were selected as characteristic spectral indicators.Peak intensity,enhancement factor,integral radiation intensity,plasma images,and the relationship between characteristic peak intensity and pressure were analyzed.Error bars were used to represent the standard deviations of repeated measurements,with uncertainties mainly originating from laser pulse energy fluctuation,local nanoparticle distribution,target surface morphology,and random plasma evolution. The results show that both Au and Ag nanoparticles enhance Cu characteristic line emission in the range of 10-4～1 Pa.The peak intensities of the Cu Ⅰ515.3 nm and 521.8 nm lines generally follow the order Au-enhanced LIBS＞Ag-enhanced LIBS＞conventional LIBS.The enhancement is reflected not only in the characteristic peaks but also in the local continuum background.Characteristic-line enhancement is related to increased laser energy deposition,enhanced Cu ablation and excitation,and local electromagnetic field enhancement induced by nanoparticles.Continuum enhancement is associated with increased electron density in the early plasma stage,which strengthens bremsstrahlung and recombination radiation. Au and Ag nanoparticles exhibit different parameter sensitivities.For Ag nanoparticles,the characteristic line intensity increases with concentration within the investigated range,indicating that higher surface coverage provides more active enhancement sites.For Au nanoparticles,stronger characteristic line emission is obtained at lower concentration,while further concentration increase may reduce the effective enhancement because of aggregation,shielding,or weakened local field coupling.Particle size also affects the two materials differently.Ag nanoparticles show stronger enhancement at 10 nm than at 5 nm,whereas Au nanoparticles exhibit higher enhancement at 5 nm than at 10 nm.The enhancement factor of 5 nm Au nanoparticles is the highest among the tested groups,especially for the CuⅠ521.8 nm line. Time-resolved integral radiation results show that Ag nanoparticles with a concentration of 0.1 mg/mL and a particle size of 10 nm produce higher overall radiation intensity and a larger luminous plasma region than the selected Au nanoparticle condition.The radiation intensity is higher at 10-3 Pa and 10-2 Pa than at 10-1 Pa and 1 Pa,and the high-radiation stage mainly appears within 100～200 ns.For vacuum characterization,the average intensity of the selected Cu peaks shows a nonlinear relationship with lg p.Quadratic fitting gives coefficients of 0.974 4 for Au and 0.941 9 for Ag,indicating that Au provides clearer characteristic-line pressure response and better pressure discrimination. Au and Ag nanoparticles therefore correspond to different enhancement pathways in low-pressure LIBS.Au is more suitable for vacuum detection based on target Cu characteristic lines and pressure fitting,while Ag is more suitable for enhancing integral radiation intensity and plasma image features.Nanoparticle material,concentration,and particle size should be selected according to the diagnostic signal used for vacuum switch monitoring.