Study on the Differences in LIBS Signal Enhancement by Au/Ag Nanoparticles under Low-Pressure Conditions and Their Applicability to Vacuum Degree Detection
Liu Jiaqi, Lü Simeng, Yuan Huan, Yang Aijun, Wang Xiaohua
School of Electrical Engineering Xi’an Jiaotong University Xi’an 710049 China
Abstract：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 CuⅠ 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 Cu Ⅰ521.8 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.
刘佳琪, 吕思濛, 袁欢, 杨爱军, 王小华. 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[J]. 电工技术学报, 2026, 41(13): 4458-4468.
Liu Jiaqi, Lü Simeng, Yuan Huan, Yang Aijun, Wang Xiaohua. Study on the Differences in LIBS Signal Enhancement by Au/Ag Nanoparticles under Low-Pressure Conditions and Their Applicability to Vacuum Degree Detection. Transactions of China Electrotechnical Society, 2026, 41(13): 4458-4468.
[1] Yao Xiaofei, Wang Jianhua, Ai Shaogui, et al.Vacuum switching technology for future of power systems[J]. Engineering, 2022, 13: 164-177. [2] 赵子玉, 宋焕生, 江秀臣, 等. 真空断路器真空度现场测量新技术[J]. 电工技术学报, 2009, 24(3): 99-103. Zhao Ziyu, Song Huansheng, Jiang Xiuchen, et al.New technology for measurement of internal pressure of vacuum breakers[J]. Transactions of China Electro-technical Society, 2009, 24(3): 99-103. [3] Feng Kaiwen, Liu Jinjun, Liu Zeng, et al.A novel communication-free carrier synchronization high-frequency circulating current suppression method based on reference prediction for parallel power converters[J]. IEEE Transactions on Power Electronics, 2025, 40(10): 15620-15637. [4] Ding Yiming, Shi Zongqian, Mo Yongpeng, et al.Study on the reignition phase and magnetic field simulation of drawn vacuum arc in 126 kV axial magnetic field contacts[J]. Physics of Plasmas, 2026, 33(2): 023503. [5] 葛国伟, 王文博, 程显, 等. 基于两间隙异步联动的一体化高压真空灭弧室电场设计[J]. 电工技术学报, 2024, 39(17): 5555-5564. Ge Guowei, Wang Wenbo, Cheng Xian, et al.Electric field design of integrated high-voltage vacuum interrupter based on two-gap asynchronous linkage[J]. Transactions of China Electrotechnical Society, 2024, 39(17): 5555-5564. [6] 袁欢, 叶哲, 王小华, 等. 真空开关真空度检测研究及其进展[J]. 高电压技术, 2022, 48(9): 3624-3635. Yuan Huan, Ye Zhe, Wang Xiaohua, et al.Research and development of vacuum degree online detection of vacuum interrupter[J]. High Voltage Engineering, 2022, 48(9): 3624-3635. [7] 韩翔宇, 纽春萍, 何海龙, 等. 电磁式断路器状态监测与智能评估技术综述[J]. 电工技术学报, 2023, 38(8): 2191-2210. Han Xiangyu, Niu Chunping, He Hailong, et al.Review of condition monitoring and intelligent assessment of electromagnetic circuit breaker[J]. Transactions of China Electrotechnical Society, 2023, 38(8): 2191-2210. [8] 李炜, 郭媛媛, 王承玉, 等. 基于X射线量变化评估真空灭弧室真空度的方法[J]. 高压电器, 2008, 44(4): 315-318. Li Wei, Guo Yuanyuan, Wang Chengyu, et al.Vacuum estimation method for vacuum interrupter based on variation of X-ray[J]. High Voltage Apparatus, 2008, 44(4): 315-318. [9] 王建华, 耿英三, 刘志远. 输电等级单断口真空断路器理论及其技术[M]. 北京: 机械工业出版社, 2017. [10] 李元钊, 丁健刚, 刘志远, 等. 并联电容对真空灭弧室内部电位分布的改善作用[J]. 电工技术学报, 2025, 40(2): 610-624. Li Yuanzhao, Ding Jiangang, Liu Zhiyuan, et al.The improving effect of parallel capacitors on the internal potential distribution of vacuum interrupters[J]. Transactions of China Electrotechnical Society, 2025, 40(2): 610-624. [11] 吴梦泽, 宋建成, 高云广, 等. 真空断路器真空度检测方法研究现状与展望[J]. 工矿自动化, 2018, 44(6): 6-10. Wu Mengze, Song Jiancheng, Gao Yunguang, et al.Research status and prospect of vacuum degree detection methods for vacuum circuit breaker[J]. Industry and Mine Automation, 2018, 44(6): 6-10. [12] Yuan Huan, Liu Dingxin, Wang Xiaohua, et al.Preliminary study on vacuum degree online detection of vacuum circuit breaker based on laser induced breakdown spectroscopy (LIBS)[C]//2016 International Conference on Condition Monitoring and Diagnosis (CMD), Xi’an, China, 2016: 135-138. [13] Yuan Huan, Gornushkin I B, Gojani A B, et al.Laser-induced plasma imaging for low-pressure detection[J]. Optics Express, 2018, 26(12): 15962. [14] Zhang Feilong, Yuan Huan, Yang Aijun, et al.On-line vacuum degree monitoring of vacuum circuit breakers based on laser-induced breakdown spectroscopy combined with random forest algorithm[J]. Journal of Analytical Atomic Spectrometry, 2024, 39(1): 281-292. [15] Ke Wei, Pan Jianbin, Yuan Huan, et al.Ensemble-learning for pressure prediction in vacuum circuit breaker using feature fusion of laser-induced plasma spectra and images[J]. Spectrochimica Acta Part B: Atomic Spectroscopy, 2025, 226: 107137. [16] Liu Zhe, Ding Jiangang, Zhang Ying, et al.A non-contact method for vacuum degree detection in simulant vacuum interrupters using coaxial optical path laser-induced plasma[J]. Discover Applied Sciences, 2026, 8(2): 102. [17] 袁欢, 柯伟, 王小华, 等. 基于激光诱导等离子体光路复用技术的真空开关真空度检测研究[J]. 高电压技术, 2022, 48(3): 1160-1167. Yuan Huan, Ke Wei, Wang Xiaohua, et al.Vacuum degree detection of vacuum switch based on laser induced plasma optical path multiplexing[J]. High Voltage Engineering, 2022, 48(3): 1160-1167. [18] 生鑫, 李争博, 付思, 等. 燃弧过程中真空旋转电弧轨迹追踪与特性[J]. 电工技术学报, 2024, 39(20): 6553-6563. Sheng Xin, Li Zhengbo, Fu Si, et al.Tracking and characterization of vacuum rotating arc trajectories during arc-firing process[J]. Transactions of China Electrotechnical Society, 2024, 39(20): 6553-6563. [19] Ke Wei, Luo Haochen, Lv Simin, et al.Air pressure prediction model based on the fusion of laser-induced plasma images and spectra[J]. Journal of Analytical Atomic Spectrometry, 2024, 39(7): 1824-1837. [20] Ke Wei, Yuan Huan, Wang Xiaohua, et al. Vacuum level prediction based on LIP using bimodal fusion and ensemble learning[J/OL]. IEEE Transactions on Dielectrics and Electrical Insulation, 2025: 1. (2025-12-15)[2026-04-01] doi: 10.1109/TDEI.2025.3644316. [21] De Giacomo A, Koral C, Valenza G, et al.Nanoparticle enhanced laser-induced breakdown spectroscopy for microdrop analysis at subppm level[J]. Analytical Chemistry, 2016, 88(10): 5251-5257. [22] De Giacomo A, Gaudiuso R, Koral C, et al.Nanoparticle enhanced laser induced breakdown spectroscopy: effect of nanoparticles deposited on sample surface on laser ablation and plasma emission[J]. Spectrochimica Acta Part B: Atomic Spectroscopy, 2014, 98: 19-27. [23] Sládková L, Prochazka D, Pořízka P, et al.Improvement of the laser-induced breakdown spectroscopy method sensitivity by the usage of combination of Ag-nanoparticles and vacuum conditions[J]. Spectrochimica Acta Part B: Atomic Spectroscopy, 2017, 127: 48-55. [24] Dell’ Aglio M, Alrifai R, De Giacomo A.Nanoparticle enhanced laser induced breakdown spectroscopy (NELIBS), a first review[J]. Spectrochimica Acta Part B: Atomic Spectroscopy, 2018, 148: 105-112. [25] Galbács G, Kéri A, Kohut A, et al.Nanoparticles in analytical laser and plasma spectroscopy-a review of recent developments in methodology and applications[J]. Journal of Analytical Atomic Spectrometry, 2021, 36(9): 1826-1872. [26] Soumyashree S, Kumar P.Influence of pressure and pulse energy on the expansion dynamics of nanoparticle-enhanced laser produced plasma[J]. Spectrochimica Acta Part B: Atomic Spectroscopy, 2023, 208: 106761. [27] 刘佳琪, 柯伟, 袁欢, 等. 不同气压下银纳米粒子增强激光诱导等离子体信号[J]. 电机与控制学报, 2024, 28(4): 1-10. Liu Jiaqi, Ke Wei, Yuan Huan, et al.Nanoparticle enhanced laser induced plasma signal technology[J]. Electric Machines and Control, 2024, 28(4): 1-10. [28] Liu Jiaqi, Ding Xiaokang, Zhang Feilong, et al.Vacuum degree detection performance improvement of vacuum switches based on NELIBS[J]. Journal of Analytical Atomic Spectrometry, 2025, 40(1): 248-258. [29] 陈家伟, 刘佳琪, 袁欢, 等. 表面纳米化提升真空开关内激光诱导等离子体信号研究[J]. 高压电器, 2025, 61(8): 32-38. Chen Jiawei, Liu Jiaqi, Yuan Huan, et al.Research on laser-induced plasma signal enhancement in vacuum circuit breaker through surface nanocrystallization[J]. High Voltage Apparatus, 2025, 61(8): 32-38. [30] Cárdenas-Escudero J, Gardette V, Villalonga A, et al.A chemically functionalized glass support for gold and silver metallic nanoparticle analysis with LIBS[J]. Journal of Analytical Atomic Spectrometry, 2024, 39(3): 962-973. [31] 国家能源局. 高压交流真空断路器: DL/T 403—2017[S]. 北京: 中国电力出版社, 2017.
2026, Vol. 41 
