金纳米与磁场作用下LIBS检测灵敏度改善研究

针对激光诱导击穿光谱技术（LIBS）中等离子体的发射光谱增强问题，提出一种磁场增强LIBS与纳米颗粒增强LIBS（NELIBS）相结合的方法。采用热蒸发法在样品表面沉积一层直径20 nm的金纳米颗粒。利用波长为1 064 nm，最大能量为200 mJ的Nd∶YAG脉冲激光器在室温，一个标准大气压下对纯铜和黄铜进行诱导击穿。调整激光能量为30~110 mJ，分别使用传统LIBS、磁场增强LIBS、NELIBS以及两种方法结合对纯铜进行激光诱导击穿，得到特征谱线(Cu Ⅰ 521.8 nm)的强度增强因子和信噪比，并对其增强机理进行分析。在相同环境下使用四种方式对黄铜和纯铜进行诱导击穿以探测样品中的微量元素。当在样品表面沉淀金纳米颗粒或者将沉淀有金纳米颗粒的样品放在磁场中进行诱导击穿时，发现纯铜样品的光谱中存在Mg元素的特征谱线Mg Ⅱ 279.569 nm，黄铜样品的光谱中存在Si元素的特征谱线 Si Ⅰ 251.611 nm。实验结果表明：单独施加磁场约束或增加纳米金颗粒均可以有效增强等离子体光谱强度，但增强效果弱于两种方法结合，磁场约束对光谱的增强效果弱于NELIBS的增强效果。当结合NELIBS与磁场约束LIBS时，谱线增强因子最高可达14.3(Cu Ⅰ 521.8 nm)，相比于磁场增强LIBS和NELIBS，最大增强因子分别提高了28%和59%。四种情况中当激光脉冲能量逐渐增大时，等离子体向外膨胀的强度增大，磁场产生的洛伦兹力束缚等离子的能力相对减弱，同时纳米金颗粒对等离子体发射光谱的增强作用被削弱，谱线强度降低，等离子体的增强因子逐渐减小后趋于稳定。通过NELIBS与磁场约束LIBS结合方式，不仅可以有效提高等离子体的发射谱线强度，改善光谱信号信噪比，而且传统LIBS方法中由于谱线强度低、背景噪声大而无法探测的微量元素可以被探测到，LIBS技术对微量元素的探测能力得到显著提高，微量元素的探测下限变得更低。NELIBS与磁场约束LIBS结合的方法具有更高的灵敏度和准确度，为激光诱导击穿光谱技术的谱线增强方法提供了新的思路，在该领域具有广阔的应用前景。

Detection Sensitivity Improvement Study of LIBS by Combining Au-Nanoparticles and Magnetic Field

In order to enhance the intensity of emission spectra of laser-induced plasma, a method of combining magnetic field enhanced laser induced breakdown spectroscopy(LIBS) with nanoparticle enhanced LIBS (NELIBS) was proposed. 20 nm in diameter Au-nanoparticles(Au NPs) was deposited on the surface of the sample by thermal evaporation. Copper and brass were induced to breakdown by a pulsed Nd∶YAG laser (1 064 nm, maximum energy 200 mJ) at room temperature and under standard atmospheric pressure. Laser-induced breakdown of copper was performed respectively using conventional LIBS, magnetic field-enhanced LIBS, NELIBS, and combining of the magnetic field enhanced LIBS and NELIBS with changing laser energy of 30~110 mJ. The enhancement factor and SNR for Cu Ⅰ 521.8 nm were obtained and the enhancement mechanism was analyzed. Brass and copper were induced to breakdown under four different constrains in the same environment to detect trace elements in the sample. When Au NPs were precipitated on the surface of the sample or the sample precipitated with the Au NPs was put in a magnetic field, the characteristic line of Mg Ⅱ 279.569 nm was found in the spectrum of the copper sample and the characteristic line of Si 251.611 nm was found in the spectrum of the brass sample. The experimental results showed that applying a magnetic field alone or add the Au NPs on the sample surface can effectively enhance the spectral intensity of the plasma, but the enhancement effect is weaker than the combination of the two methods. Magnetic field confinement enhancement of the spectrum is weaker than that of NELIBS. When the NELIBS is combined with magnetic field enhanced LIBS, the highest enhancement factor is up to 14.3 (CuⅠ 521.8 nm) and increased by 28% and 59% compared to magnetic field-enhanced LIBS and NELIBS, respectively. In the four cases, when the laser pulse energy was gradually increased, the Lorentz force that was generated by the magnetic field to restrain the plasma reduced relatively due to the increased expansion intensity of plasma, at the same time, the enhancement effect of the Au NPs on the emission spectrum of the plasma was weakened, the line intensity decreased, and the enhancement factor of plasma gradually decreased and tended to be stable. The combination of NELLBS and magnetic field enhanced LIBS can not only effectively increase the emission line intensity of the plasma and improve SNR of spectral , but also trace elements that cannot be detected in the conventional LIBS due to the low intensity of the spectral line and large background noise can be detected, and the ability of LIBS to detect trace elements is significantly improved, and the limit of detection of trace elements becomes lower. The method of combining NELIBS with magnetic field enhanced LIBS has higher sensitivity and accuracy, providing a new idea for the enhancement method of laser induced breakdown spectroscopy. It has broad application prospects in this field.