飞秒激光用作电离源的二次中性粒子质谱技术

Femtosecond Laser as Post-ionization Method for Secondary Neutral Mass Spectrometry

采用纳秒激光代替二次离子质谱中的离子束溅射金属样品,用飞秒激光电离溅射产生的中性溅射粒子,利用自行研制的反射式飞行时间质谱分析相应的离子强度分布和速度分布。研究表明,纳秒激光溅射产物中中性粒子占很大比例,飞秒激光后电离技术可以将检测灵敏度提高60倍以上;通过调节飞秒激光与溅射激光之间的延时,可以获得溅射产生的中性粒子分布,此分布符合Maxwell-Boltzmann模型。在定量分析方面,本方法获得了准确的同位素比例。合金的实验结果表明,本技术在用于成分定量分析之前需要提前标定。本方法在同位素分析应用中具有潜在应用价值。

We reported our recent attempt to apply femtosecond laser as a post-ionization method for analyzing the neutral sputtering particles,combined with a time-of-flight mass spectrometer. In the experiment,a nanosecond pulsed laser,instead of the primary ion beam in common secondary ion mass spectrometry,was applied as a sputtering source,and a focused femtosecond pulsed laser was developed as a post-ionization method for ionizing the sputtering neutral species, while a homemade reflection time-of-flight mass spectrometer was used for analyzing the intensity distributions and speed distributions of corresponding ions.Our experiments illustrated that a large amount of sputtering species were neutral. More than 60 times enhancement of sputtering ions was achieved by using femtosecond post-ionization. By varying the delay time between the sputtering laser and the post-ionization femtosecond laser,the distributions of neutral sputtering species were obtained,which were in concordance with Maxwell-Boltzmann distribution model. Accurate isotope distributions were also obtained,which implied that this post-ionization method might be a potential and powerful tool in the areas of isotope analysis,for example,isotope geological age dating. Alloy sputtering experiments indicated that pre-calibration measurements should be done before this post-ionization method was used for the quantitative analysis of different elements. Secondary neutral mass spectrometry is a novel technique used to analyze the composition of solid surfaces and thin films by sputtering the surface of the specimen.