Hirata K, Saitoh Y, Chiba A, Yamada K, Takahashi Y, Narumi K
National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.
Rev Sci Instrum. 2011 Mar;82(3):033101. doi: 10.1063/1.3541799.
We report suitable secondary ion (SI) counting for surface-sensitive chemical analysis of organic compounds using time-of-flight (TOF) SI mass spectroscopy, based on considerably higher emission yields of SIs induced by cluster ion impact ionization. A SI counting system for a TOF SI mass spectrometer was developed using a fast digital storage oscilloscope, which allows us to perform various types of analysis as all the signal pulses constituting TOF SI mass spectra can be recorded digitally in the system. Effects of the SI counting strategy on SI mass spectra were investigated for C(8) and C(60) cluster ion impacts on an organically contaminated silicon wafer and on polytetrafluoroethylene targets by comparing TOF SI mass spectra obtained from the same recorded signals with different SI counting procedures. Our results show that the use of a counting system, which can cope with high SI yields, is necessary for quantitative analysis of SI mass spectra obtained under high SI yield per impact conditions, including the case of cluster ion impacts on organic compounds.
我们报告了基于团簇离子碰撞电离诱导的二次离子（SI）发射产率显著提高，利用飞行时间（TOF）SI质谱对有机化合物进行表面敏感化学分析时合适的SI计数方法。使用快速数字存储示波器开发了一种用于TOF SI质谱仪的SI计数系统，该系统使我们能够进行各种类型的分析，因为构成TOF SI质谱的所有信号脉冲都可以在系统中进行数字记录。通过比较采用不同SI计数程序从相同记录信号获得的TOF SI质谱，研究了SI计数策略对SI质谱的影响，这些影响是针对C(8)和C(60)团簇离子对有机污染硅片和聚四氟乙烯靶材的碰撞而言的。我们的结果表明，对于在每次碰撞产生高SI产率条件下获得的SI质谱进行定量分析，包括团簇离子对有机化合物的碰撞情况，使用能够应对高SI产率的计数系统是必要的。
