Enhancing Ion Yields in Time-of-Flight-Secondary Ion Mass Spectrometry: A Comparative Study of Argon and Water Cluster Primary Beams
Enhancing Ion Yields in Time-of-Flight-Secondary Ion Mass Spectrometry: A Comparative Study of Argon and Water Cluster Primary Beams
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DOI：
10.1021/ac504191m
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发表时间：
2015-02-17
影响因子：
7.4
通讯作者：
Vickerman, John C.
中科院分区：
文献类型：
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作者：
Rabbani, Sadia Sheraz Nee;Razo, Irma Berrueta;Vickerman, John C.
继我们以前的信中关于这个问题，这篇文章报道了一个详细的研究飞行时间二次离子质谱（TOF-SIMS）正离子光谱产生的一组模型生物化合物（精氨酸，海藻糖，DPPC，血管紧张素II）的水簇初级离子束相比，氩簇束在一系列的簇大小和能量。使用氩和水束对精氨酸和Irganox 1010的溅射产率研究已经证实，使用水团簇束的溅射产率位于Seah为氩团簇束导出的相同的通用溅射曲线上。因此，使用水团簇束的增加的离子产率必须由增加的电离产生。本文报道了用团簇束在1000 ~ 10000、能量5-20 keV范围内观测到的谱线和正离子信号。它被证实，水团簇束增强质子相关的电离对氩束到一个显着的程度，使增强的检测灵敏度从1 μ m（2）在该地区的100至1000倍，相对于静态西姆斯分析与Ar-2000团簇束似乎是可访问的。这些新的研究表明，电离增强现象有一个意想不到的复杂性。而氩团簇轰击下的最佳离子产额出现在E/n >= 10 eV的区域（其中E是束流能量，n是团簇中氩原子的数目），并且当E/n < 10 eV时迅速下降;对于水簇射束，离子产额在此E/n范围内显著增加（其中n是团簇中水分子的数量）和峰值为20 keV的光束在团簇尺寸为7 000或E/n类似于3 eV。这一重要的结果进一步探讨使用D2 O团束，确认在这个低E/n制度质子化在很大程度上源于水分子。结果本身令人鼓舞，表明对于氩和水团簇束，更高能量的束，例如，40和80 keV，将使更大的集群大小被利用，具有显著的好处，离子产率，因此分析能力。
Following from our previous Letter on this topic, this Article reports a detailed study of time-of-flight-secondary ion mass spectrometry (TOF-SIMS) positive ion spectra generated from a set of model biocompounds (arginine, trehalose, DPPC, and angiotensin II) by water cluster primary ion beams in comparison to argon cluster beams over a range of cluster sizes and energies. Sputter yield studies using argon and water beams on arginine and Irganox 1010 have confirmed that the sputter yields using water cluster beams lie on the same universal sputtering curve derived by Seah for argon cluster beams. Thus, increased ion yield using water cluster beams must arise from increased ionization. The spectra and positive ion signals observed using cluster beams in the size range from 1000 to 10 000 and the energy range 5-20 keV are reported. It is confirmed that water cluster beams enhance proton related ionization over against argon beams to a significant degree such that enhanced detection sensitivities from 1 mu m(2) in the region of 100 to 1000 times relative to static SIMS analysis with Ar-2000 cluster beams appear to be accessible. These new studies show that there is an unexpected complexity in the ionization enhancement phenomenon. Whereas optimum ion yields under argon cluster bombardment occur in the region of E/n >= 10 eV (where E is the beam energy and n the number of argon atoms in the cluster) and fall rapidly when E/n < 10 eV; for water cluster beams, ion yields increase significantly in this E/n regime (where n is the number of water molecules in the cluster) and peak for 20 keV beams at a cluster size of 7 000 or E/n similar to 3 eV. This important result is explored further using D2O cluster beams that confirm that in this low E/n regime protonation does originate to a large extent from the water molecules. The results, encouraging in themselves, suggest that for both argon and water cluster beams, higher energy beams, e.g., 40 and 80 keV, would enable larger cluster sizes to be exploited with significant benefit for ion yield and hence analytical capability.