NanoSIMS Imaging of D/H Ratios on FIB Sections
NanoSIMS Imaging of D/H Ratios on FIB Sections
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DOI：
10.1021/acs.analchem.9b03134
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发表时间：
2019-11-05
影响因子：
7.4
通讯作者：
Khodja, Hicham
中科院分区：
文献类型：
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作者：
Levy, Dan;Aleon, Jerome;Khodja, Hicham
为了将纳米级二次离子质谱仪(NanoSIMS)对微米级颗粒的同位素成像与其他纳米级成像技术(如透射电子显微镜)相结合，发展了聚焦离子束(FIB)切片制备的弱水化矿物的D/H比成像。为了最大限度地提高微米级D/H比值的准确度、灵敏度、精密度和重现性，同时将表面污染降到最低，我们探索了所有已知影响现场D/H比值测量的仪器参数。最佳条件是使用(I)Cs+离子源和在低质量分辨率下检测H-和D-，(Ii)初级束流强度为100pa，(Iii)栅格尺寸在8-15微米范围内。在这些条件下，使用名义上的无水矿物来评估检测下限，并表明表面污染水平接近200ppm当量水。由于这里使用了较高的一次强度，因此驻留时间不像以前的研究中发现的那样是一个重要的参数，并且在分析过程中使用了1ms/px的驻留时间来最大限度地减少动态污染。对FIB切片的分析发现，由于样品制备，大大减少了静态污染，并且与使用不仅嵌入在环氧树脂中而且也嵌入在铟中的抛光切片相比，提高了准确性。在角闪石上，包括再现性在内的典型总体不确定度在散装FIB切片上类似于千分之20，在使用图像处理(1西格玛)的1.5亩尺度上类似于千分之50。
The D/H ratio imaging of weakly hydrated minerals prepared as focused ion beam (FIB) sections is developed in order to combine isotopic imaging by nanoscale secondary ion mass spectrometry (NanoSIMS) of micrometer-sized grains with other nanoscale imaging techniques, such as transmission electron microscopy. In order to maximize the accuracy, sensitivity, precision, and reproducibility of D/H ratios at the micrometer size, while minimizing the surface contamination at the same time, we explored all instrumental parameters known to influence the measurement of D/H ratios in situ. Optimal conditions were found to be obtained with the use of (i) a Cs+ ion source and detection of H- and D- at low mass resolving power, (ii) a primary beam intensity of 100 pA, and (iii) raster sizes in the range of 8-15 mu m. Nominally anhydrous minerals were used to evaluate the detection limits and indicate a surface contamination level of similar to 200 ppm equivalent H2O under these conditions. With the high primary intensity used here, the dwell time is not a parameter as critical as found in previous studies and a dwell time of 1 ms/px is used to minimize dynamic contamination during analysis. Analysis of FIB sections was found to reduce significantly static contamination due to sample preparation and improved accuracy compared to using polished sections embedded not only in epoxy but in indium as well. On amphiboles, the typical overall uncertainty including reproducibility is similar to 20 parts per thousand on bulk FIB sections and similar to 50 parts per thousand at the 1.5 mu m scale using image processing (1 sigma).