基于软X射线谱学显微双能衬度图像的元素空间分布研究

上海光源软X射线谱学显微实验站(BL08U)可实现30nm空间分辨的元素探测功能.实验中,对样品内要标识元素的吸收边附近两个能量(E1和E2,且E1E2)分别进行扫描成像,然后将这两幅吸收图上对应像素点的光密度相比,得到的相比双能衬度图像可有效地显示该元素的空间分布信息.相对于另一种常用的相减双能衬度图像分析法,这种方法对元素空间分布的显示更为灵敏、精确,判断空间点是否含有要标识元素的阈值的定义更为简单,物理意义更为清晰.通过对聚丙烯腈预氧化纤维截面氧元素分布的测量结果的分析计算,比较了这两种分析方法的差异,验证了相比双能衬度法的有效性.该方法为快速标识样品中的微量元素提供了一种很好的新型分析手段.

Soft X-ray spectromicroscopy dual-energy contrast image for element spatial distribution analysis

The detection of chemical speciation with spatial resolution of 30 nm has been implemented at BL08U soft X-ray spectromicroscopy endstation of Shanghai Synchrotron Radiation Facility. For each specimen, we scan two absorption images separately at two energies E₁ and E₂ near the absorption edge of the element with E₁>E₂. After calculating the signal ratio of each pair of the corresponding pixels’ optical density in the two absorption images, we can obtain the map of the spatial distribution of that element. Compared with the conventional analysis method of K-edge subtraction (KES), our ratio analysis method is more sensitive and accurate in identifying the spatial distribution of the interested elements, and the definition of the contrast threshold determining whether a pixel contains the interested element, is simpler and clearer in physics. Through the analysis and calculation of the spatial distributions of the oxygen element on a pre-oxidized polyacrylonitrile fiber cross-section, we can verify the effectiveness of the ratio analysis method compared to the traditional KES method. This ratio method provides a new analysis tool for fast mapping the distribution of trace elements.