Local sample thickness determination via scanning transmission electron microscopy defocus series
Local sample thickness determination via scanning transmission electron microscopy defocus series
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DOI：
10.1111/jmi.12284
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发表时间：
2016-05-01
影响因子：
2
通讯作者：
Volz, K.
中科院分区：
文献类型：
--
作者：
Beyer, A.;Straubinger, R.;Volz, K.
在过去的十年中，由于引入了像差校正，(扫描)透射电子显微镜(S)的可用孔径显著增大。随着会聚角的增大，焦深急剧减小，STEM中的光学切片成为可能。在这里，我们应用STEM散焦级数来推导出瞬变电磁样品的局部样品厚度。为此，获得了实验和模拟离焦系列的薄硅箔。高分辨率高角度环形暗场图像的系统模糊是通过评估散焦系列中每个图像的图像强度的标准差来量化的。导出的相关性在最佳散焦处表现出明显的最大值，并且对于较高或较低的值下降到背景值。曲线的全宽半高(FWHM)等于样品厚度大于由所用孔径的大小和显微镜的色差给出的最小厚度。用该方法得到的实验散焦序列的厚度与由其他方法得到的值符合得很好。与其他方法相比，这种方法的主要优点是空间分辨率高，而且不涉及任何耗时的模拟。
The usable aperture sizes in (scanning) transmission electron microscopy ((S)TEM) have significantly increased in the past decade due to the introduction of aberration correction. In parallel with the consequent increase of convergence angle the depth of focus has decreased severely and optical sectioning in the STEM became feasible. Here we apply STEM defocus series to derive the local sample thickness of a TEM sample. To this end experimental as well as simulated defocus series of thin Si foils were acquired. The systematic blurring of high resolution high angle annular dark field images is quantified by evaluating the standard deviation of the image intensity for each image of a defocus series. The derived dependencies exhibit a pronounced maximum at the optimum defocus and drop to a background value for higher or lower values. The full width half maximum (FWHM) of the curve is equal to the sample thickness above a minimum thickness given by the size of the used aperture and the chromatic aberration of the microscope. The thicknesses obtained from experimental defocus series applying the proposed method are in good agreement with the values derived from other established methods. The key advantages of this method compared to others are its high spatial resolution and that it does not involve any time consuming simulations.