Measurement of specimen thickness and composition in AlxGa1-xN/GaN using high-angle annular dark field images
Measurement of specimen thickness and composition in AlxGa1-xN/GaN using high-angle annular dark field images
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DOI：
10.1016/j.ultramic.2009.05.003
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发表时间：
2009-08-01
期刊：
影响因子：
2.2
通讯作者：
Lutgen, Stephan
中科院分区：
文献类型：
--
作者：
Rosenauer, Andreas;Gries, Katharina;Lutgen, Stephan
在使用高角度环形暗场探测器的扫描电子显微镜中，成像强度强烈地依赖于样品的厚度和成分。在本文中，我们证明了相对于入射电子束强度的图像强度的测量允许与模拟的图像强度直接比较，从而定量测量样品的厚度和成分。用冻结晶格和吸收势多切片方法进行了模拟。测量了探测器的径向不均匀性，并对其进行了考虑。利用聚焦离子束(FIB)制备的样品，我们首先证明了用这种方法获得的样品厚度与在FIB中用扫描电子显微镜直接测量片层厚度是非常一致的。在第二步中，我们应用这种方法来评估AlxGa1-xN/GaN层的成分。我们分别测量了未知区域和已知AI浓度x区域的图像强度比率。通过对样品厚度的估算和光强比的估算，可以定量测量样品的成分x。在高分辨率图像中，如果模拟图像与半宽为0.07 nm的高斯型图像卷积，则可以很好地描述图像的强度。(C)2009爱思唯尔B.V.保留所有权利。
In scanning transmission electron microscopy using a high-angle annular dark field detector, image intensity strongly depends on specimen thickness and composition. In this paper we show that measurement of image intensities relative to the intensity of the incoming electron beam allows direct comparison with simulated image intensities, and thus quantitative measurement of specimen thickness and composition. Simulations were carried out with the frozen lattice and absorptive potential multislice methods. The radial inhomogeneity of the detector was measured and taken into account. Using a focused ion beam (FIB) prepared specimen we first demonstrate that specimen thicknesses obtained in this way are in very good agreement with a direct measurement of the thickness of the lamella by scanning electron microscopy in the FIB. In the second step we apply this method to evaluate the composition of AlxGa1-xN/GaN layers. We measured ratios of image intensities obtained in regions with unknown and with known AI-concentration x, respectively. We show that estimation of the specimen thickness combined with evaluation of intensity ratios allows quantitative measurement of the composition x. In high-resolution images we find that the image intensity is well described by simulation if the simulated image is convoluted with a Gaussian with a half-width at half-maximum of 0.07 nm. (c) 2009 Elsevier B.V. All rights reserved.