Klenov Dmitri O, Stemmer Susanne
Materials Department, University of California, Santa Barbara, CA 93106-5050, USA.
Ultramicroscopy. 2006 Aug-Sep;106(10):889-901. doi: 10.1016/j.ultramic.2006.03.007. Epub 2006 Apr 25.
This paper reports on a study of the contributions to the image contrast of high-angle annular dark field (HAADF) images acquired in scanning transmission electron microscopy. Experimental HAADF images were obtained from a model system consisting of an epitaxial perovskite PbTiO3 film grown on a SrTiO3 single crystal. This sample allowed for the study of the intensities of a wide range of atomic numbers. The main objective of the paper was to quantify the influence of TEM foil thickness on the image contrast, but the effects of the annular detector inner angle and the probe forming lens focus were also studied. Sample thicknesses ranging from approximately 10 nm to more than 400 nm were investigated. The image contrast was relatively insensitive to changes in inner angle. The main impact of sample thickness was a rapid increase in a background intensity that contributed equally to the intensities of the atomic columns and the channels between them. The background intensity and its increase with thickness reflected the average atomic number of the crystal. Subtraction of the background intensity allowed for a quantitative interpretation of image contrast in terms of atomic numbers and comparison with multislice image simulations. The consequences for the analysis of interfaces in terms of atom column occupancies are discussed.
本文报道了一项关于扫描透射电子显微镜中高角度环形暗场（HAADF）图像的图像对比度贡献的研究。实验性的HAADF图像是从一个由生长在SrTiO3单晶上的外延钙钛矿PbTiO3薄膜组成的模型系统中获得的。该样品可用于研究广泛原子序数的强度。本文的主要目的是量化透射电子显微镜箔片厚度对图像对比度的影响，但也研究了环形探测器内角和探针形成透镜焦点的影响。研究了从约10纳米到超过400纳米的样品厚度。图像对比度对内角变化相对不敏感。样品厚度的主要影响是背景强度迅速增加，这对原子列及其之间通道的强度贡献相同。背景强度及其随厚度的增加反映了晶体的平均原子序数。减去背景强度后，可以根据原子序数对图像对比度进行定量解释，并与多层图像模拟进行比较。讨论了根据原子列占有率分析界面的结果。
