Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton NY 11973, USA.
Ultramicroscopy. 2012 Dec;123:66-73. doi: 10.1016/j.ultramic.2012.06.008. Epub 2012 Jul 4.
It has been demonstrated recently that an atomic resolution secondary electron (SE) image can be achieved with a scanning transmission electron microscope (STEM) equipped with a probe-aberration corrector. Its high sensitivity to the surface structure provides a powerful tool to simultaneously study both surface and bulk structure in the STEM, in the combination with the annular dark field (ADF) image. To quantitatively explain the atomic resolution SE image and retrieve surface-structure information, an image simulation is required. Here, we develop a method to simultaneously calculate, for the first time, the atomic resolution SE and ADF-STEM images, based on the multislice method with a frozen-phonon approximation. An object function for secondary electrons, derived from the inelastic scattering, is used to calculate the intensity distribution of the secondary electrons emitted from each slice. The simulations show that the SE image contrast is sensitive to the surface structure and the electron inelastic mean free path, but insensitive to specimen thickness when the thickness is more than 5 nm. The simulated SE images for SrTiO(3) crystal show good agreement with the experimental observations.
最近已经证明，配备有探针像差校正器的扫描透射电子显微镜（STEM）可以实现原子分辨率的二次电子（SE）图像。它对表面结构的高灵敏度提供了一种强大的工具，可与环形暗场（ADF）图像结合使用，在 STEM 中同时研究表面和体结构。为了定量解释原子分辨率的 SE 图像并获取表面结构信息，需要进行图像模拟。在这里，我们首次开发了一种基于多片方法和冻结声子近似的方法，同时计算原子分辨率的 SE 和 ADF-STEM 图像的方法。从非弹性散射中得出的二次电子的目标函数用于计算从每个切片发射的二次电子的强度分布。模拟表明，SE 图像对比度对表面结构和电子非弹性平均自由程敏感，但当厚度超过 5nm 时对样品厚度不敏感。SrTiO(3)晶体的模拟 SE 图像与实验观察结果吻合良好。
