Yu Z, Muller D A, Silcox J
Physics Department, Cornell University, Ithaca, NY 14853, USA.
Ultramicroscopy. 2008 Apr;108(5):494-501. doi: 10.1016/j.ultramic.2007.08.007. Epub 2007 Aug 14.
Annular dark field scanning transmission electron microscopy (ADF-STEM) imaging of a crystal depends strongly on specimen orientation, but for an amorphous sample it is insensitive to orientation changes. To fully investigate the effects of specimen tilt, an interface of amorphous Si (a-Si) and crystalline Si (c-Si) was rotated systematically off a zone axis in a STEM equipped with low-angle ADF (LAADF) and high-angle ADF (HAADF) detectors. The change of relative intensity across the interface shows very different trends in the LAADF and the HAADF images upon tilting. More importantly, it is found that the HAADF signal decreases much more rapidly when tilted off a zone axis than does the LAADF signal. The high-resolution lattice fringes also disappear much faster in the HAADF image than in the LAADF image. These trends reflect the fact that the channeling peaks that are responsible for scattering into the HAADF detector decrease more quickly upon tilting than the lower angle scattering to the LAADF detector does.
晶体的环形暗场扫描透射电子显微镜（ADF-STEM）成像强烈依赖于样品取向，但对于非晶样品，它对取向变化不敏感。为了全面研究样品倾斜的影响，在配备低角度ADF（LAADF）和高角度ADF（HAADF）探测器的STEM中，将非晶硅（a-Si）和晶体硅（c-Si）的界面系统地从晶带轴旋转离开。倾斜时，界面上相对强度的变化在LAADF和HAADF图像中显示出非常不同的趋势。更重要的是，发现从晶带轴倾斜时，HAADF信号比LAADF信号下降得更快。高分辨率晶格条纹在HAADF图像中也比在LAADF图像中消失得更快。这些趋势反映了这样一个事实，即导致散射到HAADF探测器中的沟道峰在倾斜时比散射到LAADF探测器的低角度散射下降得更快。
