Hyun Jerome K, Ercius Peter, Muller David A
Department of Physics, Cornell University, E13 Clark Hall, Ithaca, NY 14853, USA.
Ultramicroscopy. 2008 Dec;109(1):1-7. doi: 10.1016/j.ultramic.2008.07.003. Epub 2008 Jul 22.
Tomography using a scanning transmission electron microscope (STEM) offers intriguing possibilities for the three-dimensional imaging of micron-thick, biological specimens and assemblies of nanostructures, where the image resolution is potentially limited only by plural elastic scattering in the sample. A good understanding of the relationship between material thickness and spatial resolution is required, with particular emphasis on the competition between beam divergence (a geometrical effect from the converged STEM probe) and beam spreading (an unavoidable broadening due to plural elastic scattering). We show that beam divergence dominates beam spreading for typical embedding polymers beyond the 100-nm thickness range and that minimization of this effect leads to enhanced spatial resolution. The problems are more pronounced in spherical-aberration-corrected instruments where the depth of field is shorter.
使用扫描透射电子显微镜（STEM）进行断层扫描为微米厚的生物标本和纳米结构组件的三维成像提供了有趣的可能性，其中图像分辨率可能仅受样品中多次弹性散射的限制。需要充分理解材料厚度与空间分辨率之间的关系，尤其要关注束发散（会聚STEM探针产生的几何效应）和束展宽（多次弹性散射导致的不可避免的展宽）之间的竞争。我们表明，对于厚度超过100纳米的典型包埋聚合物，束发散主导着束展宽，并且将这种效应最小化会提高空间分辨率。在球差校正仪器中，景深较短，这些问题更为明显。
