Brown H G, Shibata N, Sasaki H, Petersen T C, Paganin D M, Morgan M J, Findlay S D
School of Physics and Astronomy, Monash University, Victoria 3800, Australia.
Institute of Engineering Innovation, School of Engineering, University of Tokyo, Tokyo 113-8656, Japan.
Ultramicroscopy. 2017 Nov;182:169-178. doi: 10.1016/j.ultramic.2017.07.002. Epub 2017 Jul 3.
Electric field mapping using segmented detectors in the scanning transmission electron microscope has recently been achieved at the nanometre scale. However, converting these results to quantitative field measurements involves assumptions whose validity is unclear for thick specimens. We consider three approaches to quantitative reconstruction of the projected electric potential using segmented detectors: a segmented detector approximation to differential phase contrast and two variants on ptychographical reconstruction. Limitations to these approaches are also studied, particularly errors arising from detector segment size, inelastic scattering, and non-periodic boundary conditions. A simple calibration experiment is described which corrects the differential phase contrast reconstruction to give reliable quantitative results despite the finite detector segment size and the effects of plasmon scattering in thick specimens. A plasmon scattering correction to the segmented detector ptychography approaches is also given. Avoiding the imposition of periodic boundary conditions on the reconstructed projected electric potential leads to more realistic reconstructions.
最近在扫描透射电子显微镜中使用分段探测器实现了纳米尺度的电场映射。然而，将这些结果转换为定量场测量涉及一些假设，而这些假设对于厚样品的有效性尚不清楚。我们考虑了三种使用分段探测器进行投影电势定量重建的方法：微分相衬的分段探测器近似以及叠层成像重建的两种变体。还研究了这些方法的局限性，特别是探测器段尺寸、非弹性散射和非周期性边界条件引起的误差。描述了一个简单的校准实验，该校准实验校正了微分相衬重建，以给出可靠的定量结果，尽管探测器段尺寸有限且厚样品中存在等离子体散射的影响。还给出了对分段探测器叠层成像方法的等离子体散射校正。避免在重建的投影电势上施加周期性边界条件会导致更现实的重建。
