Image formation in the scanning transmission electron microscope using object-conjugate detectors.

IF 1.8 4区材料科学

Acta Crystallographica Section A Pub Date : 2012-03-01 Epub Date: 2012-01-12 DOI:10.1107/S0108767311051592

C Dwyer, S Lazar, L Y Chang, J Etheridge

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引用次数: 4

Abstract

This work presents a theoretical analysis of image formation in a scanning transmission electron microscope equipped with electron detectors in a plane conjugate to the specimen. This optical geometry encompasses both the three-dimensional imaging technique of scanning confocal electron microscopy (SCEM) and a recently developed atomic resolution imaging technique coined real-space scanning transmission electron microscopy (R-STEM). Image formation in this geometry is considered from the viewpoints of both wave optics and geometric optics, and the validity of the latter is analysed by means of Wigner distributions. Relevant conditions for the validity of a geometric interpretation of image formation are provided. For R-STEM, where a large detector is used, it is demonstrated that a geometric optics description of image formation provides an accurate approximation to wave optics, and that this description offers distinct advantages for interpretation and numerical implementation. The resulting description of R-STEM is also demonstrated to be in good agreement with experiment. For SCEM, it is emphasized that a geometric optics description of image formation is valid provided that higher-order aberrations can be ignored and the detector size is large enough to average out diffraction from the angle-limiting aperture.

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用物体共轭检测器在扫描透射电子显微镜中成像。

这项工作提出了一个理论分析的图像形成在扫描透射电子显微镜配备电子探测器在一个平面共轭到试样。这种光学几何结构包括扫描共聚焦电子显微镜(SCEM)的三维成像技术和最近开发的原子分辨率成像技术，即实空间扫描透射电子显微镜(R-STEM)。从波动光学和几何光学的角度考虑了这种几何结构的成像，并利用维格纳分布分析了几何光学的有效性。提供了图像形成几何解释有效性的相关条件。对于使用大型探测器的R-STEM，证明了图像形成的几何光学描述提供了波光学的精确近似，并且这种描述为解释和数值实现提供了明显的优势。结果表明，R-STEM的描述与实验结果吻合较好。对于SCEM，强调了当高阶像差可以忽略并且探测器尺寸足够大以平均来自限角孔径的衍射时，图像形成的几何光学描述是有效的。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Acta Crystallographica Section A 化学-晶体学

自引率

11.10%

发文量

审稿时长

3 months

期刊介绍： Acta Crystallographica Section A: Foundations and Advances publishes articles reporting advances in the theory and practice of all areas of crystallography in the broadest sense. As well as traditional crystallography, this includes nanocrystals, metacrystals, amorphous materials, quasicrystals, synchrotron and XFEL studies, coherent scattering, diffraction imaging, time-resolved studies and the structure of strain and defects in materials. The journal has two parts, a rapid-publication Advances section and the traditional Foundations section. Articles for the Advances section are of particularly high value and impact. They receive expedited treatment and may be highlighted by an accompanying scientific commentary article and a press release. Further details are given in the November 2013 Editorial. The central themes of the journal are, on the one hand, experimental and theoretical studies of the properties and arrangements of atoms, ions and molecules in condensed matter, periodic, quasiperiodic or amorphous, ideal or real, and, on the other, the theoretical and experimental aspects of the various methods to determine these properties and arrangements.