Müller Knut, Krause Florian F, Béché Armand, Schowalter Marco, Galioit Vincent, Löffler Stefan, Verbeeck Johan, Zweck Josef, Schattschneider Peter, Rosenauer Andreas
1] Institut für Festkörperphysik, Universität Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany [2] Center of Excellence for Materials and Processes, Universität Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany.
EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
Nat Commun. 2014 Dec 15;5:5653. doi: 10.1038/ncomms6653.
By focusing electrons on probes with a diameter of 50 pm, aberration-corrected scanning transmission electron microscopy (STEM) is currently crossing the border to probing subatomic details. A major challenge is the measurement of atomic electric fields using differential phase contrast (DPC) microscopy, traditionally exploiting the concept of a field-induced shift of diffraction patterns. Here we present a simplified quantum theoretical interpretation of DPC. This enables us to calculate the momentum transferred to the STEM probe from diffracted intensities recorded on a pixel array instead of conventional segmented bright-field detectors. The methodical development yielding atomic electric field, charge and electron density is performed using simulations for binary GaN as an ideal model system. We then present a detailed experimental study of SrTiO3 yielding atomic electric fields, validated by comprehensive simulations. With this interpretation and upgraded instrumentation, STEM is capable of quantifying atomic electric fields and high-contrast imaging of light atoms.
通过将电子聚焦在直径为50皮米的探针上，像差校正扫描透射电子显微镜（STEM）目前正跨越界限，探索亚原子细节。一个主要挑战是使用差分相衬（DPC）显微镜测量原子电场，传统上利用衍射图样的场致位移概念。在此，我们给出了DPC的一种简化量子理论解释。这使我们能够根据在像素阵列上记录的衍射强度，而非传统的分段明场探测器，计算传递到STEM探针的动量。利用二元GaN作为理想模型系统进行模拟，完成了产生原子电场、电荷和电子密度的方法开发。然后，我们给出了对SrTiO₃产生原子电场的详细实验研究，并通过全面模拟进行了验证。通过这种解释和升级的仪器设备，STEM能够量化原子电场并对轻原子进行高对比度成像。
