Department of Physics and Astronomy, University of Missouri-St Louis, One University Boulevard, Center for Nanoscience, St Louis, MO 63121, USA.
Microsc Microanal. 2010 Aug;16(4):425-33. doi: 10.1017/S1431927610000450. Epub 2010 Jul 2.
The aberration-corrected scanning transmission electron microscope can provide information on nanostructures with sub-Angström image resolution. The relatively intuitive interpretation of high-angle annular dark-field (HAADF) imaging technique makes it a popular tool to image a variety of samples and finds broad applications to characterizing nanostructures, especially when combined with electron energy-loss spectroscopy and X-ray energy-dispersive spectroscopy techniques. To quantitatively interpret HAADF images, however, requires full understanding of the various types of signals that contribute to the HAADF image contrast. We have observed significant intensity enhancement in HAADF images, and large expansion of lattice spacings, of surface atoms of atomically flat ZnO surfaces. The surface-resonance channeling effect, one of the electron-beam channeling phenomena in crystalline nanostructures, was invoked to explain the observed image intensity enhancement. A better understanding of the effect of electron beam channeling along surfaces or interfaces on HAADF image contrast may have implications for quantifying HAADF images and may provide new routes to utilize the channeling phenomenon to study surface structures with sub-Angström spatial resolution.
经过像差校正的扫描透射电子显微镜可以提供亚埃分辨率的纳米结构信息。高角环形暗场（HAADF）成像技术相对直观的解释使其成为一种广泛应用于各种样品成像的工具，并在表征纳米结构方面有着广泛的应用，尤其是与电子能量损失谱和 X 射线能量色散谱技术相结合时。然而，要对 HAADF 图像进行定量解释，需要充分了解导致 HAADF 图像对比度的各种类型的信号。我们观察到原子级平坦 ZnO 表面的表面原子的 HAADF 图像中存在显著的强度增强和晶格间距的大幅扩展。表面共振沟道效应，即晶体纳米结构中电子束沟道现象之一，被用来解释观察到的图像强度增强。更好地理解电子束沿着表面或界面沟道对 HAADF 图像对比度的影响，可能对量化 HAADF 图像具有重要意义，并可能为利用沟道现象以亚埃空间分辨率研究表面结构提供新途径。
