Malac Marek, Beleggia Marco, Taniguchi Yoshifumi, Egerton Ray F, Zhu Yimei
National Institute for Nanotechnology, 11421 Saskatachewan Drive, Edmonton AB, Canada T6G 2M9.
Ultramicroscopy. 2008 Dec;109(1):14-21. doi: 10.1016/j.ultramic.2008.07.004. Epub 2008 Jul 23.
We evaluate the low-dose performance of parallel nano-beam diffraction (NBD) in the transmission electron microscope as a method for characterizing radiation sensitive materials at low electron irradiation dose. A criterion, analogous to Rose's, is established for detecting a diffraction spot with desired signal-to-noise ratio. Our experimental data show that a dose substantially lower than in high-resolution bright-field imaging is sufficient to determine structure and orientation of individual nanoscale objects embedded in amorphous matrix. In an instrument equipped with a cold field-emission gun it is possible to form a probe with sub-3 nm diameter and sub-0.3 mrad convergence angle with sufficient beam current to record a diffraction pattern with less than 0.2 s acquisition time. The interpretation of NBD patterns is identical to that of selected area diffraction patterns. We illustrate the physical principles underlying good low-dose performance of NBD by means of a phase grating. The electron irradiation dose needed to detect a diffraction peak in NBD is found proportional to 1/N2, where N is the number of lattice planes contributing to the peak.
我们评估了透射电子显微镜中平行纳米束衍射（NBD）的低剂量性能，将其作为一种在低电子辐照剂量下表征辐射敏感材料的方法。建立了一个类似于罗斯准则的标准，用于检测具有所需信噪比的衍射斑点。我们的实验数据表明，与高分辨率明场成像相比，低得多的剂量就足以确定嵌入非晶基质中的单个纳米级物体的结构和取向。在配备冷场发射枪的仪器中，有可能形成直径小于3 nm、会聚角小于0.3 mrad的探针，并具有足够的束流，以在小于0.2 s的采集时间内记录衍射图样。NBD图样与选区衍射图样的解释相同。我们通过相位光栅说明了NBD良好低剂量性能背后的物理原理。发现检测NBD中衍射峰所需的电子辐照剂量与1/N²成正比，其中N是对该峰有贡献的晶格平面数。
