Asano Natsuko, Lu Jinfeng, Asahina Shunsuke, Takami Seiichi
EP Business Unit, EP Application Department, SEM Team, JEOL Ltd., 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan.
Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.
Nanomaterials (Basel). 2021 Apr 2;11(4):908. doi: 10.3390/nano11040908.
Metal oxide nanocrystals have garnered significant attention owing to their unique properties, including luminescence, ferroelectricity, and catalytic activity. Among the various synthetic methods, hydrothermal synthesis is a promising method for synthesizing metal oxide nanocrystals and nanoclusters. Because the shape and surface structure of the nanocrystals largely affect their properties, their analytical methods should be developed. Further, the arrangement of nanocrystals should be studied because the properties of nanoclusters largely depend on the arrangement of the primary nanocrystals. However, the analysis of nanocrystals and nanoclusters remains difficult because of their sizes. Conventionally, transmission electron microscopy (TEM) is widely used to study materials in nanoscale. However, TEM images are obtained as the projection of three-dimensional structures, and it is difficult to observe the surface structures and the arrangement of nanocrystals using TEM. On the other hand, scanning electron microscopy (SEM) relies on the signals from the surface of the samples. Therefore, SEM can visualize the surface structures of samples. Previously, the spatial resolution of SEM was not enough to observe nanoparticles and nanomaterials with sizes of between 10 and 50 nm. However, recent developments, including the low-landing electron-energy method, improved the spatial resolution of SEM, which allows us to observe fine details of the nanocluster surface directory. Additionally, improved detectors allow us to visualize the elemental mapping of materials even at low voltage with high solid angle. Further, the use of a liquid sample holder even enabled the observation of nanocrystals in water. In this paper, we discuss the development of SEM and related observation technologies through the observation of hydrothermally prepared nanocrystals and nanoclusters.
金属氧化物纳米晶体因其独特的性质，包括发光、铁电性和催化活性，而备受关注。在各种合成方法中，水热合成是一种很有前景的合成金属氧化物纳米晶体和纳米团簇的方法。由于纳米晶体的形状和表面结构在很大程度上影响其性质，因此应开发相应的分析方法。此外，由于纳米团簇的性质很大程度上取决于初级纳米晶体的排列方式，所以还应研究纳米晶体的排列情况。然而，由于纳米晶体和纳米团簇的尺寸较小，对它们的分析仍然具有挑战性。传统上，透射电子显微镜（TEM）被广泛用于研究纳米尺度的材料。然而，TEM图像是三维结构的投影，使用TEM很难观察到纳米晶体的表面结构和排列情况。另一方面，扫描电子显微镜（SEM）依赖于样品表面的信号。因此，SEM可以可视化样品的表面结构。以前，SEM的空间分辨率不足以观察尺寸在10到50纳米之间的纳米颗粒和纳米材料。然而，包括低着陆电子能量法在内的最新进展提高了SEM的空间分辨率，使我们能够观察到纳米团簇表面目录的精细细节。此外，改进后的探测器使我们即使在低电压、高立体角的情况下也能可视化材料的元素映射。此外，使用液体样品架甚至能够观察水中的纳米晶体。在本文中，我们通过对水热制备的纳米晶体和纳米团簇的观察，讨论了SEM及相关观察技术的发展。
