Department of Physics, Arizona State University, Tempe, AZ 85281-1504, USA.
Micron. 2023 Aug;171:103482. doi: 10.1016/j.micron.2023.103482. Epub 2023 May 4.
Electron beam damage in transmission electron microscopy (TEM) is complicated because the damage phenomena can be the result of random atomic displacements or collective migrations. The former is categorized as the primary beam effects and the latter is the secondary beam effects. The mechanisms for these two distinguishing atomic processes of damage are different. The primary beam effects can be caused by the mechanisms of knock-on and/or radiolysis, while the secondary effects must be driven by a field that is induced by electron irradiation. One such field has been identified to be the electric field produced by the accumulated charges due to the ejection of secondary and Auger electrons from the irradiated region. One convincing example is the electron irradiation-induced domain switch in ferroelectric materials, in which the collective cation displacements are driven by the induced electric field. A detailed interpretation is given in this review. The sintering of metal NPs under electron irradiation is a secondary beam effect and is most likely also caused by the induced electric fields. The interactions between the charged NP and substrate, and between charged NPs, result in NP motion. Interchanging atoms between NPs during the sintering may also be driven by the electric fields. Although many beam-damage phenomena in C nanotubes and layered materials, such as graphene, BN, and transition metal dichalcogenides, are caused by the primary beam effects and have been well studied experimentally and theoretically in the literature, some phenomena from the secondary beam effects have also been identified in this review. These phenomena are sensitive to electron current density, the shape and orientation of the specimen, and even the illumination mode (i.e., TEM or STEM). Unfortunately, the mechanisms responsible for these phenomena still need to be clarified.
电子束在透射电子显微镜（TEM）中的损伤较为复杂，因为损伤现象可能是随机原子位移或集体迁移的结果。前者归为初级束效应，后者归为次级束效应。这两种有区别的原子损伤过程的机制是不同的。初级束效应可能是由碰撞和/或辐射分解机制引起的，而次级效应必须由电子辐照感应的场驱动。其中一个场已被确定为由于从辐照区域中射出的二次和俄歇电子而积累的电荷产生的电场。一个令人信服的例子是铁电材料中的电子辐照诱导畴开关，其中集体阳离子位移是由感应电场驱动的。在这篇综述中给出了详细的解释。金属 NPs 在电子辐照下的烧结是一种次级束效应，很可能也是由感应电场引起的。带电 NP 与衬底之间以及带电 NPs 之间的相互作用导致 NP 运动。在烧结过程中 NP 之间的原子交换也可能是由电场驱动的。虽然许多碳纳米管和层状材料（如石墨烯、BN 和过渡金属二卤化物）中的束损伤现象是由初级束效应引起的，并且在文献中已经进行了很好的实验和理论研究，但在这篇综述中也已经确定了一些由次级束效应引起的现象。这些现象对电子电流密度、样品的形状和取向甚至照明模式（即 TEM 或 STEM）敏感。不幸的是，这些现象的机制仍需要阐明。
