Takeguchi Masaki, Takei Toshiaki, Mitsuishi Kazutaka
National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan.
Nanomaterials (Basel). 2023 Jul 26;13(15):2170. doi: 10.3390/nano13152170.
The structural change in Pt networks composed of multiple chain connections among grains was observed in air at 1 atm using atomic-resolution environmental cell scanning transmission electron microscopy. An aberration-corrected incident electron probe with a wide convergence angle made it possible to increase the depth resolution that contributes to enhancing the signal-to-noise ratio of Pt network samples in air in an environmental cell, resulting in the achievement of atomic-resolution imaging. The exposure of the Pt networks to gas molecules under Brownian motion, stimulated by electron beams in the air, increases the collision probability between gas molecules and Pt networks, and the Pt networks are more intensely stressed from all directions than in a situation without electron irradiation. By increasing the electron beam dose rate, the structural change of the Pt networks became significant. Dynamic observation on an atomic scale suggested that the structural change of the networks was not attributed to the surface atomic-diffusion-induced step motion but mainly caused by the movement and deformation of unstable grains and grain boundaries. The oxidized surface layers may be one of the factors hindering the surface atomic step motion, mitigating the change in the size of the grains and grain boundaries.
使用原子分辨率环境池扫描透射电子显微镜在1个大气压的空气中观察了由晶粒间多个链连接组成的铂网络的结构变化。具有宽会聚角的像差校正入射电子探针能够提高深度分辨率，这有助于提高环境池中空气中铂网络样品的信噪比，从而实现原子分辨率成像。在空气中，电子束激发下处于布朗运动的气体分子与铂网络接触，增加了气体分子与铂网络之间的碰撞概率，与无电子辐照的情况相比，铂网络受到来自各个方向的更强应力。通过提高电子束剂量率，铂网络的结构变化变得显著。原子尺度的动态观察表明，网络的结构变化并非归因于表面原子扩散引起的台阶运动，而是主要由不稳定晶粒和晶界的移动和变形引起的。氧化表面层可能是阻碍表面原子台阶运动、减轻晶粒和晶界尺寸变化的因素之一。
