Understanding the growth mechanism of noble metal nanocrystals during solution synthesis is of significant importance for shape and property control. However, much remains unknown about the growth pathways of metal nanoparticles due to the lack of direct observation. Using an in situ transmission electron microscopy technique, we directly observed Ag nanocube and nanobar growth in an aqueous solution through both classical monomer-by-monomer addition and nonclassical particle attachment processes. During the particle attachment process, Ag nanocubes and nanobars were formed via both oriented and nonoriented attachment. Our calculations, along with the dynamics of the observed attachment, showed that the van der Waals force overcomes hydrodynamic and friction forces and drives the particles toward each other at separations of 10–100 nm in our experiments. During classical growth, anisotropic growth was also revealed, and the resulting unsymmetrical shape constituted an intermediate state for Ag nanocube growth. We hypothesized that the temporary symmetry breaking resulted from different growth rates on (001) surfaces due to a local surface concentration variation caused by the imbalance between the consumption of Ag⁺ near the surface and the diffusion of Ag⁺ from the bulk to the surface.

中文翻译：

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通过各向异性单体加成和颗粒附着过程的银纳米立方体和纳米棒生长

在溶液合成过程中，了解贵金属纳米晶体的生长机理对于形状和性能控制非常重要。然而，由于缺乏直接观察，关于金属纳米颗粒的生长途径仍然未知。使用原位透射电子显微镜技术，我们通过经典的逐单体添加和非经典的粒子附着过程，直接观察到了Ag纳米立方体和纳米棒在水溶液中的生长。在粒子附着过程中，Ag纳米立方体和纳米棒通过定向和非定向附着形成。我们的计算，以及观察到的附件的动态，结果表明，范德华力克服了流体动力和摩擦力，并在我们的实验中以10–100 nm的间隔将粒子彼此逼近。在经典生长过程中，还显示出各向异性生长，并且所得的不对称形状构成了Ag纳米立方体生长的中间状态。我们假设暂时的对称性破坏是由于（001）表面上不同的生长速率所致，这是由于银的消耗之间的不平衡所引起的局部表面浓度变化所致⁺在表面附近⁺和Ag ⁺从块体到表面的扩散。