A series of monolayer protected gold nanoparticle colloidal solutions have been prepared with average sizes in the 2–15nm range. If a drop of such a colloidal suspension is deposited onto a Si3N4 substrate and the solvent allowed to evaporate, the particles have a tendency to self-assemble into monolayer rafts with varying degrees of structural order depending on the initial mono-dispersity of the particles. The thermal stability of these selfassembled gold nanoparticle rafts as a function of particle size, heating method, heating rate and ligand identity have been assessed in this study. In-situ TEM studies show that sub-8nm Au nanoparticles on Si3N4 have a tendency to coarsen upon slow heating, whereas those comprised of larger particles exhibit densification. Increasing the heating rate for the smaller particles promoted densification, forcing them to form highly interconnected string-like structures. Finally, rafts of sub-4nm alkanethiol protected Au nanoparticles are shown to sinter spontaneously under ambient conditions at room temperature on the timescale of several months. This unexpected effect may have important implications for the long term structural stability of any device constructed from sub-4nm gold nanoparticles.

中文翻译：

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金纳米颗粒阵列热稳定性的电子显微镜研究

一系列单层保护的金纳米颗粒胶体溶液已制备，平均尺寸在 2-15nm 范围内。如果将一滴这样的胶体悬浮液沉积在 Si3N4 基材上并让溶剂蒸发，则粒子有自组装成单层筏的趋势，根据粒子的初始单分散性而具有不同程度的结构顺序。本研究评估了这些自组装金纳米颗粒筏的热稳定性作为粒径、加热方法、加热速率和配体特性的函数。原位 TEM 研究表明，Si3N4 上的亚 8nm Au 纳米颗粒在缓慢加热时有变粗的趋势，而那些由较大颗粒组成的则表现出致密化。增加较小颗粒的加热速率促进了致密化，迫使它们形成高度互连的弦状结构。最后，大量亚 4nm 烷硫醇保护的 Au 纳米颗粒显示出在室温和环境条件下在几个月的时间尺度上自发烧结。这种意想不到的效果可能对由亚 4 纳米金纳米粒子构成的任何设备的长期结构稳定性产生重要影响。