Size‐Dependence of the Melting Temperature of Individual Au Nanoparticles

Abstract

Nanoparticles have an immense importance in various fields, such as medicine, catalysis, and various technological applications. Nanoparticles exhibit a significant depression in melting point as their size goes below ≈10 nm. However, nanoparticles are frequently used in high temperature applications such as catalysis where temperatures often exceed several 100 degrees which makes it interesting to study not only the melting temperature depression, but also how the melting progresses through the particle. Using high‐resolution transmission electron microscopy, the melting process of gold nanoparticles in the size range of 2–20 nm Au nanoparticles combined with molecular dynamics studies is investigated. A linear dependence of the melting temperature on the inverse particle size is confirmed; electron microscopy imaging reveals that the particles start melting at the surface and the liquid shell formed then rapidly expands to the particle core.

Reversible and concerted atom diffusion on supported gold nanoparticles

“…Initially, at a dose rate of 6.6 × 10 3 e − Å −2 s −1 , column (11) is empty and events are seen in columns (12) and (21), interrupted briefly by events in column (11) where it occasionally fills. Similar behavior is seen in the next two plots, as the dose rate is increased, until late in the plot, at 29 × 10 3 e − Å −2 s −1 , where columns (13), (22) and (31) are activated. Under irradiation at a high dose rate, activity is seen in most atomic columns, corresponding to significant dynamic roughening of the observed corner of the nanoparticle.…”

“…The static morphology of Au nanoparticles has been studied for decades under various conditions, e.g. different temperature [31], gas species [4] and pressures, especially after the commercial MEMS chips launched, at pressures up to ambient pressure [32] and temperatures approaching the melting point of the nanoparticles [31]. However, these works mainly focus on the equilibrium shape of the nanoparticles, isolated or supported on oxide.…”

“…When column (11) is absent, hopping of columns (21) and (12) may occur. In a similar way, column (21) or (12) must be absent for any activity to be seen in columns (31) and (13), respectively, and both must be absent for column (22) to show activity. This is caused by the lower binding energy of the under-coordinated corner atoms.…”

Transformations of supported gold nanoparticles observed by in situ electron microscopy

“…This melting/resolidification phenomenon is suggested to be a result of the nanoscale size of the particles [2], the adsorption of oxygen on the surface [3] and the interaction with the CeO2 support [4]. All of these factors can give rise to a depression of the melting point of the Au nanoparticles.…”

Transformations of Supported Gold Nanoparticles Observed by In Situ Electron Microscopy

“…The lifetime for Type II is shorter than that of Type I, which indicates a difference in energy of the two states. This melting/resolidification phenomenon is suggested to be a result of the nanoscale size of the particles [2], the adsorption of oxygen on the surface [3] and the interaction with the CeO2 support [4]. All of these factors can give rise to a depression of the melting point of the Au nanoparticles.…”