Exploring the role of grain boundaries on the melting behavior of multi-grain gold nanoparticles

Grain boundaries play a significant role in the mechanical and thermal properties of solid polycrystalline nanoparticles. However, both experimental and theoretical investigations of their structure and properties in a multi-grain system are challenging. Modeling of nanoparticles often considers single crystals with varying sizes, which is not representative of nanoparticles formed by chemical or physical processes.

In this work, we present an extensive study of the effect of grain boundaries on the thermal properties of gold polycrystalline nanoparticles ranging from 10 nm to 23 nm, carried out using molecular dynamics modeling. We compare the findings to the properties of single-grain particles of the same diameter. The grains are obtained using different viscinals of the (111) stacking of the Au FCC structure. To quantify the changes taking place as a function of temperature, atoms with low coordination numbers in grain boundaries and at the surface of the particles are identified. Vibrational density of states, internal energy distribution as well as the Lindemann index, were considered in the different regions of the nanostructure. Low coordination in the grain boundaries contributes to the first steps of melting at temperatures below that observed for single crystals.