Direct Imaging of Surface Melting on a Single Sn Nanoparticle

Despite previous studies, understanding the fundamentalmechanismof melting metal nanoparticles remains one of the major scientificchallenges of nanoscience. Herein, the kinetics of melting of a singleSn nanoparticle was investigated using in situ transmissionelectron microscopy heating techniques with a temperature step ofup to 0.5 & DEG;C. We revealed the surface premelting effect and assessedthe density of the surface overlayer on a tin particle of 47 nm sizeusing a synergetic combination of high-resolution scanning transmissionelectron microscopy imaging and low electron energy loss spectralimaging. Few-monolayer-thick disordered phase nucleated at the surfaceof the Sn particle at a temperature & SIM;25 & DEG;C below the meltingpoint and grew (up to a thickness of & SIM;4.5 nm) into the solidcore with increasing temperature until the whole particle became liquid.We revealed that the disordered overlayer was not liquid but quasi-liquidwith a density intermediate between that of solid and liquid Sn.

Automated summary

In this study, the melting kinetics of a single Sn nanoparticle was investigated using in situ transmission electron microscopy heating techniques. It was found that a few-monolayer-thick disordered phase nucleated at the surface of the Sn particle at a temperature 25°C below the melting point and grew into the solid core with increasing temperature until the whole particle became liquid. The disordered overlayer was revealed to be a quasi-liquid with a density intermediate between that of solid and liquid Sn.