Correlation between the Melting Point of a Nanosolid and the Cohesive Energy of a Surface Atom

Size-Dependent Formation Enthalpy of Nanocompounds

A quantitative thermodynamic model for the size-dependent formation enthalpy of nanocompounds is proposed. The model reveals that the thermal stability of nanocompounds decreases because of the size dependence of formation enthalpy when the size of these nanostructures decreases. This stability loss is related to some general phenomena such as interface alloying of immiscible systems and phase segregation of miscible systems with reducing system sizes. The predictions from the model are in agreement with the results from density function theory calculation for MgH2, the experimental measurement of SnTe nanoparticles, and quantum chemistry consideration.

Surface Diffusion and Coalescence of Mobile Metal Nanoparticles

The diffusion and coalescence of metal nanoparticles play important roles in many phenomena. Here, we offer a new integrated overview of the main factors that control the nanoparticle coalescence process. Three factors are considered in our description of the coalescence process: nanoparticle diffusion across the surface, their physical and thermodynamic properties, and the mechanism of coalescence. We demonstrate that the liquid-like properties of the surface layers of the nanoparticles play an essential role in this process. We present experimental evidence for our opinion, based on the high-resolution electron microscopic analysis of several different types of nanoparticles.

Impact of Bond Order Loss on Surface and Nanosolid Mechanics

An analytical solution shows that a competition between bond order loss and the associated bond strength gain of the lower coordinated atoms near the edge of a surface dictates the mechanics of the surface and, hence, a nanosolid. Bond order loss lowers the activation energy for atomic dislocation, whereas bond strength gain enhances the energy density or mechanical strength in the region near the surface. Therefore, the surface is harder than the bulk interior at temperatures far below the melting point (T(m)), and the surface becomes softer at temperatures close to the surface T(m) that drops because of bond order loss. Matching predictions to measurements reveals that a transition happens to the Hall-Petch relationship for a nanosolid when the effect of bond order loss becomes dominant, and the critical size of the Hall-Petch transition depends intrinsically on the bond nature of the specimen and the ratio of T/T(m), where T is the temperature of operation.