The effect of heating rate on the sintering of aluminum nanospheres.

Molecular dynamics simulations have been performed to study the influence of five different heating rates on the sintering of aluminum nanoparticles with a diameter of 4-10 nm, mainly by exploring the atomic migration, radial distribution function (RDF), atomic average displacement, mean square displacement (MSD), radius ratio (i.e., the ratio of the neck radius to the particle radius), shrinkage rate, radius of gyration, sintering temperature and melting point. It is found that the displacement of surface atoms is always larger than the displacement of the internal atoms at the same heating rate during the sintering process. Radius ratio and shrinkage go through three stages as the temperature increases: (1) an abrupt increase after reaching the sintering temperature; (2) an almost plateau region within a wide temperature range; (3) finally a drastic increase again after reaching the melting point. Although the radius of gyration also goes through three stages, nonetheless the trend is opposite to radius ratio and shrinkage. For aluminum nanoparticles with the same diameter, at a lower heating rate, the atomic displacement, mean square displacement, radius ratio, shrinkage, and radius of gyration change more remarkably with increasing temperature. The lower heating rate and smaller nanoparticle diameter correspond to a lower sintering temperature and melting point.

Atomic insights into thickness-dependent deformation mechanism and mechanical properties of Ag/PMMA ultra-thin nanofilms.

In this work, the nanoindentations on bilayer composite nanofilms composed of metal Ag and polymer PMMA were simulated using molecular dynamics. The effects of the thickness of Ag and PMMA on the elastic moduli of the composite films were analyzed from Hertz contact theory, dislocation evolution and atomic migration. The results show that the maximum penetration depth that the Hertz model could well describe is about 6 Å, and this limiting value is almost independent on the film thickness. The deformation mode of the Ag films gradually changes from bending mode to indentation mode with an increase in Ag thickness, which improves the elastic modulus of the composite films. The rule of mixtures could give a theoretical prediction about the elastic modulus of the composite film close to the nanoindentation, and Hertz theory could also be used as long as the thickness of Ag films exceeded a certain value. The introduction of a PMMA layer impedes the development of dislocation in the Ag layer and improves the elastic limit of the composite films. This work provides an important basis for experimentally measuring the overall elastic modulus of metal/polymer composite film based on nanoindentation or extracting the elastic modulus of metal film from the overall indentation response of the composite film.