Influence of shell thickness on the thermal stability and melting-like behavior of Al@Fe core-shell nanoparticles from atomistic simulations: a structural and dynamic description.

Core-shell nanoparticles (CSNPs) are a class of functional materials that have received important attention nowadays due to their adjustable properties by a controlled tuning of the core or shell. Understanding the thermal response and structural properties of these CSNPs is relevant to carrying out an analysis regarding their synthesis and application at the nanoscale. The present work is aimed to investigate the shell thickness effect on thermal stability and melting behavior of Al@Fe CSNPs by using molecular dynamics simulations. The results are discussed considering the influence of the Fe shell on the Al nanoparticle and analyzing the effect of different shell thicknesses in Al@Fe CSNPs. In general, calorific curves show a smooth energy decline for temperatures greater than room temperature for different shell thicknesses and sizes, corresponding to the inward and outward atomic movement of Al and Fe atoms, respectively, that produce a mixed Al-Fe nanoalloy. Here, the thermal stability of the Al@Fe nanoparticle is gradually lost passing to a liquid-Al@solid-Fe configuration and reaching a mixed Al-Fe state by an exothermic mechanism. Combining quantities of the atomic diffusion and structural identification, a stepped structural transition of the system is subsequently observed, where the melting-like point was estimated. Furthermore, it is observed that the Al@Fe CSNPs with greater stability are obtained with a thick shell and a large size. The ability to control shell thickness and vary the size opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.

Structural properties and thermal stability of multi-walled black phosphorene nanotubes and their operation as temperature driven nanorotors.

In this paper, we explore the influence of structural properties, thermal stability, and temperature on the rotational frequency of (0,n) armchair multi-walled black phosphorene nanotubes (MWßPNTs). Using Density Functional Theory (DFT) calculations, we first determine the influence of the outer wall rotation on the structural stability of (0,12)@(0,19) DWßPNTs, and (0,12)@(0,19)@(0,26) TWßPNTs. The results indicate that the relative energies of the DW- and the TWßPNTs do not change with the rotation angle. Therefore, the outer wall rotation is not important for the structural formation of the MWßPNTs. Then, using molecular dynamics (MD) simulations, we study the structural properties, thermal stability, and rotational frequency of (0,12)@(0,19) DWßPNTs, (0,12)@(0,19)@(0,26) TWßPNTs, and (0,12)@(0,19)@(0,26)@(0,33) QWßPNTs from 1 K to 400 K. The calorific curve, the mean-squared displacement, and the radial distribution function are analyzed to characterize the temperature behavior of the MWßPNTs. In all cases, the nanotubes are rotating: they act as thermal-driven rotors as the temperature increases, with a maximum rotational frequency of 16.7 GHz (clockwise direction) at 5 K for the DWßPNTs. Our results suggest that MWßPNTs could be used to construct room temperature nanomotors.