Zhichao Wang

Molecular dynamics study on the formation of self-organized core/shell structures in the Pb alloy at the nanoscale

Herein, we report a self-organized core/shell (CS) structure consisting of an Al core and a Pb shell in the liquid Pb alloys at a constant temperature. This is contrary to a believed opinion that the thermal gradient acts as the only driving force for the formation of this kind of structure. The results show that its forming ability greatly depends on the composition and temperature. Importantly, when the alloys are placed in the confined space, a structure of Al–Pb–Al sandwich construction and a completely different CS structure composed of a Pb core and an Al shell are obtained; this suggests a new strategy for controlling the phase-separated structures at the nanoscale. More interestingly, an abnormal phenomenon in the low Pb alloys with the amorphous thin Pb shell and the crystal Al core is observed after solidification, which does not occur in the high Pb alloys that just possess a secondary wrapped structure that never appears in the liquid state. The result of this study may help to shed light on understanding the formation of this core/shell structure and controlling it at an atomic view that have a potential application in the fabrication of these structural materials through nanotechnology.

Density dependent structural phase transition for confined copper: origin of the layering

Confinement presents the opportunity for novel structural transition scenarios not observed in three-dimensional systems. Here, we report a comprehensive molecular dynamic (MD) study of the structural phase transition induced by density for an ordinary metal copper (Cu) confined between two parallel panel walls. At 4.19 g cm-3 < ρ < 4.66 g cm-3, a notable structural phase transition occurs between the triangle unit cell structure and quasi-square unit cell structure upon densification. Both the bond order parameter (BOP) and angular distribution function (ADF) can provide evidence for the transition. We highlight the fact that when the sole decrease of the atom distance cannot adapt to the further densification, the system starts to adjust the neighboring bond angle and promote the layering transition, thus inducing the structural phase transition. At the metastable coexistence zone, the viscosity exhibits a remarkable drop and the diffusion coefficient shows a notable increase, both facilitating the accomplishment of the structural transition. Our results will trigger more interest on the phase transition under confinement in a metallic system.

Electronic transport properties of heterojunction devices constructed by single-wall Fe2Si and carbon nanotubes

The electronic structures of the armchair Fe2Si nanotubes are calculated by using the SGGA+U method. Novel heterostructure devices are prepared composed of single-wall Fe2Si nanotubes (Fe2Si NTs) and carbon nanotubes (CNTs). The results indicate that the (4,4) Fe2Si NT is a ferromagnetic half metal with 100% spin-polarization ratio at the Fermi energy level. These heterojunctions have spin-polarized transport properties but their spin-polarization ratios are relatively low. Interestingly, the (13,0) CNT–(n,n) Fe2Si NT–(13,0) CNT devices are all semiconductors but others are metallic. This study suggests that adding the novel Fe2Si NTs endows the CNTs with spin-polarized property and provides very valuable results for better understanding of the electronic structures of the heterostructure.

Wetting and coalescence of the liquid metal on the metal substrate

Molecular dynamics (MD) simulations are performed to investigate the wettability of liquid metal on the metal substrate. Results show that there exists different wettability on the different metal substrates, which is mainly determined by the interaction between the liquid and the substrate. The liquid metal is more likely to wet the same kind of metal substrate, which attracts the liquid metal to one side on the hybrid substrate. Exchanging the liquid metal and substrate metal has no effect on the wettability between these two metals. Moreover, the study of metal drop coalescing indicates that the metal substrate can significantly affect the coalescence behavior, in which the changeable wettability of liquid metal plays a predominant role. These studies demonstrate that the wetting behavior of liquid metal can be controlled by choosing the suitable metal substrate.