Chong Qiao

Inhibition effect on the evolution of a twist grain boundary for an Al/Ni bimetal interface under torsion

By using a molecular dynamics method with EAM potential, we study the evolution phenomena of metal twist grain boundaries (GBs) in the [100], [111] and [110] orientations, together with their bimetal interface, under anticlockwise and clockwise torsions. Our results show that there are different evolution behaviors of the GB screw dislocations for single metals (Al and Ni) and their bimetal interface (Al/Ni) under torsion. Specifically, for the single metals in the [100] and [111] orientations, their GBs evolve toward lower or higher angle twist GBs depending on the twist direction. For Ni in the [110] orientation, the dislocations spread not only in the GB region but also in the grain interior. However, for the bimetal interface, the propagation of dislocations is not only reduced dramatically but also limited to the interface region, showing that there is an inhibition effect. Therefore, such an inhibition effect can enhance the stability of nanomaterials which is very useful for the further design of nanodevices.

Molecular dynamics simulation studies on the plastic behaviors of an iron nanowire under torsion

The plastic deformation mechanism of iron (Fe) nanowires under torsion is studied using the molecular dynamics (MD) method by applying an external driving force at a constant torsion speed. We find that the deformation behavior depends on the orientation of the wire. The dislocations in 〈100〉 and 〈111〉 oriented nanowires propagate through the nanowires under torsion, whereas those in 〈110〉 oriented nanowires divide the wire into two parts. The situation that there is a low angle twist grain boundary (GB) in the nanowires is also under consideration. The results reveal that the dislocations are concentrated on the GB in the initial state, presenting different patterns of dislocation network. The networks change depending on the twist direction. They shrink with increase in twist angle but expand with the decreasing twist angle, presenting an asymmetric phenomenon. Our findings can help us more thoroughly understand the plastic deformation mechanism of Fe nanowires under torsion.

Evolution of short- and medium-range order in the melt-quenching amorphization of Ge2Sb2Te5

Phase-change memory takes advantage of the fast phase transition between amorphous and crystalline phases of phase-change materials (e.g., Ge2Sb2Te5 or GST). To date, while the “SET” process (crystallization of GST glass) has been intensively studied, studies on the “RESET” process (melt-quenching amorphization of GST) are still limited. In this work, we explored the structural changes of GST upon rapid cooling by ab initio molecular dynamics simulations and atomistic cluster alignment (ACA) analysis. Different from other methods which only focus on the nearest bonding atoms, the ACA method can study both the short- and medium-range order clusters containing atoms beyond the first-neighboring shell and enables us to explore the changes of cluster structures in a larger scale. The results reveal that low-coordinated octahedral clusters tend to become high-coordinated ones, and Ge-centered octahedral structures change to tetrahedrons whereas Sb-centered tetrahedrons transform to octahedral structures during the amorphization process. Interestingly, tetrahedrons show aggregation in liquid and supercooled liquid in contrast to 6-fold octahedrons which present notable aggregation in amorphous GST. Moreover, our study showed that wrong bonds (Ge–Ge, Sb–Sb, Ge–Sb and Te–Te bonds) can promote the formation of large rings, and irreducible rings tend to separate into smaller and larger rings as the temperature is decreased. Our findings provide useful insights into the formation process and the structure of amorphous GST, which is valuable for facilitating the application of phase change materials.

Optical Properties and Local Structure Evolution during Crystallization of Ga 16 Sb 84 Alloy

Phase-change memory is one of the most promising candidates for future memory technologies. However, most of the phase-change memories are based on chalcogenides, while other families of materials for this purpose remain insufficiently studied. In this work, we investigate the optical properties and microstructure of Ga16Sb84 by an in-situ ellipsometer and X-ray diffraction. Our experimental results reveal that the Ga16Sb84 films exhibit a relatively high crystallization temperature of ~250 °C, excelling in long data retention. In addition, a large optical contrast exists between the amorphous and crystalline states, which may make it suitable for use in optical discs. Molecular dynamics simulations indicate that a unique local structure order in the amorphous and crystalline phases is responsible for the optical properties observed in the experiment. The similarity found in the short-range orders of the amorphous and crystalline phases is beneficial to better understanding the fast phase transition of phase-change memory.

Si-centered capped trigonal prism ordering in liquid Pd82Si18 alloy study by first-principles calculations

First-principles molecular dynamic (MD) simulation and X-ray diffraction were employed to study the local structures of Pd–Si liquid at the eutectic composition (Pd82Si18). A strong repulsion is found between Si atoms, and Si atoms prefer to be evenly distributed in the liquid. The dominate local structures around Si atoms are found to be with of a trigonal prism capped by three half-octahedra and an archimedean anti-prism. The populations of these clusters increase significantly upon cooling, and may play an important role in the formation of Pd82Si18 alloy glass.

Electronic and magnetic properties of dopant atoms in SnSe monolayer: a first-principles study

SnSe monolayer with orthorhombic Pnma GeS structure is an important twodimensional (2D) indirect band gap material at room temperature. Based on first-principles density functional theory calculations, we present systematic studies on the electronic and magnetic properties of X (X = Ga, In, As, Sb) atoms doped SnSe monolayer. The calculated electronic structures show that Ga-doped system maintains semiconducting property while In-doped SnSe monolayer is half-metal. The Asand Sbdoped SnSe systems present the characteristics of n-type semiconductor. Moreover, all considered substitutional doping cases induce magnetic ground states with the magnetic moment of 1μB . In addition, the calculated formation energies also show that four types of doped systems are thermodynamic stable. These results provide a new route for the potential applications of doped SnSe monolayer in 2D photoelectronic and magnetic semiconductor devices.A SnSe monolayer with an orthorhombic Pnma GeS structure is an important two-dimensional (2D) indirect band gap material at room temperature. Based on first-principles density functional theory calculations, we present systematic studies on the electronic and magnetic properties of X (X = Ga, In, As, Sb) atom doped SnSe monolayers. The calculated electronic structures show that the Ga-doped system maintains its semiconducting properties while the In-doped SnSe monolayer is half-metal. The As- and Sb-doped SnSe systems present the characteristics of an n-type semiconductor. Moreover, all considered substitutional doping cases induce magnetic ground states with a magnetic moment of ∼ 1 μB. In addition, the calculated formation energies also show that four types of doped systems are thermodynamically stable. These results provide a new route for the potential applications of doped SnSe monolayers in 2D photoelectronic and magnetic semiconductor devices.