Tinghong Gao

Structural Properties of Liquid SiC during Rapid Solidification

The rapid solidification of liquid silicon carbide (SiC) is studied by molecular dynamic simulation using the Tersoff potential. The structural properties of liquid and amorphous SiC are analyzed by the radial distribution function, angular distribution function, coordination number, and visualization technology. Results show that both heteronuclear and homonuclear bonds exist and no atomic segregation occurs during solidification. The bond angles of silicon and carbon atoms are distributed at around 109° and 120°, respectively, and the average coordination number is <4. Threefold carbon atoms and fourfold silicon atoms are linked together by six typical structures and ultimately form a random network of amorphous structure. The simulated results help understand the structural properties of liquid and amorphous SiC, as well as other similar semiconductor alloys.

Effects of area, aspect ratio and orientation of rectangular nanohole on the tensile strength of defective graphene – a molecular dynamics study

Molecular dynamics simulations with adaptive intermolecular reactive empirical bond order (AIREBO) potential are performed to investigate the effects of rectangular nanoholes with different areas, aspect ratios (length/width ratios) and orientations on the tensile strength of defective graphene. The simulations reveal that variation of area, aspect ratio and orientation of rectangular nanohole can significantly affect the tensile strength of defective graphene. For example, defective graphene with a larger area of rectangular nanohole shows a bigger drop in tensile strength. It was found that the tensile strength of both armchair and zigzag edged graphene monotonically decreases with area increases in rectangular nanohole. Changes in aspect ratio and orientation of rectangular nanohole, however, can either decrease or increase the tensile strength of defective graphene, dependent on the tensile direction. This study also presents information that the tensile strength of defective graphene with large area of nanohole is more sensitive to changes in aspect ratio and orientation than is defective graphene with small area of nanohole. Interestingly, variation of tensile strength of defective graphene from MD simulations is in good agreement with predictions from energy-based quantized fracture mechanics (QFM). The present results suggest that the effect of nanoholes on the tensile strength of graphene provides essential information for predictive optimization of mechanical properties and controllable structural modification of graphene through defect engineering.

Microstructural properties and evolution of nanoclusters in liquid Si during a rapid cooling process

The formation of amorphous structures in Si during the rapid quenching process was studied based on molecular dynamics simulation by using the Stillinger–Weber potential. The evolution characteristics of nanoclusters during the solidification were analyzed by several structural analysis methods. The amorphous Si has been formed with many tetrahedral clusters and few nanoclusters. During the solidification, tetrahedral polyhedrons affect the local structures by their different positions and connection modes. The main kinds of polyhedrons randomly linked with one another to form an amorphous network structures in the system. The structural evolution of crystal nanocluster demonstrates that the nanocluster has difficulty to growth because of the high cooling rate of 1012 K/s.

Properties of Icosahedral Clusters and Medium-Range Order in AlCuZr Alloy

The evolution characteristics of icosahedral clusters during the rapid solidification of Al10Cu50Zr40 alloy under cooling rates of 1.0 × 1011 K/s are investigated based on molecular dynamics simulations. The structural properties of short-range order and medium-range order of Al10Cu50Zr40 alloy are analyzed by several structural characterization methods. It is found that the icosahedral cluster is the dominant short range order structure. Simultaneously, the medium -range order structural evolutions are described in detail by quantitative method and visualization technology during the rapid solidification. The results reveal that the medium-range order icosahedral clusters are bonding with each other by chain, triangle, tetrahedral and their combination structures, and have excellent structural stability and configural continuity with the temperature decreasing. The medium-range order clusters that consist of , and interlocked with each other and built the densely packed network structures.