Jianyu Yang

The dynamic diffusion behaviors of 2D small Fe clusters on a Fe(110) surface

In this paper, the diffusion behaviors of Fe clusters on a Fe(110) surface have been investigated using molecular dynamics simulations based on a modified analytic embedded-atom method. The stable configurations of Fe clusters are predicted to be close-packed islands configuration for Fe clusters up to nine atoms or even larger in size. The activation energy of surface diffusion exhibits an interesting, oscillatory behavior as a function of cluster size. As compared to the structures with extra atoms at the periphery, compact geometric configurations of Fe clusters (four- and seven-atom clusters) have an obviously higher activation energy. The reason is that for clusters of more than two atoms the diffusion mechanisms of 2D small clusters are achieved by the migration of extra atoms at the periphery.

Simultaneous melting of shell and core atoms, a molecular dynamics study of lithium–copper nanoalloys

Melting of nanoalloys originates from the alloy surface and gradually propagates into the interior region. The thermal stability of Li cores and Cu shells nanoalloy with size of 3.5 nm is studied through molecular dynamics and embedded atom method with the use of potential energy, Lindemann index, and radial distribution function. Results show that the shell and core Li atoms are melted in two steps: first, some Li atoms in the core migrate to the nanoalloy surface and maintain a typical solid state despite that the system temperature is higher than the bulk melting point of Li because of Li solidification in the solid–liquid interface; second, the shell and core Li atoms are simultaneously melted at high temperatures. A comparative study of Li@Cu nanoalloys with different Li atomic numbers shows that thermal stability is enhanced with the decreasing number of Li atoms within the nanoalloys because of weak binding for Cu thin shells.

Effect of incident energy on the configuration of Fe–Al nanoparticles, a molecular dynamics simulation of impact deposition

The impact deposition of Al (or Fe) atoms on the rhombohedron of Fe (or the truncated octahedron of Al) nanoparticles is investigated by performing a molecular dynamics simulation using the embedded atom method. These simulations are performed in different incident energies (from 10 eV to 50 eV). The dependence of the incident energy of deposited atoms on the growth configurations of Fe–Al nanoparticles is analyzed. For the deposition of Al atoms on the Fe nanoparticle, some Al atoms are incorporated into the Fe core as the incident energy of Al increases. A nanoparticle configuration with Fe-core and Al-shell is usually observed at all incident energies considered. In this case, the substrate Fe atoms and the deposited Al atoms are arranged in body-centered cubic configuration. For the impact deposition of Fe atoms on the Al nanoparticle, an onion-like nanoparticle is observed at incident energy of 10 eV. A configuration with Al-shell and alloyed Fe–Al core is obtained as the incident energy increases. This study proposes a method of artificially controlling nanoalloy configuration.

The configurations of nanoalloy by impact deposition: atomistic simulation on Ni–Al system

The use of energetic particles can change the growth mode and provide control of nanoalloy morphology and properties. The impact deposition of Ni (or Al) on the truncated octahedral nanoparticle of Al (or Ni) is studied. The embedded atom method is used for the description of the interatomic interactions in combination with molecular dynamics method for the growth simulation. Three configurations of Ni–Al nanoparticle are obtained depending on incident energy and deposition sequence. A perfect core–shell nanoparticle with Ni-core/Al-shell is obtained as Al atoms are deposited over Ni nanoparticle. For the deposition of Ni atoms on Al nanoparticle, an onion-like nanoparticle at smaller incident energy, and a configuration with Al-shell and alloyed Ni–Al core at larger incident energy are observed, respectively. The formation energies show that the latter is energetically favorable.

Surface self-diffusion behavior of individual tungsten adatoms on rhombohedral clusters

The diffusion of single tungsten adatoms on the surfaces of rhombohedral clusters is studied by means of molecular dynamics and the embedded atom method. The energy barriers for the adatom diffusing across and along the step edge between a {110} facet and a neighboring {110} facet are calculated using the nudged elastic band method. We notice that the tungsten adatom diffusion across the step edge has a much higher barrier than that for face-centered cubic metal clusters. The result shows that diffusion from the {110} facet to a neighboring {110} facet could not take place at low temperatures. In addition, the calculated energy barrier for an adatom diffusing along the step edge is lower than that for an adatom on the flat (110) surface. The results show that the adatom could diffuse easily along the step edge, and could be trapped by the facet corner. Taking all of this evidence together, we infer that the {110} facet starts to grow from the facet corner, and then along the step edge, and finally toward the {110} facet center. So the tungsten rhombohedron can grow epitaxially along the {110} facet one facet at a time and the rhombohedron should be the stable structure for both large and small tungsten clusters.

Atomic simulations for configurations and solid-liquid interface of Li-Fe and Li-Cu icosahedra

The melting point of Li is lower than that of Fe (or Cu); thus, solid-liquid interfaces can be easily formed on Li-Fe and Li-Cu nanoalloys. In this work, the configurations and solid-liquid interfaces of Li-Fe and Li-Cu icosahedra are studied using Monte Carlo and molecular dynamics methods. The atomic interactions are described by the analytic embedded-atom method. The dependence of composition, temperature, and nanoparticle size on the configurations and thermal stabilities of nanoalloys is discussed. The behavior of the Li-Fe and Li-Cu nanoalloys in segregation, configuration, and thermal stability is investigated. A different behavior of surface segregation of Li atoms is observed for the two types of nanoalloys. The interface between the Li and Fe atoms is clear. Mixing of Li with Cu at larger nanoparticle sizes is found because of low heat of formation in the system. The configurations of the Li-Fe and Li-Cu nanoalloys are related to the competition between surface segregation and alloying. The thermal stability of Li in the two types of nanoalloys is enhanced by the support of the Fe (or Cu) solid substrate.