Two-steps versus one-step solidification pathways of binary metallic nanodroplet

The solidification of AgCo, AgNi, and AgCu nanodroplets is studied by molecular dynamics simulations in the size range of 2-8 nm. All these systems tend to phase separate in the bulk solid with surface segregation of Ag. Despite these similarities, the simulations reveal clear differences in the solidification pathways. AgCo and AgNi already separate in the liquid phase, and they solidify in configurations close to equilibrium. They can show a two-step solidification process in which Co-/Ni-rich parts solidify at higher temperatures than the Ag-rich part. AgCu does not separate in the liquid and solidifies in one step, thereby remaining in a kinetically trapped state down to room temperature. The solidification mechanisms and the size dependence of the solidification temperatures are analyzed, finding qualitatively different behaviors in AgCo/AgNi compared to AgCu. These differences are rationalized by an analytical model

Heterodiffusion of Ag adatoms on imperfect Au(1 1 0) surfaces

The hetero-diffusion of Ag adatoms on imperfect Au(1\uc2 1\uc2 0) surfaces is studied using Molecular Dynamics (MD) simulations. The atomic interactions are described by an Embedded Atom Method (EAM) potential. Static activation energies governing various diffusion processes (jumps and exchanges) are calculated by quenched MD, finding that activation energies for interlayer mobility at straight step edges are somewhat larger than those on the flat surface in the cross-channel [1\uc2 0\uc2 0]-direction, while interlayer barriers at kinks are considerably lower. Dynamic activation energies are calculated at high temperature from the Arrhenius plots of different diffusion mechanisms and compared to static barriers

Growth of size-matched nanoalloys - a comparison of AuAg and PtPd

The gas-phase growth of AuAg and PtPd clusters up to sizes ~3 nm is simulated by Molecular Dynamics. Both systems are characterized by a very small size mismatch and by a tendency of the less cohesive element to segregate at the nanoparticle surface. The aim of this work is to figure out the differences in the behavior between these two bimetallic systems at the atomic level. For each system, three simulation types are performed, in which either one species or both species are deposited on preformed bimetallic seeds. Our results show that core@shell and intermixed chemical ordering arrangements can be obtained, in agreement with the available experimental data. In the case of core@shell arrangement, the purity of the surface layer is perfect for Ag-rich and Pd-rich nanoparticles, whereas in Au-rich and Pt-rich ones, some tendency to surface migration of minority atoms (Ag or Pd) is observed. This tendency is somewhat stronger for Ag than for Pd. The analysis of the internal arrangement of the nanoparticles indicates that in the growth process the mobility of Pd and Ag minority atoms is stronger than that of Au and Pt minority atoms