Strain-induced structural transformation of a silver nanowire

We have investigated the structural characteristics of the experimentally observed phase transition of a silver nanowire into a tube under tensile strain. In the simulations, atoms are allowed to interact via a model potential extracted from the modified embedded atom method. Our calculations demonstrate that the formation of the hollow structure is governed by the nature of the applied strain, the length of the wire, and the initial cross-sectional shape. The results further offer insights into the atomistic nature of this specific structural transformation into a nanotube with the smallest possible cross-section

Vibrational Behavior of Metal Nanowires under Tensile Stress

We have investigated the vibrational density of states (VDOS) of a thin Cu nanowire with $$ axial orientation and considered the effect of axial strain. The VDOS are calculated using a real space Green's function approach with the force constant matrices extracted from interaction potential based on the embedded atom method. Results for the vibrational density of states of a strain-free nanowire show quite distinctive characteristics compared to that of a bulk atom, the most striking feature of which is the existence of high frequency modes above the top of the bulk spectrum. We further predict that the low frequency characteristics of the VDOS reveal the quasi-1 dimensional (Q1D) behavior only when the wire is extremely thin. Through decomposition of VDOS into local atoms we also exhibit that while the anomalous increase in low frequency density of states is mainly due to the corner atoms, the enhancement in high frequency modes is primarily moderated by core atoms. We, additionally, find that while the high frequency band above the top of the bulk phonon shifts to higher frequencies, the characteristics at low frequencies remains almost the same upon stretching the nanowire along the axial direction

Shape-controlled growth of metal nanoparticles: an atomistic view

Recent developments in shape-controlled synthesis of metallic nano-particles present a promising path for precisely tuning chemical activity, selectivity, and stability of nano-materials. While previous studies have highlighted the macroscopic description of synthesis processes, there is less understanding as to whether individual atomic-scale processes posses any signicant role in controlling growth of nano-products. The presented molecular static and dynamic simulations are the rst simulations to understand the underlying atomistic mechanisms of the experimentally determined growth modes of metal nano-clusters. Our simulations on Ag nano-cubes conrm that metal nano-seeds enclosed by {100} facets can be directed to grow into octopod, concave, truncated cube, and cuboctahedron when the relative surface diusion and deposition rates are nely tuned. Here we further showed that atomic level processes play a signicant role in controllably ne tuning the two competing rates: surface diusion and deposition. We also found that regardless of temperature and initial shape of the nano-seeds, the exchange of the deposited atom with an edge atom of the seed is by far the governing diusion mechanism between the neighboring facets, and thus is the leading atomistic process determining the conditions for ne tuning of macroscopic processes

The role of vibrations in thermodynamic properties of Cu-Ni alloys

We report results of a systematic study for vibrational thermodynamic functions of Cu-Ni alloys, in the harmonic approximation, using interaction potentials based on the embedded atom method with improved optimization techniques. The vibrational density of states of the systems is calculated using real space Green’s function method. From an investigation of local force fields we found that increasing Ni concentration in the alloy substantially stiffens the force experienced by Cu atoms compared to that of Ni atoms. Our calculations also reveal that vibrational entropy change between ordered and disordered crystals of Cu-Ni is negligible. However, the mixing entropy of the phonons and electronic states is found to be negative and favors un-mixing, and thus contributes to the miscibility gap