Statistical analysis of Ni nanowires breaking processes: a numerical simulation study

Abstract

We have performed the statistical analysis of the breaking behavior of Ni nanowires. Using molecular dynamic simulations based on the embedded atom method approximation, we have simulated thousands of nanocontact breakages, determining the time evolution of both the nanowire atomic structure and the nanowire minimum cross section time evolution, Sm(t). The accumulation of thousands of breaking events allows the construction of Sm histograms. These histograms allow the analysis of the influence of the temperature, the crystalline stretching direction and the initial nanowire size on the breaking processes. We have also calculated the proportion of monomers, dimers and more complex structures at the latest stages of the breaking process. We have found important differences among results obtained for different nanowire orientations and sizes, illustrating that very small wires do not capture the behavior of actual thick nanonecks obtained in experiments. Three main cases have been observed: (a) For the [111] stretching direction and large nanowire sizes, the wire gradually evolves from more complex structures to monomers and, in several cases, to dimers prior its rupture. This case presents well ordered structures during the breaking process. (b) On the other hand, for large nanowires stretched along the [100] and [110] directions the system mainly breaks directly from complex structures, with a low probability of finding monomers and dimers. In this case a clear dependence on temperature is observed. At room temperature a huge histogram peak around Sm = 5 appears, showing for first time in the literature the presence of long staggered pentagonal Ni wires with ...1-5-1-5-1-5-.... structure. Additionally, we have found for this case that nanowires have disordered regions during their breakage. (c) When the initial wire size is small strong size effects are observed independent on the temperature and stretching direction used. Finally, we have found that the local structure around monomers and dimmers do not depend on the stretching direction and that these configurations differ from those usually chosen in static studies of conductance.