[Paper Review] Statistical analysis of Ni nanowires breaking processes: a numerical simulation study

P. García‐Mochales, Ricardo Paredes+2 more|arXiv (Cornell University)|Oct 2, 2007

Molecular Junctions and Nanostructures66 references19 citations

TL;DR

This study uses molecular dynamics simulations based on the embedded atom method to statistically analyze Ni nanowire breaking processes across varying temperatures, crystallographic orientations, and initial sizes. Key findings reveal that [111]-oriented nanowires evolve through ordered monomer and dimer states before rupture, while [100] and [110] directions exhibit a prominent peak at $ S_m \sim 5 $, indicating stable staggered pentagonal chains, with increased disorder at room temperature, and size effects dominate in small wires regardless of orientation.

ABSTRACT

A statistical analysis of the breaking behavior of Ni nanowires is presented. Using molecular dynamic simulations, we have determined the time evolution of both the nanowire atomic structure and its minimum cross section (Sm(t)). Accumulating thousands of independent breaking events, Sm histograms are built and used to study the influence of the temperature, the crystalline stretching direction and the initial nanowire size. The proportion of monomers, dimers and more complex structures at the latest stages of the breaking process are calculated, finding important differences among results obtained for different nanowire orientations and sizes. Three main cases have been observed. (A) [111] stretching direction and large nanowire sizes: the wire evolves from more complex structures to monomers and dimers prior its rupture; well ordered structures is presented during the breaking process. (B) Large nanowires stretched along the [100] and [110] directions: the system mainly breaks from complex structures (low probability of finding monomers and dimers), having disordered regions during their breakage; at room temperature, a huge histogram peak around Sm=5 appears, showing the presence of long staggered pentagonal Ni wires with ...-5-1-5-... structure. (C) Initial wire size is small: strong size effects independently on the temperature and stretching direction. Finally, the local structure around monomers and dimmers do not depend on the stretching direction. These configurations differ from those usually chosen in static studies of conductance.

Motivation & Objective

• To understand the statistical behavior of Ni nanowire breaking under varying conditions such as temperature, crystal orientation, and initial size.
• To identify the atomic-scale structural evolution during nanowire rupture, particularly the formation of minimum cross-sections $ S_m(t) $.
• To determine the prevalence of monomers, dimers, and complex structures in the final stages of breaking.
• To assess the influence of temperature and size on structural order and conductance-relevant configurations.
• To compare simulated minimum cross-section histograms with experimental conductance histograms and identify discrepancies due to disorder, impurities, or magnetic effects.

Proposed method

• Molecular dynamics simulations using the embedded atom method (EAM) potential for Ni to model atomic interactions.
• Simulation of thousands of nanocontact breakage events under controlled conditions (temperature, stretching direction, initial size).
• Time-resolved tracking of nanowire atomic structure and minimum cross-sectional area $ S_m(t) $.
• Construction of $ S_m $ histograms from accumulated breaking events to analyze statistical distributions.
• Analysis of final atomic configurations, particularly monomers and dimers, to identify preferred geometries.
• Comparison of results across [111], [100], and [110] stretching directions and temperatures (4K to 300K).

Experimental results

Research questions

• RQ1 How does the crystallographic orientation of Ni nanowires affect the statistical distribution of minimum cross-sections $ S_m $ during breaking?
• RQ2 What is the role of temperature in altering the structural evolution and stability of transient configurations during nanowire rupture?
• RQ3 To what extent do initial nanowire size and size effects influence the breaking process and final atomic configurations?
• RQ4 Why do experimental conductance histograms at room temperature show broad peaks not fully explained by current simulations?
• RQ5 What atomic configurations (e.g., monomers, dimers, pentagonal chains) are most probable at the breaking point, and how do they differ across orientations?

Key findings

• For [111]-oriented nanowires with large initial size, the breaking process proceeds through well-ordered monomers and dimers, with a high probability of observing these configurations before rupture.
• In [100] and [110] directions, a strong peak in the $ S_m $ histogram appears at $ S_m \sim 5 $, indicating the formation of long, staggered pentagonal chains with a repeating …-1-5-1-5-… structure, especially prominent at room temperature.
• The presence of this $ S_m \sim 5 $ peak is confirmed to arise from stable, ordered pentagonal chains, a feature not previously reported in the literature.
• At room temperature, [100] and [110] wires exhibit significant structural disorder during breaking, unlike the ordered evolution seen in [111] wires.
• For small initial nanowire sizes, size effects dominate the breaking process regardless of temperature or orientation, leading to noisy and complex $ S_m $ histograms.
• Monomer and dimer configurations are similar across all orientations: monomers favor 2-1-3 and 2-1-4 arrangements, while dimers most commonly adopt 3-1-1-4, 3-1-1-3, and 4-1-1-4 geometries.