Phonons softening in tip-stretched monatomic nanowires

Abstract

It has been shown in recent experiments that electronic transport through a gold monatomic nanowire is dissipative above a threshold voltage due to excitation of phonons via the electron-phonon interaction. We address that data by computing, via density functional theory, the zone boundary longitudinal phonon frequency of a perfect monatomic nanowire during its mechanical elongation. The theoretical frequency that we find for an ideally strained nanowire is not compatible with experiment if a uniformly distributed stretch is assumed. With the help of a semiempirical Au-Au potential, we model the realistic nanowire stretching as exerted by two tips. In this model we see that strain tends to concentrate in the junctions, so that the mean strain of the nanowire is roughly one half of the ideal value. With this reduced strain, the calculated phonon softening is in much better agreement with experiment.

Structural changes during the formation of gold single-atom chains: Stability criteria and electronic structure

“…72 Usually, the system was considered converged when the change in total energy per atom was less than 1 ϫ 10 −6 eV and the atomic forces were less than 0.001 eV/ Å. Different effective strain rates were simulated by slightly changing the convergence criteria on the gradient of the atomic positions, similar to the procedure in Picaud et al 73 Thus, the most stringent convergence criteria produce highly converged structures that correspond to real systems that were strained slowly enough to allow complete relaxation. Slightly less stringent convergence criteria approximate higher strain rates where the system has less time to relax.…”

Elongation and breaking mechanisms of gold nanowires under a wide range of tensile conditions

“…54 Different effective strain rates were simulated by slightly changing the convergence criteria on the gradient of the atomic positions, similar to the procedure Ref. 55. In a few cases, slightly smaller or larger incremental displacements of the grip atoms were sampled as well.…”

Atomic Scale Design, Structure and Stability of Quantum Nanowires Located on Epitaxial Interfaces and Free‐Standing in Space

“…This approach yields simple approximate expressions for the time-dependent number of vacancies and holes in the nanowire, N v (t) and N h (t), Equations (8) and (9), and for the probabilities to form at least one vacancy and at least one hole, P v (t) and P h (t), Equations (12) and (13) which control the nanowire integrity. On that background, for monatomic epitaxial nanowires we find out two physically important quantities related to the temporal and permanent nanowire breakdown: the mean time τ v for appearance of the first vacancy, Equations (14) and (16), and the mean time τ h for appearance of the first hole in the nanowire, Equations (15) and (17). It is essential to point out that these two mean lifetimes are experimentally accessible via measurements of the time dependence of the nanowire conductivity at different nanowire lengths and temperatures.…”

“…[52][53][54][55][56][57] This semi-empirical TB SMA potential has been extensively used in contemporary atomistic simulations of transition metals and intermetallic alloys, including metal nanowires, too. [15,[38][39][40][41]43,44,48] Its advantage is due to the ability to faithfully reproduce real physical properties of bulk metals and their surfaces with steps, kinks, point defects, dislocations, vacancies, and grain boundaries. [53,54,56,57] The statistical distribution in the model is canonical, that is, NVT ensemble with constant number of particles, N, at fixed temperature, T, and volume, V. [52,57] Following this approach, the total interaction energy E i of atom i in the system is expressed by…”