Diversity of anisotropy effects in the breakup of metallic FCC nanowires into ordered nanodroplet chains

Abstract

We have analyzed the expressed manifestation of the anisotropy of surface energy density in the dynamics of ultrathin nanowires, which break up into disjointed clusters when annealed below their melting temperature. The breakup process is studied for different temperatures and orientations of the nanowire axis relative to its internal crystal structure using the Monte Carlo kinetic method. We have also presented an approximate analytical model of the instability of nanowires. Generally, the interpretation of experimental results refers to the theoretical model developed by Nichols and Mullins, which is based on conceptions about the Rayleigh instability of liquid jets. In both cases, the theories -which do not take into account the anisotropy of surface energy density -predict the breakup of a nanowire/liquid jet with radius into fragments with an average length Λ = 9 . However, the observed value, Λ/ , often deviates from 9 either to lower values or to substantially greater ones (up to 24-30). Our results explain various observed features of the breakup and the significant variations in the values of its parameter Λ/ depending on experimental conditions. In particular, the ambiguous role of exchange by atoms of the surface of a nanowire with the surrounding layer of free atoms formed as a result of their rather intensive sublimation, which occurs in a number of cases, has been investigated. We have shown that this exchange can lead both to a decrease, and to a significant increase, in the parameter Λ/ . The obtained results could be potentially useful in applications such as the development of optical waveguides based on ordered nanoparticles chains.

Roughening transition as a driving factor in the formation of self-ordered one-dimensional nanostructures

“…The first of them was initiated by the results with gold nanowires [32] with a radius of the order of ≈ 7𝑛𝑚. Under the influence of electron beam irradiation, modulations of the radius with the wavelength 𝜆/𝑟 0 ~5.2 − 5.6 appeared in accordance with our estimates of the data given in [48]. We attribute this to the stimulation of the roughening transition in electron bombardment of a nanowire surface.…”

“…In the described model [31], the dynamics of the nanowire is very similar to the results of the classical theory of instability of Plateau-Rayleigh liquid jets [30]. A recent work [48] took into account the possible anisotropy of 𝜎 under the assumption that the shape of a nanowire can also be presented by sinusoidal modulation of its radius along the length. The obtained qualitative results are physically transparent.…”

“…For an inverse ratio, a decrease in 𝐸 𝑠 can be achieved only by significantly reducing 𝐴 𝑛𝑤 , which corresponds to wavelengths 𝜆 > 9𝑟 0 . The experimentally observed deviations of 𝜆 [20-22, 25, 32, 38, 39, 53] on both sides of 𝜆 𝑚𝑎𝑥 are largely associated with a different type of anisotropy 𝜎, which depends on the orientation of the nanowire relative to its crystal structure [45][46][47][48]53].…”

Phase-field study of surface diffusion enhanced break-ups of nanowire junctions

“…Experimentally, it is known that single-crystalline and poly-crystalline metallic nanowires possess faceted morphologies and this preference in surface orientation is attributed to surface energy anisotropy [21]. The diverse effects of surface energy anisotropy in FCC metallic nanowires have been investigated using Monte Carlo models [18]. It has been reported that Au nanowires develop facets as a result surface diffusion in order to minimize the surface energy [30].…”

“…The effect of nanowire size, network density and temperature on the stability of metallic nanowires have been investigated experimentally [8,9,10]. The structural stability of the metallic nanowires at the nanoscale is governed by numerous factors -the most dominant factors being Rayleigh instability [11,12,13] and anisotropy in interfacial energy [14,15,16,17,18]. Thermally accelerated surface diffusion plays a central role in the resulting change in morphology of the metallic nanowires due to Rayleigh instability, and their subsequent break-up into nanodots [19,20,21,22,23,24,25].…”