Theoretical study of the formation, evolution, and breaking of gold nanowires

Abstract

Real time imaging experiments with metal nanowires ͑NWs͒, in particular gold under stress, that show their formation, evolution, and breaking, were obtained with high resolution electron microscopy. In order to understand these results, we use density functional theory ͑DFT͒ based methods to simulate the evolution of Au NWs. First we use a tight-binding molecular dynamics ͑TBMD͒ method to understand the mechanisms of formation of very thin gold NWs. We present realistic simulations for the breaking of these NWs, whose main features are very similar to the experimental results. We show how defects lead to the formation of one-atom constrictions in the Au NW, which evolves into a one-atom-thick necklace chain. Similarly to the experimental results, we obtain that these necklaces can get as long as five-atoms from apex to apex. Before breaking, we obtain relatively large Au-Au bond distances, of the order of 3.0-3.1 Å. A further pull of the wire causes a sudden increase of one of the bond distances, indicating the breaking of the NW. To get some more insight into the electronic structure aspects of this problem, we considered several of our tight-binding structures before breaking and studied them in detail using an ab initio method based on the DFT. By pulling the wire quasistatically in this case, we also observed the breaking of the wire at similar distances as in the TBMD. This result was independent of the exchange-correlation potential used-either the local density approximation ͑LDA͒ or the generalized gradient approximation ͑GGA͒. The pulling force before rupture was obtained as 2.4 nN for the LDA, and 1.9 nN for the GGA. Finally, we also present a detailed analysis of the electronic structure properties for the Au neck atoms, such as the density of states and charge densities, for some configurations before the rupture.

The uniaxial tensile deformation of Ni nanowire: atomic-scale computer simulations

“…With the strain up to 39.12%, those atoms at the 'tip' of the neck rearrange themselves into an one-atom thick, about three-atoms long necklace (see Fig. 5(b)) which is some similar to what happened in the gold nanowire [18,21]. However, this is not observed for Ni nanowire simulated by Sorensen et al [17].…”

“…However, measuring the mechanical and electrical properties of a nanowire is a difficult task due to the small dimensions [11]. In recent years, the deformation of nanowires have been studied by molecular dynamics simulations using either embodied-atom-method (EAM) [12][13][14][15] or effective-medium theory (EMT) [16,17] potentials as well as first-principles method based on the density functional theory (DFT) [18][19][20][21]. These studies focus on the correlation of the force (associated with the changes in the bonding of the nanowire) and the conductance for the metallic Au, Ni, and Na nano-contacts [17,22] and Au, Ni, Al, Na, and SiSe 2 nanowire [12,16,20,23].…”

“…At lower strain rates, the Ni nanowire shows superplasticity [12,13], and at sufficiently high strain rates, it can transform continuously to an amorphous metal at constant temperature [13,14,23]. The Au nanowires, before breaking under tensile stress, can get as thin as one-atom chains, and as long as five suspended atoms [18,21]. Sorensen et al [17] have simulated the mechanical deformation of atomic-scale metallic contacts under tensile strain, and found that various defects such as intersecting stacking faults, local disorder, and vacancies were created during the deformation.…”

Electron-vibration interaction in transport through atomic gold wires

“…We use the nineorbital spd parametrization of Papaconstantopoulos et al [22,23,24,25]. This type of spd TB approach is known to reproduce very well some nontrivial ab initio results, like the numbers of conduction channels and the formation of zigzag Au chains [38,39]. Thus we can be confident that the method gives at least good order-ofmagnitude estimates for all of the quantities which we shall be interested in.…”

Growth and properties of Au nanowires

“…Also Au nanowires promise applications in nanoelectronics, biomedicine, sensing and catalysis [13,14], especially after the discovery of quantum conductance through individual rows of suspended gold atoms [15]. Au nanowires and other nanostructures [16][17][18][19][20] with special features such as conductance [21,22] and transport properties [23,24] have been reported and also been at the focus of several theoretical studies [17, [25][26][27][28][29][30][31][32][33].…”