Yielding and fracture mechanisms of nanowires

Abstract

This paper presents a detailed analysis of atomic structure and force variations in metal nanowires under tensile strain. Our work is based on state of the art molecular dynamics simulations and ab initio self-consistent field calculations within the local density approximation, and predicts structural transformations. It is found that yielding and fracture mechanisms depend on the size, atomic arrangement, and temperature. The elongation under uniaxial stress is realized by consecutive quasielastic and yielding stages; the neck develops by the migration of atoms, but mainly by the sequential implementation of a new layer with a smaller cross section at certain ranges of uniaxial strain. This causes an abrupt decrease of the tensile force. Owing to the excessive strain at the neck, the original structure and atomic registry are modified; atoms show a tendency to rearrange in closed-packed structures. In certain circumstances, a bundle of atomic chains or a single atomic chain forms as a result of transition from the hollow site to the top site registry shortly before the break. The wire is represented by a linear combination of atomic pseudopotentials and the current is calculated to investigate the correlation between conductance variations and atomic rearrangements of the wire during the stretch. The origin of the observed ''giant'' yield strength is explained by using results of the present simulations and ab initio calculations of the total energy and Young's modulus for an infinite atomic chain.

Pentagonal nanowires: A first-principles study of the atomic and electronic structure

“…We examined the relative stability of the pentagonal geometry by performing a simple analysis based on the two-body LennardJones potential, V (r i,j ) = 4ǫ[(σ/r i,j ) 12 − (σ/r i,j ) 6 ]. We considered three structures encountered in the structure optimization of very thin wires, 16,27 namely equilateral triangle, pentagon and hexagon. The total potential, V T = i =j V i,j (r i,j ) for these structures are obtained by adding all the two-body potential energies, V i,j .…”

“…While stretching the nanowire, the number of atoms in the neck region, where the wire is thinned, and their structure exhibit sequential and step-wise changes. 13,27 It has been argued that these changes are closely related with a band moving up from the Fermi level and becoming unoccupied. 14,36 An important feature of Fig.…”

“…18,19,20,21,22,23,24,25,26 Whether the pentagonal structures predicted earlier by empirical methods 16,27,28,29 are common to other elements and can be understood from more fundamental principles have become an important issue. In this paper we address this question by using the first-principles plane wave calculations within the density functional theory.…”

Identification and characterization of icosahedral metallic nanowires

“…The formation of staggered pentagonal configurations during the stretching process has been already reported for Na [3] using first principles methods, and for Cu [4,5,6] and Au [7] nanowires with different Molecular Dynamic (MD) approaches. In particular the high stability of the Cu nanowire was confirmed with ab-initio calculations [9].…”

“…Different computational works during the last decade have showed the formation of staggered pentagonal configurations on breaking nanowires of different species [3,4,5,6,7,8,9,10,11,12]. The atomic sequence -1-5-1-5-presents a fivefold symmetry with respect the nanowire axis.…”