Vibrational Behavior of Metal Nanowires under Tensile Stress

TL;DR

This study investigates the vibrational density of states in Cu nanowires under axial strain, revealing unique vibrational features and the influence of atomic positions on vibrational modes, with implications for nanoscale material behavior.

Contribution

It introduces a real space Green's function approach to analyze vibrational states in strained nanowires, highlighting the effects of atomic structure and strain on vibrational properties.

Findings

High frequency modes exist above bulk spectrum in nanowires.

Low frequency VDOS shows quasi-1D behavior only in extremely thin wires.

Corner atoms mainly contribute to low frequency VDOS, core atoms to high frequency modes.

Abstract

We have investigated the vibrational density of states (VDOS) of a thin Cu nanowire with $<100>$ axial orientation and considered the effect of axial strain. The VDOS are calculated using a real space Green's function approach with the force constant matrices extracted from interaction potential based on the embedded atom method. Results for the vibrational density of states of a strain-free nanowire show quite distinctive characteristics compared to that of a bulk atom, the most striking feature of which is the existence of high frequency modes above the top of the bulk spectrum. We further predict that the low frequency characteristics of the VDOS reveal the quasi-1 dimensional (Q1D) behavior only when the wire is extremely thin. Through decomposition of VDOS into local atoms we also exhibit that while the anomalous increase in low frequency density of states is mainly due to the corner atoms, the enhancement in high frequency modes is primarily moderated by core atoms. We, additionally, find that while the high frequency band above the top of the bulk phonon shifts to higher frequencies, the characteristics at low frequencies remains almost the same upon stretching the nanowire along the axial direction.