Femtosecond laser-induced plasticity in CuO nanowires

Metal oxide nanowires represent promising candidates for the fabrication of nanodevices, particularly strain sensors. However, the applications have been limited by the intrinsic brittleness of these materials. We demonstrate that this limitation can be addressed through secondary treatment by femtosecond laser irradiation. We show that the mechanical properties of CuO nanowires at room temperature can be adjusted to reduce brittle failure and enhance plasticity. The micro-mechanisms involved in induced plasticity by femtosecond laser processing are addressed using transmission electron microscopy images. At moderate laser fluence, this treatment induces plasticity in CuO nanowires by generating an enhanced density of oxygen vacancies, leading to turn the nanowires configuration from fractured to mostly bent. In bent nanowires, due to high strain rate, vacancy migration from bending tension to compression region leads to localized laser-induce phase transformation from CuO to oxygen-deficient compositions. The coalescence of femtosecond laser-induced oxygen vacancies paves the way for activation of pipe diffusion mechanism which in turn facilitates dislocation movement, leading to substructure development. Moreover, nanoindentation analyses are utilized as a further support to truly demonstrate that the femtosecond processed nanowire offers a metal-like plastic behavior. This promising result can be considered to improve the nanowire performance in future application.