Selective breaking and re-joining of CuO nanowires by nanosecond laser irradiation

Nanostructures incorporating copper oxide (CuO), a narrow bandgap p-type semiconductor, are well suited for applications such as gas/biosensors, field emission devices, and photodetectors. However, the use of CuO nanocomponents in these applications is currently limited by the availability of fabrication and in situ processing techniques. In this paper, we show that the electrical and mechanical properties of CuO nanowire (NW) networks can be adjusted through sequential processing with nanosecond laser radiation. This new two-stage process involves selective breakage/cleaving of CuO NWs with an initial set of laser pulses, followed by irradiation with a second set of laser pulses applied in an optimized orientation to tailor bonding and junction formation between pairs and bundles of previously separated CuO NWs. We find that stage one processing introduces a high concentration of oxygen vacancies in NWs leading to the nucleation of dislocations and high strain. This localized strain is responsible for the breaking of individual NWs, while the high oxygen vacancy concentration modifies the electrical conductivity within each NW. The second stage involves re-orientation of the laser beam, followed by additional laser irradiation of the NW network. This has been found to result in the bonding of NWs and the creation of junctions in regions where CuO NWs are in contact. Laser-induced heating under these conditions produces melting in the contact areas between NWs and is accompanied by the reduction of CuO to form Cu2O as verified via XPS and Raman analysis. XRD and TEM observations demonstrate that plastic deformation within CuO NWs dominates in stage one laser processing. The enhancement of electrical conductivity observed, following stage two processing, is attributed due to an increase in the concentration of laser-induced oxygen vacancies as well as the formation of localized bridging and junction sites in the overall NW network.