Modulation on the twinning microstructure of Cu nanowires and its effect on oxidation behaviour

In this study, nanotwinned Cu nanowires (nt-Cu NWs) with varying twin characteristics were fabricated via pulse electrodeposition using a novel H 3 BO 3 based electrolyte, and their impact on the oxidation process was investigated. The density and direction of twin lamellas within nt-Cu NW were adjusted by modifying the concentration of H 3 BO 3 and the current density. Specifically, the average twinning thickness of Cu NWs increases from 26.7 nm to 424.5 nm as the concentration of H 3 BO 3 increases from 0 g/L to 6 g/L. Moreover, three types of nt-Cu NWs with distinct twinning directions, namely waterfall type, bevel type, and ladder type were fabricated by changing the current density from −0.16 ASD to -1.6 ASD (vs Ag/AgCl). A nanowire Winand (NWW) diagram was established to describe the change of twin density and direction based on the difference between the growth behaviour of thin films and nanowires. The thermogravimetric analysis (TGA) and transmission electron microscopy (TEM) were further used to characterize the oxidation process of nt-Cu NWs. It revealed that the oxide thickness was closely related to the thickness of twin lamellas for the ladder type nt-Cu NWs. Also, the waterfall type Cu NWs exhibited a unique bead-chain like oxide morphology and a slower oxidation rate through the impact on the nanoscale Kirkendall effect (NKE). This study provides valuable insights into the controllable fabrication of nt-Cu NWs and Cu oxide NWs.