Non-Thermal Solid-State Nanojoining of CuO Nanowires Enabled by Femtosecond Laser Shock Waves for Nanoscale Electronic Interconnects

Abstract Nanojoining of one-dimensional metal-oxide nanostructures remains challenging because their high melting temperatures and intrinsic brittleness hinder reliable integration into nanoscale electronic systems. Here, we present a two-step femtosecond-laser strategy for predominantly solid-state nanojoining of CuO nanowires through nonequilibrium defect engineering followed by shock-assisted mechanical activation. In the first step, femtosecond-laser pretreatment increases the oxygen-vacancy-related defect density, as supported by XPS measurements, which is associated with lattice softening and enhanced nanoscale plasticity. Quantitative nanoindentation shows corresponding reductions in elastic modulus and hardness, together with an increase in the H/Py ratio from approximately 2.2 to 3.1, indicating a transition toward a more plastic deformation response. In the second step, femtosecond-laser shock peening under the optimized condition generates transient compressive loading that promotes intimate inter-nanowire contact and interfacial bonding. TEM, HRTEM, localized FFT, and SAED analyses of X-type, Y-type, and end-to-end junctions reveal direct atomic-scale contact, preservation of the monoclinic CuO structure, and no observable thick amorphous interlayer, melt−resolidification morphology, or bulk phase transformation. Single-junction electrical measurements further show a current enhancement of up to approximately 35% after optimized shock peening, demonstrating improved electrical transport across the formed junctions. These results establish a vacancy-assisted, shock-mediated solid-state route for integrating brittle CuO nanowires into conductive nanoscale architectures and electronic interconnects.