Laser nanojoining of copper nanowires

Single nanowire becomes attractive as a basic component of various nanodevices. Nanowire joining is one of crucial operations in micro-nano manufacturing. Compared to other joining methods, such as electrical current heating and mechanical pressure, laser illumination can yield metallic contacts through local precision nanosoldering. In this paper, we report the joining of one single copper nanowire (CuNW) to silver film with a laser illumination method. We firstly cut the silver film on a flexible substrate to form a gap of about 1-4 µm by a 1030 nm femtosecond (fs) pulsed laser. Then we coat copper nanowires (CuNWs) by dripping nanowire solution onto the gap, bridge the gap and then join single CuNW with the fs pulsed laser. By comparison with scanning electron microscope (SEM) images after and before laser illumination, it is found that the local silver film melts, then wraps partial CuNW and finally crystallizes. So the joining is through a part of CuNW embedded in a silver film. In addition, we further analyze the joining situation by directly measuring the resistance variation between after joining (R_a) and before joining (R_b). It is demonstrated that the resistance ratio of R_a to R_b decreases from 0.835 to 0.172 with increasing laser power from 10 to 40 mW for 3 seconds of the laser illumination time. The resistance ratio of R_a to R_b decreases from 0.936 to 0.368 with increment of the laser illumination time from 1 to 4 seconds at a laser power of 30 mW. Finally, we find that the welded single CuNW enables sensing of glucose at a concentration of 10^-5 M.