Contact Annealing for Self-Soldering: In Situ Investigation into Interfaces between PVP-Coated Silver Nanoelectrodes and Carbon Nanotubes

Reliable interconnection is a primary requirement for the fabrication of electronic or electromechanical devices in the bottom-up nanotechnology. At the current stage, although the position and fixation of functional elements through various methods have been achieved, the stable fixation process is still extremely difficult given the readily oxidative properties of the metal electrodes and the method for corresponding antioxidant protection by the dielectric coating. Here, we achieved a robust fixation of polyvinyl pyrrolidone (PVP)-coated silver nanoelectrodes and PVP-coated multiwalled carbon nanotubes (MWCNTs) through PVP pyrolysis at their interface. We comprehensively investigated the interface between the PVP-coated silver nanoelectrode and the PVP-coated MWCNT to better understand the leverage of the PVP protective layer on the electrical performance and joining strength properties during the self-soldering process. This self-soldering process is performed within an environmental scanning electron microscope by a nanorobot-assisted nanomanipulation system. Our results show that the conductivity of the soldered nanostructure is enhanced by about 1000 times after a 65 s vacuum annealing process. The PVP-coated MWCNT and the PVP-coated silver nanoelectrode were soldered together with a joining strength up to 112 MPa. The PVP protective layer and the subsequently formed amorphous carbon layer from the PVP pyrolysis provide good antioxidant protection for the whole soldering process. The PVP-coated silver nanoelectrode was also successfully positioned and soldered onto the silver pad, which verifies the feasibility of the provided self-soldering method. Additionally, our in situ investigation provides a reliable method for identifying metal or semiconductor materials and a temperature estimation method without any thermal sensors on the nanoscale. Our recipe highlights the promise of soldering dielectric-coated electrodes for fabricating nanoelectronic devices and transparent conductive films.