Precise Assembly and Joining of Silver Nanowires in Three Dimensions for Highly Conductive Composite Structures

Three-dimensional (3D) electrically conductive micro/nanostructures are now a key component in a broad range of research and industry fields. Direct laser writing by two-photon polymerization (TPP) has been established as one of the most promising methods for achieving 3D fabrication in micro/nanoscales, due to its ability to produce arbitrary and complex 3D structures with sub wavelength resolution. However, the lack of TPP-compatible and functional materials represents a significant barrier to realizing the functionality of the fabricated devices, such as high electrical conductivity, high environmental sensitivity, and high mechanical strength, etc. In this work, a novel method was developed to realize metallic 3D micro/nanostructures with silver-thiol-acrylate composites via TPP followed by femtosecond laser nanojoining. Complex 3D micro/nanoscale conductive structures have been successfully fabricated with ~200 nm resolution. The loading of silver nanowires (AgNWs) and joining of junctions successfully enhanced the electrical conductivity of the composites from insulating to 92.9 S m-1 at room temperature. Moreover, for the first time, a reversible switching to a higher conductivity was observed, up to ~103-105 S m-1 at 523 K. The temperature-dependent conductivity of the composite was analyzed using the variable range hopping and thermal activation models. The as-developed nanomaterial assembly and joining method in this study paves a way toward a wide range of device applications, including 3D electronics, sensors, memristors, micro/nanoelectromechanical systems (MEMS/NEMS), and biomedical devices, etc.