2, University of California, Riverside, Riverside, California, United States
Ag nanowires (AgNWs) hold great promise for applications such as transparent and flexible displays, solar cells, chemical/biological sensors, photonic circuits and scanning probe microscopies, but their susceptibility to damage from oxidation significantly limit their device life-time and commercialization potential. To address this challenge, we developed a single-step, room-temperature, solution-phase, etch-free deposition technique to grow an ultra-thin, epitaxial layer of Au coating on the AgNW surface, which acts as a reliable and economical anti-oxidation barrier to provide long-term device stability. The Ag@Au core-shell NWs are stable in air and in physiological buffer solution for months. Transparent flexible electrodes fabricated from Ag@Au core-shell NWs shows steady performance in air at 80°C and 100% humidity for 2 months, while those fabricated with bare AgNWs died out within 2 weeks. The ultra-thin Au coating did not introduce significant Au fluorescence in the SERS spectrum, making them feasible for SERS and plasmonic sensing applications. It was also demonstrated that the ultra-thin Au coating does not have adverse effects on the propagation and coupling of surface plasmon polaritons (SPPs) in AgNW waveguides, and the device performance remains stable for weeks, a significant improvement against uncoated AgNW. AgNW-AFM probes are low-cost alternatives of high-aspect-ratio, high-resolution AFM probes, but the major drawback is their short shelf-life (typically a couple of weeks). It was demonstrated that the Ag@Au core-shell NWs functions similarly to bare-AgNW, with a much longer shelf-life for at least 4 weeks in the air.