Fabrication and characterization of next-generation soft conductors via flash-material interaction

Abstract

In chapter 2, we report a strongly adhesive (213 % higher peel strength) silver nanowire (AgNW) network with excellent performance (sheet resistance ~5 Ω·$sq^{-1}$, transmittance 90 % at λ = 550 nm) fabricated by flash-induced plasmonic welding based on theoretical studies of photothermal interactions. Self-limited plasmonic welding and improved adhesion of AgNWs were simultaneously demonstrated through finite-difference time-domain simulations. The ultraviolet spectrum of a flash lamp generated localized heat at the junctions of NWs with a self-limited photothermal reactions, enabling fully welded AgNWs. In addition, the surface plasmon po-laritons excited by near-infrared could thermally activate the AgNW/PET interface and enhance the adhesion of AgNW film. This flash-activated AgNW network was utilized as electrodes for a transparent flexible energy harvester. Despite harsh poling and bending fatigue, the device shows outstanding transmittance of ~80 % as well as high electric output performance (output voltage and current density of 38 V and 6.8 μA·$cm^{-2}$). In chapter 3, we report a high-performance Cu nanowire (NW) network (sheet resistance ~17 Ω·$sq^{-1}$, transmittance 88 %) fabricated by plasmonic-tuned flash welding (PFW) with ultrafast interlocking and photo-chemical reducing, which greatly enhance mechanical and chemical stability of Cu NWs. Xenon flash spec-trum was tuned in an optimized distribution (maximized light intensity at 600 nm wavelength) through modula-tion of electron kinetic energy in the lamp by generating drift potential for preferential photothermal interac-tions. High-intensity visible (VIS) light was emitted by the plasmonic-tuned flash, which strongly improves Cu nanowelding without oxidation. Near-infrared (NIR) spectrum of the flash induced an interlocking structure of NW/PET interface by exciting Cu NW surface plasmon polaritons (SPPs), increasing adhesion of the Cu nano-network by 208 %. In addition, ultrafast photochemical reduction of Cu NWs was accomplished in air by flash-induced electron excitations and relevant chemical reactions. The PFW effects of localized surface plasmons (LSPs) & SPPs on junction welding and adhesion strengthening of Cu-network were theoretically studied as physical behaviors by finite-difference time-domain (FDTD) simulations. Finally, a transparent resis-tive memory and a touch screen panel (TSP) were demonstrated by using the flash-induced Cu NWs, showing versatile and practical uses of PFW-treated Cu NW electrodes for transparent flexible electronics.