Feng Xu,Wei Xu,Bingxin Mao,Wenfeng Shen,Yan Yu,Ruiqin Tan,Weijie Song
In this article, silver nanowires (AgNWs) with aspect ratios of 1000 and lengths up to 200 μm are obtained by a modified polyol approach. These very long AgNWs are then utilized to prepare transparent electrodes (TEs) displaying a transmittance of 91.3% at a sheet resistance of 8.6 ohm/sq without any post-treatment. Furthermore, we also demonstrate a process for the cold welding of Ag NWs by simply dipping the AgNWs films into CTAB solutions, resulting in a further improvement for the optoelectronic performance. After the post-treatment, the AgNW-based TEs can achieve a transmittance of 93% at a sheet resistance of 9.5 ohm/sq. In addition, the electric behaviors of AgNW-based TEs are investigated. In the bulk-like regime, for the as-prepared AgNW-based TEs, the Figure of merit (FOM), DC to optical conductivity ratio reaches up to 566.8. After the cold welding process, the DC to optical conductivity ratio can reach even higher values (631.6). In the percolative regime, the as-prepared and welded AgNW-based TEs can achieve Π (FOM with percolative-like behavior) values of 166.8 and 242.1, respectively.
When a brittle nanoporous material infiltrated with water is dried in air, the capillarity-induced large volume shrinkage often leads to cracking within the material. In consequence, porous material may become more fragile or even shatter after drying. In this paper, we prepared nanoporous gold (NPG) with a low relative density by dealloying dilute Ag(Au) precursor alloys. Drying of this sample in air leads to a large volume contraction up to 22 ∼ 38%. Meanwhile, the material undergoes a ductile–brittle transition during drying: The wet sample of as-dealloyed NPG, while tested in water, shows a surprisingly large tensile strain up to 8%–10% before fracture; After drying, the fracture strain of the same material drops to around 1% in tension. This ductile-to-brittle transition is not caused by the formation of cracks as usual. Instead, it can be linked to the self-healing of microcracks during drying. We found that the plasticity of as-dealloyed NPG arises from the presence of high-density native microcracks. The bridging or deflection of these microcracks in tension leads to a diffuse failure, which accounts for the large irreversible tensile strain of the wet, as-dealloyed NPG. Further examination reveals that these native microcracks can be healed during drying, owing to the cold welding of nano-ligaments under capillary contraction force. Healing of these microcracks suppresses the diffuse failure induced by crack bridging or deflection, leading to a brittle fracture of the dried NPG in tension. Cold welding of nano-ligaments, which accounts for the anomalous crack healing and ductile–brittle transition of NPG in drying, might occur frequently in nanoporous metals under external load and contribute significantly to their mechanical performance.
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