Understanding the Effects of NaCl, NaBr and Their Mixtures on Silver Nanowire Nucleation and Growth in Terms of the Distribution of Electron Traps in Silver Halide Crystals

Abstract

In recent years, many research groups have synthesized ultra-thin silver nanowires (AgNWs) with diameters below 30 nm by employing Cl− and Br− simultaneously in the polyol process. However, the yield of AgNWs in this method was low, due to the production of Ag nanoparticles (AgNPs) as an unwanted byproduct, especially in the case of high Br− concentration. Here, we investigated the roles of Cl− and Br− in the preparation of AgNWs and then synthesized high aspect ratio (up to 2100) AgNWs in high yield (>85% AgNWs) using a Cl− and Br− co-mediated method. We found that multiply-twinned particles (MTPs) with different critical sizes were formed and grew into AgNWs, accompanied by a small and large amount of AgNPs for the NaCl and NaBr additives, respectively. For the first time, we propose that the growth of AgNWs of different diameters and yields can be understood based on the electron trap distribution (ETD) of the silver halide crystals. For the case of Cl− and Br− co-additives, a mixed silver halide crystal of AgBr1−xClx was formed, rather than the AgBr/AgCl mixture reported previously. In this type of crystal, the ETD is uniform, which is beneficial for the synthesis of AgNWs with small diameter (30~40 nm) and high aspect ratio. AgNW transparent electrodes were prepared in air by rod coating. A sheet resistance of 48 Ω/sq and transmittance of 95% at 550 nm were obtained without any post-treatment.

Rapid and Facile Synthesis of High-Performance Silver Nanowires by a Halide-Mediated, Modified Polyol Method for Transparent Conductive Films

“…In the work of Tang et al [ 32 ], uniform silver nanowires were synthesized via a green and simple hydrothermal method through fine tailoring the anions in the precursors. Additionally, the reaction time is 18 h. Rui et al [ 36 ] investigated the roles of Cl − and Br − in the preparation of AgNWs and then synthesized high aspect ratio (up to 2100) AgNWs in high yield (>85% AgNWs) using a Cl − and Br − co-mediated method in 30 min. Tetsumoto et al [ 37 ] found that, in the AgNO 3 , NaCl and lucose system, the AgNWs could be easily generated at temperature of 150 °C.…”

Synthesis of Silver Nanowires with Controllable Diameter and Simple Tool to Evaluate their Diameter, Concentration and Yield

“…In fact, a mixed silver halide crystal of AgBr 1‐X Cl X is formed, rather than the AgBr/AgCl mixture. In this type of crystal, the electron trap distribution (ETD) is uniform and it is more proper to synthesis of silver nanowires with small diameters and high aspect ratio . In addition to synthesize of thin nanowires, the positive effect of the presence of pressure during the reaction and also using an ionic liquid as soft template have been reported …”

Polyol Silver Nanowire Synthesis and the Outlook for a Green Process

“…Rui et al investigated the effect of Cland Brin the polyol synthesis of high yield (>85%) and high aspect ratio (up to 2500) of AgNWs. They used the electron trap distribution (ETD) of the silver halide crystals to investigate the simultaneous effect of Cland Brions in the synthesis of high aspect ratio AgNWs of small diameter by providing uniform EDT through formation of silver halide AgBr 1-x Cl x [111]. Bobinger et al tailored the various polyol parameters such as the temperature, PVP to the AgNO 3 ratio, rate of stirring, and type of PVP to synthesize AgNWs with an aspect ratio of 800.…”

“…They showed that by simultaneous application of NaCl and NaBr as salt mediators, AgBr 1-x Cl x would be formed as a mixed silver halide crystal with uniform EDT which is beneficial for the formation of high aspect ratio AgNWs. The x value, defined as x = ½NaCl/ð½NaCl + ½NaBrÞ, controls the diameter and yield of AgNWs [111].…”