Abstract
The focus of this research is to improve the polyol process for silver nanowires. Ethylene glycol was used as both reductant and solvent, silver nitrate as precursor, PVP as protecting agent and potassium chloride as additional chemical. The “two-step process” for silver nanowires synthesis was at 160℃. The parameters included: the ratio between different chemicals, and the concentration of reactants to obtain silver nanowires of different dimensions. By doing so, we are able to obtain nanowires of diameter about 50 to 70 nm and length between 0.7 to 15 μm. Basically, the amount of the silver nitrate added at the second step controls the length and the concentration of potassium chloride for the diameter control.And for the growth mechanism of nanowire, we collect evidence to illustrate the mechanism about the growth of a nucleus into a nanowire. A series of experimental steps including centrifuge, separation and dissolution on samples were collected at different stages of the process. During the first step, i.e. nucleation step, a number of nuclei was formed whose size was about 40 nm in diameter, together with some short rods. All silver ions were reacted at the end of the first step. Then, we added more silver nitrate solution for the second step. At this moment, about 70 percent of the silver ions were converted to particles because of the high rate of reduction at 160℃ in ethylene glycol. But those particles would become a part of the nanowire progressively by dissolution and re-growth process called “Ostwald ripening” during the reaction. Finally, there’s no particles exist in our final product. We can further modify the process by changing the temperature of the solution added at the second stage. For example, we could either decrease or preheat the solution to achieve better control on wire size and uniformity.In the last section, we choose Ag nanowires which is 12 to 15μm in length and 60 to 70nm in diameter suspending in the solution to create coating film for transparent and conductive application. Two techniques were tried here: i.e. “Tilted substrate flowing” and “Dip and drag”, which showed advantages and disadvantages respectively. We could obtain roughly regular-aligned Ag nanowires by the flowing over tilted substrate. Nevertheless, the quantity deposited by this technique was rather small if compared to the other method of “Dip and drag”. Finally we tried to combine these two methods to achieve a best transmittance of 86.9 % and conductivity of 7.66 Ω/sq respectively.