The goal of our research into nanowires is (1) understand the mechansisms by which atoms assemble into nanowires and (2) study the properties of nanowires in the context of important problems. See below for recent examples of our work in this area.
Copper Nanowires
The development of a high-performance transparent conductor that is also inexpensive, flexible, and can be deposited at low temperatures would remove a significant barrier to the development of low-cost flexible displays and solar cells. We’ve recently developed a gram-scale synthesis of copper nanowires in aqueous solution. Copper nanowires exhibit a unique growth mechanism in that they sprout and grow from spherical copper seeds. Films of copper nanowires with a sheet resistance of 15 Ω/sq had a transmittance of 65%. Films of copper nanowires remained conductive and had no change in transmittance after storage in air for one month, and exhibited no change in sheet resistance after 1000 bending cycles. Films of copper nanowires transmit ~15% more light than flexible films of carbon nanotubes, but 25% less than brittle films of indium tin oxide with the same sheet resistance. Our calculations and experimental data indicate that the transmittance of copper nanowire films is not limited by the optical properties of copper, but by aggregation. If aggregation of copper nanowires can be eliminated, the properties of films of copper nanowires should be on par with films of silver nanowires, and very close to those of indium tin oxide, the industry standard.
Reference
The Growth Mechanism of Copper Nanowires and their Properties in Flexible, Transparent Conducting Films. A. Rathmell, S. Bergin, Y. Hua, Z. Li, and B. Wiley, Adv. Mater. in press. PDF
Figure 1. Pictures of the reaction flask (a) before the synthesis and (b) after growth of CuNWs at 80˚C for 1 hr. (c) SEM image of CuNW product.
Figure 2. (a) SEM image showing copper nanorods sprouting from spherical copper seeds at a reaction time of 3.5 minutes. (b) By 20 minutes the rods had vtgrown to form longer wires. (c) TEM image of two CuNWs growing out of a nanoparticle.
Figure 3. (a) Camera image of a CuNW film (390 mg/m2) with a sheet resistance of 61 Ω/sq, and a transmittance of 67%. (b) Plot of transmittance versus sheet resistance for films of CuNWs (copper circles), silver nanowires (black triangles), ITO (blue stars), and carbon nanotubes (black open circle). (c) A plot of sheet resistance versus number of bends shows no change in CuNW conductivity after 1000 bends. (d) A plot of sheet resistance versus time in days demonstrates the stability of the CuNW films.