Aug 4, 2010
Long metallic nanowires fabricated for transparent electrode tests
Researchers at Ames Laboratory and Iowa State University, both in the US, have developed a new method for fabricating long (~1–2 cm) metallic nanowires. The technique involves physical vapour deposition of various metals on centimetre-long patterned polymer templates. The thickness and width of the nanowires can be controlled by deposition rate, time, angle and dimensions of the templates. Nanowires (straight as deposited) and nanoribbons (which curl when freestanding) are collected after chemical removal of the polymer templates.
The polymer templates are made with photoresist by laser interference holography, with an overall sample size of 2 by 2 cm (note that it is possible to make larger versions). Metals are deposited with directional e-beam evaporation. Deposited metals on the top part of the photoresist are collected as nanoribbons in solution after the photoresist is removed. The metals deposited on the substrate between the patterned photoresist remain even after removal of the photoresist. The team analysed physical, electrical and optical properties of nanowires and nanoribbons using various methods.
"There is no waste of materials, we collect all deposited material – long nanowires from the substrate and nanoribbons from the solvent," explained Dr Kai-Ming Ho, distinguished professor of physics and astronomy at Iowa State University. "Also, there is no restriction on materials, even semiconductor and insulator nanowires are possible."
The metallic nanowires show high-quality, uniform, ordered structures that are 100 nm thick, 500 nm wide and a few centimetres long. Also two-layer mesh structures have been fabricated by depositing a second layer on top of the first layer.
Mesh structures and freestanding metallic nanoribbons show high transmission and lower electrical resistivity than ITO (indium tin oxide), which is used as a transparent electrode material for light emitting devices and solar cells. The next step is to use these nanowires and nanoribbons in solar cells and light emitting devices to demonstrate their potential as transparent electrodes.
The researchers presented their work in the journal Nanotechnology.
About the author
Joong-Mok Park is a researcher at Ames Laboratory-USDOE and the Department of Physics and Astronomy, Iowa State University, US. This work is supported by the director for energy research, Office of Basic Energy Sciences. The Ames Laboratory is operated for the US Department of Energy by Iowa State University under contract no. DE-AC02-07CH11358.