Washington, April 10 : Researchers have used carbon nanotubes to make thin films that are semitransparent, highly conductive, flexible and come in a variety of colors, with an appearance similar to stained glass.
Developed by researchers at Northwestern University, US, the 'stained glass' is another important application of carbon nanotubes, which are used for many high-technology applications due to their exceptional mechanical, thermal, chemical, optical and electrical properties.
In fact, the diverse properties of carbon nanotubes have inspired a vast range of proposed applications including transistors, conductive films, infrared emitters, biosensors, scanning probes, nanomechanical devices, mechanical reinforcements, hydrogen storage elements and catalytic supports.
Among these applications, transparent conductive films based on carbon nanotubes have attracted significant attention recently.
Transparent conductors are materials that are optically transparent, yet electrically conductive. These materials are commonly utilized as electrodes in flat-panel displays, touch screens, solid-state lighting and solar cells.
With pressure for energy-efficient devices and alternative energy sources increasing, the worldwide demand for transparent conductive films also is rapidly increasing.
Indium tin oxide currently is the dominant material for transparent conductive applications. However, the relative scarcity of indium coupled with growing demand has led to substantial cost increases in the past five years.
The Northwestern team has taken an important step toward identifying an alternative transparent conductor.
Utilizing a technique known as density gradient ultracentrifugation, the researchers have produced carbon nanotubes with uniform electrical and optical properties.
Thin films formulated from these high purity carbon nanotubes possess 10-fold improvements in conductivity compared to pre-existing carbon nanotube materials.
In addition, density gradient ultracentrifugation allows carbon nanotubes to be sorted by their optical properties, enabling the formation of semitransparent conductive films of a given color.
The resulting films thus have the appearance of stained glass.
However, unlike stained glass, these carbon nanotube thin films possess high electrical conductivity and mechanical flexibility.
"Transparent conductors have become ubiquitous in modern society - from computer monitors to cell phone displays to flat-panel televisions," said Mark Hersam, professor of materials science and engineering in Northwestern's McCormick School of Engineering and Applied Science.
According to Hersam, high purity carbon nanotube thin films not only have the potential to make inroads into current applications, but also accelerate the development of emerging technologies such as organic light-emitting diodes and organic photovoltaic devices.
"These energy-efficient and alternative energy technologies are expected to be of increasing importance in the foreseeable future," he said.