'Colored glass' carbon nanotubes are conductive and flexible

Carbon nanotubes are promising materials for high-tech applications because of their rare properties of mechanics, temperature, chemistry, optics and electricity.

Researchers at Northwestern University used metal nanotubes to make semi-transparent thin films, highly conductive, flexible, and available in a variety of colors, looking like colored glass. These results, published in the journal Nano Lettes, can improve high-tech products such as flat screens and solar cells.

The diverse and standard properties of carbon nanotubes have inspired many applications including transistors, logic gates, wires, conductive films, field emission sources, infrared radiators, reinforcement. mechanical, hydrogen-containing elements and catalytic supports.

In these applications, transparent conductive films based on carbon nanotubes have attracted much attention recently. Transparent conductors are optically transparent materials, but can conduct electricity . This material is often used as an electrode in flat screens, touch screens, solid lighting and solar cells. With the urgent need of highly efficient energy devices and alternative energy sources, the demand for transparent conductive films has also increased rapidly.

Photographs of 'colored glass' carbon nanotubes are conductive and malleable on flexible substrates. Carbon nanotubes are arranged to increase the average diameter (clockwise from the lower left): 0.9, 1.0, 1.05, 1.1, 1.4, and 1.6 nanometers. The ability to control nanotube diameter forms the colors that appear on the image. (Photo: Northwestern University)

Indium Oxide is currently the main material for transparent conductive products. However, a relatively rare amount of Indi, along with increasing demand, has led to rising costs in the last 5 years. In addition, Indium Oxide Tin is also limited in optical correction and mechanical flexibility, which reduces its use in some applications such as organic light-emitting diodes and devices. photovoltaic with organic barrier.

The Northwestern team has achieved an important step in identifying another type of transparent conductor. Using a technique known as super-fast centrifugal gradient , scientists have created carbon nanotubes with unchanged electrical and optical properties. Films made from these pure carbon nanotubes are up to 10 times improved in terms of conductivity compared to carbon nanomaterials that once existed.

In addition, the high-density gradient centrifugation method allows carbon nanotubes to be classified according to their optical properties, helping to create semi-transparent film with a certain color. This lead film looks like colored glass. However, unlike colored glass, this thin film of carbon nanotubes has a high electrical conductivity and mechanical flexibility. This flexible property overcomes a major limitation in indium oxide tin, electronic and photovoltaic applications with a soft barrier.

Mark Hersam - McCormick's professor of materials science and mechanics in Northwestern's Applied Mechanical Science, and professor of chemistry at Weiberg University in science and art, and led the research team - "The transparent conductors have become very popular in modern society - from computer screens, phone screens to flat-screen TVs," said said.

"Pure carbon nanotube films are not only capable of being applied in current applications but also can accelerate the development of today's outstanding technologies such as organic light-emitting diodes or devices. photovoltaic with an organic barrier, it is predicted that high-energy energy technology and alternative energy will occupy an important position in the near future. '

In addition to Hersam, another author of the paper in Nano Letters is Alexander Green, a graduate student in materials science and engineering at Northwestern.