Jan 11, 2007
New hybrid structures make strong nanowires
Researchers in the US have created hybrid structures that combine the best properties of carbon nanotubes and metallic nanowires. The new structures could overcome some of key problems in employing carbon nanotubes in a wide variety of applications including computer chips, displays and sensors.
As chip designers seek to continually increase computing power, they are looking to shrink the dimensions of chips to the nanoscale. Carbon nanotubes and nanowires could be promising candidates to act as connections at this scale because they have exceptional mechanical, electronic and optical properties. "By combing the superlative properties of these two novel materials, such hybrid materials will offer new possibilities in areas such as interconnects and perhaps others we have not foreseen," says team member Fung Suong Ou of the Rensselaer Polytechnic Institute in New York.
Previous techniques only allowed bundles of nanotubes to be attached to macroscopic metal contacts and until now there was no way to attach metal contacts to a single nanotube. The new approach enables a single carbon nanotube to be precisely attached to an individual metal "pin" and allows precise nanoscopic metal contact to carbon nanotubes to make multi-segmented hybrid nanotube-nanowire structures for the first time.
The Rensselaer researchers begin by making their metal nanowires using an alumina template that can be designed to have pore sizes in the nanometre range. Next, they deposit copper or gold wires inside the pores and then place the entire assembly in a furnace containing a carbon-rich compound. When the furnace is heated to high temperatures, the carbon atoms arrange themselves along the wall of the template and carbon nanotubes grow directly on top of the metallic wires.
The technique is very simple and could be applied to many other materials. "The most exciting aspect is that it allows you to manipulate and control the junctions between nanotubes and nanowires over several hundred microns of length," explains Ou. Moreover, the alumina templates are readily available because they are mass-produced in the filter industry and the technique could easily be scaled up to industrial scales.
The team has already made hybrid nanowires that combine carbon nanotubes with copper and gold. It is now working on connecting carbon nanotubes to semiconductors. These devices could be used as diodes, says Ou.
The researchers reported their work in Appl. Phys. Lett..