Nanotechnology is wired

Chemists at the University of California, Irvine, have developed a method for preparing metal nanowires featuring the conductivity, strength and length necessary for use in microelectronic devices, such as diodes and transistors, designed for emerging nanotechnologies.

Reginald Penner, UCI professor of chemistry, and his team built the nanowires from molybdenum using a process dubbed step-edge decoration.

‘Metal nanowires may be important to the future of nanotechnology, but there simply hasn’t been a good general way to make them,’ said Penner

In building the wires through the step-edge decoration process, the Penner group first electrochemically deposited molybdenum dioxide onto a piece of graphite. Rudimentary wires began growing when their molecules linked onto step edges-molecular defects on the graphite surface where the emerging wires could gain a stronger atomic hold.

After the brittle molybdenum dioxide wires were formed, they were heated in hydrogen gas at 350 degrees to remove the oxygen, leaving only the molybdenum metal.

The resulting pure molybdenum wires were smaller in diameter but also stronger, more conductive and more flexible than those created in the first step of the process. The metal wires were then embedded in a polystyrene film and peeled off the graphite surface. The nanowires measured between 10 nanometers and a half-micron in diameter and up to 100 microns, or one-tenth of a millimetre, in length.

‘By heating the molybdenum oxide in hydrogen, the wires we created were 1,000 times more conductive than the wires we electroplated in the first step of the process,’ said Penner.

In developing a method to build long, uniform nanowires, Penner said that the step-edge decoration method used on graphite is proving to be more practical than using template synthesis.

‘The problem with templates is that you need a different one for every diameter of wire you want to grow,’ said Penner. ‘Also, thick templates needed to prepare long nanowires are not readily available. Our technique allows you to grow wires of any diameter you want as well as very long wires with a piece of graphite, which is something you can’t do with existing templates.’

Penner and his research team plan to continue their research by developing electronic devices with these nanowires, such as sensors, diodes and transistors.