With the use of mobile devices with touch screen displays on the rise, engineers have been trying to find lower-cost alternatives to the expensive indium tin oxide (ITO) films currently used to connect pixels in electronic screens. At Duke University (Durham, NC), researchers have developed a technique to organize copper atoms in water, resulting in long, thin, non-clumped nanowires that can be transformed onto transparent conductive films. In addition to touch screens on tablets and handheld devices, the technology may also help engineers build improved solar cells or foldable electronics.
Film made from ITO, an expensive rare earth element costing as much as $800/kg, is highly transparent, which helps it to transfer information well, but the film cracks easily and must be deposited from a vapor in an extremely slow process. An alternative process of using inks containing silver nanowires has found its way into electronics, with the first cell phone with screen made from this material due out this year, but the cost is still high, with silver at $1,400/kg. However, copper is a thousand times more abundant than silver or indium, and at a cost of $/kg, is about 100 times less expensive.
Duke University chemist Ben Wiley and his graduate student Aaron Rathmell were able to form a layer of copper nanowires on glass, creating a transparent conducting film in 2010, but the wires clumped together so the film wasn't good enough for practical applications. They developed a new technique to grow the copper nanowires and coat glass surfaces that eliminates the clumping. The copper nanowires also can maintain their form and conductivity when bent back and forth 1000 times, unlike the ITO films that break after just a few bends.
The results were published Sept. 23 online in Advanced Materials. Wiley believes that the high-performance, low-cost, flexible copper nanowires make them an ideal choice for use in solar cells and in lighter, more reliable displays. And taking both expense and weight out of medical device components is a development that will be welcomed by many design engineers.