Sturdy nanofilms beg to be touched

VANDERBILT (US)—Nanoparticle films are no longer a delicate matter. Physicists at Vanderbilt University have found a way to make them strong enough so they don’t disintegrate at the slightest touch.

In the last 25 years scientists have come up with a number of different methods to mold nanoparticles into thin films for a variety of potential applications, including semiconductor fabrication, drug delivery, solid state lighting, and flexible television and computer displays.

But until now, the films have had a common problem: lack of cohesion. Nanoparticles typically consist of an inorganic core coated with a thin layer of organic molecules, which don’t form coherent thin films unless they are encapsulated in a polymer coating or mixed with molecules called chemical “cross-linkers” that act like glue.

“Adding this extra material can complicate the fabrication of nanoparticle films and make them more expensive, says James Dickerson, assistant professor of physics at Vanderbilt. “In addition, the added material, usually a polymer, can modify the physical properties that make these films so interesting.”

The properties of the new films and the method that the researchers used to create them were published online in May in the journal Chemical Communications.

“Our films are so resilient that we can pick them up with a pair of tweezers and move them around on a surface without tearing,” says Dickerson. “This makes it particularly easy to put them into microelectronic devices, such as computer chips.”

The most straightforward applications for the films is in semiconductor manufacturing to aid in the continued miniaturization of digital circuitry and in the production of flexible television and computer screens, Dickerson says.

A key component in the transistors in integrated circuits is an insulating layer that separates the gate, which turns current flow on and off, from the channel through which the current flows. Traditionally, semiconductor manufacturers have used silicon dioxide for this purpose. As transistors have shrunk, however, they have been forced to make this layer thinner and thinner until they reached the point where electrons leak through and sap the power from the device.

The films also have properties that make them ideal for flexible television and computer screens, Dickerson says, being flexible without showing signs of cracking when they are flexed repeatedly. The technique they are made with is also well suited for creating patterned material and is compatible with fluorescent materials that can form the red, green, and blue pixels used in flat panel displays.

So far the Dickerson group has used the technique to make films out of two different types of nanoparticles, and they believe it can be used with a wide variety of other nanoparticles.

“The technique is liberating because you can make these films from the materials you want and use them where you want,” Dickerson says.

Read more in Exploration, Vanderbilt’s online research magazine.

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