Electronic Circuit Rides a Chemical Film

Chains of molecules known as conducting polymers are versatile materials that can work like electronic circuits. Potential uses include flat panel displays, solar panels, sensing devices and transistors, to name just a few. Their invention won three scientists the Nobel Prize in chemistry.

But to make useful devices from conducting polymers requires a degree of chemical wizardry that often proves elusive. University of Illinois at Chicago chemistry professor Luke Hanley has found a new and effective way around the problem.

Hanley, along with UIC doctoral candidates Sanja Tepavcevic and Yongsoo Choi, has developed a method for growing conducting polymers that he calls Surface Polymerization by Ion-Assisted Deposition, or SPIAD for short. The method is described in the online Journal of the American Chemical Society that appeared Feb. 6, and which will appear in the March 5 print edition. His research was funded through a National Science Foundation grant.

“This is the polymerization, or chemical binding, of small molecules together at the surface to form a larger molecule. This occurs by an ion-assisted deposition process,” said Hanley.

“Basically, the way it works is you have a surface upon which you want to grow a thin film. You put that into a vacuum chamber, pump all the air out, and you simultaneously deposit charged ions on to the surface and evaporate neutral molecules onto the surface. These ions and neutrals meet at the surface and form this continuous polymeric film.”

Hanley has done work on ion-surface interactions for over a decade and has published a series of papers on taking individual ions and landing them on a surface.

“We’ve been able to show we can control the chemistry and shape of the surface on a nanometer scale,” said Hanley. “It allows you to control what this thin film is on the sub-nanometer scale.”

Working with thiophene, Hanley and his group tried to land individual ions onto a surface, hoping they’d link up to form a type of conducting polymer known as polythiophene. The ions “formed something,” Hanley said, “but it wasn’t an interesting polythiophene. So we brought in both an ion beam and neutral beam at the surface.”

Using a commercially available instrument that provides a source of ions, Hanley modified the device to work with organic material, such as thiophene. “We can put organic molecules into it and get out the types of ions that we want,” he said. “We can actually grow large areas of films fairly quickly by this method. We’re not quite at manufacturing scale yet, but we’ve demonstrated that we know how to get to that point.”

Hanley has high expectations for his conducting polymers and thinks the SPIAD method may open the door to many new and useful materials.

“We’re beginning to explore different film properties using this growth method. I think it shows a lot of promise for creating a whole class of conducting polymers with applications you cannot achieve with existing methods.

“Essentially, this is another tool in the toolbox for producing these useful devices. I think we’ve demonstrated this is a new way to create these types of materials. Now we can look at trying to discover some of those newer materials by this method.”