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Polymer Light-Trapping Properties Enhanced for Photonics

Colors in an Xray spectrum (NASA)


Researchers at North Carolina State University and University of North Carolina developed a process for enhancing a polymer’s ability to trap light waves, making it a better material for photonic semiconductors. The team led by NC State materials scientist Lewis Reynolds published its findings online in a recent issue of the journal Applied Physics Letters.

The polymer known as MEH-PPV — for poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene — emits light in response to an electric current. The light-conductive properties of this low-cost polymer make it potentially attractive as an addition to silicon chips to convert electric current into lasers for new photonic semiconductors used in optical and sensor applications.

MEH-PPV has not yet lived up to its potential for lasers, however, because of its inability to confine light waves. Much higher electric currents are needed to compensate for the light escaping from the polymer, and this high current volume causes MEH-PPV to degrade.

Reynolds and colleagues devised a method for better confining light in MEH-PPV, which they say can reduce its energy threshold by half. The process sandwiches the MEH-PPV between layers of the common materials silica (silicon dioxide) and polymethyl methacrylate or PMMA, a basic polymer known as acrylic. These layers effectively reflect light back into MEH-PPV, keeping it from escaping.

In addition to holding light in MEH-PPV, the technique restricts the polymer’s exposure to oxygen, thus limiting oxidation and making it more stable. The method for producing the enhanced MEH-PPV also does not require expensive new technology. “This approach is fairly inexpensive,” says Reynolds, “and could also be easily scaled up for large-scale processing.”

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