Nanowire Combs Lase in UV
Daniel S. Burgess
Researchers at the University of California, Berkeley, have produced novel comblike arrays of zinc-oxide nanowires that produce ultraviolet laser radiation when optically stimulated. If they could be made to lase under electronic injection, the structures, which resemble nanoscale fern fronds, could have applications in high-density data storage or as sources for chemical and biological analysis, said Peidong Yang, an assistant professor of chemistry at the university.
To produce the material, the researchers used a nanowire growth process that was developed in Yang's lab. They heated zinc powder in a quartz tube filled with a 5 to 10 percent oxygen-to-argon carrier gas at 800 to 900 °C. In 10 minutes, the reaction yielded a powder of nanowires -- 90 percent taking the comb structure -- atop a silicon target substrate in the tube.
Comb structures made of ZnO nanowires display laser emission near 387 nm. Courtesy of Peidong Yang.
The uniform nanowires had diameters of 10 to 300 nm and lengths of 0.5 to 10 µm and were spaced 0.1 to 2 µm apart along the central "stem" of the frond. Characterization by To investigate the optical characteristics of the nanowires, the scientists illuminated isolated samples with the frequency-quadrupled output of an optical parametric amplifier seeded by 800-nm radiation from a home-built Ti:sapphire oscillator or with the 266-nm fourth harmonic of an Nd:YAG laser. A spectrograph and CCD collected the UV response, indicating lasing at This threshold is two to five times higher than reported for individual nanowires and two-dimensional arrays. Yang said that each nanowire acts as a classical Fabry-Perot optical cavity, and the researchers suggest that the higher threshold might be the result of near-field coupling. Other possibilities include the different cavity lengths of the structures and the lack of second mirror surfaces.
The team currently is investigating methods of electrically stimulating the comb structures, he said.
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