"In general each comb structure has more than 10 nanowire branches in parallel," lead researcher Peidong Yang told Optics.org. "The largest structure we can grow has 50 nanowire branches."

The nanowire branches have uniform diameters ranging from 10 to 300 nm and are between 0.5 to 10 microns long. The branches can be grown on either or both sides of the central stem at regular intervals of 0.1 to 2 microns. Transmission electron microscopy has shown that the nanowire combs are monolithic and single crystalline.

Yang and colleagues optically excite the structure using the fourth harmonic (266 nm) of a pulsed Nd:YAG or a femtosecond-pulsed Ti:Sapphire laser. Each nanowire branch essentially acts like a Fabry-Perot cavity and emits ultraviolet light from its tip. "Currently we do not have a quantitative number for the output power," Yang said. "But the emitted wavelength is around 380 nm."

The team synthesized the comb structure using a chemical vapour transport and condensation system. Yang says that by carefully controlling this process, his team is able to grow custom-designed structures. "The important factor here is the oxygen partial pressure and flow rate as well as the condensation temperature," he explained. "We have obtained several other interesting structures and are now investigating their properties."

Yang sees many applications for these structures and his group is now working on other designs. "The next step is to construct matrix lasers and LEDs from these comb structures," he said. "We also want to make an electron-injected version of the device."