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The scientists observed the nanowires using electron microscopy and made adjustments to the growth process based on the results. Electron tomography also enabled them to reconstruct the three-dimensional shape of individual nanoscale wires.


The team has also published work regarding the use of electron-microscopy cathodoluminescence to observe what wavelengths of light are emitted from different regions of individual nanowires.


Precisely structured nanowires could facilitate a new generation of semiconductor devices, says Gradečak. Such control of nanowire geometry and composition could enable devices with better functionality than conventional thin-film devices made of the same materials, she says.


One likely application of the materials developed by Gradečak and her team is in LED light bulbs, which have far greater durability and are more energy-efficient than other lighting alternatives. The most important colours of light to produce from LEDs are in the blue and ultraviolet range; ZnO and GaN nanowires produced by the MIT group can potentially produce these colours very efficiently and at low cost, she says.


While LED light bulbs are available today, they are relatively expensive. “For everyday applications, the high cost is a barrier,” Gradečak says. One big advantage of this new approach is that it could enable the use of much less expensive substrate materials, a major part of the cost of such devices, which today typically use sapphire or SiC substrates. The nanowire devices have the potential to be more efficient as well, she says.


Such nanowires could also find applications in solar-energy collectors for lower-cost solar panels. Being able to control the shape and composition of the wires as they grow could make it possible to produce very efficient collectors.


The individual wires form defect-free single crystals, reducing the energy lost due to flaws in the structure of conventional solar cells. Also, by controlling the exact dimensions of the nanowires, it’s possible to control which wavelengths of light they are “tuned” to, either for producing light in an LED or for collecting light in a solar panel.


Complex structures made of nanowires with varying diameters could also be useful in new thermoelectric devices to capture waste heat and turn it into useful electric power. By varying the composition and diameter of the wires along their length, it’s possible to produce wires that conduct electricity well but heat poorly. This combination is hard to achieve in most materials, but is key to efficient thermoelectric generating systems.


The nanowires can be produced using tools already in use by the semiconductor industry, so the devices should be relatively easy to gear up for mass production, the team says.


Zhong Lin Wang, the Regents’ Professor and Hightower Chair in Materials Science and Engineering at the Georgia Institute of Technology, says that being able to control the structure and composition of nanowires is vitally important for controlling their nanoscale properties. The fine- tuning in the growth behaviour of these materials opens up the possibilities for fabricating new optoelectronic devices that are likely to have superior performance.


Isofoton & Mercedes AMG Petronas partnership gets the green light


The agreement sees an Isofoton logo on the helmet visors of the Mercedes AMG Petronas drivers Michael Schumacher and Nico Rosberg


Isofoton and the Mercedes AMG Petronas Formula


1 Team are in an exciting new partnership, as the team debuts its F1 W03 car for the 2012 season today.


Malaga based company Isofoton began operations in 1981 producing photovoltaic cells based on silicon wafers. The company is now also involved in the development and manufacture of HCPV technology which uses high efficiency III-V semiconductor materials. These cover a small part of the module’s surface yet allow for the production of nearly double the energy obtained from conventional photovoltaic systems. Thirty years on and now employing close to 800 people, the company expects to increase its manufacturing


March 2012 www.compoundsemiconductor.net 115


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