March 27, 2013 feature
Semiconductor 'shish kabob' nanostructures combine properties from different dimensions
The scientists, Chun Li, et al., at North Carolina University in Raleigh, North Carolina; and Oak Ridge National Laboratory in Oak Ridge, Tennessee, have published a paper on the nanosheet-nanowire heterostructures in a recent issue of Nano Letters.
So far, most research on growing nanoscale heterostructures has focused on combining materials that have the same dimensions. Studies that involve combining materials with different dimensions have remained limited because it is much more difficult to integrate these materials into a single structure due to their different growth mechanisms.
However, as the researchers here explain, integrating materials with different dimensions is attractive because it can combine the advantages of both materials while mitigating the disadvantages. As a result, such heterostructures may enable novel functions that cannot be obtained from each of the components separately.
To synthesize the new nanosheet-nanowire structures in this study, the researchers used a two-step approach, first growing the nanowires and then growing the nanosheets at certain sites on the nanowires. They used germanium sulfide as the material for both components, but predict that the same approach will apply to other similar materials.
In order to yield nanowire-nanosheet heterostructures, the researchers exposed the grown nanowires to air for a few minutes to a few days prior to the nanosheet growth step. The air exposure likely causes mild oxidation on the surface of the nanowires, which changes its surface properties. The researchers think that these surface imperfections may facilitate the nucleation of the nanosheets better than a perfect surface can.
After the nanowires were exposed to air, the researchers could successfully grow nanosheets on the nanowire surface along the radial direction, so that they were arranged like pieces of chicken and peppers on a skewer. Besides their appeal due to this unusual architecture, the nanowire-nanosheet heterostructures also have an appealing combination of characteristics, notably a large surface area due to the 2D nanosheets and efficient charge transport due to the 1D nanowire. For these reasons, the new nanostructures could have applications in photovoltaics, supercapacitors, lithium-ion batteries, 3D optoelectronics, and chemical sensing.
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