Harvard Scientists Bend Nanowires 2-D, 3-D

Harvard Gazette is reporting that the university’s nanotechnologists developed a new methodology to produce 2-D and 3-D shaped nanowires by introducing bends through a series of stereocenters:

“We are very excited about the prospects this research opens up for nanotechnology,” said Lieber, Mark Hyman Jr. Professor of Chemistry in Harvard’s Faculty of Arts and Sciences. “For example, our nanostructures make possible integration of active devices in nanoelectronic and photonic circuits, as well as totally new approaches for extra- and intracellular biological sensors. This latter area is one where we already have exciting new results, and one we believe can change the way much electrical recording in biology and medicine is carried out.”
Lieber and Tian’s approach involves the controlled introduction of triangular “stereocenters” – essentially, fixed 120-degree joints – into nanowires, structures that have previously been rigidly linear. These stereocenters, analogous to the chemical hubs found in many complex organic molecules, introduce kinks into 1-D nanostructures, transforming them into more complex forms.
The researchers were able to introduce stereocenters as nanowires, which are self-assembled. The researchers halted growth of the 1-D nanostructures for 15 seconds by removing key gaseous reactants from the chemical brew in which the process was taking place, replacing these reactants after joints had been introduced into the nanostructures. This approach resulted in a 40 percent yield of bent nanowires, which can then be purified to achieve higher yields.
“The stereocenters appear as kinks, and the distance between kinks is completely controlled,” said Tian, a research assistant in Harvard’s Department of Chemistry and Chemical Biology. “Moreover, we demonstrated the generality of our approach through synthesis of 2-D silicon, germanium, and cadmium sulfide nanowire structures.”
The research by Lieber and Tian is the latest in the years-long efforts by scientists to control the composition and structure of nanowires during synthesis. Despite advances in these areas, the ability to control the design and growth of self-assembling nanostructures has been limited. Lieber and Tian’s work takes the formation of 2-D nanostructures a step further by enabling the introduction of electronic devices at the stereocenters.
“An important concept that emerged from these studies is that of introducing functionality at defined nanoscale points for the first time – in other words, nanodevices that can ‘self-label,’ ” Lieber said. “We illustrated this novel capability by the insertion of p–n diodes and field-effect transistors precisely at the stereocenters.”
Such self-labeled structures could open up the possibility of introducing nanoelectronics, photodetectors, or biological sensors into complex nanoscale structures.

Full story: Nanowires go 2-D, 3-D…
Abstract in Nature Nanotechnology: Single-crystalline kinked semiconductor nanowire superstructures