Because the nanowires are semiconductors, they could be used as switching devices. "These nanowires are about 10 times smaller than the smallest silicon wires, and, if used in future technology, would result in powerful energy-efficient devices," Kim said.
Using a transmission electron microscope, the researchers started with atomically thin, 2D sheets of molybdenum ditelluride. The material belongs to a class called transition metal dichalcogenides, which show promise in replacing silicon in transistors.
"We wanted to understand the thermal stability of this particular material," Kim said. "We thought it was a good candidate for next-generation nanoelectronics. Out of curiosity, we set out to see whether it would be stable above room temperature."
When they increased the temperature to 450°C, the researchers saw the molybdenum ditelluride layers began to transform into six-pointed star shapes.
The material was transitioning into hexa-molybdenum hexa-telluride, a 1D wire-like structure. This structure consisted of six central atoms of molybdenum surrounded by six atoms of tellurium.
"Then, when we examined the material more closely, we found that the transition we were seeing was not in any of the phase diagrams," Kim said. "Normally, when you heat up particular materials, you expect to see a different kind of material emerge as predicted by a phase diagram. But in this case, it formed a whole new phase."
"We would want to use the nanowires individually because we are pushing the size of a transistor as small as possible."
The researchers now have to determine how to separate out the nanowires and overcome technical challenges to manufacturing and mass production.