Nanowire casting triggers an unexpected process, Sometimes, to make big progress, you have to start small.
In particular, scientists can make many different quantum materials by creating nanoscale structures that create new properties on the surface and around the material. Cornell researchers used a simple thermomechanical nanocasting technique to create single-crystal nanowires that can make a metastable structure that would be difficult to achieve with conventional methods.
“We are really interested in this process of nanocasting synthesis because it allows us to quickly and easily change many different types of materials at the nanoscale, while we benefit from the control of the methods other aspects of nanomaterial synthesis lack, especially morphology and size control.” Judy Cha, Ph.D. ’09, professor of materials science and engineering at Cornell Engineering, who led the project.
The team’s paper, “Nanomolding of Metastable Mo4P3,” was published April 12 in Matter. The lead author of this article is postdoctoral researcher Mehrdad Kiani.
In thermomechanical nanocasting, materials are combined into a large component, placed in a hollow mold, and pressed at high temperatures for several hours. The resulting process is separated from the material used – in this case, through ultrasonic vibrations, a process known as sonication – and placed on a silicon wafer or another surface.
The advantage of this method (Nanowire Casting Triggers an Unexpected Process) is that nanoscale quantities of solids can be cast at temperatures well below their melting point, representing simple processing conditions. This allows the use of many different materials for strange, unrealized things, such as graphene to change the structure of electronics. Cha’s team tested molybdenum monophosphide (MoP), which is a topological compound.
“Topological metals should have a resistance that decreases as you go to smaller sizes, and the MoP is not only topological, but also has a high density (electrons per volume), which should help further reduce the resistance,” Kiani said.
Cha and his team have previously shown that nanocasting topological nanowires can lead to the discovery of new electronic devices for applications such as quantum computing, microelectronics and clean energy. These nanowires would be ideal for making connections between billions of transistors in integrated circuits. Last year, the team showed that MoP nanowires have such a low resistance that they are compatible with copper.
“It’s an amazing discovery,” Cha said. “But the challenge is that we have to keep making the MoP smaller and smaller, and the methods we are using are not getting us there. So, the nanocasting process came along, and we saw it as a way to make small MoP nanowires to test whether the resistivity will still be lower than copper.
Instead, they found that the process of molding the nanowires changed the crystal structure of MoP into a different material: Mo4P3.
“It’s not what we expected. And even more surprising, this Mo4P3 system is not the stable system that you usually get,” Cha said. “We now understand that this cast system can give us a metastable system.”
The resistance of metastable Mo4P3 is about 75% higher than that of MoP, so MoP remains a promising candidate for fusion.
“It expands our scope for exploring new things. But who knows what could be? Cha said. “When graphene was first discovered, it was not clear that we could use it in golf balls, for example, to think about ordinary applications. For now, we want to see the next example of Mo4P3, another metastable system that we can stop and turn into nanowires.
Source: Cornell University
