Researchers at Rice University and Oak Ridge National Laboratory (ORNL) are aiming to remake the world of two-dimensional materials, including graphene, molybdenum disulfide (MDS) and hexagonal boron nitride (hBN), so that together they constitute a trilogy of materials for the next generation of electronics.
The ultimate goal of their research is to combine these three 2D materials: a semiconductor, insulator and conductor (MBS, hBN and graphene, respectively) to create a range of electronic devices, such as field-effect transistors, integrated logic circuits, photodetectors and flexible optoelectronics. To get there the researchers have come up with a better way of producing MDS.
When research into using MDS as a 2D material for electronics first started to gain notice, scientists suggested that it would serve as a compliment to graphene, especially in applications that require a transparent semiconductor. While some have seen a rivalry between the two 2D materials developing, research has continued to pursue them as compliments to one another. In fact, recently graphene and MDS have been mated to create a new flash memory. And earlier this year, some of the same Rice University researchers in this current work showed that graphene could be weaved together with hBN to create nanoscale patterns.
While a trilogy of 2D materials might be the long-range aim, the team of researchers started their work by seeing if they could produce large, high-quality sheets of MDS through chemical vapor deposition (CVD) instead of employing the so-called “Scotch Tape” method in which layers of the material are peeled off from bulk samples.
In the research, which was published in the journal Nature Materials (“Vapour phase growth and grain boundary structure of molybdenum disulphide atomic layers”), the team discovered that they could improve the CVD process by adding artificial edges to the substrate.
“The material is difficult to nucleate, unlike hBN or graphene,” said Sina Najmaei. co-author of the paper, in a press release. “We started learning that we could control that nucleation by adding artificial edges to the substrate, and now it’s growing a lot better between these structures.”
The final material built up through CVD was sent over to ORNL where microscopy tools were used to characterize it. Among the properties they discovered in the material is what they believe to be the potential for the atoms in the MDS to bind with carbon atoms in the graphene.
“We’re working on it,” said Zheng Liu, a researcher at Rice, in the press release. “We would like to stick graphene and MDS together (with hBN) into what would be a novel, 2-D semiconductor component.”
“These are very different materials, with different electronic properties and band gaps. Putting one on top of the other would give us a new type of material that we call van der Waals solids,” said Pulickel Ajayan, an engineering professor at Rice. “We could put them together in whatever stacking order we need, which would be an interesting new approach in materials science.”
Image: Oak Ridge National Laboratory
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.