Adjacent crystal structures of rhenium diselenide (ReSe2) and molybdenum diselenide (MoSe2) form a 2D transition metal dichalcogenide heterostructure with sharply separated domains. Image: Center for Nanophase Materials Science/Ajayan Research Group.The lab of materials scientist Pulickel Ajayan at Rice University has created unique two-dimensional (2D) flakes with two distinct personalities: molybdenum diselenide (MoSe2) on one side of a sharp divide, with rhenium diselenide (ReSe2) on the other. From all appearances, the two-toned material likes it that way, growing naturally – though under tight conditions – on a substrate in a chemical vapor deposition furnace.
As Ajayan and his colleagues report in a paper in Nano Letters, the material is a 2D transition metal dichalcogenide heterostructure, a crystal with more than one chemical component. That's not unusual in itself, but the sharp zigzag boundary between the elements in the material is unique.
Dichalcogenides are semiconductors made up of transition metals and chalcogens like sulfur or selenium. They're a promising component for optoelectronic applications such as solar cells, photodetectors and sensing devices. According to Amey Apte, a Rice graduate student and lead author of the paper, dichalcogenides may also be suitable materials for quantum computing or neuromorphic computing, which emulates the structure of the human brain.
Apte said that well-known, atomically flat molybdenum tungsten dichalcogenide heterostructures are more alloy-like, with diffuse boundaries between their crystal domains. However, the new material – 2H MoSe2-1T' ReSe2 – has atomically sharp interfaces that gives it a smaller electronic band gap than other dichalcogenides.
"Instead of having one unique band gap based on the composition of an alloy, we can tune the band gap in this material in a very controllable way," Apte explained. "The strong dissimilarity between two adjacent, atomically thin domains opens up new avenues." He said the range of voltages likely spans from 1.5 to 2.5 electron volts.
Growing the materials reliably involved creating a phase diagram that laid out how each parameter – the balance of chemical gas precursor, the temperature and the time – affects the process. Rice graduate student and co-author Sandhya Susarla said the diagram serves as a road map for manufacturers.
"The biggest issue in these 2D materials has been that they're not very reproducible," she said. "They're very sensitive to a lot of parameters, because the process is kinetically controlled.
"But our process is scalable because it's thermodynamically controlled. Manufacturers don't have a lot of parameters to look at. They just have to look at the phase diagram, control the composition and they will get the product every time."
The researchers think they can gain further control over the material's form by tailoring the substrate surface for epitaxial growth. Having the atoms fall into place in accordance with the surface's own atomic arrangement would allow for far more customization.
This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.