This is a high-angle annular dark-field image of pure rhenium diselenide; in the key at bottom right, rhenium atoms are blue and selenium atoms yellow. Image: Oak Ridge National Laboratory.Substituting atoms during the process of making two-dimensional (2D) alloys not only offers a way to customize the alloys for specific applications but can also make them magnetic, according to Rice University scientists and their collaborators.
In a new paper in Advanced Materials, the scientists from Rice, Oak Ridge National Laboratory, the University of Southern California (USC) and Kumamoto University in Japan described how they used chemical vapor deposition (CVD) to make atom-thick alloy sheets. In the same step, they also tailored the properties of these alloys by adding other elements through a process known as doping. This led them to discover by surprise that doping could also give the 2D sheets magnetic properties.
The labs worked with transition metal dichalcogenides (TMDs), alloys that combine a transition metal and chalcogen atoms into a single material. Transition metals are stable elements that fall in the middle of the periodic table; chalcogens include sulfur, selenium and tellurium, also neighbors to each other in the table.
By adding a dopant element to the mix during CVD, the scientists showed it was possible to rearrange the atoms in the resulting 2D crystal sheets. They demonstrated several different configurations and found they could replace some atoms outright with the dopant. These physical changes led to changes in the mechanical and electronic properties of the flat crystals, said co-author and Rice postdoctoral researcher Chandra Sekhar Tiwary.
Led by the Rice lab of Pulickel Ajayan, this project was intended to test the theory developed by USC researchers that doping the materials would force a phase transition in the 2D crystals. The Rice team confirmed that adding rhenium in various amounts to the TMD molybdenum diselenide during growth altered its properties by changing its atomic structure. The magnetic signatures were a bonus.
"Usually, when you make a magnetic material, you start with magnetic elements like iron or cobalt," said graduate student and co-lead author Amey Apte. "Rhenium, in bulk, is not a magnetic material, but it turns out it is in certain combinations at the atomic scale. It worked fantastically in this case."
The scientists said the magnetic properties they discovered could make the 2D alloys of interest for spintronic devices that encode digital information in electron spins.
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.