Researchers have found a new method for chemically exfoliating molybdenum disulfide crystals into "high quality monolayer flakes"; the technique allows them to make larger flakes with a higher yield than has been possible in the past.
These flakes can be transformed into a "printable solution" useful in applications such as printable photonics and electronics, a University of Singapore news release reported.
The same method can also be applied to other two-dimensional materials such as tungstendiselenide and titanium disulfide.
"Transition metal dichalcogenides" are formed when chalcogens (such as sulfur) combine with transition metals (like molybdenum). These dichalcogenides have gained popularity in the scientific world because of their "unique electronic and optical properties," the news release reported.
Current single layer chalcogenide-printing processes are tedious and produce very little material. The flakes produced are also of "submicron sizes," which makes them difficult to use in electronic devices.
Many possible applications require "clean and large-sized flakes"; this need is what prompted the researchers to search for better single-layer transition metal dichalcogenide-making methods.
The team looked at various metal adducts of naphthalene such as lithium, sodium and potassium" and compared their exfoliation efficiency with molybdenum disulfide.
The researchers used a "two-step expansion and intercalation method" that proved to have the ability to produce flakes of "unprecedented size." The method also allowed the molybdenum disulfide flakes to be made into a printable solution.
"At present, there is a bottleneck in the development of solution-processed two dimensional chalcogenides. Our team has developed an alternative exfoliating agent using the organic salts of naphthalene and this new method is more efficient than previous solution-based methods. It can also be applied to other classes of two-dimensional chalcogenides," Doctor Zheng Jian, the first author of the paper, said in the news release.
"Considering the versatility of this method, it may be adopted as the new benchmark in exfoliation chemistry of two-dimensional chalcogenides," he said.
