Graphene is extremely useful in some applications owing to its lightweight and ultra-strong characteristics, but it cannot be the solution for all the world’s problems. In that regard, researchers worldwide are in search of new materials with the same level of potential. Graphene expert Mark Hersam at McCormick shows interest in molybdenum disulfide, a transition metal dichalcogenide.
Similar to graphene, atomically thin sheets can be created using molybdenum disulfide through exfoliation. The atomic-scale-thick sheet of molybdenum disulfide exhibits fluorescence property. Hence, it is a potential candidate for optoelectronic applications, including LEDs, as well as in light-absorbing devices like solar cells. As a true semiconductor, it is useful for electronic applications.
However, the challenge lies in the large scale production of atomically thin sheets of molybdenum disulfide. Hersam has devised solution-based techniques for exfoliating thin graphene layers from graphite. Centrifugal force by means of a centrifuge tube was used to isolate graphene layers based on their density. The top in the layers of densities is single layer graphene sheets, followed by sheets of higher order layers.
The comparatively low density of graphene makes this separation possible. However, it is difficult with high density materials like molybdenum disulfide. Hersam has to lower the density of molybdenum disulfide without altering the material itself. Adjusting the density of the molecules utilized for molybdenum disulfide dispersion is the way to achieve this goal.
Molybdenum disulfide’s effective density can reach the range of the density gradient when bulkier polymer dispersants are used. However, this method allows molybdenum disulfide sheets to be floated at layered positions rather than accumulating at the bottom of the centrifuge tube.
This approach is also applicable to other transition metal dichalcogenides, allowing the isolation of single layer and multiple layers of transition metal dichalcogenides in a scalable manner.