Graphene Getting More Competition
Practically since it was first discovered, graphene has been considered a wonder material for its many special properties. For perhaps not as long, researchers have been looking for other materials that replicate some of graphene's properties, but add some other, valuable properties into the mix. Researchers at Berkeley Lab have recently discovered a new contender for graphene that could see use in photonic and optoelectric technologies.
Called MX2 materials, these two dimensional semiconductors are made of a layer of a transition metal, like tungsten or molybdenum, with a chalcogen, like sulfur, sandwiching it. The result is a structure with the same hexagonal design of graphene and its highspeed electrical conductance, but also a band gap. Band gaps are the energy difference between conducting bands and non-conducting, valence bands in a material. As graphene lacks a band gap, it lacks a means to switch its conductivity on and off, like a semiconductor. By combining layers of different MX2 materials, it is possible to control their properties and now the researchers have found that they can have very short charge transfer times of under 50 femtoseconds.
A short charge transfer time, and thereby efficient charge transfer, impacts the ability to separate charges in a material. This is important in materials for photodetectors and solar cells, because if the charges recombine too early, what energy they had would be lost.
Source: Berkeley Lab