Scientists have long worked to harness the unusual properties of graphene, a two-dimensional sheet of carbon atoms. However, graphene lacks a single critical characteristic that would make it even more useful: a property known as a bandgap, which is essential for designing devices like computer chips and solar cells.
As such, researchers at MIT and Harvard University are currently experimenting with a two-dimensional material whose properties are very similar to graphene, albeit with certain distinct advantages – including the fact that this material naturally boasts a usable bandgap.
The research, just published online in the Journal of the American Chemical Society, was conducted by MIT assistant professor of chemistry Mircea Dincă and 7 co-authors.
The new material, essentially a combination of nickel and an organic compound known as HITP, also has the advantage of self-assembly. Indeed, its constituents naturally assemble themselves, a “bottom-up” approach that could lend itself to easier manufacturing and tuning of desired properties by adjusting relative amounts of the ingredients.
According to Dincă, two-dimensional materials that possess extraordinary properties is “all the rage these days, and for good reason.” To be sure, graphene offers optimized electrical and thermal conductivity, as well as considerable strength. However, lack of a bandgap forces researchers to modify it for certain uses, which tends to degrade the properties that made the material desirable in the first place.
The new compound, Ni3(HITP)2, shares graphene’s perfectly hexagonal honeycomb structure. In addition, multiple layers of the material naturally form perfectly aligned stacks, with the openings at the centers of the hexagons all of precisely the same size, approximately two nanometers (billionths of a meter) across.
During a series of initial experiments, researchers studied the material in bulk form, rather than as flat sheets. As Dincă notes, this makes the current results – including excellent electrical conductivity – even more impressive, as these properties should be better yet in a 2-D version of the material.
“There’s every reason to believe that the properties of the particles are worse than those of a sheet,” he explains. “[However], they’re still impressive.”
Perhaps most importantly, this is just the first example of what could eventually be a diverse family of similar materials built from different metals or organic compounds.
“Now we have an entire arsenal of organic synthesis and inorganic synthesis [that could be harnessed] to tune the properties, with atom-like precision and virtually infinite tunability,” he adds.
Such materials might ultimately lend themselves to solar cells whose ability to capture different wavelengths of light could be matched to the solar spectrum, or improve supercapacitors used to store electrical energy. Last, but certainly not least, the new material could lend itself to use in basic research on the properties of matter, the creation of exotic materials such as magnetic topological insulators, or materials that exhibit quantum Hall effects.
“They’re in the same class of materials that have been predicted to have exotic new electronic states. These would be the first examples of these effects in materials made out of organic molecules. People are excited about that,” Dincă concludes.