2D self-assembling semiconductor could beat out graphene
By Heidi Hoopes
May 2, 2014
Graphene may be talked about as the future wonder material (and for that matter, the present one), but it has one critical deficiency. It lacks a natural bandgap, the physical trait that puts the “semi” in “semiconductor," so it has to be doped to become effective. Enter Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 ... well, you can refer to it as a metal-organic graphene analogue for now. In addition to having a natural band gap, it’s able to self-assemble and represents a whole family of compounds that’s exciting to researchers for its novel properties.
Nickel (the metal) and HITP (the organic compound) are represented in the diagram at the top of the page, with nickel colored in green, amino groups in purple, and carbon rings in grey. The amino groups in the carbon rings are attracted to the nickel, and because of the symmetry and geometry in HITP, the overall organometallic complex almost has a fractal nature that allows this new semiconductor to self-organize perfectly. A band gap is created in the “hole” where electrons aren’t, a space that's just about 2 nm across.
The bandgap is important: graphene must be doped with other compounds to give it the properties of a semiconductor rather than a metal, but this process also negatively affects the otherwise desirable properties of graphene.
So with that chemistry and physics geek-out completed, researchers at MIT under Mircea Dincă initially studied the “bulk” form of this compound, rather than flat 2D sheets, and found even that data impressive. Pellets of Ni3(HITP)2 had a conductivity of 2 S/cm, a record for a metal-organic compound. After creating 2D sheets, the conductance was measured at 40 S/cm, also a record and among the best for any polymer.
To add to the interest even more, Ni3(HITP)2 represents an entire class of similar compounds. Dincă describes the potential as “an entire arsenal of organic synthesis and inorganic synthesis,” harnessable “with atom-like precision and virtually infinite tunability.” In other words, there could be an excellent self-assembling polymer of this type for varying applications, such as creating a solar panel tuned to multiple wavelengths of light.
The research was originally published in the Journal of the American Chemical Society.