Scooping quantum dots out of graphane

May 28, 2010 – Researchers at Rice U. say they have figured out how to carve up graphane sheets to create spaces of pure graphene with properties of semiconducting quantum dots, results that point to possible future work in nanoelectronics.

The subject material, graphane, is a sister to graphene but with hydrogen atoms attached to both sides of the matrix, making it an insulator and thus a target for research into manipulating its semiconducting properties. Removing islands of hydrogen from both sides of a 2D graphane sheet, they calculate, leaves a "well" of pure graphene that exhibits all the properties of a quantum dots — crystalline molecules with size-determinant bandgap and tunability, applicable in devices from chemical sensors to solar cells to nanoscale circuitry.

"This phase transformation (from graphene to graphane), accompanied by the change from metal to insulator, offers a novel palette for nanoengineering," states Boris Yakobson, research team leader and Rice professor of mechanical engineering and materials science and of chemistry.

When chunks of the hydrogen are removed, the area left behind is always hexagonal, with sharp interface between the graphane and graphene — which means each dot is highly contained, and very little charge leaks into the graphane host material. "You have an atom-like spectra embedded within a media, and then you can play with the band gap by changing the size of the dot," noted postdoc contributor Abhishek Singh. "You can essentially tune the optical properties."

Precise removal of the hydrogen atoms is still being determined, they admit, and more work is needed to make arrays of quantum dots in a sheet of graphane. Future use could be in optics, single-molecule sensing, and ultimately nano-transistors and semiconductor lasers. "We think the major conclusions in the paper are enough to excite experimentalists," added Singh.

Their work has been published in ACS Nano.

Click to Enlarge
Electron densities created from graphane-embedded quantum dot calculations. The isosurfaces depict electrons in the valance band that, in reality, would be confined within the quantum dot, and demonstrate that very little charge would leak from the hydrogen-defined boundaries of such a dot. (Source: Rice U.)



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