July 22, 2011 — Scientists from the A*STAR Institute of High Performance Computing and the National University of Singapore developed a method to collapse spherical carbon nanostructures into perfect quantum dots. The technique could be applied to manufacture quantum-dot-based next-generation electronics and optoelectronics.
The carbon atoms in graphite are arranged into stacked sheets that are weakly bound to one another. Single-layer graphene can be peeled from bulk graphite, but offers radically different properties. Graphene-based quantum dots, a few nanometers in diameter, must be uniformly manufactured to maintain consistent properties. The researchers took a hollow spherical carbon buckyball (carbon 60) and fragmented it to produce uniformly sized quantum dots of graphene.
The researchers deposited the buckyballs onto a ruthenium surface to catalyze the fragmentation. Heated to 725 kelvin, the carbon atoms rearranged from a sphere into a flower shape. At 825 kelvin, these dots merged into a single quantum dot 1.2nm-wide.
The image demonstrates how buckyballs can be converted into graphene quantum dots by heating them on a ruthenium substrate.
The carbon fragments diffused across the metal substrate, forming uniform nano-graphene structures, according to the research team, which noted that the experiment required low coverage of buckyballs on the ruthenium layer.
The graphene dots’ shape may be influenced by the annealing temperature and density of the carbon clusters, which would allow makers to tune the dots’ properties.
"The next step in the research will be to devise ways to extract these interesting nanostructures from the ruthenium and transfer them to a semiconducting substrate for further experiments," say the researchers.
Lu, J., Yeo, P. S. E., Gan, C. K., Wu, P. & Loh, K.P. Transforming C60 molecules into graphene quantum dots. Nature Nanotechnology 6, 247–252 (2011). Access it at http://www.nature.com/nnano/journal/v6/n4/full/nnano.2011.30.html
The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing.