Carbon-60 and graphene for vertical transistors

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By Belle Dumé

Graphene has numerous unique electronic and mechanical properties such as extremely high charge carrier mobilities and high mechanical strength, explains team member Kwanpyo Kim at UNIST and Elton Santos at Queen’s. As an atomic thick layer that is structurally sound it can also serve as an assembly template, especially for small organic molecules.

The researchers, led by Zhenan Bao of Stanford, made a vertical structure composed of C60 thin films and graphene. “We exploited the van der Waals interactions between the two materials to make molecular heterostructures and then succeeded in making high-quality transistors from these,” says Kim. “These devices boast high current on-off ratio of over 3000 – a result that has been challenging to achieve in the past considering that graphene itself does not have a bandgap in its natural state.” It is the bandgap in semiconductors that allows the devices to be switched on and off.

C60 films lie uniformly on the graphene substrate
First produced in the lab over a decade ago, graphene can now be grown as large sheets using a process called chemical vapour deposition. In their new work, Kim and colleagues began by preparing suspended graphene films. They then evaporated C60 molecules onto the films to form thin-film crystals.

Thanks to various transmission electron microscopy techniques, including selective area electron diffraction, atomic resolution TEM imaging, and van der Waals-based first principles computational methods, the researchers were able to study the structure and grain size of the crystals in detail and carefully look at the graphene-C60 interface in particular. “We also saw that the C60 films lay uniformly on the graphene substrate and that the individual molecules can assume several different molecular orientations – as confirmed by our first-principles simulations,” says Santos.

Flexible transistors and high-performance photosensors and solar cells
“Since both graphene and organic C60 thin films are good materials for flexible electronics devices, our heterostructures could readily be incorporated into flexible transistors and other such components (like wearable displays, for instance),” he tells “The organic semiconductor-graphene junction is also a unique candidate for high-performance photosensors and solar cells and we expect to see these architectures widely employed in such device applications soon.”

The team says that it will now be looking at how to grow various other organic semiconductor thin films (including polymer thin films) onto graphene. “Our approach allows us to the tune the electrical properties (such as the interfacial energy barrier between the graphene and organic films) of the vertical heterostructures we make - something that will help us develop better performing devices,” say Kim and Santos.

Read the abstract in ACS Nano here.

For the original article, please click here.