Plasmonics Used to Dope Graphene

The big push in graphene research for electronics has been overcoming its lack of an inherent band gap.  But silicon has another leg up on graphene when it comes to electronics applications: it can comparatively easily be p- and n-doped (positive and negative).

While there have been a number of approaches taken for doping graphene, researchers at Rice University believe that the idea of plasmon-induced doping of graphene could be ideal for this purpose.

The research (“Plasmon-Induced Doping of Graphene”), which was published in the journal ACS Nano, looks to use plasomonics, which exploits the fact that “photons striking small, metallic structures can create plasmons, which are oscillations of electron density in the metal.”

The Rice team placed nanoscale plasmoic antennas—dubbed nonamers—on the graphene to manipulate light in such a way that they inject electrons into the graphene, changing its conductivity. The nonamers tooks the form of eight nanoscale gold discs that encircled one large gold disc, and were placed on the graphene with electron beam lithography.

When the graphene and nonamers are exposed to light, the incident light is converted into hot electrons that transform those portions of the graphene where the nonamers are located from a conductor to an n-doped semiconductor.

“Quantum dot and plasmonic nanoparticle antennas can be tuned to respond to pretty much any color in the visible spectrum,” says Rice professor Peter Nordlander, one of the authors of the paper, in the university's press release about the research. “We can even tune them to different polarization states, or the shape of a wavefront."

Nordlander adds: “That’s the magic of plasmonics. We can tune the plasmon resonance any way we want. In this case, we decided to do it at 825 nanometers because that is in the middle of the spectral range of our available light sources. We wanted to know that we could send light at different colors and see no effect, and at that particular color see a big effect.”

While the possibility of a process that simply uses light for doping graphene seems pretty amazing, the researchers are looking ahead to a day when a flashlight in a particular pattern would replace a key for unlocking a door by triggering the circuitry of the lock to open it. “Opening a lock becomes a direct event because we are sending the right lights toward the substrate and creating the integrated circuits. It will only answer to my call,” Norlander suggests in the release.

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