Nano Lett. 12, 2470–2474 (2012)

Morphological defects in graphene layers grown on SiC can result in a strong plasmon resonance in the terahertz region, according to Iris Crassee and co-workers from Switzerland, France, Germany, Spain, Czech Republic and the USA. Furthermore, the presence of the plasmons can affect the magneto-optical response of the material — particularly the Faraday rotation. The researchers began by growing graphene epitaxially on SiC using an approach that results in uniformly distributed defects caused by a combination of substrate 'terraces' and post-graphitization thermal relaxation. They then used atomic force microscopy to show that the defects are oriented predominantly in one direction across the entire sample, and that electromagnetic absorption is 1.7 times higher when the electric field is perpendicular to the terraces, which suggests that the terraces assist plasmon excitation. The researchers probed the magneto-optical response using Fourier-transform infrared spectroscopy with a split-coil superconducting magnet at a temperature of 5 K in magnetic fields of up to 7 T. They observed a strong response at around 1.6 THz in the absence of a magnetic field, and resonance splitting in the presence of a magnetic field. Although similar plasmons have been observed on lithographically nanostructured graphene, the approach of Crassee and co-workers does not require special patterning and is a natural by-product of the growth process.