Graphene can absorb more than 2% of incident visible light, but researchers at IBM have discovered that graphene can absorb up to 40% of light in the far infrared and microwave frequency ranges. The finding confirms that the material could be ideal for terahertz applications.
Graphene
Graphene is a 2D sheet of carbon just one atom thick with unique electronic and mechanical properties. Graphene has a number of technological applications and can even replace silicon in the electronic industry. This is because electrons travel through graphene at extremely high speeds with no rest mass.
It can also absorb light over a very wide range of wavelengths, ranging from the visible to the infrared. This is unlike III-V semiconductors that do not work over such a wide range.
Infrared light
The infrared part of the electromagnetic spectrum is important for optical telecommunications, for example, and the terahertz range in areas like biological imaging, materials analysis and security screening. Characterizing graphene at these wavelengths is thus crucial for developing graphene optoelectronic devices for such applications.
Infrared radiation absorption
The IBM researchers in New York had already analyzed the infrared radiation emitted from graphene, determined the temperature distribution, carrier (electron and hole) densities and the position of band structure where the valence and conduction bands touch. The Fermi level of undoped (or intrinsic) graphene coincides with the Dirac point, and the position of this point is crucial for defining graphene's properties.
The researchers have studied few-layer wafer-scale epitaxial and single-layer CVD graphene using infrared spectroscopy and were able to obtain information on the sheet resistance and the rate at which free carriers are scattered during transport.
According to the researchers the finding opens up avenues for applications in transparent terahertz optoelectronics, terahertz infrared metamaterials, cloaking, transformation optics and photonics applications.
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