When an excitation laser beam moves from a single-layer region to a bilayer region of twisted bilayer graphene islands the Raman intensity of the G line doubles. In contrast, the Raman intensity of the 2D band becomes about four times as strong. The four-fold enhancement of the 2D Raman band is a direct manifestation of the constructive interference between two Raman paths. The intensity of the G line represents an excellent example where there is no interference between two Raman paths.

There is a striking difference in the Raman spectra between twisted bilayer graphene and conventional AB-stacking bilayer graphene. In particular between the G line and 2D band. This reveals the unique underlying electronic band structure of twisted bilayer graphene as well as the unique condition for quantum interference. This finding will help to distinguish among different types of bilayer graphene, and accelerate the exploration of new quantum phenomena in two-dimensional nanomaterials.

More information can be found in the journal Nanotechnology (in press).

Further reading

Graphyne: a two-dimensional material with thermoelectric properties (May 2014)
Graphene production goes green (Sep 2013)