Graphene has been a hot topic in both fundamental science and practical applications since it was first isolated in 2004. It is the most conductive material known and has many other attractive properties such as flexibility, transparency and impermeability. This makes it suitable for application in wide-ranging areas such as sanitation, biomedical science and electronics.
The incredible features and applications of this material can be generated by adding layers of graphene on top of a single graphene layer. The interlayer shear modes in these few-layer graphene are very important for understanding their exceptional properties. However, these modes are in very low frequency range with very weak intensities which greatly hinders exploration.
This month’s Paper of the Month comes from Nanyang Technological University, in Singapore. Cong, currently a professor of Fudan University, and Ting demonstrated methods of improving intensities of the shear modes of graphene layers which would in turn allow better probing of few-layer graphene itself and exploration of its application.
Cong and Ting discovered a way to enhance such interlayer shear modes through folding the bernal-stacked graphene layers with certain twisting angles. They used Linkam’s electrical probe stage, the HFS600E-PB4, which has a temperature range of -196°C to 600°C in their temperature dependant in-situ Raman spectroscopy experiments.
When asked to comment on the motivation behind their work, and the purpose of the Linkam stage, Dr Cong said:
“Investigations of shear modes in few-layer graphene are greatly hindered by the truth that shear modes of graphene layers are extremely weak and almost fully blocked by a Rayleigh rejecter in Raman measurements.
We found that the shear modes could be dramatically enhanced by properly folding graphene layers. Such strong signals offer the feasibility of performing systematically in-situ temperature Raman scattering measurements with the help of a Linkam stage. The vibrational symmetry, anharmonicity and electron-phonon coupling of the shear modes of graphene layers are uncovered through studies of temperature-dependent Raman spectroscopy.
The Linkam stage which is compatible with our confocal low-frequency Raman system, helps us to realize the temperature-dependent Raman measurement with liquid nitrogen”.
Their research will provide a better insight into the mechanical and electrical properties of graphene.
By Tabassum Mujtaba
Cong, C. & Ting, Y. Enhanced ultra-low-frequency interlayer shear modes in folded graphene layers. Nat Commun. 5:4709 | DOI: 10.1038/ncomms5709 (2014).