Tight-Binding Investigation of Structural and Vibrational Properties of Graphene-Single Wall Carbon Nanotube Junctions

Hybrid carbon nanostructures based on single walled carbon nanotubes (SWNT) and single layer graphene (SLG) are drawing much attention lately for their applications in a range of efficient hybrid devices. Few recent studies, addressing the interaction behavior at the heterojunction, consider charge transfer between the constituents (SWNT and SLG) to be responsible for changes in the electronic and vibrational properties in their hybrid system. We report the effect of various factors, arising due to the interactions between atoms of SWNT and SLG, on the structural and vibrational roperties of hybrid nanostructures investigated computationally within the framework of tight-binding DFT. These factors such as the van der Waal’s (vdW) forces, structural deformation and the charge transfer, are seen to affect the Raman active phonon frequencies of SWNT and SLG in the hybrid nanostructure. These factors are already known to affect the vibrational properties on SWNT and SLG separately and in this work, we have explored their role and interplay between these factors in hybrid systems. The contribution of different factors to the total shift observed in phonon frequencies are estimated and it is perceived from our findings that not only the charge transfer but the structural deformations and the vdW forces also affect the vibrational properties of components within the hybrid, with structural deformation being the leading factor. With decreasing separation between SWNT and SLG, the charge transfer and the vdW forces, both increase. However, the increase in vdW forces is relatively much higher and likely to be the main cause for larger Raman shifts observed at smaller separations.