Finite-Size Effects in the Absorption Spectra of a Single-Wall Carbon Nanotube

The determination of the optical spectrum of single-wall carbon nanotubes (SWCNTs) is essential for the development of opto-electronic components and sensors with application in many fields. Real SWCNTs are finite, but almost all the studies performed so far use infinite SWCNTs. However, the spectra of finite and infinite systems are different. In this work the optical spectrum of finite (3,3) and (5,5) SWCNTs is calculated as a function of nanotube length. For the (3,3) SWCNTs, the calculated absorption spectra for light polarised both parallel and perpendicularly to the nanotube axis are in good agreement with experimental results. However, our results indicate that the lowest energy peak present in the experimental results for light polarised parallel to the nanotube axis can be attributed to a surface-plasmon resonance that is a consequence of the finite nature of the SWCNTs and not to the presence of SWCNTs with other chiralities, as claimed by the previous theoretical works. The surface-plasmon resonance is also studied using the Aharonov-Bohm effect. Finally, this work demonstrates that the surface-plasmon resonance in finite SWCNT can be described using a 1D infinite well.