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

TL;DR

This study investigates how finite length affects the optical absorption spectra of single-wall carbon nanotubes, revealing surface-plasmon resonances that differ from infinite models and align with experimental observations.

Contribution

It provides a detailed analysis of finite-size effects on SWCNT spectra, identifying surface-plasmon resonances as key features explained by a 1D infinite well model.

Findings

Finite SWCNTs exhibit surface-plasmon resonances.

Calculated spectra agree with experimental results for (3,3) nanotubes.

Surface-plasmon resonance is explained by a 1D infinite well model.

Abstract

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.