Optical absorption in small BN and C nanotubes

TL;DR

This study uses advanced theoretical methods to analyze the optical absorption properties of small boron-nitride and carbon nanotubes, revealing effects of polarization, band-gap characteristics, and structural features on their spectra.

Contribution

It provides a detailed theoretical analysis of optical absorption in small BN and C nanotubes, highlighting the influence of local field effects and chirality on their spectra.

Findings

Perpendicular light absorption is suppressed due to local field effects.

BN nanotubes only absorb in the UV range regardless of chirality.

Additional fine-structure in spectra depends on tube chirality and diameter.

Abstract

We present a theoretical study of the optical absorption spectrum of small boron-nitride and carbon nanotubes using time-dependent density-functional theory and the random phase approximation. Both for C and BN tubes, the absorption of light polarized perpendicular to the tube-axis is strongly suppressed due to local field effects. Since BN-tubes are wide band-gap insulators, they only absorb in the ultra-violet energy regime, independently of chirality and diameter. In comparison with the spectra of the single C and BN-sheets, the tubes display additional fine-structure which stems from the (quasi-) one-dimensionality of the tubes and sensitively depends on the chirality and tube diameter. This fine structure can provide additional information for the assignment of tube indices in high resolution optical absorption spectroscopy.