Distinguishing Field Effects from Charge Effects in the Optoelectronic Properties of Carbon Nanotube Films

W Joshua Kennedy

doi:10.1155/2013/586208

Abstract

We have used charge-induced absorption to quantify the influence of injected charges on electroabsorption measurements in single-wall carbon nanotube films. The interpretations of experimental measurements of χ3 processes in nanotubes are simplified by taking into account the change in electron-electron interactions upon charge injection. Electroabsorption spectra that are properly corrected for charge-induced effects show remarkable agreement with a simple Stark shift of the exciton transitions with no notable second-derivative contributions. Thus, distinguishing electric field effects from carrier density effects allows for a more rigorous calculation of exciton polarizability from electroabsorption measurements, even in heterogeneous films. PACS: 78.67.Ch Nanotubes: optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures.

Highlights

While much attention has been given to precise optical measurements on individual single-wall carbon nanotubes (SWNTs) or monodispersed populations of SWNTs, devices made from heterogeneous mixtures of nanotubes continue to be of interest for use as field emitters, actuators and transducers, chemical sensors, transparent conductive films, and field-effect transistors [1,2,3,4,5,6]
We have shown that the EA signal in such films is a simple combination of a component proportional to the first derivative of the absorption and a component proportional to the charge-induced bleaching, with no need to include higher derivative terms or the notion of state mixing with lower lying “dark” excitons
This opens the door for refined calculations of exciton polarizability and binding energy, using the relatively simple technique of electroabsorption if a suitable measurement or calculation of the actual field experienced by the nanotubes can be obtained

Summary

Introduction

While much attention has been given to precise optical measurements on individual single-wall carbon nanotubes (SWNTs) or monodispersed populations of SWNTs, devices made from heterogeneous mixtures of nanotubes continue to be of interest for use as field emitters, actuators and transducers, chemical sensors, transparent conductive films, and field-effect transistors [1,2,3,4,5,6]. The absence of Franz-Keldysh oscillations in EA spectra of nanotubes was used as evidence of the excitonic nature of the photoexcitations in SWNTs [7,8,9]. EA spectra of heterogeneous mixtures of SWNTs suffer from a variety of complex interactions. Perturbation of π orbitals due to bundling, intertube charge transfer or trapping, and other competing effects can obfuscate individual tube responses to external fields. Because of these interactions, the analysis of SWNT EA spectra is less straightforward than for many other materials

Methods

Results

Conclusion