Influence of oxygen-defects on intraband terahertz conductivity of carbon nanotubes

TL;DR

This study investigates how oxygen-induced defects in single-walled carbon nanotubes affect their terahertz conductivity and charge transport, revealing defect-dependent plasmon shifts and potential for THz device engineering.

Contribution

It introduces a modified Drude model considering non-equilibrium carriers and demonstrates defect-controlled tuning of THz properties in SWCNTs.

Findings

Defects cause a shift in plasmon resonance to higher THz frequencies.

Increased defects lead to reduced conductivity and slower charge migration.

Higher THz field strength diminishes conductivity due to intraband absorption bleaching.

Abstract

The exceptional charge transport properties of single-walled carbon nanotubes (SWCNTs) enable numerous ultrafast optoelectronic applications. Modifying SWCNTs by introducing defects significantly impacts the performance of nanotube-based devices, making defect characterization crucial. This research tracked these effects in oxygen plasma-treated SWCNT thin films. Sub-picosecond electric fields of varying strengths and additional photoexcitation were used to assess how defects influence charge carrier transport. Changes in effective conductivity within the terahertz (THz) range were found to be strongly dependent on impurity levels. The plasmon resonance shift to higher THz frequencies aligns with the defect-induced reduction in conductivity and slowed carrier migration within the network. An increase in THz field strength resulted in diminished conductivity due to intraband absorption bleaching. To address the emergence of hot charge carriers, a modified Drude model, which considers non-equilibrium charge carrier distribution via fielddependent scattering rates, was applied. The dominant charge-impurity scattering rate in plasma-treated samples corresponded with an increase in defects. Additionally, the impact of defects on charge carrier dynamics on a picosecond timescale was examined. The modeled plasma-treated SWCNTs wire-grid polarizer for the THz range reveals the potential for multi-level engineering of THz devices to customize properties through controlled defect populations.