Directly measured optical absorption cross sections for structure-selected single-walled carbon nanotubes

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Single-walled carbon nanotubes (SWCNTs) exhibit unique optical properties crucial for electronic and photonic applications.
• Understanding the relationship between SWCNT structure and optical transitions is key to their targeted use.
• Accurate quantification of SWCNT concentrations is essential for reliable optical measurements.

Purpose of the Study:

• To measure absolute absorption cross sections for the first (E11) and second (E22) optical transitions in semiconducting SWCNTs.
• To investigate the influence of nanotube diameter and chirality on optical absorption.
• To establish a method for determining species-specific SWCNT concentrations in bulk samples.

Main Methods:

• Utilized UV-Vis-NIR absorption spectroscopy to determine optical cross sections.
• Employed short-wave infrared (SWIR) fluorescence microscopy for direct counting of SWCNTs to determine concentrations.
• Analyzed seven distinct semiconducting SWCNT species in bulk suspensions.

Main Results:

• Absolute absorption cross sections were measured for E11 and E22 transitions across seven SWCNT species.
• Species-specific SWCNT concentrations were accurately determined using SWIR fluorescence microscopy.
• A clear inverse relationship was found between absorption cross sections per atom and SWCNT diameter.
• Chirality-dependent differences were observed: E11 cross sections were larger for metallic (mod 1) species, while E22 cross sections were larger for semiconducting (mod 2) species.

Conclusions:

• The study provides fundamental optical absorption data for semiconducting SWCNTs.
• Nanotube diameter and chirality significantly impact optical transition strengths.
• SWIR fluorescence microscopy is a powerful tool for accurate SWCNT quantification in bulk samples.