Characterization of single-walled carbon nanotubes by Raman spectroelectrochemistry

Significance of the Topic

Raman spectroelectrochemistry integrates vibrational spectroscopy and electrochemical control in a single experiment, offering complementary insights into redox behavior and structural features of nanomaterials. Single-walled carbon nanotubes (SWCNTs) exhibit unique electronic, mechanical, and thermal properties, making their in-depth characterization crucial for sensor development, energy storage, and nanoelectronics.

Objectives and Study Overview

This study demonstrates how the SPELEC RAMAN instrument is applied to analyze SWCNT films during anodic electrochemical doping in aqueous solution. Key goals include:

• Determining nanotube diameter distribution via radial breathing modes.
• Tracking real-time changes in tangential (G) band intensity and position under varying potentials.
• Evaluating defect generation by monitoring D/G intensity ratios as a function of applied voltage.

Materials and Methods

SWCNT films were deposited on a screen-printed carbon electrode (110SWCNT). Electrochemical doping was carried out in 0.1 M KCl aqueous solution by scanning the potential from 0.00 V to upper limits (up to +1.80 V) and back at 0.05 V/s. Raman spectra were recorded in situ with 1 s integration times, enabling dynamic monitoring of spectral changes.

Used Instrumentation

• SPELEC RAMAN spectroelectrochemical setup combining a 785 nm Class 3B laser, a bipotentiostat/galvanostat, and a near-infrared spectrometer (785–1010 nm, 0–2850 cm⁻¹).
• 110SWCNT screen-printed electrode modified with single-walled carbon nanotubes for enhanced electroactive surface area.

Main Results and Discussion

• Diameter Distribution: Four radial breathing mode (RBM) bands at 120–300 cm⁻¹ corresponded to diameters of 1.55, 1.19, 1.07, and 0.92 nm, reflecting sample heterogeneity.
• G-Band Behavior at Moderate Doping (+1.00 V): G-band intensity at 1592 cm⁻¹ decreased steadily during anodic scan and recovered upon return to 0.00 V, indicating reversible filling/depletion of electronic states.
• High-Potential Effects (+1.80 V): G-band bleaching persisted with only partial intensity recovery and a measurable upshift in peak position, attributed to changes in C–C bond force constants and phonon renormalization under heavy p-doping.
• Defect Generation: The D/G intensity ratio rose from 0.51 at +1.00 V to 1.26 at +1.80 V, showing more than a two-fold increase in defect density due to electrochemical oxidation.

Advantages and Practical Applications of the Method

• Simultaneous electrochemical and spectroscopic monitoring enables real-time observation of redox and structural changes.
• Quantitative evaluation of nanotube diameter distribution and defect density informs quality control of CNT films.
• Applicable to sensor optimization, battery electrode evaluation, and nanoelectronic device development.

Future Trends and Potential Applications

• Integration with machine-learning algorithms for automated spectral interpretation and defect mapping.
• Multi-wavelength Raman spectroelectrochemistry to access different resonance conditions and broaden analytical scope.
• In situ monitoring of CNT-based devices under operational conditions, such as flexible electronics and electrochemical energy conversion systems.

Conclusions

Raman spectroelectrochemistry using the SPELEC RAMAN instrument provides a powerful approach for detailed characterization of SWCNT films. It reveals diameter distributions, tracks dynamic G-band responses to electrochemical doping, and quantifies defect generation through D/G ratio analysis. This method supports the development and quality assurance of CNT-based technologies.

References

1. M.S. Dresselhaus, G. Dresselhaus, R. Saito, A. Jorio, Raman spectroscopy of carbon nanotubes, Physics Reports 409 (2005) 47–99.
2. L. Kavan, L. Dunsch, Spectroelectrochemistry of carbon nanostructures, ChemPhysChem 8 (2007) 974–998.
3. M. Kalbac, L. Kavan, L. Dunsch, Effect of Bundling on the Tangential Displacement Mode in the Raman Spectra of Semiconducting Single-Walled Carbon Nanotubes during Electrochemical Charging, J. Phys. Chem. C 113 (2009) 1340–1345.