Characterization of carbon materials with Raman spectroscopy

Importance of the Topic

Carbon nanomaterials—including graphene, graphite, carbon nanotubes, and carbon black—exhibit distinct structural features that critically influence their mechanical, thermal, and electronic behavior. As these materials gain traction in diverse sectors such as energy storage, composites manufacturing, and electronic devices, reliable, rapid, and nondestructive quality control methods become essential. Raman spectroscopy offers a powerful means to probe crystallinity, defect density, and layer thickness in carbon materials, facilitating both research and industrial process monitoring.

Objectives and Overview of the Study

This application note follows ASTM E3220 guidelines to demonstrate how Raman spectroscopy can characterize various carbon allotropes. The primary goals are to:

• Illustrate the spectral signatures of key carbon nanomaterials (graphene, graphite, carbon nanotubes, carbon black).
• Detail the calculation of the intensity ratio between the D-band and G-band (ID/IG) as a proxy for structural disorder.
• Showcase a practical measurement workflow using a portable Raman system suitable for manufacturing quality control.

Methodology and Instrumentation

Raman spectra of carbon materials are dominated by three features:

• G-band (~1580 cm⁻¹): in-plane C–C bond vibrations, indicative of crystalline order.
• D-band (~1350 cm⁻¹): defect-activated ring breathing mode, its intensity reflects disorder or edge density.
• 2D-band (overtone of D-band, ~2700 cm⁻¹): sensitive to layer number and stacking.

Spectral analysis involves baseline correction to remove atmospheric contributions and subsequent peak intensity measurement. The ratio ID/IG is calculated following ASTM E3220 protocols to quantify sample quality.

Instrumentation Used

Measurements were carried out with the following setup:

• i-Raman Prime 532H portable Raman spectrometer (532 nm excitation, ~34 mW laser power)
• Fiber-optic probe with BAC150B holder
• BAC152C enclosure for Class 1 laser safety
• BWSpec software for data acquisition, baseline correction, peak fitting, and automated ID/IG reporting

Main Results and Discussion

Distinct Raman profiles were recorded for each material:

• Pristine graphene showed sharp G and 2D peaks, no detectable D-band, and I2D/IG ≈ 2, consistent with high crystallinity and monolayer character.
• Graphite exhibited asymmetric, broadened 2D features and lower I2D/IG ratios, reflecting multilayer stacking.
• Single-walled carbon nanotubes presented split G-bands (G⁺ and G⁻) due to curvature effects.
• Carbon black displayed strong, broad D- and G-bands, with ID/IG values above 0.5, indicative of high defect density.

Additional measurements on nanofiber samples revealed pronounced G-band asymmetry and elevated ID/IG ratios in certain batches, signaling substantial structural disorder.

Benefits and Practical Applications of the Method

Using Raman spectroscopy for carbon material assessment offers:

• Rapid, nondestructive analysis ideal for inline or at-line quality control.
• High specificity to crystallinity and defect concentration via simple spectral metrics.
• Portability and safety compliance for deployment in manufacturing environments.

Future Trends and Applications

Emerging directions include:

• Integration with automated production lines for real-time graphene quality monitoring.
• Development of AI-driven spectral interpretation to predict material performance.
• Expansion of handheld Raman devices capable of analysing coated or packaged samples through advanced Raman techniques.

Conclusion

Raman spectroscopy, guided by ASTM E3220, provides a straightforward and robust framework for evaluating carbon nanomaterials. The ID/IG ratio serves as a reliable indicator of structural order, enabling manufacturers and researchers to quickly distinguish high-quality graphene and graphite from disordered carbon forms.

Reference

Ferrari, A. C. Raman Spectroscopy of Graphene and Graphite: Disorder, Electron–Phonon Coupling, Doping and Nonadiabatic Effects. Solid State Communications 2007, 143 (1), 47–57. https://doi.org/10.1016/j.ssc.2007.03.052
ASTM International. Standard Guide for Characterization of Graphene Flakes; ASTM E3220-20; ASTM International, 2020.