Characterization of carbon materials with Raman spectroscopy

Importance of the Topic

Carbon nanomaterials including graphene, graphite, carbon nanotubes, and carbon black possess unique mechanical, electrical, and thermal properties that drive their adoption across industries such as energy storage, construction, and advanced manufacturing. Precise, rapid, and nondestructive characterization of these materials is critical to ensure consistent performance and quality in research and production environments.

Objectives and Study Overview

This application note outlines a standardized Raman spectroscopy approach for assessing the structural quality of carbon nanomaterials in accordance with ASTM E3220-20. Key aims include:

• Demonstrating spectral features associated with graphene layers, defects, and crystallinity.
• Describing a workflow for baseline correction, peak identification, and ID/IG ratio calculation.
• Providing practical examples of spectra for various carbon allotropes and interpretation guidelines.

Methodology

Raman spectra were collected using a 532 nm excitation source, targeting the principal carbon bands:

• G-band (~1580 cm⁻¹): In-plane vibrational mode indicative of graphitic order.
• D-band (~1350 cm⁻¹): Defect-activated breathing mode, sensitive to disorder and edge sites.
• 2D-band (~2700 cm⁻¹): Overtone of D-band, used to estimate layer thickness and stacking.

Data processing steps:

• Baseline correction to remove background and atmospheric features.
• Peak fitting to extract intensity values for D and G bands.
• Calculation of the ID/IG intensity ratio as a semi-quantitative marker of structural disorder.

Applied Instrumentation

Measurements were performed on an integrated portable Raman spectrometer system:

• i-Raman Prime 532H: 532 nm laser, TE-cooled CCD detector, embedded tablet interface.
• Probe holder (BAC150B) with fiber-optic sampling probe for stable sample positioning.
• Safety enclosure (BAC152C) ensuring Class 1 laser operation in manufacturing environments.
• BWSpec software for instrument control, baseline correction, peak fitting, and automated ID/IG reporting.

Key Results and Discussion

Distinct spectral signatures were observed for each carbon material:

• High-quality monolayer graphene exhibited a sharp G-band, prominent 2D-band (I2D/IG ≈ 2), and negligible D-band.
• Graphite showed a broadened, asymmetric 2D-band with a low I2D/IG ratio.
• Single-walled carbon nanotubes displayed a split G-band (G+ and G–) due to tubular curvature.
• Carbon black presented strong D and G bands with high ID/IG ratios (>0.5), reflecting substantial disorder.

Data from multiple samples confirmed that the ID/IG ratio increases with defect density and can serve as a rapid quality control metric. Examples of nanofiber spectra revealed asymmetric G-bands and elevated ID/IG values corresponding to higher disorder levels.

Benefits and Practical Applications

Adopting this Raman-based workflow offers several advantages:

• Nondestructive analysis suitable for research labs and manufacturing floors.
• Fast acquisition (30–90 s) and inline or offline quality checks.
• Semi-quantitative ID/IG parameter enabling pass/fail evaluation of carbon materials.
• Applicability to a wide range of carbon allotropes and powder samples.

Future Trends and Applications

Emerging directions in carbon material analytics include:

• Integration of inline Raman probes with production lines for real-time process control.
• Machine learning algorithms for automated spectral classification and defect quantification.
• Expansion to composite and functionalized carbon materials, correlating spectral markers with performance metrics.

Conclusion

Raman spectroscopy guided by ASTM E3220 offers a robust, reproducible method for assessing carbon nanomaterial quality. The ID/IG intensity ratio provides a simple yet effective indicator of structural disorder, supporting rapid quality control and material research.

References

• Ferrari AC. Raman Spectroscopy of Graphene and Graphite: Disorder, Electron–Phonon Coupling, Doping and Nonadiabatic Effects. Solid State Communications. 2007;143(1):47–57.
• ASTM International. Standard Guide for Characterization of Graphene Flakes. ASTM E3220-20; ASTM International; 2020.