Carbon Analysis with High Signal Throughput Portable Raman Spectroscopy

Significance of the Topic

Carbon nanomaterials such as graphene, graphite, carbon nanotubes and carbon black possess unique mechanical, electrical and thermal properties that are driving their adoption across industries from batteries to composite materials. As production scales up, fast, reliable and non-destructive methods for assessing structural quality and defects become critical to ensure performance and uniformity in manufacturing.

Objectives and Study Overview

This application note demonstrates the use of a portable, high signal-throughput Raman spectroscopy system for characterizing carbon allotropes. The goal is to establish a rapid quality-control workflow based on key Raman features and intensity ratios, enabling inline or offline pass/fail testing in production environments.

Methodology and Instrumentation

Raman spectra of carbon materials are dominated by three bands: the G-band (~1580 cm⁻¹) reflecting sp² lattice vibrations, the D-band (~1350 cm⁻¹) indicating structural disorder or edge defects, and the 2D-band as an overtone of the D-band. The intensity ratio I(D)/I(G) serves as a semi-quantitative measure of defect density.

• i-Raman® Prime 532H system: 532 nm laser, integrated tablet, low-noise detector.
• Probe holder: manual coarse and fine XYZ adjustments for stable sampling.
• Safety enclosure: converts class 3B laser to class 1 for safe operation at 532, 785 and 1064 nm.
• Software BWSpec®: baseline correction, peak fitting and automatic intensity ratio calculation.

Main Results and Discussion

Raman spectra were collected for pristine graphene, graphite, single-walled carbon nanotubes (SWCNTs), carbon nanofibers and carbon black powders with typical acquisition times of 30–90 s at ~3–4 mW laser power. Key observations include:

• Graphene displays sharp G and 2D bands, no detectable D-band, and I(2D)/I(G) ≈ 2, indicating high crystallinity.
• Graphite shows a broadened, asymmetrical 2D band and reduced I(2D)/I(G) due to increased layer stacking.
• SWCNTs exhibit a split G-band (G+ and G– modes) caused by tube curvature effects.
• Carbon nanofibers yield I(D)/I(G) values ranging from 0.50 to 1.57, reflecting variable defect densities.
• Carbon black samples consistently show strong D-bands with I(D)/I(G) values above 0.58, signifying low crystallinity.

The BWSpec software’s baseline removal and peak intensity measurements facilitate rapid calculation of I(D)/I(G), which can be exported for reporting and automated pass/fail decision-making.

Benefits and Practical Applications

Raman spectroscopy offers:

• Non-destructive analysis allowing subsequent use of samples.
• Minimal sample preparation and rapid measurement times.
• Portable configuration suitable for on-site and inline process monitoring.
• Quantitative defect assessment via the I(D)/I(G) ratio as a straightforward quality-control metric.

Future Trends and Opportunities

Advances are expected in multi-wavelength Raman platforms to account for dispersive band behavior, integration with machine-learning algorithms for automated spectral classification, real-time inline monitoring in battery and composite manufacturing, and extension to emerging carbon-based materials such as doped graphene and hybrid nanocomposites.

Conclusion

Portable high signal-throughput Raman spectroscopy, combined with standardized baseline correction and intensity ratio analysis, provides a robust, rapid and reliable approach for characterizing structural order and defects in carbon nanomaterials. The I(D)/I(G) parameter is a versatile pass/fail criterion applicable in both research and industrial quality-control settings.

References

1. A. C. Ferrari et al. Solid State Communications 143, 47–57 (2007)
2. ASTM E3220-20 Standard Guide for Characterization of Graphene Flakes, ASTM International, West Conshohocken, PA (2020)