Research-Grade Raman Analysis of Carbon Nanotubes

innoRam, an advanced Raman spectrometer system from B&W Tek, has been specifically developed to deliver excellent performance in both lab and mobile environments. The system offers high sensitivity and application versatility, and features a back-thinned, 2D vertically binned CCD detector with TE-cooling to -20°C to guarantee research-grade performance.

This article compares the results of Raman analysis of carbon nanotubes with the innoRam spectrometer and a Raman system with a traditional front-illuminated linear CCD detector with TE-cooling to 14°C.

Quantum Efficiency

The quantum effiency of back-illuminated or back-thinned CCDs can reach up to 90% - much higher than the ~50% typically achieved by traditional front-illuminated CCDs. The lower quantum efficiency of a front-illuminated CCD is attributed to the incident photons being reflected and absorbed by gate structures (Poly-Si, BPSG, gate oxide) while passing through the CCD’s front side.

Back-thinned CCDs are able to reduce these losses by etching the Si substrate and illuminating the CCD from the back. This aspect considerably increases the quantum efficiency of back-thinned CCD by minimizing the photon loss.

Photon Efficiency

Since the Raman phenomenon (10-8) has low photon efficiency, detectors utilized in Raman spectrometry must have very low dark noise and readout noise, so as to be able to detect the Raman signal from the sample. The dark noise is effectively reduced by thermoelectric cooling of the CCD device - the dark noise halves for each 7°C reduce in device temperature.

Moreover, the TE-cooled detector permits extended integration time - up to 16 minutes for innoRam, which significantly increases the detection limit. Another technique called 2D binning involves the combination of two or more vertical rows of the CCD array. This method considerably enhances signal-to-noise ratio.

The detector’s characteristics make the innoRam Raman spectrometer suitable for low-light level applications.

Experiment and Results

B&W Tek's innoRam Raman spectrometer system (Figure 1-a) with 785nm laser excitation was used to collect the Raman spectrum of carbon nanotubes. Figure 1 -b shows the Raman spectrum of carbon nanotubes measured from innoRam.

(a) innoRam, (b) Raman spectrum of carbon nanotubes from innoRam. (c) The Raman spectrum of the same type of carbon nanotubes using a Raman system with a front-illuminated linear CCD TE- cooled to 14°C.

Figure 1. (a) innoRam, (b) Raman spectrum of carbon nanotubes from innoRam. (c) The Raman spectrum of the same type of carbon nanotubes using a Raman system with a front-illuminated linear CCD TE- cooled to 14°C.

Figure 1-c shows the Raman spectrum of the same carbon nanotubes utilizing a Raman spectrometer with a front-illuminated linear CCD TE-cooled to 14°C.

To achieve a direct comparison, the same laser power and integration time were employed for both Raman measurements. Figure 1 (b) and (c) demonstrates clear improvement of signal-to-noise ratio as well as increased intensity in the spectrum from the innoRam.

Conclusion

The innoRam Raman spectrometer system equipped with a back-thinned 2D vertically binned CCD detector with TE-cooling to -20°C offers excellent performance with high signal-to-noise ratio and sensitivity.

The high signal-to-noise ratio and sensitivity is clearly showed by comparing the Raman analysis of carbon nanotubes between innoRam and a Raman spectrometer using a traditional front-illuminated linear CCD with TE-cooling to 14°C.

This information has been sourced, reviewed and adapted from materials provided by B&W Tek.

For more information on this source, please visit B&W Tek.

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