8. Conclusions and outlook

7. Physical properties and Raman spectra of graphene Nanoplatelets

and studied, rather than individual nanoplatelets (STREM Data Sheets) [18].

(30–150C), before and after being exposed to NO [16].

174 Raman Spectroscopy

All of the graphene nanoplatelet samples investigated in the current study (functionalized oxygen, nitrogen, argon, ammonia, carboxyl and fluorocarbon) have similar shapes (see Table 2 and Figure 19) [17]. Graphene nanoplatelet aggregates (aggregates of sub-micron platelets with diameters of <2 microns and a thickness of a few nanometers) were identified

Figure 18. Plots showing the change in Raman frequency shift, light intensity, and peak width, over a temperature range

The electronic structure of graphitic nanocarbons is linked to its structure, and Raman spectroscopy is sensitive to this intimate and unique relationship, which makes it very effective at studying the various functionalized graphene nanoplatelets used in this study. Akin to pristine

Functional species X average (μm) Y average (μm) Z average (μm)

Argon 4.8 3.9 0.50 Carboxyl 4.3 4.5 0.57 Oxygen 4.7 4.3 0.90 Ammonia 4.4 3.7 0.64 Fluorocarbon 5.0 3.6 0.55 Nitrogen 6.7 6.5 0.91

Table 2. Average x, y, z axis spatial measurements of functionalized graphene nanoplatelet aggregates.

The thermal characteristics of a variety of graphitic nanomaterials (single-walled and multi-walled carbon nanotubes, graphene and functionalized graphene in the form of nanoplatelets) have been investigated in the temperature range 24.0–200C using Raman spectroscopy for enhanced gas-sensing and optoelectronic applications. A Kataura plot analysis has been presented for the Radial Breathing Mode vibrations of single-walled carbon nanotubes and possible chiralities identified that pertain to metallic, semiconductor and type 2 semiconducting SWNTs. The effect of temperature on the Raman vibrational modes (RBM, G+ and G bands) of SWNTs has been investigated and the thermal expansion of the SWNT sample determined. A demonstrable correlation between the slope of the variation of the G+ Raman band with laser power for varying levels of SWNT purity has been obtained showing clearly that less pure samples exhibit a steeper slope variation with enhanced laser power. We have also investigated in some detail the behavior of Raman vibrational modes of graphene as a function of temperature in the range (24–150C), following exposure to a variety of toxic gases (NO, NO2 and SO2) at 500 ppm concentration in nitrogen with an eye toward developing sensitive chemical and biological sensors that are efficient, sensitive and portable.

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