This chapter showcases some of the versatility of Raman spectroscopic data as applied to the characterization of single (SWNT) and multi-walled (MWNT) carbon nanotubes, few layer graphene and functionalized graphene nanoplatelets, with an emphasis on gas-sensing applications. Specifically, water vapor and a variety of toxic gases (NO, NO2, and SO2 at 500 ppm in gaseous nitrogen) have been targeted for detection over the temperature range 24–200°C. The structure of sp2-hybridized carbon allotropes is reviewed and scanning electron microscopy (SEM) imagery utilized in conjunction with Raman spectroscopy to physically and spectrally characterize the various graphitic nanomaterials studied. A Kataura plot analysis associated with the Radial Breathing Mode (RBM) vibrations of SWNT has been used to identify possible chiralities in the graphitic samples employing 455, 532 and 780 nm laser excitation wavelengths to record the Raman spectra. The effect of temperature on the various Raman vibrational modes (RBM, G+ and G−) has been investigated, along with a determination of the thermal conductivity of SWNT samples and correlation between the purity of the sample and the variation of the slope of the G+ band with increasing laser power.
Part of the book: Raman Spectroscopy
The theoretical simplicity of sp2 carbons, owing to their having a single atomic type per unit cell, makes these materials excellent candidates in quantum chemical descriptions of vibrational and electronic energy levels. Theoretical discoveries, associated with sp2 carbons, such as the Kohn anomaly, electron-phonon interactions, and other exciton-related effects, may be transferred to other potential 2D materials. The information derived from the unique Raman bands from a single layer of carbon atoms also helps in understanding the new physics associated with this material, as well as other two-dimensional materials. The following chapter describes our studies of the G, D, and G′ bands of graphene and graphite, and the characteristic information provided by each material. The G-band peak located at ~1586 cm−1, common to all sp2 carbons, has been used extensively by us in the estimation of thermal conductivity and thermal expansion characteristics of the sp2 nanocarbon associated with single walled carbon nanotubes (SWCNT). Scanning electron microscope (SEM) images of functionalized graphene nanoplatelet aggregates doped with argon (A), carboxyl (B), oxygen (C), ammonia (D), fluorocarbon (E), and nitrogen (F), have also been recorded and analyzed using the Gwyddion software.
Part of the book: 2D Materials