Raman Spectroscopy of Carbon Materials (original) (raw)
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Raman spectroscopy of carbon materials: Structural basis of observed spectra
Chemistry of Materials, 2009
The first-and second-order Raman spectral features of graphite and related sp2 carbon materials were examined with laser wavelengths ranging from 293 to 1064 nm. A wide range of carbon materials was considered, including highly ordered pyrolytic graphite (HOPG), powdered and randomly oriented graphite, and glassy carbon prepared at different heat-treatment temperatures. Of particular interest is boron-doped highly ordered pyrolytic graphite (BHOPG), in which boron substitution decreases local lattice symmetry but does not disrupt the ordered structure. New second-order bands at 2950,3654, and -4300 cm-' are reported and assigned to overtones and combinations. The D band at 1360 cm-l, which has previously been assigned to disordered carbon, was observed in ordered boronated HOPG, and its overtone is strong in HOPG. The observed Raman shift of the D band varies with laser wavelength, but these shifts are essentially independent of the type of carbon involved. It is concluded that the D band results from symmetry breaking occurring at the edges of graphite planes in sp2 carbon materials or at boron atoms in BHOPG. The observations are consistent with the phonon density of states predicted for graphitic materials, and the fundamental and higher order Raman features are assignable to theoretically predicted lattice vibrations of graphite materials. The laser wavelength dependence of the D band frequency appears to result from scattering from different populations of phonons, perhaps through a resonance enhancement mechanism. However, the results are inconsistent with resonance enhancement of graphite microcrystallites of varying size.
Use of Raman Spectroscopy to Qualify Carbon Materials
Spectroscopy
In the last 30 to 40 years, various new types of carbon materials have been engineered for multiple industrial uses. It is now well-known that the Raman spectrum is sensitive to the structure, even though the spectrum is rather uncomplicated. Because Raman spectroscopy now has a reputation for providing good information, potential users of Raman equipment can request information on the quality of their sample. However, they are often not able to define clearly what they mean by “quality.” If they are growing diamond films, they may or may not want interstitial sp2 carbon to glue polycrystalline diamond together. If they are growing hard diamond-like carbon (DLC) films, they may want to correlate the spectral characteristics with physical characteristics of the film. In this column, I explain how the Raman characteristics can aid in characterization of carbon materials.
Raman characterization of carbon materials under non-hydrostatic conditions
Carbon, 2011
Raman spectroscopy experiments on double-wall carbon nanotube and highly oriented pyrolytic graphite (HOPG) samples subjected to non-hydrostatic conditions have been conducted in anvil cells to study the effect of the pressure/stress on the bands assigned to defects. Typical diamond anvils used in high pressure experiments have been substituted by moissanite (6H-SiC) and sapphire (Al 2 O 3 ) anvils to allow the observation of the D band (around 1350 cm À1 ) and the second-order Raman scattering without interference. We demonstrate that Raman experiments at high pressure provide unique information to probe the mechanical behaviour of carbon materials (CMs). We also show that this can be also a powerful technique to assign controversial spectral features such as those appearing in the second order region of the spectra of CMs. In HOPG samples we find that the D 0 /D band intensity ratio is independent of stress. The results indicate that an increase of non-hydrostatic stresses on HOPG generates graphitic domains with sizes around 20-30 nm when the sample is recovered to room conditions.
Raman Spectroscopy of Amorphous Carbon
1998
Amorphous carbon is an elemental form of carbon with low hydrogen content, which may be deposited in thin films by the impact of high energy carbon atoms or ions. It is structurally distinct from the more well-known elemental forms of carbon, diamond and graphite. It is distinct in physical and chemical properties from the material known as diamond-like carbon, a form which is also amorphous but which has a higher hydrogen content, typically near 40 atomic percent. Amorphous carbon also has distinctive Raman spectra, whose patterns depend, through resonance enhancement effects, not only on deposition conditions but also on the wavelength selected for Raman excitation. This paper provides an overview of the Raman spectroscopy of amorphous carbon and describes how Raman spectral patterns correlate to film deposition conditions, physical properties and molecular level structure.
Raman spectroscopy of carbon-containing particles
Vibrational Spectroscopy, 2001
Raman spectroscopy has been used to study a number of carbon-containing particles: commercial graphite of various compositions, Candle soot (CS) and Diesel soot (DS), and ambient particles. The spectra show the known D, G, D H and 2D bands with varying characteristics. An analysis of the spectra allows the inference of internal physical characteristics of the samples such as the size or degree of disorder of the carbon microcrystalline domains on a nanometer scale. The samples are also analyzed using a scanning electron microscope, revealing their structure in the 1±20 mm scale. #
Ab initio resonant Raman spectra of diamond-like carbons
Diamond and Related Materials, 2005
Raman spectroscopy is a standard tool for the characterisation of carbon materials, from graphite to diamond-like carbon and carbon nanotubes. An important factor is the dependence of the Raman spectra on excitation energy, which is due to resonant processes. Here, we calculate the resonant Raman spectra of tetrahedral amorphous carbon. This is done by a tight-binding method, using an approach different from Placzek's approximation, which allows calculation of Raman intensities also in resonant conditions. The calculated spectra confirm that the G peak arises from chains of sp 2 bonded atoms and that it correlates with the atomic and electronic structure of the samples. The calculated dispersion of the G peak position with excitation energy follows the experimental observations. Our ab initio calculations also show that the sp 3 phase can only be seen by using UV excitation above 4 eV, confirming the assignment of the T peak at~1060 cm À1 , seen only in UV Raman measurements, to CC sp 3 vibrations.
Emergent Materials, 2019
Sp 3 and sp 2 hybridised carbon materials have been exploited for myriad applications owing to their unique electronic features. Novel carbon materials and its composites are synthesised by researchers with improved physico-chemical properties for various applications. These novel materials need to be characterised to decipher the structures. Vibrational spectroscopic studies have been used to understand the lattice dynamics of such carbon materials for the last six decades. Raman spectroscopy in particular has been a unique technique in such investigations as it provides bond-specific information at a molecular level which is desirable in understanding the microstructure of carbon. In this review, we highlight the potential of Raman spectroscopy to study the microstructure of different carbon allotropes such as graphene, carbon nanotubes, fullerene, and carbon nitride and its composites. In addition, perovskites has been receiving a lot of attention recently as the scientific community has realised their potential in the areas of material science and energy storage and conversion. This review also covers a few aspects of Raman spectroscopic studies of oxide and halide perovskites.
Raman spectroscopy of closed-shell carbon particles
Chemical Physics Letters, 1993
Raman spectra of annealed carbon soot reveal strong structural changes. Downshifts of the graphite-like phonon bands to lower energies after annealing are suggested to be related to strained or curved graphitic planes. The effect of curvature on the energy of the in-plane optical phonon mode is quantitatively estimated by applying the semi-empirical interatomic Tersoff potential. A weighted average curvature corresponding to a bond bending of 2.1' is deduced for spherical shells with 20.6 A radius. These findings are consistent with high-resolution electron microscopy images which reveal closed-shell carbon particles in the same size
Raman spectroscopy of selected carbonaceous samples
International Journal of Coal Geology, 2010
This paper presents the results of Raman spectra measured on carbonaceous materials ranging from greenschist facies to granulite-facies graphite (Anchimetamorphism and Epimetamorphism zones). Raman spectroscopy has come to be regarded as a more appropriate tool than X-ray diffraction for study of highly ordered carbon materials, including chondritic matter, soot, polycyclic aromatic hydrocarbons and evolved coal samples. This work demonstrates the usefulness of the Raman spectroscopy analysis in determining internal crystallographic structure (disordered lattice, heterogeneity). Moreover, this methodology permits the detection of differences within the meta-anthracite rank, semi-graphite and graphite stages for the samples included in this study. In the first order Raman spectra, the bands located near to c.a. 1350 cm − 1 (defects and disorder mode A 1g) and 1580 cm − 1 (in plane E 2g zone-centre mode) contribute to the characterization and determination of the degree of structural evolution and graphitization of the carbonaceous samples. The data from Raman spectroscopy were compared with parameters obtained by means of structural, chemical and optical microscopic analysis carried out on the same carbonaceous samples. The results revealed some positive and significant relationships, although the use of reflectance as a parameter for following the increase in structural order in natural graphitized samples was subject to limitations.