324 research outputs found
Spectroscopic studies on nanocomposites obtained by functionalization of carbon nanotubes with conducting polymers
International audienceVibrational properties of composites based on single-walled carbon nanotubes (SWNTs) and conducting polymers of the type polyaniline (PANI) and poly (3,4-ethylene dioxythiophene) (PEDOT) are reported. For PANI-functionalized SWNTs, the intensity increase of the Raman band at 178 cm-1, associated with radial breathing modes of SWNTs bundles, indicates an additional roping of nanotubes due to the presence of the polymer. The interaction of this composite with NH4OH solution involves an internal redox reaction between PANI and SWNTs. Thus, the polymer chain undergoes a transition from the semi-oxidized state into a reduced one. The functionalization of SWNT side walls with PEDOT is invoked as well
Bromination of Graphene and Graphite
We present a density functional theory study of low density bromination of
graphene and graphite, finding significantly different behaviour in these two
materials. On graphene we find a new Br2 form where the molecule sits
perpendicular to the graphene sheet with an extremely strong molecular dipole.
The resultant Br+-Br- has an empty pz-orbital located in the graphene
electronic pi-cloud. Bromination opens a small (86meV) band gap and strongly
dopes the graphene. In contrast, in graphite we find Br2 is most stable
parallel to the carbon layers with a slightly weaker associated charge transfer
and no molecular dipole. We identify a minimum stable Br2 concentration in
graphite, finding low density bromination to be endothermic. Graphene may be a
useful substrate for stabilising normally unstable transient molecular states
Raman spectroscopy of BN-SWNTs
We present results on the vibrational properties of BN-SWNTs together with a study of the synthesis material by transmission electron microscopy. Phonon modes have been investigated by Raman spectroscopy with laser excitation wavelengths in the range from 363.8 to 676.44 nm. The assignment of the modes is guided by ab-initio calculations
Low frequency Raman studies of multi-wall carbon nanotubes: experiments and theory
In this paper, we investigate the low frequency Raman spectra of multi-wall
carbon nanotubes (MWNT) prepared by the electric arc method. Low frequency
Raman modes are unambiguously identified on purified samples thanks to the
small internal diameter of the MWNT. We propose a model to describe these
modes. They originate from the radial breathing vibrations of the individual
walls coupled through the Van der Waals interaction between adjacent concentric
walls. The intensity of the modes is described in the framework of bond
polarization theory. Using this model and the structural characteristics of the
nanotubes obtained from transmission electron microscopy allows to simulate the
experimental low frequency Raman spectra with an excellent agreement. It
suggests that Raman spectroscopy can be as useful regarding the
characterization of MWNT as it is in the case of single-wall nanotubes.Comment: 4 pages, 2 eps fig., 2 jpeg fig., RevTex, submitted to Phys. Rev.
Spectroscopic Evidence of Carbon Nanotubes’ Metallic Character Loss Induced by Covalent Functionalization via Nitric Acid Purification
A detailed characterization of covalently functionalized HiPco single-walled carbon nanotubes (SWNTs) has been carried out using several physicochemical methods (thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman scattering). The chemical process, finally leading to SWNT?ester derivatives, starts from nitric acid purification of pristine SWNTs. Besides the efficiency of the functionalization, we show that a loss of metallic character of the carbon nanotubes is initiated by the nitric acid treatment of pristine SWNTs and is maintained in the final SWNT ester derivatives. A higher reactivity of the metallic tubes is also demonstrated
Tuning the Raman Resonance Behavior of Single-Walled Carbon Nanotubes via Covalent Functionalization
We present a systematic Raman study over a range of excitation energies of arc discharge single-walled carbon nanotubes (SWCNTs) covalently functionalized according to two processes, esterification and reductive alkylation. The SWCNTs are characterized by resonance Raman spectroscopy at each step of the functionalization process, showing changes in radial breathing mode frequencies and transition energies for both semiconducting and metallic tubes. Particular attention is given to a family of tubes clearly identified in the Kataura plot for which we continuously tune the excitation energy from 704 to 752 nm. This allows us to quantify the energy shift occurring in the spacing of the van Hove singularities. We demonstrate that, independently of the functionalization technique, the type of chain covalently bound to the tubes plays an important role, notably when oxygen atoms lie close to the tubes, inducing a larger shift in transition energy as compared to that of other carbonaceous chains. The study shows the complexity of interpreting Raman data and suggests many interpretations in the literature may need to be revisited
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