Raman Spectra Of Single-walled Carbon Nanotubes Research Articles

Over Two-Fold Photoluminescence Enhancement from Single-Walled Carbon Nanotubes Induced by Oxygen Doping.

Covalent functionalization of single-walled carbon nanotubes (SWCNTs) is a promising way to improve their photoluminescent (PL) brightness and thus make them applicable as a base material for infrared light emitters. We report as high as over two-fold enhancement of the SWCNT PL brightness by using oxygen doping via the UV photodissociation of hypochlorite ions. By analyzing the temporal evolution of the PL and Raman spectra of SWCNTs in the course of the doping process, we conclude that the enhancement of SWCNTs PL brightness depends on the homogeneity of induced quantum defects distribution over the SWCNT surface.

Diameter control of single wall carbon nanotubes synthesized using chemical vapor deposition

Lack of control on the chirality or diameter of single-wall carbon nanotubes (SWCNTs) during synthesis is a major impediment in the path of their widespread commercialization. We demonstrate that the humble technique of catalytic chemical vapor deposition of methane, without any sophisticated catalyst preparation, can provide significant control on the diameter of the synthesized SWCNTs. The catalyst used is a solid solution of the bimetals Fe-Mo or Co-Mo in MgO. The radial breathing modes (RBMs) in the Raman spectra of SWCNTs were used to find out the diameters. Kataura plot along with RBMs was used to study the chirality of the tubes. High concentration of the catalysts (Co:Mo:MgO=1:0.5:15 and Fe:Mo:MgO=1:0.5:30) resulted in high yields. However, most of these carbonaceous materials were impurities. Reducing the concentration not only improved the purity and crystallinity (ID/IG ratio ∼0.1), but most importantly reduced the diameter spread of the SWCNTs. Majority of the SWCNTs grown using the low concentration catalysts (Co:Mo:MgO=1:0.5:300 and Fe:Mo:MgO=1:0.5:200) were estimated to have diameters lying between 1.13 and 1.65nm. This narrowing of diameter spread happened for both Fe and Co catalyst systems and depended only on the concentration of the catalyst.

Resonance Raman spectroscopy of carbon nanotubes: pressure effects on G-mode

We use 488 and 568 nm laser Raman spectroscopy under high pressure to selectively follow evolution of Raman G-mode signals of single-walled carbon nanotubes (SWCNTs) of selected diameters and chiralities ((6, 5) and (6, 4)). The G-mode pressure coefficients of tubes from our previous work are consistent with the thick-wall tube model. Here we report the observation of well-resolved G-minus peaks in the Raman spectrum of SWCNTs in a diamond-anvil cell. The pressure coefficients of these identified tubes in water, however, are unexpected, having the high value of over 9 cm−1 GPa−1 for the G-plus and the G-minus, and surprisingly the shift rates of the same tubes in hexane have clearly lower values. We also report an abrupt increase of G-minus peak width at about 4 GPa superposed on a continuous peak broadening with pressure.

DNA sequence detection based on Raman spectroscopy using single walled carbon nanotube

A Biosensor for detection of DNA sequence in bacterium Bacillus anthracis has been developed using Raman spectrum of single walled carbon nanotubes (SWNTs). We have utilized the fact that being hydrophobic in nature single strand of target DNA (diseased DNA) gets wrapped over SWNT surface forming single stranded DNA-SWNT complex. The sensing ability of this sensor has been studied using the dependency of G peak intensity (in the Raman spectrum of SWNTs) on the covered surface of SWNTs. When a DNA having a sequence complementary to that of the target DNA is added to DNA-SWNT complex, hybridization between these sequences takes place. This results in large covered surface area of SWNT and reducing the intensity of G peak. A slight red shift in the G peak has also been observed. The intensity of Gpeak depends on the exposed area of SWNT to the excitation beam. On the other hand with noncomplementary DNA, no significant change in intensity of G peak is observed. Finally, results were cross-checked by gel electrophoresis.

Spectroelectrochemical properties of the single walled carbon nanotubes functionalized with polydiphenylamine doped with heteropolyanions

A combined chemical–electrochemical method was used for covalent functionalization of single-walled carbon nanotube (SWNT) with polydiphenylamine (PDPA) doped with heteropolyanions of H3PMo12O40·xH2O. The functionalization process induces in Raman spectra of SWNTs the following changes: (i) an increase in relative intensity of the D band, accompanied a gradual up-shift of the G band in the case of the semiconducting tubes and a decrease in the relative intensity of band peaked at 1540cm−1 is remarked in the case of the metallic tubes; (ii) in the anti-Stokes Raman spectrum an increase in the relative intensity of Raman line of metallic tubes peaked at −1560cm−1 is remarked when the cycles number increases. The additional down-shift of the FTIR bands belonging to H3PMo12O40 heteropolyanions (at 881, 943 and 1055cm−1) and PDPA (at 688, 736 and 1016cm−1) originates in hindrance steric effects induced the covalent functionalization of SWNTs with polymer molecules. Using Raman scattering and FTIR spectroscopy we demonstrate that chemical polymerization of diphenylamine in the presence of H3PMo12O40·xH2O and SWNTs results in a composite of the type blend based on PDPA in un-doped state and SWNTs doped with H3PMo12O40 heteropolyanions.

Raman spectroscopy of strained single-walled carbon nanotubes

Due to remarkable rolling structure and distinct rolling direction, the chirality-dependent Raman spectra of single-walled carbon nanotubes (SWNTs) show two characteristic features: the radial breathing mode (RBM) and the G-band. Rich information about SWNTs presented by these Raman features makes Raman spectroscopy a general and common tool for characterizing structures and properties of SWNTs and their changes. When exerted by external forces, the geometrical structures of SWNTs will change, which further affects the electronic structures and phonon properties of SWNTs. In this article, emphasis is given to how Raman frequency and resonant-Raman intensity evolve under distinct strains, including uniaxial strain, torsional strain, radial deformation and bending deformation. It is found that depending on different structural variations, Raman spectra of SWNTs have different responses to each strain, showing that resonant-Raman spectroscopy is a suitable tool to characterize and study strains in SWNTs.

Stacking interaction of cytosine with carbon nanotubes: MP2, DFT and Raman spectroscopy study

We employed the Raman spectroscopy and the MP2 and DFT (with the MPWB1K, M05, M05-2X and MPW1B95 functionals) calculations to study the interaction of cytosine with SWCNTs (single-wall carbon nanotubes). The Raman spectra of SWCNT and SWCNT-cytosine films showed that the non-covalent interaction results in a down-shift of the frequency of the most intensive band of the SWCNT at 1590 cm −1 (the G-mode). The interaction energy in the complex formed by cytosine with a fragment of the zigzag(10, 0) SWCNT calculated at the MP2/6-311++G(2d,p) level of theory is −62.4 kJ/mol.

Anharmonic effects in single-walled carbon nanotubes

We have investigated the temperature and excitation energy dependence of Raman spectraof single-wall carbon nanotubes (SWCNTs). The measured Raman shifts for D and Gbands of SWCNTs show a softening behavior upon increasing temperature (83–733 K). Atheoretical model is developed to study the frequency shifts for these two Raman modes asa function of temperature; the calculated results agree well with the experimental data.The calculation indicates that the virtual optical-phonon couplings dominate contributionsto the temperature variance of frequency shifts for D and G bands of SWCNTs while thepure-volume effect is very weak. Measurements of peak positions and linewidths of D and Gbands are also carried out at three different excitation wavelengths (325, 514.5 and 785 nm).It is found that not only does the peak position of the D band exhibit a linear increase,but also the linewidth of the G band does upon increasing excitation energy. Inaddition, we also measure the relative intensity ratios of the D band to the G band(ID/IG) with temperature and excitation energy in this work.

A Raman probe for selective wrapping of single-walled carbon nanotubes by DNA

In this paper, we discuss nanotube diameter selectivity in DNA wrapping of single-walledcarbon nanotubes (SWNTs) under high-shear sonication and present Raman evidence forthe selective wrapping. The DNA wrapping induces an upshift (an increase in wavenumber)of the radial breathing mode (RBM) bands in the Raman spectra of SWNTs,which indicates strong interaction between nanotubes and DNA. The extent of theupshift correlates well with the change in the intensity of the RBM bands uponDNA wrapping, and larger upshifts correspond to larger intensity changes. Theintensity changes represent wrapping selectivity, and differ from tube to tube due tovarying diameters and electronic properties. The shift of the RBM bands thusrepresents a practical probe for wrapping selectivity and the extent of the shiftsindicates different electronic structures of core nanotubes hybridized with DNA.

Spectroscopic Evidence and Molecular Simulation Investigation of the <I>π</I> – <I>π</I> Interaction Between Pyrene Molecules and Carbon Nanotubes

The pi-pi interaction between pyrene molecules and single-walled carbon nanotubes (SWNTs) or multi-walled carbon nanotubes (MWNTs) was studied by fluorescence, FTIR, Raman spectroscopy and molecular simulation. The carbon nanotubes were incubated in pyrene solution and dried for characterization. A broadband fluorescence emission at 463 nm of the incubated samples was observed, which is similar to that of pyrene excimers but shifts to shorter wavelength. The typical FTIR bands of pyrene shift to lower wavenumbers in the incubated samples. D- and G-bands in Raman spectra of SWNTs also shift to low frequencies. All these spectroscopic evidences reveal the stronger pi-pi stacking interaction between the nanotubes and pyrene molecules over the pyrene dimers, which leads to the formation of pyrene-carbon nanotube complexes. The systems of SWNTs and pyrene molecules were also studied with molecular simulation. It was found from the binding energy calculation that a stronger interaction presents between the pyrene molecule and the nanotube. In addition, the simulation gives some structural information about the pyrene-nanotube complex, such as the staggered conformation of pyrene on nanotube. The effect of defects in carbon nanotube sidewall was also discussed.

The effect of catalyst concentration on the synthesis of single-wall carbon nanotubes

Single wall carbon nanotubes (SWNTs) were synthesized by electric arc discharge method with a mixture of nickel and yttrium as catalysts. The effect of the catalyst concentration on the synthesis of SWNTs was studied. Raman spectra of SWNTs have been recorded with excitation wavelengths from 476.5 to 1064 nm. The Raman peaks of the radial breathing modes (RBM) of SWNTs were assigned. The results indicate that the diameter distribution of SWNTs is in the range of 1.2–1.6 nm, and the SWNTs with diameter 1.43 nm are in the majority. The catalyst concentrations have large effect on the yield of SWNTs and little effect on the diameter distribution of SWNTs.

D-band Raman Spectra of Graphite and Single Wall Carbon Nanotubes

AbstractThe double resonance Raman spectra of the disorder-induced D-band and some other non-zone-center phonon modes are discussed for two-dimensional (2D) graphite and to some extent for single wall carbon nanotubes (SWNTs). The phonon dispersion relations of graphite can be determined using Raman spectroscopy b y measuring the non-zone center Raman phonon frequencies in combination with theoretically determined phonon q-vectors. We report a t of the phonon dispersion relations to experimental Raman spectra which were previously observed but have not y et been assigned to speci c phonon branches. We found that the D-band and the G0-band of 2D graphite consist of, respectively, two and one Raman Lorentzian peaks, while 3D graphite shows two G0-band Lorentzian peaks. The appearance of two G0 peaks in the resonance Raman spectra of SWNTs may come from resonances of one laser line with two di erent van Hov e singularities.