Effect of nitrogen doping on Raman spectra of multi-walled carbon nanotubes (original) (raw)
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FTIR studies of nitrogen doped carbon nanotubes
Diamond and Related Materials, 2006
Purified and defect free carbon nanotubes have great potential for applications in electronic, polymer composites and biological sciences. The removal of impurities (carbon nanoparticles and amorphous carbon) is an important step before the CNT applications can be realized. We report the results of FTIR and TGA/DTA studies of the impurities present in the carbon nanotubes. The multiwalled CNTs were grown using Microwave Plasma Chemical Vapor Deposition (MPCVD) technique. Fourier transform infrared (FTIR) spectroscopy was carried out in the range of 400–4000 cm− 1 to study the attachment of the impurities on carbon nanotubes. FTIR spectra of the as-grown MWCNTs show dominant peaks at 1026, 1250, 1372, 1445, 1736, 2362, 2851, 2925 cm− 1 that are identified as Si–O, C–N, N–CH3, CNT, C–O, and C–Hx respectively. The peaks are sharp and intense showing the chemisorption nature of the dipole bond. The intensity of the peaks due to N–CH3, C–N and C–H reduces after annealing and the peaks vanish on annealing at high temperature (900 °C). The presence of C–N peak may imply the doping of the CNTs with N in substitution mode. TGA/DTA measurements, carried out under argon flow, show that the dominant weight loss of the sample occurs in the temperature range 400–600 °C corresponding to the removal of the impurities and amorphous carbon.
It is frequently observed that as-grown single-walled carbon nanotubes (SWCNTs) contain defects. Controlling the defect density is a key issue for the control of nanotube properties. However, little is known about the influence of the growth conditions on the formation of nanotube defects. In addition, SWCNT samples frequently contain carbonaceous by-products which affect their ensemble properties. Raman spectroscopy is commonly used to characterize both features from the measurement of the defect-induced D band. However, the contribution of each carbonaceous species to the D band is usually not known making it difficult to separately extract the defect density and relative abundance of each. Here, we report on the correlated evolution of the D and G' bands of SWCNT samples with increasing growth temperature. In the general case, three to four Lorentzian components are required to fit them. Coupled with HRTEM characterization, the low frequency components of the D and G' can be attributed to the contribution of SWCNTs while high frequency components are associated with defective carbonaceous by-products. The nature of these defective by-products varies with the type of catalysts and with the growth conditions.
Carbon, 2009
We describe the systematic study of multi-walled carbon nanotubes with different nitrogen doping produced by aerosol chemical vapor deposition. Benzylamine:toluene mixtures of 0:100, 5:95, 10:90, 25:75, 50:50, 75:25 and 100:0 were thermally decomposed at 800-900°C under argon at atmospheric pressure, whereby the nitrogen content of the bulk material was varied between 0 and 2.2 at%. We also show how the presence of nitrogen in the precursor changed the nanotube morphology, i.e. nitrogen decreased the number of kinks incorporated into the carbon nanotubes, decreased their length and diameter and increased the proportion of 'bamboo' shaped nanotubes. Furthermore, due to the nitrogen doping, the oxidation resistance of the nanotube material was decreased. With concentrations above 10% benzylamine the increase of the reaction temperature had no significant effect on the quality of the nanotubes, however, at higher temperatures the nitrogen content was decreased. We demonstrate the control over the nanotube geometry, the nitrogen content and oxidation resistance of the nanotubes, and show that these properties are interlinked.
Nitrogen doping of CVD multiwalled carbon nanotubes: Observation of a large g-factor shift
Materials Chemistry and Physics, 2011
Nitrogen doped multi-walled carbon nanotubes (N-CNTs) and undoped multi-walled carbon nanotubes (MWCNTs) were synthesized by a chemical vapour deposition (CVD) floating catalyst method. The N-CNTs were synthesized by the decomposition of a ferrocene/N-source/toluene (N-source = triethylamine, dimethylamine, acetonitrile) mixture at 900 • C. The undoped MWCNTs were synthesized using a ferrocene-toluene mixture without a nitrogen source under similar reaction conditions. The structure of the N-CNTs and MWCNTs was ascertained using HRTEM, SEM and Raman spectroscopy. Systematic ESR measurements of the carbon products produced, in the temperature range of 293-400 K showed line widths that were in general very large ∼ kOe. Most importantly, a large g-factor shift in samples of N-CNTs from that of the free electron g-factor was observed. Further, the shift increased with increasing temperature. The large g shift has been analysed in terms of Elliott-Wagoner and Bottleneck models. The temperature dependence of the g shift in the N-CNT samples rules out the Elliott-Wagoner type spin-orbit coupling scenario. The large g shift and temperature dependence can be qualitatively explained in terms of the Bottleneck model.
Chemical Physics Letters, 2005
Thin multi-walled carbon nanotubes (t-MWCNTs) synthesized by catalytic chemical vapor deposition were characterized by transmission electron microscopy (TEM), Raman spectroscopy, and gas adsorption. TEM observations showed that the innermost diameter ranges from less than 1 to 5 nm and the outermost diameter ranges from 4 to 12 nm, which are much smaller than conventional thick MWCNTs. We observed clear radial breathing modes in Raman spectra, which are attributed to the existence of inner nanotubes in small diameters less than 3 nm. We also performed N 2 adsorption at 77 K after the tip opening of t-MWCNTs by nitric acid in order to analyze the tube inner diameters. The pores with sizes less than 4 nm corresponding to the inner empty space of t-MWCNTs were largely developed, in good agreement with TEM and Raman observations.
Carbon, 2012
High purity aligned nitrogen doped multi walled carbon nanotubes were synthesized by the catalytic chemical vapor deposition method using pyridine and Fe/Co (2:1 volume ratio) as the single C/N precursor and catalyst material. The average diameter of the synthesized tubes ranges between 29 nm and 57 nm and the nitrogen content of the tubes reaches a maximum of 9.2 (at.)% nitrogen. The effect of nitrogen doping on the Raman scattering of doped tubes and its correlation with X-ray photoelectron spectra (XPS) was investigated. The analysis is based on the investigation of the I D /I G (integrated area ratio), other nitrogen characteristic Raman modes and the type of nitrogen inclusion interpreted from the N 1s electron bonding energies in XPS. At doping levels higher than 5% the nitrogen inclusion takes place through another mechanism than at low nitrogen doping levels. Most significant is that pyridinic defects are relatively readily incorporated at low nitrogen doping levels while at nitrogen content higher than 5% the major incorporation mechanism is dominated by pyridinic and pyrrolic defects on an equal basis. Our study gives further insight into nitrogen doping effects and the relation between type of nitrogen inclusion and nitrogen doping levels.
Raman Characterization of Nitrogen Doped Multiwalled Carbon Nanotubes
MRS Proceedings, 2003
N-type multi-walled nanotubes were synthesized by nitrogen doping using pyridine and pyridine-melamine mixtures in chemical vapor deposition, and their donor states were verified by Scanning Tunneling Spectroscopy. Tunneling Electron Microscopy reveals small amounts of residual catalyst and Scanning Electron Microscopy show well aligned mats of the Nitrogen doped nanotubes. Nitrogen is present in the lattice of these MWNTs as pyridine structures and CNx structures. Raman scattering measurements were performed as a function of increasing growth temperature and the results compared to previously studied boron doped multiwalled nanotubes.
Journal of Physics D Applied Physics
The influence of nano-structure and composition of the substrate on the properties of carbon nanotubes (CNTs) is presented. The samples are obtained following a sequential in situ deposition routine. First, TiN x O y films are grown on a crystalline silicon substrate. Immediately, dispersed nickel catalyst particles are deposited on the film. The non-stoichiometric TiN x O y films and Ni particles are grown by ion beam sputtering of Ti and Ni targets, respectively. Soon after that, the CNTs are grown by feeding acetylene gas into the chamber and maintaining the substrate at 973 K. In situ x-ray photoelectron spectroscopy allows compositional and structural analysis in all the stages of the sample growth process. The CNTs are further studied by scanning and transmission electron microscopy techniques, showing different population densities, sizes and diameters as a function of the oxygen content in the TiN x O y films. The results show that oxygen influences the surface diffusion mob...
The influence of nitrogen sources on nitrogen doped multi-walled carbon nanotubes
Journal of Organometallic Chemistry, 2010
A range of nitrogen doped carbon nanotubes (N-CNTs) was produced by a nebulised floating catalyst method at 850 C using a mixture of toluene and 1e8% nitrogen containing reagents (a range of amines and amides). The carbon nanotube (CNT) products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), CHN analysis as well as Raman spectroscopy. Differences due to the different N containing reagents were noted but in general all reagents gave aligned CNTs that at low concentration (1%) were longer and wider than those produced without nitrogen. Increased N content in the reactant mixture gave doped tubes that became shorter and showed more disorder. Treatment of the N-CNTs with nitric acid (microwave, 30 min) gave samples that were chemically modified by the acid (loss of alignment, narrower tubes and more facile oxidation). It appears in general that the amount of N in the nitrogen containing reagent is more important than the source and type of the N atoms used as revealed by trends in the morphology (diameter, length) of the N-CNTs produced.
Synthesis and Characterization of Nitrogen-doped Carbon Nanotubes Derived from g-C3N4
Materials
Here, nitrogen-doped carbon nanotubes (CNT-N) were synthesized using exfoliated graphitic carbon nitride functionalized with nickel oxides (ex-g-C3N4-NixOy). CNT-N were produced at 900 °C in two steps: (1) ex-g-C3N4-NixOy reduction with hydrogen and (2) ethylene assisted chemical vapor deposition (CVD). The detailed characterization of the produced materials was performed via atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The possible mechanism of nanotubes formation is also proposed.