Nitrogen doped multi walled carbon nanotubes produced by CVD-correlating XPS and Raman spectroscopy for the study of nitrogen inclusion (original) (raw)
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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.
Incorporation of nitrogen in carbon nanotubes
Journal of Non-Crystalline Solids, 2002
Nitrogen-doped carbon nanotubes were obtained by the arc-discharge technique in a helium-nitrogen atmosphere and using iron-nickel-cobalt catalysts, The samples were analyzed using spectroscopic techniques (Raman, EELS, Xray photoelectron spectroscopy) and transmission electron microscopy (TEM). Pure helium atmosphere conditions led to bundles of single-wall nanotubes with diameters of $1.5 nm. The presence of nitrogen during tube formation produced irregular and thickly textured tubes. TEM micrographs showed that N suppresses the formation of bundles of single-wall nanotubes, giving rise to nested nanofibers. Quantum-chemical calculations were carried out to study the influence of substitutional N on the tube conformation. The calculations show that the combination of hexagons and pentagons at low N concentration produces kinks that account for the irregular shaped nanotubes. Ó
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.
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.
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.
Electronic and optical properties of nitrogen-doped multiwalled carbon nanotubes
Physical Review B, 2006
Highly nitrogen-doped carbon nanotube ͑CN x NT, x = 12 at. %͒ was synthesized by the pyrolysis of acetonitrile on Co-Mo catalysts. The electronic structures and chemical bondings of CN x NT were studied using various spectroscopic techniques: Raman, photoelectron and x-ray absorption spectroscopies. The ultrafast pump-probe measurements of CN x NT exhibited a larger third-order susceptibility ͑3͒ , a relaxation time of 2 = 1 ps and improved saturable absorption, as compared with undoped multiple-walled carbon nanotubes, which indicate that N-doping can improve all-optical switching properties of carbon nanotubes.
Structural and morphological control of aligned nitrogen-doped carbon nanotubes
Carbon, 2010
Nitrogen-doped carbon nanotubes (CN x-NTs) were prepared using a floating catalyst chemical vapor deposition method. Melamine precursor was employed to effectively control nitrogen content within the CN x-NTs and modulate their structure. X-ray photoelectron spectroscopy (XPS) analysis of the nitrogen bonding demonstrates the nitrogen-incorporation profile according to the precursor amount, which indicates the correlation between the nitrogen concentration and morphology of nanotubes. With the increase of melamine amount, the growth rate of nanotubes increases significantly, and the inner structure of CN x-NTs displayed a regular morphology transition from straight and smooth walls (0 at.% nitrogen) to cone-stacked shapes or bamboo-like structure (1.5%), then to corrugated structures (3.1% and above). Both XPS and CHN group results indicate that the nitrogen concentration of CN x-NTs remained almost constant even after exposing them to air for 5 months, revealing superior nitrogen stability in CNTs. Raman analysis shows that the intensity ratio of D to G bands (I D /I G) of nanotubes increases with the melamine amount and position of G-band undergoes a down-shift due to increasing nitrogen doping. The aligned CN x-NTs with modulated morphology, controlled nitrogen concentration and superior stability may find potential applications in developing various nanodevices such as fuel cells and nanoenergetic functional components.
The Journal of Physical Chemistry C, 2013
Nitrogen doping in carbon nanostructures has attracted interest for more than a decade, and recent implementation of such structures in energy conversion systems has boosted the interest even more. Despite numerous studies, the structural conformation and stability of nitrogen functionalities in small diameter single-walled carbon nanotubes (SWNTs), and the impact of these functionalities on the electronic and mechanical properties of the SWNTs, are incomplete. Here we report a detailed study on nitrogen doping in SWNTs with diameters in the range of 0.8−1.0 nm, with well-defined chirality. We show that the introduction of nitrogen in the carbon framework significantly alters the stability of certain tubes, opening for the possibility to selectively grow nitrogen-doped SWNTs with certain chirality and diameter. At low nitrogen concentration, pyridinic functionalities are readily incorporated and the tubular structure is well pertained. At higher concentrations, pyrrolic functionalities are formed, which leads to significant structural deformation of the nanotubes and hence a stop in growth of crystalline SWNTs. Raman spectroscopy is an important tool to understand guest atom doping and electronic charge transfer in SWNTs. By correlating the influence of defined nitrogen functionalities on the electronic properties of SWNTs with different chirality, we make precise interpretation of experimental Raman data. We show that the previous interpretation of the double-resonance G′-peak in many aspects is wrong and instead can be well-correlated to the type of nitrogen doping of SWNTs originating from the p-or n-doping nature of the nitrogen incorporation. Our results are supported by experimental and theoretical data.
Atomic configuration of nitrogen-doped single-walled carbon nanotubes
Nano letters, 2014
Having access to the chemical environment at the atomic level of a dopant in a nanostructure is crucial for the understanding of its properties. We have performed atomically resolved electron energy-loss spectroscopy to detect individual nitrogen dopants in single-walled carbon nanotubes and compared with first-principles calculations. We demonstrate that nitrogen doping occurs as single atoms in different bonding configurations: graphitic-like and pyrrolic-like substitutional nitrogen neighboring local lattice distortion such as Stone-Thrower-Wales defects. We also show that the largest fraction of nitrogen amount is found in poly aromatic species that are adsorbed on the surface of the nanotube walls. The stability under the electron beam of these nanotubes has been studied in two different cases of nitrogen incorporation content and configuration. These findings provide key information for the applications of these nanostructures.