Nitrogen-doped Single-walled Carbon Nanotubes Research Articles

Spectroscopic Characterization of N-Doped Single-Walled Carbon Nanotube Strands: An X-ray Photoelectron Spectroscopy and Raman Study

We have studied in detail the carbon and nitrogen bonding environments in nitrogen-doped single-walled carbon nanotubes (SWCNTs). The samples consisting of long strands of N-doped SWCNTs were synthesized using an aerosol assisted chemical vapor deposition method involving benzylamine-ethanol-ferrocene solutions. The studied samples were produced using different benzylamine concentrations in the solutions, and exhibited a maximum concentration of ca. 0.3%at of N, determined by X-ray photoelectron spectroscopy (XPS). In general, we observed that the ratio between substitutional nitrogen and the pyridine-like bonded nitrogen varied upon the precursor composition. Moreover, we have observed that the sp2-like substitutional configuration of the C-N bond does not exceed the 50% of the total N atomic incorporation. In addition, we have characterized all these samples using Raman spectroscopy and electron microscopy.

Movement of hydrogen molecules in pristine, hydrogenated and nitrogen-doped single-walled carbon nanotubes

Carbon nanotubes (CNT) are considered promising nano-scale materials because of their unique structural, mechanical and electronic properties. Due to their long seamless cylindrical shaped structures they could be applied as effective nano-channels for mass transfer and relevant storages for hydrogen molecules. We study hydrogen transport mechanisms in CNTs for various chiral indices and different peculiarities, using the molecular dynamics simulation and quantum mechanical approach. Various CNT models such as pristine, hydrogenated and doped by nitrogen atoms of zigzag (10,0), chiral (7,5) and armchair (6,6) types with hydrogen molecules diffusing inside are simulated at 300 K. The behaviour of hydrogen molecules inside CNTs is analysed using mean-square displacements and velocity autocorrelation functions. From the quantum mechanical approach, the electronic density distribution of CNT is calculated to verify the smooth characteristics of inner surfaces of nanotubes.

Unusual transport characteristics of nitrogen-doped single-walled carbon nanotubes

Electrical transport characteristics of nitrogen-doped single-walled carbon nanotubes (N-SWCNTs), in which the nitrogen dopant is believed to form a pyridinelike bonding configuration, are studied with the field effect transistor operations. Contrary to the expectation that the nitrogen atoms may induce a n-type doping, the electrical transports through our N-SWCNTs are either ambipolar in vacuum or p-type in air. Through the first-principles electronic structure calculations, we show that the nitrogen dopant indeed favors the pyridinelike configuration and the Fermi level of the pyridinelike N-SWCNT is almost at the intrinsic level.

Electronic Properties of Nitrogen-Doped Carbon Nanotubes with Strain: Ab initio Method Approach

A theoretical study on the electronic structure of nitrogen-doped single-walled carbon nanotubes (SWCNTs) using density functional theory based on the projector-augmented wave method is presented. It is found that the electronic properties of the CNT were determined by the nitrogen doping, uniaxial strain, and the size of the CNT. The nitrogen-doped CNTs turned out to have n-type semiconductor characteristics. However, the detailed change in electronic behavior varied with the specific condition of the CNT. Specifically, the density of states (DOS) for (5,5) nanotubes exhibited a shift of the electronic spectrum. On the other hand, for the case of (10,10) nanotubes, the band gap was narrowed by nitrogen doping owing to the existence of nitrogen states near the conduction band minimum. Interestingly, the applied strain did not affect the electronic structure of the (10,10) CNT. However, in the case of the 5% nitrogen-doped (5,5) CNT, the difference in the electronic structure was enhanced markedly with applied strain, unlike in the case of other armchair CNTs.

Growth and characterization of nitrogen-doped single-walled carbon nanotubes bywater-plasma chemical vapour deposition

Nitrogen-doped single-walled carbon nanotubes (N-SWNTs) are directly grown onSiO2/Si substratesat 450 °C with methane and ammonia gases by water-plasma chemical vapour deposition. Thestrongest radial breathing mode peak in Raman spectra of the grown N-SWNTs, probedwith a 633 nm laser excitation, was assigned to (7, 5) semiconducting nanotubes witha diameter of 0.83 nm. As the doped nitrogen content increases, the D-band toG-band ratio in Raman spectra, indicating the imperfection of nanotubes, graduallyincreases and saturates at around 4%. X-ray photoelectron spectroscopy shows thatnitrogen atoms are doped with a pyridine-like configuration in the N-SWNTs.

Boron and nitrogen-doped single-walled carbon nanotube

Boron nitride semiconducting zigzag single-walled carbon nanotube (SWCNT), B cb N cn C 1 - cb - cn , as a potential candidate for making nanoelectronic devices is investigated by first-principle full potential density functional theory (DFT). In contrast to the previous DFT calculations, where just one boron and nitrogen doping configuration is considered, here for the average over all possible configurations density of states is calculated in terms of boron and nitrogen concentrations. For example in many body techniques (MBTs) [R. Moradian, Phys. Rev. B 89 (2004) 205425] it is found that semiconducting average gap, E g , could be controlled by doping nitrogen and boron. But in contrast to MBTs where gap edge in the average density of states is sharp, the gap edge is smeared and impurity states appear in the SWCNT semiconducting gap.

Synthesis and characterization of long strands of nitrogen-doped single-walled carbon nanotubes

We describe the synthesis of N-doped single-walled carbon nanotubes (N-SWNTs), that agglomerate in bundles and form long strands (<10 cm), via the thermal decomposition of ferrocene/ethanol/benzylamine (FEB) solutions in an Ar atmosphere at 950 °C. The amount of benzylamine in the solution was varied from 0% to 26% by weight. Using Raman spectroscopy, we noted that as the N content is increased in the starting FEB solution, the growth of large diameter tubes is inhibited. We observed that the relative electrical conductivity of the strands increases with increasing nitrogen concentration. Thermogravimetric analysis (TGA) showed novel features for highly doped tubes that are related to chemical reactions on N sites.

Chirality-dependent boron-mediated growth of nitrogen-doped single-walled carbon nanotubes

A change in the relative abundance of single-walled carbon nanotubes, due to the presence of both nitrogen and boron during synthesis, has been identified through Raman and absorption spectroscopy. Raman spectroscopy shows that for two specific branches boron mediates the growth of smaller-diameter zigzag or near-zigzag nanotubes. We combine our experimental results with an improved Kataura model to identify two of the preferentially grown species as (16,0) and (14,1).

Ab initio investigations of lithium insertion in boron and nitrogen-doped single-walled carbon nanotubes

Theoretical investigations on boron and nitrogen-doped single-walled carbon nanotubes have been carried out using ab initio calculations to explore the capability of the nanotubes to incorporate Li + ion in its interior. Li-nanotube systems can improve the capacity of lithium batteries by using both nanotube exteriors and interiors. Ab initio calculations of the fully optimized nanotubes and their complexes with lithium were used to examine the lithium incorporation in the nanotube through the open-end depending on the doping. The energetic and geometric features of the complexes are studied and discussed.

A first-principles study of lithium absorption in boron- or nitrogen-doped single-walled carbon nanotubes

The lithium absorption energies and electronic structures of boron- or nitrogen-doped single-walled carbon nanotubes (SWCNT) were investigated using first-principles calculations. B-doping decreases lithium absorption energy dramatically both at inner and outer sites. B-doping forms an electron-deficient structure in SWCNT, which can stabilize the Li absorption on the tube walls; however, N-doping forms an electron-rich structure, and will hinder the Li absorption in SWCNT. The calculations suggest that B-doping in SWCNT will improve its Li absorption performance.