N-doped Single-walled Carbon Nanotubes Research Articles

Study of the electron-doping mechanism in single-walled carbon nanotubes using dimethylbenzimidazole.

Single-walled carbon nanotubes (SWCNTs) exhibit p-type properties in air, necessitating electron doping using n-dopants (e.g., reducing agents) for the development of SWCNT-based electronic devices. Dimethylbenzimidazole (DMBI-H) derivatives serve as effective electron dopants, not only for SWCNTs, but also for various organic semiconducting materials. However, the doping reaction is still a subject of debate. In this study, the electron-doping reactions of ortho-methoxy-substituted DMBI-H for SWCNTs were analyzed in protic and aprotic solvents in the presence and absence of dioxygen (O2). The presence of O2 was found to cause the reduction of O2 on the SWCNT surface in the protic solvent, resulting in the production of DMBI cations and water through proton-coupled electron transfer (PCET) from the n-doped SWCNT and ethanol. This work elucidates the mechanism behind the air-stability of n-type SWCNTs.

Pyridine-mediated B–B bond cleavage of tetrahydroxydiboron to synthesize n-doped SWCNTs with long-term air stability

Neutral radicals, including carbon radicals, are highly useful chemical species for the functionalization of semiconducting materials to change their electrical and optical properties owing to their high reactivity. However, boron radicals have been limited to synthetic and reaction chemistry, with rare utilization in materials science. In this study, a mixture of tetrahydroxydiboron (B2(OH)4) and pyridine derivatives was found to act as an electron dopant for single-walled carbon nanotubes (SWCNTs) because of the electron transfer from pyridine-mediated boron radicals generated by B–B bond dissociation to neutral radicals. In particular, the radical formed from a mixture of B2(OH)4 and 4-phenylpyridine ((4-Phpy)B(OH)2·) efficiently doped electrons into the SWCNT films; thus, n-type SWCNTs with long-term air stability for more than 50 days at room temperature were prepared. Furthermore, the experimental and theoretical surface analyses revealed that the formation of stable cations from ((4-Phpy)B(OH)2·) and the efficient interaction with SWCNTs due to their high planarity served as the mechanism for their stable doping.

Nitrogen-Doped Single-Walled Carbon Nanotubes by Floating-Catalyst CVD Process

Due to the properties of single-walled carbon nanotube (SWCNT), thin film SWCNTs have been used for many versatile applications. Direct synthesis of the nanotube films with desired electronic structures without prerequisite of post treatment process then becomes one important step. Here, we present the synthesis of nitrogen-doped SWCNTs by floating-catalyst chemical vapor deposition process. With low nitrogen level incorporated into the sp2 carbon network, substitutional and pyridinic nitrogens become predominance. The electronic structure of N-doped SWCNT film could be changed into n-type doping. The localized structures of carbon and nitrogen bonding environments were also revealed by x-ray absorption spectroscopy. The formation of p-n junction was also obtained from the I-V characteristic of N-doped SWCNT heterojunction diode revealing n-type behavior of the sample.

A Flexible NO2 Gas Sensor Based on Single-Wall Carbon Nanotube Films Doped with a High Level of Nitrogen.

Carbon nanotubes (CNTs) are considered a promising candidate for the detection of toxic gases because of their high specific surface area and excellent electrical and mechanical properties. However, the detecting performance of CNT-based detectors needs to be improved because covalently bonded CNTs are usually chemically inert. We prepared a nitrogen-doped single-wall CNT (SWCNT) film by means of gas-phase fluorination followed by thermal annealing in NH3. The doped nitrogen content could be changed in the range of 2.9–9.9 at%. The N-doped SWCNT films were directly used to construct flexible and transparent gas sensors, which can work at a low voltage of 0.01 V. It was found that their NO2 detection performance was closely related to their nitrogen content. With an optimum nitrogen content of 9.8 at%, a flexible sensor had a detection limit of 500 ppb at room temperature with good cycling ability and stability during bending.

Field-emission properties of sulfur chain-encapsulated single-walled carbon nanotubes

The encapsulation of elemental sulfur inside single-walled carbon nanotube (SWNT) and the consequent formation of sulfur chain-encapsulated SWNT (S@SWNT) is achieved. Raman spectra suggest an enhanced conductivity and electron doping of the SWNT by the sulfur chain encapsulation, which are also consistent with ultraviolet photoelectron spectra and thermoelectric measurements. Owing to the enhanced electron concentration and the reduced work function, an enhanced field-emission (FE) current is observed for S@SWNT. In addition, a gradual recovery of the suppressed FE current is observed for S@SWNT after the O2 purging in the chamber is terminated, while the permanent failure of FE is observed for the pristine SWNT. Further experimental results collectively demonstrate that the enhanced electron concentration of the relatively n-doped SWNT by sulfur chain encapsulation alleviates the damage inflicted to the emitter tip sites from the oxidative environment generated during FE measurement.

Diameter dependent doping in horizontally aligned high-density N-doped SWNT arrays

We reported the growth of horizontally aligned nitrogen-doped single-walled carbon nanotubes (SWNTs) on quartz substrates. The synthesized SWNTs were comprehensively characterized at the single nanotube level. Owing to the highly aligned nature of the nanotubes, we were able to investigate the diameter dependent doping mechanism through systematic resonant Raman spectroscopy studies. Other than the formerly found narrowing effect by N-doping, we proposed that the nanotube diameter affects the introduction of N atoms into the carbon lattice in an elaborate way. The obtained doping level increased along with the nanotube diameter but lost the increasing trend when the diameter became larger and experienced a slight decrease after reaching the local peak value. These insights about the heteroatom doping into the carbon nanotubes could benefit the development of the carbon nanotube based functional materials and extend their application in a broad range of areas.

The sensing mechanism of N-doped SWCNTs toward SF6 decomposition products: A first-principle study

In order to monitor the insulation status of SF6-insulated equipment on-line, SOF2 and SO2F2, two typical decomposition products of SF6 under electric discharge condition, are chosen as the target gases to evaluate the type and severity of discharge. In this work, single N atom doping method is adopted to improve the gas sensitivity of single wall carbon nanotubes to SOF2 and SO2F2. Single and double gas molecules adsorptions are considered to completely analyze the adsorption properties of N-doped single wall carbon nanotubes. Calculation results show that N atom doping enhances the surface activity of carbon nanotubes. When gas molecules physically adsorbed on N-doped single wall carbon nanotubes, the weak interaction between gas molecules and N-doped single wall carbon nanotubes nearly not changes the electrical property according to analysis of the density of states and molecular orbitals. While the chemisorption between gas molecules and N-doped single wall carbon nanotubes distinctly decreases the conductivity of adsorption system.

Promoting mechanism of N-doped single-walled carbon nanotubes for O2 dissociation and SO2 oxidation

Although heteroatom doping in carbon based catalysts have recently received intensive attentions, the role of the intrinsically porous structure of practical carbon materials and their potential synergy with doping atoms are still unclear. To investigate the complex effects, a range of N-doped single-walled carbon nanotubes (SWCNTs) were used to investigate their potential use for O2 dissociation and the subsequent SO2 oxidation using density functional theory. It is found that graphite N doping can synergize with the outer surface of SWCNTs to facilitate the dissociation of O2. The barrier for the dissociation on dual graphite N-doped SWCNT-(8, 8) is as low as 0.3eV, and the subsequent SO2 oxidation is thermodynamically favorable and kinetically feasible. These results spotlight on developing promising carboncatalyst via utilization of porous gemometry and heteroatom-doping of carbon materials simultaneously.

Enhanced Lithium–Oxygen Battery Performances with Pt Subnanocluster Decorated N-Doped Single-Walled Carbon Nanotube Cathodes

Achieving dramatic improvement in long-term cycling performance in Li–O2 batteries continues to remain a challenge, which is imperative for turning their alluring promise into reality. Developing a bifunctional cathode material capable of reducing overpotentials and enhancing the long-term cycling performances holds the key. Herein, bifunctional cathodes for Li–O2 batteries were prepared by electrodeposited Pt subnanoclusters on pristine as well as nitrogen-doped single-walled carbon nanotubes (SWCNTs) using rotating disk electrode voltammetry techniques. Diffraction, microscopic, and spectroscopic techniques were used to characterize the prepared materials, and the phase purity of the materials was confirmed. Microscopic analysis depicted a fine dispersion of ≤2 nm Pt nanoclusters on single-walled carbon nanotubes. Rotating disk electrode voltammetry measurements indicated low overpotentials as well as high catalytic ORR/OER activities with Pt nanocluster decorated SWCNTs in comparison to Pt-free SWCNTs....

Fully gravure printed complementary carbon nanotube TFTs for a clock signal generator using an epoxy-imine based cross-linker as an n-dopant and encapsulant.

Printed p-type single walled carbon nanotube (SWCNT) based circuits exhibit high power dissipation owing to their thick printed dielectric layers (>2 μm) and long channels (>100 μm). In order to reduce the static power dissipation of printed SWCNT-base circuits while maintaining the same printing conditions and channel lengths, complementary metal-oxide-semiconductor (CMOS) based circuits are more ideal. These circuits, however, have not been successfully implemented in a scalable printing platform due to unstable threshold voltages of n-doped SWCNT based thin film transistors (TFTs). In this work, a thermally curable epoxy-imine-based n-doping ink is presented for achieving uniform doping and sealing of SWCNT layers by gravure printing. After printing the n-doping ink, the ink is cured to initiate a cross-linking reaction to seal the n-doped SWCNT-TFTs so that the threshold voltage of the n-doped SWCNT-TFTs is stabilized. Flexible CMOS ring oscillators using such n-doped SWCNT-TFTs combined with the intrinsically p-type SWCNT-TFTs can generate a 0.2 Hz clock signal with significantly lower power consumption compared to similarly printed p-type only TFT based ring oscillators. Moving forward, this CMOS flexible ring oscillator can be practically used to develop fully printed inexpensive wireless sensor tags.

Simulating adsorption of organic pollutants on N-doped single-walled carbon nanotubes in water

N-doped carbon nanotubes (N-CNTs) are widely used in various fields due to their excellent characters. They will be inevitably released into the environment with their extensive use. The adsorption of organic compounds on N-CNTs may affect the environmental behavior and ecological risk of both N-CNTs and pollutants. However, only few studies have been performed on the adsorption of organic compounds on N-CNTs in water. In this study, we constructed 20 N-doped single-walled carbon nanotubes (N-SWNTs) with different doping configurations and doping concentrations and simulated the adsorption of aromatic pollutants on N-SWNTs by density functional theory (DFT) calculations. Our simulation results indicated that N doping can increase the adsorption affinity of aromatic compounds on SWNTs, and doping configurations and doping concentrations show significant effect. Pyrid-N doped SWNTs with vacancy defect have a good performance on adsorption. The adsorption of aromatic compounds on N-SWNTs in water is physisorption. Hydrophobic interaction and p-p stacking are the main interaction forces. Functional groups of benzene derivatives (-NO 2 , -OH, -NH 2 ), can enhance electrostatic interactions between the aromatics and N-SWNTs. Our study will provide a theoretical guide for future ecological risk assessment of N-SWNTs.

Dissociation of oxygen on pristine and nitrogen-doped carbon nanotubes: a spin-polarized density functional study

The oxygen adsorption energies for pristine and N-doped single-walled carbon nanotubes of different diameters.

N-SWCNTs production by aerosol-assisted CVD method

The insertion of dopant atoms into the carbon nanotube framework allows one to tailor their electronic properties, reactivity and structure. We investigated the effect of the reaction parameters on the yield and quality of N-doped single-walled carbon nanotubes (N-SWCNTs) produced via aerosol chemical vapour deposition. In this context, aerosols of ethanol/benzylamine mixtures in conjunction with ferrocene were pyrolysed at temperatures between 950 and 1100°C. As a result, we were able to produce N-SWCNTs with a nitrogen content of ca. 1at.%, diameters ranging between 0.9 and 1.8nm, and production rates of more than 10mg/h.

Spectroscopic Determination of the Electrochemical Potentials of n-Type Doped Carbon Nanotubes

Understanding the doping mechanism that involves substantial charge transfer between carbon nanotubes and chemical adsorbent is of critical importance for both basic scientific knowledge and nanodevice applications. Nevertheless, it is difficult to estimate the modification of electronic structures of the doped carbon nanotubes. Here we report measurements of electrochemical potentials of n-doped single-walled carbon nanotubes (SWCNTs) by using photoluminescence (PL) measurement. The change of the measured PL intensity before and after n-type doping was used to extract the electrochemical potential using the Nernst equation. The measured electrochemical potentials of SWCNTs approached the theoretical reduction potential of SWCNTs as the mole concentration of the dopant increased. The doping effect was also confirmed by the change of absorption spectroscopy. The quenching of the PL and absorption intensity was strongly correlated to the standard reduction potential of the dopant and its concentration. This investigation could be a cornerstone for SWCNTs-based electronic device applications such as solar cells, light-emitting diodes, and nanogenerators.

Origin of Bonding between the SWCNT and the Fe3O4(001) Surface and the Enhanced Electrical Conductivity

Recent experiments have demonstrated that adding single-wall carbon nanotubes (SWCNTs) to Fe3O4 nanoparticle electrodes leads to dramatically improved electrical conductivity and performance of Li ion batteries. Our density functional theory (DFT) calculations reveal that the interactions between both pristine and B- or N-doped SWCNTs and the Fe3O4(001) surface are very weak. Although C vacancies in SWCNTs can lead to stronger chemical bonding between SWCNTs and Fe3O4(001) surfaces, the binding and electrical conductivity in this case are not ideal. Interestingly, we show that transition-metal (Fe, Ni) atoms or clusters facilitate the formation of strong chemical bonding between SWCNTs and Fe3O4(001) surfaces, providing excellent channels for electrons flowing between SWCNTs and Fe3O4(001) surfaces, which is essential for improving electrical conductivity of the mixed electrodes. The calculated electron conductance of the transition-metal-decorated system is improved by more than 2 orders of magnitude, in...

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.

Methane adsorption inside and outside pristine and N-doped single wall carbon nanotubes

The internal and external adsorption of CH 4 on zigzag pristine and N-doped SWCNTs has been investigated employing first principles calculations. Two different substitutions were performed to obtain pyridinic (N py) and graphitic ( N sp 3 ) nitrogen. The adsorption of CH 4 inside SWCNTs is expected to be more favorable than on groove sites for open-ended small diameter (0.7–1.1 nm) pure SWCNTs. In general, the introduction of N atoms increases the external adsorption energies ( E ads). In the case of N py-doped SWCNTs, they are increased over a 100%. However, for the internal adsorption, the E ads can be decreased or increased when N atoms are included. For the N sp 3 -doped (9, 0) SWCNT, it is decreased with respect to the undoped tube. Thus, the optimal radius to encapsulate CH 4 is increased upon N-doping. The adsorption isotherms of CH 4 are going to be dependent on the production method of the SWCNTs, if they have open ends; this fact is in contrast with the experimental measurements on close-ended SWCNT. For undoped SWCNTs, the encapsulation inside small diameter (0.7–1.1 nm) SWCNT is going to be preferred over electric arc-SWCNTs (1.4–1.8 nm diameter). However, for N-doped SWCNTs, the opposite should be true, if enough nitrogen is introduced.

Computational study of B- or N-doped single-walled carbon nanotubes as NH 3 and NO 2 sensors

The adsorption of NH 3 and NO 2 in B- or N-doped (10, 0) single-walled carbon nanotubes (SWCNTs) was investigated by using density functional computations to exploit their potential applications as gas sensors. NH 3 can be chemisorbed only in B-doped SWCNTs with apparent charge transfer, so B-doped SWCNTs can be used as NH 3 sensors. Both B- and N-doping make NO 2 chemisorption feasible in SWCNTs, but the binding of NO 2 with B is too strong, indicating an impractical recovery time as gas sensors. Due to the medium (optimal) adsorption energy and the conductance reduction accompanied with the charge transfer between SWCNTs and gas molecules, N-doped SWCNTs are potentially good NO 2 sensors.

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.

Doping effects of B and N on hydrogen adsorption in single-walled carbon nanotubes through density functional calculations

The doping effects of B and N on atomic and molecular adsorption of hydrogen in single-walled carbon nanotubes (SWNTs) were investigated through density functional theory (DFT) calculations. The hydrogen adsorption energies and electronic structures were calculated for the pristine and B- or N-doped SWNTs. The B-doping increases the hydrogen atomic adsorption energies both in zigzag and armchair nanotubes. The B-doping forms an electron-deficient six-membered ring structure, and when hydrogen is adsorbed on top of B atom, a coordination-like B–H bond will form. The N-doping forms an electron-rich six-membered ring structure, and decreases the hydrogen atomic adsorption energies in the N-doped SWNT. In case of hydrogen molecular adsorption, both B- and N-doping decrease the adsorption energies in SWNTs.