Narrow Results

In this paper, we review the potential applications of single-walled carbon nanotubes in three areas: passives (interconnects), actives (transistors), and antennas. In the area of actives, potential applications include transistors for RF and microwave amplifiers, mixers, detectors, and filters. We review the experimental state of the art, and present the theoretical predictions (where available) for ultimate device performance. In addition, we discuss fundamental parameters such as dc resistance as a function of length for individual, single-walled carbon nanotubes.

Junction formation in crossed C(10,0) single wall carbon nanotubes under pressure has been investigated, using classical molecular-dynamics simulations at 1 K. It has been found that a stable mechanical junction was formed by means of placing two crossed single wall carbon nanotubes between two rigid graphene layers which move toward each other.

Thermal conductivity of carbon nanotubes depends on various factors. The simulation of heat transport in armchair single-walled carbon nanotube by direct nonequilibrium molecular dynamics (NEMD) method employing Tersoff–Brenner potential indicates that, thermal conductivity decreases with increase in temperature difference between two ends of the tube. Increasing the imposed temperature differential along the tube axis, leads to domination of Umklapp scattering and impacts the heat transport. The applied temperature difference does not influence the behavior of thermal conductivity vs. tube length, diameter and temperature, but changes its value.

Plasma-based accelerator technology enables compact particle accelerators. In Laser Wakefield Acceleration, with an ultrafast high-intensity optical laser driver, energy gain of electrons is greater if the electron density is reduced. This is because the energy gain of electrons is proportional to the ratio of laser’s critical density to electron density. However, an alternative path for higher energy electrons is increasing the critical density via going to shorter wavelengths. With the advent of Thin Film Compression, we now see a path to a single cycle coherent X-ray beam. Using this X-ray pulse allows us to increase the plasma density to solid density nanotube (carbon or porous alumina) regime and still be under-dense for a Laser Wakefield Acceleration technique. We will discuss some implications of this below.

The structural and electronic properties of BN(5, 5) and C(5, 5) nanotubes under pressure are studied by using first principles calculations. In our study range, BN(5, 5) undergoes obvious elliptical distortion, while for C(5, 5) the cross section first becomes an ellipse and then, under further pressure, is flattened. The band gap of BN(5, 5) decreases with increasing pressure, which is inverse to that of zinc blende BN, whereas for C(5, 5) the metallicity is always preserved under high pressure. The population of charge density indicates that intertube bonding is formed under pressure. We also find that BN(5, 5) may collapse, and a new polymer material based on C(5, 5) is formed by applying pressure.

The dislocation energy, Peierls barrier and Peierls stress of pentagon–heptagon (p–h) pair dislocation in zigzag single-walled carbon nanotube (SWCNT) are studied by the improved Peierls–Nabarro (P–N) theory. The contribution of the strain energy is considered in evaluating the dislocation energy and Peierls barrier and stress. Using the γ-surface obtained from the first-principle calculations, it is found that the misfit energies of p–h pair dislocations are weakly dependent on the perimeters of the SWCNTs, while the strain and total energies have logarithmic behaviors with the perimeters of larger SWCNTs (N>10). For the smaller SWCNTs (N⩽10), the strain and total energies have a little deviation from the logarithmic behaviors due to the curvature and size effects. The calculated Peierls barrier and Peierls stress are about 4.2–4.8 eV and 0.3μ, respectively. For the (12,0)–(11,0) carbon nanotube with different modification factors, the dislocation energy remains almost invariant (about 18 eV). The Peierls barrier and Peierls stress increase linearly with the increasing of the modification factor. When modification factor changes from 0.10 to 0.45, the Peierls barrier changes from 3.6 eV to 7.4 eV, and the Peierls stress changes from 0.2μ to 0.5μ.

Extensive studies of the geometric structures, stabilities and electronic properties of gallium nitride (GaN)_n tubelike clusters and single-walled GaN nanotubes (GaNNTs) were carried out using density-functional theory (DFT) calculations. A family of stable tubelike structures with Ga–N alternating arrangement was observed when n≥8 and their structural units (four-membered rings (4MRs) and six-membered rings (6MRs)) obey the general developing formula. The size-dependent properties of the frontier molecular orbital surfaces explain why the long and stable tubelike clusters can be obtained successfully. They also illustrate the reason why GaNNTs can be synthesized experimentally. Our results also reveal that the single-walled GaNNTs, which as semiconductors with a large bandgap, can be prepared by using the proper assembly of tubelike clusters.

On the basis of the one-particle Dirac equation, an exact solution for the problem of the energy spectrum of a relativistic electron on the surface of a tube in a magnetic field is obtained. The spectra of a relativistic rotator and a relativistic electron in a two-dimensional electron gas are obtained in limiting cases. The density of electron states and the main thermodynamic functions of a relativistic electron gas on a tube in a magnetic field are calculated. These values experience Aharonov–Bohm oscillations and oscillations of the de Haas–van Alphen type with a change of the magnetic field and parameters of the problem. The asymptotics of thermodynamic functions at low- and high-temperatures are obtained. The results can be used in studies of nanotubes of a two-dimensional electron gas and in astrophysics.

The model of electron gas situated on the two-dimensional continual cylindrical surface is suggested to describe a polaron in the single-walled nanotube made of polar material. The problem on weak-coupling polaron is solved using perturbation theory. Analytical expression for the polaron energy shift of the subband is found in the case of bulk phonon approximation and the case when longitudinal optical (LO) phonons are confined on the cylinder's surface. It is shown that in the second case the polaron effect is negligible.

Uniform and aligned ZnO nanotube arrays have been synthesized by annealing Zn nanowire arrays in anodic aluminum oxide (AAO) membrane. In our method, Zn nanowire arrays were fabricated by electrochemical deposition technique based on ordered nanoporous AAO, and then a heat-treatment method was used to convert Zn nanowire arrays to ZnO nanotube arrays. The ZnO arrays were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and absorption spectra. The results show that the polycrystalline ZnO nanotubes have a diameter of about 45 nm. This method can also be used to fabricate other metal oxide nanotube arrays.

Porous anodized aluminum oxide (AAO) template was combined with sol-gel method in this work for the fabrication of high-ordered NdVO₄ nanotube arrays. The diameter, length, and wall thickness of the nanotubes can be adjusted conveniently. The sample was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), absorption spectra, and photoluminescence spectra. The results show that these uniformly distributed, high-ordered, and parallel nanotubes have great light emission in both the visible region and near-infrared region due to their corresponding energy level transitions. With this method, future application of rare-earth hollow nanostructures will be widely extended.

Based on first-principle calculation, the geometry and electronic transport properties of the boron and nitrogen co-doping single-walled carbon nanotubes are investigated by using density functional theory combined with non-equilibrium Green's functions. The results show that the BN atoms energetically tend to form covalent bond of BN along axis in the nanotubes. In contrast to solely B or N doping, the co-doping do not generate accepter or donor subbands near the Fermi level. The co-doping give rise to the reduction of band gap in semiconducting (10, 0) tube and, furthermore, introduces the band gap to the metallic (5, 5) tube.

We investigate the effect of vacancy defect reconstruction on electron transport properties in a (4, 0) zigzag and (5, 5) armchair silicon-carbide nanotubes (SiCNTs) by applying self consistent non-equilibrium Green's function formalism in combination with the density-functional theory to a two probe molecular junction constructed from SiCNTs. The geometry optimization results show that single vacancies and di-vacancies in SiCNTs have different reconstructions. A single vacancy when optimized, reconstructs into a 5-1DB configuration in both zigzag and armchair SiCNTs, and a di-vacancy reconstructs into a 5-8-5 configuration in zigzag and into a 5-2DB configuration in armchair SiCNTs. Analysis of frontier molecular orbitals (FMO) and transmission spectrum show that the vacancy defect increases the band gap of (4, 0) metallic SiCNT and decreases the band gap of (5, 5) semiconducting SiCNT. Bias voltage dependent current characteristic show reduction in overall current in metallic SiCNT and an increase in overall current in semiconducting SiCNT.

CoFeB nanotubes were fabricated by electroless plating in magnetic field using anodized aluminum oxide template, and the structural and magnetic properties of CoFeB nanotubes were investigated. It is found that some nano-scale particles form on the wall of nanotubes. Both coercivity ratio and squareness ratio of out-of-plane to in-plane are significantly changed by the applied magnetic field during electroless plating, which indicates that directional ordering in amorphous CoFeB nanotubes are achieved during electroless plating under magnetic field. The results show that the applied field impacts the magnetic anisotropy of amorphous nanotubes. The anisotropy is stronger with the magnitude of applied field increasing.

In this paper, we report strong variations in the Raman spectra of different carbon allotropes samples, for temperatures ranging from 83 K to 1123 K. The temperature dependence of D and G peak frequencies in the Raman spectrum of diamond, graphite, graphene, and carbon nanoparticles (CNPs) with 20 nm dot-size were investigated. These effects caused by temperature can be estimated from the changes in position and in linewidth of peak full width at half maximum (FWHM) G in the Raman spectrum of each sample. The broadening for each allotrope under the same conditions of temperature were: diamond ~ 4 cm^-1, graphite ~ 50 cm^-1, graphene ~ 5 cm^-1 and nanoparticles ~ 7 cm^-1. We also used scanning electron microscopy (SEM) to study the morphology and determine the size of the samples. According to the experimental data, the residual structural disorder and stress present in the samples are enhanced with temperature and responds for the observed changes in the Raman spectra. We present a systematic study of the temperature-dependent Raman spectra of four carbon allotropes.

The helicity of stable double helical bromine chains inside single-walled carbon nanotubes (SWCNTs) was studied through the calculation of systematic interaction energy, using the van der Waals interaction potential. The results presented clear images of stable double helical structures inside SWCNTs. The optimal helical radius and helical angle of chain structure increase and decrease, respectively, with the increase of tube radius. The detailed analysis indicated that some metastable structures in SWCNTs may also co-exist with the optimal structures, but not within the same tubes. In addition, a detailed simulation of X-ray diffraction patterns was performed for the obtained optimal helical structures.

This paper proposes a new dielectrically modulated (DM) twin cavity nanotube biosensor and its sensitivity evaluation suitability by the transit time $(\tau )$ and device efficiency $(g_m/I_{\mathrm{\text{ds}}})$. In addition, the vertical structure of the device also helps the uniform spreading of biomolecules within the nanogap cavity region. The inner cavity of the proposed biosensor offers more space for the stabilization of biomolecules and uses the benefits of material solubility. In this paper, the sensing ability of the biosensor is examined in terms of $\tau$ and $g_m/I_{\mathrm{\text{ds}}}$ for five neutral biomolecules. Furthermore, the charged biomolecule and deoxyribonucleic acid (DNA) are separately investigated for positive as well as negative charge densities. Also, various optimizations on the device are analyzed for different biomolecules in this paper.

The large area, highly uniform copper nanorod arrays with cylindrical morphology in polycarbonate membranes (PC) have been successfully prepared by electrochemical deposition. The copper nanorod arrays have the length of 3 μm, the diameter of 400 nm, approximately, which correspond closely to the pore diameter and thickness of membranes. The copper nanotubes were also obtained by controlling initial voltage and polycarbonate membranes treatment process. The possible growing mechanisms of copper nanostructures in membrane pores were discussed.

Novel three-dimensional (3D) branched nanotubes of sodium niobate (NaNbO₃) were produced by a multi-step reaction, which involves the synthesis of Nb₂O₅ branched nanowires and subsequently treating these precursors in alkali solution. XRD and SEM have been used to analyze current products. All the obtained nanobranches exhibited tubular structure, which was induced by nanoscale Kirkendall effect and surface diffusion. This work demonstrates a simple and efficient pathway to design hierarchical and complex hollow nanostructures, which are expected to have important applications, such as sensors and photocatalysts.

Nanotubes and nanowires of π-conjugated polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) were synthesized using Al₂O₃ nanoporous template through electrochemical polymerization method. From the SEM and TEM photographs, the formation of conducting polymer nanotube (CPNT) and nanowire (CPNW) was confirmed. From FT-IR and UV/Vis absorbance spectra, we observed the effect of doping and de-doping through HF or NaOH dissolving of Al₂O₃ template. DC conductivity and I–V characteristics as a function of temperature and gate bias were measured for the CPNTs and CPNWs prepared with various synthetic conditions. Magnetic properties were measured through EPR experiments. Based on the results, we compare the intrinsic properties between bulk and nanoscale π-conjugated polymers.