Narrow Results

When one studies the Casimir effect, the periodic (anti-periodic) boundary condition is usually taken to mimic a periodic (anti-periodic) structure for a scalar field living in a flat space with a non-Euclidean topology. However, there could be an arbitrary phase difference between the value of the scalar field on one endpoint of the unit structure and that on the other endpoint, such as the structure of nanotubes. Then, in this paper, a periodic condition on the ends of the system with an additional phase factor, which is called the "quasi-periodic" condition, is imposed to investigate the corresponding Casimir effect. And an attractive or repulsive Casimir force is found, whose properties depend on the phase angle value. Especially, the Casimir effect disappears when the phase angle takes a particular value. High dimensional spacetime case is also investigated.

We describe calculations of the properties of quantum fluids inside nanotubes of various sizes. Very small radius (R) pores confine the gases to a line, so that a one-dimensional (1D) approximation is applicable; the low temperature behavior of 1D ⁴He is discussed. Somewhat larger pores permit the particles to move off axis, resulting eventually in a transition to a cylindrical shell phase—a thin film near the tube wall; we explored this behavior for H₂. At even larger R ~ 1 nm, both the shell phase and an axial phase are present. Results showing strong binding of cylindrical liquids ⁴He and ³He are discussed.

High-orderly nanotubes of titania were fabricated by anodic oxidation of pure titanium substrate in different electrolytes containing fluoride. Different morphological nanotubes of titania were obtained through controlling the different pH value of inorganic electrolytes, and it was found that nanotubes of titanium oxide would not formed when pH value was above 6. The morphological and structural properties of nanotublar products were characterized by SEM. The synthesized nanotubes of titania in organic electrolytic solutions containing fluoride was of 60 μm in length. The experiments demonstrated the length and orderliness of nanotubes of titanium oxide in organic solutions were much better than those in inorganic solutions.

We discuss recent measurements of the interband spectrocopy of carbon nanotubes and studies of cyclotron resonance in graphene, using these to examine the possible dependence of the band structure of graphene on the number of layers present and the role of Coulomb interactions. Cyclotron resonances gives a value for the electron velocity at the Dirac point of 1.093×10⁶ ms^-1, which is ~ 20% larger than would be expected from deductions of the band structure of carbon nanotubes. In addition, a significant asymmetry exists between band structure for electrons and holes, which gives rise to a 5% difference between the velocities at energies of 125 meV away from the Dirac point.

Quasi one-dimensional systems, including bio-polymers, nanotubes, nanowires, etc., are in focus of material science and technology for more than two decades. Using recently found quasi one-dimensional conformation classes, which are elementary building blocks of all quasi one-dimensional crystals, we make symmetry based study of their diffraction patterns. In particular, we single out the features distinguishing between the classes, thus enabling to characterize each of them. It turns out that this analysis suffices to find out chiral indices of carbon nanotubes.

Photoconductive and photorefractive characteristics of fullerene- and nanotubes-doped organic thin films based on conjugated organics, such as polyimide, polyaniline, pyridine, etc. have been studied. In addition, the liquid crystal mesophase with nanoobjects has been investigated. The increase of the charge carrier mobility of nanosensitized organics has been established. The nonlinear refraction and cubic nonlinearity have been investigated at wavelength of 532 nm via four-wave mixing technique using Raman-Nath diffraction regime. The thin holographic grating has been written at the spatial frequencies placed in the range of 90-150 mm^-1. The energy density has been chosen in the range of 0.1-0.9 J×cm^-2. The correlation between photoconductive and nonlinear optical parameters has been revealed. The nanostructured materials can be proposed for different area of nano- and microelectronic applications.

A matrix Green's function formalism is employed to study the excitations in long nanotubes where the dynamics are governed by nearest-neighbor interactions between atoms. Examples of the excitations, which can be characterized in terms of the tube circumference and a one-dimensional wave number along the length, include ferromagnetic spin waves in a Heisenberg exchange model and electronic modes in a tight-binding model with hopping. It is assumed that the system is a single-walled nanotube of negligible thickness and that the atoms are arranged on a simple square lattice. Defects in the form of substitutional impurity atoms are introduced to study localized modes as well as the propagating modes of the pure (host) material. The impurities have the form of one or more line defects parallel to the nanotube axis. The derived Green's functions provide a description of the frequencies of the discrete modes of the system and their spectral intensities. Numerical examples are presented for different mode types (magnetic and electronic), nanotube diameters and arrangements of impurity lines.

A simple procedure for one-step growing Nb₂O₅ hollow nanospheres and nanotubes was proposed. The final products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The as-obtained hollow spheres present a polycrystal surface while the nanotubes possess single crystal walls. Moreover, the factors that could impact the product morphology and crystal structure were discussed, and the corresponding mechanism was proposed accordingly. The crystal structure and morphology of products can be easily tuned by adjusting the molar ratio of Nb/Ti used, which determines the amount of F^- ions existing in the reaction system. The as-obtained Nb₂O₅ hollow nanospheres and nanotubes may exhibit enhanced applications in a wide range of areas. Additionally, it is rational to expect that this simple method can be extended to systems of other inorganic materials with desired morphologies.

Fe-doped In₂O₃ nanotubes were successfully synthesized by electrospinning technique followed by subsequent heat treatment. The as-prepared samples appeared as an apparently open-end one-dimensional (1D) and tubular-like morphology with the diameter of approximately 150 nm and the wall thickness about 20 nm. The diffraction peak of the obtained nanotubes shifts toward bigger angle direction with the increase of the Fe content. Comparing to the In₂O₃ nanotubes, the Fe-doped In₂O₃ nanotubes exhibit better sensing characteristics toward ethanol gases, including higher sensing response, lower operating temperature and higher selectivity. Enhanced sensing properties are attributed to 1D hollow nanostructures and the role of doping Fe element.

Cluster-like network structures of single-walled carbon nanotubes (SWNTs) were synthesized by chemical grafting poly 2-hydroxyethyl methacrylate (polyHEMA) to the sidewalls of SWNTs. Acid chloride-functionalized tubes were coupled with commercially available HEMA monomer, which was in turn polymerized using a radical initiator. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to identify the surface changes on the nanocomposites. Microscopic observations of the nanotube complexes by field emission scanning electron microscopy (FE-SEM) show that the tubes were dispersed and formed cluster-like network, branched structures with less bundling, thus, strongly suggesting a firm coating of the polymer on nanotube walls. The coating was further confirmed by transmission electron microscopy. The thermal properties of the nanotube complex as studied by thermal gravimetric analysis (TGA) revealed that coating enhanced stability of the complex, when compared to that of bulk polyHEMA and pristine SWNTs. The nanotube complexes showed excellent suspension stability when dispersed in organic solvent.

Carbon atoms can connect with themselves and with other atoms (both electronegative and electropositive elements) in various ways. Thanks to these abilities, the diversity of carbon compounds is increasing day by day. This growth was even faster after the discovery of carbon nanoallotropes, i.e. carbon nanotubes, fullerenes, and graphene. At present, these carbon nanoallotropes are widely studied, and new hybrid structures have been synthesized based on these nanoallotropes. Hybrid structures formed by the covalent bond of fullerenes to the outside carbon nanotubes are called carbon nanobuds (CNBs). Development of synthesis methods, computational calculations, and the study of CNB properties was much faster than other hybrid structures. However, only fewer articles on CNBs have been published in recent years. CNBs show a synergistic effect and have the unique properties of the carbon nanoallotropes from which they formed. This review discusses CNBs and reports the recent research on CNBs, mostly after 2016.

A 3D chiral nanoporous coordination framework consisting of homochiral nanotubes was synthesized. The sample was assembled from octuple helices. The chiral nanotube had a free aperture about 20 A. The structure of the sample was characterized by X-ray diffraction. The UV–Vis was used to investigate the optical property of the sample. The absorption appears in the range of 210–290 nm. Second harmonic generation (SHG) was studied by powder measurement using a YAG laser. Especially, the efficient SHG of sample is about 3.5$\times$ of urea.

AUSTRALIA — AIBN and Dow Launch Research Collaboration.

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The symmetry of single-wall carbon and inorganic tubes is reviewed. For the carbon nanotubes it is used to get the full set of quantum numbers, in the efficient precision (combined density functional and tight-binding methods) calculation of electronic bands and their complete assignation, to obtain the selection rules for optical transitions and the momenta matrix elements for the Bloch eigen-states. The optical characteristics are thoroughly found, and discussed.

A comprehensive ab-initio investigation of the stability, structural, electronic, optical and Raman-active properties has been performed for the small diameter armchair carbon nanotubes. A number of new features not discussed earlier are observed in the present study. The binding energies (BEs) for the ultrathin nanotubes with respect to the graphine sheet are negative and the magnitude of the negative BE decreases with the diameter of the tube approaching zero for the graphine sheet. The separation between the two van Hove singularities (vHs) around the Fermi level increases with the diameter of the tube. The main absorption arises from the transitions between the states at nonzero values of k_z lying in the range 0.38–0.50. There is a large variation in the magnitude of the optical matrix-element with the wave vector. The energy range of the strong optical absorption increases with the diameter of the tube. The presently predicted absorption and the RBM frequencies are in good agreement with the available experimental data. The variation of the radial breathing mode (RBM) frequency with diameter "d" of a tube obeys a relation which is very close to an experimentally determined relation obtained for a number of wide semiconducting nanotubes possessing a wide range of chiral angles.

Soft chemical routes are employed effectively for the synthesis of nanocrystals of semiconductor materials. Several methods have been developed for the synthesis of multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) and specially noteworthy are the precursor route and nebulized spray pyrolysis for the synthesis of MWNTs and junction nanotubes. Nanotubes of inorganic layered materials are obtained by ingenious chemical methods. Nanowires of inorganic materials can be synthesized not only by high-temperature methods such as the carbon-assisted route but also by soft chemical routes.

We report on a number of new effects of self-organization at nanoscale, leading to creation of new functional nanomaterials, including carbon and carbon–metal nanotoroids and nanodiscs and self-assembling of magnetic nanoparticles into helices and chains. We also extensively used a new approach of biopattern nanoengineering to create DNA-based complexes with metal or CdSe/ZnS core-shell nanorods (22 × 4.5 nm) which possess strong linearly polarized photoluminescence due to unidirectional orientation of nanorods along DNA filaments. Optical, electrical, and topological (geometrical) properties of such complexes were investigated. This work is a result of a coherent effort (since 1980s) of a consortium of Russian research groups in Nano-technology (INTC: Interdisciplinary Nanotechnology Consortium) aimed at creating molecular electronic devices based on individual and collective properties of specially designed and fabricated nanoclusters.

We demonstrate Co, Fe, and Ni encapsulated polyaniline (PAni) nanotubes using a three-step anodization and electrodeposition process. The electrodeposition process is used to create the tubes, as well as the wires, in a highly reliable manner. The metal-filled PAni structures embedded inside nanoporous alumina templates are fabricated in the form of an array. The magnetic properties of these structures are investigated as a function of temperature. These results are compared with the magnetic properties of nanowires embedded inside nanoporous alumina templates.

This work presents template synthesis of ordered arrays of nickel, cobalt and nickel hexacyanoferrates (NiHCF) with several distinct morphologies such as dots, rods, and tubes. Anodic alumina oxide (AAO) with preferred pore diameters and thickness was fabricated by electrochemical anodization of aluminum used as template. Ni and Co nanostructures inside AAO template were prepared by electrodeposition using galvanostatic method. NiHCF nanostructures were prepared by electrochemical oxidation of Ni using cyclic voltametry (CV) in the presence of hexacyanoferrate ions. The morphology, chemical, and functional properties of prepared nanostructures were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray microscopy (EDAX), and electrochemical methods. The electrocatalytic properties of NiHCF nanorod arrays electrode and their potential for the detection of hydrogen peroxide and biosensing application were demonstrated.

Ultralong zinc oxide nanotubes have been synthesized on glass substrate by a simple chemical bath deposition. The nanotubes are hexagonal with the core diameter about ~200 nm. The length of the nanotubes was about 10 μm. No specific alignment of the nanotubes on the glass substrate was observed. The morphology of the nanostructures depends highly on the concentration of zinc acetate solution, duration of mechanical stirring, and temperature during synthesis. Depending upon these experimental conditions nanorods and nanotubes were observed. The material was structurally characterized using grazing incidence X-ray diffraction, showing hexagonal unit cell structure. Transmission electron microscopy results revealed that the walls of the nanotubes are hexagonal. Room temperature photoluminescence spectrum shows a strong violet emission at ~420 nm from the ZnO nanotubes due to transition between zinc interstitial and zinc vacancy level. These results will be very useful in optoelectronic and nanophotonic device applications.