Nano

The electronic structures and transport properties of single crystalline GaN nanotubes with 0.92 nm inner diameter and different wall thicknesses of 0.08 nm, 0.26 nm and 0.54 nm are studied based on the generalized gradient approximation (GGA) of density functional theory (DFT) and the nonequilibrium green's function (NEGF). The research shows that (1) the three single crystalline GaN nanotubes have direct band gaps, decreasing with the increase of wall thickness; (2) the electronic density of state and electronic transmission spectra of two-probe system have their own pulse-type sharp peaks with almost the same location of electron energy; (3) under different bias-voltages, two-probe systems of the single crystalline GaN nanotubes have the I–V properties which reveal that the single-wall GaN nanotube and the single-layer GaN nanotube are semiconducting and the double-layer GaN nanotube appears nearly metallic.

Serious microcracks often occur on the surface of nanohydroxyapatite (n-HAP) artificial bone scaffolds prepared by selective laser sintering (SLS) technology. In this study, we found that appropriate preheating before sintering can reduce and attenuate the cracks. The microstructure and morphology of sintered n-HAP were tested at different preheating temperature and laser sintering speed with scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The experiments showed that the cracks gradually reduced and then disappeared when the preheating temperature increased from 0°C to 600°C while other parameters remain unchanged. The n-HAP particles gradually fused and grew up, while the grain size of sintered n-HAP will be attenuated with the increase of preheating temperature. As the thermal conductivity of n-HAP increases with increased preheating temperature, the temperature drops quickly, inhibiting greatly the grain growth of n-HAP. We obtained a group of optimum parameters when the sintered n-HAP still maintains nanostructure and possesses the optimal comprehensive performances, that is, laser power is 26 W, spot diameter is 4 mm, sintering speed is 200 mm/min, layer thickness is 0.4 mm, layer density is 852 kg/m³, and optimized preheating temperature is 600°C. These data illustrated that the cracks of sintered n-HAP can be eliminated at appropriate preheating temperature and sintering speed. This provided experimental optimal condition for the preparation of artificial bone scaffolds with nanohydroxyapatite ceramics.

We present an analytical method for the scattering of antiplane shear waves by a piezoelectric nanofiber surrounded by piezomagnetic matrix. Owing to their analogies, the piezoelectric surface/interface theory is extended to the magneto-electro-elastic surface/interface theory. The analytical solutions of elastic field, electric field and magnetic field are expressed by employing wave function expansion method and then the expanded mode coefficients are determined by satisfying the nanoboundary conditions around the fiber (a piezoelectric nanowire). The effects of the incident frequency are graphically illustrated and discussed. The material properties of the nanointerface, which is related to the two phases, are examined through parametric variation. A comparison with a non-nano case is also presented.

The well dispersed ZAO nanoparticle with 25–30 nm in diameter was prepared by an ultrasonic-template method. The morphologies, structures, and photoelectricity of the ZAO nanoparticles were analyzed by TEM, XRD, UV-Vis, etc. The thermochemistry behaviors of the precursor were studied by TG-DSC. The composite film with semipermeable structure made from ZAO nanoparticles and collodion can be explored firstly. The photocatalytic properties of the ZAO nanoparticles and composite film were investigated. The composite film can be applied in the sewage treatment field.

In this paper, a nonlocal Flugge shell model is utilized to investigate the axial buckling behavior of double-walled carbon nanotubes (DWCNTs) under various boundary conditions. According to the nonlocal elasticity theory, the displacement field equations coupled by the van der Waals interaction are derived. The set of governing equations of motion is then solved by the Rayleigh–Ritz method. The present analysis can treat boundary conditions in a layer-wise manner. The effects of nonlocal parameter, layer-wise boundary conditions and geometrical parameters on the mechanical behavior of DWCNTs are examined. Furthermore, molecular dynamics simulations are performed to assess the validity of the results and also to predict the appropriate values of nonlocal parameter. It is found that the type of boundary conditions affects the proper value of nonlocal parameter.

By considering excitons in a semiconductor nonparabolic quantum dot as hydrogen-atom-like quasi-particles confined in a spherical quantum box, the dot being connected to two semi-infinite conducting leads, we propose a theoretical-analytical approach by which the maximal dot-lead coupling energy is calculated in terms of the maximum Fermi velocity. In addition, numerical computations consistent with the above approach are carried out. Our results constitute a deep insight into the state of the art and agree with experimental data.

Single-walled carbon nanotube (SWCNT)/anatase TiO₂ composite materials were prepared by successive sol–gel and hydrothermal processes. The composites contained thin SWCNT bundles embedded in aggregates of ~ 12 nm anatase crystallites. A series of SWCNT/TiO₂ photocatalysts was prepared with various SWCNT contents; a SWCNT content of ~ 8 wt.% was found to be optimal for methylene blue (MB) degradation under combined UV/visible radiation. The optimized SWCNT/TiO₂ composite demonstrated substantially higher photocatalytic activity than pure nanocrystalline anatase (5.2 times) and Degussa P-25 TiO₂ powder (2.7 times). The MB degradation and mineralization processes were separately evaluated and complete decomposition of MB was shown to take place. The presence of SWCNTs caused an increase in the visible light absorbance of TiO₂; however, SWCNT/TiO₂ composites did not show any photocatalytic activity when the UV part of the UV/visible light source was filtered. Therefore SWCNTs worked as acceptors for the TiO₂ photoexcited electrons, but did not act as sensitizers for TiO₂.

Several novel organic–inorganic hybrids consisting of high performance polyimide (PI) and organically modified montmorillonite (OMMT) with trifunctional swelling agent were successfully prepared by in situ polymerization technique. In this way, at first, OMMT was prepared by surface treatment of Cloisite Na⁺ with protonated form of bioactive L-tyrosine amino acid. Amine functional groups of this swelling agent formed an ionic bond with the negatively charged silicates, whereas the remaining acidic and phenolic functional groups are available for further interaction with PI chains. Then, organo-soluble PI with benzimidazole pendent group was prepared from pyromellitic dianhydride and 4-(3, 5-diaminophenyl)-benzimidazole in dry N,N-dimethylacetamide. PI/OMMT nanocomposites enclosing 1–10 wt.% of OMMT were successfully prepared by an in situ polymerization reaction through thermal imidization up to 300°C. Also, the relationship between the properties and OMMT content of the PI hybrid films were examined using Fourier-transform infrared spectroscopy, X-ray diffraction measurements and electronic microscopy (FE-SEM and TEM). The silicate layers in the polymer matrix were exfoliated as confirmed by XRD, FE-SEM and TEM techniques. The PI/OMMT films have good optical transparencies, and are almost colorless. The thermal stability of hybrids such as the decomposition temperature and weight residue at 800°C were also increased with increasing OMMT content.

ZnO nanoparticles have been prepared by wet chemical method. The properties of the synthesized nanostructures are studied using X-ray diffraction, Transmission Electron Microscopy (TEM), Photoluminescence (PL), Ultraviolet-Visible absorption, Laser Raman and Fourier transform Infrared (FTIR) spectroscopy. The thermal decomposition is analyzed by Thermogravimetric (TG) and Differential Thermal Analysis (DTA). The influence of annealing on structural and optical properties of ZnO nanoparticles has been systematically investigated. The PL results demonstrated that the visible emission at 565 nm is associated with the combination of oxygen vacancies and OH group attached at the surface of ZnO nanoparticles. OH group is lessened from the surface of ZnO nanoparticles with annealing temperature and a blue-shift in visible emission peak is observed at 800°C annealing temperature.

We have used molecular dynamics simulation to study the influence of disclination angle on helium adsorption capacity of carbon nanocones (CNCs). Adsorption capacities of 180°, 240° and 300° CNCs have been compared at various temperatures. The results indicate that helium atoms adsorb on internal and external surfaces of the CNCs. At saturation conditions, the endohedral adsorption coverage is decreased by increasing the disclination angle, while the exohedral adsorption coverage is independent of this angle. It is also found that temperature has a considerable effect on the adsorbed amount. Comparison of the adsorption on CNCs with carbon nanotubes indicates that the adsorption capacity of cones is greater than those of tubes. Our results confirm the fact that the CNCs are good candidate for gas storage.