Nano

Various methods for the synthesis of copper nanoparticles employing chemical, physical and biological techniques considering bottom-up and top-down methods synthesis have been studied. The properties of copper nanoparticles depend largely on their synthesis procedures. The results from various investigations performed by different scientists using these methods have been summarized. The applications, characterization techniques, advantages and disadvantages of each synthesis method are also the point of discussion. A detailed study of the results reveals that chemical reduction methods are most suitable for the synthesis of copper nanoparticles. Chemical reduction of copper salts using ascorbic acid (Vitamin C) is a new and green approach in which ascorbic acid is used both as the reduction and capping agent. This approach is the most effective and is also economical. Wide applications have been reported in various fields, including heat transfer, catalyst production, electronics and medicine at a commercial scale. This process is nontoxic, environment-friendly and economical. The applications, characterization techniques, advantages and disadvantages of each synthesis method have been presented.

In this article, the small scale effect parameter e₀ of single-layered graphene sheets (SLGSs) is calibrated for the bending problem. Taking the SLGSs as a rectangular plate, the normal displacement of the simply supported plate under concentrated force was analyzed by both nonlocal elasticity theory and molecular dynamics (MD) simulations, then the small scale effect parameter e₀ of SLGSs with different size was obtained by matching the displacement of the nonlocal elasticity theory and that obtained from MD simulations. The results show that the value of e₀ is not a constant but has a relationship with the size of SLGSs, and the relationship of armchair-graphene sheets and zigzag-graphene sheets is different.

Copper, nickel and cobalt metals and oxides needle-like shape nanoclusters have been synthesized successfully by chemical reduction in solution without using a surfactant. XRD analyses showed that copper and nickel metals could be synthesized in a short time period by a microwave irradiation (MWI) — assisted step wise reduction of metal ions in basic solution using hydrazine as a reducing agent whereas cobalt was mainly precipitated in the form of either hydroxide or oxide. TEM images showed that the size of needle-like shape nanoclusters varying from about 5 nm to few hundred nanometers length. On the other hand, copper and cobalt showed high catalytic activity toward CO oxidation than that of nickel. The mechanism of catalytic oxidation reactions over unsupported metals and oxides are also discussed.

Large-area GaN-based blue light-emitting diodes (LEDs) on sapphire substrates with an omnidirectional nanostructure consisted of Ag nanoparticles and TiO₂/SiO₂ Bragg reflector were fabricated. For the LEDs without the omnidirectional nanostructure, the spectra of the P- and S-polarization light are lightly different and the peak wavelength of P- and S-polarization light was estimated to be 464 nm and 463 nm, respectively at forward current of 20 mA. In contrast, for the LEDs with the omnidirectional nanostructure, the spectra of the P- and S-polarization light are nearly the same at forward current of 20 mA and 100 mA.

The Co₃O₄ nanorod bundles are synthesized by a hydrothermal method. The samples are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED), X-ray powder diffractometer (XRD), and nitrogen adsorption. It is important that the as-obtained Co₃O₄ nanorod bundles are assembled by nanoparticles. The porous nanorod bundle electrode exhibits a higher rate capacity and a higher reverse capability for lithium ion battery than the solid nanorods, which is attributed to the high surface area and the porous structure.

By using first-principles calculations, we predict that an in-plane homogenous electrical field can induce half-metallicity in hydrogen-terminated zigzag silicene and germanene nanoribbons (ZSiNRs and ZGeNRs). A dual-gated finite ZSiNR device reveals a nearly perfect spin-filter efficiency (SFE) of up to 99% while a quadruple-gated finite ZSiNR device serves as an effective spin field effect transistor (FET) with an on/off current ratio of over 100 from ab initio quantum transport simulation. This discovery opens up novel prospect of silicene and germanene in spintronics.

Ultrafine Co₃O₄/SiO₂ nanocomposites were obtained via sol–gel (SG) method and related routes. The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ adsorption–desorption techniques. The obtained phase, size of crystallites and specific surface area of the composites vary with the Co:SiO₂ weight ratio and preparation route. Humidity sensing properties measured by monitoring the DC conductivity for the obtained nanocomposites are reported. Conductivity changes amount to four orders of magnitudes were observed in response to 10–90% relative humidity change in the measuring chamber. Results indicate that humidity sensing properties depend on Co content and specific surface area of the composite.

This paper reports the preparation and characterization of nanocomposites consisting of epoxy resin (EP) and conducting polyaniline nanowires doped with formic acid (PANI-FA). The percolation threshold of this nanocomposites was obtained at 8 wt.% of PANI-FA loading. On the other hand, 8 wt.% of PANI-FA resulted in reduction of tensile and flexural modulus up to 30% and 16%, respectively. The fracture morphological analysis revealed a distinct PANI-FA domain on the EP matrix after the percolation threshold has been reached. Using the scaling law of the percolation theory, it was found that the conductivity of the nanocomposites exhibited an exponential factor, (t) of 0.417.

We adopted the verified quantum chemistry approach to demonstrate the possible frictionless transport of solid He-4 with high shear viscosity in a confined 3 nm (diameter) nanopore. Both the sharp decrease of flow resistance and sudden increase of shear viscosity of solid ⁴He in nanodomains near the onset of possible supersolidity are illustrated.

Carbon nanotubes (CNTs) possess exceptional mechanical properties and are therefore suitable candidates for use as reinforcements in composite materials. Substantial improvements in mechanical properties of polymers have been attained through the addition of small amounts of CNTs. The CNTs, however, form complicated shapes and do not usually appear as straight reinforcements when introduced in polymer matrices. In this paper, theory of elasticity of anisotropic materials and finite element method (FEM) are used to determine effective mechanical properties of sinusoidal-nanotube reinforced polymers. The effects of CNT shape, orientation, and CNT distribution on nanocomposite effective properties are investigated by modeling different CNT-reinforced polymers. Also, the effects of interface strength on nanocomposite properties are investigated using an elastic interface model. The results indicate that even a slight nanotube curvature significantly reduces the reinforcing efficiency of sinusoidal — nanotubes compared to straight nanotubes. Also, in-plane isotropy was observed in the results obtained from the random CNT reinforced polymer. Finally, increasing the interface strength results in higher nanocomposite longitudinal modulus.