Papers by Keyword: Hollow Nanospheres

Abstract: Monodisperse CoFe₂O₄ and Co_0.4Zn_0.6Fe₂O₄ hollow nanospheres were synthesized in large scale by solvothermal method in ethylene glycol solution. The structure, shape and size of the samples were investigated by Fourier Transform infrared, X-ray powder diffraction and scanning electron microscopy. The results indicate that the products are spherical with an average diameter less than 200 nm. Magnetic studies revealed that the saturation magnetization of Co_0.4Zn_0.6Fe₂O₄ is 78.6 emu/g, higher than the CoFe₂O₄, which is 69 emu/g, while the coercivity of the Co_0.4Zn_0.6Fe₂O₄ is 184 Oe , obviously lower than that of CoFe₂O₄ which is 832 Oe. The electromagnetic parameters were measured at 2-18 GHz using HP8722ES vector network analyzer and then the microwave absorption properties were calculated through the transmission line theory. As to the Co_0.4Zn_0.6Fe₂O₄, the absorption bandwidth with reflection loss below-10 dB is up to 3GHz, from 10GHz to 13GHz with a thickness of 2 mm. A maximum reflection loss-45.6 dB was found at 12.9 GHz for the CoFe₂O₄ with a thickness of 1.8 mm. As a result, the as-prepared hollow nanospheres show good prospects of being applied in EM wave absorption materials.

Abstract: CeO₂ hollow nanospheres with average diameter of 500 nm have been fabricated through a template-assisted approach at 200 °C. A possible formation mechanism has been briefly discussed.

Abstract: Hollow TiO₂ nanospheres have been successfully prepared by templating the polymericmicelles of poly (styrene-b-[3-(methacryloylamino)propyl] trimethylammonium chloride- b-ethylene oxide) (PS-b-PMAPTAC-b-PEO), which shows a core-shell-corona structure in aqueous solutions. It was found that, in such system, the wall thickness of the hollow TiO₂ is fine tuned by varying the concentration of the TiO₂ precursor.

Abstract: CuInS2 hollow nanospheres composed of nanoparticles have been fabricated through a solvothermal reaction in ethylene glycol solution (EG) at 200 °C in the absence of any templates or surfactants. The as-obtained CuInS2 products were characterized by XRD, FESEM andTEM. Results show that the synthesized hollow nanospheres are made up of small nanoparticles with a size of 10 nm and the outer diameters of these spheres change from 200 to 400nm. The possible formation mechanism of CuInS2 hollow nanospheres is simply discussed.

Abstract: Results of kinetic Monte Carlo simulation of the formation of a hollow nanosphere by interdiffusion from a core-shell binary system are presented for the first time. The faster diffusing species is located in the core whilst the slower diffusing species form the shell. With its self-generated vacancy composition all stages of the hollow sphere formation process are observed in our model: interdiffusion, the supersaturation of the core of the nanosphere by vacancies, precipitation of pores and eventual void formation. Results of this simulation confirm the experimental conclusions that interdiffusion accompanied by the Kirkendall effect and Kirkendall porosity is one of the mechanisms responsible for the formation of hollow nano-objects.

Abstract: In this paper, a hollow random binary alloy nanosphere and initially homogeneous is considered under the approximation that the radial dependence of the vacancy formation free energy can be neglected. On the basis of a theoretical description and kinetic Monte Carlo simulations it is shown that the steady-state condition for the atomic components is not achievable during its shrinkage at any composition when the ratio of the tracer diffusion coefficients is not greater than two orders of magnitude. In the theoretical description, the dependence of the collapse time of the hollow random binary alloy nanosphere on the atomic fraction of the faster diffusing species at can be estimated by using the geometric mean of the ratios of the atomic fluxes at self-diffusion and steady-state. At the ratio of the atomic fluxes approaches the self-diffusion ratio as increases.

Abstract: A theoretical and atomistic study of diffusion and stability of a pure element hollow nanosphere and nanotube is performed. The shrinkage via the vacancy mechanism of these hollow nano-objects is described analytically. Using Gibbs-Thomson boundary conditions an exact solution of the kinetic equation in quasi steady-state at the linear approximation is obtained. The collapse time as a function of the geometrical sizes of the hollow nano-objects is determined. Kinetic Monte Carlo simulation of the shrinkage of these nano-objects is performed: it confirms the predictions of the analytical analysis. Next, molecular dynamics simulation in combination with the embedded atom method is used to investigate diffusion by the vacancy mechanism in a Pd hollow nanosphere and nanotube. It is found that the diffusion coefficient in a Pd hollow nanosphere and nanotube is larger near the inner and external surfaces compared with the middle part of a nanoshell. The molecular dynamics results provide quite a strong but indirect argument that a real pure element hollow nanosphere and nanotube may not shrink as readily via the vacancy mechanism as compared with the predictions of the analytical analysis and kinetic Monte Carlo simulations.

Abstract: Molecular dynamics simulation using the embedded-atom method is applied to study defect formation and distribution in a hollow Pd nanosphere. It is established that besides vacancies, which can nucleate on the inner or external surfaces, at the external surface, other defects (Shockley partial dislocations, twins and stacking faults) form due to its significant reconstruction by means of a/6〈112〉 shears of atomic rows. The density of the defects on the external surface grows with decreasing nanoshell size. It is demonstrated that Shockley partial dislocations can act as vehicles for the transfer of material from the external surface to the inner surface of the nanoshell thus leading to shrinking. It is shown that the vacancy concentration is higher near both surfaces than in the bulk of the nanoshell.