فصلنامه نانو مقیاس
سال دوم شماره 2 (پیاپی 6، تابستان 1394)

Citrate colloidal silver nanoparticles were synthesized with 17 nm by Lee and Meisel technique. TiO2-Ag/MWCNTs nanocomposites were synthesized by sol-gel method. The size of colloidal silver nanoparticles were estimated under 20 nm by Dynamic Light Scattering DLS and Zeta analyzer. By Raman spectroscopic methodology different loading of MWCNTs into TiO2-Ag matrix were scanned in which it is an effective factor in shifting Raman frequencies bands. G band 1583 cm-1 that is one of the main bands of MWCNTs in above matrix, was analyzed and evaluated according to the shift of this band as a function of different loading percentages of MWCNTs. According to the amount of shifting of this band, the compressive strain of MWCNTs in the matrix was calculated that is more remarkable than the amount of the reported values in similar works.

In this paper, we study the electronic transport of an infinite ladder network that a part of it is twisted by using Green’s function method at the tight-binding approach. For this purpose, we insert the effects of orbital overlapping of the neighbor atoms as well as the effect of twisting, in the tight-binding parameters of the twisted part. Moreover, due to the symmetric considerations of the system Hamiltonian, the under consider problem reduces to the problem of the two simple chains. The numerical results show that the conductance dramatically depends on amount of twisting and the coefficient of variation of orbital overlapping strength. Increasing of twisting in the center ladder causes the decreasing of its energy window and consequently the resonance region becomes smaller.

Oil contaminations are a problem that Iran, as a country having oil reserves, faces it. These contaminations mostly occur in aquatic ecosystems and cause death of many aquatic organisms, their entrance in food chain, and health problems in human societies. Many solutions have been proposed for this problem and using nanoparticles has been introduced as a new approach. In this project, iron oxide nanoparticles have been synthesized in order to be used in separating petroleum from water. These nanoparticles are biocompatible and could be directed and recovered by magnetism. Based on our experiments, nanoparticles were successful in separating petroleum from water. Furthermore, the recovered petroleum was analyzed by Gas Chromatography and showed no significant change. According to the results of current investigation, the separated petroleum could be recovered and returned to the economic cycle of the country and inhibit the loss of national wealth.

Two dimensional molybdenum disulfide nanoflakes; due to the emergence of new physical phenomena as well as promising practical applications such as field effect transistors, lithium ion batteries and gas sensors, have attracted considerable attention. However, finding new ways for large-scale production in a cost-effective way is one of the main bottlenecks in the development of these nanostructures. In this study, solvent-based exfoliation approach is introduced for the synthesis of two dimensional molybdenum disulfide nanoflakes by the use of ethanol/water mixture. Using this mixture offers distinct advantages including production of atomic scale nanoflakes, reduced residues of solvent used, high yield and high stability of suspension. Crystal phononic structure, energy gap and morphology of the synthesized nanoflakes have been investigated by using Raman scattering, absorption spectroscopy and atomic force microscopy, respectively. The optimum volume ratio for water and ethanol solvents was obtained equal to 55% and 45%, respectively. Optical characterization using absorption spectrum of the nanoflakes showed an energy gap of 1.7 eV for multilayer nanoflakes. The reported data reveals the production of two dimensional molybdenum disulfide nanoflakes.

G raphene based materials with outstanding optical and electrical characteristics attract substantial interest of the researchers to improve sensitivity and performance of sensing element of surface Plasmon resonance (SPR) based biosensors. In this research carrier density variation because of functionalized element on graphene based SPR biosensor modeling is employed. The molecular specifications such as electro-negativity, molecular mass and periodic table group effect are engaged. The refractive index shift equation is defined and related coefficients are proposed. Finally a semi-empirical model for interpretation of changes in SPR curve is suggested.

In this research, MWCNT-based nanohybrids made of functionalized multi-walled carbon nanotubes with multi-element magnetic nanocomposites Ba0.2Sr0.2La0.6MnO3/MWCNT were prepared and used to strengthen the intensity and absorbing frequency bandwidth and maximum microwaves absorption in X-band. Initially Ba0.2Sr0.2La0.6MnO3 NPs was synthesized by sol-gel method. Afterwards, the MWCNT was functionalized with carboxylic functional group by acid treating in a mixture of sulfuric/nitric acid in 3:1 ratio (V/V) using ultrasonic irradiation and mechanical stirring simultaneously. The functionalized MWCNT was then coated with these NPs using poly methyl methacrylate (PMMA) in an argon atmosphere furnace. The crystal structures and morphology of synthesized nanoparticles and suitable coating of carbon nanotubes with these nanoparticles were characterized and confirmed by FESEM, XRD, VSM, FTIR analysis. Finally absorbent samples were prepared by dispersion of magnetic NPs and nanocomposite in polyurethane in an ultrasonic bath and the absorption or reflection loss for absorbing samples was investigated at the frequency range of 8.2 – 12.4 GHz. The maximum reflection loss of Ba 0.2Sr0.2La 0.6MnO3 NPs was -14.46 dB at 10.74 GHz with a bandwidth of 1.72GHz (more than –10 dB) and the maximum reflection loss for Ba0.2Sr0.2La0.6MnO3/MWCNT nanocomposite was -22.97 dB at 11.45GHz with a bandwidth of 2.29GHz (more than –10dB). These results indicated that albeit Ba 0.2Sr0.2La 0.6MnO3 NPs has its own microwave absorption properties and could be a good absorber in X-band, but the microwave absorption properties of the hybrid Ba 0.2Sr0.2La 0.6MnO3/MWCNT nanocomposites are significantly enhanced.

In this paper we utilized a new method in definition of anisotropic permittivity function of multi-wall carbon nanotubes, which is based on cylindrical coordination. Nanotube with inner radius of 22nm and outer radius of 25nm and having its inside filled with poly-silicon as a dielectric material, utilized for guiding surface plasmon polariton waves. Thanks to adjustable Fermi level of graphene sheets in nanotube, we can change dynamic conductivity of them by applying external electric field and design a tunable plasmonic switch.