NANOSCALE
Year:2015 | Volume:2 | Issue:2|Papers Count:7

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.

Graphene 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 Ba0.2Sr0.2La0.6MnO3 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 Ba0.2Sr0.2La0.6MnO3 NPs has its own microwave absorption properties and could be a good absorber in X-band, but the microwave absorption properties of the hybrid Ba0.2Sr0.2La0.6MnO3/MWCNT nanocomposites are significantly enhanced.

In this study, we achieved to high carrier concentration (in order 1019) p-type ZnO by using N-Al co-doping. By controlling the surfactant concentration, the temperature of annealing reduced to 450oC without deterioration of electrical properties. To investigate the effect of doping, the optical and electrical properties of co-doped ZnO characteristics were compared with undoped ZnO thin film fabricated by the same method. The PL-spectra results indicate most intrinsic defects that mainly generate electron carriers, were removed by codoping. The UV-visible spectra show both films have high transmittance in visible region (over 95%), visible transmission increased by N-Al codoping. The electrical analysis results, confirm the conversion from n-type to p-type ZnO, Which is in agreement with the optical results of photoluminescence spectra.

In this work, quantum dots of different materials were used to fabricate the sensitized solar cells. The successive ionic layer adsorption and reaction (SILAR) method was used to synthesise CdS and PbS QD's. By changing the percentages of the material or changes in the number of layers the performance of individual cells was compared. Moreover, solar cells by combination of these cells so-called co-sensitized solar cells were fabricated and characterized. The use of narrow band gap semiconductors such as PbS may expand the light absorption range to the near-infrared region in quantum-dot-sensitized solar cells (QDSCs), increasing the generated photocurrent. However, the use of PbS as a sensitizer in QDSCs causes some problems of stability and high recombination. Here, it is shown that the direct growth of a CdS layer on previously deposited PbS minimizes these problems. An increase in short-circuit current density up to 8.24 mA/cm2 and the higher efficiency of 1.25% for the hybrid PbS/CdS QDSCs were obtained, compared to that of PbS QDSCs, using polysulfide electrolyte in both cells.

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 22 nm and outer radius of 25nm and having its inside filled with poly-silicon as a dielectric material, utilized for guiding surface plasmon polaritons waves. Thanks to adjustable Fermi level of graphene sheets in nanotube, we can change dynamic conductivity of them by applying external voltage or electric field and design a tunable plasmonic switch.

Optical nano-antennas have been proposed as an alternative option for solar energy harvesting. In this work the power conversion efficiency of optical antennas have been proposed as an alternative option for solar energy harvesting. In this paper, an investigation is presented into bowtie, polygonal and circle antennas for THz energy detection, with the aim of optimizing their geometrical parameters. HFSS Multiphysics based on the Finite Element Method (FEM) is used to simulate the golden nano-antennas, which are placed on a silica glass substrate with er=2.09. The dielectric properties of gold is obtained by fitting the experimental data into the Drude model. A performance comparison among these designs is presented in order to find the optimum solution for this application. The main goal of this study is to design and optimize nano-antennas for maximum solar radiation energy conversion. It is shown that increasing the edges of the patch consequently tapering of the patch, decreases the value of the converted electric field.