Manizheh Navasery

Visible Light-Induced Degradation of Methylene Blue in the Presence of Photocatalytic ZnS and CdS Nanoparticles

ZnS and CdS nanoparticles were prepared by a simple microwave irradiation method under mild conditions. The obtained nanoparticles were characterized by XRD, TEM and EDX. The results indicated that high purity of nanosized ZnS and CdS was successfully obtained with cubic and hexagonal crystalline structures, respectively. The band gap energies of ZnS and CdS nanoparticles were estimated using UV-visible absorption spectra to be about 4.22 and 2.64 eV, respectively. Photocatalytic degradation of methylene blue was carried out using physical mixtures of ZnS and CdS nanoparticles under a 500-W halogen lamp of visible light irradiation. The residual concentration of methylene blue solution was monitored using UV-visible absorption spectrometry. From the study of the variation in composition of ZnS:CdS, a composition of 1:4 (by weight) was found to be very efficient for degradation of methylene blue. In this case the degradation efficiency of the photocatalyst nanoparticles after 6 h irradiation time was about 73% with a reaction rate of 3.61 × 10−3 min−1. Higher degradation efficiency and reaction rate were achieved by increasing the amount of photocatalyst and initial pH of the solution.

Modeling of Electrical Transport in YBCO Single Layer Thin Films using Flux Motion Model

The electrical transport properties of YBCO single layers thin film have been investigated using different physical techniques. For the purpose, the physical properties are probed numerically with help of simulation modelling. The physical transport properties were also estimated with temperature and magnetic fields limits using thermally-activated flux flow model with some modifications. The result of present simulation modelling indicated that the magnitude of activation energy depends on temperature and magnetic field. The simulations revealed thickness dependent physical transport properties including electrical and magnetic properties of deposited YBCO single layers thin films. Furthermore, it shows the temperature dependence of the pinning energy. In the nutshell, the result can be used to improve the Superconducting Properties (Tc) of the YBCO single layers thin films.

Impact of Parameter Variation in Fabrication of Nanostructure by Atomic Force Microscopy Nanolithography

In this letter, we investigate the fabrication of Silicon nanostructure patterned on lightly doped (1015 cm−3) p-type silicon-on-insulator by atomic force microscope nanolithography technique. The local anodic oxidation followed by two wet etching steps, potassium hydroxide etching for silicon removal and hydrofluoric etching for oxide removal, are implemented to reach the structures. The impact of contributing parameters in oxidation such as tip materials, applying voltage on the tip, relative humidity and exposure time are studied. The effect of the etchant concentration (10% to 30% wt) of potassium hydroxide and its mixture with isopropyl alcohol (10%vol. IPA ) at different temperatures on silicon surface are expressed. For different KOH concentrations, the effect of etching with the IPA admixture and the effect of the immersing time in the etching process on the structure are investigated. The etching processes are accurately optimized by 30%wt. KOH +10%vol. IPA in appropriate time, temperature, and humidity.

Facile Synthesis of Calcium Borate Nanoparticles and the Annealing Effect on Their Structure and Size

Calcium borate nanoparticles have been synthesized by a thermal treatment method via facile co-precipitation. Differences of annealing temperature and annealing time and their effects on crystal structure, particle size, size distribution and thermal stability of nanoparticles were investigated. The formation of calcium borate compound was characterized by X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), and Thermogravimetry (TGA). The XRD patterns revealed that the co-precipitated samples annealed at 700 °C for 3 h annealing time formed an amorphous structure and the transformation into a crystalline structure only occurred after 5 h annealing time. It was found that the samples annealed at 900 °C are mostly metaborate (CaB2O4) nanoparticles and tetraborate (CaB4O7) nanoparticles only observed at 970 °C, which was confirmed by FTIR. The TEM images indicated that with increasing the annealing time and temperature, the average particle size increases. TGA analysis confirmed the thermal stability of the annealed samples at higher temperatures.

STRUCTURE, ELECTRICAL TRANSPORT AND MAGNETO-RESISTANCE PROPERTIES OF La5/8Ca3/8MnO3 MANGANITE SYNTHESIZED WITH DIFFERENT MANGANESE PRECURSORS

We synthesized the polycrystalline manganite of La5/8Ca3/8MnO3 with three different manganese routes prepared through a solid state reaction method. The effects of the manganese route selection on the structure, electrical transport and magneto-transport properties were examined in this study. The samples were characterized using X-ray diffraction (XRD) and SEM to identify their structure and morphology. XRD analysis confirmed that all samples were in single phase with orthorhombic structure and belonged to the Pnma space group. The average grain sized samples with manganese route of Mn2O3 and MnCO3 had a grain size of 1.2–8.7 μm and 2–7.5 μm, respectively. For the MnO2 route, the sample had a small melt-like shape with higher porosity. The metal–insulator transition temperature, TMI, for LCMO (Mn2O3), LCMO (MnO2) and LCMO (MnCO3) samples were 270 K, 266 K and 258 K, respectively. All the samples showed negative magneto-resistance with significant increase in value near the TMI temperature. The highest CMR (colossal magneto-resistance) ratio was found in LCMO (Mn2O3), -22.06% at 270 K, followed by -16.69% for LCMO (MnO2) at 80 K, and 15.2% for LCMO (MnCO3) at 100 K in a 1 T magnetic field.

Growth and characterization of ZnO multipods on functional surfaces with different sizes and shapes of Ag particles

Three-dimensional ZnO multipods are successfully synthesized on functional substrates using the vapor transport method in a quartz tube. The functional surfaces, which include two different distributions of Ag nanoparticles and a layer of commercial Ag nanowires, are coated onto silicon substrates before the growth of ZnO nanostructures. The structures and morphologies of the ZnO/Ag heterostructures are investigated using X-ray diffraction and field emission scanning electron microscopy. The sizes and shapes of the Ag particles affect the growth rates and initial nucleations of the ZnO structures, resulting in different numbers and shapes of multipods. They also influence the orientation and growth quality of the rods. The optical properties are studied by photoluminescence, UV-vis, and Raman spectroscopy. The results indicate that the surface plasmon resonance strongly depends on the sizes and shapes of the Ag particles.

The Synthesis and Characterization of Peach-Like ZnO

Peach-like ZnO microstructures are synthesized using vapor phase transport on MgO (001) substrates with a copper oxide (60 nm) buffer layer. The structure and morphology of the product are investigated using an x-ray diffractometer (XRD) and a field-emission scanning electron microscope. The peaches have an average diameter of 3 ?m and a wurtzite structure. To study the optical properties, photoluminescence (PL) and Raman spectroscopy are employed. A strong UV emission at 380 nm in the PL spectra is observed, and a sharp and dominant peak at 437 cm?1 in the Raman spectrum can be assigned to the good crystallization of obtained product. In addition, the growth mechanism of the peach-like ZnO structure is tentatively investigated based on the EDX analysis and growth time.

Structural, electrical and magnetic properties of polycrystalline La0.67(Ca1−x Sr x )0.33MnO3 manganites

Polycrystalline La0.67(Ca1−xSrx)0.33MnO3 with different substitution level of strontium element, were synthesized via solid state reaction. Structure of samples was characterized by X-ray diffraction (XRD). XRD patterns reveal that La0.67Ca0.33MnO3 exhibits orthorhombic structure with space group Pnma. Phase transitions from orthorhombic to rhombohedral take place as Ca ions were gradually substituted by Sr ions. The XRD data were further analyzed by Rietveld refinement technique. The data show that Mn–O–Mn bond angle increases as x increases. Microstructures obtained from SEM show that substitution of Sr ions has demoted the grain growth and densification process during sintering. The substitution of Sr ions has greatly influenced the hopping integral of electron via double exchange interaction, thus affecting the electrical properties and magnetic properties as well. The resistivity decreases and the metal–insulator transition temperature (Tp) shifts to higher temperature as x increases. The magnetoresistance (MR) effect gradually decreases and MR peak shifts to higher temperature as x increases. The magnetization measured at room temperature is found to be increasing as x increases.

Atomic force microscope base nanolithography for reproducible micro and nanofabrication

Atomic force microscopy nanolithography (AFM) is a strong fabrication method for micro and nano structure due to its high spatial resolution and positioning abilities. Mixing AFM nanolithography with advantage of silicon-on-insulator (SOI) technology provides the opportunity to achieve more reliable Si nanostructures. In this letter, we try to investigate the reproducibility of AFM base nanolithography for fabrication of the micro/nano structures. In this matter local anodic oxidation (LAO) procedure applied to pattern a silicon nanostructure on p-type (1015 cm-3) SOI using AFM base nanolithography. Then chemical etching is applied, as potassium hydroxide (saturated with isopropyl alcohol) and hydrofluoric etching for removing of Si and oxide layer, respectively. All parameters contributed in fabrication process were optimized and the final results revealed a good potential for using AFM base nanolithography in order to get a reproducible method of fabrication.

Numerical study of side gate junction-less transistor in on state

Side gate p-type Junctionless Silicon transistor is fabricated by AFM nanolithography on low-doped (105 cm-3) SOI wafer. In this work, the simulation characteristic of the device using TCAD Sentaurus in on state will be studied. The results show that the device is the pinch off transistor, works in on state for zero gate voltage in depletion mode. Negative gate voltage drives the device into on state, but unable to make significant effect on drain current as accmulation mode. Simulation results for valence band energy, electric field and hole density are investigated along the active regions. The influence of the electric field due to the applied voltages of VDS and VG on charge distribution is much more when the device operates at the saturation region. The hole quasi-Fermi level has a positive slope showing the current flows from source to drain.