فصلنامه نانو مواد
پیاپی 13 (بهار 1392)

In this paper, tin dioxide (SnO2) nanowires with different diameter have been fabricated for gas sensor applications by a chemical vapour deposition (CVD) technique. Alumina (Al2O3), quartz, and gold Au-coated silicon (Si) (100) were used as substrates. X-ray diffraction (XRD), photoluminescence spectroscopy (PL), and a scanning electron microscope were employed to characterize the synthesized products. Nanostructured gas sensor devices were fabricated using SnO2 nanowires as the active layer and gold (Au) for the electrode contacts. Gas sensing performance of synthesized SnO2 nanostructures are studied for two most widely used gases suchas liquefied petroleum gas (LPG) and ethanol (C2H5OH) vapor. The responses of SnO2 nanowires were checked at different temperatures ranging from 50 to 300 °C, so as to optimize sensing efficiency. Sensing performances were discussed for parameters such as response time, recovery time, and operating temperature. Fabricated sensor is shown a high sensitivity to low concentrations of LPG at elevated temperatures. Prepared sensor was revealed fast response and recovery time at working temperature of 200 °C for ethanol vapor detection.

This paper reports on the photo detection properties of graphene nano layer, based on the fabrication of graphene-Si Schottky diode. To fabricate this Schottky junction, a graphene nano layer has been deposited on Si substrate. The Si substrate is oxidized to 270 nm thickness and is patterned with a specific mask after Cr/Au deposition (the thickness of Cr/Au are 50 nm and 150 nm, respectively). The current-voltage (C-V) curves of the diode are analyzed under 670, 700 and 1100 nm illuminations and also under yellow light radiations. To investigate the photo detection properties of graphene nano layer in Schottky diode structure, 700 and 1100 nm radiations are also illuminated to the backside of the diode and then the photo-generated current under both front and back side illuminations are compared. The experiment results demonstrate that the generated currents in the front side mode and under 700 and 1100 nm illuminations have been increased about 23 and 17 times in comparison with the backside mode. This rise in the current shows the graphene effect in photo detection mechanism and also shows the great amount of photo generated current in graphene in the front side illuminations. The C-V curves of the diode under 670 nm and yellow light illuminations demonstrate not only the photo-generated current but also the photo voltage which shows graphene potential for being used as the solar cell. The optical properties of graphene are also discussed in this paper and many theories which can describe the generation of photo current in graphene are presented.

In this research, Nanocrystalline Zn-doped and pure tin oxide thin films were synthesized by electron beam evaporation technique. X-ray diffraction patterns indicated that as deposited thin films were amorphous SnO. Heat treatment at 500 °C for 10 h was applied to the as deposited thin films, which led to nanocrystalline tetragonal SnO2. AFM images showed that the morphology of as-deposited thin films was very smooth and fine, however, heat treatment caused that the morphology of thin films were gradually rough. Furthermore, SEM images revealed that the microstructure of thin films was compact and homogeneous. Elemental mapping of thin films proved the homogeneous distribution of zinc atoms in the structure of SnO2. Finally, electrochemical evaluation of pure and Zn-doped tin oxides as anodes for microbatteries was investigated by using galvanostatic charge/discharge in the potential range of 0-1.7 voltage. The results showed that specific capacity of pure tin oxide thin films increased from 69.5 μAhcm-2μm-1 to 137.6 μAhcm-2μm-1 for Zn-doped tin oxide thin films.

This study examined the powder synthesis characteristics of nickel and cerium oxide dopants together into yttria stabilized zirconia. A polymeric sol-gel (pechini) process has been used for preparation of nanocrystalline powder. This route has the ability to provide homogeneous products with high purity and activity. The starting materials used in this investigation werezirconium tetrachloride, yttrium nitrate, cerium nitrate and nickel nitrate. The samples (gels) after drying at 140 °C during a night (24 h), were calcined at 900 °C for 2 h. DTA-TG, XRD, SEM and TEM analyses are used respectively to investigate the phase formation temperature of nano powders, distinct the phases and investigate the microstructures. The results of thermal analysisconfirm the range of phase formation temperature that obtained from XRD analysis. Ni/Ce-YSZ powder with the mean crystallite size of 11 nm was calculated by Scherrer equation. Based on the SEM and TEM analyses, spherical morphology has been reported.

The presence of heavy metals in aqueous waste streams has become a problem due to its harmful effects on human health and to the fauna and flora of receiving water bodies. Metal immobilization through adsorption and precipitation is considered as a common mechanism to decrease the hazards of heavy metal. The objective of this study is to assess the uptake of, Cd2 from aqueous solution by nanocrystalline tri-calcium phosphate (TCP). The study also investigates the effects ofparameters such as initial concentration ion, adsorbent mass, temperature, and pH. According to the experimental results, increase in initial concentration ion, temperature and pH resulted in increase in adsorption capacity, Increasing mass adsorbent decreased the adsorption of C 2 by nanocrystalline TCP. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS° have been calculated. The thermodynamics of all ions onto nano-TCP system indicates spontaneous and endothermic nature of the process.

In this research, a super hydrophobic coating grade polypropylene (MFI6) with nanoparticles of ZnO was produced on glass by using solution casting technique and the optimal conditions were introduced as well. Solution casting as a simple and inexpensive method does not require any special equipment in order to produce super hydrophobic coatings. Therefore, the effect of two parameters namely, the concentration nanoparticles of ZnO and the drying temperature, on the final properties and performance hydrophobic coatings were investigated. Regarding the studies which have been done on coatings based on the hydrophobicity of the contact angle (CA), it was showed that the hydrophobicity of super hydrophobic coatings behavoirs were exhibited and according to observations of a scanning electron microscope (SEM) devise, a rough and hydrophobic surface was resulted. Thus, the rougher the surface, the higher contact angle is generated, and if this value reaches 150 to 180 °C, the surface would change to a super hydrophobic surface. Increasing the concentration of ZnO nanoparticles to polypropylene has led to more surface roughness. Therefore, the created surface roughness was in micro and nanoscale, while because of an extreme increase in ZnO nanoparticles, the surface roughness was reduced and hydrophobicity was decreased as well due to high accumulation.

This study will outline graphene nanosheets effects on engine oil. Viscosity, viscosity index, flash point and pour point of SAE 20W50 engine oil as four qualitative and effective parameters of oil functionality were investigated. The obtained results are shown that flash point and pour point in the sample including graphene nanosheets with 0.2wt.% concentration, improved 6.7% and 11.1%, respectively, compare with base oil. Although, nano-lubricants viscosity as a major factor in lubricating process, slightly surged when graphene added. There are various methods on dispersing of nanoparticles inside the base oil among which planetary ball mill is the best one to meet the need of graphene nanosheets stabilization.

Research study presents an experimental investigation on forced convection heat transfer of an aqueous ferro-fluid flow passing through a circular copper tube in the presence of an alternating magnetic field. The flow passes through the tube under a uniform heat flux and laminar flow conditions. The primary objective was to intensify the particle migration and disturbance of the boundary layer by utilizing the magnetic field effect on the nanoparticles for more heat transfer enhancement. Complicated convection regimes caused by interactions between magnetic nanoparticles under various conditions were studied. The process of heat transfer was examined with different volume concentrations and under different frequencies of the applied magnetic field in detail. The convective heat transfer coefficient for distilled water and ferro-fluid was measured and compared under various conditions. The results showed that applying an alternating magnetic field can enhance the convective heat transfer rate. The effects of magnetic field, volume concentration and Reynolds number on the convective heat transfer coefficient were widely investigated, and the optimum conditions were obtained. Increasing the alternating magnetic field frequency and the volume fraction led to better heat transfer enhancement. The effect of the magnetic field in low Reynolds numbers was higher, and a maximum of 27.6% enhancement in the convection heat transfer was observed.