Sharif Digital Repository

In this research, initially anodization process was used to fabricate ZnO nanorods on Zn substrate and then RF sputtering technique was applied to grow a thin layer of polytetrafluoroethylene (PTFE, Teflon) on the coated ZnO nanorods for producing a superhydrophobic surface. According to scanning electron microscopy (SEM) observations, ZnO nanorods were formed with average diameter and length of about ∼180 nm and 14 μm, respectively. Superhydrophilic property of ZnO nanorods and superhydrophobic property of PTFE/ZnO nanorods was investigated by water contact angle (WCA) measurements. It was found that the contact angle varied with the PTFE deposition time. The highest contact angle... 

In this investigation, the effect of annealing temperature and concentration of gold nanoparticles on the photoelectrochemical properties of sol-gel deposited Au : TiO2 nanocomposite thin films is studied. Various gold concentrations have been added to the TiO2 thin films and their properties are compared. All the deposited samples are annealed at different temperatures. The optical density spectra of the films show the formation of gold nanoparticles in the films. The optical bandgap energy of the Au : TiO2 films decreases with increasing Au concentration. The crystalline structure of the nanocomposite films is studied by x-ray diffractometry indicating the formation of gold nanocrystals in... 

WO3-TiO2 nano porous layers were synthesized by micro arc oxidation (MAO) process under different applied voltages in electrolytes containing sodium tungstate and phosphate salts with various concentrations. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDS) techniques were employed to study phase structure and chemical composition of the layers. According to our data analysis, the nano porous layers consisted of anatase, rutile, and tungsten oxide phases with a varying fraction depending on the voltage and electrolyte concentration. Moreover, it was found that WO3 not only dispersed in the TiO2 matrix, but also doped into the TiO2... 

In this study, pure TiO2 and Au:TiO2 nanocomposite thin films are both synthesized using sol-gel and RF reactive co-sputtering methods. Physical and photoelectrochemical properties of the thin films deposited by each method are compared. The optical density spectra and scanning electron microscopy images of the Au:TiO2 films reveal formation of gold nanoparticles in the all nanocomposite films synthesized by two methods. Moreover, the optical bandgap energy of the thin films decreases with addition of Au nanoparticles. X-ray photoelectron spectroscopy indicates that the presence of gold in metallic state and the formation of TiO2 is stoichiometric. The photoelectrochemical properties of the... 

Vertically aligned ZnO@CdS nanorod heterostructure films with various loadings of CdS nanoparticle shell were synthesized and applied in photoinactivation of Escherichia coli bacteria under visible light irradiation. While neither the bare ZnO nanorods (with band-gap energy (Eg) of ∼3.28 eV) under visible light irradiation nor the nanorod heterostructures in dark exhibited any significant antibacterial activity, the ZnO@CdS nanorod heterostructures (with Eg ∼2.5-2.6 eV) could successfully inactivate the bacteria under visible light irradiation. Furthermore, it was found that an optimum loading of the CdS shell (corresponding to the effective thickness less than ∼15 nm) is required to achieve... 

The wide utilization of nanomanipulation as a promising approach in microorganisms, nanoelectromechanical systems, and assembly of nanostructures remarks the importance of nanostructures' motion in electric fields. Here, we study the rotational dynamics of metallic and non-metallic nanowires (NWs) in a static uniform electric field in viscous dielectric liquids. For metallic NWs, it has been theoretically shown that the electric field-induced rotation is practically independent of the geometrical dimensions and the electrical properties of NWs. Our experimental results for suspended silver (Ag) NWs in microscope oil are perfectly in agreement with this model. However, in the case of TiO2... 

Correlations between electrical and thermal conduction in polymer composites are blurred due to the complex contribution of charge and heat carriers at the nanoscale junctions of filler particles. Conflicting reports on the lack or existence of thermal percolation in polymer composites have made it the subject of great controversy for decades. Here, we develop a generalized percolation framework that describes both electrical and thermal conductivity within a remarkably wide range of filler-to-matrix conductivity ratios (Y f / Y m), covering 20 orders of magnitude. Our unified theory provides a genuine classification of electrical conductivity with typical Y f / Y m ≥ 10 10 as... 

Direct solvent exfoliation of bulk MoS2 with the assistance of poly(3-hexylthiophene) (P3HT) produces a novel two-dimensional organic/inorganic semiconductor hetero-junction. The obtained P3HT-MoS2 nanohybrid exhibits unexpected optical limiting properties in contrast to the saturated absorption behavior of both P3HT and MoS2, showing potential in future photoelectric applications  

ZnO/CuO nanofibers, with different CuO concentrations, were fabricated by one-step electrospinning of the polymer precursor and annealing in air. Scanning electron microscopy (SEM) showed smooth and beadless morphology for the synthesized nanofibers, while X-ray diffraction (XRD) analysis revealed formation of hexagonal and monoclinic crystalline structure phases for ZnO and CuO nanofibers, respectively. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of CuO on the surface of ZnO nanofibers. For further confirming the formation of chemical bonds, Fourier transform infrared (FT-IR) spectroscopy was employed. The effect of Cu contents in the overall electronic band... 

Considering hydrogen as a future fuel, development of clean energy sources based on solar power is the main human challenge in recent years. Here, for the first time, Au:WO3 photoanodes are synthesized with different Au concentrations and then applied for photoelectrochemical (PEC) water splitting. A comprehensive statistical study on the prepared photoanode surface is conducted to understand the correlation between surface morphology and PEC activity, using atomic force microscopy (AFM). The results clearly justified the maximum surface area observed for the film containing 1 mol % Au. Additionally, X-ray diffraction (XRD) analysis determined that Au nanocrystals have been formed in cubic... 

A series of thiophene-based donor-acceptor-donor (D-A-D) oligomer substituted metalloporphyrins (MPors) with different 3d central metal-ions (M = Co, Ni, Cu, and Zn) were systematically investigated to screen efficient hybrid photocatalysts for CO2 reduction based on density functional theory (DFT) and time-dependent DFT simulations. Compared with base MPors, the newly designed hybrid photocatalysts have a lower bandgap energy, stronger and broader absorption spectra, and enhanced intermolecular charge transfer, exciton lifetime, and light-harvesting efficiency. Then, the introduction of D-A-D electron donor (ED) groups into the meso-positions of MPors is a promising method for the... 

Thermal stability of Ag layer on Ti coated Si substrate for different thicknesses of the Ag layer have been studied. To do this, after sputter-deposition of a 10 nm Ti buffer layer on the Si(1 0 0) substrate, an Ag layer with different thicknesses (150-5 nm) was sputtered on the buffer layer. Post annealing process of the samples was performed in an N 2 ambient at a flow rate of 200 ml/min in a temperature range from 500 to 700 °C for 30 min. The electrical property of the heat-treated multilayer with the different thicknesses of Ag layer was examined by four-point-probe sheet resistance measurement at the room temperature. Phase formation and crystallographic orientation of the silver... 

ZnO Nanorods (NRs) are deposited on glass substrate using the hydrothermal method by applying a strategic growth control to improve their aspect ratios. In this research, the aspect ratio was tuned by tailoring the synthesis parameters, including the seed layer annealing temperature, absence/presence of polyethylenimine (PEI) in the growth solution, and the solution preheating process. The effects of these parameters on the morphology, crystal structure, room temperature photoluminescence properties, and current-voltage characteristics were examined by FESEM, XRD, PL, and I-V measurements. It was demonstrated that by varying the seed layer annealing temperature and presence of PEI solution... 

In this study, the effects of TiO2 addition on the physical and photoelectrochemical properties of ZnO thin films have been investigated. The (TiO2)x-(ZnO)1-x nanocomposite thin films were dip-coated on both glass and indium tin oxide (ITO)-coated conducting glass substrates with various values of x, specifically 0, 0.05, 0.1, 0.25 and 0.5. Optical properties of the samples were studied by UV-vis spectrophotometry in the range of 300-1100 nm. The optical spectra of the nanocomposite thin films showed high transparency in the visible region. The optical bandgap energy of the (TiO2)x-(ZnO)1-x films increased slightly with increasing values of x. The crystalline structure of the nanocomposite... 

In this work, we have studied thermal stability of nanoscale Ag metallization and its contact with CoSi 2 in heat-treated Ag(50 nm)/W(10 nm)/Co(10 nm)/Si(1 0 0) multilayer fabricated by sputtering method. To evaluate thermal stability of the systems, heat-treatment was performed from 300 to 900 °C in an N 2 ambient for 30 min. All the samples were analyzed by four-point-probe sheet resistance measurement (R s ), Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD), and atomic force microscopy (AFM). Based on our data analysis, no interdiffiusion, phase formation, and R s variation was observed up to 500 °C in which the Ag layer showed a (1 1 1) preferred crystallographic... 

The physical and photoelectrochemical properties of the anodized ZnO-TiO2 thin films were investigated in this study. Impedance spectroscopy revealed a decrease in charge transfer resistance and Tafel plots determined enhancement of about 200 times in the exchange current (i 0) after anodization at high positive potential. It was found from XPS analysis that after applying the potential of 5 V to the ZnO-TiO2 photoelectrode, the lattice oxygen (O2-) in the thin film is oxidized to molecular oxygen and then, cations such as Zn2+ can be solved in the basic electrolyte and passed to the solution. Moreover, according to AFM analysis it was observed that the surface of the samples has been... 

Using multi-walled carbon nanotubes (MWCNTs), the present study focuses on their electrochemical hydrogen storage capacities. The results showed that the hydrogen desorption process is composed of two steps with voltages around -0.75 and -0.15 V. Hydrogen adsorption at -0.15 V took place at temperatures above 30 °C, and the amount of energy required for adsorbing hydrogen was 1.68 eV. The hydrogen storage capacity increased with increasing electrolyte temperature from 30 to 60 °C in both steps. The hydrogen storage capacity of the MWCNTs treated at different atmospheres showed that the decrease in the graphitization of MWCNTs led to the increase in hydrogen adsorption. The results also... 

The effects of HCl, HNO3, H2SO4 and HF acids on the purification and the electrochemical hydrogen storage of multi-walled carbon nanotubes (MWCNTs) were studied. The MWCNTs were synthesized on Fe-Ni catalyst by thermal chemical vapor deposition method. The X-ray diffraction and thermal gravimetric analysis results indicated that the MWCNTs purified by HF acid had the highest impurities as compared with the other acids. The N2 adsorption results at 77 K indicated that all the samples were mainly mesoporous and the purified MWCNTs by HF acid had the highest surface area as compared with the other acids. The hydrogen storage capacities of the purified MWCNTs by the following acids were in... 

The ZnO nanowires have been synthesized using vapor-liquid-solid (VLS) process on Au catalyst thin film deposited on different substrates including Si(1 0 0), epi-Si(1 0 0), quartz and alumina. The influence of surface roughness of different substrates and two different environments (Ar + H2 and N2) on formation of ZnO nanostructures was investigated. According to AFM observations, the degree of surface roughness of the different substrates is an important factor to form Au islands for growing ZnO nanostructures (nanowires and nanobelts) with different diameters and lengths. Si substrate (without epi-taxy layer) was found that is the best substrate among Si (with epi-taxy layer), alumina and... 

Formation and thermal stability of nanothickness NiSi layer in Ni(Pt 4 at.%)/Si(1 0 0) and Ni0.6Si0.4(Pt 4 at.%)/Si(1 0 0) structures have been investigated using magnetron co-sputtering deposition method. Moreover, to study the effect of Si substrate in formation of NiSi and its thermal stability, we have used Ta diffusion barrier between the Ni0.6Si0.4 layer and the Si substrate. Post annealing treatment of the samples was performed in an N2 environment in a temperature range from 200 to 900 °C for 2 min. The samples were analyzed by four point probe sheet resistance (Rs) measurement, X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. It was found that the annealing...