Sharif Digital Repository

CdS/TiO2/graphene (CTG) nanocomposite thin films were synthesized by a facile production route. The TiO2/graphene (TG) nanocomposite was initially fabricated by sol-gel method in such a way that TiO2 nanoparticles loaded on graphene oxide (GO) sheet via photocatalytic process. Then, CdS nanoparticles were deposited on the TG thin film by successive ion layer adsorption and reaction process (SILAR) approach. Based on atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses, the TG thin film possessed a larger surface area as compared with the pure TiO2 thin film due to presence of graphene sheet. UV/visible spectroscopy exhibited... 

The analytical treatment of an axisymmetric rigid punch indentation of an isotropic half-space reinforced by a buried extensible thin film is addressed. With the aid of appropriate displacement potential functions, Hankel transforms, and some mathematical techniques, the mixed boundary value problem under consideration is reduced to a Fredholm integral equation of the second kind. The most interesting results of the problem, including the equivalent normal stiffness of the system and the contact stress distribution beneath the rigid punch, are expressed in terms of the solution of the obtained Fredholm integral equation. Some limiting cases corresponding to inextensible and extremely... 

In this research, an attempt was made to improve TiO2 photo-catalyst properties, thus pure, N-Ce co-doped TiO2 thin films were prepared on glass-ceramic substrate using a sol-gel dip-coating technique. The samples were calcinated in air at 475 °C, 550°C, and 650°C for 2 h. The result of simultaneous thermal analysis (STA) and X-ray diffraction (XRD) showed that the presence of Ce in TiO2 could inhibit the phase transformation from anatase to rutile and enhance the thermal stability, and anatase was the dominant phase in N-Ce co-doped TiO2 samples. Also based on the results, the doping results in decreasing the size of TiO 2 crystallite. The results of ultra violet-visible light diffuse... 

In this report, crack-free nanostructured barium titanate thin films are prepared by a sol-gel processing method. Glacial acetic acid, barium acetate, titanium tetraisopropyl alkoxide, 2-propanol and deionized water are used as precursors for preparing stable precursor solution. Then very thin films (thickness=26 nm) are deposited on fused silica substrates. In order to prepare crack-free thin films of BaTiO3, much attention is given to solvent evaporation process and a controlled pre-drying process is developed. It is found that the control of the process, especially in the initial stage of drying process is crucial and important for preparation of the crack-free ultrathin nanostructured... 

Plasmonic Sierpinski nanocarpet as back structure for a thin film Si solar cell is investigated. We demonstrate that ultra-broadband light trapping can be obtained by placing square metallic nanoridges with Sierpinski pattern on the back contact of the thin film solar cell. The multiple-scale plasmonic fractal structure allows excitation of localized surface plasmons and surface plasmon polaritons in multiple wavelengths leading to obvious absorption enhancements in a wide frequency range. Full wave simulations show that 109 % increase of the short-circuit current density for a 200 nm thick solar cell, is achievable by the proposed fractal back structure. The amount of light absorbed in the... 

Particulate back-reflector films are conventionally used for the improvement of light harvesting in dye solar cells (DSC). The back-reflection of the films is directly related to the scattering efficiency of the individual particles. Inspired by the idea of multilayer optical thin films, here it is demonstrated theoretically and experimentally that putting a SiO2 shell around spherical rutile-TiO2 particles leads to improved light scattering by the particles. These dielectric core-shells not only enhance the overall diffuse reflection of the films, but they also cause a relative improvement in the red and near infrared regions. Back-reflector films of these core-shell particles employed in... 

Nanostructured TiO2-Al2O3 films and powders were prepared by a straightforward aqueous particulate sol-gel route. Titanium (IV) isopropoxide and aluminum chloride were used as precursors, and hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the porosity. The effect of Al:Ti molar ratio was studied on the crystallization behavior of the products. X-ray diffraction (XRD) revealed that the powders crystallized at 800°C, containing anatase-TiO2, rutile-TiO2 and cubic-Al2O3 phases. Furthermore, it was found that Al2O3 retarded the anatase to rutile transformation. Transmission electron microscope (TEM) image showed that one of the smallest crystallite sizes was... 

The normal indentation of a rigid circular disk into the surface of a transversely isotropic half-space reinforced by a buried inextensible thin film is addressed. By virtue of a displacement potential function and the Hankel transform, the governing equations of this axisymmetric mixed boundary value problem are represented as a dual integral equation, which is subsequently reduced to a Fredholm integral equation of the second kind. Two important results of the contact stress distribution beneath the disk region as well as the equivalent stiffness of the system are expressed in terms of the solution of the Fredholm integral equation. When the membrane is located on the surface or at the... 

Indium tin oxide (ITO) thin films have been deposited using RF sputtering technique at different pressures, RF powers, and substrate temperatures. Variations in surface morphology, optical properties, and film resistances were measured and analyzed. It is shown that a very low value of sheet resistance (1.96 ω/sq.) can be achieved with suitable arrangement of the deposition experiments. First, at constant RF power, deposition at different pressure values is done, and the condition for achieving minimum sheet resistance (26.43 ω/sq.) is found. In the next step, different values of RF powers are tried, while keeping the pressure fixed on the previously found minimum point (1-2 Pa). Finally,... 

In this study, TiO 2-SiO 2 nanocomposite films with different amounts of SiO 2 were prepared by sol-gel process and were coated onto stainless steel 316L. The effect of addition of various amount of SiO 2 in the precursor solution on the photocatalysis, photo-generated hydrophilicity and self-cleaning property of TiO 2 thin films was investigated by X-ray diffraction, Fourier transform infrared spectroscopy, water contact angle measurements and UV spectroscopy. In the tested ranges of SiO 2 content and sintering temperature, the highest photocatalytic activity and self-cleaning property were observed in the 15 mol% SiO 2 sample sintered at 750 °C. Addition of less than 30 mol% SiO 2 had a... 

The morphological characteristics and electronic structure of the BaTiO 3 films grown by pulsed-laser deposition technique have been investigated. AFM and FE-SEM images reveal columnar growth characteristic of these films. Utilizing spectrophotometer, optical band gap of the films were reckoned to be about 3.76 eV. Both dα/dE and PL vs. E plots reveal numerous luminance states in the gap. Despite the presence of many luminance faults in the gap, cations manage to preserve their electronic states  

In this study the effect of deposition temperature and thickness on the physical properties of carbon films deposited by magnetron sputtering PVD was investigated. The results of Raman spectra and grazing incidence XRD (GIXRD) patterns show that the graphitization increases by increasing the deposition temperature. There is a change in deposition mechanism at 400 °C from amorphous carbon deposition to nano-structured graphite deposition. Also by increasing substrate temperature the electrical resistance of carbon films reduces significantly up to 300 °C and then remains largely constant. High intrinsic compressive stress in low temperature deposited carbon films causes cracks and... 

TiO2 thin films containing different concentrations of Ag nanoparticles have been synthesized by sol-gel method. According to UV-visible spectra, presence of an intense surface plasmon resonance peak at 490 nm of wavelength indicated formation of silver nanoparticles in the TiO2 films. Based on atomic force microscopy (AFM) analysis, the surface roughness and the effective surface ratio increased by increasing the Ag mol%. Moreover, scanning electron microscopy (SEM) images showed formation of Ag nanoparticles on the surface for the samples containing high Ag concentration. X-ray diffraction (XRD) patterns revealed that the size of Ag nanocrystals increased by increasing the Ag content in... 

We present the results of a bolometric transition-edge sensor made of a high-Tc superconductor YBCO thin film prepared by fluorine-free metal-organic deposition. The structure of the films was characterized by X-ray diffraction and scanning electron microscopy, and the superconducting properties were determined by R-T measurements. The applicability of the resulting film as an infrared sensor is reported here. The optical response in the range of near infrared and the noise characteristics of the patterned bolometer are measured and analyzed. The dependence of device sensitivity on the bias current and modulation frequency is also investigated. As it is presented in this paper, the results... 

A simple method for synthesis of W17O47 nanothick plates by annealing sol-gel-deposited tungsten oxide thin films on soda lime substrate has been reported. After heat treatment of the dried thin films at 700 °C in N2 ambient for 60 min, W17O47 nanothick plates with [100] orientation were obtained. The synthesized product was characterized and analyzed by, X-ray diffraction (XRD), SEM, XPS and ultraviolet-visible spectrophotometery. According to SEM observations, nanothick plates grew with random orientations on the surface. In addition, it was observed that some of the nanothick plates were constituted from several nanosheets. XRD analysis determined that the nanothick plates were mainly... 

Ce-doped ZnO and pure ZnO nanocomposite thin films with different Ce/Zn ratios (0, 2, 5, 10, 15, 20, and 30 at.%) have been prepared by sol-gel method at optimum annealing temperature of 500 °C. The synthesized samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis spectrophotometry. According to our XPS data analysis, there are three major metal ions namely Ce3+, Ce4+ and Zn 2+ that coexist on the surface. The XRD measurements indicate that the ZnO thin films have a hexagonal wurtzite structure, and CeO2 crystallites formed in the Ce-doped ZnO nanocomposite thin films. Photoelectrochemical property of the samples was studied by three... 

Micro arc oxidation technique, as a facile and efficient process, was employed to grow sulfur doped titania porous layers. This research sheds light on the photocatalytic performance of the micro arc oxidized S-TiO2 nano-porous layers fabricated under pulse current. Morphological and topographical studies, performed by SEM and AFM techniques, revealed that increasing the frequency and/or decreasing the duty cycle resulted in formation of finer pores and smoother surfaces. XRD and XPS results showed that the layers consisted of anatase and rutile phases whose fraction was observed to change depending on the synthesis conditions. The highest anatase relative content was obtained at the... 

Hollow structures show both light scattering and light trapping, which makes them promising for dye-sensitized solar cell (DSSC) applications. In this work, nanoparticulate hollow TiO 2 fibers are prepared by layer-by-layer (LbL) self-assembly deposition of TiO 2 nanoparticles on natural cellulose fibers as template, followed by thermal removal of the template. The effect of LbL parameters such as the type and molecular weight of polyelectrolyte, number of dip cycles, and the TiO 2 dispersion (amorphous or crystalline sol) are investigated. LbL deposition with weak polyelectrolytes (polyethylenimine, PEI) gives greater nanoparticle deposition yield compared to strong polyelectrolytes... 

The infrared range optical absorption mechanism of carbon-copper composite thin layer coated on the diamond-like carbon buffer layer has been investigated. By consideration of weak interactions between copper nanoparticles in their network, optical absorption is modelled using their coherent dipole behaviour induced by the electromagnetic radiation. The copper nanoparticles in the bulk of carbon are assumed as a chain of plasmonic dipoles, which have coupling resonance. Considering nearest neighbour interactions for this metallic nanoparticles, surface plasmon resonance frequency (ω 0) and coupled plasmon resonance frequency (ω 1) have been computed. The damping rate against wavelength is... 

Antibacterial activity of sol-gel synthesized Ag-TiO2 nanocomposite layer (30nm) deposited on rough anatase (a) TiO2 thin film (~200nm in thickness) was investigated against Escherichia coli bacteria, in dark and also in exposure to UV light. The nanocomposite thin films were transparent with a surface plasmon resonance absorption band at a wavelength of 410nm. The metallic silver nanoparticles with an average diameter of 30nm and fcc crystalline structure were self-accumulated on surface of a mesoporous and aqueous TiO2 layer with a capillary pore structure having a pore radius of 3.0nm. By adding the silver nanoparticles in the TiO2 layer, recombination of the photoexcited electron-hole...