Sharif Digital Repository

Molecular machines, such as nanocars, have shown promising potential for various tasks, including manipulation at the nanoscale. In this paper, we examined the influence of temperature gradients on nanocar and nanotruck motion as well as C60 - as their wheel - on a flat gold surface under various conditions. We also compared the accuracy and computational cost of two different approaches for generating the temperature gradient. The results show that severe vibrations and frequent impacts of gold atoms at high temperatures increase the average distance of C60 from the substrate, reducing its binding energy. Moreover, the temperature field drives C60 to move along the temperature variation;... 

Tungsten oxide thin films on glass substrates were fabricated by pulsed laser deposition under different experimental conditions for gasochromic applications. Palladium clusters were overlaid on the film surface by the electroless plating method. Hydrogen gasochromic investigation revealed that desirable samples are amorphous deposited films in oxygen partial pressure. The maximum colouration velocity of deposited films at 13.3 Pa oxygen partial pressure and 25 °C, 150 °C and 300 °C substrate temperatures are 0.010 s-1, 0.027 s-1 and 0.030 s-1, respectively, while at 300 °C substrate temperature by increasing the oxygen partial pressure to 66.7 Pa the maximum colouration velocity enhances to... 

The hydroxyapatite coating on metal implants is a suitable method to create a bioactive surface and to increase the bone-implant bonding strength. In this research, at first the titanium surface was treated with NaOH solutions ; 5N and 10N at 60°C for 24 h and 5N at 60°C for 24 h followed by heating at 600°C for 1 h. The samples were immersed in the simulated body fluid (SBF) for 28 days to generate a calcium phosphate coating on titanium substrates. The modified substrates and coatings were characterized using SEM and XRD. According to the results obtained in this work the concentration increase of the NaOH solution has influenced the grain boundaries, whereas the heat treatment at 600°C... 

WO3-SiO2 compound thin films were deposited on glass substrates using the sol-gel method, and then all the samples were dried at 100 °C and annealed at 400 °C in air. The effect of WO3 concentration on the hydrophilicity of WO3-SiO2 compound films was studied for the first time and it was shown that the films containing 85 mol% of the concentration possessed a superhydrophilic surface without UV or visible irradiation. Optical properties of the films such as transmittance, reflectance and bandgap energy were investigated using a UV-visible spectrophotometer. According to atomic force microscopy, the surface ratio was maximized in 85 mol% concentration of WO3 similar to hydrophilicity.... 

Adhesive and cohesive properties of the plasma-sprayed hydroxyapatite (HA) coatings, deposited on Ti-6Al-4V substrates by varying the plasma power level and spray distance (SD), were evaluated by an indentation method. The crystallinity and the porosity decreased with increasing both of these two parameters. The microhardness value, Young's modulus (E) and coating fracture toughness (K C ) were found to increase with a combinational increase in spray power and SD. The Knoop and Vickers indentation methods were used to estimate E and K C , respectively. The critical point at which no crack appears at the interface was determined by the interface indentation test. This was used to define the... 

A two stage chemical deposition (TSCD) technique is used to produce ZnO films on quartz glass (QG), soda lime glass (SLG) and high purity alumina (HPA) from an aqueous solution of zinc complex. The effects of the substrate material on the chemical composition and morphology of the deposited layer are investigated. The effects of different annealing temperatures (180, 300, 500 and 800°C) on the morphology and orientation of the ZnO crystallites are also determined. X-ray diffraction diffractograms show that above 300°C, the intensity of (002) peak considerably decreases with increasing temperature. Results indicate that changing the substrate from QG to SLG does not significantly influence... 

In this investigation, the effect of coloring voltage and thickness on optical and also electrochromical properties of W O3 thin films has been studied. The W O3 thin films were grown on glass and indium tin oxide coated conducting glass substrates by e-beam evaporation at different thicknesses of 200, 400, and 700 nm. Optical properties of the deposited samples were characterized in the ultraviolet-visible range (300-1100 nm). The optical bandgap energy of the W O3 was obtained in a range of 3.3-3.5 eV showing its increase by decreasing the film thickness. The refractive index of the W O3 films was measured around 2 in the visible range. Surface chemical states of the films were studied by... 

This paper presents a mathematical model of laser powder deposition (LPD) to predict temperature field, melt pool depth and dilution. The model validated by experiments is developed using the moving heat source method. In this method, the temperature distribution inside the clad and the substrate is obtained using the superposition principle and the solution of the heat diffusion due to a point heat source. The model, which can be used in real-time applications, predicts the melt pool depth and dilution as a function of clad height and clad width, which in practice can be measured by a vision system. Numerical and experimental analyses show a non-linear behaviour of the melt pool depth as a... 

SQUID (superconducting quantum interference device) microscopes are versatile instruments for biosensing applications, in particular for magnetic nanoparticle detection in immunoassay experiments. We are developing a SQUID microscope based on an HTS rf SQUID magnetometer sensor with a substrate resonator. For the cryogenic set-up, a configuration was realized in which the cryostat is continuously refilled and kept at a constant liquid nitrogen level by an isolated tube connection to a large liquid nitrogen reservoir. The SQUID is mounted on top of a sapphire finger, connected to the inner vessel of the stainless steel cryostat. The vacuum gap between the cold SQUID and room temperature... 

We experimentally demonstrate a circularly polarized antenna that utilizes unidirectional surface waves that propagate on the boundary of a small ferrite disk. The ferrite disk is metalized on top and is mounted on a grounded dielectric substrate. The disk is normally biased by a magnetic field that is provided by two permanent magnets below and above the structure. A two-section feeding network is used to feed the antenna. The operation frequency of the antenna can be adjusted by changing the magnitude of the applied magnetic bias. The sense of polarization can be reversed by reversing the direction of the applied bias. © 2020 Elsevier B.V  

There is still an open question of how to prepare high-performance counter electrodes for dye solar cells (DSCs) at room temperature; a requirement for flexible DSCs. Here, we introduce Pt deposited cube-like chromium coating as a low-temperature highly-efficient counter electrode for DSCs. Cr is a chemically stable metal and can be easily electroplated on conductive substrates with high roughness (here ∼160 nm) and cube-like appearance. A cyclic electrochemical deposition method with optimized temperature and number of cycles is used to grow Pt nanoparticles on this surface and charge transfer resistance as low as 0.54 Ω cm2 and 0.27 Ω cm2 were obtained at 40 °C and 55 °C solution... 

Bioinspired materials can mimic the stem cell environment and modulate stem cell differentiation and proliferation. In this study, biomimetic micro/nanoenvironments were fabricated by cell-imprinted substrates based on mature human keratinocyte morphological templates. The data obtained from atomic force microscopy and field emission scanning electron microscopy revealed that the keratinocyte-cell-imprinted poly(dimethylsiloxane) casting procedure could imitate the surface morphology of the plasma membrane, ranging from the nanoscale to the macroscale, which may provide the required topographical cell fingerprints to induce differentiation. Gene expression levels of the genes analyzed... 

In this research, mathematical modelling of an anaerobic hybrid bioreactor for effluent treatment of a Poly-Ethylene Terephthalate (PET) unit in a petrochemical complex was performed. The developed model included a combination of a biofilm model for describing the substrate kinetics; a fluidized bed model for determination of species profiles along the reactor length and a bioreactor model for particle distribution inside the reactor. The reactions performed in the bioreactor included; i) the polymers hydrolysis; ii) fermentation of the resulting monomers; iii) the volatile fatty acids fermentation to Acetate and Hydrogen and iv) the Methane formation as the final product. The reactor was... 

We present a technology for the manufacturing of silicon- filled integrated waveguides enabling the realization of lowloss high-performance millimeter-wave passive components and high gain array antennas, thus facilitating the realization of highly integrated millimeter-wave systems. The proposed technology employs deep reactive-ion-etching (DRIE) techniques with aluminum metallization steps to integrate rectangular waveguides with high geometrical accuracy and continuousmetallic side walls. Measurement results of integrated rectangular waveguides are reported exhibiting losses of 0.15 dB/ at 105GHz.Moreover, ultra-wideband coplanar to waveguide transitions with 0.6 dB insertion loss at 105... 

The aim of current research is to investigate the substrate electropolishing effect on corrosion resistance of Ni-Mo thin films. For this purpose, corrosion resistance of coatings deposited on mild steel substrates, that was electropolished or mechanically polished, have been compared in 3.5 wt.% NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The structural properties of Ni-Mo thin films were evaluated using X-ray diffraction (XRD) and their morphology, microstructure and chemical composition were also investigated using scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). Temperature and acidity of deposition... 

This article proposes a tunable composite right-/left-handed transmission line consisting of a transversely magnetized ferrite substrate periodically loaded by microstrip inductors. The gapless transition between the left- and right-handed bands (balanced response) is the main characteristic of this structure. This composite right-/left-handed transmission line is proposed in both reciprocal and nonreciprocal versions. Based on periodic structure analysis, the dispersion relation is estimated theoretically and validated numerically by the finite-element method in the reciprocal case. Theoretical and numerical results demonstrate the tunability of the proposed structures by changing the DC... 

Tungsten Inert Gas (TIG) process and titanium cored wires filled with micro size TiC particles were employed to produce surface composite coatings on commercial pure Ti substrate for wear resistance improvement. Wire drawing process was utilized to produce several cored wires from titanium strips and titanium carbide powders. Subsequently, these cored wires were melted and coated on commercial pure Ti using TIG process. This procedure was repeated at different current intensities and welding travel speeds. Composite coating tracks were found to be affected by TIG heat input. The microstructural studies using optical and scanning electron microscopy supported by X-ray diffraction showed that... 

Chemical vapour deposition (CVD) at atmospheric pressure, using TiCl 4 as a precursor, was used to grow nanostructured TiO2 films on glass substrates. At relatively low temperatures (∼245 °C) and using relatively high reactant concentrations, different nano-morphologies of TiO2 were formed simultaneously, such as spheres, nanowires and mesoporous structures. The TiO2 spheres were successfully applied as light-scattering particles in dye-sensitized solar cells, either by direct deposition onto electrodes in the reactor, or by preparation of a printing paste from the deposited particles. For dye-sensitized solar cells using the organic dye D35 as sensitizer and a cobalt-complex based redox... 

Epitaxial cerium oxide (CeO2) buffer layer has been grown on lanthanum aluminate (LAO) single crystal substrates for fabrication of c-axis oriented YBa2Cu3O7-x (YBCO). Precursor solution of cerium acetylacetonates with viscosity of 0.6 centipoises was spin coated on the 1×1 cm area LAO substrates. The calcination was carried out by very slow ramp (1°C per minute) until the final temperature of 500°C in oxygen flow to remove most of the organic compounds. The final heat treatment has been done at 780°C by a ramp of 20° per minute in gas flow of mixed argon-oxygen with 5 Pa partial pressure of oxygen. The thickness of the deposited CeO2 buffer layer was 20 nm. Then, 100 nm thick YBCO film was... 

In this work, ultraviolet photodetectors based on electrodeposited ZnO sheet thin films were fabricated on a glass substrate. Before electrodeposition, a thin buffer layer of ZnO was deposited on the glass by pulsed laser deposition method. This layer not only acted as a nucleation site for ZnO sheet growth, but also made it possible to use cheap glass substrate instead of conventional fluorine-doped tin oxide (FTO) substrate. Our results showed that photoresponse properties of the photodetectors strongly depend on the sheet sizes. The smaller sheets exhibited enhanced photosensitivity, shortened fall times and decreased gain compared to larger ones. We showed that photodetectors based on...