Sharif Digital Repository

The surface plasmon effect of Au nanostructures placed on the surface of hematite has recently been used to enhance light absorption within its carrier collection distance of 10 nm from the water-hematite interface. Despite significant narrow band absorption enhancements in the visible region, the reported enhancements in the overall performance of the cell under standard AM1.5 sunlight illumination are not significant. We numerically design an array of Au stripes on the surface of an extremely thin layer of hematite to maximize the number of charge carriers that can reach the hematite-water interface and explore the optical processes involved. The lateral dimensions and in particular the... 

We report different morphologies of nanodroplets over various topographical features of the supporting substrates. The effects of different parameters such as the profile of the disjoining pressure, droplet size and the geometrical parameters are studied and discussed. Also, the effects of a coating layer on the surface of the substrate are determined. It is demonstrated that the nanodroplets at some positions are not stable and gradually move to more stable positions so that the system has less energy. For grooves this results in a series of morphology diagrams of the nanodroplets over the grooves as a function of the grooves' width and the liquid volume  

Operation of an optical system for surface profiling is reported here. Reflection signals for the plane and cylindrical surfaces with different materials are reported. To investigate the precision and sensitivity of the reported system the reflection results of the curved and flat structured surface are compared with that of a structure-free surface. Reported system provides a simple and accurate means for the object shape study through the optical reflection measurements  

Design and operation of an opto-mechanical system for surface profiling are reported in this study. The reported system consists of a double-fiber optical design and an electro-mechanical scanning system. In this arrangement one fiber transmits the source light to the object surface and the second one transmits the light reflected off the surface to a photodetector. By scanning the double-fiber assembly in one-direction, reflection properties of different curved surfaces are investigated. Reflection signals for the cylindrical surfaces made with different curvatures and materials are reported. In order to see the effect of the surface material, for a fixed radius cylinder, the surface is... 

By co-deposition via RF-Sputtering and RF-PECVD methods and using Cu target and acetylene gas, we prepared Cu@Cu2O coreshell nanoparticles on the a-C:H thin film at room temperature. Mie absorption of Cu cores, scattering from Cu2O shell and luminescence that rises from carrier transfer in Cu@Cu2O interface were employed to fit the whole range of visible extinction spectrum of these coreshells. From simulation it was found that scattering and luminescence have an important effect on the energy, width and shape of LSPR absorption peak. Shift of LSPR peak is more affected by the dielectric coefficient of shell than Cu core size particularly for Cu core diameter above 4 nm. Also, the LSPR... 

Barium strontium titanate (BST, Ba1-xSrxTiO3) thin films have been extensively used in many dielectric devices such as dynamic random access memories (DRAMs). To optimize its characteristics, a microstructural control is essential. In this paper, Ba0.6Sr0.4TiO3 thin film has been deposited on the SiO2/Si substrate by the pulsed laser deposition (PLD) technique at three different oxygen working pressures of 100, 220 and 350 mTorr. Then the deposited thin films at 100 mTorr oxygen pressure were annealed for 50 min in oxygen ambient at three different temperatures: 650, 720 and 800°C. The effect of oxygen working pressure during laser ablation and thermal treatment on the films was investigated... 

Numerical modeling of periodically patterned graphene sheets (PPGS) embedded in planar multilayered media using Fourier-based methods suffers from very slow convergence because of the fact that the conductivity is zero in unfilled areas of the patterned surface and, thus, the so-called Li's inverse rule is not applicable. In this paper, a simple and efficient approach is proposed to overcome this problem such that the exact boundary condition can be applied and the surface current density on PPGS can be obtained accurately. Here, the PPGS is modeled as a conductive surface and only its conductivity representation by the Fourier series is modified. The proposed method can be used easily for... 

Zn/Ni nanocrystalline multilayer coatings were electrodeposited using single bath method and switching current densities. Effect of deposition current densities (i1 and i2) and number of layers (n) on composition, surface morphology and roughness, microhardness, phase structure and corrosion resistance of Zn/Ni multilayers were studied and compared with that of single layer. Analyzing and optimizing the influences of mentioned parameters on corrosion resistance of multilayers carried out through Response Surface Methodology. The model based on RSM results demonstrated that improvement in corrosion resistance due to increase in “difference of deposition current densities” was more effective... 

The three-dimensional power law fluid flow through rough microchannels has been studied numerically to determine the effects of the topographic structures on the thermal and hydrodynamic characteristics of the system. Rectangular, triangular and sinusoidal element shapes have been considered in order to investigate the effects of roughness height, width, pitch and channel separation on the pressure drop and heat transfer. Uniform wall heat flux boundary condition has been applied for all the peripheral walls. The results indicate that the global heat transfer performance can be improved or reduced by the roughness elements at the expense of pressure head when compared with the smooth... 

To obtain metallic nanofingers applicable in surface acoustic wave (SAW) sensors, a mechano-chemical atomic force microscope (AFM) nanolithography on a metallic thin film (50 nm in thickness)/piezoelectric substrate covered by a spin-coated polymeric mask layer (50-60 nm in thickness) was implemented. The effective shape of cross-section of the before and after etching grooves have been determined by using the AFM tip deconvolution surface analysis, structure factor, and power spectral density analyses. The wet-etching process improved the shape and aspect ratio (height/width) of the grooves and also smoothed the surface within them. We have shown that the relaxed surface tension of the... 

Cu@Cu2O core-shell nanoparticles on a-C : H thin films are prepared by co-deposition of RF-sputtering and RF-PECVD. Samples with different copper concentrations are grown. The copper content of films increases with reduction in initial pressure and rises with increasing RF power. When the Cu/C ratio reaches 0.5, the surface plasmon resonance (SPR) peak that is a signature of the formation of Cu nanoparticles appears in visible spectra of these films. X-ray photoelectron spectroscopy (XPS) characterization indicates that the surface of the copper nanoparticles oxidizes when they are exposed to air. The results are indicative that the shell of the nanoparticle is mainly the Cu 2O phase that is... 

Large-scale K-doped ZnO nanotapers were successfully grown on an indium tin oxide (ITO) substrate using a facile electrochemical route. The structural and morphologic analysis exhibited that the K-doped ZnO nanostructures had a nanotaper morphology and strong preferential [0001] c-axis direction with a hexagonal polycrystalline structure. The optical results show that the incorporation of K+ ions as the donors in a ZnO lattice leads to substantial modulation of the band gap structure of ZnO nanotapers, which results in a redshift in the ultraviolet emission peaks. The considerable enhancement of performance in K-doped ZnO-based dye-sensitized solar cells (DSSCs) can be related to the doping... 

We analyze the process of electrowetting-induced jumping of droplets away from a substrate with a geometric heterogeneity in the form of a cone and compare the results with those of a flat substrate in different wettabilities and hydrophobicities. Our results reveal that the droplet dynamics can be enhanced through applying a topographic heterogeneity. However, increasing the height of the cones does not always provide a better condition for the jumping and there is an optimum value for the height of the cones. The enhancement is due to the fact that more liquid flowing affects the pressure gradient within the droplet leading to a higher jumping velocity. It is shown that for the flat... 

This study involves the capability of severe shot peening (SSP) as a catalyst intake for plasma nitriding process and the probability of reducing the requirement of thermal energy individually on the diffusion of interstitial atoms. To this end, combination of mechanical-thermal energy is run with pure thermal plasma assisted energy. Therefore, SSP is exposed to AISI 304 austenitic stainless steel as a former treatment and gradient structured surface (nanograined zone, ultrafine grain martensite-twin intersections zone and twin densed zone) is created. Then, plasma nitriding at 400 0 C-4h and 475 0 C-2h temperature-duration conditions. The condition of 475 0 C-2h provides the requirements of... 

The friction on the water–solid interfaces continues to be the most important factor for the energy loss in many marine and submarine applications. Therefore, different techniques have been developed and are available to reduce friction and, as a result, the overall cost. In the past decades, the use of structured surfaces has been given considerable attention because of their specific characteristics such as their abilities in pressure drop reduction. However, an appropriate optimization method is required to find the best surface structure. In the present study, we consider a microgrooved substrate and examine the performance of three shapes including rectangular, elliptical, and... 

Material design and input field properties limit high-harmonic excitation efficiency of surface-plasmon polaritons (SPPs) in a nanoscopic device. We remedy these limitations by developing a concept for a plasmonic waveguide that exploits spatiotemporal control of a weak surface polaritonic field to create efficient four-wave mixing (FWM) and periodic phase singularities. Our configuration comprises four-level double 3-type atomic medium (43 As) doped in a lossless dielectric situated above a negative-index metamaterial (NIMM) layer. We report the coherent excitation and propagation of the multiple surface polaritonic shock waves (SWs) and establish the highly efficient frequency combs by... 

The application of heat pipes with flat evaporators in cooling electronic devices has attracted a lot of attention in recent years. Increasing the rate of heat transfer in their evaporator by utilizing structured surfaces is considered as a prominent method for reducing the thermal resistance of the heat pipes. In this study, the performance of a thermosyphon heat pipe with novel radially rectangular-grooved and radially inclined triangular-grooved evaporator surfaces was evaluated experimentally. It is hypothesized that the radial grooves may enhance the performance by inducing rotational motions and increasing the heat transfer coefficients. Based on the results, the optimum filling ratio... 

Drop motion on different types of new proposed micro-structure surfaces has been numerically investigated to find the optimum structure in view point of ice formation delaying. The droplet automatically moves on the inclined surfaces due to gravity forces. To validate the numerical algorithm, three different bench mark problems have been considered. The results indicate that the present algorithm is trustable for the presented numerical simulations. Then the validated numerical approach has been used to simulate droplet motion on nine proposed superhydrophobic surfaces in the same conditions. Comparison the drop motion on different micro-structure surfaces at different time indicate that... 

Conducting interfaces and nano conducting layers can support surface electromagnetic waves. Uniform charge layers of non-zero thickness and their asymptotic behavior toward conducting interfaces of infinitely small thicknesses, where the thin charge layer is modeled via a surface conductivity σ s , are already studied. Here, the possible effects of inhomogeneity in the conductivity profile of the thin conducting layers are investigated for the first time and a new approximate yet accurate enough analytical formulation for mode extraction in such structures is given. In order to rigorously analyze the structure and justify the proposed approximate formulation, the Galerkin's method with...