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    Simultaneous optimization and simulation of a-Si1-xC x layers on n-type silicon solar cells

    , Article Solar Energy Materials and Solar Cells ; Volume 85, Issue 4 , 2005 , Pages 467-476 ; 09270248 (ISSN) Vesaghi, M. A ; Asadi, K ; Sharif University of Technology
    We have applied Rosenbrock's optimization algorithm to obtain the optimized efficiency of a solar cell and its structural parameters. To obtain these parameters, we have developed a computer program for simultaneous optimization and simulation of the solar cell. We have used experimental data on the electrical and optical properties of a-Si1-xCx layers, put them into the written code and obtained the optimized parameters of this solar cell. The maximum efficiency is 6.32% which is close to one experimental result. © 2004 Elsevier B.V. All rights reserved  

    Investigation of warm compaction and sintering behaviour of aluminium alloys

    , Article Powder Metallurgy ; Volume 46, Issue 2 , 2003 , Pages 159-164 ; 00325899 (ISSN) Simchi, A ; Veltl, G ; Sharif University of Technology
    IOM Communications Ltd  2003
    The effects of warm compaction on the green density and sintering behaviour of aluminium alloys were investigated. Particular attention is paid to prealloyed powders, i.e. eutectic and hypereutectic Al-Si alloys, regarding their potential applications in the automotive industry. The effects of chemical composition, alloying method, compacting temperature and the amount of powder lubricant were studied. The compaction behaviour was examined by an instrumented die enabling simultaneous measurement of density, die wall friction coefficient, the triaxial stresses acting on the powder during the course of compaction and ejection pressure. The sintering behaviour was studied via dilatometeric... 

    Thermal desorption of ultrathin silicon oxide layers on Si(111)

    , Article Semiconductor Science and Technology, Bristol, United Kingdom ; Volume 15, Issue 2 , 2000 , Pages 160-163 ; 02681242 (ISSN) Iraji Zad, A ; Taghavinia, N ; Ahadian, M ; Mashaei, A ; Sharif University of Technology
    IOP  2000
    The mechanism of oxide desorption from the surface of Si(111) is studied. Oxide layers formed by different chemical treatments were thermally removed in a UHV chamber and the removal process was probed by Auger electron spectroscopy. Results show that the oxide formed by HCl desorbs very fast and the desorption rate is initially almost linear in time, while for oxides formed by HNO3, H2SO4 and NH4OH the rate is initially slow, becoming faster at later times. Similarity in AES spectra of different oxides indicates that the difference in the desorption rates of different oxides cannot be attributed to the difference in chemical environment. Linear increase of void coverage with the square of... 

    Formation of Silicon Nanoparticles From Porous Silicon for LED Application

    , M.Sc. Thesis Sharif University of Technology Moeini Rizi, Mansoure (Author) ; Taghavinia, Nima (Supervisor)
    Semiconductor nanocrystals act as a good luminescent layer in new coming electroluminescence devices. Research on luminescent devices based on nanocrystals such as silicon nanoparticles, has been progressed over the last decades. In this research, silicon nanoparticles have been synthesized from porous silicon layer that was created through an electrochemical process. The effective luminescent parameters like electrolyte contents, current density and reaction time have been investigated. The maximum luminescence has been captured when the current density and reaction time were adjusted at 30 and 20 min, respectively. In addition, volume ratio Ethanol:HF 14:8 was another modified... 

    Comparison between electron-beam and chemical crosslinking of silicone rubber

    , Article Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms ; Volume 243, Issue 2 , 2006 , Pages 354-358 ; 0168583X (ISSN) Frounchi, M ; Dadbin, S ; Panahinia, F ; Sharif University of Technology
    Silicone rubber (SR) was irradiated by electron beam over a dose range of 50-300 kGy in the absence of chemical reagents. Molecular weight between crosslinks (Mc) in the network of SB was determined by two methods of solvent swelling and modulus of elasticity. The network structure of the elastomer crosslinked by electron beam irradiation and chemical vulcanization was compared. Mechanical tests were performed to determine shore hardness, tensile elongation, strength and modulus of the samples. It was found that SR is effectively crosslinked by electron beam irradiation. The tensile strength, hardness, modulus and elongation of irradiated SR were higher than peroxide-crosslinked SR. The... 

    Study and production of silicone rubber and polyethylene alloy

    , Article Journal of Thermoplastic Composite Materials ; Volume 24, Issue 5 , 2011 , Pages 669-677 ; 08927057 (ISSN) Tavakkoli, H ; Meibod, M. P ; Frounchi, M ; Dadbin, S ; Sharif University of Technology
    Linear silicone rubber and polyethylene alloy produced from extrusion-injecting process will be present in separate phases. While samples are mixed with 1% dicumylperoxide, DCP, and injected in extruder, an alloy is almost formed. In addition, when the samples containing silicon rubber with vinyl group are mixed with polyethylene and passed in the vicinity of electron beam, a similar reaction occurs, as confirmed from FTIR spectrum. The water contact angles for the samples has been listed in the article. Furthermore, the crystallinity of samples produced via electron beam method is more than that obtained from peroxide method. On the other hand, the tensile strengths of produced samples via... 

    CVD synthesis of small-diameter single-walled carbon nanotubes on silicon

    , Article Scientia Iranica ; Volume 16, Issue 1 D , 2009 , Pages 61-64 ; 10263098 (ISSN) Arjmandi, N ; Sasanpour, P ; Rashidian, B ; Sharif University of Technology
    A simple process for the chemical vapor deposition of ultra SD single-wall carbon nanotubes has been developed. In this process, an iron nitrate nonahydrate solution in isopropyl alcohol with a concentration of (400 μgr/milt) was used to catalyst nanoparticle formation on an oxidized silicon wafer. The oxide on the substrate was made of a thick layer of wet oxide sandwiched between two thin layers of dry oxide. The process results in semiconducting Single-Walled carbon Nano Tubes (SWNTs) with diameters of less than 0.7 nm and more than a 1 ev band gap energy, which are amongst the smallest diameters of SWNTs ever reported. © Sharif University of Technology, June 2009  

    Roduction of Solar Grade Silicon by Thermal Refining of Industrial Grade Silicon

    , M.Sc. Thesis Sharif University of Technology Fazlali, Reza (Author) ; Yoozbashizadeh, Hossein (Supervisor)
    The photovoltaic (PV) industry is in rapid growth and a large supply of PV feedstock materials must be provided to maintain this growth. Since silicon is still the dominant material for the fabrication of solar cells, low-cost solar-grade silicon (SoG-Si) feedstock is demanded. The most cost-effective and direct approach for producing SoG-Si is to purify and upgrade metallurgical-grade silicon. The major impurities in silicon are Al, Fe and Ca. other impurities present are Cu, Ti , Zn, Ni, Cr, Mn, Cd, B and P. In this study The effects of the acid leaching process parameters, including the particle size of silicon, the acid type (HCl, HNO3, H2SO4, and their combination), tmepreture and the... 

    Multi-scale modeling of edge effect on band gap offset in polygonal cross-section Silicon nanowires

    , Article Computational Materials Science ; Volume 79 , 2013 , Pages 262-275 ; 09270256 (ISSN) Khoei, A. R ; Dormohammadi, H ; Aramoon, A ; Sharif University of Technology
    The band gap offset is an effect of coordination numbers (CNs) of atom reduction at the edge of transversal cross-section of Silicon nanowires (SiNWs). In this paper, a hierarchical multi-scale technique is developed to model the edge effect on the band gap shift of SiNWs since the geometric effect is dominant in the energy gap due to the appearance of strain in the self-equilibrium state. The multi-scale model is performed based on the molecular dynamics approach and finite element method for the micro- (atomistic) and macro-scale levels, respectively. The Cauchy-Born (CB) hypothesis is used to relate the atomic positions to the continuum field through the deformation gradient. Finally, the... 

    Leveraging dark silicon to optimize networks-on-chip topology

    , Article Journal of Supercomputing ; Volume 71, Issue 9 , 2015 , Pages 3549-3566 ; 09208542 (ISSN) Modarressi, M ; Sarbazi-Azad, H ; Sharif University of Technology
    Kluwer Academic Publishers  2015
    This paper presents a reconfigurable network-on-chip (NoC) for many-core chip multiprocessors (CMPs) in the dark silicon era, where a considerable part of high-end chips cannot be powered up due to the power and bandwidth walls. Core specialization, which trades off the cheaper silicon area with energy-efficiency, is a promising solution to the dark silicon challenge. This approach integrates a selection of many diverse application-specific cores into a single many-core chip. Each application then activates those cores that best match its processing requirements. Since active cores may not always form a contiguous active region in the chip, such a partially active many-core CMP requires some... 

    Significant crosstalk reduction using all-dielectric CMOS-compatible metamaterials

    , Article IEEE Photonics Technology Letters ; Volume 28, Issue 24 , 2016 , Pages 2787-2790 ; 10411135 (ISSN) Khavasi, A ; Chrostowski, L ; Lu, Z ; Bojko, R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    A recent computational result suggests that highly confined modes can be realized by all-dielectric metamaterials. This substantially decreases crosstalk between dielectric waveguides, paving the way for high-density photonic circuits. Here, we experimentally demonstrate, on a standard silicon-on-insulator platform, that using a simple metamaterial between two silicon strip waveguides results in about a tenfold increase in coupling length. The proposed structure may lead to significant reduction in the size of devices in silicon photonics  

    Molten salt synthesis of a SiC coating on graphite flakes for application in refractory castables

    , Article Ceramics International ; 2016 ; 02728842 (ISSN) Masoudifar, S ; Bavand Vandchali, M ; Golestani Fard, F ; Nemati, A ; Sharif University of Technology
    Elsevier Ltd 
    A silicon carbide coating was formed on the surface of graphite flakes by reaction of molten Si with carbon at 1100-1300. °C in a 95%KCl-5%NaF molten salt under Ar atmosphere. The effect of temperature and Si/graphite ratio in the initial mixture on the quality and the amount of SiC were investigated by XRD and SEM/EDS analyses. Also, the water wettability, oxidation resistance and zeta potential of un-coated and coated graphite were examined by TGA analysis and sedimentation test. The results show the amount of coating to increase in the coated flakes with increasing temperature and Si/graphite ratio. The SiC coating improves water wettability of graphite and acts as a protective layer to... 

    Efficient mapping of applications for future chip-multiprocessors in dark silicon era

    , Article ACM Transactions on Design Automation of Electronic Systems ; Volume 22, Issue 4 , 2017 ; 10844309 (ISSN) Hoveida, M ; Aghaaliakbari, F ; Bashizade, R ; Arjomand, M ; Sarbazi Azad, H ; Sharif University of Technology
    The failure of Dennard scaling has led to the utilization wall that is the source of dark silicon and limits the percentage of a chip that can actively switch within a given power budget. To address this issue, a structure is needed to guarantee the limited power budget along with providing sufficient flexibility and performance for different applications with various communication requirements. In this article, we present a generalpurpose platform for future many-core Chip-Multiprocessors (CMPs) that benefits from the advantages of clustering, Network-on-Chip (NoC) resource sharing among cores, and power gating the unused components of clusters. We also propose two task mapping methods for... 

    A novel organic–inorganic hybrid tandem solar cell with inverted structure

    , Article Applied Physics A: Materials Science and Processing ; Volume 123, Issue 4 , 2017 ; 09478396 (ISSN) Bahrami, A ; Faez, R ; Sharif University of Technology
    Springer Verlag  2017
    A novel organic–inorganic hybrid tandem solar cell with inverted structure is proposed. This efficient double-junction hybrid tandem solar cell consists of a single-junction hydrogenated amorphous silicon (a-Si:H) subcell with n-i-p structure as front cell and a P3HT:PCBM organic subcell with inverted structure as back cell. In order to optimize the hybrid tandem cell, we have performed a simulation based on transfer matrix method. We have compared the characteristics of this novel structure with a conventional structure. As a result, a power conversion efficiency (PCE) of 6.1 and 24% improvement compared to the conventional hybrid tandem cell was achieved. We also discuss the high potential... 

    Effects of tool rake angle and tool nose radius on surface quality of ultraprecision diamond-turned porous silicon

    , Article Journal of Manufacturing Processes ; Volume 37 , 2019 , Pages 321-331 ; 15266125 (ISSN) Heidari, M ; Akbari, J ; Yan, J ; Sharif University of Technology
    Elsevier Ltd  2019
    This paper presents an investigation of the effects of tool rake angle and nose radius on the surface quality of ultraprecision diamond-turned porous silicon. The results showed that as rake angle decreases, the high-stress field induced by the tool edge increases, causing microcracks to propagate extensively near the pore walls. As a result, the ductile-machined areas shrank under a negative tool rake angle. On the other hand, brittle fracture occurred around pores released cutting pressure significantly. These trends of rake angle effects are distinctly different from those in the cutting of non-porous silicon. Finite element simulation of stress in the cutting area agreed with the... 

    Mechanics of carbon-coated silicon nanowire via second strain gradient theory

    , Article European Journal of Mechanics, A/Solids ; Volume 81 , 2020 Ojaghnezhad, F ; Shodja, H. M ; Sharif University of Technology
    Elsevier Ltd  2020
    The phenomena of surface, interface, and size effects are the determinative factors in the prediction of the mechanical behavior of multiphase nanowires. The interatomic bond lengths and charge density distribution associated with the surface and interface layers of the relaxed configuration of such nanostructures, in the absence of any external loadings, differ from those of the bulk remarkably. Second strain gradient theory due to its competency in capturing the above mentioned effects will be employed to examine the relaxation of carbon-coated silicon nanowire, carbon nanoshell, and silicon nanowire. Using this theory their effective Young's modulus will also be estimated. To this end,... 

    Evaluation of the topographical surface changes of silicon wafers after annealing and plasma cleaning

    , Article Silicon ; Volume 12, Issue 11 , 2020 , Pages 2563-2570 Stach, S ; Ţălu, Ş ; Dallaev, R ; Arman, A ; Sobola, D ; Salerno, M ; Sharif University of Technology
    Springer Science+Business Media B.V  2020
    Purpose: The morphological stability of silicon single crystal wafers was investigated, after performing cleaning surface treatments based on moderate temperature annealing and plasma sputtering. Methods: The wafer surfaces were measured by Tapping mode atomic force microscopy in air, before and after the different treatments. The 3D images were segmented by watershed algorithm identifying the local peaks, and the stereometric parameters were extracted thereof. The analysis of variance allowed to better assess the statistically significant differences. Results: All the resulting quantities were critically discussed. It appeared that the different cleaning treatments affected differently the... 

    Microbeam analysis of lateral inhomogeneity in depth penetration of Pd in porous silicon

    , Article Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms ; Volume 266, Issue 8 , 2008 , Pages 1507-1510 ; 0168583X (ISSN) Torkiha, M ; Lamehi Rachti, M ; Agha Aligol, D ; Razi, F ; Sharif University of Technology
    Porous silicon (PS) is widely utilized in gas sensors. Palladium is a good choice to sensitize the surface of PS to hydrogen. Ideally for highest sensitivity of the sensor, all the pores of PS should be completely covered with palladium. Rutherford backscattering spectroscopy (RBS) technique is routinely used to determine depth profile of elements in thin layers. By using microbeam analysis as a complementary technique, we clearly observed the lateral image of penetrated Pd in depth. In this work, we used electrochemically anodized-silicon wafer doped with Pd by the electroless process. In our analysis, we intentionally characterized both the area of PS where Electric Field is applied during... 

    Effects of HfB2 addition on pressureless sintering behavior and microstructure of ZrB2-SiC composites

    , Article International Journal of Refractory Metals and Hard Materials ; Volume 94 , 2021 ; 02634368 (ISSN) Jafari, S ; Bavand Vandchali, M ; Mashhadi, M ; Nemati, A ; Sharif University of Technology
    Elsevier Ltd  2021
    In this study the effects of HfB2 addition were investigated on the sintering behavior, densification and microstructure of ZrB2-SiC in the presence of B4C and MoSi2 as a sintering catalyst. 5, 10, 15 and 20 wt% of HfB2 was substituted with ZrB2 in ultra-high temperature ceramic composites of ZrB2-SiC. Additionally, the effect of using nano-scale against common micron size SiC was compared. All compositions were sintered for 1 h in 2100 °C and 2150 °C. Relative and bulk density and open porosity percentage of samples were calculated by Archimedes method. Dimensional changes of pellets and their weight reduction after pyrolysis and sintering proved that increasing of HfB2 leads to increasing... 

    Modeling vibrational behavior of silicon nanowires using accelerated molecular dynamics simulations

    , Article Scientia Iranica ; Volume 27, Issue 2 , 2021 , Pages 819-827 ; 10263098 (ISSN) Nejat Pishkenari, H ; Delafrouz, P ; Sharif University of Technology
    Sharif University of Technology  2021
    The classical methods utilized for modeling nano-scale systems are not practical because of the enlarged surface e ects that appear at small dimensions. Contrarily, implementing more accurate methods is followed by prolonged computations as these methods are highly dependent on quantum and atomistic models, and they can be employed for very small sizes in brief time periods. In order to speed up the Molecular Dynamics (MD) simulations of the silicon structures, Coarse-Graining (CG) models are put forward in this research. The procedure involves establishing a map between the main structure's atoms and the beads comprising the CG model and modifying the parameters of the system so that the...