Search for: nitrides
0.006 seconds
Total 123 records

    Diffraction analysis of extraction efficiency for photonic crystal based white light emitting diodes

    , Article CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, Munich, 14 June 2009 through 19 June 2009 ; 2009 ; 9781424440801 (ISBN) Khoshnegar, M ; Sodagar, M ; Eftekharian, A ; Khorasani, S ; Sharif University of Technology

    Resonant optical absorption and defect control in Ta3N 5 photoanodes

    , Article Applied Physics Letters ; Volume 102, Issue 3 , 2013 ; 00036951 (ISSN) Dabirian, A ; Van De Krol, R ; Sharif University of Technology
    In this study, we explore resonance-enhanced optical absorption in Ta 3N5 photoanodes for water splitting. By using a reflecting Pt back-contact and appropriate Ta3N5 film thickness, the resonance frequency can be tuned to energies just above the bandgap, where the optical absorption is normally weak. The resonance results in a significant improvement in the photoanode's incident photon-to-current efficiency. The Ta3N5 films are made by high-temperature nitridation of Ta2O5. The nitridation time is found to be critical, as extended nitridation result in the formation of nitrogen vacancies through thermal reduction. These insights give important clues for the development of efficient... 

    Plasma surface functionalization of boron nitride nano-sheets

    , Article Diamond and Related Materials ; Volume 77 , 2017 , Pages 110-115 ; 09259635 (ISSN) Achour, H ; Achour, A ; Solaymani, S ; Islam, M ; Vizireanu, S ; Arman, A ; Ahmadpourian, A ; Dinescu, G ; Sharif University of Technology
    Elsevier Ltd  2017
    On silicon substrates, boron nitride nanosheets (BNNS) consisting of interconnected hexagonal boron nitride nano-layers were produced via chemical vapor deposition process at 1200 °C whose roughness's are at the micrometer- and nanometer-scale. The BNNS were functionalized in argon plasma admixed with ammonia or nitrogen or oxygen. The samples were characterized to investigate the surface chemistry and structural changes after plasma treatment using X-ray photoelectron spectroscope and Micro-Raman spectroscope techniques, respectively. While no significant changes in the surface features, upon plasma treatments of the BNNS, were noticed during SEM and TEM examination, the oxygen functional... 

    Graphitic carbon nitride (g-C3N4)-based photocatalysts for solar hydrogen generation: Recent advances and future development directions

    , Article Journal of Materials Chemistry A ; Volume 5, Issue 45 , 2017 , Pages 23406-23433 ; 20507488 (ISSN) Naseri, A ; Samadi, M ; Pourjavadi, A ; Moshfegh, A. Z ; Ramakrishna, S ; Sharif University of Technology
    Royal Society of Chemistry  2017
    Graphitic carbon nitride (g-C3N4) is a metal-free conjugated polymer constructed from two-dimensional sheets with a bandgap energy of 2.7 eV, which makes it an applicable and efficient visible-active photocatalyst for H2 production. In the present study, the basic concepts and principles of photocatalytic water splitting have been discussed, and a guide for the selection of appropriate photocatalysts, focusing on the g-C3N4 nanomaterials, has been proposed. Our approach is mainly concentrated on evaluating two factors, namely the solar-to-hydrogen (STH) conversion and apparent quantum yield (AQY) for different photocatalysts, to provide an in-depth analysis and a framework for solar H2... 

    Adsorption of pollutant cations from their aqueous solutions on graphitic carbon nitride explored by density functional theory

    , Article Journal of Molecular Liquids ; Volume 260 , 15 June , 2018 , Pages 423-435 ; 01677322 (ISSN) Safdari, F ; Shamkhali, A. N ; Tafazzoli, M ; Parsafar, G ; Sharif University of Technology
    Elsevier B.V  2018
    In this study, adsorption of important pollutant cations on the surface of graphitic carbon nitride (g-C3N4) was investigated by density functional theory. The calculations indicated that N6 cavity surrounded by triazine units is the most probable adsorption site on this surface. The structural optimizations also predicted a planar surface for Cr3+, and Ni2+/g-C3N4 systems while the structure of the surface for other systems indicated a considerable distortion with strong dependency on the cation size. Also, g-C3N4 surface exhibited the high adsorption energies for Cr3+, As3+, and Sb3+ ions in the gas phase. However, formation energies of the metal-aquo complexes of these cations indicated... 

    Plasma nitriding of gradient structured AISI 304 at low temperature: Shot peening as a catalyst treatment

    , Article Vacuum ; Volume 164 , 2019 , Pages 194-197 ; 0042207X (ISSN) Unal, O ; Maleki, E ; Varol, R ; Sharif University of Technology
    Elsevier Ltd  2019
    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... 

    Review - Towards the two-dimensional hexagonal boron nitride (2D h-BN) electrochemical sensing platforms

    , Article Journal of the Electrochemical Society ; Volume 167, Issue 12 , 2020 Angizi, S ; Khalaj, M ; Alem, S. A. A ; Pakdel, A ; Willander, M ; Hatamie, A ; Simchi, A ; Sharif University of Technology
    IOP Publishing Ltd  2020
    Electrochemical sensing performance of two-dimensional hexagonal boron nitride (2D h-BN) has traditionally been suppressed by their intrinsic electrical insulation and deficient electron transportation mechanism. However, the excellent electrocatalytic activity, high specific surface area, N- and B-active edges, structural defects, adjustable band gap through interaction with other nanomaterials, and chemical functionalization, makes 2D h-BN ideal for many sensing applications. Therefore, finding a pathway to modulate the electronic properties of 2D h-BN while the intrinsic characteristics are well preserved, will evolve a new generation of highly sensitive and selective electrochemical... 

    Wear-Resistant Nickel-Titanium Nitride Composite Coating by Electrochemical Method

    , M.Sc. Thesis Sharif University of Technology Parhizkar, Nafise (Author) ; Dolati, Abolghasem (Supervisor)
    Metal matrix nanocomposites contains ceramic ultrafine particles in a metal matrix, are used to improve the mechanical properties such as hardness and wear of coatings. For developing metal matrix nanocomposites, there are many methods. Electrochemical deposition process is one of these methods that have some advantages like uniform depositions on substrates with complex shapes, low cost, good repeatability and reducing waste. In this project, for increasing the hardness and wear resistance of nickel, composite coatings of nickel - titanium nitride was created by using electrochemical deposition of Watts bath contained titanium nitride particles. In order to increase the amount of... 

    Differential quadrature method for nonlocal nonlinear vibration analysis of a boron nitride nanotube using sinusoidal shear deformation theory

    , Article Mechanics of Advanced Materials and Structures ; Volume 23, Issue 11 , 2016 , Pages 1278-1283 ; 15376494 (ISSN) Sadatshojaei, E ; Sadatshojaie, A ; Fakhar, M. H ; Sharif University of Technology
    Taylor and Francis Inc  2016
    This article presents a nonlocal sinusoidal shear deformation beam theory (SDBT) for the nonlinear vibration of single-walled boron nitride nanotubes (SWBNNTs). The surrounding elastic medium is simulated based on nonlinear Pasternak foundation. Based on the nonlocal differential constitutive relations of Eringen, the equations of motion of the SWBNNTs are derived using Hamilton's principle. Differential quadrature method (DQM) for the nonlinear frequency is presented, and the obtained results are compared with those predicted by the nonlocal Timoshenko beam theory (TBT). The effects of nonlocal parameter, vibrational modes, length, and elastic medium on the nonlinear frequency of SWBNNTs... 

    As-cast mechanical properties of vanadium/niobium microalloyed steels

    , Article Materials Science and Engineering A ; Volume 486, Issue 1-2 , 2008 , Pages 1-7 ; 09215093 (ISSN) Najafi, H ; Rassizadehghani, J ; Asgari, S ; Sharif University of Technology
    Tensile and room temperature Charpy V-notch impact tests along with microstructural studies were used to evaluate the variations in the as-cast mechanical properties of low-carbon steels with and without vanadium and niobium. Tensile test results indicate that good combinations of strength and ductility can be achieved by microalloying additions. While the yield strength and UTS increase up to respectively 370-380 and 540-580 MPa in the microalloyed heats, their total elongation range from 20 to 25%. TEM studies revealed that random and interphase fine-scale microalloy precipitates play a major role in the strengthening of the microalloyed heats. On the other hand, microalloying additions... 

    Preparation of New Titanium Nitride-Carbon Nanocomposites and Evaluation of their Electrocatalytic Behavior

    , Ph.D. Dissertation Sharif University of Technology Yousefi, Elahe (Author) ; Ghorbani, Mohammad (Supervisor) ; Dolati, Abolghasem (Supervisor)
    Titanium nitride-carbon nanocomposites are synthesized by the reaction of TiCl4 and NaN3 in supercritical benzene medium that also serves as a carbon source. In order to improve the crystallinity of the as-prepared precursor (SI), it is further heat-treated at 1000 ˚C for 3-10 h using anhydrous ammonia and UHP nitrogen atmospheres at 1000 ˚C (SIII-SV). Moreover, to improve electrochemical behavior, the synthesized nanocomposite (SIV) is modified with Pt nanoparticles using a polyol process. For better understanding of synthesized catalyst nature and justifying their variant ORR activity several analyses are done. X-ray diffraction (XRD), Raman spectrum, field emission scanning electron... 

    Synthesis and Study of Photocatalytic Properties of g-C3N4/TiO2 Nanocomposite

    , M.Sc. Thesis Sharif University of Technology Abtahi, Mohammad (Author) ; Sadrnezhaad, Khatiboleslam (Supervisor)
    In this research, synthesis and characterization of photocatalytic properties of g-C3N4 / TiO2 nanocomposite was carried out. The target of research was to increase the photocatalytic properties of g-C3N4. So at first, g-C3N4 was synthesized from melamine precursor via thermal pyrolysis. Then, TiO2 nanoparticles were synthesized via sol – gel method. g-C3N4 / TiO2 nanocomposite with heterojunction structure was synthesized in one step by thermal pyrolysis of certain amounts of melamine precursor and TiO2 nanoparticles mixture in 550 ℃. Characterization of synthesized samples was carried out by XRD, FT-IR, UV-Vis, PL, BET, DLS and FE-SEM tests. Characterization results showed that g-C3N4,... 

    The effect of gas mixture of post-oxidation on structure and corrosion behavior of plasma nitrided AISI 316 stainless steel

    , Article Applied Surface Science ; Volume 283 , 2013 , Pages 584-589 ; 01694332 (ISSN) Karimzadeh, N ; Moghaddam, E. G ; Mirjani, M ; Raeissi, K ; Sharif University of Technology
    In this research, microstructure and corrosion properties of plasma nitriding and post-oxidation treated AISI 316 austenitic stainless steel have been studied. The plasma nitriding treatment was carried out at 450 C for 5 h in a D.C. plasma setup with a gas mixture of 25% N2-75% H2 followed by post-oxidation in gas mixtures of O2/H2: 1/3, 1/5, 1/9 and 1/12 for 30 min. The treated samples were characterized by SEM, XRD and roughness testing. Potentiodynamic and cyclic polarization tests were also employed to evaluate the corrosion resistance of the samples. The results showed that plasma nitriding treatment decreases corrosion resistance of the steel substrate. However, post-oxidizing... 

    An investigation into the effect of various surface treatments on fatigue life of a tool steel

    , Article Journal of Materials Processing Technology ; Volume 174, Issue 1-3 , 2006 , Pages 318-324 ; 09240136 (ISSN) Farrahi, G. H ; Ghadbeigi, H ; Sharif University of Technology
    The effects of nitriding, nitrocarburizing and shot peening on fatigue behavior of AISI D3 cold work tool steel were investigated. Five batches of fatigue specimens were manufactured according to the ASTM E466-96 standard. All specimens were quenched and tempered to a hardness of 50 HRC. One group of specimens was shot peened with an Almen intensity of 16 A, one group was nitrocarburized, one group was gas nitrided by single stage and another group was also nitrided by double stages. Rotating-bending fatigue tests were carried out. Our results showed that nitriding and nitrocarburizing treatments did not have a beneficial effect on the fatigue resistance of D3 tool steel. Fatigue test... 

    Two-dimensional porous graphitic carbon nitride C6N7 monolayer: first-principles calculations

    , Article Applied Physics Letters ; Volume 119, Issue 14 , 2021 ; 00036951 (ISSN) Bafekry, A ; Faraji, M ; Fadlallah, M. M ; Abdolhosseini Sarsari, I ; Jappor, H. R ; Fazeli, S ; Ghergherehchi, M ; Sharif University of Technology
    American Institute of Physics Inc  2021
    The fabrication of the C6N7 monolayer [Zhao et al., Sci. Bull. 66, 1764 (2021)] motivated us to discover the optical, structural, mechanical, and electronic properties of the C6N7 monolayer by employing the density functional theory (DFT) method. We find that the shear modulus and Young's modulus of the C6N7 monolayer are smaller than the relevant values of graphene. However, Poisson's ratio is more significant than that of graphene. Applying the PBE (HSE06) functional bandgap of the C6N7 monolayer is 1.2 (1.97) eV, and the electronic dispersion is almost isotropic around the Γ point. C6N7 is more active in the ultraviolet region as compared to the visible light region. This study provides... 

    Mechanical behaviors of titanium nitride and carbide MXenes: A molecular dynamics study

    , Article Applied Surface Science ; Volume 566 , 2021 ; 01694332 (ISSN) Hatam Lee, S. M ; Esfandiar, A ; Rajabpour, A ; Sharif University of Technology
    Elsevier B.V  2021
    MXenes have recently witnessed significant evolution and advances in terms of their applications in different areas such as flexible electronics, energy storage devices, and coatings. Here, the mechanical properties of both pristine and functionalized Tin+1CnO2 and Tin+1NnO2 (n = 1, 2) are investigated utilizing classical molecular dynamics simulations. For eight different MXene structures, the stress-strain curves are calculated including Young's modulus, strength, and fracture strain. It is found that Ti2N holds the highest Young's modulus with the value of 517 GPa while Ti3C2 has the lowest one with the amount of 133 GPa. In addition, the strongest MXene structure is Ti2N while the... 

    Synthesis, Characterization and Photocatalytic Application of ZnO/g- C3N4 Composite Nanorods Fabricated by Combined Sol Gel-Hydrothermal Methods

    , M.Sc. Thesis Sharif University of Technology Soltani, Mojtaba (Author) ; Moshfegh, Alireza (Supervisor)
    Because of the working conditions of semiconductors at ambient temperature and pressure, degradation of organic pollutants through semiconductors photocatalysis has attracted the interest of many researchers. Because of its large exciton binding energy,high chemical and physical stability,high electron and hole mobility, and low cost; zinc oxide, an n-type semiconductor with 3.2 eV direct band gap, is widely used in applications such as photocatalysts, solar cells, and light-emitting diodes. Among various morphologies of ZnO, 1D nanostructures such as nanowires and nanorods have recieved much attention due to their high surface to volume ratio. However, the application of ZnO as a... 

    Manipulation of Electronic Structure in Boron Nitride Nanosheets to Improve Catalytic and Photocatalytic Properties

    , M.Sc. Thesis Sharif University of Technology Hemmati, Amir (Author) ; Simchi, Abdolreza (Supervisor)
    The variety of 2D materials and their wide range of properties, as well as numerous methods to manipulate them, have made this class of materials among prominent candidates for the future of the energy industry. Among the means available to tailor nanomaterials performance for such applications, introducing dopants and the creation of heteroatom-doped structures are of great interest. In this study, mixtures of urea, boric acid, and graphene oxide, as cheap and available precursors, were used to synthesize C-doped h-BN nanosheets. After the implementation of TGA/DSC to select a suitable calcination temperature of 950 C°, the samples were successfully synthesized with relatively precise... 

    Preparation of new titanium nitride-carbon nanocomposites in supercritical benzene and their oxygen reduction activity in alkaline medium

    , Article Electrochimica Acta ; Volume 164 , May , 2015 , Pages 114-124 ; 00134686 (ISSN) Yousefi, E ; Ghorbani, M ; Dolati, A ; Yashiro, H ; Outokesh, M ; Sharif University of Technology
    Elsevier Ltd  2015
    Titanium nitride-carbon nanocomposites are synthesized by the reaction of TiCl4 and NaN3 in supercritical benzene medium that also serves as a carbon source. The as-prepared precursors (SI, SII) are subjected to several heat treatments (SIII-SV). The synthesized nanoparticles are characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The samples are tested as electrocatalyst for oxygen reduction reaction in an alkaline electrolyte. It is shown that the electrocatalytic properties of the synthesized nanoparticles are... 

    Diffraction analysis of extraction efficiency for photonic crystal based white light emitting diodes

    , Article CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference ; 14-19 June , 2009 ; 21622701 (ISSN) ; 9781424440801 (ISBN) Khoshnegar, M ; Sodagar, M ; Eftekharian, A ; Khorasani, S ; Sharif University of Technology
    Optical Society of America  2009