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    Geometry selects highly designable structures

    , Article Journal of Chemical Physics, Woodbury, NY, United States ; Volume 113, Issue 15 , 2000 , Pages 6437-6442 ; 00219606 (ISSN) Shahrezaei, V ; Ejtehadi, M. R ; Sharif University of Technology
    American Inst of Physics  2000
    The designability of structures in a two-dimensional hydrophobic-polar (HP) pair contact lattice model in a wide range of intermonomer interaction parameters was studied by considering HP constraints. The designability of all structures was clarified by enumerating all sequences of length 20. Results confirm that changing the intermolecular interactions affects the structure designability and also chooses the search space of the native state but the set of HDSs is invariant  

    Synthesize of Graphene Nanoribbons with a Non-Zero Energy Band Gap for Inactivation of Alive Cells Using Infrared Irradiation

    , M.Sc. Thesis Sharif University of Technology Emamy, Hamed (Author) ; Akhavan, Omid (Supervisor)
    Graphene is a one layer atom thickness and zero energy gap so for using it in nano electronic and transistors baised on graphene it's energy gap should be opened.one of the methods for opening graphene band gap is creating nano scale boundaries or synthesize graphene nanoribbons. One of the new methods for graphene nanoribbon synthesize is longitudinal opening of carbon nanotube. In this thesis graphene nanoribbons synthesize with this method and analyze with AFM and Raman spectroscopy. Carbon nanotubes also have energy gap and IR absorption recently they used for living cell destruction. In this thesis we synthesize graphene nanoribbons and analyzing their optical absorption and use it for... 

    Synthesis of Doped Titania Nanotube Arrays by Anodizing of Titanium and Surveying of their band Gap

    , M.Sc. Thesis Sharif University of Technology Meftahi, Mohammad (Author) ; Ghorbani, Mohammad (Supervisor)
    In recent decade, photocatalystic properties of titania nanotube and its mechanisms has been considered greatly in many researches. One of the major ways to increase photocatalystic properties and extending the usage of TNTs is doping them with various elements and modifying their band structure. In present research doped TNTs were prepared by doping of Molybdenum, Nitrogen, and Carbon elements by anodizing method in about of 35 degrees of centigrade and constant voltage of 20V on the surface of titanium sheet. Structural and photocatalystic properties of as-prepared TNTs were studied using field emission scanning electron microscope (FESEM), x-ray diffraction (XRD), energy dispersive... 

    Photocatalytic Degradation of Dye in Wastewater Using Nanomaterials Based Zinc-iron

    , M.Sc. Thesis Sharif University of Technology Rezaei, Salar (Author) ; Kazemeini, Mohammad (Supervisor) ; Mahmudi, Niaz Mohammad (Co-Supervisor) ; Baqalha, Morteza (Co-Supervisor)
    Removing pollutants of water and, in general, wastewater treatment is one of the most important issues in the world. In this research, we synthesized a nanophotocatalyst based on znic-iron in the form of a magnetic core-shell Fe3O4@ZIF-8, and used to degrade the malachite green toxic color of wastewater. SEM, XRD and FT-IR analyzes have been taken and analyzed fore all three core, shell and core-shell composite catalysts.Due to the band gap of core-shell nanocomposite and the performance of the malachite green dye, a photocatalytic process under the visible light was obtained, which at an optimum amount of photocatalyst 0.003g, we reach 99.2% dye degradation at the 30ppm concentration. This... 

    sp 2/sp 3 bonding ratio dependence of the band-gap in graphene oxide

    , Article European Physical Journal B ; Volume 92, Issue 4 , 2019 ; 14346028 (ISSN) Akbari, E ; Akbari, I ; Ebrahimi, M. R ; Sharif University of Technology
    Springer Heidelberg  2019
    Abstract: Although the band-gap in pure graphene is zero, the oxygenated graphene could have a considerable band-gap. The D/G peak intensity ratio is known as a measure of the size of sp3∕sp2 domains in graphene oxide (GO) sheets and determines the band-gap in GO sheets. Characterization results showed that the photoluminescence (PL) spectra of GO suspensions has a peak at ~604 nm and also the I(D)/I(G) intensity ratio of GO suspensions is 1.73. After reduction, a redshift appeared at PL spectrum (at 650 nm) and the I(D)/I(G) intensity ratio decrease to 1.26. Our results showed that the band-gap in GO is related to the I(D)/I(G) intensity ratio of GO suspensions and offers a mechanism for... 

    The importance of electron correlation in graphene and hydrogenated graphene

    , Article European Physical Journal B ; Volume 88, Issue 10 , October , 2015 ; 14346028 (ISSN) Hadipour, H ; Jafari, S. A ; Sharif University of Technology
    springer berlin  2015
    Local density approximation (LDA) and Green function effective Coulomb (GW) calculations are performed to investigate the effect of electronic correlations on the electronic properties of both graphene and graphane. The size of band gap in graphane increases from 3.7 eV in LDA to 4.9 eV in GW approximation. By calculating maximally localized Wannier wave functions, we evaluate the necessary integrals to get the Hubbard U and the exchange J interaction from first principles for both graphene and graphane. Our ab-initio estimates indicate that in the case of graphene, in addition to the hopping amplitude t ∼ 2.8 eV giving rise to the Dirac nature of low lying excitations, the Hubbard U value... 

    The effect of nanocrystalline tungsten oxide concentration on surface properties of dip-coated hydrophilic WO3-SiO2 thin films

    , Article Journal of Physics D: Applied Physics ; Volume 40, Issue 7 , 2007 , Pages 2089-2095 ; 00223727 (ISSN) Naseri, N ; Azimirad, R ; Akhavan, O ; Moshfegh, A. Z ; Sharif University of Technology
    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.... 

    Effect of mono-vacant defects on the opto-electronic properties of ionic liquid functionalized hexagonal boron-nitride nanosheets

    , Article Journal of Molecular Liquids ; Volume 249 , 2018 , Pages 1172-1182 ; 01677322 (ISSN) Shakourian Fard, M ; Bayat, A ; Kamath, G ; Sharif University of Technology
    We compare and contrast the physisorption behavior of imidazolium and butyltrimethylammonium based ionic liquids (ILs) on mono-vacant nitrogen and boron defective hexagonal boron nitride nanoflakes (h-BNNF) using M06-2X/cc-pVDZ level of theory. The presence of defects on the nanoflakes results in an increase in IL binding energy by ~ 1–27 kcal/mol partly due to the lowering of the energy band in the defective nanoflakes. Imidazolium based ILs adsorb energetically more favorably on h-BNNF-VB than on h-BNNF-VN while butyltrimethylammonium based ILs prefer to adsorb on h-BNNF-VN. Upon adsorption of imidazolium ILs on the nanoflakes, an increase in both HOMO and LUMO orbital energies is observed... 

    Design of Graphene Spintronic Devices

    , M.Sc. Thesis Sharif University of Technology Barami, Soode (Author) ; Faez, Rahim (Supervisor)
    Magnetization have an important role in spintronic devices based on graphene. In this study the effect of stone-wales and vacancy defect on electrical and magnetic properties of zigzag and armchair graphene nanoribbons were investigated. Calculations are performed using tight-binding and hubard model combining with Green's function techniques. When the balance between A and B sub-lattices gets disturbed, magnetization will be appeared. In stone-wales defect we have local magnetization because of changing the position of sub-lattices and the total magnetization is zero. In addition the stone-wales defect can change and modify the band structures and band gaps. Vacancy of carbon atom in... 

    Solvothermal synthesis of CuMS2 (M=A1, In, Fe) nanoparticles and effect of coordinating solvent on the crystalline structure

    , Article Scientia Iranica ; Volume 21, Issue 6 , 2014 , Pages 2468-2478 ; ISSN: 10263098 Vahidshad, Y ; Ghasemzadeh, R ; Zad, A. I ; Mirkazemi, S. M ; Masoud, A ; Sharif University of Technology
    CuMS2 (M=A1, In, Fe) ternary compounds were synthesized via the facile polyol method in autoclave. Depending on the functional groups of solvent and surfactant, the structure of the nanocrystals can be controlled in the form of wurtzite or chalcopyrite. The chalcopyrite structure was obtained when the precursors solved in the mixture of diethylene glycol, polyethylene glycol 600 and ammonium hydroxide. When the solvent was replaced by ethylene diamine, the wurtzite was obtained along with chalcopyrite (polytypism). The products were characterized by X-Ray Diffraction (XRD) for analysis of structural properties, Transmission Electron Microscopy (TEM) for studying morphological... 

    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... 

    Semi-conducting carbon nanotube as variable capacitor

    , Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 54 , 2013 , Pages 9-14 ; 13869477 (ISSN) Ozmaian, M ; Naghdabadi, R ; Sharif University of Technology
    This paper proposes a novel, one-part, variable capacitor, using semi-conducting carbon nanotube (CNT). This variable capacitor works based on the change in the electronic structure of CNTs under applied voltage and deformations. Positive and negative charges are stored at both ends of a non-zero band gap nanotube which works as metallic electrodes in parallel plate capacitors. Also the neutral strip in the middle acts as the dielectric part of a conventional capacitor under the influence of an external electric field. Mechanical strains on carbon nanotube change its band gap energy and thus the length of neutral strip and charged regions. The lengths of these parts are primarily dependent... 

    Effect of simultaneous chemical substitution of A and B sites on the electronic structure of BiFeO3 films grown on BaTiO 3/SiO2/Si substrate

    , Article Journal of Materials Science: Materials in Electronics ; Volume 24, Issue 6 , 2013 , Pages 2128-2134 ; 09574522 (ISSN) Ahadi, K ; Nemati, A ; Mahdavi, S. M ; Vaezi, A ; Sharif University of Technology
    Electrical properties and electronic structure of Bi1-xCa xFe1-yMnyO3-δ grown by pulsed-laser deposition on BaTiO3/SiO2/Si substrate were investigated. Results showed that Ca has drastic effect on symmetry of crystal and electrical poperties of BiFeO3. On the other hand, Mn revealed to have more radical effect on optical properties and energy gap of the compound. XPS results represented that although Ca tend to decrease Fe valence state, Mn tends to stabilize it at 3+ (at least in this concentrations). UV-visible study yielded bandgap of 2.51-2.81 eV (at 300 K) for different concentrations of Ca and Mn. UV-visible spectra also revealed sub-bandgap defect transitions at 2.2 and 2.4 eV.... 

    Effect of iron oxide and silica doping on microstructure, bandgap and photocatalytic properties of titania by water-in-oil microemulsion technique

    , Article Transactions of the Indian Ceramic Society ; Volume 70, Issue 4 , Jan , 2011 , Pages 227-232 ; 0371750X (ISSN) Karbassi, M ; Nemati, A ; Zari, M. H ; Ahadi, K ; Sharif University of Technology
    The microemulsion method was successfully used to prepare a series of TiO2, Fe oxide and SiO2 doped TiO2 nanoparticles at Fe/Ti atomic ratio of 10% and Si/Ti atomic ratio of 15%. The molar ratio of water to surfactant (W0) was 2. The samples were calcinated at 350°C. The structural features of TiO2, Fe oxide and SiO 2-TiO2 were investigated by XRD, UV-Visible spectroscopy, SEM and TEM. XRD data verified the formation of typical characteristic anatase form in all the prepared Fe and SiO2-doped TiO2 samples. In comparison with the pure TiO2, Fe oxide and SiO 2-TiO2 samples were relatively large in particle size, indicating that doping with Fe oxide and SiO2 can help in increasing the particle... 

    Quantum phase transitions in the Kondo-necklace model: Perturbative continuous unitary transformation approach

    , Article Journal of Physics Condensed Matter ; Volume 27, Issue 15 , March , 2015 ; 09538984 (ISSN) Hemmatiyan, S ; Rahimi Movassagh, M ; Ghassemi, N ; Kargarian, M ; Rezakhani, A. T ; Langari, A ; Sharif University of Technology
    Institute of Physics Publishing  2015
    The Kondo-necklace model can describe magnetic low-energy limit of strongly correlated heavy fermion materials. There exist multiple energy scales in this model corresponding to each phase of the system. Here, we study quantum phase transition between the Kondo-singlet phase and the antiferromagnetic long-range ordered phase, and show the effect of anisotropies in terms of quantum information properties and vanishing energy gap. We employ the 'perturbative continuous unitary transformations' approach to calculate the energy gap and spin-spin correlations for the model in the thermodynamic limit of one, two, and three spatial dimensions as well as for spin ladders. In particular, we show that... 

    Synthesis and characterization of electrochemically grown CdSe nanowires with enhanced photoconductivity

    , Article Journal of Materials Science: Materials in Electronics ; Volume 26, Issue 3 , March , 2015 , Pages 1395-1402 ; 09574522 (ISSN) Kalhori, H ; Irajizad, A ; Azarian, A ; Ashiri, R ; Sharif University of Technology
    Springer New York LLC  2015
    CdSe nanowires were grown in polycarbonate track etched membrane with pore diameter of 80 nm by an electrochemical deposition technique. The mechanism of the growth was studied during the potentiostatic deposition of nanowires. X-ray photoelectron spectroscopy and energy dispersive spectrometry results showed binding of fragments and fraction of atoms for the CdSe nanowires. Microstructure and morphology of synthesized CdSe nanowires were observed by scanning electron microscopy. Optical spectrophotometry technique was used to determine the energy band gap of CdSe nanowires. It was found that the nanowires were resistive in the dark and exhibited a pronounced visible light photoconductivity.... 

    Effects of processing conditions on the physico-chemical characteristics of titanium dioxide ultra-thin films deposited by DC magnetron sputtering

    , Article Ceramics International ; Volume 41, Issue 6 , July , 2015 , Pages 7977-7981 ; 02728842 (ISSN) Rezazadeh Sefideh, M ; Sadeghian, Z ; Nemati, A ; Mohammadi, S. P ; Mozafari, M ; Sharif University of Technology
    Elsevier Ltd  2015
    In this research, titanium dioxide (TiO2) ultra-thin films have been successfully obtained on lamina-glass substrates by thermal oxidation of DC magnetron sputtered titanium. The as-deposited and the annealed films have been characterized by different techniques. The X-ray diffraction (XRD) results revealed the amorphous structure of as-deposited titanium and anatase crystal structure for the annealed films. The atomic force microscopy (AFM) results showed that increasing the annealing temperature could lead to rougher and larger grain size in the films. Finally, the optical data and band-gap calculations of the films were obtained using the transmittance spectrum, indicating that... 

    Electrochemical determination of CdS band edges and semiconducting parameters

    , Article Bulletin of the Chemical Society of Japan ; Volume 88, Issue 6 , February , 2015 , Pages 814-820 ; 00092673 (ISSN) Miandari, S ; Jafarian, M ; Mahjani, M. G ; Gobal, F ; Heidaripour, A ; Sharif University of Technology
    Chemical Society of Japan  2015
    Cadmium sulfide (CdS) thin film was electrodeposited on indium tin oxide (ITO) by chronoamperometry. The SEM images showed that hexagonal sheets of CdS deposited on the ITO surface. The X-ray diffraction (XRD) analysis confirmed this structure for CdS crystals and the average of crystalline size and the lattice constant parameters are approximately 39.54 and a = 0.4136, c = 0.6696 nm respectively. Photo-electrochemical investigations were performed by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) techniques. CdS band edges and density of states (DOS) were determined by CV technique. The band gap energy (Ebg) was measured... 

    analytical calculation of energy levels of mono- and bilayer graphene quantum dots used as light absorber in solar cells

    , Article Applied Physics A: Materials Science and Processing ; Volume 122, Issue 1 , 2016 , Pages 1-8 ; 09478396 (ISSN) Tamandani, S ; Darvish, G ; Faez, R ; Sharif University of Technology
    Springer Verlag  2016
    In this paper by solving Dirac equation, we present an analytical solution to calculate energy levels and wave functions of mono- and bilayer graphene quantum dots. By supposing circular quantum dots, we solve Dirac equation and obtain energy levels and band gap with relations in a new closed and practical form. The energy levels are correlated with a radial quantum number and radius of quantum dots. In addition to monolayer quantum dots, AA- and AB-stacked bilayer quantum dots are investigated and their energy levels and band gap are calculated as well. Also, we analyze the influence of the quantum dots size on their energy spectrum. It can be observed that the band gap decreases as quantum... 

    Optical absorption and electronic spectra of chlorophylls a and b

    , Article RSC Advances ; Volume 6, Issue 111 , 2016 , Pages 109778-109785 ; 20462069 (ISSN) Hedayatifar, L ; Irani, E ; Mazarei, M ; Rasti, S ; Azar, Y. T ; Rezakhani, A. T ; Mashaghi, A ; Shayeganfar, F ; Anvari, M ; Heydari, T ; Tabar, A. R ; Nafari, N ; Vesaghi, M. A ; Asgari, R ; Rahimi Tabar, M. R ; Sharif University of Technology
    Royal Society of Chemistry  2016
    Photosynthesis includes capturing sunlight by an assembly of molecules, called chlorophylls, and directing the harvested energy in the form of electronic excitations to the reaction center. Here we report, using real-space density functional theory and time-dependent density functional theory together with GW calculations, the optical and electronic properties of the two main chlorophylls in green plants, namely, chlorophylls a and b. Furthermore, we estimate the dipole and primitive quadrupole electric moments of these molecules. We employ Casida's assignment ansatz to study the absorption spectra of the chlorophylls in the two main red and blue regions at various environments with...