Search for: as-doping
Total 233 records
An Investigation on Photocatalytic Properties of Sol-Gel Produced TiO2-SiO2-Ni Nanocomposite Coatings, M.Sc. Thesis Sharif University of Technology ; Ghorbani, Mohammad
Titania is one of the photocatalytic materials , but low quantum yield and relatively high band gap of TiO2 limited its applications.There are several ways to improve the photocatalytic properties of this material relied on narrowing the band gap,by doping TiO2 with other metals and oxides or increasing its specific surface area.In this work ,TiO2-SiO2-Ni coating have been made by sol-gel process and deposited on quartz substrate by using of dip-coating method .Effect of increasing Nickel content in nanocomposite and primary sol on crystalline structure,morphol ogy, photocatalytic properties and specific surface area have been investigated by means of X-Ray diffraction method, FT-IR, SEM,...
Novel synthesis route for preparation of porous nitrogen-doped carbons from lignocellulosic wastes for high performance supercapacitors, Article Journal of Alloys and Compounds ; Volume 827 , 2020 ; Abdolmaleki, H ; Doroudian, M ; Hosseini, S. H ; Sharif University of Technology
Elsevier Ltd 2020
Porous nitrogen-doped carbons derived from biomass wastes are considered as promising materials for energy storage devices. Herein, a novel and scalable synthesis route for preparation of these materials from sugarcane bagasse waste is demonstrated. The synthesis process includes a hydrogel intermediate in which delignified bagasse and polyacrylamide networks are interlaced in molecular scale and calcium acetate serves as a hard template within the polymeric chains. After pre-carbonization and chemical activation of the hydrogel, porous nitrogen-doped carbon with high surface area of 1834.3 m2 g−1 and considerable pore volume of 1.03 cm3 g−1 was obtained with nitrogen and oxygen contents of...
M.Sc. Thesis Sharif University of Technology ; Akhavan, Mohammad
Synthesis and Investigation of Effect of Pr Doping on the Compound Y_(3-x) 〖Pr〗_x 〖Ba〗_5 〖Cu〗_8 O_(19-δ)-FInvestigation of doping of the parent compounds with different elements is important to understand the origin of high-Tc superconductivity. Several research groups have attempted to improve the properties of superconductivity and better understand the superconductivity mechanism of cuprate through doping different elements. In this research, at first, optimization of Y_3 〖Ba〗_5 〖Cu〗_8 O_(19-δ) F_z samples with z=0.2 ,0.4 ,0.6 ,0.8 ,1 ,2 ,3 ,4 have been done. By doping fluorine instead of oxygen, we expected an increase in the transition temperature, based on some the reports. But after...
Article Oriental Journal of Chemistry ; Volume 33, Issue 1 , 2017 , Pages 329-334 ; 0970020X (ISSN) ; Gholami, M. R ; Boshra, A ; Sharif University of Technology
Oriental Scientific Publishing Company 2017
The doping reaction of boron nitride and carbon nanotubes with aluminium atom was theoretically investigated. ONIOM method and PM6 method have been used to evaluate the thermochemistry of doping reactions of single walled boron nitride nanotubes and carbon nanotubes. The enthalpy changes, Gibbs free energy changes, of studied doping reactions were evaluated at different temperatures. All nanotubes were single-walled and finite length with hydrogen saturation in the terminal atoms. The thermodynamic calculations based on the ONIOM and PM6 levels results showed (8,0)CNT is the best candidate for Al-doping reaction.result suggest the aluminum doped boron nitride nanotubes and carbon nanotubes...
Article Physica Status Solidi C: Conferences ; Volume 1, Issue 7 , 2004 , Pages 1883-1886 ; 16101634 (ISSN) ; Akhavan, M ; Sharif University of Technology
The magnetoresistance of single phase polycrystalline Gd(Ba 2-xPrx)Cu3O7-δ samples have been studied within thermally activated flux creep model. The decrease of pinning energy with applied magnetic field can be scaled to two power law relations for magnetic fields, smaller and also larger than about 1 kOe. The derived pinning energy shows that the Pr-doping, similar to weak links, decreases the vortex flux pinning energy. It is also concluded that the substitution of Pr at Ba site has a more destructive effect on the flux dynamics than Pr at rare earth site. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Article Physica B: Condensed Matter ; Volume 336, Issue 3-4 , 2003 , Pages 410-419 ; 09214526 (ISSN) ; Akhavan, M ; Sharif University of Technology
The Gd(Ba2-xPrx)Cu3O7+δ single phase polycrystalline samples with 0.00 ≤ x < 1.00 were investigated for pseudogap phenomenon in comparison with the (Gd1-xPrx)Ba2Cu3O7-δ compound. The measured XRD and its Rietveld refinement show that Pr is substituted at Ba site, with its stoichiometric order, and an orthorhombic-tetragonal transition occurs at x = 0.20. For x ≥ 0.60, the solubility limit of the system exceeds. Based on the resistivity measurements, the effect of Pr substitution in 123 structure of HTSC at Gd or Ba site is to increase the pseudogap temperature Ts, although, Pr at Ba site has a stronger effect on the suppression of Ts and superconductivity. Pr-doping not only reduces the...
Article Bulletin of Materials Science ; Volume 26, Issue 1 , 2003 , Pages 105-107 ; 02504707 (ISSN) ; Chen, Z ; Kawazoe, Y ; Sharif University of Technology
Indian Academy of Sciences 2003
Effect of doping of carbon nanotubes by magnetic transition metal atoms has been considered in this paper. In the case of semiconducting tubes, it was found that the system has zero magnetization, whereas in metallic tubes the valence electrons of the tube screen the magnetization of the dopants: the coupling to the tube is usually antiferromagnetic (except for Cr)
Article Materials Letters ; Volume 65, Issue 5 , March , 2011 , Pages 840-842 ; 0167577X (ISSN) ; Aminzare, M ; Molaei, R ; Sadrnezhaad, S. K ; Sharif University of Technology
Simple synthesis of silver doped TiO2 nanostructured layers by micro arc oxidation process is reported for the first time. The layers consisted of anatase and rutile phases whose characteristic XRD-peaks shifted toward lower diffraction angles when compared to the pure micro arc oxidized TiO 2 layers. Silver-doping was confirmed by XPS technique. The anatase phase crystalline size was determined as 27.6 and 21.8 nm for the layers grown under the voltages of 350 and 500 V. Employing a UV-Vis spectrophotometer, a red shift in the absorption edge of the layers was observed when silver was incorporated into the titania lattice
Article Physica C: Superconductivity and its Applications ; Volume 470, Issue 5-6 , 2010 , Pages 309-312 ; 09214534 (ISSN) ; Manivannan, N ; Kim, K. H ; Daadmehr, V ; Akhavan, M ; Sharif University of Technology
In order to study the Hall effect in pure and CNT-doped Y-123 polycrystalline samples, we have measured the longitudinal and transverse voltages at different magnetic field (0 - 9 T) in the normal and vortex states. In the normal state, the Hall coefficient is positive and decreases with increasing temperature, and can be approximately fitted to RH = a + bT-1. We have found a sign reversal in the pure sample for the magnetic field of about 3 T, and double sign reversal of the Hall coefficient in the 0.7 wt% CNT-doped sample at about 3 and 5 T. The Hall resistivity in our samples depends on the pinning
M.Sc. Thesis Sharif University of Technology ; Baghalha, Morteza ; Ahmadpour, Ali ; Khorashe, Farhad
due to high mineralization rate of Zinc oxide، chemical and physical stability, non-toxicity and low price as the most promising photocatalysts studied, although its use is not too satisfactory. Because of the wide energy gap(3.2 ev) and for photocatalytic activity needs to UV light Unfortunately, the solar spectrum is made up only 5-7% of UV light, while 46-47% is the spectrum of visible light and infrared. Doped zinc oxide nanoparticles with metal and non-metallic atoms could increase the photocatalytic properties under visible light irradiation. In this research, nanoparticles of zinc oxide was doped by fluorine as Dopant. The results showed that photocatalytic activity of the modified...
Preparation and characterization of nanostructured TiO2thin film codoped with nitrogen and vanadium on glass surface by sol–gel dip-coating method, Article Research on Chemical Intermediates ; 2014 ; ISSN: 09226168 ; Sani, M. A. F ; Sharif University of Technology
To enhance hydrophilicity and photocatalytic activity, N-doped and N–V-codoped TiO2films were coated on glass substrates by the sol–gel dip-coating method. The substrates were previously coated with SiO2using the same method. The coated samples, after annealing at 450 °C for 30 min in air, were analyzed by an X-ray diffractometer, scanning electron microscope, Fourier transform infrared spectroscope, X-ray photoelectron spectroscope, and UV–visible spectroscope. The SiO2/N–V-codoped TiO2photocatalyst showed a narrower band gap (2.93 eV) compared to the SiO2/N-doped. Degradation tests, methyl orange under UV light and stearic acid under visible light, were performed in order to evaluate...
Optical bistability in fiber ring resonator containing an erbium doped fiber amplifier and quantum dot doped fiber saturable absorber, Article Applied Optics ; Volume 51, Issue 29 , 2012 , Pages 7016-7024 ; 1559128X (ISSN) ; Farshemi, S. S ; Sajjad, B ; Shahshahani, F ; Bahrampour, A. R ; Sharif University of Technology
In this paper we study the optical bistability in a double coupler fiber ring resonator which consists of an erbium doped fiber amplifier (EDFA) in half part of the fiber ring and a quantum dot doped fiber (QDF) saturable absorber in the other half. The bistability is provided by the QDF section of the ring resonator. The EDFA is employed to reduce the switching power. The transmitted and reflected bistability characteristics are investigated. It is shown that the switching power for this new bistable device is less than 10 mW
Article Photonics North 2009, Laval, QC, 24 May 2009 through 27 May 2009 ; Volume 7386 , 2009 ; 0277786X (ISSN) ; 9780819476685 (ISBN) ; Bahrampour, A. R ; Quebec Photonic Network; Institut National d'Optique (INO); Canadian Photonics Consortium (CPC); Universite Laval, Centre for Optics, Photonics and Lasers; Ontario Photonics Industry Network (OPIN) ; Sharif University of Technology
An Erbium-doped silica CROW can be employed as a band pass and band stop amplifier in telecommunication systems. Also it can be proposed as wide band amplifier as well as narrow band amplifier. We investigate theoretically and simulate structure of Erbium-doped CROW (EDC) with different parameters to realize its performance and possible applications as an amplifier. In this paper we try to consider effect of different parameters on gain spectrum of systems. © 2009 SPIE
Article Physica C: Superconductivity and its Applications ; Volume 466, Issue 1-2 , 2007 , Pages 157-162 ; 09214534 (ISSN) ; Javanmard, H ; Akhavan, M ; Sharif University of Technology
The bulk samples of GdBa2Cu3-xCrxO7-δ with x = 0-0.3 have been prepared by the conventional solid-state reaction method. Structural phases were determined by powder X-ray diffraction. The XRD and the unit cell parameters were obtained through Rietveld refinement of the XRD data. By increasing the doping, the c parameter decreases and the a parameter increases, and by the nearly fixed b parameter, the orthorhombic phase approaches to the tetragonal phase. The resistivity measurements show a strong effect of doping on suppression of Tc. At the first doping step of x = 0.05, Tc decreases abruptly to 57 K, but by increasing the doping, this rate slows down and becomes nearly linear for higher...
Article Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers ; Volume 44, Issue 11 , 2005 , Pages 7934-7942 ; 00214922 (ISSN) ; Akhavan, M ; Sharif University of Technology
Solid-state-reacted polycrystalline Nd(Ba2-xPr x)Cu3O7+8 materials have been prepared and investigated using X-ray diffraction and resistivity measurements. Our results show that Nd(Ba2-xPrx)Cu3O7+8 is a superconductor when x < 0.3. The Tc depression in superconductivity of Pr at Ba sites is due to both hole filling/localization and depairing effects. The normal state conductivity undergoes a dimensional crossover from two-dimensional to three-dimensional in the frame of the variable range hopping regime. The localization length of carriers shows that Pr doping localizes carriers in the normal state and causes the Tc depression. The magnetoresistance of the samples has been investigated...
M.Sc. Thesis Sharif University of Technology ; Dolati, Abolghasem
Antimony Doped tin oxide as a conductive film has found a wide range of applications and sol-gel method has so advantageous with respect to another methods for preparing ATO thin films. In this study, ATO thin film has been synthesized using a solution containing metal salts of tin chloride and antimony chloride. The microstructure of the obtained films was studied by applying scanning electron microscopy (SEM) and X-ray diffraction patterns (XRD). In diffraction patterns of the acquired ATO layers which was deposited from a sol containing SnCl4.5H2O and SnCl2.2H2O with Sb concentration of 15%mol and layers which was deposited from a sol containing SnCl4.5H2O with Sb concentration of 15%mol...
M.Sc. Thesis Sharif University of Technology ; Nemati, Ali
The main purpose of this research was simultaneous doping of carbon and nickel in the structure of barium strontium titanate, in order to investigate its dielectric and optical properties. Powders and films of BST, was synthesized by the sol-gel method in six different compositions: without any dopant, 0.04mol nickel dopant, 0.04mol nickel dopant accompanied by different amounts of carbon (0.01, 0.02, 0.03 and 0.04 mol). Suspensions were dip coated on alumina and quartz substrates. Structural features and chemical bonds, were studied through thermal analysis, XRD, FT-IR, FESEM and AFM. For electrical and optical properties, LCR-meter and UV-Vis were used. XRD and FESEM proved that nickel...
M.Sc. Thesis Sharif University of Technology ; Moshfegh, Alireza
ZnO is a wide and direct band gap (3.37 eV) semiconducting material with a large exciton binding energy (60 meV). It has been extensively studied in the last few years owing to its potential applications in various fields such as surface acoustic wave devices (SAW), transparent electrode, solar cell windows, photovoltaic devices, gas sensors and photoelectrochemical cells. Recently, much attention has been paid to rare-earth (RE) doped ZnO for possible applications in visible emitting phosphors in displays, high power lasers, and other optoelectronic devices. In this thesis, initially ZnO thin films were deposited on glass and ITO substrates using sol-gel dip-coating method. Optical and...
Effect of content silver and heat treatment temperature on morphological, optical, and electrical properties of ITO films by sol-gel technique, Article Journal of Nanoparticle Research ; Volume 16, Issue 9 , September , 2014 ; ISSN: 13880764 ; Dolati, A ; Sharif University of Technology
Silver-doped indium tin oxide thin films were synthesized using sol-gel dip-coating technique. The influence of different silver-dopant contents and annealing temperature on the electrical, optical, structural, and morphological properties of the films were characterized by means of four-point probe, UV-Vis spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscope (XPS). XRD analysis confirmed the formation of cubic bixbyte structure of In2O3with silver nanoparticles annealed at 350 °C. XPS analysis showed that divalent tin transformed to tetravalent tin through oxidization, and silver nanoparticles embedded into ITO...
Article Materials Letters ; Volume 65, Issue 19-20 , October , 2011 , Pages 3086-3088 ; 0167577X (ISSN) ; Ahadi, K ; Nemati, A ; Sharif University of Technology
Electrical conductivities in dark and light were investigated in Calcium doped Bismuth Ferrite thin films. Higher dark conductivity, in the order of 10 times higher than conductivity of bismuth ferrite, was observed for Bi 0.85Ca0.15FeO3 - δ. Structural analyses using Rietveld refinement showed a deviation from volume reduction for Bi 0.85Ca0.15FeO3 - δ which could be the reason of abnormally high conductivity for this compound. Although higher calcium doping reduced conductivity, photoconductivity was observed again. Atomic Force Microscopy investigations showed that surface roughness and grain size decreased with increasing calcium concentration. Enhanced photoconductivity is reported for...