Search for: semiconductor-doping
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    Enhancement of Mn luminescence in ZnS:Mn multi-quantum-well structures

    , Article Applied Physics Letters ; Volume 83, Issue 22 , 2003 , Pages 4616-4618 ; 00036951 (ISSN) Taghavinia, N ; Makino, H ; Yao, T ; Sharif University of Technology
    The efficiency of Mn luminescence is enhanced in low-thickness ZnS:Mn layers. While various hypotheses can be considered to explain the phenomenon, it seems more reasonable to consider the luminescence enhancement effect a result of the formation of dot-like regions with higher local Mn concentration  

    Normal state conduction in Gd(Ba2-xPrx)Cu 3O7+δ

    , Article European Physical Journal B ; Volume 33, Issue 4 , 2003 , Pages 381-390 ; 14346028 (ISSN) Mohammadizadeh, M. R ; Akhavan, M ; Sharif University of Technology
    The normal state resistivity of single phase polycrystalline Gd(Ba 2-x Pr x )Cu3O7+δ samples with 0.0 ≤ x ≤ 0.50 have been investigated. There is a distinct metal-insulator transition at xMITc = 0.2 and a superconductor-insulator transition at xSITc = 0.35 with the increase of x. The two-dimensional variable range hopping is dominant in the normal state resistivity of the samples. The localization length, hopping range, and hopping energy of carriers show that Pr doping strongly localizes the carriers in normal state, and finally causes the suppression of superconductivity. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2003  

    Enhanced inter-plane coupling of Mg doped Cu0.5Tl0.5Ba2Ca2- xMgxCu3O10-δ superconductors: XPS and FTIR studies

    , Article Physica C: Superconductivity and its Applications ; Volume 468, Issue 5 , 2008 , Pages 405-410 ; 09214534 (ISSN) Khurram, A. A ; Khan, N. A ; Ahadian, M. M ; Iraji zad, A ; Sharif University of Technology
    A comparison of X-ray photoemission spectroscopy of Mg doped Cu0.5Tl0.5Ba2Ca1.5Mg 0.5Cu3O10-δ and Mg free Cu0.5Tl0.5Ba2Ca2Cu 3O10-δ superconductor samples have been made. The main objective of these studies is to see the effect of Mg doping in developing better inter-plane coupling among the CuO2 planes and its effects on the chemical shift of the bonding species. Through these studies it is observed that thallium is in Tl+1 oxidation state in the Cu0.5Tl0.5Ba2O4- δ charge reservoir layer in both Mg doped and Mg free samples, however, the XPS line related to Ba atoms are shifted to higher binding energy side by 0.32 eV in Mg doped sample. This chemical shift is most likely due to presence of... 

    Investigation of quantum conductance in semiconductor single-wall carbon nanotubes: Effect of strain and impurity

    , Article Journal of Applied Physics ; Volume 110, Issue 6 , 2011 ; 00218979 (ISSN) Rabiee Golgir, H ; Faez, R ; Pazoki, M ; Karamitaheri, H ; Sarvari, R ; Sharif University of Technology
    In this paper the effect of strain and impurity on the quantum conductance of semiconducting carbon nanotubes (CNTs) have been studied by ab-initio calculations. The effect of strain and impurity on the CNT conducting behavior and physical characteristics, like density of states (DOS), band structure, and atomic local density of state (LDOS), is considered and discussed separately and simultaneously. Our results show that the quantum conductance of semiconductor CNTs is increased by compression strain, elongation strain, and replacing nitrogen and boron doping in its structure. The amount of increasing in the conductance depends on the type of strain and impurity. Conductance of CNT can be... 

    Micro arc oxidation of nano-crystalline Ag-doped TiO2 semiconductors

    , Article Materials Letters ; Volume 65, Issue 5 , March , 2011 , Pages 840-842 ; 0167577X (ISSN) Bayati, M. R ; 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  

    Effect of a gap opening on the conductance of graphene superlattices

    , Article Solid State Communications ; Volume 150, Issue 13-14 , 2010 , Pages 655-659 ; 00381098 (ISSN) Esmailpour, M ; Esmailpour, A ; Asgari, R ; Elahi, M ; Rahimi Tabar, M. R ; Sharif University of Technology
    The electronic transmission and conductance of a gapped graphene superlattice were calculated by means of the transfer-matrix method. The system that we study consists of a sequence of electron-doped graphene as wells and hole-doped graphene as barriers. We show that the transmission probability approaches unity at some critical value of the gap. We also find that there is a domain around the critical gap value for which the conductance of the system attains its maximum value  

    Ag doping of organometal lead halide perovskites: morphology modification and p-type character

    , Article Journal of Physical Chemistry C ; Volume 121, Issue 7 , 2017 , Pages 3673-3679 ; 19327447 (ISSN) Shahbazi, S ; Tsai, C. M ; Narra, S ; Wang, C. Y ; Shiu, H. S ; Afshar, S ; Taghavinia, N ; Wei Guang Diau, E. ? ; Sharif University of Technology
    We report a simple synthetic approach to grow uniform CH3NH3PbI3 perovskite (PSK) layers free of pinholes via varied portions of silver iodide (AgI) added to the precursor solution. XRD/EDS elemental mapping experiments demonstrated nearly uniform Ag distribution inside the perovskite film. When the 1% AgI-assisted perovskite films were fabricated into a p-i-n planar device, the photovoltaic performance was enhanced by ∼30% (PCE increased from 9.5% to 12.0%) relative to the standard cell without added AgI. Measurement of electronic properties using a hall setup indicated that perovskite films show p-type character after Ag doping, whereas the film is n-type without Ag. Transients of... 

    Isothermal LCF behavior in aluminide diffusion coated Rene 80 near the DBTT

    , Article Materials and Design ; Volume 30, Issue 4 , 2009 , Pages 1183-1192 ; 02641275 (ISSN) Rahmani, Kh ; Nategh, S ; Sharif University of Technology
    Ni-base superalloys such as René 80 are widely used for aircraft turbine blades manufacture, due to possesses suitable mechanical, oxidation and hot corrosion properties. It is usually coated in order to increase its wear, oxidation, erosion and hot corrosion properties against environmental degradation. One the most important properties of coatings is its DBTT. In this paper the behavior of uncoated and coated (CODEP-B) René 80 has been studied near the DBTT (871 °C), R = (εmin/εmax) = 0 and strain rate of about 2 × 10-3 s-1. Experimental results show that in coated specimens while the total cyclic strain is lower than 1%, coating leaves longer fatigue life, at this condition the nucleation... 

    Size variation and optical absorption of sol-gel Ag nanoparticles doped SiO2 thin film

    , Article Thin Solid Films ; Volume 515, Issue 2 SPEC. ISS , 2006 , Pages 771-774 ; 00406090 (ISSN) Babapour, A ; Akhavan, O ; Moshfegh, A. Z ; Hosseini, A. A ; Sharif University of Technology
    Elsevier  2006
    In this research, we have focused on the formation of Ag nanoparticles dispersed in SiO2 matrix using sol-gel method. The influences of the metal concentration on the size variation of Ag nanoparticles and the size effect on the surface plasmon absorption have been studied. Sol-gel silica thin films containing Ag particles were synthesized by dip-coating on soda-lime glasses. The molar ratio of Ag / Si was chosen from 0.2% to 8%. All films were dried in air at 100 °C for 1 h. Using X-ray photoelectron spectroscopy, the Ag / Si ratios in the prepared films have been measured. In addition, it was shown that the prepared matrix was a stoichiometric composition as SiO2, and the synthesized... 

    Effect of bromine doping on the charge transfer, ion migration and stability of the single crystalline MAPb(Br: XI1- x)3photodetector

    , Article Journal of Materials Chemistry C ; Volume 9, Issue 42 , 2021 , Pages 15189-15200 ; 20507534 (ISSN) Mahapatra, A ; Prochowicz, D ; Kruszyńska, J ; Satapathi, S ; Akin, S ; Kumari, H ; Kumar, P ; Fazel, Z ; Tavakoli, M. M ; Yadav, P ; Sharif University of Technology
    Royal Society of Chemistry  2021
    Organic-inorganic halide perovskites (OIHPs) have emerged as a promising semiconductor for the fabrication of efficient optoelectronic devices such as photodetectors (PDs). Among all the perovskite compositions, the mixed-halide MAPb(BrxI1-x)3 formulations have gained more attention for photodetection application thanks to their tunable optoelectronic properties and great stability. However, there is still a lack of sufficient understanding of the effect of Br doping on the stability and physical properties of MAPb(BrxI1-x)3 based PDs. In this work, we prepare a series of MAPb(BrxI1-x)3 (x = 0, 0.04, 0.08, 0.12, and 0.16) single crystals (SCs) and investigate the influence of the Br content... 

    Synthesis and characterization of co-doped TiO2 thin films on glass-ceramic

    , Article Materials Science in Semiconductor Processing ; Vol. 26, Issue 1 , October , 2014 , pp. 41-48 ; ISSN: 13698001 Ahmadi, N ; Nemati, A ; Solati-Hashjin, M ; Sharif University of Technology
    In this research, an attempt was made to improve TiO2 photo-catalyst properties, thus pure, N-Ce co-doped TiO2 thin films were prepared on glass-ceramic substrate using a sol-gel dip-coating technique. The samples were calcinated in air at 475 °C, 550°C, and 650°C for 2 h. The result of simultaneous thermal analysis (STA) and X-ray diffraction (XRD) showed that the presence of Ce in TiO2 could inhibit the phase transformation from anatase to rutile and enhance the thermal stability, and anatase was the dominant phase in N-Ce co-doped TiO2 samples. Also based on the results, the doping results in decreasing the size of TiO 2 crystallite. The results of ultra violet-visible light diffuse... 

    Effect of chemical substitution on the morphology and optical properties of Bi1-xCaxFeO3 films grown by pulsed-laser deposition

    , Article Journal of Materials Science: Materials in Electronics ; Volume 24, Issue 1 , 2013 , Pages 248-252 ; 09574522 (ISSN) Ahadi, K ; Mahdavi, S. M ; Nemati, A ; Sharif University of Technology
    The morphological characteristics as well the optical properties of Ca-doped BiFeO3 films grown by pulsed-laser deposition technique have been investigated. AFM images revealed that calcium has a radical effect on the surface features of BiFeO3 films. By utilizing spectrophotometer, transmission behaviour of the films was investigated. Local IV characteristics of the films disclosed about three orders of magnitude enhancement concerning electrical conductivity through Ca doping. X-ray photoelectron spectroscopy results revealed that Ca can reduce the valence state of iron in the compound  

    Adsorption and solar light activity of transition-metal doped TiO 2 nanoparticles as semiconductor photocatalyst

    , Article Journal of Materials Science: Materials in Electronics ; Volume 23, Issue 3 , 2012 , Pages 659-667 ; 09574522 (ISSN) Khakpash, N ; Simchi, A ; Jafari, T ; Sharif University of Technology
    There is an eminent interest to improve the photoactivity of TiO 2 nanostructures via doping with midband gap donors or acceptors to achieve a high solar absorption. In the present work, Cr- and V-doped TiO 2 nanoparticles were prepared via a facile chemical vapor synthesis method. The effect of the transition metals (TM) on the solar light activity of the semiconductor nanoparticles as photocatalyst was examined by degradation of methylene blue and acid red 27. Induced coupled plasma and X-ray photoelectron spectroscopy analyses indicated high efficiency of the doping process in the hot wall reactor without surface covering of the TiO 2 nanoparticles by the dopants. Diffuse reflectance... 

    Effect of Y2O3 and Er2O3 co-dopants on phase stabilization of bismuth oxide

    , Article Ceramics International ; Volume 37, Issue 8 , 2011 , Pages 3451-3455 ; 02728842 (ISSN) Arasteh, S ; Maghsoudipour, A ; Alizadeh, M ; Nemati, A ; Sharif University of Technology
    Bi2O3 compositions were prepared to investigate the effect of rare earth metal oxides as co-dopants on phase stability of bismuth oxide. Compositions containing 9-14 mol% of Y2O3 and Er2O3 were synthesized by solid state reaction. The structural characterization was carried out using X-ray powder diffraction. The XRD results show that the samples containing 12 and 14 mol% total dopants had cubic structure, whereas the samples with lower dopant concentrations were tetragonal. Comparing the lattice parameters of the cubic phases of (Bi 2O3)0.88(Y2O3) 0.06(Er2O3)0.06 and (Bi 2O3)0.86(Y2O3) 0.07(Er2O3)0.07 revealed that lattice parameter decreases by increasing the dopant concentration. The XRD... 

    Investigation of dark and light conductivities in calcium doped bismuth ferrite thin films

    , Article Materials Letters ; Volume 65, Issue 19-20 , October , 2011 , Pages 3086-3088 ; 0167577X (ISSN) Kianinia, M ; 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... 

    Recent progress on doped ZnO nanostructures for visible-light photocatalysis

    , Article Thin Solid Films ; Volume 605 , April , 2015 , Pages 2–19 ; 00406090 (ISSN) Samadi, M ; Zirak, M ; Naseri, A ; Khorashadizade, E ; Moshfegh, A. Z ; Sharif University of Technology
    Elsevier  2015
    Global environmental pollution and energy supply demand have been regarded as important concerns in recent years. Metal oxide semiconductor photocatalysts is a promising approach to apply environmental remediation as well as fuel generation from water splitting and carbon dioxide reduction. ZnO nanostructures have been shown promising photocatalytic activities due to their non-toxic, inexpensive, and highly efficient nature. However, its wide band gap hinders photo-excitation for practical photocatalytic applications under solar light as an abundant, clean and safe energy source. To overcome this barrier, many strategies have been developed in the last decade to apply ZnO nanostructured... 

    Impact of preparation method of TiO2-RGO nanocomposite photoanodes on the performance of dye-sensitized solar cells

    , Article Electrochimica Acta ; Volume 219 , 2016 , Pages 38-48 ; 00134686 (ISSN) Nouri, E ; Mohammadi, M. R ; Lianos, P ; Sharif University of Technology
    Elsevier Ltd  2016
    In this work, a comparative study has been performed on two ex-situ and one in-situ doping of titania photoanodes with reduced graphene oxide. The presence of finely dispersed reduced graphene oxide facilitates electron transport and reduces electron-hole recombination resulting in a better performance of doped titania photoanodes. It was found that in-situ doping, i.e. introduction of graphene oxide in solution together with titania precursor was the most performant case of graphene doping. This result was obvious by studying dye-sensitized solar cells based on such doped photoanodes but was also and mainly analytically demonstrated by subjecting the obtained materials to characterization... 

    Improved performance of low cost CuInS2 superstrate-type solar cells using Zinc assisted spray pyrolysis processing

    , Article Journal of Physics D: Applied Physics ; Volume 50, Issue 48 , 2017 ; 00223727 (ISSN) Cheshme Khavar, A. H ; Mahjoub, A. R ; Taghavinia, N ; Sharif University of Technology
    Superstrate configuration CuInS2 (CIS) solar cells are fabricated using a spray pyrolysis method. We avoided selenization process, cyanide etching and CdS buffer layer, to keep the process 'green'. CIS layers are formed by spray pyrolysis of an aqueous precursor ink containing metal chloride salts and thiourea at 350 °C. We investigated the effect of intentional Zn doping on structural, morphological and photovoltaic response of the fabricated CIS films by dissolving ZnCl2 in aqueous precursor solution. At a zinc doping level ranging between 0.25 and 1.00 mol%, Zn doping is found to improve the CIS crystal growth and surface morphology of CIS films. Compared with the performance of the... 

    Low-temperature solution-based processing to 7.24% efficient superstrate CuInS2 solar cells

    , Article Solar Energy ; Volume 157 , 2017 , Pages 581-586 ; 0038092X (ISSN) Cheshme Khavar, A.H ; Mahjoub, A. R ; Taghavinia, N ; Sharif University of Technology
    Elsevier Ltd  2017
    The fabrication of high performance, solution-processed CIGS family solar cells is based on high-temperature crystallization processes in chalcogen-containing atmosphere and/or using dangerous solvents like hydrazine. The non-hydrazine sulfurization- and selenization-free reports typically suffer from poor grain structures. We report a facile strategy to overcome grain growth limitations at very low temperature processing (250 °C). Selenium free Superstrate configuration CuInS2 (CIS) solar cells are fabricated using a nanocrystals ink which avoiding from high temperature selenization or/and sulfurization is targeted. We investigated the effect of intentional M doping (M = Sb, Zn, Cd and Sn)... 

    Role of nitrogen doping at the surface of titanium nitride thin films towards capacitive charge storage enhancement

    , Article Journal of Power Sources ; Volume 359 , 2017 , Pages 349-354 ; 03787753 (ISSN) Achour, A ; Chaker, M ; Achour, H ; Arman, A ; Islam, M ; Mardani, M ; Boujtita, M ; Le Brizoual, L ; Djouadi, M. A ; Brousse, T ; Sharif University of Technology
    We recently reported an impressive cycling stability (over 20,000 cycles) of titanium nitride (TiN) electrodes with high specific capacitance. It is anticipated that nitrogen (β−N) doping in the oxidized surface of TiN film plays a crucial role in charge storage mechanism and stability of this material. In this work, we offer an evidence on the effect of β−N doping on improvement in specific capacitance of vacuum annealed TiN thin films. The annealing of the TiN films leads to the diffusion of the excess β−N from sub-surface to oxidized TiN film surface without further oxidation of the electrode surface. We demonstrate an increase in the TiN areal capacitance upon an increase in the amount...