Papers by Keyword: Doping Effect

Abstract: The objective of the present work is the study the Ni concentration effect on the optical, structural and electrical properties of ZnO:Ni thin films deposited by pneumatic spray pyrolysis method. Un-doped and Ni-doped ZnO thin films were prepared from zinc acetate dihydrate and nickel chloride hexahydrate dissolved in distilled water onto glass substrates by pneumatic spray pyrolysis method. Solution concentration, substrate temperature and nozzle-substrate distance were kept constant during all deposition processes. Effect of nickel content on the optical, structural and electrical properties of as-prepared films obtained was investigated by UV–Vis-NIR spectrophotometry, X-ray diffraction and four-point probe technique. The results indicate that the deposited films are well adherent to the substrates, present surface roughness and have a preferential growth in the (002) direction. The observed transmittance in the visible region was situated between 60% and 70%. For Ni-doped ZnO, there are two separate phases. The Urbach energy, grain size, and electrical conductivity increase with Ni content. The same behavior for both the optical energy gap and the ZnO:Ni lattice parameters.

Abstract: We have developed a combined approach of metaheuristic optimization algorithms (MOA), such as the genetic algorithm, with an ab-initio materials simulation engine. Concurrent run of the ab-initio calculations with each different parameter set selected by the MOA searches the optimum condition within a given input-parameter space. Using this methodology, the optimum dopant and its position/structure at a graphene edge are found to be a multiple N-atoms doping at graphitic sites, which predicts to lead to better charging/discharging performance when it is used as an anode material of Li-ion battery.

Abstract: CdSe thin films doped with 10% of Indium and 10 % Zinc were prepared by electron beam evaporation technique and the films were annealed at 200 oC for 30 min. Well crystalline films were deposited and the crystallite variation was studied for doping effect and it was found to be about 48 and 52 nm respectively. Optical band gap values are found to be modified by doping as well as annealing. PEC solar cells were fabricated using CdSe:In and CdSe:Zn films which showed 1.54% and 1.88% conversion efficiency respectively. Annealed films showed considerable influence in the optoelctronic properties and its improvement in conversion efficiency to about 2.75% and 2.87% respectively. In order to increase the photo output the films were annealed at 200o C at temperature. The photo output was Voc = 0.476 V, Jsc = 9.8 mA cm^-2, ff = 0.44, η = 2.76 % at 80 mW cm^-2 . Photoetching increased the output parameters.

Abstract: Simulation of arsenic clustering in Si at a temperature of 750 degrees Celsius has been carried out. It has been shown that considering the formation of singly or doubly negatively charged clusters that incorporate one or two arsenic atoms and point defects, one obtains a good fit to the measured values of electron density. It is supposed that we have the initial stage of clustering, when the concentration of complexes with one arsenic atom incorporated is high enough and the diffusion of these mobile particles provides for the formation of more stable clusters incorporating two arsenic atoms.

Abstract: Detailed investigations of nonstoichiometry as well as chemical and self-diffusion in nickel oxide have shown that doubly ionised cation vacancies and electron holes are the predominant defects in this material. The present work is an attempt to demonstrate that aliovalent impurities (Cr, Al, Na and Li) may considerably influence the concentration of these defects and, consequently, the oxidation rate of nickel at high temperatures. It has been shown that small amounts of tri-valent impurities (Cr, Al) bring about an increase of the oxidation rate, while mono-valent ones (Li, Na) decrease the rate of oxidation. These phenomena may satisfactorily be explained in terms of a doping effect. All experiments have been carried out as a function of temperature (1373-1673 K) and oxygen pressure (1-105 Pa) and consequently, it was possible to determine the influence of impurities not only on the oxidation rate but also on the activation energy of reaction and its pressure dependence. The results of these investigations could again be elucidated in terms of doping effect.

Abstract: The Te doped NbSe2-xTex (x=0, 0.10, 0.20) single crystals were prepared by vapor transport method and the variations of structure and superconducting properties with Te content were studied. It is found that the Te substitution increases the degree of disorder and causes sharp decrease of superconducting transition temperature (Tc). The temperature dependence of upper critical field (Hc2) of pure NbSe2 crystal can be fitted by the two-band model, and the effect of Te substitution on Hc2(T) is discussed.

Abstract: Using the first-principles self-consistent discrete variational method based upon density functional theory, we investigated the energetics and the electronic structure of the 3d impurities Ni and Co in a kink on the [100](010) edge dislocation (ED) in bcc iron. The calculated results show that the interatomic energies between the impurity atom and the neighboring host atoms decrease. The bonding for the impurity atom (Ni, Co) and the neighboring host Fe atoms is weaker than that for an Fe atom at the X site and the corresponding atoms in the clean kink. These results indicate that sideways motion of the kink in the <100>{010} ED is accelerated by an impurity atom such as Ni or Co and that, consequently, the presence of impurities increases the dislocation mobility, thus leading to solid-solution softening.

Abstract: Doping effects of Sr and/or Mg on the crystal structures of LaGaO3 perovskites were investigated. The doping with Mg into Ga-site in LaGaO3 led to structural change from the orthorhombic primitive lattice (Pbnm) to the orthorhombic body-centered lattice (Ibmm) at room temperature. The orthorhombic cell (Ibmm) of LaGa0.9Mg0.1O2.95 changed to the monoclinic (I2/a) by doping with Sr into La site. Neutron powder diffraction analyses revealed that these compounds had GaO6 octahedral tilt. The GaO6 octahedral tilt angles were reduced with doping with Sr and/or Mg.

Abstract: A series of Pb(Ti1-xAlx)O3, Pb(Ti1-xNbx)O3 and Pb(Ti1-xAlx/2Nbx/2)O3 thin films were fabricated onto Pt/Ti/SiO2/Si(100) substrates using a chemical solution deposition process. The dielectric constant of the Pb(Ti1-xAlx)O3 thin films increased with increase of aluminum content, while a maximum dielectric constant value was observed for the Pb(Ti1-xNbx)O3 and Pb(Ti1 xAlx/2Nbx/2)O3 thin films when the doping contents were 10 and 20 mol%, respectively. The dielectric constant of the Pb(Ti0.8Al0.1Nb0.1)O3 thin film is about 600, being two times higher than those of Pb(Ti0.9Al0.1)O3 and Pb(Ti0.9Nb0.1)O3 thin films. The Pb(Ti0.8Al0.1Nb0.1)O3 thin film showed less than 10-7 A/cm2 current density at ±150 kV/cm, being superior to the leakage property of the PbTiO3, Pb(Ti0.9Al0.1)O3 and Pb(Ti0.9Nb0.1)O3 thin films. The co-doping of aluminum and niobium is more effective to increase the dielectric and ferroelectric properties as compared with the individual aluminum or niobium doping.