Study on structure and properties of transition metal doped BiF3 by first-principles

Structure and physical properties of BiF₃ doped with M=Cr, Cu, Fe, Mn, Ni, Ti, V and Co are calculated by the DFT+U method. Effect of metal doping on the electronic structure and optical response of host materials BiF₃ is investigated systematically. New energy levels are formed and located within the band gap, which could decrease the recombination rate of e⁻/h⁺ pairs. Furthermore, transition metal doping extends the optical absorption of BiF₃ to the visible spectral region.     

Effect of Mg doping on the electrical properties of SnO2 nanoparticles

Sol-gel derived Mg doped tin oxide (Sn_1−xMg_xO₂) nanocrystals were synthesized with x ranging between 0.5 and 7 at. %. Characteristic single phase tetragonal structure of pure and doped samples was obtained and doping saturation was inferred by X-ray diffraction analysis. Structural, morphological and phase informations were obtained by high resolution transmission electron microscope, field emission scanning electron microscope and X-ray photoelectron spectroscopy respectively whereas bonding information was obtained from Fourier transformed infrared spectroscopy. Measurement of different electrical parameters with frequency (200 Hz-10⁵ Hz) has been carried out at room temperature. Ultrahigh dielectric constant and metallic AC conductivity were observed for undoped tin oxide and the profiles reflected highly sensitive changes in the atomic and interfacial polarizability generated by doping concentrations. Relaxation spectra of tangent loss of any sample did not show any loss peak within the frequency range. Both the grain and grain boundary contributions are observed to increase as the doping concentration increased. Results of first principle calculation based on density functional theory indicated effective Fermi level (E_F) suppression due to Mg doping which is responsible for the experimentally observed conductivity variation. AC conductivity was found to depend strongly on the doping concentration and the defect chemistry of the compound. Mg doped SnO₂ may find applications as a low loss dielectric and high density energy storage material.     

The randomly fluctuating impurity strength initiated excitation in doped quantum dots

We investigate the excitation behavior of a repulsive impurity doped quantum dot under the influence of randomly fluctuating dopant potential. We have considered Gaussian impurity centers doped at different locations. The investigation reveals the interplay between dopant location and dopant’s spatial stretch in modulating the excitation pattern. Maximization in the excitation rate has been observed as a function of fluctuating dopant strength owing to the conflict between opposing influences that promote and hinder excitation.     

Electroluminescence properties of In-doped Zn2SiO4 thin films prepared by sol–gel process

The effect of In doping on the electroluminescence (EL) properties of Zn₂SiO₄:In thin films was investigated. In-doped Zn₂SiO₄ thin films were deposited on BaTiO₃ substrates and their EL properties were characterized in this study. X-ray powder diffraction patterns of In-doped Zn₂SiO₄ powders revealed a single phase of Zn₂SiO₄ for In concentrations up to approximately 1.5 mol%, whereas a secondary phase of In₂O₃ was observed for In concentrations in the range of 2–10 mol%. The maximum luminance of thin film electroluminescent (TFEL) devices varied significantly with the amount of In doping. The highest luminance with blue emission was obtained when 2 mol% In was doped. The blue emission of In-doped Zn₂SiO₄ thin film may be related to the In substitution for Zn. The 2 mol% In-doped Zn₂SiO₄ thin film exhibited blue emission with CIE color coordinates of x=0.208 and y=0.086.     

Mn site substitution of La0.67Ca0.33MnO3 with closed shell ions: Effect on magnetic transition temperature

Mn site is substituted with closed shell ions (Al, Ga, Ti, Zr and a certain combination of Zr and Al) and also with Fe and Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at %. Substitution did not change either the crystal symmetry or the oxygen stoichiometry. All substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures (T _p(ρ) and T _C, respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising due to difference in the ionic radii between the substituent (r _M) and the Mn³⁺ ion (r _Mn ³⁺) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and that of the neighboring Mn ion.     

Combinatorial synthesis and characterization of a ternary epitaxial film of Co and Mn doped Ge (0 0 1)

We report combinatorial molecular beam epitaxy synthesis and properties of a ternary epitaxial film of Co and Mn co-doped Ge grown on Ge (0 0 1) substrate. Structural effects were examined in situ by reflection high-energy electron diffraction and ex situ by microbeam X-ray diffraction techniques, and magnetic properties were probed by using magnetooptic Kerr effect. Ternary epitaxial phase diagrams have been studied for total doping concentrations up to 30 at.%, where regions of coherent epitaxy and rough disordered growth and those of near room temperature ferromagnetic ordering have been identified.     

Influence of tungsten doping concentration on the electronic and optical properties of anatase TiO2

The structural, electronic and optical properties of tungsten-doped TiO₂ have been investigated using density functional theory with plane wave basis sets and ultrasoft pseuodopotential. Substitutional W doping at Ti sites create W 5d states just below the conduction band minimum while interstitial W doping gives isolated W 5d states in the middle of forbidden region. Averaged bond lengths show that W doping at Ti sites produce minimum structural distortion as compared to the interstitial W-doped TiO₂. Substitutional W-doped TiO₂ has better visible light absorption compared to interstitial W-doped TiO₂ and has stable configuration which provide reasonable explanation for the experimental findings. Tungsten doping in TiO₂ with different doping concentrations is investigated as an enabling concept for enhancing the visible light absorption. Optical properties show that optimal W doping concentration would improve the visible light absorption. 2.08% W doping concentration gives strong visible and ultraviolet light absorption among all doped models found consistent with experiments.     

Electric field induced non-linear multisubband electron mobility in V-shaped asymmetric double quantum well structure

ABSTRACT

We study the effect of the external electric field F_ext on the low-temperature electron mobility μ in an asymmetrically doped Al_xGa_1-xAs based V-shaped double quantum well (VDQW) structure. We show that nonlinearity of µ occurs under double subband occupancy on account of intersubband effects. The field F_ext alters the VDQW potential leading to transfer of subband wave functions between the wells, which affects the scattering potentials and hence μ. In the VDQW structure, due to the alloy channel layer, the alloy disorder (Al-) scattering happens to be significant along with the ionised impurity (Imp-) scattering. The non-linear behaviour of μ is because of μ^Imp, while the overall magnitude of μ is mostly due to μ^Al. The increase of difference in the doping concentrations of the outer barriers increases the nonlinearity of μ. The oscillatory character of μ is amended by varying the width of the well and barrier and also the height of the VDQW. Our results can be used to study VDQW based nanoscale field effect transistor structures.     

Nitrogen doping in pulsed laser deposited ZnO thin films using dense plasma focus

Pulsed laser deposition synthesized ZnO thin films, grown at 400 °C substrate temperature in different oxygen gas pressures, were irradiated with 6 shots of pulsed nitrogen ions obtained from 2.94 kJ dense plasma focus to achieve the nitrogen doping in ZnO. Structural, compositional and optical properties of as-deposited and nitrogen ion irradiated ZnO thin films were investigated to confirm the successful doping of nitrogen in irradiated samples. Spectral changes have been seen in the nitrogen irradiated ZnO thin film samples from the low temperature PL measurements. Free electron to acceptor emissions can be observed from the irradiated samples, which hints towards the successful nitrogen doping in films. Compositional analysis by X-ray photoelectron spectroscopy and corresponding shifts in binding energy core peaks of oxygen and nitrogen confirmed the successful use of plasma focus device as a novel source for nitrogen ion doping in ZnO thin films.