Effect Of Oxygen Doping Research Articles

Oxygen induced p-doping of α-nickel phthalocyanine vacuum sublimed films: Implication for its use in organic photovoltaics

The effects of oxygen doping on the charge transport and photovoltaic properties of α-nickel phthalocyanine (α-NiPc) based devices are investigated using in situ and ex situ I–V measurements. I–V characteristics for devices employing gold contacts indicate ohmic conduction at low voltages, followed by space-charge-limited conduction in higher fields. Upon exposure of NiPc to dry air an increase in the hole concentration (p0) from 8.5×1010 to 2.6×1015 m−3 is observed. When the top gold ohmic cathode is replaced by lead, Schottky type behavior is evident with the junction exhibiting photovoltaic effect. The energy conversion efficiency of the cell increases following exposure to oxygen. These results suggest that fabrication of air stable electronic devices based on NiPc is feasible.

Quasiparticle tunneling properties of YBa 2Cu 3O 7− x bicrystals grown by liquid phase epitaxy

Transport properties and tunneling characteristics of 45° asymmetric grain boundary junctions, fabricated in YBa 2Cu 3O 7− δ films grown by liquid phase epitaxy, have been studied. For selected samples, with very low zero field critical current density, a conductance peak in the d I/d V vs V curves has been observed below T c. The position and amplitude of this peak depend on the magnetic field and temperature, indicating its superconducting origin. Strong oxygen doping effect on the gap energy was also found.

EFFECT OF OXYGEN DOPING AND HIGH PRESSURE ON THE ELECTRONIC STRUCTURE OF HgBa2CuO4+δ AND SUPERCONDUCTIVITY

The effects of oxygen doping (δ=0~0.19) and high pressure (P=0~5.07 GPa) on the electronic structure of HgBa2CuO4+δ have been studied by the recursion method. The hole concentration of the CuO2 layer increases monotonically as δ increases from 0 to 0.19. Each excess oxygen atom contributes about 1.9 holes to the CuO2 layer. The pressure-induced charge transfer, dn/dP, decreases for increasing δ, vanishing at over-doping level, which is consistent with the δ-dependence of dT c /dP observed in experiments.

Effect of Oxygen Doping on the IR Transmission and Cathodoluminescence of ZnSe

The effect of oxygen doping (0.9 and 4.3 vol % O2in the gas phase) on the transmission and cathodoluminescence of CVD ZnSe was studied. The incorporation of oxygen was found to reduce the transmission in the spectral range 700–1900 cm–1. Examination by scanning electron microscopy shows that Se excesses and high O2concentrations lead to tabular growth. ZnO precipitation at structural defects during cooling was observed only in the end portion of the deposit. The dimensions of microinhomogeneities are shown to have a significant effect on the transmission of ZnSe. The oxygen-containing species present in the deposits were identified using cathodoluminescence spectra. The CL spectrum of Se-enriched p-type ZnSe is dominated by the band at 490 nm (SAL) at 80 K and the band at 640 nm (SA) at 300 K. The 640-nm band is attributed to recharging of the SALcenters upon a variation of the Fermi energy with temperature. Decreasing the Se excess leads to the quenching of the SALemission and appearance of the shorter wavelength component of the SAband at 600 nm (80–300 K), characteristic of slightly Zn-enriched ZnSe. The intensity of the self-activated bands is shown to increase as the concentration of dissolved oxygen increases.

Crystallinity and transport properties in Bi2Sr2Ca1-xPrxCu2Oy single crystals

Bi2Sr2Ca1-xPrxCu2Oy (x ranging from0 to 0.5) single crystals have been grown by a self-flux method from Bi-richmelts. The crystals obtained manifest slim and plate-like shapes. Thecrystallinity is studied by x-ray diffraction. The x-ray θ-scanningrocking curve shows that the slim crystal has perfect crystal structure whilethe plate-like crystal is mosaic along the c-axis. The in-plane resistivityρab(T) has been measured for crystals with different Pr doping levels.Tc is suppressed gradually upon doping while the residual resistivityincreases strongly. A superconductor-insulator transition is observed whichis attributed to the tetragonal-orthorhombic phase transition when the Prcontent reaches about 0.5. The effect of oxygen doping on in-plane resistivityρab(T) is also studied for x = 0.22 and 0.40 crystals.

High-spin and charge-ordering state ofYBaCo2O5

The first-principles band calculations for the oxygen-deficient double perovskite ${\mathrm{YBaCo}}_{2}{\mathrm{O}}_{5}$ show that the Co ions see a weak crystal field and remain in a high-spin state. A ${\mathrm{Co}}^{2+}/{\mathrm{Co}}^{3+}$ charge-ordering (CO) state with a structure distortion appears at low temperature, and it exhibits a weak orbital ordering. The CO transition results in a variance of the Co spin moments, which is not ascribed to a low- to high-spin-state transition. In addition, the effect of oxygen doping is qualitatively accounted for.

Oxygen doping effects on the magnetization of Bi 2Sr 2CaCu 2O 8+δ single crystalline system in the mixed state

We present a systematic study of the oxygen overdoping effects on the dc magnetization loops of Bi 2Sr 2CaCu 2O 8+δ single crystalline samples. The overdoping is produced by high oxygen pressure (from 1 to 190 bar) annealing at 500°C. The superconducting critical temperature and the c-axis lattice parameter are used to identify the oxygen content of the samples. The dc magnetization loop measurements are performed with the applied magnetic field parallel to the c-axis of the crystals. The characteristic second peak in the magnetization is present for all the investigated oxygen contents. We show that the position of this second peak and the irreversibility field increase monotonically as a function of oxygen doping.

Doping dependence of the Josephson coupling in Bi2Sr2Ca1−xGdxCu2O8+δ single crystals

The Gd and oxygen doping effects on the Josephson coupling in Bi2Sr2Ca1−xGdxCu2O8+δ single crystals have been studied systematically. It was found that a pseudo-transition at temperature TcJ, attributed to the Josephson coupling between CuO2 layers, shifts dramatically to lower temperature with increasing magnetic field, and the temperature dependence of the pseudo-upper-critical-field HcJ associated with the coupling shows a clear upward curvature. For the Gd-doped as compared with the oxygen-doped crystal, the value of TcJ is smaller at the same carrier density, which implies that the substitution of Gd for Ca reduces the Josephson coupling more severely. The characteristics of the pseudo-transition associated with the Josephson coupling between CuO2 layers are different from those of the superconducting transition occurring in the CuO2 layers.

Effect of sodium and oxygen doping on the conductivity of CuInS2 thin films

Doping of Cu-poor CuInS2 thin films by sodium and oxygen species, such as O2 and O, was investigated by SIMS and conductivity measurements. Increased oxygen concentration is found for Na-doping. The SIMS signals of CuO and CuOS were detected. They coincide for O-doped films but differ for Na and O2 doped films. This is interpreted as due to grain boundary effects. Na doping leads to an increase in lateral conductivity. This finding supports the model previously proposed by L. Kronik, D. Cahen, H.W. Schoek, Adv. Mater. 10 (1998) 31] that oxygen plays a major role in Na doping. The presented results, furthermore, propose oxygen single doping for chalcopyrite films.

Effect of oxygen and indium metal doping on the thermal and optical properties of InF3/GaF3-based glasses

Effect of oxygen and indium metal doping on the thermal and optical properties of InF3/GaF3-based glasses

Oxygen doping effect on Ge–Sb–Te phase change optical disks

High performance phase change optical recording disk has been developed by using an oxygen-doped Ge–Sb–Te recording layer. The 5×105 overwrite cycles were achieved with this 6 at. % oxygen-doped phase change optical recording disk. The transmission electron microscope observation shows that the crystal grain size was enlarged and the “self-sharpening effect” disappeared with increasing of oxygen concentration. It is thought that the oxygen doping made it easy to grow the uniform large grain size without the self-sharpening effect around the amorphous mark and therefore, the overwrite cyclability of the phase change optical recording disk was improved.

Analysis of the effect of oxygen doping and pressure on superconducting transition temperature in metal oxides

The two-orbital Hubbard model is used to obtain formulas for the fermion excitation spectrum in the energy bands hybridized by the Anderson interaction. An analysis of lower part of the energy spectrum leads to a formula for the superconducting transition temperature Tc associated with the pairing of quasiparticles in one of the correlated bands. The dependence of Tc on pressure is analyzed, and the individual influence of carrier density enhancement and interaction strength is obtained as a function of oxygen concentration. The experimental discrimination made by Honma et al. [Solid State Commun 98, 395 (1996)] in Y0.9Ca0.1Ba2Cu3O7−δ by separating out the contributions due to carrier density and pairing strength can be reproduced quantitatively, and perhaps with further refinement, so can the carrier concentration. Although the prediction of the absolute value of the transition temperature using the present model is not accurate, it is clear that it furnishes a reasonably accurate description of the change in transition temperature with pressure. The component contributions due to the change in carrier concentration and due to the change in interaction strength as a function of oxygen concentration are also in reasonable agreement with the experimental results.

Solid state chemistry of Ruddlesden-Popper type complex oxides

Various criteria of formation of perovskites and K2NiF4-type compounds, which are the end members of homologous Ruddlesden-Popper series of phases, have been discussed. RP-phases show some general trends in their physical properties. Literature survey of the formation of these phases, their properties, and effect of oxygen stoichiometry and doping is presented. Some conditions for their synthesis are also described.

Spin-Wave Excitations in Oxygen Doped La2NiO4.11

Inelastic neutron scattering experiments were carried out to study the oxygen doping effect on spin-waves in La 2 NiO 4.11 . The present study revealed well-defined spin-waves appearing in the low energy regions as well as in the smaller q 2D region near the antiferromagnetic zone center which are considered to be bound magnons associated with impurities. The `host' spin-waves still persist in higher energies with a short lifetime. The `impurity' mode may result from the doped hole distribution at both Ni and O sites in NiO 2 layers.

The effects of oxygen doping and annealing on the surface and bulk electrical conductivity in planar copper phthalocyanine thin films for gas-sensing applications

In the development of gas-sensing devices based on phthalocyanine materials, it has become evident that the current drawn depends on previous exposure to oxygen, which acts as an acceptor impurity, and on the relative importance of the bulk and surface regions. The present work focuses on the effects of oxygen on α-phase thin films of copper phthalocyanine (CuPc) having a planar configuration. In unannealed samples both ohmic and space-charge-limited conductivity (SCLC) regions were observed in films of thickness 0.1 μm, whereas for films of thickness 1 μm, SCLC was not observed below a field strength of 2×10 6 V m −1. These variations may be explained in the context of the differing effects of oxygen on the surface and bulk regions of the films. Exposure to oxygen has the effect of enhancing the conductivity and increasing the threshold voltage between the ohmic and SCLC regions. In the thinner films, samples lightly doped with oxygen had a trap distribution exponentially distributed in energy, whereas long exposure to oxygen resulted in the establishment of a discrete dominant trap level. While annealing was found to reduce the conductivity due to oxygen desorption, the resulting activation energy was found to be dependent on the concentration of oxygen within the films. Observations of oxygen desorption from films of different thickness revealed that the binding energy of oxygen to the CuPc molecule is lower on the surface than in the bulk of the films. It was concluded that the adsorbed or absorbed oxygen molecules resulted in the establishment of a partial charge-transfer complex, and that the hole concentration on the surface of the films is lower than that in the bulk under vacuum.

Oxygen-doping effect on spin correlations in La 2NiO 4 + δ

We performed neutron scattering experiments on single crystals of La 2NiO 4.11 and La 2NiO 4.125. The dynamical intralayer spin correlations are depressed by oxygen doping and essentially independent of ordering of the excess oxygen atoms. The characteristic feature of the spin-wave in oxygen-doped La 2NiO 4 is that a sharp spin-wave mode exists in the lower-energy region with the reduction of the exchange interaction. Experimental results indicate that the average intralayer interaction of spin correlations is controlled by the number of holes induced by oxygen doping.

Specific heat anomalies on the vortex melting line in YBa 2Cu 3O 7−δ up to B=23 teslas: Observation of first- and second-order transitions, effect of oxygen doping, field orientation, crystal purity and detwinning

Because strong fluctuations transform the upper critical field line B c2(T) into a smooth crossover, vortex melting is now believed to be the only true phase transition of high temperature superconductors in a magnetic field. We review recent work performed by the Geneva and Grenoble laboratories in the calorimetric determination of the melting line B m(T) in YBa 2Cu 3O x. This includes three crystals showing specific heat steps upon crossing B m(T), and three crystals showing specific heat peaks. Adiabatic calorimetry (up to 23 T) and oscillating dynamic methods (up to 7 T) are used. We investigate the effect of field orientation (B//c and B⊥c), oxygen concentration x (6.95 – 6.97), and detwinning. These experiments document both processes that may occur on the B m(T) line, depending on pinning properties: the melting of a vortex lattice with a first-order transition, and the melting of a vortex glass with a second-order or continuous transition.

Effects of hydrostatic pressure and oxygen doping on the vortex phase diagram in Bi2Sr2CaCu2O8+y

We report on the effects of oxygen-doping and hydrostatic pressure on the vortex lattice melting (VLM) and the peak effect (PE) in Bi2Sr2CaCu2O8+y. Both oxygen-doping and hydrostatic pressure shift these phase boundaries towards higher fields. This change is understood by considering the fact that these processes reduce the anisotropy of the system. PE is found to show a non-monotonic temperature dependence in samples with small anisotropy.

Effects of oxygen doping and structural distortion on the superconductivity of single crystals

Effects of oxygen doping and structural distortion on the superconductivity of (Bi2212) were studied by ac susceptibility and x-ray diffraction measurements for a group of high-quality single crystals. The crystals were annealed at 600 and under different oxygen pressures ranging from to 6080 Torr. It was found that the c-axis length showed a plateau at - Torr and decreased with increasing oxygen pressure above Torr, which strongly suggested that two stages of oxygen diffusion may be involved. The full width at half maximum (FWHM) of the 00 main reflection, which reflects structural distortion in the c direction, showed a peak around the optimized oxygen doping. This implies that the structural modification may be another factor that affects apart from oxygen content. On the other hand, the period of incommensurate modulation along the b direction, s, was found to have nothing to do with the oxygen content or superconductivity. Relationships between superconductivity, oxygen content and microstructure of the Bi2212 single crystal are discussed.

Neutron Scattering Study of Oxygen Ordering and Magnetic Correlations in La2NiO4.11and La2NiO4.125

We have performed neutron scattering experiments on single crystals of La 2 NiO 4+δ (δ=0.11, and 0.125) to study the effect of oxygen doping on the structural and magnetic properties. The degree of the excess oxygen order strongly influences the local crystal structure and interlayer magnetic correlation. The intralayer magnetic correlation is depressed by doping in the commensurate region (δ≤0.11), then turns to increase in the incommensurate region (δ>0.11). Our experimental results are compared with existing results for oxygen and Sr doped La 2 NiO 4 .