Optical characterization of transparent nickel oxide films deposited by DC current reactive sputtering

In this paper, we characterize high transparency p-type semiconducting NiO thin films deposited by Direct Current Reactive Magnetron Sputtering from a pure Ni target in a mixture of oxygen and argon gases on Corning glass/SnO₂:F substrates at different oxygen contents ranging from 0% at 30%. The influence of the O₂/Ar ratio and thickness on transmittance has been examined using ultraviolet-visible spectroscopy. The results show that whatever the oxygen proportion into the discharge, the nickel oxide films exhibit a polycrystalline structure. At low oxygen content, the preferential orientation is (111), for stoichiometric films the XRD diagram is powder-like whereas the preferential orientation is (200) for higher oxygen content. For low and high oxygen content, the transmittance is low. Thanks to plasma method and its ability to tune the oxygen content in the discharge and therefore the film composition, we have been able to explore carefully the intermediate zone and obtain transparent films. The optical absorption coefficient α has been calculated from the transmittance and the variation of (αhν)² versus the photon energy (hν) for nickel oxide is presented. The optical band gap energy has been evaluated and varies from 3.2 to 3.8 eV.     

Cu2O thin films deposited by reactive direct current magnetron sputtering

The Cu₂O thin films were prepared on quartz substrate by reactive direct current magnetron sputtering. The influences of oxygen partial pressure and gas flow rate on the structures and properties of deposited films were investigated. Varying oxygen partial pressure leads to the synthesis of Cu₂O, Cu₄O₃ and CuO with different microstructures. At a constant oxygen partial pressure of 6.6 × 10^− 2 Pa, the single Cu₂O films can be obtained when the gas flow rate is below 80 sccm. The as-deposited Cu₂O thin films have a very high absorption in the visible region resulting in the visible-light induced photocatalytic activity.     

Effect of process conditions on the optoelectronic characteristics of ZnO:Mo thin films prepared by pulsed direct current magnetron sputtering

The purpose of this study is to use pulsed magnetron sputtering to deposit transparent conductive ZnO:Mo (MZO) film on a Corning 1737 glass substrate. Various process parameters, including power, work pressure, pulsed frequency, film thickness, and substrate temperature, were analyzed for their effects on the microstructure and optoelectronic characteristics of MZO thin film. Experimental results show that MZO film with a low resistivity of approximately 8.9 × 10^− 4 Ω cm and a visible light transitivity of greater than 80% can be obtained using a Mo content of 1.77 wt.%, sputtering power of 100 W, work pressure of 0.4 Pa, pulsed frequency of 10 kHz, and film thickness of 500 nm without heating. The value of optical band gap of MZO increased upon increasing the crystallinity of the MZO thin film, and the range of the optical band gap of MZO thin film is from 3.30 to 3.35 eV.     

Nanophotocatalysis using immobilized titanium dioxide nanoparticle: Degradation and mineralization of water containing organic pollutant: Case study of Butachlor

In this paper, the degradation and mineralization of Butachlor in aqueous solution by nanophotocatalysis using immobilized TiO₂ nanoparticles were investigated. Butachlor (N-butoxymethyl-2-chloro-2′,6′-diethylacetanilide) is a persistent organic pollutant in agricultural soil and watercourses. A simple and effective method was used for immobilization of titanium dioxide nanoparticles. UV-vis and Ion Chromatography (IC) analyses were employed to obtain the details of the photocatalytic degradation and mineralization of Butachlor. The effects of operational parameters such as H₂O₂, inorganic anions (NO₃⁻, Cl⁻ and SO₄²⁻) and pH were investigated. The lack of any absorbance in 254 nm was indicative of the complete degradation of aromatic intermediates. The mineralization of Butachlor was evaluated by monitoring of the formed inorganic anions (NO₃⁻ and Cl⁻). Butachlor is effectively degraded following first order kinetics model. Results show that the immobilized titanium dioxide nanoparticle photocatalysis is an effective method for treatment Butachlor from contaminated water.     

Influence of annealing temperature on the properties of ZnO:Zr films deposited by direct current magnetron sputtering

Transparent conducting zirconium-doped zinc oxide (ZnO:Zr) films were deposited on quartz substrates by direct current (DC) magnetron sputtering at room temperature. The influence of post-annealing temperature on the structural, morphological, electrical and optical properties of ZnO:Zr films were investigated. When annealing temperature increases from room temperature to 573 K, the resistivity decreases obviously due to an improvement of the crystallinity. However, with further increase in annealing temperature, the crystallinity deteriorates leading to an increase in resistivity. The films annealed at the optimum annealing temperature of 573 K in vacuum have the lowest resistivity of 9.8 × 10⁻⁴ Ω cm and a high transmittance of above 92% in the visible range.     

Highly conductive alumina-added ZnO ceramic target prepared by reduction sintering and its effects on the properties of deposited thin films by direct current magnetron sputtering

To obtain a suitable sputtering target for depositing transparent conducting Al-doped ZnO (AZO) films by using direct current (DC) magnetron sputtering, this study investigates the possibility of using atmosphere controlled sintering of Al₂O₃ mixed ZnO powders to prepare highly conductive ceramic AZO targets. Experimental results show that a gas mixture of Ar and CO could produce a sintered target with resistivity in the range of 2.23 × 10^− 4 Ω cm. The fairly low resistivity was mainly achieved by the formation of both aluminum substitution (Al_Zn) and oxygen vacancy (V_O), thus greatly increasing the carrier concentration. Compared to usual air sintered target, the thin film deposited by the Ar + CO sintered target exhibited lower film resistivity and more uniform spatial distribution of resistivity. A film resistivity as low as 6.8 × 10^− 4 Ω cm was obtained under the sputtering conditions of this study.     

Performance evaluation of the ITER Toroidal Field Model Coil phase I: Part 2: M&M analysis and interpretation

The ITER Toroidal Field Model Coil (TFMC), a large (2.7 m × 3.8 m × 0.8 m) superconducting (Nb₃Sn) DC coil designed and constructed in collaboration between EU industries and laboratories coordinated by EFDA, has been tested during 2001 in the TOSKA cryogenic facility at Forschungszentrum Karlsruhe, Germany, achieving the nominal 80 kA at 7.8 T peak field and 86 MJ stored energy as a standalone coil (Phase I). The results of the current sharing temperature (T_CS) measurements at I=80, 69 and 57 kA, presented in a companion paper (Part 1), are evaluated here using the M&M code. The critical properties best fitting the experimental voltage-inlet temperature characteristic of the P1.2 pancake are deduced from the TFMC data under the assumption of an ideal collective behaviour of the strands. The TFMC results are compared first with the expected conductor performance, showing that at the maximal current the performance was borderline with what was expected, while at the minimal current tested it was better than expected. Second, they are compared with the performance of the single strand as measured in the lab, showing that, in order to reproduce the TFMC data, one has to invoke that some degradation, larger at higher current, occurred when going from the strand to the cable.     

Electronic structure and optical properties in ZnO:M(Co, Cd): Effect of band-gap variation

ZnO doped with some transitions metals (ZnO:M) has several significant potential application. ZnO:Co is proposed to be used in advanced spintronic devices due to its high Curie temperature and large magnetic moments per transition metal. ZnO:Cd has potential applications in short-wavelength optoelectronic devices. This work focuses on an ab-initio study of the electronic and optical properties of ZnO:M doped with Co, and Cd. Theoretical calculations have been done with different computational codes, using the density functional theory (DFT) at the GGA and GGA+U level. The latter introduces a Hubbard term correction in the “d” levels of the Zn and Co. We used different supercells in order to have different realistic dilution levels which can be achieved in experiments. Doping effects on the features of the optical absorption are also studied and analysed in this work.     

Sulfamethoxazole abatement by photo-Fenton: Toxicity,inhibition and biodegradability assessment of intermediates

The objective of this work was to study the abatement of 200 mg L⁻¹ sulfamethoxazole (SMX) solution by means of photo-Fenton process. Biodegradability of the treated solutions was followed by the ratio biochemical oxygen demand at five days/chemical oxygen demand (BOD₅/COD) and toxicity by Microtox^® and inhibition tests. Experiments with different initial concentration of H₂O₂ were carried out. The initial amount of Fe²⁺ and pH of the solution were set at 10 mg L⁻¹ and 2.8 respectively. The temperature of the reactor was kept constant in all the experiments (25 ± 0.8 °C). Photo-Fenton process is thought to be a successful treatment step to improve the biodegradability of wastewater containing SMX. The complete antibiotic removal was achieved for a H₂O₂ dose over 300 mg L⁻¹. Biodegradability (BOD₅/COD) rose from zero (SMX solution) to values higher than 0.3 (treated solutions). Toxicity and inhibition tests pointed out in the same direction: oxidized intermediates for initial H₂O₂ dose over 300 mg L⁻¹ showed no toxicity effects on pure bacteria and no inhibition on activated sludge activity.     

Two-dimensional versus three-dimensional post-deposition grain growth in epitaxial oxide thin films: Influence of the substrate surface roughness

Epitaxial thin films made of nanosized yttria-stabilized zirconia islands deposited on (0001) sapphire substrates are synthesized by sol-gel dip-coating followed by a high-temperature post-deposition thermal annealing procedure. At high temperatures, a competitive growth process takes place that allows to obtain thin films made of atomically flat islands with an in-plane diameter typically ten times higher than the thickness or on the contrary inducing the formation of dome-shaped islands. Apart from having a different shape, these islands are also characterized by a different crystallographic orientation with respect to the substrates respectively (001) and (111). In this paper, we investigate the influence of the substrate surface roughness on this competitive grain growth process. The deposition on epi-polished substrates results in a two-dimensional (2D) island growth, whereas the deposition on rough substrates results in a three-dimensional (3D) growth of dome-shaped nanosized islands. The films have been characterized by atomic force microscopy and high-resolution X-ray diffraction using the reciprocal space mapping technique.     

The effect of factor interactions in Plackett-Burman experimental designs: Comparison of Bayesian-Gibbs analysis and genetic algorithms

A genetic algorithm has been developed in order to estimate not only the main effects but also the association of terms when analyzing the influence of experimental factors through a Plackett-Burman design of experiments. The results for a series of simulated systems as well as experimental examples show excellent agreement with a Bayesian-Gibbs approach. The Plackett-Burman design is usually employed for screening, but its performance depends on the assumption that the interaction effects are negligible. Simulations allow one to analyze the effect of increasing interactions on the significance of main factors when Plackett-Burman designs are processed by neglecting factor associations.     

Bending strength of silica gel with bimodal pores: II. Effect of variations in morphology and porosity

The bending strength of amorphous silica gels with bimodal pore structure was evaluated by changing macropore morphology and porosity, where the macropore morphology was controlled by inducing phase separation during gelation of silicate solution and the porosity was controlled by changing aging conditions and calcination temperature. At the same porosity, the bending strength was decreased for gels with larger macropores. In this preparation of bimodal porous silica gels, however, samples with large macropores also had many small particles in the macropores. Therefore, the decrease in bending strength with increasing macropore size was attributed to the presence of the particles that contributed to increasing bulk density but not bending strength. A power law applies to the bending strength and the bulk density of gels with the same macropore morphology, where the exponent depends on the morphology.     

Influence of spectator ions on the reactivity of divalent metal salts in molten alkali metal nitrates: Morphology of the resulting metal oxides

This work focuses on the investigation of the reaction of alkali metal nitrates (LiNO₃, NaNO₃ and KNO₃) with divalent metal salts (Cu²⁺, Ni²⁺ and Zn²⁺). Thermogravimetric analysis (TGA) was employed to study the kinetics and mechanisms of the above reactions, which led to the formation of the corresponding metal oxides. The reaction temperature was found to depend not only on the alkali metal but also on the metal salt (MCl₂ or M(NO₃)₂) involved in the reaction.SEM observations show that the spectator ions present in the reacting medium have varying degrees of influence on the morphology of the powder; the growth directions, sizes and the homogeneity of their distribution, are modified. KNO₃ generates the most significant differences compared to LiNO₃ and NaNO₃.     

Aqueous lateral epitaxy overgrowth of ZnO on (0001) GaN at 90 °C: Part II: Stress determination

In Part I, it was shown that the critical thickness required for mechanical failure of lateral epitaxial overgrown films of ZnO on GaN buffered Al₂O₃ substrates could be significantly increased by masking and patterning the substrate to produce periodic, hexagonal arrays of circular windows. It was also observed that the critical thickness could be increased by increasing the distance between the circular windows. In Part II, it is shown, using Raman piezo-spectroscopy, that a stress gradient exists within the hexagonal prisms of ZnO that grow from the circular windows. The compressive stress, due to lattice mismatch, was highest in the center of the prisms and lowest near the perimeter where they overgrow the masked region to form ‘wings’. For one orientation of the hexagonal array of circular windows, relative to the substrate, where the hexagonal prism coalesce face to face, the stress gradient persisted after the hexagonal prisms coalesced to form a continuous film because residual voids surround the base of the coalesced, hexagonal prisms. For a second orientation where the hexagonal prisms coalesce corner to corner, the stress gradient was greatly diminished due to a larger amount of coalescence at the base of the prisms. Most important, it was shown that the compressive stress for both arrays decreased with increased spacing between the circular windows. Namely, for window orientation producing face to face coalescence of the prisms, the maximum compressive stress decreases from ∼ 520 MPa for windows separated by twice their diameter to ∼ 350 MPa for windows separated by four times their diameter. These results are consistent with the critical thickness observations reported in Part I.     

On the existence of PbBi3PO8: Its synthesis and crystal structure

The title compound crystallizes in the tetragonal system, a = 11.733(2) Å, c = 15.587(3) Å, I4 mm, Z = 10. Data were collected at the Argonne National Laboratory synchrotron source at λ = 0.15359 Å. Least squares refinement on F² converged to R1 = 0.039. The oxygen coordination polyhedra around Bi and Pb display the distortions typical of 6s² lone-pair atoms. One Bi is disordered. BiO bonds vary from 2.08(2) to 2.96(1) Å. One Pb is in cubic coordination to oxygen and the second Pb is bonded to six oxygen atoms that form a rectangular pyramid and a seventh oxygen is off one of the rectangular faces of the pyramid. PbO bonds vary from 2.303(6) to 2.804(17) Å. Of the two crystallographically independent P one is in a single tetrahedral coordination while the second is at the center of two disordered tetrahedra. Units of OM₄ tetrahedra, M = Bi/Pb, articulate into a three-dimensional framework by corner and edge sharing that is strengthened by corner sharing with PO₄ moieties.     

Ductile to brittle transition of an A508 steel characterized by Charpy impact test: Part I: experimental results

This study is devoted to the ductile-brittle transition behavior of a French A508 Cl3 (16MND5) steel. Due to its importance for the safety assessment of PWR vessels, a full characterization of this steel with Charpy V-notch test in this range of temperature was undertaken. The aim of this study is to provide a wide experimental database and microstructural observations to supply, calibrate and validate models used in a local approach methodology. Mechanical and fracture properties of the steel have been investigated over a wide range of temperatures and strain-rates. Effects of impact velocity on ductile-brittle transition curve, on ductile tearing and on notch temperature rise are presented and discussed. A detailed study of ductile crack initiation and growth in Charpy specimens is also carried out. From fractographic investigations of the microvoids nucleation around carbide second phase particles, a plastic strain threshold for nucleation is determined for this material. A508 Cl3 steels undergo a transition in fracture toughness properties with temperature, due to a change in fracture mode from microvoids coalescence to cleavage fracture. A systematic investigation on the nature and the position of cleavage triggering sites and on any change in the ductile to brittle transition (DBT) range has been carried out. This leads to the conclusion that manganese sulfide inclusions do not play an increasing role with increasing test temperature as recently mentioned in other studies on A508 Cl3 steel with a higher sulfur content. In a companion paper [Tanguy et al., Engng. Fract. Mech., in press], the numerical simulation of the Charpy test in the ductile-brittle transition range using fully coupled local approach to fracture is presented.