Excited-state absorption at 1.57 μm in U:CaF2 and Co:ZnSe saturable absorbers

Appreciable excited-state absorption (ESA) in U²⁺:CaF₂ and Co²⁺:ZnSe saturable absorbers was measured at λ=1.573 μm by optical transmission versus light fluence curves of 30–40 ns long pulses. The ground- and excited-state absorption cross-sections obtained were (9.15±0.3)×10⁻²⁰ and (3.6±0.2)×10⁻²⁰ cm², respectively, for U²⁺:CaF₂, and (57±4)×10⁻²⁰ and (12.5±1)×10⁻²⁰ cm² for Co²⁺:ZnSe. Thus, ESA is not negligible in U²⁺:CaF₂ and Co²⁺:ZnSe, as previously estimated.     

Deformation behavior and microstructural evolution during the semi-solid compression of Al–4Cu–Mg alloy

The effects of the process parameters, including deformation temperature and strain rate, on the deformation behavior and microstructure of an Al–4Cu–Mg alloy, have been investigated through isothermal compression. Experiments were conducted at deformation temperatures of 540 °C, 560 °C, and 580 °C, strain rates of 1 s⁻¹, 1×10⁻¹ s⁻¹, 1×10⁻² s⁻¹, and 1×10⁻³ s⁻¹, and height reductions of 20%, 40%, and 60%. The experimental results show that deformation temperature and strain rate have significant effect on the peak flow stress. The flow stress decreases with an increase of deformation temperature and/or a decrease of the strain rate. Above a critical value of the deformation temperature, the flow stress quickly reaches a steady value. Experimental materials A and B have equiaxed and irregular grains, respectively, prior to deformation. The microstructures vary with the process parameters in the semi-solid state. For material B, the irregular grains transform to equiaxed grains in the process of semi-solid deformation, which improves the deformation behavior.     

Up-conversion dynamics in GdAlO3:Er single crystal fibre

Green fluorescence has been obtained under continuous laser excitation in the 780–860 nm range in GdAlO₃:Er³⁺. With the help of the Judd-Ofelt treatment we built a model based on population rate equations to describe its time evolution. We found the intensity parameters to be Ω₂ = 2.045 × 10⁻²⁰ cm², Ω₄ = 1.356 × 10⁻²⁰ cm² Ω₆ = 1. 125 × 10⁻²⁰ cm². Even if a two-photon absorption and a looping mechanism are necessary to well describe the dynamics, the main process responsible for up-conversion is energy transfer between erbium ions.     

The characteristics of serrated flow in superalloy IN738LC

Serrated flow was investigated in superalloy IN738LC, a nickel-base γ′ age-hardened alloy. In this material serrated flow appeared between 350 and 450 °C and strain rate of (8.77 × 10⁻⁵ to 8.77 × 10⁻³) s⁻¹. Activation energy for this process was calculated to be 0.69–0.86 eV which is in good agreement with the values reported for similar alloys. Results show that the diffusion rate of substitutional solute atoms at this temperature range is too low to cause this effect. This suggests that the interaction of solute atoms and moving dislocation is responsible for the observed serrated flow in this alloy.     

Microstructure evolution and texture development during high-temperature uniaxial compression of magnesium alloy AZ31

Texture development in magnesium alloy AZ31 was studied by uniaxial compression tests at temperatures, strain rates and final strains ranging from 573 to 773 K, 1.0 × 10⁻³ to 5.0 × 10⁻⁵ s⁻¹ and −0.2 to −1.5, respectively. Fiber texture was formed in all of the deformation conditions. The main component of the texture varied depending on deformation conditions; it appeared about 33–38° away from the basal pole after the deformation at higher temperatures and lower strain rates. This can be attributed to the increased activity of the secondary pyramidal slip system. With a decrease in temperatures and an increase in strain rate, the tilting angle of the main component (compression plane) from the basal pole decreased down to about 20°. Construction of a basal fiber texture was detected after deformations at the lowest temperature and high strain rates.     

Transparent conductive In2O3:Mo thin films prepared by reactive direct current magnetron sputtering at room temperature

An amorphous transparent conductive oxide thin film of molybdenum-doped indium oxide (IMO) was prepared by reactive direct current magnetron sputtering at room temperature. The films formed on glass microscope slides show good electrical and optical properties: the low resistivity of 5.9 × 10^− 4 Ω cm, the carrier concentration of 5.2 × 10²⁰ cm^− 3, the carrier mobility of 20.2 cm² V^− 1 s^− 1, and an average visible transmittance of about 90.1%. The investigation reveals that oxygen content influences greatly the carrier concentration and then the photoelectrical properties of the films. Atomic force microscope evaluation shows that the IMO film with uniform particle size and smooth surface in terms of root mean square of 0.8 nm was obtained.     

Atomic layer deposition growth of zirconium doped In2O3 films

Zirconium doped indium oxide thin films were deposited by the atomic layer deposition technique at 500 °C using InCl₃, ZrCl₄ and water as precursors. The films were characterised by X-ray diffraction, energy dispersive X-ray analysis and by optical and electrical measurements. The films had polycrystalline In₂O₃ structure. High transparency and resistivity of 3.7×10⁻⁴ Ω cm were obtained.     

Sintering behavior and microwave dielectric properties of Bi3(Nb1−xTax)O7 solid solutions

Solid solutions of Bi₃(Nb_1−xTa_x)O₇ (x = 0.0, 0.3, 0.7, 1) were synthesized using solid state reaction method and their microwave dielectric properties were first reported. Pure phase of fluorite-type could be obtained after calcined at 700 °C (2 h)⁻¹ between 0 ≤ x ≤ 1 and Bi₃(Nb_1−xTa_x)O₇ ceramics could be well densified below 990 °C. As x increased from 0.0 to 1.0, saturated density of Bi₃(Nb_1−xTa_x)O₇ ceramics increased from 8.2 to 9.1 g cm⁻³, microwave permittivity decreased from 95 to 65 while Q_f values increasing from 230 to 560 GHz. Substitution of Ta for Nb modified temperature coefficient of resonant frequency τ_f from −113 ppm °C⁻¹ of Bi₃NbO₇ to −70 ppm °C⁻¹ of Bi₃TaO₇. Microwave permittivity, Q_f values and τ_f values were found to correlate strongly with the structure parameters of fluorite solid solutions and the correlation between them was discussed in detail. Considering the low densified temperature and good microwave dielectric proprieties, solid solutions of Bi₃(Nb_1−xTa_x)O₇ ceramics could be a good candidate for low temperature co-fired ceramics application.     

Compression testing of a sintered Ti6Al4V powder compact for biomedical applications

In this study, the compression deformation behavior of a Ti6Al4V powder compact, prepared by the sintering of cold compacted atomized spherical particles (100–200 μm) and containing 36–38% porosity, was investigated at quasi-static (1.6×10⁻³–1.6×10⁻¹ s⁻¹) and high strain rates (300 and 900 s⁻¹) using, respectively, conventional mechanical testing and Split Hopkinson Pressure Bar techniques. Microscopic studies of as-received powder and sintered powder compact showed that sintering at high temperature (1200 °C) and subsequent slow rate of cooling in the furnace changed the microstructure of powder from the acicular alpha () to the Widmanstätten (+β) microstructure. In compression testing, at both quasi-static and high strain rates, the compact failed via shear bands formed along the diagonal axis, 45° to the loading direction. Increasing the strain rate was found to increase both the flow stress and compressive strength of the compact but it did not affect the critical strain for shear localization. Microscopic analyses of failed samples and deformed but not failed samples of the compact further showed that fracture occurred in a ductile (dimpled) mode consisting of void initiation and growth in phase and/or at the /β interface and macrocracking by void coalescence in the interparticle bond region.     

Highly conducting indium tin oxide (ITO) thin films deposited by pulsed laser ablation

Highly conducting and transparent indium tin oxide (ITO) thin films were prepared on SiO₂ glass and silicon substrates by pulsed laser ablation (PLA) from a 90 wt.% In₂O₃-10 wt.% SnO₂ sintered ceramic target. The growths of ITO films under different oxygen pressures (P_O2) ranging from 1×10⁻⁴–5×10⁻² Torr at low substrate temperatures (T_s) between room temperature (RT) and 200°C were investigated. The opto-electrical properties of the films were found to be strongly dependent on the P_O2 during the film deposition. Under a P_O2 of 1×10⁻² Torr, ITO films with low resistivity of 5.35×10⁻⁴ and 1.75×10⁻⁴ Ω cm were obtained at RT (25°C) and 200°C, respectively. The films exhibited high carrier density and reasonably high Hall mobility at the optimal P_O2 region of 1×10⁻² to 1.5×10⁻² Torr. Optical transmittance in excess of 87% in the visible region of the solar spectrum was displayed by the films deposited at Po₂≥1×10⁻² Torr and it was significantly reduced as the P_O2 decreases.     

Reactions in Au/Nb bilayer thin films

The interdiffusion and intermetallic compound formation of Au/Nb bilayer thin films annealed at 200–400 °C have been investigated. The bilayer thin films were prepared by electron beam deposition. The Nb film was 50 nm thick and the Au film was 50–200 nm thick. The interdiffusion of annealed specimens was examined by measuring the electrical resistance and depth-composition profile and by transmission electron microscopy. Interdiffusion between the thin films was detected at temperatures above 325 °C in a vacuum of 10^-4 Pa. The intermetallic compound Au₂Nb₃ and other unknown phases form during annealing at over 400 °C. The apparent diffusion constants, determined from the penetration depth for annealing at 350 °C, are 3.5 × 10⁻¹⁵ m² s⁻¹ for Nb in Au and 8.6 × 110^7minus;15 m² s⁻¹ for Au in Nb. The Au surface of the bilayer films becomes uneven after annealing at over 400 °C due to the reaction.     

Al2O3 formation on Si by catalytic chemical vapor deposition

Catalytic chemical vapor deposition (Cat-CVD) has been developed to deposit alumina (Al₂O₃) thin films on silicon (Si) crystals using N₂ bubbled tri-methyl aluminum [Al(CH₃)₃, TMA] and molecular oxygen (O₂) as source species and tungsten wires as a catalyzer. The catalyzer dissociated TMA at approximately 600 °C. The maximum deposition rate was 18 nm min⁻¹ at a catalyzer temperature of 1000 °C and substrate temperature of 800 °C. Metal oxide semiconductor (MOS) diodes were fabricated using gates composed of 32.5-nm-thick alumina film deposited at a substrate temperature of 400 °C. The capacitance measurements resulted in a relative dielectric constant of 7.4, fixed charge density of 1.74×10¹² cm⁻², small hysteresis voltage of 0.12 V, and very few interface trapping charges. The leakage current was 5.01×10⁻⁷ A cm⁻² at a gate bias of 1 V.     

Deep levels in GaInAs grown by molecular beam epitaxy and their concentration reduction with annealing treatment

X-ray diffraction (XRD), current–voltage (IV), capacitance–voltage (CV), deep-level transient Fourier spectroscopy (DLTFS) and isothermal transient spectroscopy (ITS) techniques are used to investigate the thermal annealing behaviour of three deep levels in Ga_0.986In_0.014As heavily doped with Si (6.8 × 10¹⁷ cm⁻³) grown by molecular beam epitaxy (MBE). The thermal annealing was performed at 625 °C, 650 °C, 675 °C, 700 °C and 750 °C for 5 min. XRD study shows good structural quality of the samples and yields an In composition of 1.4%. Two main electron traps are detected by DLTFS and ITS around 280 K, with activation energies of 0.58 eV and 0.57 eV, capture cross sections of 9 × 10⁻¹⁵ cm² and 8.6 × 10⁻¹⁴ cm² and densities of 2.8 × 10¹⁶ cm⁻³ and 9.6 × 10¹⁵ cm⁻³, respectively. They appear overlapped and as a single peak, which divides into two smaller peaks after annealing at 625 °C for 5 min.

Annealing at higher temperatures further reduces the trap concentrations. A secondary electron trap is found at 150 K with an activation energy of 0.274 eV, a capture cross section of 8.64 × 10⁻¹⁵ cm² and a density of 1.38 × 10¹⁵ cm⁻³. The concentration of this trap level is also decreased by thermal annealing.     

Growth and spectroscopy of Dy doped in ZnWO4 crystal

Single-crystal ZnWO₄:Dy³⁺ was grown by Czochralski technique. The XRD, absorption spectra as well as fluorescence spectrum are investigated and the Judd–Ofelt intensity parameters Ω₂, Ω₄, Ω₆ are obtained to be 7.76 × 10⁻²⁰ cm², 0.57 × 10⁻²⁰ cm², 0.31 × 10⁻²⁰ cm², respectively. Calculated radiative transition rate, branching ratios and radiative lifetime for different transition levels of ZnWO₄:Dy³⁺ crystals are presented. Fluorescence lifetime of ⁴F_9/2 level is 158 μs and quantum efficiency is 66%.The most intense fluorescence line at 575 nm correlative with transition ⁴F_9/2 → ⁶H_13/2 is potentially for application of yellow lasers.     

Change in grain size and flow strength in P/M Rene 95 under isothermal forging conditions

The changes in microstructure induced by plastic deformation in hot isostatically pressed (HIPed) P/M Rene 95 under isothermal conditions are discussed. Results of the constant true strain rate compression tests are presented for initially fine (7 μm) and coarse (50 μm) grained compacts deformed at temperatures of 1050 °C, 1075 °C and 1100 °C and at strain rates in the range from 10⁻⁴ s⁻¹ to 1 s⁻¹. Under these test conditions, both the fine and coarse-grained compacts recrystallize and their grain size are refined during flow. This grain refinement gives rise to softening in both materials. Ultimately, their microstructures transform into the same equiaxed fine-grained microduplex structure at which point their flow strength becomes identical. Continued deformation at that point produces no further change in grain size or flow strength. Under this steady state regime of deformation, the microduplex grain size and flow strength are independent of the original microstructure but are conditioned by the strain rate at a given temperature. The steady state grain size increases whereas the steady flow strength decreases with a decrease in strain rate and/or an increase in temperature.     

Exceptional superplasticity in an AZ61 magnesium alloy processed by extrusion and ECAP

Experiments were conducted on a commercial AZ61 alloy to evaluate the potential for achieving an ultrafine grain size and superplastic ductilities through the use of the EX-ECAP two-step processing procedure of extrusion plus equal-channel angular pressing. The results show that EX-ECAP gives excellent grain refinement with grain sizes of 0.6 and 1.3 μm after pressing at 473 and 523 K, respectively. The alloy processed by EX-ECAP exhibits exceptional superplastic properties including a maximum elongation of 1320% after pressing through four passes when testing at 473 K with an initial strain rate of 3.3 × 10⁻⁴ s⁻¹. This result compares with an elongation of 70% achieved in the extruded condition without ECAP under similar testing conditions.     

New transparent conducting MgIn2O4---Zn2In2O5 thin films prepared by magnetron sputtering

New materials for a transparent conducting oxide film are demonstrated. Highly transparent Zn₂In₂O₅ films with a resistivity of 3.9 × 10⁻⁴ Ω cm were prepared on substrates at room temperature using a pseudobinary compound powder target composed of ZnO (50 mol.%) and In₂O₃ (50 mol.%) by r.f. magnetron sputtering. MgIn₂O₄---Zn₂In₂O₅ films were prepared using MgIn₂O₄ targets with a ZnO content of 0–100 wt.%. The resistivity of the deposited films gradually decreased from 2 × 10⁻³ to 3.9 × 10⁻⁴ Ω cm as the Zn/(Mg + Zn) atomic ratio introduced into the films was increased. The greatest transparency was obtained in a MgIn₂O₄ film. The optical absorption edge of the films decreased as the Zn/(Mg + Zn) atomic ratio was increased, corresponding to the bandgap energy of their materials. It was found that the resistance of the undoped Zn₂In₂O₅ films was more stable than either the undoped MgIn₂O₄, ZnO or In₂O₃ films in oxidizing environments at high temperatures.     

Molecular dynamics study of the mechanical behavior of nickel nanowire: Strain rate effects

We present the analysis of uniaxial deformation of nickel nanowires using molecular dynamics simulations, and address the strain rate effects on mechanical responses and deformation behavior. The applied strain rate is ranging from 1 × 10⁸ s⁻¹ to 1.4 × 10¹¹ s⁻¹. The results show that two critical strain rates, i.e., 5 × 10⁹ s⁻¹ and 8 × 10¹⁰ s⁻¹, are observed to play a pivotal role in switching between plastic deformation modes. At strain rate below 5 × 10⁹ s⁻¹, Ni nanowire maintains its crystalline structure with neck occurring at the end of loading, and the plastic deformation is characterized by {1 1 1} slippages associated with Shockley partial dislocations and rearrangements of atoms close to necking region. At strain rate above 8 × 10¹⁰ s⁻¹, Ni nanowire transforms from a fcc crystal into a completely amorphous state once beyond the yield point, and hereafter it deforms uniformly without obvious necking until the end of simulation. For strain rate between 5 × 10⁹ s⁻¹ and 8 × 10¹⁰ s⁻¹, only part of the nanowire exhibits amorphous state after yielding while the other part remains crystalline state. Both the {1 1 1} slippages in ordered region and homogenous deformation in amorphous region contribute to the plastic deformation.     

Thermal optical properties of TiO2 films

A fibre optic experimental arrangement was used to determine the thermo-optic coefficient (dn/dT) of electron beam deposited titanium dioxide coatings on the cleaved end faces of multimode optical fibres for a wavelength range between 600 and 1050 nm. The temperature-induced change in the index of refraction (n) and extinction coefficient (k) were successfully determined from reflection spectra. Measurements of n and k at various wavelengths for different temperatures enabled the determination of dn/dT and dk/dT. It was found that dn/dT takes different values at different temperature ranges. For example, at 800 nm, dn/dT was (−1.77±0.7)×10⁻⁴ K⁻¹, between 18°C and 120°C, and took a value of (−3.04±0.7)×10⁻⁴ K⁻¹ between 220°C and 325°C.     

Destruction of carbon disulfide in aqueous solutions by sonochemical oxidation

Carbon disulfide (CS₂) is toxic to animals and aquatic organisms, and can also decompose to carbonyl sulfide (OCS) and hydrogen sulfide (H₂S) in aqueous environment. The kinetics of the sonochemical degradation of aqueous CS₂ was studied in a batch reactor at 20 kHz and 20 °C, and the effects of process parameters (e.g. concentration, ultrasonic intensity, irradiating gas) investigated. The concentrations of unbuffered CS₂ solutions used were (6.4–7.0)×10⁻⁴, 10.5×10⁻⁴ and (13.2–13.6)×10⁻⁴ M and the intensities were varied from 14 to 50 W. The reaction rate was found to be zero-order and the rate constant for the degradation at 20 °C and 14W in air was 21.1 μM/min using the largest initial concentration range studied. At the same initial concentration range but at 50 W (39.47 W/m²) the degradation rate of CS₂ was 46.7 μM/min, more than two times that at 14 W (11.04 W/m²). The rate of CS₂ sonochemical degradation in the presence of the different gases was in the order of He>air≥N₂O>Ar; the rate with helium was found to be about three times that of argon. The formation of sulfate (SO₄²⁻) as reaction product with air as the irradiating gas was enhanced in the presence of hydrogen peroxide (H₂O₂) and inhibited in the presence of 1-butanol. The sonochemical oxidation of CS₂ may prove to be an efficient and environmentally benign way for the removal of this hazardous pollutant from natural water and wastewater.