Fabrication and characterization of dual sputtered Pd–Cu alloy films for hydrogen separation membranes

In this paper, submicron thin Pd–Cu alloy films are deposited using a dual sputtering technique, which allows a high composition control of the layer. The composition, surface morphology and phase structure of the sputtered layers are investigated by energy-dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractiometry (XRD). For example, the XRD data prove that the Pd–Cu layers are an alloy of Pd and Cu. Subsequently, the characterized Pd–Cu alloy layers are deposited on a silicon support structure to create a 750-nm thin Pd–Cu membrane for hydrogen separation. The reported membrane obtained a high flux of 1.6 mol H₂/m² s at a temperature of 725 K, while the selectivity is at least 500 for H₂/He.     

Microstructural features of biomedical cobalt–chromium–molybdenum(CoCrMo) alloy from powder bed fusion to aging heat treatment

The design freedom of powder bed fusion process selective laser melting(SLM) enables flexibility to manufacture customized, geometrically complex medical implants directly from the CAD models. Cobased alloys have adequate wear and corrosion resistance, fatigue strength, and biocompatibility, which enables the alloys to be widely used in medical devices. This work aims to investigate the evolution of microstructures and their influence on tribological property of CoCrMo alloy processed by SLM and aging heat treatment. The results showed that very weak 110 texture along the building direction and microsegregation along cellular boundaries were produced. The presence of high residual stress and fine cellular dendrite structure has a pronounced hardening effect on the as-SLM and aging-treated alloys at moderate temperatures. Furthermore, the hexagonal ε phase transformed from the γ matrix during SLM became significant after subsequent aging at moderate temperatures, which further increased the nanohardness and scratch resistance. High temperature(1150℃) heating caused homogenized recrystallization microstructure free of residual stress and ε phase, which sharply decreased the hardness and scratch resistance. The material parallel to the building direction exhibited improved tribological property in both SLMed and aging-treated alloy than that of the material perpendicular to the building direction. The anisotropy in frictional performance may be considered when designing CoCrMo dental implants using laser additive manufacturing.     

AlGaAs/GaAs multiquantum-well heterostructures for long-wavelength (8–10 μm) IR photodetectors

We have studied AlGaAs/GaAs multiquantum-well heterostructures grown by molecular beam epitaxy in an STE-3532 setup (SemiTEq, St. Petersburg), which are intended for long-wavelength IR photodetectors operating on inter-subband transitions. Quantum wells (QWs) in the obtained heterostructures are highly homogeneous and possess sharp heteroboundaries, which is confirmed by the photoluminescence spectra and dark current-voltage characteristics of photodetectors based on these heterostructures. The photodetectors exhibit sensitivity in the atmospheric transparency window (8?C10 mm) and possess parameters that make possible their use in large-format photodetector arrays for a new generation of long-wavelength IR camera systems.     

Increasing output power of LEDs (λ = 1.7–2.4 μm) by changing directions of reflected light fluxes in GaSb/GaInAsSb/GaAlAsSb heterostructures

It is demonstrated, using the example of light-emitting diodes (LEDs) based n-GaSb/n-GaIn-AsSb/p-GaAlAsSb heterostructures, that the formation of a curvilinear reflecting surface consisting of hemispherical etch pits on the rear side of an LED chip leads to an increase in the output radiation power by a factor of 1.9–2 in the entire wavelength interval studied (λ = 1.7–2.4 μm) as compared to the LED chip design with a continuous absorbing ohmic contact. This increase in the LED efficiency is related to a change in the directions of reflected light fluxes upon reflection from the hemispherical etch pits.     

Modulation Transfer Function Measurement of Optical Systems in the Visible and Infra-red (5 to 20 μm) Range

The ACOFAM combines an optical method of frequency analysis with electronic data unit and display to obtain a fast and accurate measurement of the Modulation Transfer Function of lenses and complete systems in the visible range. Some extra devices are described in order to convert the standard ACOFAM to the infra-red spectral range (5–20 μm). Results of measurements on a 50 mm F/1 developed by the Optical Division of Engins MATRA are shown.     

High-power single-mode laser diodes (λ = 1.1–1.2 μm) based on quantum-confined AlInGaAs/InP heterostructures

Quantum-confined AlInGaAs/InP laser heterostructures emitting at a wavelength of 1.18 μm have been grown by metalorganic vapor-phase epitaxy. An output radiation power of 40 mW in a single-mode CW regime has been obtained using a diode based in this structure with a mesastrip width of W = 4 μm. The total maximum CW emission power amounted to 75 mW.     

Hydrogen sorption properties of 90 wt% MgH2–10 wt% MeSi2 (Me = Ti, Cr)

The hydriding/dehydriding characteristics of 90 wt% MgH₂–10 wt% MeSi₂ (Me = Ti, Cr) composites, synthesized by ball milling under argon, were studied by Sievert’s type apparatus and by high-pressure differential scanning calorimetry (HPDSC). The composites have demonstrated similar absorption kinetics and capacity at temperature of 300 °C and a pressure of 1 MPa. They showed fast kinetics and achieved absorption capacity higher than 6 wt%. Slightly higher values for the enthalpy of hydriding and dehydriding were obtained at scanning conditions in the HPDSC for the composite 90 wt% MgH₂–10 wt% CrSi₂ compared to those for the composite with addition of TiSi₂.     

The influence of Pd on growth behavior of a quaternary (Cu,Ni,Pd)6Sn5 compound in Sn–3.0Ag–0.5Cu/Au/Pd/Ni–P solder joint during a liquid state reaction

This study investigated the liquid state reaction of a Sn–3.0Ag–0.5Cu solder jointed with electroless Ni–P/immersion Au (ENIG) and electroless Ni–P/electroless Pd/immersion Au (ENEPIG) surface finishes. Treatments with various soldering temperatures (240, 250, and 260 °C) and times (60, 180, 300, and 600 s) were performed to study the microstructure evolution. Detailed interfacial images revealed that the morphology of (Cu,Ni)₆Sn₅ affects the formation of Ni₃P and the curvature of the interface between them. In addition, the growth kinetics of (Cu,Ni)₆Sn₅ and (Cu,Ni,Pd)₆Sn₅ were studied and compared. The effect of grain coarsening during extended reflow modified the diffusion transport mechanism. However, because of the refinement of Pd on the grain structure, reduced IMC growth and a lower degree of transition from grain boundary diffusion to volume diffusion could be observed in the growth kinetics of (Cu,Ni,Pd)₆Sn₅. Moreover, the activation energy of IMC growth was evaluated using the Arrhenius equation. Pd may act as heterogeneous nucleation sites in the initial stage of soldering and lower the activation energy of (Cu,Ni,Pd)₆Sn₅, compared to (Cu,Ni)₆Sn₅. The lower activation energy of (Cu,Ni,Pd)₆Sn₅ growth ensured that no phase transformation occurred in the SAC305/ENEPIG joints, which may benefit the solder joint reliability. Finally, the detailed influence of Pd on the growth kinetics of IMC formation was investigated and discussed.     

Complex impedance spectroscopy studies of PLZT (5/52/48) ceramics synthesized by sol–gel route

The polycrystalline perovskite Pb_0.95La_0.05(Zr_0.52Ti_0.48)O₃ ceramic material was prepared by sol–gel route. Structural, phase formation and thermal properties were confirmed by X-ray diffraction, thermogravimetry and differential thermal analysis. The microstructural study was carried out using scanning electron microscope. The electrical properties of the ceramics were investigated within a wide range of both temperature (from 25 to 500 °C) and frequency (from 100 Hz to 1 MHz) using complex impedance spectroscopy. The impedance spectrum results indicate the decrease in dielectric constant with increase in frequency while the dielectric loss increases with frequency. The activation energy of the sample was calculated as 0.124 eV from the Arrhenius plot of dc conductivity vs. inverse of absolute temperature. The remnant polarization (P_r) and coercive electric fields (E_c) are found out as 5.97 μC/cm² and 8.89 kV/cm from the ferroelectric loop measured at room temperature.     

Room-temperature photodiodes based on InAs/InAs<Subscript>0.88</Subscript>Sb<Subscript>0.12</Subscript>/InAsSbP heterostructures for extended (1.5–4.8 μm) spectral range

Photodiodes with a photosensitive area of 0.45 × 0.45 mm² operating at room temperature in a wavelength range bounded by 4.9 μm have been created on the basis of InAs/InAs_0.94Sb_0.06/InAsSbP/InAs_0.88Sb_0.12/InAsSbP/InAs heterostructures grown by liquid phase epitaxy. A distinguishing feature of the proposed photodiodes is extended (λ_max = 1.5–4.8 μm) spectral sensitivity range, in which the photodiode is characterized by a monochromatic responsivity of 0.5–0.8 A/W and a dark current density of 1.0–1.5 A/cm² at a reverse bias of 0.2 V. The differential resistance at zero bias reaches up to 20–100 Ω. The detection ability of photodiodes in the region of maximum sensitivity reaches (1–2) × 10⁸ cm Hz^1/2 W⁻¹.     

High-pressure Synthesis and Physical Characterization of Y-based 1222-type Niobio–Cuprate NbSr2(Y1.5Ce0.5)Cu2O10

We have successfully synthesized a new 1222-type Y-based niobio-cuprate for the first time with the chemical composition, NbSr₂(Y_1.5Ce_0.5)Cu₂O₁₀ by a high-pressure and high-temperature (HPHT) technique under different synthesis conditions. Good quality (nearly single-phase) Nb1222Y polycrystalline sample was synthesized at 1,450^?○C and 6 GPa for 2 h. It crystallizes in a tetragonal symmetry of space group I4/mmm with lattice parameters a=b=3.863(2) Å and c=28.687(5) Å, which is isostructural with the corresponding Ru1222Y (RuSr₂(Y_1.5Ce_0.5)Cu₂O₁₀) phase. The dc-magnetic susceptibility measurements show a mixed magnetic state at ～29 K, which is apparently associated with magneto-superconductivity. The magnetic moment (M) versus field (H) curve of Nb1222Y sample measured at 1.8 K looks like a hybrid and it normally ensembles for both superconducting and a ferromagnetic curve. As the field increases, a low field diamagnetic signal emerges. However, temperature dependence of electrical resistivity of Nb1222Y did not show superconductivity, but semiconducting nature with a relatively large magnetoresistance (～6% at almost entire region). No specific heat anomaly was observed at the vicinity of the transition temperature.     

Polarized spectral properties and 1.5–1.6 μm laser operation of Er:Sr3Yb2(BO3)4 crystal

Undoped and Er³⁺-doped Sr₃Yb₂(BO₃)₄ crystals were grown by the Czochralski method. Room temperature polarized spectral properties of the Er:Sr₃Yb₂(BO₃)₄ crystal were investigated. The efficiency of the energy transfer from Yb³⁺ to Er³⁺ ions in this crystal was calculated to be about 95%. End-pumped by a diode laser at 970 nm in a hemispherical cavity, a 0.75 W quasi-CW laser at 1.5–1.6 μm with a slope efficiency of 7% and an absorbed pump threshold of 3.8 W was achieved in a 0.5-mm-thick Z-cut crystal glued on a 5-mm-thick pure YAG crystal with UV-curable adhesive.     

Effect of different catalyst supports on the (n,m) selective growth of single-walled carbon nanotube from Co–Mo catalyst

Co–Mo catalysts supported on four different high surface area oxides (SiO₂, Al₂O₃, MgO, and TiO₂) were evaluated to investigate the (n,m) selectivity control in single-walled carbon nanotube (SWCNT) synthesis. Results from Raman spectroscopy and thermogravimetric analysis showed that Co–Mo catalysts supported on SiO₂ and MgO possessed good selectivity toward SWCNTs, while photoluminescence and ultraviolet–visible–near-infrared spectroscopy results indicated that these two catalyst supports induced the same (n,m) selectivity to near-armchair tubes, such as (6,5) and (7,5) tubes. Catalysts supported on TiO₂ produced a mixture of multi-walled carbon nanotubes (MWCNTs) and SWCNTs, whereas catalysts supported on Al₂O₃ mainly grew MWCNTs. Characterization of catalysts by ultraviolet–visible diffuse reflectance spectroscopy suggested that the surface morphology of metal clusters over different supports was not directly responsible for the (n,m) selectivity. Analysis of monometallic (Co or Mo) and bimetallic (Co–Mo) catalysts using temperature program reduction demonstrated that catalyst supports changed the reducibility of metal species. The interaction between supports and Co/Mo metals perturbed the synergistic effect between Co and Mo, leading to the formation of different metal species that are responsible for the observed distinction in SWCNT synthesis.     

Electrical properties of Pd–Au/(In x –Sn1 – x ) Oxide/Si(p)/Al heterojunction diodes

Current–voltage (I–V ) and capacitance–voltage – characteristics of [Pd–Au/( – ) Oxide/Si(p)/Al] semiconductor oxide semiconductor (SOS) solar cells were measured in the temperature range between 300 and 500 K. The dark forward current–voltage curves were found to be independent of temperature. Consequently, the diode quality factor was temperature dependent. Analysis of the data indicated that the predominant carrier transport mechanism of the samples in the intermediate bias voltage region was thermionic field emission and recombination tunneling. From the experimental data it was found that, the open circuit voltage – , the short circuit current – and the fill factor 0.28–0.32, under illumination of 1124 lux.     

Positional isomerism,stability, and polarizability of C20(CH2)n (n = 1–10), the cyclopropane adducts of the smallest fullerene: General formula for calculation of mean polarizability of fullerene derivatives C20XnYm and C60XnYm with fixed (n + m) number of different addends

All regioisomers of fullerene adducts C₂₀(CH₂)_n have been found and their stability and polarizability have been studied by the PBE/3ζ method. As in the case of the C₆₀ and C₇₀ adducts, mean polarizability of C₂₀(CH₂)_n quadratically depends on the number of addends and demonstrates the depression, viz. negative deviation of polarizability from the linear additive scheme. Another, linear formula is proposed for calculating mean polarizability of the C₂₀ and C₆₀ fullerene adducts with mixed functionalization C₂₀(CH₂)_nO_m and C₆₀(CH₂)_nO_m and fixed number of addends. The obtained results will be further used to work out the algorithm for counting all possible C₆₀X_n cycloadducts and searching a general formula for calculation of the C₆₀X_nY_m polarizability with variable (n + m) number of addends.