Design of a thermal tunable photonic-crystal coupler

Wavelength division multiplexing (WDM) is a common technique used to increase the capacity of optical communication networks. In this technique, data coming from different sources are transmitted through the same optical fiber using different optical carriers. We study a thermally controlled tunable photonic-crystal optical coupler. The device is designed using a triangular lattice of air holes in an epitaxially layered structure (InGaAsP/InP). In this configuration, the input and output waveguides are separated from each other, in contrast to other devices that require a reflective grating and circulators or beam splitters. We use the two-dimensional finite-difference time-domain method (2D-FDTD) to analyze the performance of this device. After optimization the parameters of this device, we study the effects of changing the temperature. Not only has the position of the resonant peak changed linearly with the temperature, but the efficiency is also doubled. A linear regression of the spectral response gives a slope of dλ/dT = +0.1 nm/°C in a temperature range of ΔT = 50°C for wavelengths close to 1550 nm. These results show the possibility of tuning this contra-directional coupler using the thermo-optical effect.     

Europium(III) Concentration Effect on the Spectroscopic and Photoluminescent Properties of BaMoO4:Eu

BaMoO₄:Eu (BEMO) powders were synthesized by the polymeric precursor method (PPM), heat treated at 800 °C for 2 h in a heating rate of 5 °C/min and characterized by powder X-ray diffraction patterns (XRD), Fourier Transform Infra-Red (FTIR) and Raman spectroscopy, besides room temperature Photoluminescence (PL) measurements. The emission spectra of BEMO samples under excitation of 394 nm present the characteristic Eu³⁺ transitions. The relative intensities of the Eu³⁺ emissions increase as the concentration of this ion increases from 0.01 to 0.075 mol, but the luminescence is drastically quenched for the Ba_0.855Eu_0.145MoO₄ sample. The one exponential decay curves of the Eu^{3+ 5}D₀→⁷F₂ transition, λ _exc = 394 nm and λ _em = 614 nm, provided the decay times of around 0.54 ms for all samples. It was observed a broadening of the Bragg reflections and Raman bands when the Eu⁺³ concentration increases as a consequence of a more disordered material. The presence of MoO₃ and Eu₂Mo₂O₇ as additional phases in the BEMO samples where observed when the Eu³⁺ concentration was 14.5 mol%.     

Electrical conductivity and chemical stability of perovskite-type BaCe0.8-xTixY0.2O3-δ

Here we report the synthesis, chemical stability, and electrical conductivity of Ti-doped perovskite-type BaCe_0.8-x Ti _x Y_0.2O_3-δ (x = 0.05, 0.1, 0.2, and 0.3; BCTY). Samples were synthesized by conventional solid state (ceramic) reaction from corresponding metal salts and oxides at elevated temperature of 1,300–1,500 °C in air. The powder X-ray diffraction confirmed the formation of a simple cubic perovskite-type structure with a lattice constant of a = 4.374(1), 4.377(1), and 4.332(1) ? for x = 0.05, 0.1, and 0.2 members of BCTY, respectively. Like BaCe_0.8Y_0.2O_3-δ (BCY), Ti substituted BCTY was found to be chemically not stable in 100% CO₂ and form BaCO₃ at elevated temperature. The bulk electrical conductivity of BCTY decreased with increasing Ti content and the x = 0.05 member exhibited the highest conductivity of 2.3 × 10⁻³ S cm⁻¹ at 650 °C in air, while a slight increase in the conductivity, especially at low temperatures (below 600 °C), was observed in humidified atmospheres.     

Photophysics, Photochemistry and Energetics of UV Light Induced Disulphide Bridge Disruption in apo-α-Lactalbumin

Continuous 295 nm excitation of whey protein bovine apo-α-lactalbumin (apo-bLA) results in an increase of tryptophan fluorescence emission intensity, in a progressive red-shift of tryptophan fluorescence emission, and breakage of disulphide bridges (SS), yielding free thiol groups. The increase in fluorescence emission intensity upon continuous UV-excitation is correlated with the increase in concentration of free thiol groups in apo-bLA. UV-excitation and consequent SS breakage induce conformational changes on apo-bLA molecules, which after prolonged illumination display molten globule spectral features. The rate of tryptophan fluorescence emission intensity increase at 340 nm with excitation time increases with temperature in the interval 9.3–29.9°C. The temperature-dependent 340 nm emission kinetic traces were fitted by a 1st order reaction model. Native apo-bLA molecules with intact SS bonds and low tryptophan emission intensity are gradually converted upon excitation into apo-bLA molecules with disrupted SS, molten-globule-like conformation, high tryptophan emission intensity and red-shifted tryptophan emission. Experimental Ahrrenius activation energy was 21.8 ± 2.3 kJ.mol⁻¹. Data suggests that tryptophan photoionization from the S₁ state is the likely pathway leading to photolysis of SS in apo-bLA. Photoionization mechanism(s) of tryptophan in proteins and in solution and the activation energy of tryptophan photoionization from S₁ leading to SS disruption in proteins are discussed. The observations present in this paper raise concern regarding UV-light pasteurization of milk products. Though UV-light pasteurization is a faster and cheaper method than traditional thermal denaturation, it may also lead to loss of structure and functionality of milk proteins.     

Fabrication of a Bi-luminophore Temperature Sensitive Coating by Embedding Europium Thenoyltrifluoroacetonate (EuTTA) and Perylene in Polystyrene

A new bi-luminophore system for optical sensing of temperature is described. The coating was fabricated by embedding europium thenoyltrifluoroacetonate (EuTTA) and perylene in polystyrene (PS) matrix. The luminescence emission of EuTTA was sensitive to temperature whereas perylene emission was temperature-insensitive and was used as a reference. Both luminophores were excited in the UV region of about 330 to 380 nm. The fluorescence emission of perylene and EuTTA occured at 474 nm and 615 nm respectively. The temperature sensitivities of both luminophores were influenced by (i) the type of polymer, and (ii) the concentration of luminophore in the matrix. Combining EuTTA and perylene in polystyrene matrix, a new bi-luminophore temperature sensing coating was developed. The temperature sensitivity of this coating was −1.80%/°C in the temperature range of 5 °C to 50 °C. The emission characteristics of this temperature sensitive coating displayed a fully reversible response to temperature.     

The sublimation growth of AlN fibers: transformations in?morphology & fiber direction

The growth of AlN fibers using sublimation method was investigated in the temperature range from 1600 °C to 2000 °C. Large-scale AlN fibers are obtained with diameters from 100 nm to 50 μm and lengths up to several millimeters. The fiber morphology and growth direction are characterized by X-ray diffraction (XRD), field emission scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), and Raman scattering. The fibers change from wire-like to prism-like in morphology and increase in diameter as rising temperatures, accompanying a transformation in axial direction from [10 ] to [0001]. The transformation in the growth direction is discussed in terms of AlN structure and supersaturation of AlN gas species. These results provide useful information for controlling the growth of large-scale AlN fibers.     

A novel anode-supported stable BaCe0.7Ta0.1Y0.2O3− δ membrane prepared by all-solid-state process for solid oxide fuel cells

BaCe_0.7Ta_0.1Y_0.2O_{3− δ} (BCTY) and BaCe_0.8Y_0.2O_{3− δ} (BCY) were synthesized by solid-state reaction method at 1,300 °C for 20 h. After being exposed in 3% CO₂ + 3% H₂O + 94% N₂ at 700 °C for 20 h, the BCTY exhibited adequate chemical stability against carbonations while BCY decomposed into BaCO₃ and CeO₂. The BCTY showed the similar thermal expansion behavior to BCY from room temperature to 1,000 °C in air. The BCTY displayed a conductivity of 0.007 S/cm at 700 °C in humid hydrogen, lower than that of BCY (0.009 S/cm). A fuel cell with 10-μm thick BCTY membrane prepared through an all-solid-state process exhibited 1.004 V for OCV, 330 mW/cm² for maximum output at 700 °C, respectively. Short-term test shows that the fuel cell performance does not degrade after 20 h.     

Pyroelectric properties of BiFeO3 ceramics prepared by a modified solid-state-reaction method

BiFeO₃ (BFO) ceramics were prepared by a modified solid-state-reaction method which adopts a higher heating/cooling rate during the sintering process than usually used. It was found that the calcination temperature T _cal (from 400 to 750°C) does not influence the BFO phase formation, while the sintering temperature T _sin (from 815 to 845°C) dominates the phase purity. The optimum sintering temperature was in the range from 825 to 835°C. The optimized samples exhibit saturated ferroelectric hysteresis loops with a remnant polarization of 13.2 μC/cm². The measured piezoelectric coefficient d ₃₃ was 45 pC/N. No remnant magnetization was observed in all of the samples. The pyroelectric properties were studied as a function of temperature and frequency. A pyroelectric coefficient as high as 90 μC/m² K was obtained at room temperature in the optimized sample. An abrupt decrease of the pyroelectric coefficient was observed at temperatures between 70 and 80°C. On the basis of our results, BFO may have the potential for pyroelectric applications.     

Determination of the optimal parameters for the fabrication of ZnO thin films prepared by spray pyrolysis method

In this work, ZnO thin films have been prepared by spray pyrolysis deposition method on the glass substrates. The effect of deposition parameters, such as deposition rate, substrate temperature and solution volume has been studied by X-ray diffraction (XRD) method, UV–Vis–NIR spectroscopy, scanning electron microscopy (SEM), and electrical measurements. The XRD patterns indicate polycrystalline wurtzite structure with preferred direction along (0 0 2) planes. Thin films have transparency around 90% in the visible range. The optical band gap was determined at 3.27 eV which did not change significantly. Evolution of electrical results containing the carriers’ density, sheet resistance and resistivity are in agreement with structural results. All the results suggest the best deposition parameters are: deposition rate, R = 3 ml/min, substrate temperature, T _s = 450°C and thickness of the thin films t = 110–130 nm.     

Proton-conducting hybrid membranes for medium temperature (>100 °C) fuel cells

Hybrid membranes doped with silicotungstic acid (STA) were prepared by sol–gel process with 3-glycidoxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, phosphoric acid, and tetraethoxysilane as chemical precursors. The thermogravimetry and differential thermal analysis measurements confirmed that the hybrid membranes were thermally stable up to 350 °C. Relatively, a high proton conductivity of 2.85 × 10⁻² S/cm was obtained for 10 mol% STA-doped hybrid membrane at 120 °C under 90% RH. The hydrogen permeability was found to decrease in the temperature range 20–120 °C from 1.64 × 10⁻¹⁰ to 1.36 × 10⁻¹⁰ mol/cm.s.Pa.     

Photoluminescence of fluoroacrylate polymers impregnated with Eu(bta)<Subscript>3</Subscript> using supercritical CO<Subscript>2</Subscript>

Optical properties (photoluminescence and absorption) of Eu(bta)₃(B) _n (B = H₂O or 1,10-phenanthroline) polycrystalline powders and fluoroacrylate polymers (FAPs) impregnated with these compounds using supercritical CO₂ (SC CO₂) were investigated. It was established that impregnation of Eu(bta)₃phen into the FAPs using an SC CO₂ solution was difficult to achieve. The type of B (ancillary ligand) and the polymer matrix were shown to influence the temperature quenching of photoluminescence of Eu³⁺ ions in the range 25–100°C. A comparative analysis of quantum yields (λ_ex = 300 and 380 nm) and photoluminescence decay times (λ_ex = 337.1 nm) for Eu(bta)₃B _n and for Eu(bta)₃B _n -doped FAPs was performed.     

Eu-doped B2O3–ZnO–PbO glass phosphor powders with?spherical shape and fine size prepared by spray pyrolysis

Eu-doped B₂O₃–ZnO–PbO glass phosphor powders with spherical shape and fine size were directly prepared by spray pyrolysis. The glass phosphor powders prepared at a temperature of 1100°C had broad XRD peak at around 28°. One glass phosphor powder was formed from one droplet at the preparation temperature range from 900 to 1100°C. The mean size of the glass phosphor powders was 0.75 μm. The glass transition temperature (T _g ) of the glass phosphor powders prepared by spray pyrolysis was 378.5°C. The excitation spectrum of the glass phosphor powders prepared at the optimum preparation temperature of 1100°C had bands at 362, 381, 392, 463, 525, and 532 nm. The glass phosphor powders had emission spectra with bands at 579, 614, and 653 nm. The glass phosphor powders with doping concentration of Eu of 7 wt% had the maximum photoluminescence intensity. The glass phosphor layer formed from the glass phosphor powders had high transparencies above 90%.     

Fluorescent Property of the Gd<Superscript>3+</Superscript>-Doped Terbium Complexes and Crystal Structure of [Tb(TPTZ)(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>]Cl<Subscript>3</Subscript>·3H<Subscript>2</Subscript>O

The complex of Tb(TPTZ)Cl₃·3H₂O was synthesized by adding the ethyl alcohol solution of TbCl₃ (1 mmol) to the solution of 2,4,6-tris-(2-pyridyl)-s-triazine(TPTZ,1 mmol) with constant stirring. The solution which had been filtered was kept at the room temperature for 4 weeks, and then a kind of transparent crystal was formed. Besides, nine kinds of solid complexes in the different molar proportion of terbium to gadolinium had been synthesized by adopting the similar method mentioned above. It was inferred from the elemental analysis and rare earth complexometry that the composition of these complexes is (Tb_xGd_y)(TPTZ)Cl₃·3H₂O (x : y = 0.9 : 0.1, 0.8 : 0.2, 0.7 : 0.3, 0.6 : 0.4, 0.5 : 0.5, 0.4 : 0.6, 0.3 : 0.7, 0.2 : 0.8, 0.1 : 0.9). The absorption spectra and photoluminescence of the complexes were determined in dimethylsulfoxide (DMF), which showed that the excitation of the complexes is mostly ligand based. The triplet state energy level of TPTZ was measured, indicating that the lowest excitation state energy level of Tb(III) and the triplet state energy level of TPTZ match well each other. The fluorescent data indicated that the fluorescent emission intensity of Tb³⁺ ions would be enhanced in the complexes after terbium was doped with Gd³⁺ ion. When x : y was 0.5 : 0.5, the fluorescent emission intensity was the largest. The result obtained by testing the X-ray diffraction of the monocrystal revealed that the molecular formula of the mono-crystal complex is [Tb(TPTZ)(H₂O)₆]Cl₃·3H₂O. The number of metal ion coordinates is nine, and the tridentate TPTZ and six water molecules are bonded with terbium respectively. Besides, it also revealed that the monocrystal belongs to the monoclinic system, and space group Cc with the following unit cell parameters is a = 1.4785 (3) nm, b = 1.0547 (2) nm, c = 1.7385 (4) nm, β = 94.42 (3)°, V = 2.7028 (9) nm³ and Z = 4.     

Fluorescent Carbon Dots Capped with PEG<Subscript>200</Subscript> and Mercaptosuccinic Acid

The synthesis and functionalization of carbon nanoparticles with PEG₂₀₀ and mercaptosuccinic acid, rendering fluorescent carbon dots, is described. Fluorescent carbon dots (maximum excitation and emission at 320 and 430 nm, respectively) with average dimension 267 nm were obtained. The lifetime decay of the functionalized carbon dots is complex and a three component decay time model originated a good fit with the following lifetimes: τ ₁ = 2.71 ns; τ ₂ = 7.36 ns; τ ₃ = 0.38 ns. The fluorescence intensity of the carbon dots is affected by the solvent, pH (apparent pK _a of 7.4 ± 0.2) and iodide (Stern-Volmer constant of 78 ± 2 M⁻¹).     

Properties of reactively sputtered W–B–N thin film as a diffusion barrier for Cu metallization on Si

Thin films of W–B–N (10 nm) have been evaluated as diffusion barriers for Cu interconnects. The amorphous W–B–N thin films were prepared at room temperature via reactive magnetron sputtering using a W₂B target at various N₂/(Ar + N₂) flow ratios. Cu diffusion tests were performed after in-situ deposition of 200 nm Cu. Thermal annealing of the barrier stacks was carried out in vacuum at elevated temperatures for one hour. X-ray diffraction patterns, sheet resistance measurement, cross-section transmission electron microscopy images, and energy-dispersive spectrometer scans on the samples annealed at 500°C revealed no Cu diffusion through the barrier. The results indicate that amorphous W–B–N is a promising low resistivity diffusion barrier material for copper interconnects.     

Synthesis, crystal structure, thermal and dielectric properties of bis(p-phenylenediammonium) chloride hexachlorobismuthate(III) monohydrate [C6H4(NH3)2]2ClBiCl6.H2O

Synthesis, crystal structure, and dielectric properties of [C₆H₄(NH₃)₂]₂ClBiCl₆.H₂O are reported. The compound crystallizes in the monoclinic system with space group P2₁/n. The unit cell dimensions are a = 9.836(5), b = 19.582(5), c = 13.082(5) ?, β = 104.731(5)° with Z = 4. The atomic arrangement can be described by an alternation of organic and inorganic layers. The anionic layer is built up of octahedral of [BiCl₆]^3- arranged in sandwich between the organic layers. The crystal packing is governed by means of the ionic N–H···Cl hydrogen bonds, forming a three-dimensional network. The dielectric properties have been investigated at temperature range from 297 to 410 K at various frequencies (10 Hz–100 kHz). Dielectric studies were performed to confirm results obtained with thermal analysis. The evolution of dielectric constant as a function of temperature and frequency of single crystal has been investigated in order to determine some related parameters.     

Low-temperature formation of nanocrystalline SiC particles and composite from three-layer Si/C/Si film for the novel enhanced white photoluminescence

In this article, nanocrystalline silicon carbide (nc-SiC) and composite have been synthesized at an annealing temperature as low as 750 °C through the thermal reaction of Si/C/Si multilayers deposited on the Si(100) substrate by ultra-high-vacuum ion beam sputtering (UHV IBS) compared with the conventional thermal formation of crystalline SiC (c-SiC) nanostructures above 1,000 °C. The evolution of microstructure and reaction between C and Si was examined by Raman spectroscopy, Fourier transform infrared spectrometer (FTIR), high-resolution field emission scanning electron microscope (HR-FESEM), and high-resolution transmission electron microscopy. The c-SiC nanoparticles (np-SiC) of around 20–120 nm in diameter appeared on the top and bottom of the three-layer film with a particle density of around 2.63 × 10¹⁰ cm⁻² after 750 °C annealing. The composite of nc-SiC and Si nanocrystals (nc-Si) size below 5 nm embedded in an amorphous SiC (a-SiC) matrix appeared at the interface between the Si and C layers. Efficient thermal energy is the driving force for the formation of nc-SiC and composite through interdiffusion between C and Si. The broad visible photoluminescence (PL) spectrum of 350–750 nm can be obtained from the annealed composite Si/C/Si multilayer and deconvoluted into four bands of blue (~430 nm), green (~500 nm), green–yellow (~550 nm), and orange (~640 nm) emission, corresponding to the emission origins from nc-SiC, sp² carbon clusters, np-SiC, and nc-Si, respectively.     

Preparation and characterization of Yb-doped Ba(Ce,Zr)O<Subscript>3</Subscript> nanopowders with high sinterability

The Ba(Ce_0.8Zr_0.2)_0.95Yb_0.05O_2.975 ceramics electrolyte was prepared via a Pechini method using metal nitrate salts as starting materials. An optimum annealing temperature of 1,400 °C was needed to obtain a pure perovskite-like phase with orthorhombic structure. Particle size distribution showed a bimodal distribution that corresponds to the loose powders and agglomerates size. Scanning electron micrograph revealed that the loose powders were in the nanosize range (70–200 nm). These ultrafine loose powders enhanced the densification of a pellet with relative density ∼95% obtained at 1,400 °C. The sample formed clear and compact grains with submicron sizes. Impedance results showed that the impedance semicircle of the grain was observed only at T ≤ 250 °C. The introduction of 20 mol% Zr improved the chemical stability of BaCe_0.95Yb_0.05O_2.975 sample in atmosphere containing carbon dioxide at 600 °C. The sample also exhibited high proton conductivity in wet hydrogen.     

Preparation of phosphors AEu(MoO4)2 (A?=?Li, Na, K and Ag) by?sol-gel method

A series of double molybdates phosphors AEu(MoO₄)₂ (A = Li, Na, K and Ag) have been prepared by sol-gel method. Their crystal structure and luminescent properties have also been investigated in a comparable way. The crystallization processes of the phosphor precursors were characterized by X-ray diffraction (XRD) and thermogravimetry-differential thermal analysis (TG-DTA). Field emission scanning electron microscopy (FE-SEM) was also used to characterize the shape and size distribution of the phosphors. Samples except KEu(MoO₄)₂ showed tetragonal scheelite structure in the range of our experiments, and no phase transition appeared. Phosphor KEu(MoO₄)₂ possessed two structures, and the phase transition took place at about 800°C. All samples with high purity could be obtained at about 500°C for 5 hours, and they all showed intense red light peaked at 616 nm originated from ⁵D₀→⁷F₂ emission of Eu³⁺ under the excitation of 465 nm or 394 nm light. The excitation spectra of phosphors AEu(MoO₄)₂ (A = Li, Na, and K) are composed of a strong broad charge transfer (CT) band and some sharp lines, and the relative intensity of CT band, the two strongest absorption lines at 395 nm and 465 nm are comparative, so these three phosphors are good red phosphor candidates for violet or blue LEDs. For the excitation spectrum of phosphor AgEu(MoO₄)₂, intensities of CT band and the absorption line at 395 nm are much weaker than that of line at 465 nm, thus phosphor AgEu(MoO₄)₂ is only suit for GaN-based blue LED.     

Performance of lithium-ion cells using 1 M LiPF<Subscript>6</Subscript> in EC/DEC (<Emphasis Type="Italic">v</Emphasis>/<Emphasis Type="Italic">v</Emphasis> = 1/2) electrolyte with ethyl propionate additive

In this work, 1 M LiPF₆:EC:DEC (v/v = 1/2) was used as a baseline electrolyte where EC is ethylene carbonate and DEC is diethyl carbonate. Ethyl propionate (EP) was used as an additive. The conductivity of the liquid electrolyte was obtained at ambient and elevated temperatures. The highest room temperature conductivity was observed at (8.05 ± 0.16) mS cm⁻¹ for the electrolyte containing 28.6 vol.% EP. Viscosity of the baseline and EP added baseline electrolytes have been measured at room and elevated temperatures. The electrolyte was also characterized by linear sweep voltammetry. The highest conducting electrolyte with 28.6 vol.% EP and the baseline electrolyte were used to fabricate several batteries. The batteries were charged and discharged at room temperature and at −20°C.