Properties of aminosilane precursors for the preparation of Si-C-N films

R _n Si(NEt₂)_{4 − n} aminosilanes have been synthesized by reacting the R _n SiCI_{4 − n} (R = H, CH₃; n = 1, 2) organylchlorosilanes with diethylamine. Using IR, UV, and NMR (¹H, ¹³C, and ²⁹Si) spectroscopies and elemental analysis, we have identified the reaction products and determined their spectroscopic characteristics. Vapor pressure measurements have been used to determine the saturated vapor pressure as a function of temperature and calculate the thermodynamic characteristics of vaporization. Thermodynamic modeling of chemical vapor deposition processes has been performed with the aim of predicting the phase composition of the deposit as a function of the nature of the precursor and process conditions.     

Hot deformation of AA6082-T4 aluminum alloy

High-temperature tensile deformation of 6082-T4 Al alloy was conducted in the range of 623–773 K at various strain rates in the range of 5 × 10⁻⁵ to 2 × 10⁻² s⁻¹. Stress dependence of the strain rate revealed a stress exponent, n of 7 throughout the ranges of temperatures and strain rates tested. This stress exponent is higher than what is usually observed in Al–Mg alloys under similar experimental conditions, which implies the presence of threshold stress. This behavior results from dislocation interaction with second phase particles (Mg₂Si). The experimental threshold stress values were calculated, based on the finding that creep rate is viscous glide controlled, based on creep tests conducted on binary Al–1Mg at 673 K, that gave n a value of 3. The threshold stress (σ _o) values were seen to decrease exponentially with temperature. The apparent activation energy for 6082-T4 was calculated to be about 245 kJ mol⁻¹, which is higher than the activation energy for self-diffusion in Al (Q _d = 143 kJ mol⁻¹) and for the diffusion of Mg in Al (115–130 kJ mol⁻¹). By incorporating the threshold stress in the analysis, the true activation energy was calculated to be about 107 kJ mol⁻¹. Analysis of strain rate dependence in terms of the effective stress (σ − σ _o) using normalized parameters, revealed a single type of deformation behavior. A plot of normalized strain rate () versus normalized effective stress (σ − σ _o)/G, on a double logarithmic scale, gave an n value of 3. Ehab A. El-Danaf—on leave from the Department of Mechanical Design and Production, College of Engineering, Cairo University, Egypt.     

LO phonon–plasmon coupled modes and carrier mobilities in heavily Se-doped Ga(As, N) thin films

We use Raman scattering to study the LO–plasmon coupled modes (LOPCMs) of n-type GaAs_1−x N _x epilayers grown by molecular beam epitaxy (0.1% ≤ x ≤ 0.36%). We find that the LOPCMs are heavily damped in n-GaAs_1−x N _x even for x as low as 0.1%. From a lineshape analysis based on the hydrodynamical model, we evaluate the lifetime of the LOPCMs in our samples. We compare the values thus obtained with the corresponding Hall mobilities. We find that both quantities decrease strongly with increasing x, which can be attributed to N-related alloy scattering of conduction band electrons in the GaAs_1−x N _x alloy.     

Doping of Bi-Sr-Ca-Cu-O superconductors with Pb,Sn and Ag

Basic and substituted superconductors in the homologous series Bi₂Sr₂Ca _n−1Cu _n O_2n+4+y , Bi_2−x/2Sr_2−x/2L _x Ca _n−1Cu _n O_2n+4+y and Bi₂Sr_2−x L _x Ca _n−1Cu _n O_2n+4+y (L=Sn, Pb or Ag,x=0−0.4,n=2, 3 or 4) have been synthesized. All the prepared ceramic samples show superconducting behaviour with zero resistance atT _c=70 to 85 K. The compounds withn=3 or 4 showed onset temperature around 115K indicating involvement of a disproportionate solid-state reaction and formation of a two-phase system. The phase involving tin or lead oxides showed similar superconducting properties. Final rapid quenching of samples contributed to preservation of the high temperature equilibria with higher solubility of tin oxide in the quaternary system Bi-Sr-Ca-Cu-O. Silver was not soluble but precipitated in a colloidal form at interfaces between the crystalline grains.     

Atmospheric effects on the thermally induced sintering of nanoparticulate gold films

Gold (Au) films were formed by sintering of Au nanoparticles (NPs) under gas flows of air, oxygen (O₂), nitrogen (N₂), or N₂ bubbled through formic acid (FA/N₂). The microstructure changes of the Au nanoparticulate films were studied when different atmospheres were applied. The Au film sintered under FA/N₂ showed the progressive agglomeration and grain growth with porosity in the film, while the film sintered under N₂ had NPs without participating grain growth. A necking between NPs was observed in the film, however, unnecked NPs were still found. The Au film sintered under O₂ atmosphere showed the NPs agglomeration with various sizes up to 50 nm. X-ray characteristic peaks of the (111)-preferred orientation were observed in all samples. All samples showed N–H stretching at 3200–3300 cm⁻¹ regardless of sintering atmosphere. Hydrocarbon chains (C–H) at 2850–3000 cm⁻¹ were detected in the film sintered under N₂. For the Au film sintered under O₂, C–H stretching at 2850–3000 cm⁻¹, C–H deformation at 1350–1470 cm⁻¹, and C–O stretching at 1200–1300 cm⁻¹ were observed. C–O stretching at 1600–1700 cm⁻¹ was observed for the film sintered under FA/N₂ atmosphere. The electrical resistance of the film was related with microstructures and organic residual materials left in the film. Even though either porosity or carbon residues were observed in the film, the sintering of NPs in FA/N₂ or N₂ showed the sheet resistance comparable to that of electroplated one.     

Supercapacitive performance of hydrous ruthenium oxide (RuO<Subscript>2</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O) thin films deposited by SILAR method

The amorphous hydrous ruthenium oxide (RuO₂·nH₂O) thin films were deposited by a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method. These films were characterized for their structural, surface morphological, and compositional study by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDAX) techniques. The wettability test was carried out by measuring the water contact angle. The scanning electron microscopy study showed small RuO₂ particles are grouped together to form porous agglomerates. The FT-IR study confirmed the formation of hydrous ruthenium oxide films. The hydrophilic nature of ruthenium oxide (RuO₂·nH₂O) thin films was observed from water contact angle measurement. The presence of Ru and O in the film was confirmed by EDAX analysis. The supercapacitor behavior of these films studied in 0.5 M H₂SO₄ electrolyte showed maximum specific capacitance of 162 F g⁻¹ at 10 mV s⁻¹ scan rate. These films exhibit 80% cycling performance after 2,000 cycles. The charge–discharge studies carried at 1 mA cm⁻² current density revealed the specific power of 3.5 KW kg⁻¹ and specific energy of 29.7 W Kg⁻¹ with 93% coulombic efficiency.     

Photoluminescence and thermal stability of yellow-emitting Sr-α-SiAlON:Eu<Superscript>2+</Superscript> phosphor

Novel α-SiAlON:Eu²⁺-based yellow oxynitride phosphors with the formula Sr_0.375−x Eu _x ²⁺Si_12−m−n Al _m+n O _n N_16−n (m = 0.75, n = x = 0.004–0.04) have been prepared by firing the powder mixture of SrSi₂, α-Si₃N₄, AlN, and Eu₂O₃ at 2,000 °C for 2 h under 1 MPa nitrogen atmosphere. The luminescence properties, the dependence of the activator concentration of Eu²⁺ and the thermal stability of Sr-α-SiAlON:Eu²⁺ phosphor have been investigated in comparison with Ca-α-SiAlON:Eu²⁺ phosphor. Similar to Ca-α-SiAlON:Eu²⁺ phosphor, Sr-α-SiAlON:Eu²⁺ phosphor has the excitation wavelength ranging from the ultraviolet region to 500 nm, and exhibit intense yellow light. The strongest luminescence was achieved at about x = 0.02 with the emission peak at 578 nm, slightly shorter than that of Ca-α-SiAlON:Eu²⁺ phosphor at 581 nm. Temperature-dependent emission intensity of Sr-α-SiAlON:Eu²⁺ phosphor is comparable to that of Ca-α-SiAlON:Eu²⁺ phosphor. The results suggest that the different position of the emission peak for Sr- and Ca-α-SiAlON:Eu²⁺ depends on the composition and the Stokes shift, and the thermal stability is nearly independent of Sr and Ca or fixed by the network of (Si, Al)–(O, N) in α-SiAlON at the same Eu²⁺ concentration.     

Heating Characteristics of Transformer Oil-Based Magnetic Fluids of Different Magnetic Particle Concentrations

The heating ability of mineral oil-based magnetic fluids with different magnetic particle concentrations is studied. The calorimetric measurements were carried out in an alternating magnetic field of 500 A · m⁻¹ to 2500 A · m⁻¹ amplitude and of 1500 kHz frequency. The revealed H ⁿ law-type dependence of the temperature increase rate, (dT/dt) _t=0, on the amplitude of the magnetic field indicates the presence of superparamagnetic and partially ferromagnetic particles in the tested samples since n > 2. The specific absorption rate (SAR) defined as the rate of energy absorption per unit mass increases with a decrease of the volume fraction of the dispersed phase. This can be explained by the formation of aggregates in the samples with a higher concentration of magnetic particles.     

Crystal structure and negative thermal expansion of solid solution Y<Subscript>2</Subscript>W<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Mo<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>12</Subscript>

A new series of solid solutions Y₂W_3−x Mo _x O₁₂ (0.5 ≤ x ≤ 2.5) were successfully synthesized by the solid state method. Their crystal structure and negative thermal expansion properties were studied using high-temperature X-ray powder diffraction and the Rietveld method. All samples of rare earth tungstates and molybdates were found to crystallize in the same orthorhombic structure with space group Pnca, and show the negative thermal expansion phenomena related to transverse vibration of bridging oxygen atoms in the structure. Thermal expansion coefficients (TEC) of Y₂W_3−x Mo _x O₁₂ were determined as −16.2 × 10⁻⁶ K⁻¹ for x = 0.5 and −16.5 × 10⁻⁶ K⁻¹ for x = 2.5 in the identical temperature range of 200–800 °C. High-temperature XRD data and bond length analysis suggest that the difference between W–O and Mo–O bond is responsible for the change of TECs after the element substitution in this series of solid solutions.     

Nonlinear optical characterization and measurement of optical limiting threshold of CdSe quantum dots prepared by a microemulsion technique

CdSe quantum dots prepared by micro emulsion technique shows quantum confinement effect and broad emission at 532 nm. These quantum dots have about 4.35 nm size, and they exhibit good nonlinear effects which are measured using z-scan technique. The samples have a reverse saturation in the nonlinear absorption as nonlinear optical absorption coefficient β is 2.545 × 10⁻¹⁰ W m⁻¹ and nonlinear optical refraction coefficient n ₂ is −1.77 × 10⁻¹⁰ esu. The third-order nonlinear optical susceptibility is found to be 4.646 × 10⁻¹¹ esu and also the figure of merit is 2.01 × 10⁻¹² esu m. The optical limiting threshold which is found to be 0.346 GW/cm² makes it a good candidate for device fabrication.     

Fe–Ga–As precipitates and their magnetic domain structures in high-dose iron implanted GaAs

The integration of ferromagnetism with semiconductors to fabricate ferromagnetic semiconductors has been believed to be a potential way to make new spintronic devices. We have synthesized ferromagnetic Fe₃Ga_2−x As _x nanoparticles in the surface of GaAs by employing ion implantation and rapid thermal annealing processes. Transmission electron microscopy revealed that these nanoparticles exist only in the top surface of the GaAs samples, with sizes from several to hundreds of nanometers. They have two orientation relationships to the GaAs matrix: [1 − 210]_p//[011]_m, (10 − 10)_p//(−42 − 2)_m and (0002)_p//(11 − 1)_m; and [1 − 210]_p//[011]_m, (−1010)_p//(42 − 2)_m and (0002)_p//(−11 − 1)_m. The magnetic structures of the precipitates were studied by magnetic force microscopy. Results indicate that most of the ferromagnetic nanoparticles have single magnetic domains with their magnetic poles randomly orientated.     

Thermal properties and crystallization of PbO–MoO3–P2O5 glasses

Thermal properties and crystallization of glasses from PbO–MoO₃–P₂O₅ ternary system were studied in three compositional series (100 − x)[0.5PbO–0.5P₂O₅]–xMoO₃ (A), 50PbO–yMoO₃–(50 − y)P₂O₅ (B), and (50 − z)PbO–zMoO₃–50P₂O₅ (C). Glass transition temperature, crystallization temperature, coefficient of thermal expansion, and dilatation softening temperature of the studied glasses were determined by differential thermal analysis and dilatometry. Crystallization products of annealed glass samples were investigated by X-ray diffraction and Raman spectroscopy. X-ray diffraction analysis of crystallized glasses revealed the formation of PbP₂O₆, Pb₃P₄O₁₃, and PbMoO₄ in the samples of the B series. In the series A and C in the samples with a high MoO₃ content, crystalline compounds of Pb(MoO₂)₂(PO₄)₂ and (MoO₂)(PO₃)₂, respectively, were identified. Raman spectra of crystalline samples confirmed the results of X-ray diffraction measurements and provided also information on thermal stability of glasses and formation of glass-crystalline phases in the studied glass series.     

Thermal properties of multicomponent tellurite glass

Quaternary tellurite glass systems of the form 80TeO₂–5TiO₂–(15 − x)WO₃ − xA_nO_m where A_nO_m is Nb₂O₅, Nd₂O₃, and Er₂O₃, x = 0.01, 1, 3, and 5 mol% for Nb₂O₅ and x = 0.01, 0.1, 1, 3, 5, and 7 mol% for Nd₂O₃ and Er₂O₃, have been prepared by the melt quenching. Density and molar volumes have been measured and calculated for every glass system. The thermal behavior of the glass series was studied by using the differential thermal analysis DSC. Glass transition temperature T _g, crystallization temperature T _c, and the onset of crystallization temperature T _x were determined. The glass stability against crystallization S (≈100 °C) and glass-forming tendency K _g (≈0.3) have been calculated. Specific heat capacity C _p (≥1.4 J/g °C) was measured from room temperature and above the T _g for every composition in each glass series. Quantitative analysis of the above thermal properties of these new tellurite glass with the structure parameters like average cross-link density (≥2.4), number of bonds per unit volume n _b (≥8 × 10²⁸ cm⁻³), and the average stretching force constant (F) have been studied for every glass composition.     

Electrochemical synthesis and characterization of a new soluble conducting polymer

Electroactive poly(4-methyl carbazole-3-carboxylic acid) (PMCCA) film was formed on Pt electrode surface by oxidative electropolymerization of a new carbazole derivative. The structure of the soluble polymer was elucidated by nuclear magnetic resonance (¹H and ¹³C NMR) and Fourier transform infrared (FTIR) spectroscopy. The average molecular weight has been determined by gel permeation chromatography (GPC) to be M _n = 51,000 for the electrochemically synthesized polymer. Characterizations of the resulting polymer were performed by cyclic voltammetry, dry conductivity measurement, scanning electron microscopy, and UV-vis spectroscopy. Spectroelectrochemical studies indicated that PMCCA films revealed a green color in the oxidized state and a high transmittance in the neutral state. The conductivities of PMCCA are in the range of 10⁻⁵–10⁻⁴ S cm⁻¹.     

Yttrium-doped effect on thermoelectric properties of La0.1Sr0.9TiO3 ceramics

Ceramic samples of La_0.1Y _x Sr_0.9–x TiO₃ with different yttrium concentration have been synthesized by conventional solid state reaction technique, and their thermoelectric properties have been investigated. X-ray diffraction characterization confirms that the main crystal structure is of perovskite, but with a small amount of second phase of Y₂Ti₂O₇ for samples with x = 0.05, 0.08, and 0.10. SEM images indicate all ceramic samples are dense and compact, and the largest grain size appears in sample with x = 0.03 and 0.05. Also the second phase can also be identified from the SEM images for x = 0.05, 0.08, and 0.10 samples. Electrical conductivity and Seebeck coefficient of samples have been measured in the temperature range between 300 and 1100 K. With increasing of yttrium concentration, electrical resistivity decreases, and reaches 0.8 mΩ cm for x = 0.10 sample at room temperature. The absolute Seebeck coefficients increase monotonically with increasing temperature in the whole temperature range. Sample with x = 0.03 exhibits the highest absolute Seebeck coefficient 219 μV K⁻¹ at 1059 K, as well as the maximum power factor 11 μW cm⁻¹ K⁻² at 624 K.     

How Grain-Boundaries Influence the Intergranular Critical Current Density of Cu1−x Tl x Ba2Ca3Cu4O12−δ Superconductor Thin Films?

The insulating and metallic behavior of the grain-boundary weak links has been studied in thallium rich and the samples with small amount of thallium in the charge reservoir layer of Cu_1−x Tl _x Ba₂Ca₃Cu₄O_12−δ superconductor thin films. The influence of the nature of grain boundaries on the inter-granular critical current density (J _c) has also been investigated. From the power law dependence of H _ac∼(1−T _p/T _c) ⁿ , it was observed that n=1 gives a best fit for the J _c of thallium rich samples and n=2 provides a best fit for the J _c of the samples with small amount of thallium. The polycrystalline thin film samples showing the power law dependence of J _c as n=1 make superconductor-insulator-superconductor (SIS) type while the samples with n=2 follow superconductor-normal metal-superconductor (SNS) types of Josephson junctions. The insulating grain boundaries decrease the inter-granular Josephson coupling and hence the transport properties are suppressed.      

New cyano-substituted copolymers containing biphenylenevinylene and bithienylenevinylene units: synthesis,optical, and electrochemical properties

Two new cyano-substituted copolymers containing biphenylenevinylene and bithienylenevinylene moieties (DCN-PPV and DCN-PTV) were synthesized by a stille condensation reaction with Pd(PPh₃)₄ as catalyst. Their structures were confirmed by ¹H NMR, IR spectroscopy, and elemental analysis. The thermal, optical, and electrochemical properties of the polymers were investigated. The results show that the polymers possess high thermal decomposition temperature and reversible n-doping/dedoping processes. In addition, DCN-PTV has higher electron affinity with a low LUMO energy level of −3.84 eV and a relatively broader absorption band covering 300–780 nm, indicating that DCN-PTV could be a potential n-type conjugated polymer in optoelectronic devices.     

Extraction of Critical Current Density and Flux Creep Exponent in the Magnetic Superconductor Ru-1212 Using the ac Magnetic Susceptibility Measurements

The ac susceptibility data was employed to extract the temperature dependence of the critical current density, J _c(T), as well as the variation of flux-creep exponent n(T,H _ac) with temperature and ac field amplitude in bulk samples of polycrystalline magnetic superconductor RuSr₂GdCu₂O₈ (Ru-1212). The critical state models and the collective flux-creep approximation model were successfully accounted to describe such behavior below the transition temperature. The calculated values of n(T,H) are well fitted to a power law of the following form: n(T,H)=n ₀(H)T ^−s(H), where s is field dependent exponent whose values varied from −2.4, −1.01 for field amplitudes ranging from 0.5 G and 3.8 G. The power law describing the frequency dependence of χ′ is found to be consistent with the results of the current-dependent effective activation energy of the form U(J)=U ₀ln (J _c/J). Additionally, the dependence of the current density is found to scale according as: J _c(T)=J _c0(1−T/T _c) ⁿ , where the exponent n values varied from 1.05 to 1.25. Such dependence is an indication of intergrain coupling that could be ascribed in terms of superconductor–insulator–superconductor junctions. The derived temperature dependence of J _c(T) is in good agreement with the data obtained from the measurements using the traditional “loss-maximum” approach. Furthermore, the flux-creep effect increased with increasing both ac fields and temperatures except at about 15–25 K below the onset of T _c, where a slowing down of the flux creep was observed.     

Experimental study of the intergranular weak link structures YBa2Cu3O7−x with the help of magnetization measurements

AC and DC virgin magnetizations of sintered YBa₂Cu₃O_7−x samples have been measured in dependence of the sintering temperature. The samples were prepared by solid state reaction of stoichiometric decarbonated mixture of Y₂O₃, BaCO₃ and CuO components. Magnetization curves were measured at 77K in the range of magnetic field (10⁻¹−2×10⁴ Am ⁻¹). The temperature of sintering was being changed in the range 910°C up to 950°C. In the range of weak magnetization fields the magnetization curves are affected by properties of the intergranular medium — the intergranular weak links. The parameters H ₁ ^w1 , H ₂ ^w1 and H ₁ ^g characterising the flux penetration into intergrain and intragrain medium were estimated from the magnetization measurements.     

Proton conduction in BaxCe0.8Y0.2O3?α?+?0.04ZnO at intermediate temperatures and its application in ammonia synthesis at atmospheric pressure

Dense ceramic samples Ba _x Ce_0.8Y_0.2O_3−α + 0.04ZnO (x = 1, 0.98, 0.96, 0.94) were successfully prepared by a solid-state reaction method, whose sintering temperature was about 573 K lower than a traditional solid state reaction method without sintering aid. XRD patterns indicated that all the samples exhibited a single-phase of orthorhombic perovskite structure. The conduction behavior was investigated by alternating current impedance in wet hydrogen atmosphere at 673–1073 K. It was found that the conductivities were affected by the nonstoichiometric amount of Ba, and increased in the order: σ (x = 0.94) < σ (x = 1) < σ (x = 0.96) < σ (x = 0.98). It was also found that the samples were almost pure ionic conductors and contributed mainly by proton and partially by oxide ion in wet hydrogen atmosphere at 773–1073 K. The ammonia synthesis at atmospheric pressure was successfully conducted using an electrolytic cell based on Ba_0.98Ce_0.8Y_0.2O_3−α + 0.04ZnO. The ammonia formation rate reached 2.36 × 10⁻⁹ mol s⁻¹ cm⁻² under the suitable conditions of 0.8 mA and 773 K.