Copper coating on coir fibres

Conditions for obtaining continuous coatings of copper (thickness range 1.5 to 5μm) on coir fibres have been reported. Activation of the surface of coir fibres was achieved by treating the surface of the fibres with NaOH-HCHO/ammoniacal AgNO₃ solution. Copper was deposited on the activated surface of coir fibres from Fehling-formaldehyde solution. The effects of variation in formaldehyde and sodium hydroxide concentrations and pressures inside the coating vessel on deposition rates were determined. The minimum concentrations of NaOH and HCHO required for maintaining a maximum rate of deposition of copper from a solution contaning 10g l⁻¹ copper sulphate were found to be 6.6 g l⁻¹ and 2.5 to 3.5 g l⁻¹, respectively. Optical and scanning electron microscope studies show that relatively more uniform and non-porous copper coatings were obtained when deposition was carried out under reduced pressures. A 5μm thick copper coating on coir fibre prevents the propagation of flame as was shown by flammability tests. Copper coating on coir fibre decreases its electrical resistivity from 2.55×10⁶Ωcm to 4.68×10⁻³Ωcm with 1.5μm thick coating and 3.76×10⁻⁵Ωcm with 5μm thick coating. Reinforcement of polyester with copper-coated coir fibre leads to an increase of about 25% in tensile strength and flexural strength as compared to polyester reinforced with plain coir fibre.     

Effects of hydrogen annealing on the structural, optical and electrical properties of indium-doped zinc oxide films

Indium-doped zinc oxide (IZO) films were fabricated by radio-frequency magnetron sputtering. The effects of hydrogen annealing on the structural, optical and electrical properties of the IZO films were investigated. The hydrogen annealing may deteriorate the crystallinity of the films. The surfaces of the films would be damaged when the annealing temperature was higher than 350 °C. After the annealing, the surface roughness of the films would decrease, and high transparency of 80–90% in the visible and near-infrared wavelength would be kept. Meanwhile, the resistivity decreased from 1.25 × 10⁻³ Ωcm of the deposited films to 6.70 × 10⁻⁴ Ωcm of the annealed films. The work function of the IZO films may be modulated between 4.6 and 4.98 eV by varying the hydrogen annealing temperature and duration.     

Structural and magnetic studies of CTAC-assisted NiZn ferrite films by spray deposition

Spinel NiZn ferrite thin films were performed on polycarbonate glass substrates by spray deposited method at low temperature (<90 °C). After addition of cetyltrimethylammonium chloride(CTAC) made the adsorptive energy of substrate surface increase, smooth surface and uniform columnar film structures were obtained. The optimum reaction temperature up to 85 °C and the solution pH up to 7.5 were obtained. When the pH solution value increases from 6.5 to 7.5, the saturation magnetization accordingly increases to 2.48 × 10⁵ A/m and resistivity to 5.6 × 10² Ω cm. The high real permeability (μ′) of 36.1 and magnetic loss (μ″) of 53.2 for the ferrite film at 500 MHz were achieved. As the ferrite plate thickness is 1 mm, the attenuating characteristics for reflection loss ≤−10 dB can be obtained in the wide range between 0.5 GHz and 2.7 GHz.     

Online in-situ control of lead zirconate titanate film growth in gas discharge chamber

Online in situ monitoring of the gas-discharge deposition of lead zirconate titanate Pb(Zr _x Ti_{1 − x} )O₃ (PZT) films onto a stainless steel substrate revealed oscillatory decay in the intensity of light with a wavelength of 0.640 μm specular reflected from the growing film. It is established that the parameters of the reflectance curves depend on the electric power deposited in discharge and correlate with the type of growing films (possessing pyrochlore or perovskite structures). Using the proposed method, it is possible to control technological parameters of the deposition process, which determine the physical characteristics of the obtained PZT films.     

Fatigue,retention and switching properties of PLZT(x/30/70) thin films with various La concentrations

We investigated the fatigue, retention and switching properties of PLZT(x/30/70) thin films with various La concentrations. By applying 10⁹ square pulse switching cycles with a voltage of ±5 V to study the fatigue properties of the film, we found that the decrease of the initial polarization is improved from 64% to 40% as the La concentration is increased from 0 mol% to 10 mol%. The retention properties are also greatly improved as the decrease of the initial polarization decrease is reduced from 47% to 9% after 10⁵ s. The switching time is decreased from 0.8 μs to 0.55 μs as the La concentration is increased. While the dielectric constant of the PLZT thin films increases from 450 to 600 as the La concentration is increased, the dielectric loss and leakage current density measured at 100 kV/cm decrease from 0.075 to 0.025 and from 5.83 × 10⁻⁷ to 1.38 × 10⁻⁷ A/cm², respectively. By analyzing the hysteresis loops of the PLZT thin film measured at 175 kV/cm, we found that the remnant polarization and coercive electric field decrease from 20.8 μC/cm² to 10.5 μC/cm² and from 54.48 kV/cm to 32.12 kV/cm, respectively, as the La concentration is increased.     

Influence of precursor solution coating parameters on structural and dielectric properties of PZT thick films

Ferroelectric PZT(70/30) thick films were fabricated by the hybrid technique adding the sol-coating process to the normal screen-printing process to obtain a good densification. The screen-printing procedure was repeated four times to form PZT(70/30) thick films, and then PZT(30/70) precursor solution was spin-coated on the PZT thick films. All PZT thick films showed the typical XRD patterns of a perovskite polycrystalline structure. The thickness of all thick films was approximately 75–80 μm. The relative dielectric constant and dielectric loss of the PZT-6 thick film were 656 and 1.2%, respectively. The remanent polarization increased and coercive field decreased with increasing the number of sol coatings and the values of the PZT-6 thick films were 28.3 μC/cm² and 13.1 kV/cm, respectively. Leakage current density of PZT-6 thick films was 2.4 × 10⁻⁹ A/cm² at 100 kV/cm.     

Effect of hydrogen and temperature on the resistivity of an aluminum-2 wt % copper thin film

Thin metallic films are required to provide interconnection between contacts on devices and between devices. As device dimensions decrease, the low electrical resistivity becomes the most important issue in microelectronics industry. Recently in thin metallic films, hydrogen has been shown to lower the electrical resistivity of thin metallic films, reduce the rate of electromigration in interconnect lines, and lower the stress generated in thin metallic films during annealing. These effects are referred to as hydrogen effects. Low temperature resistivity measurements were performed to determine the effect of hydrogen and temperature on the resistivity of an aluminum-2 wt% copper film. Low temperature control experiments were performed in helium since it has a similar thermal conductivity as hydrogen but is chemically inert. The electrical resistivity of an aluminum-2 wt% copper alloy is lowered by hydrogen even at low temperature. The temperature coefficient of resistivity (TCR) values are identical within the experimental error (±0.005 cm/K). This means that phonon scattering is identical. So the decrease of the electrical resistivity is due to the decrease in the residual resistivity. Hydrogen effects are reversible for an aluminum-2 wt% copper alloy at room temperature because the adsorption and desorption of hydrogen occur. Hydrogen effects are slowly reversible for an aluminum-2 wt% copper alloy at low temperature because the adsorption of hydrogen occurs, but the desorption of hydrogen does not occur readily.     

Optical and electrical properties of SnO2 films prepared by chemical vapour deposition

Transparent and conducting SnO₂ films are prepared at 500°C on quartz substrates by chemical vapour deposition technique, involving oxidation of SnCl₂. The effect of oxygen gas flow rate on the properties of SnO₂ films is reported. Oxygen with a flow rate from 0·8–1·35 lmin⁻¹ was used as both carrier and oxidizing gas. Electrical and optical properties are studied for 150 nm thick films. The films obtained have a resistivity between 1·72 × 10⁻³ and 4·95 × 10⁻³ ohm cm and the average transmission in the visible region ranges 86–90%. The performance of these films was checked and the maximum figure of merit value of 2·03 × 10⁻³ ohm⁻¹ was obtained with the films deposited at the flow rate of 1·16 lmin⁻¹.     

Characteristics of pulse electrodeposited PbS thin films

PbS thin films were deposited for the first time using the pulse electrodeposition technique at different duty cycles in the range of 9 to 50% and at room temperature using lead nitrate and sodium thiosulphate. The thickness of the films increased from 0.5 to 1.0 μm with increase of duty cycle. The films were polycrystalline and exhibited cubic structure. The band gap of the films deposited at 50% duty cycle is 0.42 eV. The resistivities of the films decreased from 0.9 to 0.5 × 10⁵ ohm cm as the duty cycle increased. Films with grain size in the range of 20 to 35 nm were deposited. Films with refractive index varying in the range of 4.45–3.75 with increase of wavelength were obtained. Films with higher photosensitivity and higher detectivity compared to earlier reports were obtained.     

Complete desorption of interlayer hydrogen phosphate in Mg/Al-layered double hydroxides by means of anion exchange with 1-octanesulfonate

Hydrogen phosphate intercalated Mg/Al-layered double hydroxides (LDH-HPO₄) were synthesized by a homogeneous precipitation method with urea and anion exchange. The intercalated hydrogen phosphate was removed by anion exchange with Na₂CO₃, NaOH–NaCl, and 1-octanesulfonate solutions. The phosphate removal behavior was characterized by X-ray diffraction (XRD), Fourier Transform-InfraRed (FT-IR) spectroscopy, and elemental analysis. Complete removal of interlayer hydrogen phosphate from LDH-HPO₄ was realized using 1-octanesulfonate solution. Two reasons are proposed to explain complete hydrogen phosphate removal from the interlayer space of LDH-HPO₄. Complete desorption and cyclability suggest this is a viable technique to use as an efficient adsorption/desorption system in industrial applications.     

Preparation of high dispersed nickel pastes for thick film electrodes

Ultra-thinning of Ni paste films for BME-MLCC (Base Metal Electrode Multilayered Ceramic Capacitor) internal electrode was investigated. Adding various dispersants, ball-milling powder, and using the pre-dispersion process to improve Ni paste dispersion and properties of the paste electrodes/thick films, were employed. The paste containing 200 nm sized Ni powders, ethyl cellulose vehicle (η = 2.98 × 10⁴ mPa-s at 0.1 s⁻¹), and Emphos PS-21A as a dispersant proved to be the most desirable candidate. This paste thick film showed the smallest surface roughness (R _a = 0.10 μm and R _max = 0.97 μm) at a viscosity (η = 2.80 × 10⁵ mPa-s at 0.1 s⁻¹) adaptable to screen-printing. In addition, the Ni paste/thick film had the low sheet resistivity (ρ = 1.11 × 10⁻⁴ Ωcm) and an excellent microstructure after sintering at 1,290 °C for 3 h in a 97% N₂/3% H₂ atmosphere.     

A study of the effects of process variables on the properties of PZT films produced by a single-layer sol-gel technique

Thin films of PbZr_0.53 Ti_0.47O₃ have been prepared from diol-based sols. Films up to 1 μ thick could be produced by applying a single coating on to platinized silicon substrates. A number of processing variables ranging from sol composition through to firing conditions have been examined, and their effects on film microstructure and electrical properties evaluated. Control of the lead stoichiometry was found to be of critical importance in determining dielectric and ferroelectric parameters. Values of remanent polarization and coercive field of 22–27 μC cm ⁻² and 40–45 kV cm ⁻¹, respectively, could be obtained by compensating for PbO lost by volatilization during firing; corresponding relative permittivity values were 800–1000.     

Synthesis and characterization of nanocrystalline Mg2CoH5 obtained by mechanical alloying

The stoichiometric mixture of 2MgH₂ + Co was ball milled under a hydrogen atmosphere to synthesize nanocrystalline metal hydride Mg₂CoH₅. Upon milling, the mixture was analyzed by X-ray powder diffraction (XRD) and thermal methods employing the techniques of differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermal analysis (DTA). Hydrogen absorption and desorption measured by pressure-composition-temperature (P-C-T) curves indicated that the capacity loss was small after 20 consecutive cycling tests. The enthalpies associated with hydride formation and decomposition were measured to be –69.5 and –83.2 kJ mol^–1 H₂, respectively. At the temperatures of this study (553 to 653 K), hysteresis decreases with increasing temperature.     

Processing of Fe-6.5wt.%Si alloy foils by cold rolling

Thin foils of 50 μm in thickness of Fe-6.5wt.%Si alloy were obtained by conventional hot-cold rolling method. The rolling texture and basic mechanical properties of the foils were examined. The foils were heavily work-hardened and exhibited high tensile fracture strength with some extent of plastic elongations. Their bending ductility was more remarkable.     

Ultrastiff,Strong, and Highly Thermally Conductive Crystalline Graphitic Films with Mixed Stacking Order

A macroscopic film (2.5 cm × 2.5 cm) made by layer‐by‐layer assembly of 100 single‐layer polycrystalline graphene films is reported. The graphene layers are transferred and stacked one by one using a wet process that leads to layer defects and interstitial contamination. Heat‐treatment of the sample up to 2800 °C results in the removal of interstitial contaminants and the healing of graphene layer defects. The resulting stacked graphene sample is a freestanding film with near‐perfect in‐plane crystallinity but a mixed stacking order through the thickness, which separates it from all existing carbon materials. Macroscale tensile tests yields maximum values of 62 GPa for the Young's modulus and 0.70 GPa for the fracture strength, significantly higher than has been reported for any other macroscale carbon films; microscale tensile tests yield maximum values of 290 GPa for the Young's modulus and 5.8 GPa for the fracture strength. The measured in‐plane thermal conductivity is exceptionally high, 2292 ± 159 W m^?1 K^?1 while in‐plane electrical conductivity is 2.2 × 10⁵ S m^?1. The high performance of these films is attributed to the combination of the high in‐plane crystalline order and unique stacking configuration through the thickness.     

Novel nano-structured glasses containing semiconductor quantum dots: controlling the photoluminescence with phonons and photons

Effects of temperatures and excitation intensities on the photoluminescence properties of PbS quantum dots precipitated in the glass were investigated. Peak wavelength of the near-infrared photoluminescence shifted towards the short wavelength side with an increase in temperature and excitation intensity. The largest shift in the peak wavelength of the photoluminescence bands was approximately 90 nm. The temperature coefficient of band gap energy (deduced from the photoluminescence wavelength) of quantum dots varied from 230 to 28 μeV/K under the excitation intensity of 50–600 mW. The integrated photoluminescence intensity also showed similar dependencies on temperature and excitation intensity. The shifts of the photoluminescence with changes in the temperature and excitation intensity were associated with the trapping and re-activation of charge carriers at defect sites located at the QDs/glass interface and inside the glass matrix.     

Laser Chemical Etching of Metals in Liquids

Laser-assisted chemical etching of Co, Cr, Cu and Ti w;is investigated using aqueous solutions of phosphoric acid and KOH at different concentrations. Thin metal films on glass substrates and thin foils were etched upon irradiation with a focussed Ar-laser operating at 514 nm and an output power of about 1 W. Static etch rates of the order of 10 pmμmsol;s were obtained at measured background etch rates less than 103 nm/s. The influence of the laser power on the etch rate suggests dominating thermally activated etch reactions. Due to the thermal nature of the etch process etched lines of about two times smaller width than the estimated laser spot diameter could be obtained. Etching of lines in thin Ti films on glass subsu'ates was performed by laser direct writing at speeds of about 1 mm/s and a laser power of about 0.3 W. Cutting of thin Ti foils was obtained at cutting velocities of about 30 um/s and a power of 0.8 W. The width of the etched lines was found to be controlled by laser power and writing speed. Some applications of the method are mask fabrication for lithography, drilling of small holes into metal parts and cutting of thin metal foils. Fabrication of microparts by laser etching of Ti foils is demonstrated.     

Growth and characterization of high resistivity c-axis oriented ZnO films on different substrates by RF magnetron sputtering for MEMS applications

In the present work, we report the deposition of high resistivity c-axis oriented ZnO films by RF magnetron sputtering. The deposition parameters such as RF power, target-to-substrate spacing, substrate temperature, and sputtering gas composition affect the crystallographic properties of ZnO films, which were evaluated using XRD analysis. The self-heating of the substrate in plasma during film deposition was investigated and we report that highly “c-axis oriented” ZnO thin films can be prepared on different substrates without any external heating under optimized deposition parameters. The post-deposition annealing of the film at 900 °C for 1 h in air ambient increases the intensity of (002) peak corresponding to c-axis orientation in addition with the decrease in full width at half maxima (FWHM). Bond formation of ZnO was confirmed by FTIR analysis. Grains distribution and surface roughness have been analyzed using SEM and AFM. The DC resistivity of the films prepared under different deposition conditions was measured using MIS/MIM structures and was found to be in the range of 10¹¹–10¹² Ω cm at low electric field of 10⁴ V/cm. The ZnO film of 1 μm thickness has transmittance of over 85% in the visible region. Applications of these films in MEMS devices are discussed.     

Hydriding properties of the nanocomposite 85 wt.% Mg–15 wt.% Mg2Ni0.8Co0.2 obtained by ball milling

The hydrogen sorption properties of the nanocomposite 85 wt.% Mg–15 wt.% Mg₂Ni_0.8Co_0.2 obtained by mechanical alloying in inert atmosphere were investigated. Absorption measurements were performed under a hydrogen pressure P = 1 MPa at temperartures ranging from 373 to 573 K, while desorption studies proceeded at P = 0.15 MPa and temperatures of 573 and 553 K. The addition of the intermetallic compound Mg₂Ni_0.8Co0_0.2 was shown to improve the hydriding kinetics of magnesium. The composite exhibited a high hydrogen capacity which did not decrease even after a large number of absorption–desorption cycles. Comparison of the hydriding kinetics of the intermetallic compounds Mg₂Ni and Mg₂Ni_0.8Co_0.2 indicated facilitation of the process by the presence of cobalt in the alloy. Magnetic measurement data on Mg₂Ni_0.8Co_0.2 showed formation of superparamagnetic precipitations of nickel and cobalt playing the role of active centres for dissociative chemisorption of hydrogen. The behaviour of the composite was explained by the catalytic effect of the intermetallic Mg₂Ni_0.8Co0_0.2, the existence of Ni and Co clusters on the surface and the process of mechanical alloying.     

Hydrogen transport by group 5 metals: Achieving the maximal flux density through a vanadium membrane

Hydrogen transport by 100-μm-thick vanadium and palladium membranes was studied in the pressure range from 1 × 10^?8 to 4.5 × 10^?1 MPa at a temperature of 400°C. Both sides of the vanadium membrane were covered by 2 μm of palladium (Pd-V-Pd) for facilitating the dissociative absorption and associative desorption of H₂ molecules. At low pressures, hydrogen flux densities through vanadium and palladium membranes are nearly the same; at high pressures, the flux through the vanadium membrane becomes 16 times larger than the flux through the palladium membrane and attains a value of 2.4 scc cm^?2 s^?1. This flux of permeating hydrogen is larger than all values ever observed earlier for membranes made of group 5 metals or any other unsupported metal membranes.