Table of contents

A negative-tone inorganic-organic hybrid SiO₂/TiO₂ sol-gel glass is applied to make blazed gratings using a high-energy beam-sensitive (HEBS) grey-scale mask with ultraviolet (UV) exposure. To improve the sol-gel material's linear response to the optical densities (ODs) of the HEBS grey mask, a new recipe of sol-gel synthesis is investigated to offer good linear UV response to ODs of the HEBS mask. The calibration results show that the linearity of the UV response versus ODs is significantly improved for the whole OD range between 0.12 and 1.12. The sol-gel film thickness has been increased to 3µm so that it enables us to realize 2π phase difference for diffractive optical elements in the visible and near IR wavelength range. It is seen that the transmittance curve has an UV shift, which played an important role to improve the properties of the sol-gel material.

In this paper we investigate the effect of hydrostatic pressure on the electrical conductivity of polypyrrole-polyaniline conductive (protonated) blends of various compositions. Results are presented for thermally aged blends as well. The modification of the conductivity due to pressure is more pronounced in the fresh samples than in the aged ones. The phenomenon is discussed within the frame of the granular model. The percentage variation of the conductivity upon pressure change for the polypyrrole rich blends is not influenced by the ageing process. This feature suggests that these blends could possibly be used as pressure sensors, which are insensitive to thermal ageing.

The a.c. conductivity σ_ac of polyaniline prepared with a.c. plasma polymerization was studied recently at low angular frequencies (ω⩽1 MHz) (Mathai J et al 2002 J. Phys. D: Appl. Phys.35 240). The data were analysed considering a power dependence of the a.c. conductivity on frequency σ_ac∝ωⁿ, n⩽1. It was found that the index n varies between 0.4 and 1. In this work, we show that these values conflict with the bounds of the n parameter predictions of the Austin and Mott model, which assumes a single mode of charge hopping in amorphous media. We suggest that multiple a.c. conductivity mechanisms of the Austin and Mott type may contribute to the measured a.c. conductivity. A numerical calculation for a couple of mechanisms showed that the resulting a.c. conductivity curve exhibits effectiven values which can explain the wide distribution of the indexes evaluated in polyaniline.

We report here magnetization, resistivity, colossal magnetoresistance and Nernst coefficient (Q) measurements in electron-doped manganite, Ca_0.88Sm_0.12MnO₃. A paramagnetic to a ferromagnetic transition at around T_c~105 K was observed. Q was independent of temperature and applied magnetic field (B) for 110<T<300 K. However, Q was strongly suppressed when B was increased from 0.25 to 1.8 T for T<110 K. For T<T_c, our data point to an increase in the relaxation time τ resulting from a decrease in the spin-disorder scattering of carriers.

For a fine ferromagnetic particle of a non-ellipsoidal external shape, an effective single-domain diameter is defined as a characteristic length at which the energy of a stable quasi-uniform state (usually a flower state) of the particle coincides with that of the lowest non-uniform (`multi-domain') state. The effective single-domain diameters for soft magnetic parallelepipeds and cylinders having aspect ratios 0.5⩽m⩽3 are obtained by means of numerical simulation. In particular, it is shown that the effective single-domain diameters for a cylinder and cube with aspect ratio m = 1 are approximately only 3% and 9% lower, respectively, than the single-domain diameter of an ideal sphere with the same magnetic parameters.

In this paper, the relationship between microstructural properties of steels and the material parameters in the Preisach model and in the Jiles-Atherton (JA) model is discussed, in the instance where both models describe quasi-static hysteretic magnetic behaviour. It is shown how the material parameters in both hysteresis models should be modified to reflect their dependence on dislocation density and grain size. The dependence of the Preisach material parameters on these microstructural features is identified starting from hysteresis loops calculated by the microstructurally dependent modified JA model. For the Preisach model, a Lorentzian distribution function is used for the distribution function. This makes it possible to compare predictions here to results of an earlier paper in which the Lorentzian distribution was used for Preisach fits to experimental data for steels of different grain sizes. Also, in a different earlier paper, it was shown how the Lorentzian distribution can be formulated so that it connects with salient features of the JA model. The procedure in this paper enables one to examine and predict microstructural variations of Preisach parameters in steels not only for the case of grain size variation but also for the case of variation in dislocation density.

An analytic solution is presented to the problem of designing an antireflection coating to be added to an arbitrary periodic superlattice, so as to create an optimal electron mini-band-pass filter.

We present laser-induced fluorescence (LIF) measurements, spatially and temporally resolved, of tungsten impurities eroded from the cathode of a free-burning argon arc. Saturation, but more drastically quenching processes limit a quantitative evaluation of the measurements. Applying a special measuring technique, we were able to determine relative densities and, via a Boltzmann plot, excitation temperatures. A 2D display of the metal impurity can be obtained with a planar LIF arrangement. It shows the distribution of that part of metal component being in a distinct mode of ionization and excitation. As known, the population distribution of the tungsten impurity is dominated by strong demixing effects.

Negative absorption of an electromagnetic wave (2.6 GHz) in argon afterglows has been detected over the time interval between 2 and 10 ms at the pressures ranging from 0.5 to 0.9 Torr. Since the frequency 2.6 GHz is much greater than the collision frequency of electrons-atoms, the radiation could be collisional bremsstrahlung. We have followed the proposed model (Bekefi G et al 1961 Phys. Fluids4 173-6) of the negative absorption which depends on the conditions of ∂f_e(v)/∂v>0 and ∂(v⁴Q(v))/∂v<0, and experimentally checked the existence of the these two requirements, where f_e(v) is the velocity distribution function of electrons, Q(v) a collision cross section for electrons. The former condition requires more electrons populating over higher-energy region on the electron velocity distribution function (EVDF). This may be overcome by assuming the generation of a high-energy electron hump created by ionizing collision between two metastable atoms. Experimentally, the occurrence of the high-energy electron group has been verified by the EVDF measured with the Druyvesteyn probe technique. The latter condition is satisfied by using argon gas which has a typical Ramsauer effect. We have come to a result that the calculated absorption coefficient by substituting the measured EVDF and the collision cross section into the theoretically derived formula (Bekefi G 1966 Radiation Processes in Plasmas(New York: Wiley)) agrees well with the measured value.

A general ray-trace method for calculating the effects of radiative transfer in a control volume (CV) fluid code is presented. The method makes use of the structured CV grid of the fluid code, and is suited for geometries with a point or axis of symmetry. In particular, the specific equations for spherical and cylindrical (without z dependence) configurations are developed. The application of this method to local thermal equilibrium (LTE) and non-LTE plasma models is discussed. Various opportunities for sacrificing precision for calculation speed are pointed out.

As a case study, the effects of radiative transfer in a sulphur lamp are calculated. Since an LTE description of the molecular radiation yields a computed spectrum that differs significantly from a measured one, the possibility of a non-LTE vibrational distribution of the radiating S₂-B state is investigated. The results indicate that the vibrational populations may be inversed.

An inductively coupled plasma (ICP) flame of the Ar-SiH₄-CH₄ system was investigated in situ by spectroscopic methods during chemical vapour deposition of SiC particles. In order to determine the rotational temperature of C₂ radicals, we focused on emission spectra of C₂ (0,0) Swan band located at 513.1-516.3 nm. Spectral simulations were performed before measurements of C₂ spectra, and temperatures were determined from fits of experimentally observed peak intensities before and after Abel inversions with calculated spectra. Simulations were performed in 50 K steps from 2000 to 6000 K. Since spectral intensities after Abel inversions dropped to near zero, the measurable ranges of temperature were restricted. The rotational temperatures of C₂ radicals determined varied from 2850 to 4750 K, depending on experimental conditions and radial positions from the plasma centre. The present results were comparable to various numerical analyses of ICP flames reported by many authors.

Hydroxyl radicals generated by a pulsed corona discharge are measured by laser-induced fluorescence (LIF) with a tunable KrF excimer laser. The discharge with 35 kV voltage and 100 ns pulse current occurs between needle and plate electrodes in H₂O/O₂/N₂ mixture at atmospheric pressure. The density and decay profile of OH radicals are studied. OH radicals decay with time after the discharge with a time constant of about 30-60 µs. The OH density is estimated to be about 7×10¹⁴ cm^-3 in H₂O(2.4%)/N₂ mixture 10 µs after the discharge. The OH density is approximately proportional to the energy dissipated in the discharge. The O₂ content influences the OH production. When the O₂ content is varied in H₂O(2.4%)/O₂/N₂ mixture, the OH density is maximum at an O₂ content of 2%. The spatial distribution of OH density shows that OH radicals are produced in the streamers under positive discharge.

This paper presents a two-temperature model for compressible plasma flows. This study concentrates on the behaviour of the plasma jet in the expansion region. The conditions used correspond to the conditions of low-pressure plasma spraying, with slightly supersonic conditions with thermal and chemical non-equilibrium. The flow dynamics results are analysed with different turbulence models and appear to be consistent with results previously published by the authors [3] on the dynamics of low-temperature air jets and favour the Reynolds stress turbulence model. Chemical as well as thermal non-equilibrium are studied.

Application of the inductively coupled thermal plasma (ICTP) technique was proposed for investigating plasma-quenching efficiency of various gases including the arc-quenching medium of SF₆. The ICTP enables us to study fundamentally the effect of gas injection on thermal plasma without any impurities because it has no electrode. Seven kinds of gases including CO₂, SF₆ and environmentally benign gases (N₂, O₂, air, He and H₂) were injected into Ar ICTP. Spectroscopic observation was carried out in order to investigate a change in the excited state of Ar atoms due to addition of these gases. Radial distributions of the radiation intensity of Ar spectral lines and the temperature of Ar ICTP were estimated. It was found that 10% CO₂ addition causes a remarkable decline of the radiation intensity and temperature at any radial position, similarly to 2% SF₆ addition. Two-dimensional local thermal equilibrium modelling for Ar ICTP also revealed that CO₂ causes temperature decay more than the other gases of N₂, O₂, air, He and H₂ except SF₆.

The diffuse column of a dc glow discharge in neon is a typical example of a plasma whose properties are mainly determined by the non-local non-equilibrium kinetics of the electron component. Consequently, the space-charge confinement causes a spatial variation of all plasma properties. The effects on the power balance, the ionization budget and the radiation efficiency of a cylindrical column plasma are studied by a detailed self-consistent column model based on a hybrid method. The analysis deals with the impact of discharge parameter variations over larger ranges, of an admixture of a molecular gas as well as of the superposition of a longitudinal magnetic field on the spatial plasma structure. Among others, the non-local properties of the electron power balance and their influence on the radiation efficiency are discussed. The largest influence of energy transport processes on the electron power balance has been observed in a range of the pressure times radius values from about 200 to 400 Pa cm, which nearly coincides with the range where the maximum efficiency of the resonance radiation occurs.

The propagation and branching of pulsed positive corona streamers in a short gap is observed with high resolution in space and time. The appearance of the pre-breakdown phenomena can be controlled by the electrode configuration, the gas composition and the impedance of the pulsed power circuit. In a point-wire gap the positive corona shows much more branching than in the parallel plane gap with a protrusion. In air, the branching is more pronounced than in argon. The pulsed power circuit appears to operate in two modes, either as an inductive circuit creating a lower number of thick streamers or as a resistive circuit giving a higher number of thin streamers. A possible cause for branching is electrostatic repulsion of two parts of the streamer head. The electric field at the streamer head is limited, the maximum values found are ~170 kV cm^-1 in air and ~100 kV cm^-1in argon. At these maximum field strengths, the electrons have 5-10 eV energy, so the ionization is dominated by two-step processes. Differences between argon and ambient air in the field strength at which streamers propagate are ascribed to the difference in de-excitation processes in noble and molecular gases. The fact that the pulsed power circuit can control the streamer structure is important for applications, but this effect must also be taken into account in fundamental studies of streamer propagation and branching.

YBa₂Cu₃O_7-δ (YBCO) thin films ablated from melt-textured-growth (MTG) YBCO target (containing-Y211 phases) by pulsed laser deposition were studied by transmission electron microscopy. The films grow epitaxially on the SrTiO₃ substrates in a c-axis orientation with very few large particles on the film surface: instead rectangular Y₂O₃ inclusions were embedded in the films. The crystallographic relationship was (100)Y₂O₃//(001)YBCO, [011]Y₂O₃//[010]YBCO. The inclusions do not degrade the superconducting property of the YBCO films. MTG YBCO targets result in films with lower level of large impurity particles.

Intermediate valence compound YbAl₃ has been synthesized by the Bridgman method. Temperature dependence of the Seebeck coefficient, electrical resistivity and thermal conductivity has been measured on YbAl₃ hot-pressed and single crystal samples. At temperatures below 100 K, the electrical resistivity exhibits a ρ(T) = ρ₀ + AT² dependence, while over the temperature range 300-800 K YbAl₃ exhibits metallic behaviour with a linear temperature dependence of the electrical resistivity. The Seebeck coefficient exhibits a temperature dependence typical for heavy fermion compounds and attains a maximum of its absolute value of -79 µV K^-1 at around 200-250 K. Combination of a large Seebeck coefficient and low residual resistivity of single crystalline YbAl₃ leads to the highest ever reported electrical power factor of 340×10^-6 W cm^-1 K^-2 at 80 K. Thermal conductivity as a function of temperature has a broad peak at 50 K, which originated mainly from the electronic contribution to thermal conductivity. At 300 K the total thermal conductivity of hot-pressed samples ranges from 0.085 to 0.179 W cm^-1 K^-1depending on the density of the samples. The calculated figure of merit value attains its maximum of 1×10^-3 K^-1 at 100-120 K.

Reversible modification of the optical and electrical properties of V₂O₅×nH₂O gel films under the action of an electric field is studied. It is shown that under cathodic polarization (I = 10^-6-10^-5 A, t~10min, film thickness ~10 µm), the films turn from brownish-yellow to red. This internal electrochromic (EC) effect is caused by the redistribution of hydrogen ions inside the film, instead of insertion from the outside (from an electrolyte). A local increase in the hydrogen concentration occurs near the cathode, and this in turn results in modification of the optical properties. The rise of transmittance in the long-wavelength region of the spectrum, as well as the shift of the absorption edge near hν~2.5eV towards longer wavelengths, is observed. In addition, according to the infrared data, some increase in water content also contributes to the process of colouration. The change in the optical properties is accompanied by a change in the electrical properties, namely, an increase in ionic conductivity from ~4×10^-5 to 10^-4Ω^-1 cm^-1. At higher currents, electroforming resulting from the transport of oxygen ions occurs. This process leads to the formation of a channel consisting of vanadium dioxide due to reduction of V₂O₅ to VO₂. Electrical switching with the S-type negative resistance, associated with an electrothermally driven metal-insulator transition in the channel, is observed in the sandwich M/V₂O₅×nH₂O/M devices (unlike the planar devices described in the literature). Finally, applied potentialities of these phenomena for micro- and opto-electronics (EC devices, sensors) are discussed.

Nanocomposite films containing silver particles embedded in SiO₂ matrix were prepared by high pressure (~40 Pa) d.c. sputtering technique in an argon plasma on fused silica substrate. Particle size and metal volume fraction were tailored by varying the substrate temperature (T_s~233-300 K) and deposition time (15-240 s). Reduction in size and volume fraction of metal particles culminated in blue-shift of the surface plasmon resonance peak in the optical absorbance spectra of the films. Absence of surface plasmon peak in the absorption spectra below a critical particle size and metal concentration of the nanocomposite films and appearance of sharp absorption edge in the absorbance spectra within the UV-VIS range indicated the semiconducting behaviour of the ultrafine silver particles. Experimental absorbance spectra were theoretically simulated by Mie scattering theory and Maxwell-Garnett effective medium theory.

Pure and iodine-doped polyaniline thin films are prepared by ac plasma polymerization technique. Doping of iodine is carried out in situ as well as by employing iodine chamber methods. The structural analyses of pure and iodine-doped polyaniline thin films are carried out by FTIR spectroscopic studies. Optical bandgaps of these films are evaluated from UV-VIS absorption studies. Direct and indirect transition energy gaps are determined from Tauc plots. The structural changes of polyaniline upon doping and the reduction of optical bandgap are explained on the basis of the results obtained from FTIR spectroscopic and UV-VIS absorption studies.

Solid phase crystallization of amorphous silicon thin films deposited by radio frequency plasma enhanced chemical vapour deposition (RF PECVD) has been studied. The effects of power density variation on the properties of amorphous and microcrystalline films (after crystallization) have been discussed. A fast growth rate of the amorphous layer (12.5 Ås^-1) and large grain (~350Å) microcrystalline film has been reported. A high value of electrical dark conductivity (~10^-6S cm^-1) is also obtained for the microcrystalline (intrinsic) film. It has been observed that deposition rate and bonded hydrogen content in the amorphous films play important roles in the crystallization process and properties of the crystallized films. Electron resonance spectra indicate an increase in defect density of amorphous films with increase in power density and better crystallization is obtained for films with higher density of defects. Scanning electron microscopy reveals that the nature of film surfaces and distribution of grain in the crystallized films are strongly affected by the power density regime in the deposition process.

This work investigates the grain-growth behaviour of powder compact during Stage 1 sintering (<90{%} theoretical density). It is widely accepted that grain size is an important state variable in the constitutive modelling in material sintering. However, it is noted that all the existing grain-growth laws proposed in the literature do not incorporate the effect of externally applied stress independently. In this work, a grain-growth law with externally applied stress as a variable was proposed. Alumina powders were forge-sintered at different applied stresses to examine the proposed grain-growth relationship. The proposed grain-growth law was then applied to model the grain-growth process on the sinter forging of tool steel. It is shown that the present proposed grain-growth law provides a good description on the experimental results.

This paper addresses discrepancies between the results of different measurements of the effective tensile strength (F_c) of liquids, in experiments in which a pulse of tension (or `negative pressure') is created by the reflection of a pressure pulse at a suitable boundary. We show that a key feature of the pressure records previously reported in such experiments may have been misinterpreted. The first complete account of such pressure records reported here offers an explanation for the order-of-magnitude discrepancies in F<sub>c</sub> which arise in work involving instruments such as the `Bullet-Piston' (B-P) pulse-reflection apparatus (Temperley H N V and Trevena D H 1987 J. Phys. D: Appl. Phys.20 1080). We also report a new method of estimating F_c in a modified B-P apparatus and the results obtained indicate that samples of degassed, deionized water can sustain tensions which are an order-of-magnitude greater than previously reported in B-P work. Results are also reported for work involving samples of Newtonian silicone oils, for which the dependence of F_c on shear viscosity, µ, found in this work confirms that of an earlier study although the absolute values of F_c are found to be considerably greater than previously reported.

Electrorheological (ER) fluids with microspheres and micro-rods as the component solid phase were examined experimentally to investigate the influences of particle geometry on ER performance. It is observed that for both dried and water-activated ER fluids, the shape of the constituent particles plays a significant role, i.e. for particles with same diameters, the microsphere-based ER fluids show better ER performance than micro-rod-based ER fluids. We found from experiments that the aspect ratio of particles is an important parameter for the ER activities. The tendency is that the ER effect decreases with the increase of the aspect ratio, while this phenomenon becomes much weaker in the case when dried particles were substituted for the ones with moisture.

On p1393, the second line after equation (13) is corrected to: ....column in question, (x_n - x_o)ddot x_o Delta_ad, d being the density of the fluid.