Table of contents

Nd₂Fe₁₄B and Sm₂Co₁₇ particles of submicrometre sizes have been prepared by ball milling in a magnetic field. Structural and magnetic characterization reveal that these submicrometre particles milled in a magnetic field, consisting of nanosize grains, exhibit strong magnetic anisotropy compared with the particles milled without a magnetic field. Based on in situ observations of the field-ball milling in a transparent container, the mechanism of field-induced anisotropy in the nanostructured hard magnetic particles is discussed.

It has recently been shown that the polarization of electromagnetic radiation can be completely controlled using devices constructed entirely from photonic crystals. We will review these important developments, focusing on effects that occur for propagation in the periodic plane of two-dimensional, dielectric structures. Specifically, we survey the recent experimental results demonstrating waveplates and polarizers based on two-dimensional photonic crystals.

The transmission of light through ionic ferrofluids, in which the viscosity of the carrier liquid can be modulated, is measured under an applied magnetic field. The experimental results show that the transmission intensity would not vary monotonously with time when an external magnetic field is applied. The intensity can get to a stable value if the duration for which the magnetic field applied is long enough. The relaxation time of the variation of the light intensity with time is proportional to the viscosity of the carrier liquid and inversely proportional to the strength of the field. The character of the transmitted light is explained according to a model of microstructured transition relaxing in ferrofluids under an applied magnetic field.

We use a micromechanics approach to study the magnetoelectric (ME) properties of the piezoelectric/magnetostrictive composite with a 2–2 laminate structure and a 3–1 fibrous structure. It is found that the 3–1 composite has a higher ME coefficient than the 2–2 one, if the volume ratio of piezoelectric material is the same. The reason is that the 3–1 fibrous composite makes use of the longitudinal piezoelectric response and the piezoelectric voltage constant g₃₃ is 2–3 times that of g₃₁. Generally, a smaller volume ratio of the piezoelectric material will generate a higher ME response. The tensile stress at the piezoelectric/magnetostrictive interface of the 3–1 fibrous composite, however, could be high enough to induce plastic deformation or microcracks, which leads to a ME coefficient lower than the theoretically predicted one.

We present here our latest results on high quality gate insulators for organic electronics. Ultra-thin films of n-octadecyltrichlorosilane-treated, anodized aluminium (Al) grown onto flexible, Al-sputtered polyester substrates combine low cost and manufacture under ambient conditions with excellent performance characteristics (negligible leakage and hysteresis, 400 nF cm⁻² capacitance). With pentacene as organic semiconductor, we present organic transistors with inverse subthreshold slope of approximately 200 mV dec⁻¹, threshold of the order of −2 V and >10⁵ on/off ratio. The subthreshold behaviour is significantly better than for transistors with pentacene deposited onto a gate insulator optimized for high mobility. Above the threshold, the higher capacitance compensates for the somewhat lower mobility. Crucially, the cheap, sputtered Al-on-polyester films resulted in transistors that were as good as transistors fabricated on the same substrate with evaporated Al.

A two-phase mixture (TPM) is a mixture of gas and macroparticles of high concentration. It is of interest in many different areas, such as in macroparticle-contaminated insulated systems, gas–liquid discharges, dusty plasmas and processing plasmas. Based on Townsend's theory, a physical model in analytical form for the breakdown mechanism in TPM is presented. In this model, two factors that influence the electron avalanche propagation are considered: macroparticles distorting the electric field and capture of the electrons. According to this breakdown mechanism and the dipole-enhanced model for calculating the maximum local field strength in TPM, the modified Paschen' law for TPM is presented to calculate the breakdown voltage. When the number of series of macroparticles (m) between two plate electrodes is very small, such as when m = 1, the breakdown voltage of the TPM is always lower than that of gas. With an increase in m or a decrease in the radius of macroparticles, the breakdown voltage tends to increase gradually for the same volume fraction of macroparticles. When m ≫ 1, the breakdown voltage of TPM may be lower or higher than that of gas, depending on the ratio of the number of saturation electrons captured by a macroparticle to the cell primary electrons generated at the cathode. Some other relevant factors, such as the volume fraction of macroparticles, the dielectric mismatch, the charging rate and the product of gas pressure and the gas length, are also discussed.

In this paper, the morphology, vibrational spectra and electronic properties of WO₃ films loaded with different levels of Ag, prepared by screen printing onto Si substrates and annealed in air at 600°C were investigated. AFM micrography showed that the films are grain-like, and the grain size increases with an increase in the Ag loading level. Raman spectroscopy results showed the formation of a AgWO₃ bronze structure that results in a more stable film. X-ray photoelectron spectroscopy results showed that the Ag concentration is 1.8 times higher than the nominal concentration indicating that Ag diffuses to the WO₃ grain surface. No strong electronic interaction between the Ag clusters and the WO₃ grains was found. Sensors fabricated with the WO₃ : Ag films exhibited a significant increase in their sensitivity and selectivity towards NO₂ detection.

Nanostructured NbO₂ films have been prepared on Si (001) substrates by thermally oxidizing a spiral niobium coil in a vacuum of the order of 10⁻² Torr. The film consists of single-crystalline NbO₂ nanoslices (several tens of nanometres thick) that are aligned with each other. When excited with 512 nm light, the NbO₂ film showed room-temperature photoluminescence around 700 and 825 nm. It also exhibits, interestingly, excellent dielectric properties in the frequency range from 1 kHz to 10 MHz. It has a dielectric constant comparable to that of SiO₂ and Si₃N₄, is independent of the frequency applied, and has a dielectric loss of less than 1% in the measured frequency range, making NbO₂ a potential material for applications into MOS devices. The Raman spectrum of the NbO₂ phase, for the first time, is also reported.

To predict the thermal conductivity of granite rocks the existing mixing law and empirical models have been utilized. Due to the porosity dependence in all the existing models, ASTM standard methods have been utilized to measure the porosity including specific gravity and density. The chemical composition of these samples has been analysed using the x-ray fluorescence technique. Because of the complex structure of the specimens and non-availability of data, models depending on the strict geometrical structure like the shape, size, position of the constituent mineral and the arrangement of fluid in the samples have not been used. The predicted values of the effective thermal conductivity have been compared with the experimental measurements made on the samples, using Gustafsson's probe. The calculated thermal conductivities from various models are in agreement with the experimental observations. Simple correlations between the chemical composition and specific gravity, density and porosity are also reported.

In this work, the effect of an excimer laser has been studied for presenting a method for SF₆ decomposition and simultaneous formation of a SiF₂ layer on amorphous SiO₂. Though the excimer laser did not establish a gas phase photodissociation, we have shown that UV photoablation leads strongly to molecular decomposition in the SF₆–SiO₂ system. Moreover, the dependence of the decomposition process on the exposure parameters such as the wavelength and intensity as well as the gas pressure and the focal point distance from the gas–solid interface has been investigated.

A physical model for forming the spatial photorefractive screening solitons based on the paraxial wave equation and on the Kukhtarev model in one and two transverse dimensions is studied. A numerical simulation of the interaction between two incoherent spatial photorefractive screening solitons was performed. The numerical scheme according to the Crank–Nicholson method generalized in three dimensions, accompanied by the central difference method, is introduced to solve the coupled wave and potential equations governed by the generation of solitons and their interaction. This simulation approach demonstrates theoretically the real aspect of the photorefractive screening soliton interaction in one dimension and compares it with the two-dimensional case. It is found clearly that the interaction in one dimension displays only attraction whereas in two dimensions repulsion as well as attraction are displayed. The outcome can be used in fabrication of all-optical switching elements.

Platinum is deposited into porous carbon materials relevant for fuel cell electrodes using plasma sputtering techniques. The resulting platinum concentration profile extends up to 2 µm into the porous carbon and is well fitted by a generalized stretched Gaussian function, which displays the non-thermal nature of the penetration process. Platinum deposits are observed to grow as clusters. On the outermost carbon particles, platinum nano-cluster sizes of 3.5 nm have been measured. In tests using actual PEM fuel cells, current densities as high as 1000 mA cm⁻² have been obtained at 400 mV with 25 cm² plasma electrodes. This compares favourably with commercially available electrodes but the present electrodes have a platinum density 4.5 times lower and hence can be considered to be significantly more efficient.

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