Table of contents

The emerging field of strained-Si based nanomembranes is reviewed, including fabrication techniques, strain-induced band structure engineering, electronic applications and three-dimensional membrane architectures. Elastic strain sharing between thin heteroepitaxial Si and SiGe films, enabled by techniques that allow release of these films from a handling substrate, creates a new material: freestanding, single-crystal, strained nanomembranes. These flexible nanomembranes are virtually dislocation-free and have many potential new applications. Strain engineering also provides opportunities for massively parallel self-assembly of a wide variety of three-dimensional nanostructures.

La_0.7Sr_0.3MnO₃/Nb-1 wt%-doped SrTiO₃ p–n junction, which was fabricated by the magnetron sputtering technique, exhibits excellent rectifying characteristic over the temperature range from 40 to 320 K. Moreover, it is worth noting that the rectifying behaviour is nearly independent of temperature. The modulated electrical and magnetic properties of La_0.7Sr_0.3MnO₃ by the built-in electric field near the interface of the junction is also achieved.

CoAlO composite antidot arrays were fabricated on self-organized porous anodic aluminium oxide (AAO) membranes. The effects of pore size and film thickness on the magnetism and magnetotransport properties of the CoAlO films were investigated. On increasing the pore dimensions in the arrays, an anisotropic to isotropic magnetism transition was observed. The result is discussed based on the competitive contributions from the external field induced uniaxial anisotropy and the topology-induced shape anisotropy superimposed by the stray fields from the pore channels. Magnetoresistance showed corresponding variations with increasing pore sizes, as evidenced by a magnetoresistance variation from typically anisotropic to nearly isotropic behaviour. When deposited on large-pored AAO membranes, the antidot arrays showed no obvious anisotropy at different film thicknesses. It led to negligible magnetoresistive loops in the thick films of high structural continuity. The possible reasons for spin-independent electron scatterings are discussed.

Langevin dynamics treats finite temperature effects in a micromagnetics framework by adding a thermal fluctuation field to the effective field. Several works have addressed the dependence of numerical results on the cell size used to split the ferromagnetic samples on the nanoscale regime. In this paper, some former problems dealing with the dependence on the spatial discretization at finite temperature have been revised. We have focused our attention on the stability of the numerical schemes used to integrate the Langevin equation. In particular, a detailed analysis of results was carried out as a function of the time step. It was confirmed that the mentioned dependence can be minimized if an unconditional stable integration method is used to numerically solve the Langevin equation.

The influence of residual stress on the hysteresis properties of mild steel is studied in detail. Magnetic measurements were done in different directions to investigate the stress-induced anisotropy. The hysteresis loops measured in any fixed direction at different levels of deformation crossed at two points known as the coincident points. One possible explanation of this effect is proposed and it makes an assumption about the stress-induced term in the effective field model. Loops measured in different directions at any fixed level of deformation also crossed at two points. It was found that the hysteresis loop follows a very simple formula when changing the direction of the measurement from the easy axis to the hard one. This explained not only the crossing of these loops at the two points but also the results of measurements on ring-shaped samples where all the directions are possible.

FeNiN thin films with good soft magnetic properties were synthesized on Si (1 0 0) substrates at 473 K by RF magnetron sputtering; all the films have a thickness of around 500 nm. The dependence of phase structure and magnetic properties on nickel concentrations and RF power were systematically investigated. With increasing nickel contents from X_Ni = 5.0% to X_Ni = 65.5%, FeNiN thin films deposited at turn from a main bcc α-(Fe,Ni) phase coexisting with γ'-phase to fcc γ-(FeNi₃)₄N phase. With the RF power larger than 160 W, the samples deposited at all show clear reproducible striped domains at the films' surfaces, which is explained by the high enough perpendicular anisotropy and the small stress in the film. A completely ordered structure of (FeNi)N_0.0324-phase forms at P_W = 300 W. The FeNiN thin films prepared at different RF power show smooth surfaces and good soft magnetic properties compared with corresponding FeN compounds. The optimum soft magnetic properties with M_S of ∼ 1900 emu cm⁻³, H_C of ∼1 Oe are obtained at and P_W = 300 W at 473 K.

Transmission characteristics of two-dimensional magnetized magnetic photonic crystals (MPCs) have been studied by electromagnetic simulation and experiments in microwave frequencies. MPCs with square and hexagonal lattices are made of ferrites, and their transmission coefficients are measured in the X waveband with an applied static magnetic field. For the lattices, a stop-band and a band shift with the applied static magnetic field are observed. The experimental results are in good agreement with those of electromagnetic simulations when magnetic anisotropy of ferrites is represented by a tensor but deviate from the simulation results when the anisotropy is modelled by an effective permeability of TM_z mode.

In this paper, a correlation between structural and magnetic properties of Fe-implanted ZnO is presented. High fluence Fe⁺ implantation into ZnO leads to the formation of superparamagnetic α-Fe nanoparticles. High vacuum annealing at 823 K results in the growth of α-Fe particles, but the annealing at 1073 K oxidizes the majority of the Fe nanoparticles. After a long term annealing at 1073 K, crystallographically oriented ZnFe₂O₄ nanoparticles are formed inside ZnO with the orientation relationship of ZnFe₂O₄(1 1 1)[1 1 0]//ZnO(0 0 0 1)[11 2 0]. These ZnFe₂O₄ nanoparticles show a hysteretic behaviour upon magnetization reversal at 5 K.

This paper analyses the various etching tolerances and profiles of comb-drive microstructures by using deep reactive ion etching (RIE) and studies their influence on the actuator's performance. The comb-drive actuators studied in this paper are fabricated with the silicon-on-glass (SOG) wafer process using deep RIE and wafer bonding, which present very high-aspect-ratio and high-strength microstructures. However, the deep RIE process generates some tolerances and varies the dimension and profile of comb fingers and flexures due to the process limitations. We have analysed the different etching tolerances and studied their influence on the actuator's performance, in terms of the electrostatic force, flexure stiffness, actuator's displacement, air damping and quality factor of the actuator. The analysis shows that the comb fingers with a positive slope profile generated a larger electrostatic force, and the flexures with a negative profile induced the loss of the actuator's stiffness. The combination of these two profiles leads to a great increase in the actuator's displacement and decrease in the quality factor. The measured results of the SOG fabricated actuators have demonstrated the influence of deep RIE tolerance on the actuator's performance.

In this paper, we consider the electro-optic properties of a bistable display device based upon the smectic A phase which can function without polarizers. This scheme is attractive for low-power, high-efficiency devices with indefinite storage. The bistable modes are opaque (write), due to electrohydrodynamic instabilities from motion of ionic dopant at dc/low ac frequencies, and clear (erase), due to dielectric reorientation. The two regimes are delimited by a critical frequency at which ionic motion is damped out. From consideration of current flow through the cell and contrast ratio, it is shown that the display lifetime is significantly dependent on the write mode drive frequency e.g. operation at 100 Hz extends lifetime by a factor greater than 10² compared with 1 Hz. The origin of the limited lifetime at dc/low ac applied fields is explained via an electrolytic purification mechanism; operation at frequencies above a threshold (e.g. 50 Hz) significantly reduces this process. It is also proposed that, although this phenomenon must be minimized for dynamic scattering, the technique should be of benefit generally for in situ purification of liquid crystalline samples in other electro-optic effects where ionic conductivity is an undesirable property.

The channel mobility in organic field-effect transistors that have a disordered semi-conducting layer in contact with an insulating polar dielectric material is calculated from the transconductance of the modelled transistor transfer response. The modelled transfer characteristics incorporate the additional energetic disorder that is introduced into the channel region from the polar gate dielectric, together with a carrier mobility enhancement factor due to localized state occupancy under charge accumulation conditions. A proposed mobility enhancement factor is independently determined from Monte Carlo simulations of carrier hopping through partially occupied energy landscapes that are subject to a Gaussian distribution of energetic disorder. The calculated field-effect mobility is found to be reduced relative to the bulk semiconductor mobility as the amount of energetic disorder in the channel region is increased through the use of more strongly polar gate dielectrics. The field-effect mobility is additionally found to decrease as the accumulated charge is confined to the most energetically disordered region in the vicinity of the insulator–semiconductor interface at higher gate voltages. The overall gate voltage dependence of the channel mobility is suppressed, however, by the mobility enhancement factor. Support for the model is found from recently published mobility data for a series of triarylamine field-effect devices.

Three-dimensionally ordered photonic crystals were fabricated using the vertical self-assembly method from colloidal polystyrene spheres of sub-micrometre diameters. Structural and optical characterization results indicate the extent of good ordering present in these samples. The photonic stop band was tuned by infiltrating two important oxide materials, namely, SiO₂ and ZnO. Infiltration was done using a low cost room-temperature sol–gel process which does not require any sophisticated instrumentation. The optical measurements clearly demonstrate that the infiltration is significant. The experimentally measured values of wavelength shift and peak reflectance were compared with theoretically estimated values and found to be in good agreement.

A previously published kinetic model for the production of luminescence signals in quartz is used to investigate the production of thermally transferred optically stimulated luminescence (TT-OSL) signals. This paper provides a mathematical description of the thermal transfer mechanism for two different phenomena that have been observed in previously published experiments (Aitken and Smith 1988 Quat. Sci. Rev.7 387–93). The starting point is the model proposed by Bailey (2001 Radiat. Meas.33 17–45). The numerical values of some of the parameters are varied so that they match the experimental data. The effect caused by varying these values is investigated.

The first of these phenomena takes place after storing optically bleached samples at room temperature; this involves the traps responsible for the 110 °C thermoluminescence (TL) peak of quartz acting as a refuge trap. The second phenomenon concerns OSL signals that are induced by heating the samples after the bleaching of the OSL signal and involves a putative TL peak at ∼230 °C associated with the refuge trap; specifically, the paper presents a simulation of the temperature dependence of the OSL signal measured by successively heating the quartz samples to higher temperatures up to ∼400 °C.

A solar cell junction symbolized as P⁺–i–N⁺ is examined in which amorphous silicon hydride is placed between two heavily doped, wide bandgap semiconductors. A potential barrier exists at each semiconductor interface and charge transport through the barriers occurs predominantly by tunnelling. This cell structure produces both a large built-in potential across the absorber and an increase in the average lifetime and velocity of the photogenerated carriers. Simulation of P⁺–i–N⁺ and p–i–n junctions were performed using the AMPS-1D program and the calculated conversion efficiencies were 10.0% versus 7.5%, respectively.

We designed and simulated a nonlinear directional coupler switch by using dark soliton propagation in this coupler. We utilized the optical properties of chalcogenide glasses such as their high nonlinear refractive index and positive group velocity dispersion and designed a switch having a length of 1.2 mm and an ultra-fast pulse width of 10 fs with a 100 W power input pulse. The switching characteristic shows that complete switching is possible for different ranges of lengths and pulse widths, and by using the result of the simulation we find a relation between the length and the pulse width with respect to the necessary power for complete dark soliton switching. Also the effect of two photon absorption (2PA) on dark soliton switching was studied and it was shown that the 2PA puts some limitations on the switching action but, because of the low value of the 2PA figure of merit for chalcogenide glasses, it did not have any considerable effect on dark soliton switching.

Nd³⁺ : BaGd₂(MoO₄)₄ crystal with dimensions of Ø20 mm × 28 mm has been grown by the Czochralski method. The absorption and fluorescence spectra of Nd³⁺ : BaGd₂(MoO₄)₄ crystal were investigated. The absorption band at 807 nm has a FWHM of 5 nm, which is suitable for AlGaAs diode-laser pumping. The absorption cross section σ_ab is 3.42 × 10⁻²⁰ cm²at 807 nm. The emission cross section σ_em is 2.21 × 10⁻¹⁹ cm² at 1065 nm. Based on the Judd–Ofelt theory, the spectral parameters have been calculated. The oscillator intensity parameters Ω_λ are Ω₂ = 14.96 × 10⁻²⁰ cm², Ω₄ = 5.04 × 10⁻²⁰ cm² and Ω₆ = 3.58 × 10⁻²⁰ cm² The radiative lifetime is 156 µs and quantum efficiency η_c = 83.3%. Nd³⁺ : BaGd₂(MoO₄)₄ crystals have a low fluorescence quenching effect and can be doped with more Nd³⁺ ions. The above results suggest that the Nd³⁺ : BaGd₂(MoO₄)₄ crystal may be regarded as a potential solid-state laser material for diode laser pumping.

In order to characterize a nonequilibrium molecular plasma from the point of view of translational, vibrational and rotational degrees of freedom and their interaction, the characteristic temperatures of such a plasma were measured in an ICP rf reactor. Both pure nitrogen and argon–nitrogen mixture plasmas were examined for this purpose.

The experimental results of rotational (T_r), vibrational (T_v) and electron (T_e) temperatures are presented. Vibrational and rotational temperatures were measured as a function of nitrogen content for both E and H modes of ICP discharge using a power range of 45–200 W and pressure range of 2.6–13.3 Pa. Additionally, the pressure dependence of electron temperature in a pure nitrogen discharge was studied. Results show that rotational temperature is ≈370 K for E mode and ≈470 K for H mode and almost does not depend on either the applied rf power or the nitrogen content in the discharge. Vibrational temperature groups in the range 5000–12 000 K increase with applied rf power and constantly decay with an increase of nitrogen content. The measured values and behaviour of electron temperature are comparable with those for the positive column of the dc glow discharge. The results also prove that these three temperatures obey the classical inequality T_e > T_v > T_r, as well as clarifying the differences in both vibrational and rotational temperature for different modes of the ICP discharge.

Results of the treatment of multi-crystalline silicon with low-pressure inductive plasma are presented. Plasma treatment was found to increase silicon electrical conductivity to a greater value relative to its initial state; the time to reach this maximum was found to depend strongly on temperature between 120 and 400 °C. An effect of plasma parameters on collection efficiency and diffusion length was observed by EBIC measurements. An actinometry method based on optical emission spectroscopy measurements was used to determine the molar fraction of monatomic hydrogen produced in plasma in the range between 5% and 8% during the treatment. The excitation temperature calculated by Boltzmann's method ranged between 4500 and 8000 K depending on the plasma gas composition, the pressure and the applied power. A model was developed using the CHEMKIN III® software to compute the role of operational parameters in hydrogen–silicon interactions. The aim of this work is to elucidate the relation between the plasma characteristics and the efficiency of hydrogen passivation on multi-crystalline silicon.

A method for the determination of the reduced electric field strength (E/N) in a neon discharge from the optical emission spectra was developed. This method is based on a collisional–radiative model, which was used to calculate the emission spectra of the neon plasma. In the model, populations of 30 excited levels of the neon atom were studied. Various elementary collision processes were taken into account: electron impact excitation, de-excitation and ionization of neon atoms, emission and absorption of radiation, metastable–metastable collisions, metastable and radiative dimer production, Penning ionization, etc. To determine the rates of electron collisions, the Boltzmann kinetic equation for the electron distribution function (EDF) was solved for given E/N, and thus the dependence of the emission spectra on E/N could be determined. The EDF was expanded in terms of Legendre polynomials and the first two terms of this approximation were taken into account. The theoretical emission spectra were fitted by the non-linear least-squares method to the measured spectra with respect to the unknown parameter E/N.

The method was applied to the study of low pressure dc glow discharge in neon. In such a discharge the calculated reduced electric field strength could be compared with the independent results of simultaneously performed electric probe measurements of E/N. Generally, close agreement of the calculated values with the experimental data was achieved.

A spectroscopic approach was used to study the effects of different operating parameters on st14 sheet metal welding with a 400 W maximum average power pulsed Nd : YAG laser. The parameters included pulse duration and peak power and type and flow rate of the assist gas and welding speed. Weld quality, including penetration depth and melt width, has been compared with the FeI electron temperature obtained from spectroscopic observations of a plasma plume. A correlation between the standard deviation of the electron temperature and the quality of welding has also been found.

In order to understand the influence of electrical discharges on combustion ignition processes, a wire-to-wire spark created in an air/methane mixture has been studied. The electron temperature and density of this spark discharge have been determined.

Voltage, current measurements, photography and optical emission spectroscopy have been used to characterize this discharge as a function of time, pressure and equivalence ratio. The size and shape of the phenomenon were observed using photography. Voltage and current measurement were correlated to these photos to determine the time scale of the discharge and the propagating flame.

The Boltzmann plot method was applied to the results of time-resolved spectroscopy during the discharge phase and yielded to the electron temperature the first 10 µs. Finally, from Stark broadening of H_α, H_β and copper lines, the electron density of the plasma was deduced for the first 10 µs, with values up to 10¹⁸ cm⁻³. These data will be used as the initial condition in a numerical simulation.

We show how the quasi-analytic method developed to solve linear elastic contacts to coated substrates (Perriot and Barthel 2004 J. Mater. Res.19 600) may be extended to adhesive contacts. Substrate inhomogeneity lifts accidental degeneracies and highlights the general structure of the adhesive contact theory. We explain the variation of the contact variables due to substrate inhomogeneity. The relation to other approaches based on finite element analysis is discussed.

In this work we report on the formation of pure polyaniline fibres by the electrospinning method. The fibres present diameters ranging from hundreds of nanometres to a few micrometres and have lengths of hundreds of micrometres. The fibres were collected on SiO₂/Si and Si wafer pieces in the form of isolated fibres. Morphological characterization by scanning electron microscopy shows smooth fibre surfaces and lack of failure effects such as necking and fibrillation. The current–voltage characteristics are linear and the conductivity values vary in the range usually observed for partially doped polyaniline.

Metal–insulator–metal (MIM) capacitors with atomic-layer-deposited Al₂O₃–HfO₂ laminated and sandwiched dielectrics have been fabricated and electrically compared for analog circuit applications. The experimental results indicate that the laminated dielectrics exhibit much better leakage and breakdown characteristics than the sandwiched ones while maintaining higher capacitance densities and acceptable voltage linearity. In respect of the 1 nm Al₂O₃ and 10 nm HfO₂ laminated dielectric, the resulting capacitor offers an extremely low leakage current of 2.4 × 10⁻⁹ A cm⁻² at 8 V and a breakdown electric field of ∼3.3 MV cm⁻¹ at 125 °C together with a capacitance density of ∼3.1 fF µm⁻² and voltage coefficients of capacitance of 100 ppm V⁻² and −80 ppm V⁻¹ at 100 kHz. The superiority of the laminated dielectrics correlates with inhibition of HfO₂ crystallization, discontinuity of the grain boundary channels from the top to the bottom and changes of the dielectric electronic properties due to the bonding and polarization effects at the multi-interfaces.

Thin films of tantalum, molybdenum, palladium and aluminium deposited on silicon are studied by means of atomic force microscopy. The morphology and the grain size, as well as the fractal dimension, of the thin films are deduced and compared with intrinsic stress experimental data on the same films. A correlation is found between the surface morphology, the growth mode, the fractal dimension and the intrinsic residual stress of the films.

GaSb 1 µm-thick layers were grown by molecular beam epitaxy on GaAs (0 0 1). The effects of the growth conditions on the crystalline quality, surface morphology, electrical properties and optical properties were studied by double crystalline x-ray diffraction, atomic force microscopy, Hall measurement and photoluminescence spectroscopy, respectively. It was found that the surface roughness and hole mobility are highly dependent on the antimony-to-gallium flux ratios and growth temperatures. The crystalline quality, electrical properties and optical properties of GaSb layers were also studied as functions of growth rate, and it was found that a suitably low growth rate is beneficial for the crystalline quality and electrical and optical properties. Better crystal quality GaSb layers with a minimum root mean square surface roughness of 0.1 nm and good optical properties were obtained at a growth rate of 0.25 µm h⁻¹.

Plasma-assisted reactive rf magnetron sputtering deposition is used to fabricate vanadium oxide films on glass, silica and silicon substrates. The process conditions are optimized to synthesize phase-pure vanadium pentoxide (V₂O₅) featuring a nanocrystalline structure with the predominant (0 0 1) crystallographic orientation, surface morphology with rod-like nanosized grains and very uniform (the non-uniformity does not exceed 4%) coating thickness over large surface areas. The V₂O₅ films also show excellent and temperature-independent optical transmittance in a broad temperature range (20–95 °C). The results are relevant to the development of smart functional coatings with temperature-tunable properties.

N-type semiconductor thin films of WO₃, Fe₂O₃ and the composite structure of WO₃/Fe₂O₃were prepared on FTO (SnO₂ : F on glass) substrates by the sol–gel method. Their structures and optical properties were characterized by XRD, SEM and UV–Vis spectrometry. Their photoelectrochemical properties were also investigated in a three-electrode cell system. The results showed that the photocurrent of the WO₃/Fe₂O₃ film was higher than that of WO₃ or Fe₂O₃ alone, particularly under visible light illumination (λ > 440 nm). In this case there was almost no photocurrent in the WO₃ film. A reasonable explanation was that the photo-generated electrons could transfer more easily in WO₃/Fe₂O₃ than in WO₃ or Fe₂O₃ alone due to their special conduction band structures. Therefore, the interface between WO₃ and Fe₂O₃ played an important role in improving the conversion efficiency.

During electron irradiation, the growth in the surface voltage on virgin and silver diffused polyimide sample was studied by varying electron energy from 3 to 15 keV and beam diameter from 3 to 15 mm. At a constant beam current, the surface voltage increased nonlinearly with electron energy but decreased slowly with beam diameter at fixed electron energy. At a surface voltage around saturation or beyond 3 kV, the electron beam was switched off and the decay in the surface voltage was studied for a period of 9 × 10⁴ s. The surface analysis revealed that the relative concentrations of carbon increased and that of the oxygen and the nitrogen decreased in the electron irradiated virgin and silver diffused polyimide sample, however in different proportions. Under the identical conditions of electron irradiation, the growth rate of the surface voltage, the post irradiated surface resistivity and the voltage decay constant of the silver diffused polyimide were lower than that of the virgin polyimide. The results of the present study reveal that the resistance of the silver diffused polyimide to keV electrons is higher than that of the virgin polyimide.

Intensive work has long been going on to find out the unknown origin that sets off curious tribo-physicochemical phenomena and that causes various kinds of problems in oil-lubricated sliding contacts in mechanical and processing systems. The strange tribochemical reaction is one of the such curious chemical phenomena observed in the degradation of perfluoropolyether (PFPE) lubricating oil film in a hard disk drive. Plasma (triboplasma) (Nakayama and Mirza 2006 Tribol. Trans.49 17) would be one of the most probable origins of the problems if it were generated sufficiently intensely in oil-lubricated sliding contacts, as it is in such a highly energetic state. The generation of plasma was predicted in both dry and oil-lubricated sliding (Nakayama 1997 Japan. J. Tribol.42 1077, Nakayama 2004 Surf. Coat. Technol.188–189 599). However, plasma generation in industrially important oil-lubricated contacts has not yet been proven, though it has been found in dry sliding (Nakayama and Nevshupa 2002 J. Phys. D: Appl. Phys.35 L53). Here the author reports the discovery of the predicted plasma generated in the rear part of an oil-lubricated sliding contact, together with a new finding on photon emission phenomena from inside and outside of the sliding contact in the tribosystem of a diamond pin sliding against a sapphire disc. The plasma in oil-lubricated sliding has a simple ellipse shape, while that in dry sliding has a horseshoe pattern. Visible and infrared (IR) photons are emitted from oil-lubricated sliding contact, while ultraviolet (UV), visible and IR photons are emitted from the region of plasma generation as well as from dry sliding. The UV photon spectra emitted under oil-lubrication completely coincided with those in dry sliding and air discharge, demonstrating that plasma is generated by air discharge even under oil-lubrication. Two kinds of new concepts have been proposed. One is plasma generation by discharge of air through bubble formation in decompressed oil in the rear part of the sliding contact. The other is photon emission from surface atoms and oil molecules excited by the attack of electrons accelerated in the intense tribocharge-induced electric field of the asperity gap inside the sliding contact under dry and oil-lubricated slidings. The size and intensity of the plasma and photon emission from the sliding contact under oil-lubrication increases greatly with the applied normal force and the sliding velocity.

High-quality GaN films with low dislocation density have been successfully grown on the c-plane specially treated surface of the sapphire substrate. The vapour phase epitaxy starts from the regions with no etched pits where there are some micro-sidesteps to help to nucleate and then spreads laterally with increasing V/III ratio to form continuous GaN films. The full-widths at half-maximum of the x-ray diffraction curves for the GaN films grown on the treated surface of the sapphire substrate in the (0 0 0 2) plane and the (1 0 −1 2) plane are as low as 208.80 arcsec and 320.76 acrsec, respectively, and the etch-pit density of those etched in molten KOH is reduced to 5.5 × 10⁵ cm⁻². The surface of the epilayer exhibits atomically smooth, whose root mean square roughness is found to be 0.2863 nm.The epilayer grown on the treated surface of the sapphire substrate exhibits excellent optical quality, in which the yellow luminescence is nearly invisible in the photoluminescence spectrum. Compared with the conventional epitaxial lateral overgrowth technique, the technology is much simpler and the crystallographic tilt can also be greatly decreased.

We have investigated the growth of AlGaN epilayers on a sapphire substrate by metalorganic chemical vapour deposition using various low-temperature (LT) AlN buffer thicknesses. Combined scanning electron microscopy and cathodoluminescence investigations reveal the correlation between the surface morphology and optical properties of AlGaN films in a microscopic scale. It is found that the suitable thickness of the LT AlN buffer for high quality AlGaN growth is around 20 nm. The Al compositional inhomogeneity of the AlGaN epilayer is attributed to the low lateral mobility of Al adatoms on the growing surface.

The localized dislocation at the interface induces uneven strain distribution in two wafer-bonded layers. Because of the different elastic properties of two bonding layers and this uneven strain distribution, the bilayered microstructure deflects and deflection relaxes the strains. Depending on the microstructure dimensions, elastic properties and lattice parameters, the contribution of deflection to strain field can be very significant. The interface condition also plays an important role in relaxing strain. Two models capable of describing different interface conditions are used for the analysis and offer a more comprehensive study on the dislocation-induced strain field in a wafer-bonded bilayered microstructure. The combined effect of microstructure dimensions and interface condition on the strain is presented and compared.

The frequency dependence of complex permittivity or the dielectric spectrum of a system including a cell in cell division has been simulated by a numerical technique based on the three-dimensional finite difference method. Two different types of cell division characteristic of budding and fission yeast were examined. The yeast cells are both regarded as a body of rotation, and thus have anisotropic polarization, i.e. the effective permittivity of the cell depends on the orientation of the cell to the direction of an applied electric field. In the perpendicular orientation, where the rotational axis of the cell is perpendicular to the electric field direction, the dielectric spectra for both yeast cells included one dielectric relaxation and its intensity depended on the cell volume. In the parallel orientation, on the other hand, two dielectric relaxations appeared with bud growth for budding yeast and with septum formation for fission yeast. The low-frequency relaxation was shifted to a lower frequency region by narrowing the neck between the bud and the mother cell for budding yeast and by increasing the degree of septum formation for fission yeast. After cell separation, the low-frequency relaxation disappeared. The simulations well interpreted the oscillation of the relative permittivity of culture broth found for synchronous cell growth of budding yeast.

The influence of annealing temperature on the hydrophilic property of WO₃ thin films deposited by thermal evaporation and sol–gel dip-coating methods was studied and compared for the first time. The thermal evaporated WO₃ thin films annealed at 400 °C showed a nearly super-hydrophilic property without UV and visible illumination. By analysing the O(1s) core level peak of XPS spectra, the amount of oxygen contributed at various bonds (including O²⁻, OH⁻ and H₂O) on the surface of the annealed samples at different temperatures were measured. In addition, a correlation between the hydrophilicity and the concentration of chemisorbed water on the film surface was suggested, independent of the thin film deposition method.

The glass transition in amorphous poly(ethylene terephthalate) is studied by thermally stimulated depolarization currents (TSDC) and differential scanning calorimetry (DSC). The ability of TSDC to decompose a distributed relaxation, as the glass transition, into its elementary components is demonstrated. Two fractional polarization techniques, windows polarization (WP) and non-isothermal windows polarization (NIW) are employed to assess the influence of thermal history in the results. The Tool–Narayanaswami–Moynihan model has been used to fit the TSDC spectra. The most important contributions to the relaxation comes from modes with a value of the non–linearity parameter (x) around 0.7. Activation energies yield by this model are located around 1 eV (96 kJ mol⁻¹) for polarization temperature (T_p) below 50 °C and they rise up to values higher than 8 eV (771 kJ mol⁻¹) as T_p increases (up to 80 °C). There are few differences between results obtained with WP and NIW but, nonetheless, these are discussed. The obtained kinetic parameters are tested against DSC results in several conditions. Calculated DSC curves at several cooling and heating rates can reproduce qualitatively experimental DSC results. These results also demonstrate that modelling of the non–equilibrium kinetics involved in TSDC spectroscopy is a useful experimental tool for glass transition studies in polar polymers.

We present experimental studies on the dielectric properties of amorphous cerium dioxide in Au–CeO₂–Au systems on strontium titanate substrates. From measurements of the capacitance versus contact area we calculated the dielectric constant of cerium dioxide at room temperature to be _r = 26.9 ± 0.5. These measurements also reveal an additional offset capacitance, which can be attributed to stray fields in the substrate material. I–V characteristics show that the current transport through the insulator changes from electrode-limited to bulk-limited conduction.

In the present work, solidification of a hyper-eutectic ammonium chloride solution in a bottom-cooled rectangular cavity (i.e. with stable thermal gradient) is numerically simulated. The role of finger convection and remelting on the structure of a mushy layer containing channels is studied. The numerical simulation is performed using a fixed-grid single-domain approach in which local remelting and anisotropic variation of mush permeability are taken into account. It is observed that solute-rich liquid rising in the form of finger convection causes delayed growth and localized remelting of portions of the solid/mush interface, resulting in patches of thin structure known as channels. The present study reveals the manner in which the structure of a mushy layer evolves during channel formation. Effects of bulk liquid convection on channel formation, evolution, destruction and the resulting effect on the mush structure are found to be significant. Numerical prediction with regard to variation of the number of channels with time agrees qualitatively with published experimental results.

A novel method of achieving a negative index of refraction in the far-infrared region using intrinsic material properties is proposed. SrTiO₃ has a dielectric resonance at ∼100 cm⁻¹ that can be lowered by lowering the temperature or with Ba doping. NiO has an antiferromagnetic resonance at ∼35 cm⁻¹ that can be raised with an applied field or with Co doping. These resonance frequencies can therefore be engineered to occur at the same frequency to achieve a negative index of refraction over an interval just above the coincident resonance. We show that SrTiO₃ and NiO are readily chemically compatible and non-reacting at temperatures up to 1550 °C and can be formed into polycrystalline composite bodies. Epitaxial thin film heterostructures of (SrTiO₃/NiO)_n/MgO with n = 1, 2 have also been fabricated with very high crystal quality.

Most models of solid-state thermionic devices assume that all electrons with energy in the direction of transport greater than the barrier height are transmitted and utilize the Richardson equation. Here we consider a number of thermionic systems where the electron energy spectrum differs from the Richardson model. The electron energy spectra for maximum refrigeration coefficient of performance and maximum power are presented. We then consider multilayer solid-state nanostructures with currents not given by the Richardson equation and discuss the optimization of their energy spectrum. Nanometre gap vacuum thermionic refrigerators are also treated, where significant current is provided by below the barrier tunnelling. Finally, equations are developed for devices that select electrons for emission according to their total momentum, rather than simply the value in the direction of transport as is the case with conventional devices.

This paper presents a new application of the phase field method. Two-dimensional phase field simulations of domain switching in the crack tip vicinity of a crack embedded in a ferroelectric single crystal, which was subjected to mechanical and electric loading, have been carried out. Khachaturyan–Shatalov (KS) theory [1] was adopted to account for the elastic energy. The domain switching zones induced by the mechanical and electric loading were plotted. The stress field near the crack tip was also plotted to investigate the effect of domain switching on the crack. The obtained domain switching zones are in good agreement with reported theoretical predictions and experimental observations. The stress field shows that the positive electric field inhibits while the negative field promotes the crack propagation.

Thermodynamic and hydrogen-induced structural properties of hydrogenated Ho_1−xMm_xCo₂ (x = 0, 0.1, 0.2, 0.3 and 0.4, Mm = mischmetal) alloys have been investigated. The hydrogen absorption pressure-composition isotherms were studied in the temperature range 50–200 °C and pressure range 0.001–1 bar using a Sieverts-type apparatus. The effect of Mm on the equilibrium plateau pressure and hydride stability has been discussed. Structural analyses and hydrogen-induced amorphization of Ho_1−xMm_xCo₂hydrides were performed using powder x-ray diffraction. The structural stability of these alloys upon repeated hydrogenation and dehydrogenation cycles has been investigated. At lower hydriding pressure and temperatures, Ho_1−xMm_xCo₂-hydrides retain their Laves C15 structure; however, the large lattice volume expansion about 24% is observed in the β-phase. The effect of hydrogenation pressure and temperature and Mm concentration on the hydrogen-induced transformation from crystalline Ho_1−xMm_xCo₂-H to amorphous Ho_1−xMm_xCo₂-H and recrystallization into elemental hydrides have been studied and discussed.

Longitudinal electrostrictive strains in an as-sintered and two annealed (0.4)Pb(In_1/2Nb_1/2)O₃ : (0.6)Pb(Mg_1/3Nb_2/3)O₃ relaxor ceramics were measured by laser-interferometry. The field-related electrostriction coefficients (M₃₃) of the ceramics were then determined. The electrostrictive coefficients progressively decreased with annealing and the strain responses became nonlinear. The ferroelectric hysteresis loops of the as-sintered and annealed ceramics showed progressive decrease in coercive fields and maximum polarizations with increasing annealing time. Transmission electron microscopy studies revealed enlargement of 1 : 1 B-site ordered domains with annealing. The changes in the high-field responses of the annealed ceramics are interpreted as arising from a higher degree of long-range order caused by annealing. A field-induced mechanism is proposed to explain the correlation between the B-site cation long-range order and the electrostrictive behaviour in this relaxor.

Bi_1−xLa_xFeO₃ (x = 0–0.25) multiferroic ceramics were prepared to study the compositional driven structural transformation and ferroelectric– paraelectric phase transition. Rietveld-refined crystal structure parameters revealed the existence of a rhombohedral R3c symmetry in BiFeO₃, a triclinic P1 symmetry in Bi_0.95La_0.05FeO₃, Bi_0.9La_0.1FeO₃ and Bi_0.85La_0.15FeO₃, a pseudotetragonal P4mm symmetry in Bi_0.8La_0.2FeO₃ and a pseudotetragonal P4/mmm symmetry in Bi_0.75La_0.25FeO₃. La substitution led to the ferroelectric–paraelectric phase transition accompanying abrupt changes of Raman scattering spectra in Bi_0.8La_0.2FeO₃ and Bi_0.75La_0.25FeO₃, besides the release of weak ferromagnetism in Bi_0.85La_0.15FeO₃, Bi_0.8La_0.2FeO₃ and Bi_0.75La_0.25FeO₃. Ferroelectricity with remnant polarization of >9.8 µC cm⁻² and piezoelectricity with d₃₃ coefficient of >25 pC/N were confirmed in all compositions except for Bi_0.75La_0.25FeO₃.

The understanding of melt flow in kerfs is still dominated by a simplified view of melt films travelling down the kerf wall. This is mainly due to the inherent problems of observing the melt flow in the experiment. High temperatures, high speed phenomena, high intensity irradiation by the laser combined with narrow and deep kerfs are factors hindering observation. Hence the assumption that shear is the main driving force in expelling the melt was not challenged fundamentally until now. However, initial computer experiments performed by the authors appear to, albeit not contradicting, but at least augmenting this understanding by adding a second melt expulsion mechanism. This second mechanism is dominated by stagnation pressure and an expansion fan at the melt edge. Circumstantial evidence is provided in the form of micrographs showing a solidification behaviour reminiscent of the melt flow observed in the computer experiment.

Linear and nonlinear optical properties of lanthanum-modified lead zirconate titanate (Pb_0.92La_0.08)(Zr_0.65Ti_0.35)O₃ (PLZT 8/65/35) ferroelectric thin films are presented in this paper. The PLZT ferroelectric thin films were grown on quartz substrates by radio-frequency magnetron sputtering at 650 °C. Their crystalline structure and surface morphologies were examined by x-ray diffraction and atomic force microscopy, respectively. It was found that the PLZT thin films exhibit well-crystallized perovskite structure and good surface morphology. The fundamental optical constants (the band gap energy, linear refractive index and absorption coefficient) were obtained through the optical transmittance measurements. A Z-scan technique was used to investigate the optical nonlinearity of the PLZT thin films on quartz substrates. The films display a strong third-order nonlinear optical effect. A large and negative nonlinear refractive index n₂ is determined to be 1.21 × 10⁻⁶ esu for the PLZT thin films. All results show that the PLZT ferroelectric thin films have potential applications in nonlinear optical devices.

There are some typographical errors on page 2105, in line 5 in the right-hand column. The values `8.0 mm × 1.2 mm × 1.0 mm' should read as `80 mm × 12 mm × 10 mm', and `2.0~g' should read as `1.0–2.0 g'.

In figure 5, on page 2108, the labelled wavelengths of the first peaks of curves a and b should be interchanged as in the following corrected figure:

Figure 5. Room temperature PL spectrum of the ZnO tetrapods excited at 325 nm using Xe lamp as the resource. (a) T = 630 °C, O₂: 15 sccm, Ar: 300 sccm and (b)T = 680 °C, O₂: 25 sccm, Ar: 300 sccm.