Table of contents

Introduction of a high concentration of manganese in III–V semiconductors, such as InAs and GaAs, results in carrier-induced ferromagnetism, which allows us to integrate ferromagnetism in nonmagnetic heterostructures and which modifies their magnetic properties through electric-field control of carrier concentration. The properties of ferromagnetism can in many cases be semi-quantitatively understood by the p–d Zener model, which is qualitatively different from conventional ferromagnetic metals. These ferromagnetic III–V semiconductors also offer the unique opportunity of examining spin-dependent phenomena observed so far only in metallic systems. Here, we review our experimental study on electrical manipulation of magnetization in these ferromagnetic III–V semiconductors. We first describe the results of electrically assisted magnetization reversal in ferromagnetic semiconductor (In, Mn)As field-effect transistor structures. The coercivity as well as ferromagnetic transition temperature can be controlled through the modification of carrier concentration by applied electric fields in a gated structure. We then present electrical magnetization reversal by spin-transfer torque exerted by spin-polarized currents at low threshold current density (∼10⁵ A cm⁻²) in (Ga, Mn)As-based magnetic tunnel junctions.

A cylindrical thin liquid metal layer is submitted to a uniform ac magnetic field. When the intensity of the electromagnetic field exceeds a critical value, an opening in the liquid is shaped from outside to inside. At a given intensity of the electromagnetic field, this opening is in a frozen state, that is, the liquid metal layer reaches a new equilibrium shape. In this paper, we show that this equilibrium corresponds to a minimum of the total energy of the system. This total energy is equal to the sum of the magnetic energy and the mechanical energy. The magnetic energy is computed by assuming that the induced eddy current flowing through the liquid metal layer is concentrated in the cross-section S_c equal to the product of the skin depth and the thickness of the layer. This assumption leads us to study an equivalent electrical circuit.

The mechanical energy is composed of the potential energy and the surface energy.

The effects of Co substitution for Fe on the spin reorientation temperature, magnetic properties over a wide temperature range, the thermal stability and on exchange enhancement in nanocrystalline (Nd/Pr)_z(Fe_1−xCo_x)_94−zB₆ alloys have been comprehensively studied. Such Co substitution substantially increased the Curie temperature (T_C) of the 2/14/1 phase and slightly decreased the spin reorientation temperature (T_SR) for these alloys. Despite the smaller anisotropy field for the Nd₂Co₁₄B phase, in comparison with Nd₂Fe₁₄B, a small Co substitution did not greatly decrease the room temperature (RT) coercivity _jH_C, regardless of the rare earth to transition metal ratio. The remanence J_r at RT was generally slightly improved by Co substitutions up to ∼20%, though less so for the 8 at% rare earth (RE) series having a high volume fraction of soft magnetic phase. Similarly, substitution of up to 20% Co slightly enhanced the maximum energy product (BH)_max at RT, except for the 8 at% RE alloys which showed a marked decline beyond 10 at% Co due to the strongly diminished _jH_C. In the case of the sub-ambient magnetic properties, Co substitution markedly decreased J_r and (BH)_max, though the effect on _jH_C was much smaller. In contrast, Co additions, because of the enhancement of T_c, substantially improved the elevated temperature behaviour of all experimental alloys, by decreasing the values of the temperature coefficients for J_r and _iH_c, α and β, respectively, particularly for α. Moreover, the Co also reduced the irreversible losses in J_r and _jH_C measured on ribbon samples. Analysis of microstructural parameters governing the coercivity, using the modified Brown equation, suggested that Co substitution not only reduced the stray fields, by homogenizing the grain structure and smoothing the grain boundaries, but also improved the exchange coupling between grains.

Chemical solution deposition as an alternative method for colossal magnetoresistance films is used to prepare the La_0.8Na_0.1A_0.1MnO₃ (A = Ca, Na, Sr) on single crystalline LaAlO₃ (h00) substrates. The results show that all the derived films are highly (h00)-oriented and have rather large magnetoresistance values near the room temperature. Moreover, for the three films, it is found that the insulator–metal transition temperature (T_IM) is higher than that of the paramagnetic–ferromagnetic transition (T_c). It is interesting to find that in the Na-doped manganites the maximum MR value and T_IM as well as T_c can be synchronously improved.

Carrier dynamics and optical activity of 10 MeV Ni⁺-irradiated and annealed GaInAs/InP quantum wells (QWs) have been studied using a time-resolved femtosecond up-conversion method. Quantitative results are obtained for a carrier capture time and a carrier lifetime (decay time) as a function of implantation dose. The carrier capture time decreases with the dose, while it is little affected by rapid thermal annealing (RTA). The capture time is 8 ps for the as-grown QW and 2 ps for the irradiated QW at the highest ion dose of 50 × 10¹⁰ ions cm⁻². The carrier lifetime in the as-grown QW is long, 1.19 ns, but is only 3.7 ps after ion irradiation. RTA reduces the density of irradiation-induced defects and improves the optical activity. Other than the implantation dose, the lifetime also depends on the ion implantation energy (varied from 6 to 30 MeV at a fixed dose of 5 × 10¹⁰ ions cm ⁻²): the higher the implantation energy, the longer the carrier lifetime. This is because the nuclear deposited energy decreases in the QW region with an increase in implantation energy. Hence, for an efficient defect production low-energy implantation (<10 MeV for Ni⁺) is preferred. The results obtained are compared with compressively strained GaInAs/GaAs QWs samples exposed to a similar dose and annealing conditions.

A metal-ferroelectric-semiconductor structure has been developed by depositing Li-doped ZnO thin films (Zn_1−xLi_xO, x = 0.25) on p-type Si substrates by the pulsed laser ablation technique. (002) preferential oriented films were deposited at a low growth temperature of 500 °C and 100 mTorr oxygen partial pressure. The dielectric response of the films has been studied over a temperature range 250–373 K. A dielectric anomaly was observed at 360 K. The capacitance–voltage characteristics of Ag/Zn_0.75Li_0.25O/Si exhibited clockwise hysteresis loops with a memory window of 2 V. The films deposited at 100 mTorr pressure show a stable current density and a saturated polarization hysteresis loop with a remanent polarization of 0.09 µC cm⁻² and coercive field of 25 kV cm⁻¹. Leakage current measurements were done at elevated temperatures to provide evidence of the conduction mechanism present in these films. Ohmic behaviour was observed at low voltage, while higher voltages induced a bulk space charge. The optical properties of Zn_0.75Li_0.25O thin films were studied in the wavelength range 300–900 nm. The appearance of ferroelectric nature in Li-doped ZnO films adds an additional dimension to its applications.

The thermally stimulated luminescence (TSL) arising simultaneously from localized and delocalized recombination processes is studied theoretically for a wide range of recombination and retrapping probabilities. The model proposed by Braunlich and Scharmann (BS), which considers the excitation of trapped electrons to (i) the conduction band, (ii) the excited state of the trap and (iii) the electrons from the excited state of the trap which are further raised to the conduction band during the heating phase of the TSL phosphor, has been used in the present study. The rate equations of the model, which are 'stiff', are solved numerically for a wide range of parameters using the linear heating profile. It has been found that the glow peak temperature T_m can exhibit dose dependence in localized transitions under strong retrapping, i.e. r ≫ 1 (r is the retrapping parameter for localized transitions), whereas for the other values of r, the glow peak temperature T_m is independent of dose.

The same is also true for the glow curve arising from localized recombination in the study of a semi-localized transitions model. The study shows that the order of kinetics of the TSL glow curve arising from localized recombination can be more than one as the glow peak temperature T_m can exhibit dose dependence.

However, the BS model is of approximate character because the possibility that the recombination centre, which is likely to participate in localized process, may be emptied by a recombination transition from conduction band, i.e. via delocalized recombination process, has not been included and in such situations the BS model does not hold.

Two novel polymers PQP(poly(3, 7-N-octyl phenothiozinyl cyanoterephthalylidene)) and PQM (poly(3, 7-N-octyl phenothiozinyl cyanoisophthalylidene)) containing phenothiazine were synthesized for application in red and orange light-emitting diodes. The synthesized polymers were characterized using UV-visible, photoluminescence and electroluminescence (EL) spectroscopy. The single-layer EL devices of indium tin oxide(ITO)/PQP(or PQM)/Mg : Ag and multi-layer devices of ITO/PQP(or PQM): N, N'-diphenyl-N, N'-bis(3-methylphenyl) -[1, 1'-biphenyl]-4, 4' -diamine(TPD) (44 nm)/2, 9-dimethyl-4, 7-diphenyl -1, 10-phenanthroline (BCP, 5 nm)/tris(8-hydroxyquinolinato) aluminium(AlQ₃, 20 nm)/Mg : Ag were fabricated. The EL spectra from the devices based on PQP peaked at the wavelength of 664 nm and covered red and infrared regions. The maximal brightness was measured to be about 60 cd m⁻² at the applied voltage of 17 V. The devices based on PQM gave bright orange light-emission peaking at 608 nm and the maximal luminance was 150 cd m⁻² at the applied voltage of 14 V.

Thermoluminescence (TL) of CaSO₄ : Dy phosphor, irradiated by 48 MeV ⁷Li ions with different fluences in the range 1 × 10⁹–5 × 10¹¹ ions cm⁻² has been studied. The samples from the same batch were also exposed to γ-rays from a Co⁶⁰ source for comparative studies. The TL glow curve of the material, irradiated with the ion beam has a simple structure with a prominent peak at around 494 K along with three small shoulders at around 424, 592 and 662 K. The TL saturation has been observed at around the fluence 1 × 10¹¹ ions cm⁻². As the fluence is increased from 1 × 10⁹ to 5 × 10¹¹ ions cm⁻², a shift in the peak positions towards the lower temperature side, by around 7 K was observed. However, with increasing fluence, the TL glow curve structure remains invariant with no change in the relative intensities between the 494 and 424 K peaks, while in the case of γ-irradiated samples, in contrast, the intensity ratios of these peaks increase exponentially with exposures. Theoretical analysis of the glow curves of the ion beam and γ-irradiated samples was done by the glow curve deconvolution method. The efficiency of CaSO₄ : Dy to 48 MeV ⁷Li ions has been measured relative to γ-rays of Co⁶⁰ and found to be 0.81. This result, along with the observed good linearity over a large span of fluences, shows that this phosphor is quite suitable as a dosimeter for heavy charged particles.

Non-basal surfaces of 6H-SiC, which are thought to exhibit polar behaviour, were thermally oxidized in steam. The resulting oxide thickness was determined by two methods: a non-contact measurement of the oxide capacitance and a physical measurement of the step height from an etched pattern. The surface was found to oxidize faster than its counterpart, i.e. the surface. When these results were compared with results of the oxidation of the basal {0001} and surfaces, the effective permittivity of the oxide was found to be closer to the ideal value of 3.9 for SiO₂ grown on the and surfaces. This important result for these novel crystalline surfaces could be beneficial in the fabrication of MOSFET devices on SiC.

Al-doped quasi-aligned ZnO submicro-rods were prepared on heavily doped n-type Si(111) substrates by the thermal evaporation method. Electrical transport measurements indicate the Al-doped ZnO submicro-rods have better conductivity than the undoped submicro-rods. The photoluminescence excitation spectrum of the annealed sample indicates an energy level ∼100 meV below the conduction band minimum, which may be due to the localized state of the Al impurity. The annealed sample exhibits a strong green emission centred at 2.45 eV that can be seen by the naked eye and an infrared emission centred at 1.10 eV. The intensity ratios of the deep-level green emission to the ultraviolet emission are 0.86 and 30 for the as-grown and annealed samples, respectively. Moreover, two emissions at 2.2 and 1.96 eV were discriminated from the PL spectrum of the as-grown Al-doped ZnO submicro-rods, which were not observed in the pure ZnO submicro-rods and the annealed Al-doped sample.

A bright red colour emitting Mn doped Ba₂ZnS₃ phosphor was prepared by an ecologically acceptable carbothermal reduction method without an inert gas or hazardous gas (H₂S) environment. The phosphor can be excited with UV wavelength radiation to realize emission in the visible range. X-ray diffraction studies confirm an orthorhombic structure with phase group, pnam. The photoluminescence (PL) emission spectrum shows a broad band with emission maximum at 625 nm under the host excitation of 358 nm, which lies in the near UV region. The concentration of Mn was varied from 0.0025 to 0.20 mole with respect to Zn and the optimum PL emission intensity was obtained at the concentration of 0.01 mole of Mn. The CIE (Commission Internationale de l'Eclairage) colour coordinates measurement (x = 0.654 and y = 0.321) shows that the primary emission is in the red region. The triband phosphors blend containing Sr₅(PO₄)₃Cl : Eu²⁺ (blue), ZnS : Cu,Al (green) and Ba₂ZnS₃ : Mn (red) shows white light emission under 365 nm excitation having CIE chromaticity (x = 0.292 and y = 0.251). Since phosphor excitation lies in the near UV excitable region, giving a bright red emission, it can be used for applications in near UV phosphor converted white LED lighting and display devices.

CdTe crystals grown by the Bridgman technique were irradiated by swift heavy ions (SHIs), 100 MeV Ag⁷⁺ ions, with fluences varying from 10¹¹ to 10¹⁴ ions cm⁻² and the damage is investigated by atomic force microscopy, x-ray diffraction, hall effect measurements and photoluminence. It is found that the behaviour of CdTe crystals under a SHI irradiation induces structural disorder, generation of optically active defects, decrease in the electron mobility but an increase in the carrier concentration compared with as-grown samples. The observed effects are mainly due to the intense electronic excitation created by SHIs.

By doping an erbium complex, erbium (III) 2, 4-pentanedionate (Er(acac)₃), into the ALQ layer, we fabricate a series of infrared emission organic light emitting diodes (OLED) with structures of p-Si/SiO₂/NPB/ALQ/ ALQ:Er(acac)₃/ALQ/Sm/Au, where p-Si is the anode and Sm/Au is the cathode. The 1.54 µm emission from Er³⁺ is observed. The impact of doping level of Er(acac)₃ in ALQ on 1.54 µm electroluminescence (EL) intensity is studied, and the best mass ratio of Er(acac)₃ to ALQ is found at 1 : 60. A competitive EL mechanism from the ALQ and Er(acac)₃ is found and the Er³⁺ ions excitations are attributed to energy transfer from the ligands to Er ions.

Cathodic arc attachment after a steady state anodic phase is investigated in a vertically operated 0.7 MPa mercury high intensity discharge lamp with pure tungsten electrodes. Experimental evidence of a dynamic cathodic mode change of arc attachment influenced by convective effects is documented. Finite element simulation of the temperature field in the cathode body in two and three dimensions is performed. Nonlinear surface heating using Neumann's and Benilov's models is employed. The presheath voltage drop as a function of electron temperature is proposed as a compact input parameter. For Benilov's model two alternatives are compared. All models have the ability to show transient mode changes. The models show no sharp distinction. There are strong indications that the transient spot possesses a nonzero minimum life time when it abruptly emerges at a distinct threshold. The model fairly predicts the thresholds observed in experiments for the upper and lower electrodes depending on the convection heating. The evidence is more in favour of a lower presheath voltage drop, i.e. lower electron temperatures during the spot mode. The results are applicable for the design of dimming modes of HID lamps.

High frequency (HF) stationary capillary discharge in He and He/N₂ mixtures has been studied at medium pressures. In the experimental part the spectrum of the discharge was recorded as a function of small concentration of N₂ varying the input power and pressure. The analysis of experimental data showed that in the negative glow region of discharge the dominant recombination mechanism is direct dissociative recombination. ions are formed both by charge transfer and Penning reactions but the first reaction is prevailing.

The electrical conductivity of a thin gas discharge gap (d = 60 µm) filled with atmospheric air at 60 Torr pressure and room temperature was investigated. Current–voltage characteristics of the device when both the electrodes are metals and when one of the electrodes is a high resistivity GaAs semiconductor were measured. It is shown that in the device with the semiconductor electrode, the current is registered before the breakdown of gas. The value of pre-breakdown current depends on experimental conditions: it increases drastically if gas is subjected to breakdown before the measurements. Thus, the device has a memory effect. The value of memory effect depends on the value of the ionization current and does not depend on the polarity of the applied voltage. The effect is absent in a device with two metallic electrodes, and the effect disappears after the pumping of the gas down to 0.1 Torr. The obtained results can be explained on the basis of diffusion–drift type equilibrium of charges taking into account the charging of the semiconductor near the surface. The latter is the guarantee of the stability of residual pre-breakdown current in the gas.

A frequently cited multi-fluid plasma model for the near-cathode region in thermal plasmas is investigated by a combination of analytical and graphical methods. The results presented in the literature are reproduced and confirmed for plasmas where charge exchange collisions occur more frequently than ionization collisions. For plasmas where ionization collisions are dominant, slightly different results including a different interpretation are presented. From this interpretation, possible amendments to the model are suggested. Also, conclusions about the limitations of the model are drawn.

The spatial structure, including a discharge and a remote plasma zone, of a large-scale, slot antenna excited microwave plasma source operating in Ar and N₂–Ar mixtures at 2.45 GHz has been investigated. The discharge source is sustained by the electric field of pure TM surface modes. Optical emission spectroscopy, probe diagnostic techniques and radiophysics methods are applied to measure the emission intensity of radiative states, the electron density and the microwave field intensity, respectively. The spatial distribution of the electron density and the intensity of emission lines belonging to the 2nd positive and 1st negative systems of N₂ follow the electric field pattern in the active-discharge zone of the plasma source. On the contrary, the populations in vibrational and rotational levels of the N₂(C ³Π_u) state are homogeneous irrespective of the azimuthal position.

Numerical simulations are carried out for the characterization of injection instabilities in electrohydrodynamics and, in particular, the development of electroconvection between two parallel plates. The particle-in-cell and the finite element-flux corrected transport methods are used for the simulation of the test case, as they have proved very powerful and accurate in the solution of complex transport problems. Results are presented for unipolar injection (both strong and weak injections) between two plane electrodes immersed in a dielectric liquid, and the good agreement obtained by the two methods demonstrates not only their theoretical validity but also their practical ability to deal with transport problems in the presence of steep gradients. Some differences appear mainly in the prediction of small oscillations of the velocity and consequently of the electric current. These differences are highlighted and an explanation of their source is given.

The anode boundary layer in high intensity arcs determines the anode lifetime and processing efficiency in many industrial applications and can be controlled by cold lateral gas flows (LGFs) parallel to the anode. In this paper, properties of the anode boundary layer in a high intensity argon arc with argon and nitrogen LGFs have been studied. Anode heat and current transfer and restrike frequency and restrike length have been measured using a segmented anode and a high speed camera. Electron temperature, electron density and current density have been measured by a Langmuir probe setup. The correlation between these properties and the previously defined arc attachment mode has been described and explained.

The secondary electron emission coefficient (γ_se) of ions and excited species in a plasma display panel (PDP) was studied by means of 2-dimensional fluid and 1-dimensional particle-in-cell Monte Carlo collision simulations. Relations between the driving voltage and the luminous efficiency observed in experiments are reproduced at low and high Xe concentrations. Agreement between experiments and simulations, however, requires careful selection of the γ_se of ions and excited species. The trend of the efficiency as a function of the driving voltage is particularly sensitive to the γ_se of Xe excited species. For the conditions typically encountered in PDP cells (pd = 1–10 Torr cm), the dependence of the γ_se on the energy of impinging ions can be neglected in discharges of pure gases. This is a consequence of multiple charge exchange collisions in the cathode region. In Xe–Ne mixtures, however, the ion energy distribution function on the cathode depends on the mixture ratio. Typically more energetic ions can reach the cathode in gas mixtures and the γ_se is enhanced.

Different types of carbon samples, which are used as carbon support for proton exchange membrane fuel cells electrocatalysts as well as for gas diffusion layers, are treated by various methods in order to improve the adhesion of platinum metal to the carbon as well as to reduce the ionomer loading in the electrocatalyst layers. The samples are characterized by the point of zero charge method, FTIR and x-ray fluorescence before and after various oxidation and sulfonation treatments in order to determine the nature of functional groups, linkage of sulfonic groups with carbon, etc. The extent of surface modification in Vulcan Xc 72, Acetylene black and Ensaco 250G has been investigated. In addition, the extent of sulfonation of carbons to link sulfonic groups directly onto the surface of C-particles functioning as catalysts supports has been carried out in order to investigate the reduction in the weight percentage of Nafion loading, within the catalyst layer for proton conduction. The point of neutral charge evaluation helps in identifying the platinum complex to be used for electrocatalyst synthesis based on their charge.

We have systematically investigated hydrogen sensing properties of pulsed laser deposited palladium thin films with reference to their crystallinity, surface morphology and film thickness. Thin films were deposited on clean quartz substrates at varying growth parameters. Structural and surface morphological characterizations have been carried out using X-ray diffraction, scanning electron microscopy and atomic force microscopy. Thin films with nanostructured surface morphology were achieved. Electrical resistance measurements, carried out in situ, by a two-probe technique in a chamber with a provision to introduce a known concentration of hydrogen gas and air, showed saturation on exposure to hydrogen gas. The change in electrical resistance due to hydrogen loading is found to be reversible. The sensor response time is typically 10–20 s. The Pd films are stable after several cycles of hydrogenation and dehydrogenation.

Fluorescence x-ray absorption fine structure and x-ray diffraction are used to study the structures of super-hard TiN/Si₃N₄ multilayer films deposited by reactive magnetron sputtering at temperatures of 20, 200, 500 and 800 °C. The results clearly reveal the presence of interfacial intermixing between adjacent TiN and Si₃N₄ layers. And the interlayer is composed of TiSi_xN_1−x solid solution with an NaCl-like structure. Increasing the growth temperature from 20 to 500 °C, the crystalline quality of the pure TiN layer improves significantly, and the thickness of the interlayer rises from 2.5 to 5.0 Å. For the TiN/Si₃N₄ multilayer film grown at 500°C, the interfacial layer is composed of TiSi_0.24N_0.76 solid solution, where the Ti–N bond length (2.07 Å) is largely shrunk as compared with the value (2.12 Å) in the pure TiN layer. When growth temperature rises to 800°C, the composition of the interfacial layer becomes TiSi_0.3N_0.7 and reaches a thickness of 7.8 Å. We propose that the TiSi_xN_1−x interlayer with obviously contracted Ti–N bond length is an important hardening factor for the crystalline/amorphous TiN/Si₃N₄ multilayer films grown at high temperatures.

Nanocrystalline nickel films have been deposited by microwave plasma-assisted sputtering from pure argon discharges on steel and (100)-oriented single crystal silicon wafers mounted on a water-cooled substrate holder biased to various direct current voltages ranging from 0 to −120 V. The crystallographic structure and surface morphology of films were determined by x-ray diffraction techniques and atomic force microscopy, respectively. The magnitude of compressive residual stresses (intrinsic stress) calculated from the radius of curvature of Si substrates reached a maximum value of −250 MPa in films deposited on grounded substrates and decreased with increasing negative substrate bias voltage. The hardness of films was determined by nanoindentation as a function of the substrate bias voltage. Alumina ball-on-disk tribological tests of films deposited on steel substrates were conducted in room air at 20 °C under a load of 1 N with a sliding speed of 50 mm s⁻¹. The value of the stabilized friction coefficient was in the range 0.35–0.45 for 5000 cycles. Beyond 5000 cycles, the films were worn and the friction coefficient increased rapidly. The electrical resistivity of films deduced from the thickness and sheet resistance of films determined by four point probe measurements was approximately equal to 13 µΩ cm.

The paper describes a theoretical study of adhesive friction at the contact between rough surfaces taking asperity interaction into consideration and using an elastic–plastic model of contact deformation that is based on an accurate finite element analysis of an elastic–plastic single asperity contact. The micro–contact model of asperity interactions, developed by Zhao and Chang, is integrated into the improved elastic–plastic rough surface adhesive contact analysis to consider the adhesive friction behaviour of rough surfaces. The model considers a large range of interference values from fully elastic through elastic–plastic to fully plastic regimes of contacting asperities. Two well-established adhesion indices are used to consider different conditions that arise as a result of varying load, surface and material parameters. Results are obtained for the coefficient of friction against applied load for various combinations of these parameters. The results show that the coefficient of friction depends strongly on the applied load for the no-interaction case while it becomes insensitive to the load for interaction consideration. Moreover, the inclusion of elastic–plastic asperities further reduces the friction coefficient.

Ba_1−xSr_xTiO₃ (x = 0.3, 0.5, 0.7) thin films have been prepared on (001) MgO substrates by pulsed laser deposition. Temperature-dependent permittivity and Raman spectra of the Ba_{1 − x}Sr_xTiO₃ films are compared with those of the corresponding bulk samples. Raman spectra indicate that a tetragonal structure is present in the Ba_0.5Sr_0.5TiO₃ thin film while the Ba_0.5Sr_0.5TiO₃ bulk sample shows a cubic structure. Temperature-dependent permittivity shows that the phase transition in the film occurs over a wide temperature range, which results in the co-existence of the cubic phase and tetragonal phase in the Ba_0.5Sr_0.5TiO₃ film. The smooth change of phase transition is attributed to the residual stress in the film. We demonstrate that the residual stress releases gradually with increasing thickness of the film. Furthermore, the effects of the composition and thickness on Raman spectra have also been discussed systematically.

The study deals with the ac electrical conduction of poly(methyl methacrylate)/carbon black composite of different carbon black (CB) filler concentrations (2, 6, 12 wt%). The ac electrical conductivity was studied as a function of filler concentration, frequency in the range from 100 kHz to 2 MHz, and temperature in the range from 300 to 450 K. It was found that ac electrical conductivity increases by increasing both temperature and CB concentration. The observed overall mechanism of electrical conduction has been related to the transfer of electrons through the CB aggregations distributed in the polymer matrix. The observed increase in conductivity with CB concentration was interpreted through the percolation theory.

The stress relaxation rate in irradiated high purity polycrystalline titanium was studied at room temperature. Titanium specimens of grain size 40 µm were irradiated with 18 MeV electrons for 12 min at 300 K to a dose of 0.01 dpa. The stress relaxation rate in the specimens was studied using a universal testing machine. The comparison of irradiated samples with un-irradiated ones, annealed and tested in similar conditions, revealed that the stress relaxation rate is lower in the irradiated titanium specimens than in the un-irradiated ones. The results are analysed in terms of a single barrier model of stress relaxation. The intrinsic height of the energy barrier to the movement of dislocations was found to be higher in the case of irradiated specimens than in the un-irradiated ones. This is attributed to the local pinning of dislocations with the irradiation induced defects acting as obstacles.

The notion of dielectric order of a multi-component disperse system is introduced and is bounded with the index of the power law of mixing for dielectric permittivities of different components in an electromagnetic field. Using the example of wheat grain under microwave radiation, we phenomenologically describe the effect of continuous modification of dielectric order in a disperse system as a result of its moisture alteration. It is supposed that this effect is conditioned by the known phenomenon of organization and expansion of spatially regulated water structure formations inside grain kernels when they absorb moisture. A new mixing law is established, being in good agreement with this effect. On its basis, a physically correct theory has been developed. It permits calculation of the grain dielectric permittivity over a wide range of moisture content and temperature variation.

Single orientation epitaxial erbium silicide (ErSi₂) nanowires (NWs) were fabricated by laser ablation and a post-annealing process on the Si (110) surface. The average width of the NWs is 10 nm and the maximum length is more than 10 µm. The resistivity of the NWs was measured at room temperature using two methods: AFM probe measurement and direct electrodes deposited by FIB. It was demonstrated that the resistivities of the NWs were ten times that of the ErSi₂ film material. The experimental data were compared with theoretical predictions for the strong size effect to the erbium silicide NW resistivity.

Stretched nylon 6 fibres are treated with iodine at 50 °C at different time intervals. The effects of the treatment on the optical and structural parameters are investigated. Using the double-beam Pluta polarizing interference microscope, the interference patterns are recorded for the investigated samples and used for calculating the refractive indices, birefringence and other optical properties. The refractive indices and the birefringence values are directly proportional to the time of iodine evaporation. The iodine treatment increases the isotropic refractive index, mean polarizability per unit volume, surface reflectivity and orientation function, while decreasing the orientation angle (θ). The angle (θ_m) between the chain axis and the dipole moment seems to be constant. The investigated parameters show remarkable variation for the uniaxially drawn fibres to draw ratios (3 and 3.5). Moreover, the iodinated undrawn and drawn samples reveal an increase in the magnitude of the investigated parameters compared with those only annealed at the same conditions of temperature and time. The obtained results indicate that the iodine treatment modifies the nylon 6 fibre structure and consequently the optical properties, which may be useful for different industrial purposes.

In this paper, the internal friction behaviour of Zr–Ti–Cu–Ni–Be bulk metallic glass (BMG) containing 2 at% Fe at elevated temperatures has been studied in isothermal dynamic mechanical analysis experiments. The experiments lead to the determination of metastable equilibrium internal friction , as a function of temperature, which can be well described by the Maxwell model with viscosity, η(T), following a Vogel–Fulcher–Tammann (VFT) relation or Arrehnius law. Comparison with the Zr–Ti–Cu–Ni–Be glass-forming liquid shows that a small addition of Fe results in a stronger liquid behaviour of the alloy, exhibiting a higher strength parameter as well as lower VFT temperature and therefore correlates better glass forming ability and thermal stability. From the isothermal internal friction data, the activation energies for viscous flow and primary crystallization of the Zr based supercooled metallic liquid are also derived. It is found that the former is comparable to the activation energy controlling the diffusion process of atoms, e.g. the Ni element of medium size and higher mobility among the components of this alloy, while the latter to that of atoms, e.g. the Ti element of larger size and lower mobility. Thus, it is proposed that both isothermal viscous flow and primary crystallization of the alloy in the supercooleld liquid region are atom diffusion-controlled processes. However, the dominating atomic species are different from each other in the multicomponent Zr based BMG.

A suitable plane transmission line was developed and its behaviour analysed at 900 MHz radiofrequency fields to study DNA mutability and the repair of micro-organisms. In this work, utilizing such a device, we investigated the behaviour of DNA mutability and repair of Escherichia coli strains. The transmission line was very simple and versatile in changing its characteristic resistance and field intensity by varying its sizes. In the absence of cell samples inside the transmission line, the relative modulation of the electric and/or magnetic field was ±31% with respect to the mean values, allowing the processing of more samples at different exposure fields in a single run. A slight decrease in spontaneous mutability to rifampicin-resistance of the E. coli JC411 strain was demonstrated in mismatch-repair proficient samples exposed to the radio-frequency fields during their growth on solid medium.

The time-harmonic induced current in a conductive plate has been calculated for an excitation by a normal coil near the plate edge. Using series expansions in elementary functions, the quasi-static solution for the plate is matched to the solution for the region outside the plate to ensure continuity of the tangential magnetic field and the normal magnetic flux density at the air–conductor interface. The continuity of the field is achieved by mode matching in a truncated domain. Predictions of the coil impedance as a function of position derived from this theory have been compared with experiment showing good agreement.

Three-dimensional finite element analysis of arc-welding processes is presented with emphasis on practical applications for numerical simulation. We use an implicit numerical implementation for Leblond's transformation plasticity constitutive equations, which are widely used in steel-structure welding. Several numerical examples, particularly including a large structure undergoing significant elastic–plastic deformations before welding, are presented to demonstrate the effectiveness of the three-dimensional analysis of welding processes.

Accelerator mass spectrometry measures the depth profiles of material concentration in solid samples. Crater edge effects affect the experimental data when the secondary ions are sputtered from the sidewalls of the produced crater. We present a simple mathematical unfolding procedure that removes the perturbing contribution from the measured depth profile data. Application of this procedure to experimental data is also presented.