Table of contents

Dielectrophoretic and electrohydrodynamic forces have been demonstrated in the literature to cause movement of particles across the surface of planar electrodes when exposed to low-frequency (≈1 kHz) electric fields. In this paper we describe the development of this phenomenon for collection of particles, covering a range of sizes, out of a liquid and focusing them at the centre of a novel electrode consisting of large interlocking circles. The volume of analyte across which this effect is observed is significantly larger than has been reported for conventional dielectrophoretic arrays. By altering the experimental conditions, particles can either be collected or cycled across the surface and then removed. This technique offers great scope for enhancement of surface-based detection methods.

A ZnO transparent thin-film transistor (TTFT) with a channel layer formed via spin-coating deposition is demonstrated. The TTFT is highly transparent and exhibits n-channel, enhancement-mode behaviour with a channel mobility as large as 0.20 cm² V⁻¹ s⁻¹ and a drain current on-to-off ratio of nearly 10⁷.

An analytical model was developed to determine the length of a surface-breaking defect along the direction of the applied field when using the magnetic flux leakage (MFL) non-destructive technique. The theoretical model fits the experimental MFL results from simulated defects. The extreme positions of the normal magnetic leakage field component were subsequently used for a quantitative evaluation of the defect length. Permeability variations were neglected by employing a flux density close to sample saturation. Four different defect geometries were experimentally investigated and the validity of the analytical model was verified. Good agreement between theoretical and experimental results suggests that this method can be used as an inverse MFL data interpretation technique.

We have investigated the effect of carbon addition on the structure and magnetic properties of melt-spun Sm(Co_0.9Fe_0.1)_6.8Zr_0.2C_x (x = 0, 0.03, 0.06, 0.09 and 0.12) ribbons. The samples mainly have a single TbCu₇ structure. The added carbon helps formation of a microstructure with fine and homogeneous grains. A coercivity, _iH_c, of 11.3 kOe and a maximum energy product, (BH)_max, of 6.8 MG Oe have been obtained for ribbons with x = 0 at a wheel speed of 40 m s⁻¹; a _iH_c of 14.3 kOe and a (BH)_max of 10.9 MG Oe are achieved for ribbons with x = 0.06.

A mechanism for excitation of capillary waves on a weldpool formed by a laser is shown to be due to coupling of the weldpool height with the laser beam profile. This leads to an additional low frequency mode, which has been observed and has a frequency of about an order of magnitude lower than the classically expected capillary waves. This mechanism for wave excitation on the weldpool can only happen if the focal point of the laser beam is located above the surface of the weldpool; otherwise the waves are damped.

Anisotropic in-plane strain in quantum wells leads to an optical polarization anisotropy that can be exploited for device applications. We have determined that for many anisotropic compressive strain cases, the dependence of the optical anisotropy is linear in the strain anisotropy. This result holds for a variety of well and barrier materials and widths and for various overall strain conditions. Further, the polarization anisotropy per strain anisotropy varies as the reciprocal of the energy separation of the relevant hole sub-bands. Hence, a general result for the polarization anisotropy per strain anisotropy is avialable for cases of compressive anisotropic in-plane strain.

UV-moulded microlens arrays with high replication quality were fabricated using a parametric design method. It is important to maximize replication quality because one can obtain replicated micro-optical components with desired properties by accurate control of the shape. In this study, nickel mould inserts for microlens arrays with lenses having diameters between 3 and 230 µm were fabricated by an electroforming process. The reflow method was used to make the master for the metallic mould insert. A UV-moulding system was designed and constructed, and the effects of compression pressure and UV-curing dose on the replication quality of UV-moulded microlens arrays with a diameter of 14 µm were examined experimentally. Finally, geometrical and optical properties of the replicated microlens arrays were measured and analysed.

The intersubband transitions in single, double and triple Si δ-doped GaAs structures are theoretically studied for different applied electric fields. Electronic properties such as the confining potential, the subband energies and the eigen envelope wave functions have been calculated by solving the Schrödinger and Poisson equations self-consistently. We have seen that the intersubband transitions are very sensitive to the type of structure and are dependent on the applied electric field. The electric field and structure dependence of the intersubband optical absorption is interesting for potential device applications in a class of photodetectors and optical modulators.

Laser vaporization of graphite was performed with a 308 nm excimer laser. C₂ radicals have been observed in the absorption region of the Swan band by cavity ring-down spectroscopy with spatial and temporal resolutions. Various characteristics of C₂ radicals in the plume have been studied.

By using the near field in proximity x-ray lithography (PXL), a technique is demonstrated that extends beyond a resolution of 25 nm print feature size for dense lines. 'Demagnification by bias' of clear mask features is positively used in Fresnel diffraction together with multiple exposures of sharp peaks. Exposures are performed without lenses or mirrors between the mask and wafer, and 'demagnification' is achieved in a selectable range, 1 × –9 ×. The pitch is kept small by multiple stepped exposures of sharp, intense image peaks followed by single development. Low pitch nested lines are demonstrated. The optical field is kept compact at the mask. Since the mask–wafer gap scales as the square of the mask feature size, the mask feature sizes and mask–wafer gaps are comparatively large. Because the features are themselves larger, the masks are more easily manufactured. Meanwhile, exposure times for development levels high on sharp peaks are short, and there are further benefits including defect reduction, virtual elimination of sidebands, etc. A critical condition (CC) has been identified that is typically used for the highest resolution. Many devices, including batches of microprocessors, have been demonstrated previously by traditional 1 × PXL, which is the only next generation lithography developed and which is now further extended. For two-dimensional near field patterning, temporal and spatial incoherence at the CC have been used to show not only that peculiarities in the aerial pattern, such as 'ripple' and 'bright spots', can be virtually eliminated but also that there is an optimum demagnification, around 3 ×, in the Fresnel diffraction, where the contrast and, therefore, critical dimension control are highest. In the simulation of a bridge pattern, 'ripple' is likewise controlled. Blur and run-out are compared for various sources. Magnification corrections can be applied by various means. Extension to 15 nm printed features is predicted.

We show how colour tunability (including white) can be achieved by controlling non-radiative intermolecular energy transfer from the donor to the acceptor in binary blends of oligomeric compounds. Blends of different concentrations of a novel functionalized thiophene-based oligomer and a low-molar-mass diamine derivative (N, N'-diphenyl-N, N'-bis(3-methylphenyl)-1, 1'-biphenyl-4.4'diamine) are used to tune both the photoluminescence and the electroluminescence (EL) from red to blue, including balanced white, according to the standards of the Commission Internationale de l'Eclairage. The single-active-layer light-emitting devices, realized by spin-coating, exhibit good EL performance. In particular, the white-emitting device shows an EL efficiency of 5 × 10⁻¹ cd A⁻¹ and a luminance of more than 180 cd m⁻².

In this paper a theoretical model for transient behaviour analysis of the discharge current pulse in the transversely excited atmospheric pressure CO₂ laser with dielectric corona pre-ionization is presented. The laser discharge tube is modelled by a non-linear distributed RLC electric circuit. The transmission line method is applied to the non-linear distributed circuit and it is approximated by a lumped non-linear RLC circuit. By this method the governing partial differential equations are reduced to a system of ordinary differential equations. The governing ordinary differential equations of the lumped non-linear RC electric circuit are solved numerically. On the basis of this model the pre-ionization and main discharge energies are evaluated. Our theoretical results are in good agreement with the published experimental observations.

A new approach is presented for calculation of photoionization rates, in fully three-dimensional grids, that improves the accuracy of the secondary processes calculation without significantly compromising the efficiency of the numerical algorithm. The method is based on generating a coarser secondary grid and interpolating the photoionization values between the two meshes, in order to overcome the enormous effort required for calculation of photoionization in gas discharge problems.

A comprehensive study of the effects of photoionization, photoemission and background ionization in a short point-plane gap in air at atmospheric pressure is then presented, by using the above approach for the secondary processes in two dimensions, in conjunction with the two-dimensional axisymmetric finite-element flux-corrected transport algorithm. The secondary processes are modelled individually within a wide range of parametric values to reflect the uncertainty in the experimental data, and their effect on streamer development and propagation is investigated. The significant reduction in time required for the calculations makes numerical modelling an essential tool for better understanding of the very important yet not well understood physical processes central to the propagation and development of streamers.

Finally, numerical branching is observed under certain conditions in the absence of an adequate supply of electrons in high field regions.

We have measured the mobility of negative ion species drifting in mixtures of SF₆ with N₂, O₂ and air. The pulsed Townsend experiment was used for this purpose. The conditions of the experiment, high pressures and low values of the reduced electric field, E/N, ensured that the majority species drifting in the gap was , to which the present mobilities are ascribed. The extrapolated, zero field mobilities for several mixture compositions were used to test them successfully with Blanc's law. Moreover, the measured zero field mobilities in air could also be explained in terms of the measured mobilities for this ionic species in N₂ and O₂.

The results of the electrical breakdown time-delay as a function of the relaxation time τ, known as 'the memory curve', are presented. The memory curve was experimentally established for the relaxation times from 3 ms to 300 s, for the Ne-filled diode at 7 mbar pressure. Statistical analysis was used to analyse the obtained time-delay values. The results show that for the relaxation times τ ⩽ 0.1 s the dominant part of the total time-delay is the breakdown formative time (t_f ∼ 0.1 ms). The breakdown formative time obtained in this investigation shows the same 'memory effect' as the breakdown total time-delay, because it slowly increases with τ. For τ > 0.1 s, the statistical time-delay makes up the dominant part of the total time-delay, as was reported earlier.

Using a simple discharge circuit, we have investigated effects of the circuit parameters on glow-to-arc transition behaviour. A direct current power source is used with a capacitor and resistors. Plasma is generated between thoriated tungsten electrodes at atmospheric pressure in argon. Current and voltage are recorded while capturing plasma images.

A variation of the charge on the capacitor causes a fluctuation in discharge current. Due to the current fluctuation, the electric power dissipated between the electrodes increases during a temporary glow phase and decreases during a temporary arc phase. The cathode tip has been heated in the glow mode and a glow-to-arc transition occurs finally. The current fluctuation can be reduced by increasing the resistance. The temporary arc and glow durations are affected by the time constant of the circuit.

The external electrode fluorescent lamp (EEFL) is operated in a high frequency mode because the lamp lighting is basically a dielectric barrier discharge. The self-discharge synchronization is defined by synchronizing the self-discharge time of the dielectric wall charge with the voltage rising and falling time. It is shown that for the self-discharge synchronization a high brightness is obtained in the multi-lamps backlight connected in parallel with the EEFLs operated with square waves from a switching inverter. The frequency for self-discharge synchronizing is also shown to increase as the driving voltage increases.

In this study, the reaction kinetics and material properties of polycrystalline CuGaSe₂ thin films are reported. The films were prepared by the rapid thermal processing of thermally evaporated glass/Ga/Se/Cu//Ga/Se stacked precursors. In order to gain insight into the chalcopyrite formation process, stacked elemental layers with different Cu/Ga atomic ratios were annealed in an Ar/Se atmosphere under different thermal conditions. For typical annealing temperatures below 600°C, x-ray fluorescence studies indicated that a homogeneous element distribution could only be obtained for stoichiometric or near-stoichiometric samples. Systematic studies indicated that temperatures above 600°C are required in order to enhance the crystallinity and in-depth compositional uniformity of Ga-rich CuGaSe₂ thin films. These results also highlighted the structural limitation of high gallium containing chalcopyrite thin films.

The backscattering process of 8–28 keV electrons from a thick tungsten target is studied. Measurements on the variation of the backscattering coefficient, η, with angle of incidence α and with diffusion range x_d for different impact energies are presented and discussed. Simple analytical expressions based on continuous energy-loss and diffusion of incident electrons inside the target are used to examine the above variations. Over the entire ranges of impact energy and angle of incidence of the present studies, the predictions of the analytical relations are found to be in good agreement with most of our data and with those of earlier workers within experimental errors of measurement.

We report on the successful fabrication of transparent and uniform aluminium nitride (AlN) III–V semiconductor films using an ion-beam assisted filtered cathodic vacuum arc technique at room temperature. A nitrogen-ion beam with energy varying from 200 to 650 eV has been employed to assist the deposition of AlN films. Effects of the nitrogen-ion-beam energy on optical and structural properties of AlN films have been investigated using an optical spectrophotometer, visible Raman spectroscopy, x-ray diffraction, atomic force microscopy and nanomechanical test instruments. The optical and structural properties of the AlN films depend significantly on the nitrogen-ion-beam energy. The AlN films deposited under ion energies below 300 eV are all amorphous and enhanced polycrystalline AlN films are obtained for energies above 400 eV.

In this paper, the infrared optical properties of diamond films grown on silicon substrates by means of the microwave plasma chemical vapour deposition (MPCVD) method were first studied by infrared spectroscopic ellipsometry in the photo energy range of 0.1–0.4 eV. Using the effects of annealing treatment on the extinction coefficient k and refractive index n of diamond films, the infrared optical quality of the diamond film can be significantly improved by thermal annealing treatment in N₂ atmosphere. After annealing the value of k was about 10⁻¹²–10⁻¹⁵. However, for the non-annealed diamond film, the value of k varied in a large range, about 10⁻³–10⁻¹⁴. After annealing the refractive index n of the diamond film increased and was close to that of a single crystal, Type IIa natural diamond. The graphite on the diamond surface can be removed to some extent after surface oxidizing treatment of the diamond film in a solution of H₂O₂ and H₂SO₄, which causes the obvious decrease of the leakage current of the CVD diamond detector. Based on these diamond films, diamond x-ray detectors with a response time of about 3 ns were fabricated. From the temperature behaviour and the time response of the CVD diamond detector to x-ray irradiation, we find that the various defects or impurities that exist in the film may be responsible for the long fall time.

In this paper, the process of thin film photopolymerization using evanescent waves is used and the adaptability of this process to pattern replication is studied. Variable frequency patterns are copied on film by an imaging process. After photopolymerization, a thin polymer image is obtained, and the shape of the polymer parts is studied. The main limitation to this process is the loss of fidelity between the light profile just after the target and after the imaging set-up. Taking into account optical considerations, the theoretical shape of the polymer parts obtained by this method is calculated and then compared with experimental results. The general shape can be predicted by this approach, but a finer analysis indicates that the response of the formulation has also to be taken into account.

Electromagnetic (EM) flow control of boundary layers refers to the use of 'wall-flush' electrodes (j, current density) and 'sub-surface' magnets (B, magnetic induction) used in combination to create local Lorentz body forces (j × B). In the present application the working fluid is seawater. Close to the boundary wall, these j × B forces can act directly on velocity and vorticity. In this paper, the characterization of a wall-normal EM actuator (i.e. j × B forces are mainly wall-normal above the central axis of the actuator) is considered. An idealized inertial and integral approach leads to the definition of characteristic EM numbers in term of velocity, time, acceleration and length-scales. These numbers are useful in introducing an EM parameter similar to the Froude number. Furthermore, two asymptotic EM flow regimes, which depend on flow velocity and on EM force intensity, are also discussed.

In an effort to progress in our understanding of the ageing mechanisms of high voltage cables submitted to electrical and thermal stresses, we present a quantitative study of voids, the defects which are considered to be partly responsible for cable failure. We propose a method based on large data sets of transmission electron microscopy (TEM) observations of replicated samples allowing for the determination of void concentration distribution as a function of void size in the mesoscopic to microscopic range at any point in the cable insulation. A theory is also developed to calculate the effect of etching on the apparent size of the voids observed. We present the first results of this sort ever obtained on two industrial cables, one of which was aged in an AC field. Results clearly indicate that a much larger concentration of voids occur near the inner semiconductor compared to the bulk of the insulation, independently of ageing. An effect of ageing can also be seen near the inner semiconductor, resulting in an increase in the total void internal surface area and a slight shift of the concentration curve towards larger voids, with the peak moving from about 40 nm to about 50 nm.

The movement and behaviour of particles suspended in aqueous solutions subjected to non-uniform ac electric fields is examined. The ac electric fields induce movement of polarizable particles, a phenomenon known as dielectrophoresis. The high strength electric fields that are often used in separation systems can give rise to fluid motion, which in turn results in a viscous drag on the particle. The electric field generates heat, leading to volume forces in the liquid. Gradients in conductivity and permittivity give rise to electrothermal forces and gradients in mass density to buoyancy. In addition, non-uniform ac electric fields produce forces on the induced charges in the diffuse double layer on the electrodes. This causes a steady fluid motion termed ac electro-osmosis. The effects of Brownian motion are also discussed in this context. The orders of magnitude of the various forces experienced by a particle in a model microelectrode system are estimated. The results are discussed in relation to experiments and the relative influence of each type of force is described.