Table of contents

Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) thin film capacitors were fabricated using a metalorganic decomposition method, and the process of polarization reversal was investigated using a switching current testing technique. The switching time (50–600 ns) and the reversible polarization were measured at different voltages in the range 0–5 V. The effect of gas environment and annealing temperature on the switching time was systematically investigated. It was found that the switching time was not significantly affected by the annealing gas environment at 700°C, which indicates that oxygen vacancies have no influence on the switching time. However, the annealing temperature has a significant effect on the switching time. It increases with an increase in annealing temperature below 750°C, and decreases above 750°C. Several hypotheses have been given to explain this phenomenon and a growth-dominated switching process is proposed in BNT thin films.

The influence of an ac magnetic field and the induced magnetic anisotropy (by field annealing and torsion annealing) on the magnetoimpedance (MI) tensor in an amorphous wire has been analysed. The experimental measurements were carried out in an amorphous wire of composition (Co_0.94Fe_0.06)_72.5Si_12.5B₁₅, with a negative, nearly zero magnetostriction constant, excited either by an ac circular, h_ϕ, or an axial, h_z, magnetic field created by an ac electric current passing along the wire or through an exciting coil mounted on the wire, respectively. The ac current amplitude was changed from 7.5 to 40 mA and the current frequency f was varied from 1.5 to 20 MHz. The induced magnetic anisotropies modify the MI response drastically. The field annealed sample shows a unique peak of the MI effect, while the torsion annealed sample presents an asymmetric giant magnetoimpedance ratio associated with the induced magnetic anisotropy which provokes such thermal treatments.

Giant magnetoimpedance (GMI) effects were studied in multilayered films with a structure of (F/SiO₂)₃/Ag/(SiO₂/F)₃, where F represents the amorphous soft ferromagnetic layer having a composition of Fe_71.5Cu₁Cr_2.5V₄Si₁₂B₉. The samples were deposited by radio-frequency sputtering under an applied magnetic field of 900 Oe in the plane of the film and then annealed at an optimum temperature of 230°C for 1.5 h. Longitudinal and transverse GMI ratios of up to 251% and 277% were obtained at a frequency of 8.5 MHz. Maximum GMI sensitivities of 12.5% Oe⁻¹ and 9.2% Oe⁻¹ were achieved in longitudinal and transverse fields, respectively. For the as-deposited state, the maximum GMI ratios were about 45% and 44% in the longitudinal and transverse cases, respectively. These values are much higher than those obtained for FeCuCrVSiB/Ag (or Cu)/FeCuCrVSiB sandwiched films. These very large GMI responses are attributed to the superior soft magnetic alloy and SiO₂ layers used in the magnetic layers and the magnetic field used in the preparation process.

In this work electron-beam-induced potentials are analysed theoretically and experimentally for semiconductors. A theoretical model is developed to describe the surface potential distribution produced by an electron beam. The distribution of generated carriers is calculated using semiconductor equations. This distribution causes a local change in surface potential, which is derived with the help of quasi-Fermi energies. The potential distribution is simulated using the model developed and measured with a scanning probe microscope (SPM) built inside a scanning electron microscope (SEM), for different samples, for different beam excitations and for different cantilever voltages of SPM. In the end, some fields of application are shown where material properties can be determined using an SEM/SPM hybrid system.

The luminescence of synthetic rare earth (RE)-doped zircons and three natural zircons has been studied by ion beam excitation (ion beam luminescence or ionoluminescence (IL)). Luminescence results from electronic transitions between energy levels of the RE ions, giving emissions with characteristic energies. Studies of co-doped Ho : Dy zircon show that electronic cascades from Ho³⁺ to Dy³⁺ ions result in intense Dy³⁺ luminescence even when Ho is far more abundant. Dy³⁺ ions have the greatest luminescence cross-section of common RE³⁺ ions. Implantation of heavier N⁺ ions into zircon, chosen to mimic accelerated radiation-induced structural modification, causes significant sample degradation. Frenkel-type defects and groups in the zircon are associated with a broad luminescence band of ∼600 nm, and these defects modify energy cascades between RE³⁺ ions, thereby reducing the efficiency of energy deposition via the Dy³⁺ luminescence decay pathway. The broad band of ∼600 nm created by implantation is common in natural zircons and is attributed primarily to intrinsic Frenkel defects caused by natural radiation. Dy³⁺ luminescence is apparent from natural zircons even though Dy is one of the least abundant RE ions in zircon, and this behaviour is explained by the high luminescence cross-section of Dy³⁺ in zircon. Radiation-induced structural damage reduces the efficiency of energy transport between different RE³⁺ ions. IL provides key insights into both the interactions between defects and the nature of luminescence centres in zircon.

Ion bombarding conditions were used to modify glass properties in silica-on-silicon systems during plasma enhanced chemical vapour deposition (PECVD). The induced structural modifications in the SiO₂/Si system resulted in different photosensitive responses when irradiated by ArF pulsed laser operating at 193 nm wavelength. Fourier transform infrared spectroscopy was used to study the structural modifications triggered by ion bombarding conditions during film growth. The results were further confirmed by additional characterizations with regard to density (etch rate), refractive index and surface topographic measurements. The demonstrated method could be used not only to engineer UV-photosensitivity but also to control and compensate birefringence in planar lightwave devices.

A SnO₂ transparent thin-film transistor (TTFT) is demonstrated. The SnO₂ channel layer is deposited by RF magnetron sputtering and then rapid thermal annealed in O₂ at 600°C. The TTFT is highly transparent, and enhancement-mode behaviour is achieved by employing a very thin channel layer (10–20 nm). Maximum field-effect mobilities of 0.8 cm² V⁻¹ s⁻¹ and 2.0 cm² V⁻¹ s⁻¹ are obtained for enhancement- and depletion-mode devices, respectively. The transparent nature and the large drain current on-to-off ratio of 10⁵ associated with the enhancement-mode behaviour of these devices may prove useful for novel gas-sensor applications.

Micro-Raman spectroscopy and capacitance–voltage (C–V) measurements have been used to investigate 2 in GaN epitaxial wafers grown by hydride vapour phase epitaxy on sapphire substrates. The position and line shape of the A₁ longitudinal optical (LO) phonon mode were used to determine the carrier concentration at different locations across the wafer. The line-shape fitting of the Raman A₁ (LO) coupled modes taken from horizontal lateral-different positions on the wafer yielded a rudimentary spatial map of the carrier concentration. These data compare well with a carrier density map of the wafer obtained by C–V measurements, confirming the non-uniform distribution of carrier concentration in the GaN epitaxial film and that Raman spectroscopy of the LO phonon–plasmon mode can be used as a reliable and production friendly wafer quality test for GaN wafer manufacturing processes.

An experimental investigation into the initial phases of laser-induced breakdown in air, with and without an external field, is presented. The plasma is produced by focusing the light of a Nd : YAG laser between two parallel plates connected to a dc bias supply. The diagnostics employed included fast photography and electric field measurements with a D-dot field probe. It is found that the laser power threshold required to initiate breakdown increases when an external field transverse to the laser beam is applied; the effect is not observed when the field is parallel to the beam. Measurements performed with a field probe show that the plasma produces a dipolar electric field that is proportional to the strength of the bias. The dipole is caused by charge redistribution over the plasma surface rather than by charge creation at separate points. The estimated plasma-polarizability coefficient associated with the dipole is a function of the beam energy and focal lengths employed only.

We report optical emission spectroscopy (OES) measurements in cylindrical inductively coupled plasma (ICP) discharges, focusing on E-to-H mode transition in rare gases (Ar, Kr, Xe). The discharge configuration is designed primarily as a radical source for treatment in a high vacuum system, but little is known about its characteristics. Two discharge modes are observed in Ar and Kr on increasing the power injected into the discharge (E-mode at low injected power and H-mode at high injected power). In this paper, we use OES measurements and calculations to infer rare gas discharge characteristics and mode transitions for this geometry in rare gases. It is shown that emission line intensity ratios from the OES signal of a level that is strongly coupled to a metastable state with one whose principal production mechanism is by direct excitation can be used to infer information about the electronic parameters of the discharge.

The formation of titanium nanoparticles from plasmas in mixtures of titanium tetrachloride, argon and hydrogen is examined using three approaches: chemical equilibrium calculations, chemical kinetic calculations and a nucleation-coupled model of particle formation coupled to chemical kinetic equations. The results indicate that production of solid titanium particles requires a non-equilibrium process, such as is obtained using a rapid quench of the plasma. It is calculated that titanium yields approaching 100% are possible for sufficiently large residence times at a high temperature, and sufficiently rapid quench rates. The residence time and quench rate conditions are less stringent for high ratios of argon to titanium tetrachloride in the initial gas mixture. Adding hydrogen to the gas mixture leads to less stringent residence time, but more stringent quench rate conditions.

The 35 W D2 automotive headlight lamp with an electrode gap of around 4 mm is a well known example of a short-arc high-intensity discharge (HID) lamp. It has a filling of xenon, mercury, and sodium/scandium iodide and is driven by a rectangular-wave current of 0.4 A, 400 Hz. Other fields of application of HID lamps are video projection (UHP), street and industrial lighting, floodlighting, etc. Due to their small size and short timescales, HID lamps are often experimentally difficult to investigate or even inaccessible. Thus modelling gets more and more important. The challenges in modelling such lamps are e.g. the important plasma–electrode interaction, the time dependence (electrodes change with 400 Hz from anode to cathode phase and vice versa in the case of D2 lamps), and the complex plasma composition (Xe, Hg, NaI, ScI₃ in the case of D2 lamps). Additionally the electrodes might change their well-defined tip geometry during operation, causing substantial changes in electrode temperature or electrode fall voltages. This paper intends to address all these questions and compare results of numerical simulations with measurements of plasma and electrode temperatures. Special focus is directed towards the important electrode–plasma interaction, which, even after seven decades of HID lamps, has not been understood satisfactorily. The results presented in this paper are very important for a better understanding of dc and ac HID lamps including the treatment of complex plasma compositions, the choice of the work functions, and the effect of different electrode geometries. Furthermore the results of the numerical simulations will lead to improved or new HID lamps.

Application of power higher than the optimum operation value to an external electrode fluorescent lamp (EEFL) leads to the formation of pinholes, which subsequently leads to lamp failure. Small holes, called pinholes, are formed through the external electrode and the glass tube when a high voltage with a high power is applied. The phenomenon of pinhole formation has been investigated, including the conditions under which they occur and the characteristics such as size and location on the electrode. Pinhole formation has been analysed and shown to be the insulation layer breakdown of glass in the dielectric barrier discharge of capacitively coupled EEFLs.

A one-dimensional reaction–diffusion model was used to study periodic filament formation in a laterally coupled gas discharge. Our results demonstrate three types of pattern formation (localized solitary filaments, small oscillation and intermediate), which deform into one another subject to a control parameter θ(φ_a/pd) and a boundary condition (where pd is the pressure–distance and φ_a is the applied voltage). The work shows the same qualitative dependence as the experimental work of Guikema et al (2000 Phys. Rev. Lett.85 3817).

Micro-arcing and breakdown of the wall plasma sheath in radio frequency (RF) plasmas is studied in a hollow cathode system, using a Langmuir probe to measure the floating potential. Micro-arcing was induced reproducibly by controlling the floating potential. By dc grounding the hollow cathode, a negative current can flow to ground resulting in a higher voltage sheath between the plasma and the earthed vacuum vessel. The wall arcing threshold of the plasma potential in this system is in the vicinity of 50 V. In the present system, the charging process to rebuild the plasma potential, which is about a few tens of milliseconds, is much slower than the microsecond discharge. The arcing frequency was found to depend strongly on the plasma potential and the pressure. We propose a mechanism for the dependence of the frequency of periodic micro-arcing based on the development of electron field emission sites. The measurement of floating potential is suggested as a useful parameter to monitor and prevent micro-arcing in RF plasmas.

A self-consistent model of a non-equilibrium spherical microwave discharge is presented. We use a two-temperature plasma model. Numerical experiments are carried out for the discharge in argon at atmospheric pressure. Results are presented for the characteristics of the discharge plasma against the external parameters (the power and frequency of the applied electromagnetic field and the size of the discharge chamber).

As length scales decrease, adhesive forces become increasingly important. These adhesive forces contribute to the normal load in experiments conducted on thin layered systems using micro-probe instruments such as the surface force apparatus (SFA) and the atomic force microscope (AFM). Adhesion between these thin-layer systems was analysed by Sridhar et al (1997 J. Phys. D: Appl. Phys.30 1710) for the SFA geometry and Johnson and Sridhar (2001 J. Phys. D: Appl. Phys.34 683) for AFM using a numerical SJF (Sridhar–Johnson–Fleck) version of the JKR (Johnson–Kendal–Roberts) theory. In this paper, adhesion mechanics between a compliant elastic coating and a spherical probe is investigated using the SJF model in detail. When the substrate is rigid, the non-dimensional pull-off force may differ from the JKR value of −0.5 by as much as 90%. Computations of the contact size at zero load and pull-off force are presented for a range of values of adhesion energy. Finally, empirical relations for the contact load and contact compliance as a function of contact radius were obtained from the numerical data for practical layer-substrate material systems.

We investigated the structural and electrical properties of HfO₂ films fabricated by the pulsed laser deposition technique. HfO₂ films were deposited directly on n-Si (100) substrates and Pt coated silicon substrates, respectively, at 300°C in a 20 Pa N₂ ambient, and in situ post-annealed in a 20 Pa N₂ ambient. X-ray diffraction indicates that films post-annealed at temperatures more than 500°C exhibit a polycrystalline monoclinic structure. High-resolution transmission electron microscopy images clearly show that an interfacial layer (IL) between an amorphous HfO₂ layer and the Si substrate exists. An x-ray photoelectron spectroscopy measurement was performed to identify this IL as nonstoichiometric Hf-silicate. The dielectric constant of amorphous HfO₂ was determined to be about 26 by measuring the Pt/HfO₂/Pt capacitor structures. Capacitance–voltage measurements show that a small equivalent oxide thickness of 1.26 nm for the 5 nm HfO₂ film on the n-Si substrate, with a leakage current of 2.2 mA cm⁻² at 1 V gate voltage was obtained.

The Hugoniots of the polymers polyethylene, polypropylene and polystyrene have been measured in terms of stress, shock velocity and particle velocity. All three materials have been shown to have a linear shock velocity–particle velocity relationship. This has been used to determine the hydrodynamic response, and compared with the measured shock stress. The results show that agreement between the two in all three materials is good, but at higher stresses, the hydrodynamic pressure is significantly lower. It has been suggested that this is due to an increasing shear strength with increasing impact stress. We have also observed that the difference between these two parameters increases with an increase in the size of the side group from the main polymer chain. We believe that this is due to an increasing resistance to compression caused by these side groups.

The charge transport properties of chemically synthesized, DNA-doped polypyrrole (PPY) are described here. The polymer showed a significant change in microstructural morphology and optical absorption spectra with increase in DNA concentrations (0.36–14% w/v). Both the dark and photo-induced I–V characteristics of the polymers showed an increase in the degree of linearity with increase in DNA concentration. The temperature-dependent dc electrical conductivity (σ) exhibited a significant dependence on the nature of carrier hopping dominant in this DNA-doped PPY: σ showed a change from T^−1/4 to T^−1/2 dependence on temperature as the degree of doping increased from 0.36% to 3%, respectively. Further increase in DNA doping to 14% led to a T⁻¹ dependence of the dc electrical conductivity. The results were interpreted in terms of the localized polaronic and bipolaronic states caused by the disorder in polymeric chains, variation in chain length, interchain interactions, etc.

Domain structures investigation in (110)-oriented Pb(Mg_1/3Nb_2/3)O₃–33% PbTiO₃ (PMN–33% PT) single crystals has been performed by piezoresponse force microscopy. Submicron-sized fingerprint pattern and tweed pattern domains (TPDs) have been observed in large parallel domains with typical sizes of 20–30 µm. Based on the existence of gradual transition regions between fingerprint pattern domains and TPDs in the same large ferroelectric domain, the relationship between the two pattern domains is discussed and a possible formation mechanism of the domain structure in PMN–33% PT single crystal is proposed.

Scattering of coherent light by a droplet of water fullerene suspension was investigated. Two light wavelengths were used simultaneously. The evolution of the radius and refractive index of a droplet was examined. Resonant scattering was detected and analysed by means of a simple model and some conclusions were drawn on the microscopic properties of the suspension. The study was supplemented with atomic force microscopy measurements of samples obtained by drying the suspension.

The results of interaction of single and multiple 200 fs laser pulses with thick stainless steel and HgCdTe samples are reported. The threshold laser energy density required to produce surface melting is measured. The melt dynamics and evolution of surface morphology are observed for different pulse energies and number of laser pulses. It is observed that, as with a long laser pulse interaction, a layer of melt can be produced at the sample surface. Melt ejection in the radial direction towards the periphery of the interaction zone is observed when the pulse energy is increased. The observed melt dynamics resembles the evaporation recoil melt removal typical of the laser interactions in the range from nanoseconds to continuous wave (CW). The observed melt ejection is attributed to a nanosecond component of the laser pulse with an estimated energy of approximately 25% of the total laser pulse energy. The measured melting threshold energy density for stainless steel is comparable with the published theoretically predicted threshold for nickel computed using a two-temperature model.

Scanning electron microscopic techniques were employed to study the surface morphological changes of oxide cathodes and nickel caps as a result of cathode activation extending over periods of 1–12 h. Elemental analysis of barium, strontium, tungsten, magnesium and aluminium was performed using energy dispersion x-ray spectroscopy. An abrupt change was observed after activation longer than 3 h. Conduction through well activated cathode assemblies was found to be due to intergranular electron tunnelling at low temperatures (T ⩽ 500 K), while trapping and detrapping at grain boundaries becomes the dominant mechanism at high temperatures (T ⩾ 500 K). The contribution of the interfacial layer to conductivity was found to be significant for cathodes activated for smaller periods.

Thermal processes are important in areas ranging from biological to advanced materials processing. Here, we present a method for measuring temperature profiles in three dimensions using a combination of two-photon microscopy and calibrated temperature-dependent fluorescent dyes, or 'molecular thermometers'. We have found that the dye, tris(2,2'-bipyridine)ruthenium(II) ( ) possesses both a strong temperature dependence in the range 0–60°C and a large cross section for two-photon induced fluorescence, making it ideal for two-photon thermal imaging. The technique is used to map out the temperature profile in a thick polyacrylate film containing an embedded wire heater, and, from that, the thermal properties of the polymer are determined.