Table of contents

A review of the evolution of electronic information processing from small-scale integration to ultra-large-scale integration and beyond is presented recalling the milestones achieved in the development of electronic hardware. Physical principles which limit the size and performances of electronic circuits and the rate of information processing are discussed. In order to explore the new courses offered by organic molecular materials towards atomic-scale integration, the elementary computational capabilities of molecules are discussed by casting the quantum dynamic equations in the framework of system theory. Bond dynamics in polymeric networks is considered, thus showing the possibility of obtaining molecular probabilistic circuits.

Electrically conducting films have been prepared by casting aqueous dispersions of mixed polymer lattices on supporting glass microscope slides; one of the lattices is conducting (polypyrrole or polyaniline) and the other film-forming (a 1:1 co-polymer of polymethylmethacrylate and polybutylacrylate). The polypyrrole particles, being roughly spherical in shape, give a percolation threshold where the conductivity rises sharply at a weight fraction of about 20%, whereas the polyaniline particles, being needle-shaped, have a much lower percolation threshold at about 5%. In addition, the preparation of composite beads, having a non-conducting polymer core (e.g. polymethylmethacrylate) and a conducting shell (polypyrrole), has been carried out.

The title compound was prepared by reducing octadecanoyl-TTF with lithium aluminium hydride and subsequent complexation with TCNQ. Langmuir-Blodgett films of the complex could be built-up on glass or calcium fluoride substrates. These multilayer films have been characterised by UV-visible and infrared spectral measurements. Conductivity values at room temperature of around 10^-3 S cm^-1 were obtained, with an activation energy of 0.27 eV over the temperature range 80-320 K.

The morphology, density and electrochemical characteristics of electrodeposited polyvinylferrocene have been studied as part of work directed towards the development of electrochemical microdevices. A constant current deposition method has been found to produce better quality films than those obtainable using the standard constant potential method. Marked differences in film density and morphology were observed, dependent on the type of electrolyte used in electrodeposition. Tetrabutylammonium hydrogen sulphate (TBAHS) provided the best quality films, which also exhibited unusual electrochemical properties.

A study has been made of the electrochromic behaviour of polyaniline films of potential use in passive display devices, and a preliminary examination of the properties of substituted polyanilines has also been carried out. Films of 'emeraldine-type' conducting polyanilines have been grown electrochemically from aqueous solutions onto glass substrates coated with gold or indium tin oxide. The authors have studied the electrochemistry of their redox reactions in acidic media to examine the kinetics and reversibility. Cyclic voltammetry was used to determine the electrode potentials for growth and redox switching and to obtain information on the electrode kinetics. The effect of electrode potential on the optical absorption spectra was observed, and was found to be consistent with polaron and bipolaron formation. The electrochromic colour contrast and switching times were measured as a function of pH; the requirements were somewhat conflicting, but a satisfactory compromise could be obtained around pH=0. By switching the electrodes over a constant potential step but from a variety of starting potentials, the influence on switching times of the initial oxidation state, and hence of the film conductivity, was investigated. Under suitable circumstances electronic conductivity, ionic transport or interfacial charge-transfer can limit the switching speed, but response times (for 50% transmission change) as short as 15 ms have been obtained without full optimisation. Of the numerous substituted polyanilines tried, only simple alkyl and alkoxy derivatives formed good polymeric films, and only the 2-ethoxy and 2-methoxy polymers gave good electrochromic behaviour. Switching times for these two were very fast, being less than 2.5 ms for both oxidising and reducing potential changes.

The surface pressure versus area isotherm of a Langmuir film of ytterbium bisphthalocyanine on water subphases of pH 2.1 to 9.2 has been investigated and an average area per molecule of 70 AA² measured. The monolayer was found to collapse at a rate of 29%/hour. A dipping regime has been established for the deposition of Langmuir-Blodgett films with transfer ratios of unity. These deposited films were found to be electrochromic and their spectra are discussed.

A number of novel, functionalised, diarylalkynes have been prepared which are capable of forming non-centrosymmetric Langmuir-Blodgett films by Z-type deposition. The nonlinear optical behaviour of these layers has been investigated using both second-harmonic generation and surface plasmon resonance techniques.

Using the finite difference method, rotationally symmetrical field strengths are calculated in a coaxial microwave resonator, such as used for the production of optical fibres. A linear relation between electron density and microwave power consumption at each position inside the plasma is assumed. In this way the electron density distribution can be calculated in a self-consistent manner. The energy parameter involved (MW power per electron-ion pair sustained in the plasma) is adjusted so that experimentally obtained emission spectra with local resolution in axial and radial directions are reproduced within reasonable limits. The increase in gas temperature in the discharge has been taken into account. This simple model reproduces the most important relationships found experimentally, the MW-power dependence, the pressure dependence and the axial and radial variation of the emitted light intensity. It can easily be extended to other geometries and plasma gases. Fully three-dimensional calculations are also possible provided enough computer capacity is available.

The authors present a numerical calculation of the edge capacitance corrections for thin unguarded disc electrodes placed on opposite faces of a dielectric sheet or film. As a function of the ratio (a/h) of electrode radius to sample thickness, the correction grows logarithmically for small values of the sample dielectric constant epsilon ₂, but for epsilon ₂>or=20 the correction is almost independent of (a/h). In all cases, the correction decreases in relative importance as (a/h) increases. These calculations yield upper limits for experimental measurements, and provide a theoretical base for modifying the empirical expressions which are currently found in various national and international standards.

Measurements have been made of the erosion rate of helical cathodes in copper ion laser gas discharges, as a function of the current density j on the cathode surface. The rate was found to be proportional to j⁵2/. On the basis of the authors' measurements a cathode lifetime of 1000 h is estimated for a current density of 0.2 A cm^-2.

Density variations in the air associated with, e.g. turbulence or quasi-stationary temperature gradients can seriously hamper high-precision optical alignment or levelling. The refraction effects due to quasi-stationary temperature gradients seem to be particularly harmful as, unlike turbulence, their influence cannot be reduced by measuring longer periods of time. In this contribution the authors describe a successful attempt to measure and correct for the atmospheric refraction effects using a so-called 'two-colour method'. It is found that not only can the quasi-static effects be compensated for, but also the effect of low-frequency turbulence is significantly reduced, even under strongly turbulent conditions (C_n²=10^-13 m^-23/) and for path lengths of at least one hundred, but probably several hundred, metres.

The general wear performance and boundary lubrication properties of a silicone-oil-based electro-rheological (ER) fluid are presented. The tribological characteristics are derived from the results of an extensive series of tests on a two-disc machine. By comparison with a commercial lubricating oil working under the same conditions it is concluded that the ER fluid tested is likely to cause severe wear problems in some engineering situations. This is so even though the active particulate matter of the fluid mixture appears to act as a solid lubricant which enhances the performance of the base liquid phase.

The drying of a limestone block was studied by analysing one-dimensional projections (profiles) and three-dimensional (3D) NMR images as well as free induction decay (FID), as a function of the amount of water remaining in the sample at various stages of the drying process. From these results, the water repartition in the sample stays continuous and fairly uniform down to a water content W of the order of 2% in weight of water per weight of rock. However, at the end of the drying, for W<2%, water is no longer uniformly distributed. The remaining water is concentrated in the centre of the block where the NMR signal is intense, whereas in the surrounding region the NMR signal is drastically weaker. This is the first report on drying of a porous stone monitored by NMR imaging through to its late stage. These first results show spatial compartmentation and modification of the physicochemical state of the protons during the drying, which would be difficult to observe with other techniques. The authors suggest a two-compartment model which is consistent with images and profiles.

The time-averaged Poisson equation has been solved in the space charge sheaths of a parallel-plate RF plasma reactor. The frequency of the applied electric field is assumed to be greater than the ion plasma frequency. The time-averaged electron density profile and the stationary ion density profile have been calculated in the space charge sheaths of the RF plasma. The time-averaged sheath thickness and the time-averaged voltage drop across the sheath have been calculated as functions of the relevant discharge parameters. The calculated averaged electron density is compared with experimental data. The model is developed in order to describe the sheath properties for both a collisional and a collisionless sheath.

A kinetic simulation of various neutral species created by the corona effect in dry or humid oxygen is presented. The physical conditions of the pulsed electrical discharge used are: atmospheric pressure, a gas discharge channel temperature in the 200 to 800 K range and an electron density N_e=5*10¹⁵ cm^-3 or 10¹⁶ cm^-3 with the electron energy assumed to be larger than 5 eV. The presence of water vapour leads to a non-negligible H₂O₂ production. Temperature and humidity have a cumulative effect on the O₃ production. With multiple pulses, the maximal O₃ concentration is obtained for a finite number of pulses.

Optimisation of volume-produced H^- ions is studied by using a set of particle balance equations in a steady-state hydrogen plasma with a single-chamber system. The dependence of production of both H^- ions and vibrationally excited hydrogen molecules H₂* (vibrational level V") on plasma parameters (i.e. electron temperature T_e, electron density n_e, hydrogen gas pressure p, density ratio n_fe/n_e of fast primary electrons e_f to slow plasma electrons e, energy of fast electron E_fe, etc.) is explored because it is expected that H^- ions are produced by the following two-step process, i.e. H₂+e_f to H₂*(V")+E_f; H₂*(V")+e to H^-+H. Particular attention is also paid to wall effects, i.e. neutral particles-wall interaction, on H^- production. So, a wall recombination coefficient gamma ₁ for H and a wall de-excitation collision parameter gamma ₂ for H₂*(V") are treated as numerical parameters. It is confirmed that most H^- ions are produced by the above-mentioned two-step process, and that the presence of e_f with energies in excess of 40 eV is reasonable for H₂*(V") production. With increasing T_e (above 1 eV), H^- yield decreases monotonically. Besides, n_e, n_fe/n_e and p have some optimum values for H^- production. However, the optimum condition for H^- formation is not compatible with that for H₂*(V") production. Another significant point is that the ion species ratios depend strongly on the wall parameters, i.e. gamma ₁ and gamma ₂. For H^- production, the optimum condition is that gamma ₁ approximately=1 and gamma ₂<<1.

The electron energy distribution function in H₂ and the vibrational distribution function of H₂(X, v) molecules have been self-consistently calculated for the typical operating conditions of a low-pressure, moderate current, hydrogen positive column by solving the Boltzmann equation together with a system of rate balance equations for the vibrational levels. This system takes into account e-V, V-V and V-T processes, the latter including both intermolecular and molecule-atom processes. The formulation provides a relationship between the characteristic vibrational temperature, T_v, the degree of ionisation, delta _e, the fractional concentration of dissociated atoms, delta _a, and the ratio of the electric field to the gas density, E/N. At low E/N the superelastic e-V collisions strongly enhance the high-energy tail of the electron energy distribution which results in a significant increase in the electron excitation rates, especially in the rate of dissociation by electron impact. The authors present calculations of electron transport parameters and excitation rates, of the power transfer by the electrons via the various collisional mechanisms, of the total power transferred to the translational and rotational modes by electron collisions and V-T and non-resonant V-V processes, and of the total dissociation rate.

A free-burning, high-intensity argon arc at atmospheric pressure was modelled during the evaporation of copper from the cathode. The effect of cathode evaporation on the temperature, mass flow, current flow and Cu concentration was studied for the entire plasma region. The copper evaporates from the tip of the cathode with an evaporation rate of 1 mg s^-1. The copper vapour in the cathode region has a velocity of 210 m s^-1 with a mass concentration of above 90% within 0.5 mm from the arc axis. The vapour passes from the cathode toward the anode with a slight diffusion in the argon plasma. Higher temperatures and current densities were calculated in the core of the arc caused by the cathode evaporation.

An experimental investigation of ablation-stabilised arcs in ice has been carried out with measurements of arc diameter, voltage and pressure for 50 Hz currents ranging from 1 to 13 kA. A key advantage in the use of ice for the confining enclosure was the absence of solid materials within the outer regions, thus permitting photographic estimates of the arc diameter. The results are in agreement with a two-zone isothermal arc model.

The ablation properties of a selection of insulating materials including PTFE, boric acid, nylon and polymethylmethacrylate have been studied experimentally and theoretically for arc lengths up to 150 mm, arc diameters in the range 6 to 20 mm and currents up to 16 MA. The results are in good agreement with previously available for PTFE, but show a trend with increasing current density that does not support a linear model for theoretical predictions.

An exact solution for dislocations interacting with a surface crack in a thin plate material is derived. This solution is compared with the approximate solution proposed by Lung (1987). However, his result is only valid for a material with a sufficiently large thickness. It is found that the thinner materials have high toughness. Finally, the ratio of volume to area related to fracture is discussed.

A calorimetric study of the effect of thermal cycling on the martensitic transformation of Cu-Zn-Al shape-memory alloys is presented. The transformation kinetics become smoother when the number of cycles increases, and start progressively at higher temperatures and finish at lower ones. The use of a high-sensitivity calorimeter has, for the first time, enabled the study of the evolution of the elastic and frictional energies involved in the thermoelastic balance. It is shown that dislocations created in thermal cycling do not result in an indefinite increase of such contributions.

A stainless steel container, filled with 1 g of water and sealed with a copper plug, was repeatedly heated and cooled over an appropriate temperature range (temperature cycles). Negative pressures, although scattered, increased with temperature cycle repetition through two stages. The cavitation history effect persisted for continued temperature cycles after renewal of only the water. The authors found two efficient means of raising the negative pressure by the cavitation history effect: (i) a high repetition rate of the conditioning cycles and (ii) using a sealing metal melted and cast under vacuum. Aided by these means, negative pressure was raised to -87 bar at 49 degrees C after 392 cycles repeated over a period of one week, while the maximum value of -76 bar at 46 degrees C was attained after a total of 850 cycles continued for over a month. The results can be interpreted by the gas-trapping crevice model supplemented with a working assumption that crevices on the metal surface are supplied with gas from sources in the metal bulk. A more recent maximum value of -125 bar at 47 degrees C, the highest value ever reported for water in a metal tube, supports the assumption.

A new set of expressions is derived to evaluate thermal activation energy E to TSC peaks with non-constant recombination lifetime. The validity of these expressions is discussed by calculating thermal activation energy E of a number of numerically computed TSC peaks using the present set of expressions and comparing them with those calculated using the formula of Chen. It has also been shown that the value of the parameter mu _g characterising the geometrical shape of these TSC peaks is a function of U_m=E/kT_m demonstrating that mu _g is not a unique parameter.

The optoelectronic properties of polyester polymer-CdS composite were investigated, as a function of component weight ratio, electric field strength and light intensity. Cl and Cu activated CdS powder as well as unactivated CdS powder were added to polyester polymer. It has been shown that the composite containing 60-70 wt.% of CdS has the best photoelectric properties. The ratio of photocurrent to dark current was greater than 10⁸ for white illumination of approximately 225 mW cm^-2. The electrophotographical layers of this composite exhibited a photosensitivity as high as 1.25 lx^-1 s^-1. The results have been explained in terms of the reduction in interparticle barrier height assisted by the localised trapping of photoexcited or field excited holes.

The DC electrical resistances of certain chloroprene rubbers with carbon black filling exhibit positive temperature coefficients (PTC effect) for certain concentrations of the conductive filler. The electrical noise exhibited by these rubbers has been studied. The thermal noise is shown to obey Nyquist's theorem to a good approximation. The current noise shows a 1/f frequency dependence, and the noise power is proportional to the square of the applied bias voltage. This applies to samples exhibiting a wide range of resistivities, from over 10⁷ Omega cm (20% carbon black) to under 100 Omega cm (35% carbon black by weight).

The coercivity of epitaxial magnetic garnet films measured by the domain-wall-oscillation methods depends on the size of the sample. It is shown that this effect is characteristic of only the wall-oscillation method. A direct, empirical correlation was found between the mechanical stresses of the sample and its magnetic parameters. It was concluded that any effect of a modification of mechanical stresses resulting from cutting of the sample can be disregarded as a possible contribution to the effect of sample size on coercivity.

Polarisation currents were investigated in polycrystalline BaTiO₃ in order to investigate its I-V characteristics. All but one of the measurements were performed at temperatures below the Curie point, for voltages between 1 V and 1000 V. The experimental curves consist of three parts of different shape: a region in which Ohm's law is valid, a region in agreement with the Fridkin-Kreher theory and a region showing a rapid increase in current for the highest applied fields. Comparison of the SCLC theory for ferroelectrics with the results obtained allows an estimate to be made of the temperature dependence of the carrier mobility in the sample. It increases from 10^-8 cm V^-1 s^-1 at 25 degrees C to 10^-5 cm V^-1 s^-1 at 140 degrees C.

Kinetics parameters of BeO thermoluminescent material are presented. Thermoluminescence emission from irradiated BeO shows two well separated peaks. Using a linear heating rate of 8.07 K s^-1, the peak temperatures at maximum are 495 and 642 K respectively. Various methods have been used for trap parameter determination, including the initial rise and Ilich (1979) methods, the peak shape and glow curve area measurements and the fitting method. A kinetics order of about two has been determined for the first peak, whereas the second peak follows first-order kinetics. The energy activation values as found using different kinds of measurements are in good agreement.

A new type of radiation dosimeter for large radiation doses is described, which is based on silica fibre material. Conventional radioluminescence or thermoluminescence of silica produces emission in the blue region of the spectrum. However, in this new material irradiation, in conjunction with a heat treatment, generates a green emission band. The intensity of the green band can be monitored by either radioluminescence or thermoluminescence using a test dose. The signals are directly related to the total irradiation history of the material. The dosimeter is therefore rereadable. The production mechanism of the green emission centre requires a thermal processing stage, with an activation energy of 0.52 eV. Further, the dosimeter is effective at recording radiation during high-temperature exposure, to at least 400 degrees C, with the subsequent dosimetry being performed below 200 degrees C.

Surface-processed TiC(110) tips have been developed to obtain highly stable emission as a cold field-electron emission source. The surface processing consists of heating the tip at 1000-1100 degrees C in a gas such as ethylene, oxygen or hydrogen sulphide, and the subsequent continuous emission of 10 mu A for 30 minutes. The field-emission pattern and the current stability of surface-processed TiC(110) tips have been investigated for several kinds of surface processing.

ZnO films were grown using an RF sputtering technique and a hot-pressed oxide target. Glass and single-crystal silicon substrates were used. The substrate temperature T_s was varied from room temperature (300 K) to 625 K. The sputtering ambient was argon and 80% argon+20% oxygen gas mixture. At room temperature the films grown in pure argon showed good c axis orientation for both glass and Si substrates, i.e. reflections from the (002) plane. The strong reflections of the (100) and (101) planes show up with the introduction of the oxygen at room temperature, and they remain dominant even when the substrate temperature is increased to 373 K. However, with a further increase in substrate temperature to 625 K the films become highly oriented to the c axis. The change in grain size and lattice constants with sputtering parameters (especially substrate temperature) can be explained by assuming incorporation of oxygen neutrals at low substrate temperatures and their out-diffusion at high substrate temperatures. The effect of sputtering parameters on the electrical conductivity and optical band gap are also reported.

This paper outlines an investigation into monitoring the moisture condition of cement-based materials using impedance spectroscopy techniques. Impedance measurements are made over the frequency range 20 Hz-110 MHz, and several parameters identified which could characterise the moisture condition of such materials.

The mathematical relation between volume fraction RuO₂ and the resistance of RuO₂-glazed thick-film resistors has been deduced in terms of the diameters of the RuO₂ particles and glass frits and some physical properties of the glass. The equation obtained can qualitatively describe the relation between RuO₂ volume fraction and the resistance values. Therefore, valuable information can be obtained for the design of thick-film resistors.

Measurements of the DC breakdown voltage U_s of 1,1,1,2-C₂H₂F₄ (Arcton 134a) in a uniform-field gap are reported. Over the range 1<or=pd/(bar mm)<or=10, where P is the gas pressure and d the gap length, the results indicate that U_s is a function of pd only for 0.1<or=p/bar<or=0.7, to within the scatter in the breakdown measurements; i.e., Paschen's law is obeyed in this pressure range. A regression analysis of the experimental data is used to obtain an empirical expression relating U_s and pd.

Effects of the physical constants of a viscoelastic liquid on leaky surface acoustic waves (LSAWS) propagating on liquid/piezoelectric film/glass structures are studied theoretically. It is found that the radiation loss is very much affected by the change in the physical constants of the liquid, and that it increases with increasing density, bulk modulus of elasticity and viscosity coefficient of the liquid. On the contrary, it slightly decreases with increasing permittivity. All the physical constants of glycerin act to increase the radiation loss compared with the case of water and hence the maximum loss for glycerin/ZnO/Pyrex glass structures is 66% larger than that for water loading.

The target voltage hysteresis with nitrogen flow of NbN films reactively sputtered in a DC planar magnetron system has been studied. The hysteresis characteristic was found to provide a reliable indication of the best operating point for deposition of NbN films with high superconducting critical temperatures. Films deposited at the top elbow in the hysteresis curve were of the cubic B1 crystal structure and had critical temperatures up to 15.6 K.