Table of contents

The thermal expansion of zircon-type gadolinium vanadate (GdVO₄) was determined by the high-temperature X-ray powder diffraction method. The thermal expansion is anisotropic, having a larger coefficient of expansion along the c axis than that along the a axis ( alpha _c> alpha _a). The mean values of alpha _a and alpha _c, evaluated in the temperature range 300-809K, are found to be 2.16*10^-6 K^-1 and 8.92*10^- K^-1 respectively. The temperature dependence of alpha _c is unusual, for its decreases with increasing temperature.

It is shown that the exchange of Li⁺ ions in LiNbO₃ by protons leads to a large decrease of the (group) velocity of surface acoustic waves propagating in the x-direction on Y- and Z-cut samples. Changes up to about 20% were measured at a frequency of 180 MHz. This effect can be used to construct strip waveguides for surface acoustic waves.

Conductivity, photoconductivity and Hall measurements have been carried out on vacuum evaporated, air exposed SnSe films of different thicknesses in the temperature range 300K-85K to probe into the mechanism of photoconduction in these films. Photoconductivity has been explained by the trapping of majority carriers at the crystallite boundaries.

Experimental results on the evolution of two magnetic parameters (magnetisation energy and the a₁ coefficient of the ( mu ₀H)^-1 term of the law of approach to ferromagnetic saturation) with annealing treatments in the metallic glass Fe₄₀Ni₄₀P₁₄B₆ are presented. The results are interpreted in terms of an activation energy spectrum model.

The optical and electrical efficiencies of thioindigo and six BASF dyes, all doped in PMMA, were determined. Optical efficiencies of about 10.7% for thioindigo and 11.3% for the BASF dye no.339 were obtained. Consequently the efficiency of an attached silicon solar cell was raised by about 1.7%; these values were better than those measured for any other dyes tested.

This article review the theory of local contrast in field-ion images, as it has developed over the last 15-20 years. The issue has been: how do we see atoms? The question has partly been whether contrast formation is dominated by a rate-constant or by a gas-concentration mechanism. But there has also been difficulty in establishing any satisfactory numerical explanation of the long-known resolving power of the field-ion microscope. Views on these issues have fluctuated, as understanding of the complicated physical situation has changed and as better models of various parts of the problem have been built. Recent work, involving new analyses of charged-surface models and JWKB-type rate-constant formulae, has much clarified the solution. It now seems probable that local contrast at normal operating temperatures (near 20K or above) is rate-constant determined, whereas local contrast at temperatures near 5K is dominated by imaging-gas distribution effects. Across-surface variations in the mean electric field in the forbidden ionization zone are very much greater than previously realised: the electron from the field-ionised atom has to tunnel through this zone, and these field variations lead to much greater rate-constant variations than previously estimated. Although much numerical modelling remains to be done, it is now possible to give a coherent, quantitatively justifiable, physical explanation of how the field-ion microscope works: we now know how men first saw atoms.

The transit time effect (TTE) on stroboscopic waveform measurements in the scanning electron microscope is analysed. Here the TTE means the voltage contrast variation due to the time-varying surface electric field near the measurement electrode. The results show that the TTE on waveform rise and fall times or amplitude measurements cannot be disregarded for waveforms with a time variation of the order of 100 ps or less. The TTE on pulse width measurements does not appear to be so large.

Heterodyne photon correlation has been used to study bilayer lipid membranes. It is shown that the intensity of light scattered by thermally excited fluctuations of the membrane can be deduced from the correlation measurements. The measured intensities vary with scattering angle in good accord with theoretical expectation. In this work the reference beam used was not well controlled, unlike normal heterodyne optical detection.

A pimple or dimple on an otherwise uniform oil film on a flat surface decays under the action of surface tension and viscosity. The process is followed analytically from the Navier-Stokes equation, and by optical experiments employing interferometry and the observation of caustics of refraction. Point or line disturbances give a range of recognisable oil hills and ridges, and the theory predicts their shapes and how these scale with time. If the surface is disturbed in a distributed random way, the interferometric contour map shows a random oilscape. The statistics of the oilscape develop self-similarly by changes in lateral and vertical scales which may be predicted and observed. The theory is well verified for the hills, ridges and oilscapes.

The reversal of diffusion of a dispersive wave packet is studied theoretically and the possibilities of application of this effect to increase the range of signals travelling through highly absorbing media, are discussed.

This paper describes an experimental study of the friction generated between compacted maize and smooth ridge counterfaces. The influence of compaction conditions and the normal load is presented for a hemispherical compact in contact with a smooth rigid plane. The data are analysed using the approaches which have been widely adopted to interpret the friction of rough solid bodies. The compact surface is an interesting and structurally simple case of a rough solid surface. These analyses are shown to provide a good prediction of the friction and its load dependence.

The authors have developed an arbitrary-collision sampling technique for Monte Carlo calculations of the diffusion term in the density gradient expanded energy distribution functions. The technique is shown to provide for an alternative and accurate Monte Carlo calculation of the diffusion coefficients. Comparisons of the diffusion distribution function for the cases of electron swarm transport in the ramp model gas and CH₄ show excellent agreement with the results obtained by the Boltzmann method of Pitchford and Phelps (1982). However, there remains a discrepancy for the case of N₂.

This paper describes a computer simulation of the development of an electron avalanche under an induced toroidal electric field. The simulation was based on solving the continuity equations for electrons and positive ions. These equations were solved numerically by a two-dimensional treatment and the space-charge field was directly calculated using the net charges within a quarter of the torus in front of and behind the mesh point whose field was required. The time variation of the calculated instantaneous luminosity agreed well with the photomultiplier output of the corresponding experiment and the distribution of the particle densities in the discharge volume was obtained. Under the condition of a 'growing' avalanche (e.g. E₀=86.8 V cm^-1 and p=0.5 Torr) the space-charge field is negligible in the first half-circuit round the torus. When the avalanche develops near the end of the first full circuit, the radial space-charge field increases to a value giving an electron drift velocity comparable with the diffusion velocity. In the second circuit, a toroidal space-charge field of >25% of the induced field appears, and it promotes the discharge development.

The calculation of collision processes in He shows that for electrons with energies of hundreds of electron volts the momentum transfer cross-section is less than the total cross-section for inelastic collisions. Thus, the electron energy distribution relaxes faster than their angular distribution. Neglecting the secondary electrons created in ionisations and assuming that in every inelastic collision an electron loses the same energy, a simple one-dimensional kinetic equation for the energy distribution function of the electrons is deduced. This equation is solved numerically for He when the cathode is the source of electrons with an initial energy of 250 eV. The calculations give the rate of ionisation at different distances from the cathode. The distribution of the rate of ionisation in a rectangular (double) hollow cathode is found. It is shown to be uniform at gas pressures P<1 Torr but becomes nonuniform at higher pressures. The spatial distribution of the electron concentration in a rectangular cathode at 'low' and 'high' pressures is also obtained.

Oscillations in subnormal glow discharges under DC excitation at different pressures have been studied. A residual current has been observed in these oscillations. A study of this current is presented. A possible method for measuring the characteristic loss time for ions and electrons, under given experimental conditions, is also indicated.

This paper proposes several equations to calculate the effective work-function and the average cooling energy of electrons emitted from an arc cathode root in both the high temperature region and the high electric field region. It is shown that the average cooling energy consists of the effective work-function and the kinetic energy carried by escaping electrons due to their motion normal to the cathode surface. The numerical results of average cooling effect agree well with Lee's results (1960) which were calculated under other assumptions. From numerical solutions of these simple equations, it is evident that the average cooling energy and the effective work-function are strongly dependent on the temperature and the electric field at the position of electron emission, and the normal work-function of the cathode material.

Derivatives of mesoporphyrin IX dimethylester, poly(octadec-1-ene-maleic anhydride) and poly(styrene-maleic anhydride) have been prepared as Langmuir-Blodgett (LB) films. Examining their layer structure using X-ray diffraction analysis has led to several interesting and important conclusions about their packing arrangement.

A two-layer structure (PbO_x/In₂O₃/Pb alloy) in lead alloy thermal oxides has been verified by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses in combination with a reoxidation technique. Following initial formation of oxides to a thickness of about 20 AA at 4*10^-2 Torr oxygen at room temperature, a 7 AA surface region is removed by a sophisticated short-time sputtering technique. Reoxidation is then performed at 5*10^-2 Torr oxygen in a time range below 215 min, resulting in the formation of a single layer of In₂O₃ having the same thickness as the initial In oxide. The two-layer formation mechanism is discussed with reference to the uneven nature of the PbO_x-In₂O₃ and In₂O₃-alloy interfaces.

This paper presents an empirical decay relationship containing five parameters depending on field strength and temperature for describing the isothermal surface potential kinetics of high-density polyethylene (HDPE) over a wide range of field strength and temperature for samples of different thickness subjected to positive or negative corona discharge. Based on a mathematical model describing the hopping mechanism, modulated by surface and bulk traps, of injected charge carriers, a theoretical explanation of the relationship is provided, the model parameters being determined by a fitting procedure. The transport parameters obtained, as charge carrier mobility, hopping distance, trap concentration, trap depth and attempt-to-escape frequency, are discussed.

A precise model deriving electron tunnel current in a metal-tunnel insulator-semiconductor thyristor (MIST) is presented, taking into account the effect of fast interface states. The model is then used to determine the tunnelling transmission probability and the surface potential in the thyristor for various oxide thicknesses. It is found that the tunnelling transmission probability is very sensitive to the oxide thickness and is dependent on the voltage drop across the oxide layer. The surface potential is increased with increasing bias voltage, but becomes saturated at a value corresponding to (E_gs/2q)+ theta _Fn.

For pt.I see J.A.J. Lourens and E.C. Reynhardt, ibid., vol.12, p.1963 (1970). The proton spin-lattice relaxation time and the liquid content of polycrystalline hard wax, average chain length m=50 carbon atoms and chain length disorder Delta m=15.7, were determined as a function of temperature (385>T>118K). In the low-temperature phase (T<308K) the activation energy and pre-exponential factor of threefold reorientations of methyl groups are 7.9+or-0.4 kJ mole^-1 and 1.46*10^-12 s respectively. All methyl groups have the same correlation time. The motional parameters associated with this motion in waxes are independent of chain length or chain length disorder. In the high-temperature region of the low-temperature phase, T₁ is dominated by reorientational-translational (RET) motions. The activation energy is 21.3+or-0.8 kJ mole^-1. A linear relationship exists between ( Delta m/m)^1/2 and the activation energies for RET motions in waxes. The high-temperature phase (T>308K) is dominated by the gradual melting of the crystalline phase of the wax. Linear relationships exist between the percentage liquid in the wax and the specific volume and thermal conductivity of the wax. The thermogram of the wax is discussed in terms of the melting process of the wax and the effect of this process on the average chain length and chain length disorder.

Using a standing wave X-band microwave technique, the dielectric constant ( epsilon ") and dielectric loss ( epsilon ') of dilute solutions of N,N-dimethylformamide (DMF), acetronitrile (AN) and four binary mixtures of DMF and AN have been measured. Measurements were carried out in benzene solution at 9.885 GHz and 15 degrees C. Similar measurements have also been made on a (DMF+AN) mixture containing 50 mol.% AN at 15, 20, 25 and 30 degrees C. Following the single-frequency concentration variational method, the dielectric relaxation times ( tau ) for all these systems have been evaluated. The variation of relaxation time as a function of AN molar fraction in (DMF+AN) mixtures shows a solute-solute type of molecular association between DMF and AN at all compositions. The energy parameters ( Delta F_epsilon , Delta H_epsilon , Delta S_epsilon ) for the dielectric relaxation of the 50:50 mol.% mixture at various temperatures have been found to be in fairly good agreement with the corresponding energy parameters for the viscous flow. The entropy of activation for the relaxation process and for the viscous flow has been found to be negative.

The dielectric responses of mica along the cleavage planes has been measured in the frequency range between 0.01 Hz and 100 kHz and in the temperature range between 368K and 173K. The loss parallel to the planes is two to three orders of magnitude higher that that measured normal to the planes. The response is due to relaxation of ions along the cleavage planes, including interlaminal and surface water molecules.