Table of contents

We consider the approximate calculating methods of the electron transit time for a vacuum microelectronics (VME) triode, on the basis of comparison and analysis of some results given by our predecessors. We summarize all the calculating methods of the electron transit time by four types - the method of mean transit time, the method of average electric field, the method of the equivalent electric field and the method of composite voltage. We discuss the common features of these four methods, unify all the calculating formulae, draw some related curves for convenience to research and calculate new VME devices for use in the future.

Magnetron sputtering of transparent conductive oxides (zinc oxide, indium tin oxide, tin oxide) is a promising technique which allows the deposition of films at low temperatures with good optical and electronic properties. A special advantage is the scalability to large areas. The principles underlying magnetron sputtering are reviewed in this paper. The growth process during magnetron sputtering is characterized by the bombardment of the growing film with species from the sputtering target and from the plasma. In addition to sputtered atoms with energies in the eV range, ions from the plasma (mostly argon) and neutral atoms (also argon) reflected at the target hit the growing film. Depending on the energy of these species and on the ion-to-neutral ratio the properties of the films vary. High energies ( 100 eV), which occur mainly at low sputtering pressures lead to damage of the growing film, connected with mechanical stress, small crystallites and bad electrical parameters. Ion assisted growth with low ion energies (below about 50 eV) is advantageous as is a high ion-to-neutral ratio. A compilation of resistivities of magnetron sputtered zinc oxide films yields a limiting resistivity of 2 × 10^-4 cm for polycrystalline films. Based on the correlation between plasma parameters and film properties new research fields are anticipated.

Development of biomaterials for use as bone substitute requires better control of the process of materials degradation and bone substitution. At present, composite implants of alloy coated with bioceramic are being developed. In this paper, a cylinder made of TiAl₆ V₄alloy coated with hydroxyapatite is used to simulate a hip prosthesis integration. Physico-chemical evaluations are needed to determine such an implant osseointegration process. Use of the particle induced x-ray emission (PIXE) method with histological sections results in quantitative cartography of elements at the bone-implant interface. The sensitivity of the PIXE method in measuring low concentrations of elements gives information to better understand bioresorption of calcium phosphate ceramics and events occurring at this dynamic interface. However, concentration evolution in different elements is still going on and reflects the ceramic resorption. In our case, the alpha parameter method based on experimental determination of the correction of matrix effects is useful as it allows data corrections to be calculated without hypotheses about matrix composition. In the present paper, we propose an expression to calculate directly the correction factor and an application to the characterization of the interface between hydroxyapatite coating film and bone.

Heavily Cu⁺ -doped amorphous PbCl₂has been obtained by quench deposition of the mixture of PbCl₂and CuCl. Upon crystallization, the large majority of Cu⁺ions aggregate to form CuCl precipitates embedded in the crystalline PbCl₂matrix. The present experiment opens up the possibility of producing densely dispersed CuCl clusters in a controlled manner in PbCl₂films.

We present a new method for the determination of the magnetic moment distribution (µ) of ferrofluid particles from the magnetization curve measured on diluted ferrofluid samples in the liquid state. The method employs the solution of the standard integral equation describing the magnetization of a non-interacting particle system in the given external field as a convolution of the Langevin function with the distribution of particle moments. No a prioriassumptions concerning the shape of the corresponding distribution are required. We present the reconstruction results obtained both for the computer simulated magnetization curves and for real experimental data. In the latter case we compare the distributions found using our algorithm with those calculated from the particle size distributions obtained via the electron microscopy images of the ferrofluid particles.

The effects of a partial substitution of Mo, Ga, Si or Al, respectively, for Fe on the structure and magnetic properties of Nd_8.4 Fe_87.1 B_4.5alloy prepared by mechanical alloying have been studied in detail. The addition of 1.1 at% Mo, Si or Ga results in the improvement of the intrinsic coercivity of the nanocomposite magnets. In contrast, the substitution of 1.1 at% Al is unfavourable for improving the magnetic properties. The optimum average grain size d_opof the -Fe is different for various element substitutions. It is found that in addition to the grain size of -Fe, the grain size of Nd₂ Fe₁₄ B is another important factor in determining the magnetic properties of nanocomposite magnets. The main effects of these substitutions on the magnetic properties of the nanocomposite magnets originate from modifications of the grain sizes of the soft magnetic phase and the hard magnetic phase. The best magnetic properties: µ₀H_c= 0.4 T (4 kOe), J_r= 1.07 T (10.7 kGs), (BH )_max= 93.2 kJ m^-3(11.7 MGOe), J_r /J_s= 0.68, are achieved for the Nd_8.4 Fe₈₆ Ga_1.1 B_4.5alloy.

We present a technique for generating short far-infrared (FIR) laser pulses, with a linewidth close to the Fourier transform limit, changing the reflectivity of an InSb crystal by the photoelectric effect. The crystal is irradiated with an optically pumped CW FIR laser and its reflectivity at an FIR frequency is changed by the ionizing radiation of a pulsed Nd-YAG laser. A reflectivity change, from 18 to 90%, has been obtained. Shorter FIR pulses can be obtained using shorter ionizing laser pulses. Finally, double pulses separated by an arbitrary time interval and of chosen amplitude are obtained.

The temporal frequency response of water supplemented with scattering particles was deduced from the measurement of the optical backscattering of a short (100 ps) blue-green (532 nm) optical pulse given by a frequency-doubled Nd:YAG laser. Indeed, this backscattering measurement gave the water impulse response from which the transfer function was computed by taking the power spectrum. This backscattering frequency response had a low-pass filter-like response which enabled us to estimate the medium cut-off frequency. As the backscattered signal shape depends on the value of the water attenuation coefficient, the ocean water cut-off frequency varies with the amount of scattering particles its contains. The aim was to define the variations of the cut-off frequency as a function of the attenuation coefficient.

The use of the new concept of a saving functionas a measure of possible reductions of undesired side effects in heat engine operation is proposed. Two saving functions are introduced, one associated with fuel consumption and another associated with thermal pollution. Two optimization paths including the maximization of power output and these saving functions are presented. The first is based on a linear formalism and the second is based on a power-law formalism. When these optimization criteria are applied to a Curzon-Ahlborn heat engine, both criteria lead to a very similar optimum efficiency, _opt= 1-^3/4 , where is the ratio between the temperatures of the cold and the hot external reservoirs. A numerical comparison with the efficiency of some modern nuclear power plants is reported.

In this paper a method to determine spatially-resolved profiles of the electron temperature T_eand density n_ein an electron-cyclotron-resonance (ECR) discharge is presented. This technique is based on the observation of line emission from a neutral Li atom beam, which is injected into the plasma and excited by electron collisions. A collisional-radiative model valid for the injected Li atoms is used to predict the emission intensities as function of n_eand T_efor several lines theoretically. In contrast to the electron temperature regime representative for the edge of tokamak discharges (T_e >5 eV), the ECR discharge offers a T_erange where selected line intensity ratios strongly depend on the electron temperature. Therefore, a comparison of the measured ratios with the calculated ones yields T_eprofiles for the first time. The n_emeasurement is performed as in tokamaks by observing the attenuation of the beam due to ionization in the plasma. We present radial profiles of T_eand n_efor discharges in argon and xenon under different operating conditions. These results are compared with results obtained by Thomson scattering. Our measurements give evidence for a satisfying agreement between the two methods.

The axisymmetric energy fluxes in an arc cathode are calculated by a commercial finite-element analysis code. The model decouples the sheath from the arc. Exclusively a spot mode exists at small integral loads by heat flux in the steady state for a cathode in 1 MPa xenon and direct currents below 10 A. The diffuse mode occurs at high loads by heat flux or current. In-between multiple solutions are possible. A spot mode is favoured by lower thermal conductivity, higher emissivity, lower support temperature, greater diameter and a smaller length of the cathode. This conforms with experiments. The method provides a design tool for cathodes.

The electron energy distribution function and the electron drift velocity are studied numerically in a decaying plasma in the external electric field in the mixture Ar:F₂= 1:0.005 at atmospheric pressure. For a reduced electric field strength over the range 0.055-0.55 Td the negative electron mobility was predicted earlier by the solution of the Boltzmann equation using the two-term approximation for the velocity distribution function. The applicability of this approximation for calculations of negative mobility is discussed. The Monte Carlo simulation method is used to verify results obtained from Boltzmann equation analysis. It is shown that there is a reasonable agreement between the Boltzmann equation and Monte Carlo results.

Laser-induced fluorescence spectroscopy is used to measure spatially- and time-resolved SiH₂radical densities in pure SiH₄ , H₂ /SiH₄and Ar/SiH₄radio-frequency glow discharges used for amorphous silicon thin film deposition. Absolute density calibration is obtained by a Rayleigh scattering experiment in pure nitrogen. Typical SiH₂densities on the plasma axis are 1-10 × 10¹⁶m^-3 . Measurements of the SiH₂decay in the afterglow of argon/silane discharges are used to determine for the first time the SiH₂loss probability on a-Si:H surfaces and to confirm the reaction rate coefficient of SiH₂with SiH₄ . We find = 0.6±0.15 and k_r= (2.3±0.5) × 10^-17m³s^-1molecule^-1at T= 500 K and p= 9 Pa. The measured SiH₂densities are compared to those calculated by a previously published two-dimensional plasma simulation code.

This is a sequel to a recently published companion paper (Jones J E 1999 J. Phys. D: Appl. Phys.321243) on variational principles for the passive inter-electrode regions of all corona discharges. The earlier work considered extremal principles for the ionic-flow regions and the outer Laplacian domains of these phenomena, but did not apply these methods to the ionization zones that give rise to the charge flow. It is with the search for integral forms whose optimization corresponds to the charge-separation and creation terms in the field equations that the present paper is concerned. The work is fundamental to the theoretical analysis of the practical and engineering uses of corona discharges. It relates to any electrode geometry, e.g. point-plane, wire-to-plane, cylindrical and ducted flows; and also to dc, ac and other time-dependent glows. Although they are usually physically relatively small, the active regions are a significant part of the overall high-voltage manifestation. In particular, if current-creation calculations rather than measurements are being used in an analysis, the modelling of these terms is crucial to the overall success or failure of the theory. The power of the variational calculus would be a considerable asset if it can be shown to work in these analyses. The preceding paper showed that there is only one approach to simultaneous variational methods for the potential and charge distribution of the non-active regions, and that there are additional difficulties associated with the location of free boundaries between domains. The present work shows that current-creation terms can be incorporated into simultaneous variational methods for the glow region, but only if the electric-field dependency of these terms is ignored. A proof that integrands giving field-dependent separation rates do not exist is given, so that other methods must be used for the modelling of these effects. The results are of primal importance to the construction of global finite-element methods in electrical discharge problems.

We investigated emission spectrum of LiH molecules from an electric discharge in a heat-pipe oven. The optimal conditions for the most intense LiH emission regarding the vapour pressures of helium, hydrogen and lithium were found to be 2.5 Torr, 8.5 Torr and 0.9 mTorr, respectively. The important role of helium gas in increasing the LiH emission intensity is described. The number density of the lithium atoms in the first excited state, Li(2p) and the LiH emission, was measured for different hydrogen pressures and currents through the discharge. We found that one part of the LiH molecules formed in the discharge is created in chemical quenching of excited lithium atoms by H₂ . We performed the theoretical simulations for observed LiH A ¹⁺ -X ¹⁺emission band. The rotational temperature and the population distribution of vibrational levels in the LiH A ¹⁺state were determined. We also describe the search for emission from the LiH C ¹⁺electronic state in the spectrum, which at present is unsuccessful.

The design of a digitally controlled impedance probe for the fast absolute measurement of the ionospheric plasma density aboard a sounding rocket is described. Instrument performance is tested in a large plasma chamber. The first results from two flights within the DEOS-campaign are reported, and discussed with respect to spatial resolution and wake effects. The resulting density profiles have the same shape as ground-based ionosonde measurements. The in situimpedance probe measurements yield absolute electron densities that are lower by a factor of 1.5-2.

Processes affecting the emission of the cathode zone plasma of a N₂ /Ti dc discharge were studied experimentally and theoretically. Light maxima occurring at the negative glow head (maximum II) are due to the electron-molecule excitation. Emission characteristics of this region, space distributions of lighting, dependence of the line intensity (I ) on the gas pressure (p ) and current density (j_d ) can be fully explained by the Monte Carlo (M-C) simulation of electron motion in this region. Emission characteristics of the space close to the cathode surface (maximum I) are complex, depending on the emitting species. Molecular lines are found to be emitted mostly due to the fast ion-N₂interactions. The results of the analytical modelling of this process confirm the experimentally observed almost linear dependences of the intensities of these lines on the pressure and current density. Lines of atomic nitrogen are found to be due to the fast ion-N₂interactions as well as to the fast ion-solid excitation, both accompanied by a dissociation. Particular attention was paid to the emission of sputtered material lighting in the space close to the cathode surface. This lighting results from the fast ion-sputtered atom interaction as well as from that of the sputtered atom with `hot' atoms of the cathode surface layer. The experimentally observed dependences of the sputtered atom line intensity on the gas pressure (I ~1/p ) and the discharge current density (I ~j_d× j_d ) are qualitatively explained with a complex model that takes into account the analytical assessment of the energy distribution of bombarding ions, the M-C simulation of the ion-solid interaction and the M-C simulation of the motion of atoms roaming in the plasma phase. The plasma of the space close to the cathode surface (maximum I) of low-pressure discharges (~0.1 Torr) is an effective light source for the optical emission spectroscopy of buffer gas and solid species.

The effect of nitrogen ion implantation on the wear behaviour and the change of structure of single-crystal SiO₂was investigated by SEM, TEM and XPS. The results show that the tribological properties of single-crystal SiO₂under dry friction conditions change with the nitrogen ion implantation. At low implanted doses, the hardness and critical peeling load for single-crystal SiO₂varies inconspicuously and the tribological properties are also not improved. However, the wear resistance is greatly improved at doses of 5 × 10¹⁶and 1 × 10¹⁷N cm^-2 . When the dose reaches 5 × 10¹⁷N cm^-2 , the tribological properties of single-crystal SiO₂decrease again. The possible friction and wear mechanisms for single-crystal SiO₂were discussed.

We report complementary studies of space-charge distributions in electron-beam irradiated fluoroethylene propylene (FEP) (thicknesses of 13 and 26 µm) using the thermal pulse (TP) method and the laser-induced pressure-pulse (LIPP) method. The distributions obtained by the two methods are compared to show the strengths of both methods, the high near-surface resolution of the TP method (better than 100 nm) and the nearly constant resolution versus depth of the LIPP method (1-2 µm). In addition to the expected implanted negative charge at a depth governed by the electron energy, a negative near-surface charge layer was found close to the metal/FEP interface if the electron beam entered the dielectric through that interface. This finding provides new insights into the charging of dielectrics using electron beams.

The sensitivity changes of the 110 °C TL peak in response to temperature, time, irradiation dose and UV exposure were studied. The observations are explained by a modified model with proposed existence of multiple levels of holes (R traps). It is found that the degree of the sensitivity change, and hence the OSL efficiency, relates to many factors. The relevance of the 110 °C TL peak to OSL dating is discussed.

The ac conductivity of La_0.95 Sr_0.05 MnO_3.08has been measured at temperatures between 20-77 K, and for frequencies up to 100 kHz. A comparison of the measured ac conductivity ( ) has been made with some of the models of hopping conductivity proposed earlier in the literature. It is observed that in La_0.95 Sr_0.05 MnO_3.08the measured ac conductivity, over the entire frequency and temperature region, can be explained reasonably well by assuming two contributions ₁ ( ) and ₂ ( ) to the measured ( ). The first, ₁ ( ), which dominates at low temperatures (T <40 K), may be due to the impurity conduction in small polarons of ligand holes (L ); the second, ₂ ( ), which dominates at higher temperatures (T >40 K), depending on the frequency of measurement, may be due to hopping of small polarons and is responsible for the activated dielectric loss peak.

A general theoretical model for the photoinduced discharge of a charged photoreceptor is developed by considering non-dispersive charge transport in a high-resistivity semiconductor (insulator in the dark), point form representations of Ohm's law, Gauss's law and Maxwell's equations for the total current, and the trapping and release rate equations. The rate equations incorporate arbitrary strengths of trapping, release, and trap saturation for a single level of traps. In contrast to most previous works, the trap filling effect is fully incorporated into the model which allows its effects to be studied. These equations were combined to create a single general second-order nonlinear partial differential equation which governs the behaviour of the electric field during photoinduced discharge.

The general differential equation for the field was then solved numerically using boundary conditions that are representative of pulsed illumination. Solutions were obtained under low injection (0.1% of surface charge) and high injection (10%, 50%, and 99% of surface charge) conditions. Trapping parameters in the model could be adjusted to represent a wide range of trapping conditions including trap saturation. In each case, the time evolution of the discharge was monitored by calculating the trapped and untrapped charge densities at regular intervals throughout the discharge. By differentiating the calculated surface voltage V , the rate discharge dV /dtwas also monitored, because it is an experimentally accessible quantity that is widely used in xerographic time-of flight measurements.

Results obtained under low injection conditions demonstrated that the dispersion in the charge packet increased with larger values of the mobility reduction factor and smaller values of the trapping and release rates, and r , respectively. Increased charge packet dispersion was seen to cause increased dispersion in dV /dtnear the transit time. The temporal spread of arrival times analytically predicted by the Schmidlin equation was found to be in good agreement with the present model in the small signal mode.

High injection results illustrated that the dispersion of the charge packet and |dV /dt | increased dramatically with increased injection strength. Under extremely high injection, the dispersion is primarily determined by the amount of injection. The effect of trap saturation under high injection conditions was also investigated. Increased trap saturation caused the packet to become more spread out during the early stages of the discharge. This caused significant decay in |dV /dt | before the shallow-trap controlled transit time, but did not significantly affect the overall dispersion in |dV /dt |.

Molecular structure, morphological characteristics and electrical conduction in syndiotactic polypropylene (sPP) are studied. sPP is found to be highly resistant to thermal oxidation. The crystallinity measured by the x-ray diffraction meter is very low and shows no significant change with annealing, compared with that in isotactic polypropylene (iPP). The development of spherulites occurs at a lower temperature than in iPP and the size of spherulites is much smaller than that in iPP, even though the number of spherulites increases drastically. The influence of the morphological change on electrical conduction in sPP is negligibly small, in contrast to iPP, where the breakdown strength decreases markedly due to spherulite growth upon heat treatment. In electrical conduction in the high field region above 10⁷V m^-1 , the predominant conduction mechanism is interpreted to be the Schottky effect in the low temperature region below 70 °C. But in the high temperature region above 70 °C, the conduction is considered to be ionic conduction, with the jump distance estimated to be 3.3 nm smaller than that in iPP. These results are discussed in terms of the molecular structure differences between sPP and iPP.