Showing papers in "Journal of Physics D in 1979"
TL;DR: In this paper, a study of the spreading of silicone oil drops is presented, with particular attention to the dominant effect of the conditions near the edge and the surface tension forces acting there.
Abstract: A study of the spreading of silicone oil drops is presented, with particular attention to the dominant effect of the conditions near the edge and the surface tension forces acting there. It is shown that the drop profiles can be predicted and that this leads to a relation between the edge velocity and the maximum slope, which occurs at an inflection point close to the edge. This relation leads to others governing the variation of drop size and slope with time. The predictions are compared with experiment, using silicone oils, and good agreement obtained. The lubrication approximation theory gives no solution for thicknesses below a value varying from 2 to 9*10-8 m at the drop edge. At thicknesses of this order, or possibly even larger, other effects become important, and some observations on edge behaviour are included.
1,229 citations
TL;DR: In this article, a transient hot-strip method has been developed for use with solids and fluids with low electrical conductivity, where the hot strip is used both as a constant plane heat source and a sensor of the temperature increase.
Abstract: A transient hot-strip method has been developed for use with solids and fluids with low electrical conductivity. The hot strip (thin metal foil) is used both as a constant plane heat source and a sensor of the temperature increase. The accuracy of the method is so good that it might even be used for the measurement of the specific heat especially under difficult experimental conditions when the standard methods cannot be used or would be very inconvenient. This method has been tested in measurements on fused quartz, glycerine and Araldite at room temperature. The experimental conditions that cause deviations from the mathematical solution of the thermal conductivity equation are discussed and estimates for their maximum influence on the measured quantities are given.
326 citations
TL;DR: In this article, the mechanism of ozone generation in the silent discharge of air-fed ozonisers has been studied theoretically and experimentally, and the electron impact dissociation coefficients of O2, N2 and O3 and the gas temperature of O3 were estimated by the computer matching of the theoretical calculations to experimental results.
Abstract: The mechanism of ozone generation in the silent discharge of air-fed ozonisers is studied theoretically and experimentally. The nitrogen oxides (NOx) formed in the silent discharge have been found to play an important role in the process of ozone generation due to the catalytic cycle for O3 destruction: NO+O3 to NO2+O2 and NO2+O to NO+O2. Taking this catalytic cycle into account, a mechanism is proposed to explain the characteristics of ozone generation in air-fed ozonisers. The electron impact dissociation coefficients of O2, N2 and O3 and the gas temperature in the silent discharge are estimated by the computer matching of the theoretical calculations to experimental results.
202 citations
TL;DR: In this paper, a wave-launching structure called a surfatron is proposed for long plasma columns, in many instances preferable to the positive columns of DC discharges, can be obtained by means of a UHF surface wave propagating along the column.
Abstract: Long plasma columns, in many instances preferable to the positive columns of DC discharges, can be obtained by means of a UHF surface wave propagating along the column. This is possible through the use of a novel wave-launching structure, called a surfatron. The launcher is compact and located on the outside of the dielectric tube containing the plasma. The surfatron is described and analysed in terms of an equivalent circuit theory. Guidelines for its design and operation are given.
187 citations
TL;DR: In this paper, the principal characteristics of free burning arcs were derived from the controlling physical equations to predict the radius, voltage, central temperature, electric field, and center plasma velocity.
Abstract: Analytic formulae are derived from the controlling physical equations to give the principal characteristics of free burning arcs. Predictions of arc radius, voltage, central temperature, electric field and centre plasma velocity are in reasonable agreement with published experimental results for arcs in air from 1 A to 20,000 A at a pressure of 1 atmosphere and an electrode spacing of 1 cm. The theory enables useful predictions to be made for applications of arcs in welding, switchgear and arc furnaces.
114 citations
TL;DR: In this article, strong electric double layers are produced in a low-density plasma column confined by an axial magnetic field and maintained by single-ended inflow of plasma along the magnetic field.
Abstract: Strong electric double layers are produced in a low-density plasma column confined by an axial magnetic field and maintained by single-ended inflow of plasma along the magnetic field The double layer evolves from an anode sheath, and ionisation within the sheath is shown to be a significant process in this conversion Once the double layer has been formed, its axial position can be controlled by the external electric circuit The layer exhibits an axial motion back and forth with amplitudes somewhat larger than the layer thickness
103 citations
TL;DR: In this article, the amount of energy involved for impacts where the metal is deformed plastically, and is typically only a few per cent of the initial kinetic energy, was calculated for impact cases.
Abstract: During the normal impact of a hard particle on a metal surface, some of the kinetic energy of the particle is radiated into the target as elastic waves. The amount of energy involved is calculated for impacts where the metal is deformed plastically, and is found to be typically only a few per cent of the initial kinetic energy.
95 citations
TL;DR: In this article, the electron swarm development in SF6 gas is studied for E/p20 values from 15 approximately 200 V cm-1 Torr-1 (E/N=45.6-607 Td) by a Boltzmann equation method in which the effect of ionisation and electron attachment is considered properly.
Abstract: The electron swarm development in SF6 gas is studied for E/p20 values from 15 approximately 200 V cm-1 Torr-1 (E/N=45.6-607 Td) by a Boltzmann equation method in which the effect of ionisation and electron attachment is considered properly. The momentum transfer, vibration, ionisation and attachment cross-sections are taken from experiments, but the electronic excitation cross-section is determined by fitting the calculated ionisation and attachment coefficients to previous measurements. The calculation is performed for the steady-state Townsend, pulsed Townsend and time-of-flight experiments. The results show that the deduced electron drift velocities and diffusion coefficients agree reasonably well with experiment and the value of a swarm parameter should depend on the type of experiment not only at high E/p20 values, at which ionisation is appreciable, but also at low E/p20 values, at which electron attachment is appreciable. The electron energy distribution, which is found to have depressions at low E/p20 values, the electron mean energy and the excitation coefficients are also calculated and discussed.
95 citations
TL;DR: In this article, the authors derived a closed system of transport equations for an anisotropic plasma of arbitrary degree of ionisation, which is based on a bi-Maxwellian species distribution function and should provide a better description of flow conditions characterised by large temperature anisotropies.
Abstract: The authors have derived a closed system of transport equations for an anisotropic plasma of arbitrary degree of ionisation. The system is based on an anisotropic bi-Maxwellian species distribution function, and therefore, should provide a better description of flow conditions characterised by large temperature anisotropies. The method used to derive the transport equations is an extension of Grad's method and corresponds to a 16-moment approximation for the species distribution function. The relevant collision terms were calculated for an arbitrary inverse-power interaction potential and for a resonant charge exchange interaction between an ion and its parent neutral. In the collisionless limit, the system of equations reduces to the collisionless transport equations which include the effects of collisionless 'viscosity' and heat flow.
91 citations
TL;DR: In this paper, the authors considered the effect of back-tunnelling on the amount of charge acquired by an insulator when it is contacted to a metal, and also the extent to which it can lose charge by back-tunneling during separation.
Abstract: Tunnelling of electrons between a metal and localised states in an insulator is considered, with a view to determining the charge that an insulator can acquire by this mechanism when it is contacted to a metal, and also the extent to which it can lose charge by back-tunnelling during separation. Traps at a single energy are considered primarily, but some attention is given to traps distributed over a range of energy. Back-tunnelling is likely to be significant only at the very highest observed charge densities.
85 citations
TL;DR: In this article, the formation of local regions of the high-temperature, high-pressure plasma, "hot-spots", in a vacuum spark was studied using X-ray spectroscopy and holography.
Abstract: The formation of local regions of the high-temperature, high-pressure plasma, 'hot-spots', in a vacuum spark is studied using X-ray spectroscopy and holography. Measurements of the dimensions of the hot-spots, of the absolute flux of radiation and of the spectral composition of the X-ray emission, have been analysed to give order-of-magnitude values for the local electron density, temperature and plasma lifetime. It appears that the plasma pressure is >or approximately=107 atm and that the formation of the hot spots requires intense heating rates more commonly associated with focused laser beams, i.e. >or approximately=1015 W cm-3. It is probable that in the vacuum spark electron beams are responsible for plasma heating. Possible mechanisms for concentrating energy deposition in localised regions are discussed.
TL;DR: In this article, the secondary electron emission yield delta due both to primary and back-scattered electrons is derived as functions of three parameters such as atomic number Z, first ionisation energy I and backscattering coefficient r, which are found to be in good accordance with the results obtained experimentally.
Abstract: Based on the energy retardation power formula concerning the penetration and the energy loss of an electron probe into solid targets, the secondary electron emission yield delta due both to primary and back-scattered electrons is derived as functions of three parameters such as atomic number Z, first ionisation energy I and back-scattering coefficient r, which are found to be in good accordance with the results obtained experimentally. Notable in such theoretical procedures are the maximum yield delta m and the primary energy Em, giving delta m=0.12Z1/15I4/5(1+1.26r) for Em=57.9Z115/I4/5(1+5r2)4/5 (eV) which substantially agree with the miscellaneous experiments of many authors. The energy dependence of the yield-energy distributions, the yield of thin films and the lateral distribution of secondary yield at the distance from the centre of the beam are given as functions of the back-scattering coefficient and the primary energy.
TL;DR: In this article, the piezoresistivity coefficients in p-and n-channel MOS transistors manufactured on silicon wafers cut parallel to the (111) and (100) planes as a function of VD, VG and of the temperature, between -20 and 120 degrees C, have been measured with the particular aim of investigating the possible application of MOS Transistors for strain measurements, by comparing the advantages and the disadvantages with bulk and diffused resistors.
Abstract: The piezoresistivity coefficients in p- and n-channel MOS transistors manufactured on silicon wafers cut parallel to the (111) and (100) planes as a function of VD, VG and of the temperature, between -20 and 120 degrees C, have been measured with the particular aim of investigating the possible application of MOS transistors for strain measurements, by comparing the advantages and the disadvantages with bulk and diffused resistors. The characteristics of the MOS devices can be consistently better than the corresponding ones of bulk semiconductor strain gauges, particularly as regards the temperature stability of the resistivity and of the electrical characteristics.
TL;DR: In this article, the current peaks due to transient SCLC were observed both in high-density polyethylene (HD-PE) and in oxidised HD-PE in the temperature range 50-90 degrees C.
Abstract: Current peaks due to transient SCLC were observed both in high-density polyethylene (HD-PE) and in oxidised HD-PE in the temperature range 50-90 degrees C. From the time at which the current peak occurs, carrier mobilities ranging from 10-11 to 10-9 cm2 V-1 s-1 were obtained. The mobility values obtained agree well with those evaluated from surface-charge decay measurements. They strongly depend upon applied field and temperature. The charge carriers have a much lower mobility in oxidised HD-PE than in non-oxidised HD-PE. This is attributed to the introduction of deep traps by the oxidation.
TL;DR: In this article, the authors demonstrate that the order of kinetics of the TL process can change with the dose received by a sample, and that the activation energies E of the two peaks are determined using peak shape, and initial rise methods.
Abstract: The authors demonstrate that the order of kinetics of the TL process can change with the dose received by a sample. In LiF the order of kinetics becomes constant only when the dose given to the sample is smaller than the saturation dose by at least an order of magnitude. The order of kinetics followed by glow peaks V (190 degrees C) and XII (385 degrees C) of LiF TLD-100 is determined using two methods: (i) peak shape, and (ii) isothermal decay. The former gives the values as 1.4 for peak V and 1.35 for peak XII and the latter 1.6 for peak V and 1.5 for peak XII. For the saturation exposure of 105 R when no empty traps are available, peak V decays exponentially in the beginning (first-order kinetics) and as the decay progresses the order of kinetics continuously increases. After 3 min of decay at 165 degrees C, when the intensity has fallen to less than 20% of initial value, the order of kinetics stabilises at 1.6. The activation energies E of the two peaks are determined using (i) peak shape, and (ii) initial rise methods. The initial rise method is found to give lower values of E than the peak shape method. This is explained on the basis of a thermal effect on luminescence efficiency.
TL;DR: In this paper, the scattering and absorption efficiencies of chains of spheres in the Rayleigh approximation were compared with individual particles, and significant differences were found for the scattering case which arise due to multiple scattering and coherent phase effects.
Abstract: Scattering and absorption efficiencies are calculated for chains of spheres in the Rayleigh approximation, and compared with individual particles. For aligned chains significant differences are found for the scattering case which arise due to multiple scattering and coherent phase effects. The absorption efficiency is not influenced by the latter, but the changes are found to be of the same proportion as those in the scattering efficiency due to multiple scattering alone. For randomly oriented chains the effects of multiple scattering are small within the range considered.
TL;DR: In this paper, it was shown that the Stark profile is related to the electron current density rather than to electron density Ne, and the current density j is derived and from total current i a characteristic radius r 0 of the filamentary discharge is obtained.
Abstract: The discharge is operated in oxygen with a 1 cm gap between a positive point and a plane at a pressure near 300 Torr. The discharge has been found to have a behaviour similar to that in atmospheric air. By introducing traces of hydrogen it has been possible to study the Halpha and Hbeta lines broadening which is mainly connected to the Stark effect. However, due to the presence of a macroscopic field the usual theory does not apply, i.e. it is shown that the Stark profile is related to the electron current density j rather than to the electron density Ne. The current density j is derived and from total current i a characteristic radius r0 of the filamentary discharge is obtained. A value of the macroscopic field Fe is then determined from a numerical simulation of the discharge, leading in turn to the electron density. All these measurements are time resolved and are given as a function of time during the glow-to-arc transition. Typical values are j approximately 3*103 A cm-2, r0 approximately 20 mu m, Ne approximately 1015 cm-3. Some indications concerning the primary streamer, the nature of the discharge plasma and the glow to arc transition are derived from these measurements.
TL;DR: In this paper, theoretical calculations and experimental observations on electron scattering by gases in the specimen chamber of a scanning electron microscope are presented, in good agreement with theoretical calculations based on elastic and inelastic electron scattering.
Abstract: Presents theoretical calculations and experimental observations on electron scattering by gases in the specimen chamber of a scanning electron microscope. The observed scattering is in good agreement with theoretical calculations based on elastic and inelastic electron scattering. For normal surface inspection work, good resolution is retained in back-scattered imaging when gas is deliberately introduced into the specimen chamber. Experimental and calculated beam profiles are discussed for 25 keV electrons in nitrogen gas. Guidelines for choosing operating conditions for higher than normal gas pressures in the specimen chamber are also presented. Micrographs are provided to illustrate the image clarity attainable under high electron scattering conditions.
TL;DR: In this paper, the rotary diffusion coefficient of ferrofluid particles was measured by observing the decay of their birefringence after a magnetic field pulse, and it was concluded that it was predominantly due to the shape anisotropy of the particles.
Abstract: For pt.I see ibid., vol.12, p.311 (1979). A method is described for measuring the rotary diffusion coefficient of ferrofluid particles, and hence their hydrodynamic size, by observing the decay of their birefringence after a magnetic field pulse. Details of the pulse amplifier used to produce field pulses of from 8*10-3 to 8*10-2 T with decay times of 3.6 to 36 mu s are given. The origin of the birefringence in ferrofluids is discussed and it is concluded that it is predominantly due to the shape anisotropy of the particles: particles in which Neel rotation occurs do not contribute to the birefringence. The existence of Faraday rotation in Co and Fe3O4 ferrofluids is also reported.
TL;DR: In this article, the authors measured the time delays of electrical breakdown in a gas-filled diode (td) as a function of the time between two successive measurements ( tau ) at cathode temperatures of 300K, 523K and 673K.
Abstract: Time delays of electrical breakdown in a gas-filled diode (td) were measured as a function of the time between two successive measurements ( tau ) at cathode temperatures of 300K, 523K and 673K. The diode was filled with nitrogen at 4 mbar with an oxygen impurity of about 10 ppm. It is shown that the breakdown time delays at 673K are one order of magnitude smaller than those at 300K.
TL;DR: In this paper, the Monte Carlo technique has been used to simulate the electron swarm motion in carbon dioxide and nitrogen, and electron swarm parameters have been evaluated in the range of E/N varying from 14 to 3000 Td (1 Td=10-17 V cm2).
Abstract: The Monte Carlo technique has been used to simulate the electron swarm motion in carbon dioxide and nitrogen, and electron swarm parameters have been evaluated in the range of E/N varying from 14 to 3000 Td (1 Td=10-17 V cm2). These parameters, namely ionisation coefficient, drift velocity, ratios of both radial and longitudinal diffusion coefficients, to mobility (also attachment and dissociation coefficients in the case of carbon dioxide) have been compared with the available experimental data. A set of elastic and inelastic cross-sections has been collected for each gas such that the computed and experimental values gave good agreement for each swarm parameter over the entire E/N range. In addition the percentage of energy lost by different types of inelastic collisions and also the mean swarm energy have been given as a function of E/N for each gas.
TL;DR: In this article, the dispersion equation of capillary wave on a liquid surface is discussed, and the results for water compare favourably with the predictions of hydrodynamic theory over a wider range of surface wave vector than hitherto examined.
Abstract: Photon correlation spectroscopy has been applied to the study of thermally excited capillary waves on a liquid surface. The technique of using a diffraction grating as a local oscillator has been refined for use with photon correlation; the combination has considerable advantages. Results for water compare favourably with the predictions of hydrodynamic theory over a wider range of surface wave-vector than hitherto examined. Data for glycerine agree with theoretical predictions based on a viscosity appropriate to about 1.5% absorbed water. A novel discussion of the dispersion equation of capillary waves on a liquid surface is presented.
TL;DR: In this article, the friction and adhesion developed between nominally clean monofilaments of polyethylene-terephthalate in a crossed-cylinder configuration are determined by the free surface energy of the fibres and by the contact geometry.
Abstract: The friction and adhesion developed between nominally clean monofilaments of polyethylene-terephthalate in a crossed-cylinder configuration. The adhesion is determined by the free surface energy of the fibres and by the contact geometry. A single region of contact is assumed, this provides a means of estimating the effective geometry of the fibres in the contact zone. From the deduced contact geometry, the area of contact as a function of normal load may be calculated using classical elasticity equations. The friction as a function of normal load may be deduced assuming that it arises primarily from shear of polymer at the interface. The calculated values are in good agreement with friction measurements carried out over a wide range of positive and negative loads. However, the friction experiments at negative loads are best considered as a special case of adhesive failure.
TL;DR: In this paper, an experimental investigation and a theoretical analysis of the behavior of a quartz crystal microbalance with coatings of varying viscosity and modulus of elasticity are presented. And the analysis is based upon the analogy with electrical waves propagating in a lossy transmission line.
Abstract: Presented is an experimental investigation and a theoretical analysis of the behaviour of a quartz crystal microbalance with coatings of varying viscosity and modulus of elasticity. The analysis is based upon the analogy with electrical waves propagating in a lossy transmission line.
TL;DR: In this article, it is shown that small indentations and scratches can be made in highly brittle materials such as glass or silicon without any associated fracture, and that this effect is governed by a strain energy criterion which can be defined quantitatively if the tensile field which initiates fracture is known.
Abstract: Small indentations and scratches can be made in highly brittle materials such as glass or silicon without any associated fracture. It is proposed that this effect, which is usually explained in terms of flaw statistics, is in fact governed by a strain energy criterion which can be defined quantitatively if the tensile field which initiates fracture is known. Using a model of the field of residual stress around an indentation proposed by Swain and Hagan (1976), it is shown that the critical size of indentation for fracture to occur should be about 12(ET/Y2), where E is Young's modulus, Gamma fracture surface energy, and Y the yield stress for plastic flow in uniaxial compression. The critical size parameter is evaluated for silicon.
TL;DR: In this article, two recently developed techniques have been used sequentially in an attempt to define the nature of high- beta field emission sites on a commercial-alloy, broad-area, electrode surface.
Abstract: Two recently developed techniques have been used sequentially in an attempt to define the nature of high- beta field emission sites on a commercial-alloy, broad-area, electrode surface. The techniques involved were: (i) an in-situ electron optical method for locating and examining the emission site; and (ii) a high-resolution spectrometer for determining the energy spectra of the electrons field emitted from this site. Furthermore, following these measurements, the elemental composition of the emission area was determined by electron microprobe X-ray analysis. Observations, which cast further doubt upon the traditional concept of field-enhancing microprojections, indicate that the sites are non-metallic and probably consist of impurities located at cracks or grain boundaries in the surface. Tentative hypotheses are proposed for the emission mechanism and include provision for an unstable situation caused by the effects of adsorbed gas atoms.
TL;DR: In this article, the anti-Stokes rotational Raman scattering from nitrogen gas at near atmospheric pressure and room temperature has been used to calibrate the intensity of ruby laser light Thomson scattered from a plasma in a transverse magnetohydrodynamic shock tube.
Abstract: Anti-Stokes rotational Raman scattering from nitrogen gas at near atmospheric pressure and room temperature has been used to calibrate the intensity of ruby laser light Thomson scattered from a plasma in a transverse magnetohydrodynamic shock tube. The main limit to the accuracy of this calibration method is the uncertainty in the available Raman cross section for nitrogen.
TL;DR: In this paper, the diffusion length of p-type silicon implanted with 400 kV boron ions to a dose of 1014 B+ cm-2 and annealed to temperatures in the range 700-1000 degrees C was evaluated.
Abstract: The SEM operated on the EBIC model is used to evaluate the diffusion length in p-type silicon implanted with 400 kV boron ions to a dose of 1014 B+ cm-2 and annealed to temperatures in the range 700-1000 degrees C. The method is to fabricate a Schottky diode on the irradiated surface of the implanted sample, and then place the sample in the SEM in such a way so that the beam is incident normal to the sample surface partly covered with the Schottky diode metal film; the diffusion length is found by slowly scanning the beam away from the Schottky diode and analysing the resulting EBIC decay. It is found that the effect of the implantation is to reduce the diffusion length with reference to an unimplanted sample subjected to the same heat treatment. The reduction is approximately 53% at 700 degrees C, and as the annealing temperature increases it gradually decreases to approximately 21% at 1000 degrees C. This shows that the effect of the damage on the diffusion length decreases with increasing annealing temperature.
TL;DR: In this article, the effective ionisation coefficient alpha /p20 is measured for E/p20 from 70 to 160 V cm-1 Torr-1, and the static breakdown voltage Vs between parallel plates for p20d from 8 to 130 Torr cm, for SF6 and nitrogen mixtures.
Abstract: The effective ionisation coefficient alpha /p20 is measured for E/p20 from 70 to 160 V cm-1 Torr-1, and the static breakdown voltage Vs between parallel plates for p20d from 8 to 130 Torr cm, for SF6 and nitrogen mixtures. It is found that the alpha /p20 of the mixtures may be approximated by a linear function of the partial pressure of SF6 at fixed E/p20 and that Paschen's law holds for the p20d may be estimated with good accuracy from the Vs of the respective pure gases using an experimental formula of Takuma et al. (1972) which has been used for much larger p20d.
TL;DR: In this article, the interband absorption coefficient, the free carrier absorption cross-section and the surface reflectivity in the same experimental set-up were determined, together with an analysis of the experimental data.
Abstract: Describes and experimental method together with an analysis of the experimental data, which makes it possible to determine the interband absorption coefficient, the free carrier absorption cross-section and the surface reflectivity in the same experimental set-up. The experiments were performed on samples of pure silicon at T=294K using a pulsed Nd-YAG laser, which gave pulses of 10-15 ns duration at lambda =1.06 mu m. The maximum carrier concentration achieved was about 3*1019 cm-3. Effects of laser beam inhomogeneities are also discussed and included in the absorption model.