Table of contents

The various macromolecular parameters such as the radius of gyration of cross section, the radius of gyration of thickness, the specific surface, the range of inhomogeneity, the length of coherence, the molecular volume and the molecular weight of the insoluble protein particles present inside wool fibres (Merino from Australia) are experimentally evaluated from the analysis of the low-angle X-ray scattering curve due to the sample. The air-fraction and the characteristic number of the wool sample are also determined. The low-angle scattering camera, due to Kratky et al., is used with the photographic registration technique. Monochromatized Cu K_α radiation is obtained by reflecting the copper radiation from a Johansson-Guinier bent crystal monochromator.

This paper deals with the study of surface charge formation and decay characteristics of thermoelectrets of polyvinyl chloride and polyvinyl acetate prepared at different polarizing temperatures from 30°C to 180°C. It has been found that the polarizing temperature has a major influence in deciding the magnitude of the initial as well as the final charge as well as the mode of decay of the surface charge. It has also been found that the moulding and stripping charge contribution during the formation of an electret is equally important in deciding the characteristics of an electret. The behaviour of these thermoelectrets based on the contribution from (i) the type of the degradation products produced at various temperatures, (ii) the moulding and stripping charge, (iii) the dipolar orientation and (iv) the spray charge mechanism from the electrode to the electret surface under high-field conditions, is explained in the paper.

Grazing-incidence electron diffraction is used to show the surface structure and mode of growth of silver films condensed in vacuum, in relation to film thickness H, rate of deposition, substrate temperature and, especially, the residual gas nature and pressure p. In air at 7 × 10⁻⁶ to 7 × 10⁻³ torr, on glass at room temperature, silver deposited at 30-35 Å s⁻¹ showed random polycrystalline initial structure up to a certain thickness, then {111} orientation, then additional {111} twinning, followed by {110} and later {110}+{211} orientation, at all these pressures. Additionally some hexagonal silver was present in films at 10⁻³ to 10⁻² torr of air or nitrogen, but not oxygen. The thickness at which these orientations were first observed is approximately H=Kprime ln (p0/p), where Kprime and p0 are constants, p0 being approximately 2 × 10⁻² torr.

The {111} orientation results from {111} crystal faces being formed, and more rapid lateral growth and predominance of crystals with this face normal to the vapour stream. The {110} and {211} orientations appear to be due to secondary twinning combined with presence of {110} or {211} faces on the twins.

A theory is developed which accounts well for the (H, ln p) rectilinear locus in terms of a Temkin isotherm for adsorption of the oxygen, and indicates a stepped nature of the {111} faces. The coverage fraction θ of the oxygen adsorption is estimated.

At 60-160 Å s⁻¹, the {111} orientation develops slightly earlier, but little or no twinning occurs at up to 12 000 Å film thickness.

Films of InAs have been prepared by evaporation of the elements, using the `three temperature' method, on to Corning 0211 glass substrates at temperatures from ambient to 630°C, in a range of thicknesses from 0·1 to 1·4 μm. Electrical measurements have indicated a dependence of carrier concentration on thickness, but not on substrate temperature; the lowest concentration observed was 9 × 10²³ m⁻³ at the greatest thickness. The mobility was found to increase both with thickness and substrate temperature; a maximum value of 0·225 m²V⁻¹s⁻¹ was found. For films prepared on substrates held at temperatures greater than 450°C, optical reflection measurements in the infrared enable plasma data to be obtained by comparison with computed curves. Combining this data with electrical measurements on the same sample gave the variation of effective mass with carrier concentration up to greater concentrations than have been reported for bulk material, a value of m^* of0·12 being obtained for a concentration of 7 × 10²⁵m⁻³. The changes of mobility in this range were indicated to be due to changes both in the carrier effective mass and in their relaxation times.

The plasma reflection edge exhibited by semiconducting material is shown to be considerably modified when the material is of low mobility and in thin film form. The interpretation of reflectance data requires a knowledge of the film thickness and is obtained with reference to curves computed for standard conditions. The refractive index and extinction coefficient have been calculated from parameters of the free charge carriers, using Drude theory, and used in the calculation of reflectance from a thin absorbing film, taking account of reflectance and phase changes induced by the absorbing nature of the material. The conditions were chosen for measurements in the wavelength range 5-30 μm with films up to 1 μm in thickness. Precise information can only be obtained for values of τ, the relaxation time, above 10⁻¹⁴s, with a suitable carrier density for the frequency range.

The application is reported of these computed curves to the interpretation of reflection spectra and refractive index measurements of InAs to give values for τ and the relative effective mass.

Films of InSb have been prepared by the evaporation of the elements on to heated glass substrates up to a thickness of 5 μm. The use of a semiclosed system has allowed material, initially evaporated on to the container walls, to getter the residual gas of active impurities before the substrates are exposed. Carrier densities of just over 10²² m⁻³ were obtained which were constant with film thickness; the electron mobility increased with film thickness to a value of 1·7 m²V⁻¹s⁻¹ at about 2 μm, above which it remained approximately constant. Hall element sensitivities of 350 V A⁻¹ T⁻¹ were obtained, though with a considerable temperature dependence.

The effect of applying a rounded stylus to thin metallic films on glass substrates has been investigated using diamond and steel styli with tip radii of approximately 25 μm and loadings of up to 230 g. The films were vacuum-deposited indium, tin, lead, gold, copper, aluminium, nickel, chromium and molybdenum of various thicknesses up to 3·2 μm. Scanning electron microscope and optical interference microscope observations showed that the process of scratch formation was generally very complex and varied with the film material, indicating that it is not possible to deduce absolute values of adhesion forces using a simple general theoretical model. The method can, however, be used with caution for qualitative comparisons under certain restricted conditions.

A method for utilizing the `dual transverse' Pockels effect with cubic crystals, classes 4bar, above 3m, 23 is given. The light path is along the [110] axis, and the two field signals are applied in the [11bar, above 0] and [001] directions. This configuration is suitable for producing duplex polarization modulation, single sideband modulation and for changing the frequency of light. Simultaneous modulation of a laser beam by two independent signals has been demonstrated using a ZnS crystal class 4bar, above 3m.

This paper discusses static orientation patterns in nematic liquid crystals in the presence of magnetic fields. Some solutions of the equations of a continuum theory are presented, and these suggest experiments for the evaluation of coefficients in the theory due to Frank in 1958.

Measurements of ac losses in superconducting niobium strips by the helium boil-off method have been made with a view to assessing the effects of sample thickness, surface finish and metallurgical hardness on prospective superconducting cable conductor materials. The method of preparing the strip edges has been shown to have considerable effect upon the level of measured losses. The measurement technique is described in some detail.

Liquid-filled, flexible, open cell foams exhibit large mechanical damping when subjected to oscillatory compressions because of the flow of liquid through the foam matrix. The theory which has been proposed by Gent and Rusch in 1966 to explain this phenomenon is extended to take into account the effects of inertia. An apparatus is described which has been used to study the dynamic behaviour of liquid-filled foams. It operates in the compression tension deformation mode over a frequency range of nearly five decades (3 × 10⁻³-2 × 10² Hz) at temperatures between −50 and +70°C. Experimental data are presented showing how the mechanical properties of the matrix and the liquid and the sample geometry affect the dynamic behaviour of the liquid-filled foam system. In general the observed behaviour is in agreement with that predicted theoretically. Deviations from the theory are attributed to the sample configuration used.

It is shown that in a thoroughly degassed oil each impulse discharge generates a definite amount of gas. Under the conditions of the measurements this was about 3·6 × 10⁻⁹ moles per discharge. A large fraction of the gas is hydrogen. Over a small range of temperatures the rate rises exponentially with the absolute temperature, the energy in the Boltzmann factor being about 8·1 kcal mol⁻¹, and roughly the same as that for the conductivity of the oil. As an explanation of the association of a definite yield of gas with each impulse breakdown, it is proposed that the breakdown avalanche can be generalized to include gas molecules as well as ions and electrons (stage I). After the avalanche has developed sufficiently a gas-phase channel forms and is propagated between electrodes by a space charge at its tip (stage II). When the interelectrode gap is bridged, conduction is entirely in the gas phase (stage III). Most of the breakdown current flows during stage III; most of the gas is produced during stage II. This three-stage model seems to be consistent with breakdown behaviour. Self-terminating alternating current breakdowns generate not more than several times as much gas as single impulse discharges.

An experimental investigation of visible and ultraviolet laser action in a small argon Z-pinch plasma has been made. The effect of initial gas pressure on the peak laser output power, implosion time, time of ultraviolet laser action and axial electron density is described, and streak photographs of the discharge are presented. Laser action at 4765 Å due to Ar⁺ is observed in the initial stages of the discharge at pressures below 7 mtorr. Laser action at 3511 Å due to Ar²⁺ occurs as a short pulse at higher initial gas pressures just after the imploding current sheath reaches the axis of the discharge tube. Typically, the axial electron density at the time of peak ultraviolet laser action was found to be 1·0 × 10¹⁵ electrons cm⁻³, although at certain gas pressures slightly larger values were found. Large electron density gradients occur just after ultraviolet laser action.

Experiments are described in which time-resolved spectroscopic measurements have been made on arcs of 250 to 1000 A between 0·5 and 3·1 cm in length, moving due to a transverse magnetic field at speeds up to 80 m s⁻¹ in argon at a pressure of 2 atm. On the assumption that the arc cross section did not depart appreciably from a circle, it has been possible to convert the photomultiplier signals of an atomic argon line to radial temperature distributions. By measuring the ratio of the intensities of two lines, the temperature at the arc axis has been found to be nearly constant over a number of revolutions of the arcs around circular electrodes for the range of arc current and speed in which measurements were made.

From the measured peak temperatures, values of average column electric field and the radius beyond which little conduction will occur have been calculated. These have been found to be in good agreement with electric fields estimated from arc voltage measurements, and radii estimated from aerodynamic drag force considerations.

The measurements of the first ionization coefficient α/p for air, without and with transverse magnetic fields, are reported in this paper. These were carried out using coaxial cylindrical electrodes to reduce the loss of electrons due to their drift in the E×H direction. The range of measurement covered the values of E/p between 200 and 600 V cm⁻¹ torr⁻¹ and those of H/p between 200 and 1400 G torr⁻¹. The validity of the equivalent pressure concept was tested for the complicated medium like air. It has been shown that a satisfactory agreement between the theoretical and experimental values of α/p, H/p and E/p was obtained for low values of E/p (<300 V cm⁻¹ torr⁻¹) provided the collision frequency was taken to be an increasing function of E/p, instead of a constant as was assumed for hydrogen. At higher values of E/p (> 300), however, the observed values of α/p, H/p and E/p were below those calculated on the basis of the equivalent pressure concept. A few measurements of α/p were also carried out using the pressure variation technique, and its operational utility has been established from the identical nature of the results.

The mobilities and Townsend's energy factor k_T of negative ions in SF₆ have been measured over the range 10<E/p<80 V cm⁻¹ torr⁻¹ (normalized to 20 °C) with gas pressures varying between 1 and 10 torr. Using the measured mobilities, values of k_T have been calculated from Wannier's simplified theory and are found to be in excellent agreement with the observed values over the entire E/p range studied.

D/μ values (diffusion coefficient/mobility), drift velocities and attachment coefficients of electrons in oxygen have been measured over the range 5<E/p<50 V cm⁻¹ torr⁻¹ at 20 °C with gas pressures varying between 3 and 5 torr using a modified drift tube. For E/p>25, the measurements have also yielded values of Townsend's primary ionization coefficient. If electron detachment is neglected, the D/μ values and drift velocities are in good agreement with the available data, while the attachment coefficients differ substantially from some of the reported values. The overall accuracy of the D/μ values and the drift velocities is estimated to be better than ±3%, while the accuracy of the attachment coefficients obtained varies from ±3% for E/p<20 to about ±10% at higher E/p values.

The energy distribution of electrons in a part of the electron beam selected by two apertures situated on the axis was measured using a wienfilter-type energy analyser. These measurements gave brightness values for electrons in specific energy intervals of the distribution which fitted the theory extremely well. The influence of the measuring system on the energy distribution was also demonstrated and it indicated that the discrepancy between experiment and theory observed by Nottingham and Hutson was due to a crude approximation in the electron optics of the theory rather than a large electron reflection effect.

The anomalous broadening of the energy distribution (Boersch effect) was found to be independent of the measuring system and had no influence on the brightness. Energy gains were also observed in the broadening process.

Barium has been purified by repeated distillation onto an induction heated condenser. The increase in resistance ratio from 6 to 900 over 5 distillations is in qualitative agreement with a simple model of a single-plate still.

The dc electrical conductivity of single-crystal and polycrystalline alumina has been measured in the temperature range 600-1573 K using an apparatus designed to avoid errors due to extraneous conductance paths. Experimental data are presented which cast serious doubts on values published hitherto.

Third harmonic components in the reflected and transmitted waves produced by non-linear interaction of a plane-polarized electromagnetic wave with a semiconducting sample of finite thickness have been studied. It is found that the sample thickness should be a little less than half the skin depth at the fundamental frequency for optimum harmonic output.