Table of contents

Outlines the physical basis of semiconductor electroluminescent diodes and describes how various forms of display device are made. At the present time most of the available devices are made from gallium phosphide or gallium arsenide phosphide and the properties of these are compared. The application of electroluminescent devices to form display systems is described. The design of a system depends on the devices which are available, and this is discussed bearing in mind not only the form of the display device to be used but also the logic circuits used to drive the display.

A cone and plate air turbine viscometer is described which is suitable for the rheological testing of biological materials. The instrument produces a minimum shear stress of about 0.027 N m^-2.

Problems associated with the calibration of photoelectron spectrometers are discussed in the light of current calibration techniques, and an alternative method is presented.

A circuit is described, based on a gated photomultiplier, which allows differential and direct light intensity measurements over 4-6 orders of magnitude with a time resolution between 0.03 and 40 mu s.

The charge-energy, Q-W, relation for a planar vacuum photodiode was investigated experimentally using a ruby laser as energy source and a cone calorimeter for reference energy measurement. High accuracy was obtained by operating the calorimeter over a restricted energy range and by using digital read-outs for both charge and energy. The energy incident on the photodiode was varied over three decades and the results fitted to a relation of the form Q=aWⁿ. There was found to be no significant departure of the index n from unity and no significant variation with energy; the mean value was n=0.994+or-0.015.

A simple module is described which enables a Stereoscan stage, Series 100 or similar, to accept large specimens for examinations where only translational stage movements are necessary. The modification is based upon a component incorporated in the original state.

A method is described whereby the Edwards VPC1 gas pressure control device can be modified to enable it to be used in quasi-static situations where the gas flow is very low and where use of the standard device is prevented by control valve seepage. The new performance characteristics are briefly discussed.

Two micrometeoroid experiments based on the plasma emission caused by impacting hypervelocity dust particles are described. Since 31 January 1972 the first has been flying on the HEOS 2 satellite orbiting the earth in a highly eccentric polar orbit. The second experiment will be flown in 1974 on the HELIOS probe which will orbit the sun with a perihelion of about 0.3 AU. The aim of these experiments is to measure the mass and speed of micrometeoroids and to determine their approximate orbital elements.

A torsional creep apparatus incorporating a novel linear bearing to permit simultaneous application of axial and torsional creep stresses to small nonrigid specimens is described. The results of a detailed examination of the capabilities of this apparatus and a comparison of shear creep and recovery compliance data is made (as measured direct in torsion and calculated from the axial and lateral strain data in tension). The measurements were made on isotropic and oriented sheets of low-density polyethylene and the use of oriented, as well as the more usual isotropic, material in such trials is illustrated.

A method is described for the determination of the transmission function of an ultraviolet photoelectron spectrometer of spherical design. Such a function may be determined by this method for any given electron.

An electrodeless method for determining electrical conductivity at various frequencies is presented. Two sinusoidal magnetic fields of equal amplitude and a constant phase displacement of 180 degrees are balanced, and the resultant eddy current field perturbation produced by the insertion of a sample in a specified region of the system is measured. A mathematical expression relating the conductivity of the sample to the circuit parameters is derived and tested on a system of equivalent 'sample loops' whose conductivities are known for annuli of samples placed in the position of the same loop. Also presented are preliminary results obtained for determination of conductivities of aqueous solutions of hydrochloric acid by the 'difference-field method'.

A new principle applicable to the Rowland circle mechanisms of X-ray spectrometers is formulated, and is based on the geometry of the circle considered in terms of its polar coordinates relative to the pole of the grating. It allows continuous adjustment of the Rowland radius scanned; it confers flexibility in operation, yet simplifies construction of the instrument. A soft X-ray spectrometer, designed on the new principle, is described and covers the wavelength range 1-20 nm for concave gratings of any radius between 0.5 and 5 m. Results obtained using an electron microprobe source are presented.

By introducing a transparent plane parallel plate into an open Fabry-Perot cavity and counting the change in the interference order while the plate is rotated, it is possible to measure the thickness or refractive index of the material with a high degree of accuracy. The method of multipass interferometry can be applied by using a He-Ne laser of 632.8 nm wavelength.

A reflectance unit is described which enables the spectra of corrosive melts to be recorded between the near ultraviolet and far infrared regions of the electromagnetic spectrum at temperatures up to 1300 K. The unit is designed for use with a Perkin-Elmer model 457 spectrophotometer, but could readily be adapted to suit other instruments. Measurements on semitransparent samples can be used to derive reflection and absorption coefficients; the reflectivity of an opaque sample can be measured directly.

A novel method is proposed for the acute determination of magnifications in the in-line method of holography. The method is completely general but is described with particular emphasis on its use in measurements on rapidly moving aerosols. The method allows the size distribution of such an aerosol to be determined without the use of optical components. Preliminary experiments have confirmed that the method is feasible, and more exhaustive tests are in progress.

An AC circuit and sample apparatus have been devised which enable the temperature dependence of impurity resistivity of metals and deviations from Matthiessen's rule to be measured simply and directly, the latter with an accuracy hitherto unobtainable. By means of two transformers the difference of two resistivities is essentially obtained, and by interchanging the positions of the two samples in a specially designed sample holder, uncertain apparatus constants are eliminated from the expression for Delta rho / rho ₀. The circuit consists essentially of an amplifier and phase-sensitive detector applied to the out-of-balance signal between an AC potentiometer and the potential to be measured in such a way that the entire measurement becomes independent of current. An example of the temperature dependence of the deviation from Matthiessen's rule in Cu+0.1 at.% Au is given.

It is shown how the rate of change of anemometer voltage with windspeed can be accurately computed from coarsely spaced static calibration data. The calibration of an approximately linearized anemometer is then discussed and appropriate formats for data presentation are described. Experimental results from cylinder wakes at the same Reynolds number demonstrate the validity of the calibration procedure when an analogue linearizer is used.

Describes a regulator of hydrogen pressure-and therefore of hydrogen flow-whose parts have been designed to ensure a fast response. It uses a directly heated palladium hydrogen leak and a thermistor gauge. The dynamic behaviour of the regulator is analysed. The desired gas flow value is obtained in about 20 s. The temperature coefficient of the regulator is low, and it shows an excellent long-term stability.

A reentrant cavity coupling system successfully used for hypersonic, especially spin resonance, investigations is described in detail. The influence of seven parameters of the system is studied, and the conditions are established for obtaining in different samples optimal piezoelectric excitation and detection of coherent hypersound. The usefulness of the system for hypersonic spin resonance is demonstrated.

The field homogeneity requirements for observing the de Haas-van Alphen effect are discussed in some detail. It is demonstrated how field inhomogeneity can cause interaction between different de Haas-van Alphen frequencies. A method for measuring the absolute amplitude of de Haas-van Alphen oscillations using a known field gradient is proposed.

The use of helical resonant cavities for the piezoelectric generation of sound in the frequency range 0.1-1 GHz is described and illustrated with some ultrasonic attenuation measurements in a nickel crystal. Equations for the design of these cavities are presented and show to give a good description of their performance.

An image intensification system, based on a commercially available channeltron plate, has been constructed for a JEM 200 electron microscope. Contrast and resolution of the system is comparable to that which one obtains by direct photographic recording from the phosphor observation screen of the microscope, but with specimen current densities which are approximately a factor 200 lower than for the conventional electron microscope system. The improvement over previously reported image intensification systems based on channeltron plates is due to the removal of secondary scattered electrons and residual gas ions from the input of the intensifier.

Two super-regenerative oscillators for an NQR spectrometer have been built covering the frequency range from 250 up to 1100 MHz. The two oscillators of microstrip type use ¹/₄ lambda or ¹/₂ lambda resonators, possess sideband suppression and automatic gain control and allow insertion of a finger dewar for low temperature investigations. A series of nitrogen-iodine charge-transfer compounds have been studied.

Analytical expressions which include all parameters are derived for the signal response and noise of the pneumatic nondispersive infrared detector in terms of the membrane displacement. The polytropic exponent for the infrared absorption compartment expansion process is defined as a function of the system parameters. Numerical experiments are performed to characterize the detector IR chopping frequency response with membrane spring constant and thermal power losses of the absorption compartment. Brownian bombardment noise and membrane mass and damping are negligible in these experiments. Absorption compartment thermal power fluctuations is the single source of noise considered. It is shown that the analytical model can be extensively used to outline the design of a detector. In addition, it can be employed in conjunction with detector hardware to aid in the interpretation of experimental results, determine the relative importance of the detector parameters, demonstrate feasibility of design changes, and establish the detector theoretical performance limits.

The rather broad peaks obtained with a Si(Li) detector often necessitate extrapolation of background over a considerable energy range. In many samples no background readings free of interference from peaks can be obtained below 2.7 keV. A procedure for calculating background over the whole spectrum for measurements at 2.96 keV (Ar K alpha ) and 9.87 keV (Ge K alpha ) is described. For samples consisting of elements below 30 in atomic number the background correction can be determined with an error not exceeding an equivalent concentration of 0.1 wt %.

A system for the measurement of time-varying ellipticity and axis orientation of polarized light has been developed and specifically applied to the analysis of the birefringence of macromolecular solutions in a Kerr electro-optic cell. The method of measurement is based upon the passing of the elliptical light through a rapidly rotating analysing prism, ahead of photodetector. When elliptical light results from the passage of circularly polarized light through a material having slowly changing birefringence and optical axis orientation, these material properties may be continuously monitored. In the application of the Kerr effect, the steady and alternating components of the birefringence are separated in the frequency domain of the photodetector output. The measurement system provides a high degree of discrimination against problems due to light intensity variations and small residual birefringence in Kerr cells.

It is shown that polymer electret films can be used to sense the arrival of shock and detonation waves. Time-of-arrival detectors can be constructed which have excellent signal-to-noise ratios, even for shock pressure rises as small as 10 Torr, and which are very insensitive to precursor stress waves in the vessel walls and to electron precursors from very strong shock waves. Rise times of less than 5 mu s and triggering responses within 1 mu s are readily attainable.

X-ray intensity measurements in a narrow range of the spectrum can be achieved by means of Ross filters. Nearly always they are used in connection with ionization detectors (especially pulse counters). With regard to certain applications, however, the employment of photographic film is of great interest, e.g. in microradiography or diffraction studies on amorphous materials. If the Ross-filter technique is combined with the photographic method instead of the counter method, the random error (arising from variations of the thickness or the speed of the emulsion, from nonuniform development, the graininess, etc.) becomes of paramount importance. Its dependence on filter thickness and X-ray voltage is discussed for Ni-Co and Zr-Sr filter pairs. Practical rules, which take into consideration the random error, as well as the error of monochromatism, are given.

A technique has been evolved for the growth of single-crystal films on silicon surfaces. The films were grown by condensation of vapour sublimed from an electron-beam heated source of zinc sulphide in ultrahigh vacuum. Careful control was maintained of the substrate temperature and the deposition rate. Films up to 1.5 mu m thick, exhibiting varying degrees of epitaxy, were grown on the (100), (110) and (111) faces of silicon, using both pure and doped sources. The best epitaxy was obtained by condensation, on a (100) surface held close to 300 degrees C, of vapour from a pure zinc sulphide source having an arrival rate at the substrate of the order of 4*10¹⁹ molecules/m²s. Mass spectrographic analyses of the starting materials, the residual pressure within the vacuum system before, during and after film deposition, and in some cases of the films produced were undertaken to monitor system cleanliness during the depositions of the films.

A calibrated detector system developed for a program of ultraviolet intensity measurements is described. The detector uses a tungsten photodiode as a secondary standard in the wavelength range 50-120 nm, together with a vacuum photocell sensitized by a fluorescent coating of sodium salicylate which extends the detector sensitivity to 300 nm. The intensity calibration has been checked against the stabilized arc source developed by Boldt at Garching, and the calibration errors are estimated to be within +or-15% limits. The calibrated detector has been used to measure the sensitivity of various types of photographic film (Kodak SC5, SC7 and 101-01) and to obtain an intensity calibration for spectrographic instrumentation used in rocket payloads. A monochromatic collimated light source and a polarization analyser developed for these vacuum ultraviolet calibration measurements are also described briefly.

A modification of a Varian TE 104 dual sample cavity is described. With this modified cavity, sample temperatures of up to 1300 K are reached without loss in sensitivity. The performance of this cavity allows one to measure the temperature dependence of very weak broad ( Delta H approximately=1 kG) ESR signals. Moreover, it is possible to carry out spin concentration measurements reliably. The ideas underlying this modification can be used in general for making type TE 104 or TE 102 cavities suitable for sensitive ESR measurements at high temperatures.