Table of contents

A critical discussion is given of the Kelvin method of measuring work functions and surface potentials. There is a short description of the theory and a review of the technical development of the method. The practical limits to its precision are discussed in turn: these are noise, the effects of stray capacitance, and variations in the work function of the reference surface. Suggestions are made for a new technical variation of the method, and for a new type of reference surface that should have advantages for measuring the surface potentials of gases on metals.

In measuring residence times of potassium ions desorbed from a tungsten surface in an atomic beam experiment, a correlation technique is used to measure the residence time distribution. The advantage of this method over other techniques mentioned is the high efficiency of the modulation and detection process. In this experiment the atomic beam is modulated by a random sequence, and the cross-correlation function of this sequence and the detected ion signal from the tungsten target is computed simultaneously for a hundred different delay points. From the measured residence time the desorption energy can be calculated, which for the potassium-tungsten system in this experiment has a value of 2·3 eV in accordance with the data of Kaminsky.

The balance described is intended for isothermal studies of moderately fast gas-solid interactions, such as adsorption, in which the heat of reaction is not negligible. The sample of solid is contained in a chamber which is integral with a hollow balance beam. The gas flow rate through the chamber is adjusted to minimize the resistance to heat and mass transfer in the boundary layer. The excess gas flow acts as a heat sink. The deflection of the beam under load changes is sensed by a frequency modulation capacitance system. Load changes of 15-250 mg give full scale deflection on a chart recorder and direct calibration and range reset by riders are available at any time. The balance has been used extensively in measurements of gas adsorption and diffusion in porous solids.

A servo-controlled axial-loading fatigue machine is described. Its performance has been evaluated for both load and strain control, and shown to be suitable for short-endurance fatigue testing. The results of some initial fatigue tests are presented.

A simple tilting stage has been constructed which can be mounted in conventional Philips EM 200 and EM 300 electron microscopes. The stage guarantees high resolution and is able to rotate the object 180° in the electron beam.

A differentially pumped specimen stage is described which allows thin film deposition studies to be carried out inside an electron microscope. The pressure in the specimen vicinity can be reduced to about 10 ntorr after 16 hours pumping, and it is shown that meaningful studies of thin film growth of reactive materials are now possible.

An improved magnetic reluctance transducer of high sensitivity is developed for use with laboratory disk-machine which simulates conditions associated with elastohydrodynamic lubrication. It measures the change in the magnetic flux across the contacts of a double rimmed disk in contact with a solid disk when a film is introduced. Details of the design principles and procedures of optimization are discussed. The transducer is particularly suited for the study of the film thickness of lubricating grease because, unlike their dielectric constants, the permeabilities of greases, being nonferromagnetic, are close to unity. This simplifies the calibration.

An apparatus is described for precise measurement of creep properties in specimens with gauge lengths down to 1·2 cm. An extensometer has been developed which is supported independently of the specimen, and exerts a load on the specimen of less than 5 g. It can thus be used with small non-rigid specimens. The extensometer will detect strains down to 2×10⁻⁶. However, in practice we have found that the smallest strain that can be measured reproducibly is 5×10⁻⁴ with a gauge length of 1·2 cm. The stability is excellent. An adaptation of the system which allows simultaneous measurement of tensile strain and lateral strain during creep is also described. The apparatus was designed for the measurement of anisotropy of creep properties in oriented thermoplastics and reference to such measurements is given. It is however entirely suitable for general application to small specimens.

An apparatus capable of measuring, by direct current methods, very high resistances in the temperature range between 300 K and 4·2 K is described. It is shown that a current of 5×10⁻¹⁶ A can be measured to within an accuracy of 5%.

The apparatus is designed to measure the properties of photodetectors used for the measurement of pulsed laser power and energy. Repetitively pulsed lasers at 0·694, 0·91, 1·06 μm are used to give pulse lengths in the range 5-400 ns. The beam power is varied by a slowly rotating polarizer and, after division, produces photocurrents in both the test cell and a standard monitor cell. The signals are integrated electronically and used to produce Y and X deflections of a cathode ray oscilloscope spot. The spot is brightened after a few microseconds to give a point on a plot of photoelectric charge against pulse energy. Alternatively, the test cell output is time-sampled electronically to give a plot of photocurrent against pulse energy (or power). Departures from linearity of 3% can be detected over a range of 10⁵ in photoelectric charge with better accuracy for smaller ranges.

For the GaAs laser at 0·91 μm a single optical pulse, of approximately 30 ps long, can be generated. This is used for rise-time measurements.

An ultra high-speed camera (with a framing rate of the order of 10⁶ pictures per second) is described. This camera was constructed to observe the transient events occurring during the breaking of electrical contacts. Because of the unpredictable nature of the exact moment of break it was highly desirable to have an instrument capable of producing a large number of photographs. On account of the comparatively low light levels encountered during the breaking of the microscopic molten metal bridge, the system had to be capable of producing the maximum amount of illumination on the film, thus excluding systems in which the beam of light is split into several beams. The camera described consists in principle of two rotating mirror cameras in series, so that the total number of photographs produced is approximately the square of that obtained with conventional rotating mirror cameras.

Spin-lattice relaxation time measurements in solids by decay of the absorption magnetic resonance signal are discribed. The signal decay method is improved by synchronization of the measurements to the trigger mechanism of a computer of average transients.

A constant load creep testing machine has been designed and built for operation under high frequency (1 to 10⁻² S⁻¹) thermal cycling conditions. The apparatus can be operated at loads up to 7 kg with temperatures up to 1000°C, and under vacuum to better than 10 μtorr. A twin creep stage enables differential creep measurements. Preliminary results on foil specimens of Inconel 718 are presented.

An instrument is described which enables the resistivity of metals or metallic alloys to be continuously monitored with the accuracy of 1 part in 10⁴. By using a square current waveform the thermal emf and contact potential contributions are eliminated. The use of integrated circuit operational amplifiers allows for an overall design simplicity and relatively low cost to be achieved.

An electron bombardment oven is described which operates at temperatures of about 2500 K. A calculation of the power requirement is given together with a calculation of the (unstable) current-voltage characteristic. Measurements are in good agreement with these calculations.

A method for measuring the thermal characteristics of natural rocks at low temperature is developed. The advantage of the experimental technique is that both thermal conductivity and thermal diffusivity are obtained from the same run by interpreting two parts of the temperature profiles. The quasi-steady state is used for thermal conductivity, and the thermal diffusivity is obtained from the asymptotic transient state (Fourier transient state).

The present device can be used as an accessory to any Schulz x-ray goniometer. It is connected to the output of the electronic integrator so that the texture diagram normally obtained with the original equipment remains available.

The pole figure is thus obtained in addition, without delay, by drawing a spiral with pens of different colours (10 maximum), each of them corresponding to a specific counting rate range. The levels of the different counting rates at which the colours change can be adjusted at will by the operator.

A simply constructed oil manometer is described which can be used to measure the vapour pressure of liquid helium between temperatures of 4·2 and about 1·5 K. In this manometer the space above the liquid level in the closed arm is occupied by gas not vacuum.

A method is described for the observation of electron spin resonance spectra from transient free radicals that are formed photolytically by the use of a pulsed ultraviolet laser. A fast response esr spectrometer system enables measurements to be made to within 1 μs of the photolysis flash. Alternative methods of operation are described which yield either a complete time profile of the esr spectrum, or a more rapidly obtained spectrum at a single predetermined time after the photolytic flash.

The focal loci of a number of three-element lenses have been measured and compared with calculations made using the design procedure of Heddle. Very good agreement is found provided that only paraxial rays are used.

Very simple instrumentation, using the properties of balanced resistance bridges, can be used to measure directly the polarization of luminescence, emission anisotropy and other parameters. The incorporation of these circuits into a simple manually operated polarization photometer suitable for routine measurements or teaching purposes, and also into a more elaborate automated instrument for research use, is outlined.

An automatic system for the measurement of charge storage in metal-silicon nitride-silicon dioxide-silicon (MNOS) capacitor structures is described. The operation of the system is based on the fact that the capacitance of these structures remains constant at any flat-band voltage. The system speeds up the characterization of MNOS capacitors and allows the study of the transient (ramp) and near steady-state response of these structures.

In real-time holographic interferometry, misregistration of the reconstructed image due to emulsion shrinkage produces a residual initial fringe pattern which must be subtracted from the observed pattern to obtain accurate data on changes that occur in the object. A method of reducing the emulsion shrinkage, thus permitting accurate registration of the image and object with no residual fringes, is described.

An apparatus is described which permits potential profile measurements to be made in large semiconducting samples using pulsed currents of up to 90 A and a maximum voltage of 40 V.

An air-driven turbine, running up to 10⁵ rev min⁻¹ has been developed for high speed optical applications (Q-switching of lasers in particular). A general disadvantage of working with turbines, the high noise level, has been eliminated completely.

A load cell has been developed for the verification of indenter forces in low-load and micro-indentation hardness testers for metals, and hardness testers for rubbers. The elastic element is a triple-beam spring, the deflection under load being measured either electrically or pneumatically. The cell is calibrated in situ by the application of a special weight to provide a known force, and is used as a comparator in verifying the corresponding force of a hardness tester. Methods of use are described and examples of pen recordings are given.

A simple, reliable system, using carbon resistors as level sensors, for maintaining liquid nitrogen in cold traps is described.

The sensitivities of two S1 photocathodes to the laser wavelengths 0·694 μm and 1·06 μm have been measured over a period of a year with 1% relative accuracy. A change of 45% at 1·06 μm occurred in seven weeks during hot weather. The introduction of temperature control and constant biasing reduced the variations after a settling down period. With this form of stabilization the sensitivity probably stays within 10% of the mean at 1·06 μm, and within 5% of the mean at 0·694 μm.

Small thin-walled components which are difficult to construct by conventional techniques may be produced simply and efficiently by electroforming methods. Some of the advantages of construction by electroforming are outlined and a summary is given of the general principles that should be followed. These principles are illustrated by reference to one particular design of calorimeter for specific heat determination.

Modifications and performance are given for a glove box with high purity atmosphere by absorption of H₂O, O₂, N₂ and other impurities.

A small, simple x-ray plane-crystal monochromator used with a horizontally mounted x-ray tube is described. The monochromator is designed to produce a high intensity beam of characteristic radiation in the wavelength range from CrKα to MoKα.

A spectrophotometric cell for the direct observation of chemical reactions at pressures and temperatures in the ranges 1-1000 atm and −30-200°C respectively is described. The combination of appropriate windows and metal spacers facilitates the measurement of either infrared or visible-ultraviolet spectra.

Special features of the design and construction of a small internally heated pressure vessel with a working volume of 30 cm³ are briefly described and an indication is given of its usefulness over a range of research topics. The adaptation of commercially available heating elements simplifies the pressure vessel design and use, and provides an internal furnace with rapid response. The satisfactory performance of all features of the equipment has been established in continual use in more than 100 experiments with a total operating time of 2000 hours.

A bolometer detector for atomic beams is described. It consists of a cage, whose shape ensures nearly complete dissipation of the beam power, and a thermistor attached to it. A convenient calibration procedure with ion beams is provided by simultaneous operation as thermal detector and as Faraday cup. The smallest detectable power is 10⁻⁸ W. Absolute currents of neutral particle beams with energies down to 100 eV have been measured.

An apparatus has been constructed for contact angle measurements between liquid metals and solids, and for measurement of the surface tension of liquid metals at high temperature by the sessile drop method. Measurements may be performed under dynamic vacua better than 1 μtorr to at least 1600°C, or under a reduced pressure of inert gas.