Table of contents

The paper is an introduction to a series of papers to be published in the journal, which will review and discuss the basic principles of instrument science. It surveys the principal features of our present understanding of instrument science from the point of view of the author.

A survey is presented of the most important methods for producing mass or energy spectra with characteristic peaks of single chemical elements in the uppermost monatomic layers of solid surfaces. Some special problems are discussed, such as surface selectivity, surface layer destruction, sensitivity and the possibility of quantitative measurements. The references include some of the most instructive review papers on particular methods and important special topics.

Using an integrated circuit multiplier, the authors have developed a wattmeter capable of measuring watts, VA and VAR in the same instrument. Its power factor range and frequency response together with its cheapness have enabled this instrument to be used in a model power system.

Lithium fluoride windows have been sealed helium-tight to thin-walled cylinders made of copper or gold with lead fluoride. Lead fluoride is stable against ultraviolet radiation. The seals do not introduce undue mechanical stress in the window and support atmospheric pressure difference up to temperatures of at least 300 degrees C. If necessary they can be heated to 400 or 500 degrees C to cure the effect of ultraviolet light on LiF (solarization).

A new method of manufacturing Mollenstedt electron spectrometer entrance slits is described. The new slits have radically improved performance and service life.

The characteristics and performance of a simple directional coupler for radiofrequency applications are described. Measurements on two prototypes show that coupling factors between -4 and -20 dB can be easily obtained in the frequency range 100-500 MHz.

There is an optimum characteristic impedance for the coaxial transmission line in an NMR probe.

A cell design for AC conductance measurements at various temperatures is described. The cell does not require external spring-loaded or screwed supports, permitting the accurate identification of phase transition points irrespective of coincidental large changes in molar volume (e.g. for compounds such as AgI, TlI and organic substances showing phase-mesophase transitions).

The AC signal from a Wien bridge oscillator using an operational amplifier is controlled by negative DC feedback through an opto-isolator. This results in a low-noise DC output related to the value of a resistance (e.g. that of a conductivity cell) forming part of the bridge. Performance is superior to that of conventional circuits using more components; a possible reason is given.

A filtration device for gaseous and liquid media is described; the filter is backed by a perforated support and clamped in a mount which provides protection and can be snapped in and out of a holder in the supply line.

A compact, low-cost atmospheric pressure UV nitrogen laser employing photoionization stabilization techniques is described. The device yields peak output power of 200 kW in subnanosecond pulses. Average output power is 200 mW at a repetition rate of 1.7 kHz.

A simple adsorption apparatus for a quick and reproducible determination of Brunauer-Emmett-Teller (BET) surface areas is described. The justification of proposing this device lies particularly in its flexibility, simplicity of construction and low price. The dimensions and the influence of external variables are discussed quantitatively. An adsorption measurement proceeds as follows: the adsorbate (argon) passes through a capillary tube into the adsorption vessel, the flow being constant. The increase of pressure with time is recorded and compared with the blank (empty adsorption vessel). The blank does not depend on the adsorbent. It takes about one hour to determine a surface area of 100 m². The reproducibility and accuracy are 3% or better for surface areas larger than 10 m². Surface areas down to 1 m² can be measured by a suitable decrease of the argon flow.

A new experimental method is presented by which the density and electrical conductivity of fluids can be measured on the same or closely adjacent samples over wide ranges of temperature and pressure. The emphasis is on isochoric investigation and the variation of conductivity with temperature at constant volume is given directly. An application is given to expanded liquid mercury at temperatures up to 1350 degrees C and pressures up to 0.2 GPa.

The measurement of the variation of the voltage across a silicon p-n junction through which a constant current is flowing is a simple and inexpensive method of measuring the temperature. By linearization of this voltage, direct display of the temperature may be achieved. A circuit is given for operation between -50 and +100 degrees C with an absolute accuracy of 0.1 degrees C.

A pulsed Raman spectrometer is described, based on mode-locked Ar⁺ laser excitation and gated detection using time-amplitude conversion techniques. The equipment has been used to suppress unwanted fluorescence relative to Raman signal, and improvements by a factor of 6 for Rhodamine 6G ( tau =3.9 ns) and acridine orange ( tau =9.5 ns) have been obtained with negligible change in signal-to-noise ratio. These figures are better than those from previous attempts because electronics jitter in timing has been reduced so that the limit is set by the transit time spread in the photomultiplier tube. Large random fluctuations in fluorescence are also significantly reduced, which is of great importance when accurate Raman data are required in fluorescing solutions.

A simple, inexpensive method is proposed to measure the aperture and wire sizes of wire screens for sieves using diffraction, interference and statistical techniques. The method offers substantial savings of time when compared to traditional methods of measuring such screens, while increasing the size of the sampled population by up to four orders of magnitude. Experimental comparisons with conventional methods are presented.

In the viscosity balance method of skin friction measurement an oil film is placed on the surface over which gas is flowing, and moves under the influence of skin friction. The oil thickness variation with time at a fixed point is measured by interferometry. The paper gives a comparison of this method with the well known Preston tube method in conditions (thick, turbulent boundary layer) favourable to the latter. The results show no significant difference between the methods. The Preston tube method is simpler and probably more accurate when conditions are suitable for its use. The advantage of the viscosity balance method is that it is independent of conditions in the boundary layer. It can be used whether the boundary layer is thick or thin, laminar, transitional or turbulent, two- or three-dimensional, on flat or curved surfaces, in compressible or incompressible flow, with or without pressure gradients.

A spectrophotometer cell is described which can be used for fluorescence or absorption measurements of organic solvents or liquids in the UV or visible range. The cell can withstand pressure as high as 20-25*10⁵ Pa, and is suitable for measurements in the temperature range from about 20 degrees C to 230 degrees C. It can also be easily dismantled for cleaning purposes and can be conveniently coupled to a deoxygenation system. A suitable sample cell holder is also described.

The design and operation of a sensitive self-nulling automatic ellipsometer based on the application of Faraday effect modulation are described. A number of desirable features of previously reported instruments are combined in the design. In particular, the use of a phase plate is obviated; and strain birefringence is minimized by the use of benzene in the Faraday cells. Various sources of systematic error are considered and measurements on thin films of gold to test the reliability of the instrument are discussed.

A simple, rapid experimental method is proposed for obtaining the parameters of each MOS device from the profile of the derived curve dC_n/dV_g of the capacitance-voltage characteristic, which is closely correlated to the level of disorder existing in the I-S interfacial region. A simple reading of the experimental graphs provides the information allowing the systematic, instantaneous characterization of the devices at the time of manufacture or immediately after stress (electron irradiation, temperature).

The safe operating area of a power transistor is one of its most important ratings, yet only a few methods exist to evaluate it. Systems which involve testing a sample of devices under controlled breakdown conditions are limited by the time involved and the need for elaborate protection systems. The method described uses the collector cut-off current as a heat sensor to control the temperature of the collector-base junction. This temperature is sampled at a defined repetition rate and is kept constant during the test. The advantage of the system is that is allows description of the safe operating area for direct current as well as for pulsed operation without subjecting the transistor to break-down. Both n-p-n and p-n-p devices in hermetic or plastic packages can be evaluated, and the complete safe-operating-area curve can be described automatically in a short time.

A facility for electron irradiation of metallic resistivity samples is described which allows quasi-continuous irradiation and fast measurement of the residual resistivity. The heat generated in the specimen during irradiation is transferred via the specimen surface to flowing helium gas. Temperatures between 300 and 700K are accessible due to preheating of the gas. A temperature stability of +or-0.1K with the electron beam off and of +or-1K with the beam on could be achieved. The temperature increase of the specimen was measured as a function of electron flux density. From this the heat transfer coefficient could be determined.

A new sample-loading technique is described for emitters covered with microneedles as used in field desorption mass spectrometry. An increase in ion sensitivity of about two orders of magnitude over the standard syringe technique can be obtained with tne new method. It consists essentially in loading the sample only on to a small portion of the needles in front of the counter electrode opposite the field anode.

An earlier system for voltage measurement in the scanning electron microscope (SEM) used a hemispherical retarding field analyser comprising two grids and a solid outer collector. A new electron energy analyser is described which uses two extra grids in place in the solid hemisphere, and thus allows high-energy backscattered primary electrons to escape from the analyser. This modification enables an image of the specimen to be easily obtained and, in conjunction with a modified feedback control loop, reduces the magnitude of the unwanted topographic and compositional contrast signals. The performance of the voltage measurement system using this 'four-grid' analyser is discussed and compared with that obtained from the solid hemisphere analyser.

Observation of the primary beam and scattered electrons is important for centring the electron beam and establishing the optimum conditions in a gas electron diffraction experiment. Electronic control utilizing the beam stop and the rotating sector (see e.g. Schafer 1976) as electron collectors seems to be a suitable method. Such a detecting device, using a centrally friction driven sector which needs no additional contacts, is described.