Table of contents

The methods of protecting and etching surface areas to obtain lateral pattern dimensions of <0.5 mu m to >50 mu m are reviewed. Protection materials, resists, which can be selectively dissolved, i.e. developed, after exposure to UV, electron beam, X-ray or ionic radiation are considered. The techniques available for etching the unprotected surface areas, i.e. liquid chemicals, physical bombardment methods (RF sputtering, ion beams) and recent plasma etching processes are compared.

A photocapacity technique for observing defect centres in semiconducting material is described. It is advantageous in not requiring the formation of a permanent diode junction in the semiconductor.

A simple algorithm is developed for the analysis of Wollaston prism schlieren interferometer data for axisymmetric flow fields. An Abel Fourier transform pair is utilised and a closed form analytical expression is derived whereby the density (or temperature) field can be directly calculated from fringe shift data. The present method thus eliminates any iterative or 'stepping' solutions that were required for all previous techniques. The method is applied to a specified density field and shown to be within 1%, but a previous method is in error by more than 20%. The method is also applied to previous experimental free convection data and shown to be within 2%, but a previous analysis yielded a 6% error. Thus the present method is both much easier to use and more accurate than previous methods.

A small, lightweight furnace for a kappa-phi configuration neutron single-crystal diffractometer is described. Sample temperatures between room temperature and 700K can be attained and maintained to within 0.03K of the set temperature. Temperature gradients of less than 0.05K over the sample are found in the whole temperature region.

A brief review of the existing circuits for input protection of low-current DC amplifiers is followed by a suggestion that GaAsP diodes are suitable for designing protection circuits. Experimental results and the corresponding theory show that these diodes are the best protecting devices applied so far since they are very fast devices and the large energy gap of the GaAsP_xP_1-x semiconductor ensures extremely low leakage currents.

In rheology, torsionally vibrating quartz crystals are in use to determine dynamic shear moduli of liquids in the sonic and ultrasonic frequency range. A computer controlled measuring system using such crystals is described. The main advantages of this system are high measuring speed with respect to the manual AC bridge method and on-line data reduction. As an illustration measurements of a solution of polystyrene in toluene in the 10-100 kHz range are presented.

A description of a new technique-PENKER (Pendulum electronically balanced Knudsen-effusion recoil)-for vapour pressure measurements based on the Knudsen effusion method is given. The determination of vapour pressures by means of the suggested method is based on the recoil momentum of the evaporating species: the displacement of a pendulum, caused by the recoil of the escaping molecular beam, is automatically counteracted by an electromagnetic compensation system which is electronically controlled. The suggested method has clear advantages over the TORKER technique. It shows better mechanical stability, no oscillations, symmetrical furnace-cell configurations are possible, and there are no problems with electromagnetically induced cell rotations.

A simple, economic but accurate device is described which enables the double integration of curves to be obtained.

In order to follow long-lasting kinetics (up to several weeks) a microcomputer-based system was organised around a low-cost spectrophotometer. The system makes effective use of available building blocks and follows simultaneously up to three independent samples, at different or equal temperatures. At programmable time intervals (e.g. equidistant on a log scale), temperature and optical absorbance at programmable wavelengths are acquired, printed, plotted and recorded for each of the three samples. Availability of both assembly and BASIC languages provides the system with great programming flexibility for both I/O control and complex computation for on-line analysis of experimental data. The system is completely backed-up against power failures by battery.

Describes the development of a simple CW CO₂ waveguide laser with a watt level output power at more than 70 emission lines. It employs a Pyrex guide with improved cooling and a resonator with an intracavity lens. Its power and stability performance have been tested in an optoacoustic saturation spectroscopy experiment.

Describes the measurements made with differential particle detectors in a laboratory 'ionospheric' plasma. The plasma in the ionospheric plasma facility of the Centre de Recherches en Physique de l'Environment Terrestre et Planetaire (CRPE) plasma physics group at Orleans, France, was investigated with suprathermal plasma analysers (SPAs) identical to those flown by the Mullard Space Sci. Laboratory (MSSL) on the ESA GEOS satellites.

A reference interferometer based on an earlier design has been developed, in which a reference wedge is rotated by a direct-drive position servo-system. The reference interferometer is used to set the spacing of Fabry-Perot interferometer plates in a narrow bandwidth optical filter. The instrument is designed to contain a nitrogen atmosphere and to operate under adverse conditions.

Describes a new spectrometer for investigation of paramagnetic gases in the millimeter range (50 to 120 GHz) using the resonant Faraday effect and circular dichroism induced by a longitudinal magnetic field. The interaction between molecules and a linearly polarised resonance radiation produces a change in the polarisation of the transmitted light. A heterodyne detector is used to observe this modification on a black background by monitoring the transmitted wave through a crossed polariser. Possibilities of the spectrometer are discussed, especially its sensitivity (about 7*10^-11 mm^-1 at 60 GHz), and its application to the measurement of absolute line intensity are pointed out. Typical results on O₂ molecules and SO free radicals both in linear and nonlinear spectroscopy are given.

A Johann-type reflection spectrometer with a wavelength resolution of 15000 at 0.229 nm (CrK_alpha ) is described. The diffracting crystal is a (310)-quartz plate with 50*30 mm² total and useful area, bent to a radius of 1380 mm. The use of a novel, simple crystal bending device and of a position-sensitive proportional counter makes this instrument interesting also for other domains of X-ray spectroscopy. Results of extended calculations on diffraction properties of quartz as a function of diffraction plane index and wavelength are also presented.

Describes a fully automated pendulum balance for measurements of magnetic susceptibility between room temperature and 1700 degrees C. It is especially designed for investigations on liquid metals and alloys. A novel system for the control of the pendulum position gives the apparatus a high reproducibility and reliability. The crucible containing the molten sample can be manufactured from almost any material, e.g. Al₂O₃, BeO, W.

An electronic circuit which measures parameters such as peak over-pressure, positive duration and impulse simultaneously and displays them in digital form, is described.

A method is demonstrated for measuring small departures from true cylindricity of a tube by using it as a microwave cavity and then applying a perturbation method to the observed resonant frequencies. The technique is also applicable to other geometries.

A simple and inexpensive instrument for deep level transient spectroscopy (DLTS) is described. When used with a pulse generator and a capacitance meter, it permits studies of defects in semiconductor junctions. A detection limit N_T/N_D of about 10^-5 is obtained, where N_T is the concentration of the deep level impurity and N_D that of the shallow level dopant. The rate window is easy to change over more than three decades for determination of activation energies. Additional features are included for measurement of carrier capture cross sections. Examples of measurements are given.

A data-only interface between the microcomputer and waveform recorder is described. Details of the necessary hardware and software are given. The software reads the 8100 memory and performs signal averaging. This system is compared with other signal-averaging systems.

Describes a computer-controlled system capable of measuring a wide range of semiconductor resistivities and Hall coefficients, as well as their dependences upon temperature (4.2-600K), magnetic field (0-1.8 T), and monochromatic light irradiation (up to 2*10¹⁸ photons cm^-2 s^-1, held constant over the range 0.76-2.5 mu m). With the use of a guarded cable configuration, the response time for a 10¹³ Omega sample is less than 10 s. The system uses commercial components whenever possible and is built around a PDP 11-03 computer with a standard IEEE-488 I/O bus. The only important noncommercial piece of apparatus used is a wavelength scan and intensity control system for a popular, ¹/₄ m, high intensity monochromator.

A two-dimensional angular correlation spectrometer based on position sensitive Anger camera detectors is described. The specification of the machine includes an angular resolution of 0.65 mrad FWHM by 0.65 mrad FWHM over an angular field of order 21*21 mrad² and an exceptionally high efficiency for counting coincidence events. The spectrometer design is discussed in the light of the basic measurement problem and its performance is illustrated with the aid of the results of explicit test measurements and some representative results.

The apparatus described is built on a fully pneumatic system with bearings, thrust bearings and impulse system. It needs only one energy source-compressed air. Its use and fabrication are especially easy in any laboratory with a small mechanical workshop. The results obtained for calibration and visualisation on a ventilator with constant rotation speed or on a disc of variable speed are easy to reproduce and of great interest for later use with other rotating machines.

A nanosecond laser spectrophotometer with a tunable dye laser probe pulse continuously delayed up to about 100 ns with respect to the nitrogen laser pump pulse is described. A time scale synchronisation method for reconstruction of the time-resolved transient absorption spectra is employed. Transient spectra of anthracene in acetonitrile from 415 to 630 nm are given as examples.

Measurements of the discharge V-I characteristics of a pulsed HF laser initiated by a Blumlein circuit indicate that the discharge is attachment dominated operating at a reduced field magnitude E/N constant with the normalised current density J/N. A simple model of the combined circuit-discharge network is developed which is capable of accurately describing the pressure dependence of peak current and discharge resistance and the conditions to be verified for an efficient energy transfer into the laser plasma. Experimental results are given that strongly support the model used for the analysis, which therefore should prove useful in the design and optimisation of current-pulse generation networks.

The system described is built around a very accurate positioner into which a sensitive transducer and the object of analysis is mounted. The properties of the applied magnetoresistive transducer are described. This transducer, a very narrow permalloy strip placed at the edge of a glass substratum, can be used to measure both components of the field distribution. The analysis of the measured results can be accomplished with the help of a computer simulation of the transducer response curves. The performance of the system is demonstrated by measurements on a number of ferrite heads and conclusions about the so called 'dead layer'-structures on these heads are given.

An adaptation of a TI 59 programmable calculator to a home-made digital system, described earlier by the authors (see ibid., vol.13, p.346, March 1980), is described. Further valuable features of the system have been established: (i) automatic evaluation of delta values together with information about their precision and the sample pressure in the inlet system, (ii) on-line correction of biases and calculation of absolute delta values, (iii) increase in analytical efficiency to over 30 samples daily with a routine precision of 0.05 per mil. Details of the new modifications, the calculator program and instrumental precision are included.