Table of contents

A silicon surface-barrier detector is used to measure the distribution of secondary electrons, ejected from the ion-secondary electron converter of a Daly detector. It appears that the pulse-height distribution at the output of this detector is affected by electrons which, after initial penetration into the detector, turn back into the vacuum. The response for single electrons is measured with an electron microscope. Assuming a linear response of the detector and a Poisson distribution for the secondary electrons, the pulse-height distribution can be calculated. It appears that these distributions agree very well with the measured ones.

A sealed-off CW waveguide CO₂ laser employing longitudinal electrical excitation has been constructed, using an alumina waveguide formed by hard anodising an Al-2% Mg alloy substrate. The breakdown strength of the unsealed oxide film was in excess of 2 kV. This constructional technique offers promise as a cheap and simple means for the fabrication of rugged waveguide lasers.

A new value of the parameter r_m of the exponential-six potential for neon is derived from the viscosity values of Maitland and Smith (1972) and is employed, in conjunction with the values suggested by Cunha and Laranjeira (1977) for alpha and epsilon /k, to predict the transport properties of neon over a wide temperature range with quite high accuracies.

The dielectric behaviour of water-in-hexadecane microemulsions (potassium oleate being the surfactant and hexanol the cosurfactant) has been investigated for different values of the mass fraction of water p between 20 degrees C and 45 degrees C and over the frequency range 100 kHz-2000 MHz. A dielectric relaxation of the Cole-Cole type was found. Upon increasing the temperature T, the low-frequency relative permittivity epsilon ₁ passes through a maximum whilst the critical frequency nu _c passes through a minimum. The maximum of the epsilon ₁ versus T curve decreases and shifts towards higher temperatures upon decreasing p.

Ion exchange currents (microdischarges) have been observed in short lengths of accelerator tube. The occurrence of these discharges can be related to the trajectories of ions in the tube. High-resolution mass spectra of the negative and positive ion components have been obtained.

Dielectric boundary conditions are applied to the gyrotropic waveguide magnetised along the direction of propagation. The secular equation, which defines the dispersion, is derived in the form of a 4*4 determinant which is used to compute the dispersion curves of a pure YIG guide on a GGG substrate with air above. Computed field profiles permit the classification of the normal modes into two families, one approaching TE characteristics and the other TM. The classification applies only to waveguide materials having a small off-diagonal tensor element delta (or small Faraday rotation).

A direct determination of the temperature dependence of the refractive index of water has been performed in the range -3 degrees to +80 degrees C. In this range delta n/ delta t shows an exponential behaviour. Attempts have been made to obtain a relation between delta n/ delta t and the molecular polarisability of water.

An analogue technique for the approximate solution of the biharmonic equation is used to determine the viscous drag at Reynolds number approaching zero for cylinders falling symmetrically in a liquid between parallel walls. Results obtained show good agreement with numerical solutions, with results by direct experiment and with the work of other authors. Streamlines are obtained with a maximum error of 2% and vorticities and viscous drag forces with a maximum error of approximately 10%.

For pt.VII see ibid., vol.10, p.2423 (1977). The capillary network model has been used to examine the effects of connectivity and radius distribution on the minimum in the transition from Knudsen to Poiseuille flow. It was found that, using formulae for infinitely long capillaries, the minimum persisted in two-dimensional random networks for all the structures examined. When short-tube formulae were used to describe the flow in network elements minima were absent even when the length to (mean) radius ratio was as large as 20. It is concluded that the limitation of diffusion path lengths, rather than network topology, is the significant factor influencing the Knudsen minimum. On the other hand, information about network structure can be obtained from structure factors at low- and high-pressure limits.

The transmission coefficients are calculated for Gamma and L conduction band electrons incident on GaP(111)B negative-electron-affinity surfaces within the abrupt-step model. For large band-bending, the transmission coefficient for Gamma electrons is found to be 0.83 compared with 0.22 for L electrons. These results provide an explanation for the lower quantum yields observed by Escher and Antypas (Appl. Phys. Lett., vol.30, p.314 (1977)) for negative-electron-affinity photocathodes using indirect-gap GaAsP compared with those observed using direct-gap GaAsP.

It is shown that thermoelectric voltage measurements in the mixed-conduction region can be used to determine accurately the extrinsic hole concentration p_77K in Pb_0.8Sn_0.2Te. For the p_77K range, 10¹⁶-10¹⁸ cm^-3, this can be achieved by a thermoelectric voltage measurement over the temperature range 295-395K. From such measurements on bulk crystals the thermoelectric power of Pb_0.8Sn_0.2Te has been determined and the intrinsic carrier density estimated to be 8*10¹⁶ cm^-3 at 295K, with an electron/hole mobility ratio of 2.0.

That component of the terminal current of Schottky diodes due to the high fringing fields at the metal periphery is discussed. Special device structures are described which enable the peripheral current to be measured unambiguously. Reasonable qualitative agreement is obtained with a theoretical estimate of the peripheral current using thermionic and thermionic-field emission theories.

Dielectric dispersion properties of evaporated silicon oxide films sandwiched between Al electrodes are reported for the frequency range from 0.1 Hz to 20 kHz and the results are analysed by comparing them with the ETSC (electrically excited thermally stimulated current) and the DC current-voltage characteristics. It is shown that the total conductance measured by the AC bridge method is constructed of DC and AC conductivities, as expressed by the empirical relation sigma ( omega )= sigma _dc+ sigma _ac( omega ). Only the AC conductivity is related to the dielectric dispersion properties, which are Debye-like. The activation energy and the frequency factor of the relaxation frequency are in good agreement with those deduced from the ETSC results. At a frequency moderately higher than the relaxation frequency, the AC conductivity obeys the empirical relation sigma _ac varies as omega 0.66. The frequency range over which the empirical relation holds is about four decades, which is much narrower than the results of Frost and Jonscher (1975).

The Sondheimer model for electrical conduction in thin films, in the presence of a transverse magnetic field, is generalised to incorporate the Lucas problem for unlike surfaces. The authors' computations for the ratios of thin film conductivity ( sigma ) to bulk conductivity ( sigma ₀) as a function of magnetic field parameter beta and specularity parameters P and Q are found to be logically consistent with both the Sondheimer and Lucas models. A further qualitative extension of their model suggests that oscillations are developed when beta approximately=10k, where k is the ratio of thickness of the film to the mean free path of the electrons, and they are absent for higher and lower values of beta . The results could be further interpreted to give two discrete magnetomorphic spectra with different harmonics in contrast to a single discrete spectrum obtained from the Sondheimer model alone.

This study presents a systematical investigation of the effects of a variable degree of supercooling and of a variable rotation rate on the parameters of (Sm,Y)₃(Fe,Ga)₅O₁₂ magnetic layers grown by LPE. Significant differences with published data of the (Eu,Y) system are revealed. An important discontinuity of the growth kinetics in the 920-980 degrees C temperature range is reflected directly in the behaviour of the distribution coefficients. The analysis shows that the site selectivity of Ga is in the first place dependent on the growth temperature. For Sm this parameter and its distribution coefficient are growth-rate-dependent.

The modulus of elasticity, Poisson's ratio, coefficient of thermal expansion and material fringe value of Araldite CT200 with hardener HT907 have been determined over the temperature range -10 degrees C to 70 degrees C with a view to establishing a suitable working temperature range for photothermoelastic investigations. The greatest variation in the derived photothermoelastic figures of merit of the specimens studied, in both plane stress and plane strain, over the temperature range -5 degrees C to 40 degrees C, was 3.0% and this range is considered appropriate for photothermoelastic work. Cast-to-cast property variations over five samples were of the order +or-4%. The temperature dependence of the refractive indices of this material and of the constituents of an immersion liquid used with photoelastic models and slices (medicinal paraffin and Aroclor 1242) has also been studied.