Table of contents

It is shown that vertical-junction solar cells can always be designed to have larger open circuit voltages than comparable horizontal-junction cells, in contrast to the conclusions of a recent analysis, by Dhariwal et al. (1975).

Water can induce a high-temperature thermally stimulated current peak (295 degrees C at 1 degrees C s^-1) in G163 PTFE. This current is produced by the movement of positive charge carriers. The peak is eliminated by annealing at 320 degrees C for 3 h but gradually reappears over many weeks. It appears to be due to water being both adsorbed and absorbed.

The approximate coupling efficiency equation for prism-film couplers in planar optical waveguides gives incorrect results under certain conditions. Using a rectangular-profile and a Gaussian-profile beam separately, the author presents an exact ray-optical analysis of the coupling efficiency especially when N is small and T is large. The Goos-Haenchen effect is discussed. Experimental results are compared with theoretical ones using both the exact and approximate coupling equations.

A thermodynamical calculation scheme is worked out to study radial and axial transport of tungsten in a halogen incandescent lamp. The approximations of a common diffusion coefficient for all gaseous components and local chemical equilibrium are used. Non-blackening is connected to an inequality forbidding deposition of tungsten onto the bulb wall. Chemical attack or growth of a given part of the coil is characterized by the second derivative of the global pressure of tungsten along the coil. The gettering effect of carbon on oxygen is shown to be limited by partial deposition of carbon as well as the formation of CO₂ that decomposes at the coil releasing active oxygen.

A mechanism is proposed whereby dust is removed from a flat deposit by an airflow; it involves the interaction of the laminar sub-layer of the boundary layer with individual particles. Results of experiments on an isolated deposit are presented to show how the mass of dust removed with the airflow velocity and with time. Results obtained with a continuous deposit show that erosion varies not only with time but also with distance along the deposit; this suggests that saltation of larger grains may be taking place.

Pieranski and Guyon (1973) describe a shear-induced instability in a nematic liquid crystal when the anisotropic axis is initially normal to the plane of shear, and present a simple calculation which supports their experimental results. A more detailed theoretical analysis of the stability of this flow arrangement to certain time-dependent perturbations is given, and the theory predicts the onset of an instability at a critical shear rate not greatly different from that calculated by Pieranski and Guyon, and therefore in good agreement with their experimental observations.

The BCC-to-FCC phase transformation which occurs in alloys of the copper-zinc system of composition 37-43 at.% zinc, when they are cold-worked after quenching, has been studied by analysing the X-ray powder diffraction line broadening and the peak shifts which occur as the transformation progresses. The major part of the particle size broadening is due to the effects of stacking faults. Peak shifts are due to stacking faults and macrostresses. Estimates of the dislocation densities and stacking fault energies are given for the alloys investigated. The results are compared with those of other workers.

Capacitance-voltage characteristics have been obtained for Schottky barrier diodes, formed on polished surfaces of natural p-type semiconducting diamond, before and after illumination with radiation capable of neutralizing ionized donors in the depletion layer. Plots of 1/C² versus V for the two cases have yielded values for both the acceptor concentration N_A and the donor concentration N_D. Comparison of these data with those obtained from Hall effect measurements indicate that the latter overestimate the value of N_A-N_D by almost a factor of 2. The boron concentration has been determined in approximately the same surface layer as the capacitance measurements by detecting the alpha -particles emitted during irradiation with 700 keV protons using the reaction ¹¹B(p, alpha ₁)⁸Be* to 2 alpha ₂. A quantitative correlation has been obtained between the boron and acceptor concentrations.

Rutherford backscattering of energetic ⁴He⁺ ions has been used to study the composition and depth profile of silicide layers formed when thin nickel films evaporated on (111) and (100) silicon surfaces are heated in a nitrogen-hydrogen ambient. In the temperature range 297 to 430 degrees C two phases are seen to form sequentially. The growth of the first phase, Ni₂Si, is parabolic with time, whilst the second, NiSi, grows linearly with time. The simultaneous presence of both diffusion and reaction-rate-limiting mechanisms is implied by the parabolic and linear growth laws. An investigation of the electrical characteristics of diodes which were metallized and heat-treated simultaneously shows little change in the barrier height.

The variation in the film conduction during vapour deposition in UHV reflects the different growth stages: discontinuous structure; formation of stable metallic paths; and metallic continuous structure. If the deposition is stopped with R_{Square Operator} 1 M Omega the resulting film is discontinuous with a temperature-dependent conduction activation energy varying between 2 and 70 MeV, and a surface coverage f of typically 50%. When the resistance has decreased to less than 1 M Omega Square Operator ^-1 the film exhibits metallic conductance with f>or=75%. The resistance change in the discontinuous stage has been explained by a model where the applied field stretches the particles causing a decrease in the tunnelling length and making the films metallic continuous at an average thickness of 53+or-13 AA.

The surface charge distributions resulting from the partial discharges in a perspex-air insulation system have been measured and subjected to statistical analyses. The charge patterns cannot be correlated either with the erosion tracks or the puncture locations. Substantial changes in the distribution of surface charges occur before and after puncture.

The acousto-optic interaction in the Raman-Nath regime was used to study sound waves propagating in the principal planes of piezoelectric lithium niobate. Complete cuts of the inverse phase velocity surfaces were obtained for surface waves on reflection and for three bulk waves and one surface wave on transmission through the surface acoustic wave (SAW) propagation surface. It is also shown how simple diffraction can be used to measure the group velocity direction and the electro-mechanical coupling coefficient for surface waves. A modified schlieren technique was used to visualize bulk waves generated by a finite transducer and to observe shear waves reflecting and mode converting to longitudinal waves at an interface.

A detailed study has been made of the effect of cooling rate on (a) the thermoluminescent sensitivity of TLD-100 and Harshaw pure LiF, and (b) the Mg⁺⁺V associated pair concentration in TLD-100. The thermoluminescence of TLD-100 at the lower cooling rates appears to be strongly affected by precipitation of a second phase, whereas changes at higher cooling rates appear to be a consequence of Mg⁺⁺V clustering. In particular there is evidence to show that peaks II and III are probably associated with the same trapping centre and that this is the Mg⁺⁺V pair.

The construction of a parallel-plate electrostatic energy-analyser equipped with a channel-plate focal-plane detector and a novel acceleration electrode assembly has allowed the intrinsic energy losses of field-evaporated ions to be measured for the first time, under effectively steady-state conditions. It is found that the ions have energy losses which are considerably less than originally predicted by the Lucas plasmon-loss theory (1971); the losses are shown to be of the same order as those expected from the charge-exchange or image-potential theories of field evaporation, but exact numerical agreement is not easily attained at present.

The DC electrical conductivity of composites made from Epikote 828 resin filled with Cu, Ag, Au, Al, Sn, Pb, bronze and stainless steel powders has been measured at room temperature. Apart from specimens containing Al and stainless steel, all others with a volume concentration of metal of about 20% of more showed switching behaviour. The normally high resistance of the composite was reduced to a few hundred ohms when a potential of about 100 V was applied across the sample and this low resistance was retained as the potential was reduced to zero. The high-resistance state could be recovered by passing a current of a few hundred mA through the sample.

The potential engineering advantages of two-part core/sheath reinforcing elements in which core fracture is prevented by means of a stress-controlled decoupling mechanism are outlined. Studies have been made of the longitudinal stress distributions occurring between core and sheath in various loading conditions. A very significant enhancement of the core longitudinal stiffness is observed when it is contained within the tube. It is suggested that this is due to the large residual lateral strains developed in the two parts of the reinforcing member coupled with the very large effective Poisson's ratio of the core.

The stress intensity term is interpreted to be the volume of activation for the submicroscopic crack formation which initiates fracture.

The deformation and fracture of poly(ethylene terephthalate) (PET) film was studied as a function of draw ratio, birefringence and degree of crystallinity. Tear tests were employed to determine the fracture surface energy ( gamma ) of PET in the isotropic and anisotropic, unannealed and annealed states. It was found that for tearing parallel to the draw direction, the value of gamma for unannealed PET decreased by a factor of 13 with increasing orientation. For the unoriented material and at draw ratios greater than about 2.5, the effect of annealing was to reduce the value of gamma . No definite effect was established in the intermediate range. These results suggest that an increase in the degree of crystallinity reduces the value of gamma .

The ultrasonic particle displacement and stress amplitude along a solid body of revolution with a circular profile is obtained. In the calculation, a hyperbolic cosine function is approximated to the arc of circle profile, and it is shown that there is negligible error in this approximation. The results are used in the design of specimens for ultrasonic fatigue testing.

A method for ultrasonic fatigue testing of specimens much shorter than the testing-frequency half-wavelength of the material is described. A bimetallic unit is used in which the specimen under test can have practically any shape. A theoretical calibration of stress is given for specimens with circular profiles and it is shown that knowledge of the acoustic parameters of the material under test is not required for this calibration. The method is particularly useful for the testing of materials which are only available in short lengths, and it has the added advantage of providing large stress magnification factors.