Table of contents

It is shown that the orientation of locus of daylight chromaticities with respect to the Planckian locus may be explained in terms of the dust content and other atmospheric conditions responsible for the absorption features in the long-wavelength part of the daylight spectrum.

The transmission probability for electrons incident on the (1,1,0) face of GaAs activated to negative electron affinity has been calculated for electrons at the same energy within the X and Gamma minima. The two transmission probabilities obtained are found to be both fairly small, suggesting that multiple reflection within the surface space charge region plays an important role in this system.

The primary difficulty in the attempt to observe direct optical excitation of interface states in the Si-insulator system is the good thermal communication between the interface states and the two energy bands.

The photochromic effect in erbium-doped tellurite glass at 479 nm is strongly influenced by the erbium-ion concentration and the presence of other rare-earth oxides. The effect is substantially more pronounced and has a shorter half-life in silicate glasses at erbium-ion concentrations below 1.4*10²¹ cm^-3. The exponential dependence of the lifetime on erbium-ion concentration is compared with that for silicate glasses. The effect in tellurite glass can be enhanced by the addition of 2-4 wt.% ytterbium oxide.

A relation used in the calculation of the dipole correlation function for a rigid rotator by means of the Langevin equation is proved.

A uniform-field magnetic spectrometer, of pole boundaries designed to focus monoenergetic electrons emitted by a point source, without aberrations in a median plane is considered. Electron trajectories in the median plane of the spectrometer are calculated. Electron equations of motion are solved numerically on a computer using the Runge-Kutta method. The dependence of aberrations on the width and strength of the fringe fields and on the equivalent angular divergence of the electron beam is determined. The aberrations place a lower limit on the energy resolution of the spectrometer, which is in the range of 0.005-0.113 eV for the spectrometer geometries investigated at 100 keV and changes very little with beam energy. The structure of dynamic focus is obtained and compared with the previously investigated point source case.

The absorption correction model proposed by Bishop (1974) is evaluated by making use of a large number of published microanalysis results. From a best-fit analysis on these data, constants are derived for use in the expression for the mean mass depth of X-ray generation. Microanalysis results corrected using the Bishop model are compared with those obtained by applying the more widely used Philibert equations (1963). It is shown that Bishop's method combines the best features of both the full Philibert model for elements with Z<12 and the simplified Philibert treatment where Z>or=12. In addition, methods of averaging h, a parameter accounting for the effect of atomic number of absorption, are discussed.

Angle-dependent spectra of neutrons, emitted by a thick lithium target when bombarded with protons in the energy range 1.881-3 MeV, have been evaluated from experimental and theoretical values of the angular distribution of neutrons emitted in the ⁷Li(p,n)⁷Be reaction. The variation of d²N/dE_nd Omega with proton energy at different angles of emission, and with angle of emission for different neutron energies, is presented for the ground and excited state reactions. The angle-integrated neutron spectrum is given for different incidence proton energies.

Micrographs of polished diamond surfaces show that even well polished surfaces are rough on a microscopic scale, with height variations of the order of 5 nm over distances of the same order. The geometric structure of this roughness is not fully resolved but clearly depends on the crystallographic orientation of the polished surfaces. This unusual topography arises from the exceptionally brittle nature of diamond, and correlates with the unusual properties observed in other experiments on the abrasion resistance and friction of diamond.

Theoretical calculations are presented for surface-state loss under the transfer electrodes in three-phase charge-coupled devices, using the published data for N_SS and sigma for the two substrate orientations, namely (100) and (111). Inefficiency values are compared and performance limitations are discussed for these orientations.

The GaAs negative electron affinity photoemission mechanism is studied using the full Bloch wave nature of the incident electron. It is found that the experimentally observed anisotropy between A and B faces is a basic result of the heteropolar nature of the GaAs, contrary to previous interpretations. The physical principles behind the numerical results are illustrated and analysed using a simple method for the scattering which illustrates the origin of the very large anisotropy observed.

A preceding quantum and electronic theory of the metal-semiconductor interface is used to compute several physical quantities of contacts between silicon and various metals. The parameters of the contacts, such as the energy barrier heights, the electric field at the interface, the abscissa of the energy barrier peak, the depletion layer width, the interfacial dipole contribution to the energy barrier, the capacitance built-in-voltage and so on, are computed as functions of the metal work-function, of the silicon Fermi level and of the voltage biasing the contact. The theoretical values obtained prove to be in agreement with the published experimental results.

Electrical measurements on pressure contacts between pairs of semiconductor crystals are reported with a view to understanding the properties of grain-grain contacts in powdered semiconductors. The materials used were Ge and GaAs, their surfaces being prepared chemically and exposed to room atmosphere. It is thus necessary to consider three contributions to the contact resistance-bulk spreading resistance, oxide film resistance and semiconductor surface barrier effects. By studying the contact resistance, shape of current voltage curves and the a.c. impedance, and comparing semiconductor-semiconductor and semiconductor-metal contacts, the following conclusions were reached: (i) for GaAs and light doped n-Ge surface barrier effects are dominant; (ii) for lightly doped p-Ge bulk spreading resistance is probably the controlling factor; (iii) for heavily doped p-Ge and oxide resistance is important.

TSD current studies of thin films (thickness approximately 7000 AA) of iodine-doped polyvinyl-acetate have been made as a function of the polarizing field E_p. Polarized PVAc:I₂ films exhibit two TSD peaks at 327 and 398K with activation energies of 0.19 and 0.27 eV. At 300K, they show relaxation times of 8.40*10² and 6.54*10³ s respectively. The magnitude of the 327K peak increases with the increase of E_p from 0 to 1 kV cm^-1. Above this value of E_p, the peak starts decreasing and ultimately vanishes for E_p>or approximately=7 kV cm^-1. However, the 398K peak continues to increase as E_p increases from 0 to 9 kV cm^-1. Only one TSD peak (at 398K) has been observed in unpolarized PVAc:I₂ films. This has been attributed to the formation of the charge-transfer complexes between iodine and the main molecular chain of PVAc.

The electrical resistivity, temperature coefficient of resistance (TCR) and thermoelectric power are measured on systematically annealed copper films formed by the vacuum evaporation method. From the measured quantities the scattering coefficient and the bulk mean free path of the conduction electrons are calculated. The electron mean free path is found to be 410+or-100 AA. The energy dependence of mean free path U and the energy dependence of Fermi surface area V are calculated from the thermoelectric power measurements as a function of thickness. Both U and V are found to be negative and thickness-dependent.

New observations of the optical and electrical disturbances associated with pre-breakdown events in n-hexane with a point-plane electrode configuration are reported. The sequence of events leading to the previously described black spots or trees at the tip is analysed, and a tentative interpretation accounting for the polarity effects is offered.

A new Monte Carlo approach to the direct simulation of scattering process of a penetrating electron in matter has been attempted. The theoretical stopping powers for elementary excitation processes (conduction-electron, plasmon and L-shell electron excitations) were used instead of Bethe's stopping power equation to describe the energy loss process in the electron penetration. The result obtained for aluminium describes the energy as well as the angular distribution of the transmitted electrons satisfactorily. This approach has also been applied to copper as a preliminary example. The theory describes qualitatively the energy and angular distributions of the transmitted electrons fairly well, but there is some discrepancy between theory and experiment in the energy distribution.

The effect of fibre/matrix interface strength on the tensile strength of the discontinuous fibre composites is studied theoretically. The equation for longitudinal stress distribution in a fibre which has perfect adhesion to the matrix is extended to the case of imperfect adhesion. The effect of fibre/matrix debonding was introduced by using an adhesion parameter, K, describing the extent of slip between the fibre and the matrix, which depended on matrix strain. Three fracture modes were assumed: (i) matrix fracture, (ii) fibre fracture, and (iii) fibre/matrix interface debond. The fracture conditions were derived theoretically. The tensile strength of composites in which fibres of various lengths are randomly distributed, are simply formulated.

The paper outlines three approaches which were used to study the frictional properties of explosive substances. The techniques involved sliding (i) single crystals on single crystals, (ii) single crystals on glass and (iii) glass surfaces over thin films of the explosive which were deposited on glass substrates. The latter technique in conjunction with the adhesion model of friction is shown to be capable of predicting accurately the coefficients of friction in the other two cases within certain ranges of load. Data are also presented on the hardness of certain explosive materials. The paper concludes by speculating the likely effects of temperature and sliding velocity on the friction of single-crystal contacts.