A number of chalcogenide glasses, representing the complete glass forming regions of the· three binary systems Selenium-Arsenic·, Selenium- Tellurium, and Tellurium-Arsenic were prepared in bulk form. For each of the glasses in each of the three systems, measurement of d.c. conductivity over a large temperature range, and optical absorption also over a large temperature range were completed. The Hall effect was looked for in the glasses from the Tellurium-Arsenic system. Other supporting experiments, namely, space charge limited current measurements in representative glasses from two systems, and density measurement of all glasses were carried out. X-Ray diffraction tests were· used to identify each material as amorphous. A description is given of the material and specimen preparation techniques, as are details of experimentation. A consideration of some current theoretical ideas is shown to point .to a density of states model which should apply to a .large range of amorphous semiconductors. Based upon this model certain computer calculations are made: The temperature dependence, of the density of free carriers in the conduction and valence bands, and the position of the Fermi energy as a function of temperature are determined. The calculations assume, acceptor, and donor, character for the localized states (proposed in the model) associated with the conduction and valence bands respectively. A second group of calculations is made to determine the variation of optical absorption coefficient with incident photon energy, assuming band to band transitions to be the dominant absorption mechanism. A comparison between the calculated and empirically determined functions for the above two cases plus those of the space charge limited current measurement is made so that a number of conclusions can be drawn. These include amongst others, the 'universal' nature of the density of states model, the existence and role of localized states, the nature of the conductivity, i.e. intrinsic or extrinsic, and the validity of the calculations. An anomolous low temperature, conductivity - temperature – electric field, characteristic is found in annealed specimens of certain glasses. This effect is discussed and is thought to be associated with 'hopping conduction'. Other questions concerning, variation of properties with composition, the difference bulk and thin film produced samples, and quality of electrical contacts are raised and discussed.

In this thesis an attempt is made to formulate closed sets of transport equations which are applicable to inhomogeneous and time-dependent situations in semiconductor hot electron transport problems. The basis of the formalism is the Boltzmann Transport Equation from which macroscopic, phenomenological transport . Equations are generated by the Moments Balance Method. The equations describe the behaviour of the electron distribution function in terms of the spatial and time-dependence of its moments. When the behaviour of the electron system is assumed to be typified by that of a finite number of its moments, the components of momentum and energy being the most important members of the set, then closed systems of transport equations are obtained. In the regime of small and slowly-varying density gradients, a theory of electronic diffusion has been developed. For isotropic, single valleys it is possible to derive a set of generalised Einstein relations which express the diffusion coefficients of the electrons in terms of their mobility, differential mobility and temperature. For many valley, ellipsoidal band structures, the results cannot in general be expressed in terms of simple relations such as the generalised Einstein relations although the theory does provide a semi-analytical' framework within which diffusion may be understood in terms of macroscopic quantities. The theory is applied to n-type gallium,arsenide and silicon. The effects of anisotropic electron-phonon scattering and electron-electron scattering in silicon have also been examined in some detail and were found to be small in determining the values of the velocity characteristic and diffusion coefficients. The transport equations derived from the Moment Balance formalism may be modified to form the basic of constitutive equations for the Gunn Effect. These equations are able to give a unified account for the roles of diffusion, intervalley scattering and energy transport in the propagation properties of Gunn Domains, in a manner that is consistent with the Boltzmann Equation. The dynamics of domain propagation are studied. by a simulation technique. It is found that heat currents and intervalley scattering have a crucial effect on domain shapes and propagation velocity.

The electron paramagnetic resonance (E.P.R.) and photosensitivity of silver chloride and silver bromide doped with a number of transition metal ions" has been investigated. The valent state, lattice position and site symmetry of the impurities are discussed in relation to the E.P.R. spectra and the chemical properties of the ions. The E.P.R. spectra of trivalent chromium in AgCl and AgBr are analysed. The principal spectrum at 95K in both halides has orthorhombic symmetry with axes in the < 100> directions. Subsidiary spectra are also observed with tetragonal and orthorhombic symmetries. The possible arrangements of the two charge compensating silver ion vacancies around the trivalent ion are discussed. The principal spectrum is shown to be consistent with a centre in which the Cr3+ ion is associated with a nearest and a next nearest cation vacancy. The lines joining the vacancies to the Cr3+ ion are at an angle of 1350 • Other centres are proposed to explain the subsidiary spectra. The Cr3+ resonances are studied at temperatures up to 500K. The broadening of the fine structure lines at high temperatures is used to . determine the activation energy for vacancy motion around the C~ ion in each of the centres observed. A set of lines which increase in intensity as the sample is warmed above room temperature is assigned to the Cr3+ ion associated with a single next nearest cation vacancy. The spin Hamiltonian parameters of the spectra of Cr3+ in the chloride and the bromide are compared. The substitutional incorporation of the Cr3+ ion is contrasted with the interstitial incorporation of the Fe 3 + ion which has a similar radius. A dewar and cavity for use at 4.2K are described. The E.P.R. spectra of ytterbium, erbium and dysprosium in AgCl are presented. The resonances are assigned to the trivalent state of these ions and the ground states are derived from the experimental g-values. The symmetries of the spectra are used to derive the probable arrangements of vacancies about the rare earth ions. Preliminary investigations of the E.P.R. and optical properties of the remaining rare earths and the 4d and 5d series ions in AgCI are presented. The rare earths other than europium are thought to be present only in the trivalent state in AgCI. The stable valent state is discussed in relation to the chemical properties of the rare earths. The E.P.R. and electrical measurements available to date on the lattice site and vacancy association of transition ions in AgCI and AgBr are summarised. The results are used to show that association with nearest neighbour vacancies is most likely for ions which are relatively large compared with the Ag+ ion. Small impurity ions are shown to be more likely to be associated with next nearest cation vacancies.

Measurements of optical absorption, dielectric loss, photoconductivity and photolysis have been used to investigate the properties of silver chloride containing gold. The gold enters the silver chloride lattice either substitutionaly or as a separate phase of aurous or auric chloride depending on the method of preparation. The most interesting properties are shown by the aurous chloride phase which is produced by annealing in chlorine or nitrogen at 673º K and quenching to room temperature. The temperature and concentration dependences of the optical absorption of the aurous chloride phase indicate that the energy for the formation of a separate phase of aurous chloride approaches a minimum near 673º K. The incorporation of gold sensitises silver chloride for colloid formation. The photolysis of silver chloride is determined by measuring the optical absorption during irradiation. In silver chloride containing substitutional Au or auric chloride as a separate phase, the photolysis occurs mainly on the. surface. The incorporation of a separate phase of aurous chloride results in strong volume sensitivity to both blue and red light. The volume sensitivity is explained in terms of the spectral sensitisation of silver chloride by the aurous chloride. At temperatures above 170ºK irradiation results in the formation of silver and gold colloid and the conversion of aurous chloride to auric chloride. The thermal development which occurs at 423°K is attributed to the thermal decomposition of the aurous chloride phase. The properties of the deep hole and electron traps in silver chloride sensitised with europium have been studied by measuring both the photoconductivity and the thermally stimulated conductivity at low temperatures. The slow growth in the photoconductivity which occurs' on blue irradiation at 130º K is shown to be due to the effects of deep hole trapping and the gradual filling of intrinsic electron traps. Dielectric loss measurements are used to determine the binding energy of cation vacancies to impurity ions and the activation energy for reorientation of cation vacancies about impurity ions in silver chloride and bromide containing chromium and in silver chloride containing europium. These measurements and those of photoconductivity and thermally stimulated conductivity are made on a spectrometer developed for the continuous measurement of complex permittivity.

In this investigation, an attempt is made to correlate magnetic susceptibility and nuclear magnetic resonance properties in a wide variety of metallic systems. Such an approach is adopted in order to obtain greater insight into the atomic and electronic structure of these systems. The magnetic susceptibility of several pure metals in the solid and liquid phases is presented and it is shown that in the liquid at least these can be understood in terms of free interacting conduction electrons. Thus, in these metals the spin contribution to the susceptibility (related to the Knight shift) can be confidently estimated. The measured values of the Knight shifts in these pure liquid metals are then compared with those calculated from the susceptibility and the conduction electron wave function density at the nucleus, found using a pseudopotential method. It is seen that the temperature variations of the shifts are better explained than their absolute values. In view of the greater success of the prediction of fractional changes the approach is extended to the concentration dependence of the shift upon alloying. Experimental results are presented for the 113 Cd and 119 Sn resonance shifts and the magnetic susceptibility in tin-cadmium alloys (a system chosen for its simplicity). These shifts are compared with values calculated using either the pseudopotential method or the more limited partial wave analysis. Good agreement is found and the method of correlation is extended to less simple systems. It is used with success to separate spin and orbital contributions to the shift and susceptibility in the transition metal oxide, V0 2 , but is of more limited use in heavy metal alloys and in those suspected of liquid atomic ordering or of localised magnetic moment formation.

This work develops the semiclassical theory of electrical conduction due to electrons in localized states, and compares the resultant formulae with a variety of experimental data. We begin by using the equivalent electrical network, derived from the phenomenological rate equations, to deduce the dc conductivity of a number of model systems. Percolation arguments are used to derive both the exponent and the prefactor when the dc conductivity is written in the form a = a exp [-sp]. In particular, we derive formulae for the cases when the energies of the electron states are distributed over a very narrow range, a very wide range and an intermediate range. In the first two cases the formulae are in excellent agreement with computer generated data obtained by numerical solutions of Kirchhoff's equations for the equivalent network. Experimental data obtained from studies of a number of systems are analysed, namely, impurity conduction in crystalline germanium and amorphous silicon, the conductivity of evaporated films of amorphous germanium and finally the conductivity due to electrons in an inversion layer formed in a metal-oxide-silicon-field-effecttransistor. In all cases very good agreement is found between experiment and theory. Formulae are also derived for the ac conductivity. Comparison of these formulae with computer data again shows good agreement between theory and experiment. We show how detailed considerations indicate that the ac data obtained from evaporated films of amorphous germanium cannot be due to hopping at the Fermi level, as is normally assumed. In conclusion, this work develops the simple hopping theory which adequately describes experimental data obtained from a variety of systems. Various problems are isolated; which relate to the model adopted rather than any approximation inherent in the deduction of the analytical formulae.

The conditions under which submicroscopic defects can be revealed due to decoration by the precipitation of vacant lattice sites from a supersaturated solution have been investigated in aluminium. Two particular defects , rows of loops along<110> directions end narrow faulted dipoles with their axes along the same direction, were studied in specimens quenched to and deformed at low temperatures and subsequently aged up to room temperature. The primary observations an! that the visibility of these defects is favoured by high purity end a moderate quenching temperature, i.e. by conditions where a moderate supersaturation of vacancies is present after quenching, without the existence of many nuclei for the formation of self-sinks. Thus the conditions under which the faulted dipoles and rows of loops are observed are just those where a decoration phenomenon would be expected. The decoration technique has been used in quenched and deformed single crystals oriented for single slip to investigate the mechanism of formation of these defects. It is suggested that the observed narrow dipoles along <110> grew from similar submicroscopic dipoles produced from sessile jogs on moving screw dislocations. It is then proposed that the observed rows of loops along <ll0> are formed in two ways: from the break-up of these submicroscopic dipoles at an early stage, and/or from the break-up of vacancy platelets formed .long <110> by the same mechanism. This hypothesis is confirmed by the single crystal experiments which show that the faulted dipoles lie along a particular <110> direction. A 90º jog in a screw dislocation can produce a faulted dipole along either of the <110> directions in the slip plane not parallel to its Burgers vector. The observed dipole direction, for a given tensile axis, was always found to coincide with that predicted from the known stress on the jog. The occurrence of a high density of helical dislocations is reported in zone-refined aluminium quenched to temperatures above room temperature and deformation during the quench. The conditions of quenching and deformation indicate that helices are not normally seen in pure metals partly due to the presence of effective competing sinks and partly due to the annihilation of screw dislocations by cross-slip during plastic deformation. The helices observed in aluminium are not circular helices tut consist of straight segments. It is shown that these helices are approximately the geodesics on a right prism with a rhombus base, whose generator is the Burgers vector b and whose faces are the (111) planes containing b. This configuration is attributed to the effect of dislocation core energy, the core energy being lowest if the dislocation lies in a (111) plane containing b. i.e. a glide plane. This observation is used to estimate the ratio of the core energy of a dislocation when it is not on its glide plane and when it is on it. Finally, a sensitive technique for the detection of radiation damage. , by the annihilation of small quenched-in vacancy loops during irradiation, is described. An increase in certain inelastic scattering processes is known to occur under anomalous absorption conditions due to higher electron density at the atom positions. Using the detection technique mentioned above. a similar expected enhancement in displacement damage during anomalous absorption was investigated in the 200 kV electron microscope. Preliminary results suggest that this effect, if present, is small.

When an e1eotromagnetio wave enters a medium having an effective negative resistance, it may be expected to grow spatially. The conditions under which such growth may be observed are examined, and an experimental regime chosen where it should be possible to observe these effects. Suchh observations can throw light not only upon the negative resistance travelling wave amplification process, but also upon the transport process giving rise to the host negative resistance. The experimental work is therefore divided between a study of a new negative differential conductivity process recently discovered in n-Ge and a study of the negative résistancee travelling wave amplification process in GaAs. The diagnostic measurements upon n-Ge provide new data relating to the negative resistance process in that material; data such as the maximum negative slope mobility of 300 cm 2 /V.sec. at 77°K (E / / <100» the threshold electric field for N.D.C. of 2.95KV/cm. (E //<100»), and the ceiling frequency of 5 GHz beyond which N.D.C. disappears, all of which have been subsequently corroborated by other workers. Observations of the emission spectrum from GaAs, when the amplified electromagnetic wave begins to experience round trip gain within the specimen cavity, have allowed some fairly detailed discussion to be undertaken concerning the nature of the emission process, which rely upon careful measurements of the spectral power and line width. Although the maximum pulse power observed of 4mW is low, such observations of emission do provide anew mechanism by which microwave power may be extracted from a suitably biased material having a negative differential conductivity. Finally, attention is directed towards some potentially profitable areas for future work.

Although Low Energy Electron Diffraction (LEED) has become relatively well established aa a technique for the study of' some aspects of' the surfaces of crystalline systems, it is only comparatively recently that close aattention has been paid to the physics of the diffraction process. The work presented in this thesis was therefore carried out in an attempt to elucidate some of these aspects of the process. Firstly, we show that it is not necessary tor the surface under examination to be an atomically perfect crystal surface, or even a macroscopically perfect surface over the entire area sampled by the electron beam, by a consideration of the diffraction patterns produced from faceted metal toils. This shows that provided the ssurface contains small area of good crystal order larger than the coherence area of the electron beam used to produce the diffraction pattern only as little as 10% of the sampled area of surface need be occupied by these areas of good crystalline order to produce no visible degradation of the diffraction pattern. A short discussion of the properties of' an ideal set of experimental data against which theoretical calculations or LEED intensity-energy spectra should be checked is followed by a set of 'experimental results which goes some way towards meeting these criteria. This comprises a complete set of intensity-energy spectra tor the specular LEED beam from a single crystal copper (100) surface in an azimuth close to (110) , covering a large planar area of k-space bounded by the approximate energies 20 and 350eV,and the angles of incidence 6 and 22º , the spectra being taken at 1º intervals, together with a similar set of data tor the (111) surface in a (112) azimuth, the spectra being taken in this case at 2° intervals. The (110) surface of copper proved to be impossible to clean satisfactorily in a UHV environment, and a sshort discussion of its adsorption properties in that environment is given. These sets of spectra demonstrate that although the main features or the intensity-energy spectrum lie close to the kinematical Bragg scattering conditions, the details of the spectra can only be explained by the use of proper dynamical calculations, in accord with the latest theories of LEED. Some correlations between the features of the spectra and the emergence of new non-specular diffraction beams are discussed. Finally, a detailed discussion is presented on the effects of specimen temperature on the intensity-energy spectra obtained from the Cu(100) surface and the Cu(111) surface, the results for the (100) surface being rather more detailed than those for the (111) surface. These results demonstrate that the principal effect of temperature is the diminution in intensity of the diffraction peaks in the intensity-energy spectra, and that this diminution in intensity can be characterised by an effective Debye temperature. As the specimen temperature is changed, these peaks also shift in energy in a non-simple way, which, while not in itself important when comparing experimental results with rigid lattice theoretical spectra, must be taken into account in evaluating the Debye temperature for each peak. However, the width and overall shape of diffraction peaks which are well isolated from other peaks in the spectra appear to be independent of temperature. The detailed study of the measured Debye temperatures and peak shifts tor all the diffraction peaks as a function or the experimental diffraction parameters - energy and crystal orientation - proves them to be highly sensitive to the diffraction conditions. Such results cannot therefore be interpreted in the traditional kinematical manner, and hence cannot be used with confidence in extracting information about surface atom vibrations, surface lattice expansions, etc. The importance of including thermal effects when comparing theory with experiment is emphasised, and a particularly interesting experimental result is discussed in the light of a very recent calculation.

The strong interaction within a nucleon has been the focus of much theoretical and experimental work in nuclear and particle physics. Theorists have been improving lattice QCD calculations and developing quark models that define the inter-quark interactions, and experimentalists have spent years gathering data to support and improve these models. Finding nucleon resonance states provides essential information for the development of these theories and improves our understanding of the excited nucleon spectrum. There are a variety of quark models that have been proposed which each predict a unique resonance spectrum. Currently, these models predict resonances that have not been observed experimentally. It is important to experimentally determine which of these resonances exist. Historically, many of the existing measurements came as a result of nucleon-pion scattering experiments. It has been suggested, however, that some resonances may couple more strongly to other reaction channels, such as the KΛ strangeness reaction channel analysed here. Pseudoscalar meson photoproduction experiments can be used to analyse such a reaction channel. In these experiments, a photon beam is incident on a stationary nucleon target and the reaction products are detected. The polarisation of the recoiling particle can often be determined or measured. In the KΛ channel, the recoiling baryon is a Λ whose polarisation can be obtained without the use of any additional hardware through the self-analysing properties of the hyperon. These experiments can be completely described by four complex amplitudes, which can be accessed experimentally through sixteen polarisation observables. The polarisation observables are bilinear combinations of the amplitudes and as such have nontrivial correlations. They are dependent on the polarisations of the beam, target and recoiling particle. By selecting different polarisations of the beam or target, or by using a combination of polarisations, different observables can be measured. The amplitudes can be obtained once a sufficient selection of observables is determined. Currently, analyses of pseudoscalar meson photoproduction data is done using a binned fitting method. The use of binned fitting inevitably leads to some information from the data being lost. In this thesis, a new analysis method is presented, based on Bayesian statistics. The aim of such an approach is to maximise the information yield from data. An event-by-event likelihood function reduces the information lost through histogram binning. It is shown that the use of a prior distribution in amplitude space can preserve the correlations between observables, also increasing the information yield. It is found that such an analysis programme leads to a significant extraction of information from existing data. It is also found that datasets from different experiments could be concatenated and analysed together using the programme presented in this work, and successfully extract observables. Information on observables to which the experiment is not directly sensitive can be found and visualised graphically. The development of this analysis programme is detailed in this thesis. Previously analysed data from two experiments are analysed using this analysis method, and the results are compared to those obtained in the past. It is shown that this Bayesian approach produces results that are consistent with accepted results and provides information on observables that are not directly measurable by a particular experiment. The data from two experiments is combined and analysed together, and it is shown that the results of the combined analysis are consistent with those obtained through separate analyses.