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Polymers have ideal bulk properties for many applications. However, adhesion to many polymers is poor without surface pretreatment. This can result, for example, in peeling paint and printing, adhesive joint failure and bio-incompatibility. In applications such as painting, printing, adhesive bonding and biocompatibility, various cleaning or surface chemical modifications may be employed. A commodity polymer where pretreatment IS sometimes needed is polystyrene. This project investigated, in detail, the effects of a novel method of modification namely mediated electrochemical oxidation (MEO), as a mode of surface modification on polystyrene and a comparison was made with other polymers. The resulting modification was investigated using a range of surface analysis techniques to obtain complementary information. These included; X-ray photoelectron spectroscopy, contact angles, static secondary ion mass spectrometry, atomic force microscopy, chemical derivatisation, scanning electron microscopy, attenuated total reflection Fourier Transform infrared spectroscopy and composite lap shear joint testing. It has been shown that MEO modifies the surface of polystyrene introduced oxygen mainly as hydroxyl groups, and a small number of carbonyl groups, that are positioned only on the backbone hydrocarbon chain. This modification improved adhesion, was stable and samples could be stored in aqueous media. The resulting hydroxylation was further derivatised using an - amino acid to provide a specialised surface. This was very different from the multiple oxygen functionalities introduced in the comparison studies by UV/ozone and plasma treatments.

Electrical conduction properties of thin co-evaporated SiO/B2C3 (borosilicate) films in the form of sandwich structures of M-SiO B203 –M (diode) and M-SiOx/B2O3-N-SiOx/B2O3-M (triode) have been studied. Diode and triode systems show electroforming effects and subsequently electron emission, voltage-controlled negative resistance, electroluminescence, and switching phenomena. Previous work in this field is reviewed. By making certain modifications to the filamentary conduction theory of Dearnaley, the time dependence of the circulating current and electron emission may be explained. The theory is also supported by topographical studies 0 of the structures in a scanning electron microscope. The voltage breakdown strength in borosilicate glasses is found to be very high, in particular for devices which carry aluminium electrodes in comparison to those carry silver, copper or gold electrodes. Breakdown depends on both the electrode and insulating materials and on the insulator thickness. Since the circulating current in borosilicate films which carry noble metal electrodes such as Ag or Au, is much higher than those which carry reactive electrode materials such-ac Al, i. e. the device temperature is very high (400-700 oC), and these have led us to the conclusion that this type of breakdown in fact is at least partly thermal in origin. Experiments on triode systems yielded extremely interesting results such as dependence of potential distribution on the forming direction, non-uniformity of conducting filaments, and finally controllability of the circulating and emission currents by the grid voltage. The films deposited between Al electrodes, show evidence of electroforming and of electron emission. Formed devices also showed a region of differential negative resistance at high voltages. These devices could withstand high voltages and give improved emission efficiency. Diode and triode systems having thickness greater than 10,000 R were formed. The effects of electrode materials, by using combinations of Al, Ag and Cu in triode electrodes were studied. Peak voltage and peak current showed a dependence on the electrode materials. Scanning electron microscope observations of films showed localised effects at the electrode surfaces and physical changes in the dielectric structure, while the sandwich structures were being operated as electron emitters. Consequently electroforming is believed more likely to take place 4y means of the production of filaments of mostly electrode and insulator materials by diffusion and electrolytic processes. Since borosilicate films show a high sensitivity to water vapour for concentrations of B2O3 greater than 50%, a 30% concentration of B2O3 was found experimentally suitable to work with, and therefore all devices made use of 70% SiOx and 30%. B2O3 insulating films.

This study is concerned with the problem of calculating electronic band structures of solids from a priori potentials, in particular potentials which are not spherically symmetric about the centre of the Wigner-Seitz cell. Band structure calculations are performed using the Cellular Method, and the adaptation of this method to deal with non-spherical potentials is a major concern of this work. A review is presented of the work so far published on non-spherical potentials in the OPW, APW and KKR methods, and the ideas to be built on in the present work are considered more carefully. The details of the Cellular Method are expounded, paying particular attention to the stages which require modification in the non-spherical treatment. The superposition method introduced by Mattheiss, and by which many of the potentials used in band structure calculations are constructed from the appropriate atomic potentials, is extended to include non-spherical terms, and a general expression for the potential is obtained for the f.c.c. lattice. This expression takes the form of an expansion in spherical harmonics correctly orientated with respect to the crystal axes. We then proceed to consider the non-spherical corrections introduced when the potential used in the Cellular Method is the true potential within the whole circumscribing sphere of the Wigner-Seitz cell, which overlaps the neighbouring cells. These non-spherical corrections to the potential are non-zero in the region between the inscribed and circumscribing spheres of the cell, and therefore affect the radial wave functions over this region - the very region over which their values are required in order to perform the boundary condition fitting of the Cellular Method. Methods are developed for the treatment of general non-spherical potentials which can be written in terms of a reasonably convergent expansion in spherical harmonics. First of all a rigorous treatment, in v;hich it is found necessary to label the radial functions with two sets of angular momentum quantum numbers is developed. This treatment involves the calculation of many more radial functions than the usual spherical treatment and the form of trial function produced necessitates certain changes and generalisations of the Cellular Method, It is, therefore, important to look for possible approximations which might be employed to facilitate a quicker, and more simple solution to the problem Two such methods are explored. A suite of computer programs is set up to deal with the calculations necessary to employ the methods developed, and these programs are described in some detail. The methods are then applied to the non-spherical correction arising from the strict division of the potential field into cells mentioned above, using the potential of Chodorow for f.c.c. copper as a basis. Various tests of the methods developed are undertaken. An iterative approach to the problem, much quicker to compute than the rigorous treatment, is shown to give results in excellent agreement with those of the rigorous" treatment for the case considered, and is certainly worthy of further investigation in cases where the non-spherical corrections are larger. Both of these treatments are shown to retain adequate convergence of the cellular expansion. The corrections due to the newly proposed potential scheme are shown to be often negligible, and never more than 0,008 Rydbergs, for the lower lying band energies at the symmetry points in k-space calculated.

Epitaxial rare earth films and superlattices grown by molecular beam epitaxy, MBE, can be designed to investigate theoretical predictions of the magnetic and electronic properties of the metals. These investigations ideally require smooth epitaxial layers with atomically flat interfaces and therefore the microstructure of selected epitaxial rare earth systems has been characterised by a combination of techniques. These systems were grown on a (110) niobium || (112‾0) sapphire substrate. Because the crystallographic quality of the subsequent layers is influenced by the quality of the substrate, the niobium-sapphire interface was studied with transmission electron microscopy, TEM, and high resolution electron microscopy, HREM, to identify uniquely the misfit dislocation network. Conventional TEM specimen preparation techniques were inappropriate for the preparation of metallic foils, and so appropriate specimen preparation techniques were developed. HREM was used to characterise the strain relief mechanisms within a partially relaxed holmium/yttrium superlattice. Rare earth hydrides are also of interest because of the ability of some rare earths to absorb up to three hydrogen (H) atoms per rare earth atom. Loading between RH₂ (R - rare earth) and RH₃ is completely reversible and the system undergoes a metal-insulator transition. A film subjected to such H-loading is observed to switch from mirror-like to transparent. TEM specimens of RH₂ (R = Ho, Y) were characterised and the structural changes that occur during H-loading were investigated using controlled environment TEM and a combination of scanning probe techniques. The applicability of electron diffraction for the characterisation of structures containing hydrogen is presented. Finally single crystal neutron diffraction techniques have been applied to epitaxial samples of HoD₂ to probe the effect of the addition of extra deuterium atoms on the magnetic properties.

This thesis describes some Raman scattering experiments on solids in the temperature range 1.8 - 300°K. The three main problems studied were : (a) the phase transitions in PrAlO₃; (b) the Jahn-teller phase transitions in the series of mixed crystals Tb_cGd_1-cVO₄; (c) the Two-Magnon excitations in the mixed crystals Mn_1-cZn_cF₂. Chapter 2. reviews the theory of phonons, magnons (both ferromagnetic and anti-ferromagnetic) and electronic excitations in solids. The mechanisms which cause light scattering from these excitations are discussed, together with the selection rules for Raman scattering. Chapter 3- describes the experimental techniques that were used. The spectra were excited using an Argon-ion laser. A 90° scattering geometry was employed, and the spectra analysed by a double-grating spectrometer. Detection was by means of a photomultiplier tube used in the pulse-counting mode. The sample was mounted in a conventional helium cryostat. Optical birefringence was used to study Tb_cGd_1-cVO₄; the experimental arrangement is described in this chapter. A superconducting magnet dewar was built in this laboratory for magneto-optical work, and is briefly described in Chapter 3. In Chapter 4. some experiments on PrAlO₃ are discussed, The Raman spectra were measured between 4.2 and 300°K and used to study the low temperature phase transitions at 146 and 196°K. The Hainan data were compared with the predictions of a theoretical model of PrAlO₃, based on molecular field theory; this model was found to give a reasonable qualitative description of the observed behaviour. It was concluded that below 99°K PrAlO₃ has only a very small deviation from tetragonal symmetry. Optical fluorescence and EPR experiments reinforce this conclusion. In the vicinity of the phase transition at 146°K the anomalous behaviour of two of the low frequency Raman lines was found to be due to coupling between an electronic level of Pr³⁺ and a phonon. Chapter 5. deals with some Raman and optical birefringence studies on the series of mixed crystals Tb_cGd_1-cVO₄. The Jahn-Teller phase transition temperatures were measured usinf" the optical birefringence method and found to be in good agreement with the predictions of Molecular Field theory. In addition, this theory predicted a unique type of phase transition for a certain range of c, and this was observed in the crystals with c = 0.365. On cooling, these crystals underwent a Jahn-Teller phase transition to a lower symmetry at 8.5±0.5°K; further cooling resulted in a second phase transition at 2.3±0.1°K temperature at which the crystals reverted to their original high-temperature symmetry. These crystals therefore had a high and low- temperature phase of the same symmetry, with an intermediate phase of lower symmetry. Raman scattering was used to measure the E_g phonon splittings below the transition temperature in the mixed crystals as a function of temperature. Comparison of experiment with predictions of a Molecular Field theory showed that this theory gave an excellent description of the behaviour of the system. This indicated that the electron-phonon interaction in the mixed crystals was of long range. Chapter 6. describes the results of some Two-Magnon Raman scattering experiments on Mn_1-cZn_cF₂ alloys. The peak-frequencies and linewidths of the Two-Magnon lines at helium temperature were measured over the whole concentration range. These were compared with the predictions of two different theories. The first theory involved calculation of the first three moments of the Magnon lineshape, while the second was a cluster-model theory based on the Ising model. Both theories gave reasonable agreement with the experimental results. The phonon frequencies were also measured at low temperature as a function of c. The E_g phonon exhibited two-mode behaviour for c<0.25, and one-mode behaviour for the rest of the concentration range. This anomaly was attributed to a local mode effect. Appendix 1. gives a brief description of some attempts to subtract the background Rayleigh scattering from Magnon spectra in order to measure the true lineshape. The experiments failed, but had they been successful, would have enabled a direct comparison between experimentally and theoretically determined moments to be made. Finally, Appendix 2. describes some phonon and electronic Raman scattering experiments on HoF₃, and TbF₃. The frequencies of all but two of the Reman active phonons were measured in both materials. At low temperatures electronic transitions between the levels of the ground-state multiplets of the Ho³⁺ and Tb³⁺ were observed. A level scheme for some of the electronic levels within the ⁵I₈ multiplet of Ho³⁺ was derived from these results, but the results for Tb³⁺ have so far proved difficult to interpret.

Conventional strong-beam imaging techniques have been widely applied in the study of crystal defects, the main advantage being the high intensity of the images which reduces photographic exposure times to a few seconds at most, thus avoiding problems of drift and contamination. However, such images have the disadvantage of not being related in any simple way to the defect geometry, and they are relatively insensitive to small changes in the strain field. The width of a peak from a dislocation can be ~100 &Aring; for 100keV electrons, and so the study of dislocations separated by the much smaller distances that are found in dissociated dislocations or faulted dipoles in pure metals is very difficult, even with careful computed image matching techniques. The weak-beam technique of electron microscopy (Cockayne, Ray and Whelan 1969) overcomes this problem by tilting the specimen so that only the highly-strained regions near dislocation cores contribute to the final image; narrow (~15 &Aring;) , relatively intense peaks which lie close to the defects are obtained by this approach, and such images are ideal for investigating closely-spaced dislocations. This thesis describes the study of various dislocation geometries by the weak-beam technique and the calculation of equivalent images. Chapter 1 reviews the theories of electron diffraction which are needed both to understand the properties of weak-beam images and also to compute the images required for comparison with experimental micrographs. Such calculations require a knowledge of the displacement field of a dislocation, and in most cases if any useful information is to be derived from weak-beam observations of dislocation networks (e.g. the stacking-fault energy) the stress fields are also required. Chapter 2. discusses the anisotropic theory of infinite straight dislocations as given by Stroh (1958); the only defects considered here are those for which this infinite straight approximation is reasonable, e.g. the partial dislocations in a faulted dipole, or the dissociated straight edge of a very large loop. Chapter 3 applies the weak-beam technique to the study of faulted dipoles in copper and it is shown that such images define the dipole geometry with a greater accuracy than hitherto possible using conventional techniques. Previous strong-beam studies of faulted dipoles are also discussed. An upper limit for the stacking-fault energy of copper of &gamma;_max = 47 &plusmn; 8 erg cm^-2 is obtained. It is concluded that similar studies are potentially very useful for estimating the stacking-fault energy of materials for which &gamma; and the elastic constants are such that the dissociation of single dislocations cannot be resolved. The rest of the thesis considers the effect that a finite divergence in the illuminating beam of electrons has on weak-beam images. The oscillatory effects dependent on depth and thickness which are often observed in weak-beam image computations when assuming a parallel beam can be damped or removed altogether when calculations are performed which make allowance for a finite divergence. Chapter 4 considers divergent illumination from a theoretical point of view and it is shown that effective damping of the depth and thickness oscillations should occur if the defect is greater than a distance d = ¹&frasl;_2&Delta;s from either surface, where &Delta;s = g&Delta;&theta; is the spread in the deviation parameter s introduced by a finite divergence &Delta;&theta; in the incident beam. Chapter 5 calculates the images of single undissociated and dissociated dislocations in copper including the effect of a finite beam divergence. The predictions of Chapter 4 concerning the damping of the oscillations and the above formula for d are shown to be valid in these cases. The effect of anisotropy on the symmetry of images of dissociated dislocations is considered and the results of the image calculations are also used to analyse the author's experimental observations of dissociated dislocations in copper. The result obtained for the stacking-fault energy is &gamma; = 44 erg cm^-2. This result is dependent on the assumption that the partial dislocation cores are singular. The effect of a finite core extension on this value is discussed, and it is argued that the good agreement between this figure and that deduced from the studies of faulted dipoles in Chapter 3 is evidence supporting the view that core extension effects are negligible in faulted dipoles and dissociated edge dislocations in this material. Chapter 6 considers the dissociation of the Frank partial dislocation into a stair-rod and a Shockley partial. Such a dissociation is thought to occur in small Frank loops in heavy-ion irradiated copper, but previous weak-beam investigations have not resolved the partials due to the presence of stacking-fault contrast. In theory {113} reflections at the (110) pole should image both partials but not the stacking faults. To simplify the computer simulation of experimental micrographs when investigating these new diffraction conditions, very large faulted Frank loops in copper and copper-aluminium alloys were grown by electron irradiation at elevated temperatures in a high-voltage electron microscope. The partials in any one dissociated side can then be simply represented by two infinite straight dislocations and the effect of the rest of the loop is ignored. The weak-beam images in general show two peaks corresponding to the two partials; as the dissociation always produces an obtuse fault bend, the ribbon of fault between the partials is intrinsic in nature, which suggests that the intrinsic stacking-fault energy is less than the extrinsic in these materials. The images calculated assuming a parallel incident beam of electrons do not agree with the experimental images since two, three or four peaks which are very sensitive to small changes in defect depth and foil thickness are predicted; these effects are not observed in practice. However, with a finite value of beam divergence the images become more uniform and only two peaks are predicted which exhibit inside-outside contrast effects on reversing g. Therefore the assumption of a finite beam divergence has proved essential in understanding the images of a dissociated Frank partial, and suitable diffraction conditions have been developed for studying such dissociations which may be applicable to small loops. Chapter 7 contains general conclusions and suggestions for further work.

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