Ultraviolet photoelectron spectroscopy measurements are presented from a variety of metals and alloys in the liquid state. For the metals, the optical density of states function is extracted from the photoemission data, by using an extended version of the three step model of Berglund and Spicer and compared to theoretical liquid density of states calculations based on a weak scattering approach which show only small deviations from the free electron parabola. The experimentally derived results for liquid lead and liquid tin reveal deviations from the simple picture with some of the solid state density of states features persisting into the liquid phase. By contrast, liquid lithium is shown to adhere more closely to the free electron model, showing a weaker deviation from the parabolic form for its experimentally derived density of states, while the same function for liquid silver is shown to be a smeared version of the solid state curve which, as explained, is not unexpected because of structural considerations. Photoemission data from liquid germanium is presented and discussed in comparison with published data for crystalline and amorphous germanium in terms of local atomic ordering. Data is presented from the liquid semiconducting lithium-lead alloy system and the similar lithium-tin alloy system which is shown incompatible with a simple ionic bonding model, and a stoichiometric structure is proposed where the unlike atom bonding is taken to be more covalent in character. Photoemission spectra are also presented from the silver- germanium alloy system which has a deep eutectic composition indicating enhanced glass forming qualities. Some change with composition can be seen in the valence band region but this cannot account for the above behaviour.

It has been demonstrated that reactive magnetron sputtering can be controlled in low pumping speed vacuum system through observation of the spectral line emission by the plasma emission monitor (PEM). Confining the deposition process in an enclosed volume has provided the gettering-pumping action needed to deposit films with good quality reducing the active contamination that low pumping vacuum system suffers. TiN films of specular quality has been optimised by observing the emission line of the sputtered titanium. It was shown that optimum TiN film is formed when the consumption of nitrogen flow at the metal line set point is a maximum. This optimisation is characterised by a clear minima of ultimate resistivity and better selective optical properties. Films of TiN deposited using the balanced magnetron source had higher resistivity than the metal titanium in contrast to its bulk properties. That was explained by their lower densities. The lack of activation energy of the growing film during deposition resulted in a columnar structure separated by voids which is a normal microstructure of low film density. By adding activation energy, from an unbalanced magnetron source, a plasma beam was leaked to the substrate subjecting the growing film to energetic ions of sufficient energy to modify the structure of the film. Films were shown to have resistivities lower than the metal titanium. This characterisation was verified by examining their structure by SEM which showed dense films. The reactive gas consumption gave also a good indication of the process control and the optimisation of dielectric films of Ti02 and Zr02. Optimum films characterised by lowest absorption and high refractive index were shown to form when the consumption of oxygen is low at the lowest metalline set point within the limit of the plasma emission monitor. This shift occurred because the much tighter control of reactive gas pressure which is consequently higher for oxides than for nitrides. Films of TiN were also deposited at a low magnetTon potential. Increasing electron injection reduced the operating potential of the sputtered titanium resulting eventually in a reduction of sputtering rate and consequently a reduction in nitrogen consumption. Films made at lower target potentials had lower resistivities due to the enhanced reactivity and increasing ion current density bombarding the film.

The research presented in this thesis is on the application of the injection-locked oscillator technique to microwave balanced oscillators. The balanced oscillator design is primarily analysed using the extended resonance technique. A transmission line is connected between the two active devices, so that the active device resonate each other. The electrical length of the transmission line is also analysed for the balanced oscillation condition. The balanced oscillator can be viewed with the negative resistance model and the feedback model. The former model is characterised at a circuit plane where the feedback network is cut. By using both the negative-resistance oscillator model and the feedback model, the locking range of the oscillator is analysed by extending Kurokawa's theory. This analysis demonstrates the locking range of the injection phenomenon, where the injection frequency is either close to the free-running frequency, close to (lin) x freerunning frequency or close to n x the free-running frequency. It also reveals the effect of different injection power levels on the locking range. Injection-locked balanced oscillators for subharmonic and fundamental modes are constructed. When the balanced oscillator is in the locking state, it is clearly shown that the output signal is better stabilised and the phase noise is attenuated. The experimental results agree with the analysis. Furthermore, the spurious signal suppression in a cascaded oscillator is investigated. The other focus of this research is on the design of frequency doublers. A balanced douber is designed and integrated with a balanced injection-locked oscillator. The experimental result shows that the output signal is clean and stabilised. The other important frequency doubler design technique studied is the use of the feedforward technique to significantly eliminate the fundamental frequency component. The design and the experiment show that the fundamental component can be suppressed to better than 50 dBc.

Hexaferrites are still a very important component of the permanent magnets market because of their low price combined with reasonably attractive magnetic properties. In such a context, any improvement of the magnet data would be of great importance. In recent years, work has been carried out on improving the magnetic properties by a combined substitution of La and Co into the Sr-ferrite composition. This improvement was largely associated with an increase of coercivity and the underlying magneto-crystalline anisotropy. The possibility of replacing Sr by La and the subsequent improvement of the magnetic properties of the M-type ferrite stimulated our interest in studying other rare-earth ion substitutions. This thesis focuses on the effects of rare-earth element substitutions on the magnetic properties of strontium hexaferrite, SrM (SrFe12O19b)y chemical co-precipitation and by hydrothermal synthesis,a s well as on the properties-microstructure relationship. In order to produce the nanosized SrM powder, chemical co-precipitation was employed and subsequently proved to be an effective route for producing nanosized single domain SrM powder, where the SrM phase crystallises from the mainly amorphous co-precipitates through an exothermic reaction after calcination at >650°C. A very high intrinsic coercivity of 518. OkA/m (6509 Oe) with magnetisation at I IOOkA/m of 67 J/T. kg was obtained for the sample calcined at 850°C for 2h in air. The coercivity is close to the theoretical limit and is one of the highest values reported so far for isotropic SrM particles. Nanosized SrM powders with Sm and La-Zn additives were also studied. It was found that Sm doping increased slightly the coercivity of SrM and exhibited higher values than those of the corresponding samples with La additives. However, the values of magnetisation decreased slightly with the increase of the Sm/Sr ratio, which can be correlated with the increased proportion of weakly magnetic SrFeO3_pxh ase in the Sm doped SrM. Sm doping slightly increasedt he ferritization temperatureo f SrM. In the case of the La-Zn substitution, single phase Sri_,(,L aZn),,F e12_XO19 nanosized powders were produced successfully for all x, where x varied from 0 to 0.4. La-Zn substitution caused a decrease of the Curie temperature. The values of magnetization, remanence and coercivity decreased with La-Zn content. Unlike the results of La-Zn doped SrM particles prepared by conventional ceramic methods and the results of La-Zn doped SrM film prepared by rf sputtering, no improvement of the magnetisation was observed, which suggested that the properties of these materials are strongly processing-dependent and that the site preference of the Zn 2+ cation is not identical in all cases but would be affected by the processing route. Mainly single phase RE (RE=Sm, Nd, Pr and La) substituted SrM plate-like particles with the magnetoplumbite structure could be produced by hydrothermal synthesis and subsequent calcination. Under the particular hydrothermal conditions, RE elements did not substitute totally into the SrM structure and this resulted in incomplete reactions between Fe 3+ and Sr2+, indicated by traces of a-Fe2O3 and RE203 in all the RE substituted SrM samples. The presence of a-Fe2O3 and RE203 increased with the increase of the RE/Sr ratio. High temperature calcination homogenizes the materials and promotes the substitution of RE elements, resulting generally in the disappearance of a-Fe2O3 and RE203 after calcinations at >_ 1100°C. A higher calcination temperature was required to obtain the SrM single phase for a high RE/Sr ratio. The SrFe03_xp hase was found to be present in most of the RE substituted samples after calcination above 1100°C. Except for the La substitution, the other RE elements reduced the rate of grain growth during the calcination. Generally, the magnetization values of the RE substituted samples were almost the same as that of SrM. On the other hand, their intrinsic coercivities generally increased upon RE doping. Thus, an appropriate amount of RE substitution resulted in a useful increase in the intrinsic coercivity (18% for Sm, 14% for Pr, 11 % for Nd and 5% for La) without causing any significant deterioration in the saturation magnetisation or in the remanence. The improvement in the coercivity as a result of the RE substitutions is discussed in terms of the extrinsic effect associated with the microstructure and the intrinsic effect associated with an increase in the magnetocrystalline anisotropy. Finally, anisotropic SrM magnets with Sm substitution, which is observed to have the largest enhancement of coercivity among the other elements, were studied. All the magnets with Sm additions exhibit a bigger coercivity and remanence than those of the SrM magnet and the coercivity of the magnets increases with increasing Sm/Sr ratio. The average grain size of the samples decreases with increasing Sm/Sr ratio. EDX quantitative analysis suggests that the solubility of Sm 3+ in the SrM-type structure is very small and that the Sm3+ preferably goes into SrFe03_Xw, hich is probably located around the SrM grain boundaries. The coercivity mechanism of the magnets is nucleation controlled. The formation and the distribution of the SrFe03_x phase around the SrM grain boundraies probably provides the inhibition of SrM grain growth, the reduction of the reverse domain nucleation at the grain surface and the isolation of the SrM grains. All these factors would contribute to the improvements of the coercivity of the magnets with Sm additions.

The physical and electrical properties of highly thermally conductive materials have long been of interest, especially to power electronics manufacturers for the improvement of device efficiencies by better substrate cooling. This thesis provides a resume of the findings on high thermal conductivity materials and reports in detail on the results of an investigation undertaken to evaluate the suitability of Anodized Aluminium as a high thermal conductivity substrate material. Special anodic film fabrication techniques were developed to produce substrates on which thick film components could be directly printed. These studies were implemented in conjunction with a selection of low temperature Thick Film (TF) conductor and resistor pastes (inks) to achieve the optimum combination of Anodized Aluminium substrate and paste system. Test circuits of these chosen pastes were then printed and fired on Anodized Aluminium, Aluminium Nitride, Beryllia, Porcelain on Steel and Alumina substrates. The circuits were used to investigate the physical and electrical properties of the substrates, such as thermal conductivity, thermal expansion, thermal coefficient of resistance, dielectric constant and adhesion of the pastes to the substrates. The resultant anodized aluminium substrates were shown to:- be insulating to over 500 volts, able to withstand firing temperature of 500°C, and have a thermal conductivity very close to that of aluminium (240Wm-1K"1 at room temperature). Unfortunately electrical measurements have shown the anodic films to be humidity dependent, as the resistivity of the films is greatly reduced by an increase in humidity. The substrates are compatible with Heraeus C180-5554 conductor paste and the ESL 15511 resistor paste series. A low power hybrid device with surface mounted components was employed to validate the substrate/paste combinations. To conclude, this thesis has shown that anodized aluminium is suitable as a high thermal conductivity substrate for high power hybrid microelectronics.

Forward focussing of medium energy Auger and photoelectrons have been used along with LEED and Auger electron spectroscopy to investigate the initial stages of growth of both Cr and Co on Ag(001). Cr was found to grow epitaxially on Ag in the bcc phase up to ~2ML, in agreement with previous results. Co also grows epitaxially on Ag up to 3ML although it is proposed that the Co lattice is in the FCC phase but no comment can be made as to whether the overlayer is laterally expanded. Polarised Neutron Reflection measurements have been made on Ag/Cr/Ag sandwich structures with varying thicknesses of Cr. It is shown that for Cr thicknesses of 2 and 3.3ML the Cr is ordered non-ferromagnetically and it is proposed that at these thicknesses the Cr has reverted to its bulk antiferromagnetic order. However measurements on samples with Cr thicknesses of 0.33ML indicate ferromagnetic ordering with a greatly enhanced magnetic moment per atom over the bulk Cr value, in partial agreement with previous theoretical predictions. PNR measurements on a Ag/Fe/Ag (001) structure with thickness of Fe of 8ML have yielded an accurate measurement of the magnetic moment per atom for the Fe film of 1.0 +; 0.15microB, indicating a reduced value from that of bulk Fe of 2.22microB. x-ray scattering from a Ge (001) surface has been used to show that the surface undergoes a reversible phase transition at T = 954 +; 7K. It is proposed that the transition occurs due to the formation of vacancy-adatom pairs as some of the surface dimers break with increasing temperature. The data is explained in terms of a three level model used to describe the vacancy-adatom creation. The three level model results are compared with results from a simple Monte-Carlo simulation and an energy of 0.41 +; 0.05eV is deduced as the energy required to break the dimer bonds on the surface of Ge (001). Further X-ray scattering from a miscut Ge (001) surface shows that the surface is made up of regularly spaced steps of double atomic height, in agreement with theoretical and previous experimental studies. It is shown that perpendicular to the steps the reconstructed domains are limited in dimension by the steps, although both orientations of the reconstruction are possible.

The surface sensitive techniques of LEED, Auger electron spectroscopy (AES), ultra-violet photoelectron spectroscopy (UPS) and electron energy loss spectroscopy (EELS) were combined in order to study the electronic structure of well characterised overlayers of Pb, T? and Mn on Cu(l00). LEED and AES showed that Pb and T? atoms are adsorbed initially in linear chains lying in the (001) furrows between rows of copper atoms in the substrate surface. Both overlayers form an hop structure at the dense monolayer coverage. Thallium forms an intermediate overlayer structure in which the linear chains have moved closer together. Beyond the dense monolayer coverage both overlayers grow in the Stranski- Krastanov mode. In the case of Pb on Cu(l00) the LEED and AES results confirm the results of earlier work (Sepulveda and Rhead, 1977). Manganese initially forms a c(2 x 2) structure which is interpreted as an overlayer with Mn atoms lying in four-fold hollow sites. Further growth occurs in a disordered layer by layer mode. UPS shows that Pb and T? atoms are bonded mainly by the interaction of their 6s-p electrons with the Cu 4s-p electrons. There is little interaction between the overlayer 6s-p electrons and the Cu 3d electrons. In the case of T?, an analysis of work function measurements shows that the linear chains formed at low coverages do not interact appreciably with each other, whereas there is a strong interaction between the chains when they move closer together to form the next ordered overlayer. The transition from the first ordered T? overlayer structure to the second therefore involves a transition from a one dimensional to a two dimensional electronic interaction. For Mn overlayers there is a strong interaction between the Mn and Cu 3d electrons. At low coverages (?0.25 monolayers) a resonant bound state is observed just above the Cu 3d bands in agreement with a recent calculation. Such a state has not been observed in previous photoemission studies of dilute CuMn alloys. The photoemission spectra of thick Mn overlayers resemble the density of states of bulk Mn. EELS shows that Pb overlayers perturb the Cu 4s band confirming that bonding of the overlayer occurs via the Cu 4s orbitals. The existing models of plasmons in overlayers fail to predict the energies of the discrete losses observed in the EEL spectra of Pb and T? overlayers.

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