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Zinc oxide (ZnO) is a II–VI compound semiconductor with a wide direct band-gap of 3.3 eV and a hexagonal structure. ZnO is often used in the paint, paper, rubber, food and drug industries. It is also a promising material in nanotechnology applications, for example in nano-electronics and nano-robotic technology. With its wide band-gap, high exciton binding energy and high breakdown strength, ZnO can be utilized for electronic and photonic devices, as well as for high-frequency applications. To produce such optoelectronic devices, control of electronic properties, such as the nature of conduction and carrier density, is required. However, such control has proved difficult for ZnO. Much research has been done to pursue p type ZnO using different processing techniques, however, there are few reports addressing the relationships of microstructure on optical and electrical properties, ion implantation doping of ZnO and nano-ZnO polymer composites. The objectives of this project are to study the processing, composition, microstructure, electronic, optical, UV and electromagnetic shielding properties of ZnO thin films and composites; to explore ion implantation as a method to dope Al, Ag, Sb, Sn and TiN into ZnO thin films or single crystals; to develop conducting, transparent oxide films and/or p-type semiconductor for potential device applications; and to study the relationships of doping, microstructure and electro-optical properties of ZnO thin films and nano-ZnO polymer composites. The experimental work included annealing, characterizing and implantation of magnetron sputtering ZnO thins films and ZnO single crystals. Ion implantation was employed to dope ZnO thin films or single crystals with Ti, N, Sb, Al, Sn and Ag. The diffusion behaviour of implanted and annealed ZnO and the ellipsometry of implanted ZnO thin films were investigated. The relationship of microstructure and properties of as-deposited, annealed and implanted ZnO was studied. The results show that compared to direct current (d.c.) sputtering, the films produced using radio frequency (r.f.) have significantly lower resistivity, porosity and stress. The residual stress can change the band gap of ZnO thin films. Conductivity experiments suggest that the conduction mechanism of sputtered ZnO thin films involves charge transport in the conduction band and electronic hopping between the nearest neighbour donor levels. Furthermore, the optical transmission of ZnO thin films is high in the visible, with excellent UV absorption properties. It is also found that annealing alters the grain size and composition, and reduces the stress of ZnO thin films. Moreover, ion implantation causes partial amorphousness of ZnO films in the implantation zone and introduces stress and interstitial dopants. Transport of Ions in Matter (TRIM) modelling and Secondary Ion Mass Spectrometer (SIMS) analysis confirm that lighter elements implant deeper than heavy elements. The implanted ZnO shows some p type tendency and evidence of photoluminescence. Lastly, the nano-ZnO and polymer composites show excellent mechanical, good UV barrier properties.

Zinc oxide (ZnO) is a II–VI compound semiconductor with a wide direct band-gap of 3.3 eV and a hexagonal structure. ZnO is often used in the paint, paper, rubber, food and drug industries. It is also a promising material in nanotechnology applications, for example in nano-electronics and nano-robotic technology. With its wide band-gap, high exciton binding energy and high breakdown strength, ZnO can be utilized for electronic and photonic devices, as well as for high-frequency applications. To produce such optoelectronic devices, control of electronic properties, such as the nature of conduction and carrier density, is required. However, such control has proved difficult for ZnO. Much research has been done to pursue p type ZnO using different processing techniques, however, there are few reports addressing the relationships of microstructure on optical and electrical properties, ion implantation doping of ZnO and nano-ZnO polymer composites. The objectives of this project are to study the processing, composition, microstructure, electronic, optical, UV and electromagnetic shielding properties of ZnO thin films and composites; to explore ion implantation as a method to dope Al, Ag, Sb, Sn and TiN into ZnO thin films or single crystals; to develop conducting, transparent oxide films and/or p-type semiconductor for potential device applications; and to study the relationships of doping, microstructure and electro-optical properties of ZnO thin films and nano-ZnO polymer composites. The experimental work included annealing, characterizing and implantation of magnetron sputtering ZnO thins films and ZnO single crystals. Ion implantation was employed to dope ZnO thin films or single crystals with Ti, N, Sb, Al, Sn and Ag. The diffusion behaviour of implanted and annealed ZnO and the ellipsometry of implanted ZnO thin films were investigated. The relationship of microstructure and properties of as-deposited, annealed and implanted ZnO was studied. The results show that compared to direct current (d.c.) sputtering, the films produced using radio frequency (r.f.) have significantly lower resistivity, porosity and stress. The residual stress can change the band gap of ZnO thin films. Conductivity experiments suggest that the conduction mechanism of sputtered ZnO thin films involves charge transport in the conduction band and electronic hopping between the nearest neighbour donor levels. Furthermore, the optical transmission of ZnO thin films is high in the visible, with excellent UV absorption properties. It is also found that annealing alters the grain size and composition, and reduces the stress of ZnO thin films. Moreover, ion implantation causes partial amorphousness of ZnO films in the implantation zone and introduces stress and interstitial dopants. Transport of Ions in Matter (TRIM) modelling and Secondary Ion Mass Spectrometer (SIMS) analysis confirm that lighter elements implant deeper than heavy elements. The implanted ZnO shows some p type tendency and evidence of photoluminescence. Lastly, the nano-ZnO and polymer composites show excellent mechanical, good UV barrier properties.

Zinc oxide (ZnO) is a II–VI compound semiconductor with a wide direct band-gap of 3.3 eV and a hexagonal structure. ZnO is often used in the paint, paper, rubber, food and drug industries. It is also a promising material in nanotechnology applications, for example in nano-electronics and nano-robotic technology. With its wide band-gap, high exciton binding energy and high breakdown strength, ZnO can be utilized for electronic and photonic devices, as well as for high-frequency applications. To produce such optoelectronic devices, control of electronic properties, such as the nature of conduction and carrier density, is required. However, such control has proved difficult for ZnO. Much research has been done to pursue p type ZnO using different processing techniques, however, there are few reports addressing the relationships of microstructure on optical and electrical properties, ion implantation doping of ZnO and nano-ZnO polymer composites. The objectives of this project are to study the processing, composition, microstructure, electronic, optical, UV and electromagnetic shielding properties of ZnO thin films and composites; to explore ion implantation as a method to dope Al, Ag, Sb, Sn and TiN into ZnO thin films or single crystals; to develop conducting, transparent oxide films and/or p-type semiconductor for potential device applications; and to study the relationships of doping, microstructure and electro-optical properties of ZnO thin films and nano-ZnO polymer composites. The experimental work included annealing, characterizing and implantation of magnetron sputtering ZnO thins films and ZnO single crystals. Ion implantation was employed to dope ZnO thin films or single crystals with Ti, N, Sb, Al, Sn and Ag. The diffusion behaviour of implanted and annealed ZnO and the ellipsometry of implanted ZnO thin films were investigated. The relationship of microstructure and properties of as-deposited, annealed and implanted ZnO was studied. The results show that compared to direct current (d.c.) sputtering, the films produced using radio frequency (r.f.) have significantly lower resistivity, porosity and stress. The residual stress can change the band gap of ZnO thin films. Conductivity experiments suggest that the conduction mechanism of sputtered ZnO thin films involves charge transport in the conduction band and electronic hopping between the nearest neighbour donor levels. Furthermore, the optical transmission of ZnO thin films is high in the visible, with excellent UV absorption properties. It is also found that annealing alters the grain size and composition, and reduces the stress of ZnO thin films. Moreover, ion implantation causes partial amorphousness of ZnO films in the implantation zone and introduces stress and interstitial dopants. Transport of Ions in Matter (TRIM) modelling and Secondary Ion Mass Spectrometer (SIMS) analysis confirm that lighter elements implant deeper than heavy elements. The implanted ZnO shows some p type tendency and evidence of photoluminescence. Lastly, the nano-ZnO and polymer composites show excellent mechanical, good UV barrier properties.

Zinc oxide (ZnO) is a II–VI compound semiconductor with a wide direct band-gap of 3.3 eV and a hexagonal structure. ZnO is often used in the paint, paper, rubber, food and drug industries. It is also a promising material in nanotechnology applications, for example in nano-electronics and nano-robotic technology. With its wide band-gap, high exciton binding energy and high breakdown strength, ZnO can be utilized for electronic and photonic devices, as well as for high-frequency applications. To produce such optoelectronic devices, control of electronic properties, such as the nature of conduction and carrier density, is required. However, such control has proved difficult for ZnO. Much research has been done to pursue p type ZnO using different processing techniques, however, there are few reports addressing the relationships of microstructure on optical and electrical properties, ion implantation doping of ZnO and nano-ZnO polymer composites. The objectives of this project are to study the processing, composition, microstructure, electronic, optical, UV and electromagnetic shielding properties of ZnO thin films and composites; to explore ion implantation as a method to dope Al, Ag, Sb, Sn and TiN into ZnO thin films or single crystals; to develop conducting, transparent oxide films and/or p-type semiconductor for potential device applications; and to study the relationships of doping, microstructure and electro-optical properties of ZnO thin films and nano-ZnO polymer composites. The experimental work included annealing, characterizing and implantation of magnetron sputtering ZnO thins films and ZnO single crystals. Ion implantation was employed to dope ZnO thin films or single crystals with Ti, N, Sb, Al, Sn and Ag. The diffusion behaviour of implanted and annealed ZnO and the ellipsometry of implanted ZnO thin films were investigated. The relationship of microstructure and properties of as-deposited, annealed and implanted ZnO was studied. The results show that compared to direct current (d.c.) sputtering, the films produced using radio frequency (r.f.) have significantly lower resistivity, porosity and stress. The residual stress can change the band gap of ZnO thin films. Conductivity experiments suggest that the conduction mechanism of sputtered ZnO thin films involves charge transport in the conduction band and electronic hopping between the nearest neighbour donor levels. Furthermore, the optical transmission of ZnO thin films is high in the visible, with excellent UV absorption properties. It is also found that annealing alters the grain size and composition, and reduces the stress of ZnO thin films. Moreover, ion implantation causes partial amorphousness of ZnO films in the implantation zone and introduces stress and interstitial dopants. Transport of Ions in Matter (TRIM) modelling and Secondary Ion Mass Spectrometer (SIMS) analysis confirm that lighter elements implant deeper than heavy elements. The implanted ZnO shows some p type tendency and evidence of photoluminescence. Lastly, the nano-ZnO and polymer composites show excellent mechanical, good UV barrier properties.

Zinc oxide (ZnO) is a II–VI compound semiconductor with a wide direct band-gap of 3.3 eV and a hexagonal structure. ZnO is often used in the paint, paper, rubber, food and drug industries. It is also a promising material in nanotechnology applications, for example in nano-electronics and nano-robotic technology. With its wide band-gap, high exciton binding energy and high breakdown strength, ZnO can be utilized for electronic and photonic devices, as well as for high-frequency applications. To produce such optoelectronic devices, control of electronic properties, such as the nature of conduction and carrier density, is required. However, such control has proved difficult for ZnO. Much research has been done to pursue p type ZnO using different processing techniques, however, there are few reports addressing the relationships of microstructure on optical and electrical properties, ion implantation doping of ZnO and nano-ZnO polymer composites. The objectives of this project are to study the processing, composition, microstructure, electronic, optical, UV and electromagnetic shielding properties of ZnO thin films and composites; to explore ion implantation as a method to dope Al, Ag, Sb, Sn and TiN into ZnO thin films or single crystals; to develop conducting, transparent oxide films and/or p-type semiconductor for potential device applications; and to study the relationships of doping, microstructure and electro-optical properties of ZnO thin films and nano-ZnO polymer composites. The experimental work included annealing, characterizing and implantation of magnetron sputtering ZnO thins films and ZnO single crystals. Ion implantation was employed to dope ZnO thin films or single crystals with Ti, N, Sb, Al, Sn and Ag. The diffusion behaviour of implanted and annealed ZnO and the ellipsometry of implanted ZnO thin films were investigated. The relationship of microstructure and properties of as-deposited, annealed and implanted ZnO was studied. The results show that compared to direct current (d.c.) sputtering, the films produced using radio frequency (r.f.) have significantly lower resistivity, porosity and stress. The residual stress can change the band gap of ZnO thin films. Conductivity experiments suggest that the conduction mechanism of sputtered ZnO thin films involves charge transport in the conduction band and electronic hopping between the nearest neighbour donor levels. Furthermore, the optical transmission of ZnO thin films is high in the visible, with excellent UV absorption properties. It is also found that annealing alters the grain size and composition, and reduces the stress of ZnO thin films. Moreover, ion implantation causes partial amorphousness of ZnO films in the implantation zone and introduces stress and interstitial dopants. Transport of Ions in Matter (TRIM) modelling and Secondary Ion Mass Spectrometer (SIMS) analysis confirm that lighter elements implant deeper than heavy elements. The implanted ZnO shows some p type tendency and evidence of photoluminescence. Lastly, the nano-ZnO and polymer composites show excellent mechanical, good UV barrier properties.

The deployment of third generation (3G) cellular systems is resulting in a transition from cellular systems that predominantly carry constant-bit-rate (CBR) voice traffic to multi-service packet based systems that predominantly carry variable-bit-rate (VBR) traffic. With 3G DS-CDMA cellular systems there is a direct relationship between user traffic and propagation dependent performance as additional traffic causes increased system interference. This thesis investigates the impact of VBR traffic on the propagation dependent performance of DS-CDMA cellular systems that utilise frame-by-frame dynamic resource allocation on the radio channel. A DS-CDMA cellular system model is developed and the downlink performance of both outdoor macro-cellular and indoor pico-cellular systems is evaluated with a variety of traffic types. Both traffic scheduling performance and propagation dependent performance are evaluated as the two are inter-linked. Scenarios are identified where propagation dependent performance is sensitive to the statistical properties of the user traffic streams and it is shown that a significant performance difference potentially exists between different traffic types when the number of users per cell is low. When a significant performance difference does exist, burstier more variable traffic generally results in superior propagation dependent performance. The base transceiver station (BTS) transmitter power mean and variance provides a good indication of the level of propagation dependent performance regardless of the specific traffic type. Traffic scheduling policies that deliberately reduce the variability of user traffic streams are considered and in terms of propagation dependent performance these are shown to have a minimal impact on the performance difference between different traffic types. The implications of VBR traffic on DS-CDMA cellular system design are outlined and it is shown that VBR traffic can be approximated as CBR traffic in many scenarios and this is a convenient approximation as it simplifies system design and detailed traffic models do not need to be developed.

The motivation for this research is a proposed UHF surface wave communication system in which the waveguides are the stranded, overhead earth wires of Power System transmission lines. Attention is confined largely to an investigation of certain aspects which affect the overall surfaces wave transmission loss, a full-scale system having been set up in the laboratory for experimental purposes. For the prediction of transmission loss the stranded conductor is assumed to be equivalent to a solid conductor of the same diameter but with surface anisotropy in the form of two mutually orthogonal surface impedances the major reactive component of which is attributed to the effects of the helical stranding. This reactance is determined from a consideration of the fields which are assumed to exist within the cavities between the strands, and externally. From a comparison between experimental and theoretical loss characteristics there is sufficient inducement to accept the anisotropic model of the stranded conductor for practical design purposes. Approximate equations are developed to simplify the calculation of transmission loss and the notion of ‘capture cross-section’ is employed for the estimation of the efficiency of conical horn launchers. It is deduced from ‘sensitivity’ relationships that the horn loss is relatively insensitive to small changes in the fictitious surface reactance representing the effects of helical stranding, which tends to justify the assumptions upon which the anisotropic model is based. On the other hand, variations in the helix angle are shown to have a marked effect upon the calculated horn loss. This influences the choice of the stranded conductor used as the waveguide for the experimental verification of the model. The Author’s experimental research is described at length, the principal objective being to establish the anisotropic model as an acceptable theoretical substitute for the stranded conductor. To reduce the horn loss, dielectric sheaths are ted to the waveguide in the vicinity of the horn apertures. The discrepancies which then appear between theory and experiment are attributed both to the scattering of the surface wave by the boundary discontinuities at the ends of the sheaths and to the anomalous behaviour of commercial-grade PVC dielectric. Considering the increase in the transmission efficiency which may be realised by fitting dielectric sheaths to the conductor near the horn apertures it is concluded that a theoretical investigation of the scattering properties of the discontinuities s in order. Thus, the remainder of the Thesis is devoted, to this scattering effect as it may be encountered in the proposed scheme, the theoretical analysis following the lines of earlier documented research. A short-cut method is applied for the determination of certain ‘half-plane’ functions which appear in the expressions for the scattered power. Theoretical results are presented together with a discussion of some experimental measurements and a brief theoretical examination of the effects on the horn loss of varying the thickness of the dielectric sheaths. It is argued that the horn loss may be reduced if the dielectric thickness is graded in steps to a value at the horn apertures consistent with the desired ‘power capture’. The Thesis is concluded with an Addendum which outlines a number of topics suggested by the Author for future research.

The motivation for this research is a proposed UHF surface wave communication system in which the waveguides are the stranded, overhead earth wires of Power System transmission lines. Attention is confined largely to an investigation of certain aspects which affect the overall surfaces wave transmission loss, a full-scale system having been set up in the laboratory for experimental purposes. For the prediction of transmission loss the stranded conductor is assumed to be equivalent to a solid conductor of the same diameter but with surface anisotropy in the form of two mutually orthogonal surface impedances the major reactive component of which is attributed to the effects of the helical stranding. This reactance is determined from a consideration of the fields which are assumed to exist within the cavities between the strands, and externally. From a comparison between experimental and theoretical loss characteristics there is sufficient inducement to accept the anisotropic model of the stranded conductor for practical design purposes. Approximate equations are developed to simplify the calculation of transmission loss and the notion of ‘capture cross-section’ is employed for the estimation of the efficiency of conical horn launchers. It is deduced from ‘sensitivity’ relationships that the horn loss is relatively insensitive to small changes in the fictitious surface reactance representing the effects of helical stranding, which tends to justify the assumptions upon which the anisotropic model is based. On the other hand, variations in the helix angle are shown to have a marked effect upon the calculated horn loss. This influences the choice of the stranded conductor used as the waveguide for the experimental verification of the model. The Author’s experimental research is described at length, the principal objective being to establish the anisotropic model as an acceptable theoretical substitute for the stranded conductor. To reduce the horn loss, dielectric sheaths are ted to the waveguide in the vicinity of the horn apertures. The discrepancies which then appear between theory and experiment are attributed both to the scattering of the surface wave by the boundary discontinuities at the ends of the sheaths and to the anomalous behaviour of commercial-grade PVC dielectric. Considering the increase in the transmission efficiency which may be realised by fitting dielectric sheaths to the conductor near the horn apertures it is concluded that a theoretical investigation of the scattering properties of the discontinuities s in order. Thus, the remainder of the Thesis is devoted, to this scattering effect as it may be encountered in the proposed scheme, the theoretical analysis following the lines of earlier documented research. A short-cut method is applied for the determination of certain ‘half-plane’ functions which appear in the expressions for the scattered power. Theoretical results are presented together with a discussion of some experimental measurements and a brief theoretical examination of the effects on the horn loss of varying the thickness of the dielectric sheaths. It is argued that the horn loss may be reduced if the dielectric thickness is graded in steps to a value at the horn apertures consistent with the desired ‘power capture’. The Thesis is concluded with an Addendum which outlines a number of topics suggested by the Author for future research.

The motivation for this research is a proposed UHF surface wave communication system in which the waveguides are the stranded, overhead earth wires of Power System transmission lines. Attention is confined largely to an investigation of certain aspects which affect the overall surfaces wave transmission loss, a full-scale system having been set up in the laboratory for experimental purposes. For the prediction of transmission loss the stranded conductor is assumed to be equivalent to a solid conductor of the same diameter but with surface anisotropy in the form of two mutually orthogonal surface impedances the major reactive component of which is attributed to the effects of the helical stranding. This reactance is determined from a consideration of the fields which are assumed to exist within the cavities between the strands, and externally. From a comparison between experimental and theoretical loss characteristics there is sufficient inducement to accept the anisotropic model of the stranded conductor for practical design purposes. Approximate equations are developed to simplify the calculation of transmission loss and the notion of ‘capture cross-section’ is employed for the estimation of the efficiency of conical horn launchers. It is deduced from ‘sensitivity’ relationships that the horn loss is relatively insensitive to small changes in the fictitious surface reactance representing the effects of helical stranding, which tends to justify the assumptions upon which the anisotropic model is based. On the other hand, variations in the helix angle are shown to have a marked effect upon the calculated horn loss. This influences the choice of the stranded conductor used as the waveguide for the experimental verification of the model. The Author’s experimental research is described at length, the principal objective being to establish the anisotropic model as an acceptable theoretical substitute for the stranded conductor. To reduce the horn loss, dielectric sheaths are ted to the waveguide in the vicinity of the horn apertures. The discrepancies which then appear between theory and experiment are attributed both to the scattering of the surface wave by the boundary discontinuities at the ends of the sheaths and to the anomalous behaviour of commercial-grade PVC dielectric. Considering the increase in the transmission efficiency which may be realised by fitting dielectric sheaths to the conductor near the horn apertures it is concluded that a theoretical investigation of the scattering properties of the discontinuities s in order. Thus, the remainder of the Thesis is devoted, to this scattering effect as it may be encountered in the proposed scheme, the theoretical analysis following the lines of earlier documented research. A short-cut method is applied for the determination of certain ‘half-plane’ functions which appear in the expressions for the scattered power. Theoretical results are presented together with a discussion of some experimental measurements and a brief theoretical examination of the effects on the horn loss of varying the thickness of the dielectric sheaths. It is argued that the horn loss may be reduced if the dielectric thickness is graded in steps to a value at the horn apertures consistent with the desired ‘power capture’. The Thesis is concluded with an Addendum which outlines a number of topics suggested by the Author for future research.