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No description available.

No description available.

No description available.

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This thesis discusses the development of an ion beam generation and transport system for the purpose of high current ion implantation and presents a method to achieve high quality beam generation and high transport efficiency. An advanced method of achieving ideal space charge neutralization of an ion beam as well as charge neutralization of implanted targets has also been developed and presented. This study was carried out in five main categories as described below. 1. Beam optics: The optical properties of the ion beam have to be well controlled through various beam transport devices. Beam transfer matrix calculation and Poisson's equation solver were used to determine beam optics. 2. Plasma generation: The ion beam is extracted from a plasma generated in the ion source. Therefore, the quality of ion beams depends largely on the characteristics of the source plasma. Plasma diagnostic tools were used to understand the desired plasma conditions. 3. Space charge neutralisation: Space charge neutralisation is essential to transport high perveance beams because a beam without neutralisation develops a high electric potential in itself that would scatter beam ions away. A plasma based charge neutraliser "Plasma Flood System" was developed to maintain space charge neutrality during implantation. 4. Low energy beam extraction and transport: Beam extraction and transport become difficult at lower energy due to growth of emittance and space charge. Beam divergence had to be minimized by tight optical control. 5. Microwave plasma sources as ultimate ion source: A microwave source was developed to obtain high current, ultra clean ion beams and long source life. The characteristics of microwave plasmas differ significantly from whose generated by other methods such as DC excitation. The source achieved the highest recorded beam currents for various species. All the technology and the methods described above were combined to develop a state-of-the-art high current ion implanter that has achieved world leading beam performance.

Phononic crystals are composite media, with two different elastic materials modulated in a periodic fashion. The two-dimensional system under study is comprised of an array of cylindrical tubes arranged in a square Bravais lattice. The propagation of a time-harmonic acoustic Bloch waves is investigated experimentally and the findings compared with those obtained from the finite element method. The band structure, that is a well-known characteristic of Bloch wave dispersion, is also determined. This demonstrates the existence of band gaps of forbidden transmission at certain frequency ranges. These arise due to the interference when the wavelength of the incident wave is comparable to the periodic spacing of the modulated media. A second phononic crystal with slotted steel tubes is also studied. The opening in the tube permitting air to flow to the internal cavity, and constituting a Helmholtz resonator. The band structure of such a structure possesses additional band gaps, which arise due to the excitation of the resonators. Furthermore, it has recently been shown that periodically distributed Helmholtz resonator structures, can exhibit negative refraction phenomena. Using the transmission line technique, as outlined by Y.Cheng et al. we demonstrate this behaviour for our experimental system. It is shown that, at certain frequency ranges, the locally resonant phononic crystal exhibits negative effective density and bulk modulus, the two conditions required to obtain a negative index of refraction.

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The technological importance of hard thin films is well established. There is growing recognition that nanometre-scale surface structures can be controlled to the benefit of function. In-process structuring brings these ideas together. This study explores how the morphology, especially the surface topography, and microtribological behaviour of Cr-N films can be controlled during unbalanced magnetron (UBM) sputtering. Experiments varying the sputter power, bias voltage, temperature, total pressure and Ar/N2 ratio during UBM sputtering generated different compositions, crystallite orientations and microstructures, and six associated topography types: pyramidal (type P), grain-like (G), crater-like (CR), ribbon-like (R), conical (C) and hillock-like (H). A new empirical zone model consistently relates these topography types to process parameters. The feature dimensions are also controlled by the deposition parameters. The films have closely reproducible topographical and mechanical properties. The microtribological behaviour for three topography types (P, C and CR) is studied under different conditions relevant to unlubricated contacts, lubricated contacts, and humid environments. Nanostructured surfaces show significantly lower friction than smooth ones, with actual reductions depending on the topography type. Friction strongly correlates with summit density (Ssd). Low friction (Ssd ~ 3 #/µm2) was measured on all type CR surfaces, but only by increasing the lateral dimensions of types P and C. Unlubricated friction is attributed principally to solid-solid adhesion, influenced by the density and curvature of summits. Wear is influenced by the density, shape and size of the surface features and by the mechanical properties of the film. Boundary lubrication reduced friction, with slight dependence on lubricant. Alongside the summits parameters, friction correlates with core fluid retention index. Applying hydrophobic and hydrophilic treatments shows that appropriate nanostructuring reduces the dependence of friction on humidity and sliding velocity, principally by controlling the summit density. In-process structuring is clearly very useful for creating nanostructures in order to enhance the microtribological behaviour of surfaces. Further investigations are recommended into friction optimization by nanostructuring.

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