Semiconductor nanowire fabrication via bottom-up & top-down paradigms

Semiconductor nanowires are pseudo 1-D structures where the magnitude of the semiconducting material is confined to a length of less than 100 nm in two dimensions. Semiconductor nanowires have a vast range of potential applications, including electronic (logic devices, diodes), photonic (laser, photodetector), biological (sensors, drug delivery), energy (batteries, solar cells, thermoelectric generators), and magnetic (spintronic, memory) devices. Semiconductor nanowires can be fabricated by a range of methods which can be categorised into one of two paradigms, bottom-up or top-down. Bottom-up processes can be defined as those where structures are assembled from their sub-components in an additive fashion. Top-down fabrication strategies use sculpting or etching to carve structures from a larger piece of material in a subtractive fashion. This seminar will detail a number of novel routes to fabricate semiconductor nanowires by both bottom-up and top-down paradigms. Firstly, a novel bottom-up route to fabricate Ge nanowires with controlled diameter distributions in the sub-20 nm regime will be described. This route details nanowire synthesis and diameter control in the absence of a foreign seed metal catalyst. Additionally a top-down route to nanowire array fabrication will be detailed outlining the importance of surface chemistry in high-resolution electron beam lithography (EBL) using hydrogen silsesquioxane (HSQ) on Ge and Bi2Se3 surfaces. Finally, a process will be described for the directed self-assembly of a diblock copolymer (PS-b-PDMS) using an EBL defined template. This section will also detail a route toward selective template sidewall wetting of either block in the PS-b-PDMS system, through tailored functionalisation of the template and substrate surfaces.

Conversion as transformative experience: a sociological study of identity formation and transformation processes

This thesis contributes to the understanding of the processes involved in the formation and transformation of identities. It achieves this goal by establishing the critical importance of ‘background’ and ‘liminality’ in the shaping of identity. Drawing mainly from the work of cultural anthropology and philosophical hermeneutics a theoretical framework is constructed from which transformative experiences can be analysed. The particular experience at the heart of this study is the phenomenon of conversion and the dynamics involved in the construction of that process. Establishing the axial age as the horizon from which the process of conversion emerged will be the main theme of the first part of the study. Identifying the ‘birth’ of conversion allows a deeper understanding of the historical dynamics that make up the process. From these fundamental dynamics a theoretical framework is constructed in order to analyse the conversion process. Applying this theoretical framework to a number of case-studies will be the central focus of this study. The transformative experiences of Saint Augustine, the fourteenth century nun Margaret Ebner, the communist revolutionary Karl Marx and the literary figure of Arthur Koestler will provide the material onto which the theoretical framework can be applied. A synthesis of the Judaic religious and the Greek philosophical traditions will be the main findings for the shaping of Augustine’s conversion experience. The dissolution of political order coupled with the institutionalisation of the conversion process will illuminate the mystical experiences of Margaret Ebner at a time when empathetic conversion reached its fullest expression. The final case-studies examine two modern ‘conversions’ that seem to have an ideological rather than a religious basis to them. On closer examination it will be found that the German tradition of Biblical Criticism played a most influential role in the ‘conversion’ of Marx and mythology the best medium to understand the experiences of Koestler. The main ideas emerging from this study highlight the fluidity of identity and the important role of ‘background’ in its transformation. The theoretical framework, as constructed for this study, is found to be a useful methodological tool that can offer insights into experiences, such as conversion, that otherwise would remain hidden from our enquiries.

Resonant power conversion topologies for inductive charging of electrical vehicle batteries

This thesis is concerned with inductive charging of electric vehicle batteries. Rectified power form the 50/60 Hz utility feeds a dc-ac converter which delivers high-frequency ac power to the electric vehicle inductive coupling inlet. The inlet configuration has been defined by the Society of Automotive Engineers in Recommended Practice J-1773. This thesis studies converter topologies related to the series resonant converter. When coupled to the vehicle inlet, the frequency-controlled series-resonant converter results in a capacitively-filtered series-parallel LCLC (SP-LCLC) resonant converter topology with zero voltage switching and many other desirable features. A novel time-domain transformation analysis, termed Modal Analysis, is developed, using a state variable transformation, to analyze and characterize this multi-resonant fourth-orderconverter. Next, Fundamental Mode Approximation (FMA) Analysis, based on a voltage-source model of the load, and its novel extension, Rectifier-Compensated FMA (RCFMA) Analysis, are developed and applied to the SP-LCLC converter. The RCFMA Analysis is a simpler and more intuitive analysis than the Modal Analysis, and provides a relatively accurate closed-form solution for the converter behavior. Phase control of the SP-LCLC converter is investigated as a control option. FMA and RCFMA Analyses are used for detailed characterization. The analyses identify areas of operation, which are also validated experimentally, where it is advantageous to phase control the converter. A novel hybrid control scheme is proposed which integrates frequency and phase control and achieves reduced operating frequency range and improved partial-load efficiency. The phase-controlled SP-LCLC converter can also be configured with a parallel load and is an excellent option for the application. The resulting topology implements soft-switching over the entire load range and has high full-load and partial-load efficiencies. RCFMA Analysis is used to analyze and characterize the new converter topology, and good correlation is shown with experimental results. Finally, a novel single-stage power-factor-corrected ac-dc converter is introduced, which uses the current-source characteristic of the SP-LCLC topology to provide power factor correction over a wide output power range from zero to full load. This converter exhibits all the advantageous characteristics of its dc-dc counterpart, with a reduced parts count and cost. Simulation and experimental results verify the operation of the new converter.

Keeping their heads down: Shame and pride in the stories of Protestants in the Irish Republic

This study draws on a number of in-depth interviews to explore the ethnic aspect of Protestantism in the Republic of Ireland. We explore themes of shame and pride around issues of identity, together with a sense of loss of a minority rapidly losing cultural distinctiveness. Following Ireland‘s division, the ordinary Protestants of the south, comprising a range of religious denominations bound by history, intermarriage and culture, found themselves in a society in which their story was rarely told. The dominant narrative was one of a Catholic people, long oppressed by a wealthy Protestant minority. The story of ordinary Protestants, including those in rural and urban poverty, went largely unheard. Today, ordinary Protestants – small farmers, shop keepers, housewives – tell the story of Ireland as seen through their family‘s narratives. Themes of pride and shame, often intertwined, form a thread that binds their testimony, drawing on family, personal and local history, folklore and statements of identity.