7 resultados para Antenna Fabrication and Experimental

em CORA - Cork Open Research Archive - University College Cork - Ireland


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One-dimensional semiconductor nanowires are considered to be promising materials for future nanoelectronic applications. However, before these nanowires can be integrated into such applications, a thorough understanding of their growth behaviour is necessary. In particular, methods that allow the control over nanowire growth are deemed especially important as it is these methods that will enable the control of nanowire dimensions such as length and diameter (high aspect ratios). The production of nanowires with high-aspect ratios is vital in order to take advantage of the unique properties experienced at the nanoscale, thus allowing us to maximise their use in devices. Additionally, the development of low-resistivity interconnects is desirable in order to connect such nanowires in multi-nanowire components. Consequently, this thesis aims to discuss the synthesis and characterisation of germanium (Ge) nanowires and platinum (Pt) interconnects. Particular emphasis is placed on manipulating the nanowire growth kinetics to produce high aspect ratio structures. The discussion of Pt interconnects focuses on the development of low-resistivity devices and the electrical and structural analysis of those devices. Chapter 1 reviews the most critical aspects of Ge nanowire growth which must be understood before they can be integrated into future nanodevices. These features include the synthetic methods employed to grow Ge nanowires, the kinetic and thermodynamic aspects of their growth and nanowire morphology control. Chapter 2 outlines the experimental methods used to synthesise and characterise Ge nanowires as well as the methods used to fabricate and analyse Pt interconnects. Chapter 3 discusses the control of Ge nanowire growth kinetics via the manipulation of the supersaturation of Ge in the Au/Ge binary alloy system. This is accomplished through the use of bi-layer films, which pre-form Au/Ge alloy catalysts before the introduction of the Ge precursor. The growth from these catalysts is then compared with Ge nanowire growth from standard elemental Au seeds. Nanowires grown from pre-formed Au/Ge alloy seeds demonstrate longer lengths and higher growth rates than those grown from standard Au seeds. In-situ TEM heating on the Au/Ge bi-layer films is used to support the growth characteristics observed. Chapter 4 extends the work of chapter 3 by utilising Au/Ag/Ge tri-layer films to enhance the growth rates and lengths of Ge nanowires. These nanowires are grown from Au/Ag/Ge ternary alloy catalysts. Once again, the supersaturation is influenced, only this time it is through the simultaneous manipulation of both the solute concentration and equilibrium concentration of Ge in the Au/Ag/Ge ternary alloy system. The introduction of Ag to the Au/Ge binary alloy lowers the equilibrium concentration, thus increasing the nanowire growth rate and length. Nanowires with uniform diameters were obtained via synthesis from AuxAg1-x alloy nanoparticles. Manifestation of the Gibbs-Thomson effect, resulting from the dependence of the mean nanowire length as a function of diameter, was observed for all of the nanowires grown from the AuxAg1-x nanoparticles. Finally, in-situ TEM heating was used to support the nanowire growth characteristics. Chapter 5 details the fabrication and characterisation of Pt interconnects deposited by electron beam induced deposition of two different precursors. The fabrication is conducted inside a dual beam FIB. The electrical and structural characteristics of interconnects deposited from a standard organometallic precursor and a novel carbon-free precursor are compared. The electrical performance of the carbon-free interconnects is shown to be superior to that of the organometallic devices and this is correlated to the structural composition of both interconnects via in-situ TEM heating and HAADF-STEM analysis. Annealing of the interconnects is carried out under two different atmospheres in order to reduce the electrical resistivity even further. Finally, chapter 6 presents some important conclusions and summarises each of the previous chapters.

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The concept of a biofuel cell takes inspiration from the natural capability of biological systems to catalyse the conversion of organic matter with a subsequent release of electrical energy. Enzymatic biofuel cells are intended to mimic the processes occurring in nature in a more controlled and efficient manner. Traditional fuel cells rely on the use of toxic catalysts and are often not easily miniaturizable making them unsuitable as implantable power sources. Biofuel cells however use highly selective protein catalysts and renewable fuels. As energy consumption becomes a global issue, they emerge as important tools for energy generation. The microfluidic platforms developed are intended to maximize the amount of electrical energy extracted from renewable fuels which are naturally abundant in the environment and in biological fluids. Combining microfabrication processes, chemical modification and biological surface patterning these devices are promising candidates for micro-power sources for future life science and electronic applications. This thesis considered four main aspects of a biofuel cell research. Firstly, concept of a miniature compartmentalized enzymatic biofuel cell utilizing simple fuels and operating in static conditions is verified and proves the feasibility of enzyme catalysis in energy conversion processes. Secondly, electrode and microfluidic channel study was performed through theoretical investigations of the flow and catalytic reactions which also improved understanding of the enzyme kinetics in the cell. Next, microfluidic devices were fabricated from cost-effective and disposable polymer materials, using the state-of-the-art micro-processing technologies. Integration of the individual components is difficult and multiple techniques to overcome these problems have been investigated. Electrochemical characterization of gold electrodes modified with Nanoporous Gold Structures is also performed. Finally, two strategies for enzyme patterning and encapsulation are discussed. Several protein catalysts have been effectively immobilized on the surface of commercial and microfabricated electrodes by electrochemically assisted deposition in sol-gel and poly-(o-phenylenediamine) polymer matrices and characterised with confirmed catalytic activity.

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By using Si(100) with different dopant type (n++-type (As) or p-type (B)), it is shown how metal-assisted chemically (MAC) etched silicon nanowires (Si NWs) can form with rough outer surfaces around a solid NW core for p-type NWs, and a unique, defined mesoporous structure for highly doped n-type NWs. High resolution electron microscopy techniques were used to define the characteristic roughening and mesoporous structure within the NWs and how such structures can form due to a judicious choice of carrier concentration and dopant type. Control of roughness and internal mesoporosity is demonstrated during the formation of Si NWs from highly doped n-type Si(100) during electroless etching through a systematic investigation of etching parameters (etching time, AgNO3 concentration, %HF and temperature). Raman scattering measurements of the transverse optical phonon confirm quantum size effects and phonon scattering in mesoporous wires associated with the etching condition, including quantum confinement effects for the nanocrystallites of Si comprising the internal structure of the mesoporous NWs. Laser power heating of NWs confirms phonon confinement and scattering from internal mesoporosity causing reduced thermal conductivity. The Li+ insertion and extraction characteristics at n-type and p-type Si(100) electrodes with different carrier density and doping type are investigated by cyclic voltammetry and constant current measurements. The insertion and extraction potentials are demonstrated to vary with cycling and the occurrence of an activation effect is shown in n-type electrodes where the charge capacity and voltammetric currents are found to be much higher than p-type electrodes. X-ray photo-electron spectroscopy (XPS) and Raman scattering demonstrate that highly doped n-type Si(100) retains Li as a silicide and converts to an amorphous phase as a two-step phase conversion process. The findings show the succinct dependence of Li insertion and extraction processes for uniformly doped Si(100) single crystals and how the doping type and its effect on the semiconductor-solution interface dominate Li insertion and extraction, composition, crystallinity changes and charge capacity. The effect of dopant, doping density and porosity of MAC etched Si NWs are investigated. The CV response is shown to change in area (current density) with increasing NW length and in profile shape with a changing porosity of the Si NWs. The CV response also changes with scan rate indicative of a transition from intercalation or alloying reactions, to pseudocapactive charge storage at higher scan rates and for p-type NWs. SEM and TEM show a change in structure of the NWs after Li insertion and extraction due to expansion and contraction of the Si NWs. Galvanostatic measurements show the cycling behavior and the Coulombic efficiency of the Si NWs in comparison to their bulk counterparts.

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The absence of rapid, low cost and highly sensitive biodetection platform has hindered the implementation of next generation cheap and early stage clinical or home based point-of-care diagnostics. Label-free optical biosensing with high sensitivity, throughput, compactness, and low cost, plays an important role to resolve these diagnostic challenges and pushes the detection limit down to single molecule. Optical nanostructures, specifically the resonant waveguide grating (RWG) and nano-ribbon cavity based biodetection are promising in this context. The main element of this dissertation is design, fabrication and characterization of RWG sensors for different spectral regions (e.g. visible, near infrared) for use in label-free optical biosensing and also to explore different RWG parameters to maximize sensitivity and increase detection accuracy. Design and fabrication of the waveguide embedded resonant nano-cavity are also studied. Multi-parametric analyses were done using customized optical simulator to understand the operational principle of these sensors and more important the relationship between the physical design parameters and sensor sensitivities. Silicon nitride (SixNy) is a useful waveguide material because of its wide transparency across the whole infrared, visible and part of UV spectrum, and comparatively higher refractive index than glass substrate. SixNy based RWGs on glass substrate are designed and fabricated applying both electron beam lithography and low cost nano-imprint lithography techniques. A Chromium hard mask aided nano-fabrication technique is developed for making very high aspect ratio optical nano-structure on glass substrate. An aspect ratio of 10 for very narrow (~60 nm wide) grating lines is achieved which is the highest presented so far. The fabricated RWG sensors are characterized for both bulk (183.3 nm/RIU) and surface sensitivity (0.21nm/nm-layer), and then used for successful detection of Immunoglobulin-G (IgG) antibodies and antigen (~1μg/ml) both in buffer and serum. Widely used optical biosensors like surface plasmon resonance and optical microcavities are limited in the separation of bulk response from the surface binding events which is crucial for ultralow biosensing application with thermal or other perturbations. A RWG based dual resonance approach is proposed and verified by controlled experiments for separating the response of bulk and surface sensitivity. The dual resonance approach gives sensitivity ratio of 9.4 whereas the competitive polarization based approach can offer only 2.5. The improved performance of the dual resonance approach would help reducing probability of false reading in precise bio-assay experiments where thermal variations are probable like portable diagnostics.

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This paper investigates the effects of antenna detuning on wireless devices caused by the presence of the human body,particularly the wrist. To facilitate repeatable and consistent antenna impedance measurements, an accurate and low cost human phantom arm, that simulates human tissue at 433MHz frequencies, has been developed and characterized. An accurate and low cost hardware prototype system has been developed to measure antenna return loss at a frequency of 433MHz and the design, fabrication and measured results are presented. This system provides a flexible means of evaluating closed-loop reconfigurable antenna tuning circuits for use in wireless mote applications.

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Integrated nanowire electrodes that permit direct, sensitive and rapid electrochemical based detection of chemical and biological species are a powerful emerging class of sensor devices. As critical dimensions of the electrodes enter the nanoscale, radial analyte diffusion profiles to the electrode dominate with a corresponding enhancement in mass transport, steady-state sigmoidal voltammograms, low depletion of target molecules and faster analysis. To optimise these sensors it is necessary to fully understand the factors that influence performance limits including: electrode geometry, electrode dimensions, electrode separation distances (within nanowire arrays) and diffusional mass transport. Therefore, in this thesis, theoretical simulations of analyte diffusion occurring at a variety of electrode designs were undertaken using Comsol Multiphysics®. Sensor devices were fabricated and corresponding experiments were performed to challenge simulation results. Two approaches for the fabrication and integration of metal nanowire electrodes are presented: Template Electrodeposition and Electron-Beam Lithography. These approaches allow for the fabrication of nanowires which may be subsequently integrated at silicon chip substrates to form fully functional electrochemical devices. Simulated and experimental results were found to be in excellent agreement validating the simulation model. The electrochemical characteristics exhibited by nanowire electrodes fabricated by electronbeam lithography were directly compared against electrochemical performance of a commercial ultra-microdisc electrode. Steady-state cyclic voltammograms in ferrocenemonocarboxylic acid at single ultra-microdisc electrodes were observed at low to medium scan rates (≤ 500 mV.s-1). At nanowires, steady-state responses were observed at ultra-high scan rates (up to 50,000 mV.s-1), thus allowing for much faster analysis (20 ms). Approaches for elucidating faradaic signal without the requirement for background subtraction were also developed. Furthermore, diffusional process occurring at arrays with increasing inter-electrode distance and increasing number of nanowires were explored. Diffusion profiles existing at nanowire arrays were simulated with Comsol Multiphysics®. A range of scan rates were modelled, and experiments were undertaken at 5,000 mV.s-1 since this allows rapid data capture required for, e.g., biomedical, environmental and pharmaceutical diagnostic applications.

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This paper reports the results of the on-body experimental tests of a set of four planar differential antennas, originated by design variations of radiating elements with the same shape and characterized by the potential for covering wide and narrow bands. All the antenna designs have been implemented on low-cost FR4 substrate and characterized experimentally through on-body measurements. The results show the impact of the proximity to the human body on antenna performance and the opportunities in terms of potential coverage of wide and narrow bands for future ad hoc designs and implementations through wearable substrates targeting on-body and off-body communication and sensing applications.