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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Solid state contacts to ion sensitive glass

Wilson, James Charles January 1991 (has links)
There have been a number of attempts since the inception of the glass electrode to replace the internal filling solution with a solid state form of contact. These have included both metallic and non-metallic materials. In the present work such contacts are reviewed, the nature of the materials, and conduction mechanisms between the contact and glass are discussed. Noble metal contacts alone are not expected to give a reproducible performance because of the lack of a common charge carrier which would allow conduction across the interface. However insertion of a non-metallic transition material which contains charge carriers common to both metal and glass may lead to more predictable performance. The materials, sodium tungsten bronze, iron-aluminium-sodium silicate glass, and various silver salts were interposed between a metal conductor and ion sensitive glass. Potentiometric measurements were made to determine sensitivity and time dependence of the output potential. These revealed that both the sodium tungsten bronze and iron-aluminium-sodium silicate glass gave improved performance over noble metal contacts. The silver salt contacts gave variable performance but it was shown that composite silver salts led to greater predictability of the value of the potential. Spectroscopic measurements were made to allow association of the observed concentration changes at the interface with potentiometric data and contribute to elucidation of reaction mechanisms. It was possible to relate the observed potential changes for silver halides with the increase in silver metal content in the halide layer. Interfacial conduction mechanisms remain unclear but charge transfer is most likely to occur through ionic conduction of sodium or silver ions across the interface. Sodium containing contacts, particularly iron-aluminium-sodium silicate glass, appeared to give a more stable output potential than silver containing contacts. Fabrication of an all-solid-state glass electrode from the former class of materials may be both simpler and more likely to achieve a reliable sensor than from the latter.
2

MCP optics

Brunton, Adam North January 1994 (has links)
This thesis is an account of research into a novel type of X-ray optic - the microchannel plate (MCP). Experiments to determine the point to point focusing properties of square pore MCPs manufactured by Galileo Electro-Optics and Philips Photonics are reported. These were performed both in a test chamber at Leicester with an electron-bombardment X-ray source and with a laser-plasma X-ray source at the Rutherford Appleton Laboratory. A resolution of 6 arcmin and an intensity gain of 20 were recorded using a Galileo focusing MCP. An invesigation into the focusing action of MCPs which have been curved to a spherical figure is detailed. Such curved MCPs may, in a manner reminiscent of a conventional refractive lens, be used to focus a parallel X-ray beam to a point forming the basis of an X-ray telescope, or conversely to convert the diverging beam from a point-like X-ray source to a quasi-parallel one. The curving experiments were performed by Philips Photonics on standard circular pore MCPs. Tests on these plates were performed at Leicester; the results appear favourable. The technique has been applied to MCPs of up to 4mm thickness, curving them to a radius of 1.4m (0.7m focal length). A comprehensive Monte Carlo ray-tracing model is presented. This was initially developed to facilitate an understanding of the geometry of MCP focusing and to produce idealised images corresponding to a given experimental set up. These perfect images may be compared with, or used to predict experimental results. Comparison with experimental results led to incorporation of MCP distortions into the code. These distortions have been found by a programme of metrology which is also described. The model has led to a clear insight into the causes of poor image quality and their relative importance.
3

Scanning near-field optical lithography and microscopy of conjugated polymer structures

Fenwick, Oliver January 2007 (has links)
This thesis is concerned with the use of the scanning near-field optical microscope (SNOM) to pattern and image conjugated polymer structures. The SNOM is one of just a few optical instruments which are capable of breaking the diffraction limit which limits conventional microscopes to a resolution of approximately half a wavelength. It does so by directing light onto a sub-wavelength aperture at the apex of a probe, establishing a local evanescent field of subwavelength dimensions around the aperture. Conjugated polymers on the other hand are an interesting class of materials which have semiconducting properties and a rich photophysics making them suitable for use in novel light-emitting diodes, transistors and solar cells. I demonstrate direct patterning of several conjugated polymers using the SNOM with a resolution extending below 100 nm and attempt to explain the resolution of the lithography through simulations using the Bethe-Bouwkamp model of the field surrounding a sub-wavelength aperture. In particular the modelling focuses on the role of the film thickness and reflections from the substrate. Further experiments demonstrate that thermal effects which can be caused by heating of the SNOM probe do not play a role in lithography with the SNOM in this case. However, I demonstrate the use of a scanning thermal microscope to do a novel and purely thermal lithography on one of the same conjugated polymers. Resolutions of 120 nm are demonstrated, and finite element analysis is used to show that significant improvements in resolution should be possible by optimisation of the probe and the polymer film. In addition, I present simulations of imaging artefacts caused by topography on samples under SNOM investigation, and use the same model to look at the potential of the SNOM to obtain information about sub-surface objects. SNOM images are presented of blends and supramolecular fibres of conjugated polymers.
4

Non-invasive imaging of metal structures using electric potential probes

Debray, Atanu January 2002 (has links)
No description available.
5

The metal photodissolution effect in spin-coated As-S films and its application in grating fabrication

Hajto, Eva January 1991 (has links)
The deposition of chalcogenides from their solutions using the spin-coating technique offers a new possibility for preparing technologically useful thin films in an easier way than the conventional vacuum techniques. This study descibes the use of the spin-coating technique to prepare chalcogenic thin films from their propylamine solutions. The composition range As<SUB>15</SUB>S<SUB>85</SUB>-As<SUB>40</SUB>S<SUB>60</SUB> was investigated. Infrared transmittance measurements show that the main structural unit of the spin-coated films is the AsS<SUB>3</SUB> pyramid. IR Spectroscopy also indicates that the amine group of the solvent propylamine molecule plays the dominant role in the dissolution process. The solvent/chalcogenide interaction was found to occur at the S-sites of the AsS<SUB>3</SUB> structural units of the chalcogenide. The dispersion of the refractive index, n(λ), for undoped and Ag-doped spin-coated As-S films was measured and shows that these films are transparent in the λchar61 1-10 μm spectral region. The refractive index values were fitted with the single oscillator expression and the oscillator energy, E<SUB>o</SUB>, and the oscillator dispersion energy, E<SUB>d</SUB>, for spin-coated films were determined. These values provide further information about the structure of these films. The values of the absorption coefficient, α, for a range of compositions of spin-coated As-S films and also for silver photodoped spin-coated As-S films at the optical absorption edge were calculated, and the band gap energy, E_g, for these films determined. The compositional dependence of E_g is explained by the bond strengths of the different bonds in the films. The preparation of holographic diffraction gratings in spin-coated As-S films by silver photodissolution and subsequent selective etching using CF_4 plasma is described. The diffraction efficiency of the surface relief gratings yielded a similar value to that for gratings prepared in vacuum-evaporated films.
6

Advances in gas-phase electron diffraction

Fender, Robert Scott January 1996 (has links)
A new gas-phase electron diffraction apparatus is reported in this thesis. The machine complements the existing electron diffraction set-up at Edinburgh University. The new apparatus utilises an electron counting device consisting of a pair of stacked microchannel plates and a novel, position-sensitive anode counter rather than the photographic plate-rotating sector method more commonly used in electron diffraction studies. The work carried out with this detector is discussed together with results from a simulation program designed to evaluate the operational capabilities of the device under a range of experimental conditions. The molecular target source was provided by a Campargue-type molecular beam and the electron beam was produced by a telefocus electron gun. Both of these beams have been fully characterised and the results are presented in this work. A short review is given of the current developments in gas-phase electron diffraction. Finally, the structural refinements of two molecules studied using the photographic method are reported. These are 1,2-di-<I>tert</I>-butyldisilane and 1,2-dicarbapentaborane(7).
7

Spatially resolved laser desorption mass spectrometry and femtosecond laser photoionisation studies

Hollingsworth, Alison January 1998 (has links)
A new instrument has been developed to perform spatially resolved molecular analysis using laser mass spectrometry. The instrument, a "laser mass microscope", incorporates a differentially pumped load-lock for rapid sample introduction, a precision computer controlled XYZ stage for accurate sample positioning, and a high resolution reflecting geometry single field time-of-flight mass analyser. The technique of two-step laser desorption laser photoionisation mass spectrometry (L2MS) is used in order to enable separate optimisation of sample desorption and ionisation. The spatial resolution of the instrument, primarily determined by the diffraction limited spot size at the desorption wavelength employed, ranges from 10 μm (532 nm) to 40 μm (10.6 μm). The mass resolution of the instrument is typically <I>M</I> ≥ 1400 for coronene (m/z = 300), with a detection limit at 266 nm of 0.7x10<SUP>-18</SUP> mole per shot. The range of molecules amenable to L2MS has been extended to include non-aromatic amino acids and aliphatic polymers, by employing femtosecond laser photoionisation as an alternative to single photon ionisation. A detailed description of the instrument and the L2MS technique is given together with the underlying background theory. The instrument has been characterised in terms of achievable spatial resolution, mass resolution, and detection sensitivity using a variety of desorption and photoionisation lasers as well as different photoionisation schemes. Desorption effects, such as any photochemical or photophysical consequences of employing UV desorption laser wavelengths as well as effects due to different methods of sample presentation have been investigated. An extensive set of experiments has been carried out (initially to explore the feasibility of employing femtosecond laser photoionisation) to investigate the possibility of achieving enhanced detection sensitivity for large molecules due to more efficient laser photoionisation. For such systems, fast intramolecular decay channels frequently inhibit the attainment of high ionisation efficiency using laser photoionisation on a nanosecond timescale. These experiments were carried out at the Lasers for Science Facility at the Rutherford Appleton Laboratory, Didcot. Several large molecules of analytical interest, such as porphyrins, biological molecules such as hemin and chlorophyll <I>a</I>, as well as amino acids and synthetic polymers have been efficiently ionised in this way using near-infrared radiation (λ = 750 nm). The mechanism of femtosecond ionisation for an aromatic amino acid tryptophan and for nickel octaethylporphyrin have been investigated.
8

Luminescence stimulated from quartz by green light : developments relevant to dating

Hong, Duk-Geun January 1998 (has links)
Since the introduction, in 1985, of optically stimulated luminescence (OSL) for age determination, the technique has become increasingly common as a method of dating. Light emitting diodes (LEDs) are a convenient and economical light source for the optical stimulation of luminescence. However for work with quartz, green light stimulation with an argon ion laser as light source is usual, particularly because of the low light intensity of light emitting diodes. Replacement of the original green light emitting diodes by newly developed high intensity green light emitting diodes allowed this limitations to be overcome. The new arrangement was shown to be of comparable sensitivity to the traditionally used argon ion laser system. The optically stimulated luminescence dating method has been advanced with the introduction of the "single aliquot method", which uses one disc prepared from the sample to carry out all the measurements to determine the equivalent dose. A method based on a single aliquot has the advantages of avoiding normalization problems and reducing effort. The original version of this method concerned the infrared stimulation of feldspar and showed success with an additive dose method, in which correction was made for less of luminescence signal due to repeated preheating and reading of the same aliquot. A similar single aliquot approach has been applied to the stimulation of quartz by green light, involving an alternative method of analysis of single aliquot data. This approach provides comparable accuracy to conventional equivalent dose determination by the multiple aliquot technique.
9

Extended dynamic range from a combined linear-logarithmic CMOS image sensor

Storm, Graeme George January 2004 (has links)
Dynamic Range determines the ability to see detail in scenes with varying illumination intensities, whether the viewing element is an eye, conventional film, or a digital image sensor. There are two distinct measures of dynamic range:  interscene and intrascene. The first is the absolute range viewable, where the viewing mechanism has time to adapt to the full range of sensitivity to incident illumination and the second is the range achievable in just a single setting and time. The research reported in this Thesis investigates how to combine linear and logarithmic modes of circuit operation to improve CMOS imager intrascene dynamic range. A single chip, 360x288 pixel image sensor has been designed, fabricated and characterized to demonstrate the ideas developed during the research. The pixel circuits are switchable between linear and logarithmic modes: after the set exposure period the linear result is readout then the logarithmic mode is switched in and read-out. Single or two parameter calibration can be performed to reduce the relatively high level of FPN in the raw logarithmic data. The settling time of the logarithmic mode of operation is identified as an important constraint on this approach and is optimized by the inclusion of an amplifier. To permit a pixel pitch of 5.6µm in a 0.18µm technology and achieve a 33% fill-factor, circuit and layout architectures have been devised to place the majority of the amplifier in the column in a way that allows it to be switchable between rows. The combining of linear and logarithmic data in a single image provides an intrascene dynamic range in excess of 120dB. The sensor can operate at 26 frames per second when employing single parameter calibration of the logarithmic mode. Comprehensive characterization of both modes and the overall performance of the sensor is also outlined. Critical discussion and suggestions on further research conclude the Thesis.
10

Diagnostic and statistical modelling techniques applied to an aluminium plasma etch process

Hannah, James Robertson January 1992 (has links)
Dry etching processes are crucial to the fabrication of VLSI and ULSI circuits and are likely to continue so for the foreseeable future. However, the technique remains difficult to implement and is not well understood. To a great extent, this is a result of the use of novel machine configurations and chemical recipes which are employed far in advance of any real understanding of the interactions occurring within the process chamber. Historically, process development in this field has proceeded as a result of improvements in vacuum technology coupled to empirical one-dimensional trend analyses. These traditional approaches to process development have become severely limited with the advent of ULSI. This project addressed the requirement for improved process characterisation by investigating diagnostic techniques and rigorous statistical modelling as applied to one of the most challenging leading edge processes: the BCl<SUB>3</SUB>/Cl<SUB>2</SUB>/He dry etching of aluminium alloys. Optical emission spectroscopy, electrostatic Langmuir probes and mass spectrometry were used to investigate the dry etch behaviour. During this research, a novel in-situ SIMS implementation of the mass spectrometer was used to investigate plasma generated positive ions. Details of detected ions and intensities during etching are presented. A CCF experimental design was formulated from the major RIE machine parameters of rf power, system pressure and % Cl<SUB>2</SUB>/BCl<SUB>3</SUB>. The final quadratic model covered 3 manipulated machine variables, 3 process parameters and 6 performance parameters. This is the first time that rigorous statistical modelling techniques have been applied to the BCl<SUB>3</SUB>/Cl<SUB>2</SUB>He based process or to an aluminium dry etch process in order to systematically characterise both the process and performance behaviour. This work presents these models, along with an estimate of each model's accuracy.

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