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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.
41

Multi-microscopy characterisation of III-nitride devices and materials

Ren, Christopher Xiang January 2017 (has links)
III-nitride optoelectronic devices have become ubiquitous due to their ability to emit light efficiently in the blue and green spectral ranges. Specifically, III-nitride light emitting diodes (LEDs) have become widespread due to their high brightness and efficiency. However, III-nitride devices such as single photon sources are also the subject of research and are promising for various applications. In order to improve design efficient devices and improve current ones, the relationship between the structure of the constituent materials and their optical properties must be studied. The optical properties of materials are often examined by photoluminescence or cathodoluminescence, whilst traditional microscopy techniques such a transmission electron microscopy and scanning electron microscopy are used to elucidate their structure and composition. This thesis describes the use of a dual-beam focussed ion beam/scanning electron microscope (FIB/SEM) in bridging the gap between these two types of techniques and providing a platform on which to perform correlative studies between the optical and structural properties of III-nitride materials. The heteroepitaxial growth of III-nitrides has been known to produce high defect densities, which can harm device performance. We used this correlative approach to identify hexagonal defects as the source of inhomogeneous electroluminescence (EL) in LEDs. Hyperspectral EL mapping was used to show the local changes in the emission induced by the defects. Following this the FIB/SEM was used to prepare TEM samples from the apex of the defects, revealing the presence of p-doped material in the active region caused by the defect. APSYS simulations confirmed that the presence of p-doped material can enhance local EL. The deleterious effects of defects on the photoelectrochemical etching of cavities were also studied. We performed TEM analysis of an edge-defect contained in unetched material on the underside of a microdisk using FIB/SEM sample preparation methods. The roughness and morphology of microdisk and nanobeam cavities was studied using FIB-tomography (FIBT), demonstrating how the dual-beam instrument may be used to access the 3D morphology of cavities down to the resolution of the SEM and the slicing thickness of the FIB. This tomography approach was further extended with electron tomography studies of the nanobeam cavities, a technique which provided fewer issues in terms of image series alignment but also the presence of reconstruction artefacts which must be taken into account when quantitatively analysing the data. The use of correlative techniques was also used to establish the link between high Si content in an interlayer running along the length of microrods with changes in the optical emission of these rods. The combination of CL, FIB/SEM and TEM-based techniques has made it possible to gain a thorough understanding of the link between the structural and optical properties in a wide variety of III-nitride materials and devices.
42

A light and electron microscopic analysis of the sacral parasympathetic nucleus after labelling primary afferent and efferent elements with HRP /

Mawe, Gary M. (Gary Michael) January 1984 (has links)
No description available.
43

Histogenesis of proventricular submucosal glands of the chick as revealed by light and electron microscopy /

Thomson, Dale Stirling January 1965 (has links)
No description available.
44

Fluorescence lifetimes of free and intracellular fluorescein as measured at the cellular level in Saccharomyces cerevisiae

Page, Steven Joseph January 2011 (has links)
Digitized by Kansas Correctional Industries
45

Ice thickness estimation using low frequencies, and an investigation of diffraction of sound in samples with micro structures using ultrasound

Shaw, Anurupa 07 January 2016 (has links)
In the first section, the thickness of ice on the lakes and canals is estimated by analyzing the sound spectrum generated by dispersion of Lamb type waves propagating in ice. In winters when the lakes and canals freeze, it is important to know the thickness of the ice layer before setting foot on it. When a stone is thrown on the ice layer, a fluting sound can be heard. This is recorded for different thicknesses of ice, and the sound spectrum is compared with the results simulated using a parameterized model. This model is created using a combination of plane waves for different incident angles and frequencies to generate dispersion curves for different thicknesses of ice. The frequencies of the reflected sound are then compared with the frequencies of musical instruments in order to assign different musical notes to different thicknesses of ice. The technique enables thickness estimation without the use of specialized equipment or time consuming drilling and may therefore be of practical value in the preservation of the lives of ice skaters and playing children. In the second half of the study, high frequencies (400 MHz and 1 GHz) are used to investigate samples with micro structures. Acoustic microscopy is a well established technique as far as smooth surfaces are concerned. V (z) curves are obtained from which, through surface wave generation, important features concerning elasticity and related properties can be extracted. Recently, high resolution imaging using high frequency focused transducers, based on acoustic microscopy has appeared. The surface profiles of the samples used in this study, have periodic structures but lack smoothness. The periodicity causes sound diffraction and the roughness influences the acoustic microscopic investigation. The small acoustic contrast between the substrate and the periodic corrugation on the material, gives us information about the additional stresses which develop and affect the bonding between the two materials. In this study, experiments are conducted using samples with corrugations of different periodicity, and a comparison is made between the results for smoother surfaces and results for the periodic structures of the same material. An attempt is made to analyse the effects described above.
46

Quantitative morphological studies of the parathyroid gland

Larsson, Hans-Olov January 1983 (has links)
This work is based upon a series of quantitative morphological studies of the parathyroid glands of Mongolian gerbils and rats. Standard stereological methods were used on light and electron microscopical levels. Subclassification of the chief cells based on the staining affinity and electron density of the cytoplasm was not correlated with contents (volume and surface densities) of organelles. Compared to fixation by immersion, fixation by perfusion caused a remarkable reduction in the number of light chief cells and atrophic cells, indicating that the occurrence of those kind of cells is dependent on factors of artifactual nature. The early response of the parathyroid gland to altered concentrations of extracellular calcium was studied in vitro. At six hours of "incubation, enlargement of the Golgi zone (Golgi complex and presecretory granules), but unaltered endoplasmic reticulum, was seen in glands incubated in low (0,5 mM) compared to those incubated in high (3,0 mM) calcium concentrations. Prolonged hypocalcemia induced in vivo by intraperitoneal injections of ethylenediaminetetraacetate and calcium deficient diet for eight days, did not give rise to any major quantitative morphological changes in the individual parathyroid cell, and furthermore, the quantitative morphology of the parathyroid cell was unchanged in experimentally induced hyperparathyroidism (calcium deficient diet for 16 weeks). The morphological data do not support the opinion of a functional cycle in the parathyroid chief cell, but suggest that the early response of this cell to altered extracellular calcium may be funtional activities associated with the Golgi zone. / <p>S. 1-48: sammanfattning, s. 49-170: 5 uppsatser</p> / digitalisering@umu
47

Scanning probe energy loss spectroscopy

Eves, Brian John January 2002 (has links)
No description available.
48

Advanced optical microscopy for three dimensional deformation, profile and tomography measurement

Pan, Zhipeng 27 May 2016 (has links)
Deformation, profile and tomography measurement is critical for engineering materials characterization and engineering structure component design, analysis and biomedical application. The current existing 3D measurement method, such as stylus based profilometry, 3D optical stereo imaging and focus stacking, either suffers from low sampling speed from spatial scanning or maximum thickness of the specimen that could be imaged due to physical constraints. This thesis is dedicated to develop a hybrid 3D measurement method that can be easily implemented with fast imaging speed for dynamic process at the microscale. Also, at the microscale, the reduced depth of focus of existing microscope system greatly limits the maximum depth of the specimen that could be imaged, especially at high magnification. In this study, a 3D tomography system will be developed with extended depth of focus and improved axial resolution.
49

Secondary electron emission in coincidence with primary energy losses

Muellejans, Harald January 1992 (has links)
No description available.
50

Development of methods for the analysis of structure and composition of biological tissues using low temperature electron microscopy

Oates, Kenneth January 1984 (has links)
No description available.

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