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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.
31

Measurement of low concentration and nano quantity hydrogen sulfide by carbon nanotube

Wu, Xiao Chu 17 December 2007
Traditionally, hydrogen sulfide (H2S) has been regarded as toxic. It can affect the various human systems and even cause death. However, research in the 1990s has shown that H2S can be endogenously generated by many cells and tissues in mammalian bodies, and that H2S also may play physiological roles such as those of neuromodulator and vasorelaxant in the biological system. As such, the precise measurement of the amount of H2S in a mammalian body has generated researchers strong interest. The ultimate goal of such a measurement should be conducted in-vivo and in real time.<p>The existing methods for H2S measurement require both a large quantity of tissue samples and a complex procedure, so they are not highly practicable for the purpose of achieving the aforementioned goal. In this dissertation, a new method that uses carbon nanotube as an absorbent or transducer and laser-based microscopy techniques (Raman and confocal laser scanning microscopy) as signal excitation and acquisition is proposed and developed. Experimental studies are described of using this new method for analysis of both distilled water samples and serum samples in which a group of proteins are present. <p>The study concludes that the new method (1) can measure H2S in water solutions down to a low level of concentration of 10 µM, (2) can measure H2S in sera down to a low concentration of approximately 20 µM), and (3) has a high feasibility for being used in the clinical context. Regarding (3), this is confirmed by presenting a control system that allows the laser microscopy to track carbon nanotube in a solution that has Brownian motion.<p>While not having reached the ultimate goal as mentioned above, this work advances the state-of-the-art of the measurement of low concentration and nano-quantity of H2S in water and serum samples, in particular providing a promise toward a real-time and in-vivo H2S measurement.
32

Measurement of low concentration and nano quantity hydrogen sulfide by carbon nanotube

Wu, Xiao Chu 17 December 2007 (has links)
Traditionally, hydrogen sulfide (H2S) has been regarded as toxic. It can affect the various human systems and even cause death. However, research in the 1990s has shown that H2S can be endogenously generated by many cells and tissues in mammalian bodies, and that H2S also may play physiological roles such as those of neuromodulator and vasorelaxant in the biological system. As such, the precise measurement of the amount of H2S in a mammalian body has generated researchers strong interest. The ultimate goal of such a measurement should be conducted in-vivo and in real time.<p>The existing methods for H2S measurement require both a large quantity of tissue samples and a complex procedure, so they are not highly practicable for the purpose of achieving the aforementioned goal. In this dissertation, a new method that uses carbon nanotube as an absorbent or transducer and laser-based microscopy techniques (Raman and confocal laser scanning microscopy) as signal excitation and acquisition is proposed and developed. Experimental studies are described of using this new method for analysis of both distilled water samples and serum samples in which a group of proteins are present. <p>The study concludes that the new method (1) can measure H2S in water solutions down to a low level of concentration of 10 µM, (2) can measure H2S in sera down to a low concentration of approximately 20 µM), and (3) has a high feasibility for being used in the clinical context. Regarding (3), this is confirmed by presenting a control system that allows the laser microscopy to track carbon nanotube in a solution that has Brownian motion.<p>While not having reached the ultimate goal as mentioned above, this work advances the state-of-the-art of the measurement of low concentration and nano-quantity of H2S in water and serum samples, in particular providing a promise toward a real-time and in-vivo H2S measurement.
33

Exploring Atomic Force Microscopy To Probe Charge Transport Through Molecular Films And For The Development Of Combinatorial Force Microscopy

Chisholm, Roderick A. 06 1900 (has links)
Since the invention of the atomic force microscope (AFM), this technology has had profound implications in the study of material science and molecular biology. The ability to visualize and perform quantitative analysis of the nanoscale properties of surfaces has provided great insights into these nanoscale landscapes. The present dissertation manuscript exploits this technology for the measurement of charge transport through molecular films and the development of combinatorial force microscopy. Firstly, this work probed, for the first time, charge transport through molecular films derived from diazonium salts grafted to carbon electrodes using conductive atomic force microscopy. We found the charge transport properties of a molecular junction are dependent upon the chemical structure of the molecular film. We also investigated the effect of molecular film compression and deformation has on charge transport. In this, we observed increases in current densities associated with increases in applied load to the molecular film. Furthering these initial findings, PPF/NAB/Cu molecular junctions were fabricated having junction sizes ranging between micro-scale and nanoscale. The charge transport experiments reveal an agreement of electron transport properties between the metal deposited PPF/NAB/Cu junction and a PPF/NAB/Cu AFM tip junction at an applied load of approximately 60nN. This form of molecular layer charge transport control may potentially open new horizons for integration of molecular films into the microelectronics industry. This dissertation manuscript also describes the development of the quantitative interrogation opposing chemical libraries involved in combinatorial inverted atomic force microscopy. Tipless cantilevers were patterned with chemically modified nanorods. These modified nanorods were then used as chemical identifiers during a combinatorial force microscopy experiment and for the first time 16 interactions were monitored within one experiment in a continuous medium. Thus, providing excellent for the validation that combi-AFM is a truly quantitative high-throughput technology.
34

Variable-temperature scanning tunneling microscopy studies of atomic and molecular level surface phenomena on semiconductor and metal surfaces /

Fitts, William Patrick, January 2001 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 337-351). Available also in a digital version from Dissertation Abstracts.
35

Crossed and uncrossed retinal fibres in normal and monocular hamsters : light and electron microscopic studies /

Yu, Enhua. January 1990 (has links)
Thesis (Ph. D.)--University of Hong Kong, 1991.
36

The point emitter as a positive-ion source

Herron, Russell Gardner. January 1955 (has links)
Thesis (M.S. in Physics)--United States Naval Postgraduate School, California. / Includes bibliographical references (p. 23). 9
37

Theoretical aspects of scanning transmission electron microscopy /

Findlay, Scott David. January 2005 (has links)
Thesis (Ph.D.)--University of Melbourne, Dept. of Physics, 2005. / Typescript. Includes bibliographical references (leaves 205-223).
38

Development of spectral imaging microscope for single molecule studies in complex biological systems /

Girirajan, Thanu Prabha Kalambur, January 2007 (has links)
Thesis (M.S.) in Electrical Engineering--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaf 75).
39

Development of Spectral Imaging Microscope for Single Molecule Studies in Complex Biological Systems

Girirajan, Thanu Prabha Kalambur January 2007 (has links) (PDF)
No description available.
40

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.

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