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Title: Charge writing on nanocrystalline tin dioxide nanoparticles
Author: Loke, Wing Lup David
Awarding Body: Swansea University
Current Institution: Swansea University
Date of Award: 2007
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Nanotechnology is an emerging field that shows the potential to bring the development in the various aspects of research to a new level. However, this evolution relies on the advancement in fabricating and locating material on surfaces with nanoscale precision. Self assembly is believed to be the solution to overcome the challenges and is presently being pursued in various guises, one of which is nanopatteming. Nanocrystalline tin dioxide is an n-type wide band gap semiconductor, which is commonly used for gas sensing applications. In Swansea University, the research on gas sensors had led to the discovery that by applying negative voltage pulses from a Scanning Tunnelling Microscope (STM) tip, it is possible to pattern the 8nm nanocrystalline tin dioxide grains. This results in features that are of average size of about 5nm in height and 17nm in width. Further research reveals that close to 100% success rate can be obtained with -6.0V tip voltage for 100?s, and the features patterned could be erased by scanning with a positive tip voltage. Moreover, the apparent height of the features on STM scans is dependent on the scanning tip voltage; and the grid Scanning Tunnelling Spectroscopy (STS) revealed a higher current flow into the patterned features. These experiments are in agreement and suggest that the patterned features are electronic in nature, as opposed to topographic. This thesis investigates the nanopatteming phenomena exhibited by tin dioxide grains at high temperature using the techniques of STM/STS, and with the aid of oxidising and reducing gases. At elevated temperature, nanopatteming on tin dioxide reveals a "charge spreading" effect, resulting in bigger feature size and lower current flowing through the patterned features. The studies also demonstrated the possibility to trigger the charge writing mechanism whilst scanning with a higher magnitude of tip voltage, charging large areas of the surface. The research on gas exposures with oxygen (oxidising) and carbon monoxide (reducing) gas favours the proposal that patterned features are electronic in nature; as well as acting as a feasibility study for the possibility of using the patterns for molecular docking applications. The investigation on the erasing process showed that a high magnitude voltage will result in removal of individual charged tin dioxide grains from the surface instead of extraction of electrons. Suggestions for future work that could be explored based on the findings presented in this study are presented in the last section of the thesis.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available