Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

In this study, the properties of nickel and antimony doped tin oxide (NATO) electrode materials were investigated in relation to the electrochemical generation of ozone. The performance of NATO materials was correlated to ·OH radical generation and oxygen adsorption properties. Long-time ozone generation results suggested that surface property changes, including surface morphology, chemical composition and electro-catalyst thickness, could lead to ozone production rate decreased from 137 to 0 mg·h-1 and the current efficiency declined from 18% to 0. The loss of Ni in the electrode was suggested for the decrease in ozone generation. Moreover, material characterization results indicated the presence of NiOOH and multiple oxidation states of Sb (+3 and +5), which were proposed as the critical sites for the electrochemical generation of ozone. In addition, NATO nanocrystals of 3.5 ~ 7.5 nm in size prepared by the hydrothermal method were used as an alternative route to fabricate electrodes. The highest current efficiency of 41% was achieved on NATO material of 6% Sb in the precursor, which led to the lowest resistivity of 2.38 ± 0.03 Ω·cm in the product NATO material. This further demonstrated the applicability of NATO materials used as electro-catalysts for the electrochemical generation of ozone. Hydroxyl free radicals (·OH) can be regarded as one of the most important intermediates for ozone generation. The presence of ·OH radicals was quantified by fluorescence spectroscopy with terephthalic acid as probes. Quantitative analysis results showed that Ni dopant could significantly enhance ·OH generation, while over-doping of Sb and Ni can decrease the generation of ·OH radicals. An oxygen chemisorption study on NATO materials showed that more active sites available for oxygen chemisorption lead to higher catalytic activity for ozone generation. The highest oxygen chemisorption capacity of 49.76 μmol·g-1 was achieved on NATO-5 (Sn:Sb:Ni=1000:16:2), which showed the highest current efficiency of 43%. In addition, temperature programmed oxygen adsorption and desorption showed different patterns on different NATO materials. This suggested that oxygen adsorption on NATO materials has a correlation to the electrochemical generation of ozone. In addition, oxygen adsorption was further investigated with near ambient oxygen adsorption. Oxygen adsorption isotherm results indicated that both physisorption and chemisorption can occur on the surface of SnO2 based material (NATO-5) with or without hydrogen pretreatment. When NATO-5 was treated with hydrogen, adsorption was mainly in the form of chemisorption. However, it was mainly in the form of physisorption without hydrogen pretreatment. By comparing NATO-6 (Sn:Sb:Ni=1000:16:0) with NATO-7 (Sn:Sb:Ni=1000:0:2), it was found that Sb was more important in the oxygen adsorption ability of NATO materials compared to Ni doping. Based on the findings in this study, two active sites (Sb and Ni sites) were proposed for ·OH generation and oxygen adsorption in order to explain the mechanism of ozone generation on NATO materials. Also, electrochemical generation of ozone was correlated with oxygen adsorption and ·OH generation. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

No description available.

No description available.

This study uses clusters formed in a UHV-compatible cluster apparatus, which was built and commissioned during this thesis. The design and operation of the cluster deposition system is described. This system is optimised for high clus- ter fluxes and for the production of cluster assembled nanoscale devices. One key feature of the system is a high degree of flexibility, including interchangeable sputtering and inert gas aggregation sources, and two kinds of mass spectrome- ter, which allow both characterisation of the cluster size distribution and deposi- tion of mass-selected clusters. Another key feature is that clusters are deposited onto electrically contacted lithographically defined devices mounted on an UHV- compatible cryostat cold finger, allowing deposition at room temperature as well as at cryogenic and at elevated temperatures. The electrically contacted nanoscale cluster devices were fabricated using a novel template technique. Hereby, clusters are placed between two electrodes separated only by ∼100 nm. The width of the cluster ensemble is in the order of a few cluster diameters, which means that the assembled clusters form a cluster wire bridging the electrode separation. During this thesis, the design and layout has been optimised to be able to measure electrical properties of the cluster devices and in particular to investigate the interaction between the cluster ensemble and the contact electrodes. In-situ electrical characterisation of cluster assembled nanoscale devices are performed in the temperature range 4.2 K to 375 K. The samples are provided with a backgate, which in principle allows modification of the conduction through the cluster ensemble by applying a gate voltage. However, no change in conduc- tion with changes in gate voltages was seen. The main focus of the electrical measurements is on the current voltage char- acteristics. It was noticed that the nanoscale bismuth (and antimony) cluster devices exhibited non-linear current voltage characteristics, which were in stark contrast to the linear current voltage characteristics measured for cluster films previously. Investigations into the causes of this non-linearity suggests that tun- nelling conduction occurs between the cluster ensemble (wire) and the contact electrodes. The non-linear current voltage characteristics were fitted using three models of tunnelling conduction and appear to be best fitted using a model in- volving fluctuation-assisted tunnelling through barriers of different heights. Further, measurements of the temperature dependent resistance are performed showing an increase of resistance with decreasing temperature for bismuth and antimony assembled cluster devices. The temperature dependence of bismuth as- sembled cluster wires can be explained by the decrease of the carrier concentration in bismuth for decreasing temperature. Annealing of the cluster ensemble and the cluster contact connection resulted in an increase in conduction. This increase of conduction can be explained due to the current flow through the cluster wire. Locally, at the bottlenecks, the current flow causes resistive heating and subsequently coalescence of two (or more) clusters.

Thesis (Master)--İzmir Institute of Technology, İzmir, 2005 / Includes bibliographical references (leaves 35-37).

Thesis (M.S.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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Thesis (Ph. D.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on June 29, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Chemistry, University of Alberta." Includes bibliographical references.