This thesis is a study of the development of new methods for the quantitative determinations of bismuth and amines.

An experimental Nernst effect measuring system is designed and constructed. The ability to measure the Nernst effect allows completion of a thermoelectric suite of measurements consisting of electrical conductivity, the Seebeck effect, the Hall effect, and the Nernst effect. This suite of measurements gives information about electron transport, carrier concentration, and electron scattering within a thermoelectric sample. Programs were designed in LabView to control the various instruments in the measuring system. Measurements of the Nernst effect were taken on two thermoelectric samples, bismuth nickel telluride and bismuth antimony telluride. These measurements were taken at both constant temperature and constant magnetic field. An error analysis of the Nernst effect measuring system is also presented, with consideration as to future work that can be done to improve the quality of Nernst effect measurements taken from the system.

Graduation date: 1999

Typescript. Includes vita and abstract. Includes bibliographical references (leaves 130-137). Abstract also available online in ProQuest, free to University of Oregon users.

published_or_final_version / Chemistry / Master / Master of Philosophy

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.

No description available.

Several bismuth-containing transition metal perovskites that are of interest as potential multiferroic materials have been synthesised and studied. These materials have been structurally characterised and their physical properties have been examined at varying temperatures and pressures. The new series of substituted bismuth ferrite perovskites BixCa1-xFeO3, where x = 0.4 - 1.0, has been prepared. A disordered cubic phase (x = 0.4 - 0.67) and the coexistence of rhombohedral and cubic phases (x = 0.8 and 0.9) have been observed. The x = 0.8 sample is located at the phase boundary and shows a transformation from cubic to rhombohedral symmetry at 473 - 573 K. All samples are antiferromagnets at room temperature and have Néel temperature of 623 - 643 K. Ferroelectric order is suppressed in the disordered cubic phase. BixLa1-xMnO3 materials with x = 0.8, 0.9 and 1.0 were synthesised at 3 - 6 GPa. For x = 1.0 and 0.9 samples a highly distorted perovskite structure with monoclinic space group C2/c was adopted and ferromagnetic behaviour was observed with Curie temperatures of 101 and 94 K, respectively. Bi0.8La0.2MnO3 shows an O'-type orthorhombic Pnma structure and canted A-type antiferromagnetic ordering below 80 K. A new phase of BiNiO3 has been discovered at 4 - 5 GPa below 200 K, in which a Pb11 symmetry has been revealed with a = 5.2515(2) Å, b = 5.6012(3) Å, c = 7.6202(4) Å and β = 90.20(1) º at 4.3 GPa and 100 K. This new Phase Id is derived from the ambient Phase I Bi3+ 0.5Bi5+ 0.5Ni2+O3, where the charge disproportionated Bi3+/Bi5+ cations become disordered. The updated P-T phase diagram of BiNiO3 is presented. BiCu3Mn4O12 has been studied by neutron diffraction from 5 to 400 K. The incorporation of Mn3+ into the Cu site has been observed, showing that the true composition is BiCu2.5Mn4.5O12. The ordering of Mn and Cu moments below transition temperature 320 K is found to be ferromagnetic rather than ferrimagnetic as proposed previously.

If a physical dimension of a metallic specimen is comparable with, or smaller than, the mean free path of the conduction electrons, then the observed electrical conductivity will be less than that of a conventional bulk sample. This phenomenon is called a size effect, and is the result of electron scattering from the specimen surfaces. In the present investigation, measurements were made on electropolished monocrystalline specimens ranging from matchbox geometry to thick-film geometry in order to obtain further information on the size effect in bismuth at liquid helium temperatures.

Cheung Ching Ying. / Bibliography: leaf 126 / Thesis (M.Phil.)--Chinese University of Hong Kong