Dr Pierre Couture

Aluminium-doped ZnO (AZO) thin films were deposited by remote plasma sputtering of a ZnO:Al2O3 98:2 wt.% ceramic target in a pulsed DC configuration. The target power was kept constant at 445 W and the RF plasma power was varied between 0.5 and 2.5 kW. The as-deposited AZO thin films exhibited an optimum resistivity of 6.35 x 10-4 .cm and optical transmittance of 92 % at a RF plasma power 1.5 kW. The thin film microstructure, chemical composition, and residual stress were investigated using SEM, RBS, XPS and XRD. Accurate determination of the chemical composition and correct interpretation of GIXRD data for AZO thin films are a particular focus of this work. The AZO layer thickness was 500 - 700 nm and Al content in the range of 2.3 - 3.0 at.%, determined by RBS. The AZO thin films exhibited a strong (002) preferential orientation and grain sizes between 70 and 110 nm. The (103) peak intensity enhancement in GIXRD is proven to be a result of the strong (002) preferential orientation and GIXRD geometrical configuration rather than a change in the crystallite orientation at the surface. XPS depth profiles show preferential sputtering of O and Al using a 500 eV Ar+ beam, which can be reduced, but not eradicated using an 8 keV Ar150+ beam. The preferential sputtering can be successfully modelled using the simulation software TRIDYN. A plasma power of 1.5 kW corresponds to a highly ionised plasma and various microstructural and compositional factors have all contributed to the optimum low resistivity occurring at this plasma power. The grain size exhibits a maximum in the 1.25 - 1.5 kW range and there is improved (002) orientation, minimising grain boundary scattering. The highest carrier concentration and mobility was observed at the plasma power of 1.5 kW which may be associated with the maximum in the aluminium doping concentration (3.0 at.%). The lowest residual stress is also observed at 1.5 kW.

BiFeO3 and BiCrO3 films were made by room temperature sputtering followed by thermal annealing in a partial oxygen atmosphere. The annealed films were found to be nanocrystalline, with an average particle size of 11 nm for BiFeO3 and 8 nm for BiCrO3. The saturation moment per formula unit is 0.39 µB for BiFeO3 which is significantly greater than that found in bulk BiFeO3 (0.02 µB). A similar enhancement was also found in previous studies of BiFeO3 nanoparticles where the nanoparticle size was small. However, no large enhancement of the saturation moment per formula unit was identified for the annealed BiCrO3 films. The annealed BiFeO3 films displayed superparamagnetic behaviour and the particle size estimated from the blocking temperature is comparable to that estimated from the X-ray diffraction data. Our results show that sputtering and oxygen annealing is a method that can be used to make nanocrystalline BiFeO3 and BiCrO3 films.

Starbursts are found through the whole Universe and represent an important phase in the evolution of galaxies. Distant starbursts may be easily observed and study in the ultraviolet light because of their massive stars. I will present magnitude and color simulations of young stellar populations in order to characterize their age, metallicity, initial mass function, and star formation rate and history. These simulations take into account the filters available with the Ultraviolet Imaging Telescope.

Multiferroic nanocrystalline BiFeO3films have been successfully made by room temperature sputtering and thermal annealing in oxygen at 500C. Nanocrystalline Bi was seen before annealing as well asb-Bi2O3 and the iron oxide phases, magnetite, maghemite, and FeO. Superparamagnetism was observed that can be attributed to magnetite and maghemite nanoparticles. The thermally annealed film contained BiFeO3 nanoparticles and magnetite, maghemite, and hematite as well as unidentified BiFexOyphases. Superparamagnetism was also seen after annealing and the magnetic properties are predominately due to magnetite and maghemite nanoparticles rather than from multiferroic BiFeO3. The saturation magnetic moment was 60% lower after annealing, which was due to some of the Fe in the iron oxide nanoparticles being incorporated into the BiFeO3nanoparticles. An exchange bias was observed before and after annealing that cannot be attributed to a structure that includes BiFeO3. It is likely to arise from magnetite and maghemite cores with spin-disordered shells.