The preparation & properties of inorganic nanometer particles

Brooks, Lindsay (1998) The preparation & properties of inorganic nanometer particles. (PhD thesis), Kingston University, .


This thesis presents the findings obtained from a comprehensive investigation into experimental techniques for producing conducting and semiconducting colloidal sols, of carefully controlled particle size and narrow size distribution. Particle size distributions were determined using Transmission Electron Microscopy (TEM)and Image Analysis software. Evidence for the loss of bulk metal and semiconducting properties caused by the onset of quantum size effect, as energy levels become discrete and quanti sed, was monitored using optical spectroscopy, and then equated with the corresponding particle size distribution. Semiconducting iron disulphide was produced in nanometer dimensions using a novel synthetic route. Intensive studies into earlier investigations, alongside our own methods, revealed discrepancies in the literature. The control of colloidal FeS2 within reverse micelles, using sodium bis(2-ethylhexyl) sulfosuccinate and heptane as the reverse micellar solution, was also found to be an unreliable technique for cluster size control. Monodisperse silver sols were found to be difficult to form. Optical properties and particle size relationships were found when poly (ethylene glycol) was employed as a stabilising agent. However, the study showed a randomness associated with silver sol formation and a minimal correlation between experimental conditions and resultant particle sizes was found. Gold sols displayed greater relationships between reagent conditions and particle size, as well as between particle size and the associated optical properties. Gold sols stabilised with poly (vinylpyrrolidone) formed well defined gold particles, displaying quantum size effects. Studies into the mechanisms for colloidal nucleation and growth provided further evidence for the different processes involved for gold and silver sols. Stopped-flow kinetic apparatus was utilised to observe the changing optical spectrum of the particles, as a function of time. Gold sol kinetics' showed a process for rapid nucleation and slow growth, with an absorbance versus time profile similar to previous gold investigations explained by the Organiser Theory. Silver sols had optical lineshape suggesting continuing nucleation and aggregation. Computer simulations were carried out, demonstrating the different mechanisms. The gold sol profile has been reproduced using simple steady state treatment, rather than using the rather complex Organiser Theory. Hence, a new hypothesis has been proposed to explain the formation of gold sols. The silver sol kinetics spectra-have also been reproduced based upon models involving aggregative cluster reactions. Conduction Electron Spin Resonance (CESR) studies were performed upon dehydrated sols of silver, gold, and platinum. Quantum size effects were observed for Pt, with border-line quantum/classical effects displayed by gold and silver samples. All observed lineshapes were consistent with the literature, and could be rationalised in terms of the theory. The asymmetrical lineshapes and temperature effects have been accounted for using calculated simulations based upon a new model which allowed for quantum behaviour of the linewidth and the classical behaviour of the g-shift. Flaws were shown in earlier calculations for the asymmetric lineshape of colloidal silver.

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