|dc.contributor.author||Aghili Yajadda, Mir Massoud||-|
|dc.description.abstract||In this thesis the electrical conduction mechanism and some of the optical properties of thin films (TFs) of gold nanoislands (GNIs) are studied to utilize them for applications in nanoelectronics, sensors, solar cells, and plasmonics.
In a regular array of GNIs where NIs have an identical size and tunnel gap, the tunnel current can be calculated by using a relatively simple formula (provided in chapter one). In discontinuous GTFs, there are distributions of GNI sizes and tunnel gaps. Therefore, calculating the tunnel current in such systems at low and high applied voltages over a wide temperature range will be challenging. Here, we introduce a conduction percolation model where uncorrelated broad probability distributions for both the tunnel junction gaps and the Coulomb blockade energies are assumed. An excellent agreement is achieved between model calculations and experimental results at low and high applied voltages over a wide temperature range (2-300 K).
In discontinuous GTFs where the Coulomb blockade energies become significantly small such that the tunnel resistance is not much higher than the GNI resistance, the metallic behaviour of GNIs and the thermal expansion of the substrate can play an important role in the temperature dependent resistance of discontinuous GTFs. In this thesis, the temperature dependence of the electrical resistance of discontinuous GTFs at temperatures between 2 K and 300 K is studied experimentally and by model calculations. We show that the tunnel junctions and the Coulomb blockade energies are important at low temperatures and that the thermal expansion of the substrate and the resistance of the GNIs affect the resistance at high temperatures. We obtain a simple expression for the temperature at which the resistance changes from non-metal-like behaviour into metal-like behaviour.
To show an application of the discontinuous GTFs in nanoelectronics, we measure their resistances over a temperature range of 10-300 K. One of the samples essentially shows a temperature independent resistance (~ 2% resistance variation over a temperature range of 10-300 K). We find that such behaviour corresponds to the minimized Coulomb blockade energy (approximately 0.3 meV). This is achieved by reducing the nearest neighbour distance and increasing the size of the GNIs. It is shown that the temperature independent resistor operates in a regime where the thermally activated electron tunnelling is compensated by the metallic behaviour of the GNIs.
Generally, z-scan measurements can be used to demonstrate the nonlinear light absorption in gold, but in TFs, scattering of light from the surface due to its roughness can introduce inaccuracy in measuring absorption nonlinearity. We overcome this problem by developing an experimental technique where a GTF is irradiated by a Nd-YAG pulsed laser at the wavelength of 532 nm in near resonance with the d-band transition of gold. The temperature increase in the GTF is estimated for different light intensities by electrical measurement. Then, the temperature increase is calculated by using a 1D heat transport equation by assuming a constant absorbance for the GTF at the low laser intensities. The comparison between results of the calculations revealed the nonlinear absorption in the GTF. We employed this deviation from the linear behaviour to determine the nonlinear absorption coefficient. It is shown that the nonlinear absorption is due to smearing of the Fermi distribution, and scattering of the light from the surface dose not play a major role in the temperature increase of the GTF.
To demonstrate an application of discontinuous GTFs in opto-electronics, we use a discontinuous GTF to rectify an oscillating tunnel current at ultra high frequency (optical frequency). This is done by irradiating the GTF with a Nd-YAG pulsed laser at the
wavelength of 532 nm while a high DC voltage is applied to the sample. The tunnel current is found to be strongly enhanced by partial rectification of the plasmon-induced AC tunnel currents flowing between adjacent GNIs. In addition, our technique shows that the enhancement is due to the plasmon oscillation and the thermal effects seem not to contribute to the tunnel current enhancement.||en_AU|
|dc.publisher||University of Sydney||en_AU|
|dc.publisher||Faculty of Science||en_AU|
|dc.publisher||School of Physics||en_AU|
|dc.rights||The author retains copyright of this thesis. It may only be used for the purposes of research and study. It must not be used for any other purposes and may not be transmitted or shared with others without prior permission.||en_AU|
|dc.subject||Coulomb Blockade Effect||en_AU|
|dc.subject.other||POST DG EXPORT SUBMISSION||en_AU|
|dc.title||An investigation on the electrical and optical properties of thin films of gold nanoislands||en_AU|
|dc.type.pubtype||Doctor of Philosophy Ph.D.||en_AU|
|Appears in Collections:||Sydney Digital Theses (Open Access)|