In this thesis, I present an excitonic approach to treating the coherent dynamics of optically generated charge carriers in semiconductor nanostructures. The main feature of this approach is that it includes exchange interactions and phase space filling effects, which have generally been omitted in previous excitonic treatments of coherent dynamics, so that it can go beyond the low excitation limit. In contrast to the well-known semiconductor Bloch equations, this approach treats intraband correlations without factorization. The excitonic formalism and the obtained excitonic equations are shown to be particularly advantageous in systems where bound excitons dominate the optical response and where intraband correlations play a central role. To demonstrate the application of the excitonic approach, we simulate the coherent carrier dynamics of an optically-excited, updoped AlGaAs superlattice in the presence of a terahertz pulse, where 1s excitonic states as well as higher in-plane excited states are included. We find that gain coefficients greater than 20/cm can be achieved over a tuning range of 3-11THz and that due to the coherent cascading of the carriers down the excitonic Wannier-Stark ladder, the gain coefficients have much higher gain saturation fields than comparable two-level systems. To investigate the effects of phase space filling and exchange interaction on exciton dynamics, we then apply the excitonic formalism to a simple model of a quantum ring as well as a realistic model of a quantum well. For the quantum ring, we have obtained numerical results regarding exciton population and interband polarization. We also compared our excitonic approach to the semiconductor Bloch equations in detail using this simple model. For the quantum well, in addition to the investigation of exciton dynamics, we propose and examine several approximations that can make our excitonic dynamic equations very efficient. The excitonic formalism presented in this thesis is an efficient approach that can be applied in a wide range of systems, which makes it a potential alternative to the standard miconductor Bloch equations for many systems where the intraband correlations are crucial. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2008-12-01 18:21:17.181

<p>The main aim of this study was to develop a novel strategy for harnessing the properties of electroconductive polymers in sensor technology by using polymeric nanostructured blends in the preparation of high performance sensor devices.</p>

Electron scattering by a single or multiple impurities affects the quantizaton of conductance of a semiconductor nanochannel. The theoretical model of electron transport in a hardwall nanostructure with an impurity requires an analysis of the electronic transverse energy levels, eigenfunctions and hopping integrals resulting from cross channel or transverse confinement. Theoretical equations for the electronic transverse energy levels, wavefunctions and hopping integrals in the case of a repulsive, finite strength rectangular barrier arbitrarily positioned in the nanochannel are presented. The effects of size, strength and location of the impurity are discussed.In order to find the electronic transverse energy levels, wavefunctions and hopping integrals, two FORTRAN computer programs were developed. The first, called Program Data Input, writes the computational parameters to a data file. The second, Program Single Impurity, uses this data file in performing the calculations of the electronic transverse energy levels, eigenfunctions and hopping integrals. / Department of Physics and Astronomy

Transport in nanostructures and on-chip detection using nanohole arrays are investigated using a combination of analytical, numerical and experimental techniques. The first half of the thesis describes a fundamental theoretical contribution to the study of nanofluidic species transport. The second half of the thesis describes an applied experimental application of nanostructure-based species detection in a microfluidic framework. A continuum based analytical solution and numerical model are developed to quantify ionic dispersion of charged and neutral species in nanochannels and identify fundamental dispersion mechanisms unique to nanoscale flows. Ionic dispersion for circular cross-section nanochannels is quantified as a function of a valance parameter. the relative electrical double layer thickness. and the form of the velocity profile. Two unique mechanisms governing ionic dispersion in both pressure- and electrokinetically driven flows are identified. The results of the analytical solution are supported and extended by the results of the numerical model. Collectively, these results indicate that dispersion of ionic species in nanoscale channels is markedly charge dependent and substantially deviates from that of neutral solutes in the same flow. A microfluidic device with a set of embedded nanohole array surface plasmon resonance sensors is developed and successfully demonstrated experimentally as a chemical/biological sensor. The device takes advantage of the unique optical properties. the surface-based sensitivity, the transmission mode operation. relatively small footprint, and repeatability characteristic of nanohole arrays. Proof-of-concept measurements are performed on-chip to detect changes in liquid refractive index at the array surface. proportional to change in near wall concentration or indicative of a surface binding event. Employing a cross-stream array of nanohole arrays. the device is applied to detect microfluidic concentration gradients as well as to detect surface binding in the assembly process of a cysteamine monolayer-biotin-streptavidin system.

A new nanostructure for enhancing transmission and local field intensity in thin metal films is presented. The novel double-hole array design was numerically modelled using a finite-difference time-domain technique. Simulations were performed for different array periodicities and hole spacing to optimize the structure for maximum enhancement capabilities. An optimum double-hole array was able to produce simultaneous increase in transmission and near-field intensity. The local field enhancement was found to be 4 orders of magnitude greater than the incident field and strongly localized to a nanoscale area which is promising for a variety of applications. Arrays of the double-hole design were fabricated using a focussed-ion beam on a thin gold film. Linear measurements through the milled arrays showed the predicted enhancement in transmission for the optimum double-hole configuration. Finite-difference time-domain calculations were also done to study an isolated rectangular aperture to show the dependence of transmission on polarization of the incident beam and width of the aperture. Fabry-Perot resonances were shown to exist for different film thicknesses and the phase of reflection was calculated from the transmission results. A microfluidic device with an embedded surface plasmon sensor was developed and its sensitivity to changes in refractive index was shown.

This thesis addresses one of the major outstanding problems in the study of self-assembled InAs quantum dots (QDs): their physical profile after deposition of a capping layer and post-growth processing. The optical properties of QDs depend critically on the shape, composition and strain profile, yet these parameters are inaccessible to most experimental techniques once the dots are buried. Data from various x-ray scattering experiments are presented here, along with a novel approach to simulating diffuse scattering using an atomistic model based on Keating energy minimisation. The size and position of the diffuse scattering on the low-Q side of the Bragg peak, which are strongly influenced by the shape and composition of the QDs, has been used to determine that the QDs are truncated pyramids with a diagonal base length of 28 nm, with their edges aligned along the [100] and [010] directions. The composition profile varies from pure InAs at the top to 40-60% InAs at the base. These properties all agree with recent cross-sectional scanning tunnelling microscopy (X-STM) measurements by Bruls et al. It was shown that post-growth annealing causes a reduction in the In content of the QDs, primarily by diffusion from the base of the dot into the wetting layer. Grazing incidence small angle x-ray scattering (GISAXS) measurements have been made from samples of QDs produced with varying growth interruptions (GI) before deposition of the capping layer. The QDs were found to be highly diffuse. After a GI, the dots have been shown to change shape anisotropically, with two facets becoming sharper. An investigation of the use of resonant scattering to study buried QDs has shown that the method of contrast variation is of limited use for enhancing the measurement of diffuse features away from the Bragg peak. It is unsuitable for the study of buried nanostructures.

The high performance of bone implants depends on the positive response of osteoblasts to the surface of the materials manufactured for the implant. Cell response in turn strongly depends on the nature of the initial interaction of macromolecules involved in cell adhesion and proliferation with the atomic structure of the surface of the material used for the implant. The initial interaction between bone specific extracellular matrix proteins and the solid substrate influences cell response at the cell-implant interface. This interaction is crucial for implant stability, long-term durability, and osseointegration. Despite extensive research undertaken to develop high-quality material for implants in order to improve the cell-substrate interaction, little is known about the significance of the atomic structure of the substrate and the role of molecular machinery involved in cell-substrate interaction. Using a combined approach involving material sciences and cell and molecular biology, the objectives of this research are to evaluate the response of pre-osteoblast and fibroblast cell lines to novel bulk polycrystalline and single crystal titanium based material and assess the role of crystal size and orientation. / Novel bulk nano-structured titanium substrates were produced by the process of high-pressure torsion (HPT). These materials have a significant advantage compared to conventional titanium-based materials by having higher surface wettablity, mechanical properties as well as a distinct surface oxide layer and atomic structure. A co-culture system was adapted to investigate the differential response of pre-osteoblast and fibroblast cell lines to titanium and titanium dioxide single-crystal substrates. / The results of this study provide clear evidence that crystal size and specific crystallographic orientation can be used to improve cell adhesion and proliferation. The nanostructured titanium substrates show strong interaction with pre-osteoblast cells as evident by the higher expression of fibronectin and the formation of extensive focal adhesion. Differential cell behaviour of pre-osteoblasts and fibroblasts are observed in cultures grown on the substrates with specific crystallographic orientations. The degree of cell attachment of the pre-osteoblasts is considerably higher on Ti-(1120) crystal face compared with the fibroblasts. These findings have profound implications for the improved osseointegration and inhibition of fibrosis leading to long-term implant consolidation and stability.

No description available.

<p>The main aim of this study was to develop a novel strategy for harnessing the properties of electroconductive polymers in sensor technology by using polymeric nanostructured blends in the preparation of high performance sensor devices.</p>

Novel carbon materials such as carbon onions, nanotubes and amorphous carbon (a-C) are technologically important due to their useful properties. Normally synthesised using plasmas, their growth mechanisms are not yet fully understood. For example, the growth mechanism of the high density phase of a-C, tetrahedral amorphous carbon (ta-C), has been a subject of debate ever since its discovery. The growth mechanism of carbon nanostructures such as carbon onions and nanotubes is also not well known. The aim of this thesis is two-fold. Firstly, to provide insight into the growth of carbon films, in particular, the driving force behind the formation of diamond-like bonding in a-C which leads to ta-C. Secondly, to investigate the growth of carbon onions and other sp2 bonded carbon nanostructures such as nanotubes. To achieve the first aim, carbon thin films were deposited using cathodic arc deposition at a range of ion energies, substrate temperatures and Ar background gas pressures. These films were characterised using electron microscopy techniques to examine their microstructure, density and sp3 content. It was found that the formation of the ta-C is due to a stress-induced transition whereby a critical stress of 6.5±1.5 GPa is needed to change the phase of the film from highly sp2 to highly sp3. Within this region, a preferentially oriented phase with graphitic sheets aligned perpendicular to the substrate surface was found. By investigating the role of elevated temperatures, the ion energy-temperature