Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6872. Adviser: Richard M. Martin. Includes bibliographical references (leaves 104-109) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--Indiana University, Dept. of Physics, 2008. / Title from home page (viewed on Oct 8, 2009). Source: Dissertation Abstracts International, Volume: 70-02, Section: B, page: 1098. Adviser: William Michael Snow.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3850. Adviser: Vijay Pandharipande. Includes bibliographical references (leaves 118-122) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6459. Adviser: David M. Ceperley. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

<p> Interactions between particles and their environment can alter the dynamics of biological systems. In crowded media like the cell, interactions with obstacles can introduce anomalous subdiffusion. Active matter systems, <i>e.g. </i>, bacterial swarms, are nonequilibrium fluids where interparticle interactions and activity cause collective motion and dynamical phases. In this thesis, I discuss my advances in the fields of crowded media and active matter. For crowded media, I studied the effects of soft obstacles and bound mobility on tracer diffusion using a lattice Monte Carlo model. I characterized how bound motion can minimize the effects of hindered anomalous diffusion and obstacle percolation, which has implications for protein movement and interactions in cells. I extended the analysis of binding and bound motion to study the effects of transport across biofilters like the nuclear pore complex (NPC). Using a minimal model, I made predictions on the selectivity of the NPC in terms of physical parameters. Finally, I looked at active matter systems. Using dynamical density functional theory, I studied the temporal evolution of a self-propelled needle system. I mapped out a dynamical phase diagram and discuss the connection between a banding instability and microscopic interactions.</p><p>

<p> Cooper pairs are known to tunnel through a barrier between superconductors in a Josephson junction. The spin states of the pairs can be a mixture of singlet and triplet states when the barrier is an inhomogeneous magnetic material. The purpose of this thesis is to better understand the behavior of pair correlations in the ballistic regime for different magnetic configurations and varying physical parameters. We use a tight-binding Hamiltonian to describe the system and consider singlet-pair conventional superconductors. Using the Bogoliubov-Valatin transformation, we derive the Bogoliubov-de Gennes equations and numerically solve the associated eigenvalue problem. Pair correlations in the magnetic Josephson junction are obtained from the Green's function formalism for a superconductor. This formalism is applied to Josephson junctions composed of discrete and continuous magnetic materials. The differences between representing pair correlations in the time and frequency domain are discussed, as well as the advantages of describing the Gor'kov functions on a log scale rather than the commonly used linear scale, and in a rotating basis as opposed to a static basis. Furthermore, the effects of parameters such as ferromagnetic width, magnetization strength, and band filling will be investigated. Lastly, we compare results in the clean limit with known results in the diffusive regime.</p><p>

<p> The magnetic properties of Metallo-organic heterostructure interfaces are studied. These heterostructures are built with manganese phthalocyanine (MnPc) and iron phthalocyanine (FePc). Previously, the powder of each material is reported to be an Ising-like chain magnet with Arrhenius relaxation. The relaxation is slow enough to exhibit magnetic hysteresis at low temperatures. Each layer of the heterostructure is investigated separately by depositing a thin film of either iron phthalocyanine (FePc) or manganese phthalocyanine (MnPc) on a Silicon substrate heated to 150 &deg;C. FePc thin films show magnetic hysteresis below 5K with a typical coercivity of 1850 &plusmn; 50 Oe and moment of about 1.9 &micro;B in agreement with values from the literature. Similarly, the MnPc thin film deposited at 150 &deg;C shows magnetic hysteresis at 2.5 K, and no hysteresis at 5K and 10 K. A coercive field of 390 Oe is recorded at 2.5 K. The saturation magnetization is near 9 emu cm^&ndash;3, which corresponds to an effective magnetic moment per Mn ion of about 0.5 &micro;B. For the MnPc/FePc thin film bilayer, the FePc is deposited at 150 &deg;C onto the Silicon substrate, the sample is cooled to room temperature followed by the MnPc deposition in situ. The magnetic moment of this heterostructure is consistent with contributions from the FePc layer only, since the room temperature deposited MnPc has antiferromagnetic characteristics. This heterostructure has magnetic hysteresis with a coercivity of 910 Oe. No measurable shift of the hysteresis loops&mdash;as expected for an antiferromagnetic-ferromagnetic coupled interface&mdash;is observed in this set of bilayers.</p><p>

<p> We have investigated the Faraday effect of bismuth-doped rare-earth iron-garnets with varying doping levels of gallium from z = 1.0 to 1.35. We used lutetium to control the film's in-plane magnetic properties and found that gallium doping levels above the compensation point caused a loss of anisotropy control, a canted out-of-plane magnetization in the film, and an extremely weak but linear coercivity above 10 micro-Tesla fields. Using these results we focused on in-plane films to create 8 layer stacks of 500 um thick films to achieve a minimum detectable field of 50 pT at 1 kHz. Unlike previous Magneto-Optic (MO) studies that typically used thin films of approximately 1um thickness, we used approximately 400um thick films to allow experimentation with the final, robust, ideal form the MO sensor would take. We measured what most other MO studies with garnets neglected: the magnetic anisotropy axis or structure within the film. Knowledge of this structure is essential in improving the sensitivity of a stacked MO probe. Studying thick films proved to be key to understanding the magnetic anisotropy and domain properties that can degrade or enhance the sensitivity of the Faraday rotation in bismuth doped rare-earth iron-garnets to an applied magnetic field and to pointing the direction of future research to develop the conditions for rugged magnetometer sensors. </p><p>

Block copolymers (BCP) are a unique class of polymers, which can self-assemble into ordered microdomains with sizes from 3 nm to about 50 nm making BCPs an appealing meso-scale material. In thin films, arrays of BCP microdomains with long-range lateral order can serve as ideal templates or scaffolds for patterning nano-scale functional materials and synthesizing nanostructured materials with size scales that exceed the reach of photolithography. Among many annealing methods, solvent vapor annealing (SVA) is a low-cost, highly efficient way to annihilate defects in BCP thin films and facilitates the formation of highly ordered microdomains within minutes. Directing the self-assembly of BCPs could, in principle, lead to the formation of domains with near perfect lateral ordering. The mechanism of SVA of BCPs, however, is still ill-understood, albeit it has been widely adopted in research laboratories around the world for the past decade. In the first part of this thesis, the ordering process of BCP thin films during annealing in neutral solvents was investigated mainly by in situ synchrotron X-ray scattering. Briefly, the solvent molecules impart mobility to the BCP and enable a marked improvement in the lateral ordering of the BCP microdomains. Both, BCP concentration in the swollen film and the rate of solvent removal play a key role in obtaining films with well-ordered microdomains. The amount of swelling in a BCP thin film during SVA depends on the chemical nature of the blocks, the quality of the solvent, and the molecular weight of the BCP. A high degree of swelling - still low enough to prevent solvent-induced mixing (disordering) of BCP microdomains,- provides a high chain mobility, and thus results in the formation of arrays of ordered microdomains with large grain sizes after SVA in neutral solvents. The rate of solvent removal is another critical parameter for obtaining long-range lateral order in BCP thin films after SVA in neutral solvents. While in the swollen state ordered structures form with exceptional order, removal of the solvent results in a deterioration of order due to the confinement imposed to a BCP in a thin film by the rigid silicon substrate. It was found, however, that an instantaneous solvent removal can minimize disordering to preserve the order formed in the swollen state. Self-assembled BCP microdomains also serve as ideal template to pattern other materials with exceptional lateral resolution. In this thesis, two examples of BCP lithography was also demonstrated. A reconstruction process was used to enhance the etch contrast between two organic blocks. In one example, a BCP pattern was transferred to a silicon substrate to form high aspect ratio, 5:1, sub-10nm silicon lines or holes with high fidelity. While in a second example, I demonstrated the fabrication of silicon oxide dots with an areal density as high as 2 Tera dots per inch2 by BCP templates, which has the potential to serve as etch mask for bit pattern media applications.

Experimental investigations of the optical properties of InGaN/GaN quantum dots are presented. A pulsed laser is used to perform time-integrated and time-resolved microphotoluminescence, photoluminescence excitation, and polarisation-resolved spectroscopy of single InGaN quantum dots under a non-linear excitation regime. The first micro-photoluminescence results from InGaN/GaN quantum dots grown on a non-polar crystal plane (11^-<sub style='position: relative;left: -.4em;'>2</sub>0) are presented. Time-resolved studies reveal an order of magnitude increase in the oscillator strength of the exciton transition when compared to InGaN quantum dots grown on the polar (0001) plane, suggesting a significantly reduced internal electric field in non-polar InGaN quantum dots. Polarisation resolved spectroscopy of non-polar InGaN quantum dots reveals 100% linearly polarised emission for many quantum dots. For quantum dot emissions with a polarisation degree less than unity, a fine structure splitting between two orthogonal polarisation axes can be resolved in an optical setup with a simple top-down excitation geometry. A statistical investigation into the origins of spectral diffusion in polar InGaN quantum dots is presented, and spectral diffusion is attributed to charge carriers trapped at threading dislocations, and itinerant and trapped carriers in the underlying quantum well layer which forms during the growth procedure. Incorporating quantum dots into the intrinsic region of a p-i-n diode structure and applying a reverse bias is suggested as a method to reduce spectral diffusion. Coherent control of the excited state exciton in a non-polar InGaN quantum dot is experimentally demonstrated by observation of Rabi rotation between the excited state exciton and the crystal ground state. The exciton ground state photoluminescence is used as an indirect measurement of the excited state population.