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Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / An X-ray diffraction study of tri-(p-aminophenyl) carbonium perchlorate, (H2NC6H4)3C.ClO4, was carried out in order to determine (1) the effects of substituents on the structure of triphenylcarbonium ion, and (2) the effect of crystal symmetry on the configuration of the triarylcarbonium ions. [TRUNCATED] / 2031-01-01

by Mok Siu Wah. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references. / Text in English; abstract also in Chinese. / by Mok Siu Wah. / Chapter Chapter I --- Introduction / Chapter 1.1 --- Solidification --- p.1-1 / Nucleation A. Homogenous nucleation --- p.1-2 / B. Heterogeneous nucleation --- p.1-3 / Crystal growth and dendrites formation --- p.1-4 / Planar growth --- p.1-5 / Dendrite formation --- p.1-5 / Growth far from equilibrium --- p.1-5 / Chapter 1.2 --- Grain refinement --- p.1 -6 / Models of grains refinement --- p.1-6 / Dynamic nucleation --- p.1-7 / Dendrite remelting --- p.1-8 / Objectives of the present project --- p.1-12 / References --- p.1-13 / Figure --- p.1-14 / Chapter Chapter II --- Experimental method / Experimental methods --- p.2-1 / Specimen preparation --- p.2-1 / Metallography --- p.2-2 / Analysis --- p.2-3 / Reference --- p.2-4 / Figures --- p.2-5 / Chapter Chapter III --- Grain refinement in a system with solubility gap / Abstract --- p.3-1 / Introduction --- p.3-2 / Experimental --- p.3-4 / Results --- p.3-5 / Discussion --- p.3-8 / Reference --- p.3-11 / Figure Caption --- p.3-12 / Figures --- p.3-13

A series of hydrophobic and hydrophilic self-assembled monolayers (SAMs) were deposited by the adsorption of 1- dodecanethiol (SAM I), 11-mercapto-1-undecanol (SAM II), 16- mercaptohexadecanoic acid (SAM III), 5-(10-mercaptodecyloxy) benzene-1,3-dioic acid (SAM IV) and 4-(10-mercaptodecyloxy)- pyridine-2,6-dicarboxylic acid (SAM V) on gold substrates. Crystallization experiments were carried out on SAMs I-V, on control surfaces (bulk gold, glass and PDMS (polydimethlysiloxane)) and in microfluidic devices to screen the polymorphs of two well known drugs, acetaminophen and barbital. Microfluidic devices consist of PDMS (polydimethlysiloxane) patterned with microchannels and then bonded to self-assembled monolayers (SAMs) of organic molecules on gold substrates. The crystallization of acetaminophen was carried out under thermodynamic conditions from solutions at room temperature and under kinetic conditions by rapid cooling. The results of crystallization experiments and the influence of self-assembled monolayers (SAMs) in controlling polymorphism by acting as nucleation sites, or templates, are discussed.

For the last 20 years, there has been considerable interest in chiral nematic liquid crystal band edge lasers. The birefringent molecules of chiral nematic liquid crystals form a periodic helical structure, which results in a photonic bandgap for circularly polarised light with the same sense of rotation as the helix. A large increase in effective gain is seen for a fluorescent gain medium within the liquid crystal at the band edges, resulting in lasing. Applications of liquid crystal lasers could include miniature medical diagnostic tools, large-area holographic laser displays, and environmental sensing. The wavelength of emission from dye-doped chiral nematic liquid crystals is highly flexible, with lasers demonstrated across the visible range and near infra-red. This thesis investigates two routes for improving the functionality of chiral nematic liquid crystal lasers, supported by mathematical modelling of expected lasing wavelengths based on reflection and transmission by anisotropic layers. Perovskite is tested as a replacement for fluorescent laser dyes as a gain medium,both in the form of quantum dots dispersed in liquid crystal, and as films placed in liquid crystal structures. It is shown that while the perovskite tested provides some emission, it is not compatible for lasing in these devices, and suggestions for building on these results are made. In-plane switching is tested and developed as a means to achieve tuning of the laser wavelength, demonstrating a continuous wavelength shift of 15 nm, from 600.71 nm to 585.03 nm, over a voltage range of 100 V. This is an improvement on previous tuning in related devices, and may be extended with optimisation of cell thickness,electrode geometry, and initial lasing wavelength. Accurate descriptions of the refractive index profile of the liquid crystal and perovskite are developed and included in mathematical modelling, in addition to descriptions of the wavelength-dependent gain of a laser dye and perovskite. Suggestions for developing this modelling are made, particularly by the inclusion of accurate modelling of the distortion caused by in-plane switching.

Doctor of Philosophy (PhD) / Photonic crystals are optical structures that contain a periodic modulation of their refractive index, allowing them to control light in recent years of an unprecedented capacity. Photonic crystals may take on a variety of configurations, in particular the photonic crystal cavity, which may “hold” light in small volumes comparable to the light’s wavelength. This capability to spatially confine light opens up countless possibilities to explore for research in telecommunications, quantum electrodynamics experiments and high-resolution sensor applications. However, the vast functionality potentially made available by photonic crystal cavities is limited due to the difficulty in redefining photonic crystal components once they are formed in their (typically) solid material. The work presented in this thesis investigates several approaches to overcome this issue by reconfiguring photonic crystal cavities.

In the medical world the precise identification of a disease can take longer than it is safe to wait to start treatment so there is a need for faster and more precise biosensors. Bond Rupture is a new sensor technique that maybe able to improve disease detection. It does this by inducing bonds to rupture from the surface, and also measuring the point at which this rupture occurs this enables the forces to be measured on the surface. Specifically, this project has focused on the application of Bond Rupture to detecting antigens when bound to a surface using their specific antibodies, and the idea that the rupture force of these antigens can also be measured. The sensor that this project is based around is the Quartz Crystal Microbalance (QCM), which oscillates horizontally when a voltage is applied, and can also be used to measure mass change on its surface via change in resonant frequency. The aim of this project was to investigate possible Bond Rupture detection methods and techniques and has involved the development of a high speed digital electronics system, for the purposes of inducing and detecting Bond Rupture. This has involved the development of a FPGA based high speed transceiver board which is controlled by a Digital Signal Processor (DSP), as well as the development of various graphical user interfaces for end user interaction. Bond rupture testing was carried out by rupturing beads from the surface of a QCM in an experiment taking as little as 20 seconds. The Bond Rupture effect has been observed via the high accuracy measurement of the frequency change while inducing Bond Rupture on the sensor, proving that the Bond Rupture effect indeed exists. The research performed is believed to be a world first in terms of the method used and accuracy acquired.

The use of optics in the fields of nano-technology, telecommunication and medicine has been growing exponentially in recent years. Application of liquid crystals within optics has been a growing trend from flat screen displays to variable focus lenses in a digital versatile discs. One area of the recent developments within optics has been the development of two-photon fluorescence microscopy and high-density three-dimensional optical data storage. In such applications, where a light beam has to be focused deep within the volume of bulk media, aberrations are introduced. The most dominant aberration is spherical aberration which results from the mismatch in refractive indices of the immersion and recording media. The aim of this thesis is to design a liquid crystal lens for dynamic tube length compensation of the spherical aberration. Liquid crystal phase plates are used in everyday liquid crystal displays (LCDs) such as mobile phones and calculators. The technologies required to manufacture a liquid crystal phase plate are well understood. However, an application like three-dimensional data storage requires different properties in the liquid crystal phase plate, which are investigated in this thesis. To fabricate our liquid crystal phase plate we used ZLI-5049-000 from MERCK as the liquid crystal medium, with poly-vinyl alcohol (PVA) and Indium Tin Oxide (ITO) providing the insulating and conducting layers, respectively. It has been demonstrated that vacuum vapour deposition can be used to coat a glass substrate with ITO. However, in order for the ITO coating to be conductive a method is developed where the substrate is heated to 300oC before, during and after the coating. Similarly, a method has been developed for producing a uniform 10 μm coating of PVA on top of the ITO. In order to produce a liquid crystal lens with the properties required to compensate for spherical aberration an investigation into the properties of the liquid crystals is first conducted. A liquid crystal phase plate described in chapter 3 is characterised to determine the effect of the rubbing direction of the insulating layer and the effective refractive index change with applied voltage. It has been demonstrated that an effective change in refractive index of 0.11 can be achieved with 30 volts applied across the ITO electrodes. Based on the characterisation of the liquid crystal phase plate four different liquid crystal lens designs have been proposed and tested. The lens designs are based upon convergent and divergent lenses with different refractive index lens substrates. It is determined that a liquid crystal lens with a divergent lens substrate with a refractive index of 1.785 can be used to effectively compensate for spherical aberration. This has been confirmed experimentally by using the liquid crystal lens in a two-photon confocal microscope and measuring a increase in detected intensity at a depth below the surface of a sample. The research conducted in this thesis shows the ability to dynamically compensate for spherical aberration introduced by a mismatch in the refractive indices between the immersion and sample mediums. It has also been demonstrated that new methods for fabricating the conductive and insulating layers are suitable for producing a liquid crystal lens. A liquid crystal lens based on the research in this thesis could be used in three-dimensional data storage or microscopy applications.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 79-81). Also available in electronic version.

In this thesis, we use E-Beam lithography to finish the process of DBR laser, 2D Photonic crystal, and Metallic nanoelectrodes. We use the new E-Beam system to define array patterns. By this test, we obtain the minimum linewidth of 50nm, and the maximum working range is 250£gm*250£gm. We fabricated the 2D photonic crystal microcavity and DBR laser on the InGaAs/InAlGaAs which was grown by molecular beam epitaxy (MBE) on InP substrate. For the DBR laser, the length of Multi-mode Interference (MMI) was 90£gm to satisfied the emission wavelength and optical modes. We apply a coupled DBR reflector on both sides of MMI. The mirror width was 361nm and the air gap was 388nm. For the 2D photonic crystal (2D PhC) microcavity, a triangular array of air columns was adopted. The lattice constant and air columns radius are 1137nm and 456nm, respectively. The TE-mode photonic band gap of this structure is corresponding to wavelength range in 1517.01 nm~1617.81 nm. We leave a single defect in the 2D PhC to form 2D PhC microcavity and the corresponding defect modes are 1546.32nm and 1547.74nm. The Micro-PL measurement shows that a defect mode at 1547nm (a/£f=0.74), a surface state at 1351nm (a/£f=0.85), and a standing wave at 1480nm (a/£f=0.78). The maximum Q value is about 400 for the defect mode.