published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

Optical filters and thin film optical devices play an important role in Science and Industry. Several significant applications have emerged in optics, microelectronics and computer technology. In this work, we study some aspects of their design and applications. One class of optical fibers, known as Christiansen filters, are based on scattering phenomena in suspensions of solid particles in a liquid medium. Some new scattering filters in the visible and the near UV regions and their performance characteristics are reported here. Feasibility to fabricate such optical filters in solid matrix form is established. Some applications of these scattering filters are discussed. After an introduction to the optics of homogeneous and isotropic thin films, I discuss the general design of anisotropic thin film media and a scheme implemented to calculate their performance. Optical anisotropy, produced by the growth-induced columnar microstructure in thin films and its effects on the performance of optical filters are studied. Large shifts in the peak wavelength of a typical narrow band filter are predicted. Magneto-optical (MO) thin film media of great importance to erasable optical data storage technology are studied. An approximate technique based on a 2 x 2 matrix formalism is developed to calculate the normal incidence performance of these media. To investigate anisotropic effects, to incorporate more than one magnetic film with arbitrary orientations of magnetization, and to study oblique incidence performance, a completely general 4 x 4 matrix technique is implemented in a computer program. Effects of substrate/superstrate birefringence in the read-out signal of MO media are investigated. Several optimizing design criteria, particularly, the effectiveness in employing appropriate metal or dielectric reflector layers are studied. The influence of the plasma edge of metals in enhancing the polar Kerr rotation of MO media is discussed with illustrations. A contour plot of the Kerr rotation and reflectance is developed to help in the design of these media. An explanation is given for the observation of Kerr rotation enhancement near the plasma reflection edge of the reflector layer adjacent to the active MO layer and in general, where the reflectance spectrum shows a steep gradient.

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Highly efficient LEDs and photovoltaic cells based on spin coated films of layered Ruddlesden-Popper hybrid perovskites (RPP) have been recently reported. The electronic structure and phase composition of these films remains an open question, with diverse explanations offered accounting for the excellent device performance. Here we report x-ray and optical characterization of hot cast RPP thin films, emphasizing the distribution of structural and electronic properties through the film depth. Our results indicate an at least 70% phase pure n=3 film results from casting a stoichiometric solution of precursors, with minor contributions from n=2 and n=4 phases. We observe a strong correspondence between the predicted single-crystal RPP reciprocal lattice and measured RPP film wide angle scattering pattern, indicating a highly ordered [101] oriented film. This correspondence is broken at the air-film interface where new scattering peaks indicate the existence of a long wavelength structural distortion localized near the films surface. Using transient absorption spectroscopy, we show that the previously detected luminescent mid-gap states are localized on the films surface. Investigating films of varying thickness, we determine the photo-excited carrier dynamics are dominated by diffusion to this interface state, and extract an excitonic diffusivity of 0.18cm2s-1. We suggest that the observed surface distortion is responsible for the creation of luminescent mid-gap states.

by Hui Koon-chung = 由電子束照射引起氧化金屬膜覆蓋的氧化鋅之光學特性 / 許冠中. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 87-89). / Text in English; abstracts in English and Chinese. / by Hui Koon-chung = You dian zi shu zhao she yin qi yang hua jin shu mo fu gai de yang hua xin zhi guang xue te xing / Xu Guanzhong. / ABSTRACT --- p.i / ACKNOWLEDGMENTS --- p.iii / TABLE OF CONTENTS --- p.iv / LIST OF FIGURES --- p.vi / LIST OF TABLES --- p.x / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Motivation --- p.1 / Chapter 1.2 --- Overview of ZnO / Chapter 1.3 --- Overview of the Thesis / Chapter 2. --- Experimental conditions and procedures --- p.11 / Chapter 2.1 --- Samples preparation / Chapter 2.2 --- Optical and electrical Characterizations of ZnO / Chapter 2.2.1 --- Setup of cathodoluminescence (CL) spectroscopy / Chapter 2.2.2 --- Setup of photoluminescence (PL) spectroscopy / Chapter 2.2.3 --- Setup of photoconductivity measurement / Chapter 2.2.4 --- Setup of atomic force microscopy AFM / Chapter 2.2.5 --- X-ray photoelectron spectroscopy (XPS) / Chapter 3. --- Experimental results and data analysis --- p.21 / Chapter 3.1 --- The luminescence of ZnO --- p.21 / Chapter 3.2 --- Effects of metal capped layer in luminescence --- p.24 / Chapter 3.3 --- Optical memory effect of A1 capped ZnO --- p.28 / Chapter 3.4 --- The XPS study ofAl capped ZnO --- p.33 / Chapter 3.5 --- Optical properties and photoconductivity studies of AlOx-capped ZnO --- p.35 / Chapter 3.6 --- Time- and Electron-dose dependent CL of AlOx capped ZnO --- p.41 / Chapter 3.7 --- Dependence of band-edge enhancement on Deep Level to band-edge emission ratio --- p.53 / Chapter 3.8 --- Temperature-dependent CL of AlOx capped ZnO --- p.56 / Chapter 3.9 --- Electrical measurement of luminescence enhanced ZnO --- p.64 / Chapter 4. --- Discussion --- p.69 / Chapter 4.1 --- General discussion --- p.69 / Chapter 4.2 --- The effect of AlOx capping on the optical properties of ZnO --- p.70 / Chapter 4.3 --- The action of e-beam irradiation on the enhancement of band-edge emission --- p.73 / Chapter 4.4 --- The function of AlOx layer when under electron irradiation --- p.83 / Chapter 5. --- Conclusions --- p.85 / Reference --- p.87

Xu Yan = 納米銅(銅的氧化物)與三氧化二鋁復合物薄膜的製備和特性研究 / 許燕. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 50-51). / Text in English; abstracts in English and Chinese. / Xu Yan = Na mi tong (tong de yang hua wu) yu san yang hua er lv fu he wu bo mo de zhi bei he te xing yan jiu / Xu Yan. / Abstract --- p.i / 摘要 --- p.ii / Acknowledgements --- p.iii / Table of Contents --- p.iv / List of Figures --- p.viii / List of Tables --- p.xi / Chapter CHAPTER 1 --- Introduction / Chapter 1.1 --- Nanostructured Materials --- p.1 / Chapter 1.2 --- Objective of this Work --- p.1 / Chapter CHAPTER 2 --- Background / Chapter 2.1 --- Correlation of AES-CuLMM spectrum and Cu nanocluster size --- p.3 / Chapter 2.1.1 --- Typical AES-CuLMM spectra --- p.3 / Chapter 2.1.2 --- A simplified model --- p.4 / Chapter 2.1.3 --- correlation of AES-CuLMM spectra and the simplified model --- p.4 / Chapter 2.2 --- Previous works --- p.5 / Chapter CHAPTER 3 --- Instrumentation / Chapter 3.1 --- Sputtering --- p.6 / Chapter 3.1.1 --- Principles of sputtering --- p.6 / Chapter 3.1.1.1 --- Concepts of sputtering --- p.6 / Chapter 3.1.1.2 --- Initiating the plasma --- p.8 / Chapter 3.1.1.3 --- Depositing a film onto the substrate --- p.8 / Chapter 3.1.2 --- Radio-frequency (RF) magnetron sputtering --- p.9 / Chapter 3.1.2.1 --- RF sputtering --- p.9 / Chapter 3.1.2.2 --- Magnetron Sputtering --- p.10 / Chapter 3.2 --- Deposition system --- p.10 / Chapter 3.2.1 --- Instrumentation --- p.11 / Chapter 3.2.1.1 --- Vacuum system --- p.11 / Chapter 3.2.1.2 --- Sputter target and power supplies --- p.12 / Chapter 3.2.1.3 --- Substrate mounting --- p.13 / Chapter 3.2.2 --- Experimental --- p.13 / Chapter 3.3 --- X-ray Photoelectron Spectroscopy (XPS) --- p.14 / Chapter 3.3.1 --- Basic Principles --- p.14 / Chapter 3.3.2 --- Instrumentation --- p.17 / Chapter 3.3.3 --- Qualitative and quantitative analysis --- p.17 / Chapter 3.3.3.1 --- Spectra interpretations --- p.17 / Chapter 3.3.3.2 --- X-ray emission line width --- p.18 / Chapter 3.3.3.3 --- Qualification --- p.18 / Chapter 3.3.3.3.1 --- Chemical composition --- p.18 / Chapter 3.3.3.3.2 --- Sputter depth profiling --- p.18 / Chapter 3.3.3.3.3 --- Auger parameter --- p.19 / Chapter 3.4 --- Transmission Electron Microscopy (TEM) --- p.19 / Chapter 3.4.1 --- An overview of TEM --- p.19 / Chapter 3.4.2 --- Imaging mode and diffraction mode --- p.21 / Chapter 3.4.3 --- Electron-Specimen interactions --- p.21 / Chapter 3.4.3.1 --- Elastic scattering --- p.22 / Chapter 3.4.3.2 --- Inelastic scattering --- p.22 / Chapter 3.4.4 --- Imaging mechanisms for TEM --- p.23 / Chapter 3.4.4.1 --- Mass-thickness contrast --- p.23 / Chapter 3.4.4.2 --- Diffraction contrast --- p.23 / Chapter 3.4.5 --- TEM sample preparation --- p.25 / Chapter CHAPTER 4 --- Chemical and Structure Characterization of Cu(CuOx)/Al2O3 Composite Thin Films / Chapter 4.1 --- Overview --- p.26 / Chapter 4.2 --- Results and discussions --- p.26 / Chapter 4.2.1 --- Set I: Achieving the stoichiometry of A1203 matrix --- p.26 / Chapter 4.2.2 --- Set II: keeping A1203 stoichiometry and studying on the correlation of CuLMM spectra and average Cu cluster size --- p.32 / Chapter 4.2.2.1 --- Chemical information obtained by XPS --- p.32 / Chapter 4.2.2.2 --- Nanostructure studied by TEM --- p.38 / Chapter 4.2.2.3 --- Mechanical properties inspected by nano-indentation --- p.43 / Chapter 4.2.2.4 --- Optical properties --- p.43 / Chapter 4.2.3 --- Set III: Duration of deposition --- p.44 / Chapter 4.2.4 --- Set VI: Pressure effect on the average size of Cu nanoclusters --- p.45 / Chapter CHAPTER 5 --- Conclusions --- p.48 / References --- p.50

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The mirrors used in high energy laser systems have at least two requirements that are uncommon in optical engineering: the reflectance of such mirrors must be very high (> 0.999), and the level of aberrations introduced by the mirrors is desired to be very low, typically λ/50 peak at 3.8 μ. The first requirement can be met by using multilayer thin film coatings, but such coatings can themselves produce aberrations in an optical system. One possible effect in multilayers is that such coatings produce an optical phase change on reflection that varies with angle of incidence and polarization of the illuminating beam. On a strongly curved mirror, such as an f/1.5 parabola used as a collimator, these effects may be appreciable for some coatings (e.g., λ/13 for a broadband all-dielectric reflector), but for an enhanced silver coating the effects are small, typically λ/400 of error that is almost entirely in the form of a small focus shift. If this same parabola is tested at its center of curvature, the coating-caused aberration due to angle of incidence effects are nearly zero (e.g., λ/50,000 for the broadband reflector that gave λ/13 when the parabola was used as a collimator). The wavefront errors due to coating nonuniformities are usually more important than angle of incidence effects. The simplest type of coating nonuniformity to analyze is a proportional error, i.e., an error where the ratios of the thicknesses of the layers are fixed but the thin film stack varies in total thickness across a surface. For a six-layer enhanced reflector for use at 3.8 μ, a 1% thickness error produces an approximate λ/100 wavefront error. At visible wavelengths, however, the aberration produced by such a coating error can be very different because of the optical interference nature of the coating. Means may be developed to estimate the performance of such an infrared reflector from measurements at visible wavelengths. If the errors produced by the coating are to be distinguished from those existing in the test due to misalignment or gravitational flexure of a large mirror, two or more wavelengths must be chosen. There are ambiguities in such a test that may be resolved by choice of an appropriate coating design or by using enough wavelengths in the visible, and both means have been studied. A technique was found where the infrared wavefront can be determined for a coating with proportional thickness errors if the coating prescription is known: interferograms of the mirror are made at three visible wavelengths, and the IR wavefront error due to the coating error is determined in a way that is insensitive to any errors caused by distortion of the substrate or even fairly large misalignments in the optical test of a mirror's figure.

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