published_or_final_version / abstract / Physics / Master / Master of Philosophy

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

This dissertation reports on the development of a nonlinear surface spectroscopy and the observation of nonlinear optical phenomena using sputtered zinc oxide waveguides. The first is known as Surface Coherent Raman Spectroscopy, or SCRS, and is capable of monolayer sensitivity. The second, discovered during the development of SCRS, is optical limiting and a previously unobserved form of optical switching based on an absorptive nonlinear coupling mechanism. Overviews of the theories of waveguiding, linear coupling, and SCRS are given. Experiments showing that the spectrum of a monolayer coverage of molecules on the surface of a metal oxide waveguide can be obtained using SCRS are reported. For this purpose ZnO waveguides were fabricated using rf magnetron sputtering; the details of which are presented. The results of the characterization of these films, using an optical loss technique, Rutherford backscattering, and X-ray diffraction, are also presented. Experiments are described and data are presented to show the existence of optical limiting and optical switching phenomena in ZnO waveguides. The experimental dependence of these phenomena on input pulse energy, wavelength, temporal pulse width, and type of distributed coupling mechanism is described. Existing nonlinear distributed coupler theory is extended to include the effect of an absorptive nonlinearity and the results of this theory are used to explain some of the characteristic features of the experimental results. A value of n₂ ≅ 2 x 10⁻¹⁶ m²/W for the nonlinear coefficient of sputtered ZnO films is obtained.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the academic requirements for the degree of Master of Science. Johannesburg, March 2016. / Zinc oxide (ZnO) continues to receive widespread attention due to its excellent optical and electronic properties; it demonstrates the combined characteristics of high transmittance and electrical conductivity. Despite the tremendous drive for its application in optoelectronic devices, the full nature of the point defects and defect complexes have not been characterised comprehensively. In this work, luminescence characteristics of the intrinsic defects in ZnO thin films and the rare-earth ions Eu3+ and Tb3+ in ZnO powders are investigated under blue-laser excitation. The thin films used in this study were deposited using the radio-frequency magnetron sputtering method over a 2 hour duration under varied power and substrate bias conditions. The powders were synthesized by the chemical bath deposition method with dopant concentrations of 1.0 mol%. Grazing incidence X-ray diffraction (XRD) was used to determine the lattice properties of the samples. Photoluminescence studies were primarily conducted at room temperature (300 K) with the 457.9 nm, 476.5 nm and 488.0 nm laser lines as excitation sources. For the ZnO thin films, XRD patterns of a hexagonal wurtzite structure with a c/a ratio of about 1.60 and a u-parameter of 0.38 were obtained. Photoluminescence measurements show a broad emission band in the 500.0-900.0 nm range, centred at 656.0 nm. Annealed films yielded relatively more intense photoluminescence spectra than the as-prepared films. The intrinsic point defects and defect level transitions responsible for the broad emission are discussed. For the ZnO powders, the XRD patterns of the annealed samples of pristine ZnO, ZnO:Eu3+ and ZnO:Tb3+ are similarly consistent with a hexagonal wurtzite ZnO phase. Energy dispersive spectroscopy (EDS) confirmed the presence of the Eu3+ and Tb3+ dopants in the respective ZnO host while scanning electron microscopy (SEM) measurements showed the morphology of the sample powders. Photoluminescence spectra of pelletized samples, obtained in the 460.0-900.0 nm range, exhibit relatively intense Eu3+ and Tb3+ emission bands superimposed on a broad emission background. The RE3+ emission bands are attributed to the 5D0 → 7FJ (J = 0, 1, 2, 3, 4) and the 5D4 → 7FJ (J = 0, 1, 2, 3, 4, 5, 6) electronic transitions of Eu3+ and Tb3+, respectively, while the background emission is attributed to intrinsic defects. Crystal-field energy levels for the Eu3+ ion and the Tb3+ ion occupying a C3v symmetry site were deduced from fitting Gaussian curves to the RE3+ emission bands. Possible channels for transfer of energy from the intrinsic defects to Eu3+ and Tb3+ are discussed. / LG2017

Lai Chung Wing = 金屬膜覆蓋在氧化鋅上之光學變化 / 黎頌榮. / Thesis submitted in: July 2005. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Lai Chung Wing = Jin shu mo fu gai zai yang hua xin shang zhi guang xue bian hua / Li Songrong. / Acknowledgements --- p.i / Abstract --- p.ii / 摘要 --- p.iii / Table of contents --- p.iv / List of Figures --- p.vi / Chapter Chapter 1 --- Introduction / Chapter 1.1. --- Motivation --- p.1-1 / Chapter 1.2. --- Literature Review --- p.1-2 / Chapter 1.3. --- Our Study --- p.1-4 / References --- p.1-6 / Chapter Chapter 2 --- Methodology and Experiments / Chapter 2.1. --- RF sputtering --- p.2-1 / Chapter 2.1.1. --- Setup of RF sputtering --- p.2-2 / Chapter 2.1.2. --- Sample preparation --- p.2-3 / Chapter 2.2. --- Scanning electron Microscope --- p.2-4 / Chapter 2.3. --- Cathodoluminescence --- p.2-5 / Chapter 2.3.1. --- Background of CL --- p.2-6 / Chapter 2.3.2. --- Room temperature CL studies --- p.2-7 / Chapter 2.3.3. --- Software: Casino --- p.2-8 / Chapter 2.3.4. --- Depth resolved CL studies --- p.2-10 / Chapter 2.3.5. --- Power dependent CL studies --- p.2-11 / Chapter 2.4. --- Photoluminescence / Chapter 2.4.1. --- General background of PL --- p.2-11 / Chapter 2.4.2. --- Room temperature PL studies --- p.2-12 / Chapter 2.4.3. --- Quantum efficiency measurement --- p.2-13 / Chapter 2.5. --- Optical transmission measurement --- p.2-13 / References --- p.2-15 / Chapter Chapter 3 --- Experimental Results and Data Analysis / Chapter 3.1. --- Study of Optical emissions of bare and Au-capped ZnO --- p.3-1 / Chapter 3.1.1. --- RT-luminescence of ZnO --- p.3-1 / Chapter 3.1.2. --- RT- Luminescence of Au- capped ZnO films --- p.3-2 / Chapter 3.2. --- RT-luminescence of metal capped ZnO --- p.3-7 / Chapter 3.3. --- Power dependent and depth Resolved CL --- p.3-10 / Chapter 3.3.1. --- Dependence of the CL on beam energy --- p.3-10 / Chapter 3.3.2. --- Dependence of the CL intensity on beam energy --- p.3-13 / Chapter 3.4. --- Dependence of metal thickness on the RT- luminescence --- p.3-17 / References --- p.3-19 / Chapter Chapter 4 --- Discussions / Chapter 4.1. --- General discussions --- p.4-1 / Chapter 4.2. --- Surface recombination Velocity / Chapter 4.2.1. --- Quantum Efficiency --- p.4-2 / Chapter 4.2.2. --- Simulation of the dependence of surface recombination velocity on the CL intensity of ZnO --- p.4-5 / Chapter 4.3. --- Effects of metallization on MgZnO/ZnO bilayer --- p.4-10 / Chapter 4.4. --- Surface plasmon --- p.4-13 / Chapter 4.5. --- PL measurement from the backside of substrate --- p.4-18 / Chapter 4.5.1. --- Au and Ag coating by sputtering --- p.4-19 / Chapter 4.5.2. --- Au and Ag coating by thermal evaporation --- p.4-21 / Chapter 4.6. --- Au coating spaced by MgO --- p.4-23 / Chapter 4.7. --- Optical transmission of Au-capped ZnO --- p.4-25 / Chapter 4.8. --- Cross Section images by AFM and TEM --- p.4-27 / Chapter 4.9. --- Application: optical improvement of semiconductor --- p.4-30 / Chapter 4.10. --- Summary --- p.4-32 / References --- p.4-34 / Chapter Chapter 5 --- Conclusions --- p.5-1 / Appendix I --- p.A / Appendix II --- p.K

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Vita. / Includes bibliographical references. / by Elaine Paula Rothman. / M.S.

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