We established measurement and analysis techniques necessary to investigate the optical properties of some transition metal compounds: specifically the carbides and nitrides of Ti, Zr, and Hf. Two distinct techniques determined the optical constants of these films: a Nestell-Christy method to invert measurements of thickness, reflection, and transmission and a Kramers-Kronig analysis of reflection. The compositions of the samples were evaluated by X-ray diffraction, Auger spectroscopy, scanning electron microprobe analysis, and nuclear analysis. We found it possible to correlate these materials' optical and electronic properties and relate these to compositional changes. The ability to engineer a specific optical response of materials is discussed. Additions of carbon and nitrogen change the optical properties in a specific manner; the roles of these elements as electron donors and their effect on the location and population of the d electron bands with respect to the Fermi level are postulated.

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

Wang Juan = 納米金顆粒與氧化鋁複合物薄膜光學吸收譜中的尺寸和濃度效應 / 王娟. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 55-58). / Text in English; abstracts in English and Chinese. / Wang Juan = Na mi jin ke li yu yang hua lv fu he wu bo mo guang xue xi shou pu zhong de chi cun he nong du xiao ying / Wang Juan. / Abstract --- p.i / 摘要 --- p.ii / Acknowledgment --- p.iii / Table of contents --- p.iv / List of Figures --- p.vii / List of Tables --- p.ix / Chapter CHAPTER 1: --- Introduction --- p.1 / Chapter CHAPTER 2: --- Background --- p.3 / Chapter 2.1 --- Optical response of metal-particle/matrix composite system in an electronic field --- p.3 / Chapter 2.1.1 --- The concept of plasmon and the dielectric function of metal particle --- p.3 / Chapter 2.1.2 --- The concept of surface plasmon resonance --- p.4 / Chapter 2.2 --- The theories describing the optical absorption properties of metal particle/matrix composite system --- p.5 / Chapter 2.2.1 --- The Mie theory --- p.5 / Chapter 2.2.2 --- The Maxwell-Garnett (M.G.) effective medium theory --- p.6 / Chapter 2.3 --- Previous experimental works in the field --- p.7 / Chapter CHAPTER 3: --- Experimental and instrumentation --- p.8 / Chapter 3.1 --- Fabrication of the Au-nanoparticle /A12O3-matrix composite thin films --- p.11 / Chapter 3.1.1 --- Sputtering techniques and radio-frequency magnetron sputtering --- p.11 / Chapter 3.1.2 --- Experimental set up and the deposition process --- p.13 / Chapter 3.2 --- The chemical and structural characterizations of the films --- p.14 / Chapter 3.2.1 --- X-ray Photoelectron Spectroscopy (XPS) --- p.14 / Chapter 3.2.2 --- X-ray Diffraction (XRD) --- p.15 / Chapter 3.2.3 --- Transmission Electron Microscopy (TEM) --- p.17 / Chapter 3.3 --- The optical absorption measurement: UV spectrometer --- p.21 / Chapter CHAPTER 4: --- Results and discussions --- p.23 / Chapter 4.1 --- General description of the as-prepared samples --- p.23 / Chapter 4.1.1 --- Chemical composition of the films --- p.23 / Chapter 4.1.2 --- General microstructure of the films and the relationship between the deposition parameters --- p.25 / Chapter 4.2 --- The optical absorption: relationship between the SPR absorption and the microstructure --- p.27 / Chapter 4.2.1 --- The shifting of the surface plasmon resonance --- p.27 / Chapter 4.2.1.1 --- The size effect on the SPR frequency shifting --- p.27 / Chapter 4.2.1.2 --- The concentration effect on the SPR frequency shifting --- p.42 / Chapter 4.2.2 --- The broadening of the surface plasmon resonance: size dependence of the relaxation time of free electrons --- p.51 / Chapter CHAPTER 5: --- Conclusions --- p.53 / Appendix --- p.54 / Reference --- p.55

Two-photon optical bistability in commercial thin-film interference filters with ZnS and ZnSe spacers is observed with switching times ≳ 200 μs. The accompanying drifting of the bistability loop in time and laser-induced "damage" indicate a thermal mechanism. The problem of water vapor absorption in such filters must be addressed before the inherent potential and advantages of these devices in two-dimensional image processing applications can be realized. Trans- verse effects in GaAs superlattice etalons are observed which cannot be explained on the basis of a plane-wave analysis. The optical nonlinearity in GaAs and diffraction combine to produce drastic effects on the measured beam profiles and bistable loops, due to an intensity-dependent virtual focus. Lastly, the first observation of optical bistability due to a biexcitonic nonlinearity in CuCl etalons is reported with detector-limited switching times of 600 ps. In addition, lasing action along the pump axis in a cavity defined by the end mirrors is observed in a very thin (2.0 μm) CuCl etalon. The lasing transition is unique in that it involves the creation of a virtual excitation of biexcitons which decay to the longitudinal exciton state.

Nearly all the deficiencies of conventional vacuum evaporated coatings trace to a single physical property of condensed films: low packing density. One way to increase packing density is to bombard the growing film with ions during deposition, called ion-assisted deposition (IAD). The beginning chapters of this dissertation analyze IAD as a perturbation of the conventional vacuum evaporation process. The experimental chapters begin with an examination of the effect on moisture penetration behavior of oxygen-ion bombarding completed optical filters. Moisture adsorption and desorption is retarded after bombardment in filters composed of titania and silica, but not in those of zirconia and silica. Bombardment evidently induces a crystalline-to-amorphous transition in titania, causing the surface to swell and occluding the pores. The transition in zirconia is the reverse, and no impediment to moisture appears. Argon-ion-assisted magnesium fluoride (MgF₂) can show ultraviolet (UV) absorption. The primary mechanism is probably the formation of F-centers (single fluorine-ion vacancies), although an unsaturated oxygen bond may also be responsible. Absorption can be removed by baking and often by irradiation with UV. After baking, fluorine is lost and replaced by oxygen. Absorption-free MgF₂ films can be deposited by minimizing the substrate temperature and bombardment flux. Ion-assisted films contain up to 2% argon and up to 170 parts-per-million of tungsten from the ion gun filaments. They show a slightly higher refractive index, are much less porous, and are much more resistant to damage by abrasion and exposure to fluorine gas. Ion-assisted aluminum oxide (alumina, Al₂O₃) films show a small increase in UV absorption after argon-ion bombardment; however, a mixture of argon and oxygen ions avoids the problem. Excess oxygen is often incorporated into alumina films, and depresses both the mass density and the refractive index. IAD increases refractive index and decreases porosity. Ion-assisted alumina films are somewhat more stable in humid environments. Ion-assisted deposition has been shown by this study to cause substantial improvements in many of the physical and some of the optical and chemical properties of evaporated magnesium fluoride and aluminum oxide films.

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The goal of the thesis is to make contributions to the development of two new technologies for data storage: perpendicular recording and magneto-optic recording. CoCr and rare earth-transition metal multilayers are the most suitable media for perpendicular recording and magneto-optic recording technologies, respectively. In part A of the thesis, magnetic properties of CoCr thin films produced by dc magnetron sputtering are studied for various deposition conditions. Dielectric constants and extraordinary Hall effect are also studied to provide information complementary to magnetic properties. In part B, new methods are developed for theoretical analysis of the magneto-optics of rare earth-transition metal multilayers, which can be used to optimize the readout of the recording system. Part A For dc magnetron sputtered CoCr films the perpendicular and parallel magnetic coercivities are found to be mainly controlled by the substrate temperature during film growth. Substrate temperatures between 180 and 300 C are necessary to fabricate CoCr thin films for recording media. Films produced in this manner have magnetic anisotropy constants ranging from —1.0 to +0.5 10⁶erg/cc. The magnetic anisotropy has a complicated dependence on a large number of deposition parameters and can be best controlled by the dc sputtering power and the target-to-substrate distance. Based on microstructural analysis film properties are interpreted in terms of the adatom diffusion during film growth. It is found that high adatom mobility and low deposition rate promote positive magnetic anisotropy. The dielectric constants measured by ellipsometry are found to depend on the film thickness because of the change in film morphology during film growth. The effects of asymmetric sputtering are analyzed, and the relationship between the extraordinary Hall effect and the magnetic properties is investigated. Part B The 4x4 matrix method proposed by Lin-Chung and Teitler[P. J. Lin-Chung and S. Teitler, J. Opt. Soc. Am. A 1 703(1984)] is applied to the magneto-optics of the rare earth-transition metal multilayer system. Based on a plane wave model, the above method enables one to calculate the sensitivity of the readout to the layer thicknesses as well as effects of oblique angle of incidence, anisotropy in the nonmagnetic part of the dielectric constants and misalignment of the magnetization. Finally, an improved model is presented to take into account the fact that the reading laser is a strongly focused beam instead of a plane wave. This new model is used to optimize the magneto-optic multilayer system. When the focal spot size of the reading laser beam is less than about three wavelengths, significantly different results are obtained from the focused beam and the plane wave models. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This dissertation reports on the study of black molybdenum, a new cermet consisting of small Mo particles embedded in MoO₂. As with most two-phase materials, the optical properties of black molybdenum are significantly different from those of either constituent, and can be adjusted within wide limits through modifications of composition and microstructure due to variations of the fabrication process parameters. The subject of this work is to understand the exact relationships, to allow reproducible production of films with chosen optical properties. Theoretical interpretation of the optical properties of two-phase materials has in the past been hampered by insufficient microstructural characterization. Recent theoretical work by others has lifted the requirements of detailed microstructural knowledge, leaving only two required parameters for characterization of cermet reflectance: the optical properties of the constituent phases and their volume fractions in the cermet. Better characterization is obtained when structural considerations, such as film topology, surface texture and the presence of a possible amorphous phase, are taken into account. We adopted this approach to the study of black molybdenum, and accomplished satisfactory agreement between theoretical and observed reflectances. Black molybdenum films were prepared using two separate chemical vapor deposition (CVD) techniques, involving deposition from either Mo(CO)₆ or MoO₂Cl₂. We found the influence of composition through a comparison of films with different Mo:MoO₂ ratios, while the influence of structure on film reflectance was determined by comparing films from these two deposition techniques. During this investigation we produced black molybdenum films which display a spectrally selective profile--low visible reflectance combined with high infrared reflectance, and which may be applied to photothermal solar energy conversion. The versatility of CVD in adjusting film composition and structure resulted in another film of interest in photothermal conversion--black tungsten, a tungsten-tungsten oxide composite material. The black molybdenum and black tungsten systems studied here establish the utility of CVD for the production of high temperature thin film optical devices.

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy