No description available.

The columnar microstructure of most thermally evaporated thin films detrimentally affects many of their properties through a reduction in packing density. In this work, we have investigated ion-assisted deposition as a means of disrupting this columnar growth for a number of coating materials. A Kaufman hot-cathode ion source bombarded thermally evaporated films with low-energy (< 1000 eV) positive ions during deposition in a cryopumped box coater. We have investigated MgF₂, Na₃AIF₆, AIF₃, LaF₃, CeF₃, NdF₃, Al₂O₃, and AIN. Argon ion bombardment of the fluoride coatings increased their packing densities dramatically. We achieved packing densities near unity without significant absorption for MgF₂, LaF₃, and NdF₃, while Na₃AIF₆, AIF₃, and CeF₃ began to absorb before unity packing density could be achieved. Fluorine was preferentially sputtered by the ion bombardment, creating anion vacancies. The films adsorbed water vapor and hydroxyl radicals from the residual chamber atmosphere. These filled the vacancy sites, eliminating absorption in the visible, but the oxygen complexes caused increased absorption in the ultraviolet. For LaF₃ and NdF₃, a sufficient amount of oxygen caused a phase transformation from the fluoride phase to an oxyfluoride phase. The refractive indices of Al₂O₃ films increased with ion bombardment. Values as high as 1.70 at 350 nm were achieved with bombardment by 500 eV oxygen ions. Since all of the Al₂O₃ films had packing densities near unity and were amorphous, we postulate that the increase in refractive index was due to a change in amorphous networking. Aluminum nitride was deposited by bombarding thermally evaporated aluminum with nitrogen ions. Films with N:Al ratios of 0.5-1.5 could be deposited by varying the deposition conditions. Films with low absorption for wavelengths longer than 1 μm could be deposited. Annealing the films at 500°C eliminated absorption at wavelengths longer than 500 nm.

The development of materials for optical thin film application is essential to progress in fields such as optical data storage and signal processing. Samarium sulfide (SmS) thin films were prepared by reactive evaporation of samarium in hydrogen sulfide (H₂S). These displayed optical switching properties despite the presence of large amounts of carbon and oxygen. They are therefore potentially useful for data storage. The semiconductor to metal phase transition was characterized by x-ray diffraction and spectrophotometry. The observed optical response was modelled by a Bruggeman effective medium calculation. Success with this analysis suggests it as a means for predicting performance in subsequent applications. Zinc sulfide (ZnS) thin films were prepared by molecular beam epitaxy (MBE). Implimentation of an H₂S treated silicon surface provided good chemical bond match in addition to a good lattice match. Atomic layer epitaxy was unsuccessfully explored as a means to grow ZnS from zinc and H₂S reactants, therefore other reactants are proposed. Both the MBE and ALE work is directed at the long term goals of producing p-type ZnS, which is suitable for semiconductor lasing at short wavelengths, and high quality SmS thin films.

Materials in the form of thin films that have been deposited from the vapor phase are significantly different from similar bulk materials, both optically and mechanically, because of their columnar structure and consequent porosity. Their porosity have been verified in different ways. The effects of the pores on optical and mechanical performance and, in particular, the influence of water adsorption, have also been demonstrated. Three techniques used for investigating optical instabilities in thin films are given. They all involve sharp resonances. The resonances are associated either with surface plasmons, metal-dielectric narrowband filters, or all dielectric narrowband filters. These resonances are very sensitive functions of layer properties and hence can be used to detect and measure changes in the layers, particularly those that are induced by adsorption of moisture. Moisture adsorption in thin films is a complex process that occurs unevenly in patches. Using resonance techniques, the adsorption isotherms of change in refractive index, of growth rate in patch size, and of peak wavelength shift, which are all important in characterizing the porosity of films, have been measured. Some effects that locally increase film porosity and create central pores that permit water to penetrate into multilayer structures have been investigated. Based on these results, some suggestions for preventing water adsorption in films are then made. Moisture penetration into thin film structures is the major source of optical coating instability and it is therefore very important that the mechanisms of penetration by understood. Some deductions of the mechanisms are made from the experimental results.

We consider in this work the contribution of anisotropic microstructure to polarization effects in thin films. The microstructure is pictured by a simple model as composed of identical columns with elliptical cross section elongated in a direction perpendicular to that of the vapor incidence. The asymmetry in columnar structure that results from oblique deposition is identified as the common source for the significant dichroism and birefringence observed in metal and dielectric films, respectively. A four-dimensional theory for multilayer systems is presented that starts from first principles, unifies previous treatments for particular cases of film anisotropy, and properly handles the most general case of elliptically polarized mode propagation. In this framework and from a set of polarimetric measurements, a simple method is devised, with explicit consideration of the anisotropic microstructure, for the determination of the physical thickness and principal refractive indices of a single dielectric film. A sequence of transmittance measurements is performed with a zirconium oxide film deposited at 65° and, substrate role and instrumental errors considered, good agreement is obtained between theory and experiment. Spectrophotometer data for a narrowband filter with 21 layers deposited at 30° is shown to confirm theoretical predictions of peak positions with Angstrom resolution. A hypothetical metal film is discussed that reproduces the essential features observed in the optical behavior of an aluminum film deposited at 85°. Potential applications and suggestions for future work are included.

Surface-plasmon polaritons propagating on thin metal films bounded by dielectrics of nearly equal refractive indexes comprise two bound modes. Calculations indicate that, while the modes are degenerate on thick films, both the real and the imaginary components of the propagation constants for the modes split into two branches on successively thinner films. Considering these non-degenerate modes, the mode exhibiting a symmetric (antisymmetric) transverse profile of the longitudinally polarized electric field component, has propagation constant components both of which increase (decrease) with decreasing film thickness. Theoretical propagation constant eigenvalue (PCE) curves have been plotted which delineate this dependence of both propagation constant components on film thickness. By means of a retroreflecting, hemispherical glass coupler in an attenuated total reflection (ATR) configuration, light of wavelength 632.8 nm coupled to the modes of thin silver films deposited on polished glass substrates. Lorentzian lineshape dips in the plots of reflectance vs. angle of incidence indicate the presence of the plasmon modes. The real and imaginary components of the propagation constraints (i.e., the propagation constant and loss coefficient) were calculated from the angular positions and widths of the ATR resonances recorded. Films of several thicknesses were probed. Results which support the theoretically predicted curves were reported.

No description available.

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.

Dans cette étude, nous avons préparé deux matériaux composites conducteurs par le procédé d’électropolymérisation. Lebut de la première partie de la thèse était l’élaboration de films composites polyaniline /LiMn2O4 pour leur applicationcomme matériau de cathode dans les batteries lithium-ion. Les analyses par diffraction des rayons X, analyse EDX etspectrométrie IRTF ont confirmé l'incorporation de LiMn2O4 dans les films composites. Les analyses électrochimiquesdes films obtenus ont mis en évidence une conductivité plus élevée des films composites comparée à la conductivité desfilms de PANI. La deuxième partie a été consacrée à la préparation de l’oxyde de graphène (OG) à partir de graphiteselon 2 méthodes de synthèse dérivées de la méthode de Hummers. Les résultats obtenus ont montré que le de gréd’oxydation des feuillets n’était pas le seul critère à prendre en compte pour évaluer la stabilité du OG dans l’eau. Lesfeuillets d’OG obtenus ont été incorporés à la polyaniline par électropolymérisation d’une suspension d’OG et d’anilineen milieu neutre. Le milieu électrolytique neutre conduit à des chaînes oligomères de PANI de faible masse molaire avecune proportion significative d’unités aromatiques mono et 1,2-disubstituées dans la structure finale. Différents substratsmétalliques ont été testés et les films ont été en particulier déposés sur fer afin d’évaluer leur protection anticorrosion. / In this study, we prepared two conductive composite materials based on polyaniline (PANI) byelectrodeposition. First, we investigated the development of new polyaniline/LiMn2O4 composite films forapplication as cathode material in lithium-ion batteries. Analysis by X-ray diffraction, EDS analysis and FTIRspectroscopy confirmed the incorporation of LiMn2O4 in composite films. The electrochemical analysis of thefilms obtained showed a higher conductivity of the composite films compared to the conductivity of the filmsof PANI. The second part was devoted to the preparation of oxidized graphene (GO) from graphite by 2methods of synthesis derived from the method of Hummers. The results showed that the degree of oxidation ofthe graphene sheets was not the only criterion in assessing the stability of GO in water. Electropolymerizationof aniline in a neutral electrolyte containing GO sheets was carried out to prepare PANI-GO composite films.The neutral electrolytic medium leads to PANI oligomer chains of low molecular weight with a significantproportion of aromatic mono units and 1,2-di-substituted units in the final structure. The electrodeposition wasperformed on inert and oxidizable metals. The corrosion protection efficiency of PANI/GO composite filmswas studied in HCl corrosion medium.

by Poon Chun Yu. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 110-112). / Abstracts in English and Chinese. / ACKNOWLEDGEMENTS --- p.2 / ABSTRACT --- p.3 / TABLE OF CONTENTS --- p.5 / LIST OF FIGURES --- p.8 / LIST OF TABLES --- p.13 / Chapter CHAPTER 1 --- INTRODUCTION --- p.14 / Chapter 1.1 --- Overview --- p.14 / Chapter 1.2 --- Ferromagnetism --- p.15 / Chapter 1.3 --- Ferromagnetic granular thin film --- p.16 / Chapter 1.4 --- Ferromagnetism-magnetization --- p.17 / Chapter 1.5 --- Ferromagnetism - magnetization of a polycrystalline --- p.18 / Chapter 1.6 --- Soft and hard magnetic materials --- p.21 / Chapter 1.7 --- Preparation methods --- p.22 / Chapter 1.8 --- This thesis --- p.24 / Chapter CHAPTER 2 --- SAMPLE PREPARATION AND EXPERIMENTAL METHODS --- p.25 / Chapter 2.1 --- Sample preparation --- p.25 / Chapter 2.1.1 --- The pulsed filtered cathodic arc co-deposition system --- p.25 / Chapter 2.1.2 --- Details of sample preparation --- p.27 / Chapter 2.1.3 --- Improvement of the target holder --- p.30 / Chapter 2.2 --- Rutherford backscattering spectrometry (RBS) --- p.30 / Chapter 2.3 --- X-ray diffraction (XRD) --- p.32 / Chapter 2.3.1 --- Diffraction technique --- p.32 / Chapter 2.3.2 --- Scherrer's formula --- p.35 / Chapter 2.4 --- Raman spectroscopy --- p.35 / Chapter 2.5 --- Transmission electron microscopy (TEM) --- p.36 / Chapter 3.5.1 --- The technique of transmission electron microscopy (TEM) --- p.36 / Chapter 3.5.2 --- Transmission electron microscopy (TEM) sample preparation --- p.37 / Chapter 2.6 --- X-ray photoelectron spectroscopy (XPS) --- p.41 / Chapter 2.6.1 --- The principle of XPS --- p.41 / Chapter 2.6.2 --- Qualitative analysis of XPS (chemical shift) --- p.43 / Chapter 2.7 --- Scanning probe microscopy (SPM) --- p.43 / Chapter 2.7.1 --- The principle of atomic force microscopy (AFM) --- p.43 / Chapter 2.7.2 --- Tapping mode atomic force microscopy --- p.44 / Chapter 2.7.3 --- Magnetic force microscopy (MFM) --- p.46 / Chapter 2.8 --- Vibrating sample magnetometer (VSM) --- p.47 / Chapter 2.8.1 --- The principle of VSM operation --- p.47 / Chapter 2.8.2 --- Useful of the pick up coils --- p.49 / Chapter 2.8.3 --- M-H Loop --- p.50 / Chapter 2.9 --- Four-contacts technique --- p.51 / Chapter CHAPTER 3 --- CHARACTERIZATION OF CO-DEPOSITED CO-C SAMPLES --- p.53 / Chapter 3.1 --- Introduction --- p.53 / Chapter 3.2 --- Results and discussion --- p.54 / Chapter 3.2.1 --- NRBS measurements --- p.54 / Chapter 3.2.2 --- X-ray diffraction --- p.57 / Chapter 3.2.3 --- Raman spectroscopy --- p.59 / Chapter 3.2.4 --- AFM and MFM measurements --- p.64 / Chapter 3.2.4.1 --- AFM result --- p.64 / Chapter 3.2.4.2 --- MFM result --- p.68 / Chapter 3.2.5 --- Vibrating sample magnetometer (VSM) measurements --- p.73 / Chapter 3.3 --- Summary --- p.78 / Chapter CHAPTER 4 --- CHARACTERIZATION OF CO-DEPOSITED FE-C SAMPLES --- p.79 / Chapter 4.1 --- Introduction --- p.79 / Chapter 4.2 --- Results and discussion --- p.80 / Chapter 4.2.1 --- NRBS measurement --- p.80 / Chapter 4.2.2 --- X-ray diffraction --- p.81 / Chapter 4.2.3 --- x-ray photoelectron spectroscopy (XPS) --- p.84 / Chapter 4.2.4 --- AFM results --- p.87 / Chapter 4.2.5 --- MFM results --- p.91 / Chapter 4.2.6 --- Vibrating sample magnetometer (VSM) measurements --- p.95 / Chapter 4.2.7 --- Resistivity --- p.99 / Chapter 4.2.8 --- Transmission electron microscopy (TEM) --- p.100 / Chapter 4.3 --- Application potential --- p.101 / Chapter 4.4 --- Summary --- p.104 / Chapter CHAPTER 5 --- CONCLUSION --- p.106 / Chapter 5.1 --- Main results of this work --- p.106 / Chapter 5.2 --- Future work --- p.108 / REFERENCE --- p.110 / PUBLICATIONS --- p.112 / APPENDIX --- p.113