Both the optical and physical properties of thin film optical interference coatings depend upon the microstructure of the deposited films. This microstructure is strongly columnar with voids between the columns. Computer simulations of the film growth process indicate that the two most important factors responsible for this columnar growth are a limited mobility of the condensing molecules and self-shadowing by molecules already deposited. During the vacuum deposition of thin films, the microstructure can be influenced by many parameters, such as substrate temperature and vacuum pressure. By controlling these parameters and introducing additional ones, thin film coatings can be improved. In this research, ultraviolet irradiation and ion bombardment were examined as additional parameters. Past studies have shown that post-deposition ultraviolet irradiation can be used to relieve stress and reduce absorption in the far ultraviolet of silicon dioxide films. Ion bombardment has been used to reduce stress, improve packing density, and increase resistance to moisture penetration. Three refractory oxide materials commonly used in thin film coatings were studied; they are silicon dioxide, titanium dioxide, and zirconium dioxide. Both single-layer films and narrowband filters made of these materials were examined. A 1000-watt mercury-xenon lamp was used to provide ultraviolet irradiation. An inverted magnetron ion source was used to produce argon and oxygen ions. Ultraviolet irradiation was found to reduce the absorption and slightly increase the index of refraction in zirconium oxide films. X-ray diffraction analysis revealed that ultraviolet irradiation caused titanium oxide films to become more amorphous; their absorption in the ultraviolet was slightly reduced. No changes were noted in film durability. Ion bombardment enhanced the tetragonal (lll) peak of zirconium oxide but increased the absorption of both zirconium oxide and titanium oxide films. The titanium oxide films were found to become amorphous with even slight ion bombardment. Little effect was noted in silicon oxide films.

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.

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.

No description available.

Optical, electrical, and microstructural effects of Ar ion bombardment and Ar incorporation on thermally evaporated Ag and Al thin films were investigated. The results show that as the momentum supplied to the growing films by the bombarding Ar ions per arriving metal atom increases, refractive index at 632.8 nm increases and extinction coefficient decreases, lattice spacing expands, grain size decreases, electrical resistivity increases, and trapped Ar increases slightly. In Ag films, stress reverses from tensile to compressive; in AI films compressive stress increases. In both films, the change in optical constants can be explained by variation in void volume. The reversal of stress from tensile to compressive in Ag films requires a threshold level of momentum. The increase in electrical resistivity is related to the increase in the void fraction, decrease in the grain size, and increase in trapped Ar in both types of films. Many of these properties correlate well with the momentum transferred, suggesting that the momentum is an important physical parameter in describing the influence of ion beams on growing thin films and determining the characteristics of thin metal films prepared by ion-assisted deposition (IAD). With a low energy ion beam, the Ar concentration in IAD Ag films was negligible. When the bombarded film thickness was less than 5 nm, the electrical resistivity of IAD Ag films tended to decrease slightly from that of the non-IAD film. Using the Bruggeman effective medium theory, a formula for the void fraction at any given wavelength was derived. We investigated optical properties, stoichiometry, chemical bonding states, and structure of aluminum oxynitride thin films prepared by reactive ion-assisted deposition. Variations of optical constants and chemical bonding states are related to the stoichiometry. We found that our amorphous aluminum oxynitride film is not simply a mixture of aluminum oxide and nitride but a compound. A rugate filter using a step-index profile of aluminum oxynitride films was fabricated by nitrogen ion beam bombardment of a growing Al film with backfilled oxygen pressure as the sole variable. The effects of ultrasound-assisted deposition (UAD) on the optical properties of ZrO₂, Ta₂O₅, and MgF₂ films were investigated. UAD is likely to induce oxygen and fluoride deficiencies in oxide and fluoride films and increase the packing density of films.

Previous work has shown that laser-induced desorption (LID) can prove useful for the determination of surface contamination. However, because of the nature of small-spot sampling utilized in the previous work, it proved rather difficult to gather statistically significant data. A solution to this problem that still allowed sampling the surface with small focused laser spots was to automate the sample manipulation, laser control, and data acquisition of the system. With the automation of the LID facility in place, a detailed study of the LID of water/heavy water (H₂O/D₂O) was undertaken. As in the earlier work, samples were irradiated with a hydrogen fluoride/deuterium fluoride (HF/DF) laser beam focused inside an ultrahigh vacuum (UHV) chamber. The molecules desorbed from the sample surface were partially contained in a glass envelope that also contained a quadrupole mass analyzer. Samples consisted of bulk-etched CaF₂ and optical thin-film coatings of CaF₂--undosed or H₂O/D₂O dosed--on a variety of substrates. Some analysis was performed on cleaved, single-crystal alkali halides. The focused laser spot size was 155 μm (l/e² diameter) for the HF laser and 138 μm (l/e² diameter) for the DF laser. Between 400 and 800 sites per sample were tested for each desorption onset analysis. A study was also performed to test the possibility of correlation between (1) laser-induced damage and defects and (2) laser-induced desorption and adsorption sites for some of the samples listed above. Attempts to deuterate and hydrate CaF₂ thin films met with limited success as laser-induced desorption samples. Other analysis techniques showed that dosing during the coating process produced a more ordered coating; in fact, dosing with H₂O reduced the optical absorption in the "H₂O" band, modified the damage morphology, and, along with a low temperature bakeout, raised the laser-damage threshold.

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.

Thesis (M.S.)--Rochester Institute of Technology, 1991. / Typescript. Includes bibliographical references.

The plasmonic properties of silver-based alloy thin films were studied. Silver-ytterbium (Ag-Yb) and silver-magnesium (Ag-Mg) prepared by thermal co-evaporation were investigated extensively for various thin film properties. The optical properties were intensively analyzed and discussed because the dielectric response of a material is particularly significant in terms of its plasmonic properties. The study of silver-based alloy thin films has been mostly about Ag alloying with other transition metals, but the results of Ag-Yb and Ag-Mg in this work showed that the intensity of plasma resonance is tunable, in which the idea may also apply to other silver-rich binary alloy thin films regardless of the kind of second metal components. In our research, the Ag plasma resonance was weakened with respect to the concentration of Yb and Mg in the alloy thin films. The change in the optical characteristics around Ag plasma resonance frequency was attributed to an increase in “resonance damping. This is confirmed from modeling using classical free-electron theory. The increase in the damping was experimentally corroborated by the concentration dependence of electrical conductivity and estimated average crystallite size of Ag-Yb and Ag-Mg thin films. The reduction in electrical conductivity was not only caused by introducing less conductive Yb or Mg but also through disturbing the Ag lattice structure to promote additional electron scattering at grain boundaries. The Ag-Yb and Ag-Mg alloys carried intermediate properties between their pure components despite the presence of Yb or Mg oxides. Besides optical and electrical properties, changes in the electronic work function were also assessed since it is also important in applications. Plasmonic nanostructures and transparent organic light-emitting diodes (OLEDs) were fabricated to demonstrate their potential applications. Two-dimensional disc-arrays nanostructures composed of pure Ag and Ag-Yb were implemented to evaluate the plasmonic properties. The damping loss in Ag-Yb caused weakened coupling of incident photons and surface plasmons when compared to pure Ag without altering the coupling wavelengths, suggesting potential plasmonic materials for tuning the coupling strength of surface plasmons by controlling the concentration of Yb which may also apply to Ag-Mg. Ultrathin Ag-Yb and Ag-Mg films were used as cathodes in transparent OLEDs for demonstration, which was beneficial by virtue of overall device transmittance though sacrificing electrical conduction leading to poor light emission unless inserting additional ultrathin lithium fluoride to modify the ultrathin cathodes.

The physical properties of single crystals of samarium monosulfide exhibit a first order semiconductor-to-metal transition near 6.5 kbar. However, thin films of SmS show only a gradual change in their properties on applying pressure and this renders the technical utilization of the material difficult. Several mechanisms have been proposed as the cause of the smoothing of the transition. They include intrinsic stress, impurities, grain size, improper stoichiometry, and porosity, all of which can be traced to the physical vapor deposition techniques employed in preparing the films. In contrast, chemical vapor deposition was employed in this study because previous work had shown that it could minimize these detrimental modifications in thin films. A new CVD system was tested using a volatile organometallic as the samarium source and reacting it with H₂S. The deposited films contained considerable amounts of oxygen as evidenced by structure analysis, and the origin was traced to the samarium organometallic. The reaction of oxygen-free samarium tricyclopentadienyl with H₂S as well as chemical transport are suggested for deposition of stress-free SmS thin films in future work.