Dianne J. Coleman

Effects of Hydrolysis On Metallo-Organic Solution Deposition of PZT FILMS

The effects of hydrolysis on the degree of polymerization during metallo-organic solution deposition of lead zirconate titanate (PZT) films have been investigated. The reaction of lead 2-ethylhexanoate, zirconium n-tetrapropoxide, and titanium tetrabutoxide in isopropanol with water were studied using thermogravimetry, specular reflectance Fourier transform infrared spectroscopy (FTIR) and optical and electron microscopy. Films prepared from coating solutions having varying amounts of water exhibited dramatic differences in morphology. The films were spin-coated on platinum coated fused silica substrates and annealed at 525°C for 30 minutes. Unhydrolyzed coating solutions and solutions with a mole ratio of water to total metal of 0.5 yielded perovskite films with 0.5–5μm grains. A mole ratio of 1.5 (the amount of water required to completely hydrolyze the metallo–organics in the solution) formed amorphous, porous films. The stability of the prepolymerized films inhibits crystallization and densification at moderate temperatures.

Surface mediated radical recombination luminescence: O+NO+Ni

Results of an experimental investigation of the chemiluminescence produced by the interaction of atomic oxygen and nitric oxide on a nickel foil surface are reported. Visible luminescence which depends linearly on the atomic oxygen and nitric oxide fluxes, on the substrate temperature, and on the substrate temperature history has been observed under conditions for which the three‐body gas‐phase reaction of O and NO is negligible. The intensity of the luminescence is greater than can be accounted for by the gas‐phase two‐body radiative recombination reaction of O and NO. The time, flux, and temperature dependences, along with the intensity of the emission support strongly the notion that the observed luminescence stems from excited species, most probably electronically excited NO2, formed in a surface mediated reaction.

Surface-mediated chemiluminescent reaction of O and NO

Abstract Deep-red chemiluminescence occurs when beams of O and NO react on metal surfaces. Of the metals studied (Ni, Co, Pt; Kovar, Invar, and Monel), nickel was the most effective at promoting the chemiluminescent reaction. The rate depends inversely on the surface temperature. The reaction rate appears to be controlled by the flux of NO to the surface, and does not depend strongly on the NO beam temperature. These behaviors indicate that the chemiluminescence arises not from a gas-phase reaction near the surface, but from a surface-mediated reaction of O and NO to produce electronically excited gas-phase NO 2 , most probably of the Langmuir—Hinshelwood variety.

Photochemical deposition of spacecraft material outgassing products

Laboratory measurements of photochemical deposition rates of outgassing products from Tefzel insulation have been conducted. We show that outgassing products from Tefzel insulation photodeposit under conditions of surface temperature and arrival rates for which bulk condensation will not occur. Normalized to the sample size, the photodeposition rate exceeds the reported condensable material outgassing rate. The result reported here strongly support the conclusion that photochemical deposition of contaminants from Tefzel is potentially a significant mechanism for degradation of thermal control surfaces on spacecraft.

Metalloorganic solution deposition of ferroelectric PZT films

The metallo-organic solution deposition (MOSD or sol-gel) technique can be used for preparing lead zirconate titanate (PZT) ceramics with a wide range of compositions and crystal structures for electrooptical applications. Film morphology is affected by the stoichiometry of the film, hydrolysis and polymerization of the sol-gel solution, and thermal treatment of the deposited material. The lattice parameter decreases with the amount of titanium in the PZT, in agreement with ceramic data. A slight initial excess of lead in the coating solution is found to improve film morphology. Unlike traditional powder ceramic processing techniques, MOSD permits the growth of small uniform grains that are conducive to achieving consistent electronic and optical properties. Results show that the properties of films prepared by the MOSD process can be tailored to meet the needs of device applications.<<ETX>>

Ultraviolet laser contamination of quartz optics.

Laboratory experiments were conducted to determine the cause of degradation of two quartz polarizers used in conjunction with a cw UV laser. UV transmission spectra and x-ray photoelectron spectroscopic measurements of the damaged optic and laser-induced photolysis of one of the adhesives used to hold the polarizer in position indicate that the degradation is most probably a result of UV photolysis of adhesive residue. It would therefore be prudent to avoid use of all organic adhesives in UV laser optics. An alternative method of holding a quartz beam splitter without adhesives is described and is currently being used.

Contaminant film deposition on VUV-modified surfaces

Mechanisms for molecular contaminant droplet formation are investigated. The tendency for droplet formation is evaluated in terms of the surface tension of the liquid-like outgassed species and the surface energy of the collector. Results are presented indicating that VUV irradiation of the surface prior to contaminant deposition eliminates some droplet formation completely. This finding is discussed in terms of the removal of hydrocarbon and carbonyl-structured compounds from oxidized silicon surfaces.

Photochemical processes in a two-component molecular contaminant film

Previously, significant laboratory work has been performed on the photochemical deposition and darkening of molecular contaminant films. Much of this work addresses single, purified molecular species to understand fundamental photochemical processes. However, some of this work disagrees with other studies involving mixed, real spacecraft materials. There are also points of disagreement with contaminated returned optics from the Hubble Space Telescope where mixed contaminants were found. In this paper, we describe a method for vacuum depositing a controlled, reproducible contaminant film containing two molecular species: tetramethyl-tetraphenyl trisiloxane (DC 704) and dioctyl phthalate (DOP). We use this film to show differences in photochemical processes compared to a pure film of DC 704. We show that some photopolymerization processes occur more slowly in a two-component, mixed film during accelerated exposure to vacuum ultraviolet (VUV) radiation.

Digital Imaging of Particulate Contamination

The use of digital cameras and digital imaging software for the measurement of particle obscuration is discussed. Novel calibration standards are used to evaluate the sensitivity and accuracy of commercially available digital cameras for detecting microscopic dust particles and other contaminant features on surfaces. Lighting and illumination effects are also illustrated and discussed. The digital image histogram of particles on a surface is shown to give good results for the percent area coverage.

Optical properties of contaminant droplets

Novel light scattering properties of molecular films in a “droplet” configuration are presented and discussed. The illuminated films are shown to disappear when viewed at particular angles. The phenomenon is discussed in the context of Germer’s analysis of out-of-plane scattering from particles and surface micro-roughness.