Ann F. Whitaker

The interaction of atomic oxygen with thin copper films

A source of thermal, ground‐state atomic oxygen has been used to expose thin copper films at a flux of 1.4×1017 atoms/cm2 s for times up to 50 min for each of five temperatures between 140 and 200 °C. Rutherford backscattering spectroscopy was used to characterize the oxide formed during exposure. The observations are consistent with the oxide phase Cu2O. The time dependence and the temperature dependence of the oxide layer thickness can be described using oxide film growth theory based on rate limitation by diffusion. Within the time and temperature ranges of this study, the growth of the oxide layers is well described by the equation L(T,t)=3.6×108 exp(−1.1/2kBT)t12, where L, T, and t are measured in angstroms, degrees Kelvin, and minutes, respectively. The deduced activation energy is 1.10±0.15 eV, with the attendant oxidation rate being greater than that for the corresponding reaction in molecular oxygen.

The oxidation of polycrystalline silver films by thermal, ground-state atomic oxygen

Abstract Experimental results indicate a linear relationship between oxide layer thickness and exposure time for thin Ag films exposed to thermal, ground-state atomic oxygen fluxes of the order of 10 17 atoms/(cm 2 s). Exposure times ranged between 10 and 120 s, and all exposures were made at ambient temperature. The techniques of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) were used to characterize stress-induced damage in the thickest oxide layers. This damage was also observed using RBS (Rutherford backscattering spectroscopy) techniques which were applied to determine oxide layer thicknesses as a function of exposure time. Results are compared with data recently obtained from similar measurements using thin, polycrystalline Cu films.

Environmental Effects on Composites

Composite usage has increased dramatically over the last three decades due to the advantages of light weight, specific strength and stiffness, dimensional stability, tailorability of properties such as coefficient of thermal expansion and high thermal conductivity. Environmental effects on these properties may compromise a structure and must be considered during the design process.

Tribology Experiment in Zero Gravity

A tribology experiment in zero gravity was performed during the orbital flight of Spacelab 1 to study the motion of liquid lubricants over solid surfaces. The absence of a significant gravitational force facilitates studies of the motion of liquid lubricants over solid surfaces as controlled by interfacial and capillary forces. Observations were made of phenomena associated with the liquid on one solid surface and also with the liquid between a pair of closely spaced surfaces. Typical photographic records obtained on Spacelab 1 are described.

In Situ Measurements of Scattering from Contaminated Optics in the Vacuum Ultraviolet

NASAs In Situ Contamination Effects Facility has been used to measure the time dependence of the angular reflectance from molecularly contaminated optical surfaces in the vacuum ultraviolet. The light scattering measurements are accomplished in situ on optical surfaces in real time during deposition of molecular contaminants. The measurements are taken using noncoherent VUV sources with the predominant wavelengths being the krypton resonance lines at 1236 and 1600 angstroms. Detection of the scattered light is accomplished using a set of three solar blind VUV photomultipliers. An in-plane VUV BRDF (bidirectional reflectance distribution function) experiment is described and details of the on-going program to characterize optical materials exposed to the space environment is reported.