P. N. Peters, J. C. Gregory, and J. T. Swann, "Effects on optical systems from interactions with oxygen atoms in low earth orbits," Appl. Opt. 25, 1290-1298 (1986)
Modifications of material surface properties due to interactions with ambient atomic oxygen have been observed on surfaces facing the orbital direction in low earth orbits. Some effects are very damaging to surface optical properties while some are more subtle and even beneficial. Most combustible materials are heavily etched, and some coatings, such as silver and osmium, are seriously degraded or removed as volatile oxides. The growth of oxide films on metals and semiconductors considered stable in dry air was measured. Material removal, surface roughness, reflectance, and optical densities are reported. Effects of temperature, contamination, and overcoatings are noted.
James B. Hadaway, Anees Ahmad, J. Larry Pezzaniti, Russell A. Chipman, Donald R. Wilkes, Leigh L. Hummer, David G. Crandall, and Jean M. Bennett Appl. Opt. 40(16) 2755-2768 (2001)
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Results were influenced by both contamination and temperature as described in the text; results shown are for ambient temperature believed to be between 273 and 300 K.
Films were deposited on fused silica flats described in text unless noted otherwise.
See text for details; 6-nm Pt/Os was poorly protected; we were unable to make measurements of the 6-nm Pt/Os because the back of the substrate was rough ground.
Table III
Some Effects Observed on Bulk Samples Exposed to 3.5 × 1020 Oxygen Atoms cm−2 in Low Earth Orbitsa
Sample
Effects
Polished tungsten carbide
No detectable change; surface roughnesses on exposed and unexposed areas ∼10 nm.
Diamond
Least affected carbon. Etched 75 nm deep; etched surface not smooth but covered with a weak layer which was easily scraped off.
Edge oriented graphite
Etched ∼2300 nm deep; very rough, separated, striated structure produced.
Basal oriented graphite
Etched ∼2200 nm deep; smoother, orange-peel effect on surface.
Vitreous carbon
Etched ∼4500 nm deep; rough surface resembling grass, misshapen cones or pyramid, etch depth slightly dependent on manufacturer and/or preparation and mounting.
CR-39 plastic
Heavily etched samples: 22,000 nm. Etched surface very rough (cones resembling grass, see Fig. 2).
Polymethyl methacrylate
Heavily etched: ∼17,000 nm. Very rough surface also.
Silver
Thin films of optical quality are typically converted to transparent oxide with the film thickness expanding greatly (∼55%). Results on bulk silver seem to vary. Beautiful interference colors are observed for the thin oxides. Thick oxide formations appear to create stress levels which produce buckling or scaling which limit, or modify, further oxidation. The oxide is not too stable. The oxide apparently has a high index of refraction, but attempts to measure its optical properties by ellipsometry have given very poor inconsistent results possibly due to inhomogeneities or instability effects.
Osmium
Etched ∼1100 nm; polycrystalline structure made visible by slight preferential etching.
Silicon
No measurable effect.
Germanium
Visual discoloration, ellipsometer indicated 159-nm film with index of 1.53; stylus gave no distinguishable step; one form of GeO2 (tetra) has a density of 6.239 g/cm3, which exceeds the density of Ge.
Copper
Polished OFHC copper disk exhibited a very slight surface discoloration estimated to be ∼3.5 nm thick from step measurements.
Effects are temperature dependent. Temperatures were ambient for listed materials.
Table IV
Ultraviolet Reflectance Measurements Made on a 10-nm Pt/Os Film on Fused Silica with a Portion Exposed to 3.5 × 1020 Atoms cm−2 of Atomic Oxygen
Results were influenced by both contamination and temperature as described in the text; results shown are for ambient temperature believed to be between 273 and 300 K.
Films were deposited on fused silica flats described in text unless noted otherwise.
See text for details; 6-nm Pt/Os was poorly protected; we were unable to make measurements of the 6-nm Pt/Os because the back of the substrate was rough ground.
Table III
Some Effects Observed on Bulk Samples Exposed to 3.5 × 1020 Oxygen Atoms cm−2 in Low Earth Orbitsa
Sample
Effects
Polished tungsten carbide
No detectable change; surface roughnesses on exposed and unexposed areas ∼10 nm.
Diamond
Least affected carbon. Etched 75 nm deep; etched surface not smooth but covered with a weak layer which was easily scraped off.
Edge oriented graphite
Etched ∼2300 nm deep; very rough, separated, striated structure produced.
Basal oriented graphite
Etched ∼2200 nm deep; smoother, orange-peel effect on surface.
Vitreous carbon
Etched ∼4500 nm deep; rough surface resembling grass, misshapen cones or pyramid, etch depth slightly dependent on manufacturer and/or preparation and mounting.
CR-39 plastic
Heavily etched samples: 22,000 nm. Etched surface very rough (cones resembling grass, see Fig. 2).
Polymethyl methacrylate
Heavily etched: ∼17,000 nm. Very rough surface also.
Silver
Thin films of optical quality are typically converted to transparent oxide with the film thickness expanding greatly (∼55%). Results on bulk silver seem to vary. Beautiful interference colors are observed for the thin oxides. Thick oxide formations appear to create stress levels which produce buckling or scaling which limit, or modify, further oxidation. The oxide is not too stable. The oxide apparently has a high index of refraction, but attempts to measure its optical properties by ellipsometry have given very poor inconsistent results possibly due to inhomogeneities or instability effects.
Osmium
Etched ∼1100 nm; polycrystalline structure made visible by slight preferential etching.
Silicon
No measurable effect.
Germanium
Visual discoloration, ellipsometer indicated 159-nm film with index of 1.53; stylus gave no distinguishable step; one form of GeO2 (tetra) has a density of 6.239 g/cm3, which exceeds the density of Ge.
Copper
Polished OFHC copper disk exhibited a very slight surface discoloration estimated to be ∼3.5 nm thick from step measurements.
Effects are temperature dependent. Temperatures were ambient for listed materials.
Table IV
Ultraviolet Reflectance Measurements Made on a 10-nm Pt/Os Film on Fused Silica with a Portion Exposed to 3.5 × 1020 Atoms cm−2 of Atomic Oxygen