Engineering topics

Christl, Ligia C.

Publications and source records attributed to Christl, Ligia C..

8 records

NASA NTRS1995

Changes in chemical and optical properties of thin film metal mirrors on LDEF

Thin films of the metals Cu, Ni, Pt, Au, Sn, Mo, and W deposited on fused silica flats were exposed at ambient temperature on the leading and trailing faces of the LDEF. Reflectances of these films were measured from 250 to 2500 nm and compared with controls. The exposed films were subjected to the LDEF external environment including atomic oxygen, molecular contamination, and solar ultraviolet. Major changes in optical and infrared reflectance were seen for Cu, Mo, Ni, and W films on the leading face of LDEF and are attributed to partial conversion of metal to metal oxide. Smaller changes in optical properties are seen on all films and are probably caused by thin contaminant films deposited on top of the metal. The optical measurements are correlated with film thickness measurements, x-ray photoelectron spectroscopy, optical calculations, and, in the case of Cu, with x-ray diffraction measurements. In a few cases, comparisons with results from a similar UAH experiment on STS-8 have been drawn.

Peters, Palmer N.↗

NASA NTRS1993

The interaction of atomic oxygen with copper: An XPS, AES, XRD, optical transmission, and stylus profilometry study

The University of Alabama in Huntsville (UAH) experiment A-0114 was designed to study the reaction of material surfaces with low earth orbits (LEO) atmospheric oxygen. The experiment contained 128 one-inch circular samples; metals, polymers, carbons, and semiconductors. Half of these samples were exposed on the front of the Long Duration Exposure Facility (LDEF) and remaining on the rear. Among metal samples, copper has shown some interesting new results. There were two forms of copper samples: a thin film sputter-coated on fused silica and a solid piece of OFHC copper. They were characterized by x-ray and Auger electron spectroscopies, x-ray diffraction, and high resolution profilometry. Cu 2p core level spectra were used to demonstrate the presence of Cu2O and CuO and to determine the oxidation states.

Raikar, Ganesh N.↗

NASA NTRS1992

Interaction of atomic oxygen with thin film and bulk copper: An XPS, AES, XRD, and profilometer study

The University of Alabama in Huntsville (UAH) experiment A-0114 was designed primarily to study degradation of material surfaces due to low earth orbital (LEO) atmospheric oxygen. The experiment contained 128 one inch circular samples: metals, polymers, carbons, and semiconductors. Among metal samples, copper has shown some interesting new results. Two types of copper samples, a film sputter coated on fused silica and a bulk piece of OFHC copper, were characterized employing a variety of techniques such as X-ray and Auger electron spectroscopies, X-ray diffraction, and high resolution profilometry. Cu 2p core level spectra were used to characterize the presence of Cu2O and CuO in addition to Cu Auger LMM lines. These results are supported by our recent X-ray diffraction studies which clearly establish the presence of Cu oxides which we were unable to prove in our earlier work. Profilometry showed an increase in thickness of the film sample where exposed to 106.7 +/- 0.5 nm from an initial thickness of 74.2 +/- 1.1 nm. Further studies with SEM and ellipsometry are underway.

Raikar, Genesh N.↗

NASA NTRS1992

Measurements of erosion characteristics for metal and polymer surfaces using profilometry

The surfaces of many materials exposed in low earth orbit are modified due to interaction with atomic oxygen. Chemical changes and surface roughening effects can occur which alter optical and other properties. The experiment A0114 contained 128 solid surface samples, half of which were exposed on the front and half on the rear of LDEF. Each sample has been subjected to many analyses, but only the methods and techniques used to measure the changes in roughness, erosion depths, and material growth using profilometry are described.

Christl, Ligia C.↗

NASA NTRS1992

Interactions of atomic oxygen with material surfaces in low Earth orbit: Preliminary results from experiment A0114

The atomic oxygen experiment consisted of two trays (one-sixth of a Long Duration Exposure Facility (LDEF) tray each) of 64 one inch diameter solid samples. It was intended that the effects of atomic oxygen and solar ultraviolet irradiation on the surface properties of each material could be distinguished from each other and from the effects of aging. Sixteen of the samples were placed on a thermally isolated plate of highly polished aluminum, while the main plate was coated with the thermal control coating S13-GLO. Though the experiment was entirely passive, it was hoped that the effects of thermal activation might be observed, if present. The plates were expected to stabilize at temperatures differing by 20-30 C. The samples included thin films of metals Os, Ir, Pt, Ni, Mo, and Al coated onto silica optical flats, metal carbides (WC, SiC), solid carbons of various types, eight polymers, and some other coatings of various types. Analysis is essentially complete using stylus profilometry with high sensitivity Talystep and lower sensitivity Talysurf machines. Though the integrated fluence of O atoms on the LDEF was 30 times that of previous missions, etch depths of the polymers such as the polyimide Kapton show excellent agreement with extrapolations from previous flight data. However, some new effects were observed. We demonstrated on a previous experiment on STS-8 that profilometry of this kind can show steps of 50 A (for example those due to oxide film growth on metals) and this is now the preferred method for estimating etch depth (or mass loss) of erodible substances.

Gregory, John C.↗

NASA NTRS1992

Effects on LDEF exposed copper film and bulk

Two forms of copper were exposed to the Long Duration Exposure Facility (LDEF) Mission 1 environment: a copper film initially 74.2 plus or minus 1.1 nm thick sputter coated on a fused silical flat and a bulk piece of oxygen free, high conductivity (OFHC) copper. The optical density of the copper film changed from 1.33 to 0.70 where exposed and the film thickness increased to 106.7 plus or minus 0.5 nm where exposed. The exposed area appears purple by reflection and green by transmission for the thin film and maroon color for the bulk copper piece. The exposed areas increased in thickness, but only increase in the thickness of thin film samples could be readily measured. The increase in film thickness is consistent with the density changes occurring during conversion of copper to an oxide. However, we have not been able to confirm appreciable conversion to an oxide by x ray diffraction studies. We have not yet subjected the sample to e-beams or more abusive conditions out of concern that the film might be modified.

Peters, Palmer N.↗

NASA NTRS1991

Effects on LDEF exposed copper film and bulk

Two forms of copper were exposed to the Long Duration Exposure Facility (LDEF) Mission 1 environment: a copper film, initially 74.2 plus or minus 1.1 nm thick sputter coated on a fused silica flat and a bulk piece of oxygen-free, high conductivity (OFHC) copper. The optical density of the copper film changed from 1.33 to 0.70 where exposed, and the film thickness increased to 106.7 plus or minus 0.5 nm where exposed. The exposed area appears purple by reflection and green by transmission for the thin film and maroon color for the bulk copper piece. The exposed areas increased in thickness, but only increase in the thickness of the thin film sample could be readily measured. The increase in film thickness is consistent with the density changes occurring during conversion of copper to an oxide. However, we have not been able to confirm appreciable conversion to an oxide by x-ray diffraction studies. We have not yet subjected the sample to e-beams or more abusive investigations out of concern that the film might be modified.

Peters, Palmer N.↗

NASA NTRS1991

Measurements of erosion characteristics for metal and polymer surfaces using profilometry

The surfaces of many materials exposed in low earth orbit are modified due to interaction with atomic oxygen. Chemical changes and surface roughening effects can occur which alter optical and other properties. The experiment A0114 contained 128 solid surface samples, half of which were exposed on the front and half on the rear of Long Duration Exposure Facility. Each sample was subjected to many analyses, but only the methods and techniques are described which were used to measure the changes in roughness, erosion depths, and material growth using profilometry.

Christl, Ligia C.↗