The following description is taken from Simon C.G., Hunter J.L.,
Wortman J.J., Griffis D.P., ION MICROPROBE ANALYSES OF IMPACT FEATURES
ON INTERPLANETARY DUST EXPERIMENT SENSOR SURFACES, in:
LDEF-69 Months in Space, NASA CP-3134,
1992 pp. 529-548
Germanium Witness Plates
Twelve 1.25 inch (3.175 cm) diameter, 250 micrometer thick semiconductor
device quality single crystal Ge wafers were glued to Al plates with
silicone RTV, mounted on tray B12, and exposed to the orbital environment
during the entire mission. These wafers were intended to serve as witness
plates both for hypervelocity impacts and surface contaminants. However,
during optical examination it was noted that the surfaces of these wafers
were covered with solid contaminants with condensate rings at a density of
approximately 400 features (> 10 micrometer diameter) per square centimeter.
Optical surveys of three other similar sized witness plates (one zirconia
and two silicon) mounted adjacent to the Ge witness plates revealed only 10-27
similar contaminants per square centimeter on these surfaces. This is taken as
conclusive evidence that the majority of the contaminants on the Ge wafers
were deposited before they were mounted on the spacecraft with the other
witness plates. Auger, EDS and SIMS analyses of dozens of these contaminant
features showed a dominance of alkali-chlorides, hydrocarbons, Mg, Si, Ca,
S, Ti, some Fe, and very little Al.