Thin-film semiconductor sensors for hyperthermal oxygen atoms

In Earth orbit, atomic oxygen (AO) erodes and degrades many spacecraft mate rials. Several sensors have been employed to make in situ measurements of t hese oxygen atom fluxes, yet none has proved suitable for general applicati on to microsatellites. We have investigated the potential of thin-film zinc oxide (ZnO) AO sensors. It is known that single crystal and thin-film semi conductor sensors may be used to measure fluxes of low-energy (thermal) oxy gen atoms. This work extends the principle to the measurement of hypertherm al (high energy) oxygen atoms ina ground-based simulation facility. It is f ound that, upon exposure to AO, the conductance of the ZnO sensors decrease s. Moreover, the rate of sensor conductance change is proportional to the f lux of oxygen atoms. Two sensors, which were manufactured simultaneously, d emonstrated very similar responses when exposed concurrently to hypertherma l AO. Further experiments showed that the sensors were not affected by flux es of molecular oxygen, but were influenced by ultraviolet (UV) radiation. A ZnO film covered with silica - to prevent the action of AO - was used to examine the influence of UV, which was shown to cause a small, permanent ch ange of the conductance of the semiconductor (C) 2000 Elsevier Science S.A. All rights reserved.