Development of a reusuable atomic oxygen sensor using oxide thick films

Abstract

The aim of this project was to develop a thick film sensor made of zinc oxide that would accurately respond to various fluxes of atomic oxygen (AO), allowing it to be regenerated after saturation. The sensors were manufactured using a thick film technique of screen printing over a substrate (alumina) that is inert to the action of AO; some of sensors were developed with pure ZnO while others used a binder to the substrate. The expectation has been that impinging atomic oxygen is captured upon the zinc oxide which will consequently increase its resistance; this change is an indicator of the AO flux. By suitable heating, the adsorbed atomic oxygen atoms are released from the sensor and its original properties are then restored.

This thesis describes the manufacturing of the sensors as well as all the tests conducted so as to characterize and determine the performance of the thick film ZnO sensors. It also includes the relevant conclusions to this work.

It has been concluded that the sensors respond to AO by increasing the overall DC resistance of the sensors; impedance spectroscopy reveals that an increase of the resistance of the grain boundaries of the crystallites that make-up the sensors to be the dominant process. AO flux can be measured by both resistance and impedance spectroscopy measurements. Sensors can be regenerated by suitable heating. However, each sensor needs to be independently calibrated before AO measurements can be achieved. A model to relate the change of DC conductance with AO flux is described, as well as an adaptation to use with impedance spectroscopy. UV radiation does not seem to have an effect on the resistance of the sensors, despite evidence provided by other researchers.

This is the first time that thick film ZnO sensors have been used to measure AO flux, and also the first time that impedance spectroscopy has been used for this purpose and to characterize thick film ZnO sensors for outer space applications.

Screen-printing of pure ZnO has not produced a sensor robust enough for outer space applications; the use of a glass binder shows promise to overcome this limitation.

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