|
Although silver-based telescope mirrors excel over other materials such as gold and aluminum in the visible-infrared spectral range, they require robust protective coatings to overcome their inherent low durability. Our research shows that a single-layer of aluminum oxide (AlOx) deposited through thermal atomic layer deposition (ALD) using trimethylaluminum (TMA) and water (H2O) at low temperatures (~60°C) serves as an acceptable protection coating without adversely impacting the optical performance of the mirrors. While the use of TMA and H2O as precursors in thermal ALD offers AlOx that performs decently in the field, it degrades quickly in environmental tests under high-humidity at high-temperature conditions, suggesting that there is room to improve. In this paper, two approaches by which ALD processes of AlOx protection coatings can be improved are investigated: exploring another precursor for oxygen and implementing a pre-deposition conditioning. The study is carried out by introducing two new processes – the use of Pure Ozone (PO) and Ozone-Ethylene Radical (OER) in comparison to thermal ALD with TMA and H2O. Our study shows that samples prepared by PO have the initial spectral reflectance lower than that of those prepared by the thermal ALD; however, reflectance of the PO samples remains nearly constant 1.6 times longer in the environmental test, suggesting promising characteristics of AlOx prepared with PO.
|
