Coatings Made by Atomic Layer Deposition for the Protection of Materials from Atomic Oxygen in Space

Atomic Layer Deposition (ALD) has been investigated for the possible protection of various materials against atomic oxygen (ATOX) at ESTEC Materials and Electrical Components Laboratory facility. ALD is a conformal coating process, that can be used to apply ultra-thin films of metal oxides on various materials, that may have a sophisticated three-dimensional shape, such as the internal and external components of satellites. The challenge with metal oxides on soft and/or flexible surfaces arises from the brittle nature of these ceramic films if their thickness exceeds 30 nm. Different substrates, including silicon, Printed Circuitry Board (PCB), polyimide, and Carbon Fibre Reinforced Polymers (CFRP) were coated by ALD with 20 nm thick metal oxide films at 125 °C, then exposed to ATOX and characterized by photographing, reflectance measurement and scanning electron microscopy (SEM). The studies showed good performance of protective films prepared by ALD on polymer substrates, which suggests that the nanometer-scale coatings can improve the lifetime of these materials at low Earth orbit, where they are inevitably exposed to ATOX. In contrast, the uncoated substrates suffered near-surface damage after exposure to ATOX, which resulted in microscopic features on their surface that were visible in SEM. Damage caused by ATOX to the uncoated substrates was also visible in photographs and observable in reflectance studies. In the latter case, the changes in the reflectance spectrum were caused by the change of surface morphology and/or chemical and elemental composition due to corrosion by ATOX.