Spacecrafts nowadays are important technology giving us the chance to do space exploration as well as for monitoring the global environmental changes. They gather the required data based on light observation. Unfortunately, the outgas from the spacecraft materials result in the contamination and degradation of the optical systems such as lenses and optical filters. To this end, researchers are looking for appropriate solutions to the contamination problem to enhance the accuracy of the obtained data during various spacecraft missions.
To date, photocatalysts have shown great potential for solving the aforementioned contamination problem since they can decompose organic contaminants using photon energy. Among the available photocatalysts materials, titanium oxide has particularly been used to decompose contaminants and suppress deterioration in orbital optical systems. However, due to severe space environment, high resistance materials are required. This can be achieved through electron beam irradiation of titanium oxide despite the limited study on the impact of electron beam irradiation of titanium oxide for use as spacecraft materials.
Therefore, Sophia University researchers in Japan: Dr. Naoki Shimosako, Kosuke Yoshino and Professor Hiroshi Sakama in collaboration with Dr. Kazunori Shimazaki and Dr. Eiji Miyazaki from the Japan Aerospace Exploration Agency investigated the effects of electron beam irradiation on anatase titanium oxide thin films. The main objective was to evaluate the resistance of titanium oxide to the electron beam in space. The work is published in the journal, Thin Solid Films.
To begin with, the titanium oxide films were irradiated in a vacuum with an electron beam with energy less than 480eV and irradiation dose of 2.4MGy. The authors further investigated the chemical properties, surface morphology and photocatalytic activity of the thin films before and after electron beam irradiation and compared the results.
Electron beam causes ionization damage and atomic displacement thus the properties of the titanium films may depend on the available defects. The energy loss due to atomic displacement was determined by calculating the non-ionization energy loss. The threshold displacement energy for oxygen atoms was observed to be smaller than that for titanium atoms thus it was much easier to knock down oxygen atoms from the titanium oxide. Besides, the small non-ionization energy loss value in R1 signified a negligible rate of atomic displacement. It was also noted that for R1 the electron-hole pairs generated in titanium oxide recombined to produce heat while for R2 only oxygen atoms were displaced.
The electron beam exhibited little effects on the basic properties of the titanium oxide. Except for surface roughness that experienced small relative change, all other properties remained unchanged. The increase of surface roughness was slightly high in R2 as compared to R1 owing to the temperature increase in the surface region. This showed that titanium oxide has sufficient resistance to electron beams with an energy of < 480kV.
In summary, the research team successfully demonstrated the tolerance to electron beams of titanium oxide film photocatalyst. Dr. Naoki Shimosako, the first author in a statement to Advances in Engineering stated that the study will be a key contributor in solving the contamination problem in the spacecraft through the use of titanium oxide as a potential photocatalyst for contamination decomposition in space.
Shimosako, N., Yoshino, K., Shimazaki, K., Miyazaki, E., & Sakama, H. (2019). Tolerance to electron beams of TiO2 film photocatalyst. Thin Solid Films, 686, 137421.