NUST MISIS scientists create a protective coating for the space industry

The MISIS University scientists have developed a new wear-resistant optically transparent coating to protect solar cells installed on spacecraft and elements of optical devices on aircraft equipment. The Ta-Si-N (tantalum-silicon-nitrogen) coating will enable to deal with a global issue related to the impact of space debris particles and micrometeoroids on spacecraft.

Photovoltaic converters (PVCs) of solar cells are exposed to intensive destruction from collisions in space. Thin glasses are commonly used to protect PVCs from microparticles. However, their application is limited by low strength characteristics, such as hardness and fracture toughness, and they add significant weight to solar cells. Optical devices (windows, PVCs, solar collectors, etc.) may be protected from destructive effects through the use of a wear-resistant Ta-Si-N coating with high transmission of up to 80-90%. The research findings are detailed in in the international scientific Surfaces and Interfaces journal (Q1).

“The Ta-Si-N system coatings outperform famous optical semiconductor oxide coatings in terms of growth rate by 2–7 times and in terms of resistance to abrasive particles by 1.5–5 times, rendering their use promising for increasing the service life and operating features of such items, as photovoltaic converters of solar cells, parts of optical devices and components of laser equipment,” Philip Kiryukhantsev-Korneev, Dr. Sci. (Engin.), Head of the MISIS-ISMAN SHS Center In situ Diagnostics of Structural Transformations Laboratory, Professor of the MISIS Department of Powder Metallurgy and Functional Coatings, said.

Ta-Si-N coatings were obtained in vacuum using the magnetron sputtering technology, when the plasma is formed over the cathode surface as a result of collision of electrons with atoms of the working gas. Positive argon ions (Ar+) formed in the discharge are accelerated towards the cathode, bombarding its surface and knocking out atoms, which are further transported and deposited on the product. The research was supported by a grant from the Russian Science Foundation (No. 19-19-00117-P).

“Specific optical characteristics are due to flexible control of coating deposition parameters, including the partial pressure of the reaction gas. Nitrogen atoms react with tantalum and silicon to generate a wear-resistant optically transparent layer having an amorphous structure,” Alina Sytchenko, Junior Researcher at the MISIS SHS Center In situ Diagnostics of Structural Transformations Laboratory, commented.

Ta-Si-N coatings have a unique combination of properties and are marked by high optical transmission, wear resistance, thermal stability of up to 1,200°C, refractive index in the range of 2.0–2.5 and oxidation resistance. Improved properties are thanks to a high volume fraction of the amorphous phase based on silicon nitride (a-SiNx) and an amorphous structure lacking grain boundaries that serve as light scattering centers and channels of accelerated oxygen diffusion.

NUST MISIS Rector Alevtina Chernikova noted, “The aerospace industry is one of the most high-tech and knowledge-intensive industries in Russia’s economy, and its advancement is of national importance. The MISIS University scientists have been involved in pilot projects for the space industry for several years already. University researchers create new materials with specified properties for use in extreme conditions, develop breakthrough technologies related to space exploration, production and operation of spacecraft for various purposes. The wear-resistant coating created by our scientists will protect optical elements and improve functional features of spacecraft.”

In these days, scientists are working on improving the properties of coatings and their deposition technology. They believe that the work in progress is of paramount importance for the development of the sector of oxygen-free optical coatings. The research at issue is a continuation of earlier work on the creation of erosion-resistant and antireflection optical coatings obtained by magnetron sputtering of ceramic cathodes. The authors first discovered the “optical transparency” effect in Zr-B-N (zirconium-boron-nitrogen) films and described it in the scientific Surface and Coatings Technology journal (Q1).