Physics of nanostructures

Sapphire surface layer structure and transmission in visible after sputtering in H$_2$–N$_2$ RF discharge

A. E. Gorodetsky^a, L. A. Snigirev^b, A. V. Markin^a, V. L. Bukhovets^a, T. V. Rybkina^a, R. Kh. Zalavutdinov^a, A. G. Razdobarin^b, E. E. Mukhin^b, A. M. Dmitriev<sup>b

a</sup> Institute of Physical Chemistry and Electro Chemistry, Russian Academy of Sciences, Moscow, Russia
^b Ioffe Institute, St. Petersburg, Russia

Abstract: Leucosapphire ($c$-LS) structure and transmission in visible after surface treatment in 90%H$_2$–10%N$_2$ RF discharge are studied. According to AFM, the number of scratches of the mechanically polished surface decreased significantly after removal of about a 300 nm layer (exposure time of 12 h) under unchanged rms of roughness. According to TEM, a two-layer structure formed in the near-surface region consists of an outer 10 nm amorphous layer followed by a crystalline layer of 40–50 nm with a high defect density. The $c$-LS transmission in the angle of 400–1000 nm either slightly increased or remained unchanged. The demonstrated transmission stability during exposure in 90%H$_2$–10%N$_2$ RF discharge allows us to consider the plasma sputtering as a promising technique for cleaning contaminated windows protecting first mirror of divertor Thomson scattering being developed for ITER divertor.

Keywords: leucosapphire, RF discharge, hydrogen, nitrogen, AFM, TEM, surface layer structure, visible transmission.

Received: 15.04.2022
Revised: 27.05.2022
Accepted: 28.05.2022

DOI: 10.21883/JTF.2022.10.53252.108-22

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