Be/Al-based multilayer mirrors with improved reflection and spectral selectivity for solar astronomy above 17nm wavelength

Publication date: 1 June 2017
Source:Thin Solid Films, Volume 631
Author(s): N.I. Chkhalo, D.E. Pariev, V.N. Polkovnikov, N.N. Salashchenko, R.A. Shaposhnikov, I.L. Stroulea, M.V. Svechnikov, Yu.A. Vainer, S.Yu. Zuev
It is shown that in the vicinity of 17nm wavelength, Be can be used as an optically contrasting material with Al in periodic multilayer mirrors. At the same time, due to the low absorption of both Be and Al, we can expect a unique combination of reflective characteristics: record high peak reflectivity and spectral selectivity simultaneously. Although the theoretical reflectivity of a Be/Al multilayer is 78% at normal incidence and at the 17.14nm wavelength, we recorded only 46% for a pure Be/Al structure. The introduction of 1nm Si on top of the Be layers in each period increases the reflection up to 61% at normal incidence. The increase of the reflection coefficient of Be/Si/Al multilayer mirrors is conditioned by smoothing the interfaces from root-mean-square value of 1.3nm in pure Be/Al structures to 0.6nm in Si-containing samples. We suppose that the smoothing effect is connected with the amorphization of Al films in the presence of Si.