Optical index of refraction n is studied by spectroscopic ellipsometry in epitaxial nanofilms of NaNbO3 with thickness ∼10 nm grown on different single-crystal substrates. The index n in the transparency spectral range (n ≈ 2.1 - 2.2) exhibits a strong sensitivity to atmospheric-pressure gas ambience. The index n in air exceeds that in an oxygen ambience by δn ≈ 0.05 - 0.2. The thermo-optical behaviour n(T) indicates ferroelectric state in the nanofilms. The ambience-sensitive optical refraction is discussed in terms of fundamental connection between refraction and ferroelectric polarization in perovskites, screening of depolarizing field on surfaces of the nanofilms, and thermodynamically stable surface reconstructions of NaNbO3.

Institute of Physics Academy of Sciences of the Czech Republic Na Slovance 2 182 21 Prague 8 Czech Republic

Microelectronics and Materials Physics Laboratories University of Oulu PO Box 4500 FI 90014 Oulun yliopisto Finland; Institute of Physics Academy of Sciences of the Czech Republic Na Slovance 2 182 21 Prague 8 Czech Republic

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