Surface oxide on thin films of yttrium hydride studied by neutron reflectometry

Abstract

The applicability of standard methods for compositional analysis is limited for H-containing films. Neutron reflectometry is a powerful, non-destructive method that is especially suitable for these systems due to the large negative scattering length of H. In this work we demonstrate how neutron reflectometry can be used to investigate thin films of yttrium hydride. Neutron reflectometry gives a strong contrast between the film and the surface oxide layer, enabling us to estimate the oxide thickness and oxygen penetration depths. A surface oxide layer of 5-10 nm thickness was found for unprotected yttrium hydride films.

Yttrium oxyhydrides for photochromic applications: Correlating composition and optical response

“…[14] Additionally, an oxygen-enriched surface layer has been reported from combined Rutherford Backscattering Spectroscopy and neutron reflectometry studies. [15] A thin surface oxide, as well as impurities of light elements, are the number of oxygen atoms per yttrium atom. This implies that oxygen atoms replace hydrogen in the film during the oxidation process.…”

Engineering of the band gap and optical properties of thin films of yttrium hydride

“…14 The large band gap increase can be explained by the level of oxygen incorporated into the films. As we have demonstrated earlier, 8,9 films prepared by reactive sputtering deposition and not capped by a Pd protection layer contained a substantial amount of oxygen, even though the oxygen incorporation in the film was not done intentionally. Earlier Rutherford backscattering spectrometry and neutron reflectometry measurements indicated a surface oxide layer of 5-10 nm thickness and an oxygen content in the bulk of the film in the range of 8-32 at.…”

“…8 These films will, upon exposing to air, form a thin oxide layer at the surface and substantial amount of O impurities was found to be incorporated into the bulk of the films. 9,10 The O impurities might play an important role in the optoelectronic properties of YH x. The O-containing YH x (hereafter YH:O) films studied in Ref.…”

Role of oxygen in materials properties of yttrium trihydride

“…Our theoretical efforts will be concentrated on the evolution of the YHO crystalline structure in terms of the oxygen content. From analysis of experimental data [3,6,12] one can summarize that: (i) oxygen is incorporated into yttrium hydride films during a deposition process; simultaneously, there occurs some moderate deficiency of hydrogen atoms; (ii) oxygen demonstrates high reactivity with respect to yttrium; (iii) metalinsulator transition when the unstable metallic form of f cc YH 3 transfers into the semiconducting one takes place upon oxygenation process and is irreversible; (iv) the new phase corresponds to a stable solid with a similar f cc lattice structure; and (v) to date, none of the scientific reports have given any information concerning arrangements of O-impurities in the f cc lattice of YH 3 .…”