Yttrium is known to form two hydrides: YH 2 , a metal, and YH 3 , which is dielectric. However, the stability of YH 3 is not fully understood, especially in the context of thin films, where the yttrium layer must be coated to protect it from oxidation. In this work, we show that the stability of a YH 3 thin film depends on the capping layer material. Our investigation reveals that YH 3 appears to be stabilized by hydrogen that is adsorbed to the capping layer surface. This is evidenced by the YH 3-YH 2 transition temperature, which was found to be correlated with the desorption temperature of hydrogen from the surface. We posit that surface-adsorbed hydrogen prevents hydrogen from diffusing out of the thin film, which limits YH 3 dissociation to the solubility of hydrogen in the YH 2 /YH 3 thin film.
Thin films of CeCoIn 5 were deposited on a-plane (1120)-and r -plane (1102)oriented Al 2 O 3 substrates by using molecular beam epitaxy and were found to be superconductive with transition temperatures about 2 K. Their transport properties are comparable with those of the bulk material and the resistivity shows typical heavy-fermion behaviour. The growth characteristics were studied by means of x-ray diffraction and scanning tunnelling microscopy and revealed (001)-oriented growth with pronounced island formation. Based on the chemical composition of the films obtained using energy dispersive x-ray analysis, a ternary phase formation diagram was deduced.
The structural changes in Ru-coated Y films during hydrogenation were studied in this work. In situ XRD data were used to show that the Y to YH 2 transition requires significant hydrogen loading of the Y lattice. By comparing the XRD data with the in situ spectroscopic ellipsometry data, an effective medium model for the transition was obtained. This model describes the Y to YH 2 transition well. The YH 2 to YH 3 transition is also described by an effective medium model, however, with reduced accuracy around the midpoint of the transition. By comparing the YH 2 and YH 3 crystal sizes, we show that these deviations may be due to a surface plasmon resonance. The improved understanding of the ellipsometry measurements is important for optical hydrogen sensing applications.
In this work, the authors expose transferred multilayer graphene on a yttrium based hydrogen sensor. Using spectroscopic ellipsometry, they show that graphene, as well as amorphous carbon reference films, reduce diffusion of hydrogen to the underlying Y layer. Graphene and C are both etched due to exposure to atomic H, eventually leading to hydrogenation of the Y to YH 2 and YH 3 . Multilayer graphene, even with defects originating from manufacturing and transfer, showed a higher resistance against atomic H etching compared to amorphous carbon films of a similar thickness.
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