The absorption of deuterium from the gas phase into two Pd thin films 668 Å and 1207 Å thick was measured at room temperature with in situ neutron reflectometry. Room-temperature solubility isothermal curves, out-of-plane film expansion, and deuterium depth profiles were determined from fits to the neutron reflectivity data. The measurements demonstrate that the deuterium solubility behavior, both in solid solution and within the two-phase region, is strongly perturbed by the thin-film geometry, consistent with previous solubility measurements in the published literature. The phase behavior investigated here was observed to depend on film thickness and on deuterium cycling through the two-phase region. The 668-Å film exhibited the greatest initial phase perturbation and most significant changes upon cycling. Upon repeated cycling, both films approach nearly identical deuterium isothermal solubility and out-of-plane expansion behaviors. The observed equilibrium out-of-plane expansion behavior was consistent with the films expanding under an in-plane clamping constraint imposed by the substrate. The effect of this substrate constraining force is to amplify the out-of-plane expansion beyond that expected in bulk Pd. Taken together, these measurements implicate the film/substrate interfacial clamping interaction as the origin of the perturbed hydrogen phase behavior in thin-film geometry.
|Original language||English (US)|
|Number of pages||7|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - 1998|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics