Achieving reversibility of ultra-high mechanical stress by hydrogen loading of thin films

Abstract

Nano-materials are commonly stabilized by supports to maintain their desired shape and size. When these nano-materials take up interstitial atoms, this attachment to the support induces mechanical stresses. These stresses can be high when the support is rigid. High stress in the nano-material is typically released by delamination from the support or by the generation of defects, e.g., dislocations. As high mechanical stress can be beneficial for tuning the nano-materials properties, it is of general interest to deduce how real high mechanical stress can be gained. Here, we show that below a threshold nano-material size, dislocation formation can be completely suppressed and, when delamination is inhibited, even the ultrahigh stress values of the linear elastic limit can be reached. Specifically, for hydrogen solved in epitaxial niobium films on sapphire substrate supports a threshold film thickness of 6 nm was found and mechanical stress of up to (−10 ± 1) GPa was reached. This finding is of basic interest for hydrogen energy applications, as the hydride stability in metals itself is affected by mechanical stress. Thus, tuning of the mechanical stress-state in nano-materials may lead to improved storage properties of nano-sized materials.

Ferromagnetic resonance investigation of physical origins of modification of the perpendicular magnetic anisotropy in Pd/Co layered films in the presence of hydrogen gas

“…Thicker (30 nmþ) Pd layers clamped to substrates can develop folds, cracks, and even peel off. 17 Thinner films (as in our case) can withstand much larger deformations, 18 however for both thicker and thinner films, one may also expect an effect of hydrogen annealing 19 which may modify the crystal structure of Pd. Our previous studies showed that some irreversible changes to our films can indeed occur during their first exposure to hydrogen gas, especially diluted H 2 (see e.g., Fig.…”

“…17 Thin films, as in our case, can withstand huge stresses due to the clamping effect without deformation. 18 In contrast to single-layer Pd films used in Refs. 17 and 18, our films represent multilayers.…”

Mechanical stress and stress release channels in 10–350 nm palladium hydrogen thin films with different micro-structures

“…4. Note that all films leave the elastic regime at certain H concentrations, leaving De elast as an upper bound, not reached here [52]. In detail, at De plast (Ds plast ) the channel of plastic stress relaxation opens in the films, e. g. by the emission of new dislocations at the film-substrate interface.…”

Nanopatterning‐Enhanced Sensitivity and Response Time of Dynamic Palladium/Cobalt/Palladium Hydrogen Gas Sensors

“…On the contrary, similar to other interface effects, the overall effect of PMA on macroscopic material parameters (e.g., on its FMR response) does not noticeably depend on Pd thickness above some critical thickness for the onset of PMA (on the order of several atomic layers) and increases with a decrease in Co thickness. Thin Pd layers can withstand huge compressive stresses without buckling . Hence, by exploiting an interface effect instead of a bulk one the problem of irreversible deformations can be naturally avoided.…”