Nanoscale Metal Hydrides from MeV-Ion Perspectives: A Unique View

• This thesis work set out to investigate interstitial hydrogen in material systems of reduced dimensionality or high loading capacities. Experimental methodologies utilizing MeV-ions were developed addressing metal hydride formation in various transition metal alloys and in the presence of interfaces and lattice strain. Enhanced concentration measurement accuracy by 15N-resonant nuclear reaction analysis (NRA) in hydrogen-rich transition metal films was achieved by examining the influence of hydrogen on electronic excitations by 15N-ions. A non-iterative method combining NRA with Rutherford backscattering spectrometry (RBS) revealed the energy deposition of 15N-ions in various hydrogenated V/Zr-alloys, promoting reliable energy loss predictions. The findings imply the potential for indirect hydrogen concentration measurements via RBS, increasing accessibility across multiple facilities as a broader range of ion species can be utilized.To identify locations of interstitial hydrogen within thin single-crystalline films, the applicability of different MeV-ions species was explored, performing channeling experiments on Fe/V-superlattices as model systems. 4He-ions reveal hydrogen-induced anisotropic lattice expansion by RBS, while dechanneling effects and hydrogen recoils provide insights into lattice site locations. However, challenges for unambiguous site-location extraction were identified concerning deflections from channeling trajectories and limitations of simulations confined to backscattering geometry. Employing 15N-ions for channeling NRA and RBS, combined with Monte-Carlo simulations, enables quantitative real-space investigation of subsurface hydrogen site locations and thermal vibrational motion in nanosized transition metals. The 15N-channeling method was applied to study the influence of different adjacent metals on vanadium hydrides, comparing hydrogenated Fe/V- to Cr/V-superlattices. In combination with in-situ measurements of electrical resistivity and optical transmission – which serve as indirect measures for hydrogen order and concentration, respectively – the investigation revealed significant proximity effects. Specifically, Fe/V absorbs smaller integral amounts of hydrogen, and the critical temperature is lower than for Cr/V. Thereby, hydrogen atoms occupy octahedral z-sites with identical thermal vibrational amplitudes of 0.20-0.25 Å in both samples over an extensive range of hydrogen concentrations. The findings are consistent with the effects of a size reduction induced by hydrogen-depleted layers at interfaces, larger toward Fe than to Cr.The developed methodologies offer unique insights into alloying and boundary effects on metal hydride formation, which can control phase transitions and enhance the loading capacity, providing avenues to optimize material properties for sustainable energy solutions. 

Ämnesord

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

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