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Nanoscale Metal Hydrides from MeV-Ion Perspectives: A Unique View
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.ORCID iD: 0000-0002-5406-2659
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2024. , p. 80
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2381
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-525548ISBN: 978-91-513-2081-6 (print)OAI: oai:DiVA.org:uu-525548DiVA, id: diva2:1846553
Public defence
2024-05-17, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2024-04-25 Created: 2024-03-22 Last updated: 2024-04-25
List of papers
1. Accurate measurement of hydrogen concentration in transition metal hydrides utilizing electronic excitations by MeV ions
Open this publication in new window or tab >>Accurate measurement of hydrogen concentration in transition metal hydrides utilizing electronic excitations by MeV ions
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2024 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 57, p. 583-588Article in journal (Refereed) Published
Abstract [en]

This study focuses on enhancing the accuracy of hydrogen content verification in hydrogen-rich ultrathin materials relevant for sustainable energy applications. Ion beams are used for distinctive real-space detection leveraging elastic and inelastic interactions with hydrogen atoms. However, the lack of experimental reference data on electronic interactions poses a challenge to the accuracy of analytical techniques. We investigate the effect of absorbed hydrogen on the electronic energy deposition of 15N-ions in amorphous transition metal compounds, specifically V and Zr, covering concentrations >1H/M. Employing resonant nuclear reactions and Rutherford backscattering, the energy loss is found to increase considerably with hydrogen content, in line with Bragg's additivity. The electronic energy loss cross section for 15N-ions at 6.5 MeV measured (64.55±3.38) eV cm2/1015 atoms. Results are compared to semi-empirical and theoretical models. The findings improve hydrogen profiling accuracy using 15N-nuclear reaction analysis and enable unprecedented methods for hydrogen quantification by other, commonly available ion beams.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Hydrogen detection, Ion beam analysis, Transition metal hydrides, Hydrogen-rich materials, Electronic excitations, Hydrogen storage
National Category
Atom and Molecular Physics and Optics Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-524600 (URN)10.1016/j.ijhydene.2024.01.032 (DOI)001163507100001 ()
Funder
Swedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research, RIF14-0053
Available from: 2024-03-12 Created: 2024-03-12 Last updated: 2024-03-12Bibliographically approved
2. Hydrogen induced lattice expansion and site occupation analyzed by ion beam methods
Open this publication in new window or tab >>Hydrogen induced lattice expansion and site occupation analyzed by ion beam methods
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2021 (English)In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 486, p. 63-67Article in journal (Refereed) Published
Abstract [en]

We study the absorption of H in ultrathin crystalline Fe/V stacks using elastic recoil detection (ERD) and resonant nuclear reaction analysis (NRA) combined with Rutherford backscattering spectrometry (RBS). Probing with the resonant H-1 (N-15,alpha gamma) C-12 nuclear reaction allows us to profile the hydrogen concentration with high depth resolution, while ERD permits us to quantify the integral hydrogen inventory while minimizing possible ionbeam induced hydrogen desorption. We perform angular scans in order to directly identify the interstitial site occupancy. A detailed analysis of channeling patterns permits us the deduction of crystal strain in as-deposited films as well as H-loaded targets. We observe tetragonal strain formation resulting in c/a = 1.06 and find qualitative indications for tetrahedral site occupation.

Place, publisher, year, edition, pages
ElsevierELSEVIER, 2021
Keywords
Metal hydride, Hydrogen site occupancy, Channelling, Vanadium, Strain analysis
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-430577 (URN)10.1016/j.nimb.2020.09.017 (DOI)000595666300009 ()
Funder
Swedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2021-01-14 Created: 2021-01-14 Last updated: 2024-03-22Bibliographically approved
3. Interstitial Hydrogen in Fe/V Superstructures: Lattice Site Location and Thermal Vibration
Open this publication in new window or tab >>Interstitial Hydrogen in Fe/V Superstructures: Lattice Site Location and Thermal Vibration
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2021 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 127, no 13, article id 136102Article in journal (Refereed) Published
Abstract [en]

We report real space location of hydrogen in single crystalline Fe/V superstructures. Anisotropic strain is quantified versus hydrogen concentration by using the yield of backscattered primary 2 MeV He-4 ions for incidence in different crystallographic directions. From a comparison of ion channeling in combination with H-1(N-15, alpha gamma)C-12 nuclear reaction analysis and Monte Carlo simulations we show that hydrogen is located in octahedral z sites and quantify its vibrational amplitude of 0.2 angstrom.

Place, publisher, year, edition, pages
American Physical SocietyAmerican Physical Society (APS), 2021
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-457943 (URN)10.1103/PhysRevLett.127.136102 (DOI)000704680000013 ()34623839 (PubMedID)
Funder
Swedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2021-11-08 Created: 2021-11-08 Last updated: 2024-03-22Bibliographically approved
4. Hydrogen site location in ultrathin vanadium layers by N-15 nuclear reaction analysis
Open this publication in new window or tab >>Hydrogen site location in ultrathin vanadium layers by N-15 nuclear reaction analysis
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2019 (English)In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 455, p. 57-60Article in journal (Refereed) Published
Abstract [en]

We present a method using resonant nuclear reaction analysis combined with optical transmission and heavy-ion Rutherford backscattering spectrometry to study the absorption of hydrogen in single crystalline thin vanadium films. Probing with the resonant H-1(N-15,alpha gamma)C-12 reaction allows for highly resolved hydrogen depth profiling, while measurements along the crystal axes render possible the direct identification of the interstitial site occupancy. First experiments were performed on thin vanadium hydrides in Fe(Cr)/V superlattices revealing differences in site occupancy.

Place, publisher, year, edition, pages
ELSEVIER, 2019
Keywords
NRA, Metal hydride, Site occupancy, Channeling, N-15, Vanadium
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-392120 (URN)10.1016/j.nimb.2019.05.033 (DOI)000477786500010 ()
Funder
Swedish Research Council, 821-2012-5144Swedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2019-09-06 Created: 2019-09-06 Last updated: 2024-03-22Bibliographically approved
5. Lattice site location in metal hydride thin films: Ion channeling and phononic properties
Open this publication in new window or tab >>Lattice site location in metal hydride thin films: Ion channeling and phononic properties
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We investigate the relationship between lattice vibrations and ion channeling in hydrogenated strained thin V films within Fe/V- and Cr/V-superlattices, performing 15N-ion channeling experiments and Monte-Carlo simulations with the program FLUX7. Comparing simulated 15N-nuclear encounter probabilities (NEP) to Fe/V-atoms to the yield of backscattered 15N-ions demonstrates a correlation between the influence of beam divergence and Debye temperatures and provides insights into distinguishing them quantitatively from planar channeling patterns. Simulations of 15N-NEP to interstitial hydrogen and comparison to 1H(15N, αγ)12C nuclear reaction yield highlights the importance of analyzing multiple crystal symmetries to determine vibrational motions and impurity site locations accurately. The analysis of thermal vibrational motions in hydrogenated Fe/V- and CrV-superlattices reveal a reduction in Debye temperatures for Fe/V- and CrV-superlattices, emphasizing the influence of defect, surface, and interface effects on lattice vibrations.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-525547 (URN)
Available from: 2024-03-22 Created: 2024-03-22 Last updated: 2024-03-22
6. A new setup for optical measurements under controlled environment
Open this publication in new window or tab >>A new setup for optical measurements under controlled environment
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2023 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 94, no 3, article id 035104Article in journal (Refereed) Published
Abstract [en]

We present a new analytical instrument for studying the optical properties of materials in different gaseous environments at room and controlled elevated temperatures. The system consists of a vacuum chamber, which is equipped with temperature and pressure controllers, a heating band, and a residual gas analyzer and is connected to a gas feeding line via a leak valve. Two transparent view ports located around a sample holder allow for optical transmission and pump-probe spectroscopy using an external optical setup. The capabilities of the setup are demonstrated by conducting two experiments. In the first experiment, we study the photodarkening and bleaching kinetics of photochromic oxygen-containing yttrium hydride thin films illuminated in ultra high-vacuum and correlate it with changes in partial pressures inside the vacuum chamber. In the second study, we investigate changes in the optical properties of a 50 nm V film upon hydrogen absorption.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2023
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-499891 (URN)10.1063/5.0142068 (DOI)000942555100006 ()
Funder
Swedish Research Council, 2017-00646-9Swedish Research Council, 2019-00191Swedish Foundation for Strategic Research, RIF14-0053Olle Engkvists stiftelse, 207-0423
Available from: 2023-04-11 Created: 2023-04-11 Last updated: 2024-03-22Bibliographically approved
7. Proximity and dimensionality effects on interstitial hydrogen
Open this publication in new window or tab >>Proximity and dimensionality effects on interstitial hydrogen
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

In this study, we investigate the proximity effects on hydrogen distribution in ultrathin single crystalline vanadium films, by comparing the absorption in Fe/V- and Cr/V-superlattices. Pressure concentration isotherms show higher absolute solubility of hydrogen in a Cr/V-superlattice. Isotherms of excess resistivity are used to locate phase boundaries which yielded a higher critical temperature and concentration in Cr/V. Measurements of hydrogen site location and thermal vibrations using 15N-nuclear reaction analysis demonstrate identical site occupation of 0Z at room temperature with a vibrational amplitude of 0.20‑0.25 Å over a wide range of hydrogen concentrations in both superlattices. The analysis excludes changes in site occupancy as the primary cause for variations in thermodynamics across different temperatures due to proximity. Our findings are consistent with a more extended region of hydrogen depletion in the vicinity of Fe and resolve previously puzzling differences in the hydrogen loading of Fe/V- and Cr/V-superlattices, implying an inverse spillover effect.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-525542 (URN)
Available from: 2024-03-22 Created: 2024-03-22 Last updated: 2024-03-22
8. The influence of the distribution of interstitial hydrogen on optical transmission of vanadium hydride
Open this publication in new window or tab >>The influence of the distribution of interstitial hydrogen on optical transmission of vanadium hydride
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Hydrogen-induced changes of optical absorption in Fe/V (001) and Cr/V (001) superlattices are found to be dominated by the distribution of microscopic lattice expansions in vanadium. We relate optical transmission spectra between 400-1000nm to hydrogen distribution and site location in vanadium determined with 15N-NRA and compare to first-principles calculations of a uniaxial lattice expansion. An energy shift of a broad absorption peak induces non-trivial changes in the absorbance as a function of wavelength and hydrogen-induced strain. Differently sized hydrogen-depleted layers in otherwise structurally similar vanadium films containing equal hydrogen inventory [H/V], introduce a different optical response due to differing distribution of the induced microscopic volume change. 

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-525529 (URN)
Available from: 2024-03-22 Created: 2024-03-22 Last updated: 2024-03-22
9. Correlation of optical transmittance and hydrogen concentration in Cr/V superlattices
Open this publication in new window or tab >>Correlation of optical transmittance and hydrogen concentration in Cr/V superlattices
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-525546 (URN)
Available from: 2024-03-22 Created: 2024-03-22 Last updated: 2024-03-22
10. Influence of deuterium-induced volume changes on optical transmission in Fe/V (001) and Cr/V (001) superlattices
Open this publication in new window or tab >>Influence of deuterium-induced volume changes on optical transmission in Fe/V (001) and Cr/V (001) superlattices
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2022 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 19, article id 195438Article in journal (Refereed) Published
Abstract [en]

The deuterium-induced changes of the optical transmission in Fe/V (001) and Cr/V (001) superlattices are found experimentally to be dominated by the volume changes of the vanadium layers and thus indirectly linked to concentration. The deuterium-induced expansion is 67% larger in Cr/V 2/14 monolayers (ML) as compared to Fe/V 2/14 ML. This large difference can be explained by a difference in the site of deuterium from tetrahedral in Fe/V to octahedral in Cr/V. First-principles calculations based on this assumption give quantitative agreement with both the measured optical transmission and the deuterium-induced expansion coefficient. Placing hydrogen in the middle of the vanadium layers results in total energies at 0 K that favor tetrahedral occupancy at low concentrations, although the energy difference is of the order of the thermal energy available in the experiments. Hence small changes in strain, defect concentration, and/or vibrational spectrum of the superlattices may tip the balance to octahedral occupancy at low concentrations. Given this link to concentration and the linear scaling, optical transmission can, therefore, be used in a straightforward way to obtain pressure-composition isotherms also in thin metal films that do not undergo metal-insulator transitions upon hydrogenation.

Place, publisher, year, edition, pages
American Physical SocietyAmerican Physical Society (APS), 2022
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-478582 (URN)10.1103/PhysRevB.105.195438 (DOI)000809498100007 ()
Funder
Swedish Foundation for Strategic Research, ICA16-0037Swedish Research Council, 2018-05973Swedish Research Council
Available from: 2022-06-27 Created: 2022-06-27 Last updated: 2024-03-22Bibliographically approved

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