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- Komander, Kristina
(författare)
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Nanoscale Metal Hydrides from MeV-Ion Perspectives: A Unique View
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
- Saini, Apurve
(författare)
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Magnetically governed self-assembly of soft matter : A look into interfacial layering, crystallization and percolation
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Self-organisation is the key route for assembling colloidal particles into well-defined structures. Decisive for this are the interactions between the constituents, which are amongst others steric, electrostatic or magnetic. A deep knowledge on the underlying physical processes during self-assembly is crucial for the design and fabrication of well-defined hierarchical architectures from a nanometer scale as well as for realizing smart, functional or stimuli responsive synthetic materials. In this dissertation, the self-assembly of colloidal magnetic particles into organized and multi-layered structures is studied. Particular emphasis is given to solid-liquid boundaries and the response to applied magnetic fields. Particle coatings with specific functional molecules stabilize the nanoparticles (NPs) in the solvent and can simultaneously promote their assembly at a substrate. An example in this context is N-hydroxysuccinimide interacting with (3-aminopropyl)triethoxy silane at the substrate. As a result of this chemical affinity, uniform and densely packed particle wetting layers are seeded which then instate the layering process. As an alternative to chemical binding, the magnetic stray field of a ferrimagnetic (Tb15Co85 film) deposited on a substrate induces particle self-assembly with dense layers as well. The application of an external magnetic field further promotes densification, particle layering and leads to variations in the assembly characteristics such as quasi-domain formation of closely packed layers. At an interface with a magnetic field applied in the plane of the interface, Brownian motion and Neel relaxation of the NPs are decisive for the layering and give raise to these domains. For a magnetic field oriented along the surface normal similar structural layering but denser packing is found. The self-assembly is a relatively slow process and evolves over hours and is maximized, most ordered and dense for superparamagnetic NPs which are single domain and having a large remanent moment and reduced thermal mobility. Small quantities of magnetic micelles in a hybrid magnetic polymer nanocomposite, facilitate the crystallization of Pluronic F127 micelles dissolved in water into single crystalline structures via a micro-shear effect under applied magnetic field. Also, a magnetic field applied to a colloidal dispersion of conducting magnetic and non-magnetic polystyrene microbeads suspended in an oil-based ferrofluid can lead to percolated structures. This allows current transmission and switching. A working contact for possible applications in automotive, switchboard and telecommunications is demonstrated.
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