Regensburg 2019 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 24: Plasmonics & Nanooptics I: Metastructures and Novel Techniques (joint session O/CPP)

O 24.6: Vortrag

Dienstag, 2. April 2019, 11:45–12:00, H8

In-Situ Magnesium Thin Film Nanoscale Hydrogenography — •Julian Karst, Florian Sterl, Heiko Linnenbank, Mario Hentschel, and Harald Giessen — 4th Physics Institute and Research Center SCoPE, University of Stuttgart, Germany

During the hydrogenation of Magnesium (Mg), a phase change from the metallic Mg to dielectric magnesium hydride (MgH2) occurs, rendering it highly interesting for switchable optical systems. In such active systems, the nanoscale hydrogen diffusion mechanism is clearly of utmost importance, yet, so far, the details are not well understood.

To this end, we perform scattering-type scanning near-field optical microscopy to image the phase transition from Mg to MgH2 on the nanometer scale in an in-situ environment. Additionally, we perform nanoFTIR spectroscopy and identify a phonon resonance which aids in our experimental scheme. The resonance causes a very high material contrast between Mg and MgH2 in 2D near-field scattering phase images.

Our results reveal that the phase transition is nucleated at grain boundaries. From these sites, the hydrogenation front progresses into the adjoining nanocrystallites. Most interestingly, the hydrogenation seems to saturate before the entire films is hydrogenated, leaving areas of metallic Mg within the dielectric MgH2. Our results constitute an important step forward in the understanding of the hydrogen loading process in Mg and are expected to help improving the diffusion kinetics as well as the efficiency of hydrogen storage in a variety of metals.