In the search of a truly high-temperature superconductor we tried to metalize dirty (i.e. yttrium doped) hydrogen under high pressure. Shining light during hydrogenation of an yttrium film in a diamond anvil cell was the key ingredient of our discovery of switchable mirrors. Since then the transition from shiny metal to transparent semiconductor or from metal to highly absorbing black has been observed in many hydrides. Even in metals that remain metallic during hydrogenation, the optical changes induced by absorption of hydrogen are easily observable. This opened the way to Hydrogenography, a new high-throughput optical technique to measure optically and simultaneously on thousands of (nano)structured samples, pressure-composition isotherms, enthalpies and entropies of hydride formation. We demonstrated for example that the thermodynamics of hydrogen absorption in Mg/TM (TM: transition metal) (multi)layers can be tuned by engineering suitable elastic constraints or by reducing particle sizes down to 1 nm. Hydrogenography provides also unique possibilities to determine the intrinsic hydrogen permeability of alloys and to explore whether or not observed enthalpy-entropy correlations are phantom effects.
Reaction kinetics and catalytic activities, long-range diffusion, switchable metal-hydrides for smart windows, fiber optic H sensors and nanoantennas for active plasmonics are also efficiently investigated with Hydrogenography.
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