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Germanium has one of the highest refractive indices and extinction coefficients in the optical range, making it attractive material to study Mie resonance induced absorption in subwavelength structures. In this work, at first mode analysis of a subwavelength sphere in a complex permittivity plane is provided to simultaneously examine the Mie and plasmon resonances at once which are often discussed separately. Electromagnetic calculations show enhanced absorption of germanium nanospheres at Mie resonances. To experimentally confirm the predicted results, germanium nanoparticles are successfully fabricated through reactive thermal arc plasma method. The size distribution of germanium nanoparticles enables broad extinction from UV to near infrared even though Mie resonance peak of individual nanoparticle is rather narrow. Enhanced absorption is confirmed by solar photothermal experiment. Our work has proven the applicability of strong Mie resonances excited at subwavelength germanium particles.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

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We report that hydrogen gas can be easily produced from water at room temperature using a Mg nanopowder (30-1000 nm particles, average diameter 265 nm). The Mg nanopowder was produced by dc arc melting of a Mg ingot in a chamber with mixed-gas atmosphere (20% N 2 -80% Ar) at 0.1 MPa using custom-built nanopowder production equipment. The Mg nanopowder was passivated with a gas mixture of 1% O 2 in Ar for 12 h in the final step of the synthesis, after which the nanopowder could be safely handled in ambient air. The nanopowder vigorously reacted with water at room temperature, producing 110 ml of hydrogen gas per 1 g of powder in 600 s. This amount corresponds to 11% of the hydrogen that could be generated by the stoichiometric reaction between Mg and water. Mg(OH) 2 flakes formed on the surface of the Mg particles as a result of this reaction. They easily peeled off, and the generation of hydrogen continued until all the Mg was consumed.

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