We have fabricated phototubes with photocathodes consisting of the Mg-doped GaN films. The spectral shapes of the response and the quantum efficiency (QE) strongly depend on the Mg-doping concentration. The calibrated QE of the photocathode is maximized to be 71.9% at a photon energy of 5.4 eV by a Mg-doping concentration of 3.0×1019cm−3. Consequently, a phototube with the GaN-based photocathode is realized to demonstrate a very high QE, more than 50% and sharp cutoff characteristic over three orders of magnitude.

Molecular crystals have attracted increasing attention as a candidate for innovative solid electrolytes with solid-state Mg-ion conductivity. In this work, we synthesized a novel Mg-ion-conducting molecular crystal, Mg{N(SO2CF3)2}2(CH3OC5H9)2 (Mg(TFSA)2(CPME)2), composed of Mg bis(trifluoromethanesulfonyl)amide (Mg(TFSA)2) and cyclopentyl methyl ether (CPME) and elucidated its crystal structure. We found that the obtained Mg(TFSA)2(CPME)2 exhibits solid-state ionic conductivity at room temperature and a high Mg-ion transference number of 0.74. Contrastingly, most Mg-conductive inorganic solid electrolytes require heating above 150–300°C to exhibit ionic conductivity. These results further prove the suitability of molecular crystals as candidates for Mg-ion-conducting solid electrolytes.

An extremely high quantum photoyield, as high as 70% at the photon energy of 10 eV, was observed from cesiated polycrystalline diamond films. The threshold photon energy of 5.5 eV or less was observed. The results suggest that the cesiated polycrystalline diamond surface has a true negative electron affinity. In contrast, a quantum photoyield of 17% at the photon energy of 10 eV was observed for a hydrogenated polycrystalline diamond film. The threshold photon energy of 5.5 eV or less was also observed, as in the cesiated one. It seems that the hydrogenated polycrystalline diamond surface has an effective negative electron affinity.

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