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By combining hydrogen and sulfur within diamond-anvil cells we synthesize (H 2 S) 2 H 2 at 5 GPa and 373 K. Through a series of Raman spectroscopy, infrared spectroscopy, and synchrotron x-ray diffraction experiments we have constrained the phase diagram of (H 2 S) 2 H 2 within a wide P-T range. On compression we observe the phase transition sequence of I-II-II-III, where II is a previously unreported phase; at room temperature this sequence spans from 5 to 47 GPa, while the application of low temperatures stabilizes this sequence to 127 GPa (< 80 K). Above these pressures we propose that phase III of (H 2 S) 2 H 2 transforms to a nonmolecular H 3 S network. Our Raman and infrared measurements indicate that the transition from (H 2 S) 2 H 2 to H 3 S is reversible at room temperature. X-ray diffraction reveals that the symmetry of the underlying S lattice of (H 2 S) 2 H 2 and H 3 S is retained along this compression path up to at least 135 GPa.

Dias and Silvera (Research Article, 17 February 2017, p. 715) claim the observation of the Wigner-Huntington transition to metallic hydrogen at 495 gigapascals. We show that neither the claims of the record pressure nor the phase transition to a metallic state are supported by data and that the data contradict the authors' own unconfirmed previous results.

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Concave palladium nanocrystals are attractive for their superior catalytic ability arising from high densities of atomic steps and kinks. However, it is still a challenge to generate the concave surface, which is not favored by thermodynamics owing to its higher surface energy. In this study, concave palladium nanocubes have been synthesized kinetically in high yield via a facile one-step wet chemical method using sodium ascorbate (NaA) as the reductant in an aqueous solution. This process allows independent control of the average edge length and the surface curvature of the nanocubes, respectively. The particle morphology can be tuned by changing the reducing rate during the reaction. Right bipyramids and 5-fold twinned nanorods with concave surfaces have also been synthesized with two reductants at the different stages or an appropriate amount of ascorbic acid only. Remarkable enhancements in both electrocatalytic activity and stability are observed on concave Pd nanocubes and twinned nanocrystals over conventional Pd nanocrystals with flat surfaces and commercial Pd/C.

In this work, we experimentally demonstrate energy transfer from a single negatively charged nitrogen-vacancy (NV) center in nanodiamond to a graphene monolayer. The mode values of lifetime and intensity of the fluorescence from the single NV center in nanodiamond on monolayer graphene are shorter and weaker than that on bare quartz substrate. The energy transfer efficiency is measured about 40%, consistent with our theoretical estimation.

Raman spectroscopy demonstrates that the rotational spectrum of solid hydrogen, and its isotope deuterium, undergo profound transformations upon compression while still remaining in phase I. We show that these changes are associated with a loss of quantum character in the rotational modes, ie. with increasing pressure, the angular momentum J gradually ceases to be a good quantum rotational number. Through isotopic comparisons of the rotational Raman contributions, we reveal that hydrogen and deuterium evolves from a quantum rotor to a harmonic oscillator. We find that the mechanics behind this transformation can be well described by a quantum mechanical single inhibited rotor, accurately reproducing the striking spectroscopic changes observed in phase I.

We make use of inherent vacancies and nitrogen substitutions in nanodiamonds to generate nitrogen-vacancy (NV) centers by high temperature annealing. After 800 °C annealing, low temperature photoluminescence intensity of nanodiamonds shows more than eight times improvement compared with that of unannealed samples. Confocal microscope images of well dispersed nanodiamonds indicate a dramatically increased proportion of nanodiamonds containing NV centers after annealing. Optically detected magnetic resonance spectrum of single NV center demonstrates that the resultant nanodiamonds are suitable for further application as magnetic field sensor. The annealing-oxidation method could be an attractive option for NV center generation in nanodiamonds.