[en] The cooperation between theoretical and experimental investigations broke the record for the superconducting critical temperature T_c in hydrogen sulfide at a high pressure at the end of 2014. Surprisingly, the material improved its highest T_c by more than 30K and showed conventional superconductivity, which can be explained by the Bardeen-Cooper-Schrieffer theory. Recent experimental works have gradually clarified the instability of the H_2S molecule and the pathway to the high-T_c phase with a three-dimensional conductive structure unlike high-T_c superconductors thus far. In this review, the present progress on a sulfur hydride system is reported. (author)

[en] The effects of cationic growth parameters of molecular beam epitaxy on the crystalline and magnetic properties of Mn-doped ZnSnAs_2, (Zn,Sn,Mn)As_2, thin films were investigated in order to control ferromagnetism at room temperature. The combination of cationic beam equivalent pressures of Zn, Sn, and Mn atoms was varied at an optimal substrate temperature of 320°C. Clear hysteresis loops were observed for the samples at 300 K, indicating ferromagnetism at room temperature. We found that the change in Zn flux does not significantly affect the composition of (Zn,Sn,Mn)As_2 thin films and ferromagnetic properties and that ferromagnetic properties definitely depend on the amounts of Mn and Sn fluxes. X-ray photoelectron spectroscopy analysis revealed that the sum of the amounts of Mn"2"+ and Mn"4"+, which may contribute to the ferromagnetism in (Zn,Sn,Mn)As_2 thin films, was approximately 60–70% of the total Mn amount with respect to ferromagnetic (Zn,Sn,Mn)As_2 samples. This result indicates that the ferromagnetic properties could be controlled in multilayered (Zn,Sn,Mn)As_2 by changing the combination of Zn, Sn, and Mn fluxes. (author)

[en] Graphene oxide (GO) with a large surface area was synthesized by the direct growth of GO on porous alumina using chemical vapor deposition to study the Cs adsorption mechanism in aqueous solutions. Electronic structure analysis employing in situ near-edge X-ray absorption fine structure spectroscopy and X-ray photoelectron spectroscopy measurements clarifies the Cs atoms bond via oxygen functional groups on GO in the aqueous solution. The Cs adsorption capacity was found to be as high as 650–850 mg g⁻¹, which indicates that the GO/porous alumina acts as an effective adsorbent with high adsorption efficiency for radioactive nuclides in aqueous solutions. (author)

[en] The electronic structure change after plasma exposure in representative materials used in electronic devices — crystalline Si substrate and Si₃N₄ film — is investigated by a first-principles approach. We prepared the starting structures of Si, α-, and β-Si₃N₄ with various key species (Ar, Br, Cl, N, and O) in processing plasmas. We investigated the electron charge density distribution and density of state (DOS) with the interstitial species after optimizing the prepared initial structures. Model predictions showed that the interstitial species create the DOSs, and that the energy-band edge extends to the midgap. The creation of the DOSs was clearly found in the β-Si₃N₄ structure model, while no obvious creation was obtained in the α-Si₃N₄ structure. This creation of the DOSs is consistent with the current-voltage (I–V) characteristics of the damaged Si₃N₄ films presumably consisting of α- or β-Si₃N₄ local structure. The distortion of the I–V curves was considered to be attributed to the creation of the DOSs, which play a role as carrier trapping/detrapping sites. (author)

[en] We developed an intense coherent transition radiation (CTR) at the Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University. A rectangular titanium screen with dimensions of 80 x 60 mm"2 was used as the target, and the backward CTR generated on the screen was extracted through a crystal quartz window to air. We observed an intense terahertz (THz) radiation and confirmed it to be the CTR by measuring the spatial distribution and the dependence of the power on the electron charge. The CTR spectrum measured using a Martin-Puplett-type interferometer showed a maximum at a frequency of 0.3 THz and was emitted up to 1.6 THz. The CTR energy and peak power of a micropulse were approximately 80 nJ and 100 kW, respectively. The CTR energy during a 4.5 μs macropulse was approximately 1 mJ, indicating that this broadband THz light source is one of the most powerful coherent radiation sources in normal conducting linac facilities. (author)

[en] (La,Ce)OBiS₂ single crystals are successfully grown using CsCl flux. The obtained single crystals have a plate-like shape with a size of 0.5–2.0 mm and a well-developed ab-plane. The thickness of the crystals increases with a decrease in the Ce content. The (La,Ce)OBiS₂ single crystals exhibit superconducting properties. Moreover, the superconducting transition temperature increases with an increase in the Ce content. The obtained (La,Ce)OBiS₂ single crystals exhibit a tetragonal structure and the valence state of Ce in the crystals is determined to be mixed with Ce³⁺ and Ce⁴⁺ based on X-ray absorption fine structure spectroscopy. (author)

[en] In this paper, we demonstrate the feasibility of a method combining scanning tunneling microscopy (STM) and atom probe tomography (APT). In this method, an atomically smooth or flat surface for STM observation is prepared by field evaporation using an APT system. The chemical composition of the surface obtained by APT can be used to analyze the results of STM. By developing this method, it is expected that local and very fine structures inside materials can be observed with true atomic resolution. We also demonstrate that nanoscale corrugation, which has a strong effect on the reconstruction procedure in the analysis of APT data, can be observed by STM. (author)

[en] At around room temperature and higher, thermal conductivity of single crystal commonly decreases as temperature increases and shows negative temperature dependence. Crystals with positive temperature dependence, which is often preferred in thermal management, requires high Debye temperature. While this narrows the selection of material candidate, the effective Debye temperature can be enhanced through nanostructuring the single crystals. By investigating heat conduction in nanocrystalline silicon, silicon carbide, and diamond, we here demonstrate that shift of temperature dependence of heat capacity and decrease in magnitude of negative temperature dependence of relaxation time by nanostructuring lead to positive temperature dependence of thermal conductivity. (author)

[en] The local environment of W and Mo atoms in CaW_1−x Mo_xO₄ (x = 0.12) solid solution (mixed crystal) scintillator crystal was analyzed by X-ray diffraction (XD), extended X-ray absorption fine structure (EXAFS), and X-ray fluorescence holography (XFH). The XD analysis revealed that W and Mo atoms occupy the same crystallographic site. The analyzes of XFH and EXAFS exhibited that the local environment of Mo atoms is different from that of W atoms. Atomic images of neighbor atoms around the Mo and W atoms were reconstructed using their positional fluctuations. The positional fluctuation of the W atoms was apparently larger than that of Mo atoms. This feature explained the absence of the peak due to next nearest neighbor O atoms around W atoms in the Fourier transfer magnitudes for the W-L₃ edge EXAFS spectrum. It is, therefore, most likely that the different positional fluctuations of the Mo and W atoms are responsible for different atomic images of neighbor atoms between them. (author)

[en] With the increase in the brilliance of synchrotron radiation sources, diffraction techniques have grown and expanded the scientific field of application. Surface X-ray diffraction (SXRD) is one of the state-of-the-art techniques to determine the constellations of atoms on crystal surfaces including adsorbates, thin films, and relaxed layers. We briefly overview SXRD and review the recent advances over decades from both experimental and theoretical viewpoints, including fast observations and imaging surface atoms. (author)