RESUMEN
Two-dimensional materials have wide ranging applications in electronic devices and catalysts owing to their unique properties. Boron-based compounds, which exhibit a polymorphic nature, are an attractive choice for developing boron-based two-dimensional materials. Among them, rhombohedral boron monosulfide (r-BS) has recently attracted considerable attention owing to its unique layered structure similar to that of transition metal dichalcogenides and a layer-dependent bandgap. However, experimental evidence that clarifies the charge carrier type in the r-BS semiconductor is lacking. In this study, we synthesized r-BS and evaluated its performance as a semiconductor by measuring the Seebeck coefficient and photo-electrochemical responses. The properties unique to p-type semiconductors were observed in both measurements, indicating that the synthesized r-BS is a p-type semiconductor. Moreover, a distinct Fano resonance was observed in Fourier transform infrared absorption spectroscopy, which was ascribed to the Fano resonance between the E(2) (TO) phonon mode and electrons in the band structures of r-BS, indicating that the p-type carrier was intrinsically doped in the synthesized r-BS. These results demonstrate the potential future application prospects of r-BS.
Asunto(s)
Boro , Electrónica , Electrones , Excipientes , SemiconductoresRESUMEN
A new iron-based superconductor, (Ca,Pr)FeAs2, was discovered. Plate-like crystals of the new phase were obtained, and its crystal structure was investigated by single-crystal X-ray diffraction analysis. The structure was identified as the monoclinic system with space group P21/m, composed of two Ca(Pr) planes, Fe2As2 layers, and As2 zigzag chain layers. Plate-like crystals of the new phase showed superconductivity, with a T(c) of ~20 K in both magnetization and resistivity measurements.
RESUMEN
Most of previous photocatalysts contain metal species, thus exploring a metal-free photocatalyst is still challenging. A metal-free photocatalyst has an advantage for the development of economical and non-toxic artificial photosynthesis system and/or environmental purification applications. In this study, rhombohedral boron monosulfide (r-BS) was synthesized by a high-pressure solid-state reaction, and its photocatalytic properties were investigated. r-BS absorbed visible light, and its photocurrent action spectrum also exhibited visible light responsivity. The r-BS evolved hydrogen (H2) from water under ultraviolet (UV) as well as under visible light irradiation, and its internal quantum efficiency reached 1.8% under UV light irradiation. In addition to the H2 evolution reaction, the r-BS photocatalyst drove carbon dioxide (CO2) reduction and dye oxidation reactions under UV irradiation. Although bare r-BS was not so stable under strong light irradiation in water, cocatalyst modification improved its stability. These results indicate that r-BS is a new class of non-metal photocatalyst applicable for H2 production, CO2 reduction, and environmental purification reactions.
RESUMEN
Iron-based superconductors are expected to be used in strong magnet applications owing to their excellent superconducting properties. The process of sintering a mechanically alloyed precursor powder is effective in achieving a high upper critical field and critical current density in BaFe2As2 (Ba122) polycrystalline bulk materials. However, when this process is applied to K-doped Ba122, which shows the highest critical temperature in the Ba122 family, suppressing the vaporization of potassium is challenging. In this study, spark plasma sintering (SPS) method was applied to K-doped Ba122 to achieve fast densification. In contrast to the conventional synthesis method, which requires several tens of hours, optimally K-doped bulks with near theoretical density were obtained after only 5 min of SPS, and the magnetic critical current density reached 105 A/cm2 at 5 K. The demonstrated superconducting properties suggest that this fast densification technique is a useful tool for applying K-doped Ba122 to bulk trapped field magnets.