HfS2 is the novel transition metal dichalcogenide, which has not been experimentally investigated as the material for electron devices. As per the theoretical calculations, HfS2 has the potential for well-balanced mobility (1,800 cm2/V·s) and bandgap (1.2 eV) and hence it can be a good candidate for realizing low-power devices. In this paper, the fundamental properties of few-layer HfS2 flakes were experimentally evaluated. Micromechanical exfoliation using scotch tape extracted atomically thin HfS2 flakes with varying colour contrasts associated with the number of layers and resonant Raman peaks. We demonstrated the I-V characteristics of the back-gated few-layer (3.8 nm) HfS2 transistor with the robust current saturation. The on/off ratio was more than 104 and the maximum drain current of 0.2 μA/μm was observed. Moreover, using the electric double-layer gate structure with LiClO4:PEO electrolyte, the drain current of the HfS2 transistor significantly increased to 0.75 mA/μm and the mobility was estimated to be 45 cm2/V·s at least. This improved current seemed to indicate superior intrinsic properties of HfS2. These results provides the basic information for the experimental researches of electron devices based on HfS2.

Tantalum and nitrogen co-doped rutile TiO2 nanorods were developed as a visible-light-active water oxidation photocatalyst for solar-driven Z-scheme water splitting.

Mixed-anion compounds (e.g., oxynitrides and oxysulfides) are potential candidates as photoanodes for visible-light water oxidation, but most of them suffer from oxidative degradation by photogenerated holes, leading to low stability. Here we show an exceptional example of a stable, mixed-anion water-oxidation photoanode that consists of an oxyfluoride, Pb 2 Ti 2 O 5.4 F 1.2 , having a band gap of ca. 2.4 eV. Pb 2 Ti 2 O 5.4 F 1.2 particles, which were coated on a transparent conductive glass (FTO) support and were subject to postdeposition of a TiO 2 overlayer, generated an anodic photocurrent upon band gap photoexcitation of Pb 2 Ti 2 O 5.4 F 1.2 (λ <520 nm) with a rather negative photocurrent onset potential of ca. −0.6 V vs NHE, which was independent of the pH of the electrolyte solution. Stable photoanodic current was observed even without loading a water oxidation promoter such as CoO x . Nevertheless, loading CoO x onto the TiO 2 /Pb 2 Ti 2 O 5.4 F 1.2 /FTO electrode further improved the anodic photoresponse by a factor of 2−3. Under AM1.5G simulated sunlight (100 mW cm −2 ), stable water oxidation to form O 2 was achieved using the optimized Pb 2 Ti 2 O 5.4 F 1.2 photoanode in the presence of an applied potential smaller than 1.23 V, giving a Faradaic efficiency of 93% and almost no sign of deactivation during 4 h of operation. This study presents the first example of photoelectrochemical water splitting driven by visible-light excitation of an oxyfluoride that stably works, even without a water oxidation promoter, which is distinct from ordinary mixed-anion photoanodes that usually require a water oxidation promoter.

The structure of cobalt oxide (CoO) nanoparticles dispersed on rutile TiO (R-TiO) was characterized by X-ray diffraction, UV-vis-NIR diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, X-ray absorption fine-structure spectroscopy, and X-ray photoelectron spectroscopy. The CoO nanoparticles were loaded onto R-TiO by an impregnation method from an aqueous solution containing Co(NO)·6HO followed by heating in air. Modification of the R-TiO with 2.0 wt % Co followed by heating at 423 K for 1 h resulted in the highest photocatalytic activity with good reproducibility. Structural analyses revealed that the activity of this photocatalyst depended strongly on the generation of CoO nanoclusters with an optimal distribution. These nanoclusters are thought to interact with the R-TiO surface, resulting in visible light absorption and active sites for water oxidation.