Kenji Sakamaki

Imaging the phenol molecule adsorbed on TiO2(110) by scanning tunneling microscopy

Abstract The image of a phenol molecule adsorbed on a TiO2(110) single crystal was obtained, for the first time, by using the STM. TiO2(110) has a tunneling active free region from + 1.35 eV below the Fermi level to −0.25 eV above the Fermi level. This region was found after measuring the surface density of states by using tunneling spectroscopy. The phenol molecule was fixed on TiO2 utilizing the amphoteric nature of the TiO2 surface. The image of the phenol molecule was measured at a dp bias of + 443 mV, which almost matches the energy of the OH and C-H stretching bond of the phenol molecule, in the free of energy levels region of the TiO2(110) substrate. The electron density of phenol ring is apparent in the STM picture.

Photoelectrochemical in situ observation of n‐MoS2 in aqueous solutions using a scanning tunneling microscope

A scanning tunneling microscope under potentiostatic control in visible light illumination was used in aqueous solutions to investigate an in situ dynamical light‐induced morphological transformation of n‐MoS2, a representative layer‐type semiconductor electrode. In a KCl solution, light‐induced corrosion originated from ‘‘layer‐island’’ structures, island edges, and depressions, all of which served as active reaction sites. The electrode surface was then morphologically transformed by photoelectrochemical processes into a stable van der Waals’ surface. Additionally, the effect of I− ions on the suppression of photocorrosion of n‐MoS2 was investigated.

Adding H2O to study in situ anisotropically enhanced photo-oxidation at n-MoS2/CH3CN interfaces using a scanning tunneling microscope

Abstract Evidence for the existence of an anisotropically enhanced photoelectrochemical reaction at an n-MoS 2 (0001) electrode surface is presented to investigate in situ photoelectrochemical processes using a scanning tunneling microscope (STM) under potentiostatic control. By the addition of H 2 O to CH 3 CH, the photo-oxidation reaction under anodic polarization significantly enhanced. The photocorrosion processes around surface defects were continuously observed. A well-ordered (0001) face was found to be stable against the photoelectrochemical reaction in a CH 3 CN solvent containing 4 vol% H 2 O. However, when 4 vol% H 2 O was added, both photo-oxidation and photocorrosion occurred with significant anisotropy at surface depressions and vacancies which served as active reaction sites. The reaction proceeded preferentially along the van der Waals basal plane.

Evidence for superconductivity in Nb2SC0.90 carbosulfide

Abstract Evidence for bulk superconductivity in Nb2SC0.90 carbosulfide is presented. Diamagnetic volume fraction of Nb2SC0.90 was precisely determined with low applied magnetic fields which were corrected by 6N lead rod as an internal standard. Based on magnetic field dependence of magnetic moment at several constant temperatures below TC = 5 K, Nb2SC0.90 is found to be a type II superconductor with relatively high H C2 and low HC1.

DEFINITIVE STRUCTURE OF A STACKING BOUNDARY OF CHARGE DENSITY WAVES IN 1T-TAS2 USING A SCANNING TUNNELING MICROSCOPE

Abstract Definitive structure of a “stacking” boundary of nearly commensurate charge-density-waves (CDWs) in 1T-TaS 2 , caused by self-intercalated Ta atoms into a van der Waals (vdW) gap, was clearly observed at room temperature by a scanning tunneling microscope (STM). Charge density contours between the two parts were clearly seen to be markedly different. No distortions were found in either the wavelength or positions of CDWs over the area where self-intercalated Ta atoms were located in the vdW gap. However, their contour and amplitude were quite different from the commonly observed CDW structure.

Electrochemical Reduction of Ag4Hf3S8 in a Nonaqueous Lithium Cell

Abstract A basic nature of cubic Ag4Hf3S8 for electrochemical Li insertion was examined with relation to cell properties and Rietveld analyses for ex-situ X-ray powder diffraction patterns observed at several discharge steps. The composition dependence of cell voltage curves observed in the closed type Li/lM-LiPF6 in PC/Ag4Hf3S8 cell showed a long plateau at around 2.2–2.0 V up to LixAg4Hf3S8 (x ≤ 3). The cell voltage decreased with an increase of Li intercalation and final lithiated phase was assigned to cubic LixAgyHf3S8 (x > 3, × + y = 7). The electrochemical lithiation of Ag4Hf3S8 at low constant current densities proceeded topochemically. The structures of lithiated phases were solved without changing the space group P4332 (No. 212) for Ag4Hf3S8 host, indicating that Hf3S8 framework structure was kept through the lithiation.

Electrochemical and structural characterization of silver hafnium sulfide cathodes

Abstract Cubic Ag 4 Hf 3 S 8 treated with n -butyl lithium was found to function as the cathode in a lithium cell. The structure model of cubic lithiated Ag 4 Hf 3 S 8 was reconstructed on the basis of Rietveld analysis of XRD data. Its space group was assumed to be identical with that of the source, P4 3 32 . It was clarified that XRD profiles of lithiated phase can be well explained by the presence of a rigid framework structure of Hf 3 S 8 not broken by lithium. Comparative studies on electrochemical lithium insertion into Ag 4 Hf 3 S 8 were carried out in non-aqueous organic solvents. The electrochemical behavior and structural change of Ag 4 Hf 3 S 8 cathode were investigated. Effect of electrolytes on discharge behavior was examined for solutions, such as (1) 1 M LiI, (2) 1 M LiClO 4 and (3) 1 M LiPF 6 in propylene carbonate (PC). The initial cell voltage was found to differ with the electrolyte used: 2.4 V for case (1), 2.4 V for case (2) and 3.0 V for case (3).