Showing papers by "Akira Fujishima published in 1990"

Photoelectrochemical information storage using an azobenzene derivative

Abstract: HIGH-DENSITY information storage is becoming an increasingly important technological objective. The 'heat-mode' storage techniques (in which only the thermal energy of laser light is used in the recording process and hence information usually stored as a physical change of the storage media) that are used in current optical memories are limited by the diffraction properties of light1, and the alternative 'photon-mode' (in which information is stored as a photon-induced chemical change of the storage media) has attracted attention recently for high-density storage. The most promising candidates for realizing this mode seem to be photochro-ism and photochemical hole burning; but these have some intrinsic drawbacks1,2. Here we present a novel 'photon-mode' technique that uses the photoelectrochemical properties of a Langmuir-Blodgett film of an azobenzene derivative. The system can be interconverted photochemically or electrochemically between three chemical states, and this three-state system is shown to provide a potential storage process that allows for ultra-high storage density, multi-function memory and non-destructive information readout.

Hydrogen-bonded liquid crystals. A novel mesogen incorporating nonmesogenic 4,4'-bipyridine through selective recognition between hydrogen bonding donor and acceptor.

Abstract: Selective recognition between a benzoic acid derivative and nonmesogenic 4,4′-bibyridine through intermolecular hydrogen bonds results in a novel molecular structure with liquid crystalline properties, in which 4,4′-bipyridine functions as a core unit.

Self-Assembly of a Twin Liquid Crystalline Complex through Intermolecular Hydrogen Bondings

Abstract: A new type of twin liquid crystalline complex having two terminal mesogenic units and a central flexible spacer has been formed through intermolecular hydrogen bonds between a nonmesogenic aliphati...

Excellent reversible photochromic behavior of 4-octyl-4'-(5-carboxyl-pentamethyleneoxy)-azobenzene in organized monolayer assemblies

Abstract: We report the first observation of a photochromic behavior of an amphiphilic azobenzene derivative in the close-packing LB films on a solid support. The excellent reversibility was achieved only after the LB films were ‘pretreated’ with UV irradiation.

Surface density of states of TiO2(110) single crystal and adsorbed molecular observation by scanning tunneling microscopy and tunneling spectroscopy

Abstract: We present the evidence for the surface density of states (SDOS) of the hydroxylated and reduced rutile TiO2 (110) single crystal different from the bulk electronic property by tunneling spectroscopy using scanning tunneling microscopy technique (STM/TS). The surface band gap energy (SEg) was 1.6 eV as the tunneling‐active free states. This experimentally obtained SEg (1.6 eV) was quite different from the bulk band gap energy (3.05 eV). The chemisorbed OH− on the Ti3+ –O vacancy state is located 1.35 eV below the EF . The observed tunneling current rectification originates in the surface electronic structure, band bending and surface coordination property. It became clear that the photo‐oxidation of the chemisorbed OH− by photogenerated holes was energetically feasible through the study of SDOS using the STM/TS. Phenol molecules were adsorbed onto the hydroxylated TiO2 surface. The image of the phenol molecule was measured at a tip bias of +443 mV which is within the surface band gap and slightly larger than the vibration energy of phenol ring. The electron density of the phenol ring was apparent in the STM picture.

Removal of thallium from waste water by using the iron metal and hydrogen peroxide.

Abstract: Thallium in waste water can be removed effectively by DOWA Iron Powder Method which uses Fe metal powder and H2O2. The concentration of Tl in waste water was decreased by a factor of about 100 from the initial concentration with each treatment.

A Novel Electrochemical Quantification Method for Trans/Cis Interconversion of Azo Compounds in a Solid Monolayer Film

Abstract: A direct electrochemical quantification method for the trans/cis interconversion reaction of some azobenzene derivatives in a solid monolayer film was developed, on the basis of the photoelectrochemical hybrid phenomenon that we found.

In situ scanning tunneling microscopy observation of surface roughness of electrochemically modified Ag under potentiostatic control in conjunction with surface‐enhanced Raman scattering

Abstract: A morphological transformation of Ag electrode in 0.1 mol dm −3 KCl has been studied by in situ STM observation by controlling the electrode potential during a single electrochemical oxidation–reduction cycle (ORC) treatment in conjunction with SERS. Prior to the oxidation the Ag electrode surface has ellipsoidal structures. After the single oxidation treatment electrochemical formation of AgCl clusters and adatoms occurred at the edge of ellipsoidal structures. These species were stripped by the reduction processes. A single ORC treated Ag surface has roughness on an atomic scale due to the presence of residual AgCl clusters, adatoms, and adsorbed chloride ions. The ORC treated surface has roughness characteristics more suitable for observing the SERS effect than the electrochemically untreated surface.

Electroluminescence at n ‐ SiC / Electrolyte Interface under Cathodic Polarization Observation of EL Transients in a Short Time Scale and Further Evidence for a Donor‐Acceptor Transition

Abstract: Electroluminescence (EL) at electrolyte junction was studied under cathodic polarization. Various redox electrolytes including current doubling reagents like persulfate were employed to understand the nature of EL. When the cathodic bias is higher than the flatband potential of electrode, species like persulfate are reduced by the conduction band electrons to form highly oxidizing intermediates which inject holes into the valence band to produce light . In the case of redox electrolytes like , , etc., the EL emission is weak and occurs at a higher cathodic bias, i.e., when the cathodic bias exceeds the bandgap energy of . Here, an electron transfer occurs from the valence band to the redox electrolyte. This indicates that the minority carrier injection (hole) is an important process in obtaining high EL intensities. The emission appears greenish‐yellow and the peak energy of the spectrum is smaller by 1.1 eV than the bandgap of (3.2 eV, calculated from photoresponse measurements), suggesting that the radiative recombination occurs through the impurity luminescent centers. Even under continuous polarization the EL intensity is steady for longer time duration and the electrodes are highly stable. The spectral distribution and increase in the EL intensity with different cathodic pulsed bias potentials were observed and explained by a donor‐acceptor (D‐A) mechanism. The charge transfer at the interface and the radiative recombination of electrons and holes inside the semiconductor are explained from the characteristics of EL and current intensities vs. time obtained under various pulsed polarized conditions. Moreover, the electrodes are highly stable under cathodic steady‐state polarization for several hours. Time resolved measurements (using our present system) seem to indicate the EL transients are limited by the current flow.

In Situ Observation of a Dynamically Light-Induced Morphological Transformation at an n-MoS2 Electrode Surface by a Scanning Tunneling Microscope

Abstract: A scanning tunneling microscope (STM) under photoelectrochemical control was used to investigate an in situ dynamically light-induced morphological transformation at an n-MoS2 electrode surface in CH3CN by the addition of I− ions. The anistropic photocorrosion rate around the “disk-like” cavities was extremely slow due to the effects of the added I− ions when compared to the results achieved by adding only H2O.

Crystal Growth and Photoelectrochemical Characterization of Cd4BSe6 (B = Si or Ge)

Abstract: Single crystals of Cd 4 BSe 6 (B=Si, Ge) (ARGYRODITES) were grown by CVT method using a three zone furnace. As-grown crystals were of n-type and they have been characterized by photoelectrochemical (PEC) measurements in aqueous electrolytes. The current-potential curves, Mott-Schottky plots and action spectra were examined. From the analysis of spectral response measurements the band gaps (indirect) for Cd 4 SiSe 6 and Cd 4 GeSe 6 were found to be 1.68 and 1.5 eV, respectively. The opencircuit photopotentials for these semiconductor electrodes were as high as 1.1 V vs. SCE in some of the electrolytes used.

Photochromic and Electrochromic Behavior of Electrodeposited MoO3 Thin Films.

Abstract: Etude du comportement electrochromique et photochromique d'un film d'oxyde de molybdene (VI) depose electrolytiquement ou evapore sous vide

Photoelectrochemical Study of n-InP: Redox Processes Using Electroluminescence as Mechanistic Probe

Abstract: Electroluminescence (EL) due to band-band transition was observed for n-InP single crystal electrodes in solutions containing current doubling reagents like peroxodisulfate and various redox electrolytes. The mechanism for the EL emission in relation to surface properties of n-InP crystals in these electrolytes is presented. The cathodic decomposition process of n-InP electrodes involved in various electrolytes especially in peroxodisulfate medium has been analyzed from the EL emission as a function of electrode potential under steady state as well as pulsed conditions. The intensity of the EL signal depends on the electron density at the interface which is controlled by the potential and on the chemical composition of the electrode surface. Moreover, a hydrogen evolution reaction reduces the EL efficiency at higher cathodic potentials. Though the potential has no effect on the shape of the EL spectra, a significant change in EL intesity was observed. In all the electrolytes used the InP electrodes seem t...

Highly Sensitive Analysis of SnO2/Solution Interface by Internal Reflection–Fluorescence Spectroscopy

Abstract: Internal reflection-fluorescence Spectroscopy was applied to the analysis of SnO2/solution interface. Changes in the fluorescence intensity of 1,3-di-n-butyl-5-[4-[3,3-dimethyl-1-(-sulfopropyl)-2-indolinylidene]-2 -butenylidene]-2-thiobarbituric acid sodium salt were measured at very low dye concentration as a function of pH. The point of zero charge and the distribution of the positive charge sites of SnO2 thin film surface were investigated. The electrochemical potential of SnO2/solution interface was estimated.

Electrochemical behavior of high transition temperature superconducting oxides

Abstract: Typical high transition temperature (high-Tc) superconducting oxides were used as electrodes in order to investigate their electrochemical behavior at room temperature. Chemical stability of these materials in various solutions was also tested. These superconducting oxides were stable in nonaqueous solutions, but is was very difficult to protect electrical contacts from the solvents because of porous structures of these oxides. These materials were rather stable in highly concentrated alkaline solutions while unstable in neutral and acid solutions. Electrochemical experiments were carried out in alkaline solutions, and the following results were obtained: (1) All of the high-Tc superconducting oxides were unstable at cathodic polarization. (2) Oxygen evolution was observed under anodic polarization. (3) These oxides behaved like p-type semiconductros though no photocurrents were detected. (4) [Fe(CN)6]3−⁄4− served as a redox couple for all of these high-Tc oxides.

Observation of Tip-Induced Ordered Molecular Arrangement on Graphite Surfaces by Scanning Tunneling Microscopy

Abstract: Ordered molecular structure has been observed by scanning tunneling microscopy (STM) in the disordered films of an azobenzene derivative on highly oriented pyrolytic graphite (HOPG) surfaces. The disordered films were formed by a direct deposition method. The present result gives the first report on the observation of tip-induced ordered molecular structure from disordered films by STM, and it demonstrates the possibility of orderly arranging molecules on surfaces through the action of an STM tip.

Investigation of Nickel Plating by Photoacoustic Spectroscopy (PAS) and Scanning Tunneling Microscopy (STM)

Abstract: Photoacoustic technique was employed to study the plating of Nickel. And on the other hand, Scanning Tunneling Microscopy (STM) cleared the difference of the surface in the presence and in the absence of the brightener. Also Scanning Electron Microscopy (SEM) was used for supporting the data of STM.

Electrochemical Behavior of High Transition Temperature Superconducting Oxides.

Abstract: Typical high transition temperature (high-Tc) superconducting oxides were used as electrodes in order to investigate their electrochemical behavior at room temperature. Chemical stability of these materials in various solutions was also tested. These superconducting oxides were stable in nonaqueous solutions, but is was very difficult to protect electrical contacts from the solvents because of porous structures of these oxides. These materials were rather stable in highly concentrated alkaline solutions while unstable in neutral and acid solutions. Electrochemical experiments were carried out in alkaline solutions, and the following results were obtained: (1) All of the high-Tc superconducting oxides were unstable at cathodic polarization. (2) Oxygen evolution was observed under anodic polarization. (3) These oxides behaved like p-type semiconductros though no photocurrents were detected. (4) [Fe(CN)6]3−⁄4− served as a redox couple for all of these high-Tc oxides.

Electroluminescence at n-SiC/Electrolyte Interface Under Cathodic Polarization. Observation of EL Transients in a Short Time Scale and Further Evidence for a Donor-Acceptor Transition

Abstract: Electroluminescence (EL) at electrolyte junction was studied under cathodic polarization. Various redox electrolytes including current doubling reagents like persulfate were employed to understand the nature of EL. When the cathodic bias is higher than the flatband potential of electrode, species like persulfate are reduced by the conduction band electrons to form highly oxidizing intermediates which inject holes into the valence band to produce light . In the case of redox electrolytes like , , etc., the EL emission is weak and occurs at a higher cathodic bias, i.e., when the cathodic bias exceeds the bandgap energy of . Here, an electron transfer occurs from the valence band to the redox electrolyte. This indicates that the minority carrier injection (hole) is an important process in obtaining high EL intensities. The emission appears greenish‐yellow and the peak energy of the spectrum is smaller by 1.1 eV than the bandgap of (3.2 eV, calculated from photoresponse measurements), suggesting that the radiative recombination occurs through the impurity luminescent centers. Even under continuous polarization the EL intensity is steady for longer time duration and the electrodes are highly stable. The spectral distribution and increase in the EL intensity with different cathodic pulsed bias potentials were observed and explained by a donor‐acceptor (D‐A) mechanism. The charge transfer at the interface and the radiative recombination of electrons and holes inside the semiconductor are explained from the characteristics of EL and current intensities vs. time obtained under various pulsed polarized conditions. Moreover, the electrodes are highly stable under cathodic steady‐state polarization for several hours. Time resolved measurements (using our present system) seem to indicate the EL transients are limited by the current flow.

In Situ Observations of Electrode/Solution Interfaces Using a Scanning Tunneling Microscope

Abstract: The review presented here concentrates on recent advances in observing in situ electrode/ solution interfaces using a scanning tunneling microscope (STM) under potentiostatic control. In situ observation with the STM is important to gain insights into electrochemical processes at electrode/solution interfaces. The locally manufactured electrochemical STM apparatus/ system is briefly described. Attention is then focused on the in situ observations of the under potential deposition (UPD) of metals, various structural changes and reconstructions induced electrochemically, adsorbates on electrode surfaces, and photoelectrochemical processes on semiconductor electrodes. Additionally presented are electrochemical micro-fabrication processes which use a scanning electrochemical microscopy, the topography of nonconducting surfaces using a scanning ion-conductance microscope, and studies of the UPD of Cu onto Au surfaces using an atomic force microscope.