Michiko Shimura

Photo-electrochemical solar cells with a SnO2-liquid junction sensitized with highly concentrated dyes

The sensitization of a SnO2-liquid junction cell with highly concentrated dyes was investigated. The dyes used were Crystal Violet, Methyl Violet B, Malachite Green, Pararosaniline, and Rhodamine B. Anomalous or positive photovoltages were obtained in the system when Fe(CN)63− was added. The performance of the photovoltaic cells showed an open-circuit photovoltage,Voc, of 175 mV, a short-circuit photocurrent,Isc, of 12 μA, and a fill factor of 0.42. The action spectra resembled the absorption spectra of the aggregated dyes. A D-D mechanism is introduced to explain the anomaly of the photovoltage of the SnO2 electrode sensitized with the dyes. This behaviour is relevant to the practical usage of such photo-electrochemical cells and merits further investigation.

GaAs Schottky diodes with ideality factor of unity fabricated by in situ photoelectrochemical process

Schottky contacts to n-GaAs have been fabricated by means of a photoelectrochemical process in which in situ anodic etching of the substrate surface was performed in the same electrolytic solution as for electroplating of metals (Ni, Au, Sn and Pb). Measurement of the cyclic voltammogram was helpful in determining the applied voltages for in situ etching as well as metal deposition, and thus in fabricating good Schottky contacts reproducibly. The ideality factor (n value) of the fabricated diodes was unity for the substrate with an electron density of 2×1016 cm-3. The values of Schottky barrier heights determined by means of the I-V and C-V methods were in close agreement, and the chemical trend was clearly observed.

Effect of substrate temperature in chloroaluminum phthalocyanine thin films deposition studied by scanning tunneling microscopy and tunneling spectroscopy

Abstract The AlPcCl films deposited on a KCl substrate at two different substrate temperatures (Ts, −120°C and 180°C) with the average film thickness of 100 nm were investigated using scanning tunneling microscopy (STM) and tunneling spectroscopy (TS). The films were transferred onto HOPG in order to make STM and TS measurements possible. The STM as well as the electron diffraction measurement exhibited the amorphous and crystalline structures for Ts of −120°C and 180°C, respectively. The potential region with low conductance (conductance well) in the dI/dV curve was smaller (Ts, −120°C) and larger (Ts, 180°C) when compared with the band gap value of the AlPcCl film (Ts, 180°C) which we previously evaluated from the optical absorption measurement. We estimated the band bending with the assistance of the carrier concentration obtained from the ESR measurement. It is supposed that the electronic states created within the band gap caused the vanishing of band bending change for Ts of −120°C, leading to the decrease of conductance well. On the other hand, the band bending was found to be crucial for Ts of 180°C, which possibly resulted in the widening of conductance well.

Stabilization of Photoluminescence of Porous Silicon with Nonaqueous Anodic Oxidation

In order to prevent the reduction of photoluminescence from porous silicon, we tried to form stable Si–O bonds by anodization in nonaqueous electrolyte at room temperature. Extremely strong, stable, and blue-shifted photoluminescence was obtained in porous silicon that was prepared in 1:1 solution of 49% HF and EtOH and subsequently anodized in KNO3-ethylene glycol electrolytes. The optimum condition was anodization at 20 mA cm-2 for 5 min in 0.02 M KNO3-ethylene glycol. For the formation of Si–O bonds on nanostructured surfaces, it is suggested that the electric field across the surface/electrolyte plays an important role because oxidation becomes more effective when the electrolyte is more resistive. Si–OH, which is formed as a precursor at subsequent anodization, stabilizes the nanostructured surface, converting itself to more stable Si–O bond with photoexcitation. The high current density introduced destroys nanostructured silicon by clustering with surrounding SiO2. With this clustering, wall sizes of the nanostructured silicon remain constant with anodization.

Electrical Abruptness of Ni/GaAs Interfaces Fabricated by In Situ Photoelectrochemical Process

We have fabricated Ni Schottky–contacts to n–GaAs by an in situ photoelectrochemical process, in which anodic etching of GaAs was carried out under illumination just prior to electroplating of a metal overlayer. We examined the abruptness of the fabricated interfaces by electrical characterization as well as in situ STM observation. The measured values of the ideality factor (n= 1.00± 0.004) as well as the effective Richardson constant (A**=7.03-8.63 Acm−2K−2) suggested that the interface was, at least, electrically ideal. The STM data also supported that the in situ photoelectrochemical process is effective in realizing a smooth and clean surface of GaAs substrates just prior to metal deposition.

Fluoroaluminium 2,3‐Naphthalocyanine, Preparation and Electric Conductivity

Synthese du complexe cite dans le titre et mesure de quelques-unes de ses proprietes electriques

Effect of nonaqueous anodic oxidation on the intensity of photoluminescence of porous silicon

Porous silicon (PS) was anodized for short periods in 0.02 m KNO3–ethylene glycol electrolyte to improve the maximum intensity of its photoluminescence (PL) by changing surface –Si–H bonds to –Si–OH or –Si–O-related compounds. A PS sample prepared in 1:1 (49% HF:99.5% EtOH) electrolyte gave 15-fold PL intensity as well as stabilized luminescence with 5 min anodization. Prolonged anodization, however, peeled off the nano-ordered silicon particles and resulted in a decrease in PL intensity. The PL intensity of the PS sample prepared in 1:2 electrolyte decreased with 1min anodization but increased with 30 s anodization. During anodization, the nano-ordered silicon particles reacted with water, an impurity in ethylene glycol, to give Si–OH and Si–O-related compounds. Ethylene glycol proved to be the best anodization solvent for nano-ordered silicon particles because of its high resistivity, high viscosity, and good electrochemical stability. However, ethylene glycol had to be removed completely from the PS surface by rinsing with pure water, because polyhydroxy alcohols such as ethylene glycol behaved as quenchers for excited electrons formed in Si–OH-related compounds on the nano-ordered silicon as a result of illumination.

In Situ Surface Treatment of GaAs ( 100 ) Wafer in Metal Salt Electrolytes for Fabrication of Schottky Contact

The electrochemical behavior of n-type GaAs(100) was investigated to find an optimum condition for in situ surface treatment in Ni salt electrolytes prior to the fabrication of Ni/GaAs Schottky contacts by the wet method. Commercial machine-polished GaAs wafers with damaged crystal lattices did not show photoresponse and behaved exactly the same as a Ga metal electrode in the region of -0.1 to +0.5 V vs. Ag/AgCl. Photoresponse was observed after the removal of the damaged surface layer in H 2 SO 4 -H 2 O 2 -H 2 O. The in situ surface treatment of GaAs was done by photoelectrochemical etching at +0.1 V in acidic nickel salt electrolyte followed by the fabrication of a GaAs/Ni Schottky contact by applying negative potentials

Die farbanodisierung des aluminiums und seiner legierungen —grundsätzliche untersuchungen und anwendungen in Japan☆

Abstract Recent advances in Japanese research on the colour anodising of aluminium and its alloys are reviewed.