Electrodeposition of gold from cyanide solutions on different n-GaAs crystal faces

The initial stages of the electrodeposition of gold from $\mathrm{Au}(\mathrm{CN}{)}_2^{?}$-solutions on n-GaAs were investigated by means of chronoamperometry and ex situ atomic force microscopy (AFM). Three different crystal orientations were examined, i.e. (1 1 1), $(\overline{1}\overline{1}\overline{1})$ and (1 0 0) n-GaAs. Analysis of the experimental current transients showed that the nucleation mechanism of Au on n-GaAs depends strongly on the surface orientation and the deposition potential, which was confirmed by AFM measurements. This can be explained by differences in chemical composition of the surface. Further, it was observed that the Au nuclei grow laterally, which results in a flat morphology.     

Novel photocathodic characteristics of organic bilayer composed of a phthalocyanine and a perylene derivative in a water phase containing a redox molecule

An organic bilayer composed of metal-free phthalocyanine (H₂Pc, p-type semiconductor) and perylene derivative (PTCBI, n-type semiconductor) was found to involve novel characteristics of photoelectrode working in the water phase. When the photoelectrode characteristics were investigated when the PTCBI has contact with water containing the redox molecule (${\mathrm{Fe}}^{\mathrm{III}}(\mathrm{CN}{)}_6^{3-}$ (electron acceptor)), it was shown by voltammetry that the photocathodic current due to the ${\mathrm{Fe}}^{\mathrm{III}}(\mathrm{CN}{)}_6^{3-}$ reduction occurs at the present electrode, which is different from the ordinary characteristics at the n-type semiconductor/water interface of the Schttoky junction. Separate voltammetric studies showed that the photocathodic characteristics of the H₂Pc/PTCBI bilayer are consistent with those of the H₂Pc single layer, indicating that there are pin-holes in the PTCBI layer of the bilayer; that is, the H₂Pc has direct contact with ${\mathrm{Fe}}^{\mathrm{III}}(\mathrm{CN}{)}_6^{3-}$ dissolved in water. Thus, it is inferred that the photocathodic current occurs at the H₂Pc surface. However, the action spectrum for the photocathodic current indicated that a broad visible light absorption (400–750 nm) by only PTCBI can also induce photocurrent generation especially at wavelengths shorter than 500 nm where absorption of the H₂Pc is absent or relatively weak. This is supported by the previous knowledge that the PTCBI exciton alone can contribute to carrier generation through charge separation at the H₂Pc/PTCBI interface. This study showed the novel photocathodic characteristics at the organic solid/water interface coupled with electron conduction through the n-type semiconductor, in addition to the ordinary characteristics at the p-type semiconductor/water interface.     

Effect of niobium on the electronic properties of passive films on zirconium alloys

The effects of niobium on the structure and electronic properties of passive films formed on zirconium alloys in pH 8.5 buffer solution were examined by photo-electrochemical analysis. For Zr–xNb alloys (x = 0, 0.45, 1.5, 2.5 wt%), the photocurrent began to increase at an incident energy of 3.5–3.7 eV and exhibited the first peak at 4.3 eV and the second peak at 5.7 eV. From the (I_ph hν)^1/2 vs. hν plot, indirect band gap energies of $E_{\mathrm{g}}^1=3.01''–''3.47\mathrm{eV}\mathrm{and}{E}_{\mathrm{g}}^2=4.44''–''4.91\mathrm{eV}$ were obtained. With increasing Nb content, the relative photocurrent intensity of the first peak increased significantly. Compared with the photocurrent spectrum of the thermal oxide of Zr–2.5Nb, it was revealed that the first peak in the photocurrent spectrum for the passive film formed on Zr–Nb alloy was generated by two types of electron transitions; one caused by hydrous ZrO₂ and the other created by Nb. Two electron transition sources were overlapped over the same range of incident photon energy. In the photocurrent spectrum for passive film formed on Zr–2.5Nb alloy in which Nb is dissolved into the matrix by quenching, the relative photocurrent intensity of the first peak increased, implying that dissolved Nb acts as another electron transition source.     

Investigation of the electrochemical behavior of metallo-tetraazaporphyrin modified silver and pyrolytic graphite electrodes in aqueous nitrite solution

Five new complexes of the type [M(OBTTAP)] (where M = Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺; OBTTAP = 2,3,7,8,12,13,17,18-octakis(benzylthio)-5,10,15,20-tetraazaporphyrin(2?)) were used to prepare modified silver and pyrolytic graphite electrodes and their electrochemical behavior towards the reduction of aqueous nitrite solution was investigated in acidic, neutral and alkaline medium. Of these electrodes, [Co(OBTTAP)] and [Cu(OBTTAP)] modified electrodes showed affinity for ${\mathrm{NO}}_2^{-}$ ions and thereby exhibited significantly altered cathodic responses. The [Co(OBTTAP)]/Ag electrode in acidic, neutral and also in alkaline nitrite solutions, exhibited a new one electron irreversible reduction wave at E_p,c ～ ?0.2 V vs. Ag|AgCl. The [Cu(OBTTAP)]/Ag electrode in acidic and neutral nitrite solutions also behaved in a similar manner. However, in alkaline aqueous nitrite solution it showed two successive one electron reductions, the first reversible reduction at E_1/2 = ?0.26 V and the second irreversible reduction at E_p,c = ?0.73 V vs. Ag|AgCl. Controlled potential electrolysis of alkaline nitrite solutions using a [Cu(OBTTAP)]/Ag cathode led to isolation of a nitrosyl complex. The peak current, particularly with [Cu(OBTTAP)]/Ag microelectrode in alkaline medium, showed a linear response to $[{\mathrm{NO}}_2^{-}]$ and could be exploited in the electrochemical sensing and determination of ${\mathrm{NO}}_2^{-}$.