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ZnO thin films with various surface morphologies were prepared on glass substrates by spray pyrolysis, and the influence of the morphology on the adhesion of the electroless deposited Cu films was investigated. Results showed that the adhesive strength of the electroless Cu deposits was greatly affected by the surface morphology of the ZnO thin films, which can be controlled by changing the preparation parameters, e.g., substrate temperature, precursor solution composition, and spray time. Cu deposits with high adhesion were achieved on ZnO thin films with rougher, more porous morphologies. The latter were mainly composed of small ball‐like structures, with diameters on the order of 0.2–1.0 μm. Upon electroless Cu deposition on these ZnO films, in addition to the strong van der Waals force acting at the Cu/ZnO interface caused by the large surface area on a rough, porous surface, the Cu penetrates deeply into the film, giving rise to a strong mechanical, anchoring effect ("dovetail" or ball‐and‐socket joint effect), which also greatly improves adhesive strength. Such porous structures, which are difficult to obtain by chemical etching of the substrate in the conventional electroless metal deposition process, were obtained by spraying 0.05 M zinc acetate/ethanol solution onto glass substrates at temperatures above 380°C. © 1999 The Electrochemical Society. All rights reserved.

Photoelectrochemical characterization of semiconducting diamond was carried out in a weakly UV-absorbing aqueous electrolyte using suprabandgap illumination in order to examine the influence of electrochemical oxidative surface treatment on the energetic positions of bandedges. Anodic treatment of diamond photoelectrodes resulted in a positive shift in both the photocurrent onset potential and the flatband potential obtained from Mott-Schottky plots, indicating the displacement of the bandedges. A corresponding increase in the photovoltage was also observed. The pH dependence of the flatband potential of anodically treated diamond indicates an acid-base equilibrium at the interface, suggesting the formation of oxygen-containing groups. The presence of the latter was confirmed using X-ray photoelectron spectroscopy. These results suggest that the changes in the potential drop in the Helmholtz layer are due to oxygen functional groups, and the loss of surface and subsurface hydrogen are mainly responsible for the observed shifts in the flatband potentials.

The formation process of highly dispersed Pd on ZnO thin films as a catalyst for electroless metal deposition was studied in detail by means of adsorption experiments combined with X-ray photoelectron spectroscopy measurements. The chemical state of the yellow-brown species adsorbed on ZnO thin film during the catalyzation process in acidic PdCl 2 solution (pH 2.5) was determined to be Pd(OH) 2 . It was found that the adsorption of Pd on the ZnO thin film is closely related to the partial dissolution of ZnO in acidic solution, which results in an increase of the pH in the vicinity of ZnO surface, while the pH of the overall PdCl 2 solution remains essentially unchanged (-2.5) within the period of the catalyzation treatment (

Highly conductive boron-doped polycrystalline diamond thin films (ρ ≃ 10 -3 Ω cm) reduction prepared via microwave plasma chemical vapor deposition (CVD). The electrochemical behavior for oxygen reduction was examined in 0.1 M KOH using linear sweep voltammetry. Oxygen reduction was found to be highly inhibited, the cathodic voltammetric peak being observed at ∼ -1.2 V vs. Ag/AgCl, compared with the standard potential for the two-electron reduction of oxygen (O 2 + H 2 O + 2e - = HO 2 - + OH - , E°' = -0.234 V vs. Ag/AgCl at pH 13). This demonstrates that, even in the presence of dissolved oxygen, diamond retains a relatively wide potential window, which could be advantageous in certain types of analytical applications. Possible interpretations for the high overpotential for oxygen reduction include a lack of adsorption sites for oxygen and/or reduced intermediates, a low density of states or a potential drop within a thin were nm) surface layer, all of which have also been proposed for highly ordered pyrolytic graphite. The experimental data were fitted using digital simulation, which showed that the reduction peak appearing at ca. -1.2 V also consistent with an nantly due to the reduction of oxygen to peroxide. Rotating disk electrode measurements were also consistent with an overall two-electron process. Experiments involving the addition of superoxide dismutase also supported this conclusion. The oxygen reduction reaction is proposed to occur on the sp 3 carbon component of the surface, with a very small contribution from sp 2 carbon impurities at smaller overpotentials.

Electroless Cu layers with pull strengths of greater then 2.5 kg/mm 2 were fabricated on smooth ceramic substrates (glass, Al 2 O 3 , AlN) without surface etching (R a ≤ 0.05 μm). High adherence was achieved using ZnO thin films (ca. 1 μm thickness), prepared by spray pyrolysis as an intermediate layer between the ceramic substrates and the Cu layers. It was shown from the interfacial analysis that the high adherence was due to both strong van der Waals forces acting at the Cu/ZnO interface and a chemical-type bond acting at the ZnO/ceramic interface. The adhesive forces at the Cu/ZnO interface were enhanced by numerous small pores

Micropattern formation on ZnO thin films has been carried out using a photodissolution reaction. ZnO thin films were prepared on glass and on transparent, conductive SnO 2 -coated glass by spray pyrolysis. The dissolution rates of the ZnO films were measured under illumination (υ light ) and in the dark (υ dark ) under various conditions. The υ light and υ dark values were determined by measuring the zinc content in the ZnO film before and after the dissolution reaction using x-ray fluorescence spectroscopy. The dissolution rate became larger under UV illumination under various conditions. Both υ dark and υ light depended strongly on the pH value of the electrolyte solution and the bias voltage. The best conditions to form the ZnO film micropattern were determined by measuring both υ light and υ dark . Under the best conditions, a micropattern was obtained on the ZnO thin films on SnO 2 -coated glass substrates under illumination through a photomask. The linewidth of the micropattern can be as low as about 130 μm.

The reaction mechanism of electroless metal deposition proceeding selectively on a ZnO thin film coated on a glass substrate was investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma measurements. The ZnO thin film was activated for electroless metal deposition just by immersion in 1.1 mM PdCl{sub 2} solution adjusted to pH 2.5. In this process, PD(II) was selectively adsorbed on the ZnO thin film while simultaneously the ZnO underwent dissolution. The dissolution of ZnO thin film easily occurred on the (002) face with polarity. The strongly adsorbed Pd(II) was reduced to Pd(0) by a reducing agent in the electroless plating bath and this served as a catalyst center. As a result, metal layers were obtained selectively on the ZnO thin film in the electroless plating bath.

A series of the absorption spectrum changes in polypyrrole films were analyzed using the Nernst equation by two models. One is the "monomer unit model" and the other is the "polaron/bipolaron model." In the first model, formal electrode potentials and the n-values were obtained and usec~ to fit calculated hAbs vs. E curves to the experimental plots at three wavelengths. In the second model, the "apparent" excess chemical potentials were introduced to correct for the large deviations between the Nernst equation and the Nernst plots obtained from the absorption spectra. The calculated hAbs vs. E curves were then fitted to the experimental plots. The "apparent" excess chemical potentials were assigned as corrections for species concentrations. Advantages of the monomer unit model over the polaron/bipolaron model are pointed out in the precise analyses of the spectroelectrochemical behavior of the films.

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.

Electrochemical reduction was investigated on 32 metal electrodes in aqueous medium. The current efficiency of reduction on Ni, Ag, Pb, and Pd increases significantly with lowering the temperature. The ratio of reduction products are also changed by lowering temperature. Potential dependence of and on an Hg electrode supports the electron transfer mechanism for production. Formation of methane and ethylene is observed on almost all metal electrodes used, although the efficiency is mainly very low except for Cu. A periodic table for reduction, which is drawn based on the dependence of reduction products on various metals, suggests the existence of a systematic rule for the electrocatalytic reduction of on metal surfaces.

High-rate cathodic photoelectrolysis of CO{sub 2} was conducted in a high pressure CO{sub 2} + methanol medium at p-InP electrodes. Current densities up to 100 mA/cm{sup 2} were achieved, with current efficiencies up to 93% for CO production. The photoelectrochemical reduction of CO{sub 2} in the highly concentrated CO{sub 2}-methanol solution was limited at the higher current densities (50--100 mA/cm{sup 2}) by light intensity and not by the mass transport of CO{sub 2}.

Reversible photoinduced magnetization was observed in a cobalt iron cyanide thin film. Magnetic properties of the prussian blue analog, K 0.4 Co 1.3 [Fe(CN) 5 ].5H 2 O, can be switched between ferrimagnetic and paramagnetic by visible and near-IR light illumination. The critical temperature after illumination was about 26 K. This material, obtained via an electrochemical route in the form of thin films on an electrode, provides a new system whose magnetic properties can be controlled by both photochemical and electrochemical redox reactions.

A new, fully additive-based, electroless plating process for the formation of fine Cu patterns without using a conventional photoresist has been developed which utilizes a photocatalytic reaction of ZnO thin films prepared on ceramic substrates for printed circuit boards. The ZnO layer serves both as an adhesive layer and as a photosensitive layer. The Cu patterns could be easily fabricated in an electroless Cu plating bath after Pd nuclei, which act as catalytic sites for the electroless plating, were patterned via an area-selective photocatalytic reaction. This was achieved by adsorbing Pd(II) onto the ZnO surface and selectively exposing the surface with UV light through a photomask. The unexposed regions can be freed of Pd(II) using ethylenediamine, which can form a stable complex with Pd(II). Cu patterns 17 {micro}m wide, with adhesion strengths suitable for practical use, have been achieved on alumina substrates with this electroless plating method.

A novel electrochemical CO[sub 2] reduction system has been developed in which liquid CO[sub 2] was reduced electrochemically at a Cu electrode producing CO, CH[sub 4], C[sub 2]H[sub 4], and HCOOCH[sub 3]. The authors have succeeded in reducing CO[sub 2] with a current density of 420 mA/cm[sup 2] and a current efficiency of 85%; the former is higher than that used in industrial electrolysis such as in the chloralkali industry. The Tafel plots indicate that the supply of CO[sub 2] is no longer limited by its mass transfer.

A new electroless plating process for preparing a copper layer with strong adhesion to glass substrates was developed. This process incorporates a ZnO thin film on the glass substrate, instead of etching and sensitizing the substrate surface as in a conventional electroless plating process. The copper layer so obtained had a mirror-like finish while maintaining strong adhesion, even on a very smooth glass surface (Ra

A radio frequency sputtering technique was used to fabricate nitrogen-doped titanium dioxide thin films with dopant concentrations of 1.0-2.9 mol %. UV-visible absorption spectra and calculations of the estimated density of states indicated that the changes in the band structure depended on the dopant concentrations. The nitrogen-doped TiO 2 films underwent hydrophilic conversion and approximately 1.9 mol % was the optimal dopant concentration for hydrophilic properties when irradiating with visible light. When irradiating with UV light, the hydrophilic properties increased as the dopant concentration decreased, which reflected the changes in the band structure. Photoelectrical and electrochemical analyses of the nitrogen-doped TiO 2 suggested that it was an n-type semiconductor, and the carrier concentrations increased as the nitrogen concentration increased. Based on these findings, a mechanism for the visible light response, which involves nitrogen incorporation at some of oxygen sites, is proposed.

We have observed the generation of second harmonic (SH) light from electrochemically synthesized (Fe II x Cr II 1-x ) 1.5 [Cr III (CN) 6 ].7.5H 2 O films. The X-ray diffraction spectra of these films showed that the (110) and (111) crystalline planes were oriented parallel to the film plane, and that the crystal structures were not the typical face-centered cubic of Prussian blue analogs but they possessed a noncentrosymmetric monoclinic C2 symmetry. The SH intensity vs. x plots showed that only the ternary metal films (0 < x ≤ 0.42) emitted SH radiation with an intensity that grew with increasing x. Maker's fringe pattern showed that the electric polarization was oriented perpendicular to the film plane. Furthermore, the excitation wavelength dependence on the SH intensity showed that this SH wave was resonant with the intervalence transfer band between Fell and Cr III . These SH properties are explained through the analysis of preferred orientation and noncentrosymmetric structure of electrochemical-deposited crystalline films, and by the electric polarization due to the CN-Fe-OH 2 site.

We have investigated the change in surface wettability of n-type semiconductor TiO 2 electrode surfaces induced by cathodic polarization. While the wettability of polycrystalline anatase electrode surfaces did not change remarkably regardless of the electrode potential, the surface of amorphous TiO 2 electrodes became highly hydrophilic under cathodic conditions without UV light irradiation. We conclude that the increase in the number of hydroxyl groups due to electron addition to the near-band-edge trap sites accompanied by proton intercalation is responsible for the present hydrophilic conversion under cathodic conditions.

On propose un modele decrivant la reponse transitoire a une courte impulsion lumineuse d'un circuit contenant une interface electrolyte-semiconducteur