Photoelectrochemistry of electrochemically deposited cadmium-rich cadmium mercury telluride films.

The potentiostatic deposition of cadmium-rich CMT films onto Ti, Mo, Ni substrates from an aqueous bath was carried out. The photoelectrochemical properties of film electrodes were investigated when used in a solid-liquid junction photoelectrochemical cell (PEC). A.C. capacitance was determined.     

Study of electrochemically deposited thin poly(N-vinylcarbazole) films

In this paper, the influence of the water content in the acetonitrile/LiClO(4) system on the electrosynthesis and the properties of poly(N-vinylcarbazole), PNVC, films is examined. By using conventional resonant frequency and impedance measurements of an electrochemical quartz crystal microbalance (EQCM), information about the electrochemical, morphological and adhesive properties of the thin conducting films were obtained. By changing the water content of the background electrolyte, the degree of cross-linking (through the vinyl group), the doping level and the morphology of PNVC films vary simultaneously. Two limiting cases of film properties were observed: for less than 10 Vol.% water, a highly doped, porous and cross-linked polymer is synthesized. Above 10 Vol.% water content, a dense and smooth film is deposited. The growth at a constant potential was found to be limited by the diffusion of monomers to the electrode. Films grown from a system containing 20 Vol.% water exhibit better adhesive properties to the substrate than those grown from 2 Vol.% water.     

Polypyrrole-poly(3-methylthiophene) bilayer films electrochemically deposited onto tin oxide

We report the electrochemical successive deposition of layers of polypyrrole and poly(3-methylthiophene), forming conjugated polymer heterostructures onto a tin oxide-covered glass substrate. The polymer bilayer thickness and roughness were determined as a function of deposition conditions, varying the sequence of deposition of the conjugated polymer layers. The charge transport characteristics of these bilayer devices were investigated and an effective charge carrier mobility of the order of 10^–10 cm² V^–1 s^–1 was determined. Electronic Publication     

Surface plasmon resonance of electrochemically deposited Au-black

Au-black, a kind of gold nanostructure, was electrochemically deposited on a Au-vapor-deposited glass plate, and its optical properties were evaluated with a surface plasmon resonance (SPR) measurement system. The Au-black was found to exhibit an extraordinary high resonance angle (minimum reflectance angle) compared to that of the Au-vapor-deposited glass plate. We proposed a five-layer model, which consists of glass, Cr, Au, Au-black, and solution layers, to explain the high resonance angle of the Au-black plate. The calculation was based on the Fresnel formulas extended for multilayers. When the Bruggeman formula was used to obtain a refractive index of the Au-black layer, the numerical simulation could qualitatively explain the experimental observations. The curve fitting method by the five-layer model enabled us to simultaneously estimate the thickness of the Au-black layer and the volume fraction of Au in Au-black.     

X-ray spectroscopy of electrochemically deposited iridium oxide films: detection of multiple sites through structural disorder

We report the results of X-ray absorption spectroscopy studies on electrochemically deposited iridium oxide films. The emphasis of the study is the correlation of X-ray derived structural data with electrochemically controlled charge state. Data were acquired for films subject to redox cycling in neutral and alkaline aqueous media. In both cases, cyclic voltammetric responses show two redox couples, coulometrically of roughly equal magnitude. Assays of the iridium population (based on the iridium L(3) absorption edge amplitude) and the charge injected (based on integration of the voltammetric response) show that overall an average of ca. one electron per iridium atom is transferred. The absorption edge shifts indicate that the formal charge on the iridium changes, on average, from ca. 3.5+ to ca. 4.5+ across the entire process. EXAFS-derived changes in mean Ir-O distance and their mean square variation have been interpreted in terms of a two-site model, in which the two types of site have distinct redox potentials. Variations of local structure and disorder with potential are discussed and a generic model for structural disorder (parameterized via Debye-Waller factor) with diagnostic capability is developed.     

Characterization of gold nanoparticles electrochemically deposited on amine-functioned mesoporous silica films and electrocatalytic oxidation of glucose

This study reports the preparation and characterization of gold nanoparticles deposited on amine-functioned hexagonal mesoporous silica (NH₂–HSM) films and the electrocatalytic oxidation of glucose. Gold nanoparticles are fabricated by electrochemically reducing chloroauric acid on the surface of NH₂–HSM film, using potential step technology. The gold nanoparticles deposited have an average diameter of 80 nm and show high electroactivity. Prussian blue film can form easily on them while cycling the potential between −0.2 and 0.6 V (vs saturated calomel electrode) in single ferricyanide solution. The gold nanoparticles loading NH₂–HSM-film-coated glassy carbon electrode (Au–NH₂–HSM/GCE) shows strong catalysis to the oxidation of glucose, and according to the cathodic oxidation peak at about 0.16 V, the catalytic current is about 2.5 μA mM⁻¹. Under optimized conditions, the peak current of the cathodic oxidation peak is linear to the concentration of glucose in the range of 0.2 to 70 mM. The detection limit is estimated to be 0.1 mM. In addition, some electrochemical parameters about glucose oxidation are estimated.     

Properties of cadmium sulphide thin films deposited from a chemical solution

Cadmium sulphide thin films have been deposited chemically at different temperatures from 50 °C to 100 °C. The composition of the solution was [CdCl₂] = 0.01 M, [Thiourea] = 0.17 M, [NH₄Cl] = 0.036 M and [NH₃] = 0.36 M. Structural, electrical and optical properties were investigated as a function of deposition parameters. The films showed strongly oriented structures and were highly transmitting in the infrared region. Their absorption coefficient was in the range 10⁴ to 10⁵ cm⁻¹ in the visible region. The direct forbidden band had an energy gap of 2.48 eV and the refractive index for high wavelengths was equal to 2.116. The dark resistivities of as-deposited films thicker than 0.5 μm had values from 10³ to 10⁵ Ωcm. These resistivities decreased to about 10 Ωcm after annealing in vaccum or in argon atmosphere at 200 °C for one hour.     

An XPS depth-profile study on electrochemically deposited TaO x

Through the use of XPS and controlled Ar⁺ etching, the surface composition and oxide species of tantalum oxides (TaO _x ), which were electrodeposited on glassy carbon electrodes by cyclic voltammetric and constant-potential electrolyses, are quantified along the depth profile. Electrodeposition exhibits efficacy in depositing TaO _x with a distribution of various TaO _x : TaO, TaO₂, and Ta₂O₅. The distribution gradient from the outer surface of TaO _x is such that Ta₂O₅?>?TaO₂?>?TaO. TaO is found to be the dominant species in the underlying layer of TaO _x . Such a unique structure of the electrode surface is analogous to that of nanoparticles with a core–shell structure, with the core being suboxides and the surface being that of the saturated pentoxide, Ta₂O₅. The electrochemically induced nonhydrolytic condensation route is proposed to be capable of producing TaO _x with a distribution gradient of Ta₂O₅, TaO₂, and TaO in the depth direction.     

Anionic responses of electrochemically synthesized polypyrrole films

Conducting polypyrrole films with thickness of about 8 mum were prepared on platinum by continuous scanning in 0.1M pyrrole and 0.1M electrolyte (LiCl, LiBF(4) or NaBF(4)). Scan-rates of 10, 20 and 50 mV/sec with scan-times of 30, 45 and 60 min were used. The potentiometric response of the films was tested over a range of anions. Films were found to be anion-sensitive but very non-selective. The influence of the doping cation was also investigated.     

High catalytic activity of nanostructured Pd thin films electrochemically deposited on polycrystalline Pt and Au substrates towards electro-oxidation of methanol

Nanostructured Pd thin films are directly formed on polycrystalline Pt and Au substrates in the absence of hard and soft templates by using a cyclic potential sweep technique, which is confirmed by both SEM observation and their unusual cyclic voltammetric characteristics in H₂SO₄ solution. Interestingly, the bimetallic electrodes obtained after the deposition of ultrathin Pd films onto Pt and Au substrates display much higher catalytic activity towards the electro-oxidation of methanol than the bulk Pt electrode. Besides, it is found that the foreign metal substrate has great influence on the electro-catalytic behavior of the Pd films.     

Specific orientation of electrochemically deposited PbO2 crystals

Lead dioxide anodes were prepared by electrodeposition of Pb²⁺ on titanium in acidic Pb(NO₃)₂ solutions at 30, 50, 70, 90 and 130°C. The electrodes plated at higher temperatures revealed a progressive increase in the content of β-PbO₂ relative to α-PbO₂. The individual crystals were larger and a higher $\text{O}{}_2\text{O}{}_3$ overpotential was observed during the electrolysis of water on such anodes in 0.5 M HClO₄. At higher temperatures the 110 orientation parallel to the geometrical plane of the electrode predominates for the crystallographic planes. An opposite trend can be established for the crystallographic planes 200 and 101.     

Structural investigation of electrochemically synthesized ZnCuTe thin films

pZnCuTe thin films were prepared by electrochemical synthesis in aqueous solution. Cyclic voltammetric analysis allowed us to single out the potential region where deposition of the species occurs. Upon annealing at 400 °C, formation of cubic ZnCuTe was confirmed by X-ray diffraction. The patterns were modelled using a MarqX algorithm which allows direct refinement of lattice parameters over the entire pattern instead of single-peak profile analysis. Electronic Publication     

Chemical composition,structure, and properties of electrochemically deposited cobalt-boron coatings

Polycrystalline and amorphous cobalt-boron coatings were electrochemically deposited. The effect of the boron content and heating temperature on the physicomechanical properties of the coatings was studied. A relationship between the composition, structure, and properties of the coatings was established.     

Palladium nanoparticles and nanowires deposited electrochemically: AFM and electrochemical characterization

Palladium nanoparticles and nanowires electrochemically deposited onto a carbon surface were studied using cyclic voltammetry, impedance spectroscopy and atomic force microscopy. The ex situ and in situ atomic force microscopy (AFM) topographic images showed that nanoparticles and nanowires of palladium were preferentially electrodeposited to surface defects on the highly oriented pyrolytic graphite surface and enabled the determination of the Pd nanostructure dimensions on the order of 50–150 nm. The palladium nanoparticles and nanowires electrochemically deposited onto a glassy carbon surface behave differently with respect to the pH of the electrolyte buffer solution. In acid or mild acid solutions under applied negative potential, hydrogen can be adsorbed/absorbed onto/into the palladium lattice. By controlling the applied negative potential, different quantities of hydrogen can be incorporated, and this process was followed, analysing the oxidation peak of hydrogen. It is also shown that the growth of the Pd oxide layer begins at negative potentials with the formation of a pre-monolayer oxide film, at a potential well before the hydrogen evolution region. At positive potentials, Pd(0) nanoparticles undergo oxidation, and the formation of a mixed oxide layer was observed, which can act as nucleation points for Pd metal growth, increasing the metal electrode surface coverage. Depending on thickness and composition, this oxide layer can be reversibly reduced. AFM images confirmed that the PdO and PdO₂ oxides formed on the surface may act as nucleation points for Pd metal growth, increasing the metal electrode surface coverage. Dedicated to Professor Dr. Algirdas Vaskelis on the occasion of his 70th birthday.     

Epifluorescence imaging of electrochemically switchable Langmuir-Blodgett films of Nafion

A combination of electrochemistry and luminescence methods was exploited to obtain information on the electrochemical activity and homogeneity of Nafion Langmuir-Blodgett films. The redox behavior of the Ru(bpy)3(2+) probe incorporated in the Nafion film was monitored by epifluorescence microscopy. The photoluminescent images, recorded by a charge-coupled device (CCD) camera, reflect the distribution of the probe in the film, which resulted as very uniform, particularly in comparison with spin-coated films. Apparent diffusion coefficients (Dapp) determined by cyclic voltammetry for films of less than 10 layers are in the range of 1 x 10(-12) to 8 x 10(-12) cm(2) s(-1), that is, 2 orders of magnitude lower than values reported in the literature for spin-coated Nafion films. The application to the electrode of a potential able to oxidize the luminescent Ru(bpy)3(2+) to the nonluminescent Ru(bpy)3(3+) switched off the photoluminescence with a response time that for the LB films was much shorter than that for the spin-coated ones. Experimental evidence and calculations indicate that lowering of the film thickness down to the nanometric level is very effective in shortening the switching time, notwithstanding the lowering of the Dapp value in LB films.     

Disruption processes in films grown and reduced electrochemically on metals

New aspects characterizing the disruption process are discussed, based on an analysis of a proposed disruption model and on a review of previously reported voltammetric and galvanostatic anodic growths of films on metals and their consequent reduction. For voltammetric cases of Pb and Zn, it is shown that the formation charge is not always recoverable, leading to irreversible processes. The total formation charge of Zn can never be totally recovered, but that of Pb is totally recoverable if the reduction rate trends to zero, rendering the process reversible. Furthermore, disruption always causes part of the film to remain adhered to the metal, which is why it is only partially disrupted. Increasing the reduction rate causes the disruption process to increase and the remaining film adhered to the metal to trend toward a minimum constant value, which differs in Pb and Zn but is equal in voltammetric and galvanostatic experiments with Pb. The conclusions are the same with regard to the galvanostatic results for Pb, except that the film charge density is always totally reversibly recovered if the reduction rate is lower than the formation rate. Moreover, the reduction rate does not necessarily have to trend to zero in this case. It needs only to be lower than or equal to the formation rate. All these facts are discussed based on the disruption model. The paper also discusses in detail how to experimentally obtain highly reproducible measurements, which are fundamental for the conclusion’s validity. These experimental discussions and propositions are also based on the disruption model. High reproducibility is achieved even in the case of Pb, a metal whose reproducibility is notoriously difficult. This paper is dedicated to Professor Francisco Carlos Nart, in memoriam.