p-Type behaviour of electrodeposited ZnO:Cu films

Cu-doped ZnO (ZnO:Cu) thin films and ZnO/ZnO:Cu homojunction devices were electrodeposited on conductive glass substrates in a non-aqueous electrolyte containing Cu and Zn salts. The Cu content of the films is proportional to the Cu/Zn precursor ratio in the deposition electrolyte. ZnO:Cu was found to be of a hexagonal wurtzite structure with (002) preferred orientation. A transition from n-type to p-type was observed for ZnO:Cu films with a Cu/Zn ratio higher than 2% as inferred from the change in the direction of the photocurrent. The rectifying characteristics shown by homojunction devices further confirm the p-type conductivity of ZnO:Cu layers.     

Photopatterned nanoporosity in polyelectrolyte multilayer films

We report on spatial control of nanoporosity in polyelectrolyte multilayer (PEM) films using photopatterning and its effects on film optical and adsorption properties. Multilayers assembled from poly(acrylic acid-ran-vinylbenzyl acrylate) (PAArVBA), a photo-cross-linking polymer, and poly(allylamine hydrochloric acid) (PAH) were patterned using ultraviolet light followed by immersion in low pH and then neutral pH solutions to induce nanoporosity in unexposed regions. Model charged small molecules rhodamine B, fluorescein, and propidium iodide and the model protein albumin exhibit increased adsorption to nanoporous regions of patterned PEM films as shown by fluorescence microscopy and radiolabeling experiments. Films assembled with alternating stacks of PAH/poly(sodium-4-styrene sulfonate) (SPS), which do not become nanoporous, and stacks of PAH/PAArVBA were patterned to create nanoporous capillary channels. Interdigitated channels demonstrated simultaneous, separate wicking of dimethyl sulfoxide-solvated fluorescein and rhodamine B. In addition, these heterostack structures exhibited patternable Bragg reflectivity of greater than 25% due to refractive index differences between the nanoporous and nonporous stacks. Finally, the PEM assembly process coupled with photo-cross-linking was used to create films with two separate stacked reflective patterns with a doubling in reflectivity where patterns overlapped. The combined adsorptive and reflective properties of these films hold promise for applications in diagnostic arrays and therapeutics delivery.     

ZnO thin films electrodeposited in propylene carbonate under a magnetic field

Electrochemical processing of ZnO films on fluorine-doped indium tin oxide (FTO/ITO) substrate was investigated in organic propylene carbonate electrolyte solutions containing Zn(NO₃)₂·6H₂O. Much finer and more uniform morphologies of the ZnO films were obtained in comparison with those in aqueous electrolyte solutions. The effects of superimposing a magnetic field to the ZnO films were further examined. Superimposing a magnetic field considerably influenced the transient current density in the initial stage, especially in the mass transfer controlled region at −1.5 V vs Zn wire reference electrode. It also introduced substantially no drastic influence on the microstructure in spite of the appearance of considerably significant morphological variations. Contribution to special issue on Magnetic field effects in Electrochemistry.     

Dependence of the photoelectrochemical performance of sensitised ZnO on the crystalline orientation in electrodeposited ZnO thin films

The influence of the crystal orientation in porous crystalline films of ZnO electrodeposited on the photoelectrochemical characteristics of the films is studied. For differently oriented ZnO thin films following removal of the respective structure-directing agent (SDA) and adsorption of a sensitiser, time-resolved photocurrent measurements, intensity modulated photocurrent spectroscopy (IMPS), intensity modulated photovoltage spectroscopy (IMVS) and current-voltage curves were measured in acetonitrile-based electrolytes containing I(3)(-)/I(-) as the redox electrolyte. The crystal orientation has a significant influence on the charge transport across such films and hence is reflected in the observed electrode kinetics. Films originally grown in the presence of, e.g., Coumarin 343 as a SDA, showed a significantly faster response to illumination. Increased electron diffusion coefficients and diffusion lengths were calculated from the results of IMPS and IMVS, caused by a faster electron movement in the films. Implications of these findings on further improvements of sensitised ZnO films prepared by electrochemical deposition are discussed.     

Improved photoelectrochemical performance of electrodeposited ZnO/EosinY hybrid thin films by dye re-adsorption

Dye desorption and re-adsorption post treatments on electrochemically self-assembled nanoporous ZnO/eosinY hybrid thin films lead to a large improvement of the dye-sensitized photoelectrochemical performance, achieving an incident photon to current conversion efficiency up to 90%.     

Characterization of electrodeposited uranium films

Films containing uranium obtained by electrodeposition and used in alpha spectroscopic analysis were characterized by absorption spectroscopy, Raman spectroscopy, X-ray diffraction analysis and thermoanalysis. The electrodeposition method produced thin, adherent films with a yield near 100%. The analysis indicated that these films contained uranyl groups isolated or attached to other uranyl groups by oxygen bridges. Hydration water, hydroxyl groups linked by hydrogen bonds and ammonium radicals were also present. According to the X-ray diffraction analysis the films showed low crystallinity, characteristic to electrodeposited materials. The results of the thermogravimetric and differential thermal analysis did not correspond to any known pattern. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular orientation in electrodeposited polypyrrole films

The molecular arrangement in electrodeposited polypyrrole films was studied by means of linear dichroism in the near-edge X-ray absorption fine structure (NEXAFS) spectra measured at the K absorption edges of carbon and nitrogen. It has been found that the change of the exciting radiation incidence from normal to grazing leads to an increase in the intensity of π*-related resonances with simultaneous decrease in the intensity of σ*-related resonances in the spectra. Similar changes in the spectra measured for both absorption edges indicate a pronounced conjugation of π-bonds in the polypyrrole chains in the grown films. Preferential in-plane orientation of pyrrole rings relative to the substrate surface is observed for all the deposited films. The linear dichroism is more pronounced at the initial stages of deposition (2D growth) than at later stages characterized by “cauliflower”-like morphology of the grown film.     

Evaluation of N719 amount in TiO2 films for DSSC by thermogravimetric analysis

The aim of this work is to evaluate the amount of N719 dye in TiO₂ films for DSSCs by thermogravimetric analysis coupled with mass spectrometry (TG-MS) in comparison with the traditional method based on the dye extraction in NaOH solutions. The characterization was carried out on TiO₂ films applied on FTO glasses by automatic screen printing method. For all the samples, TG-MS showed three well defined steps. The first, below 100 °C and coupled to an endothermic signal was due to water release. From 200 to about 300 °C, there was the release of CO₂ coming from decarboxylation reaction of N719. The last exothermic step was due to the combustion of organic residues. As the decarboxylation reaction occurs with release of 4 moles of CO₂ per mole of N719, it was used to determine the dye loading of the samples that resulted in the range 7?15 wt% well agreeing the relevant content of dye obtained by desorption with NaOH.     

A study on electrodeposited of ZnO/ZnS heterostructures

ZnO/ZnS heterostructures were synthesized by a two steps electrochemical deposition method. Firstly, ZnS layer was deposited from an aqueous solution containing Na₂S₂O₃ and ZnSO₄ onto indium-doped tin oxide (ITO) coating glass substrate at two deposition potentials. Then, ZnO nanostructures were deposited from an aqueous solution of Zn(NO₃) onto ZnS surface. The as-obtained samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman and UV-visible analysis. The results indicate that the electrodeposition of ZnS layer at ?0.9 V give the best proprieties of ZnO/ZnS heterostructures. Homogeneous and uniform surface of ZnO/ZnS heterostructure was confirmed by AFM images. The XRD patterns indicates a high crystallinity of ZnO/ZnS. A high transmittance of 65% was also noted from UV-Visible spectra and band gap energy as large as 3.6?eV was found.     

Impedance measurements for nickel deposition in sulfate and chloride electrolytes

From the analysis of the impedance of nickel deposition, the electrode kinetics is shown to be dependent on the type of anion. In chloride electrolytes a slow electrode activation with cathodic polarization is predominant. In sulfate solutions a low-frequency capacitive feature, favored by a pH decrease, appears to result from interactions between the nickel and hydrogen discharges. An interpretation is proposed where the ad-ion Ni_ads^I acts as both a reaction intermediate and a catalyst associated with a propagating kink site, and where the adsorbed species H_ads^*, generated by the presence of Ni_ads^I, inhibit the hydrogen evolution. It is concluded that the active area is closely connected to the coverages by adsorbates.     

ZnO nanowire arrays coating on TiO2 nanoparticles as a composite photoanode for a high efficiency DSSC

A novel composite photoanode with ZnO nanowire arrays coating on the top of TiO(2) nanoparticles is fabricated, and an efficiency of 4.52% is achieved for the composite cell, far higher than both 0.90% of the ZnO nanowire cell and 3.56% of the TiO(2) nanoparticle cell. The improved efficiency is resulted from the high surface area of nanoparticles, as well as fast electron transport and light scattering effect of nanowires.     

Conductivity and photoelectric response of electrodeposited thallic oxide films

Highly conductive polycrystalline and amorphous Tl₂O₃ films are prepared by electrodeposition method. The resistivity of the polycrystalline film is lower than that of the amorphous one. A resisitivity of only 3.2×10^-4 Ω cm was obtained for the polycrystalline film. It is found that the electrodeposited Tl₂O₃ films exhibit photoelectric response of n-type semiconductors. This photoelectric response may find use for further application of the Tl₂O₃ films.     

Slope analysis and scaling analysis of electrodeposited thin films

We introduce slope analysis as a straightforward complement to scaling analysis for characterizing the morphology of electrodeposited thin films. The surface slope θ, defined as the angle between the local surface normal and the film normal, is calculated as a function of position for electrodeposited Cu films of increasing thickness t. We show that the mean value of θ increases with t and demonstrate the close relationship between this observation and the increase in local roughness found in previous studies from scaling analysis.     

Impedance measurements for determination of pore texture of a carbon membrane

The pore texture of a carbon membrane was determined by impedance measurements carried out over a wide frequency range. The impedance obtained could be characterised by a resistance Ω and a double layer capacitance Cn. Ω is the third of electrolyte resistance in pores and Cn is the double layer capacitance corresponding to the developed pore surface. Membrane samples of different length but with the same thickness were studied. As expected, it was shown that the Cn value is proportional to the weight of the membrane whereas the Ω value is inversely proportional. Cn value allowed us to evaluate the specific area of the porous membrane from the value of the double layer capacitance per unit area determined for a plain carbon electrode. Moreover, impedance diagrams obtained were found to be very similar to those of cylindrical pore even though the pore texture is very intricate. Thus, impedance measurements can be applied to porous electrodes of more intricate pore texture and evaluate the radius, depth and pore number of its equivalent cylindrical pore electrode.     

Secondary ion mass spectrometry and alpha-spectrometry of electrodeposited thorium films

The main aim of this work was the preparation of samples with thorium content on the steel discs by electrodeposition for determination of natural thorium isotope by alpha spectrometry and secondary ion mass spectrometry and finding out their possible linear correlation between these methods. The analysis of the composition of surface was other aim of study. Discs were measured by alpha spectrometer. After that, alpha spectrometry discs were analyzed by TOF-SIMS IV, which is installed in the International Laser Centre in Bratislava. The integral and normalized intensities of isotope of ²³²Th and intensities of ions of ThO⁺, ThOH⁺, ThO₂H⁺, Th₂O₄H⁺, ThO₂ ^?, ThO₃H^?, ThH₃O₃ ^? a ThN₂O₅H^? were measured. The linear correlation is between surface’s weights of Th and intensities of ions of Th⁺ from identified in SIMS spectra. We found out the chemical binding between thorium and oxygen and hydrogen on the surface of samples by SIMS method. Obtained intensities of ions ²³²ThO⁺, ²³²ThOH⁺, ²³²ThO₂H⁺ prove the presence of oxidized forms of thorium in the upper layers of surface. The oxidized ions predominate in univalent form of thorium up to deep about 3,000 nm.     

The formation and reduction of anodic films on electrodeposited ruthenium

The formation and reduction of anodic films on bright ruthenium was investigated using substrates prepared by electrodeposition onto gold-plated platinum from a commercial ruthenium bath operated at 70°C. Anodic films formed on the ruthenium may be reduced by maintaining the electrode at potentials below 0.2 V. The reduction behaviour was markedly affected by the anodization potential and, at short times, by the period of anodization. The bell-shaped cathodic current-time curves observed with films produced at potentials in the region of 1.2 V, suggest that the process in this case involves nucleation of reduction centres on a relatively stable surface layer. The influence of potential, time, and both the concentration and nature of the electrolyte on the extent of anodic film formation was investigated. The results are discussed in terms of the formation of stable phase oxides in the relatively thick anodic film produced on the ruthenium surface.     

EXAFS structural studies of electrodeposited Co and Ni hexacyanoferrate films

XAS (EXAFS and XANES), XPS and IR spectroscopies were used to extract redox compositional and structural information on films of electrodeposited Co and Ni hexacyanoferrates whose redox state was manipulated electrochemically. The X-ray methods provided direct information on the metal species and IR provided indirect information via the behaviour of the ligand vibration. XPS responses showed that the electrochemical response of Co hexacyanoferrate is attributable to Co (except for a small amount of Fe^II oxidation at very positive potentials), and of Ni hexacyanoferrate to Fe; XANES edge shifts confirm these deductions. Local structure around the metal atoms was extracted from EXAFS data in terms of M′–N, M′–C and M′–Fe (M′ = Co or Ni) distances and the associated Debye-Waller factors as functions of film charge state. For Co hexacyanoferrate, the redox variation of static disorder was consistent with a molecular model involving discrete Co^II and Co^III sites, whose populations respond to potential, but not with a solid-state model.