P. Herrasti

Polypyrrole layers for steel protection

Abstract This report describes the behaviour of polypyrrole and polypyrrole/carboximethylcellulose (Ppy/CMC) prepared by different methods in order to prevent the corrosion of steel. Potentiodynamic polarization curves and open circuit potential were used to evaluate the capacity of these materials to protect the surface. The results obtained allowed to assume that Ppy/CMC is better material to prevent corrosion than polypyrrole (Ppy) and potentiostatic method better than galvanostatic to obtain the deposit.

Self-affine fractal vapour-deposited gold surfaces characterization by scanning tunnelling microscopy

The morphological evolution of the surfaces of gold deposits grown from the vapour on smooth glass under nonequilibrium conditions and incident angle near substrate normal is studied at the nanometer level by scanning tunnelling microscopy. For an average film thickness equal to or greater than 500 nm, the interface thickness (ξ) reaches a steady state. Under these conditions, ξ depends on the scan length (L) as ξ ∝ Lα with α = 0.35 ± 0.05 for L > ds, where ds is the columnar size, and α = 0.89 ± 0.05 for L ds agrees with the prediction of ballistic deposition models without restructuring, whereas that for L < ds exceeds the prediction of ballistic models including restructuring.

Electroactive polymer films for stainless steel corrosion protection

Electroactive polymer films of polyaniline, poly-o-toluidine and a composite of both were deposited on stainless steel and their performance as protective coatings against corrosion was evaluated. Open circuit potential and potentiodynamic studies of the polymer-coated stainless steel in a corrosive medium showed a significant shift in the corrosion potential towards more positive values. Mechanical characteristics of the films were evaluated by means of microhardness measurements, revealing nonelastic films in all cases and low hardness values that increased from polyaniline to poly-o-toluidine to the composite. The best results were obtained in the case of the polyaniline-o-toluidine composite.

Synthesis and characterization of CoFe2O4 ferrite nanoparticles obtained by an electrochemical method

Uniform size cobalt ferrite nanoparticles have been synthesized in one step using an electrochemical technique. Synthesis parameters such as the current density, temperature and stirring were optimized to produce pure cobalt ferrite. The nanoparticles have been investigated by means of magnetic measurements, Mössbauer spectroscopy, x-ray powder diffraction and transmission electron microscopy. The average size of the electrosynthesized samples was controlled by the synthesis parameters and this showed a rather narrow size distribution. The x-ray analysis shows that the CoFe(2)O(4) obtained presents a totally inverse spinel structure. The magnetic properties of the stoichiometric nanoparticles show ferromagnetic behavior at room temperature with a coercivity up to 6386 Oe and a saturation magnetization of 85 emu g(-1).

Scale-dependent roughening kinetics in vapor deposited gold

Abstract The roughening kinetics of gold deposits grown from vapor was studied by scanning tunneling microscopy. The dynamic scaling yielded the following growth exponents α(I)=0.90±0.06 and β(I)=0.25±0.06 for Ls ds, where Ls is the scan length and ds is the average diameter of columns. The scaling properties of the domain-dependent-surface roughness exponents allowed us to give the rationale for experimental data on the fractal behavior of thin metal films.

A comparative study of electrodeposited and vapour deposited gold films: Fractal surface characterization through scanning tunnelling microscopy

Abstract The surfaces of Au deposits grown under non-equilibrium conditions from either the electroreduction of Au oxide or from the vapour have been analysed as fractals by measuring the perimeter (P) and the area (A) of intergranular voids. The values of P and A were determined from scanning tunnelling microscopy (STM) topographic imaging of the deposit surfaces. A fractal behaviour P ∝ A D 2 was found with D = 1.5 ± 0.1 and D = 1.7 ± 0.1 for the electrodeposited and vapour deposited Au films, respectively. These figures remain constant for film thicknesses between 100 and 1000 nm. The value of Ds, the fractal dimension of the surfaces, is 2.5 ± 0.1 for the Au electrodeposits, and 2.7 ± 0.1 for the Au vapour deposited films. The former value is consistent with either a diffusion or an electric field controlled growth model, whereas the latter is in agreement with a ballistic growth model.

Determination of the flat band potential for In2S3/electrolyte interfaces

Abstract Flat band potentials ( V fb ) of In 2 S 3 polycrystalline thin films obtained by chalcogenization of electroplated metallic indium films on Ti substrates with a flowing stream of H 2 S gas have been obtained. The variation of this potential with different redox couples, solution concentration and pH values has been studied. Photoelectrochemical characterization of the electrodes was accomplished in aqueous polysulphide solutions and the application of the Gartner—Butler model to the semiconductor/electrolyte interface makes it possible to obtain the semiconductor energy gap. The value obtained is 2.06 eV, corresponding to a direct allowed transition.

Voltammetric study of the electrodeposition of CdS films from propylene carbonate solutions

Abstract The mechanism of electrodeposition of CdS on Pt and Au electrodes has been studied in proplyene carbonate solutions by performing cyclic voltammetry at stationary electrodes in solutions containing both Cd(II) ions and elemental sulphur. The formation of an initial layer of CdS by underpotential deposits of Cd reacting with chemisorbed sulphur is suggested. The growth of the films takes place afterward by reduction of sulphur to sulphide, which forms the deposit with Cd(II) from the solution.

Structural configurations of thin dried polyaniline films on gold(111) from scanning tunneling microscopy

Abstract The early stages of growth of polyaniline films electrodeposited on Au were studied by conventional electrochemical techniques, X-ray diffraction and ex situ scanning tunneling microscopy (STM). From high resolution STM imaging it appears that the first step of polyaniline formation involves the adsorption of aniline monomers on Au(111) terraces leading to domains with hexagonal arrays involving a phenyl-phenyl distance in the range 0.70 nm ⩽ d ⩽ 1.0 nm. The second step corresponds to the initiation of the polymer growth yielding typically 10 × 10 nm 2 crystalline domains consisting of either 0.45 × 0.6 nm 2 rectangular arrays or 0.75 × 0.45 nm 2 arrays forming 120 ° angles. The crystalline domains coexist with highly disordered polymer domains. At advanced stages of growth, the formation of polymer fibers 2 nm in average width takes place leading to a full substrate coverage by a polymer deposit with an irregular surface.

STM study of fractal scaling in evaporated gold films

Fractal characterization of vacuum-evaporated gold films on glass substrates with thicknesses (h) comprised between 30 and 850 nm is made from STM data by using the dynamic scaling approach for surface growth. The rms roughness (ξ) and the scan length (L) obey a ξ versus L α relationship with a depending on h. For h≥500 nm and L>d s , the average column diameter, α≃1/3 in agreement with the predictions of ballistic deposition models without restructuring. For L<D s , α≃0.9 approaching a euclidean value. The STM method is verified through its application to several computer-generated surfaces, leading to a good agreement with the theoretical values