Experimental evidence on the development of scale invariance in the internal structure of self-affine aggregates

It is shown that an alternative approach for the characterization of growing branched patterns consists of the statistical analysis of frozen structures, which cannot be modified by further growth, that arise due to competitive processes among neighbor growing structures. Scaling relationships applied to these structures provide a method to evaluate relevant exponents and to characterize growing systems into universality classes. The analysis is applied to quasi-two-dimensional electrochemically formed silver branched patterns showing that the size distribution of frozen structures exhibits scale invariance. The measured exponents, within the error bars, remind us those predicted by the Kardar-Parisi-Zhang equation.Comment: 11 pages, 4 figure

Roughening kinetics of chemical vapor deposited copper films on Si(100)

3 pages, 3 figures.The roughening kinetics of copper films synthesized by low pressure chemical vapor deposition (LPCVD) on Si(100) substrates was investigated by scanning tunneling microscopy (STM). By applying the dynamic scaling theory to the STM images, a steady growth roughness exponent (alfa)=0.81 ± 0.05 and a dynamic growth roughness exponent (beta)=0.62 ± 0.09 were determined. The value of (alfa) is consistent with growth model predictions incorporating surface diffusion. The value of (beta), while higher than expected from these models, can be related to LPCVD processing conditions favoring growth instabilities.This work was partially supported by the CSICCONICET cooperation program and by a grant from the NASA New Jersey Space Grant Consortium.Peer reviewe

Kinetics of the cathodic discharge of ammonium ion dissolved in dimethylsulfoxide on platinum

The cathodic discharge of ammonium ion dissolved in DMSO solution on platinum electrodes in the temperature range from 25 to 44 °C yields ammonia and hydrogen at the ratio 2 : 1. The kinetics of the reaction was studied both under stationary and non-stationary conditions and reveals an influence of the treatment of the electrode surface. The kinetic parameters were interpreted with a reaction mechanism involving the participation of adsorption competition between either solvent or impurity molecules and hydrogen atoms, assuming the recombination of these adatoms is rate determining.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Kinetics and mechanisms of electrochemical reactions on platinum with solutions of iodine-sodium iodide in acetonitrile

The kinetics of the iodine-tri-iodide-iodide electrode in acetonitrile has been investigated in the temperature range from 0 to 30°C. Current/voltage curves were determined using a platinum rotating disk electrode working at 200 to 3000 rpm. The anodic and cathodic current/voltage curves are characterized by two well defined waves. The total reactions related to the first and second anodic waves are respectively 3I− = I3− + 2 e and 2I3− = 3I2 + 2 e, while the reverse reactions represent the second and first cathodic waves respectively. The diffusion coefficients of the diffusing species have been evaluated. Current/voltage curves in the region preceding the limiting cd exhibit a measurable irreversibility. The kinetic parameters related to the activated process were determined, and the kinetics of the reactions interpreted in terms of reaction mechanisms that involve an ion plus atom reaction as rate determining step for the anodic process and the reverse reaction for the cathodic process.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Kinetics and mechanisms of electrochemical reactions on platinum with solutions of iodine-sodium-iodide in dimethylsulphoxide

The kinetics and mechanisms of the iodine and tri-iodide ion reduction and iodide and tri-iodide ion oxidation on platinum have been determined, from a study of the electrochemical kinetic behaviour of DMSO solutions containing an iodine/sodium-iodide ratio greater than one. The likely mechanisms are the same as those recently discussed for the iodine—sodium-iodide solutions in acetonitrile, and all comprise consecutive reaction schemes involving, for the processes in the anodic direction, an ion-plus-atom reaction as rate-determining step, and the reverse reaction for the cathodic processes.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Chronopotentiometry of solutions containing sodium iodide and iodine in dimethylsulphoxide

Chronopotentiometric waves of solutions of sodium iodide, and sodium iodide with added iodine in dimethylsulphoxide, were determined on platinum electrodes. Sodium perchlorate was used as supporting electrolyte. The concentration range was from 2 × 10−3 to 4 × 10−2 M and the temperature from 25·0 to 45·0°C. The anodic waves exhibit two well-defined steps characterized by definite transition times, while only one step is observed for the cathodic waves given by the solutions with added iodine. The cathodic waves are irreversible. The first anodic wave shows a larger irreversibility than the second. The results are discussed in comparison with previous information gathered for the same systems by employing a platinum rotating disk electrode. Diffusion coefficients for tri-iodide and iodide ions in solutions of DMSO obtained from chronopotentiometry are in agreement with those earlier reported derived from the rotating disk electrode.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Kinetics and mechanisms of electrochemical reactions on platinum with solutions of iodine-sodium iodide in acetonitrile

The kinetics of the iodine-tri-iodide-iodide electrode in acetonitrile has been investigated in the temperature range from 0 to 30°C. Current/voltage curves were determined using a platinum rotating disk electrode working at 200 to 3000 rpm. The anodic and cathodic current/voltage curves are characterized by two well defined waves. The total reactions related to the first and second anodic waves are respectively 3I− = I3− + 2 e and 2I3− = 3I2 + 2 e, while the reverse reactions represent the second and first cathodic waves respectively. The diffusion coefficients of the diffusing species have been evaluated. Current/voltage curves in the region preceding the limiting cd exhibit a measurable irreversibility. The kinetic parameters related to the activated process were determined, and the kinetics of the reactions interpreted in terms of reaction mechanisms that involve an ion plus atom reaction as rate determining step for the anodic process and the reverse reaction for the cathodic process.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

The electrochemical kinetic behaviour of nickel in acid aqueous solutions containing chloride and perchlorate ions

The electrochemical behaviour of polycrystalline nickel in acid solutions containing large excess either of NaCl or NaClO4 has been investigated, at potentials either more positive or negative than the rest potential of the metal. The electrode reactions were studied over a wide range of experimental conditions (pH, nickelous ion activity, temperature), and the influence of each variable on the experimental kinetic parameters has been determinedInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Effect of heat treatment on the periodic current oscillation of polycrystalline zinc in alkaline solution

The phenomenology of the periodic oscillations of the faradaic current of zinc electrodes in alkaline solutions offers the possibility of investigating the influence of the non-uniformity of the polycrystalline metal surface on the periodic effect because the grain size of zinc can be easily controlled by the annealing temperature and time. Zinc rods (0.6 cm dia., Leico 99.999% purity) were annealed at 390°C during a period of between 2 and 6 h and cooled down for about 18 h. Each annealed rod was axially embedded in a PTFE rod to make a still zinc disc working electrode in contact with 1.5 M NaOH at 25°C. Other experimental details are as described in a previous publication. The morphology of the attack of the different electrode surfaces is shown in Fig. 1. From these pictures the surface density of grains at the electrode was calculated.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Current oscillations in austenitic stainless steel induced by the presence of chloride ions

The conditions for current oscillations in austenitic stainless steel (AISI Type 303) in 1M H2SO4, containing CI- ions are given. The periodic oscillations are produced in a close potential range determined at the active-passive transition region. It requires a non-homogeneous distribution of inclusions and carbides at the metal surface and a concentration range of CI- ion where active and passive areas coexist on the metal surface. The constraints at the surface determining these two regions are related to the CI- ion competitive adsorption and the local accumulation of corrosion products. Electrochemical data and SEM observations are correlated.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada