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

Effect of temperature on the electrical conductance of hydrogen chloride in dimethylsulphoxide

The electrical conductance of solutions of hydrogen chloride in dimethylsulphoxide at temperature from 25 to 45°C has been studied. Results have been interpreted with the Fouss theory for associated 1-1 type electrolytes. Values of the association constant KA and the J parameter have been computed at each temperature. The temperature dependence of the molar conductance is inferred from the theoretical equation and related to the temperature dependence of viscosity.La conductance électrique des solutions de chlorure d'hydrogène dans le diméthylsulfoxyde à des températures de 25 a 45°C a été étudiée. Les résultats ont et́é inteprétés par la théorie de Fuoss pour de electrolytes associées du type 1-1. Les valeurs de la constante d'association KA et du paramètre J ont été calculées à chaque température. La dépendance de la conductivité molare avec la température est déduite de l'équation théorique et référée a la dépendance de la viscosité avec la température.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Electrical conductance of hydrogen chloride in dimethylsulphoxide at 25°C

The electrical conductance of hydrogen chloride solutions in DMSO at 25°C has been studied. The limiting molar conductance is 38·7 int mho cm2 int mho cm2/mol. Conductivity data were interpreted with the Fuoss' theory for associated 1-1 type electrolytes. The association constant related to pair formation is 115·7 l/mol. The mechanism of electricl conduction of HCl in DMSO at infinite dilution resembles that of other 1-1 type electrolytes in the same solvent, in which charges are transported by simple entities in a viscous continuum.On a étudié la conductivité électrique des solutions de chlorure d'hydrogéne dans le DMSO à 25°C. La conductivité limite molare est de 38,7 mho int cm2/mol. Les données expŕimentalles de la conductivité furent interprétées d'aprés la théorie de Fuoss pour des électrolytes associé du type 1-1. La constante d'association liée à la formation de paires ioniques simple est 115,7 l/mol. Le mechanisme de la conduction électrique du HCl dans le DMSO à dilution infinie ressemble celui des autres électrolytes du type 1-1 dans le même dissulvant, puisque les charges sont transportées par des entités simples dans un milieu visqueux continu.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

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 and mechanism of the electrochemical oxidation of nitrite ion dissolved as sodium nitrite in dimethylsulphoxide solutions on platinum electrodes

The kinetics of the electrochemical oxidation of NO2− ion dissolved in DMSO has been studied on Pt electrodes at temperature ranging from 25 to 44°C, by means of potentiostatic E/I curves and by relaxation techniques. The oxidation reaction is explained in terms of a consecutive reaction scheme which involves, as rate-determining step, nitrite-ion discharge on an adsorbed intermediate at the reaction interface, the latter apparently obeying a Langmuir isotherm.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

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

Fractal surfaces of gold and platinum electrodeposits. Dimensionality determination by scanning tunneling microscopy

The structure of gold and platinum deposits grown on gold and platinum wire cathodes, respectively, by electroreduction of the corresponding oxide layers has been analyzed in terms of surface fractals by measuring the perimeter L and area A of intergranular voids. Perimeter and area were determined from scanning tunneling microscopy (STM) topographic images of the deposit surfaces. Fractal behavior, L ∞ AD'/2 with D'= 1.5 ± 0.1, is found for both platinum and gold deposits. From these measurements, the fractal dimension of the surfaces was 2.5. The D' value of the gold deposits decreases by aging in the electrolyte at 325 K as a consequence of surface diffusion processes.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Fractal surfaces of gold and platinum electrodeposits. Dimensionality determination by scanning tunneling microscopy

The structure of gold and platinum deposits grown on gold and platinum wire cathodes, respectively, by electroreduction of the corresponding oxide layers has been analyzed in terms of surface fractals by measuring the perimeter L and area A of intergranular voids. Perimeter and area were determined from scanning tunneling microscopy (STM) topographic images of the deposit surfaces. Fractal behavior, L ∞ AD'/2 with D'= 1.5 ± 0.1, is found for both platinum and gold deposits. From these measurements, the fractal dimension of the surfaces was 2.5. The D' value of the gold deposits decreases by aging in the electrolyte at 325 K as a consequence of surface diffusion processes.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Scanning tunneling microscopy of amorphous alloy electrocatalysts for water electrolysis

The surface topography of amorphous metals useful as electrocatalysts in water electrolysis, denoted as G16 (Cos50Ni25Si15Bu10) and G14 (Fe60Co20Si10B10), are studied at the gm scale with a conventional SEM, and at the nm scale with the STM. Both untreated specimens as well as those employed as electrodes for a relatively prolonged time exhibit the same microstructure with amorphous and crystalline surface regions. The microcrystallite reduced size structure, probably involving a very compact structure, appears to be of the greatest importance concerning the electrocatalytic activity of these materials.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

The evaluation of surface diffusion coefficients of gold and platinum atoms at electrochemical interfaces from combined STM-SEM imaging and electrochemical techniques

A simple method is presented for measuring the surface diffusion coefficients of Au and Pt atoms at electrodispersed electrodes of the same metals in contact with 0.5M H2SO4. The technique is based upon the time dependence of the surface roughness factor of electrodispersed metal overlayers. The method requires a model for the surface roughness of the metal structure. The model is deduced from microscopic measurements by a STM integrated into a conventional SEM microscope. This allows the relationship between the roughness factor and the area of the surface structure to be obtained. For Au and Pt in contact with an electrolyte solution, the values of our diffusion coefficients are higher than those reported in vacuum at the same temperature.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta