Verlag des Forschungszentrums Jülich
JUEL-3861
Different possible mass transport mechanisms and the characteristic time dependence of the time correlation function are briefly presented. The mobility at the electrode surface increases with temperature and may depend on the applied electrode potential in a liquid environment.
An activation energy for the underlying dominant mass transport may be deduced from an Arrhenius plot of the increase of the time correlation function, i.e. the increase of the mobility of atoms on the surface. Given a strong monotonous potential dependence of the step fluctuations, an activation energy for the dominant mass transport may be obtained from a potential dependent analysis of the time correlation functions at a given temperature.
Measurements performed on Ag(111) in sulfuric acid yield a dominant diffusion mechanism, which is mediated by an exchange of silver atoms with the electrolytic double layer at positive potentials with respect to the saturated calomel electrode. With increasing electrode potential an enhanced mobility of atoms manifests itself in a stronger step frizziness of the monoatomic steps. From a temperature dependent analysis of the step frizziness an activation energy is obtained. This value is comparable to a result obtained from a potential dependent analysis of the increase of the time correlation function at increasingly positive potentials.
In contrast to Ag(111), equilibrium step fluctuations on an unreconstructed vicinal Cu(111) electrode in diluted hydrochloric acid are independent of the electrode potential in a wide potential range. An increasing electrode potential leads eventually to the formation of an Quadratwurzel 3 x Quadratwurzel 3- reconstruction of the surface. From the time dependence of the fluctuations a terrace limited diffusion mechanism could be deduced. This special kind of diffusion mechanism was observed experimentally for the first time within the framework of the presented thesis. Using temperature variable measurements the activation energy for the diffusion mechanism was measured and yield slightly lower value than comparable studies perfomed under ultrahigh vacuum conditions.
Baier, Axel Sascha
Potential- und temperaturvariable Experimente zur atomaren Bewegung auf Ag- und Cu-Elektroden in wässrigen Elektrolyten
VI, 104 S., 2001
This thesis deals with the study of the atomic mass transport on the surface of single crystal electrodes in contact with aqueous electrolytes. The study was performed using time correlation functions as a result of a quantitative analysis of equilibrium step fluctuations. In scanning tunneling microscope images equilibrium step fluctuations give rise to a frizzy appearance of the monoatomic step edges. The experiments discussed were performed on vicinal Ag(111) electrodes in sulfuric acid containing copper ions and on vicinal Cu(111) in diluted hydrochloric acid. The experimental setup and the modifications of the microscope for temperature variable experiments are presented.
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