Local characterization and modification of surfaces with the in-situ STM

Abstract

The topic of this thesis is the use of the in-situ electrochemical STM beyond the imaging of electrode surfaces. The use of the in-situ STM for the study of a faceted Ir(210) surface reveals the presence of pyramids showing two (311) and one (110) facets and allows for some considerations about the faceting mechanism and for a meaningful description of the electrochemical behavior of the cyclic voltammograms of such electrodes. The STM has been also used for the controlled deposition of metal nano-clusters based on the so called Jump-to-contact (JC) (Chapter 5). In this method, a metal-loaded tip is made to approach the surface close enough, so that the JC occurs. By retracting the tip a small cluster is left on the surface. Tip-generated clusters contain less that 100 atoms and show a surprisingly high stability against the anodic dissolution. The clusters act like nucleation centres and retain a memory of the process upon dissolution of the deposits. In Chapter 6 the results of a Tunneling Spectroscopy study of the electrified interface are presented. With this method the Effective Tunneling Barrier (EBH) can be calculated from the experimental results. With the help of theoretical calculations, the EBH has been directly related to the charge distribution in the STM gap yielding detailed information about the structure of the interface at different potentials. These measurements allowed also for an estimation of the absolute width of the STM gap. In the Voltage Tunneling Spectroscopy (VTS) the current is measured as function of the electrode potential at a fixed distance. Its application at the liquid/solid interface allows for the study of the transformation of the electronic structure with the applied potential. Furthermore, the VTS has revealed processes occurring at the interface which was not possible to detect with the classical techniques used in electrochemistry.