AVS 51st International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP46
First Stages of Water Absorption on Alkali Halides Surfaces Studied by Scanning Polarization Force Microscopy

Tuesday, November 16, 2004, 4:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: A. Verdaguer, Lawrence Berkeley National Laboratory
Authors: A. Verdaguer, Lawrence Berkeley National Laboratory
G.M. Sacha, Lawrence Berkeley National Laboratory
M. Salmeron, Lawrence Berkeley National Laboratory
Correspondent: Click to Email
Adsorption of water on sodium chlorite has been studied using scanning polarization force microscopy. A crystal is cleaved at low humidity (10% RH) and then humidity is increased as topography, contact potential and mobility of the ions is measured. At a critical humidity (40% for NaCl) important changes in the surface potential and ionic mobility occurred. Topographical changes occurred as well, in the form of step motion. We focused our study on the changes on the surface immediately before this critical humidity is reached. The evolution in the topographical and electrical properties and the ion mobility on the steps and the terraces as we approach to that point has been studied. An increase in the topographic contrast on the steps appears as we approach to the critical humidity. The increase in topographic electrostatic contrast is due to an increase in ionic mobility at step, indicative of ionic dissolution. As the mobility increases the difference between the local potential at the steps and on the terraces, measured from the Kelvin Probe signal, decreases. This supports the model deduced from the topography and indicates that the initial potential at the steps disappears due to the increased ionic mobility. The data obtained suggest us a model for the first stages of the dissolution of the crystal.