AVS 46th International Symposium
    Surface Science Division Thursday Sessions
       Session SS3+AS+NS-ThM

Paper SS3+AS+NS-ThM7
Ionization Mechanisms of Water in High Interfacial Electric Fields

Thursday, October 28, 1999, 10:20 am, Room 604

Session: Novel Surface Probes & Technique Enhancement
Presenter: D.L. Scovell, University of Washington
Authors: D.L. Scovell, University of Washington
V.K. Medvedev, University of Washington
C.J. Rothfuss, University of Washington
E.M. Stuve, University of Washington
Correspondent: Click to Email
High surface fields (Ã1 V/Å) drive many important processes, such as electrochemistry and field emission. The behavior of water in these fields is important because water is the primary component in electrochemical processes and a major contaminant in the vacuum surrounding field emitter arrays in flat panel displays. It is usually assumed that water amplifies the field at the electrode surfaces, but little is known about how water affects the electric field distribution. Field emitter tips lend themselves to the study of the dielectric properties of water because they produce fields as high as 5 V/Å. To better understand the effect of high electric fields on water, numerical analyses have been conducted to model the electric field distribution around a water-covered emitter tip. The calculations include the field-dependence of the relative permittivity of the water adlayer. The model predicts that the dominant field occurs at the vacuum interface in thin water layers and at the metal surface in thick layers. In very thick layers the field at the tip surface is predicted to be greater than the applied electric field. This response is analogous to that assumed for a traditional electrode/electrolyte interface. Experiments have been conducted to verify the predicted trends for thin water layers. In these experiments water was adsorbed onto a platinum field emitter tip under field-free conditions in ultrahigh vacuum. Ionization was examined by isothermal ramped field desorption (RFD) performed as a function of temperature and water layer thickness. The experimental results are consistent with the predicted trends. This work was supported by the Office of Naval Research.