AVS 52nd International Symposium
    Surface Science Friday Sessions
       Session SS1-FrM

Paper SS1-FrM8
Consequences of Exposing Ionic Single Crystals to UV Laser Light, keV Electrons, and Low Pressure Water Vapor@footnote 1@

Friday, November 4, 2005, 10:40 am, Room 202

Session: Surface Modification through Etching
Presenter: S.C. Langford, Washington State University
Authors: J.T. Dickinson, Washington State University
K. Kjelgaard, Washington State University
S.C. Langford, Washington State University
Correspondent: Click to Email
At low pressures, water often does not stick to clean, room temperature surfaces, including surfaces of insulating inorganic materials. Nevertheless sorption, including dissociative sorption, can be strongly enhanced by defects, such as atomic steps, vacancies, and adatoms. We have examined the consequences of exposing ionic, single-crystal surfaces simultaneously to energetic radiation (UV photons, keV electrons) and relatively low pressures of water vapor. Dramatic synergisms are observed, presumably due to chemisorption-induced bond weakening. We describe mechanistic studies of this phenomenon, including time-resolved measurements of the response of the radiation-induced particle emission to transients in water pressure (@DELTA@P@sub H2O@ 10@super -9@ to 10@super -5@ Pa). Both ion and neutral particle emission rates respond to these transients on time scales of micro- to milli-seconds. We use scanning electron and atomic force microscopies to image the surface modifications associated with this loss of material, beginning with the removal of single atomic layers along step edges and eventually yielding micron-scale pits. We present AFM evidence that material removal is highly localized and defect mediated. We suggest that radiation-induced defects produce atomic-scale structures along steps (e.g., kinks) that peel off when the associated chemical bonds are weakened by sorbed, water-derived radicals. Supporting evidence from spectroscopic and microscopic data on exposed surfaces will be presented. We also show novel nanostructures produced by exposure to energetic radiation in the presence of water vapor. @FootnoteText@ @footnote 1@This work was supported by the Department of Energy.