IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Processing at the Nanoscale Monday Sessions
       Session PN-MoA

Paper PN-MoA8
Generation of Self Organized Nanometer Structures on Surfaces of Ionic Solids Generated by Electron and Laser Beam Irradiation - The Role of Water

Monday, October 29, 2001, 4:20 pm, Room 133

Session: Nanostructures from 0 to 3 Dimensions
Presenter: K. Nwe, Washington State University
Authors: K. Nwe, Washington State University
S.C. Langford, Washington State University
J.T. Dickinson, Washington State University
Correspondent: Click to Email
Radiation effects on hydrated single crystals are poorly understood. We find that dense ordered arrays of nanoscale conical structures, with aspect ratios greater than 200, are produced when single crystal brushite (CaHPO4.2H2O) is exposed to energetic electrons (2 keV). All cones are pointed directly towards the incident electron beam. Other three dimensional nanostructures are generated by exposing brushite to excimer laser irradiation. We show that the mechanism involves: (a) photo/electron stimulated decomposition of the matrix, and (b) thermally stimulated migration of water (in this case, crystalline) and ionic material. We have isolated these factors and present plausible mechanisms for structure formation where water plays a dominant role. In addition, we have recently exposed non-hydrated ionic crystals to radiation in the presence of background water at partial pressures of 10-7 Torr, which yields exceedingly fine structures (sub-10 nm). These materials show very interesting optical and luminescence properties which we will present. Finally, we show that in the presence of water vapor, the rates of both laser and electron beam induced decomposition/desorption increase by as much as an order of magnitude. We present evidence that this is a highly localized, defect mediated mechanism.