AVS 45th International Symposium
    Surface Science Division Monday Sessions
       Session SS-MoP

Paper SS-MoP16
Electron-Stimulated Desorption of Na from SiO@sub 2@ Films

Monday, November 2, 1998, 5:30 pm, Room Hall A

Session: Surface Science Division Poster Session
Presenter: B.V. Yakshinskiy, Rutgers University
Authors: B.V. Yakshinskiy, Rutgers University
T.E. Madey, Rutgers University
Correspondent: Click to Email
As part of a program to probe the mechanisms by which Na atoms are produced in tenuous planetary atmospheres (e.g., Mercury, The Moon, etc.) we have studied the electron-stimulated desorption (ESD) of sodium ions and neutral atoms from ultrathin amorphous stoichiometric silica films (~100Å thick) grown on a Re(0001) surface. The desorbing neutral Na flux is detected by using a novel surface ionization detector, which also permits measurements of energy distributions of neutral atoms by means of a time-of-flight method. Sodium ions, desorbing from the surface under electron bombardment, are analyzed by a guadrupole mass spectrometer. Approximately the same appearance threshold (~25eV) is found for both Na@super+@ and Na@super0@ desorption, corresponding to O2s core level excitation. A Coulomb pair O@super+@- Na@super+@ forms as a result of intraatomic Auger decay in the oxygen atom, leading to Na@super+@ desorption. The sodium neutral atom desorbs due to Pauli repulsion between Na and the neutralized oxygen ion. The total ESD cross section for Na is ~3x10@super-19@cm@super2@ at an electron energy of 300eV. The yield of Na atoms grows linearly with increasing sodium concentration in the monolayer, whereas the yield of Na@super+@ ions passes through a maximum at ~0.5ML. Velocity and energy distributions of desorbing sodium neutrals demonstrate evidence for the ESD of "hot" atoms, with most probable kinetic energies of ~0.5eV. The results are compared with recent photon stimulated data from oxides, and with observations of Na in planetary atmospheres.