AVS 46th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS-WeP

Paper SS-WeP24
Electron- and Photon-stimulated Desorption of Alkali Atoms from Silicon Dioxide Surfaces

Wednesday, October 27, 1999, 5:30 pm, Room 4C

Session: 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 and K atoms originate in the atmospheres of the planet Mercury and the Moon, we are studying the electron- and photon-stimulated desorption of Na deposited on model mineral surfaces: amorphous SiO@sub2@ thin films, grown on a Re(0001) substrate. The measurement scheme for electron- stimulated desorption (ESD) of Na atoms includes an efficient pulsed low energy electron source, a highly sensitive detector of Na based on surface ionization, and a time-of-flight technique. For photon-stimulated desorption (PSD), a 500 W Hg arc lamp photon source, a mechanical chopper, and appropriate filters are used. We find that bombardment of Na / SiO@sub2@ surface by ultraviolet photons or by low energy electrons (E > 4 eV) causes desorption of 'hot' Na atoms with the velocity distribution peak at 1000 m/s. The desorption cross section is ~ 10@super-20@ cm@super2@ at 5 eV excitation energy for both ESD and PSD. The ESD yield demonstrates a resonance-like feature at ~11 eV. We interpret the ESD / PSD of Na as occuring via a substrate mediated charge transfer process, in which ionic Na@super+@ is converted to neutral Na, which desorbs. These data provide evidence that DIET mechanisms (e. g., PSD) may contribute as source processes for Na in tenuous planetary atmospheres. Although there are insufficient electrons in the solar wind to produce the observed lunar sodium atmosphere, there appear to be sufficient UV solar photons to maintain the atmosphere by desorbing Na from the surface.