AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP21
Electron- and Photon-stimulated Desorption of Alkali Atoms from Silicon Dioxide and Ice Surfaces

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: B.V. Yakshinskiy, Rutgers University
Authors: B.V. Yakshinskiy, Rutgers University
T.E. Madey, Rutgers University
Correspondent: Click to Email
To investigate mechanisms for the origin of K and Na in the tenuous atmospheres of the Moon, Mercury and Europa, we are studying the electron- and photon-stimulated desorption (ESD and PSD) of alkali atoms from model surfaces: amorphous SiO@sub 2@ and water ice films (both crystalline and amorphous) grown on a metal substrate. The measurement scheme for ESD and PSD of alkali atoms includes a highly sensitive detector based on surface ionization, and a time-of-flight technique. For PSD measurements, a mercury arc light source (filtered and chopped) is used. In the present work, we focus on ESD and PSD of K atoms, and compare with our previous studies of Na desorption from SiO@sub 2@.@footnote 1@ We find that bombardment of the alkali covered surfaces by ultraviolet photons or by low energy electrons (E>4 eV) causes desorption of "hot" K and Na atoms. The velocity distributions (VD) of K and Na desorbing from the silica surface are peaked at 650 and 1000 m/s, respectively, whereas the corresponding VD for desorption from the ice surfaces have maxima at 500 and 800 m/s. These values are consistent with the "hot" components of the lunar, Mercurian and Europian atmospheres. The mechanism of desorption is identified as an electronically excited charge-transfer from the silica or the ice substrate to neutralize alkali ion, followed by desorption of the alkali atom. We conclude that PSD by UV solar irradiation is a dominant source process for K and Na in tenuous planetary atmospheres. @FootnoteText@ @footnote 1@ BVY and TEM, Nature, Vol. 400, 642 (1999).