IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Thursday Sessions
       Session SS2-ThP

Paper SS2-ThP5
A Molecular Beam Study of Helium Absorption and Diffusion in Amorphous and Crystalline Ice

Thursday, November 1, 2001, 5:30 pm, Room 134/135

Session: Beam Interactions with Surfaces Poster Session
Presenter: J.L. Daschbach, Pacific Northwest National Laboratory
Authors: J.L. Daschbach, Pacific Northwest National Laboratory
P. Ayotte, Pacific Northwest National Laboratory
G.A. Kimmel, Pacific Northwest National Laboratory
Z. Dohnalek, Pacific Northwest National Laboratory
R.S. Smith, Pacific Northwest National Laboratory
B.D. Kay, Pacific Northwest National Laboratory
Correspondent: Click to Email
Molecular beam and thermal desorption techniques are employed to study the absorption and diffusion of He atoms in thin amorphous and crystalline ice films at low temperatures (20-100 K). The He absorption probability increases strongly with increasing translational energy (0.065 - 0.23 eV) and decreases dramatically as the incident angle is moved away from the surface normal (0-60°). These findings are indicative of a large activation barrier and a strong steric effect for the insertion of the He atoms into the bulk. Comparison between crystalline and amorphous ice suggests that absorption into the bulk occurs through hexagonal ring structures existing at the ice surface. Diffusion of He in ice is studied by growing ice films of varying thickness on top of a He impregnated ice substrate, and subsequently measuring the He permeation through the overlayer using temperature programmed desorption (TPD). The resultant He TPD data is analyzed using a coupled diffusion/desorption model to extract the temperature dependent diffusivity. The diffusion exhibits Arrhenius behavior with a diffusion barrier of 0.14 eV. The details of the experimental findings and their implications will be presented. @FootnoteText@ Pacific Northwest National Laboratory is a multiprogram National Laboratory operated for the U.S. Department of Energy by Battelle Memorial Institute under contract DE-AC06-76RLO 1830.