AVS 51st International Symposium
    Surface Science Thursday Sessions
       Session SS3-ThM

Invited Paper SS3-ThM1
Ultra-Low Coverage Spontaneous Etching and Hyperthermal Desorption of Aluminum Chlorides from Cl2/Al(111)

Thursday, November 18, 2004, 8:20 am, Room 213B

Session: Halogen and Oxygen Surface Reactions and Etching
Presenter: A.C. Kummel, University of California, San Diego
Authors: A.C. Kummel, University of California, San Diego
T.J. Grassman, University of California, San Diego
G.C. Poon, University of California, San Diego
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Non-resonant multiphoton ionization and time-of-flight mass spectrometry have been used to monitor the desorption of aluminum chloride (AlxCly) etch products from the Al(111) surface at 100 K and 500 K during low-coverage (< 5% monolayer) monoenergetic Cl2 (0.11 eV to 0.65 eV) dosing. The desorption products in this low-coverage range show predominantly hyperthermal exit velocities under all dosing conditions. For example, with 0.27 eV incident Cl2, the etch product was found to have a most-probable velocity of 517 ± 22 m/s at an Al(111) surface temperature of 100 K. This corresponds to 22 times the expected thermal desorption translational energy for AlCl3. Sticking probability measurements and AlxCly etch rate measurements show etching even at Cl2 coverages of less than 5% monolayer at surface temperatures between 100 K and 500 K. These experimental results are consistent with a combination of fast-time-scale surface agglomeration of the adsorbed chlorine to form aluminum chlorides and the presence of activated aluminum chloride chemisorption states having potential energies above the vacuum level. Density functional theory calculations yield results that are consistent with both our experimental findings and mechanistic descriptions.