AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoM

Paper SS1-MoM6
Ultra-Low Coverage Spontaneous Etching and Hyperthermal Desorption of Aluminum Chlorides from Cl@sub 2@ on Al(111)

Monday, November 3, 2003, 10:00 am, Room 326

Session: Gas-Surface Dynamics
Presenter: T.G. Grassman, University of California, San Diego
Authors: T.G. Grassman, University of California, San Diego
G.C. Poon, University of California, San Diego
A.C. Kummel, University of California, San Diego
Correspondent: Click to Email
Non-resonant multiphoton ionization (MPI) and time-of-flight mass spectrometry (TOF-MS) have been used to monitor the desorption of aluminum chloride (Al@sub x@Cl@sub y@) etch products from the Al(111) surface at 100 K and 500 K during low-coverage (<5% monolayer) monoenergetic Cl@sub 2@ dosing. Three pulsed molecular beams of Cl@sub 2@ were prepared with translational energies ranging from 0.11 eV to 0.65 eV. The desorption products showed predominantly hyperthermal exit velocities under all dosing conditions, regardless of etch product species assignment (AlCl, AlCl@sub 3@, or Al@sub 2@Cl@sub 6@). For example, with an incident beam of Cl@sub 2@ seeded in neon (0.27 eV) at normal incidence dosing and normal detection, the etch product was found to have a most probable velocity of 532 ± 29 m/s at an Al(111) surface temperature of 100 K. This corresponds to nearly 7 times the expected thermal kinetic energy even if one assumes that the etch product is AlCl, and 30 times expected if one considers the more likely etch product, Al@sub 2@Cl@sub 6@. Sticking probability and transient etch rate profile measurements show etching even at Cl@sub 2@ coverages of less than 5% monolayer at all surface temperatures. High-temperature (500 K) etch rate profiles reach steady-state etching at equally small doses. These experimental results seem to indicate 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.