title: Low coverage spontaneous etching and hyperthermal desorption of aluminum chlorides from Cl2/Al(111).
abstract: Nonresonant multiphoton ionization with time-of-flight mass spectrometry has been used to monitor the desorption of aluminum chloride (Al(x)Cl(y)) etch products from the Al(111) surface at 100 and 500 K during low-coverage (<5% monolayer) monoenergetic Cl(2) (0.11-0.65 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 Cl(2), 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 AlCl(3). Cl(2) sticking probability measurements and Al(x)Cl(y) etch rate measurements show etching even at Cl(2) coverages of less than 5% monolayer at surface temperatures between 100 and 500 K. These experimental results are consistent with a combination of fast-time-scale surface diffusion and agglomeration of the adsorbed chlorine to form aluminum chlorides and the presence of activated AlCl(3) 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.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, Mail Code 0358, La Jolla, California 92093-0358, USA.
authors.forename: Tyler J
authors.initials: TJ
authors.lastname: Grassman
authors.forename: Gary C
authors.initials: GC
authors.lastname: Poon
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Kummel
mesh_terms: D000327:Adsorption; D000535:Aluminum / Q000737:chemistry*; D000077410:Aluminum Chloride; D017607:Aluminum Compounds / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods*; D002712:Chlorides / Q000737:chemistry*; D002713:Chlorine / Q000737:chemistry*; D004058:Diffusion; D006358:Hot Temperature; D008956:Models, Chemical; D015233:Models, Statistical; D017785:Photons; D012984:Software; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors
chemical_list: D017607:Aluminum Compounds; D002712:Chlorides; D000077410:Aluminum Chloride; D002713:Chlorine; D000535:Aluminum