H adsorption and the formation of alane oligomers on Al(111)

Complementary scanning tunneling microscopy and surface infrared measuremen ts show that H reacts strongly with Al(111), producing a variety of new ala ne (aluminum hydride) surface species. Alane oligomers, ranging in size fro m the monomer to 30-mers, form through a sequence of surface etching and co ndensation reactions. Atomic hydrogen initiates production by extracting al uminum atoms from the surface lattice to create mobile monohydride monomers (ad-Al-H), which predominate in the low-coverage regime. At higher hydroge n coverages, multihydride oligomers form in coexistence with the ad-Al-H. T hese alane oligomers are more thermally stable, remaining on the surface at room temperature, where they are directly imaged. The mass transfer of alu minum to surface alanes is discussed in relationship to alane stoichiometry . (C) 1999 Elsevier Science B.V. All rights reserved.