title: Towards Direct Synthesis of Alane: A Predicted Defect-Mediated Pathway Confirmed Experimentally.
abstract: Alane (AlH3 ) is a unique energetic material that has not found a broad practical use for over 70 years because it is difficult to synthesize directly from its elements. Using density functional theory, we examine the defect-mediated formation of alane monomers on Al(111) in a two-step process: (1) dissociative adsorption of H2 and (2) alane formation, which are both endothermic on a clean surface. Only with Ti dopant to facilitate H2 dissociation and vacancies to provide Al adatoms, both processes become exothermic. In agreement, in situ scanning tunneling microscopy showed that during H2 exposure, alane monomers and clusters form primarily in the vicinity of Al vacancies and Ti atoms. Moreover, ball milling of the Al samples with Ti (providing necessary defects) showed a 10 % conversion of Al into AlH3 or closely related species at 344 bar H2 , indicating that the predicted pathway may lead to the direct synthesis of alane from elements at pressures much lower than the 10(4)  bar expected from bulk thermodynamics.
authors.affiliation: Ames Laboratory, U.S. Department of Energy, Ames, IA, 50011-3020, USA.
authors.forename: Lin-Lin
authors.identifier: 0000-0003-0965-3246
authors.initials: LL
authors.lastname: Wang
authors.affiliation: Ames Laboratory, U.S. Department of Energy, Ames, IA, 50011-3020, USA.
authors.forename: Aditi
authors.initials: A
authors.lastname: Herwadkar
authors.affiliation: Ames Laboratory, U.S. Department of Energy, Ames, IA, 50011-3020, USA.|Department of Chemistry, University of Illinois Urbana-Champaign, 505 South Mathews Ave., Urbana, IL, 61801, USA.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Reich
authors.affiliation: Ames Laboratory, U.S. Department of Energy, Ames, IA, 50011-3020, USA. ddj@ameslab.gov.|Department of Materials Science & Engineering, Iowa State University, 2200H Hoover Hall, Ames, IA, 50011-2300, USA. ddj@ameslab.gov.|Department of Materials Science & Engineering, University of Illinois Urbana-Champaign, 1304 W. Green St., Urbana, IL, 61801, USA. ddj@ameslab.gov.
authors.forename: Duane D
authors.identifier: 0000-0003-0794-7283
authors.initials: DD
authors.lastname: Johnson
authors.affiliation: Department of Materials Science & Engineering, University of Illinois Urbana-Champaign, 1304 W. Green St., Urbana, IL, 61801, USA.|Department of Chemical and Petroleum Engineering, University of Pittsburgh, 3700 O'Hara St., Pittsburgh, PA, 15261, USA.
authors.forename: Stephen D
authors.identifier: 0000-0003-2035-6373
authors.initials: SD
authors.lastname: House
authors.affiliation: Department of Materials Science & Engineering, University of Illinois Urbana-Champaign, 1304 W. Green St., Urbana, IL, 61801, USA.
authors.forename: Pamela
authors.initials: P
authors.lastname: Peña-Martin
authors.affiliation: Department of Materials Science & Engineering, University of Illinois Urbana-Champaign, 1304 W. Green St., Urbana, IL, 61801, USA.
authors.forename: Angus A
authors.initials: AA
authors.lastname: Rockett
authors.affiliation: Department of Materials Science & Engineering, University of Illinois Urbana-Champaign, 1304 W. Green St., Urbana, IL, 61801, USA.|Department of Materials Science & Engineering, University of Wisconsin-Madison, 1415 Engineering Dr., Madison, WI, 53706, USA.
authors.forename: Ian M
authors.identifier: 0000-0002-4923-0400
authors.initials: IM
authors.lastname: Robertson
authors.affiliation: Ames Laboratory, U.S. Department of Energy, Ames, IA, 50011-3020, USA.
authors.forename: Shalabh
authors.initials: S
authors.lastname: Gupta
authors.affiliation: Ames Laboratory, U.S. Department of Energy, Ames, IA, 50011-3020, USA. ntkp@ameslab.gov.|Department of Materials Science & Engineering, Iowa State University, 2200H Hoover Hall, Ames, IA, 50011-2300, USA. ntkp@ameslab.gov.
authors.forename: Vitalij K
authors.identifier: 0000-0001-9503-7567
authors.initials: VK
authors.lastname: Pecharsky
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D017607:Aluminum Compounds / Q000737:chemistry*; D060326:Chemistry Techniques, Synthetic / Q000379:methods*; D008958:Models, Molecular; D008968:Molecular Conformation; D013499:Surface Properties
chemical_list: D017607:Aluminum Compounds; D000535:Aluminum
keywords: alane; ball milling; catalysis; density funcitonal theory; scanning tunneling microscopy