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Title: A transmission electron microscopy and X-ray photoelectron spectroscopy study of annealing induced γ-phase nucleation, clustering, and interfacial dynamics in reactively sputtered amorphous alumina thin films

Pure α-Al{sub 2}O{sub 3} exhibits a very high degree of thermodynamical stability among all metal oxides and forms an inert oxide scale in a range of structural alloys at high temperatures. We report that amorphous Al{sub 2}O{sub 3} thin films sputter deposited over crystalline Si instead show a surprisingly active interface. On annealing, crystallization begins with nuclei of a phase closely resembling γ-Alumina forming almost randomly in an amorphous matrix, and with increasing frequency near the substrate/film interface. This nucleation is marked by the signature appearance of sharp (400) and (440) reflections and the formation of a diffuse diffraction halo with an outer maximal radius of ≈0.23 nm enveloping the direct beam. The microstructure then evolves by a cluster-coalescence growth mechanism suggestive of swift nucleation and sluggish diffusional kinetics, while locally the Al ions redistribute slowly from chemisorbed and tetrahedral sites to higher anion coordinated sites. Chemical state plots constructed from XPS data and simple calculations of the diffraction patterns from hypothetically distorted lattices suggest that the true origins of the diffuse diffraction halo are probably related to a complex change in the electronic structure spurred by the a-γ transformation rather than pure structural disorder. Concurrent to crystallization within the film,more » a substantially thick interfacial reaction zone also builds up at the film/substrate interface with the excess Al acting as a cationic source.« less
Authors:
;  [1] ;  [2] ;  [3] ;  [4]
  1. ECMS Division, Central Electro Chemical Research Institute, Karaikudi (India)
  2. Department of Physics, PSG College of Technology, Coimbatore (India)
  3. Department of Physics, PSG Institute of Technology and Applied Research, Coimbatore (India)
  4. Department of Instrumentation, Indian Institute of Science, Bangalore (India)
Publication Date:
OSTI Identifier:
22399358
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 12; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM IONS; ALUMINIUM OXIDES; ANIONS; ANNEALING; CHEMICAL STATE; CHEMISORPTION; CRYSTALLIZATION; DIFFRACTION; ELECTRONIC STRUCTURE; INTERFACES; MICROSTRUCTURE; NUCLEATION; PHASE STABILITY; SPUTTERING; SUBSTRATES; THIN FILMS; TRANSMISSION ELECTRON MICROSCOPY; X-RAY PHOTOELECTRON SPECTROSCOPY