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

Kumar, Nanda AK and Prasanna, S and Subramanian, B and Jayakumar, S and Rao, Mohan G (2015) A transmission electron microscopy and X-ray photoelectron spectroscopy study of annealing induced gamma-phase nucleation, clustering, and interfacial dynamics in reactively sputtered amorphous alumina thin films. In: JOURNAL OF APPLIED PHYSICS, 117 (12).

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Official URL: http://dx.doi.org/10.1063/1.4916331

Abstract

Pure alpha-Al2O3 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 Al2O3 thin films sputter deposited over crystalline Si instead show a surprisingly active interface. On annealing, crystallization begins with nuclei of a phase closely resembling gamma-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 approximate to 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-gamma transformation rather than pure structural disorder. Concurrent to crystallization within the film, a substantially thick interfacial reaction zone also builds up at the film/substrate interface with the excess Al acting as a cationic source. (C) 2015 AIP Publishing LLC.

Item Type: Journal Article
Additional Information: Copy right for this article belongs to the AMER INST PHYSICS, 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA
Keywords: CHEMICAL-VAPOR-DEPOSITION; TRANSITION ALUMINAS; GRAIN-GROWTH; RANGE ORDER; OXIDE FILMS; TRANSFORMATION; GAMMA-AL2O3; OXYGEN; CRYSTALLIZATION; ALPHA-AL2O3
Department/Centre: Division of Physical & Mathematical Sciences > Instrumentation Appiled Physics
Depositing User: Id for Latest eprints
Date Deposited: 06 May 2015 05:08
Last Modified: 06 May 2015 05:08
URI: http://eprints.iisc.ac.in/id/eprint/51483

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