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

Abstract

Pure α-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 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, a substantially thick interfacial reaction zone also builds up at the film/substrate interface with the excess Al acting as a cationic source.

Phase transitions and in situ dynamics of crystal grain formation of alumina nanotubes templated by vertically aligned carbon nanotubes

“…This has been utilized in literature to determine the oxidic nature of annealed alumina lms. 23 As listed in Table 1, DBE is largest for the amorphous (456.90 eV), as-deposited alumina with an initial decrease with stage I annealing and subsequent restoration of DBE separation with stage II and II 0 annealing processes. Stage II 0 DBE (456.88 eV) approaches the as-deposited alumina with a nearly matching value.…”

“…22 Besides binding energy shis, other methods have been reported to differentiate alumina phases including the FWHM of the Al2p peak where it is approximately 1.35 for a-alumina and 2.5 for g-alumina phases. 23 The most marked shi in binding energy is seen in the Al2p peak aer the stage I annealing process. The shi from 73.11 eV to 72.79 eV suggests a more metallic nature of the aluminum present within the nanotubes.…”

Self-Assembly of Metal Oxide Nanoparticles in Liquid Metal toward Nucleation Control for Graphene Single-Crystal Arrays

“…A weak peak located at 532.81 eV, possibly corresponding to carbon oxide adsorbates from the atmosphere, disappears. 25 Figure 2H shows the signal for the O 1s band collected at the subsurface, which is almost undetectable. Therefore, the density gradient of the alumina in the normal direction along the Cu surface, which is responsible for the establishment of the vertical field in the liquid metal, can be confirmed.…”

A Review on Adhesively Bonded Aluminium Joints in the Automotive Industry

“…In case of heat treatment at higher temperatures (>400 • C) the amorphous oxide may crack due to thermal expansion and nuclei of crystalline γ-Al 2 O 3 can be formed. If the enucleation of crystalline alumina lead to the loss of cohesion of the oxide with the metal substrate then it may have a detrimental effect on the total adhesion [32,33]. The presence of Mg also promotes the crystalline oxide growth as it acts as a nucleant for γ- [32].…”