Abstract
The possibility of a new technique for fabricating nanoparticles from thin films using selective oxidation in an atmosphere mixture of water vapor and hydrogen was investigated. Fe-5wt.%Al films were RF-sputtered and annealed in the atmosphere mixture at 900°C for up to 200 min, in order to oxidize aluminum selectively. Thermodynamics simulation showed that temperatures exceeding 800°C are necessary to prevent iron from being oxidized, as confirmed by the depth profile of XPS. As the annealing time increased, the morphology of the 200-nm Fe-Al films changed from the continuous to the discontinuous type; thus, particulate Fe-Al films formed after 100 min. The particulate 10- to 100-nm Fe-Al films showed super-paramagnetic behavior after the oxidation. Thus, a new technique for fabricating nanoparticles was successfully introduced using selective oxidation.
Highlights
Aluminum oxide, Al2O3, formed on the surface can be used as a mechanically protective, oxidation-resistive, electricity-insulating film
It was reported that in Fe-Al-X bulk alloys, the aluminum elements outdiffused along the α-Al2O3 grain boundary formed in an alumina network on the boundary by the selective oxidation of aluminum when the alloys were annealed in the atmosphere [1]
Assputtered films were annealed at 900°C for up to 200 min in an atmosphere mixture of water vapor and hydrogen, for which hydrogen passed through a copper pipe whose temperature was kept at −17°C at flow rates of 500 and 1,800 sccm (Figure 1)
Summary
Al2O3, formed on the surface can be used as a mechanically protective, oxidation-resistive, electricity-insulating film. It was reported that the Fe depletion zone appeared in the annealed Fe films on an Al2O3 substrate [4]. This indicates that continuous Fe films changed to discontinuous films, i.e., particulate films. They did not focus on the morphological change of the Fe/Al2O3 films, nor the reasons for it. It is interesting to investigate the morphological changes and related properties of Al2O3/ Fe-Al films, in which oxide is formed on the surface of Fe-Al films by the selective oxidation of aluminum in Fe-Al films in a mixed atmosphere
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