Fluctuation Microscopy Studies of Aluminum Oxides Exposed to CL Ions
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FLUCTUATION MICROSCOPY STUDIES OF ALUMINUM OXIDES EXPOSED TO CL IONS Xidong Chen *, John Sullivan**, Charles Barbour**, Craig Johnson**, Guangwen Zhou***, Judith Yang *** *
Cedarville University, Cedarville, OH 45314 & Materials Science Division, Argonne National Laboratory, Argonne, IL 60439 ** Sandia National Lab, Albuquerque, New Mexico 87185-1421 *** Univ of Pittsburgh, Pittsburgh, Pennsylvania
Abstract Fluctuation electron microscopy studies have been performed on several aluminum oxides exposed to different electrochemical conditions. Little is known about amorphous aluminum oxide structures and their relationship with their passivation behaviors. Corrosion studies have shown that exposure of aluminum oxide films to Cl ions in solution reduces the oxide's passivity, and this results in the onset of pitting corrosion. The physical changes that occur in the oxide as a result of Cl exposure have not been previously identified due to the difficulty in investigating the structure of this amorphous material. Fluctuation microscopy is a new electron microscopy technique that is able to detect the presence of medium range order structures in amorphous systems. In this paper, we will report fluctuation microscopy results on amorphous aluminum oxides that have been exposed to Cl ions in solution and compare them with oxides that have seen no electrolyte exposure or that have been exposed to electrolytes that do not contain Cl-, such as SO42- containing electrolytes. We will also compare the Cl-exposed oxides with oxides that have been implanted with Cl ions. The differences in pitting behaviors for these oxides are consistent with our previous speculation on the effect of medium range order on the passivation behavior of aluminum oxides grown using ozone.
Introduction Ultrathin films of aluminum oxide are important for a variety of solid state electronic devices, including superconducting Josephson junctions [1], single electron transistors [2], and magnetic tunnel junctions [3]. Thin aluminum oxide films passivate the surface of aluminum and provide resistance against corrosion [3]. Therefore, understanding of aluminum oxides structures is very desirable, as structures determine properties. There are however many open questions regarding amorphous aluminum oxides. Part of the reason is that it is hard to perform diffraction studies on those thin films. Even diffraction studies can only provide information on short-range order structures, which is not enough to describe amorphous structures. Medium-range order is any structure order that falls into the range from 10 Å to 300 Å. There has been abundant evidence of the existence of such order. Until recently there have not been any experimental techniques that can directly characterize such structures quantitatively. However, medium-range structures do affect properties as we will show later this paper. In this paper, we apply fluctuation microscopy technique to directly measure medium range order
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structures in several aluminum oxides exposed to diffe
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