Atom probe tomography (APT) analysis of chemically pure nanofilms of zero-valent iron (Fe(0), or ZVI) and their thermal oxide nano-overlayers reveals the presence of dendritic iron oxide features that extend from the oxide nano-overlayer surface into the ZVI bulk. The dendrites are observed by APT to be in the 5 nm x 10 nm size range and form quickly under natural atmospheric conditions. Their growth into the ZVI lalyer is, within the limit of our three-month long study, self-limiting (i.e. their initial growth appears to quickly discontinue). The atomistic views presented here shed first light on the atmospheric corrosion process of Fe(0)-bearing engineered nanostructures and their surfaces in the limit of low bulk impurities. Possible roles of the newly identified oxidized iron dendrites are also discussed in the context of passivation processes limiting technological applications of Fe(0).
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