  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).
