Abstract
A significant proportion of the nanoparticles of chromium prepared by plasma gas condensation are nanocubes. We have found by electron diffraction and high-resolution transmission electron microscopy that each nanocube of chromium is enclosed by an epitaxial passive oxide film. The oxide film has been identified as fcc Cr
2
O
3
with a lattice parameter of 0.407 nm. This cubic passive oxide, found in nanocubes of chromium that have remained unchanged in water for more than 4 years, may have important implications for protective oxide films involving chromium.