Step Faceting: Origin of the Temperature Dependent Induction Period in Ni(100) Oxidation

Scanning tunneling microscopy observations reveal a new mechanism for Ni(100) surface oxidation. It is dominated by nucleation at steps and lateral growth of 2D oxide islands. At 300 K nucleation is facile and oxidation starts at rather low exposures. At higher temperatures the interaction between chemisorbed O and Ni substrate causes the steps to facet into {001} segments. These steps are stabilized by the $c(2\times 2)\mathrm{O}$ and almost inert against oxide nucleation. The activation barrier for step faceting causes a pronounced temperature dependence of the induction period for oxide formation.