Understanding the behavior and energetics of oxygen atoms on the silicon surface is important, and therefore water molecules dissociatively adsorbed on the $\mathrm{Si}\left(111\right)\text{−}7\times 7$ surface were studied. At elevated temperatures, complete decomposition of a water molecule into two hydrogen atoms and one oxygen atom was directly observed by scanning tunneling microscopy. The methodology employed in this study provided an opportunity to examine the dynamic behavior of single oxygen atoms. We found that an oxygen atom has at least four bonding states between 290 and $340°\mathrm{C}$. The majority state appeared as an intensely bright spot located at an adatom site. At room temperature, this state can also be formed by stimulation of tunneling electrons at a water-reacted site. The hopping barriers between equivalent surface sites were determined from Arrhenius plots to be in the range of $1.8–2.0\mathrm{eV}$, indicating that the diffusion barrier for oxygen atoms into the bulk of Si(111) was higher than $2.0\mathrm{eV}$.

• Received 17 October 2005

DOI:https://doi.org/10.1103/PhysRevB.73.075427