Water and Atomic Hydrogen Adsorption on Magnetite (001)

We investigated structural changes of the magnetite (001) surface upon exposure to water vapor at pressures up to 10 mbar as well as upon exposure to atomic hydrogen using surface X-ray diffraction, scanning tunneling microscopy, infrared spectroscopy, and X-ray photoelectron spectroscopy. Following a full structural analysis, we found for both adsorbates that the surface is roughening on an atomic level, indicating significant iron diffusion at the surface and in the near-surface region at room temperature. We found that this process is accompanied for both adsorbates by a lifting of the subsurface cation vacancy reconstruction present after preparation under ultrahigh vacuum conditions. In the case of water vapor, the lifting process arises in a pressure range between 10(-4) and 10(-3) mbar. We also observe an enhanced reactivity of the atomic hydrogen exposed surface with carbon species from the residual gas even at ultrahigh vacuum conditions.