Surface valence states and stoichiometry of non-superconducting and superconducting FeTe films

► Surface electronic structure and stoichiometry of non- and super-conducting FeTe films ► Oxygen incorporation changes initial valence state from Fe 0 to mainly 3 +. ► The Te changes valence from initially 0 to mixed 0 and 4 +. ► The rate of valence changes is seen to depend on the method of oxygen incorporation. ► The surface of the FeTe is left in a Te deficient state with any exposure to oxygen.