Growth and structure of ultra-thin epitaxial chromium and iron oxide films on silver(001) and silver(111): A comprehensive study accomplished by x-ray photoelectron diffraction and low energy electron diffraction.

摘要

The epitaxial growth of transition metal oxide films (CrO_x and FeO_x) on Ag(001) and Ag(111) metal surfaces was investigated using XPS, XPD, and LEED techniques. The film growth was accomplished by repeated cycles of metal deposition and subsequent oxidation, and by oxidizing multilayer metal films grown on the silver substrates.; The two oxidation methods result in the growth of different α-Cr ₂O₃ surfaces on Ag(001). Oxidation of the bcc Cr(001) films grown on Ag(001) results in the growth of α-Cr₂O₃(210), while sequential deposition-oxidation results in α-Cr₂O ₃(111). The α-Cr₂O₃(210) films are structurally very similar to the α-Cr₂O₃(111) films. The (111) oxide films are formed from the initial deposition-oxidation step and persist to the thickest oxide film grown (about 30 Å).; Iron deposition on Ag(111) results in the growth of poorly ordered Fe(110) films. Oxidation of these films results in FeO(111) growth. The sequential deposition method produces oxide films with significantly better order. For iron oxide films grown in this fashion FeO(111) is observed up to a thickness of about 10 Å with thicker films identified as Fe₃O ₄(111). Simulations of the XPD data from the Fe₃O₄ films indicate that the iron oxide structure is best described as rotationally twinned domains of Fe₃O₄(111) with a surface termination most likely being oxygen-capped Fe_oct-O-Fe_tet-Fe _oct.