Role of steps in oxide formation on stepped Cu surfaces using a hyperthermal O molecular beam

Okada, Michio*; Vattuone, L.*; Savio, L.*; Moritani, Kosuke*; Teraoka, Yuden; Kasai, Toshio*; Rocca, M.*

We report the detailed studies on the initial oxidation process of the CuO and CuO formation on stepped surfaces of Cu(410). From high-resolution electron energy-loss spectroscopy, CuO formation is verified at high temperature for thermal O exposure. However, from synchrotron radiation photoemission spectroscopy we found the efficiency of CuO formation to be quite low for thermal O exposure. On the contrary, hyperthermal oxygen molecular beam (HOMB) at 2.2 eV was efficient for the fabrication of CuO even at room temperature. The O-1s and valence-band XPS spectra clearly demonstrated the CuO formation induced by the HOMB. Furthermore, such CuO formation depended strongly on the azimuthal direction of the incident HOMB, impinging dominantly either on a terrace or on a step. At low temperature of around 100 K, we found the nucleation of a metastable CuO phase which evolved into stable CuO when the crystal was heated.