Metal oxides are ubiquitous in industrially relevant applications such as heterogeneous catalysis, corrosion science and modern microelectronics. In recent years a lot of effort has been put into resolving the microscopic properties of oxidation of metal and metal alloy surfaces [1, 2] in order to gain insights into the initial stages of nanoscale oxide film formation.
In this study the properties of nitrogen covered Cu(100) surface have been characterized before and after oxygen exposures by employing low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and temperature programmed desorption (TPD). N/Cu(100) surface was prepared by bombarding a cleaned Cu(100) surface with 2-3 keV nitrogen ions and subsequent annealing. The resulting nitrogen coverage is below 0.5 monolayers.
Both STM and LEED results indicate that the N/Cu(100) phase and nitrogen-oxygen coadsorption phase are well ordered. The size of the nitrogen-copper nano-islands directly correlates with the reactivity of the surface towards oxidation. Depending on the oxygen exposure and the surface temperature it is possible to induce extremely thin O-Cu stripes between the nitrogen rich nano-islands. Following an oxygen exposure at elevated surface temperature, these stripes reconstruct to a (2√2×√2)R45-O structure which is known to form on clean Cu(100) upon oxygen adsorption. TPD measurements on N+O/Cu(100) indicate recombinative desorption of oxygen and nitrogen most likely from the island edges.
[1] M.P. Ryan, D.E. Williams, R.J. Chater, B.M. Hutton and D.S. McPhail, Nature 415 (2002) 770.
[2] H. Over and A.P. Seitsonen, Science 297 (2002) 2003. |