Atomic Scale Insights into the Initial Oxidation of Ru(0001) Using Molecular Oxygen: A Scanning Tunneling Microscopy Study

作者：Herd Benjamin; Knapp Marcus; Over Herbert^*

来源：Journal of Physical Chemistry C, 2012, 116(46): 24649-24660.

DOI：10.1021/jp3085155

The initial oxidation of Ru(0001) has been studied by scanning tunneling microscopy (STM) using molecular oxygen as the oxidizing agent The initial oxidation Process reveals a complex behavior in which three-dimensional RuO2 domains (clusters) are exclusively formed at multiple steps, and only few of these clusters are able to initiate the growth of flat RuO2 domains with its (110) orientation along the (0001) direction of the Ru substrate. The oxide formation requires a minimum temperature of 500 K and a minimum pressure of about 1 x 10(-5) mbar of oxygen. Below 1 x 10(-5) mbar, oxide growth is very slow, although even at pressure of 10(-6) mbar oxidation in step bunching regions is occasionally observed The modified nucleation and growth mode of Ru(0001) oxidation is corroborated by growing the oxide in two separate steps: Starting with oxygen exposure of 1.5 x 10(-5) mbar of O-2 for 960 s at a sample temperature of 680 K, RuO2 nuclei are preferably formed. Subsequently, the further growth of flat oxide domains at 680 K is conducted by O-2 pressures of 2.5 x 10(-7) mbar, a pressure which is far below the threshold pressure for cluster formation. Chemical reduction experiments of ultrathin oxide layers by exposing CO at 600 K sample temperature allows to determine precisely the local thickness of the ultrathin RuO2(110) films. This reduction experiment reveals that these flat oxide layers penetrate into the topmost Ru layer starting from step edges.

• 出版日期2012-11-22