Structure of W( 111) for NO and O₂ coadsorption studied by ESDIAD

Nitric oxide and oxygen coadsorbed on W( 111) surface structures under various conditions have been studied by means of electron-stimulated desorption ion angular distribution (ESDIAD) and low energy electron diffraction (LEED) at room temperature. Only O⁺ ions are detected by electron-stimulated desorption (ESD) from the NO-and/or the O₂-adsorbed W( 111) surface. The ESDIAD patterns consist of three bright spots. With increasing temperature, the intensities of the ESDIAD pattern from the O₂/W( 111) decrease monotonically, and disappear around 700 K. However, the intensities of the patterns from the NO + O₂/W( 111) decrease rapidly above 700 K, and disappear around 850 K. The ESDIAD spots from the NO + O₂/W( 111) become sharp up to 500 K, with increasing temperature. The surface, following the NO and/or the O₂ adsorption under any condition, has a (1×1) structure with a high background intensity, and the surface structure changes into a (3×3) structure after the disappearance of intensities of the ESDIAD patterns. The O atoms on the surface diffuse into the bulk with increasing temperature, but the diffusion is blocked by the N atoms, in the case of the NO-adsorbed surfaces under any condition.