The geometry of the saturated (2 × 2)-NO adlayer on Ru(001): a structure with three different sites

• Published in: Surface science Vol. 391; no. 1; pp. 47 - 58
• Main Authors: Stichler, Markus, Menzel, Dietrich
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 26.11.1997; Amsterdam Elsevier Science; New York, NY
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Low energy electron diffraction (LEED); Low index single crystal surfaces; Metals. Metallurgy; Nitrogen oxides; Physics; Ruthenium; Solid surfaces and solid-solid interfaces; Solid-fluid interfaces; Surface structure and topography; Surface structure, morphology, roughness, and topography; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Low energy electron diffraction (LEED); Nitrogen oxides; Ruthenium; Surface structure, morphology, roughness, and topography; Low index single crystal surfaces; Inorganic adsorbate; Gas solid adsorption; Transition elements; Nitric oxide; Gas solid interface; Metallic adsorbent; Adsorption structure; LEED; Experimental study; Bond lengths; Surface structure
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/S0039-6028(97)00453-6

The geometry of the ordered (2 × 2)-3NO structure formed on Ru(001) at saturation has been studied by a detailed LEED- IV analysis. NO is found to adsorb on three different adsorption sites, NO top, NO hcp, and NO fcc, in upright orientation with the N end down. NO top with an NO bond length of r e = 1.13 ± 0.06 A ̊ is identified with the previously defined v 2-NO δ+ species, whereas NO on the two hollow sites with intramolecular bond lengths of r e = 1.24 ± 0.07 1.22 ± 0.06 A ̊ can be attributed to the known v 1-NO δ− species. The significant variations of the NO bond length can be understood in terms of the different NO charge states which are connected with corresponding variations of occupancy of the antibonding 2π∗-orbital. These results are in good agreement with density functional cluster calculations [Neyman et al., J. Chem. Phys. 100 (1994) 2310] performed in conjunction with HREELS measurements. A considerable response of the Ru substrate to the NO adsorption is found: the average first substrate spacing is expanded to d 12 = 2.19 ± 0.05 A ̊ (clean Ru(001): 2.09 Å), whereas the next layer distance is contracted to d 23 = 2.08 ± 0.05 A ̊ (bulk value d B = 2.14 A ̊ . In addition, there is significant outward buckling of the NO top-bonded Ru top atom of Δz 1 = 0.19 ± 0.02 A ̊ with respect to the adjacent Ru hollow atoms.