Surface morphology of atomic nitrogen on Pt(111).

The surface morphology of chemisorbed N on the Pt(111) surface has been studied at the atomic level with low temperature scanning tunneling microscopy (STM). When N is coadsorbed with O on the surface, they form a mixed (2 × 2)-N+O structure. When the surface is covered with N atoms only, isolated atoms and incomplete (2 × 2) patches are observed at low coverages. In a dense N layer, two phases, (√3 × √3)R30°-N and p(2 × 2)-N, are found to coexist at temperatures between 360 and 400 K. The (√3 × √3)R30° phase converts to the (2 × 2) phase as temperature increases. For both phases, nitrogen occupies fcc-hollow sites. At temperatures above 420 K, nitrogen starts to desorb. The p(2 × 2)-N phase shows a honeycomb structure in STM images with three nitrogen and three platinum atoms forming a six-membered ring, which can be attributed to the strong nitrogen binding to the underlying Pt surface.