Structural and morphological changes accompanying the reaction of ammonia with Ag(1 1 0)–p(2×1)-O: an STM study

We have investigated the reaction of ammonia with the oxygen-covered Ag(1 1 0)–p(2 × 1)-O surface using scanning tunneling microscopy (STM). The Ag(1 1 0)–p(2×1)-O surface has a well established structure, with added –Ag–O– rows running in the [0 0 1] directions separated by two lattice units in the [1 1̄ 0] directions. The reaction of ammonia with the preadsorbed oxygen forms NH(a) structures at 300 K and frees Ag atoms, leading to the recrystallization of large islands spread over the surface. The nucleation process involved in island formation is affected by ammonia pressure. A local reaction front was observed in real time to progress across the surface, forming new, small islands of adsorbate-covered silver in its wake. Heating the surface to 450 K produces mixed N(a) and compressed O(a) structures with higher coverage. Structural models are proposed based on the STM images.