Topographic nano-restructuring: Structural and morphological changes accompanying reaction on single-crystal metal surfaces

Using atomic resolution scanning tunneling microscopy (STM), we have recently shown that certain metal surfaces undergo dramatic restructuring while forming adsorbed reaction intermediates, resulting in nanometer scale changes to the surface topography. Such cases of topographic nano-restructuring have been elucidated by the local power of STM. Both pitting, where substrate atoms removed from the surface in a dynamic steady state are incorporated into the adsorbate structure, and islanding, where the adsorbate induces precipitation of metal atoms from the initial surface to form islands on top of the surface, have been observed in reactions on Cu(110), Ni(110), Ag(110) and Ag(111). These findings are suggestive of a grater role of metal atoms in surface catalyzed processes than has previously been envisioned.; On Cu(110) SO2 disproportionates into sulfur and sulfite, i.e. 3 SO2(g) + Cu(surface) → S(a) + 2 CuSO 3(a). This process produces a pitted surface. On Ag(110)-p(2x1)-O sulfur dioxide reacts according to 6 SO2(g) + 6 Ag-O → 4 AgSO 3(a) + 2 SO3(a) + 2 Ag(surface). Sulfite adsorption is concomitant with island formation. Adsorption of hydrogen and formation of the Ni-H "added" row chains on the Ni(110) surface involves removal of Ni atoms from steps and terraces, forming pits. Overall the reaction is described by H2(g) + 2 Ni (surface) 4 → Ni-H(a). Upon dissolution of the Ni-H overlayer, the Ni is released to agglomerate on the surface into plateaus of step height. Adsorption of formate and acetate on Ni(110) parallel surface pitting as a stoichiometric quantity of Ni atoms are incorporated into the carboxylate structures, i.e. 2 RCOOH(g) + 2 Ni(surface) → 2 RCOO-Ni(a) + H2 (g). Formation of the Ag(111)-p(4 x 4)-O trilayer structure is concomitant with the release of Ag from the surface to form plateaus amid the oxide structure. Exposure of this surface to NO2(g) adsorbs nitrate, a reaction that pits the surface. Overall, NO2(g) + O(a) + Ag(surface) → AgNO3(a). Sulfur dioxide reacts with oxygen on Ag(111) according to SO2(g) + O(a) + Ag(surface) 4 AgSO3(a). Heating the sulfite-covered surface decomposes sulfite according to 10 AgSO3(a) → 5 SO2(g) + 2 AgSO4(a) + 3 SO4(a) + 8 Ag(surface).