Chemisorption, diffusion and reactions on surfaces by scanning tunnelling microscopy

We discuss several applications of scanning tunneling microscopy (STM) to studies of chemisorption and surface reactivity. These include: (i) adsorbate-adsorbate interactions and diffusion phenomena. We illustrate this with the example of S on Re(0001), where the hopping (diffusion) of S atoms across surface sites was viewed by use of STM. The observed atomic motion was found to be highly correlated, as in a lattice 'liquid', (ii) interaction between different co-adsorbed species, including S and CO, and benzene and CO, that display both repulsive and attractive interactions leading to the segregation or intermixing of the adsorbates; and (iii) adsorbate-substrate interactions that lead to various surface reconstructions, step restructuring and faceting. We give recent results showing CO and S inducing step restructuring and reconstruction of a Pt(111) crystal substrate. Finally, we illustrate the unique capability of STM of operating in virtually any environment by studying the structure of Pt(110) and Pt(111) surfaces in various gas environments (H-2, O-2, CO2 propylene) and at pressures of up to 1.6 atm.