Direct scanning tunneling microscope (STM) observation of Cr(III) complexes on hematite (001) surfaces

Scanning tunneling microscopy (STM) is used to observe, at the atomic scale, Cr(III) adsorbed to hematite (001) surfaces from aqueous solution. The Cr(III) adsorbates are relatively immobile, but estimated activation energies for surface self-diffusion are lower than those for water or hydroxyl substitution in aqueous Cr(III). Possible causes are effects of STM imaging (artifacts), high ligand-substitution rates for adsorbed species, or participation of substrate Fe (III) ligand exchange. STM imaging of suitable aqueous surface complexes is shown to be feasible, and constitutes a new way to study the relationships between microscopic and macroscopic chemical behavior of adsorbed species in aqueous systems.