Identification of ordered CO structures on Cu(211) using low temperature scanning tunneling microscopy

We report on imaging of CO molecules in random dilute phases and on several dense ordered CO phases using a scanning tunneling microscope at temperatures between 30 and 80 K. Images of the1×2,1×3 and1×4 ordered phases on Cu(211) allow absolute coverage determinations as well as conclusions on the registry of the absorbates with respect to the substrate. The strikingly different appearance of the CO molecules as bumps or dips is traced back to different tip compositions.