Scanning tunneling microscopy of molecules on metals

Abstract

Scanning Tunneling Microscopy (STM), a relatively new technique capable of observing atom-sized features, has recently made significant inroads into observations of molecules on surfaces. We illustrate the recent success of STM at this new task with the imaging of a few organic molecules on metal surfaces. Our first studies of molecules involved ordered coadsorbed CO and benzene on Rh(111) surfaces. The sharpest images possessed only 3-fold symmetry, presumably because 3 of the 6 C-C bonds are above substrate metal atoms. Further reductions in the image symmetry associated with asymmetric tips were frequently observed. Subsequent observations of the c(2√3 ×4)rect structure revealed the three domains present for this structure and frequent domain changes at step edges. For this system we also found small protrusions to occupy the sites assigned to CO in the LEED model so that this molecule can also be imaged. In subsequent measurements we studied Cu-phthalocyanine, whic of interest due to the catalytic activities of its central metal atom, on different substrates in order to better understand and exploit the consequences of variations in the molecule-surface interaction. Although it is still in its infancy, these results suggest that STM will become increasingly important for studies of surface chemistry.