Low coverages of ${\mathrm{C}}_{60}$ on Cu(111) and K/Cu(111) have been investigated by scanning tunneling microscopy and spectroscopy at 10 K. By combining topographic imaging and mapping of the spectral intensity $\mathrm{}(dI/dV),$ we have analyzed the evolution of the $t_{1u}$-derived [lowest-unoccupied molecular orbital (LUMO)] electronic states resulting from the difference in adsorption geometry on Cu(111) as well as the difference in bonding when the substrate is precovered by a K monolayer. The spatial distribution and the spectral width of the LUMO-derived states are observed to be particularly sensitive to the adsorbate-substrate interaction.

• Received 28 October 2003

DOI:https://doi.org/10.1103/PhysRevB.69.115434