Mapping antibonding electron states of a Pb adatom on Pb(111)

We have used low-temperature scanning tunneling spectroscopy to spatially map the energy-resolved electron density of a single Pb adatom on a Pb(111) surface. We observe a clear spatial inhomogeneity of the spectral density of the Pb adatom. This spatial inhomogeneity is rotated with bias voltage, reflecting the modification of the structure and symmetry of the adatom orbitals by the substrate. The simulated spectral maps of the Pb adatom based on density-functional-theory calculations agree well with experimental observations. This spatial inhomogeneity originates from the local extension of antibonding Pb states and the coupling to the substrate.