Adsorbate-determined field emission resonances in STM current/voltage characteristics

The interaction of oxygen with Al(1 0 0) at 300 K was studied by STM operated in the field emission mode. The superlong series of field emission resonances corresponding to multiquantum vibrational excitation of oxygen clusters were initially observed. The measured energies of vibrational transitions (0.04, 0.08 and 0.12 eV) are in agreement with data known from HREELS measurements. For Cu/O system the exchange splitting of some spectra due to interaction of tunneling electron with the adsorbed ion-radical O2− was detected.