HIGH-RESOLUTION SPECTROSCOPY OF WEAKLY CHEMISORBED SPECIES USING A LOW-TEMPERATURE SCANNING TUNNELING MICROSCOPE (STM) - CO CU(III)/

High-resolution spectroscopy with an STM (STS) concerning the electron ic aspects of adsorption is presented. Comparing spectra taken directl y at an adsorbate and in its vicinity with microscopically identical t ips allows to separate tip-induced features from such originating from the chemical interaction of the adsorbate with the substrate. The eff ects of tip contamination are studied by comparing spectra taken with bare and CO-functionalized tips. It is found that STS can have resolut ion power not only in the direct vicinity of the Fermi edge but also a few eV into the occupied and unoccupied states. We present exemplary measurements on CO/Cu(111) where as a new feature an unoccupied, proba bly Sa-derived state was found. (C) 1998 Elsevier Science B.V. All rig hts reserved.