Scanning tunneling microscopy, orbital-mediated tunneling spectroscopy, and ultraviolet photoelectron spectroscopy of nickel(II) octaethylporphyrin deposited from vapor

Thin films of vapor-deposited Ni(II) octaethylporphyrin (NiOEP) were studied supported on gold. Thin films thermally deposited onto flame-annealed Au(111) were analyzed by ultraviolet photoelectron spectroscopy (UPS) using He I radiation and by X-ray photoelectron spectroscopy (XPS) using Mg Kalpha radiation. Reflectance absorption infrared spectroscopy (RAIRS) was used to study NiOEP films on polycrystalline gold. Scanning tunneling microscopy (STM) and orbital-mediated tunneling spectroscopy (STM-OMTS) were performed on submonolayer films of NiOEP supported on Au(111). The highest occupied pi molecular orbitals of the porphyrin ring were seen in both STM-OMTS and in UPS at about 6.4 and 6.8 eV below the vacuum level. The lowest unoccupied pi* molecular orbital of the porphyrin ring also was observed by STM-OMTS to be located near 3.4 eV below the vacuum level.