SCANNING-TUNNELING-MICROSCOPY OF METAL PHTHALOCYANINES - D(7) AND D(9) CASES

Scanning tunneling microscopy (STM) images of cobalt(II) phthalocyanin e (CoPc), copper(II) phthalocyanine (CuPc), and mixtures of the two ad sorbed on the Au(111) face are reported. Based upon the stability and ease of obtaining molecular images, CoPc appears to adsorb more strong ly than CuPc on Au(111), but both species provide images showing submo lecular structure. The mixed CoPc and CuPc films also provide high-qua lity images showing details of the internal structure of the metal pht halocyanine. A particularly exciting aspect of this work is the strong influence of the metal ion valence configuration on the observed tunn eling images. Unlike CuPc, wherein the central metal appears as a hole in the molecular image, the cobalt atom in CoPc is the highest point (about 0.3 nm) in the molecular image. These data are interpreted as i ndicating that the Co(II) d(7) system has significant d-orbital charac ter near the Fermi energy while the Cu(II) d(9) system does not. This interpretation is consistent with theoretical calculations that predic t a large contribution of cobalt d-orbitals near the Fermi energy, and with inelastic electron tunneling spectra that show d-orbital-related bands within 1 eV of the Fermi energy. An intriguing aspect of this w ork is that it may be possible to chemically identify the different me tal phthalocyanines simply by their appearance. This can be used to ad vantage in the study of surface diffusion, 2-d sublimation, and the su rface thermodynamics and kinetics of adlayer formation.