Physical properties and metal ion specific scanning tunneling microscopy images of metal(II) tetraphenylporphyrins deposited from vapor onto gold (111)

Thin films of vapor deposited Cu(II), Ni(II), and Co(TI) complexes of tetraphenylporphyrin (CuTPP, NiTPP, and CoTPP) supported on gold are studied by Reflectance Absorption Infrared Spectroscopy (RAIR) and X-ray photoelectron spectroscopy (XPS). In addition, scanning tunneling microscopy (STM) images of ultrathin (submonolayer) thermally deposited films of CoTPP and NiTPP on Au(lll) are reported. The constant current STM images show a remarkable bias dependence that allows for the selective identification of different metallotetraphenylporphyrins (MTPPs). High resolution STM data are presented that clearly show the individual MTPP molecules and allow easy differentiation between NiTPP and CoTPP, even when mixed monolayer structures are studied. The strong tunneling enhancement through the Co(II) d(z2) orbital at intermediate bias values parallels what is observed in Co(II) phthalocyanines and is especially interesting since the cobalt ion in CoTPP is presumed to be located several Angstroms above the Au(lll) plane relative to the cobalt ion in CoPc.