Scanning tunneling microscopy investigation of Tris(phthalocyaninato) yttrium triple-decker molecules deposited on Au(111)

We studied triple-decker tris(phthalocyaninato)yttrium (Y ₂Pc₃) molecules deposited on a Au(111) surface with a low-temperature scanning tunneling microscope (STM). It is shown that the triple-decker molecule can be successfully transferred to the Au(111) surface by a sublimation method in the ultrahigh vacuum condition. A monolayer film of Y₂Pc₃ is observed with a height of ∼0.55 nm from the bare Au(111) surface. The molecules are adsorbed with a flat-lying configuration and a pseudosquare lattice is formed. Inside each molecule, eight bright protrusions were observed in the occupied-state images, which correspond to the high density-of-state (DOS) area on both sides of four phenyl rings in the top phthalocyanine (Pc). Scanning tunneling spectroscopy (STS) data show distinct features both in occupied and in unoccupied states. The variation of STS spectra when the tip moved from the ligand position to the center of the molecule was small, showing a limited contribution from the center metal.