On-Surface Structural and Electronic Properties of Spontaneously Formed Tb2Pc3 Single Molecule Magnets
Abstract
The single molecule magnet (SMM) bis(phthalocyaninato)terbium (III) (TbPc2) has attracted steady research attention as an exemplar system for realizing molecule-based spin electronics. In this paper, we report on the spontaneous formation of Tb2Pc3 species from TbPc2 precursors via sublimation in ultrahigh vacuum (UHV) onto an Ag(111) surface. The molecules on the surface are inspected using combined scanning tunneling (STM) and non-contact atomic force microscopies (nc-AFM) at 5 Kelvin. Submolecular resolution and height dependent measurements supported by density functional theory (DFT) calculations unambiguously show the presence of both TbPc2 and Tb2Pc3 species. The synthesis of Tb2Pc3 species under UHV conditions is independently confirmed by chemical analysis. The high-resolution AFM imaging allows us to register the orientation of the topmost Pc ligand in both Tb2Pc3 and TbPc2 relative to the underlying Ag(111) surface. Measurements of the electronic structure reveal the selective appearance of a Kondo signature with temperature 30K in the Tb2Pc3 species, localized to the Pc ligand lobes. We attribute the presence of the Kondo resonance on select Tb2Pc3 molecules to the orientation of internal molecular ligands. High-resolution AFM imaging identifies geometric distortions between Tb2Pc3 molecules with and without the Kondo effect, the result of the complex interplay between structural and electronic differences.
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