Impact of Potassium Doping on a Two-Dimensional Kagome Organic Framework on Ag(111).

Alkali element doping has significant physical implications for two-dimensional materials, primarily by tuning the electronic structure and carrier concentration. It can enhance interface electronic interactions, providing opportunities for effective charge transfer at metal-organic interfaces. In this work, we investigated the effects of gradually increasing the level of K doping on the lattice structure and electronic properties of an organometallic coordinated Kagome lattice on a Ag(111) surface. With the introduction of K dopants into the 4-fold N-Ag coordinated Kagome lattice, the highly periodic Kagome lattice gradually tends to become discrete. Combining synchrotron radiation photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and density functional theory calculations, we revealed the mechanism of structural transformation of the lattice, i.e., the change in thermodynamically favored structures caused by competition of electron donors. As an electron donor with a lower ionization energy, K adatoms tend to replace the Ag adatoms and form a more thermodynamically stable N-K coordination structure. Moreover, enhanced charge transfer from K to the Kagome lattice induced a rigid shift of the Fermi level. Our investigation provides new insights for the study of alkali-doped organometallic nanostructures.