Tunable Single-Atomic Charges on a CleavedIntercalated Transition Metal Dichalcogenide, Co_1/3NbS₂

Manipulating the charge state of an individual atom and arranging the charge-modified atoms in a desired manner can provide an ideal platform for the simulation and understanding of atomic charge interactions and the exploitation for atomic-scale devices. Ever since the first demonstration of charge manipulation from a single gold atom deposited on thin insulating layer using scanning tunneling microscopy (STM) probe, charge manipulation of atoms/molecules deposited by evaporation techniques have been established as a toolkit to explore atomic charging-related phenomena. We demonstrate that such a charge state control is possible for intercalant ions exposed on a surface after cleaving/exfoliation of intercalated layered material without any evaporation technique. After cleaving of Co-intercalated NbS₂, each Co ion left on the surface can maintain a metastable charge state manipulated by voltage pulse from STM probe despite the direct contact with the metallic NbS₂. Density functional theory calculation confirms that this unexpected metastable charge state is possible by the limited Co and Nb a_1g orbital hybridization due to the modified crystal field at the surface. We anticipate that this could be a new step towards realizing single-atom-level electronics/spintronics in 2D material.