Reversibly Switching the Charge State and Adsorption Location of A Single Potassium Atom on Ultrathin CuO Films

Potassium (K) cations are spontaneously formed upon thermal deposition of low-coverage K onto an ultrathin CuO monolayer grown on Cu(110) and they were explored by low-temperature scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy. The formed K cations are highly immobile and thermally stable. The local work function around an individual K cation decreases by 1.5 +/- 0.3 eV, and a charging zone underneath it is established within about 1.0 nm. The cationic and neutral states of the K atom are switchable upon application of an STM bias voltage pulse, which is simultaneously accompanied by an adsorption site relocation.