Hydroxide Modified Synthesis of Atomically-Doped Photoluminescent WS₂ Monolayers

Atomically doping in thin film poses a significant challenge due to the potential for dopant precipitation caused by self-purification effects. This challenge is particularly pronounced in the case of doping monolayers of photoluminescent transition metal dichalcogenides, where high energy barriers are also required to break the in-plane bonds between the transition metal (TM) and chalcogen atoms. To address this issue, this study introduces hydroxide ions to adsorb onto the surface of WS2 monolayers. This results in a significant reduction in the formation energy of the TMS bonds, enabling them to substitute for W sites and overcoming the self-purification effect of WS2 monolayers. The in-plane doping of TMs including Cr, Mn, Fe, Co, and Ni atoms is confirmed through precise atomic-scale chemical imaging using scanning transmission electron microscopy with electron energy loss spectroscopy mapping. Photoluminescence measurements reveal that the band structure of WS2 monolayers can be systematically modulated by different doping metals, owing to their distinct atomic sizes. In addition, the atomically-doped WS2 monolayers exhibit room-temperature ferromagnetism, which has never been seen in pristine WS2 monolayers. The modulation of the band structure and the emergence of magnetism in TMs-doped WS2 monolayers hold significant promise for optoelectronic and magnetoelectric applications.