  The electrical and optoelectronic properties of transition-metal
dichalcogenides (TMDs), such as MoS2, are highly dependent on carrier doping
and layer thickness. The ability to selectively control these two critical
characteristics is of great importance to develop TMD-based multifunctional
device applications, which remains challenging. Here, we report a strategy for
controllable surface modification and layer thinning of MoS2 via ultraviolet
(UV) light irradiation in a silver ionic solution environment. The results show
that by adjusting UV irradiation time, nanostructured silver ultrathin films
(~2.9 nm) are uniformly deposited on monolayer MoS2 and can lead to
controllable p-type doping effect, while the thickness of MoS2 from few-layer
to bulk crystals could be thinned down to the atomic monolayer limit. Both
silver nanostructure deposition and layer thinning process have been evidenced
to initiate from the edges of MoS2, and independent of the edge type, thus
revealing a unique UV light-assisted defect-induced surface modification and
layer thinning mechanism. Overall, this study provides a new methodology for
selective control of doping and layer thickness in TMDs, paving the way for
developing novel 2D nanoelectronics and integrated optoelectronics.
