Electron Doping of Semiconducting MoS₂ Nanosheets by Silver or Gold Nanoclusters

Semiconducting two-dimensional (2D) materials have potential applications as ultrathin optoelectronic materials. Therefore, being able to precisely modulate the band gap is useful to improving their applicability. Electron doping of the semiconducting materials is one of the successful techniques used to modulate their band gap. Silver nanoclusters (AgNCs) or gold nanoclusters (AuNCs) a few nanometers in size can generate a high density of highly energetic hot electrons with relatively long lifetimes when photoexcited. The optical band gap of 2D MoS2 nanosheets shows different responses when integrated with different amounts of AgNCs or AuNCs due to the electron doping effect. Introducing a small amount of the nanoclusters to the surface of a MoS2 nanosheet lowered its optical band gap. Further reduction of the optical band gap of MoS2 is obtained upon tripling the amount of integrated nanoclusters. Conversely, the optical band gap of MoS2 was increased when integrated with 5 times the concentration of AuNCs and AgNCs. The optical band gap of the MoS2 nanosheets was significantly increased when integrated with an even higher concentration of AuNCs or AgNCs. The magnitude of the shift of the optical band gap of MoS2 induced by AgNCs is higher than that induced by AuNCs because the energy of LUMO of the AgNCs is higher than that of the AuNCs.