Extraordinary Room-Temperature Photoluminescence in Triangular WS₂ Monolayers

Abstract

Individual monolayers of metal dichalcogenides are atomically thin two-dimensional crystals with attractive physical properties different from those of their bulk counterparts. Here we describe the direct synthesis of WS2 monolayers with triangular morphologies and strong room-temperature photoluminescence (PL). The Raman response as well as the luminescence as a function of the number of S–W–S layers is also reported. The PL weakens with increasing number of layers due to a transition from direct band gap in a monolayer to indirect gap in multilayers. The edges of WS2 monolayers exhibit PL signals with extraordinary intensity, around 25 times stronger than that at the platelet’s center. The structure and chemical composition of the platelet edges appear to be critical for PL enhancement.

Edge and confinement effects allow in situ measurement of size and thickness of liquid-exfoliated nanosheets

“…6h). This suggests that the band gap of the edge region in liquid-exfoliated WS 2 is smaller than that of the centre, in agreement with previous results 56 . Most importantly, neither very small (B50 nm), nor reasonably sized (B300 nm) few-layer species show a notable PL signal further supporting that the nanosheets with a nominal AFM height of 3 nm are monolayered nanosheets.…”

Booming Development of Group IV–VI Semiconductors: Fresh Blood of 2D Family

“…For example, it has been reported that MoS 2 has emerged with a direct bandgap of 1.8 eV when reduced the thickness to monolayer 25. Because of this merit, Few layered 2DLMCs such as transition metal dichalcogenides (TMDs) (MoS 2 ,26, 27, 28 WS 2 ,29, 30, 31, 32, 33, 34, 35, 36 TiS 3 ,37 etc.) and group III–VI nanomaterials (InSe,38, 39, 40, 41, 42 GaSe,43, 44, 45, 46, 47, 48 etc.)…”

Atomic layer deposition on 2D transition metal chalcogenides: layer dependent reactivity and seeding with organic ad-layers

“…1,2 The synthesis of these materials has been vastly improved over the last few years and many possible devices have been proposed and realised. [3][4][5][6] But to finally achieve their large-scale integration and production, it is necessary to make TMDs fully CMOS processable. One prerequisite for this is the deposition of subsequent layers on top of the TMD for gating and passivation as the performance and stability of TMD based devices hugely depends on their dielectric environment.…”

“…8 The most common ALD process is the deposition of Al 2 O 3 from alternating exposures of trimethylaluminium (TMA, Al(CH 3 ) 3 ) and water according to the reaction: 9 2Al(CH 3 ) 3 …”