Liquid Phase Isolation of SnS Monolayers with Enhanced Optoelectronic Properties

Recent advances in atomically thin two dimensional (2D) anisotropic group IV_A -VI metal monochalcogenides (MMCs) and their fascinating intrinsic properties and potential applications are hampered due to an ongoing challenge of monolayer isolation. Among the most promising MMCs, tin (II) sulfide (SnS) is an earth-abundant layered material with tunable bandgap and anisotropic physical properties, which render it extraordinary for electronics and optoelectronics. To date, however, the successful isolation of atomically thin SnS single layers at large quantities has been challenging due to the presence of strong interlayer interactions, attributed to the lone-pair electrons of sulfur. Here, a novel liquid phase exfoliation approach is reported, which enables the overcome of such strong interlayer binding energy. Specifically, it demonstrates that the synergistic action of external thermal energy with the ultrasound energy-induced hydrodynamic force in solution gives rise to the systematic isolation of highly crystalline SnS monolayers (1L-SnS). It is shown that the exfoliated 1L-SnS crystals exhibit high carrier mobility and deep-UV spectral photodetection, featuring a fast carrier response time of 400 ms. At the same time, monolayer-based SnS transistor devices fabricated from solution present a high on/off ratio, complemented with a responsivity of 6.7 × 10^-3 A W^-1 and remarkable stability upon prolonged operation in ambient conditions. This study opens a new avenue for large-scale isolation of highly crystalline SnS and other MMC manolayers for a wide range of applications, including extended area nanoelectronic devices, printed from solution.