Decoupling the Interaction between Wet-Transferred MoS2 and Graphite Substrate by an Interfacial Water Layer

The nondestructive and clean transfer of 2D-layered materials from growth onto target substrates is a key step in their practical applications. Some nonetching transfer methods are developed to avoid contaminations from chemical etchants, while the influences of other transfer media, such as the commonly used water, are rarely explored. Herein, a one-step polymer-free transfer of monolayer MoS2 from glass onto a graphite substrate by using only ultrapure water as the working medium is reported. Based on room-temperature observations, it is revealed that the MoS2-graphite interface is not atomically flat due to the trapping of water clusters, and even extended ultrahigh-vacuum annealing processes cannot easily remove the trapped water. More interestingly, the intensive scanning tunneling microscopy/spectroscopy investigations show that the interfacial water can be converted into an insulating layer by sample cooling down to approximate to 78 K, leading to a weakened interfacial interaction of MoS2/graphite and a more intrinsic bandgap of MoS2. This work hereby provides fundamental insights into the effect of wet-transfer-induced water intercalation on the structural and electronic properties of 2D-layered materials, which should inspire the development of more clean transfer routes for achieving improved device performances.