Van der Waals Encapsulation by Ultrathin Oxide for Air-Sensitive 2D Materials.

The ambient stability is one of the focal points for applications of 2D materials, especially for those well-known air-sensitive ones, such as black phosphorus (BP) and transitional metal telluride. Traditional methods of encapsulation, such as atomic layer deposition of oxides and heterogeneous integration of hexagonal boron nitride, can hardly avoid removal of encapsulation layer when the 2D materials are encapsulated for further device fabrication, which causes complexity and damage during the procedure. Here, a van der Waals encapsulation method that allows direct device fabrication without removal of encapsulation layer is introduced using GaO from liquid gallium. Taking advantage of the robust isolation ability against ambient environment of the dense native oxide of gallium, hundreds of times longer retention time of (opto)electronic properties of encapsulated BP and MoTe devices is realized than unencapsulated devices. Due to the ultrathin high-κ properties of GaO, top-gated devices are directly fabricated with the encapsulation layer, simultaneously as a dielectric layer. This direct device fabrication is realized by selective etching of GaO, leaving the encapsulated materials intact. Encapsulated 1T' MoTe exhibits high conductivity even after 150 days in ambient environment. This method is, therefore, highlighted as a promising and distinctive one compared with traditional passivation approaches.