Mechanical Thinning Of Black Phosphorus Using AFM

Black phosphorus,a new two-dimensional semiconductor material has drawn much attention because of its excellent optical and electrical characteristics in recent years.Similar to graphene,each atom covalently link together with the three adjacent atoms and form a puckered honeycomb structure in-layer.With weak van der Waals force,monolayer BP connect each other and form a stacked Multi-layer BP.BP has a direct bandgap which is thickness dependent while the bandgap type is not.The asymmetry structure of the black phosphorus leads to an apparent anisotropy in terms of carrier mobility,switching regulation ratio,and Young's modulus.Two-dimensional black phosphorus is very sensitive to visible light and infrared light,and the response can be modulated by the thickness of BP and the properties of incident light.Therefore,black phosphorus has a limitless application in photoelectric detection.The excellent properties above is all thickness dependent,single layer or few layer BP FET?filed effect transistor?device shows an excellent characteristics with a large on/off ratio of 10⁵.The ultra-thin BP degrade faster than the bulk one under oxygen,water and light condition.Thus,it is very difficult to obtained the ultra-thin BP by traditional mechanical Scotch Type method in laboratory.In this paper,a new AFM-based layer-by-layer mechanical thinning method of BP is proposed.Combined with the AFM probe calibration system,we have studied the mechanism of the thinning method.The main contents are as follows:1.As the traditional method can not controllably obtain the BP flake with a certain thickness,we proposed a new method based on AFM after systematically analyzed the research status of BP.2.Combine with the motorized position system,we developed a new all-dry transfer platform to transfer the aim BP flake to the Si/SiO₂ substrate precisely.3.A new optical structure was developed for the calibration system after analyzing the shortcomings of the original system which makes the system more compact and more stable.4.The mechanism of the thinning method was systematically studied.The interaction between AFM probe and black phosphorus surface has been analyzed in energy and mechanics respectively.We introduce the software and hardware platform of the BP thinning mrthod.The influence of the cutting force and direction of the single-line mode cutting have been systematically studied.After systematically studied the thinning method,we drawn the conclusion that we can thin the BP layer-by-layer using AFM.5.A two layers BP flake was obtained from an eight layers one by using the thinning method.A black phosphorus FET device has been fabricated to analyze the output before and after thinning.The oxide surface can also be removed using the mechanical method and will obtain a new and clean surface.Two different three-dimensional steps structure were made since the thinning method can be traded as a nano-manufacturing method.