Basic And Applied Research Of Surface And Interface Of Molybdenum Disulfide

As a transition metal chalcogenide,molybdenum disulfide is an important twodimensional material.Monolayer molybdenum disulfide is not only a direct bandgap semiconductor,but also has excellent mechanical properties and chemical stability.It has broad applications in microelectronics and other fields.The thickness of monolayer molybdenum disulfide is only 0.65 nm,and its properties are very sensitive to its surface and interface.The research and application of molybdenum disulfide cannot be separated from the exploration of its surface and interface properties.There are various defects on the surface of molybdenum disulfide,which largely determine the properties of molybdenum disulfide.At present,defects in molybdenum disulfide can be detected by electron microscope or optical means,etc.,but these methods for detecting defects also have their own shortcomings: Although we can obtain the atomic structure information of defects using electron microscopy,it is not suitable for the characterization of large-area molybdenum disulfide samples because its observation range is too small;Optical detection methods can only obtain qualitative information about defects.Rapid and accurate detection of defects in molybdenum disulfide is important for understanding and regulating its properties.The interface between layers of molybdenum disulfide and the interface between molybdenum disulfide and the substrate can serve as nanoscale channels for intercalation of molybdenum disulfide by liquid or ions,and the liquid and ions in the interface can regulate the properties of molybdenum disulfide.The regulation of the molybdenum disulfide interface can not only control the intercalation behavior of liquids or ions in the nano-scale channels composed of the molybdenum disulfide interface,but also can construct nano-and micro-scale channels with molybdenum disulfide as the inner wall.The regulation of the interface is very important to study the transport behavior of liquid or ions on the surface of molybdenum disulfide and to promote the application of molybdenum disulfide in the field of microfluidics and nanofluidics.This paper focuses on the surface and interface of molybdenum disulfide,which mainly includes the following two parts:1.The defects on the surface of molybdenum disulfide are visually and quantitatively detected rapidly by the method of defect amplification.We used calcium hypochlorite solution to etch molybdenum disulfide.Point defects in molybdenum disulfide are the starting points of etching due to their high chemical reactivity.The molybdenum disulfide etched by the calcium hypochlorite solution has triangular pits formed by the etching effect at the positions of the original defects.These pits can be observed by ordinary optical microscope.From the observation of pits,we can obtain the defect density and defect distribution of molybdenum disulfide.Combining with the results of fluorescence and Raman spectra of molybdenum disulfide before and after etching,as well as the atomic structure information of molybdenum disulfide obtained by scanning transmission electron microscopy,it can be confirmed that the calcium hypochlorite solution etched only the intrinsic defects in molybdenum disulfide without introducing new defects.This method for characterizing defects in molybdenum disulfide is not only simple,but also can give quantitative information of the defects in molybdenum disulfide,which is suitable for rapid characterization of large-area molybdenum disulfide quality.2.The interface between the molybdenum disulfide and the substrate is regulated by controlling the stress in the molybdenum disulfide,and the microfluidic and nanofluidic channels are further prepared.To strain the molybdenum disulfide,we applied additional compressive stress to the molybdenum disulfide on the sapphire substrate by depositing a compressive-stressed film on the surface of the molybdenum disulfide.Microfluidic and nanofluidic channels were created at the interface between the strained region of molybdenum disulfide and the sapphire substrate.The size and orientation of the newly created channels can be tuned by controlling the stress applied on molybdenum disulfide.While preparing the channel,we also studied the transport behavior of water into the interface between molybdenum disulfide and the substrate,and found that water can propagate rapidly between the interface of molybdenum disulfide and the substrate,and its speed can reach 2.5 mm/s.