Synthesis, Characterization And Optoelectronics Properties' Regulation Of TMDs And Black Phosphorus 2D Materials And Devices

Two-dimensional materials,are crystal materials with only one or several atomic layer in thickness.All atoms are bonded in the two-dimensional plane,and only van der Waals interaction excists in the interlayer.The first discovered two-dimensional material was graphene that isolated from the graphite in 2004.Later,people have discovered a large number of two-dimensional materials,covering the conductors,semiconductors and insulators,in which,the two-dimensional semiconductor materials,such as transition metal dithioates?TMDs?and black phosphorus are the most popular.Numerous family members and rich features of two-dimensional materials contain all the basic elements for buinding a complex Nano Electro Mechanical Systems?NEMS?.The unprecedented physical,optical and electrical properties of two-dimensional materials enable them a very broad application prospects.The single atomic layer thickness and perfect crystal structure make them have the ability to be used in ultra-small nano devices and large integrated circuits.Superior mechanical strength and mechanical flexibility can ensure the reliability and flexibility of their devices.The development and application of devices with two-dimensional materials are the research focus all over the world recently.After nearly a decade of research and development,new challenges are still emerging in the preparation,characterization and development of two dimensional materials and their optoelectronic devices,due to the constant discovery of new members and new applications directions,although great progress has been made so far.Aiming at these challenges,in this paper,we have systematically studied the new preparation and characterization methods of TMDs and black-phosphorus two-dimensional materials.And some two-dimensional optoelectronic devices were developed based on micro-nano fabrication technology.On this basis,their performance regulation methods and related theories were studied.The main contents and achievements of this paper are as follows:1.An optical non-contact rapid measurement new method based on optical phase shift interferometry?PSI?was proposed.Firstly,the relationship between the optical path length difference?OPL?and the number of layers of MoS₂ and black phosphorus was measured by PSI measurement and atomic force microscopy,and the validity of the method was verified.Then,the theoretical calculation of the OPL values of 1-4 layers MoS₂ and black phosphorous samples were obtained by modeling the measuring process and generating the simulation program.The measured values were in good agreement with the calculated values,indicating the correctness of the theoretical model.This theoretical model can therefore be applied to the prediction of OPL values of other two-dimensional materials.2.A new method for black phosphorous nanosheets and their device preparation based on oxygen plasma etching was proposed.This method can achieve fabricating phosphorene films with a designated number of layers ranging from a few-down to a mono-layer.During the etching process a phosphorus oxide capping layer is formed which acts as a protective coating onto which we can subsequently add an Al₂O₃ passivation layers by atomic layer deposition.This method has solved the difficulty in preparing high-quality,air-stable few-or mono-layer phosphorene films and could make black phosphorus a practical material for fundamental research and optoelectronic devices.Moreover,in a stabilized phosphorene monolayer,we were able to precisely engineer defects for the first time.This led to efficient emission of photons at new frequencies in the near-infrared?NIR?at room temperature.Additionally we demonstrate the use of an electrostatic gate to tune the photon emission from the defects in a monolayer phosphorene.This could lead to new broadband NIR lighting devices operating at room temperature.3.Based on the micro-nano fabrication technology of two-dimensional materials,several critical process improvements were proposed.And a fabrication process of two-dimensional material metal-oxide-semiconductor?MOS?device and freestanding device was designed.By changing the process sequence of device preparation,the cycle and efficiency of device preparation are reduced.The efficiency of device preparation is improved.And a dry and fast fabrication process of different kinds of two-dimensional material devices is achieved,which effectively avoiding the contamination and damage of the two-dimensional material sample during the device preparation process.4.Based on the fabricated MoS₂ MOS device,the energy band modulation in bilayer MoS₂ was achieved and its exciton and trion dynamics were studied for the first time.Owing to the indirect band gap nature in bilayer molybdenum disulphide?MoS₂?,the optical properties of bilayer MoS₂ were found to lack of electrical tunability at room temperature.Here we demonstrate the valley control of exciton and trion dynamics in bilayer MoS₂,via the co-modulations by both temperature and electric field.From numerical calculations,we show that we could use temperature to tune the valley positions in bilayer MoS₂ and make its electronic band structure approaching direct band gap manner.More importantly,this indirect-to-direct transition in bilayer MoS₂ at low temperature provides the electrical tunability of the K-K direct PL transition,which enables the exploration of exciton and trion dynamics in bilayer MoS₂.Our findings will enable new applications of excitonic devices based on bilayer MoS₂.5.Based on the fabricated MoSe₂ freestanding device,the biexciton emission in MoSe₂ was stimulated for the first time and its Theoretical model was proved.The emission of biexcitons in atomically thin MoSe₂ was successfully triggered for the first time,via the engineering of three critical parameters:dielectric screening,density of trions and excitation power.The observed binding energy and formation dynamics of these biexcitons strongly support the model that the biexciton emissions are from excited state biexciton.More importantly,we found the excited state biexcitons can not only exist at cryogenic temperatures,but can also be triggered at room temperature in a freestanding bilayer MoSe₂.The demonstrated capability of biexciton engineering in atomically thin MoSe₂ opens a new route for exploring fundamental many-body interactions and enabling novel device applications,such as bright entangled-photon sources operating at room temperature.