Preparation Of Black Phosphorus Single Crystal And Its Quantum Dots

Since the successful preparation of graphene in 2004,two-dimensional materials have attracted extensive attention due to their excellent physical and chemical properties.In recent years,people have successively discovered and successfully prepared some new graphene-like two-dimensional materials,such as MoS₂,Graphene,Silene,etc.These two-dimensional materials can partially compensate for the defects of graphene,but there are still some deficiencies,such as the low mobility of MoS₂ and the greater fluctuation of the stability of Silene with the substrate.In view of this,the search for new two-dimensional materials to make up for the shortage of existing materials has become a target for people to explore.Black phosphorus is p-type semiconductor lamellar material with a direct bandgap,which can be obtained by adjusting the number of layers?block bandgap0.3ev,monolayer 2.0ev?.Black phosphorus also has high electron mobility and is expected to become a core material for the new generation of semiconductor industry.At the same time,because the structure leads to significant planar anisotropy,it has important research value in electron-phonon interaction,thermoelectric materials and nervous system.The early preparation method of monolithic black phosphorus single crystal has the disadvantages of high cost,complex device and low crystallinity.At present,two-dimensional black phosphorus and zero-dimensional black phosphorus quantum dots are usually formed by physical or chemical methods from the stripping of block black phosphorus,so it is particularly important to prepare high-quality black phosphorus single crystal.However,the liquid phase stripping method is the most commonly used method for the preparation of low-dimensional black phosphorus.Unfortunately,the selected solvent has the disadvantages of toxicity and high boiling point,which is not conducive to large-scale production.Black phosphorus quantum dots are easy to be oxidized,which limits their application space to some extent,while the longer preparation time reduces the crystallinity and produces structural defects.Therefore,it is urgent to innovate the existing methods and develop a new method for the preparation of black phosphorus quantum dots.The preparation and properties of black phosphorus single crystal and quantum dots are studied in this paper.The specific research work is as follows:1.High quality black phosphorus single crystal was successfully obtained by mineralization method,with tin and iodine as mineralization agents and vacuum sealed in quartz tube.Compared with banded black phosphorus,the black phosphorus obtained in this paper is more likely to grow into large-sized single crystal.2.The effects of different temperatures on the growth of black phosphorus single crystal were studied through four different temperature and rise/drop procedures.The results showed that purple phosphorus was generated at 620-500?during the cooling process.500?is the key temperature for the growth of black phosphorus,and the proper extension of its heat preservation time is conducive to the growth of black phosphorus single crystal.The growth process of black phosphorus without gas transport was described.The heterogeneous phenomenon of nucleation during the growth of black phosphorus was explained by the nucleation theory of crystal growth.3.The high quality black phosphorus single crystal prepared by the mineralization method is used as the raw material,which is ground and placed in the microwave synthesizer.The microwave-assisted liquid phase stripping method is used to prepare the high quality black phosphorus quantum dots in a short time.By studying the effect of different microwave time on the performance of black phosphorus quantum dots,the formation process of black phosphorus quantum dots was revealed.Preliminary results showed that the BPQDs prepared had good stability,with an average size of 2.5 nm and a height of 2.19 nm,corresponding to 1-4 layers of black phosphorus quantum dots.Compared with block black phosphorus,the three Raman characteristic peaks of BPQDs were all accompanied by weakening and redshift,which were 1.3,2.4 and 3.1 cm^-1,respectively.UV-vis showed three characteristic absorption peaks at 219,278,and 323 nm.