Study On Phase Transition And Properties Of Black Phosphorus Nanosheets

Black phosphorus is the most stable elemental element in the allotrope of phosphorus,and is an orthorhombic structure at normal temperature and atmospheric pressure.Because the atomic layer is quasi-two-dimensional folds and the adjacent atomic layers are connected by vander Waals force,Through the mechanical stripping method can get less black phosphorus,also known as black phosphorus.Low-layer black phosphorus at room temperature and pressure under the P-type semiconductor properties,not only has a similar performance of graphene,but also with the transition metal chalcogenide unique regulatory bandgap characteristics.As the black phosphorus has a unique lattice structure,excellent electrical and optical properties and gradually become a two-dimensional material industry research hotspot.Although there have been many studies reported that the body material black phosphorus under high pressure suppression phase change law,but for the black phosphorus nanoplate structural phase transition and metallization phenomenon is still not clear,because when the size of the material After the nanometer scale,due to the small size effect will cause the material in the electronic distribution and energy band structure changes,in the macro to make the material appear new physical properties,so based on the above problems,we launched the black phosphorus nanosheets under high pressure structure and the nature of the study,the results are as follows:1.The black phosphorus samples in this paper were analyzed by scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The films were characterized by a lamellar structure with a size of about 1?m to 10?m and a thickness of about 70 nm.In addition,we have obtained that the black phosphorus nanosheets have good lattice structure and the lattice has the swelling phenomenon through the micro-zone XRD experiment under normal pressure.Then,by collecting atmospheric pressure Raman spectroscopy of black phosphorus nanosheets,The black phosphor nanosheets have three Raman vibrations,which are Ag1 modes that characterize out-of-plane vibrations,represent the B2 g in-plane vibration mode in the direction of the armchair and the Ag2 in-plane vibration mode in the zigzag direction;we performed the low wave number Raman spectroscopy tests showed no interaction between the layers that characterize the interaction between the respiration modes.2.The lattice phase transition of the black phosphorus nanosheets under high pressure was investigated by using the in situ Raman spectroscopy at high pressure and the synchrotron radiation X-ray diffraction technique under high pressure.The XRD and Raman peaks were analyzed with the change of pressure behavior law,the process of structural phase change made a reasonable explanation.The results show that the black phosphorus nanosheets undergo two structural phase changes in the pressure range of 0-20 GPa.First,when the pressure is about 8GPa,the first structural phase transition occurs,and the orthorhombic orthogonal structure is transformed into the rhombic phase structure,and the phase transition is complete.Then,as the pressure continues to rise,the black phosphorus nanometer The phase transition pressure point is about 16 GPa.The pressure-relief spectroscopy clearly shows that the black phosphorus nanosheet is a reversible structural phase transition under high pressure.In addition,the use of high-pressure infrared light reflection Technology,that black phosphorus nanoplate in the pressure of about 4GPa when the phenomenon of metallization.Finally,we conclude that the phase transition pressure point of the black phosphorus nanoplate under high pressure is higher than that of the bulk material black phosphorus,compared with the previous study.The difference of the size of black phosphorus nanosheets and bulk black phosphorus is the main reason that the phase change pressure point of the two is different.In this paper,the lattice of black phosphorus nanoplate has the phenomenon of expansion,the micro-size decreases,Nano-scale,with a large surface area and more surface defects,the surface energy can increase,resulting in the occurrence of structural phase change requires more energy,so the structural phase of the pressure point will rise.