First-principles Study Of The Two-dimensional Blue Phosphorus And Its Related Structures

Since the discovery of graphene in 2004,a growing number of new two-dimensional materials,including Mo S₂,silicones,boron nitride and phosgene,have come to the attention of researchers because of their excellent physical properties.These two-dimensional materials offer better controllability and higher surface area than conventional block materials and one-dimensional materials,and hold great promise for applications in spintronic devices.An isomeric isomer of black phosphorus,blue phosphorus,has been successfully isolated experimentally,and in this thesis,the properties of blue phosphorus and its related structures have been investigated using the VASP package and ATK software,mainly using the first nature principle calculation method based on density general function theory.The main research elements and conclusions of this thesis are as follows.（1）In this paper,the electronic structure and magnetic properties of transition metal atoms（Sc,Ti,V,Mn,Fe,Co,Ni,Cu and Zn）adsorbed on the surface of blue phosphorus monolayer are systematically investigated using the first-principles calculation method based on density ubiquitination theory.Based on the structural symmetry of blue phosphorus,we selected three different adsorption sites,namely the vacant site of the phosphorus hexamerocycle,the top site of the top phosphorus atom and the top site of the bottom phosphorus atom,and found by the binding energy calculation that all the 3D transition metal atoms,except the Zn atom,can be stably adsorbed on the surface of the blue phosphorus monomolecular layer,and this adsorption is more stable than the adsorption of 3D transition metal atoms on the surface of graphene.In addition to Ni atoms,the adsorption of Sc,Ti,V,Cr,Mn,Fe,Co and Cu atoms on the blue phosphorus monomolecular layer causes the blue phosphorus to become magnetic with a magnetic moment in the range of 1 to 5μB,making the originally non-magnetic blue phosphorus monomolecular layer exhibit magnetic semiconductor properties.The origin of the magnetic moment is determined by the P-D hybridization mechanism between the 3D transition metal atoms and the blue phosphorus monomolecular layer.The effect of biaxial strain on the magnetism of the blue phosphorus adsorption system was also studied.The results show that the Sc-,Cr-,Mn-,Fe-,Co-,and Ni-adsorption systems have stable magnetic strains after applying biaxial elastic stresses,which is beneficial for spintronics applications,but the magnetic moments of Ti,V,and Cu adsorption systems are more sensitive to strain when adsorbed on blue phosphorus monomolecular layers,and they have the potential to be used in strain-sensitive spintronics devices such as sensors.These indicate that stress can effectively modulate the magnetism of 3D transition metal atoms adsorbed into the blue phosphorus system.（2）In addition,we have theoretically constructed a new two-dimensional material,As P,based on the first-principles calculation by replacing the phosphorus atoms at the top of blue phosphorus with arsenic atoms.In this part of the work,we have systematically investigated the two-dimensional material As P,and firstly,the two-dimensional material As P was confirmed to have specific dynamic and thermodynamic stability through phononon calculations and calculations from molecular mechanics simulation experiments.The electronic properties of the material were then investigated and the energy band structure showed that the two-dimensional As P material is a direct bandgap semiconductor with a bandgap value of 1.08 e V and does not show magnetic properties.The state density,on the other hand,reveals a strong hybridization between the P-3p orbitals and the As-4p orbitals.In order to investigate the application of As P in optoelectronic devices,we applied biaxial stress to achieve a modulation of its band structure,with the bandgap value decreasing when compressive stress is applied,and disappearing when compressive stress is5%,changing to a metallic state.In the process of applying tensile stress,the bandgap value is gradually increasing,but after the tensile stress of 6%,the valence band between M and K points gradually becomes the new valence band top,so that As P is transformed into an indirect bandgap semiconductor,and with the decline of the guide band part,the bandgap value is also gradually decreasing.Finally,the light absorption coefficients of As P two-dimensional materials were investigated and it was found that As P has a certain absorption capacity in the visible region,but it mainly absorbs UV light,so it can be used in UV detectors and so on.（3）Finally,the structural and electronic properties of novel heterogeneous junction materials consisting of two-dimensional materials As P and graphene were also studied using density function theory.It was found that the As P/graphene heterogeneous junction retained some interesting properties of As P and graphene under the van der Waals interaction and formed an n-type Schottky contact in the base state of the As P/graphene heterogeneous structure.Furthermore,by applying a biaxial stress of-5%to 5%,we can find that the nature of the direct bandgap of the two-dimensional As P material in the heterogeneous structure is not transformed and,at stresses greater than 2%,the controllability of the Schottky barrier height can be achieved by adjusting the position of the Dirac cone of graphene relative to the As P band edge,inducing a transformation of the heterogeneous junction from n-type Schottky contact to p-type Schottky contact.Our findings may provide physical mechanisms to improve and regulate the electrical properties of nanodevices and may also contribute to practical applications of As P/graphene heterogeneous structures.