First-principles Calculation Of Two-dimensional Hexagonal Titanium Nitride

Since the single-layer hexagonal graphite(called graphene)was successfully exfoliated from the layered graphite,the unique physical and chemical properties and superior performance of graphene have stimulated people's enthusiasm for the research of other two-dimensional materials.Among them,the magnetic two-dimensional materials can be widely used in high-energy-efficiency ultra-compact spintronics devices(such as high-density data storage,high integration density,low power consumption and high operating speed).Therefore,finding and designing stable two-dimensional materials with intrinsic magnetism is very necessary,this is also one of the current research hotspots.Recently,some two-dimensional layered materials with clear ferromagnetism have been discovered experimentally,which has aroused great interest in the development of new low-dimensional magnetic materials.Especially,the two-dimensional intrinsic ferromagnetic semiconductor,they have the dual properties of ferromagnetism and semiconductor.The application of silicon-based semiconductor technology to two-dimensional intrinsic ferromagnetic semiconductors will enable the development of modern chips that may bring together a variety of functions(such as computing,storage,communication,and information processing).With much faster data transmission,less energy loss and less loss of stored data,these chips have the potential to revolutionize information technology.With the development of density functional theory and the continuous improvement of first-principles calculation methods,it is also very meaningful to design new two-dimensional(2D)magnetic materials with a purpose and basis in theory,and to guide the synthesis of experiments.In this thesis,two-dimensional(2D)graphene-like TiN(h-TiN)is predicted to be a stable 2D intrinsic magnetic semiconductor through the calculations of the electronic and magnetic using first-principles based on density functional theory,and further,the effect of the train on electronic and magnetic properties is examined,and transport properties of h-TiN is explored by employing deformation potential theory and Boltzman transport theory.The main contents include the following points:(1)The stability and feasibility of the h-TiN are first examined by calculating the phonon dispersion,binding energy,formation energy and dissociation energy of h-TiN.No virtual frequency in phonon dispersion indicates that the honeycomb structure of h-TiN is dynamically stable.The higher binding energy implies that the bonding degree of Ti-N bond of the h-TiN is relatively strong.Negative formation energy indicates that the h-TiN can be synthesized by certain means(the most common molecular beam epitaxy).The mechanical exfoliation of the h-TiN from its bulk crystal seems to be the least possible according to the high dissociation energy.Further,the h-TiN is thermal stable up to 700 K by moleculae dynamics(AIMD)simulations.(2)The electronic and magnetic properties of h-TiN are calculated,including the band structure,total density of states(TDOS)and partial wave local density of states(PDOS).The h-TiN is predicted to be an intrinsic magnetic semiconductor.The band gaps are 1,33 and 4.42 e V for spin-up and–down channels,respectively.The total magnetic moment is 1?_Bwhich is fully contributed by Ti atoms.The easy axis of magnetization is in the two-dimensional plane due to the lower energy of h-TiN in the plane than that of out-of-plane,and the magnetic anisotropy is far larger compared with some common three-dimensional magnetic materials.The Curie temperature of h-TiN is estimated to be about 205 K by the average field approximation.(3)Then the effect of iso-biaxial strain on the electronic structure and magnetic properties of h-TiN,is performed with iso-biaxial train from-4%to 4%.The Curie temperature cannot be enhanced by the train,and decreases in parabola-type with the increase of the trains.The band gap of the h-TiN increases and decreases roughly linearly for spin-up and–down channels,respectively,but the magnetic moment of the h-TiN remain unchanged when the train changes from-4%to 4%.Thus,the magnetic semiconducting behavior of the h-TiN is robust against the train.(4)Finally,the transport properties,including elastic modulus,effective carrier mass,carrier mobility,relaxation time and conductivity of the h-TiN are calculated by using deformed potential theory and carrier transport theory.The two-dimensional h-TiN has a relative larger hardness,the migration rate of electrons is much greater than the migration rate of holes,and the electrical conductivity is much greater than that of some conventional semiconductors.