First-Principles Study On Nucleation Process Of Hexagonal Boron Nitride On The Surfaces Of Transition Metals

Hexagonal boron nitride(h-BN)is a two-dimensional layered material with a graphene-like honeycomb structure.It has a wide band gap of about 5.97 e V and excellent physical and chemical properties.It has great application potential in the fields of nanoelectronic devices and deep ultraviolet optoelectronic devices,and has received extensive attention from many researchers.The difficulty in preparing high-quality and large-size h-BN films limits its wide application.Chemical vapor deposition(CVD)is considered to be the most promising synthesis method for controllable preparation of h-BN film,and understanding its growth mechanism is crucial for improving the quality of h-BN film.Based on density functional theory(DFT)and classical crystal growth theory,the nucleation of h-BN and the influence of substrate surfaces on the growth of h-BN were systematically studied.The metal substrates suitable for the growth of h-BN film were designed and screened,and provides some theoretical references for experimental workers.The specific research contents and results are as follows:1.The nucleation process of h-BN on the Ni(111)surface was studied,and the results show that h-BN undergoes a stable configuration transition from a one-dimensional chain to an two-dimensional sp~2 honeycomb structure during the nucleation process.When the cluster contains BN pairs less than 8,the chain configuration is the most stable,while when the cluster n is larger than 7,the honeycomb configuration is stable.Due to the adding continually of BN pairs,the energy of the clusters continue to decrease,and the clusters continue to grow on the Ni surface until the h-BN film completely covers the entire Ni substrate.The critical size of stable structure transition can be regulated by changing the chemical potential.2.The stability of(BN)_n(n=1-12)clusters on Ni(100),Ni(110)and Ni(111)surfaces was studied.The results show that the three surfaces have undergone structure transformation from a chain to an honeycomb except that the critical sizes are different.The low-index surface(100)is more suitable for h-BN nucleation at the initial stage,and with the growth of h-BN,Ni(111)surface becomes energetically preferred.This difference is mainly attributed to the stacking density of metal atoms,the symmetry of the substrate,the deformation of BN clusters,and the lattice matching between BN clusters and different metal surfaces.Their synergistic effect ensures the effective charge transfer between the BN cluster and the underlying substrate,and determines the nucleation of the BN cluster.The nucleation barrier and critical size of BN clusters can be controlled by adjusting the ratio of B to N in the feedstock.3.The stability and equilibrium morphology of various h-BN edges terminated by isolated Ni atoms on Ni(111)surface were studied.The results show that most of the edges terminated by isolated Ni atoms have lower formation energy than those only passivated by Ni(111)surface,and the zigzag edge terminated by N atoms(ZZN)is the most stable one.Combined with Wulff crystal growth theory,the equilibrium morphology of the h-BN domain is predicted.In the N-rich environment,it may be a triangle enclosed by ZZN edges,while in the B-rich environment,it may be a triangle enclosed by ZZB edges.The shape of the h-BN equilibrium domain can be adjusted by changing the ratio of B and N.4.The magic clusters of h-BN on Ni(111)and Cu(111)surfaces are studied.The results show that the magic clusters on Ni(111)are hexagonal core-shell structures formed by alternating connections of B and N atoms,such as structure containing 7 hexagons,while the magic clusters on Cu(111)contain more six-membered rings and closed four-membered rings.The coupling effect of the highly symmetric structure,edge atoms,metal substrates and adsorption sites ensures effective charge transfer between the magic cluster and the substrate metal atoms,which determines the high stability of the magic clusters.5.The nucleation process of h-BN clusters on different metal surfaces was studied.The results show that BN on different metal surfaces has a ground-state structure transition at the initial stage of nucleation,and the critical size of structure transformation is different.It was found that the critical sizes of h-BN clusters on Ag(111),Cu(111),Pd(111)and Co(0001)surfaces from a chain-like to an honeycomb configuration are 12,8,7 and 8,respectively.The stability ability of four metals to BN clusters is Ag<Cu<Pd<Co.There are 71 pictures,3 tables and 126 references in this paper.