First-Principles Calculation Study On The Growth Mechanism Of Low-Dimensional SnSe

With the successful preparation of single-layer graphene,extensive research on two-dimensional nanomaterials has begun worldwide.This type of material has become a hot spot in scientific research today due to its excellent thermal,mechanical,electrical and other properties.At the same time,the growth mechanism that plays a key role in the morphology of two-dimensional materials has also become an important research direction.The ?-? layered semiconductor compound tin selenide(SnSe)exhibits impressive physical properties in different fields.Because of its huge application potential,SnSe has been thoroughly studied in all aspects in recent years.Experiments have shown that there is a certain pattern in the growth of SnSe two-dimensional crystals,but there is no relevant report on its growth mechanism.This subject adopts first-principles calculations based on density functional theory,selects appropriate functionals,and studies the growth mechanism of two-dimensional SnSe from the perspectives of thermodynamics and kinetics.The main work is as follows:(1)For the common morphologies of low-dimensional SnSe nanostructures in the experiment,the(100),(010),(001),(011)and(0(?)1)crystal planes of SnSe crystals were modeled and calculated respectively.By studying the relationship between the crystal surface energy E_f and the number of atomic layers,it is found that the crystal surface energy of the above crystal surface will increase with the increase of the number of layers when the number of layers is small,and reach a convergence value after reaching a certain number of layers.The E_f of each crystal plane satisfies the following relationship:E_f(100)<E_f(011)=E_f(0(?)1)<E_f(001)<E_f(010),which provides a reasonable explanation for the nanostructure morphology observed in the experiment.(2)Aiming at the phenomenon that the quasi-one-dimensional SnSe nanoribbons always grow along the(010)direction in the experiment,from a dynamic point of view,the CI-NEB method was used to study Snsingle atoms,Se single atoms,and SnSe atom pairs along(010)direction and(001)direction diffusion barriers.It is calculated that the diffusion barriers of the above-mentioned atoms or atom pairs along the(001)direction are significantly smaller than the diffusion barriers along the(010)direction.Combining the above thermodynamic calculation results,it is concluded that the formation of quasi-one-dimensional SnSe nanoribbons is mainly caused by kinetic factors.