First-principles Calculaitons On The Growth Mechanism And Electronic Properties Of Two-dimensional Materials Stanene On Different Topological Insulators

Since the discovery of graphene,investigation of 2D materials has surged to the forefront of condensed mater of physics.As a highly appealing new member of the two-dimensional?2D?materials family,stanene has attracted much attention because of its enhanced spin-orbit coupling?SOC?and many other expected exotic properties.Stanene was first epitaxially grown on a three-dimensional topological insulator of Bi₂Te₃;yet,to date,a standing challenge is to drastically improve the overall quality of such stanene overlayers for a wide range of potential applications in next-generation quantum devices.In this thesis,the growth mechanism and electronic properties of two-dimensional materials stanene on some representative topological insulators were studied by first-principles calculations.Our results are of great significance for the study of the growth mechanism and topological properties of stanene on substrates.The research content in this thesis is mainly divided into the following three parts:In the first part,chapter 3,state-of-the-art first-principles approaches are used to explore the atomistic growth mechanisms of stanene on different Bi₂Te₃?111?-based substrates,with intriguing discoveries.We first show that,when grown on the experimentally studied Te-terminated Bi₂Te₃,stanene would follow an unusual partial-layer-by-partial-layer growth mode,characterized by short-range repulsive pairwise interactions of the Sn adatoms;the resultant stanene overlayer is destined to contain undesirable grain boundaries.More importantly,we find that stanene growth on Bi₂Te₃?111?pre-covered with a Bi bilayer will follow a highly desirable nucleation-and-growth mechanism,strongly favoring single crystalline stanene.We further show that both systems exhibit pronounced Rashba spin-orbit couplings,while the latter system also provides new opportunities for potential realization of topological superconductivity in 2D heterostructures.The novel kinetic pathways revealed here will be instrumental in achieving mass production of high-quality stanene with emergent physical properties of technological significance.In chapter 4,we study the growth mechanism of 1-ML and multiple ML stanenes on Bi?111?substrate with even stronger SOC effect as comparted to Te-Bi₂Te₃?111?.First,we examined the preferred adsorption site and configurations of one and two Sn atoms on Bi?111?substrate,and then focus on the the stable configuration of single-layer stanene on the substrate.In addition,the growth mode and the energetics of the multi-layered stanenes grown on the substrate are also extensively investigated.It is found that the two Sn adatoms on Bi?111?substrate tend to nucleate into Sn dimer.However,the growth behavior of stanene on such a substrate is Sn coverage dependent.On Bi?111?,the 1ML stanene possesses a single most stable phase,which effectively minimizes the formation of grain boundary and facilitates in growing large scale of single crystalline Sn structure.However,we discover that when multiple layers?N>2-ML?of stanene is formed on the Bi?111?substrate,there are at least two staking forms close in energy,which may lead to undesirable grain boundaries.In Chapter 5,we examine the effect of H passivation on the staking configurations and electronic energy band structures of 1-ML stanene on the three substrates?Bi₂Te₃?111?,Bi?111?,and PbTe?111??.For the 1-ML stanene,its stable configuration on the substrate Bi₂Te₃?111?is significanlty related to the H passivation,neverthless,on the substrates of both Bi?111?and PbTe?111?,H passivation leads to negiligible change in the staking form of the most stable structures.However,the introduction of the hydrogen passivation significantly reduces the energy difference between the most stable and metastable phases,which definitely enhances the possibility in formation of grain boundaries.We predicted that stanene growth on the substrate Bi?111?better than the other substrates PbTe?111?and Bi₂Te₃?111?.In the process of stanene growth,introducing H may realize the superconducting properties of stanene.It is expected that future experiments will confirm the above theoretical predictions.