The Preparation And Properties Of Hybrid Dirac Materials

Graphene and topological insulators, as a representative Dirac materials, are new two-dimensional quantum functional materials in recent year. The effective mass of carriers is zero and both the energy and momentum comply with linear relationship, using Dirac equation to describe it. It has attracted extensive scientific interests from experimental to theoretical communities benefiting from its unique band structure and physical properties. Bi₂Se₃,an ideal topological insulator（TI） with precise chemical ratio, is easy to be synthesis. It has become the focus of attention and research in recent years, as the most approximate ideal state of topological insulators. Layerstructured Bi₂Se₃ materials may be applied for the future spintronics and quantum computing devices due to large ratio of surface-to-volume. Graphene film, a 2-D atomic-scale honeycomb lattice made of carbon atoms, can be used to fabricate the high-quality epitaxial layer benefiting from that the van der Waals interactions between epitaxial layer and graphene can efficiently suppress the negative effects of the lattice mismatch. So graphene provide a good substrate for the growth of Bi₂Se₃.This paper includes the research development, fabrication method and properties of the hybrid Dirac materials. Graphene and Bi₂Se₃ become the most representative Dirac materials. We fabricated the sandwich hybrid structure Dirac materials via chemical vapor deposition（CVD） method. Its effective and economy has been proved. The research as follows:（1） In our case, the Bi₂Se₃ was directly grown on the SiO₂ substrate in Se rich conditions via chemical vapor deposition method. We try to explore the effect of the Se-rich conditions on the Bi₂Se₃ nanostructure growing quality. Bi₂Se₃ powder mixed with Se powder in ratio of 6:1serving as the precursor for evaporation, Se evaporate firstly because of its lower melt-boiling point, so that the reaction is carried out under the Se-rich environment. During the growth process, the environmental Se atom adsorbing to the surface dangling bonds of Bi₂Se₃, promote the Bi₂Se₃ nanosheets growing along the lateral direction. In addition, the Se-rich conditions is utilized to fill the Se vacancies.In our case, Bi₂Se₃ thin film was grown on the graphene/SiO₂（G/SiO₂） substrate via CVD method. We try to explore the effect of the graphene substrate on the Bi₂Se₃ thin film growing quality. Graphene film, a 2-D atomic-scale honeycomb lattice made of carbon atoms, can be used to fabricate the high-quality epitaxial layer benefiting from that the van der Waals interactions between epitaxial layer and graphene can efficiently suppress the negative effects of the lattice mismatch. The 2D band representing for the graphene in-plane vibration peak occurs red shift due to van der Waals interaction between graphene and Bi₂Se₃.（3） The Se was deposited on the G/SiO₂ substrate serving as growing point via the similar CVD method. We try to explore its impact on Bi₂Se₃ thin film growth quality. It prove that serving Se as growing point contribute to the lateral growth of Bi₂Se₃ thin film. In addition, atomic ratio Se:Bi is nearly equal to 1.5（the stoichiometric ratio of for Bi₂Se₃）.（4） The fabricated Bi₂Se₃/G is immediately covered by another graphene layer to get the G/Bi₂Se₃/G sandwich hybrid structure. The covering graphene can be mixed with Bi₂Se₃ thin film at a molecular level to maximize the contact between them by the van der Waals interaction. The G/Bi₂Se₃/G sample is different from the changes of the Bi₂Se₃/G sample and remains unchanged continuously. There are two advantages of this heterostructure:（1） the 2D growth single-crystal Bi₂Se₃ thin film can be successfully deposited on the graphene film;（2） the oxidation process of the Bi₂Se₃ is significantly delayed compared with that without the protection of the graphene.