Study On Electrical Transport And Microwave Dielectric Properties Of Bismuth Based Topological Insulator Nanomaterials

Topological insulators can achieve less dissipative transport due to the existence of gapless surface states protected by time-reversal symmetry on the surface,and in particular,the bismuth-based topological insulators Bi₂Te₃ and Bi₂Se₃ have topologically insulated electronic phases and non-zero integer Chern Number by strong spin-orbit coupling,which will make them potential for electronic devices and information transmission materials,and because the surface states are conductive and the The conductivity and dielectric properties can be controlled by adjusting the surface state,which is also promising for electromagnetic functional material applications.Therefore,it is important to study the electrical transport properties and microwave dielectric properties of bismuth-based topological insulators.In this thesis,Bi₂Te₃ nanorods and Bi₂Se₃ nanosheets were prepared by polyol reduction method,respectively.These two types of topological insulator nanomaterials exhibit a strong nonlinear electrical transport behavior with a gradual increase in conductivity with increasing voltage and a great change in conductivity with the application of a small electric field,and this unique electrical transport property is due to the disordered distribution of nanostructures causing a change in the Fermi energy level within the energy band structure of most topological insulators due to the effective gate voltage.This unique nonlinear electrical transport behavior leads to bismuth-based topological insulators with bias voltage-dependent dielectric response behavior,where the dielectric constant gradually decreases with increasing dc bias voltage,thus observing a maximum capacitance change of 800%for Bi₂Te₃nanomaterials and 4200%for Bi₂Se₃ nanomaterials in the 0-10 V range.These properties make the nanomaterials will be of great value in applications such as phase shifters,variable capacitors,smart storage,integrated circuits and microelectronic devices.Two types of bismuth-based topological insulator nanomaterials were investigated for morphology regulation,and the dielectric properties of the materials in the microwave band were achieved by varying the diameter of the nanowires and the thickness of the nanosheets.Since the topological insulator is conductive in the surface state and insulating in the bulk state,the finer the nanorods the higher the dielectric constant,and the thinner the nanosheets the higher the dielectric constant,therefore,the dielectric properties of topological insulator have more freedom of regulation and it is easier to obtain excellent microwave absorption performance compared with ordinary materials.The results show that the Bi₂Te₃ nanocomposite has a broadband microwave absorption performance of 6.8 GHz at a thickness of 1.6 mm;the Bi₂Se₃nanocomposite has an effective absorption bandwidth of 2.8 GHz at a thickness of 0.7 mm,which is an ultrathin microwave absorption material with excellent performance.These properties indicate that bismuth-based topological insulator nanomaterials have great potential for applications in coating absorbing materials and integrated microwave devices.