Preparation And Dielectric Properties Of Topological Insulator Bi₂Te₃ Nanomaterials

Electromagnetic interference inevitably produced by the massive usage of electronic devices and digital systems has resulted in an increasingly serious issue that affects our daily lives.To address the problem,considerable efforts have been devoted to the highly efficient microwave absorption materials which can attenuate the microwave by converting it into thermal energy.However,most microwave absorbing materials usually suffer from a thicker thickness(above millimeter order)to attenuate enough electromagnetic waves.The thinner matching thickness(?1mm)is in urgent demand in the field of microwave absorption due to the rapidly growing integrated microwave circuits and absorbing coatings.Therefore,it is of great significance to explore ultra-thin absorbers,and the key to decreasing the absorber thickness is to increase permittivity or permeability of absorbing materials.For magnetic materials,permeability is usually difficult to increase at high frequency due to Snoek's limit,and then high-permittivity materials are considered as a potential competitor for ultra-thin microwave absorber at high frequency.Nevertheless,most high-permittivity materials are usually accompanied by excessive dielectric loss that will result in too much reflection on material surface.Therefore,ultra-thin absorbing materials(?1 mm)are still one of the difficulties in microwave stealth material design,due to the mismatch between high dielectric constant and dielectric loss.Topological insulators show great potential in the field of electronics and semiconductors due to their unique surface states.Based on the adjustable electrical transmission characteristics of the conductive surface state,most topological insulators would be a promising candidate for ultra-thin absorber.Compared to other topological materials,Bi2Te3 as a topological insulator consists of a single Dirac cone with a simple surface state and a narrow band gap(about 0.145 eV).This work studies Bi2Te3 nanomaterials with different structures,explores the ultra-thin microwave absorption properties,and proposes an input impedance matching coefficient Mz,based on transmission line theory and which can characterize any materials.The Bi2Te3 nanosheets were prepared by solvothermal method,and the formation mechanism of nanosheets based on the content of polyvinylpyrrolidone(PVP)was explored further.Due to the unique surface conductivity characteristics of topological insulators,a single nanosheet is equivalent to a microcapacitor,while the stack of multiple nanosheets are equivalent to parallel connection of microcapacitors,and the change of thickness and quantity are closely related to the dielectric constant.Benefit from the conductivity characteristics of the topological insulator thickness dependence,the adjustment of the nanosheets' size can further regulate the dielectric loss.Different from the single adjustment of the dielectric parameters of traditional materials,the independent adjustment of the dielectric constant and dielectric loss of the topological insulator is easier to achieve impedance matching,and ultra-thin microwave absorption with only 0.77 mm sub-millimeter thickness is obtained.It has been the thinnes matching thickness among the absorbers reported to date.The Bi2Te3 nanorods were prepared by template-free chemica synthesis,and the growth mechanism of one-dimensional nanorod structure based on ethylene glycol was explored.The dielectric loss of the Bi2Te nanorods is determined by the migration conductance of the surface state an the jump conductance between the disordered nanorods,which is easier t achieve an ideal match with the high dielectric constant.The uniqu conductive surface state provides convenience for impedance matching achieving ultra-thin microwave absorption at the thickness of 0.9 mm unde low load.