The Preparation And Properties Of Topological Insulators Bi₂Te₃ And Bi₂Se₃ Nanomaterials

In this paper,the second-generation three-dimesional topological insulator thin film materials and nanostructured materials were prepared by chemical vapor deposition(CVD)technology,and their structural properties and electrical transport properties were systematically studied.The transport properties of a series of Bi2(TexSe1-x)3 films were investigated.Compared with the undoped sample Bi2Se3,when the doping amount reaches a certain concentration,the insulating behavior is exhibited at low temperature.The magnetoresistance(MR)of the Bi2(TexSe1-x)3 films(x=0,0.1,0.24,0.4 and 0.6)at vertical and parallel magnetic fields at different temperatures was also investigated.In the Bi2(Te0.4Se0.6)3 film,it was observed that the magnetoresistance of the vertical and parallel magnetic fields showed weak anti-localization characteristics in the low field.In particular,under the application of a high magnetic field parallel to the surface of the film,a negative magnetoresistance behavior similar to the weak local area(WL)is found,which is mainly caused by the bulk electrons leading the entire transport process.Bi2Se3 nanosheets,Bi2(TexSe1-x)3 nanowires and Bi2Te3-Bi2(Te1-xSex)3(x=25±5%)core-shell nano wires were prepared.The morphology and characteristics of the samples were analyzed by optical microscopy and scaning electronical microscopy(SEM).The nanostructures are found to have good morphology,considerable size and uniform contrast.The thickness of the nanostructures was quantitatively characterized by Atomic Force Microscope(AFM),and the thinnest nanostructured samples are found to be around 3nm and the length is up to 130?m.For Bi2Se3 nanosheets,the sample resistance appears to be metallic.In the MR curve,a sharp peak of the weak anti-localization phenomenon of the surface state is observed under a small field,and the peak phenomenon disappeares with increasing magnetic filed or temperatuere.For Bi2(TexSe1-x)3 nanowires sample,it is found that when the Se content is 25±5%,the sample exhibites the behavior of semiconductor characteristics.Changing the gate voltage allows regulation of the type of carriers in the sample;the thinner the sample the smaller the gate voltage required to change the carrier type.At the same time,it is found that changing the temperature and the gate voltage can realize the regulation of the MR.In addition,Bi2Te3-Bi2(Te1-xSex)3(x=25±5%)core-shell nanowires also exhibit semiconductor behavior.By changing the external gate voltage,the regulation of the carrier type in the sample can be achieved.The MR dependence of different gate voltages and temperatures is different from that of uncoated samples.