Synthesis Of Bismuth Selenide Topological Insulator And Investigation Of Mechanical And Electrochemical Performance

Bi₂Se₃ was recently discovered to be an unconventional three-dimensional topological insulator with many excellent electrical properties, having potential application prospects in the field of low-energy electronic devices. Bi₂Se₃ nanomaterial has become the research focus recently while the synthesis technology is still incomplete, especially the preparation of jumbo-size Bi₂Se₃ nanostructures which are used for the microelectronic devices. Meanwhile Bi₂Se₃ won’t present the topological insulator property unless the thickness is small enough. The dependence of surface electric property on the thickness of nanoplates is explored through mechanical measures, having guilding significance for the synthesis of Bi₂Se₃ nanomaterial with topological insulator property in control. Besides, mechanical property of commercial bulk Bi₂Se₃ has a significant impact on the service life of devices. In addition, Bi₂Se₃ has a layered structure whose interlayer spacing is much larger than the radius of lithium ion, having potential storage capacity for lithium ion. Based on the research background above, we investigate Bi₂Se₃ nanomaterials from these aspects of controllable synthesis, mechanical property and its relationship with the thickness of nanoplates, and storage capacity of lithium ion, promoting the application process in microelectronic devices.Singel crystal Bi₂Se₃ nanoplates, nanoribbons and nanowires with jumbo size are synthesized on silicon and Bi₂Se₃ sheets substrates respectively via improved vapor transportation. The influence of growth temperatures and substrates on morphologies are discussed in detail. It is found that diverse nanostructures mainly result from the difference of binding energy alone different crystal orientation. Bi₂Se₃ tends to grow along< 001>and< 1010>directions with high binding energy under relatively high temperature to form Bi₂Se₃ nanoplates, while it grows along< 1120>direction in lower temperature to get Bi₂Se₃ nanoribbons. Jumbo-size Bi₂Se₃ nanowires will form when Bi₂Se₃ sheets serve as substrates, playing the function as catalyst to induce nucleation. Ultrathin Bi₂Se₃ nanoplates and self-assembled Bi₂Se₃ nanospheres are prepared with polyol method, and the temperature, time, surfactant of the reaction are investigated concretely. The optimum condition for Bi₂Se₃ nanoplates is 190 ℃/11 h. The crystal lattice atom arrangement and twin boundaries formed by （104） crystal face are observed clearly with TEM. Nanocrystallines are absorbed on the active groups of surfactant, aggregrate to form the self-assembled nanosphere structures. Furthermore, self-assembled Bi₂Se₃ nanospheres are composited with graphene oxide （GO）.Nanomechanical properties of bulk Bi₂Se₃ and Bi₂Se₃ nanoplates are investigated with nanoindentor and AFM respectively. Firstly, nanomechanical property of two different Bi₂Se₃ sheets exfoliated from bulk Bi₂Se₃ is measured, the hardness and elastic modulus are much smaller than that of traditional alloy materials. Besides, there is a great difference of hardness and elastic modulus between the two Bi₂Se₃ sheets, possibly resulting from the defects in bulk Bi₂Se₃. Furthermore, indentation size effect mainly caused by stress concentration on surface and large surface tension takes place in both two Bi₂Se₃ sheets. Then, micro-frictional behavior of Bi₂Se₃ with different thickness is explored with AFM. Atomic stick-slip friction is observed, which mainly stems from periodic crystal lattice structure of Bi₂Se₃. Furthermore, the thinner Bi₂Se₃ has stronger frictional force under same vertical load compared to thicker specimen. The reason lies in the fact that the thinner specimens possess more freedom electrons, resulting to more intense electrostatic force. Electron-phononic coupling energy dissipation mechanism can account for this phenomenon too.The electrochemical performance of lithium ion battery with self-assembled Bi₂Se₃ nanospheres and the composites with GO as cathode materials are investigated respectively, exploring the storage capacity for lithium ion. It is found that the electrochemical performance will improve a lot when Bi₂Se₃ nanospheres are composited with GO. The reasons can be concluded as below:GO not only acts as the holder, relieving structural expansion and reducing collapse, providing more storage spaces for lithium ion, but also improves the conductivity, thus enhancing the electrochemical performance drastically.