The Transport Properties Of Two Dimensional Carbon Materials And Spintronic/Spin Caloritronic Device Design

Carbon, a marvelous element on earth, has many unique properties and many allotropes since it have three hybridization states. Although only two naturally existing allotropes are known today, which are graphite and diamond, a series of new carbon allotropes have been successfully synthesized, such as C60fullerene, carbon nanotube and graphene. Since graphene was first made in2004, the research field of graphene-based materials has generated worldwide concerns and grown rapidly due to the excellent electrical properties of graphene. Plenty of researches indicate that graphene is the most important candidate for the new generation of electronics device. Up to now, many graphene-based electronics and spintronics devices have been realized both in theoretical and experimental research, such as graphene-based FET, rectifier, spin filter, spin valve and GMR. Recently, a research indicated that graphyne, a new allotrope of carbon, may have better electrical properties than graphene, and one of whose family-graphydine has been successfully synthesized in experiment by Chinese scientists. Therefore, our research mainly focuses on these two-dimensional structures of carbon, which contains graphene, graphyne and bilayer graphene. The computational method we used was first-principles calculations, which adopts spin density functional theory combined with nonequilibruim Green’s function.Spin caloritronics, which focus on heat and spin transport, are very important for future development of low-power-consumption technology. Since only a few researches of graphene-based spin caloritronics devices had been reported, we discussed the relationship of temperature differences and spin-dependent currents in a ZGNR-based heterojunction. Successfully, we attained ideal spin seebeck effect and indicated the possibility of thermally induced pure spin current. In addition, the differences of the thermal currents are tremendous in the device with or without external magnetic field, which caused thermal colossal magnetoresistance. Therefore, the GNR-based spin caloritronics device is feasible theoretically.We chose two different allotropes of graphyne:6,6,12-graphyne and a-graphyne, and cut them into several nanoribbons to investigate the transport properties. We found that the nanoribbons cutting from different structures and directions had radically different electrical properties:some showed metallic properties and some were typical semiconductor. Some of the nanoribbons also showed negative differential resistance effect and spin-polarized transmission. Based on these graphyne nanoribbons, we designed several nanowire electronics devices, such as:rectifier, spin filter diode, spin FET and spin caloritronics device. These results indicate that graphyne is a potential candidate for spintronics and spin caloritronics.At last, we chose bilayer graphene with different stacking patterns to investigate the electrical properties, and we got different interlayer spacing and band structures with different stacking patterns. In the research of interlayer transport properties of zigzag bilayer graphene nanoribbons, the negative differential resistance effect and spin-polarized transmission were successfully found, which are essential to the development of bilayer graphene based spintronics devices.