Study On Electrical Transport Properties Of Low Dimensional Multi-membered-ring Chalcogenide-and Carbon-based Nanostructures

Recently,traditional materials are difficult to meet the needs of highly integrated devices due to their own limitations.Fortunately,nanotechnology has made great progress,especially the technology of preparing nano-materials in experiments.With the preparation of various nanomaterials with excellent characteristics,such as multi-membered-ring chalcogenide-and carbon-based nano materials,there are possibilities to improve the integration of devices.Based on this,density functional theory combined with non-equilibrium Green’s function is used to study the electron transport properties of multi-membered-ring chalcogenide-and carbon-based nanomaterials,and constructs a pratical new nano-materials.This thesis summarizes the characteristics of nano-material structure and the application of various new nano-materials,introduces the theoretical research methods,and reveals the electroinc structure characteristics and the physical mechanism of multi-membered-ring chalcogenide-and carbon-based nano-materials.Firstly,we studied the structure of C-H doped tungsten disulfide nanoribbons.By calculating the energy bands of the ribbons with different nanoband widths,it is found that the energy band gap oscillations and decreases with the increase of band width.At the same time,it is found that the system exhibits odd-even effect: when doping is an even number of hydrocarbon units,the structure is metallic;when the doping is odd,the structure is semiconductor,and with the increase of band width,the band gap of the structure decreases gradually.When it reaches a certain width,the structure exhibits metallic behavior.Obviously,doping and constructing nanoribbons are of great help to build devices with adjustable band gap.Secondly,the magnetic tunnel junction is constructed by using one-dimensional transition metal compounds such as WTe and Fe O,and its tunneling magnetoresistance(TMR)ratio is calculated.The results show that the magnetic tunnel junction presents a huge TMR ratio,which is about two orders of magnitude higher than that of the traditional magnetic tunnel junction.At the same time,by adjusting the length of the intermediate insulating layer,the TMR ratio of the magnetic tunnel junction changes accordingly,and the TMR ratio of each magnetic tunnel junction is very stable and exhibits good robustness.This is of great significance for the construction of magnetic random access memory.Finally,we use a ternary-and quaternary-ring carbon-based molecule to construct a single molecule device.The IV characteristic curve of undoped structure is studied,and it is found that it exhibits obvious negative differential resistance(NDR).Secondly,two kinds of structures doped with Ge atoms at different positions are studied.When doping on the side branch,it is found that the negative differential resistance characteristics of the undoped structure are similar to those of the undoped structure,indicating that doping on the side branch has little effect on the negative differential resistance properties of the undoped structure.However,when doping lies on the main branch parallel to the transport direction,the negative differential resistance characteristics of the system greatly change,indicating that doping at this position has a great regulation effect on the negative differential resistance properties of the system.Finally,through further analysis,it is concluded that the nonlocalized attenetion of the energy state at the Fermi level is the main reason for the negative differential resistance of the structure.