The new three-dimensional structure that the graphene connected with SWCNTs (G-CNTs, Graphene Single-Walled Carbon Nanotubes) can solve graphene and CNTs′ problems. A comprehensive study of the mechanical and electrical performance of the junctions was performed by first-principles theory. There were eight types of junctions that were constituted by armchair and zigzag graphene and (3,3), (4,0), (4,4), and (6,0) CNTs. First, the junction strength was investigated. Generally, the binding energy of armchair G-CNTs was stronger than that of zigzag G-CNTs, and it was the biggest in the armchair G-CNTs (6,0). Likewise, the electrical performance of armchair G-CNTs was better than that of zigzag G-CNTs. Charge density distribution of G-CNTs (6,0) was the most homogeneous. Next, the impact factors of the electronic properties of armchair G-CNTs were investigated. We suggest that the band gap is increased with the length of CNTs, and its value should be dependent on the combined effect of both the graphene’s width and the CNTs’ length. Last, the relationship between voltage and current (U/I) were studied. The U/I curve of armchair G-CNTs (6,0) possessed a good linearity and symmetry. These discoveries will contribute to the design and production of G-CNT-based devices.

The effects of graphene stacking are investigated by comparing the results of methane adsorption energy, electronic performance, and the doping feasibility of five dopants (i.e., B, N, Al, Si, and P) via first-principles theory. Both zigzag and armchair graphenes are considered. It is found that the zigzag graphene with Bernal stacking has the largest adsorption energy on methane, while the armchair graphene with Order stacking is opposite. In addition, both the Order and Bernal stacked graphenes possess a positive linear relationship between adsorption energy and layer number. Furthermore, they always have larger adsorption energy in zigzag graphene. For electronic properties, the results show that the stacking effects on band gap are significant, but it does not cause big changes to band structure and density of states. In the comparison of distance, the average interlamellar spacing of the Order stacked graphene is the largest. Moreover, the adsorption effect is the result of the interactions between graphene and methane combined with the change of graphene’s structure. Lastly, the armchair graphene with Order stacking possesses the lowest formation energy in these five dopants. It could be the best choice for doping to improve the methane adsorption.

In order to regulate thermal transfer characteristics of graphene/silicon carbide heterogeneous interface, the influence of temperature, size and material defect rate on thermal conductance of heterogeneous interface are studied by the non-equilibrium molecular dynamics method. The sandwich model of graphene/silicon carbide heterostructures with different lengths and thickness is built by Material Studio. The reasons for the change of thermal conductance are analyzed from the two aspects of phonon density of states and phonon participation rate. When the system temperature is below the Debye temperature of silicon carbide and graphene, the quantum corrections is used to calculate the thermal conductance of heterostructure in the paper. The results show that the thermal conductance increases with the increase of temperature under both interfacial forces, but the thermal conductance of heterogeneous interface under covalent bond is higher than under van der Waals force. The main reason is that the density of states of graphene in a range of 10—30 THz increases significantly with the increase of temperature. The thermal conductance of heterogeneous interface decreases with the increase of silicon carbide layers, and decreases by 30.5% when the number of silicon carbide layers increases from 10 to 20. The thermal conductance of heterostructure is the lowest in the thermal conductances of 4 layers, it is considered that more phonons are transferred from local to delocalized mode in the middle and low frequency band. The introduction of vacancy defects can effectively improve the interface thermal conductance. At different temperatures, the interfacial thermal conductance first increases and then decreases with the increase of graphene defects, and the defect rate when the interfacial thermal conductance reaches the maximum value and the degree of interfacial thermal conductance decrease after reaching the maximum value is related to temperature. When the defect rate of silicon carbide and graphene are 20% and 35% respectively at 300 K, the interface thermal conductance reaches a maximum value. When the temperature is 900 K, the thermal conductance of graphene/silicon carbide heterogeneous interface reaches a maximum value when the defect rate is 30%. It is considered that the introduction of defects will hinder the medium frequency phonons from realizing the heat transport. The results show that the size effect and vacancy defect can be utilized to modify the heterogeneous interface, which is beneficial to the design and thermal management of the third-generation semiconductor micro-nano devices.

为了探究氮化镓/石墨烯/碳化硅异质界面热输运特性，采用非平衡分子动力学方法从温度、尺寸以及空位缺陷三个方面研究其对界面热导的影响，通过声子态密度和声子参与率对界面热导的变化进一步阐述分析。研究表明：温度升高使界面热导增大，分析认为随着温度升高晶格振动加剧，低频声子态密度变大，参与热输运声子数量增加；其中单层石墨烯层结构界面热导的改变要高于多层石墨烯结构的界面热导。当热输运方向的结构尺寸变化时，同时改变氮化镓和碳化硅的层数，界面热导无明显变化，界面热输运声子散射几乎不受影响；但中间石墨烯层从1层增加至5层时，界面热导率先减小后缓慢增大，由于在4层时低频声子参与率变小，更多的声子局域化，不参与传热声子数量更多，故界面热导到达最小值0.024 GW/m²K。随空位缺陷浓度增加界面热导先逐步增大后减小，区别在于单空位缺陷在浓度为10 %时，界面热导达到最大值0.063 GW/m²K；而双空位缺陷在浓度为12 %时，界面热导率达到最大值0.065 GW/m²K，分析认为更多的声子从局域进入离域，参与该传热声子较多，导致界面热导增大。研究结果有助于调控氮化镓器件的热输运性能，可以为异质界面器件的设计提供理论依据。