A First Principle Study Of The Double-layer Graphene Nanoribbons

In this dissertation, we have investigated the electronic band structure and transport properties of double-layer graphene nanoribbons employing a simulation method based on the first principle density functional theory and the non-equilibrium Green’s function method. The study focuses on the calculation of the electronic transport in partially stacked zigzag graphene nanoribbons (ZGNRs) with different width. Interesting results such as negative differential resistance (NDR) has been observed and discussed.In the text, we at first review the discovery, the experimental preparation, and the electronic properties of graphene. Then we briefly present the experimental preparation and electronic properties of graphene nanoribbons. Later on, we introduce the simulation method based on the first principle density functional theory with the non-equilibrium Green’s function method. After these introductions, we present the works carried out during my graduate study in the following two parts.(A) The electronic band structure of double-layer graphene nanoribbons. There are two kinds of different overlapping modes—a type and β type in double-layer graphene nanoribbons. If spin polarization is neglected, the electronic band structure of double double-layer graphene nanoribbons is similar to that of single-layer graphene nanoribbons. In this case, zigzag nanoribbons behavior as conductor and armchair nanoribbons as semiconductor. However, if we take the spin polarization into account, the band structure of zigzag nanoribbons has a band gap at the Fermi level and the systems are always semiconductors.(B) The electronic quantum transport in double-layer graphene nanoribbons. Compared to single-layer ZGNRs, partially stacked ZGNRs have an interface in the stacked areas. Therefore, it is possible to further manipulate the electronic properties in these systems. We simulate the electronic transport properties of a two-probe system which is composed of two electrodes, the left and right regions with one single-layer zigzag graphene nanoribbons, and a central region, the area with upper and lower single-layers stacked in the a-type stack. In the computational study, we mainly focus on the effect of the ribbon width and the stack length on the electronic transport, especially the current-voltage curve. Our result shows that:(1) In nanoribbons narrower than1nm, the current-voltage curve of the system shows a serious small oscillations. The number of oscillations decreases in wider nanoribbons but their amplitude increases. Negative differential resistance (NDR) effect then may appear in various cases.(2) The peak current increases with the stacking length in the central region, and the NDR effect is enhanced accordingly.