Theoretical Study About The Structure And Properties Of Low Dimensional Layered Materials

The successful fabrication of graphene has motivated the research fever for other low dimensional materials, including graphene nanoribbon,2D BN compounds, transition metal sulfides, blackphosphrus and so on. Owing to the rapid development of scientific computation, computer softwares have become an important method to investigate the properties of graphene and other low dimensional materials. In this thesis, the basical properties of some low dimensional materials have been investigated by using first principles caculation with Vienna Ab-initio Software Package (VASP), including the electronic propertyand magnetic property of Z shape graphene nanoribbons, the electronic property of carbon atomic chains with ring structure, and the electronic property of few layered phosphrenes with two different kinds of stacking fault structures, that is the shifting stacking fault and the rotational stacking fault. The specific research contents and results are as follows:(l)Changing the length of zigzag segments and armchair segments is an effective way to modulate the electronic property and magnective property of Z type graphene nanoribbon. Especially, it is found that A4A4Z5Z0 is a special structrue with zero gap and the magnetic ground state of A4A4Z5Z0 is antiferrimagnetic. Based on this stucture, we found the rule of the Z shape graphene with zero gap. The system will open its gap and become antiferromagnetic when the zigzag length LI and L2 are extended. However, the system still remains to be nonmagnetic with zero gap when the armchair’s width is widen. In addition, for the situation that L1 of single part is lengthened or W2 of single part is widen, the results are still cosistent with the above. It means that if the number of missing dimer lines is 3, no matter the stem is widen or the side is widen, the system will be nonmagnetic and metallic. These Z shape graphene nanoribbons with zero gap have better conductance than normal graphene nanoribbon, thus providing a prospect to be wire with better conductance in nanoelectrnoc devices.(2)The carbon atomic chains with ring structure (Cm-GNR) can be either semiconductor or metal, which is related with the atomic number on the ring chains. The atomic number on the straight line is fixed to be even. Except for the systems with small ring, when the atomic number on the half side of the ring (m) is odd, the middle part of the ring appears cumulene with double bonds throughout the chain. The systems are metallic and its magnetic ground state will be antiferrimagnetic as the ring become larger. On the contrary, if m is even, the middle part of the ring appears polyyne with alternating single and triple bonds. The system will be semiconductor and its magnetic ground state will be antiferromagnetic.(3)We simulated the growth process of a narrow carbon atomic chain. Originally, the zigzag graphene nanoribbons were connected by a narrow nanoribbon. Later on, the narrow ribbon became two carbon atomic chains.The next, the chains changed into a Y shape chain and the two branch chains became smaller and smaller. Finally, it turned into a straight chain. The results of our simulation confirmed that the average energy of this process lowered gradually, which is consistent with the experiment.(4)Few layered phosphorenes (FLPs) with shifting stacking fault have been investigated with a lot of work in this thesis. Interestingly, We have not only found the most stable AB stacking,, but also a special metastable stacking named A δ stacking fault. This A δ stacking fault with an indirect gap can be a defect existed in FLPs and black phosphrus (BP), which has a great reference value for some related researches. Especially, the A δ stacking fault enriches the electronic of blackphosphrenes. The different stacking faults with different layers enables the fabrication of some lateral junctions like type-Ⅰ, Ⅱ, and Ⅲ semiconductor heterojunction.(5) For the rotational stacking fault, rotational angle θ=15°,30°,45°,60°,75°,90° are researched and it is found that they are all semiconductors. The most stable structure of them is the system with 0=75°, but it is still less stable than AB stacking and A δ stacking. The shifting stacking fault and rotational stacking fault can combine with MoS2 to form type Ⅱ heteroj unctions which can be used in thin film solar cells.