The STM Researches Of Molybdenum (Mo) Dopants And Defects In Graphene Systems

Abstract:Graphene, a one-atom-thick sheet of carbon atoms in honeycomb arrangement, has sparked much interest in both fundamental studies and technological applications in the past10years due to its outstanding physical, electronic, and optical properties. The development of graphene or graphene-related nanoscale devices requires simple methods to tune their electronic and magnetic properties. However, Impurities and defects, which are always present in graphene and the classes of two-dimension(2D) systems, have a strong influence on their electronic, optical, thermal, and mechanical properties. Therefore, the study of defects in graphene system will be of great significance. In this thesis, the double-layer graphene incorporated with molybdenum (Mo) atoms will first be studied, to explore the introduced features of specific transition metal atom in graphene. In addition, the defects generated through self-assembled graphene-related supermolecule structures is simply be discussed, expecting to extend the researches of defects existing in the classes of two-dimensional graphene-like materials. The thesis mainly contains two parts:(1)A simple method is first developed to incorporate isolated Mo atoms into BLEG on SiC(0001). We investigate the Mo incorporating sites and corresponding electronic properties of Mo-doped BLEG by means of LT-STM (T=77K) and first principles calculations. LT-STM and first principles calculations reveal that isolated substitutional Mo atoms prefer the a-sites of the upper graphene layer and to be embedded between the graphene bilayers. The Mo atoms are stable above-1100K because of covalent bonding with neighboring carbon atoms. The first principles calculations show that the Mo atom embedded between graphene bilayers is energetically more stable than that located above the graphene surface. Furthermore, each substitutional Mo atom introduces a magnetic moment of1.81μB into bilayer graphene and such effect can be widely used in spintronic devices.(2)As similar with the single atom adsorption on or doping into graphene to control its properties, the method of molecular self-assembly can also be used to control the physical properties within the smllest length scale accessible. In the thesis, high resolution scanning tunneling microscope (STM) was also used to study the adsorption of Halogenated aromatic compounds1,3,5-tris(4-bromophenyl)benzene (TBB) on the active substrate of Ag (111). It has revealed that.the annealing of smple will lead to C-Br bond scission of TBB and onnect neighboring fragments with C-Ag-C bonds, where the Ag atoms coming from the substrate, and then the2D networks consisting of hexagon macrocycles are formed. The researches of the2D networks have revealed that, there are many structure defects in this kind of supermolecular structures, which is similar to the structure defects in graphene. It has proposed that, the small deviation from the equilibrium geometry is responsible for the high number of polygons different from hexagons. The study can offer guidence for the development of graphene-like molecular devices.