Investigations On The Growth Of Graphene And Related Structures

Because of the unusual structural and electronic properties, such as half integer quantum Hall effect, quantization of electrical resistivity, and long ballistic mean free path at room temperature, graphene have attracted much attention experimentally and theoretically. The high carrier mobility and the possibility of chemical doping make this material a potential building block for future electronic devices. The uniformity of the superstructure with periodicity and its stability at high temperatures make graphene moires on an underlying densely-packed metal surface a good candidate as template for engineering nanostructures. Highly ordered monodispersed metallic nanostructures on a flat substrate have perspective applications in ultrahigh density information storage, catalysis, sensing, etc.Epitaxial growth of graphene on Ru(0001) was investigated in detail by using scanning tunneling microscopy(STM). Graphene on Ru(0001) was prepared by the procedures of direct exposure of the hot substrate at 1000 K (chemical vapor deposition (CVD)) as well as thermal annealing of ruthenium single crystal containing carbon (high temperature segregation (HTS)). The CVD growth parameters of graphene on Ru(0001) have been identified. Furthermore smaller superstructures are commonly observed on the edges region of the graphene islands in during HTS growth of graphene on Ru(0001), and those superstructures can be recognized as intermediate state.The oxidation of graphene layer on Ru(0001) has been investigated by means of scanning tunneling microscopy. Graphene overlayer can be formed by decomposing ethyne on Ru(0001) at a temperature of about 1000 K. The lattice mismatch between the graphene overlayer and the substrate causes a moire pattern with a superstructure in a periodicity of about 30 A. The oxidation of graphene/Ru(0001) was performed by exposure the sample to O2 gas at 823 K. The results showed that, at the initial stage, the oxygen intercalation between the graphene and the Ru(0001) substrate takes place at step edges, and extends on the lower steps.The oxygen intercalation decouples the graphene layer from the Ru(0001) substrate. More oxygen intercalation yields wrinkled bumps on the graphene surface. The oxidation of graphene, or the removal of carbon atoms can be attributed to a process of the combination of the carbon atoms with atomic oxygen to form volatile reaction products. Finally, the Ru(0001)-(2 x 1)-O phase was observed after the graphene layer is fully removed by oxidation.Regularly sized Co nanoclusters have been grown on a graphene moire on Ru(0001). Using scanning tunneling microscopy, we demonstrate that the monodispersed Co clusters nucleate at both the fcc and hcp regions at RT. Co forms finely dispersed small 3D clusters on graphene/Ru(0001), and a defined long-range ordering of Co nanoclusters with increasing coverage is not observed. The size of the clusters is tunable, and the growth exhibits a self-limited growth mode in diameter without coalescence. The absorbed Co begins to intercalate between the graphene layer and the Ru(0001) substrate for annealing the sample with a temperature up to about 473 K.Deposition of cobalt on graphene/Ru(0001) at 873 K leads to the intercalation of cobalt underneath graphene layer, and the intercalation of Co between graphene layer and Ru(0001) is associated with Co diffusion at steps and dislocations. The morphology on graphene/Co/Ru(0001) shows moire pattern as on graphene/Ru(0001), and the bright maxima areas covering Co islands is the hcp regions of the graphene/Ru(0001). The intercalated Co islands have a pseudomorphic structure superimposed on Ru(0001).