Perpustakaan Digital ITB

Graphene flake, grown by Chemical Vapor Deposition (CVD), is a single layer graphene with two-dimensional geometrical edges, with comparable ratio between its diameter and its thickness. In this work, we simulate graphene flakes with disordered edges, i.e. the edges are mixture of both zigzag and armchair shape as well as another type of edges with asymmetric positioning. This kind of disorder can also be viewed as edge defect or addition of atom by atom in CVD nucleation process. Both triangular and hexagonal flakes are simulated in this work using Quantum ESPRESSO software to obtain the band gap trend with addition of certain edge types while maintaining the hexagonal unit cell symmetry. The convergence of the calculation will be analyzed from the cutoff radii of the carbon atom pseudopotential. The flake outline width, the asymmetry and the amount of certain disordered edge types will contribute to the band gap opening. The band gap trend resulted is generally decreasing as we add more atom on the edge. Band gap is of the order of ~0.1 eV. The hexagonal flake have a band gap to total atom curve facing upward or downward simultaneously for armchair edge subtraction. For hexagonal flakes with concave zigzag edge subtraction, the band gap to total atom curve for spin up states is facing upward, while facing downward for spin down states. Both edge subtraction is viewed as we add atoms. Moreover, triangular flakes follow the same trend as the concave zigzag edge, as approaching symmetry. This trend, however, is still being studied to obtain an even more detailed picture of graphene flake band gap opening. On the other hand, the flake magnetism will be identified through the asymmetry of projected density of states (PDOS). Midgap states are also observed in the PDOS plot. This study reveals the midgap states induced by overlap that modify transport properties of semiconducting graphene flake.