The Characterization Of The Surface Micro-morphology Of Graphene By STM

Graphene is a two-dimensional material of monatomic layer. Its unique two-dimensional structure and electronic properties have attracted tremendous research interest. However, due to the lack of bandgap, so its application is limited. To resolve this issue, researchers pay a lot of effort in order to open the bandgap in graphene, the most common of which is the introduction of defective structure so as to effectively control the electronic structure of graphene. The chemical vapor deposition (CVD) method using copper as the substrate is an important method for the preparation of graphene. At the same time, scanning tunneling microscopy (STM) can be used as a powerful and intuitive method to characterize the structure and electronic properties of graphene at atomic scale.This thesis focuses on the characterization of the surface micro-morphology of CVD-grown graphene on copper foil. In the first chapter, the structure and unique electronic properties of graphene are introduced. In the second chapter,several commonly used experimental techniques for characterizing graphene are introduced, among which the scanning tunneling microscope/spectroscopy(STM/S) is a powerful tool to investigate the atomic structure and electronic properties. The third chapter shows that CVD-grown graphene on copper foil substrate has two types of one-dimensional stripes: one has a linear boundary with 1.28nm period and another has a zigzag boundary with 1.2nm period. It is discovered that the one-dimensional stripes are moiré patterns due to the lattice mismatch of hexagonal structure of the graphene and underlying square structure of the copper. The corresponding graphene STS spectra reveal that the formation of moiré pattern makes interlayer coupling effect between the copper substrate and graphene relatively strong. Further dI/dV mapping shows that the bright and dark stripes are reversed at two different bias voltages,proving that the one-dimensional moiré pattern has an effect on the electronic structure of graphene. In the fourth chapter, the atomic structure and electronic properties of graphene defects are observed by STM and STS which reveal a local defect state near the Fermi energy.