Study Of Graphene Nanoribbon With Scaning Tunneling Spectroscopy

Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. As the thinnest and the strongest material in the world, this strictly2D material exhibits exceptionally high crystal and electronic quality, showing enormous potential for applications. Graphenenanoribbon (GNR), another quasi-1D material in the graphite family except for carbon nanotube, shows unique electronic properties that depend on their edge structure. The emergence of graphene and graphenenanoribbon makes it possible to realize some quantum electrodynamics related experiments that should be carried out under extreme conditions, which provides versatile methods to verify existing theories.Utilizing scanning tunneling microscopy (STM), we present the width dependent edge study of GNRs unzipped from multiwall nanotubes (MWNTs). Owing to its atomic resolution, STM provides one of the best tools to explore the edge structures of GNRs. By comparing the atomic resolution images of STM with the lattice structure of graphene, the edge structures of the nanoribbons are identified. The GNRs prefer to have edge structure close to the armchair type when their widths are below10nm. Above20nm, the opposite behavior is found. The ribbons have edges close to the zigzag type. In between, a more random distribution of the edges is found.We present the study of the coulomb blockade effect based on the quantum tunneling through a vertical two-barrier structure with GNR as the middle electrode. The structure is formed by positioning a STM tip on top of the GNRs suspended by small molecules on a Au(111) single crystal. STM measurements of the GNRs show staircase I-U characteristics and pronounced oscillations in the dl/dU spectra. To identify the physical origin of the observed effect, we varied the tip to GNR distance through tuning the tunneling resistance of the tip-GNR junction and found a tip to GNR distance dependent oscillating period change. Further numerical analysis confirms that the resonances in the spectroscopy of GNR arise from the coulomb blockade effect.We report the measurement of Landau levels (LLs) arising from large strain-induced pseudo-magnetic fields in bilayer GNR by STM, which revealed pseudo-magnetic fields of20T. And the pseudo-quantum Hall effect (QHE) we observe matches well with former theory and experiment results of QHE in bilayer graphene. Such large strain-induced pseudo-magnetic fields may allow the electronic properties of bilayer graphene to be controlled through various schemes for applying strain, as well as the exploration of new high-field physical regimes.