We produce precise chiral-edge graphene nanoribbons on Cu{111} using self-assembly and surface-directed chemical reactions. We show that, using specific properties of the substrate, we can change the edge conformation of the nanoribbons, segregate their adsorption chiralities, and restrict their growth directions at low surface coverage. By elucidating the molecular-assembly mechanism, we demonstrate that our method constitutes an alternative bottom-up strategy toward synthesizing defect-free zigzag-edge graphene nanoribbons.

Success in isolating a 2D graphene sheet from bulky graphite has triggered intensive studies of its physical properties as well as its application in devices. Graphite intercalation compounds (GICs) have provided a platform of exotic quantum phenomena such as superconductivity, but it is unclear whether such intercalation is feasible in the thinnest 2D limit (i.e., bilayer graphene). Here we report a unique experimental realization of 2D GIC, by fabricating calcium-intercalated bilayer graphene C 6 CaC 6 on silicon carbide. We have investigated the structure and electronic states by scanning tunneling microscopy and angle-resolved photoemission spectroscopy. We observed a free-electron-like interlayer band at the Brillouin-zone center, which is thought to be responsible for the superconductivity in 3D GICs, in addition to a large π* Fermi surface at the zone boundary. The present success in fabricating Ca-intercalated bilayer graphene would open a promising route to search for other 2D superconductors as well as to explore its application in devices.ARPES | STM | band structure G raphene has attracted considerable attention because it exhibits a variety of unusual physical properties such as the massless charge carriers and the quantum Hall effect (1). Bipolar supercurrent (2) and spin injection at room temperature (3, 4) demonstrate its high potential for application in spintronic devices. To fabricate practical devices based on graphene, it is essential to modify and control electronic parameters such as the sign and concentration of carriers as well as the band gap at the Dirac point. In fact, several attempts have been made to achieve material engineering by introducing an external electric field (5-9) or by depositing atoms or molecules on a graphene sheet (10, 11). In graphite, however, intercalation of guest atoms and molecules into graphite layers (12-15) is known to considerably modify the electronic structure, leading to unique physical properties and technological applications such as superconductivity and rechargeable batteries. It is thus quite challenging to fabricate the thinnest limit of a graphite intercalation compound (GIC), namely, intercalated bilayer graphene, and to investigate its electronic structure to promote graphene engineering.

Scanning tunneling microscopy reveals the relationship between nematicity and superconductivity in an iron-based superconductor.

The spatial variation of electronic states was imaged in the lightly doped Mott insulator Ca2−xNaxCuO2Cl2 using scanning tunneling microscopy / spectroscopy (STM/STS). We observed nano-scale domains with a high local density of states within an insulating background. The observed domains have a characteristic length scale of 2 nm (∼4-5a, a : lattice constant) with preferred orientations along the tetragonal [100] direction. We argue that such spatially inhomogeneous electronic states are inherent to slightly doped Mott insulators and play an important role for the insulator to metal transition.

No abstract