Edge Structures for Nanoscale Graphene Islands on Co(0001) Surfaces

Abstract

Low-temperature scanning tunneling microscopy measurements and first-principles calculations are employed to characterize edge structures observed for graphene nanoislands grown on the Co(0001) surface. Images of these nanostructures reveal straight well-ordered edges with zigzag orientation, which are characterized by a distinct peak at low bias in tunneling spectra. Density functional theory based calculations are used to discriminate between candidate edge structures. Several zigzag-oriented edge structures have lower formation energy than armchair-oriented edges. Of these, the lowest formation energy configurations are a zigzag and a Klein edge structure, each with the final carbon atom over the hollow site in the Co(0001) surface. In the absence of hydrogen, the interaction with the Co(0001) substrate plays a key role in stabilizing these edge structures and determines their local conformation and electronic properties. The calculated electronic properties for the low-energy edge structures are consistent with the measured scanning tunneling images.

Hexagonal Boron Nitride–Graphene Heterostructures: Synthesis and Interfacial Properties

“…Interestingly, a monotonic decrease of the intensity of the “V–type” conductance (from the graphene side) was observed when the tip was positioned close to the interface region (within 20 nm). This phenomenon was possibly due to the quantum confinement effect at the zigzag edge of graphene, as similarly reported for graphene on Ir(111) . These results indicated that graphene and h‐BN inside the in‐plane heterostructures maintained their local electronic properties and are not electronically doped by the underlying Ir (111) substrates as well.…”

Strain Relaxation in CVD Graphene: Wrinkling with Shear Lag

“…This passivation would involve a strong interaction between the dangling bonds of the edge carbon atoms and free electrons in the transition metal substrate, which stabilizes the edge on the substrate, especially on cobalt. 40,43 As a consequence we find enhanced strain levels at the graphene edges. Figure 2e gives the variation in G peak position and Full Width at Half Maximum (FWHM) of the peak along the purple arrow in Figure 2a,b.…”

Structure of graphene and its disorders: a review

“…(d) CC-STM image of edges of graphene on Ir(111), with crystallographic directions of the Ir substrate denoted at the top-right side [89]. (e) STM image of graphene structures on Co substrate, and schematic of triangular and hexagonal corners, respectively, for zigzag-edged graphene structures on Co(0001) [90]. (f) 20 × 20 nm 2 STM image and (g) 2.5 × 2.5 nm 2 rendered STM topography of graphene island on 6H-SiC(0001) substrate.…”

“…For example, graphenenano-islands that are epitaxially grown on monocrystalline metal surfaces (i.e. Ir(111) [76,89], Co(0001) [77,90] and Pt(111) [91]) have mostly zigzag terminations, whereas those grown on 6H-SiC(0001) are dominated by armchair edges [75]. The constant-current STM (CC-STM) image of edges of graphene on Ir(111) can be seen in Figure 5(d), where the gray mesh indicates the moire superstructure on graphene, and the blue and yellow arrows represent the zigzag graphene edges on substrate surface and at substrate step edges respectively.…”

“…A detailed analysis of the on-top registry reveals that the straight edges of graphene on clean Co surface are mainly terminated in zigzag directions. With fixed edge chirality, commensurate graphene can form islands on Co(0001) substrate with either triangular or hexagonal corners, as seen in Figure 5(e) [90]. In the first case, the peripheral atoms maintain the same registry, whereas, in the second case, adjacent edges exhibit opposite configurations.…”