Thinning Segregated Graphene Layers on High Carbon Solubility Substrates of Rhodium Foils by Tuning the Quenching Process

We report the synthesis of large-scale uniform graphene films on high carbon solubility substrates of Rh foils for the first time using an ambient-pressure chemical vapor deposition method. We find that, by increasing the cooling rate in the growth process, the thickness of graphene can be tuned from multilayer to monolayer, resulting from the different segregation amount of carbon atoms from bulk to surface. The growth feature was characterized with scanning electron microscopy, Raman spectra, transmission electron microscopy, and scanning tunneling microscopy. We also find that bilayer or few-layer graphene prefers to stack deviating from the Bernal stacking geometry, with the formation of versatile moiré patterns. On the basis of these results, we put forward a segregation growth mechanism for graphene growth on Rh foils. Of particular importance, we propose that this randomly stacked few-layer graphene can be a model system for exploring some fantastic physical properties such as van Hove singularities

Tunable Spin–Orbit Interaction in Trilayer Graphene Exemplified in Electric-Double-Layer Transistors

Taking advantage of ultrahigh electric field generated in electric-double-layer transistors (EDLTs), we investigated spin–orbit interaction (SOI) and its modulation in epitaxial trilayer graphene. It was found in magnetotransport that the dephasing length <i>L</i>_ϕ and spin relaxation length <i>L</i>_so of carriers can be effectively modulated with gate bias. As a direct result, SOI-induced weak antilocalization (WAL), together with a crossover from WAL to weak localization (WL), was observed at near-zero magnetic field. Interestingly, among existing localization models, only the Iordanskii–Lyanda-Geller–Pikus theory can successfully reproduce the obtained magnetoconductance well, serving as evidence for gate tuning of the weak but distinct SOI in graphene. Realization of SOI and its large tunability in the trilayer graphene EDLTs provides us with a possibility to electrically manipulate spin precession in graphene systems without ferromagnetics

Atomic-Scale Morphology and Electronic Structure of Manganese Atomic Layers Underneath Epitaxial Graphene on SiC(0001)

We report the fabrication of a novel epitaxial graphene(EG)/Mn/SiC(0001) sandwiched structure through the intercalation of as-deposited Mn atoms on graphene surfaces, with the aid of scanning tunneling microscope, low energy electron diffraction, and X-ray photoelectron spectroscopy. We found that Mn can intercalate below both sp³-hybridized carbon-rich interface layer and monolayer graphene, along with the formation of various embedded Mn islands showing different surface morphologies. The unique trait of the sandwiched system is that the strong interaction between the carbon-rich interface layer and SiC(0001) can be decoupled to some degrees, and contemporaneous, an <i>n</i>-doping effect is observed by mapping the energy band of the system using angle-resolved photoemission spectroscopy. Moreover, what deserves our special attention is that the intercalated islands can only evolve below monolayer graphene when a bilayer coexists, accounting for an intriguing graphene thickness-dependent intercalation effect. In the long run, we believe that the construction of graphene/Mn/SiC(0001) systems offers ideal candidates for exploring some intriguing physical properties such as the magnetic property of two-dimensional transition metal systems

Grain Boundary Structures and Electronic Properties of Hexagonal Boron Nitride on Cu(111)

Grain boundaries (GBs) of hexagonal boron nitride (h-BN) grown on Cu(111) were investigated by scanning tunneling microscopy/spectroscopy (STM/STS). The first experimental evidence of the GBs composed of square-octagon pairs (4|8 GBs) was given, together with those containing pentagon-heptagon pairs (5|7 GBs). Two types of GBs were found to exhibit significantly different electronic properties, where the band gap of the 5|7 GB was dramatically decreased as compared with that of the 4|8 GB, consistent with our obtained result from density functional theory (DFT) calculations. Moreover, the present work may provide a possibility of tuning the inert electronic property of h-BN via grain boundary engineering

Toward Single-Layer Uniform Hexagonal Boron Nitride–Graphene Patchworks with Zigzag Linking Edges

The atomic layer of hybridized hexagonal boron nitride (h-BN) and graphene has attracted a great deal of attention after the pioneering work of P. M. Ajayan et al. on Cu foils because of their unusual electronic properties (Ci, L. J.; et al. Nat. Mater. 2010, 9, 430−435). However, many fundamental issues are still not clear, including the in-plane atomic continuity as well as the edge type at the boundary of hybridized h-BN and graphene domains. To clarify these issues, we have successfully grown a perfect single-layer h-BN-graphene (BNC) patchwork on a selected Rh(111) substrate, via a two-step patching growth approach. With the ideal sample, we convinced that at the in-plane linking interface, graphene and h-BN can be linked perfectly at an atomic scale. More importantly, we found that zigzag linking edges were preferably formed, as demonstrated by atomic-scale scanning tunneling microscopy images, which was also theoretically verified using density functional theory calculations. We believe the experimental and theoretical works are of particular importance to obtain a fundamental understanding of the BNC hybrid and to establish a deliberate structural control targeting high-performance electronic and spintronic devices

Quasi-Freestanding Monolayer Heterostructure of Graphene and Hexagonal Boron Nitride on Ir(111) with a Zigzag Boundary

In-plane heterostructure of hexagonal boron nitride and graphene (h-BN-G) has become a focus of graphene research owing to its tunable bandgap and intriguing properties. We report herein the synthesis of a quasi-freestanding h-BN-G monolayer heterostructure on a weakly coupled Ir(111) substrate, where graphene and h-BN possess distinctly different heights and surface corrugations. An atomically sharp zigzag type boundary has been found to dominate the patching interface between graphene and h-BN, as evidenced by high-resolution Scanning tunneling microscopy investigation as well as density functional theory calculation. Scanning tunneling spectroscopy studies indicate that the graphene and h-BN tend to exhibit their own intrinsic electronic features near the patching boundary. The present work offers a deep insight into the h-BN-graphene boundary structures both geometrically and electronically together with the effect of adlayer-substrate coupling