6 research outputs found
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 moireĢ 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 SpināOrbit 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 spināorbit interaction
(SOI) and its modulation in epitaxial trilayer graphene. It was found
in magnetotransport that the dephasing length <i>L</i><sub>Ļ</sub> and spin relaxation length <i>L</i><sub>so</sub> 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
IordanskiiāLyanda-GellerāPikus 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 sp<sup>3</sup>-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 NitrideāGraphene 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, 430ā435). 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