80 research outputs found
Substrate-induced band gap opening in epitaxial graphene
Graphene has shown great application potentials as the host material for next
generation electronic devices. However, despite its intriguing properties, one
of the biggest hurdles for graphene to be useful as an electronic material is
its lacking of an energy gap in the electronic spectra. This, for example,
prevents the use of graphene in making transistors. Although several proposals
have been made to open a gap in graphene's electronic spectra, they all require
complex engineering of the graphene layer. Here we show that when graphene is
epitaxially grown on the SiC substrate, a gap of ~ 0.26 is produced. This gap
decreases as the sample thickness increases and eventually approaches zero when
the number of layers exceeds four. We propose that the origin of this gap is
the breaking of sublattice symmetry owing to the graphene-substrate
interaction. We believe our results highlight a promising direction for band
gap engineering of graphene.Comment: 10 pages, 4 figures; updated reference
Directed self-organization of graphene nanoribbons on SiC
Realization of post-CMOS graphene electronics requires production of
semiconducting graphene, which has been a labor-intensive process. We present
tailoring of silicon carbide crystals via conventional photolithography and
microelectronics processing to enable templated graphene growth on
4H-SiC{1-10n} (n = 8) crystal facets rather than the customary {0001} planes.
This allows self-organized growth of graphene nanoribbons with dimensions
defined by those of the facet. Preferential growth is confirmed by Raman
spectroscopy and high-resolution transmission electron microscopy (HRTEM)
measurements, and electrical characterization of prototypic graphene devices is
presented. Fabrication of > 10,000 top-gated graphene transistors on a 0.24 cm2
SiC chip demonstrates scalability of this process and represents the highest
density of graphene devices reported to date.Comment: 13 pages, 5 figure
Giant Faraday rotation in single- and multilayer graphene
Optical Faraday rotation is one of the most direct and practically important
manifestations of magnetically broken time-reversal symmetry. The rotation
angle is proportional to the distance traveled by the light, and up to now
sizeable effects were observed only in macroscopically thick samples and in
two-dimensional electron gases with effective thicknesses of several
nanometers. Here we demonstrate that a single atomic layer of carbon - graphene
- turns the polarization by several degrees in modest magnetic fields. The
rotation is found to be strongly enhanced by resonances originating from the
cyclotron effect in the classical regime and the inter-Landau-level transitions
in the quantum regime. Combined with the possibility of ambipolar doping, this
opens pathways to use graphene in fast tunable ultrathin infrared
magneto-optical devices
Surface Chemistry Involved in Epitaxy of Graphene on 3C-SiC(111)/Si(111)
Surface chemistry involved in the epitaxy of graphene by sublimating Si atoms from the surface of epitaxial 3C-SiC(111) thin films on Si(111) has been studied. The change in the surface composition during graphene epitaxy is monitored by in situ temperature-programmed desorption spectroscopy using deuterium as a probe (D2-TPD) and complementarily by ex situ Raman and C1s core-level spectroscopies. The surface of the 3C-SiC(111)/Si(111) is Si-terminated before the graphitization, and it becomes C-terminated via the formation of C-rich (6√3 × 6√3)R30° reconstruction as the graphitization proceeds, in a similar manner as the epitaxy of graphene on Si-terminated 6H-SiC(0001) proceeds
Laser-induced etching of few-layer graphene synthesized by Rapid-Chemical Vapour Deposition on Cu thin films
The outstanding electrical and mechanical properties of graphene make it very
attractive for several applications, Nanoelectronics above all. However a
reproducible and non destructive way to produce high quality, large-scale area,
single layer graphene sheets is still lacking. Chemical Vapour Deposition of
graphene on Cu catalytic thin films represents a promising method to reach this
goal, because of the low temperatures (T < 900 Celsius degrees) involved during
the process and of the theoretically expected monolayer self-limiting growth.
On the contrary such self-limiting growth is not commonly observed in
experiments, thus making the development of techniques allowing for a better
control of graphene growth highly desirable. Here we report about the local
ablation effect, arising in Raman analysis, due to the heat transfer induced by
the laser incident beam onto the graphene sample.Comment: v1:9 pages, 8 figures, submitted to SpringerPlus; v2: 11 pages,
PDFLaTeX, 9 figures, revised peer-reviewed version resubmitted to
SpringerPlus; 1 figure added, figure 1 and 4 replaced,typos corrected,
"Results and discussion" section significantly extended to better explain
etching mechanism and features of Raman spectra, references adde
Control and Characterization of Individual Grains and Grain Boundaries in Graphene Grown by Chemical Vapor Deposition
The strong interest in graphene has motivated the scalable production of high
quality graphene and graphene devices. Since large-scale graphene films
synthesized to date are typically polycrystalline, it is important to
characterize and control grain boundaries, generally believed to degrade
graphene quality. Here we study single-crystal graphene grains synthesized by
ambient CVD on polycrystalline Cu, and show how individual boundaries between
coalescing grains affect graphene's electronic properties. The graphene grains
show no definite epitaxial relationship with the Cu substrate, and can cross Cu
grain boundaries. The edges of these grains are found to be predominantly
parallel to zigzag directions. We show that grain boundaries give a significant
Raman "D" peak, impede electrical transport, and induce prominent weak
localization indicative of intervalley scattering in graphene. Finally, we
demonstrate an approach using pre-patterned growth seeds to control graphene
nucleation, opening a route towards scalable fabrication of single-crystal
graphene devices without grain boundaries.Comment: New version with additional data. Accepted by Nature Material
Laser-induced phase separation of silicon carbide
Understanding the phase separation mechanism of solid-state binary compounds induced by laser-material interaction is a challenge because of the complexity of the compound materials and short processing times. Here we present xenon chloride excimer laser-induced melt-mediated phase separation and surface reconstruction of single-crystal silicon carbide and study this process by high-resolution transmission electron microscopy and a time-resolved reflectance method. A single-pulse laser irradiation triggers melting of the silicon carbide surface, resulting in a phase separation into a disordered carbon layer with partially graphitic domains (???2.5 nm) and polycrystalline silicon (???5 nm). Additional pulse irradiations cause sublimation of only the separated silicon element and subsequent transformation of the disordered carbon layer into multilayer graphene. The results demonstrate viability of synthesizing ultra-thin nanomaterials by the decomposition of a binary system.open
Quantum Resistance Standard Based on Epitaxial Graphene
We report development of a quantum Hall resistance standard accurate to a few
parts in a billion at 300 mK and based on large area epitaxial graphene. The
remarkable precision constitutes an improvement of four orders of magnitude
over the best results obtained in exfoliated graphene and is similar to the
accuracy achieved in well-established semiconductor standards. Unlike the
traditional resistance standards the novel graphene device is still accurately
quantized at 4.2 K, vastly simplifying practical metrology. This breakthrough
was made possible by exceptional graphene quality achieved with scalable
silicon carbide technology on a wafer scale and shows great promise for future
large scale applications in electronics.Comment: Submitte
Repeated growth and bubbling transfer of graphene with millimetre-size single-crystal grains using platinum
Large single-crystal graphene is highly desired and important for the applications of graphene in electronics, as grain boundaries between graphene grains markedly degrade its quality and properties. Here we report the growth of millimetre-sized hexagonal single-crystal graphene and graphene films joined from such grains on Pt by ambient-pressure chemical vapour deposition. We report a bubbling method to transfer these single graphene grains and graphene films to arbitrary substrate, which is nondestructive not only to graphene, but also to the Pt substrates. The Pt substrates can be repeatedly used for graphene growth. The graphene shows high crystal quality with the reported lowest wrinkle height of 0.8 nm and a carrier mobility of greater than 7,100 cm2 V−1 s−1 under ambient conditions. The repeatable growth of graphene with large single-crystal grains on Pt and its nondestructive transfer may enable various applications
Graphene Photonics and Optoelectronics
The richness of optical and electronic properties of graphene attracts
enormous interest. Graphene has high mobility and optical transparency, in
addition to flexibility, robustness and environmental stability. So far, the
main focus has been on fundamental physics and electronic devices. However, we
believe its true potential to be in photonics and optoelectronics, where the
combination of its unique optical and electronic properties can be fully
exploited, even in the absence of a bandgap, and the linear dispersion of the
Dirac electrons enables ultra-wide-band tunability. The rise of graphene in
photonics and optoelectronics is shown by several recent results, ranging from
solar cells and light emitting devices, to touch screens, photodetectors and
ultrafast lasers. Here we review the state of the art in this emerging field.Comment: Review Nature Photonics, in pres
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