14 research outputs found
Wafer-scale integration of graphene for waveguide-integrated optoelectronics
As the focus of graphene research shifts from fundamental physics to applications, the scalability and reproducibility of experimental results become ever more important. Graphene has been proposed as an enabling material for the continuing growth of the telecommunications industry due to its applications in optoelectronics; however, the extent of its adoption will depend on the possibility to maintain the high intrinsic quality of graphene when processing it using the industry-standard approaches. We look at the challenges of scalable graphene integration and the opportunities presented by the recent technological advances
Stretching graphene using polymeric micro-muscles
The control of strain in two-dimensional materials opens exciting
perspectives for the engineering of their electronic properties. While this
expectation has been validated by artificial-lattice studies, it remains
elusive in the case of atomic lattices. Remarkable results were obtained on
nanobubbles and nano-wrinkles, or using scanning probes; microscale strain
devices were implemented exploiting deformable substrates or external loads.
These devices lack, however, the flexibility required to fully control and
investigate arbitrary strain profiles. Here, we demonstrate a novel approach
making it possible to induce strain in graphene using polymeric micrometric
artificial muscles (MAMs) that contract in a controllable and reversible way
under an electronic stimulus. Our method exploits the mechanical response of
poly-methyl-methacrylate (PMMA) to electron-beam irradiation. Inhomogeneous
anisotropic strain and out-of-plane deformation are demonstrated and studied by
Raman, scanning-electron and atomic-force microscopy. These can all be easily
combined with the present device architecture. The flexibility of the present
method opens new opportunities for the investigation of strain and
nanomechanics in two-dimensional materials
Strain-Induced Plasmon Confinement in Polycrystalline Graphene
Terahertz spectroscopy is a perfect tool to investigate the electronic intraband conductivity of graphene, but a phenom-enological model (Drude-Smith) is often needed to describe disorder. By studying the THz response of isotropically strained polycrystalline graphene and using a fully atomistic computational approach to fit the results, we demonstrate here the connection between the Drude-Smith parameters and the microscopic behavior. Importantly, we clearly show that the strain-induced changes in the conductivity originate mainly from the increased separation between the single-crystal grains, leading to enchanced localization of the plasmon excitations. Only at the lowest strain values explored, a behavior consistent with the deformation of the individual grains can instead be observed
Scalable High-Mobility Graphene/hBN Heterostructures
Graphene-hexagonal boron nitride (hBN) scalable heterostructures are pivotal
for the development of graphene-based high-tech applications. In this work, we
demonstrate the realization of high-quality graphene-hBN heterostructures
entirely obtained with scalable approaches. hBN continuous films were grown via
ion beam-assisted physical vapor deposition directly on commercially available
and used as receiving substrates for graphene single-crystal
matrixes grown by chemical vapor deposition on copper. The structural,
chemical, and electronic properties of the heterostructure were investigated by
atomic force microscopy, Raman spectroscopy, and electrical transport
measurements. We demonstrate graphene carrier mobilities exceeding in ambient conditions, 30% higher than those directly measured on
. We prove the scalability of our approach by measuring more than
100 transfer length method devices over a centimeter scale, which present an
average carrier mobility of . The reported high-quality
all-scalable heterostructures are of relevance for the development of
graphene-based high-performing electronic and optoelectronic applications
Ultrafast, Zero-Bias, Graphene Photodetectors with Polymeric Gate Dielectric on Passive Photonic Waveguides.
We report compact, scalable, high-performance, waveguide integrated graphene-based photodetectors (GPDs) for telecom and datacom applications, not affected by dark current. To exploit the photothermoelectric (PTE) effect, our devices rely on a graphene/polymer/graphene stack with static top split gates. The polymeric dielectric, poly(vinyl alcohol) (PVA), allows us to preserve graphene quality and to generate a controllable p-n junction. Both graphene layers are fabricated using aligned single-crystal graphene arrays grown by chemical vapor deposition. The use of PVA yields a low charge inhomogeneity ∼8 × 1010 cm-2 at the charge neutrality point, and a large Seebeck coefficient ∼140 μV K-1, enhancing the PTE effect. Our devices are the fastest GPDs operating with zero dark current, showing a flat frequency response up to 67 GHz without roll-off. This performance is achieved on a passive, low-cost, photonic platform, and does not rely on nanoscale plasmonic structures. This, combined with scalability and ease of integration, makes our GPDs a promising building block for next-generation optical communication devices
Moir\'e-Induced Transport in CVD-Based Small-Angle Twisted Bilayer Graphene
To realize the applicative potential of 2D twistronic devices, scalable
synthesis and assembly techniques need to meet stringent requirements in terms
of interface cleanness and twist-angle homogeneity. Here, we show that
small-angle twisted bilayer graphene assembled from separated CVD-grown
graphene single-crystals can ensure high-quality transport properties,
determined by a device-scale-uniform moire\'e potential. Via low-temperature
dual-gated magnetotransport, we demonstrate the hallmarks of a
-twisted superlattice, including tunable regimes of interlayer coupling,
reduced Fermi velocity, large interlayer capacitance, and density-independent
Brown-Zak oscillations. The observation of these moir\'e-induced electrical
transport features establishes CVD-based twisted bilayer graphene as an
alternative to 'tear-and-stack' exfoliated flakes for fundamental studies,
while serving as a proof-of-concept for future large-scale assembly.Comment: This is the unedited authors' version of the submitted article,
published in its final form on Nano Letters 2022 at
https://pubs.acs.org/doi/full/10.1021/acs.nanolett.2c01114 , main text, 17
pages, 4 figure
Magnetic and Electric Field Dependent Charge Transfer in Perovskite/Graphene Field Effect Transistors
International audienceStable all-inorganic CsPbX3 perovskite nanocrystals (PNCs) with high optical yield can be used in combination with graphene as photon sensors with high responsivity (up to 106 A W−1) in the VIS-UV range. The performance of these perovskite/graphene field effect transistors (FET) is mediated by charge transfer processes at the perovskite – graphene interface. Here, the effects of high electric (up to 3000 kV cm−1) and magnetic (up to 60 T) fields applied perpendicular to the graphene plane on the charge transfer are reported. The authors demonstrate electric- and magnetic-field dependent charge transfer and a slow (>100 s) charge dynamics. Magneto-transport experiments in constant (≈0.005 T s−1) and pulsed (≈1000 T s−1) magnetic fields reveal pronounced hysteresis effects in the transfer characteristics of the FET. A magnetic time is used to explain and model differences in device behavior under fast (pulsed) and slowly (continuous) changing magnetic fields. The understanding of the dynamics of the charge transfer in perovskite/graphene heterostructures developed here is relevant for exploitation of these hybrid systems in electronics and optoelectronics, including ultrasensitive photon detectors and FETs for metrology
Wafer-Scale Integration of Graphene-Based Photonic Devices.
Graphene and related materials can lead to disruptive advances in next-generation photonics and optoelectronics. The challenge is to devise growth, transfer and fabrication protocols providing high (≥5000 cm2 V-1 s-1) mobility devices with reliable performance at the wafer scale. Here, we present a flow for the integration of graphene in photonics circuits. This relies on chemical vapor deposition (CVD) of single layer graphene (SLG) matrices comprising up to ∼12000 individual single crystals, grown to match the geometrical configuration of the devices in the photonic circuit. This is followed by a transfer approach which guarantees coverage over ∼80% of the device area, and integrity for up to 150 mm wafers, with room temperature mobility ∼5000 cm2 V-1 s-1. We use this process flow to demonstrate double SLG electro-absorption modulators with modulation efficiency ∼0.25, 0.45, 0.75, 1 dB V-1 for device lengths ∼30, 60, 90, 120 μm. The data rate is up to 20 Gbps. Encapsulation with single-layer hexagonal boron nitride (hBN) is used to protect SLG during plasma-enhanced CVD of Si3N4, ensuring reproducible device performance. The processes are compatible with full automation. This paves the way for large scale production of graphene-based photonic devices
Synthesis of large-area rhombohedral few-layer graphene by chemical vapor deposition on copper
Rhombohedral-stacked few-layer graphene (FLG) displays peculiar electronic properties that could lead to phenomena such as high-temperature superconductivity and magnetic ordering. To date, experimental studies have been mainly limited by the difficulty in isolating rhombohedral FLG with thickness exceeding 3 layers and device-compatible size. In this work, we demonstrate the synthesis and transfer of rhombohedral graphene with thickness up to 9 layers and areas up to ∼50 μm2. The domains of rhombohedral FLG are identified by Raman spectroscopy and are found to alternate with Bernal regions within the same crystal in a stripe-like configuration. Near-field nano-imaging further confirms the structural integrity of the respective stacking orders. Combined spectroscopic and microscopic analyses indicate that rhombohedral-stacking formation is strongly correlated to the underlying copper step-bunching and emerges as a consequence of interlayer displacement along preferential crystallographic orientations. The growth and transfer of rhombohedral FLG with the reported thickness and size shall facilitate the observation of predicted unconventional physics and ultimately add to its technological relevance