Table of contents

A new strategy for the integration of graphene electronics with silicon complementary metal–oxide–semiconductor (Si-CMOS) technology is demonstrated that requires neither graphene transfer nor patterning. Inspired by silicon-on-insulator and three-dimensional device hyper-integration techniques, a thin monocrystalline silicon layer ready for CMOS processing is bonded to epitaxial graphene (EG) on SiC. The parallel Si and graphene electronic platforms are interconnected by metal vias. In this method, EG is grown prior to bonding so that the process is compatible with EG high temperature growth and preserves graphene integrity and nano-structuring.

A novel lateral all-graphene tunnel field-effect transistor (FET) with superior ON/OFF current switching ratio is proposed and simulated. The structure consists of two coplanar graphene layers serving as source and drain separated by a narrow tunnel gap. Both barrier transparency and tunnel density of states are controlled by top and bottom gates made of graphene too. The proposed FET exhibits an ultrahigh frequency performance inherent to graphene along with a subthreshold slope approaching the thermionic limit and current saturation inherent to common semiconductor FETs.

A practical wide bandgap was induced in bilayer graphene using a perpendicular electric field. A self-assembled gate insulator was used to apply a large electric field. The wide bandgap allows the operation of fundamental logic gates composed of bilayer graphene transistors. The results reviewed here indicate the potential for graphene electronics to be realized as emerging transistors with an atomically thin semiconductor.

We have studied the static and dynamical properties of a graphene microwave nanotransistor to be used as sensitive fast charge detectors. The channel consists of exfoliated graphene on SiO₂ with a 120 nm long, 900–1500 nm wide top-gate deposited on 5 nm AlO_x dielectric. The scattering parameters were measured up to 60 GHz from which we deduce the gate capacitance, the drain conductance and the transconductance as a function of gate voltage. The broad measuring band allows us to measure the current gain and to map its full spectrum so as to extract reliable values of the transit frequency f_T. From these measurements, we could estimate the carrier mobility, the doping of the access leads, the gate capacitance and the transconductance. The transconductance per unit width and bias voltage is larger than 1 mS µm⁻¹ V⁻¹ which compares with the performance of high electron mobility transistors. High-frequency characterization is achieved using microwave probe stations. Finally, using recent noise thermometry measurements, we estimate the charge resolution of graphene nanotransistors.

First selective bio-molecule sensing was achieved using a graphene field-effect transistor. For selective sensing, the surface of the graphene was modified by a receptor, such as an immunoglobulin E aptamer, and a fragment antibody, to take into account the height of the receptor and the Debye length. For higher sensitivity, it was found that the concentration of the receptor on the graphene surface was important and should be optimized.

This paper reviews recent advances in graphene active plasmonics for terahertz (THz) device applications. Two-dimensional plasmons in graphene exhibit unique optoelectronic properties and mediate extraordinary light–matter interactions. It has been discovered theoretically that when the population of Dirac fermionic carriers in graphene are inverted by optical or electrical pumping, the excitation of graphene plasmons by the THz photons results in propagating surface plasmon polaritons with giant gain in a wide THz range. Furthermore, when graphene is patterned into a micro- or nanoribbon array by grating metallization, the structure acts as an active THz plasmonic amplifier, providing a superradiant plasmonic lasing with a giant gain at the plasmon modes in a wide THz frequency range. These new findings can lead to the creation of new types of plasmonic THz emitters and lasers operating even at room temperature.

We study several graphene devices able to generate non-linear effects in the current–voltage characteristics and in particular negative differential resistance (NDR) effects. This theoretical investigation is based on numerical charge transport simulation in the Green's function approach applied to a tight-binding Hamiltonian for particles in graphene. Depending on the device, the physical mechanism involved in the NDR effect may be different: (i) the mismatch of modes between left and right sides of a P⁺/P zigzag ribbon junction, (ii) the modulation of interband tunnelling in P/N junctions (tunnel diodes and tunnel field-effect transistors) or (iii) the modulation of chiral tunnelling in 'conventional' graphene transistors. We emphasize the advantages of exploiting different approaches of bandgap engineering in the form of graphene nanoribbons (GNRs) or nanomesh lattices (GNM), the latter resulting from a periodic array of nanoholes in graphene sheets. In particular, such nanostructuring allows us to design position-dependent bandgaps in devices, which is shown to make possible the optimization of device operation and, here, to get very high peak-to-valley ratio of the NDR. In the case of GNR nanostructuring, it is shown that appropriate bandgap engineering can even make the current–voltage characteristics of tunnel diodes weakly sensitive to the atomic edge disorder. Finally, GNM lattices are shown to be a very promising way to open large bandgaps in wide sheets of graphene and to introduce bandgaps locally with a view to optimizing the device operation and performance.

Transient absorption properties of aqueous graphene oxide (GO) have been studied by use of femtosecond pump–probe spectroscopy. Excited state absorption and photobleaching are observed in the wide spectral range. The observed fast three lifetime components are attributed to the absorption of upper excited states and localized states, which is confirmed by both laser induced absorption and transmission kinetics. The longest time component is assigned to the lowest excited state of GO, which mainly originates from the sp2 domains. With the increase of the excitation power, two-quantum absorption occurs, which results in an additional rise-time component of the observed transients.

We review some of the electric properties of self-organized graphene monolayers on the carbon face of SiC. From sparse surface defects acting as nucleation centres, isolated graphene layers grow in the shape of triangles or ribbons on the step bunched SiC surface. Using e-beam lithography, standard Hall bars have been made. At low magnetic fields, conductance fluctuations, weak localization, electron–electron interactions are usually observed. At higher magnetic fields, the anomalous quantum Hall (QHE) effect typical of monolayer graphene is also observed. In this regime, the breakdown of the QHE appears at moderate currents, which we attribute to the persistence of impurities in the vicinity of the graphene layer. Moderate heating (150 °C) is not sufficient to overcome this issue, and moreover, the carrier concentration cannot be controlled. In order to control the carrier concentration, bottom-gated samples are also presented. In these devices, the carrier concentration can be modulated, but the breakdown current remains very small.

We have observed propagation of edge magnetoplasmon (EMP) modes in graphene in the quantum Hall regime by performing picosecond time-of-flight measurements between narrow contacts on the perimeter of micrometric exfoliated graphene. We find the propagation to be chiral with low attenuation and to have a velocity which is quantized on Hall plateaus. The velocity has two contributions, one arising from the Hall conductivity and the other from carrier drift along the edge, which we were able to separate by their different filling factor dependence. The drift component is found to be slightly less than the Fermi velocity as expected for graphene dynamics in an abrupt edge potential. The Hall conduction contribution is slower than expected and indicates a characteristic length in the Coulomb potential from the Hall charge of about 500 nm. The experiment illustrates how EMP can be coupled to the electromagnetic field, opening the perspective of GHz to THz chiral plasmonics applications to devices such as voltage controlled phase shifters, circulators, switches and compact, tunable ring resonators.

This article presents the current puzzling controversy between theory and experimental results concerning the mechanisms leading to spin relaxation in graphene-based materials. On the experimental side, it is surprising that regardless of the quality of the graphene monolayer, which is characterized by the carrier mobility, the typical Hanle precession measurements yield spin diffusion times (τ_s) in the order of τ_s ∼ 0.1–1 ns (at low temperatures), which is several orders of magnitude below the theoretical estimates based on the expected low intrinsic spin–orbit coupling in graphene. The results are weakly dependent on whether graphene is deposited onto SiO₂ or boron-nitride substrates or is suspended, with the mobility spanning 3 orders of magnitude. On the other hand, extraction form two-terminal magnetoresistance measurements, accounting for contact effects results in τ_s ∼ 0.1 µs, and corresponding diffusion lengths of about 100 µm up to room temperature. Such discrepancy jeopardizes further progress towards spin manipulation on a lateral graphene two-dimensional platform. After a presentation of basic concepts, we here discuss state-of-the-art literature and the limits of all known approaches to describe spin transport in massless-Dirac fermions, in which the effects of strong local spin–orbit coupling ceases to be accessible with perturbative approaches. We focus on the limits of conventional views of spin transport in graphene and offer novel perspectives for further progress.

Graphene nanoribbon (GNR) is a recently discovered carbon allotrope, which can be described as a stripe of graphene. Pseudo-one-dimensionality exerts additional confinement on the electrons resulting in the formation of a band gap relevant for electronic devices. Due to distinct physical and chemical properties it is a promising material for several applications. To expand the range of potential applications and to improve processability, chemical functionalization of GNRs is required. This review aims to provide a concise and systematic coverage of recent work in chemical functionalization of GNRs. We will focus on longitudinal carbon nanotube unzipping, functionalization with aryl diazonium salts, non-covalent functionalization, bottom-up synthesis and one pot carbon nanotube unzipping with in situ edge functionalization.

Epitaxial graphene (EG) on SiC has been proven to be an excellent material to investigate the fundamental physical properties of graphene and also to directly implement new findings into devices realized on the versatile platform of SiC. Within this framework, this work aims to review some of the recent major achievements accomplished in the field of EG on SiC, related to the growth of EG on the SiC(0 0 0 1) surface, the control of its doping level, the decoupling of the graphene from the substrate and the intercalation of foreign atomic species at the interface.

We present a comparative high-resolution electron energy-loss spectroscopy study on the interaction of atomic hydrogen and deuterium with various reconstructions of SiC(0 0 0 1). We first show that on both the (3 × 3) and $(\sqrt {{3}} \times \sqrt {{3}})R30^{\circ}$ reconstructions, deuterium atoms only bind to silicon atoms, thereby confirming the silicon-rich appellation of these reconstructions. Deuterium passivation of the (3 × 3) is only reversible when exposed to atomic deuterium at a surface temperature of 700 K since tri- and dideuterides, necessary precursors for silicon etching, are not stable. On the other hand, we show that the deuteration of the $(\sqrt {{3}} \times \sqrt {{3}} )R30^{\circ}$ is always reversible because precursors to silicon etching are scarce on the surface. Then, we demonstrate that hydrogen (deuterium) adsorption at 300 K on both the $({6}\sqrt 3 \times {6}\sqrt 3 )R30^{\circ}$ (buffer-layer) and the quasi-free-standing graphene occurs on carbon atoms justifying their carbon-rich appellation. Comparison of the deuterium binding in the intercalation layer of quasi-free-standing graphene with the deuterated $(\sqrt {{3}} \times \sqrt {{3}} )R30^{\circ}$ surface provides some indication on the bonding structure at the substrate intercalation layer. Finally, by measuring C–H (C–D) vibrational frequencies and hydrogen (deuterium) desorption temperatures we suggest that partial sp²-to-sp³ rehybridization occurs for the carbon atoms of the buffer-layer because of the corrugation related to covalent bonding to the SiC substrate. In contrast, on quasi-free-standing graphene hydrogen (deuterium) atoms adsorb similarly to what is observed on graphite, i.e. without preferential sticking related to the underlying SiC substrate.

Graphene films were formed on sapphire surfaces using polymethylmethacrylate (PMMA) polymer films as a carbon source and characterized by Raman spectroscopy. For large-scale, uniform growth, a spin-on-glass (SOG)/Cu-catalyst/PMMA/sapphire layered structure was annealed in Ar–H₂ flow at atmospheric pressure. We found that the SOG cover layer is effective to suppress evaporation and agglomeration of the Cu film. We also confirmed that morphology and quality of grown graphene films are dramatically improved by hydrogen etching of buried bulky carbon produced by the polymer pyrolysis at the Cu/sapphire interfaces. Quality of graphene films grown at the catalyst-layer/sapphire interface was compared with that on the catalyst surface using Ni/PMMA, PMMA/Ni and Ni/PMMA/Ni layered structures. Quality of graphene films grown at the Ni/sapphire interfaces was found to be lower than that on the Ni surfaces, suggesting that strain engineering at the buried Ni/graphene/sapphire interfaces and/or etching technique to remove the wastes of polymer pyrolysis should be improved.

By forming a thin 3C-SiC film on Si substrates and by annealing it at ∼1500 K in vacuo, few-layer graphene is formed epitaxially on Si substrates. In this graphene-on-silicon (GOS) technology, graphene grows at least on three major low-index Si surfaces: (1 1 1), (1 0 0) and (1 1 0), which allows tuning of structural and electronic properties of epitaxial graphene by simply controlling the crystallographic orientation of the surface. A typical example can be found in the two types of graphene formed on 3C-SiC(1 1 1) surfaces; the one on 3C-SiC(1 1 1)/Si(1 1 1) shows a Bernal stacking with an interfacial buffer layer, while the one on 3C-SiC(1 1 1)/Si(1 1 0) shows a non-Bernal stacking without an interfacial buffer layer. Inserting an AlN interlayer between Si and 3C-SiC significantly contributes to improvement of the GOS quality. Moreover, thanks to the sealing effect of the AlN layer against Si out-diffusion, we can apply chemomechanical polishing of SiC surface to reduce the surface roughness, which can further accentuate the effect of H₂ annealing of the surface. As a result, a D to G band intensity ratio as low as 0.4 is obtained.

We investigated the atomic-scale structural properties of graphene epitaxially grown on SiC {0 0 0 1} surfaces by high-resolution transmission electron microscope observations. In this review paper, we summarize our results about the interface structure, the growth mechanisms and the growth techniques. Graphene on the Si-terminated surface has a buffer layer that is strongly bonded to the substrate and has a low carbon atom density. Multilayer graphene on the Si-face exhibited an ABC-stacking selectively. Graphene on the Si-face nucleates at the step-edge, and grows layer-by-layer over the upper terrace. Based on the mechanism, we succeeded in growing high-quality and homogeneous monolayer and bilayer graphene on the Si-terminated surface with low-height and low-density steps using our original technique. Graphene on the C-face has weaker bonds with the substrate, and the resulting multilayer contains the rotational stacking disorder. The origin of the rotational stacking is closely related to the growth mechanism, where graphene layers nucleate on a terrace at a lower temperature and grow in all directions on the surface.