Single-layer graphene (SLG) obtained by chemical vapor deposition is applied between membrane and electrodes by a wet chemical transfer method to study its effect on the performance and durability of polybenzimidazole membranes in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). After accelerated stress testing (AST), the membrane electrode assembly (MEA) loaded with SLG at different positions exhibits higher peak power density, lower electrode resistances, and larger electrochemical active surface area than pure polybenzimidazole membranes with high phosphoric acid doping level. The peak power density of the MEAs with both cathode and anode loaded with SLG is 480 mW cm(-2) after AST, while those based on pure membranes is 249 mW cm(-2). Lab-based X-ray micro-computed tomography combined with Raman spectroscopic mapping was applied for the first time to study the effect of SLG on controlling phosphoric acid leaching. In addition, samples containing SLG on an ultra-thin membrane (7.5 mu m) were also tested to explore its influence on hydrogen crossover. After 100 h of galvanostatic discharging, the hydrogen crossover of samples loaded with single-layer graphene on the anode does not exceed 1.75 x 10(-4) mol s(-1), which is much lower than that of MEAs made using pure ultra-thin membranes (8.16 x10(-4) mol s(-)(1)).

Advanced materials such as graphene and the family of two-dimensional crystals are very attractive because of the myriad of applications that could be developed based on their outstanding properties. However, as soon as material development reaches enough maturity for production to be scaled up and to enter the market within products, it is crucial to place the technology in the context of possible risks to economic well-being, social equity and environmental harm. This review aims at highlighting the current state of art on sustainable development of graphene-related materials and related environmental impact assessment studies using life cycle assessment (LCA). We show that sustainable development has focused mostly on the use of waste or low cost materials as precursors. However, the findings from relevant LCA studies reveals the limits of this approach, which does not take into account that waste recycling is often very energy intensive. We provide an overview on the life cycle environmental impact assessment, with a focus on global warming potential and energy demand, carried out on different graphene productions methods for specific applications, ranging from composites to electronics. Finally, an outlook is given focussing on the comparison of the different production routes and the results from the LCA.

The COVID-19 pandemic highlighted the need for rapid tools and technologies to combat highly infectious viruses. The excellent electrical, mechanical and other functional properties of graphene and graphene-like 2D materials (2DM) can be utilized to develop novel and innovative devices to tackle COVID-19 and future pandemics. Here, the authors outline how graphene and other 2DM-based technologies can be used for the detection, protection, and continuous monitoring of infectious diseases including COVID-19. The authors highlight the potential of 2DM-based biosensors in rapid testing and tracing of viruses to enable isolation of infected patients, and stop the spread of viruses. The possibilities of graphene-based wearable devices are discussed for continuous monitoring of COVID-19 symptoms. The authors also provide an overview of the personal protective equipment, and potential filtration mechanisms to separate, destroy or degrade highly infectious viruses, and the potential of graphene and other 2DM to increase their efficiency, and enhance functional and mechanical properties. Graphene and other 2DM could not only play a vital role for tackling the ongoing COVID-19 pandemic but also provide technology platforms and tools for the protection, detection and monitoring of future viral diseases.

We present a combined atomic force microscopy and Raman spectroscopy study of wrinkle formation in chemical vapour deposition graphene. Graphene was grown on copper and repeatedly transferred onto a SiO2 substrate to form a four-layer graphene stack. By means of depositing two electrodes with a small gap of 1 μm on top of graphene, we can generate a long wrinkle along the channel. Such a wrinkle is pronounced and seems to form at the expense of other wrinkles otherwise present. Along the wrinkle, the strain measured by both atomic force microscopy and polarized Raman is revealed to be of a biaxial type, which is shown, through atomistic modelling, is predicted to produce a sizeable bandgap opening of up to 0.4 eV. Since graphene is normally a zero bandgap material, its applications as an electronic material for devices can be limited. The approach presented in this work could lead to graphene exhibiting a controllable bandgap similar to a semiconductor material that could, therefore, be exploited for the fabrication of graphene-based electronic devices.

Graphene was grown on copper and repeatedly transferred onto a GaAs semi-insulating substrate to form multilayers (1–10). These manually stacked graphene layers resulted in appreciable local variations of optical properties due to the local differences of stacking orders. In addition, most of the observed 2D/G intensity and area ratios of an n-multilayer CVD graphene is consistent with the characteristics of a single layer repeated n-times. However, multilayer graphene has many kinds of advantages for applications to optoelectronic devices. First, the G band shift is not related to the stacking order, proving that multilayer graphene reduces doping and strain effect from the substrate, which is confirmed by Raman results after metal electrode deposition. Second, the sheet resistance decreases with increasing number of layers and after thermal annealing. Another benefit of multilayer graphene is that each layer can be annealed after transfer, which greatly improves the sheet resistance and its lateral uniformity without intentional doping. We therefore conclude that multilayer CVD graphene is a good candidate for various GaAs-based electrical applications and its good electrical uniformity allows fabrication of devices on large scales.

Here, we evaluate the electrochemical performance of sparsely studied natural crystals of molybdenite and graphite, which have increasingly been used for fabrication of next generation monolayer molybdenum disulphide and graphene energy storage devices. Heterogeneous electron transfer kinetics of several redox mediators, including Fe(CN)6(3-/4-), Ru(NH3)6(3+/2+) and IrCl6(2-/3-) are determined using voltammetry in a micro-droplet cell. The kinetics on both materials are studied as a function of surface defectiveness, surface ageing, applied potential and illumination. We find that the basal planes of both natural MoS2 and graphite show significant electroactivity, but a large decrease in electron transfer kinetics is observed on atmosphere-aged surfaces in comparison to in situ freshly cleaved surfaces of both materials. This is attributed to surface oxidation and adsorption of airborne contaminants at the surface exposed to an ambient environment. In contrast to semimetallic graphite, the electrode kinetics on semiconducting MoS2 are strongly dependent on the surface illumination and applied potential. Furthermore, while visibly present defects/cracks do not significantly affect the response of graphite, the kinetics on MoS2 systematically accelerate with small increase in disorder. These findings have direct implications for use of MoS2 and graphene/graphite as electrode materials in electrochemistry-related applications.

The deformation of monolayer graphene, produced by chemical vapor deposition (CVD), on a polyester film substrate has been investigated through the use of Raman spectroscopy. It has been found that the microstructure of the CVD graphene consists of a hexagonal array of islands of flat monolayer graphene separated by wrinkled material. During deformation, it was found that the rate of shift of the Raman 2D band wavenumber per unit strain was less than 25% of that of flat flakes of mechanically exfoliated graphene, whereas the rate of band broadening per unit strain was about 75% of that of the exfoliated material. This unusual deformation behavior has been modeled in terms of mechanically isolated graphene islands separated by the graphene wrinkles, with the strain distribution in each graphene island determined using shear lag analysis. The effect of the size and position of the Raman laser beam spot has also been incorporated in the model. The predictions fit well with the behavior observed experimentally for the Raman band shifts and broadening of the wrinkled CVD graphene. The effect of wrinkles upon the efficiency of graphene to reinforce nanocomposites is also discussed.

Using a novel interatomic force field, called MMP, we study the morphology of Graphene layers under a variety of strain conditions. We report that strain induced ripples possess the "right" kind of elastic deformation that is necessary in order to produce appreciable bandgap opening, which we calculate using Tight Binding, even for low enough strain that can be accessed through realistic means. At the same time the vibrational properties, calculated from analytic derivatives of the MMP force field and used within the dynamics matrix method, can be easily linked to strain obtained from Molecular Dynamics, opening the way for accurate modelling of Raman data. We also show that our models have allowed us to realize in practice novel devices based on our predictions.

When a crystal is subjected to a periodic potential, under certain circumstances it can adjust itself to follow the periodicity of the potential, resulting in a commensurate state. Of particular interest are topological defects between the two commensurate phases, such as solitons and domain walls. Here we report a commensurate–incommensurate transition for graphene on top of hexagonal boron nitride (hBN). Depending on the rotation angle between the lattices of the two crystals, graphene can either stretch to adapt to a slightly different hBN periodicity (for small angles, resulting in a commensurate state) or exhibit little adjustment (the incommensurate state). In the commensurate state, areas with matching lattice constants are separated by domain walls that accumulate the generated strain. Such soliton-like objects are not only of significant fundamental interest, but their presence could also explain recent experiments where electronic and optical properties of graphene-hBN heterostructures were observed to be considerably altered. A single layer of graphene on top of a hexagonal boron-nitride sheet can stretch to form a commensurate structure, or not — depending on the rotation angle between the two layers. In the case of commensurability, strain gets concentrated in domain walls, resulting in soliton-like structures.

Plasmonics has established itself as a branch of physics which promises to revolutionize data processing, improve photovoltaics, and increase sensitivity of bio-detection. A widespread use of plasmonic devices is notably hindered by high losses and the absence of stable and inexpensive metal films suitable for plasmonic applications. To this end, there has been a continuous search for alternative plasmonic materials that are also compatible with complementary metal oxide semiconductor technology. Here we show that copper and silver protected by graphene are viable candidates. Copper films covered with one to a few graphene layers show excellent plasmonic characteristics. They can be used to fabricate plasmonic devices and survive for at least a year, even in wet and corroding conditions. As a proof of concept, we use the graphene-protected copper to demonstrate dielectric loaded plasmonic waveguides and test sensitivity of surface plasmon resonances. Our results are likely to initiate wide use of graphene-protected plasmonics.

One of the challenges associated with the development of next-generation electronics is to find alternatives to silicon oxide caused by the size-reduction constraints of the devices. The dielectric properties of two-dimensional (2D) crystals, added to their excellent chemical stability, mechanical and thermal properties, make them promising dielectrics. Here we show that liquid-phase exfoliation (LPE) in water by using low-cost commercial organic dyes as dispersant agents can efficiently produce defect-free 2D nanosheets, including mono-layers, in suspensions. We further show that these suspensions can be easily incorporated into current practical graphene-based devices. In particular, it is found that boron nitride thin films made by LPE are excellent dielectrics that are highly compatible with graphene-based electronics.

The new paradigm of heterostructures based on two-dimensional (2D) atomic crystals has already led to the observation of exciting physical phenomena and creation of novel devices. The possibility of combining layers of different 2D materials in one stack allows unprecedented control over the electronic and optical properties of the resulting material. Still, the current method of mechanical transfer of individual 2D crystals, though allowing exceptional control over the quality of such structures and interfaces, is not scalable. Here we show that such heterostructures can be assembled from chemically exfoliated 2D crystals, allowing for low-cost and scalable methods to be used in device fabrication.

We exploit the low density of electronic states of graphene to modulate the tunnel current flowing perpendicular to the atomic layers of a multi-layer graphene-boron nitride device. This is achieved by using the electric field effect to raise the Fermi energy of the graphene emitter layer and thereby reduce the effective barrier height for tunneling electrons. We discuss how the electron charge density in the graphene layers and the properties of the boron nitride tunnel barrier determine the device characteristics under operating conditions and derive expressions for carrier tunneling in these highly anisotropic layered heterostructures.

Non-trivial topology of phase is crucial for many important physics phenomena such as, for example, the Aharonov-Bohm effect 1 and the Berry phase 2. Light phase allows one to create "twisted" photons 3, 4 , vortex knots 5, dislocations 6 which has led to an emerging field of singular optics relying on abrupt phase changes 7. Here we demonstrate the feasibility of singular visible-light nanooptics which exploits the benefits of both plasmonic field enhancement and non-trivial topology of light phase. We show that properly designed plasmonic nanomaterials exhibit topologically protected singular phase behaviour which can be employed to radically improve sensitivity of detectors based on plasmon resonances. By using reversible hydrogenation of graphene 8 and a streptavidin-biotin test 9, we demonstrate areal mass sensitivity at a level of femto-grams per mm2 and detection of individual biomolecules, respectively. Our proof-of-concept results offer a way towards simple and scalable single-molecular label-free biosensing technologies.

We present a joint theoretical and experimental investigation of charge doping and electronic potential landscapes in hybrid structures composed of graphene and semiconducting single layer molybdenum disulfide (MoS2). From first-principles simulations, we find electron doping of graphene due to the presence of rhenium impurities in MoS2. Furthermore, we show that MoS2 edges give rise to charge reordering and a potential shift in graphene, which can be controlled through external gate voltages. The interplay of edge and impurity effects allows the use of the graphene-MoS2 hybrid as a photodetector. Spatially resolved photocurrent signals can be used to resolve potential gradients and local doping levels in the sample.

Heterostructures fabricated from atomically thin crystalline layers are new materials which offer exciting possibilities for next-generation electronic and optoelectronic sensors and devices. The idea of heterostructures is not new and traditional semiconductor heterostructures have already played an important technological role in many modern electronic components. It is possible to fabricate new and exciting structures by stacking single atomic layers of different materials into heterostructures. This technology can be used to create materials and devices with a wide variety of properties. The stacking order, thickness, doping and crystal orientation play the major roles in determining the characteristics of these new materials. The experimental work for this thesis involves the electrical characterisation of several different heterostructures.i Investigation of boron nitride as an atomically thin tunnel barrier, including its homogeneity across micron sized areas. The area normalised conductance was found to depend on boron nitride thickness, changing by 1.5 decades per layer.ii Graphene-based tunnelling transistors which exhibit current modulation by external gate voltage. With boron nitride as the tunnel barrier an on-off ratio of up to 40 was acheived.iii Resonant tunnelling devices which show negative differential conductivity in their current-voltage characteristics.iv Photodetection and solar cell devices using semiconducting tungsten disulfide. The maximum external quantum efficiency observed was 0.1 A/W which was approximately constant across the visible spectrum. The enormous array of possibilities made available by this technology means that there is huge scope for further investigation with more exploratory research to make proof-of-principle functional devices for application in technology.

The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created a new paradigm in materials science: heterostructures based on 2D crystals. Such a concept has already proven fruitful for a number of electronic applications in the area of ultrathin and flexible devices. Here, we expand the range of such structures to photoactive ones by using semiconducting transition metal dichalcogenides (TMDCs)/graphene stacks. Van Hove singularities in the electronic density of states of TMDC guarantees enhanced light-matter interactions, leading to enhanced photon absorption and electron-hole creation (which are collected in transparent graphene electrodes). This allows development of extremely efficient flexible photovoltaic devices with photoresponsivity above 0.1 ampere per watt (corresponding to an external quantum efficiency of above 30%).