Publications

The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (~0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed.

Printed graphene supercapacitors have the potential to empower tomorrow's wearable electronics. We report a solid-state flexible supercapacitor device printed on textiles using graphene oxide ink and a screen-printing technique. After printing, graphene oxide was reduced in situ via a rapid electrochemical method avoiding the use of any reducing reagents that may damage the textile substrates. The printed electrodes exhibited excellent mechanical stability due to the strong interaction between the ink and textile substrate. The unique hierarchical porous structure of the electrodes facilitated ionic diffusion and maximised the surface area available for the electrolyte/active material interface. The obtained device showed outstanding cyclic stability over 10 000 cycles and maintained excellent mechanical flexibility, which is necessary for wearable applications. The simple printing technique is readily scalable and avoids the problems associated with fabricating supercapacitor devices made of conductive yarn, as previously reported in the literature.

The energy dissipation issue has become one of the greatest challenges of the modern electronic industry. Incorporating graphene into the electronic devices has been widely accepted as a promising approach to solve this issue, due to its superior carrier mobility and thermal conductivity. Here, using Raman spectroscopy and infrared thermal microscopy, we identify the energy dissipation behavior of graphene device with different thicknesses. Surprisingly, the monolayer graphene device is demonstrated to have a comparable energy dissipation efficiency per unit volume with that of a few-layer graphene device. This has overturned the traditional understanding that the energy dissipation efficiency will reduce with the decrease of functional materials dimensions. Additionally, the energy dissipation speed of the monolayer graphene device is very fast, promising for devices with high operating frequency. Our finding provides a new insight into the energy dissipation issue of two-dimensional materials devices, which will have a global effect on the development of the electronic industry.

Central to most applications involving monolayer graphenes is its mechanical response under various stress states. To date most of the work reported is of theoretical nature and refers to tension and compression loading of model graphenes. Most of the experimental work is indeed limited to the bending of single flakes in air and the stretching of flakes up to typically ∼1% using plastic substrates. Recently we have shown that by employing a cantilever beam we can subject single graphenes to various degrees of axial compression. Here we extend this work much further by measuring in detail both stress uptake and compression buckling strain in single flakes of different geometries. In all cases the mechanical response is monitored by simultaneous Raman measurements through the shift of either the G or 2D phonons of graphene. Despite the infinitely small thickness of the monolayers, the results show that graphenes embedded in plastic beams exhibit remarkable compression buckling strains. For large length (l)-to-width (w) ratios (≥0.2) the buckling strain is of the order of −0.5% to −0.6%. However, for l/w < 0.2 no failure is observed for strains even higher than −1%. Calculations based on classical Euler analysis show that the buckling strain enhancement provided by the polymer lateral support is more than 6 orders of magnitude compared to that of suspended graphene in air.

The electrostatic confinement of massless charge carriers is hampered by Klein tunneling. Circumventing this problem in graphene mainly relies on carving out nanostructures or applying electric displacement fields to open a band gap in bilayer graphene. So far, these approaches suffer from edge disorder or insufficiently controlled localization of electrons. Here we realize an alternative strategy in monolayer graphene, by combining a homogeneous magnetic field and electrostatic confinement. Using the tip of a scanning tunneling microscope, we induce a confining potential in the Landau gaps of bulk graphene without the need for physical edges. Gating the localized states towards the Fermi energy leads to regular charging sequences with more than 40 Coulomb peaks exhibiting typical addition energies of 7-20 meV. Orbital splittings of 4-10 meV and a valley splitting of about 3 meV for the first orbital state can be deduced. These experimental observations are quantitatively reproduced by tight binding calculations, which include the interactions of the graphene with the aligned hexagonal boron nitride substrate. The demonstrated confinement approach appears suitable to create quantum dots with well-defined wave function properties beyond the reach of traditional techniques.

Semiconducting ferromagnet-nonmagnet interfaces in van der Waals heterostructures present a unique opportunity to investigate magnetic proximity interactions dependent upon a multitude of phenomena including valley and layer pseudospins, moiré periodicity, or exceptionally strong Coulomb binding. Here, we report a charge-state dependency of the magnetic proximity effects between MoSe 2 and CrBr 3 in photoluminescence, whereby the valley polarization of the MoSe 2 trion state conforms closely to the local CrBr 3 magnetization, while the neutral exciton state remains insensitive to the ferromagnet. We attribute this to spin-dependent interlayer charge transfer occurring on timescales between the exciton and trion radiative lifetimes. Going further, we uncover by both the magneto-optical Kerr effect and photoluminescence a domain-like spatial topography of contrasting valley polarization, which we infer to be labyrinthine or otherwise highly intricate, with features smaller than 400 nm corresponding to our optical resolution. Our findings offer a unique insight into the interplay between short-lived valley excitons and spin-dependent interlayer tunneling, while also highlighting MoSe 2 as a promising candidate to optically interface with exotic spin textures in van der Waals structures.

The increasing demand for health monitoring, voice detection, electronic skins, and human-computer interaction has accelerated the development of highly sensitive, flexible, and miniaturized pressure and acoustic sensors. Among various sensing technologies, piezoresistive sensors offer advantages such as simple fabrication, low power consumption, and broad detection ranges, making them well-suited for detecting subtle vibrations and acoustic signals. However, traditional piezoresistive materials, including metals and semiconductors, are inherently stiff and brittle, limiting their integration into wearable electronics and bio-integrated devices. To overcome these challenges, we introduce a graphene oxide (GO)/deoxyribonucleic acid (DNA) aerogel, synthesized via a self-assembly approach using pre-formed hydrogel membranes. This biodegradable and biocompatible aerogel features tunable pore sizes, low density, and excellent mechanical resilience. Upon reduction, the GO/DNA aerogel exhibits high piezoresistive sensitivity (1.74 kPa-1) in the low-pressure range (0-130 Pa), surpassing conventional pressure sensors. Additionally, it detects acoustic signals, achieving a sensitivity of 74.4 kPa-1, outperforming existing acoustic sensors. These findings highlight the potential of rGO/DNA aerogels as materials for next-generation wearable electronics, biomedical diagnostics, and soft robotics.

In this work, we first screen print thin GO laminates on Kapton film and then chemically reduce to rGO with desired sheet resistance by controlling printing cycles and reduction time. The thin rGO laminates have a wide range of conductivity from 2.8 S m−1 up to 1.3×104 S m−1, exhibiting excellent consistency of electric performance even after 50000 times bending. Commonly used rGO reduction level characterization methods have been compared with the proposed sheet resistance method. It is revealed that the later has higher variation with reduction time, providing a new method for reduction monitoring of rGO. Benefiting from the tunability of its sheet resistance, the rGO laminate not only can be used in flexible electronic circuits as conductors or resistors, but also highly efficient to absorb microwave radiations with proper design. Therefore, a printed, three-layer, Jaumann structured microwave absorber has been designed, fabricated and characterised. The maximum microwave absorption rate is up to 99.9997% where the −10 dB fractional bandwidth is over 153%, which covers L, S and C bands. Moreover, the fabricated absorber can absorb efficiently even when the incident angle is as low as 20°. Full design procedure, simulation and measurement results are presented.

Textile thermoregulation and thermal protection are crucial for human health and safety. Individual thermophysiological comfort control and flame retardancy are lacking in traditional garments. Novel nanomaterial innovations have solved these limitations and have facilitated the development of next‐generation intelligent textiles. Smart textiles based on graphene and graphene derivatives material have attracted substantial attention owing to its superior electrical conductivity, high thermal conductivity, and flexibility. This review provides an overview of the current progress on the smart textiles using graphene and graphene derivative material with a focus on personal thermal management and flame retardancy. It covers mechanics, material developments, fabric designs, and on‐body applications, offering a comprehensive knowledge and scope of the entire area. Innovations in chemistry and materials with worldwide collaboration will push the frontiers of graphene‐based smart textiles, promoting the development of genuine commercial goods on the market.

No abstract is provided for this article.

Natural fibers composites are considered as sustainable alternative to synthetic composites due to their environmental and economic benefits. However, they suffer from poor mechanical and interfacial properties due to a random fiber orientation and weak fiber-matrix interface. Here we report nano-engineered graphene-based natural jute fiber preforms with a new fiber architecture (NFA) which significantly improves their properties and performances. Our graphene-based NFA of jute fiber perform enhances Young modulus of jute-epoxy composites by ~324% and tensile strength by ~110% more than untreated jute fiber composites, by arranging fibers in parallel direction through individualisation and nano surface engineering with graphene derivatives. This could potentially lead to manufacturing of high performance natural alternatives to synthetic composites in various stiffness driven high performance applications.

Two-dimensional materials offer a promising platform for the next generation of (opto-) electronic devices and other high technology applications. One of the most exciting characteristics of 2D crystals is the ability to tune their properties via controllable introduction of defects. However, the search space for such structures is enormous, and ab-initio computations prohibitively expensive. We propose a machine learning approach for rapid estimation of the properties of 2D material given the lattice structure and defect configuration. The method suggests a way to represent configuration of 2D materials with defects that allows a neural network to train quickly and accurately. We compare our methodology with the state-of-the-art approaches and demonstrate at least 3.7 times energy prediction error drop. Also, our approach is an order of magnitude more resource-efficient than its contenders both for the training and inference part.

The growing family of two-dimensional (2D) materials that are now available can be used to assemble van der Waals heterostructures with a wide range of properties. Of particular interest are tunnelling heterostructures, which have been used to study the electronic states both in the tunnelling barrier and in the emitter and collector contacts. Recently, 2D ferromagnets have been studied theoretically and experimentally. Here we investigate electron tunnelling through a thin (2-6 layers) ferromagnetic CrBr3 barrier. For devices with non-magnetic barriers, conservation of momentum can be relaxed by phonon-assisted tunnelling or by tunnelling through localised states. In the case of our ferromagnetic barrier the dominant tunnelling mechanisms are the emission of magnons at low temperatures or scattering of electrons on localised magnetic excitations above the Curie temperature. Tunnelling with magnon emission offers the possibility of injecting spin into the collector electrode.

In this paper, we present scanning gate microscopy (SGM) measurements on a graphene quantum point contact, carried out under ambient conditions. Images obtained in SGM display two-dimensional maps of sample resistance, as a function of the position of a biased AFM tip and the voltage applied to the tip. In our studies, a graphene quantum point contact was fabricated using local anodic oxidation. Performing SGM imaging on the resulting device structure shows that the resistance through the graphene QPC is strongly affected by the electric field of the AFM tip at the position of the QPC.