Publications

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We report large-yield production of graphene flakes on glass by anodic bonding. Under optimum conditions, we counted several tens of flakes with lateral size around 20-30 {\mu}m and few tens of flakes with larger size. 60-70% of the flakes have negligible D peak. We show that it is possible to easily transfer the flakes by wedging technique. The transfer on silicon does not damage graphene and lowers the doping. The charge mobility of the transferred flakes on silicon is of the order of 6000 cm^2/V s (at carrier concentration of 10^12 cm^-2), which is typical for devices prepared on this substrate with exfoliated graphene.

Modern nano-optics and nanophotonics rely heavily on the precise formation of nanostructured light fields. Accurate and deterministic light field formation and characterization are indispensable for device operation as well as for revealing the underlying physical mechanisms involved. Despite a significant progress made in detection of scattered light with extremely high precision down to 1 nm resolution, there are only a limited number of techniques for direct subwavelength light mapping which do not rely on measurements of light scattering, fluorescence, or non-linear light conversion. Hence, techniques for direct conversion of light to electrical signals with precise and non-destructive imaging of nanoscale light would be of great benefit. Here, we report a nanoscale light field imaging approach based on photodetection with a p-n junction that is induced and moved inside a graphene probe by gate voltage, formed by a set of external electrodes. The spatial resolution of this electrical scanning technique is determined by p-n junction width, reaching ~ 20 nm. The developed approach is demonstrated with mapping the electric field distribution of a plasmonic slot-waveguide at telecom wavelengths. Our method provides a non-invasive nanoscale light field imaging that ensures extremely high spatial resolution and precision.

Personal protective clothing is critical to shield users from highly infectious diseases including COVID-19. Such clothing is predominantly single-use, made of plastic-based synthetic fibres such as polypropylene and polyester, low cost and able to provide protection against pathogens. However, the environmental impacts of synthetic fibre-based clothing are significant and well-documented. Despite growing environmental concerns with single-use plastic-based protective clothing, the recent COVID-19 pandemic has seen a significant increase in their use, that could result in a further surge of oceanic plastic pollution, adding to mass of plastic waste that already threatens marine life. In this review, we briefly discuss the nature of the raw materials involved in the production of such clothing, as well as manufacturing techniques and the PPE supply chain. We identify the environmental impacts at critical points in the protective clothing value chain from production to consumption, focusing on water use, chemical pollution, CO2 emissions and waste. On the basis of these environmental impacts, we outline the need for fundamental changes in the business model, including increased usage of reusable protective clothing, addressing supply chain bottlenecks, establishing better waste management, and the use of sustainable materials and processes without associated environmental problems.

Graphene-based printable inks are advanced and promising candidates for flexible printed electronic devices. To develop large-scale graphene-based highly conductive electronics based on existing printing approaches of the material, it is imperative to scale up its ink production methods and optimize the electrical properties of the printed films. Here, a sustainable approach is reported for preparing high-conductive screen-printing graphene ink by recycling cellulose solvents. The ink uses Cyrene solvent in circulation and produces highly concentrated and conductive graphene ink to conquer the limitation of graphene inks in massive industrial production brought by the high cost of the cellulose solvents. A systematic study of the sheet resistance variation with the number of cycles has been carried out. The average conductivity of the ink can exceed 3 × 104 S m−1, with only a 2-hours shear exfoliation process, which exhibits about the same conductivity of recent works (using toxic NMP solvent, complex centrifugation, ultrasonication, etc.) but with much more straightforward and cost-effective fabrication process. The formulation of graphene inks allows flexible metal-free far-field tag antenna to be screen-printed and integrated with an off-the-shelf sensory chip to achieve battery-free wireless UHF RFID far-field temperature sensing. The high responsiveness, accuracy, and sensitivity of the RFID sensing tag were observed with instantaneous detection of accurate and reliable wireless data transmission.

We present a compelling evidence for the opening of a bandgap in exfoliated bottom-gated bilayer graphene by fitting the gate-voltage modulated infrared reflectivity spectra in a large range of doping levels with a tight-binding model and the Kubo formula. A close quantitative agreement between the experimental and calculated spectra is achieved, allowing us to determine self-consistently the full set of Slonczewski-Weiss-McClure tight-binding parameters together with the gate-voltage dependent bandgap. The doping dependence of the bandgap shows a good agreement with the existing calculations that take the effects of self-screening into account. We also identify certain mismatches between the tight-binding model and the data, which can be related to electron-electron and electron-phonon interactions.

We demonstrated that chemical vapor deposition of graphene on Cu films strongly enhances their thermal diffusivity and thermal conductivity. Deposition of graphene increases the thermal conductivity of 9 micrometer (25 micrometer) thick Cu films by up to 24% (16%) near room temperature. Interestingly, the observed improvement of thermal properties of graphene coated Cu films is primarily due to changes in Cu morphology during graphene deposition and associated with it temperature treatment rather than graphene's action as an additional heat conducting channel. Enhancement of thermal properties of metal films via graphene coating may lead to applications in electronic circuits and metallurgy.

Uncontrolled mobile anions and proton transport result in many issues, including interfacial anion depletion, irregular multi‐physics fields fluctuations, space charge layer‐induced interfacial Zn dendrites, and hydrogen evolution reaction (HER), which seriously exacerbates the cycling stability of zinc‐ion batteries. Herein, this work constructs an efficient D‐valine anion interface structure to reversely regulate the Zn2+/H+ dynamic chemistry and unlocks the multiple regulation effects of this anionic interface by investigating interfacial proton transport and complex concentration/electric fields distribution of Zn anode through dynamic in‐situ spectroscopy analysis, static energy calculations, and molecular dynamics simulation. We unravel core factors affecting complicated interfacial HER processes and the generation of the space charge layer. This anionic interfacial layer severs proton hopping transport by rupturing the initial water‐water hydrogen bond, which effectively restrains uncontrolled HER processes. Further, the anion‐immobilized interfacial layer accelerates Zn2+ transfer to optimize the interfacial concentration fields. Also, the anionic interface restrains the formation of the anion depletion layer by relieving rapid Zn2+ ions exhaustion and strengthening the uniformity of interfacial electrical field distribution, which suppresses space charges‐induced Zn dendrite growth. Consequently, Zn||Zn symmetric cells deliver an ultra‐long cycle life of 4150 h. Importantly, the multiple regulation effects enable Zn||I2 cells exhibit long‐term stable life.

Marcus-Hush theory of electron transfer is one of the pillars of modern electrochemistry with a large body of supporting experimental evidence presented to date. However, some predictions, such as the electrochemical behavior at microdisk electrodes, remain unverified. Herein, we present a study of electron tunneling across a hexagonal boron nitride barrier between a graphite electrode and redox levels in a liquid solution. This was achieved by the fabrication of microdisk electrodes with a typical diameter of 5 µm. Analysis of voltammetric measurements, using two common redox mediators, yielded several electrochemical parameters, including the electron transfer rate constant, limiting current, and transfer coefficient. They show a significant departure from the Butler-Volmer behavior in a clear manifestation of the Marcus-Hush theory of electron transfer. In addition, our system provides a novel experimental platform, which could be applied to address a number of scientific problems such as identification of reaction mechanisms, surface modification, or long-range electron transfer.

Personal protective equipment (PPE) is critical to protect healthcare workers (HCWs) from highly infectious diseases such as COVID-19. However, hospitals have been at risk of running out of the safe and effective PPE including personal protective clothing needed to treat patients with COVID-19, due to unprecedented global demand. In addition, there are only limited manufacturing facilities of such clothing available worldwide, due to a lack of available knowledge about relevant technologies, ineffective supply chains, and stringent regulatory requirements. Therefore, there remains a clear unmet need for coordinating the actions and efforts from scientists, engineers, manufacturers, suppliers, and regulatory bodies to develop and produce safe and effective protective clothing using the technologies that are locally available around the world. In this review, we discuss currently used PPE, their quality, and the associated regulatory standards. We survey the current state-of-the-art antimicrobial functional finishes on fabrics to protect the wearer against viruses and bacteria and provide an overview of protective medical fabric manufacturing techniques, their supply chains, and the environmental impacts of current single-use synthetic fiber-based protective clothing. Finally, we discuss future research directions, which include increasing efficiency, safety, and availability of personal protective clothing worldwide without conferring environmental problems.

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.

Graphene oxide relative dielectric permittivity, both its real and imaginary parts, have been measured under various humidity conditions at GHz. It is demonstrated that the relative dielectric permittivity increases with increasing humidity due to water uptake. This electrical property of graphene oxide was used to create a battery-free wireless radio-frequency identification (RFID) humidity sensor by coating printed graphene antenna with the graphene oxide layer. The resonance frequency as well as the backscattering phase of such graphene oxide/graphene antenna become sensitive to the surrounding humidity and can be detected by the RFID reader. This enables batteryless wireless monitoring of the local humidity with digital identification attached to any location or item and paves the way for low-cost efficient sensors for Internet of Things applications.

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.