Graphene-based Electronics Research Articles

Electrical Contacts to Graphene by Postgrowth Patterning of Cu Foil for the Low-Cost Scalable Production of Graphene-Based Flexible Electronics.

Numerous studies have focused on graphene owing to its potential as a next-generation electronic material, considering its high conductivity, transparency, superior mechanical stiffness, and flexibility. However, cost-effective mass production of graphene-based electronics based on existing fabrication methods, such as graphene transfer and metal formation, remains a challenge. This study proposes a simple and efficient method for creating electrical contacts with graphene. The method involves patterning a Cu foil after graphene growth, enabling the low-cost scalable production of graphene-based flexible electronics. The fabricated graphene devices exhibited linear current-voltage characteristics, indicating good electrical contact between the postgrowth-patterned Cu electrodes and graphene. The proposed postgrowth patterning method allows for the fabrication of Cu-contacted graphene devices on large areas and various flexible substrates, including ultrathin and stretchable films (<10 μm). The feasibility of the proposed method for electronic devices was demonstrated by implementing gas and flexible force sensors. The proposed approach advances the field of graphene-based electronics and holds potential for practical applications in various electronic devices, paving the way for scalable, cost-effective, and flexible technology solutions.

Twenty Years of Graphene: From Pristine to Chemically Engineered Nano-Sized Flakes.

It is a celebratory moment for graphene! This year marks the 20th anniversary of the discovery of this amazing material by Geim and Novoselov. Curiously, it coincides with the century mark of graphite's layered structure discovery. Since the discovery of graphene with the promise that its outstanding properties would change the world, society often wonders where is graphene? In this context, their discoverers said in 2005, "despite the reigning optimism about graphene-based electronics, "graphenium" microprocessors are unlikely to appear for the next 20 years". Today, possibilities for graphene are endless! It can be used in electronics, photonics, fuel cells, energy storage, artificial intelligence, biomedicine, and even cultural heritage or sports. Additionally, the electronic properties of this material have been modified in fascinating ways. Bilayer graphene sheets have been found to be superconductive when twisted at a "magic angle", leading to a new and exciting field of research known as "moiré quantum materials" or "twistronics". Additionally, small graphene fragments with nanometer sizes undergo a quantum confinement effect of electrons, affording semiconductive materials with applications in optoelectronics. Organic synthesis allows the preparation of molecules with a graphene-like pattern with total control of the shape and size, exhibiting a big catalog of chiroptical and optoelectronic properties. This Perspective shows some of the fascinating milestones raised in the field of graphene-like materials from a chemical point of view, including functionalization strategies employed to chemically modify the topology and the properties of pristine graphene as well as the rising molecular graphenes.

Direct Induction of Porous Graphene from Mechanically Strong and Waterproof Biopaper for On-Chip Multifunctional Flexible Electronics.

Graphene with a 3D porous structure is directly laser-induced on lignocellulosic biopaper under ambient conditions and is further explored for multifunctional biomass-based flexible electronics. The mechanically strong, flexible, and waterproof biopaper is fabricated by surface-functionalizing cellulose with lignin-based epoxy acrylate (LBEA). This composite biopaper shows as high as a threefold increase in tensile strength and excellent waterproofing compared with pure cellulose one. Direct laser writing (DLW) rapidly induces porous graphene from the biopaper in a single step. The porous graphene shows an interconnected carbon network, well-defined graphene domains, and high electrical conductivity (e.g., ≈3Ω per square), which can be tuned by lignin precursors and loadings as well as lasing conditions. The biopaper in situ embedded with porous graphene is facilely fabricated into flexible electronics for on-chip and paper-based applications. The biopaper-based electronic devices, including the all-solid-state planer supercapacitor, electrochemical and strain biosensors, and Joule heater, show great performances. This study demonstrates the facile, versatile, and low-cost fabrication of multifunctional graphene-based electronics from lignocellulose-based biopaper.

Design and Modelling of Graphene-Based Flexible 5G Antenna for Next-Generation Wearable Head Imaging Systems.

Arguably, 5G and next-generation technology with its key features (specifically, supporting high data rates and high mobility platforms) make it valuable for coping with the emerging needs of medical healthcare. A 5G-enabled portable device receives the sensitive detection signals from the head imaging system and transmits them over the 5G network for real-time monitoring, analysis, and storage purposes. In terms of material, graphene-based flexible electronics have become very popular for wearable and healthcare devices due to their exceptional mechanical strength, thermal stability, high electrical conductivity, and biocompatibility. A graphene-based flexible antenna for data communication from wearable head imaging devices over a 5G network was designed and modelled. The antenna operated at the 34.5 GHz range and was designed using an 18 µm thin graphene film for the conductive radiative patch and ground with electric conductivity of 3.5 × 105 S/m. The radiative patch was designed in a fractal fashion to provide sufficient antenna flexibility for wearable uses. The patch was designed over a 1.5 mm thick flexible polyamide substrate that made the design suitable for wearable applications. This paper presented the 3D modelling and analysis of the 5G flexible antenna for communication in a digital care-home model. The analyses were carried out based on the antenna's reflection coefficient, gain, radiation pattern, and power balance. The time-domain signal analysis was carried out between the two antennas to mimic real-time communication in wearable devices.

The development of graphene and its use in flexible electronics

In recent years, graphene has been deeply studied by scholars, and has attracted high attention in the field of flexible electronics. In order to better understand the properties and application of graphene, this article systematically summarized and analyzed the applications in the field of flexible electronics from multiple angles to better display its characteristics. It mainly introduces the development, preparation method, classification, and application of graphene. Since its discovery in 2004, it has become a special and useful nanomaterial. Graphene has been widely used in the field of flexible electronics in the past few years due to its excellent mechanical properties, electrical conductivity, and transparency. Moreover, we specifically show the development trends and application characteristics of graphene in flexible solar cells, field-effect transistors, nanogenerators. In addition, the problems facing graphene are also mentioned. Finally, the development prospects of graphene-based flexible electronics are presented and suggested for further studies.

Fabrication and Characterization of Pre-Defined Few-Layer Graphene

Graphene is one of the most well-known two-dimensional (2D) materials that has attracted significant interest due to its unique electrical and optical properties. Being a van der Waals substrate, the fabrication of few-layered graphene by stacking a pre-defined number of graphene monolayers is essential in the field. The thickness can influence the interface interaction and therefore tune the surface electronic properties. In the study, we demonstrate a bottom-up synthesis of pre-defined few-layer graphene on SiC substrate using the thermal decomposition method and carefully characterize its thickness by the non-damageable synchrotron-radiation-based X-ray photo-electron spectroscopy (SR-XPS). By varying the photon energy, we acquire different probe depths, resulting in the different intensity ratios of graphene to SiC substrate, which is then used to estimate the thickness of the few-layer graphene. Our calculation demonstrates that the thermal decomposition method in the study can repeatedly fabricate graphene samples with expected thickness. We further compare the obtained few-layer graphene to the single-layer graphene and HOPG using the scanning tunneling microscopy (STM) technique. Our work provides accurate methods for fabricating and characterizing pre-defined few-layer graphene, providing essential knowledge in future graphene-based thin film electronics.

Epitaxial growth of ultrathin two-dimensional pentacene film with standing-up molecular geometry on nano-size-curved graphene surface

Molecule packing behavior at organic and graphene interface is essential for graphene-based organic electronics since charge carriers are transported within the very few organic layers nearest to graphene substrate. Although organic molecules especially the ones with planar aromatic rings usually adopt recumbent geometry on graphene substrate owning to the maximized π-π interaction, the alignment of organic molecules may be influenced by modifying the interfacial nature between organic molecules and graphene. Here, epitaxy growth of two-dimensional ultra-thin pentacene film with standing-up molecular geometry was observed for the first time on graphene with periodic nano-sized buckling structure. The curvature and strain of graphene was found collectively responsible for the standing-up geometry of pentacene and its oriented growth on graphene surface. This study provides a feasible way for controlling molecular epitaxy on 2D materials interfaces toward functional heterostructures.

Highly stable self-passivated MoO3-doped graphene film with nonvolatile MoO layer

The realization of high-performance graphene-based electronics, including transparent electrodes, flexible devices, and energy storage, is often hindered by the lack of adequate doping, which provides a stable and low sheet resistance. In this study, we demonstrate a highly stable MoO 3 -doped graphene obtained simply through a self-passivation. Graphene deposited with a 5-nm-thick MoO 3 exhibited a significant decrease in sheet resistance upon annealing at 400 °C under a hydrogen atmosphere. Surface and structural analyses confirmed that MoO 3 was converted to MoO x by thermal annealing, which consisted of mainly crystalline MoO 3 and Mo 4 O 11 with coexisting MoO 2 . A field-effect transistor fabricated using the MoO x -doped graphene exhibited a p-type characteristic similar to that of the MoO 3 -doped graphene. However, unlike the MoO 3 -doped graphene severely degraded by environment, the MoO x -doped graphene exhibited stable electrical properties after air exposure and chemical immersion owing to the chemically inert Mo 4 O 11 and MoO 2 acting as passivation layers while maintaining the p-type doping by MoO 3 . Thus, we expect that the highly stable MoO x -doped graphene obtained via the simple method will facilitate the fabrication and contribute to the performance reliability of various graphene-based electronic devices. • Highly stable MoO 3 -doped graphene through self-passivation by oxygen deficient MoO x • Simple way of thermal annealing for the synthesis of oxygen deficient MoO x -doped graphene • MoO x -doped graphene with p-type semiconducting characteristics • Excellent stability and chemical durability of MoO x -doped graphene

Wearable and Flexible Multifunctional Sensor Based on Laser-Induced Graphene for the Sports Monitoring System.

The conversion of diverse polymeric substrates into laser-induced graphene (LIG) has recently emerged as a single-step method for the fabrication of patterned graphene-based wearable electronics with a wide range of applications in sensing, actuation, and energy storage. Laser-induced pyrolysis technology has many advantages over traditional graphene design: eco-friendly, designable patterning, roll-to-roll production, and controllable morphology. In this work, we designed wearable and flexible graphene-based strain and pressure sensors by laminating LIG from a commercial polyimide (PI) film. The as-prepared LIG was transferred onto a thin polydimethylsiloxane (PDMS) sheet, interwoven inside an elastic cotton sports fabric with the fabric glue as a wearable sensor. The single LIG/PDMS layer acts as a strain sensor, and a two-layer perpendicular stacking of LIG/PDMS (x and y laser-directed films) is designed for pressure sensing. This newly designed graphene textile (IGT) sensor performs four functions in volleyball sportswear, including volleyball reception detection, finger touch foul detection during blocking the ball from an opponent player, spike force measurements, and player position monitoring. An inexpensive sensor assists athletes in training and helps the coach formulate competition strategies.

Assessment of graphene-based polymers for sustainable wastewater treatment: Development of a soft computing approach

Since graphene possesses distinct electrical and material properties that could improve material performance, there is currently a growing demand for graphene-based electronics and applications. Numerous potential applications for graphene include lightweight and high-strength polymeric composite materials. Due to its structural qualities, which include low thickness and compact 2D dimensions, it has also been recognized as a promising nanomaterial for water-barrier applications. For barrier polymer applications, it is usually applied using two main strategies. The first is the application of graphene, graphene oxide (GO), and reduced graphene oxide (rGO) to polymeric substrates through transfer or coating. In the second method, fully exfoliated GO or rGO is integrated into the material. This study provides an overview of the most recent findings from research on the use of graphene in the context of water-barrier applications. The advantages and current limits of graphene-based composites are compared with those of other nanomaterials utilized for barrier purposes in order to emphasize difficult challenges for future study and prospective applications.

Graphene oxide and manganese thiophosphate modifications induced by lasers, ion beams and intercalation process

At present graphene is the most exciting star in the materials science but graphene oxide, GO, that is its low-cost precursor attracts researchers from various fields because it is very easily produced at low cost. GO is an electrical insulator than can be transformed into graphene through the ‘reduction’ process. The oxygen functional groups it contains can be removed by various ways, also using lasers, ion beams and the intercalation process. The intensive research on graphene has allowed the rediscovery of various graphite-like layered materials with composition other than carbon, but properties are not yet fully known and with interesting possible applications. Among them, manganese thiophosphate, MnPS3, is a layered inorganic host matrix for making, through the intercalation-exfoliation-restacking technique, multi-functional hybrid thin films that can find application as optical switches, transparent coatings, in catalysis and photocatalysis, as lubricants, to create new multilayer structures, as dielectric substrates for graphene-based electronics and so on. If exfoliated at few layers, MnPS3 allows to realize good ultraviolet photodetectors with a gate tunable photoresponsivity and high photo gain. Recent progress in these graphene-like materials will be presented and discussed together with measurements based on the use of lasers, ion beams and intercalation emphasizing their potential applications.

Achievements and Challenges of Graphene Chemical Vapor Deposition Growth (Adv. Funct. Mater. 42/2022)

Chemical Vapor Deposition In article number 2203191, Feng Ding and co-authors report the vapor-liquid-solid growth of graphene nanospears and graphene nanoribbons on Cu surface. The vapor-liquid-solid growth of graphene nanostructures is enabled by liquid Si-Cu catalysts and opens a platform for excellent graphene-based electronics.

Interlayer shear coupling in bilayer graphene

The interfacial shear coupling (ISC) governs the relative in-plane deformations of layered two-dimensional (2D) van der Waals (vdW) materials, which is significant for both the fundamental theory of solid mechanics and the stability design of 2D devices. Here we study the representative ISC of 2D vdW stacks using bilayer graphene (BLG) and isotope-labeled Raman spectroscopy. The results show that under uniaxial tensile strain, the ISC between two graphene layers evolves sequentially with bonding, sliding and debonding process, and the corresponding interfacial shear strength is inversely proportional to the sample size. Molecular dynamics (MD) simulations demonstrate the origin of this inverse proportionality as stronger interlayer vdW interaction induced by the edge lattices and atoms of BLG that have more degrees of freedom. These results not only provide new fundamental insights into the multiscale interpretation of macroscopic interfacial shear properties of 2D vdW stacks but also have great potential in guiding the design of graphene-based composite materials and flexible 2D electronics.

3D printing stretchable core-shell laser scribed graphene conductive network for self-powered wearable devices

Graphene-based flexible electronics, particularly those with self-powered ability and stretchability, are greatly promising candidates in the applications of portable and wearable devices. However, complicated deformation of human body and harsh environment inevitably leads to the degradation of conductivity of wearable electronics due to the intrinsic brittleness and crack sensitivity of graphene. Herein, a metamaterial-inspired stretchable and stable conductive network fabricated by 3D printing polyether-ether-ketone (PEEK) and double-side laser scribing graphene (LSG) techniques is demonstrated, which is called LSGCN. The double-side LSG covers the outer surfaces of printed PEEK filaments and forms a special core-shell structure, and its conductivity is 2.72 times of traditional flat graphene. Moreover, the parametric design of LSGCN can increase the stretchability of the structure from 20% to 118%, while ensuring that the change rate of resistance is limited to 1.06 within the 60% strain range. Based on the triboelectric effect, we also demonstrate LSGCN-based self-powered devices, including wearable smart belts and human-computer interaction gloves. Particularly, the LSGCN glove integrates 21 interactive channels, and it can work as the input equipment to control the simulated calculator, display the slides and even play the 3D games. This hybrid-fabricating method of LSGCN provides a novel strategy to fabricate stretch-stable conductive structures for applications in bio-energy harvesting and self-powered sensing devices, which opens up a new avenue for the future Internet of Things.

Surface charge transfer doping of graphene using a strong molecular dopant CN6-CP

Surface charge transfer doping of graphene plays an important role in graphene-based electronics due to its simplicity, high doping efficiency, and easy-controllability. Here, we demonstrate the effective surface charge transfer hole doping of graphene by using a strong p-type molecular dopant hexacyano-trimethylene-cyclopropane (CN6-CP). The CN6-CP exhibits a very high intrinsic work function of 6.37 eV, which facilitates remarkable electron transfer from graphene to CN6-CP as revealed by in situ photoelectron spectroscopy investigations. Consequently, hole accumulation appears in the graphene layer at the direct contact with CN6-CP. As evidenced by Hall effect measurements, the areal hole density of graphene significantly increased from 8.3 × 1012 cm−2 to 2.21 × 1013 cm−2 upon 6 nm CN6-CP evaporation. The CN6-CP acceptor with strong p-doping effect has great implications for both graphene-based and organic electronics.

Assessing the Figures of Merit of Graphene-Based Radio Frequency Electronics: A Review of GFET in RF Technology

Graphene has been extensively investigated in the context of electronic components due to its attractive properties, such as high carrier mobility and saturation velocity. In the past decade, the graphene field-effect transistor (GFET) has been considered one of the potential devices to be used in future radio frequency (RF) applications and can help usher in the Internet of Things and the 5G communication network. This review presents recent developments of GFETs in RF applications with a focus on components such as amplifiers, frequency multipliers, phase shifters, mixers, and oscillators. Initially, the figures of merit (FoMs) for the GFET are briefly described to understand how they affect these RF components. Subsequently, the FoMs of GFET-based RF components are compared with other non-GFET-based RF components. It is found that, due to its zero-band gap and ambipolar characteristics, GFETs are more suitable for use in frequency multiplier and phase shifter applications, outperforming non-GFET-based RF components. Finally, future research on GFETs themselves as well as GFET-based RF components is recommended. This review provides valuable insights into such components that could give rise to innovative applications in industry.

A universal current-mode current conveyor filter based on GFET inverter

ABSTRACT CMOS technology faces significant challenges at the nanoscale. Graphene-based electronics has emerged as a feasible promising to continue obeying Moore’s law. In this paper, a positive-type second-generation current conveyor (CCII+) builds with Graphene FET (GFET) inverters is proposed. A universal current-mode active filter is presented which can realise all standard filter functions employing CCII+ as an active element. The performance of the GFET filter was simulated and analysed with 0.18um GFET technology using ADS tools. The simulation results demonstrate that the proposed GFET filter consumes 1.2 mW at 10 MHz with ±0.5 V supply voltage. Furthermore, the centre frequency of the proposed filter can be tuned electronically. As an application, a quadrature oscillator example is given. The performance of first active filter based on GFET Current conveyor is compared with CMOS technology.

A Molecular Dynamics Simulation Study: The Inkjet Printing of Graphene Inks on Polyimide Substrates

Inkjet printing-based 2D materials for flexible electronics have aroused much interest due to their highly low-cost customization and manufacturing resolution. However, there is a lack of investigation and essential understanding of the surface adhesion affected by the printing parameters at the atomic scale. Herein, we conducted a systematic molecular dynamics simulation investigating the inkjet printing of graphitic inks on polyimide substrates under various conditions. Simulations under different temperatures, inkjet velocities, and mechanical loadings such as pressure and deformation are performed. The results show that the best adhesion is achieved in the plasma-modified polyimide/graphene-oxide (mPI/GO) interfacial system (the interaction energy (Ein) between mPI and GO is ca. 1.2 times than with graphene). The adhesion strength decreases with increasing temperature, and higher inkjet velocities lead to both larger impact force as well as interfacial fluctuation, while the latter may result in greater interfacial instability. When loaded with pressure, the adhesion strength reaches a threshold without further improvement as continuing compacting of polymer slabs can hardly be achieved. The detachment of the interfaces was also explored and mPI/GO shows better resistance against delamination. Hopefully, our simulation study paves the way for future inkjet printing-based manufacturing of graphene-based flexible electronics.

Numerical Evaluation of the Effect of Geometric Tolerances on the High-Frequency Performance of Graphene Field-Effect Transistors.

The interest in graphene-based electronics is due to graphene’s great carrier mobility, atomic thickness, resistance to radiation, and tolerance to extreme temperatures. These characteristics enable the development of extremely miniaturized high-performing electronic devices for next-generation radiofrequency (RF) communication systems. The main building block of graphene-based electronics is the graphene-field effect transistor (GFET). An important issue hindering the diffusion of GFET-based circuits on a commercial level is the repeatability of the fabrication process, which affects the uncertainty of both the device geometry and the graphene quality. Concerning the GFET geometrical parameters, it is well known that the channel length is the main factor that determines the high-frequency limitations of a field-effect transistor, and is therefore the parameter that should be better controlled during the fabrication. Nevertheless, other parameters are affected by a fabrication-related tolerance; to understand to which extent an increase of the accuracy of the GFET layout patterning process steps can improve the performance uniformity, their impact on the GFET performance variability should be considered and compared to that of the channel length. In this work, we assess the impact of the fabrication-related tolerances of GFET-base amplifier geometrical parameters on the RF performance, in terms of the amplifier transit frequency and maximum oscillation frequency, by using a design-of-experiments approach.

Molten Ga-Pd alloy catalyzed interfacial growth of graphene on dielectric substrates

Direct growth of graphene on insulating substrate is highly desired for practical applications in two-dimensional electronics and optoelectronics. However, the controllable synthesis of large scale graphene films on dielectrics is still limited in thickness and crystallinity by the absence of catalyst. Here we develop a transfer-free method to synthesize continuous graphene films on various insulating substrates by using molten Ga-Pd alloy and silicon carbide (SiC) as catalyst and carbon source. The catalytic Ga-Pd alloy induces the decomposition of SiC bonds and promotes the formation of C-C sp2 at relatively low temperature around 1000 °C. The suitable carbon solubility of Ga-Pd alloy could also promote the fabrication of few-layer graphene films on the interface between alloy and SiC substrate as well as the upper surface of alloy. Furthermore, this strategy could be extended to the interfacial growth of graphene on other dielectrics by simply placing the substrate face down to the surface of molten alloy. The progress of this work may help to understand the mechanism of molten Ga-Pd alloy catalyzed interfacial growth of transfer-free graphene and benefit the application of graphene-based electronics and photonics in the future.