Few-layer Graphene Research Articles

A Qualitative Study of Defects with Enhanced Transport Properties of Graphene Exfoliated from Gum Arabic by Rapid Sonication Method

Graphene‐like materials are utilized to make electrical devices, thermal sensors, biosensors, and energy storage batteries. Herein, an efficient and cost‐effective approach is demonstrated by modulating the sonication time duration for producing a few layers of graphene using the emulsification qualities of low‐cost and environmentally friendly gum Arabic. By implementing the modified approach, the production time for graphene synthesis is significantly reduced to a short duration as compared to preliminarily reported methodologies. XRD, field‐emission scanning electron microscopy, and Raman spectroscopic results of graphene samples are presented in order to study the nature of defects. The flakes are thin enough (20 nm) to seem semitransparent under the FESEM. From the combination of both I2D/IG and FWHM (2D), a predominant formation of 3–7 graphene layers is observed. It is identified that mainly foreign adatom defects are present, with a density of ≈1010 cm−2, which results in an increasing Hall carrier concentration (≈2 × 1023 m−3) and mobility (≈27 800 cm2 Vs−1). Furthermore, graphene has a higher electrical conductivity of ≈550 S cm−1, which is far better than previously reported. This research opens the way for the mass manufacturing of simple, green, and cost‐effective graphene with better quality and physical attributes.

Chemically doped-graphene FET photodetector enhancement via controlled carrier modulation with an iron(III)-chloride

Graphene is an excellent material among the family of 2D materials due to its electronic and optoelectronic properties. The intentional modification of its electronic structure via doping processes holds immense significance regarding tailoring its properties for specific applications. We comprehensively investigated p-type doping in few-layer graphene field-effect transistors (FETs) on SiO2/Si substrates by utilizing Iron(III)-chloride (FeCl3) dopant solutions with varying concentrations that range from 5 mM to 50 mM in this study. The successful doping was confirmed via a meticulous Raman spectroscopy analysis, which revealed notable shifts in the peak positions and peak broadening post-doping. Electrical measurements, which include transfer curves at a fixed biasing voltage, provided further confirmation, which demonstrates a distinctive shift in the Dirac point from −1 V to +25 V when the FeCl3 concentrations were changed from 5 mM to 50 mM. The impact of doping on the photoresponse of the graphene device was systematically explored. The device exhibited a significant increase in responsivity and external quantum efficiency following the p-type doping, which indicates an enhanced performance in photodetection. This research validates the successful p-type doping of graphene and underscores its implications regarding optimizing the electrical and optoelectronic properties of graphene-based devices, which confirms its potential for advanced applications for electronic and optoelectronic technologies.

The Influence of a Commercial Few-Layer Graphene on the Photodegradation Resistance of a Waste Polyolefins Stream and Prime Polyolefin Blends

This work investigated the photostabilizing role of a commercially available few-layer graphene (FLG) in mixed polyolefins waste stream (MPWS), ensuring extended lifespan for outdoor applications. The investigation was conducted by analyzing carbonyl content increase, surface appearance, and the retention of mechanical properties of UV-exposed MPWS/FLG composites. Despite the likely predegraded condition of MPWS, approximately 60%, 70%, 80%, and 90% of the original ductility was retained in composites containing 1, 4, 7, and 10 wt.% FLG, respectively. Conversely, just 20% of the original ductility was retained in unfilled MPWS. Additionally, less crack density and lower carbonyl concentrations of the composites also highlighted the photoprotection effect of FLG. For prime polyolefin blends, only 0.5 wt.% or 1 wt.% FLG was sufficient to preserve the original surface finishing and protect the mechanical properties from photodegradation. Hence, it was observed that MPWS requires more FLG than prime polyolefin blends to get to comparable property retention. This could be attributed to the poor dispersion of FLG in MPWS and inevitable uncertainties such as the presence of impurities, pre-degradation, and polydispersity associated with MPWS. This study outlines a potential approach to revalorize MPWS that possess a minimal intrinsic value and would otherwise be destined for landfill disposal.

Few-layer graphene production through graphite exfoliation in pressurized CO2 assisted by natural surfactant

Graphene research has captivated researchers worldwide, propelling innovation across diverse industries. Through the liquid-phase exfoliation methodology of graphite powder, we have demonstrated a rapid route for obtaining few-layer and multi-layer graphene using a natural surfactant, cardanol. Aqueous phase exfoliation of graphite in the presence of cardanol as a surfactant was conducted to obtain pre-exfoliated graphite suspensions. The influence of different ultrasonication times, 10, 20, and 30 min, and contact times with the surfactant, 1 and 60 min, on the stability and concentration of dispersed exfoliated graphite was evaluated. Results indicate that ultrasonication for 20 min resulted in improved stability and reduced graphene flake sizes, making it suitable for scalable graphene production. Subsequently, the most stable dispersions of exfoliated graphite were subjected to CO2-pressurized treatment. Promising results were obtained when employing cardanol at its critical micelle concentration. The graphene exhibited good structural quality, low defect density, and small stacking, with an average size of 15 nm, where 40 % of the stacked graphene was smaller than 5 nm. The findings provide valuable recommendations for the scalable production of graphene with multilayers and a few layers (FLG/MLG), using cardanol, a friendly surfactant, and a novel method of exfoliation utilizing supercritical CO2. This technology represents an innovative approach, with potential applications in supercapacitors, solar cells, biosensors, polymer composites, and advanced materials.

Ultrasensitive Near-Infrared Polarization Photodetectors with Violet Phosphorus/InSe van der Waals Heterostructures.

Near-infrared (NIR) polarization photodetectors with two-dimensional (2D) semiconductors and their van der Waals (vdW) heterostructures have presented great impact for the development of a wide range of technologies, such as in the optoelectronics and communication fields. Nevertheless, the lack of a photogenerated charge carrier at the device's interface leads to a poor charge carrier collection efficiency and a low linear dichroism ratio, hindering the achievement of high-performance optoelectronic devices with multifunctionalities. Herein, we present a type-II violet phosphorus (VP)/InSe vdW heterostructure that is predicted via density functional theory calculation and confirmed by Kelvin probe force microscopy. Benefiting from the type-II band alignment, the VP/InSe vdW heterostructure-based photodetector achieves excellent photodetection performance such as a responsivity (R) of 182.8 A/W, a detectivity (D*) of 7.86 × 1012 Jones, and an external quantum efficiency (EQE) of 11,939% under a 1064 nm photon excitation. Furthermore, the photodetection performance can be enhanced by manipulating the device geometry by inserting a few layers of graphene between the VP and InSe (VP/Gr/InSe). Remarkably, the VP/Gr/InSe vdW heterostructure shows a competitive polarization sensitivity of 2.59 at 1064 nm and can be integrated as an image sensor. This work demonstrates that VP/InSe and VP/Gr/InSe vdW heterostructures will be effective for promising integrated NIR optoelectronics.

Sorption of Radium-226 on Few-Layer Graphene Synthesized under Conditions of Self-Propagating High-Temperature Synthesis

Sorption of Radium-226 on Few-Layer Graphene Synthesized under Conditions of Self-Propagating High-Temperature Synthesis

Nickel composite film for terahertz wave broadband absorption

Due to the poor response of natural materials in the terahertz (THz) frequency band, ultra-broadband absorption of THz waves is a challenge. In this work, a nickel-composite film (NCF) is experimentally demonstrated for the ultra-broadband absorption of THz waves. The NCF consists of nickel foam, polydimethylsiloxane (PDMS), and few-layer graphene. The nickel foam has a three-dimensional structure that can be filled by the PDMS and few-layer graphene. By controlling the mass fraction of few-layer graphene in the PDMS, we can reduce the surface reflection of THz waves and achieve broadband absorption. For a 0.5-mm-thick NCF, when the mass fraction of doped few-layer graphene is 2%, the qualified bandwidth (with an absorption rate more than 90%) reaches 3.2 THz. More importantly, for different thicknesses of nickel foams, the absorption bandwidth can be enhanced by changing the mass fraction of few-layer graphene.

Plasma-Treated Cobalt-Doped Nanoporous Graphene for Advanced Electrochemical Applications

Metal–carbon nanocomposites are identified as key contenders for enhancing water splitting through the oxygen evolution reaction and boosting supercapacitor energy storage capacitances. This study utilizes plasma treatment to transform natural graphite into nanoporous few-layer graphene, followed by additional milling and plasma steps to synthesize a cobalt–graphene nanocomposite. Comprehensive structural characterization was conducted using scanning and transmission electron microscopy, X-ray diffraction, Raman spectroscopy, gas sorption analysis and X-ray photoelectron spectroscopy. Electrochemical evaluations further assessed the materials’ oxygen evolution reaction and supercapacitor performance. Although the specific surface area of the nanoporous carbon decreases from 780 to 480 m2/g in the transition to the resulting nanocomposite, it maintains its nanoporous structure and delivers a competitive electrochemical performance, as evidenced by an overpotential of 290 mV and a Tafel slope of 110 mV/dec. This demonstrates the efficacy of plasma treatment in the surface functionalization of carbon-based materials, highlighting its potential for large-scale chemical-free application due to its environmental friendliness and scalability, paving the way toward future applications.

Robust wear performance of graphene-reinforced high entropy alloy composites

The expected excellent tribological performance of high-entropy alloys (HEAs) is rarely achieved due to the absence of self-lubricating ability on the worn surface. In particular, the situation is more challenging in HEAs with face-centered cubic structure because of the inferior yield strength when used in dry sliding conditions. Unlike conventional soft-solid lubricants, which deteriorate the mechanical properties of HEA matrix, in this study we demonstrate in a protocol model alloy that the proper incorporation of few-layer graphene as reinforcement in CoCrFeNiMn can lead to both surface strengthening and lubrication. This is achieved by a partially chemical interface reaction between graphene and HEA via a tunable fabrication process, resulting in a reduction of wear rate and friction coefficient of 86.03% and 23.87%, respectively. As a result of the interfacial in-situ carbide strengthening together with the self-lubrication of graphene, this tailored composite structure also exhibits superior tribological properties over most HEA-based self-lubrication composites. Besides, the subsurface structure evolution and deformation mechanisms that influence the wear resistance are systematically clarified through microscopic exploration and atomistic simulation. The present study presents an effective strategy for the development of innovative HEA composites suitable for safety-critical applications, which overcomes the inherent compromise and achieves exceptional tribological performance, i.e., self-lubricating and anti-wear.

Graphene nanomechanical vibrations measured with a phase-coherent software-defined radio

Software-defined radios (SDRs) are radio frequency transceivers designed to facilitate digital signal processing through the use of vast libraries of open-source software. Here, we assemble a simple data acquisition system whose architecture, based on SDR, allows us to develop a comprehensive suite of tools to study the vibrations of a few-layer graphene nanomechanical resonator. Namely, we measure the cross-spectrum of vibrations in the frequency domain, we measure their energy decay rate in the time domain, we perform vector measurements of their in-phase and quadrature components, and we control their phase using a time-dependent strain field –all with a single measurement platform. Our approach allows us to tailor our experiments at will and gives us control over every stage of data processing. Overall, our versatile system enables measuring a wide range of nanomechanical properties of graphene by customizing the signal acquisition and replacing some analog electrical circuits, such as filters, mixers, and demodulators, by blocks of code.

Regulating the aspect ratio of bulk few-layer graphene to improve the field emission performance

Owing to its excellent electrical conductivity and local electric field enhancement capability from abundant electron tunneling edges, graphene is a promising material for field emission. However, graphene thin-film emitters mostly emit in planar structures, and due to the flexibility of the thin film, it is commonly challenging to achieve vertical structure emission with large aspect ratios. Therefore, the emission performance of current graphene field emitters is difficult to meet the requirements of high current applications. In the present investigation, bulk few-layer graphene cathodes are formed by cold pressing to achieve upright structural field emission, and the emission performance is enhanced by appropriately adjusting the aspect ratio. The obtained bulk few-layer graphene emitters exhibit a higher conductivity of 2498 S/cm and tensile strength of 6.02 MPa. The turn-on electric field (at 1 mA/cm2) and threshold electric field (at 10 mA/cm2) in order are determined to be 1.78 V/μm and 2.66 V/μm, with a maximum current density of 986 mA/cm2 (at 6.65 V/μm) and a maximum field enhancement factor of 14,891. Excellent emission stability is achieved over a continuous period of 110 h at 5 mA @ 526 mA/cm2. With the increase of emission current, the bulk few-layer graphene with large aspect ratios exhibits better emission stability. This work provides valuable insights into the application of graphene-based field emitters at high currents.

Co, N, and P co-doped few-layer graphene derived from cobalt phthalocyanine-based covalent organic polymers as bifunctional electrocatalysts for overall water splitting

Water electrolysis is considered to be one of the most promising approaches for developing sustainable energy technologies, however, the high cost and lack of stability of traditional precious metal electrocatalysts have hindered the development of the field of water electrolysis. Covalent organic polymers have greater potential for the preparation of low-cost electrocatalysts with high efficiency and long-term stability due to their low cost, controllable chemical composition, and rich pore structure. Cobalt phthalocyanine-based covalent organic polymers were loaded onto few-layer graphene by a hydrothermal method and then pyrolyzed to produce Co, N, and P co-doped few-layer graphene (Co–N/P-FG-700). Co–N/P-FG-700 demonstrates superior performance for oxygen evolution reaction (OER) due to the synergistic effect of abundant active sites and conductive carriers, with an overpotential of 358 mV at a current density of 10 mA cm−2 and 90% of the current density after 50,000 s of stability testing. Co–N/P-FG-700 exhibits excellent results for hydrogen evolution reaction (HER) with an overpotential of −275 mV at a current density of −10 mA cm−2 and a current density retention of 93% after a 50,000 s stability test. This study provides a rational pathway for the design of low-cost, high-performance, stable bifunctional OER/HER electrocatalysts.

Interface and Morphology Engineered Amorphous Si for Ultrafast Electrochemical Lithium Storage.

Ultrafast high-capacity lithium-ion batteries are extremely desirable for portable electronic devices, where Si is the most promising alternative to the conventional graphite anode due to its very high theoretical capacity. However, the low electronic conductivity and poor Li-diffusivity limit its rate capability. Moreover, high volume expansion/contraction upon Li-intake/uptake causes severe pulverization of the electrode, leading to drastic capacity fading. Here, interface and morphology-engineered amorphous Si matrix is being reported utilizing a few-layer vertical graphene (VG) buffer layer to retain high capacity at both slow and fast (dis)charging rates. The flexible mechanical support of VG due to the van-der-Waalsinteraction between the graphene layers, the weak adhesion between Si and graphene, and the highly porous geometry mitigated stress, while the three-dimensional mass loading enhanced specific capacity. Additionally, the high electronic conductivity of VG boosted rate-capability, resulting in a reversible gravimetric capacity of ≈1270mAhg-1 (areal capacity of ≈37µAhcm-2) even after 100 cycles at an ultrafast cycling rate of 20C, which provides a fascinating way for conductivity and stress management to obtain high-performance storage devices.

Diffusive and ballistic transport in thin InSb nanowire devices using a few-layer-graphene-AlO x gate

Quantum devices based on InSb nanowires (NWs) are a prime candidate system for realizing and exploring topologically-protected quantum states and for electrically-controlled spin-based qubits. The influence of disorder on achieving reliable quantum transport regimes has been studied theoretically, highlighting the importance of optimizing both growth and nanofabrication. In this work, we consider both aspects. We developed InSb NW with thin diameters, as well as a novel gating approach, involving few-layer graphene and atomic layer deposition-grown AlO x . Low-temperature electronic transport measurements of these devices reveal conductance plateaus and Fabry–Pérot interference, evidencing phase-coherent transport in the regime of few quantum modes. The approaches developed in this work could help mitigate the role of material and fabrication-induced disorder in semiconductor-based quantum devices.

Ultra-high-performance graphene-based bulk materials strengthened by Y-type connection structure

The strategic design and assembly of bulk graphene materials represent a pivotal advancement for harnessing the inherent properties of graphene in practical applications. However, fabricating high-strength graphene-based bulk materials from graphene powders presents a significant challenge, primarily due to interlayer slippage between the graphene layers. Here, a unique Y-type connection structure was found in few-layer graphene synthesized by self-propagating high-temperature synthesis (SHS) and subsequently retained in graphene-based bulk materials prepared by spark plasma sintering (SPS) process. The Y-type connection structure and defect-induced linkages serve to cross-link the graphene-based bulk materials. Consequently, the bulk material exhibited an ultra-high compressive strength, reaching 2.14 GPa, supported by Molecular dynamics (MD) simulations which demonstrated that the Y-type connection structure increases the shear modulus and the load transfer rate. The Y-type connection structure plays a vital role in reinforcing the strength of graphene-based bulk materials, offering valuable insights for the microstructural design and property augmentation of other graphene-derived materials. Besides it’s ultra-high compressive strength, the graphene-based bulk material also performs a low thermal expansion coefficient (0.5 × 10−6 K−1), high electrical conductivity (1.47 × 105 S·m−1) and exceptional EMI shielding capability.

In Situ Polymer-Solution-Processed Graphene-PDMS Nanocomposites for Application in Intracranial Pressure Sensors.

Polydimethylsiloxane (PDMS) has emerged as a promising candidate for the dielectric layer in implantable sensors due to its exceptional biocompatibility, stability, and flexibility. This study introduces an innovative approach to produce graphene-reinforced PDMS (Gr-PDMS), where graphite powders are exfoliated into mono- and few-layer graphene sheets within the polymer solution, concurrently forming cross-linkages with PDMS. This method yields a uniformly distributed graphene within the polymer matrix with improved interfaces between graphene and PDMS, significantly reducing the percolation threshold of graphene dispersed in PDMS from 10% to 5%. As-synthesized Gr-PDMS exhibits improved mechanical and electrical properties, tested for potential use in capacitive pressure sensors. The results demonstrate an impressive pressure sensitivity up to 0.0273 kpa-1, 45 times higher than that of pristine PDMS and 2.5 times higher than the reported literature value. The Gr-PDMS showcases excellent pressure sensing ability and stability, fulfilling the requirements for implantable intracranial pressure (ICP) sensors.

Centimeter-sized diamond composites with high electrical conductivity and hardness

Achieving high-performance materials with superior mechanical properties and electrical conductivity, especially in large-sized bulk forms, has always been the goal. However, it remains a grand challenge due to the inherent trade-off between these properties. Herein, by employing nanodiamonds as precursors, centimeter-sized diamond/graphene composites were synthesized under moderate pressure and temperature conditions (12 GPa and 1,300 to 1,500 °C), and the composites consisted of ultrafine diamond grains and few-layer graphene domains interconnected through covalently bonded interfaces. The composites exhibit a remarkable electrical conductivity of 2.0 × 104 S m-1 at room temperature, a Vickers hardness of up to ~55.8 GPa, and a toughness of 10.8 to 19.8 MPa m1/2. Theoretical calculations indicate that the transformation energy barrier for the graphitization of diamond surface is lower than that for diamond growth directly from conventional sp2 carbon materials, allowing the synthesis of such diamond composites under mild conditions. The above results pave the way for realizing large-sized diamond-based materials with ultrahigh electrical conductivity and superior mechanical properties simultaneously under moderate synthesis conditions, which will facilitate their large-scale applications in a variety of fields.

Bubble-Mediated Production of Few-Layer Graphene via Vapor-Liquid Reaction between Carbon Dioxide and Magnesium Melt.

It is urgent to develop novel technologies to convert carbon dioxide to graphene. In this work, a bubble-mediated approach via a chemical reaction between carbon dioxide gas and magnesium melt to fabricate a few-layer graphene was illustrated. The morphology and defects of graphene can be regulated by manipulating the melt temperature. The preparation of graphene at 720 °C exhibited an excellent quality of surface and graphitization degree. The high-quality few-layer graphene can be grown under the combined effect of carbon dioxide bubbles and in-situ grown MgO. This preparation method possesses the advantages of high efficiency, low cost, and environmental protection, which may provide a new strategy for the recovery and reuse of greenhouse gases.

An open-source robust machine learning platform for real-time detection and classification of 2D material flakes

The most widely used method for obtaining high-quality two-dimensional (2D) materials is through mechanical exfoliation of bulk crystals. Manual identification of suitable flakes from the resulting random distribution of crystal thicknesses and sizes on a substrate is a time-consuming, tedious task. Here, we present a platform for fully automated scanning, detection, and classification of 2D materials, the source code of which we make openly available. Our platform is designed to be accurate, reliable, fast, and versatile in integrating new materials, making it suitable for everyday laboratory work. The implementation allows fully automated scanning and analysis of wafers with an average inference time of 100 ms for images of 2.3 Mpixels. The developed detection algorithm is based on a combination of the flakes’ optical contrast toward the substrate and their geometric shape. We demonstrate that it is able to detect the majority of exfoliated flakes of various materials, with an average recall (AR50) between 67% and 89%. We also show that the algorithm can be trained with as few as five flakes of a given material, which we demonstrate for the examples of few-layer graphene, WSe2, MoSe2, CrI3, 1T-TaS2 and hexagonal BN. Our platform has been tested over a two-year period, during which more than 106 images of multiple different materials were acquired by over 30 individual researchers.

Stacking-induced phonon transport engineering of siligene

Tunable phonon transport properties of two-dimensional materials are desirable for effective heat management in various application scenarios. Here, we demonstrate by first-principles calculations and Boltzmann transport theory that the lattice thermal conductivity of siligene could be efficiently engineered by forming various stacking configurations. Unlike few-layer graphene, the stacked siligenes are found to be covalently bonded along the out-of-plane direction, which leads to unique dependence of the thermal conductivity on both the stacking order and layer number. Due to the restricted flexural phonon scattering induced by the horizontal reflection symmetry, the AA stacking configuration of bilayer siligene exhibits obviously higher thermal conductivity compared with the AB stacking. In addition, we observe increasing thermal conductivity with the layer number, as evidenced by the reduced phonon scattering phase space and Grüneisen parameter. Interestingly, the Fuchs-Sondheimer model works well for the thickness-dependent thermal conductivity of stacked siligenes.