Few-layer Graphene Research Articles

Al–Si–Cu–Mg Matrix Composites with Graphene: PM‐Based Production, Microstructural, and Mechanical Properties

Few‐layered graphene (FLG)‐reinforced Al‐Si(10 wt%)‐Cu(2 wt%)‐Mg(1 wt%) matrix composites are prepared by the high‐energy mechanical alloying (MA) method, which is a branch of powder metallurgy. Al‐10Si‐2Cu‐1Mg matrix is reinforced with varying amounts of FLG (0, 0.5, 1, 2, and 5 wt%) via MA for different durations (0, 2, 4, and 8 h), and consolidation is conducted by pressureless sintering. Microstructural, mechanical, and tribological characterizations are applied to nonmechanically alloyed (non‐MAed) and mechanically alloyed (MAed) powder and bulk composites comparatively. The bulk composites produced via the MA‐containing processing route illustrate more homogeneous phase distributions and higher densification rates. The FLG/AlSiCuMg composites exhibit enhanced materials properties compared to their unreinforced counterparts. The addition of 1 and 2 wt% FLG to the Al‐10Si‐2Cu‐1Mg alloy, respectively, improved the mechanical properties in terms of microhardness (155 and 162 HV), compression strength (441 and 412 MPa), and wear rate (11.5 × 10−4 and 9.2 × 10−4 mm3 N−1 m). Therefore, the experimental results show that graphene ensures a reinforcing effect on the Al matrix, at least provided by some of the ceramic particles.

Stability of Graphene/Nafion Composite in PEM FC Electrodes.

Ensuring the stable operation of proton exchange membrane fuel cells is conducive to their real-world application. A promising direction for stabilizing electrodes is the stabilization of the ionomer via the formation of surface compounds with graphene. A comprehensive study of the (electrochemical, chemical, and thermal) stability of composites for fuel cell electrodes containing a modifying additive of few-layer graphene was carried out. Electrochemical stability was studied by cycling the potential on a disk electrode for 5000 cycles. Chemical stability was assessed via the resistance of the composites to H2O2 treatment using ion-selective potentiometry. Thermal stability was studied using differential thermal analysis. Composites were characterized by UV-Vis spectroscopy, Raman spectroscopy, EDX, and SEM. It was shown that graphene inhibits Nafion degradation when exposed to heat. Contrariwise, Nafion is corrosive to graphene. During electrochemical and chemical exposure, the determining change for carbon-rich composites is the carbon loss (oxidation) of the carbon material. In the case of carbon-poor composites, the removal of fluorine and sulfur from the Nafion polymer with their partial replacement by oxygen prevails. In all cases, the F/S ratio is stable. The dispersity of Nafion in a sample affects its chemical stability more than the G/Nafion ratio does.

Modulation of Electrokinetic Potentials Using Graphene-Based Surfaces and Variable Substrate Charge Density.

Enhanced electrokinetic phenomena, manifested through the observation of a large streaming potential (Vs), were obtained in microchannels with single-layer graphene (SLG)-coated and few-layer graphene (FLG)-coated surfaces. In comparison to silicon microchannels, the Vs obtained for a given pressure difference along the channel (ΔP) was higher by 75% for the graphene-based channels, with larger values in the SLG case. Computational modeling was used to correlate the surface charge density, tuned through plasma processing, and related zeta potential to measured Vs. The implications related to deploying lower dimensional material surfaces for modulating electrokinetic flows were investigated.

Sustainable graphene production for solution-processed microsupercapacitors and multipurpose flexible electronics

The growing demand for portable and wearable electronics, Internet of Things microdevices, and wireless sensor networks has led to the development of miniaturized energy storage devices, such as microsupercapacitors (mSCs). With excellent electrical conductivity and high surface area in a layered structure, graphene materials are ideal for mSCs, but current manufacturing methods still hinder their widespread integration. Here, we propose a sustainable approach for the rapid and eco-friendly production of few-layer graphene flakes based on the exfoliation of graphite in water by a combination of high-shear mixing and a high-pressure airless spray. An all-carbon composite paste with high electrical conductivity and tunable viscosity was designed to fabricate planar, interdigitated mSCs on polyethylene terephthalate (PET). The flexible, metal-free mSCs achieved a Coulombic efficiency close to 100%, with areal and volumetric capacitances of 6.16 mF cm−2 and 2.46 F cm−3, respectively. The maximum energy density exceeds 200 μWh cm−3 with 91.5% capacitance retention after 10000 galvanostatic chargedischarge cycles. The mSCs retain the same performance when subjected to a wide bending range and can be easily modularized to adjust the voltage and capacitance outputs. Finally, high-performance coatings for electromagnetic interference shielding and wearable strain sensors are also fabricated to demonstrate the multipurpose applicability of the graphene-based paste.

Depolarization Field-Induced Photovoltaic Effect in Graphene/α-In2Se3/Graphene Heterostructures.

The ferroelectric photovoltaic effect (FPVE) enables alternate pathways for energy conversion that are not allowed in centrosymmetric materials. Understanding the dominant mechanism of the FPVE at the ultrathin limit is important for defining the ultimate efficiency. In contrast to the wide band gap conventional thin-film ferroelectrics, 2D α-In2Se3 has an ideal band gap of 1.3 eV and enables the fabrication of ultrathin and stable heterostructures, providing the perfect platform to explore FPVE in the nanoscale limit. Here, we study the ferroelectric layer thickness-dependent FPVE in vertical few-layer graphene/α-In2Se3/graphene heterostructures. We find that the short-circuit photocurrent is antiparallel to the ferroelectric polarization and increases exponentially with decreasing thickness. We show that the observed behavior is predicted by the depolarization field model, originating from the unscreened bound charges due to the finite density of states in semimetal few-layer graphene. As a result, the heterostructures show enhancement of the power conversion efficiency, reaching 2.56 × 10-3% under 100 W/cm2 in 18 nm thick α-In2Se3, approximately 275 times more than the 50 nm thick α-In2Se3. These results demonstrate the importance of the depolarization field at the nanoscale and define design principles for the potential of harnessing FPVE at reduced dimension.

Advancing carbon dioxide capture: Unravelling structure-property-performance dynamics in graphene related two-dimensional materials

Efficient design of adsorbents for carbon dioxide (CO2) capture is imperative in addressing the challenges caused by climate change. In this study, a comprehensive exploration of solid adsorbents derived from graphene-related two-dimensional materials (GR2Ms) with tunable surface chemistry and structures was undertaken to unravel the intricate structural-property-activity relationships essential for optimizing their CO2 adsorption. Nine key GR2Ms and carbon materials, including two types of (few-layer graphene (FLG), graphene oxide (GO) reduced graphene oxide (rGO) materials), expanded graphite (Exp Gft), rGO-Exp Gft and graphite (Gft), were methodically characterized alongside benchmarked materials such as activated carbon (AC) and molecular sieves (MS). Characterization parameters, i.e. morphology, particle size, interlayer distance, crystallite size, defect density, specific surface area (SSA), total pore volume, micropore volume and pore size, are correlated with CO2 adsorption capacity. Results revealed that the dominant properties influencing CO2 adsorption in GR2Ms are hierarchical porous morphology, defect density (up to 2.38 × 1011 cm−2), SSA (up to ∼271 m2/g), total pore volume (up to 0.86 cm3/g), and micropore volume (up to 0.03 cm3/g), all of which have established positive linear relationships. Conversely, crystallite size (0.38–48 nm) exhibited an inverse (non-linear) relationship with CO2 adsorption capacity under ambient conditions (25 °C and 1 atm). Particle size (8–52 μm), interlayer distance (0.33–0.89 nm) and pore size (4.2–13.3 nm) of GR2Ms showed negligible impact on CO2 adsorption capacity. Remarkably, porous rGO emerged as the top-performing CO2 adsorbent with an enhanced adsorption capacity (5.38 mmol/g) , in comparison with activated carbon (AC, 1.79 mmol/g) and molecular sieve (MS, 1.48 mmol/g). This study establishes a comprehensive structure-property-performance relationship, highlighting the significance of a three-dimensional (3D) hierarchical, open and interconnected pore structure within the graphene network, along with the largest pore volume and minimum crystallite size of rGO. These findings underscore the critical role of structural and porosity attributes of GR2Ms in CO2 adsorption, providing fundamental insights into the interplay between the structure and properties on their CO2 adsorption behavior. This study emphasizes the key pillars for effective adsorbent design and underlines the necessity of optimised control over the structural characteristics and porosity of GR2Ms to enhance their CO2 adsorption capabilities, contributing towards the ambitious net-zero target by 2050.

In-situ observation of hydrogen nanobubbles formation on graphene surface by AFM-SECM

Gas bubble evolution is an important phenomenon in many electrochemical processes and it is highly sensitive to the surface properties. Here we visualize the gas bubble dynamics on the surface of different graphene substrates during hydrogen evolution reaction (HER) using atomic force microscopy combined with scanning electrochemical microscopy. The low overpotential and low surface hydrophobicity of few-layer graphene formed on C-phase SiC causes the uniform distribution of hydrogen nanobubbles, which easily depart from the surface during the reaction. Conversely, the high overpotential and more hydrophobic surface of HOPG induces hydrogen bubbles to linger on the surface for an extended duration, leading to its accumulation and the subsequent formation of microbubbles. This in-situ nanoscale electrochemical mapping of hydrogen bubble dynamics provides new insight into electrocatalytic HER that occurs on non-metal electrodes.

Cost-effective synthesis of stable CoxC@few-layered graphene nanostructures embedded in a carbon matrix

In this study, a two-step surfactant sol-gel strategy is developed to synthesize Co particles with confined sizes in the nanoscale using organic precursors. This approach does not require the use of vacuum techniques or strong reducing atmospheres, making it a simple approach economically attractive. The strategy involves the generation of few-layered graphene shells to provide chemical stability, prevent oxidation and aggregation tendencies. Additionally, the study investigates the use of precursors based on nitrates and acetates, exploring their structural and magnetic properties in densified samples. Remarkably, magnetic properties are competitive for both approaches, with coercivities reaching up to 300 Oe and saturation magnetization of ∼60 and ∼80 emu/g for samples based on nitrates and acetates prepared at 650 °C, respectively. However, it is observed that smaller and more uniformly sized nanoparticles (around ∼10 nm) are obtained with nitrate-based precursors due to an effective ligand decomposition process. Therefore, this chemical approach offers effective nanoscale confinement with intriguing magnetic properties through a cost-effective and reproducible synthesis.

Ultrasensitive textile strain sensors redefine wearable silent speech interfaces with high machine learning efficiency

This work introduces a silent speech interface (SSI), proposing a few-layer graphene (FLG) strain sensing mechanism based on thorough cracks and AI-based self-adaptation capabilities that overcome the limitations of state-of-the-art technologies by simultaneously achieving high accuracy, high computational efficiency, and fast decoding speed while maintaining excellent user comfort. We demonstrate its application in a biocompatible textile-integrated ultrasensitive strain sensor embedded into a smart choker, which conforms to the user’s throat. Thanks to the structure of ordered through cracks in the graphene-coated textile, the proposed strain gauge achieves a gauge factor of 317 with <5% strain, corresponding to a 420% improvement over existing textile strain sensors fabricated by printing and coating technologies reported to date. Its high sensitivity allows it to capture subtle throat movements, simplifying signal processing and enabling the use of a computationally efficient neural network. The resulting neural network, based on a one-dimensional convolutional model, reduces computational load by 90% while maintaining a remarkable 95.25% accuracy in speech decoding. The synergy in sensor design and neural network optimization offers a promising solution for practical, wearable SSI systems, paving the way for seamless, natural silent communication in diverse settings.

Influence of Few-Layer Graphene on Frictional Properties of Lithium Compound Grease

The frictional properties of lithium compound grease (LCG) with different percentage compositions of few-layer graphene (FLG) were investigated, and the mechanisms of temperature and loading effects on LCG containing FLG are also considered. The concluding effect shows that 1 wt% FLG is more appropriate for friction and wear modifiers for lithium compound grease at elevated temperatures and less suitable at ordinary temperatures. Thickener chemisorption film, FLG layering film, and tribo-reaction film consisting of FeO(OH), Fe2O3, Fe3O4, Li2O, and other oxides assist in the establishment of a lubricating boundary film on the friction interfaces lubricated with LCG containing FLG. The poor fluidity of lithium compound grease at low temperatures leads to poor dispersion of FLG, decreasing friction reduction capability. Under elevated temperature and low load condition, adding 1wt% FLG to LCG can only improve its wear-resistant property, the abrasion volume of steel plate reduced by 24.49%. Under elevated temperature and high load condition, adding 1wt% FLG to LCG can only enhance its anti-friction characteristics.. Conversely, FLG is unsuitable as an anti-friction and wear-resistant additive for LCG at low-temperature conditions.

Upconversion electroluminescence in 2D semiconductors integrated with plasmonic tunnel junctions.

Plasmonic tunnel junctions are a unique electroluminescent system in which light emission occurs via an interplay between tunnelling electrons and plasmonic fields instead of electron-hole recombination as in conventional light-emitting diodes. It was previously shown that placing luminescent molecules in the tunneling pathway of nanoscopic tunnel junctions results in peculiar upconversion electroluminescence where the energy of emitted photons exceeds that of excitation electrons. Here we report the observation of upconversion electroluminescence in macroscopic van der Waals plasmonic tunnel junctions comprising gold and few-layer graphene electrodes separated by a ~2-nm-thick hexagonal boron nitride tunnel barrier and a monolayer semiconductor. We find that the semiconductor ground exciton emission is triggered at excitation electron energies lower than the semiconductor optical gap. Interestingly, this upconversion is reached in devices operating at a low conductance (<10-6 S) and low power density regime (<102 W cm-2), defying explanation through existing proposed mechanisms. By examining the scaling relationship between plasmonic and excitonic emission intensities, we elucidate the role of inelastic electron tunnelling dipoles that induce optically forbidden transitions in the few-layer graphene electrode and ultrafast hot carrier transfer across the van der Waals interface.

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.