Conductivity Of Graphene Research Articles

Thermal properties of carbon-based materials

Phonons and related processes govern the thermal properties of materials. They can be excited externally using light, heat, mechanical energy, etc. This article aims to elucidate the methodology used in studying thermal properties, specifically employing temperature-dependent Raman spectroscopy. However, unique challenges arise when applying these techniques to low-dimensional materials. We summarize theoretical and experimental studies highlighting the significance of phonon hydrodynamics—a phenomenon typically observed only at low temperatures in bulk materials, but now found at room temperature in 2D materials like graphene. This discovery calls for caution when utilizing temperature-dependent Raman spectroscopy-based techniques, such as the optothermal Raman method, which has been extensively employed to experimentally determine the thermal conductivity of graphene. Moreover, temperature-dependent Raman spectroscopy remains a valuable tool for investigating phonon anharmonicity, a key factor governing phonon transport and decay processes in a wide array of emerging 2D materials and their heterostructures.

Facile production of graphene-based ternary composite coatings on metallic bipolar plates

Graphene-based composite coatings can be applied on metallic bipolar plates (BPs) of PEMFC for corrosion protection and electron conduction, benefited from the high electrical conductivity, chemical stability and physical barrier properties of graphene. To reach the high electrical conductivity requirement, the composite coatings shall have high graphene content, which brings challenges including dispersion, processability and interface compatibility. In this work, polyisocyanate was grafted on graphene surfaces to enhance the compatibility with polyurethane (PU). Carbon black was introduced as conductive bridging, which filled in defects of graphene/PU coatings. The corrosion current density of the ternary composite coatings with 60 % functionalized graphene, 30 % PU and 10 % carbon black was 0.43 μA·cm−2 in H2SO4 solution of pH 3 at 80 °C, while the interfacial contact resistance was 6.75 mΩ·cm2 and the in-plane conductivity was 137.4 S·cm−1. The composite coatings provided an efficient and cost-effective solution for up-scaling production of metallic BPs.

Water adsorption kinetics on graphene controlled by surface modification of supporting substrates

Sensing layers with an increased affinity for water molecules are essential for the development of highly sensitive humidity sensors. Graphene possesses superior electrical properties that make it suitable for the fabrication of low-noise miniaturized sensors. However, the enhancement of water affinity by introducing surface defects such as covalently attached hydrophilic groups reduces the electrical conductivity of graphene. In this study, we exploit the wetting transparency of graphene to increase its water affinity without introducing defects. Kinetic measurements using a Kelvin probe with a large-diameter tip showed that the rate constant of water adsorption was higher for graphene deposited on a hydrophilic substrate. These findings suggest that the wetting transparency of graphene can be exploited to reduce defect introduction into the graphene sensing layer, and has potential applications in sensor technologies.

Bi2S3 Confined by Covalent Organic Frameworks Enables High‐Rate High‐Capacity Potassium Storage

AbstractPotassium‐ion hybrid capacitors (PIHCs) are highly promising as an energy‐storage system. However, the rate performance and cycling performance of most materials with high capacity cannot simultaneously meet the requirements of PIHCs. In this work, a composite material of Bi2S3 nanoparticles in situ confined within a sulfur‐doped covalent organic framework (COF) and combined with graphene (Bi2S3@SCOF/G) is synthesized. Due to the synergistic effect of the stability of COF to buffer large mechanical stresses and the high electronic conductivity of graphene, the Bi2S3@SCOF/G anode reveals a high reversible capacity (503.8 mAh g−1 at 100 mA g−1 after 100 cycles) and favorable rate performance (223.9 mAh g−1 even at 5000 mA g−1). Furthermore, the PIHCs assembled with activated carbon show excellent energy density and cycling performance, indicating their potential for practical applications.

Promoting Thermal Conductivity of Alumina-Based Composite Materials by Systematically Incorporating Modified Graphene Oxide

Small amounts of thermally conductive graphene oxide (GO) and modified GO are systematically introduced as a second filler to thermal interface materials (TIMs) consisting of alumina (Al2O3) particles and polydimethylsiloxane (PDMS). The surface of GO is covalently linked with an organic moiety, octadecylamine (ODA), to significantly improve the miscibility and dispersity of GO across the TIM matrix. Subsequently, two series of PDMS-Al2O3 composite TIMs are manufactured as a function of GO and ODA-GO content (0.25 wt%–2.5 wt%) to understand the effect of these second additives. The incorporation of GO into the Al2O3-PDMS composite materials generally increases the thermal conductivity (TC), ranging from 18% to 29%. Conversely, the use of ODA-GO further enhances the overall performance of TIMs (22–54%) by facilitating the dispersion degree of GO across the composite matrix. The great improvement in TC is presumably related to the formation of conductive pathways by uniformly integrating 2D-type GO flakes across spherical Al2O3 particle networks. The ability to simply regulate the polarity of the thermally conductive second filler can provide an idea for designing cost-effective and practical TIM-2-type pads that can be commercially applicable in between an integrated heat spreader and a heat sink.

Pure and doped graphene as a suitable material for the detection of hazardous gases

The need for highly sensitive toxic gas sensors is significant, and achieving this sensitivity is possible. Researchers have utilized density functional theory (DFT) computations to examine adsorption of different gas molecules (COX2, where X is F, Cl, or Br) over Au-doped and pristine graphene. This investigation aims to determine possibility of employing Au-doped graphene as a basis for gas sensors. Multiple adsorption positions and orientations were examined for each gas molecule. The configuration that exhibited the highest stability was identified, and adsorption energy (Eads) values, considering van der Waals (vdW) interactions, have been computed using NCI analyses. In addition, the electronic properties, including LUMOHOMO orbital density and charge transfer, were analyzed to acquire a deeper understanding of process by which adsorption occurs. Findings indicated that gas molecules under investigation exhibited weak adsorption on pristine graphene, with low Eads values. In contrast, Eads values of every gas molecule on Au-doped graphene displayed varying degrees of increase. Notably, COX2 exhibited a high sensitivity to Au-doped graphene. Furthermore, in the effect of doping Au into graphene, the Eads absorption of COCl2 gas has increased from 0.155 to 1.028 eV. This indicates the strong tendency of Au-doped graphene to interact with gas COCl2 compared to two other COX2 gas species. This strong adsorption can be ascribed to significant substantial charge transfer (CT) between COCl2 and Au-doped graphene and orbital hybridization. The charge transfer amount of the doped states has increased by more than double compared to the pure state. The band gap of Au-doped graphene has decreased from 2.14 to 1.83 eV due to the absorption of gas COCl2, indicating the highest amount of reduction compared to other gases. Moreover, the enhanced electrical conductivity of Au-doped graphene renders it more valuable and sensitive in the context of sensing COX2 gases.

Rechargeable zinc-air battery with bifunctional electrocatalyst of copper oxide and graphene nanoplatelets

Rechargeable zinc-air batteries have been identified as promising technologies for energy storage. However, developing cost-effective electrocatalysts that can efficiently facilitate the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is crucial for their advancement. This work investigates synthesized electrocatalysts composed of graphene-Cu2O deposited on carbon cloth by doctor blading casting method as bifunctional electrodes in a rechargeable Zn-air battery. The battery integrated with graphene-Cu2O as the air-cathode electrocatalyst showed superior performance in terms of cycling stability compared to that without Cu2O. This enhanced performance is attributed to the reversibility of Cu+/Cu2+ species during the redox reactions facilitated by the high electrical conductivity of graphene. Therefore, the results suggest the potential of the synthesized electrodes for advancing the development of rechargeable Zn-air batteries.

Heat Flow Overshooting in Suspended Graphene

ABSTRACT In this work we found that when the hydrodynamic heat conduction in suspended graphene is in the under-damped free oscillation regime the disturbance of heat flux at the boundaries of graphene and the joint action of the initial heat flux and its time change rate can cause the heat flow overshooting which refers to the excess heat flux established in the heat conduction medium when two heat flow wave-fronts meet. The overshooting can make the maximum amplitude of the heat flux more than twice that of the initial heat flux, which poses a great danger to the next high-frequency and high-efficiency electronic devices based on graphene, such as the graphene field-effect transistors. Interestingly, results show that when the scale ratio of graphene with rectangular shape in the heat flow direction to its vertical direction is greater than a certain value, the overshooting caused by the disturbance of the heat flux at the boundaries no longer occurs. For the overshooting induced by the uneven distribution of the initial heat flux and its time change rate, it is shown that if the length in the region with the higher heat flux and time change rate in the direction of heat flow is less than a critical value the overshooting phenomenon can be avoided. These findings provide a new way for thermal management of electronic devices based on graphene.

The multiple faces of graphene on anticorrosion: Advances and prospects

In recent years, graphene has remarkably enhanced the protective performance of anticorrosive organic coatings, yielding increasingly frequent exciting results and perspectives. This paper reviews the latest research advancements that we have gathered on the influences of conductivity, modification, dispersion methods and controllable orientation of graphene; the graphene-based smart anticorrosive coatings; the current understandings on the designs of the anticorrosive coating and the action mechanisms of graphene in the coating. It is concluded that there would be greater opportunities for the gravitational field-induced method to play the shielding effect of graphene; noncovalent modification methods may not ensure satisfactory attachment of the modifiers to the surface; green modification methods are expected to reduce the electrical conductivity of graphene and covalently modify graphene; the self-healing and early-warning graphene-based anticorrosive coatings are becoming a trend in the development of anti-corrosive coatings. The current-faced challenges and the future development prospects of the graphene-based anticorrosive coating were also proposed. Although graphene performs well in anticorrosive coatings, there is still considerable room to improve the performance, and a new round of industrial optimisation and upgrading in the anti-corrosion coating industry is inevitable with the rapid development of the anticorrosive graphene-based filler.

Modulating Thermal Conductivity via Targeted Phonon Excitation.

Thermal conductivity is a critical material property in numerous applications, such as those related to thermoelectric devices and heat dissipation. Effectively modulating thermal conductivity has become a great concern in the field of heat conduction. Here, a quantum modulation strategy is proposed to modulate the thermal conductivity/heat flux by exciting targeted phonons. It shows that the thermal conductivity of graphene can be tailored in the range of 1559 W m-1 K-1 (decreased to 49%) to 4093 W m-1 K-1 (increased to 128%), compared with the intrinsic value of 3189 W m-1 K-1. The effects are also observed for graphene nanoribbons and bulk silicon. The results are obtained through both density functional theory calculations and molecular dynamics simulations. This novel modulation strategy may pave the way for quantum heat conduction.

Enhancing thermal conductance between graphene and epoxy interfaces through non-covalent cation-π interactions

Although graphene has high thermal conductivity, its application in thermal management remains challenging because of the large interfacial thermal resistance between graphene and adjacent materials. This work demonstrates that non-covalent cationic-π interaction can significantly improve the thermal conductance between graphene and substrate interfaces. Cationic polyacrylamide (CPAM) bridges substrate and graphene with hydrogen bonding and cation-π interaction, respectively. The cation-π interaction between graphene and CPAM is confirmed by Raman, UV–Vis and NMR spectroscopy. The results show that CPAM increases the interfacial adhesion of graphene/epoxy from 18.7 ± 2.2 mN to 37.4 ± 7.6 mN (100.0 % improvement) and improves the interfacial thermal conductivity (ITC) from 22 ± 2 MW/m2K to 51 ± 5 MW/m2K (131.8 % improvement). Enhancing the ITC of graphene/epoxy by introducing CPAM assembled layer has advantages over covalent modifications because it provides a similar level of ITC improvement rate, but has little effect on the intrinsic thermal conductivity of graphene. Finally, it is demonstrated that the sample with graphene/cationic polyelectrolyte/substrate structure exhibits great potential for applications in the area of thermal management and printed circuit boards.

Dual-indicators machine learning assisted processing high-quality laser-induced fluorine-doped graphene and its application on droplet velocity monitoring sensor

Laser-induced graphene (LIG) is widely used in electron devices owing to its characteristics of fine patterning and high precision. Doping is a commonly used approach to improve the quality of LIG. Thanks to the excellent superhydrophobicity and high electrical conductivity of laser-induced fluorine-doped graphene (F-LIG), it shows promising potential in developing electrodes for electron devices. However, it remains a major challenge to rapidly search for the optimal laser processing parameter space that can process high-quality F-LIG. In this work, a dual-indicators predictive machine learning (ML) method for optimizing the F-LIG process was proposed, utilizing a Gaussian process regression (GPR) algorithm. The mean square error (MSE) between the actual and predicted values of the data used for the model test was 0.00814, while the mean absolute percentage error (MAPE) was 10.33 %, demonstrating a certain degree of generalization without overfitting. Importantly, the F-LIG processed using parameters predicted by the ML model achieved excellent superhydrophobicity and conductivity simultaneously. Based on this high-quality F-LIG, a self-powered droplet velocity monitoring sensor was developed. This sensor can accurately work after 20,000 cycles, showing excellent stability. The proposed dual-indicator ML model assisted the optimization of the F-LIG process, which will provide a feasible and economical way to process high-quality graphene and related electron devices.

A unified hybrid micromechanical model for predicting the thermal and electrical conductivity of graphene reinforced porous and saturated cement composites

Graphene fillers have gained widespread attention as functional reinforcements for cement composites due to their excellent physical properties. The prediction of the thermal and electrical properties of graphene reinforced cement composites (GRCCs) is of great importance for developing intelligent and multifunctional civil engineering materials and structures. In this current work, a unified hybrid micromechanical model combining effective medium theory (EMT) and Mori-Tanaka-Benveniste (MTB) is developed to simultaneously predict the thermal and electrical conductivity of the GRCCs with considering pores and saturation, in which mechanisms including phonon transport, electron tunnelling and Maxwell-Wagner-Sillars (MWS) polarization are incorporated. Graphene nanoplatelets (GNPs) reinforced cement composites (GNPRCCs) samples are prepared and tested to validate the developed unified model. The results show that the electrical conductivity of the GNPRCCs is more sensitive to saturation than the thermal conductivity. When the porosity n = 0.2 and the GNP concentration is 1 wt%, the relative thermal and electrical conductivity increases by 5 % and 193 %, respectively, when the saturation index increases from 0.6 to 1. Elongated pores are more favorable for the formation of ionic networks for electrical conductivity in the saturated GNPRCCs, while spherical pores are more beneficial for heat transport. Elongated graphene fillers are preferred for enhancing both the thermal and electrical conductivity of dry and saturated GNPRCCs. The work is envisaged to provide guidelines for developing multifunctional cement composites.

Ultra-strong and conductive graphene fiber via sacrificial layer technology

Microfluidic spinning technology (MST) is an emerging method specialized in the construction of multi-component and multi-structure fibers. In this study, we designed an ultra-strong coaxial graphene oxide (GO) fiber by employing sodium alginate (SA) as sheath flow via MST. The diameter of the fiber and the arrangement of GO molecules could be controlled by adjusting process parameters. More importantly, the outer SA layer could be removed during a subsequent reduction process of GO, which served as a sacrificial layer to GO fiber formation and enhanced the fiber strength. Ultimately, this could achieve a conductive graphene fiber with a maximum strength of 365.2 MPa and electrical conductivity of 52 Ω/cm via a common wet spinning mechanism.

Prototyping a wearable and stretchable graphene-on-PDMS sensor for strain detection on human body physiological and joint movements.

In the era of wearable electronic devices, which are quite popular nowadays, our research is focused on flexible as well as stretchable strain sensors, which are gaining humongous popularity because of recent advances in nanocomposites and their microstructures. Sensors that are stretchable and flexible based on graphene can be a prospective 'gateway' over the considerable biomedical speciality. The scientific community still faces a great problem in developing versatile and user-friendly graphene-based wearable strain sensors that satisfy the prerequisites of susceptible, ample range of sensing, and recoverable structural deformations. In this paper, we report the fabrication, development, detailed experimental analysis and electronic interfacing of a robust but simple PDMS/graphene/PDMS (PGP) multilayer strain sensor by drop casting conductive graphene ink as the sensing material onto a PDMS substrate. Electrochemical exfoliation of graphite leads to the production of abundant, fast and economical graphene. The PGP sensor selective to strain has a broad strain range of ⁓60%, with a maximum gauge factor of 850, detection of human physiological motion and personalized health monitoring, and the versatility to detect stretching with great sensitivity, recovery and repeatability. Additionally, recoverable structural deformation is demonstrated by the PGP strain sensors, and the sensor response is quite rapid for various ranges of frequency disturbances. The structural designation of graphene's overlap and crack structure is responsible for the resistance variations that give rise to the remarkable strain detection properties of this sensor. The comprehensive detection of resistance change resulting from different human body joints and physiological movements demonstrates that the PGP strain sensor is an effective choice for advanced biomedical and therapeutic electronic device utility.

Влияние электронного дрейфа в графене на преобразование поляризации нормально падающей волны

The polarization conversion of an electromagnetic wave normally incident on graphene with a direct electric current is investigated in the hydrodynamic approach. It is shown that the dynamic conductivity of graphene depends on the direction of electron drift even in the absence of spatial dispersion (i.e., for long electromagnetic waves). This changes the polarization of electromagnetic radiation at terahertz frequencies. The real part of the dynamic conductivity of graphene with electron drift can be negative, which leads to amplification of terahertz wave.

Computational fluid dynamics simulations of the heat transfer properties of graphene-based nanolubricants and application to hydrodynamic lubrication

In this paper, we consider experimental data available for graphene-based nanolubricants to evaluate their convective heat transfer performance by means of computational fluid dynamics (CFD) simulations. Single-phase models with temperature-dependent properties are employed for this purpose. The base fluid is a polyalkylene glycol, and we show the effect of the addition of carbon nanohorns and graphene nanoplatelets (GNPs), in different volume fractions, on the convective heat transfer coefficient between two parallel plates. Then, an application to hydrodynamic lubrication is discussed. The extreme in-plane thermal conductivity of graphene allows a smaller temperature rise of the GNP-based nanolubricant, i.e., a more effective heat removal. To the best of our knowledge, this work represents the first application of single-phase nanofluid models to hydrodynamic lubrication.

Mechanical Control of Quantum Transport in Graphene.

2D materials (2DMs) are fundamentally electro-mechanical systems. Their environment unavoidably strains them and modifies their quantum transport properties. For instance, a simple uniaxial strain can completely turn off the conductance of ballistic graphene or switch on/off the superconducting phase of magic-angle bilayer graphene. This article reports measurements of quantum transport in strained graphene transistors which agree quantitatively with models based on mechanically-induced gauge potentials. A scalar potential is mechanically induced in situ to modify graphene's work function by up to 25 meV. Mechanically generated vector potentials suppress the ballistic conductance of graphene by up to 30% and control its quantum interferences. The data are measured with a custom experimental platform able to precisely tune both the mechanics and electrostatics of suspended graphene transistors at low-temperature over a broad range of strain (up to 2.6%). This work opens many opportunities to harness quantitative strain effects in 2DM quantum transport andtechnologies.

Graphene conductance modulation through controlled molecular release in a hybrid coordination polymer/graphene field-effect transistor

Coordination polymers, including metal-organic frameworks (MOFs), present a wide range of functionalities ranging from sensing to energy storage. Despite this, many coordination polymers are typically insulating which prevents their implementation into nanoscale electronic devices. Besides, the hybridization of MOFs with other conducting materials, like graphene, is rather unexplored. Here we introduce the grafting of a soft non-porous coordination polymer, the 1·2CH3CN, on a single-layer graphene to form a hybrid 1·2CH3CN/graphene field effect transistor. Electron transport measurements show that the sharp structural transformations in 1·2CH3CN, triggered at two specific temperatures, are detected in graphene as two sharp increments in the electrical current. Gate spectroscopy measurements show that the origin of the electrical modulation is an abrupt p-doping due to the sudden release of acetonitrile right at the structural transition temperatures. Reciprocally, the sensitivity of graphene to external perturbations allows to detect additional transformations in the coordination polymer not observed in direct transport measurements across crystals. Finally, the results have been reproduced in in-situ grown 1·2CH3CN nanoscale films on CVDG FETs. This simple method optimizes the contact area between graphene and 1·2CH3CN and facilitates the integration of coordination polymers with van der Waals materials and electronic devices. Further, a selective doping at specific temperatures could be obtained by modifying the nature of the interstitial molecule in 1.

Tunable quantized spin Hall effect of light in graphene

The spin Hall effect of light is an appealing toolset for metrology that holds incredible potential for precision measurements due to its high sensitivity to the refractive index and nanostructure physical parameters. Here, we theoretically examine the quantized spin Hall effect of light on the surface of a monolayer graphene–substrate system subjected to an external perpendicular magnetic field. We discuss the impact of Landau levels induced by the external magnetic field B and the photon energy on magneto-optical conductivities and Fresnel reflection coefficients. We find that the spin-dependent splittings in graphene exhibit quantized characteristics due to the Landau levels quantization of the magneto-optical conductivities and Fresnel’s reflection coefficients near the Brewster angle. Moreover, the spin-dependent shifts are quantized and show oscillatory behavior with changes in the magnetic field and the photon energy. Our results manifest that the quantized photonic spin-dependent separations are sensitive to variations in the incidence angle, magnetic field, and incident photonic energies. The quantized spin-dependent splitting opens a promising route to find the quantized Hall conductivity and discrete Landau levels in the monolayer graphene by a direct optical weak measurement.