Electrical Conductivity Of Graphene Research Articles

DFT assessments of optical and thermoelectric characteristics of (III/V)-doped elements into graphene sheets

First-principles simulations are conducted to explore the structural stability, electronic properties, and optical responses of pristine and boron- or nitrogen-doped monolayers graphene. The computed electronic density of states revealed that the substitutional doping of boron impurity atoms on monolayer graphene (MLG) shifts the Dirac point upward, although the substitution of nitrogen impurity atoms in graphene pushes the Dirac point downward the Fermi level. This could exhibit that upon the doping of MLG with boron or nitrogen, respectively, p-type or n-type semimetal is acquired. The overall optical spectral properties of the substituted graphene with boron or nitrogen atoms are simulated and compared with the optical spectra results of pure graphene. The optical features of pristine and doped MLG are determined by taking the interband and intra-band transitions into account ranging from the far-infrared to the ultraviolet regime of the electromagnetic radiation. A remarkable red shift in the optical spectra of the doped MLG towards the visible regime of radiation is established. An enhanced reflectivity illustrated that concentration-dependent optical properties of boron and nitrogen-doped MLG happen at lower electromagnetic radiation regimes. In addition, we explored the thermoelectric behaviors of the pristine/doped graphene monolayers with [Formula: see text] supercells. We found a significant improvement in the electrical conductivity of graphene when doped with boron or nitrogen impurities. However, an increase in the electrical conductivity has textured a decrease in the Seebeck coefficients. Improvement in the electrical conductivity is attributed to an interesting effect on the graphene monolayers’ power factor (PF). These findings indicate a positive impact of the dopants on the thermoelectric properties of graphene monolayers and reveal that they are potential materials for thermoelectric applications and nanodevices.

Passivating Grain Boundaries via Graphene Additive for Efficient Kesterite Solar Cells.

Grain boundaries (GBs)-triggered severe non-radiative recombination is recently recognized as the main culprits for carrier loss in polycrystalline kesterite photovoltaic devices. Accordingly, further optimization of kesterite-based thin film solar cells critically depends on passivating the grain interfaces of polycrystalline Cu2 ZnSn(S,Se)4 (CZTSSe) thin films. Herein, 2D material of graphene is first chosen as a passivator to improve the detrimental GBs. By adding graphene dispersion to the CZTSSe precursor solution, single-layer graphene is successfully introduced into the GBs of CZTSSe absorber. Due to the high carrier mobility and electrical conductivity of graphene, GBs in the CZTSSe films are transforming into electrically benign and do not act as high recombination sites for carrier. Consequently, benefitting from the significant passivation effect of GBs, the use of 0.05wt% graphene additives increases the efficiency of CZTSSe solar cells from 10.40% to 12.90%, one of the highest for this type of cells. These results demonstrate a new route to further increase kesterite-based solar cell efficiency by additive engineering.

Design and Realization of Ni Clusters in MoS2@Ni/RGO Catalysts for Alkaline Efficient Hydrogen Evolution Reaction.

Due to their almost zero relative hydrogen atom adsorption-free energy, MoS2-based materials have received substantial study. However, their poor electronic conductivity and limited number of catalytic active sites hinder their widespread use in hydrogen evolution reactions. On the other hand, metal clusters offer numerous active sites. In this study, by loading Ni metal clusters on MoS2 and combining them with the better electrical conductivity of graphene, the overpotential of the hydrogen evolution reaction was reduced from 165 mV to 92 mV at 10 mA·cm-2. This demonstrates that a successful method for effectively designing water decomposition is the use of synergistic interactions resulting from interfacial electron transfer between MoS2 and Ni metal clusters.

N-Doped Graphene and Its Derivatives as Resistive Gas Sensors: An Overview

Today, resistance gas sensors which are mainly realized from metal oxides are among the most used sensing devices. However, generally, their sensing temperature is high and other materials with a lower operating temperature can be an alternative to them. Graphene and its derivatives with a 2D structure are among the most encouraging materials for gas-sensing purposes, because a 2D lattice with high surface area can maximize the interaction between the surface and gas, and a small variation in the carrier concentration of graphene can cause a notable modulation of electrical conductivity in graphene. However, they show weak sensing performance in pristine form. Hence, doping, and in particular N doping, can be one of the most promising strategies to enhance the gas-sensing features of graphene-based sensors. Herein, we discuss the gas-sensing properties of N-doped graphene and its derivatives. N doping can induce a band gap inside of graphene, generate defects, and enhance the conductivity of graphene, all factors which are beneficial for sensing studies. Additionally, not only is experimental research reviewed in this review paper, but theoretical works about N-doped graphene are also discussed.

Electromagnetic coupling and transport in a topological insulator–graphene heterostructure

The electromagnetic coupling between hetero-structures made of different materials is of great interest, both from the perspective of discovering new phenomena, as well as for its potential applications in novel devices. In this work, we study the electromagnetic coupling of a hetero-structure made of a topological insulator (TI) slab and a single graphene layer, where the later presents a diluted concentration of ionized impurities. We explore the topological effects of the magneto-electric polarizability (MEP) of the TI, as well as its relative dielectric permittivity on the electrical conductivity in graphene at low but finite temperatures.

Study on the Effect of Freeze-Thaw Action on the Electrical Conductivity and Sensing Properties of Graphene-Based Cement Composites.

Graphene can effectively improve the mechanical and electrical properties of cement-based materials due to its excellent tensile strength, thermal conductivity and electrical conductivity. In this paper, the effects of freeze-thaw on the conductivity and sensing properties of graphene-based cement materials were investigated. After the preparation of graphene-based cement materials, they were subjected to different times of freeze-thaw action. The experiments were designed to analyze the influence of freeze-thaw on the electrical conductivity, humidity sensitivity, thermosensitivity and pressure sensitivity of graphene-based cement composites. The results show that the influence of freeze-thaw on the electrical conductivity of graphene is mainly manifested in the influence on the resistivity and the extension of the polarization time, and the influence on the percolation transition zone is small. After freeze-thaw, the polarization time of the specimen decreases with the increase of the relative water content. The temperature has a great influence on the polarization effect of graphene-based cement composites and the composites with graphene content of the zone B still show satisfactory pressure-sensitive property after freeze-thaw.

Graphene-Assisted Electromagnetically Induced Transparency-like Terahertz Metabiosensor for Ultra-Sensitive Detection of Ovalbumin

Terahertz (THz) metamaterial (MM) biosensors are a potential method of biomolecule detection. However, there have been few reports on the detection of trace proteins. In this study, we designed a novel THz biosensor consisting of graphene, polyimide (PI), and electromagnetically induced transparency-like (EIT-like) MMs for the ultra-sensitive detection of ovalbumin (OVA). The doping analyte can influence the Fermi level and electrical conductivity of graphene, as well as the coupling of resonators in MMs. These changes are reflected in the magnitude, phase, and frequency changes in the transmission spectra. The biosensor achieved a high sensitivity function for OVA and reached a limit of detection (LoD) of 8.63 pg/mL. The results showed that by regulating the Fermi level of graphene between the valence band, Dirac point, and conduction band, the sensitivity and LoD of MM-based THz biosensors can be enhanced. Such biosensors have the potential to be used in the high-sensitivity detection of trace proteins in biomedical fields.

Sulfonated Starch-Graft-Polyaniline@Graphene Electrically Conductive Nanocomposite: Application for Tyrosinase Immobilization

The interaction of tyrosinase with sulfonated starch-graft-polyaniline@graphene (SSt-g-PANI@G) nanocomposite was investigated by electrochemical methods. The activity of the immobilized tyrosinase (Tyase) was proved by the electrochemical detection of three substrates (L-dopa, caffeic acid, and catechol). The SSt-g-PANI@G nanocomposite was characterized by Fourier-transform infrared spectra (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray analysis (EDX), and thermogravimetric analysis (TGA). To immobilize tyrosinase on the surface of the nanocomposite, a simple drop-casting technique was used. The presence of sulfuric acid and hydroxyl groups in SSt, amine groups in PANI, and high surface-to-volume ratio and electrical conductivity of graphene in the prepared nanocomposite led to good enzyme immobilization on the electrode surface. The modified electrode showed a suitable catalytic effect on the electrochemical redox agent, compared with the bare electrode. The peak current responses for three substrates were studied with a calibration curve derived using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). In addition, the fabricated SSt-g-PANI@G/Tyase/GCE showed a more suitable response to catechol, L-dopa, and caffeic acid substrates, respectively.

Polydopamine-coated graphene for supercapacitors with improved electrochemical performances and reduced self-discharge

Graphene-based supercapacitors have attracted significant attention owning to the high specific surface area and electrical conductivity of graphene with the potential to deliver superior energy and power performances than other supercapacitor materials. However, graphene-based supercapacitors inevitably have self-discharge behavior like any other supercapacitors, resulting in rapid voltage drop and limiting their applications for long-term energy storage. Reported methods for mitigating the self-discharge of graphene-based supercapacitors are often associated with deteriorated performances such as decreased specific capacitances or rate performances. Here we report that self-polymerized dopamine on the surface of graphene can reduce the self-discharge of supercapacitors while achieving improved specific capacitance and rate performance. Specifically, a 40% increase in specific capacitance (150.8 vs. 108.0 F g–1 at 0.1 A g–1), much improved capacitance retention at high currents (80% vs. 55% at 10 A g–1), and a 37% reduction in open circuit voltage (OCV) decay rate (0.33 V vs. 0.52 V in 12 h) were attained simultaneously after PDA-coating on graphene. Analysis of the open circuit potential attenuation of both positive and negative electrodes of the supercapacitors suggests that the coating of PDA suppressed the self-discharge caused by diffusion-controlled faradaic reaction process. This can be attributed to the catechol and amine functional groups of PDA which not only offered additional pseudocapacitance when the electrodes were charged but also served as trapping sites for dissolved impurity ions and oxygen molecules so that the reactions of these species on graphene surface were impeded during open circuit test, leading to both improved energy storage performances and reduced self-discharge rate.

Improving Effect of Graphene on Electrochemical Properties of Fe2O3 Anode Materials

Transition metal oxides have a high initial charge-discharge capacity of 800–1000 mAh/g, the electrochemical performance, cyclic performance and rate performance of the composite of transition metal oxide and graphene have been improved due to the unique two-dimensional structure and excellent electrical conductivity of graphene. In this paper, iron oxides materials with different morphs were prepared by different hydrothermal reaction temperatures, and rGO/Fe2O3-175 °C composites with different graphene ratios were synthesized and used in the anode of lithium ion batteries. The results show that nanorod-shaped Fe2O3 had better electrochemical performance than spherical Fe2O3. 0.2rGO/Fe2O3-175 °C had the best cyclic performance, the first cyclic discharge capacity reaches 1372 mAh/g under the current density of 100 mA/g, and the cyclic reversible capacity remained at about 435 mAh/g after 50 cycles, illustrating that nanorods Fe2O3 and graphene composites can greatly buffer the volume expansion of Fe2O3.

Enhanced electrical conductivity in graphene–copper multilayer composite

For many years, researchers have been trying to make a material more conductive than silver by incorporating carbon nanotubes or graphene into copper to form a composite material. However, after a decade-long effort, only a few groups reported successful results, raising concerns about the feasibility of this composite approach. Here, we report our effort to validate the multilayer graphene–copper composite approach for improving electrical conductivity. We demonstrate that, with an estimated 0.008 vol. % graphene addition, copper’s electrical conductivity was improved to 104.2% of International Annealed Copper Standard (IACS) at room temperature. If the copper substrate used to make the multilayer composite is discounted using the parallel resistance model, the conductivity is calculated to be 185% IACS. This result could be further improved if the thickness of the copper layers can be further reduced.

Concurrent and Selective Determination of Dopamine and Serotonin with Flexible WS2 /Graphene/Polyimide Electrode Using Cold Plasma.

Makers of point-of-care devices and wearable diagnostics prefer flexible electrodes over conventional electrodes. In this study, a flexible electrode platform is introduced with a WS2 /graphene heterostructure on polyimide (WGP) for the concurrent and selective determination of dopamine and serotonin. The WGP is fabricated directly via plasma-enhanced chemical vapor deposition (PECVD) at 150°C on a flexible polyimide substrate. Owing to the limitations of existing fabrication methods from physical transfer or hydrothermal methods, many studies are not conducted despite excellent graphene-based heterostructures. The PECVD synthesis method can provide an innovative WS2 /graphene heterostructure of uniform quality and sufficient size (4 in.). This unique heterostructure affords excellent electrical conductivity in graphene and numerous electrochemically active sites in WS2 . A large number of uniform qualities of WGP electrodes show reproducible and highly sensitive electrochemical results. The synergistic effect enabled well-separated voltammetric signals for dopamine and serotonin with a potential gap of 188mV. Moreover, the practical application of the flexible sensor is successfully evaluated by using artificial cerebrospinal fluid.

Study on the nonreciprocal absorption properties of cylindrical photonic crystals embedded in graphene cascaded by periodic and Rudin–Shapiro sequences at large incident angles

Using the transfer matrix method, the absorption, reflection, and nonreciprocity of the cylindrical photonic crystals (CPCs) consisting of graphene and two layers of ordinary medium cascaded by a periodic sequence and a Rudin–Shapiro quasiperiodic sequence are investigated under a large incidence angle of electromagnetic wave. By comparing the cascade of two periodic structures and the case of a single periodic structure, it is concluded that the structure proposed in this paper has better nonreciprocal phenomena and wider relative absorption bandwidth at a large incidence angle, reaching 162.2%, which is also much higher than the general planar photonic crystals. The absorption performance of this structure in TE and TM modes is compared at different angles and it is found that TM mode has a wider absorption bandwidth and has an ideal bandwidth in a large range of incident angle from 20° to 80°. Meanwhile, the optimum parameters of chemical potential and medium thickness are discussed, which can meet the requirements of large absorption bandwidth and significant nonreciprocity at a large incident angle. The CPCs embedded in graphene adopted in this paper are structures that have never been studied before. The electrical conductivity of graphene can be adjusted by the chemical potential, which can more conveniently realize many optical phenomena and provide reference and application values for optical sensing, optical filtering, and optical detection.

Preventing Graphene from Restacking via Bioinspired Chemical Inserts: Toward a Superior 2D Micro-supercapacitor Electrode

Graphene-based composites are promising materials for supercapacitors due to the high specific surface area and electrical conductivity of graphene. Reduction of graphene oxide (GO) is a practical approach to obtain a graphene-like material, but it suffers from restacking of the graphene sheets. Herein, a two-dimensional composite electrode based on electrochemically reduced GO (ERGO) and polydopamine (PDA) is reported, where PDA is used as a “bioinspired chemical insert” to tackle with the restacking issue of graphene layers. This green and facile electrochemical fabrication method starts from electroreduction of GO followed by electro-oxidation of dopamine (DA), present in the same electrolyte, by a simple switch between a cathodic and an anodic potential. The optimized ERGO-PDA composite electrode possesses combined features of excellent capacitive behavior, with a relaxation time (τ0) of 0.88 s, high gravimetric and volumetric capacitances (178 F·g–1 and 297 F·cm–3, respectively, at 10 mV·s–1), and finally an excellent cycling stability at 100–2000 mV·s–1 at least for 30,000 cycles. The DA electropolymerization yield monitored by a quartz crystal microbalance and X-ray diffraction measurements demonstrate that PDA is formed between the graphene sheets which prevents the sheets from restacking and facilitates species diffusion inside the composite, leading to a volumetric energy density of 8.6 mWh·cm–3 for a power density of 7.8 W·cm–3. Additionally, the electrochemical quartz crystal microbalance demonstrates a dominant cationic charge compensation and a very efficient interfacial transfer characteristic since a totally reversible mass response during charge/discharge was observed for the optimized ERGO-PDA electrode.

Highly Efficient n-Type Doping of Graphene by Vacuum Annealed Amine-Rich Macromolecules.

Flexible transparent conducting electrodes (FTCE) are an essential component of next-generation flexible optoelectronic devices. Graphene is expected to be a promising material for the FTCE, because of its high transparency, large charge carrier mobilities, and outstanding chemical and mechanical stability. However, the electrical conductivity of graphene is still not good enough to be used as the electrode of an FTCE, which hinders its practical application. In this study, graphene was heavily n-type doped while maintaining high transmittance by adsorbing amine-rich macromolecules to graphene. The n-type charge-transfer doping of graphene was maximized by increasing the density of free amine in the macromolecule through a vacuum annealing process. The graphene adsorbed with the n-type dopants was stacked twice, resulting in a graphene FTCE with a sheet resistance of 38 ohm/sq and optical transmittance of 94.1%. The figure of merit (FoM) of the graphene electrode is as high as 158, which is significantly higher than the minimum standard for commercially available transparent electrodes (FoM = 35) as well as graphene electrodes doped with previously reported chemical doping methods. Furthermore, the n-doped graphene electrodes not only show outstanding flexibility but also maintain the doping effect even in high temperature (500 K) and high vacuum (~10−6 torr) conditions. These results show that the graphene doping proposed in this study is a promising approach for graphene-based next-generation FTCEs.

Hybrid nanomaterial of ZnFe2O4/α-Fe2O3 implanted graphene for electrochemical glucose sensing application

Nonenzymatic electrochemical glucose sensing of ZnFe2O4/α-Fe2O3 implanted graphene (ZFGr) was investigated by exploiting the electrocatalytic property of ZnFe2O4/α-Fe2O3 nanocomposite and electrical conductivity of graphene. The ZnFe2O4/α-Fe2O3 nanocomposite was implanted on graphene sheets with a process involving combustion and characterized using XRD, FTIR, Raman, XPS, FESEM, and TEM analyses. The electron microscopic images demonstrated the implantation of ZnFe2O4/α-Fe2O3 nanocomposite on graphene and the effects of implantation on the optical, magnetic and electrochemical properties of ZnFe2O4/α-Fe2O3 nanocomposite were discussed. The electrocatalytic efficiency of ZFGr hybrid nanomaterial towards glucose was investigated by employing EIS, CV, and chronoamperometry techniques. The electrochemical analysis revealed the application prospects of this hybrid nanomagnetic materials in electrochemistry due to its significant amperometric response for the electrochemical detection of glucose with a sensitivity of 609 μA(mM)−1 cm−2.

Behavior of the Energy Spectrum and Electric Conduction of Doped Graphene.

We consider the effect of atomic impurities on the energy spectrum and electrical conductance of graphene. As is known, the ordering of atomic impurities at the nodes of a crystal lattice modifies the graphene spectrum of energy, yielding a gap in it. Assuming a Fermi level within the gap domain, the electrical conductance diverges at the ordering of graphene. Hence, we can conclude about the presence of a metal–dielectric transition. On the other hand, for a Fermi level occurring outside of the gap, we see an increase in the electrical conductance as a function of the order parameter. The analytic formulas obtained in the Lifshitz one-electron strong-coupling model, describing the one-electron states of graphene doped with substitutional impurity atoms in the limiting case of weak scattering, are compared to the results of numerical calculations. To determine the dependence of the energy spectrum and electrical conductance on the order parameter, we consider both the limiting case of weak scattering and the case of finite scattering potential. The contributions of the scattering of electrons on a vapor of atoms to the density of states and the electrical conductance of graphene with an admixture of interstitial atoms are studied within numerical methods. It is shown that an increase in the electrical conductance with the order parameter is a result of both the growth of the density of states at the Fermi level and the time of relaxation of electron states. We have demonstrated the presence of a domain of localized extrinsic states on the edges of the energy gap arising at the ordering of atoms of the admixture. If the Fermi level falls in the indicated spectral regions, the electrical conductance of graphene is significantly affected by the scattering of electrons on clusters of two or more atoms, and the approximation of coherent potential fails in this case.

Effect of impurities ordering in the electronic spectrum and conductivity of graphene

By carrying out a computation in the Lifshitz tight-binding one-electron model, we obtain the energy spectrum and electrical conductance of graphene, in the presence of substitutional impurity atoms, thus assessing the influence of the latter. In the weak-scattering approximation, we study specific features of the electron energy spectrum in the gap region having width η|δ| and centered at the point yδ, arising because of the ordering of substitutional impurity atoms on nodes of the crystal lattice. Here η is the parameter of ordering, δ is the difference of the scattering potentials of impurity atoms and carbon atoms, and y is the impurity concentration. It is shown that if the ordering parameter η is close to ηmax=2y,y<1/2, the plot of the density of electron states has peaks on the edges of the energy gap. Those peaks correspond to impurity levels. As the ordering parameter η decreases, the impurity levels split into the impurity bands. The regions of localization of electron impurity states, which arise at the edges of the spectrum and edges of the energy gap, are investigated.

The energy spectrum and the electrical conductivity of graphene with substitution impurity

The effect of substitution atoms on the energy spectrum and the electrical conductivity of graphene was investigated in a Lifshitz one-electron tight-binding model. It is established that the ordering of impurity atoms results in a gap in the energy spectrum of electrons whose width depends on the order parameter and on the magnitude of the scattering potential. It is shown that if the order parameter is close to its maximum value, there are peaks associated with localized impurity states on the energy curve of the electron states density at the edges of the energy gap. At the electron concentration at which the Fermi level enters the gap region, the electrical conductivity is zero, and the metal-dielectric transition occurs. If the Fermi level falls in the region of the energy band, the electron relaxation time and electrical conductivity tend to infinity when the order parameter reaches its maximum value. The analytical calculations of the electron density and of the electrical conductivity of graphene, made in the limiting case of weak scattering, are compared with the results of the numerical calculations for different scattering potentials.

Highly Conductive Graphene Electronics by Inkjet Printing

Graphene is currently emerging as an alternative to traditional conductive materials, such as copper and silver because of its excellent electrical conductivity and earth's carbon abundance. Graphene can be applied in many different electronic fields with different manufacturing methods to meet their specific requirements, which promote the development of advanced manufacturing technology in graphene electrical applications. Inkjet printing, as an environmentally friendly, low-cost and simple-to-operate advanced manufacturing method, has broad development prospects especially in the field of flexible electronics. In this review, several factors affecting the electrical conduction property of graphene applications in the inkjet-printed graphene process are listed as follows: the preparation method of ink, material and treatment of substrate, thickness of print, and annealing, especially whether a coffee ring is produced. In addition, this paper also cites some examples of inkjet-printed graphene in electrical conductivity. In order to continuously improve the procedure designs of graphene electronics fabrication, more accurate relationships between electrical conductivity of graphene and these parameters can be built. Based on the excellent prospect of inkjet printing technology in the field of conductive electronics, there will be some further research about the perfect implementation of graphene’s electrical conductivity.