No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Electronic properties of graphene
Abstract
Graphene is the first example of truly two-dimensional crystals – it's just one layer of carbon atoms. It turns out that graphene is a gapless semiconductor with unique electronic properties resulting from the fact that charge carriers in graphene obey linear dispersion relation, thus mimicking massless relativistic particles. This results in the observation of a number of very peculiar electronic properties – from an anomalous quantum Hall effect to the absence of localization. It also provides a bridge between condensed matter physics and quantum electrodynamics and opens new perspectives for carbon-based electronics. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
... Quantum graphity is a model of quantum gravity, where spacetime is made up of discrete lattice, and this is based on the analogy with condensed matter systems like graphene [5,6]. Like graphene, at large distance the Planck scale latter can be approximated using continuum field theories like Dirac equation [7][8][9], it is proposed that spacetime at large distances scales is a continuum in quantum graphity [10,11]. The mean field theory has been used to study the properties of spacetime described by quantum graphity at low temperature [12]. ...
... Additionally, materials based on graphene exhibit exceptional physical and chemical characteristics, including a high surface area (2630m 2 /g) [90,91], excellent electrical conductivity (1738siemens/m) [90,92], strong mechanical strength (about 1100GP a) [90], unparalleled thermal conductivity (5000W/m/K) [90], ultra-high charge carrier mobility and a linear dispersion band structure [93]. Due to these unique properties, graphene is considered a promising subject of research in several fields, including biomedical [90] and biotechnology [94], chemistry and catalysis [95], energy technology and environment [96], nanoscience [9,93]. These have been studied using linear approximation to the tight-binding model in graphene, and by going beyond linear approximation, we improve all these applications of graphene. ...
We study the $f(Q, T)$ gravity in the framework of Weyl geometry (known as Weyl-type $f(Q, T)$ gravity), where $Q$ denotes the non-metricity scalar, and $T$ denotes the energy-momentum tensor trace. In this work, we consider the $f(Q,T)$ model, which is defined as $f(Q,T)=\alpha Q^{m+1}+\frac{\beta}{6\kappa^2}T$ and investigating two scenarios: $(I)$ $m=0$ (linear model) and $(II)$ $m\neq 0$ (nonlinear model). For both scenarios, we find the explicit solution for the field equations by using the barotropic equation of state as $p=\omega\rho$, where $\omega$ is the equation-of-state (EoS) parameter. Further, we study the obtained solutions statistically using the $Pantheon^+$ dataset with 1701 data points. For both models, the best-fit values of model parameters for $1-\sigma$ and $2-\sigma$ confidence level are mentioned in table 1 and 2. We statistically compare our models to the $\Lambda$CDM model using ${{\chi}^2_{min}}$, ${{\chi}^2_{red}}$, $AIC$ and $\Delta AIC$. We also examined the current values of cosmological parameters such as deceleration and EoS parameters to determine the current acceleration expansion of the universe. Furthermore, we test our model using $Om$ diagnostic and compare it to the $\Lambda$CDM model to determine its dark energy profile. Finally, we draw the conclusion that, statistically speaking, Weyl $f(Q,T)$ model I (linear model) is more compatible with the $\Lambda$CDM model than Weyl $f(Q,T)$ model II (nonlinear model).
... Quantum graphity is a model of quantum gravity, where spacetime is made up of discrete lattice, and this is based on the analogy with condensed matter systems like graphene [5,6]. Like graphene, at large distance the Planck scale latter can be approximated using continuum field theories like Dirac equation [7][8][9], it is proposed that spacetime at large distances scales is a continuum in quantum graphity [10,11]. The mean field theory has been used to study the properties of spacetime described by quantum graphity at low temperature [12]. ...
... Additionally, materials based on graphene exhibit exceptional physical and chemical characteristics, including a high surface area (2630m 2 /g) [90,91], excellent electrical conductivity (1738siemens/m) [90,92], strong mechanical strength (about 1100GP a) [90], unparalleled thermal conductivity (5000W/m/K) [90], ultra-high charge carrier mobility and a linear dispersion band structure [93]. Due to these unique properties, graphene is considered a promising subject of research in several fields, including biomedical [90] and biotechnology [94], chemistry and catalysis [95], energy technology and environment [96], nanoscience [9,93]. These have been studied using linear approximation to the tight-binding model in graphene, and by going beyond linear approximation, we improve all these applications of graphene. ...
In this letter, we analyze low energy implications of discrete spacetime, which is motivated from quantum gravity. We first investigate the effects of leading order Planckian lattice corrections on the deformation of the low energy effective Heisenberg algebra. Then we study the corrections to such an algebra from higher order Planckian lattice corrections. These include quantum gravitational terms, which break the rotational symmetry. Finally, we propose a similar deformation of the covariant form of the Heisenberg algebra using a four dimensional Euclidean lattice.
... It is used in a myriad of applications, for example, electronics, sensors, energy storage, biomedical devices, etc [6][7][8][9][10]. Graphene emerges among other materials because of its unique electronic properties, including its massless Dirac fermions, quantum Hall effect with half-integer, Klein paradox, and ultrahigh carrier mobility [2,3,[11][12][13]. These properties are assigned to the linear band dispersion near the Fermi level at the Dirac points. ...
This study investigates the structural, optical, and electronic properties of multilayer carbon (C) and boron nitride (BN) corographene structures using first-principles calculations. The results confirm that these sheets, kept together through van der Waals forces, are energetically favorable and thermally stable. Mono-, bi-, and tri-layer C corographene sheets display semiconducting behavior, while the multilayer BN corographene sheets are insulators. Controlling the band gap can be achieved by increasing the number of layers. The optical characteristics of the sheets are anisotropic when applying electric fields polarized perpendicular or parallel to the sheets. They exhibit a high constant of static dielectric, as well as optical absorption with optical conductivity that increases according to the increase in the number of layers. The reflection and transmission constants showed that multilayer C and BN corographene sheets exhibit transparency, especially in the high-energy range. These findings suggest promising capabilities of C and BN corographene sheets for use in optoelectronic devices.
... 6,7 From a theoretical point of view, the study of electronic transport in graphene-based materials could trigger ongoing progress in the physics of this two-dimensional material. 8 Application of graphene-based materials for electrochemical sensing offers advantages such as high sensitivity, rapid response time, and accelerated electron transfer. Before we came across the stepwise current at room temperature, we planned on decorating noble metallic (gold or silver) nanoparticles on GF to be applied as SERS substrates 6,7 and highly sensitive electrodes. ...
In this work, we report a new phenomenon in electrochemical systems whereby uniform current steps of 1 mA per 0.5 × 0.5 × 0.1 cm3 (width × width × depth) of electrode volume occurred during the electrodeposition of gold and silver nanoparticles onto 3D microporous graphene on nickel layers (GF/Ni) at room temperature. The effect was exhibited only at specific applied electrical potentials. The experiments (magnetic interference, temperature dependence, and surface area dependence) were repeated, and the results were reproducible. Finally, we proposed classical electrochemical theory using the Butler–Volmer equation and quantum theory using the Landauer formalism to describe this new effect. Both theories could be used to explain the experimental results: temperature dependence, surface area dependence, blocking effects, and external magnetic field dependence. In addition, the stepwise current presented in this work facilitates the trapping and supplying of a large amount of electric charge via an inherent magnetic field in a sharp time step (∼1 s). A video clip of the recorded effect can be found at https://youtu.be/pPJh45w1sUQ.
... Various graphene structures viz., graphene quantum dots (o-dimension) [1,2], graphene nanoribbon (1-dimension) [3], and graphene nanosheet (2-dimension) [4,5] possess several unique features. For example, its electron mobility and conductivity are found to be high compared to any conductors, say copper [6,7]; its thermal conductivity is better than diamond [8]; it has high transmission coefficient of 97.7% [9,10] and large surface area of 2630 m 2 /gram [11,12]. ...
We report the synthesis of CeO2-rGO nanocomposites by hydrothermal method for display and forensic applications. The prepared CeO2/rGO nanocomposites were subjected to powder X-ray diffraction (PXRD), Scanning Electron Microscopy (SEM), Field Emission Scanning Electron Microscopy, UV–Visible spectroscopic analysis, Photoluminescence study (PL), and Fourier-transform infrared analysis (FTIR). The PXRD image reveals cubic in structure. The SEM image reveals spherical structure of nanocomposites. The energy bandgap of nanocomposites is found to be 2.94 eV using optical absorption study. FTIR spectroscopy analysis showed the purity of synthesized specimens.The PL of nanocomposites shows three prominent emission peaks at 425, 512, and 594 nm. The observed Commission Internationale de I’Eclairage (CIE) results were found to be near white region. The charge-transfer kinetics were investigated through electrochemical impedance spectroscopy. A CeO2-rGO composite was found to be a substitute to luminescent powder for protected discovery and subjective improvement of latent fingerprints kept onto glassplate.
... This two-dimensional material constitutes a flat structure with six carbon (C) atoms situated at the hexagon vertices. Owing to the exceptional attributes of graphene, such as superior electrical and thermal conductivity, remarkable durability and ultra-lightweight characteristics, it has found extensive application across domains including energy storage, sensors, transistors, biomedicine and various other sectors [1][2][3][4][5]. Presenting strong contenders to graphene are germanene (Ge) [6][7][8][9] and silicene (Si) [10][11][12][13], promising to unlock myriad potential applications in the future. ...
Research into nanomaterials yields numerous exceptional applications in contemporary science and technology. The subject of this investigation is a one-dimensional nanostructure, six atoms wide, featuring hydrogen-functionalized edges. The theoretical foundation of this study relies on Density Functional Theory (DFT) and is executed through the utilization of the Vienna Ab initio Simulation Package (VASP). The outcomes demonstrate the stability of adsorption configurations, along with the preservation of a hexagonal honeycomb lattice. The pristine configuration, characterized by a wide bandgap, is well-suited for optoelectronic applications, whereas adsorption configurations find their application in gas sensing. Nitrogen (N) adsorption transforms the semiconducting system into a semimetallic one, with the spin-up state showing semiconductor characteristics and the spin-down state exhibiting metallic attributes. The intricate multi-orbital hybridization is explored through the analysis of partial states. While the pristine system remains non-magnetic, N adsorption introduces a magnetic moment of 0.588 μB. The examination of charge density differences indicates a significant charge transfer from N to the CGe substrate surface. Optical properties are systematically investigated, encompassing the dielectric function, absorption coefficient and electron–hole density. Notably, the real part of the dielectric function exhibits negative values, a result that holds promise for future communication applications.
... Table 1. The linear dispersion (E) relation of graphene is expressed in Eq. (9) [32], [33]. ...
Understanding the atomic behaviour of pure graphene is crucial in manipulating its properties for achieving optoelectronics with high absorption indexes and efficiencies. However, previous research employing the DFT approach emphasised its zero-band gap nature, not its unique optical properties. Therefore, this study employed ab initio calculations to revisit the electronic, magnetic, and optical properties of pristine graphene using the WIEN2K code. The results reveal that the PBE-GGA valence and conduction bands cross at -0.7 eV. Our calculations demonstrated that the absorption coefficient of graphene has the strongest light penetration in the parallel direction. Furthermore, our results not only present the best possible propagation of light in pure graphene but also reveal that the linear relationship between the formation of the free electron carriers and the energy absorption is responsible for the high optical conductivity observed in pure graphene, as indicated by the peaks. Lastly, the metallic properties of graphene are reflected by the variation in spin up and down that appears, as evidenced by the total and partial densities of states, and the large refractive index attributed to its high electron mobility confirms its metallic nature.
... Fortunately, recent advances in materials science have led to the emergence of novel materials that break away from these limitations. Graphene, a two-dimensional material with properties intermediate between metals and dielectrics, exhibits high electron mobility and unique doping possibilities [27][28][29]. Its optical properties can be easily altered by an external bias voltage due to its high electrical conductivity [30,31]. ...
We investigate the Goos-Hänchen (GH) shift in a hyperbolic metamaterial (GHMM) comprising graphene and vanadium dioxide (VO 2 ) as the dielectric. Our study reveals that the dispersion type of GHMM can be controlled via Fermi energy of graphene and temperature, modulating wavelength intervals. Notably, the GH shift in type I dispersion surpasses that in elliptical and type II dispersions. This suggests GH shift control by altering dispersion in GHMM. Thickness variations in VO 2 and the number of graphene/VO 2 layers minimally affect GH shift. In contrast, graphene thickness significantly impacts GH shift, with thicker graphene yielding minor shifts. Meanwhile, we discover that substantial GH shift enhancement by surface plasmon resonance (SPR) excitation, with sensitivity to refractive index changes in the sensing layer. Based on the above conclusions, we theoretically propose a highly tunable biosensor uniting GHMM with SPR and use it to distinguish normal cells from cancer cells. This work advances optical biosensors and precise physical quantity measurements.
... Graphene, as an additive, has superior mechanical properties, excellent lubricating properties, and electrical conductivity. [33][34][35][36] Therefore, graphene is considered a high-quality, conductive lubricating additive. However, studies have demonstrated that during friction, graphene alone is prone to puckering and produces disordered accumulation at the friction interface owing to its insufficient interfacial adsorption capacity, significantly affecting its function. ...
Herein, improving the conductivity of the lubricant itself is the main idea behind current‐conductive lubricant designs. However, as per previous studies, the interface state has a more dominant influence on the interface conductivity than the conductivity of the lubricant. Therefore, improving the interface state is a more direct and effective way to improve the interface conductivity. In this study, improving the interface state is the primary idea underlying the design of a conductive lubricant. Multilayer graphene/ionic liquid (MG/IL) composites with excellent interfacial adsorption properties are prepared using IL non‐covalently modified graphene. Subsequently, corresponding conductive greases are synthesized using MG, IL, and MG/IL as additives. The lubricating and conductive properties of these greases are characterized by performing current‐carrying friction tests. In the results, it is shown that when MG/IL is used as an additive, the grease exhibits excellent lubricating performance and the lowest average contact resistance. This finding is primarily attributed to the MG and IL in MG/IL acting synergistically to improve the interface state significantly, which decreases the contact resistance and increases the conductivity of the friction interface. In this work, a novel idea is provided for the design of conductive lubricants.
... Among conductive inorganic fillers, graphene oxide (GO) has been paid enormous attention because of distinguished properties such as low density, large surface area, high modulus, high electrical and thermal conductivity [20][21][22]. Furthermore, GO contains functional groups such as hydroxyl, carbonyl, carboxyl, etc., which may interact with functional groups of the cellulose hydrogel to prevent the aggregation of GO. ...
An attempt to prepare a conductive hydrogel from recyclable and renewable resource as wastepaper was made. The suspension of a laboratory-made graphene oxide (GO) was introduced to the wastepaper paste. The preparation of hydrogel from the GO suspension/wastepaper mixture was performed in the presence of ammonium persulfate (APS) as the initiator, acrylic acid (AA) as the monomer, and N, N′-methylenebisacrylamide (MBA) as the crosslinking agent. The structural and morphological characterization of cellulose/GO hydrogel were carried out through Fourier-transform infrared spectroscopy and focused ion beam scanning electron microscopy. The properties of the material were characterized through the swelling degree, thermogravimetric analysis, differential scanning calorimetry, electrical conductivity, and mechanical properties. The effect of GO content on the properties of the materials was investigated. The results indicated that the hydrogel based on wastepaper and GO exhibited unique swelling, mechanical, thermal and electrical properties. The chemical linkage formed by GO and cellulose hydrogel may play an important role to improve properties of the hydrogel. It was found that the hydrogel achieved the outstanding properties when the GO content was 1.6 g/kg cellulose in the presence of 1.0 g APS/kg cellulose, 1.6 g AA/kg cellulose, and 0.2 g MBA/kg cellulose. In this condition, the thermal resistance of the obtained material was the best. The Young’s modulus, tensile strength, elongation at break, Charpy impact of the obtained material was 7.3 MPa, 12.3 MPa, 411.1 5 and 10.2 kJ/m², respectively. The best electrical conductivity was 0.013 S/cm. The material may be suitable for the application in flexible electronics field.
... Two-dimensional materials with a hexagonal structure of group-IV elements have been studied intensively due to their potential applicability in different devices [1][2][3][4]. Some types of these 2D materials are very prominent, such as graphene [5][6][7][8], silicene [9][10][11], and germanene [12,13]. In addition, 2D materials containing atoms of different elements also attract much attention. ...
Formation of two-dimensional (2D) crystalline silicon carbide (SiC) from the melt is studied using molecular dynamics (MD) simulations. Model containing 11040 atoms interacted via the Vashishta interaction potential is cooled from 4500 to 300 K to investigate the change in structure and thermodynamic properties. We find evidence that crystallization of 2D SiC from the melt undergoes over some stages as follows. At temperature high enough, liquid 2D SiC exhibits the chain-like structure and further cooling leads to the formation of 2D SiC liquid with the ring-like structure. After that massive occurrence/growth of solid-like atoms occurs in the system leading to the formation of 2D SiC with a honeycomb structure. Moreover, out-of-plane displacements of atoms in the SiC nanoribbons at the selected temperatures are found and discussed.
Graphical abstract
... Since the discovery of graphene in 2004, there is a rapid growth of interest in graphene and analogous 2D materials due to their remarkable properties (Ref [1][2][3][4]. 2D layered materials like hBN attained enormous attention owing to their very high thermal conductivity, mechanical properties and non-toxic and non-reactive chemical stabilities. Boron nitride nanosheets (BNNSs) are one of the important class of materials with a wide range of applications spanning from automotive, aero-space, healthcare and medicine and energy storage ( . ...
Large-scale synthesis of hexagonal boron nitride (hBN) by a liquid exfoliation technique has been demonstrated in the present study. It is a low-cost and efficient method for exfoliating 2D materials like hBN. Here, a two-step approach was acquired to exfoliate the bulk hBN. In the first step, the bulk hBN was dispersed using a probe sonicator in a solution of gelatin, potassium chloride (KCl) and zinc chloride (ZnCl2), and in the second step, further exfoliation was achieved by centrifugation process. Exfoliation was achieved by both centrifugation and intercalation of Zn2+ and K+ ions within the layers of hBN. The supernatant obtained after centrifugation was heated to 600 °C for a duration of 1 h in an air atmosphere to eliminate the gelatin which was again heat treated for the same duration at 800 °C in an Ar atmosphere to improve its crystallinity. The hBN nanoplatelets obtained from the bulk hBN were characterized using various analytical techniques such as x-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), differential scanning calorimetry and thermogravimetric analysis (DSC/TGA) and atomic force microscopy (AFM) to determine their properties. The hBN nanoplatelets showed a thickness range of ~ 50-270 nm and a lateral dimension range of ~ 1-3 μm. FTIR analysis confirmed the presence of hydroxyl (OH) functional group attached to the hBN nanoplatelets due to the absorption of surface moisture. The hBN nanoplatelets showed excellent thermal stability up to a temperature of ~ 726.16 °C. The liquid exfoliation approach used in the present work was found to be a highly effective method and shows potential for producing hBN nanoplatelets with a few layers.
... 2D-CN materials are now subjects of extensive study across physics, chemistry, and materials science due to their exceptional properties. However, inherent weaknesses in these nanostructures, such as graphene's lack of band gap [18], silicene's instability [19] and MoS 2 's limited mobility [20], can hinder their utility in gas sensing applications. To address these limitations, researchers have embarked on a quest to discover 2D materials possessing optimal physical and chemical characteristics to enhance gas-sensing performance [21]. ...
The absorption properties of molecules NOx onto C6N8 monolayer were researched thoroughly with density functional theory (DFT) calculations. Detailed MEP, FMO, and reactivity analysis on C6N8 cluster have shown that NO2 and NO were successfully adsorbed onto the C6N8 monolayer with considerable amount of adsorption energy and charge transfer. The electric conductivity of the C6N8 monolayer significantly increased due to the adsorption of the NO2 and NO, resulting in the semiconducting behavior of the material being turned into conducting behavior. It has been established that the absorption rate of NO2 and NO onto the C6N8 nano-cluster is moderate, making their desorption fairly simple, indicating potential in terms of C6N8 sensor's reusability. Hence, C6N8 monolayer could be a promising candidate for sensing NO and NO2, which can be validated through further experimental studies.
... Graphene sheets with inimitable thermal [69], electronic [63], and strong mechanical properties [52] have wide applications; for example, they are used for making lithium-ion batteries, flexible supercapacitors, transistors, photodetectors, flexible displays for devices, a variety of sensors, and corrosion resistance coatings. ...
Plastic plays a significant role in most sectors of the economy. Its widespread applicability leads to its massive scale production and alarming consumption rates, positioning it as the primary pollutant and ecological toxin. In addition, this plastic waste takes hundreds of years to degrade, threatening global biodiversity. To mitigate this burning issue, the nanotechnological approach offers a plethora of methods that can be harnessed to effectively manage waste plastic. One prominent approach involves creation of value-added nanomaterials like graphene sheets, CNTs, carbon spheres, and nanocomposites through a range of meticulously designed physical and chemical treatments (constructive approach). Another eco-friendly approach highlighted in this review revolves around the augmentation of plastic waste degradation through synergistic action of microbes and nanoparticles (degradative approach). Such nanotechnological innovations could be a milestone toward sustainable environmental practices offering economic and green solutions. This review article presents a framework for managing plastic waste through current nanotechnological interventions with special emphasis on its role in the circular economy. The approaches discussed in this review are in line with the SDG-2030 goal of stepping toward environmental sustainability.
Graphical abstract
... Furthermore, graphene holds tremendous potential as a future nanoelectronic system, making it a highly intriguing material for next-generation technologies [12,13]. Its unique physical characteristics and two-dimensional honeycomb lattice structure grant it special electronic properties [14,15]. Graphene exhibits a property where its electrons have an extended spin relaxation time [16], resulting in the stability of their spin state over prolonged periods [17,18]. ...
This research delves into the influence of intrinsic decoherence on the behavior of quantum correlations and coherence between two interacting qubits in a graphene-based system. To evaluate the amount of non-classical correlations in the system, we employ local quantum uncertainty (LQU), and to assess quantum coherence we use the relative entropy of coherence (C_r) and l1-norm (C_l1). We assume that the system is initially prepared in an Extended-Werner-Like (EWL) state, and we investigate how these quantifiers evolve over time and examine their sensitivity to various graphene layer system parameters, the mixture parameter of the initial state, and the intrinsic decoherence rate. Our results indicate that by adjusting the wave number operators, decreasing the intrinsic decoherence rate, and increasing the initial state mixing parameter, it is possible to enhance both quantum correlations and coherence within the two-dimensional honeycomb lattice system. In addition, we found that quantum coherence is more resilient to intrinsic decoherence than local quantum uncertainty; moreover, the l 1-norm is more robust than the relative entropy of coherence.
... In the framework of the development and application of advanced materials, increasing attention was devoted to 2D materials, especially to graphene, thanks to its distinctive band structure and extraordinary physical properties: strong mechanical strength, lightness, flexibility, stable chemical properties, impermeability, excellent thermal, and electrical conductivity [1][2][3][4]. In fact, since the discovery of the first mechanically exfoliated graphene layers, by Geim and coworkers [5], many research groups have been competing in using graphene and its derivatives for a wide range of applications such as in electronics, in the food industry, for energy storage, and in the biotechnology field [6][7][8][9][10][11][12]. ...
Understanding and regulating DNA interactions with solvents and redox-active centers opens up new possibilities for improving electrochemical signals and developing adequate biosensors. This work reports the development of a modified indium tin oxide (ITO) electrode by chemical vapor deposition (CVD) of graphene for the detection of double-stranded DNA. The modified electrode shows a better electrical conductivity than ITO, as confirmed by electrochemical impedance spectroscopy (EIS), where a drastic decrease in the charge–transfer resistance, Rct, from ~320 to ~60 Ω was observed. Sequences of double-stranded genomic DNA with a different number of base pairs are evaluated through differential pulse voltammetry (DPV), using ferri/ferrocyanide ([Fe(CN)6]3−/4−) as a mediator in the solution. Variations in the electrochemical response of the [Fe(CN)6]3−/4− probe are observed after introducing redox inactive double-stranded DNA ions. The redox-active [Fe(CN)6]3−/4− probe serves as a scaffold to bring DNA into the graphene-modified ITO electrode surface, provoking an increase in the current and a change in the potential when the number of base pairs increases. These results are confirmed by EIS, which shows a variation in the Rct. The calibration of DPV intensity and Rct vs. DNA base pairs (bps) number were linear in the 495–607 bps range. The proposed method could replace the nucleic acid gel electrophoresis technique to determine the presence of a DNA fragment and quantify its size.
... Thus, the crystal's Fermi surface degenerates into a single point of the electronic band structure [1,2]. Such a degeneracy enables us to tune the density of electronic states at E F , as well as the system's electrical and thermal conductivity, via external electric fields or tunable doping, which leads the carrier density to increase by orders of magnitude upon small fluctuations of E F [14,15]. These Fermi-level shifts are also expected to dramatically alter the strength of the interaction between charge carriers and lattice phonons [16,17], which may have profound effects on the applicability of the Born-Oppenheimer approximation, leading to highly specific dielectric properties from electrons strongly correlated with acoustic phonons in 2D Dirac crystals [18][19][20]. ...
The unique structure of two-dimensional (2D) Dirac crystals, with electronic bands linear in the proximity of the Brillouin-zone boundary and the Fermi energy, creates anomalous situations where small Fermi-energy perturbations critically affect the electron-related lattice properties of the system. The Fermi-surface nesting (FSN) conditions determining such effects via electron–phonon interaction require accurate estimates of the crystal’s response function ( χ ) as a function of the phonon wavevector q for any values of temperature, as well as realistic hypotheses on the nature of the phonons involved. Numerous analytical estimates of χ ( q ) for 2D Dirac crystals beyond the Thomas–Fermi approximation have been so far carried out only in terms of dielectric response function χ ( q , ω ) , for photon and optical-phonon perturbations, due to relative ease of incorporating a q -independent oscillation frequency ( ω ) in calculation. Models accounting for Dirac-electron interaction with acoustic phonons, for which ω is linear to q and is therefore dispersive, are essential to understand many critical crystal properties, including electrical and thermal transport. The lack of such models has often led to the assumption that the dielectric response function χ ( q ) in these systems can be understood from free-electron behavior. Here, we show that, different from free-electron systems, χ ( q ) calculated for acoustic phonons in 2D Dirac crystals using the Lindhard model, exhibits a cuspidal point at the FSN condition. Strong variability of ∂ χ ∂ q persists also at finite temperatures, while χ ( q ) tend to infinity in the dynamic case where the speed of sound is small, albeit non negligible, over the Dirac-electron Fermi velocity. The implications of our findings for electron-acoustic phonon interaction and transport properties such as the phonon line width derived from the phonon self-energy will also be discussed.
... Now attention is paid to the study of quantum, low-dimensional, and topological materials [13][14][15][16] successfully used in electronic [17] and optical [18] spintronic devices. A number of low-dimensional materials like graphene [19], nitrides [20], and chalcogenides (-Hal) [21] exhibit unique properties prospective for applications in spintronics. Just recently a family of low-dimensional materials is replenished by MXenes [22], i.e., 2D transition metal carbides and nitrides [23]. ...
... Boasting high strength, exceptional conductivity, elevated carrier mobility (2 × 10 5 cm 2 /V·s) for monolayer graphene, a bandgap of zero, broad spectral response, and limited surface dangling bonds, it has garnered significant attention in the field of photonics [14][15][16][17][18][19]. The exceptional properties of graphene make it well-suited for use in visible light, infrared, and THz frequency regimes, offering high-sensitivity detection capabilities [20][21][22]. Additionally, the small electron heat capacity of graphene leads to a substantial temperature change and elevated photocurrent upon absorbing the same amount of heat. ...
Graphene, known for its high carrier mobility and broad spectral response range, has proven to be a promising material in photodetection applications. However, its high dark current has limited its application as a high-sensitivity photodetector at room temperature, particularly for the detection of low-energy photons. Our research proposes a new approach for overcoming this challenge by designing lattice antennas with an asymmetric structure for use in combination with high-quality monolayers of graphene. This configuration is capable of sensitive detection of low-energy photons. The results show that the graphene terahertz detector-based microstructure antenna has a responsivity of 29 V·W−1 at 0.12 THz, a fast response time of 7 μs, and a noise equivalent power of less than 8.5 pW/Hz1/2. These results provide a new strategy for the development of graphene array-based room-temperature terahertz photodetectors.
... However, graphene has a gapless band structure, and the total absorption and quantum efficiency are still poor. Therefore, for graphene to realize its potential a sizeable band gap must be created to enhance the optical properties for application in electronic devices with optimized stability and performance while widening the scope for novel electronic designs [67][68][69][70][71]. ...
Graphene has received tremendous attention among diverse 2D materials because of its remarkable properties. Its emergence over the last two decades gave a new and distinct dynamic to the study of materials, with several research projects focusing on exploiting its intrinsic properties for optoelectronic devices. This review provides a comprehensive overview of several published articles based on density functional theory and recently introduced machine learning approaches applied to study the electronic and optical properties of graphene. A comprehensive catalogue of the bond lengths, band gaps, and formation energies of various doped graphene systems that determine thermodynamic stability was reported in the literature. In these studies, the peculiarity of the obtained results reported is consequent on the nature and type of the dopants, the choice of the XC functionals, the basis set, and the wrong input parameters. The different density functional theory models, as well as the strengths and uncertainties of the ML potentials employed in the machine learning approach to enhance the prediction models for graphene, were elucidated. Lastly, the thermal properties, modelling of graphene heterostructures, the su-perconducting behaviour of graphene, and optimization of the DFT models are grey areas that future studies should explore in enhancing its unique potential. Therefore, the identified future trends and knowledge gaps have a prospect in both academia and industry to design future and reliable optoelectronic devices.
... Graphene, as a truly independent two-dimensional material realized for the first time, has created many new research directions. Due to the unique electronic and thermal transport properties, it has been widely concerned by many scientific disciplines and technical application fields since its discovery [1][2][3]. In addition, graphene also shows extremely high thermal conductivity (> 2000 W·mK −1 ) at room temperature, which is dominated by phonons [4][5][6]. ...
Based on the first-principles calculations of the phonon Boltzmann transport equation (pBTE) under the framework of the three-phonon scattering theory, we characterized the temperature and size dependence of the lattice thermal conductivity of monolayer silicene under the tensile strain. Our research shows that the lattice thermal conductivity of silicene has obvious strain dependence, and demonstrates the great potential of thermal management by applying strain in silicene. The TA phonon mode contributes the most to the thermal conductivity of silicene, while the contribution of the ZA phonon is suppressed. With the increase in tensile strain, the contribution of LA mode phonons to the thermal conductivity increases rapidly, and eventually become the dominant phonon mode of the silicene lattice thermal conductivity. We suspect that this phenomenon is caused by the reduction of the warpage of the silicene and the restoration of the crystal symmetry due to the tensile strain. When the characteristic size is less than 10 nm, the lattice thermal conductivity of silicene is no longer sensitive to temperature, and with the increase in tensile strain, the effective phonon mean free path (MFP) of silicene also increases, and the size effect is more obvious. The characterization of the scattering channel reveals its significant influence on the characteristics of thermal transport capacity of different phonon modes. These findings deepen the understanding of the phonon dynamics of the monolayer silicene-like structure, and provide the reference and theoretical basis for the research on the heat management of the corresponding material combined with strain and size and the development of thermal management technology.
... But graphene wasn't considered as an alternative for existing silicon based semiconducting materials because of its instability and rolling over tendency. With the repetition of exfoliation, mechanically, with a scotch tape on a highly ordered pyrolytic graphite (HOPG), a single atomic-layer of carbon was separated and deposited on a silicon dioxide substrate (Figure 3a) [21,22]. This top-down process is capable of producing graphene sheets of different thicknesses as necessary. ...
Graphene, ostensibly the strongest material to date, has been a topic of interest for engineers, scientists and researchers since its first isolation through mechanical exfoliation through forming mechanical cleavage of a graphite. The thickness of the sp2 hybridized carbon framework is only one atomic layer. The unique physical, electrochemical and optical properties, such as room temperature hall effect, large surface area, and excellent electrical conductivity caused from high electron mobility, make graphene become an attractive material in the fields of nanoelectronics, biosensing, biomedical engineering and related applications. The high demand of this material has led to the development of many synthesis methods and different characterization methods, and towards ensuring lower defects, high quality and large-scale production. In this paper, a comprehensive overlook of the electronic, physical and optical characteristics of graphene, synthesis methods, characterization techniques, and integration level applications are reviewed with solely focusing on pristine graphene.
... Further, these NR are classified as bare and pristine (passivated by hydrogen (H) on both the edges). The bare zigzag SiC nanoribbons (ZSiCNR) are found to be metallic due to the presence of dangling bonds at the edges, whereas the pristine is found to be semiconducting due to the passivation of dangling bonds at the edges [37,49] be semiconducting in bare and pristine case [50,51]. The electronic properties of SiCNR have been reported in the first principles study [39,52]. ...
Nanoribbons with different edge functionalization display interesting electronic properties for various device applications. It requires the necessity of exploring the novel passivating elements commensurate to various technological applications. In this direction, here we have compared the effect of H and F-passivation on the edges of zigzag SiC nanoribbons (ZSiCNR) using density functional theory based calculations. Remarkably, present study reveals that F could be used as an effective passivating element for ZSiCNR similar to widely explored H-passivations. Various possible combinations of F/H are found to have stable structural integrity for practical applications. The effect of F-adatom adsorption is also discussed which present peculiar electronic properties. The half-metallic behavior is observed to be realized via F-adsoprtion which is further confirmed with the transport calculations. The obtained negative differential resistance along the spin dependent electron transport pledges towards wide spread applications of considered ZSiCNR interacting with F.
... The two graphene conduction and valence bands touch each other at two asymmetric points noted (K, K ) are called Dirac points. In the vicinity of these Dirac points, the energy dispersion is linear, which is the origin of graphene's unique electronic properties like high electrical conductivity [5,8]. At normal incidence, the electrons transmit completely, which is due to a Klein tunneling effect, and it is therefore difficult to control them with external fields in the graphene [9][10][11]. ...
Understanding the numerous crucial properties of Dirac crystals, such as their thermal conductivity, necessitates the use of models that consider the interaction between Dirac electrons and persistent acoustic phonons in which the oscillation frequency ω depends on the phonon wave vector q and is therefore dispersive. It is commonly assumed that the exceptionally high thermal conductivity of two-dimensional (2D) Dirac crystals is due to the near ideality of their phonon quantum gasses with undesired limitations originating from phenomena such as electron-phonon (e-ph) interactions. Electrons transferred to Dirac crystals from metal nanoparticles through doping have been shown to affect and limit the thermal conductivity of Dirac crystals due to e-ph interactions at distances up to several microns from the nanoparticle. Notably, the e-ph thermal conductivity is directly linked to the phonon scattering rate, demonstrating a proportional relationship. Customarily, when calculating the phonon scattering rate, it is common to overlook phonons with short-dispersive wavelengths since in metals q is significantly smaller than the Fermi surface dimensions. However, this approach proves insufficient for analyzing 2D Dirac crystals. Furthermore, the in-plane phonon scattering rate is calculated up to the first order of magnitude consisting of two electrons and one phonon, i.e., three-particle interaction. In these calculations, only processes involving the decay of an electron and phonon, leading to the creation of a new electron (EP-E*), are considered. However, processes that involve the decay of an electron and the creation of a new electron and phonon (E-E*P*) are not taken into consideration. In this paper, we present an accurate expression for the phonon scattering rate and the e-ph thermal conductivity in 2D Dirac crystals for in-plane phonons considering phonons with short-dispersive wavelengths. We further demonstrate that even at room temperature, when calculating the phonon scattering rate and e-ph thermal conductivity, in the case of first-order e-ph interactions, the E-E*P* process assumes significance. In the end, we show the importance of incorporating second-order e-ph interactions, particularly the (EP-E*P*) interaction involving the decay of an electron and phonon and the creation of a new pair for in-plane phonons, when determining the phonon scattering rate and e-ph thermal conductivity at high temperatures and low Fermi energies. This four-particle interaction process proves significant in accurately characterizing these properties.
This study examines the operational parameters of field-effect transistors (FETs) using single-gate (SG) and double-gate (DG) graphene nanoribbons (GNRs) within the analog/RF domain. A detailed exploration is conducted through an atomistic pz orbital model, derived from the Hamiltonian of graphene nanoribbons, employing the nonequilibrium Green’s function formalism (NEGF) for analysis. The atomic characteristics of the GNRFETs channel are accurately described by utilizing a tight-binding Hamiltonian with an atomistic pz orbital basis set. The primary focus of the analysis revolves around essential analog/RF parameters such as transconductance, transconductance generation factor (TGF), output resistance, early voltage, intrinsic gain, gate capacitance, cut-off frequency, and transit time. Furthermore, the study assesses the gain frequency product (GFP), transfer frequency product (TFP), and gain transfer frequency product (GTFP) to evaluate the balance between transistor efficiency, gain, and cut-off frequency. The research outcomes indicate that double-gate GNRFETs exhibit superior analog/RF performance in comparison to their single-gate counterparts. However, both types of devices demonstrate cut-off frequencies in the gigahertz range. The extensive data presented in this study provides valuable insights into the characteristics of SG and DG GNRFETs, particularly in terms of the figure-of-merit (FoM) for analog/RF performance, offering a comprehensive analysis of the trade-offs in analog applications. In addition, the analysis has been extended be performing a high-performance hybrid 6T static random-access memory (SRAM) to get the impact in their circuit level variation as well as improvement in their circuit performance.
The field of modern biosensor development holds immense promise for clinical diagnostic. Projections indicate that the biosensor market will exceed $28 billion by 2024. In recent years, the integration of 2D materials with optical biosensors has emerged as a cutting-edge research area, owing to the unique optical, electrical, electrochemical, and physical properties of 2D materials. These materials offer an exceptionally high density of active sites over large areas, making them highly suitable for biochemical sensing applications. Optical biosensors have numerous advantages over conventional analytical techniques, including real-time, direct, and label-free detection of a wide range of biological and chemical compounds. 2D material-equipped optical biosensors have outperformed conventional sensors in terms of sensitivity and detection limitations. Significant progress has been made in the biomedical and healthcare applications of 2D materials, with research concentrating on biomimicry systems, brain interfaces, wearable technologies, and optogenetics, among other areas. These advancements might transform clinical diagnosis and enhance patient care. The importance of environmentally friendly techniques for the development and use of optical biosensors based on 2D materials is emphasized in this study. This study provides a picture of the current status of the subject and establishes the groundwork for future research endeavors that are in line with ecological responsibility by fusing technology improvements with sustainability considerations.
The unprecedented demand for sophisticated, self-powered, compact, ultrafast, cost-effective,
and broadband light sensors for a myriad of applications has spurred a lot of research, precipitat�ing in a slew of studies over the last decade. Apart from the photosensing ability of an active
element in the light sensor, the device architecture is crucial in terms of photoinduced charge
carrier generation and separation. Since the inception of graphene and the subsequent research
growth in the atomically thin 2D materials, researchers have developed and adapted different
families of 2D materials and device architectures, including single element 2D, 0D/2D, 2D/2D, 1D/
2D stacked structures, and so on. This review discusses the recent reports on the light-sensing
properties of various 2D materials, their heterostructures, and characteristics applicable to the
ultraviolet-near infrared (UV-NIR), short-wave IR (SWIR), mid-wave IR (MWIR), long-wave IR (LWIR),
and terahertz (THz) spectral ranges. It highlights the novelty of the burgeoning field, the height�ened activity at the boundaries of engineering and materials science, particularly in the gener�ation of charge carriers, their separation, and extraction, and the increased understanding of the
underpinning science through modern experimental approaches. Devices based on the simultan�eous effects of the pyro-phototronic effect (PPE) and the localized surface plasmon resonance
(LSPR) effect, the photothermoelectric effect (PTE)-assisted photodetectors (PDs), waveguide-inte�grated silicon-2D PDs, metal-2D-metal PDs, and organic material PDs are examined rigorously.
Theoretical treatment utilizing various computational approaches to investigate 2D materials and
heterostructures for photodetection applications is also briefly discussed. At the end, current
challenges and solutions to enhance the figures of merit of photodetectors are proposed
In recent years, the research on the preparation and categorization of the composites from graphene is increasing widely as graphene has so many interesting properties. The amazing characteristics of graphene occur because of the stretched series of π conjugation that results in high charge mobility, high conductivity, and high Young’s Modulus value. Due to these attractive properties, graphene has gained a lot of attention. Graphene also has some interesting properties in the biomedical field such as drug delivery, tissue engineering, biosensors, etc. The in-vivo and in-vitro study of graphene-based materials is an interesting subject for research. Graphene polymers can also be used for filler matter. These can be classified into two categories—(a) graphene-non-conducting polymer composites; (b) graphene-conducting polymer composites. The nanocomposite of the graphene-based polymer has three morphological states—(a) phase-separated micro composites; (b) intercalated nanocomposites; (c) exfoliated nanocomposites. Various techniques such as sol–gel process, in-situ polymerization, microwave-assisted process, electrochemical processes, etc. are used to prepare the composites of graphene. This chapter highlights some main findings related to graphene polymers that can be used as electrochemical devices and have applications in the fields of coatings, solar cells, light-emitting diodes (LEDs), sports equipment, aircrafts. The development of graphene in the form of nanofiller has been proved as a new source of the production of low-cost and high-performance composites for a wide range of applications.
The interlayer bonding of graphene is a modification method of graphene, which can change the mechanical and conductivity of graphene, but also affect its thermal properties. In this paper, the non-equilibrium molecular dynamics method is used to study the thermal conductivity of bilayer graphene nanoribbon which is local carbon sp³ hybridization (covalent bond formed between layers) under different concentration and angle of interlayer Covalent bond chain and different tensile strain. The mechanism of the change of the thermal conductivity of bilayer graphene nanoribbon is analyzed through the density of phonon states. The results are as follows. The thermal conductivity of bilayer graphene nanoribbon decreases with the increase of the interlayer covalent bond concentration due to the intensification of phonon scattering and the reduction of phonon group velocities and effective phonon mean free path. Moreover, the decrease rate of thermal conductivity depends on the distribution angle of covalent bond chain. With the increase of interlayer covalent bond concentration, when the interlayer covalent bond chain is parallel to the direction of heat flow, the thermal conductivity decreases the slowest because the heat transfer channel along the heat flow direction is gradually affected; when the interlayer covalent bond chain is at an angle to the direction of heat flow, the thermal conductivity decreases more rapidly, and the larger the angle, the faster the thermal conductivity decreases. The rapid decline of thermal conductivity is due to the formation of interfacial thermal resistance at the interlayer covalent bond chain, where strong phonon-interface scattering occurs. In addition, it is found that the thermal conductivity of bilayer graphene nanoribbon with interlayer bonding will be further reduced by tensile strain due to the intensification of phonon scattering and the reduction of phonon group velocities. The results show that the thermal conductivity of bilayer graphene nanoribbon can be controlled by interlayer bonding and tensile strain. These conclusions are of great significance for the design and thermal control of graphene based nanodevices.
Optical modulation and switch are crucial in photonics technologies, and microscope electron sources are essential in imaging. However, it is an obstacle to integrating those devices with conventional techniques. Moreover, they cannot function in ultrafast communication and signal processing systems. The surface plasmon resonance phenomenon is of wide interest due to its abundant physics, such as the local field enhancement enabling strong light-matter interactions, breaking the diffraction limit to realize subwavelength structures, and going beyond the speed limit intrinsic to conventional semiconductor materials and devices. Here, by reviewing the various advantages of surface plasmons in different nanostructures or materials, we intend to propose the development trend and designed configuration of such ultrafast devices (usually induced by ultrafast laser) such as modulators, switches, and microscope electron sources. Based on the surface plasmons, ultrafast devices will tend to be more energy-efficient, low-energy consumption, and miniature. We also envision the development of surface plasmons with alternative materials or structures. This review will facilitate the development of ultrafast devices.
In the present study, a novel and unconventional two‐dimensional (2D) material with Dirac electronic features has been designed using sulflower with the help of density functional theory methods and first principles calculations. This 2D material comprises of hetero atoms (C, S) and belongs to the tetragonal lattice with P4/nmm space group. Scrutiny of the results show that the 2D nanosheet exhibits a nanoporous wave‐like geometrical structure. Quantum molecular dynamics simulations and phonon mode analysis emphasize the dynamical and thermal stability. The novel 2D nanosheet is an auxetic material with an anisotropy in the in‐plane mechanical properties. Both composition and geometrical features are completely different from the conditions necessary for the formation of Dirac cones in graphene. However, the presence of semi‐metallic nature, linear band dispersion relation, massive fermions and massless Dirac fermions are observed in the novel 2D nanosheet. The massless Dirac fermions exhibit highly isotropic Fermi velocities (vf=0.68×10⁶ m/s) along all crystallographic directions. The zero‐band gap semi metallic features of the novel 2D nanosheet are perturbative to the electric field and external strain.
This research delves into the influence of intrinsic decoherence on the behavior of quantum correlations and coherence between two interacting qubits in a graphene-based system. To evaluate the amount of nonclassical correlations in the system, we employ local quantum uncertainty (LQU), and to assess quantum coherence we use the relative entropy of coherence [Formula: see text] and [Formula: see text]-norm [Formula: see text]. We assume that the system is initially prepared in an extended-Werner-like (EWL) state, and we investigate how these quantifiers evolve over time and examine their sensitivity to various graphene layer system parameters, mixture parameter of the initial state and the intrinsic decoherence rate. Our results indicate that by adjusting the wave number operators, decreasing the intrinsic decoherence rate, and increasing the initial state mixing parameter, it is possible to enhance both quantum correlations and coherence within the two-dimensional honeycomb lattice system. In addition, we found that quantum coherence is more resilient to intrinsic decoherence than LQU, moreover, the [Formula: see text]-norm is more robust than the relative entropy of coherence.
Two-dimensional transition metal dichalcogenides (2D-TMDs) have been proposed as novel optoelectronic materials for space applications due to their relatively light weight. MoS2 has been shown to have excellent semiconducting and photonic properties. Although the strong interaction of ionizing gamma radiation with bulk materials has been demonstrated, understanding its effect on atomically thin materials has scarcely been investigated. Here, we report the effect of gamma irradiation on the structural and electronic properties of a monolayer of MoS2. We perform Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) studies of MoS2, before and after gamma ray irradiation with varying doses and density functional theory (DFT) calculations. The Raman spectra and XPS results demonstrate that point defects dominate after the gamma irradiation of MoS2. DFT calculations elucidate the electronic properties of MoS2 before and after irradiation. Our work makes several contributions to the field of 2D materials research. First, our study of the electronic density of states and the electronic properties of a MoS2 monolayer irradiated by gamma rays sheds light on the properties of a MoS2 monolayer under gamma irradiation. Second, our study confirms that point defects are formed as a result of gamma irradiation. And third, our DFT calculations qualitatively suggest that the conductivity of the MoS2 monolayer may increase after gamma irradiation due to the creation of additional defect states.
The objective of this chapter is basically related to preparation process and characterization of emerging two-dimensional materials (2DMs), its fabrication into hetero-structures and application perspectives. 2DMs have capability of replicate infinitely in two directions (i.e., x-y direction) with limited atomic-level thickness at in the third direction (i.e., z-direction). Moreover, the materials dimensionality is the most promising parameters to define desired properties. Over the last decade, an interdisciplinary interest in these unique materials has emerged, because of their unique geometry, physicochemical and optoelectronic properties. 2DMs are promising candidate for electrode materials for widespread application in electrochemical sensors, energy storage, optoelectronics and spintronic etc. For next-generation electronic components, 2DMs offer facile exposure with novel physics due to their reduced dimension. The current chapter has addressed such of many aspects associated with 2DMs. In this regard, authors have been classified the chapter in three sections and are described briefly with relevant literature. In Section 1, a brief introduction, classification and synthetic approaches for 2D materials are addressed. The carbon allotrope i.e., graphene (GR) and beyond GR 2DMs and relevant synthetic methods are explored. Two classical methods; top-down and bottom-up methods are elaborated to prepare different 2DMs and their van der Waals heterostructures (vdWHs). In Section 2, different functionalization or modification methods to ensure feasible chemistry to be a part of components are discussed. Different fabrication approaches for designing vdWHs also summarized along with associated detects. The Section 3, deals with 2DMs characterization methods, special aspects of fabrication of 2DMs oriented electrochemical sensors for potential sensing of foreign species and future prospects are discussed. To monitor low-molecular weight molecules which are released (and/or up-taken) by living cells, an electrochemical sensors (ESs) are a perfect tool. To explore the possibility of 2DMs some of more microscopic techniques are needed to exploit to investigate of 2DMs. The current chapter is explored the latest literature related to 2DMs and their structures, although the area of 2DMs is too much wide. We are unable to cover all aspects associated with 2DMs but has been trying to justify the pros and cons of 2DMs structures based on available e-contents as well as library issue.
Copper (Cu) is the electrical conductor of choice in many categories of electrical wiring, with household and building installation being the major market of this metal. This work demonstrates the coating of Cu wires-with diameters relevant for low-voltage (LV) applications-with graphene. The chemical vapor deposition (CVD) coating process is rapid, safe, scalable, and industrially compatible. Graphene-coated Cu wires display good oxidation resistance and increased electrical conductivity (up to 1% immediately after coating and up to 3% after 24 months), allowing for wire diameter reduction and thus significant savings in wire production costs. Combined spectroscopic and diffraction analysis indicates that the conductivity increase is due to a change in Cu crystallinity induced by the coating process conditions, while electrical testing of aged wires shows that graphene plays a major role in maintaining improved electrical performances over long periods of time. Finally, graphene coating of Cu wires using an ambient-pressure roll-to-roll (R2R) CVD reactor is demonstrated. This enables the in-line production of graphene-coated metallic wires as required for industrial scale-up.
Graphene (G)-plasmonic nanoparticles (NPs) systems have found immense nanoscale applications via utilizing the sensitive optical response of graphene to the photo-induced electrons transferred from attached NPs. These electrons are emitted from the plasmonic metal NPs under the influence of a Localized Surface Plasmon Resonance (LSPR). Here, we first present theoretical investigations of the photoemission electrons in the G-plasmonic NPs system influenced by the LSPR of NPs. A rigorous theoretical approach is used to determine the level of photo-exited electrons and the optimal parameters for achieving a highest photoemission yield. The photoemission of electrons is mainly driven by the surface photoelectric effect in which an electron near the particle surface absorbs photon energy and overcomes the potential barrier at the metal–graphene boundary. For a thorough investigation, we study the effects of the material and geometry of NPs and the intensity of the LSPR field on the rate of photoemission. It is shown that silver nanoparticles combined with graphene are more effective in enhancing light–matter interaction in graphene owing to the lower interfacial energy barrier and higher field enhancement. Finally, we verify that the photo-induced electron density predicted by our calculations is matched with that obtained by combining theoretical and Raman-based experimental results.
For the first time, we report the enhancement of the Raman scattering signal of monolayer graphene films (MGFs) on Cu foils using a single optical microsphere-assisted Raman microscopic (SOMRM) technique. Initially, the Raman scattering spectra of MGF on Cu foil are recorded using the conventional Raman microscopic (CRM) technique, where the excitation laser is directly focused on the MGFs with the help of a different microscopic objective lens. The obtained spectra are observed to consist of only the low-intensity G and 2D bands but not the D band, known as the disorder or defect band. However, the intensity of all three bands is enhanced significantly using the SOMRM technique. Finally, the numerical investigation is performed on the SOMRM technique to understand the origin of the enhancement of the Raman scattering signal of MGF on the Cu substrates. The role of the substrate for MGF and the radius of the microsphere on the enhancement of the Raman scattering signal of MGFs is also investigated numerically in detail.
Graphene nanoribbons (GNRs) are emerging materials inheriting excellent properties from graphene while potentially exhibiting semiconducting behavior. All these features sparked numerous efforts to insert GNRs in nanoelectronics. As a result, synthesis routes with atomic resolution are now a reality. Recently, the rise of heterojunction (HJ) engineering pushed even further the prospects, allowing the blending of different GNRs as building blocks. However, much of the potential behind it remains untouched for some junctions. In this work, the consequences of forming a cove‐type GNR (CGNR) HJ by assembling specimens with borders of different zig‐zag/armchair ratios are explored. The nanoribbons are simulated using the extended two‐dimensional Su–Schrieffer–Heeger model with electron–phonon coupling. The findings show that manipulating the junction creates multiple routes for smooth monotonic gap tuning. Moreover, the changes in the hopping mechanism, mobility, and effective mass are reported leading to variations up to 10 000 cm² V⁻¹ s⁻¹ and 0.425 me. This work reveals a pathway to expand the modularity of CGNRs through smooth control of the charge carrier's properties. Future applications can explore this feature to design devices with highly specific charge transport characteristics. The study also serves as theoretical background, potentially inspiring new tuning strategies in other GNRs.
Nanomaterials with enzyme-like activity (nanozymes) are known to be suitable alternatives for natural enzymes tolerating unfavorable pH and temperature conditions. The enzyme-like activity of CeO2 nanoparticles was already reported and used in electrochemical sensing, where the peroxidase or oxidase-like activities of CeO2 NPs are mainly used. This work aims to justify the role/s that CeO2 may play in electrochemical sensing as a nanozyme and acts as a mediator. To this end, a reduced graphene oxide-CeO2 was prepared and used in two electrochemical sensing configurations. In first configuration, H2O2 reduction was catalyzed at the glassy carbon electrode modified with the rGO-CeO2 nanocomposite (rGO-CeO2 NC). The reduction current obtained upon the presence of H2O2 was attributed to a mediator role having a linear range of 100.0–800.0 µmol L−1 with a limit of detection (LOD) and limit of quantification (LOQ) of 15.9 µmol L−1 and 52.9 µmol L−1, respectively. In another configuration, glucose oxidase was used as a model enzyme with the rGO-CeO2 NC. The oxidation signal obtained upon adding glucose was attributed to the electron-accepting role of the CeO2 NPs. The analytical figures of merit obtained for both configurations indicated their high sensitivity, selectivity, and reproducibility. The linear detection range for the nanozyme-enzyme cascade system was 100.0–800.0 µmol L−1 with a LOD and LOQ of 18.7 µmol L−1 and 62.3 µmol L−1, respectively. Moreover, the flow injection analysis was enabled due to the short response time in analysis with the prepared sensor. The possibility for applying the developed nanozyme in nanozyme-enzyme cascade system in clinical and food analysis for determination of glucose was verified by studying the interference of various compounds similar to glucose in structure and typical drugs taken by diabetic patients.
For the first time, stable aqueous dispersions of polymer-coated graphitic nanoplatelets can be prepared via an exfoliation/in-situ reduction of graphite oxide in the presence of poly(sodium 4-styrenesulfonate).
In this article, we have reviewed the recent progress of the experimental studies on ultra-thin films of graphite and hexagonal boron nitride (h-BN) by using angle-resolved electron spectroscopy together with other techniques. The fundamental properties of these high-quality films are discussed on the basis of the data on dispersion relations of valence electrons, phonon dispersion etc. The interfacial orbital mixing of the -state of the monolayer graphite (MG) with the d states of the reactive substrates is the origin for the phonon softening, expansion of the nearest-neighbour C - C distance, modification of the -band, low work function, and two-dimensional plasmons with high electron density, etc. In the cases of weak mixing at the interface between the MG and relatively inert substrates, the observed properties of the MG are very close to the bulk ones. In contrast to the case for MG, the interfacial interaction between the h-BN monolayer and the substrate is weak.
Monolayer graphite films, or graphene, have quasiparticle excitations that can be described by (2+1)-dimensional Dirac theory. We demonstrate that this produces an unconventional form of the quantized Hall conductivity sigma(xy) = -(2e2/h)(2n+1) with n = 0, 1, ..., which notably distinguishes graphene from other materials where the integer quantum Hall effect was observed. This unconventional quantization is caused by the quantum anomaly of the n=0 Landau level and was discovered in recent experiments on ultrathin graphite films.
When electrons are confined in two-dimensional materials, quantum-mechanically enhanced transport phenomena such as the quantum Hall effect can be observed. Graphene, consisting of an isolated single atomic layer of graphite, is an ideal realization of such a two-dimensional system. However, its behaviour is expected to differ markedly from the well-studied case of quantum wells in conventional semiconductor interfaces. This difference arises from the unique electronic properties of graphene, which exhibits electron-hole degeneracy and vanishing carrier mass near the point of charge neutrality. Indeed, a distinctive half-integer quantum Hall effect has been predicted theoretically, as has the existence of a non-zero Berry's phase (a geometric quantum phase) of the electron wavefunction--a consequence of the exceptional topology of the graphene band structure. Recent advances in micromechanical extraction and fabrication techniques for graphite structures now permit such exotic two-dimensional electron systems to be probed experimentally. Here we report an experimental investigation of magneto-transport in a high-mobility single layer of graphene. Adjusting the chemical potential with the use of the electric field effect, we observe an unusual half-integer quantum Hall effect for both electron and hole carriers in graphene. The relevance of Berry's phase to these experiments is confirmed by magneto-oscillations. In addition to their purely scientific interest, these unusual quantum transport phenomena may lead to new applications in carbon-based electronic and magneto-electronic devices.
Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrödinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.
Graphene is a two-dimensional carbon material with a honeycomb lattice and Dirac-like low-energy excitations. When Zeeman and spin-orbit interactions are neglected, its Landau levels are fourfold degenerate, explaining the 4e(2)/h separation between quantized Hall conductivity values seen in recent experiments. In this Letter we derive a criterion for the occurrence of interaction-driven quantum Hall effects near intermediate integer values of e(2)/h due to charge gaps in broken symmetry states.
We calculate the mode-dependent transmission probability of massless Dirac fermions through an ideal strip of graphene (length L, width W, no impurities or defects) to obtain the conductance and shot noise as a function of Fermi energy. We find that the minimum conductivity of order e2/h at the Dirac point (when the electron and hole excitations are degenerate) is associated with a maximum of the Fano factor (the ratio of noise power and mean current). For short and wide graphene strips the Fano factor at the Dirac point equals 1/3, 3 times smaller than for a Poisson process. This is the same value as for a disordered metal, which is remarkable since the classical dynamics of the Dirac fermions is ballistic.
Graphene is the two-dimensional building block for carbon allotropes of every other dimensionality. We show that its electronic structure is captured in its Raman spectrum that clearly evolves with the number of layers. The D peak second order changes in shape, width, and position for an increasing number of layers, reflecting the change in the electron bands via a double resonant Raman process. The G peak slightly down-shifts. This allows unambiguous, high-throughput, nondestructive identification of graphene layers, which is critically lacking in this emerging research area.
The quantum Hall effect (QHE), one example of a quantum phenomenon that occurs on a truly macroscopic scale, has attracted
intense interest since its discovery in 1980 and has helped elucidate many important aspects of quantum physics. It has also
led to the establishment of a new metrological standard, the resistance quantum. Disappointingly, however, the QHE has been
observed only at liquid-helium temperatures. We show that in graphene, in a single atomic layer of carbon, the QHE can be
measured reliably even at room temperature, which makes possible QHE resistance standards becoming available to a broader
community, outside a few national institutions.
The mechanism of delocalization of two-dimensional Dirac fermions with random mass is investigated, using a superfield representation. Although localization effects are very strong, one fermion component can delocalize due to the spontaneous breaking of a special supersymmetry of the model. The delocalized fermion has a non-singular density of states and is decribed by a diffusion propagator. Supersymmetry is restored if the mean of the random mass is sufficiently large. This is accompanied by a critical boson component. Comment: 4 pages
There are known two distinct types of the integer quantum Hall effect. One is the conventional quantum Hall effect, characteristic of two-dimensional semiconductor systems, and the other is its relativistic counterpart recently observed in graphene, where charge carriers mimic Dirac fermions characterized by Berry's phase pi, which results in a shifted positions of Hall plateaus. Here we report a third type of the integer quantum Hall effect. Charge carriers in bilayer graphene have a parabolic energy spectrum but are chiral and exhibit Berry's phase 2pi affecting their quantum dynamics. The Landau quantization of these fermions results in plateaus in Hall conductivity at standard integer positions but the last (zero-level) plateau is missing. The zero-level anomaly is accompanied by metallic conductivity in the limit of low concentrations and high magnetic fields, in stark contrast to the conventional, insulating behavior in this regime. The revealed chiral fermions have no known analogues and present an intriguing case for quantum-mechanical studies.
It has been recently demonstrated experimentally that graphene, or single-layer carbon, is a gapless semiconductor with massless Dirac energy spectrum. A finite conductivity per channel of order of $e^{2}/h$ in the limit of zero temperature and zero charge carrier density is one of the striking features of this system. Here we analyze this peculiarity based on the Kubo and Landauer formulas. The appearance of a finite conductivity without scattering is shown to be a characteristic property of Dirac chiral fermions in two dimensions.
Two-dimensional carbon, or graphene, is a semi-metal that presents unusual low-energy electronic excitations described in terms of Dirac fermions. We analyze in a self-consistent way the effects of localized (impurities or vacancies) and extended (edges or grain boundaries) defects on the electronic and transport properties of graphene. On the one hand, point defects induce a finite elastic lifetime at low energies with the enhancement of the electronic density of states close to the Fermi level. Localized disorder leads to a universal, disorder independent, electrical conductivity at low temperatures, of the order of the quantum of conductance. The static conductivity increases with temperature and shows oscillations in the presence of a magnetic field. The graphene magnetic susceptibility is temperature dependent (unlike an ordinary metal) and also increases with the amount of defects. Optical transport properties are also calculated in detail. On the other hand, extended defects induce localized states near the Fermi level. In the absence of electron-hole symmetry, these states lead to a transfer of charge between the defects and the bulk, the phenomenon we call self-doping. The role of electron-electron interactions in controlling self-doping is also analyzed. We also discuss the integer and fractional quantum Hall effect in graphene, the role played by the edge states induced by a magnetic field, and their relation to the almost field independent surface states induced at boundaries. The possibility of magnetism in graphene, in the presence of short-range electron-electron interactions and disorder is also analyzed. Comment: 20 pages, 18 Figures. This paper is the long version of the paper cond-mat/0506709
The conduction-electron magnetic susceptibility of graphite has been calculated by using the Wallace two-dimensional band structure. The energy levels induced by the magnetic field are calculated by the method of Luttinger and Kohn, taking into account the large (in this case) effects of band-to-band transitions which are not included in the Landau-Peierls treatment. Agreement with the susceptibility observed at high temperatures is obtained with a choice of 2.6 ev for the resonance-integral parameter γ0. The details of the de Haas-van Alphen effect cannot be reproduced, indicating that a more complicated band structure is needed to account for the low-temperature experiments.
A broad review of recent research work on the preparation and the
remarkable properties of intercalation compounds of graphite, covering a
wide range of topics from the basic chemistry, physics and materials
science to engineering applications.
Tight-binding calculations, using a two-dimensional model of the graphite lattice, lead to a point of contact of valence and conduction bands at the corner of the reduced Brillouin zone. A perturbation calculation which starts with wave functions of the two-dimensional lattice and is applied to the three-dimensional lattice is described. Some general features of the structure of the $$\pi${}$ bands in the neighborhood of the zone edge are obtained and are expressed in terms of appropriate parameters.
The structure of the electronic energy bands and Brillouin zones for graphite is developed using the "tight binding" approximation. Graphite is found to be a semi-conductor with zero activation energy, i.e., there are no free electrons at zero temperature, but they are created at higher temperatures by excitation to a band contiguous to the highest one which is normally filled. The electrical conductivity is treated with assumptions about the mean free path. It is found to be about 100 times as great parallel to as across crystal planes. A large and anisotropic diamagnetic susceptibility is predicted for the conduction electrons; this is greatest for fields across the layers. The volume optical absorption is accounted for.
Graphite intercalation compounds (GICs) are of interest to chemists and physicists because of their unusual properties. Much attention has been focused on the preparation and the properties of GICs themselves and on their utilization. In recent years, there have been attempts to intercalate two guest species together into graphite to study the behavior of the first intercalated component towards the second intercalated component in the two-dimensional gallery of the graphite interlayer, where a strong influence is expected by graphene layers. As an example of inorganic reactions in the interlayer spacing of graphite, we reduced metal chloride with lithium [1, 2]. Atoms of zero-valent metal generated by the reduction start moving in the interlayer spacing of graphite and aggregate. This process results in the production of metallic particles in the graphite matrix. It is interesting to note that the size of the metallic particles produced could be explained on the basis of the movement of the metallic atoms in the graphite interlayer. For an example of organic reactions in the graphite interlayer, anionic polymerization of unsaturated hydrocarbon is studied. In the course of the characterization of the products, we have found a new morphology of graphite, which was given by the polymerization in the interlayer and the subsequent removal of polymer. In this letter we discuss a new method to cleave graphite with a unit of graphene, hexagonal monoatomic sheet of carbon. The host graphite used was a highly oriented pyrolytic graphite (HOPG) from Advanced Ceramics Corp. A sample of stage 1 potassium-GIC KC8 (ca. 2.5 mg) was allowed to react with unsaturated hydrocarbons. The liquid hydrocarbons, isoprene and styrene, were dehydrated with a molecular sieve and purified by vacuum distillation. The reaction of potassium-GICs with the vapor of liquid hydrocarbons was carried out at room temperature. The gas pressure of the gaseous hydrocarbon, 1,3-butadiene, in the reaction chamber was kept constant at 67 kPa, and potassium-GICs were allowed to react at room temperature [3‐5]. Several tens of minutes after contact with the vapor of isoprene, KC8 was found to have expanded along the c-axis direction. The expansion proceeded slowly for several hours until the source of about 1 g isoprene was exhausted. The product grew to fill a glass tube with a diameter of 1 cm which was used as a reaction chamber. The product of a black color resembles exfoliated graphite in morphology. The bulk density of the product is not as low as for exfoliated graphite but almost identical to that of commercially available polyisoprene. The product was elastic, like commercially available polyisoprene. It is thought that molecules of isoprene are introduced into the interlayer spacing of KC8 and polymerized progressively. In the X-ray powder diffraction patterns of the products from KC8 no diffraction line for graphite or GIC was observed, and the broad peak with a shoulder resembles the pattern of the commercially available polyisoprene used as a control. The curves of thermogravimetry (TG) and differential thermal analysis (DTA) for the products are quite similar to those for the control polyisoprene. The polymers were vaporized or decomposed and completely removed at about 400 ‐ C and the residue originated from the HOPG. Similar products were obtained when KC8 was allowed to react with the vapor of styrene or the gas of 1,3-butadiene. X-ray powder patterns and the TG data of the products were quite similar to those for the control polymer, as in the case of isoprene. The expansion of potassium-GICs depends on the
If N classical particles in two dimensions interacting through a pair potential Φ(r⃗) are in equilibrium in a parallelogram box, it is proved that every k⃗≠0 Fourier component of the density must vanish in the thermodynamic limit, provided that Φ(r⃗)-λr2|∇2Φ(r⃗)| is integrable at r=∞ and positive and nonintegrable at r=0, both for λ=0 and for some positive λ. This result excludes conventional crystalline long-range order in two dimensions for power-law potentials of the Lennard-Jones type, but is inconclusive for hard-core potentials. The corresponding analysis for the quantum case is outlined. Similar results hold in one dimension.
Within a self-consistent Born approximation, the Hall conductivity of a two-dimensional graphite system in the presence of a magnetic field is studied by quantum transport theory. The Hall conductivity is calculated for short- and long-range scatterers. It is calculated analytically in the limit of strong magnetic fields and in the Boltzmann limit in weak magnetic fields. The numerical calculation shows that the Hall conductivity displays the quantum Hall effect when the Fermi energy is in low-lying Landau levels and the scattering is weak. When the Fermi energy becomes away from ɛ=0, it tends to the Boltzmann result.
In order to clarify the existence of a single sheet of carbon six-membered-ring plane (graphene) this letter presents a method by which the stacking number of the sheets in a carbon nanofilm (CNF) can be exactly counted, based on the quantitative analysis of electron diffraction intensity. Using the method we can detect a single graphene sheet in a CNF. © 2004 American Institute of Physics.
LEED and AES experiments of the SiC{0001} crystal surfaces show that on heat-treatment these surfaces are easily “covered” with a layer of graphite by evaporation of silicon. The graphite layer, which has a distinct crystallographic relation to the SiC crystal, is monocrystalline on the Si-face and mostly polycrystalline on the C-face. A speculation about the mechanism of the initial graphitization of the basal faces of SiC is given.
The preparation of a new type of finite carbon structure consisting of
needlelike tubes is reported. Produced using an arc-discharge
evaporation method similar to that used for fullerene sythesis, the
needles grow at the negative end of the electrode used for the arc
discharge. Electron microscopy reveals that each needle comprises
coaxial tubes of graphitic sheets ranging in number from two up to about
50. On each tube the carbon-atom hexagons are arranged in a helical
fashion about the needle axis. The helical pitch varies from needle to
needle and from tube to tube within a single needle. It appears that
this helical structure may aid the growth process. The formation of
these needles, ranging from a few to a few tens of nanometers in
diameter, suggests that engineering of carbon structures should be
possible on scales considerably greater than those relevant to the
fullerenes.
The critical behavior of disordered degenerate semiconductors is studied within a mean-field theory valid when the number of degeneracy points is large. I show that above two dimensions there is a semimetal-metal transition at a critical impurity concentration. The mean free path and the one-particle density of states exhibit scaling behavior with universal exponents. The transition is smeared at nonzero temperature. An equation of state, relating temperature, disorder, and bare conductivity, is presented. In two dimensions, the semimetallic phase is unstable. I show that a localization transition follows except in two dimensions where all states are localized. The bare conductivity appears to be a universal number in two dimensions. Applications to zero-gap semiconductors and other systems are discussed.
We introduce and analyze a class of model systems to study transitions
in the integer quantum Hall effect (IQHE). Even without disorder our
model exhibits an IQHE transition as a control parameter is varied. We
find that the transition is in the two-dimensional Ising universality
class and compute all associated exponents and critical transport
properties. The fixed point has time-reversal, particle-hole, and parity
invariance. We then consider the effect of quenched disorder on the IQHE
transition and find the following. (i) Randomness in the control
parameter (which breaks all the above symmetries) translates into bond
randomness in the Ising model and is hence marginally irrelevant. The
transition may equally well be viewed as a quantum percolation of edge
states localized on equipotentials. The absence of random-phase factors
for the edge states is responsible for the nongeneric (Ising) critical
properties. (ii) For a random magnetic field (which preserves
particle-hole symmetry in every realization) the model exhibits an
exactly solvable fixed line, described in terms of a product of a
Luttinger liquid and an SU(n) spin chain. While exponents vary
continuously along the fixed line, the longitudinal conductivity is
constant due to a general conformal sum rule for Kac-Moody algebras
(derived here), and is computed exactly. We also obtain a closed
expression for the extended zero-energy wave function for every
realization of disorder and compute its exact multifractal spectrum
f(α) and the exponents of all participation ratios. One point on
the fixed line corresponds to a recently proposed model by Gade and
Wegner. (iii) The model in the presence of a random on-site potential
scales to a strong disorder regime, which is argued to be described by a
symplectic nonlinear-sigma-model fixed point. (iv) We find a plausible
global phase diagram in which all forms of disorder are simultaneously
considered. In this generic case, the presence of random-phase factors
in the edge-state description indicates that the transition is described
by a Chalker-Coddington model, with a so far analytically inaccessible
fixed point.
A two-dimensional condensed-matter lattice model is presented which exhibits a nonzero quantization of the Hall conductance sigmaxy in the absence of an external magnetic field. Massless fermions without spectral doubling ccur at critical values of the model parameters, and exhibit the so-called ``parity anomaly'' of (2+1)-dimensional field theories.
Impurity scatterers, particularly in the unitary limit, produce low energy quasiparticles in a two-dimensional d-wave superconductor. We argue that even if the impurity concentration is small so that the wave functions in the normal state are essentially extended, the quasiparticles in the superconducting state become strongly localized for a short coherence length d-wave superconductor. An effective mobility gap then leads to thermally activated behavior for the microwave conductivity and possibly for the London penetration depth. We argue that this observation allows some puzzling data on oxide superconductors to be reconciled with the hypothesis of d-wave pairing.
Current theories suggest that multiwalled nanotubes may form through a scrolling mechanism ([1][1], [2][2]). The concept that scrolling could lead to nanotube-like structures ([3][3]) inspired us to extend our recent work on making colloidal suspensions of layered compounds ([4][4]) to graphite.
We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions,
metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between
valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in
concentrations up to 1013 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by
applying gate voltage.
We report free-standing atomic crystals that are strictly 2D and can be viewed as individual atomic planes pulled out of bulk crystals or as unrolled single-wall nanotubes. By using micromechanical cleavage, we have prepared and studied a variety of 2D crystals including single layers of boron nitride, graphite, several dichalcogenides, and complex oxides. These atomically thin sheets (essentially gigantic 2D molecules unprotected from the immediate environment) are stable under ambient conditions, exhibit high crystal quality, and are continuous on a macroscopic scale.
We present Raman spectroscopy measurements on single- and few-layer graphene
flakes. Using a scanning confocal approach we collect spectral data with
spatial resolution, which allows us to directly compare Raman images with
scanning force micrographs. Single-layer graphene can be distinguished from
double- and few-layer by the width of the D' line: the single peak for
single-layer graphene splits into different peaks for the double-layer. These
findings are explained using the double-resonant Raman model based on ab-initio
calculations of the electronic structure and of the phonon dispersion. We
investigate the D line intensity and find no defects within the flake. A finite
D line response originating from the edges can be attributed either to defects
or to the breakdown of translational symmetry.
Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.
We have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically 3 graphene sheets, were grown by thermal decomposition on the (0001) surface of 6H-SiC, and characterized by surface-science techniques. The low-temperature conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kOhm to 225 kOhm at 4 K, with positive magnetoconductance). Low resistance samples show characteristics of weak-localization in two dimensions, from which we estimate elastic and inelastic mean free paths. At low field, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of density 10^{12} cm^{-2} per graphene sheet. The most highly-ordered sample exhibits Shubnikov - de Haas oscillations which correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nano-patterned epitaxial graphene (NPEG), with the potential for large-scale integration.
CrossRef, CAS, Web of Science® Times Cited: 26, ADS Link to full text at IDL
- R F Curl
- R F Curl
CrossRef, CAS, Web of Science® Times Cited: 86, ADS Link to full text at IDL
- C Oshima
- A Nagashima
- C Oshima
- A Nagashima
Link to full text at IDL
- R E Peierls
- Ann Inst
- R E Peierls
- Ann Inst
CrossRef, CAS, Web of Science® Times Cited: 48, ADS Link to full text at IDL
- R E Smalley
- R E Smalley
CAS Link to full text at IDL
- R E Peierls
- Helv Phys
- R E Peierls
- Helv Phys
CrossRef, CAS, Web of Science® Times Cited: 9098, ADS Link to full text at IDL
- S Iijima
- S Iijima
- L D Landau
- E M Lifshitz
L. D. Landau and E. M. Lifshitz, Statistical Physics, Part I (Pergamon Press, Oxford, 1980).
- R E Peierls
R. E. Peierls, Ann. Inst. Henri Poincare 5, 177 (1935).
- J W Mcclure
J. W. McClure, Phys. Rev. 104, 666 (1956).
- K S Novoselov
- E Mccann
- S V Morozov
K. S. Novoselov, E. McCann, S. V. Morozov et al., Nature Physics 2, 177 (2006).
- L M Viculis
L. M. Viculis et al., Science 299, 1361 (2003).
- C Oshima
- A Nagashima
C. Oshima and A. Nagashima, J. Phys.: Condens. Matter 9, 1 (1997).
- N M R Peres
- F Guinea
- A H Castro Neto
N. M. R. Peres, F. Guinea, and A. H. Castro Neto, Phys. Rev. B 73, 125411 (2006).
- J C Slonczewski
- P R Weiss
J. C. Slonczewski and P. R. Weiss, Phys. Rev. 109, 272 (1958).