GRAPHENE: THE ADVANCED MATERIAL (original) (raw)

Properties of graphene: a theoretical perspective

Advances in Physics, 2010

The electronic properties of graphene, a two-dimensional crystal of carbon atoms, are exceptionally novel. For instance the low-energy quasiparticles in graphene behave as massless chiral Dirac fermions which has led to the experimental observation of many interesting effects similar to those predicted in the relativistic regime. Graphene also has immense potential to be a key ingredient of new devices such as single molecule gas sensors, ballistic transistors, and spintronic devices. Bilayer graphene, which consists of two stacked monolayers and where the quasiparticles are massive chiral fermions, has a quadratic low-energy band structure which generates very different scattering properties from those of the monolayer. It also presents the unique property that a tunable band gap can be opened and controlled easily by a top gate. These properties have made bilayer graphene a subject of intense interest.

Graphene: The Material of Today and Tomorrow

International Journal of Sciences: Basic and Applied Research, 2021

Graphene has astounding aptitudes owing to its unique band structure characteristics outlining its enhanced electrical capabilities for a material with the highest characteristic mobility known to exist at room temperature. Graphene, one-atom-thick, a planar sheet of carbon atoms densely packed in a honeycomb crystal lattice, has grabbed considerable attention due to its exceptional electronic and optoelectronic properties. Reported properties and applications of this two-dimensional form of carbon structure have opened up new opportunities for the future devices and application in various fields. Though graphene is recognized as one of the best electronic materials, synthesizing single sheet of graphene has been less explored. This review article aims to present an overview of the progression of research in graphene, in the area of synthesis, properties and applications. Wherever applicable, the limitations of present knowledge base and future research directions have also been discussed

Physics of Graphene: Status and Perspectives

Sensor Electronics and Microsystem Technologies, 2010

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GRAPHENE: STATUS AND PROSPECTS

Graphene is a wonder material with many superlatives to its name. It is the thinnest material in the universe and the strongest ever measured. Its charge carriers exhibit giant intrinsic mobility, have the smallest effective mass (it is zero) and can travel micrometer-long distances without scattering at room temperature. Graphene can sustain current densities 6 orders higher than copper, shows record thermal conductivity and stiffness, is impermeable to gases and reconciles such conflicting qualities as brittleness and ductility. Electron transport in graphene is described by a Dirac-like equation, which allows the investigation of relativistic quantum phenomena in a bench-top experiment. What are other surprises that graphene keeps in store for us? This review analyses recent trends in graphene research and applications, and attempts to identify future directions in which the field is likely to develop. Graphene research has developed a truly relentless pace. Several papers appear every day and, if the bibliometrics predictions (1) are to be trusted, the amount of literature on graphene will keep rapidly increasing over the next few years. This makes it a real struggle to keep up with the developments. Newcomers are left without a broad perspective and are largely unaware of previous arguments and solved problems, whereas the community's doyens already show signs of forgetting their earlier papers. To combat this curse of success, many reviews have appeared in the last two years, and books on graphene are in the making. Among those, let me recommend our review (2) that provides a good introductory material and is far from being obsolete. The electronic properties of graphene were recently discussed in an extensive theory review (3), and this basic information is unlikely to require any revision soon. Also, I recommend more specialized papers discussing the quantum Hall effect in graphene, its Raman properties, epitaxial growth on SiC, etc. which are collected in (4). Despite or, perhaps, because of the vast amount of available literature, graphene research has now reached the stage where a strategic update is needed to cover the latest progress, emerging trends and opening opportunities. This paper is intended to serve this purpose without repeating, whenever possible, the information available in the earlier reviews. Growing Opportunities Graphene is a single atomic plane of graphite, which-and this is essential-is sufficiently isolated from its environment to be considered free-standing. Atomic planes are of course familiar to everyone as constituents of bulk crystals but one-atom-thick materials such as graphene remained unknown. The basic reason for this is that nature strictly forbids the growth of low-dimensional (D) crystals (2). Crystal growth implies high temperatures (T) and, therefore, thermal fluctuations that are detrimental for the stability of macroscopic 1D and 2D objects. One can grow flat molecules and nm-sized crystallites, but as their lateral size increases, the phonon density integrated over the 3D space available for thermal vibrations rapidly grows, diverging on a macroscopic scale. This forces 2D crystallites to morph into a variety of stable 3D structures. The impossibility to grow 2D crystals does not actually mean that they cannot be made artificially. With hindsight, this seems trivial. Indeed, one can grow a monolayer inside or on top of another crystal (as an inherent part of a 3D system) and then remove the bulk at sufficiently low T such that thermal fluctuations are unable to break atomic bonds even in macroscopic 2D crystals and mold them into 3D shapes. This consideration allows two principal routes for making 2D crystals (Fig. 1). One is to mechanically split strongly-layered materials such as graphite into individual atomic planes (Fig. 1A). This is how graphene was first isolated and studied. Although delicate and time consuming, the handcraft (often referred to as a scotch tape technique) provides crystals of high structural and electronic quality, which can currently reach sizes of a couple of mm. It is likely to remain the technique of choice for basic research and making proof-of-concept devices in the foreseeable future. Instead of cleaving graphite manually, it is also possible to automate the process by employing, for example, ultrasonic cleavage (5). This leads to stable suspensions of submicron graphene crystallites (Fig. 1B), which can then be used to make polycrystalline films and composite materials (5,6). Conceptually similar is the ultrasonic cleavage of chemically "loosened" graphite, in which atomic planes are partially detached first by intercalation, making the sonification more efficient (6). The sonification allows graphene production on industrial scale. The alternative route is to start with graphitic layers grown epitaxially on top of other crystals (7) (Fig. 1C). This is the 3D growth during which epitaxial layers remain bound to the underlying substrate and the bond-breaking fluctuations suppressed. After the epitaxial structure is cooled down, one can remove the substrate by chemical etching. Technically, this is similar to making, for example, SiN membranes but one-atom-thick crystals were deemed impossible to survive, and no one tried this route until recently (8-10). The isolation of epitaxial monolayers and their

Graphene: synthesis and applications

The low energy bandstructure of graphene involves its π electrons. The first bandstructure calculations were performed in 1947 by P.R. Wallace 1 and the bandstructure is shown in Fig. 1a. The valence band is formed by bonding π states, while the conduction band is formed by the anti-bonding π* states. These states are orthogonal; there is no avoided crossing, and valence and conduction bands touch at six points, the so-called Dirac points. Two of these points are independent and are indicated in Fig. 1a as the K and K' points. For energies below about 1 eV, which are relevant in most electrical transport properties, the bandstructure can be approximated by two symmetric cones representing valence and conduction bands touching at the Dirac point. Electron dispersion in this energy region is to a large extent linear, similar to that of light and unlike other conventional 2D systems with parabolic dispersion 2-8. This linear dispersion has profound implications regarding the properties of graphene. Also, unlike the conventional 2D electron systems, which are usually formed at buried semiconductor interfaces, graphene is a single atomic layer directly accessible to experimental observation, but also very susceptible to external perturbations which can interact directly with its π-electron system. The unit cell of graphene contains two carbon atoms and the graphene lattice can be viewed as formed by two sub-lattices, A and B, evolving from these two atoms (see Fig. 1b). The electronic Hamiltonian describing the low energy electronic structure of graphene can then be written in the form of a relativistic Dirac Hamiltonian: H = v F σ⋅h-k, where σ is a spinor-like wavefunction, v F is the Fermi velocity of graphene, and k the wavevector of the electron 2-8. However, the spinor character of the graphene wavefunction arises not from spin, but from the fact that there are two atoms in the unit cell. We can define a pseudo-spin that has the same direction as the group velocity and describes the electron population in the A and B sites. As with real spin, pseudo-spin reversal is not allowed during carrier interactions. This underlies the inhibition of Graphene, since the demonstration of its easy isolation by the exfoliation of graphite in 2004 by Novoselov, Geim and co-workers , has been attracting enormous attention in the scientific community. Because of its unique properties, high hopes have been placed on it for technological applications in many areas. Here we will briefly review aspects of two of these application areas: analog electronics and photonics/optoelectronics. We will discuss the relevant material properties, device physics, and some of the available results. Of course, we cannot rely on graphite exfoliation as the source of graphene for technological applications, so we will start by introducing large scale graphene growth techniques.

Graphene and its one-dimensional patterns: from basic properties towards applications

Advances in Natural Sciences: Nanoscience and Nanotechnology, 2010

Graphene, a carbon material discovered in 2004 by a group of scientists at the University of Manchester, UK, has been attracting significant attention in both fundamental and applied studies. Due to the rapid increase in the number of articles on this material since its discovery, a range of readers, particularly those just beginning to learn about this material, are turning

Graphene: A New Era of Technology

The aim of this literature indicate that graphene composites are promising multifunctional materials with improved tensile strength and elastic modulus, mechanical strength, optical property, electrical and thermal conductivity. Its unique quality light weight, high strength, excellent electric conductivity makes it differ from any other material. It has ability to replace the silicon and change the scenario of semiconductor devices. It is a base of nano technology. Due to its unique properties, it will sets the new dimension in the nano techno world.