One-dimensional (1D) nanofibers of polypyrrole (PPY) are fabricated on glass substrates in the presence of different dopants, namely, hydrochloric acid (HCl), ferric chloride (FeCl3·6H2O), p-toluene sulfonic acid, camphor sulfonic acid, and polystyrene sulfonic acid using a simple in situ vapor phase chemical oxidative polymerization method. Preliminary morphological details investigated using light microscopic study reveal 1D configuration for all the doped PPY structures, indicating a fibrous/tubular appearance. Furthermore, scanning electron microscopy confirms preferential growth of these PPY structures as fine fibers arranged in a brush-/comb-like pattern, having an average diameter of 70 nm. Such brush-like growing pattern observed for the PPY nanostructures without the aid of nanoporous membranes and/or sophisticated techniques is not very commonly reported in the literature. The undertaken work suggests applications of nanodimensioned fabricated PPY structures in the practical nanodevices and/or functional glass for sensing, optoelectronic, photocatalysis, and solar energy systems.

The gapless energy spectra and linear dispersion relations of electrons and holes in graphene lead to nontrivial features such as a high carrier mobility and a flat, broadband optical response. This article reviews recent advances in graphene-based materials and devices for terahertz science and technology. After an introduction to the fundamental basis of the optoelectronic properties of graphene, the synthesis and crystallographic characterization of graphene materials are described, with a particular focus on the authors’ original heteroepitaxial graphene-on-silicon technology. The nonequilibrium dynamics of carrier relaxation and recombination in optically or electrically pumped graphene is discussed to introduce the possibility of negative dynamic conductivity over a wide terahertz range. Recent theoretical advances toward the creation of current-injection graphene terahertz lasers are described, followed by the unique terahertz dynamics of two-dimensional plasmons in graphene. Finally, the advantages of graphene materials and devices for terahertz applications are summarized.

Accelerating global energy consumption makes the development of clean and renewable alternative energy sources indispensable. Nanotechnology opens up new frontiers in materials science and engineering to meet this energy challenge by creating new materials, particularly carbon nanomaterials, for efficient energy conversion and storage. Since the Nobel Prize winning research on graphene by Geim and Novoselov, considerable efforts have been made to exploit graphene as an energy material, and tremendous progress has been achieved in developing high-performance devices for energy conversion and energy storage. This article reviews recent progress in the research and development of graphene materials for advanced energy-conversion devices, including solar cells and fuel cells, and energy-storage devices, including supercapacitors and lithium-ion batteries, and discusses some challenges in this exciting field.

Because of its fascinating electronic properties, graphene is expected to produce breakthroughs in many areas of nanoelectronics. For spintronics, its key advantage is the expected long spin lifetime, combined with its large electron velocity. In this article, we review recent theoretical and experimental results showing that graphene could be the long-awaited platform for spintronics. A critical parameter for both characterization and devices is the resistance of the contact between the electrodes and the graphene, which must be large enough to prevent quenching of the induced spin polarization but small enough to allow for the detection of this polarization. Spin diffusion lengths in the 100-μm range, much longer than those in conventional metals and semiconductors, have been observed. This could be a unique advantage for several concepts of spintronic devices, particularly for the implementation of complex architectures or logic circuits in which information is coded by pure spin currents.

The effect of crystallographic orientation and sample volume on incipient plasticity of commercially pure polycrystalline nickel 200 was investigated using electron back scatter diffraction (EBSD) and nanoindentation. A nickel sample was annealed, and grain orientations were determined using EBSD. Specifically oriented grains were indented using tips of nominal radii 100, 1000, and 1300 nm. The onset of plasticity in relatively defect-free small volumes is characterized by a sharp “pop-in” event during load-controlled nanoindentation. Grains in the (001) orientation yield at higher pressures; larger radii tips are more sensitive to orientation effects but yield at lower stresses. Subsurface defects may result in the dominance of tip radius over orientation, indicated by statistical analysis of yield points. An activation volume analysis, in conjunction with the yield pressure as a function of tip size, suggests that dislocation loops may play a critical role in causing these effects.

We present an introduction to the rapidly growing field of epitaxial graphene on silicon carbide, tracing its development from the original proof-of-concept experiments a decade ago to its present, highly evolved state. The potential of epitaxial graphene as a new electronic material is now being recognized. Whether the ultimate promise of graphene-based electronics will ever be realized remains an open question. Silicon electronics is based on single-crystal substrates that allow reliable patterning on the nanoscale, which is an absolute requirement for any new electronic material. That is why epitaxial graphene is based on single-crystal silicon carbide. We also present recent results on nanopatterned graphene produced by etching the silicon carbide before annealing so that the graphene structures are produced in their final shapes. This avoids postannealing patterning, which is known to greatly affect transport properties on the nanoscale. Creating such structured graphene is an elegant method for avoiding pervasive patterning problems.

Recently, transmission electron microscopy (TEM) and related techniques have brought unique insights to graphene research, demonstrating remarkable flexibility in characterizations ranging from atomic ordering to charge distribution. Such TEM studies have helped advance areas including the understanding of graphene growth and the effects of defects and dopants on the mechanical and electrical properties of graphene. Electron microscopy has proved particularly useful in determining the structure of crystals and grain boundaries across six orders of magnitude—from the shapes, arrangements, and stacking sequences of grains to the atomic arrangements at grain boundaries. Meanwhile, graphene is becoming a promising two-dimensional laboratory bench for electron microscopy, for example, turning graphene into a medium for nanosculpting by transforming buckyballs into graphene and vice versa. Finally, graphene has been used as an ultrathin support membrane for TEM, enabling studies of the motion of single atoms, direct imaging of two-dimensional amorphous materials, and even formation of nano-aquaria for imaging bacteria or nanoparticles in liquid media. Rapid developments in the fields of both electron microscopy and graphene will continue to provide a rich ground for future insights.

A novel hybrid titania paste comprising aqueous-synthesized anatase (A) nanocrystalites and submicrometer-sized “sea urchin”-like rutile (R) particles that enables the construction of thin (5–6 μm) single-layer photoanodes with competitive power conversion efficiency is described. Owing to the high surface area of the dye (N719)-coated anatase film, the scattering properties of the unique rutile particulates, and the incorporation of P25 particles, the constructed bifunctional electrode films exhibit excellent electron transport properties (long electron lifetime) and no electrolyte diffusion resistance. Dye-sensitized solar cell devices built with the thin (5–6 μm) hybrid electrodes showed greatly improved power conversion efficiency (PCE), namely 7.04%, when compared to devices based on single anatase (4.20%), double-layer (A + R), or double thickness commercial benchmark paste (6.74%). This is an impressive result as less than 1/2 material was used in a single printed layer. Thinner films as the ones built here may prove particularly advantageous in using new noniodide electrolytes associated with slow diffusion rates.

As graphene technologies progress to commercialization and large-scale manufacturing, issues of material and processing safety will need to be more seriously considered. The single word “graphene” actually represents a family of related materials with large variations in number of layers, surface area, lateral dimensions, stiffness, and surface chemistry. Many of these materials have aerodynamic diameters below 5 μm and can potentially be inhaled into the human lung. Graphene materials show several unique modes of interaction with biological molecules, tissues, and cells. The limited literature suggests that graphene materials can be either benign or harmful and that the biological response varies according to a material’s physicochemical properties and biologically effective dose. The present article reviews the current literature on the graphene–biological interface with an emphasis on the mechanisms and fundamental biological responses relevant to material safety and also to potential biomedical applications

The optical properties of graphene-based nanomaterials have attracted much recent attention. This article provides an overview of recent advances in the study of linear and nonlinear optical transitions associated mostly with tailored energy bandgaps. In particular, the optical absorption characteristics and photoluminescence emissions due to various induced bandgaps and, in some cases, the formation of graphene quantum dots are highlighted. Nonlinear optical properties of these materials are reviewed with an emphasis on optical limiting through both nonlinear absorption and scattering mechanisms.

Graphene is a two-dimensional (2D) material with over 100-fold anisotropy of heat flow between the in-plane and out-of-plane directions. High in-plane thermal conductivity is due to covalent sp2bonding between carbon atoms, whereas out-of-plane heat flow is limited by weak van der Waals coupling. Herein, we review the thermal properties of graphene, including its specific heat and thermal conductivity (from diffusive to ballistic limits) and the influence of substrates, defects, and other atomic modifications. We also highlight practical applications in which the thermal properties of graphene play a role. For instance, graphene transistors and interconnects benefit from the high in-plane thermal conductivity, up to a certain channel length. However, weak thermal coupling with substrates implies that interfaces and contacts remain significant dissipation bottlenecks. Heat flow in graphene or graphene composites could also be tunable through a variety of means, including phonon scattering by substrates, edges, or interfaces. Ultimately, the unusual thermal properties of graphene stem from its 2D nature, forming a rich playground for new discoveries of heat-flow physics and potentially leading to novel thermal management applications.

Graphene is a material with outstanding properties that make it an excellent candidate for advanced applications in future electronics and photonics. The potential of graphene in high-speed analog electronics is currently being explored extensively because of its high carrier mobility, its high carrier saturation velocity, and the insensitivity of its electrical-transport behavior to temperature variations. Herein, we review some of the key material and carrier-transport physics of graphene, then focus on high-frequency graphene field-effect transistors, and finally discuss graphene monolithically integrated circuits (ICs). These high-frequency graphene transistors and ICs could become essential elements in the blossoming fields of wireless communications, sensing, and imaging. After discussing graphene electronics, we describe the impressive photonic properties of graphene. Graphene interacts strongly with light over a very wide spectral range from microwaves to ultraviolet radiation. Most importantly, the light–graphene interaction can be adjusted using an electric field or chemical dopant, making graphene-based photonic devices tunable. Single-particle interband transitions lead to a universal optical absorption of about 2% per layer, whereas intraband free-carrier transitions dominate in the microwave and terahertz wavelength range. The tunable plasmonic absorption of patterned graphene adds yet another dimension to graphene photonics. We show that these unique photonic properties of graphene over a broad wavelength range make it promising for many photonic applications such as fast photodetectors, optical modulators, far-infrared filters, polarizers, and electromagnetic wave shields. These graphene photonic devices could find various applications in optical communications, infrared imaging, and national security.

The superlative electronic, optical, mechanical, and chemical properties of graphene suggest broad technological opportunities for graphene-based materials and composites. However, the transition from the research laboratory to widespread commercial utilization requires economical methods for the mass production of graphene and graphene-based materials. Among the emerging methods for synthesizing graphene, solution-based processing holds particular promise because of its low cost, high throughput, chemical versatility, and scalability to large quantities. Furthermore, solution-processed graphene can be seamlessly integrated with other nanomaterials or polymers to yield composites for a wide array of applications such as energy conversion and storage, catalysis, electronics, and high-strength materials. This article highlights the range of techniques being developed for processing graphene in solution with a specific emphasis on solution-based methods for realizing graphene-based composites. In addition to fundamental principles, representative applications for these materials are presented.

Graphene came to the forefront in the nanosciences in the early 2000s, in particular, when high-quality graphene with atomic thickness and two-dimensional extension in the micrometer range was isolated and the resulting novel electronic properties were demonstrated. Graphene has two unique features: lateral size up to tens of micrometers or larger and quantum confinement in an atomically thin sheet. It provides an excellent platform for exploring novel material properties, designing new materials, and enhancing material performance. Now, after extensive research for nearly a decade, graphene research has moved well beyond electronic applications and has begun to extend into a wide variety of disciplines. This expanded issue of MRS Bulletin is focused on graphene and consists of 20 articles and three commentaries that collectively address the major impact of graphene on materials science, highlight the newest advances, discuss challenging issues, explore applications, and reveal future directions.