The richness of optical and electronic properties of graphene attracts enormous interest. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental stability. So far, the main focus has been on fundamental physics and electronic devices. However, we believe its true potential lies in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, even in the absence of a bandgap, and the linear dispersion of the Dirac electrons enables ultrawideband tunability. The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light-emitting devices to touch screens, photodetectors and ultrafast lasers. Here we review the state-of-the-art in this emerging field.

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Graphene photonics and optoelectronics

Worldwide commercial interest in carbon nanotubes (CNTs) is reflected in a production capacity that presently exceeds several thousand tons per year. Currently, bulk CNT powders are incorporated in diverse commercial products ranging from rechargeable batteries, automotive parts, and sporting goods to boat hulls and water filters. Advances in CNT synthesis, purification, and chemical modification are enabling integration of CNTs in thin-film electronics and large-area coatings. Although not yet providing compelling mechanical strength or electrical or thermal conductivities for many applications, CNT yarns and sheets already have promising performance for applications including supercapacitors, actuators, and lightweight electromagnetic shields.

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Carbon Nanotubes: Present and Future Commercial Applications

Transparent, conductive, and ultrathin graphene films, as an alternative to the ubiquitously employed metal oxides window electrodes for solid-state dye-sensitized solar cells, are demonstrated. These graphene films are fabricated from exfoliated graphite oxide, followed by thermal reduction. The obtained films exhibit a high conductivity of 550 S/cm and a transparency of more than 70% over 1000−3000 nm. Furthermore, they show high chemical and thermal stabilities as well as an ultrasmooth surface with tunable wettability.

Transparent, Conductive Graphene Electrodes for Dye-Sensitized Solar Cells

The integration of novel materials such as single-walled carbon nanotubes and nanowires into devices has been challenging, but developments in transfer printing and solution-based methods now allow these materials to be incorporated into large-area electronics1,2,3,4,5,6. Similar efforts are now being devoted to making the integration of graphene into devices technologically feasible7,8,9,10. Here, we report a solution-based method that allows uniform and controllable deposition of reduced graphene oxide thin films with thicknesses ranging from a single monolayer to several layers over large areas. The opto-electronic properties can thus be tuned over several orders of magnitude, making them potentially useful for flexible and transparent semiconductors or semi-metals. The thinnest films exhibit graphene-like ambipolar transistor characteristics, whereas thicker films behave as graphite-like semi-metals. Collectively, our deposition method could represent a route for translating the interesting fundamental properties of graphene into technologically viable devices.

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Large-area ultrathin films of reduced graphene oxide as a transparent and flexible electronic material

Rechargeable lithium-sulfur batteries.

We describe a simple process for the fabrication of ultrathin, transparent, optically homogeneous, electrically conducting films of pure single-walled carbon nanotubes and the transfer of those films to various substrates. For equivalent sheet resistance, the films exhibit optical transmittance comparable to that of commercial indium tin oxide in the visible spectrum, but far superior transmittance in the technologically relevant 2- to 5-micrometer infrared spectral band. These characteristics indicate broad applicability of the films for electrical coupling in photonic devices. In an example application, the films are used to construct an electric field-activated optical modulator, which constitutes an optical analog to the nanotube-based field effect transistor.

http://science.sciencemag.org/content/sci/305/5688/1273.full.pdf

Transparent, Conductive Carbon Nanotube Films

The problems posed by the synthesis and purification of single-walled carbon nanotubes (SWNTs) have inhibited progress in the field. In this article, we review the methods available for measuring the purity of SWNTs and the current status of processes designed to purify them.We emphasize the hierarchy of the purification steps that must be developed in order to obtain high-quality material suitable for the full range of advanced applications that are envisioned for the ultimate carbon nanofiber.We review two strategies for SWNT purification, the assessment of SWNT purity by use of near-IR spectroscopy and its application to the thermal oxidation of thin films of SWNTs, as well as recent advances in the separation of metallic and semiconducting SWNTs. While substantial progress has been made in the purification and separation of SWNTs, we note the need for quality control and quality assurance within the industry. Much work remains before pure SWNTs of specific lengths, diameters, and chirality can be made available for applications.

Purification and Separation of Carbon Nanotubes

To stabilize nanotube-modified atomic force microscopy tips and extend their functionality, a method for conformal polymer coating of the tips and removal of the polymer from just the probing nanotube end is described. Expressions quantifying stabilization of the tips against buckling and bending due to stresses encountered while imaging are developed. Electrical conductivity of the probes is demonstrated by their use in scanned conductance microscopy, where a substantial sensitivity advantage over standard tips is realized and explained. Further advantages of these electrically insulated (save for the tip) probes are discussed, including their proposed application in bioelectrochemical research.

Enhanced Functionality of Nanotube Atomic Force Microscopy Tips by Polymer Coating

Perhaps the most wonderful feature of carbon nanotubes is that they are synthesized in both metallic and semiconducting variants, and perhaps the most problematic feature is that they are synthesized in both metallic and semiconducting variants. The intimate mixture hampers numerous envisioned applications and separation of the nanotubes into their respective electronic transport classes has emerged (after high yield synthesis and purification) as the next great materials challenge. Recently, several groups (us among them) have shown progress in attacking the problem. We will elaborate on our bromine exposure/centrifugation based method and the evidence leading to our conclusion that the separation results from an interplay between the nanotubes, bromine and the surfactant. We will also elaborate on our method for production of ultra‐thin (and thereby transparent), optically homogeneous, nanotube films used in the spectroscopic absorbance based assay of the metallic/semiconducting nanotube content. Such films, by virtue of their electrical conductivity constitute a new class of electrically conducting, transparent electrode that may one day rival ITO in the ubiquity of its applications. The potential significance of the nanotubes in solving contact barrier problems between metals and semiconductors is also discussed.

Metallic/Semiconducting Nanotube Separation and Ultra‐thin, Transparent Nanotube Films

The excess noise of single‐walled carbon nanotubes is studied over the 77K to 300K temperature range. Lorentzian shaped spectra along with 1/f noise spectra are observed. From the Lorentzian noise components activation energies of 0.21 and 0.46eV for the associated fluctuation mechanisms are obtained.

Jennifer Sippel

Papers

Transparent, Conductive Carbon Nanotube Films

Purification and Separation of Carbon Nanotubes

Enhanced Functionality of Nanotube Atomic Force Microscopy Tips by Polymer Coating

Metallic/Semiconducting Nanotube Separation and Ultra‐thin, Transparent Nanotube Films

Excess Noise In Carbon Nanotubes