Graphene-based optically transparent electrodes for spectroelectrochemistry in the UV-Vis region

Solution-based Supramolecular Hierarchical Assembly of Frenkel Excitonic Nanotubes Driven by Gold Nanoparticle Formation and Temperature

Translating nature's successful design principle of solution-based supramolecular self-assembling to broad applications─ranging from renewable energy and information technology to nanomedicine─requires a fundamental understanding of supramolecular hierarchical assembly. Though the forces behind self-assembly (e.g., hydrophobicity) are known, the specific mechanism by which monomers form the hierarchical assembly still remains an open question. A crucial step toward formulating a complete mechanism is understanding not only how the monomer's specific molecular structure but also how manifold environmental conditions impact the self-assembling process. Here, we elucidate the complex correlation between the environmental self-assembling conditions and the resulting structural properties by utilizing a well-characterized model system: well-defined supramolecular Frenkel excitonic nanotubes (NTs), self-assembled from cyanine dye molecules in aqueous solution, which further self-assemble into bundled nanotubes (b-NTs). The NTs and b-NTs inhabit distinct spectroscopic signatures, which allows the use of steady-state absorption spectroscopy to monitor the transition from NTs to b-NTs directly. Specifically, we investigate the impact of temperature (ranging from 23 °C, 55 °C, 70 °C, 85 °C, up to 100 °C) during in situ formation of gold nanoparticles to determine their role in the formation of b-NTs. The considered time regime for the self-assembling process ranges from 1 min to 8 days. With our work, we contribute to a basic understanding of how environmental conditions impact solution-based hierarchical supramolecular self-assembly in both the thermodynamic and the kinetic regime.

Recent State and Challenges in Spectroelectrochemistry with Its Applications in Microfluidics

This review paper presents the recent developments in spectroelectrochemical (SEC) technologies. The coupling of spectroscopy and electrochemistry enables SEC to do a detailed and comprehensive study of the electron transfer kinetics and vibrational spectroscopic fingerprint of analytes during electrochemical reactions. Though SEC is a promising technique, the usage of SEC techniques is still limited. Therefore, enough publicity for SEC is required, considering the promising potential in the analysis fields. Unlike previously published review papers primarily focused on the relatively frequently used SEC techniques (ultraviolet-visible SEC and surface-enhanced Raman spectroscopy SEC), the two not-frequently used but promising techniques (nuclear magnetic resonance SEC and dark-field microscopy SEC) have also been studied in detail. This review paper not only focuses on the applications of each SEC method but also details their primary working mechanism. In short, this paper summarizes each SEC technique's working principles, current applications, challenges encountered, and future development directions. In addition, each SEC technique's applicative research directions are detailed and compared in this review work. Furthermore, integrating SEC techniques into microfluidics is becoming a trend in minimized analysis devices. Therefore, the usage of SEC techniques in microfluidics is discussed.

Printing Polymeric Convex Lenses to Boost the Sensitivity of a Graphene-Based UV Sensor

Ultraviolet (UV) is widely used in daily life as well as in industrial manufacturing. In this study, a single-step postprocess to improve the sensitivity of a graphene-based UV sensor is studied. We leverage the advantage of electric-field-assisted on-demand printing, which is simply applicable for mounting functional polymers onto various structures. Here, the facile printing process creates optical plano-convex geometry by accelerating and colliding a highly viscous droplet on a micropatterned graphene channel. The printed transparent lens refracts UV rays. The concentrated UV photon energy from a wide field of view enhances the photodesorption of electron-hole pairs between the lens and the graphene sensor channel, which is coupled with a large change in resistance. As a result, the one-step post-treatment has about a 4× higher sensitivity compared to bare sensors without the lenses. We verify the applicability of printing and the boosting mechanism by variation of lens dimensions, a series of UV exposure tests, and optical simulation. Moreover, the method contributes to UV sensing in acute angle or low irradiation. In addition, the catalytic lens provides about a 9× higher recovery rate, where water molecules inside the PEI lens deliver fast reassembly of the electron-hole pairs. The presented method with an ultimately simple fabrication step is expected to be applied to academic research and prototyping, including optoelectronic sensors, energy devices, and advanced manufacturing processes.

Graphene as a Transparent Conductive Electrode in GaN-Based LEDs

Graphene combines high conductivity (sheet resistance down to a few hundred Ω/sq and even less) with high transparency (>90%) and thus exhibits a huge application potential as a transparent conductive electrode in gallium nitride (GaN)-based light-emitting diodes (LEDs), being an economical alternative to common indium-based solutions. Here, we present an overview of the state-of-the-art graphene-based transparent conductive electrodes in GaN-based LEDs. The focus is placed on the manufacturing progress and the resulting properties of the fabricated devices. Transferred as well as directly grown graphene layers are considered. We discuss the impact of graphene-based transparent conductive electrodes on current spreading and contact resistance, and reveal future challenges and perspectives on the use of graphene in GaN-based LEDs.

Oriented Nickel Nanonetworks and Their Submicron Fibres as a Basis for a Transparent Electrically Conductive Coating

The paper demonstrates a technique for applying an oriented nickel network to a glass surface. The method is based on the chemical reduction of nickel salt. The shaping and orientation of the resulting system are carried out using a micellar template of a surfactant and a magnetic field. Submicron nickel fibres are used to impart unity to the plurality of individual-oriented nickel nanonetworks. The result is a single conductive coating on the surface of the glass, which has a transparency in the optical range. Investigations of the structure, chemical composition, morphology and electrical conductivity of the coating were performed.

Ultra-Thin Conductive Graphitic Carbon Nitride Assembly through van der Waals Epitaxy toward High-Energy-Density Flexible Supercapacitors

Graphitic carbon nitride is an ordered two-dimensional stability. However, its bulk structure with low electrical conductivity (less than 1 S cm^-1) restricts the applications in electrochemical energy storage. This is because conventional synthesis methods lack effective thickness control, and the excessive nitrogen doping (∼50%) leads to poor electrical conductivity. Here, we report an ultrathin conductive graphitic carbon nitride assembly (thickness of ∼1.0 nm) through graphene-templated van der Waals epitaxial strategy with high electrical conductivity (12.2 S cm^-1), narrow pore-size distribution (5.3 nm), large surface area (724.9 m² g^-1), and appropriate nitrogen doping level (18.29%). The ultra-thin structure with nitrogen doping provided numerous channels and active sites for effective ion transportation and storage, while the graphene layers acted as micro current collectors; subsequently, it exhibits high energy storage capability of 936 mF cm^-2 at 1 mA cm^-2 with excellent stability of over 10 000 cycles. Moreover, the all-solid-state supercapacitors showed an ultra-high energy density of 281.3 μWh cm^-2 at 1 mA cm^-2 with high rate capability, Coulombic efficiency, and flexibility. This work represents a general framework for the bottom-up synthesis of ultrathin 2D materials, which may promote the application of graphitic carbon nitride in energy storage.

Wettability of graphene: from influencing factors and reversible conversions to potential applications

As a member of the carbon material family, graphene has long been the focus of research on account of its abundant excellent properties. Nevertheless, many previous research works have attached much importance to its mechanical capacity and electrical properties, and not to its surface wetting properties with respect to water. In this review, a series of methods are put forward for characterization of the water contact angle of graphene, such as experimental measurements, classic molecular dynamics simulations, and formula calculations. A series of factors that affect the wettability of graphene, including defects, controllable atmosphere, doping, and electric field, are also discussed in detail, and have rarely have been covered in other review articles before. Finally, with the developments of smart surfaces, a reversible wettability variation of graphene from hydrophobic to hydrophilic is important in the presence of external stimulation and is discussed in detail herein. It is anticipated that graphene could serve as a tunable wettability coating for further developments in electronic devices and brings a new perspective to the construction of smart material surfaces.

Transparent to Black Electrochromism-The "Holy Grail" of Organic Optoelectronics

In the rapidly developing field of conjugated polymer science, the attribute of electrochromism these materials exhibit provides for a multitude of innovative application opportunities. Featuring low electric potential driven colour change, complemented by favourable mechanical and processing properties, an array of non-emissive electrochromic device (ECD) applications lays open ahead of them. Building up from the simplest two-colour cell, multielectrochromic arrangements are being devised, taking advantage of new electrochromic materials emerging at a fast pace. The ultimate device goal encompasses full control over the intensity and spectrum of passing light, including the two extremes of complete and null transmittance. With numerous electrochromic device architectures being explored and their operating parameters constantly ameliorated to pursue this target, a summary and overview of developments in the field is presented. Discussing the attributes of reported electrochromic systems, key research points and challenges are identified, providing an outlook for this exciting topic of polymer material science.

Smart Portable Devices Suitable for Cultural Heritage: A Review

This article reviews recent portable sensor technologies to apply in the Cultural Heritage (CH) fields. The review has been prepared in the form of a retrospective description of the sensor's history and technological evolution, having: new nanomaterials for transducers, miniaturized, portable and integrated sensors, the wireless transmission of the analytical signals, ICT_Information Communication Technology and IoT_Internet of Things to apply to the cultural heritage field. In addition, a new trend of movable tattoo sensors devices is discussed, referred to in situ analysis, which is especially important when scientists are in the presence of un-movable and un-tangible Cultural Heritage and Art Work objects. The new proposed portable contact sensors (directly applied to art work objects and surfaces) are non-invasive and non-destructive to the different materials and surfaces of which cultural heritage is composed.

Rheo-optical Analysis of Functionalized Graphene Suspensions

Wet processing of graphene sheets is a potentially interesting route for the economically viable creation of graphene-based composites. In the present work, flow dichroism and small-angle light scattering are used to investigate the dispersion of functionalized graphene sheets in a suspension and their response to shear flow. In line with expectations from scaling theory at rest, the functionalized graphene sheets are present as Brownian flat sheets, and there is no evidence of significant crumpling. More surprisingly, we find that the rate-dependent orientation of these molecularly thin sheets can be described by numerical predictions for hard spheroidal sheets, making quantitative predictions of the flow-induced orientation possible. Further comparison of the flow-induced orientation of thick gold decahedra with the thin graphene sheets shows that, except for effects of polydispersity, the flow-induced orientation is predicted well quantitatively. Adequate prediction of the effects of flow on the orientation of graphene sheets makes it possible to design wet processed graphene-based composite materials.

Influence of water on the surface of graphene

We have studied how water modifies the surface of graphene and in particular how the surface conductivity of graphene is affected. According to the literature, two types of interactions should be distinguished: physical, where a water molecule remains intact and is located at some distance from the mesh, and chemical, where a water molecule is imbricated in the graphene bond structure. We have developed theoretical models for both types of interactions using the density functional theory (DFT) with the B3LYP hybrid functional combined with the 6-31G(d) basis set. Our calculations show that the surface conductivity of graphene is reduced in the presence of water.

Room-Temperature Nanowelding of a Silver Nanowire Network Triggered by Hydrogen Chloride Vapor for Flexible Transparent Conductive Films

High contact resistance between silver nanowires (AgNWs) is a key issue in widespread application of AgNW flexible transparent conductive films as a promising candidate to replace the brittle and expensive indium tin oxide. A facile, room-temperature nanowelding method of an AgNW network triggered by hydrogen chloride (HCl) vapor is demonstrated to reduce the sheet resistance of the AgNW network. Under the visible light, O₂ and HCl vapor serving as an etching couple induced silver atoms to be transferred from the bottom AgNW at the junction to the top one, and then, these silver atoms epitaxially recrystallized at the contact position with the lattice of the top AgNW as the template, ultimately resulting in the coalescence of the junction between AgNWs. Polydimethylsiloxane (PDMS) was spin-coated onto the HCl-vapor-treated (HVT) AgNW network on the polyethylene terephthalate substrate to fabricate PDMS/HVT AgNW films. The fabricated film with low sheet resistance and high transmittance retained its conductivity after 4000 bending cycles. Furthermore, excellent heating performance, electromagnetic interference shielding effectiveness, and foldability were obtained in the PDMS/HVT AgNW film. Thus, the role of the simple nanowelding process is evident in enhancing the performance of AgNW transparent conductive films for emerging soft optoelectronic applications.

Bipolar Spectroelectrochemistry

Bipolar electrochemistry is receiving growing attention in the last years, not only because it is an important tool for studying electron transfer processes, but also because it is really fruitful in the development of new analytical sensors. Bipolar electrodes show promising applications as a direct analytical tool since oxidation and reduction reactions take place simultaneously on different parts of a single conductor. There are several electrochemical devices that provide information about electron transfer between two immiscible electrolyte solutions, but to the best of our knowledge, this is the first time that a bipolar device is able to record two spectroelectrochemical responses concomitantly at two different compartments. It allows deconvolving the electrochemical signal into two different optical signals related to the electron transfer processes occurring at two compartments that are electrically in contact. The combination of an electrochemical and two spectroscopic responses is indeed very useful, providing essential advantages in the study of a huge variety of systems. The study of three different electrochemical systems, such as reversible redox couples, carbon nanotubes, and conducting polymers has allowed us to validate the new cell and to demonstrate the capabilities of this technique to obtain valuable time-resolved information related to the electron transfer processes.

Influence of Substrate Microstructure on the Transport Properties of CVD-Graphene

We report the study of electrical transport in few-layered CVD-graphene located on nanostructured surfaces in view of its potential application as a transparent contact to optoelectronic devices. Two specific surfaces with a different characteristic feature scale are analyzed: semiconductor micropyramids covered with SiO2 layer and opal structures composed of SiO2 nanospheres. Scanning tunneling microscopy (STM) and scanning electron microscopy (SEM), as well as Raman spectroscopy, have been used to determine graphene/substrate surface profile. The graphene transfer on the opal face centered cubic arrangement of spheres with a diameter of 230 nm leads to graphene corrugation (graphene partially reproduces the opal surface profile). This structure results in a reduction by more than 3 times of the graphene sheet conductivity compared to the conductivity of reference graphene located on a planar SiO2 surface but does not affect the contact resistance to graphene. The graphene transfer onto an organized array of micropyramids results in a graphene suspension. Unlike opal, the graphene suspension on pyramids leads to a reduction of both the contact resistance and the sheet resistance of graphene compared to resistance of the reference graphene/flat SiO2 sample. The sample annealing is favorable to improve the contact resistance to CVD-graphene; however, it leads to the increase of its sheet resistance.

Flattening sol–gel nanospheres into a carbon sheet-intercalated cobalt/carbon/cobalt sandwich-nanostructure

Uniform cobalt/carbon/cobalt sandwich-like nanosheet stacks have been constructed by using sol–gel nanospheres covered with Co^II–Co^III–LDH as a precursor.

Hybridization of inorganic CoB noncrystal with graphene and its Kubas-enhanced hydrogen adsorption at room temperature

In this work an archetypical hybrid material has been prepared by the reaction of an inorganic CoB noncrystal with graphene by a high-energy ball-milling process, which showed an enhanced electrochemical hydrogen storage ability induced by the Co–B–C structure.

Nanomaterial-enabled stretchable conductors: strategies, materials and devices

Stretchable electronics are attracting intensive attention due to their promising applications in many areas where electronic devices undergo large deformation and/or form intimate contact with curvilinear surfaces. On the other hand, a plethora of nanomaterials with outstanding properties have emerged over the past decades. The understanding of nanoscale phenomena, materials, and devices has progressed to a point where substantial strides in nanomaterial-enabled applications become realistic. This review summarizes recent advances in one such application, nanomaterial-enabled stretchable conductors (one of the most important components for stretchable electronics) and related stretchable devices (e.g., capacitive sensors, supercapacitors and electroactive polymer actuators), over the past five years. Focusing on bottom-up synthesized carbon nanomaterials (e.g., carbon nanotubes and graphene) and metal nanomaterials (e.g., metal nanowires and nanoparticles), this review provides fundamental insights into the strategies for developing nanomaterial-enabled highly conductive and stretchable conductors. Finally, some of the challenges and important directions in the area of nanomaterial-enabled stretchable conductors and devices are discussed.

In situ and nonvolatile photoluminescence tuning and nanodomain writing demonstrated by all-solid-state devices based on graphene oxide

In situ and nonvolatile tuning of photoluminescence (PL) has been achieved based on graphene oxide (GO), the PL of which is receiving much attention because of various potential applications of the oxide (e.g., display, lighting, and nano-biosensor). The technique is based on in situ and nonvolatile tuning of the sp(2) domain fraction to the sp(3) domain fraction (sp(2)/sp(3) fraction) in GO through an electrochemical redox reaction achieved by solid electrolyte thin films. The all-solid-state variable PL device was fabricated by GO and proton-conducting mesoporous SiO2 thin films, which showed an extremely low PL background. The device successfully tuned the PL peak wavelength in a very wide range from 393 to 712 nm, covering that for chemically tuned GO, by adjusting the applied DC voltage within several hundred seconds. We also demonstrate the sp(2)/sp(3) fraction tuning using a conductive atomic force microscope. The device achieved not only writing, but also erasing of the sp(2)/sp(3)-fraction-tuned nanodomain (both directions operation). The combination of these techniques is applicable to a wide range of nano-optoelectronic devices including nonvolatile PL memory devices and on-demand rewritable biosensors that can be integrated into nano- and microtips which are transparent, ultrathin, flexible, and inexpensive.

Direct growth of ZnO nanowire arrays on UV-irradiated graphene

The influences of UV light to graphene for ZnO nanowire growth were discussed.

Two-dimensional layered semiconductor/graphene heterostructures for solar photovoltaic applications

Schottky barriers formed by graphene (monolayer, bilayer, and multilayer) on 2D layered semiconductor tungsten disulfide (WS2) nanosheets are explored for solar energy harvesting. The characteristics of the graphene-WS2 Schottky junction vary significantly with the number of graphene layers on WS2, resulting in differences in solar cell performance. Compared with monolayer or stacked bilayer graphene, multilayer graphene helps in achieving improved solar cell performance due to superior electrical conductivity. The all-layered-material Schottky barrier solar cell employing WS2 as a photoactive semiconductor exhibits efficient photon absorption in the visible spectral range, yielding 3.3% photoelectric conversion efficiency with multilayer graphene as the Schottky contact. Carrier transport at the graphene/WS2 interface and the interfacial recombination process in the Schottky barrier solar cells are examined.

Reversible hydrophobic to hydrophilic transition in graphene via water splitting induced by UV irradiation

Although the reversible wettability transition between hydrophobic and hydrophilic graphene under ultraviolet (UV) irradiation has been observed, the mechanism for this phenomenon remains unclear. In this work, experimental and theoretical investigations demonstrate that the H2O molecules are split into hydrogen and hydroxyl radicals, which are then captured by the graphene surface through chemical binding in an ambient environment under UV irradiation. The dissociative adsorption of H2O molecules induces the wettability transition in graphene from hydrophobic to hydrophilic. Our discovery may hold promise for the potential application of graphene in water splitting.

Optical transmission of nematic liquid crystal 5CB doped by single-walled and multi-walled carbon nanotubes

Comparative studies of optical transmission of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), dispersed in nematic liquid crystal matrix 5CB, were carried out. The data evidence violations of Beer-Lambert-Bouguer (BLB) law both in cell thickness and concentration dependencies. The most striking is the fact that optical transmission dependencies for SWCNTs and MWCNTs were quite different in the nematic phase, but they were practically indistinguishable in the isotropic phase. Monte Carlo simulations of the impact of aggregation on direct transmission and violation of BLB law were also done. The results were discussed accounting for the tortuous shape of CNTs, their physical properties and aggregation, as well as strong impact of perturbations of the nematic 5CB structure inside coils and in the vicinity of CNT aggregates.

GaN-based light-emitting diodes on graphene-coated flexible substrates

We demonstrate GaN-based thin light-emitting diodes (LEDs) on flexible polymer and paper substrates covered with chemical vapor deposited graphene as a transparent-conductive layer. Thin LEDs were fabricated by lifting the sapphire substrate off by Excimer laser heating, followed by transfer of the LEDs to the flexible substrates. These substrates were coated with tri-layer graphene by a wet transfer method. Optical and electrical properties of thin laser lift-offed LEDs on the flexible substrates were characterized under both relaxed and strained conditions. The graphene on paper substrates remained conducting when the graphene/paper structure was folded. The high transmittance, low sheet resistance and high failure strain of the graphene make it an ideal candidate as the transparent and conductive layer in flexible optoelectronics.

Spectroscopic and electrochemical characterization of nanostructured optically transparent carbon electrodes

The present paper describes the results related to the optical and electrochemical characterization of thin carbon films fabricated by spin coating and pyrolysis of AZ P4330-RS photoresist. The goal of this paper is to provide comprehensive information allowing for the rational selection of the conditions to fabricate optically transparent carbon electrodes (OTCE) with specific electrooptical properties. According to our results, these electrodes could be appropriate choices as electrochemical transducers to monitor electrophoretic separations. At the core of this manuscript is the development and critical evaluation of a new optical model to calculate the thickness of the OTCE by variable angle spectroscopic ellipsometry. Such data were complemented with topography and roughness (obtained by atomic force microscopy), electrochemical properties (obtained by cyclic voltammetry), electrical properties (obtained by electrochemical impedance spectroscopy), and structural composition (obtained by Raman spectroscopy). Although the described OTCE were used as substrates to investigate the effect of electrode potential on the real-time adsorption of proteins by ellipsometry, these results could enable the development of other biosensors that can be then integrated into various CE platforms.

Antireflection properties of graphene layers on planar and textured silicon surfaces

In this study, theoretical and experimental investigations have been carried out to explore the suitability of graphene layers as an antireflection coating. Microwave plasma enhanced chemical vapor deposition and chemically grown graphene layers deposited on polished and textured silicon surfaces show that graphene deposition results in a large decrease in reflectance in the wavelength range of 300-650 nm, especially in the case of polished silicon. A Si3N4/textured silicon reference antireflection coating and graphene deposited polished and textured silicon exhibit similar reflectance values, with the graphene/Si surface showing lower reflectance in the 300-400 nm range. Comparison of experimental results with the finite difference time domain calculations shows that the graphene along with a SiO2 surface layer results in a decrease in reflectance in the 300-650 nm range, with a reflectance value of <5% for the case of graphene deposited textured silicon surfaces. The monolayer and inert character along with the high transmittance of graphene make it an ideal surface layer. The results of the present study show its suitability as an antireflection coating in solar cell and UV detector applications.

Graphene in light: design, synthesis and applications of photo-active graphene and graphene-like materials

Graphene functionalized with photo-active units has become one of the most exciting topics of research in the last few years, which remarkably sustains and expands the graphene boom. The rise of photo-active graphene in photonics and optoelectronics is evidenced by a spate of recent reports on topics ranging from photodetectors, photovoltaics, and optoelectronics to photocatalysis. For these applications, the fabrication of photo-active graphene through appropriate chemical functionalization strategies is essential as pristine graphene has zero bandgap and only weak absorption of photons. Written from the chemists' point of view, up-to-date chemical functionalization of graphene with various small organic molecules, conjugated polymers, rare-earth components, and inorganic semiconductors is reviewed. Particular attention is paid to the development of graphene functionalized with light-harvesting moieties, including materials synthesis, characterization, energy/charge-transfer processes, and applications in photovoltaics. Challenges currently faced by researchers and future perspectives in this field are also discussed.

Ultrathin optically transparent carbon electrodes produced from layers of adsorbed proteins

This work describes a simple, versatile, and inexpensive procedure to prepare optically transparent carbon electrodes, using proteins as precursors. Upon adsorption, the protein-coated substrates were pyrolyzed under reductive conditions (5% H2) to form ultrathin, conductive electrodes. Because proteins spontaneously adsorb to interfaces forming uniform layers, the proposed method does not require a precise control of the preparation conditions, specialized instrumentation, or expensive precursors. The resulting electrodes were characterized by a combination of electrochemical, optical, and spectroscopic means. As a proof-of-concept, the optically transparent electrodes were also used as substrate for the development of an electrochemical glucose biosensor. The proposed films represent a convenient alternative to more sophisticated, and less available, carbon-based nanomaterials. Furthermore, these films could be formed on a variety of substrates, without classical limitations of size or shape.

Utilizing redox-chemistry to elucidate the nature of exciton transitions in supramolecular dye nanotubes

Supramolecular assemblies that interact with light have recently garnered much interest as well-defined nanoscale materials for electronic excitation energy collection and transport. However, to control such complex systems it is essential to understand how their various parts interact and whether these interactions result in coherently shared excited states (excitons) or in diffusive energy transport between them. Here, we address this by studying a model system consisting of two concentric cylindrical dye aggregates in a light-harvesting nanotube. Through selective chemistry we are able to unambiguously determine the supramolecular origin of the observed excitonic transitions. These results required the development of a new theoretical model of the supramolecular structure of the assembly. Our results demonstrate that the two cylinders of the nanotube have distinct spectral responses and are best described as two separate, weakly coupled excitonic systems. Understanding such interactions is critical to the control of energy transfer on a molecular scale, a goal in various applications ranging from artificial photosynthesis to molecular electronics.

Transparent conductive graphene electrode in GaN-based ultra-violet light emitting diodes

We report a graphene-based transparent conductive electrode for use in ultraviolet (UV) GaN light emitting diodes (LEDs). A few-layer graphene (FLG) layer was mechanically deposited. UV light at a peak wavelength of 368 nm was successfully emitted by the FLG layer as transparent contact to p-GaN. The emission of UV light through the thin graphene layer was brighter than through the thick graphene layer. The thickness of the graphene layer was characterized by micro-Raman spectroscopy. Our results indicate that this novel graphene-based transparent conductive electrode holds great promise for use in UV optoelectronics for which conventional ITO is less transparent than graphene.

Graphene-based nanomaterials and their electrochemistry

Graphene-based nanomaterials are in the forefront of chemical research. This tutorial review provides an introduction to their electrochemistry, its fundamentals and applications. Selected examples of applications in energy storage and sensing are presented. The synthetic methods for preparing graphenes as well as their materials chemistry are thoroughly discussed, as they have a profound influence on the electronic and electrochemical behavior of graphene-related nanomaterials. Inherent electrochemistry and spectroelectrochemistry of graphene nanomaterials is discussed thoroughly. Important application in sensing and energy storage areas are highlighted.