Single Graphene Sheet Research Articles

Mapping Activity-Dependent Quasi-stationary States of Mitochondrial Membranes with Graphene-Induced Energy Transfer Imaging.

Graphene-induced energy transfer (GIET) was recently introduced for sub-nanometric axial localization of fluorescent molecules. GIET relies on near-field energy transfer from an optically excited fluorophore to a single sheet of graphene. Recently, we demonstrated its potential by determining the distance between two leaflets of supported lipid bilayers. Here, we use GIET imaging for mapping quasi-stationary states of the inner and outer mitochondrial membranes before and during adenosine triphosphate (ATP) synthesis. We trigger the ATP synthesis state in vitro by activating mitochondria with precursor molecules. Our results demonstrate that the inner membrane approaches the outer membrane, while the outer membrane does not show any measurable change in average axial position upon activation. The inter-membrane space is reduced by ∼2 nm. This direct experimental observation of the subtle dynamics of mitochondrial membranes and the change in intermembrane distance upon activation is relevant for our understanding of mitochondrial function.

Second Floor of Flatland: Epitaxial Growth of Graphene on Hexagonal Boron Nitride.

In the studies presented here, the subsequent growth of graphene on hexagonal boron nitride (h-BN) is achieved by the thermal decomposition of molecular precursors and the catalytic assistance of metal substrates. The epitaxial growth of h-BN on Pt(111) is followed by the deposition of a temporary Pt film that acts as a catalyst for the fabrication of the graphene sheet. After intercalation of the intermediate Pt film underneath the boron-nitride mesh, graphene resides on top of h-BN. Scanning tunneling microscopy and density functional calculations reveal that the moiré pattern of the van-der-Waals-coupled double layer is due to the interface of h-BN and Pt(111). While on Pt(111) the graphene honeycomb unit cells uniformly appear as depressions using a clean metal tip for imaging, on h-BN they are arranged in a honeycomb lattice where six protruding unit cells enframe a topographically dark cell. This superstructure is most clearly observed at small probe-surface distances. Spatially resolved inelastic electron tunneling spectroscopy enables the detection of a previously predicted acoustic hybrid phonon of the stacked materials. Its' spectroscopic signature is visible in surface regions where the single graphene sheet on Pt(111) transitions into the top layer of thestacking.

Transmembrane β-peptide helices as molecular rulers at the membrane surface.

β-Peptides are known to form 14-helices with high conformational rigidity, helical persistence length, and well-defined spacing and orientation regularity of amino acid side chains. Therefore, β-peptides are well suited to serve as backbone structures for molecular rulers. On the one hand, they can be functionalized in a site-specific manner with molecular probes or fluorophores, and on the other hand, the β-peptide helices can be recognized and anchored in a biological environment of interest. In this study, the β-peptide helices were anchored in lipid bilayer membranes, and the helices were elongated in the outer membrane environment. The distances of the covalently bound probes to the membrane surface were determined using graphene-induced energy transfer (GIET) spectroscopy, a method based on the distance-dependent quenching of a fluorescent molecule by a nearby single graphene sheet. As a proof of principle, the predicted distances were determined for two fluorophores bound to the membrane-anchored β-peptide molecular ruler.

Molecular dynamics studies on the exfoliation of graphene in room temperature ionic liquids

The theoretical principle of choosing suitable room temperature ionic liquids (RTILs) for liquid phase exfoliation of graphene sheet remains a challenge. A simple thermodynamic model is proposed to show the vital role of the solvation energy as an indication of solvent quality for spontaneous exfoliation. The solvation energy of ten ILs surrounding a single graphene sheet has been determined by molecular dynamics (MD) simulations. It is found to be strongly correlated with surface excess, sheet deformation and surface tension. From the MD simulations [BMIM][TF2N] (-580.86 mJ.m−2), [BPY][ TF2N] (-565.19 mJ.m−2) and [BMP][TF2N] (-551.77 mJ.m−2) shows stronger affinity with graphene surfaces as compared to other ILs. On the basis of the established mechanism, one is able to predict and screen suitable IL for spontaneous exfoliation of graphene.

Dirac cones for graph models of multilayer AA-stacked graphene sheets

Abstract We propose an extension, of a quantum graph model for a single sheet of graphene, to multilayer AA-stacked graphene and also to a model of the bulk graphite. Spectra and Dirac cones are explicitly characterized for bilayer and trilayer graphene, as well as for graphite. For weak layer interaction (as proposed in the text), simple perturbation arguments also cover any number of layers and it mathematically recovers basic cone existences from the theoretical and experimental physics literature; its main strength is its simplicity.

Single sheets of graphene for fabrication of fibers with enhanced mechanical properties.

This paper reports the fabrication and mechanical properties of macroscale graphene fibers (diameters of 10 to 100 μm with lengths upwards of 2 cm) prepared from a single sheet of single-layer graphene grown via chemical vapor deposition (CVD). The breaking strength of these graphene fibers increased with consecutive tensile test measurements on a single fiber, where fiber fragments produced from a prior test exhibited larger breaking strengths. Additionally, we observed an overall reduction of surface folds and wrinkles, and an increase in their alignment parallel to the tensile direction. We propose that a foundation of this property is the plastic deformations within the fiber that accumulate through sequential tensile testing. Through this cyclic method, our best fiber produced a strength of 2.67 GPa with a 1 mm gauge length.

Retracted] Graphene: A Multifunctional Nanomaterial with Versatile Applications

Graphene is a 2D material of high quality obtained from a single atom with unique electronic properties. Graphene has the potential to improve the efficiency, versatility, and durability of a wide range of materials and their applications, but its commercial exploitation will require further study. Due to its flatness and semiconductivity in addition to its high surface area, high mechanical rigidity, high thermal stability, superior thermal conductivity, and electrical conductivity, good biocompatibility, and easy functionalization, graphene is the best candidate for multifunctional applications which opened up new possibilities for potential devices and systems. Every type of graphene material is found to exhibit different and unique tunable properties. Graphene is the best candidate in making nanocomposite‐based electrochemical sensors. Graphene is among the best electronic materials, but synthesizing a single sheet of graphene has received less attention. The objective of this chapter is to bring awareness to readers on the synthesis, properties, and applications of graphene. The limitations of the current knowledge base and prospective research directions related to graphene materials have also been illustrated.

High-resolution imaging of catalytic activity of a single graphene sheet using electrochemiluminescence microscopy.

Here, the electrocatalytic activity of a single graphene sheet is mapped using electrochemiluminescence (ECL) microscopy with a nanometer resolution. The achievement of this high-spatial imaging relies on the varied adsorption of hydrogen peroxide at different sites on the graphene surface, leading to unsynchronized ECL emission. By shortening the exposure time to 0.2 ms, scattered ECL spots are observed in the ECL image that are not overlaid with the spots in the consecutive images. Accordingly, after stacking all the images into a graph, the ECL intensity of each pixel could be used to reflect the electrocatalytic features of the graphene surface with a resolution of 400 nm. This novel ECL method efficiently avoids the long-standing problem of classic ECL microscopy regarding the overlap of ECL emissions from adjacent regions and enables the nanometer spatial resolution of ECL microscopy for the first time.

Wetting and Drying Transitions of Water Nanodroplets on Suspended Graphene Bilayers

Room-temperature wettability of a single graphene sheet has long been a controversial subject. To gain a better understanding of the problem, temperature dependence of the contact angle (CA) of wat...

A comparison of single and double Co sites incorporated in N-doped graphene for the oxygen reduction reaction

Metal and nitrogen co-doped carbons (M-N/Cs) are promising alternatives to platinum-based catalysts for the oxygen reduction reaction (ORR). Here, density functional theory calculations are used to compare the ORR activity of Co single and double sites embedded in N-doped carbon. Two different models of a Co double site are investigated, one in which two single sites are stacked on top of each other and one which has two Co atoms next to each other in a single graphene sheet. For both it is found that the ORR can proceed via a dissociative mechanism that splits the ∗OOH intermediate into ∗O and ∗OH, but only for the double site in the graphene sheet does it result in a significant deviation from the scaling relations. The adsorption energies of the ORR intermediates are investigated using different implicit and explicit solvent models, showing some variation in the results. In particular, the addition of explicit water on the same side of the catalyst as the ORR intermediate can result in stabilisation due to hydrogen bonding, while an explicit water molecule adsorbed on the opposite side of the Co atom can have an effect due to the change in coordination which affects the splitting of the Co d orbitals.

Dirac cones for bi- and trilayer Bernal-stacked graphene in a quantum graph model

A quantum graph model for a single sheet of graphene is extended to bilayer and trilayer Bernal-stacked graphene; the spectra are characterized and the dispersion relations explicitly obtained; Dirac cones are then proven to be present only for trilayer graphene, although the bilayer has a gapless parabolic band component. Our model rigorously exhibits basic facts from tight-binding calculations, effective two-dimensional models and a π-orbital continuum model with nearest-neighbour tunnelling that have been discussed in the physics literature.

Graphene gets bent

Graphene gets bent

A compact multi-band notched characteristics UWB microstrip patch antenna with a single sheet of graphene

A rectangular tuneable Ultra-wideband (UWB) Microstrip Patch (MP) antenna based on a Single Sheet of Graphene (SSG) is designed in this study. The antenna band can be tuned by applying a DC voltage bias perpendicular to the SSG at various values via adjusting the input impedance. The antenna has been analyzed by Computer Simulation Technology (CST) Microwave Studio (MWS) software using an FR4 substrate of thickness 1.6 mm with a dielectric permittivity =4.4 and loss tangent tan =0.02 fed by a 50 Ω microstrip line frequency. The design is compact since the antenna consists mostly of copper and the SSG. Graphene’s low weight, high flexibility, and strength make it more attractive than other semiconductor materials. Then, the study investigates the effects of applying the electrical characteristics of graphene to the antenna’s length, which varies with the ON and OFF states. This UWB MP antenna is also designed with notch characteristics so that it can reject undesired interference signals. Subsequently, this compact UWB MP antenna with tuneable resonance frequency is suitable for most wireless communication applications. The simulation results work in the 3.1 to 10 GHz range, as required for UWB technology.

An Ultra-Wideband Terahertz Metamaterial Absorber Utilizing Sinusoidal-Patterned Dielectric Loaded Graphene

In this paper, a non-structured graphene sheet loaded with a sinusoidal-patterned dielectric is introduced as an ultra-wideband metamaterial absorber in terahertz regime. Regardless of conventional structures with multilayered-graphene, a single layer sheet of non-structured graphene is used whereas the proposed structure benefits from dielectric width modulation and cavity method in order to excite continuous graphene plasmon resonances. The structure comprises four layers that two Fabry-Perot cavity mirrors are constructed by upper sinusoidal-patterned dielectric and a gold film. Full wave simulation results demonstrate that a broadband over 90% absorption with absolute bandwidth of 6.58 THz and central frequency of 3.97 THz is achieved under normal TE/TM incident plane wave. The designed structure yields 166% relative bandwidth. According to the symmetric configuration, the absorption spectra of mentioned polarizations are thoroughly close to each other resulting to a polarization insensitive structure. The stability of bandwidth and absorbance of the structure versus angle of incidence, θ, up to 35°/65° for TM/TE polarizations, respectively, and azimuth angle, φ, shows an interesting capability for utilization as detectors and sensors. The simple geometry of utilized graphene layer results in easy fabrication. The designed structure has wideband absorption in THz regime. Moreover, it is more compact than conventional broadband THz absorbers.

Strain Modulated Superlattices in Graphene.

Numerous theoretically proposed devices and novel phenomena have sought to take advantage of the intense pseudogauge fields that can arise in strained graphene. Many of these proposals, however, require fields to oscillate with a spatial frequency smaller than the magnetic length, while to date only the generation and effects of fields varying at a much larger length scale have been reported. Here, we describe the creation of short wavelength, periodic pseudogauge-fields using rippled graphene under extreme (>10%) strain and study of its effects on Dirac electrons. Combining scanning tunneling microscopy and atomistic calculations, we find that spatially oscillating strain generates a new quantization different from the familiar Landau quantization. Graphene ripples also cause large variations in carbon-carbon bond length, creating an effective electronic superlattice within a single graphene sheet. Our results thus also establish a novel approach of synthesizing effective 2D lateral heterostructures by periodically modulating lattice strain.

Detecting the morphology of single graphene sheets by dual channel sampling plasmonic imaging.

Due to their excellent physical and chemical properties, graphene sheets are widely used in industry, which makes detection important to guarantee their performance. Atomic force microscopy, scanning electron microscopy, and Raman spectroscopy are the most common detection methods, which is either time-consuming or easily destructive. In this work, we presented a fast and nondestructive method to detect single graphene sheets by using plasmonic imaging. Dual channel sampling plasmonic imaging combining the image processing algorithm is used to improve the deterioration from propagation length of surface plasmon polaritons and reconstruct the complete morphology of single graphene sheets. The fast and nondestructive detection method paves the way to applications of graphene, and can be extended to the detections of two-dimensional materials, single biological molecule, viruses, and nanomaterials.

Graphene Liquid Cells Assembled through Loop‐Assisted Transfer Method and Located with Correlated Light‐Electron Microscopy

AbstractGraphene liquid cells (GLCs) for transmission electron microscopy (TEM) enable high‐resolution, real‐time imaging of dynamic processes in water. Large‐scale implementation, however, is prevented by major difficulties in reproducing GLC fabrication. Here, a high‐yield method is presented to fabricate GLCs under millimeter areas of continuous graphene, facilitating efficient GLC formation on a TEM grid. Additionally, GLCs are located on the grid using correlated light‐electron microscopy (CLEM), which reduces beam damage by limiting electron exposure time. CLEM allows the acquisition of reliable statistics and the investigation of the most common shapes of GLCs. In particular, a novel type of liquid cell is found, formed from only a single graphene sheet, greatly simplifying the fabrication process. The methods presented in this work—particularly the reproducibility and simplicity of fabrication—will enable future application of GLCs for high‐resolution dynamic imaging of biomolecular systems.

Green hydrothermal synthesis of high quality single and few layers graphene sheets by bread waste as precursor

Graphene and its derivatives are ideal candidates for a variety of applications due to their distinctive optical, thermal, mechanical, and electronic properties, but its high price limits its application. Because of scalable graphene production method still stands as a serious barrier for its broad use. Here we develop a simple method to produce high quality single layer graphene with approximately 3 $/m2 in cost, while current price is about 56,000 $/m2. Food waste (bread waste) is used as starting material. Therefore, our introduced method also can serve as a valuable alternative to recycle food waste. Precursor concentration, pH and reaction temperature can create significant effects on the quality of final products. Single layer graphene sheet is achieved when concentration, reaction temperature and pH is used in 2 g/L, 180 °C and 7, respectively. Reaction is performed in ambient condition which is an advantage for scale up this method.

Unusual magnetotransport properties in graphene fibers.

Graphene, purely sp2-hybridized, has already been extensively studied for magnetoelectronics, however, the magnetotransport properties of graphene fibers (GrFib) have not been explored very well to date. Herein, unique magnetotransport properties of graphene fibers are detected. All the GrFib-samples show the highest positive magnetoresistance (MR ∼ 60%) at room temperature (300 K) that gradually decreases (MR ∼ 37%) at low temperature (5 K), indicating quite different behavior for a graphene derivative. The MR of three different morphologies are compared: single graphene sheet (60-100% at 300 K and 100-110% at 5 K under an applied magnetic field of 5 T), graphene foam (GF-100% at 300 K and 158% at 5 K under an applied magnetic field of 5 T), and graphene fiber (60% at 300 K and 37% at 300 K under an applied magnetic field of 5 T), and found that each morphology has a different magnitude of MR under similar magnitude of magnetic field and temperature. Unlike graphene and GF, GrFib shows a decreasing trend of MR at low temperatures, violating commonly used weak anti-localization phenomena in graphene. Technologically, each morphology of graphene has a unique set of magnetotransport properties that can be considered for particular magnetoelectronic devices depending upon the mechanical, electrical, and magnetotransport properties.

Graphene nanoparticles: The super material of future

Graphene (GR) resembles as a planar sheet having thickness equivalent to almost one atom of carbon in which carbon atoms are closely packed representing a honeycomb lattice. In the domain of material science and condensed matter, graphene is a fast growing star with good potential for real time application in diverse scientific and technical fields. The documented characteristics and scope of this unique two-dimensional structure opened new possibilities for wide range of devices and systems. Although GR has been established as well-known electronic material, there has been less exploration of the synthesis of single sheet GR. This state of art is an attempt to have overview of recent research in field of GR related to its synthesis and scope in multifarious applications in context to electronics and energy in general and related to field emission and sensors in particular. The scope of graphene nanoparticles in tribology and industrial automation has also been explored. Where applicable, the weaknesses of the existing knowledge base and future directions for study have also been emphasised.