Science.gov

Sample records for mechanically exfoliated graphene

  1. Hydrogen storage in platinum decorated hydrogen exfoliated graphene sheets by spillover mechanism.

    PubMed

    P, Divya; Ramaprabhu, S

    2014-12-28

    Development of lightweight materials with high hydrogen storage capacities is a great challenge for the hydrogen economy. Here, we report high pressure hydrogen adsorption-desorption studies of platinum-decorated hydrogen-exfoliated graphene sheets (Pt-HEG). Pt-HEG shows a maximum hydrogen uptake capacity of 1.4 wt% at 25 °C and 3 MPa. Analysis of the isosteric heat of adsorption provides evidence of spillover mechanism.

  2. Synthesis of ZnO Nanocrystal-Graphene Composite by Mechanical Milling and Sonication-Assisted Exfoliation

    NASA Astrophysics Data System (ADS)

    Arora, Sweety; Srivastava, Chandan

    2017-02-01

    A ZnO nanocrystal-graphene composite was synthesized by a two-step method involving mechanical milling and sonication-assisted exfoliation. Zn metal powder was first ball-milled with graphite powder for 30 h in water medium. This ball-milled mixture was then subjected to exfoliation by sonication in the presence of sodium lauryl sulfate surfactant to produce graphene decorated with spherical agglomerates of ultrafine nanocrystalline ZnO. The presence of a few layers of graphene was confirmed by Raman spectroscopy and atomic force microscopy measurements. The size, phase identity and composition of the ZnO nanocrystals was determined by transmission electron microscopy measurements.

  3. Liquid exfoliation of defect-free graphene.

    PubMed

    Coleman, Jonathan N

    2013-01-15

    Due to its unprecedented physical properties, graphene has generated huge interest over the last 7 years. Graphene is generally fabricated in one of two ways: as very high quality sheets produced in limited quantities by micromechanical cleavage or vapor growth or as a rather defective, graphene-like material, graphene oxide, produced in large quantities. However, a growing number of applications would profit from the availability of a method to produce high-quality graphene in large quantities. This Account describes recent work to develop such a processing route inspired by previous theoretical and experimental studies on the solvent dispersion of carbon nanotubes. That work had shown that nanotubes could be effectively dispersed in solvents whose surface energy matched that of the nanotubes. We describe the application of the same approach to the exfoliation of graphite to give graphene in a range of solvents. When graphite powder is exposed to ultrasonication in the presence of a suitable solvent, the powder fragments into nanosheets, which are stabilized against aggregation by the solvent. The enthalpy of mixing is minimized for solvents with surface energies close to that of graphene (∼68 mJ/m(2)). The exfoliated nanosheets are free of defects and oxides and can be produced in large quantities. Once solvent exfoliation is possible, the process can be optimized and the nanosheets can be separated by size. The use of surfactants can also stabilize exfoliated graphene in water, where the ζ potential of the surfactant-coated graphene nanosheets controls the dispersed concentration. Liquid exfoliated graphene can be used for a range of applications: graphene dispersions as optical limiters, films of graphene flakes as transparent conductors or sensors, and exfoliated graphene as a mechanical reinforcement for polymer-based composites. Finally, we have extended this process to exfoliate other layered compounds such as BN and MoS(2). Such materials will be

  4. Multilayered graphene efficiently formed by mechanical exfoliation for nonlinear saturable absorbers in fiber mode-locked lasers

    NASA Astrophysics Data System (ADS)

    Chang, You Min; Kim, Hyungseok; Lee, Ju Han; Song, Yong-Won

    2010-11-01

    An efficiently prepared graphene from a bulk graphite using mechanical exfoliation is experimentally investigated for the first practical application to ultrafast photonics. Overcoming the limitations of the method in its size and atomic layer control, the multilayered graphene guarantees a nonlinear intensity modulation. After confirming its excellent crystal quality and few-layered nanostructure employing Raman analysis and atomic force microscopy the graphene layer is introduced into a fiber laser as an intracavity saturable absorber to realize the passive mode-locking that produces picosecond pulses at the repetition rate of 10.9 MHz. Extinction ratio of the resultant pulsed output is higher than 40 dB.

  5. Uniaxial Drawing of Graphene-PVA Nanocomposites: Improvement in Mechanical Characteristics via Strain-Induced Exfoliation of Graphene.

    PubMed

    Jan, Rahim; Habib, Amir; Akram, Muhammad Aftab; Zia, Tanveer-Ul-Haq; Khan, Ahmad Nawaz

    2016-12-01

    Polyvinyl alcohol (PVA)-stabilized graphene nanosheets (GNS) of lateral dimension (L) ~1 μm are obtained via liquid phase exfoliation technique to prepare its composites in the PVA matrix. These composites show low levels of reinforcements due to poor alignment of GNS within the matrix as predicted by the modified Halpin-Tsai model. Drawing these composites up to 200 % strain, a significant improvement in mechanical properties is observed. Maximum values for Young's modulus and strength are ~×4 and ~×2 higher respectively than that of neat PVA. Moreover, the rate of increase of the modulus with GNS volume fraction is up to 700 GPa, higher than the values predicted using the Halpin-Tsai theory. However, alignment along with strain-induced de-aggregation of GNS within composites accounts well for the obtained results as confirmed by X-ray diffraction (XRD) characterization.

  6. Uniaxial Drawing of Graphene-PVA Nanocomposites: Improvement in Mechanical Characteristics via Strain-Induced Exfoliation of Graphene

    NASA Astrophysics Data System (ADS)

    Jan, Rahim; Habib, Amir; Akram, Muhammad Aftab; Zia, Tanveer-ul-Haq; Khan, Ahmad Nawaz

    2016-08-01

    Polyvinyl alcohol (PVA)-stabilized graphene nanosheets (GNS) of lateral dimension ( L) ~1 μm are obtained via liquid phase exfoliation technique to prepare its composites in the PVA matrix. These composites show low levels of reinforcements due to poor alignment of GNS within the matrix as predicted by the modified Halpin-Tsai model. Drawing these composites up to 200 % strain, a significant improvement in mechanical properties is observed. Maximum values for Young's modulus and strength are ~×4 and ~×2 higher respectively than that of neat PVA. Moreover, the rate of increase of the modulus with GNS volume fraction is up to 700 GPa, higher than the values predicted using the Halpin-Tsai theory. However, alignment along with strain-induced de-aggregation of GNS within composites accounts well for the obtained results as confirmed by X-ray diffraction (XRD) characterization.

  7. Stability of melamine-exfoliated graphene in aqueous media: quantum-mechanical insights at the nanoscale.

    PubMed

    Rodríguez, Antonio M; Muñoz-García, Ana B; Crescenzi, Orlando; Vázquez, Ester; Pavone, Michele

    2016-08-10

    In recent experiments, melamine (1,3,5-triazine-2,4,6-triamine) has been proposed as an effective exfoliating agent to obtain high quality graphene from graphite. After washing out the melamine in excess, small amounts (ppm) are still needed to stabilize the dispersion of graphene flakes in aqueous media. To understand the origin of this behaviour, we investigated the melamine-graphene-water system and the fundamental interactions that determine its structure and energetics. To disentangle the subtle interplay of hydrogen-bonding and dispersive forces we used state-of-the-art ab initio calculations based on density functional theory. First, we focused on the case of water molecules interacting with melamine-graphene assemblies at different melamine coverages. We found that water-melamine interactions provide the driving force for washing off the melamine from graphene. Then, we addressed the interaction of single and double layers of water molecules with the graphene surface in the presence of an adsorbed melamine molecule. We found that this melamine acts as a non-covalent anchor for keeping a number of water molecules conveniently close to the graphene surface, thus helping its stabilization in aqueous media. Our analysis helps understanding how competing weak forces can lead to a stable graphene water suspension thanks to small amounts of adsorbed melamine. From our results, we derive simple indications on how the water-graphene interfacial properties can be tuned via non-covalent adsorption of small functional molecules with H-bond donor/acceptor groups. These new hints can be helpful to prepare stable graphene dispersions in water and so to unlock graphene potential in aqueous environments.

  8. Synthesis and characterization of exfoliated graphene oxide

    NASA Astrophysics Data System (ADS)

    Muhamad, Ku Sarah Syahidah Ku; Mohamed, Faizal; Radiman, Shahidan; Hamzah, Ainon; Sarmani, Sukiman; Siong, Khoo Kok; Yasir, Muhammad Samudi; Rahman, Irman Abdul; Rosli, Nur Ratasha Alia Md.

    2016-11-01

    Graphene oxide has many applications such as in electronic devices, as storage energy device, biosensor, biomedical application, water purification, coating technology, as a composite and paper like materials. Hummer's method is one of the most common methods used in synthesizing graphene oxide. Graphene is different in size and structure because of oxidized layered of graphene oxide hence, the expanded interlayer structure of graphene oxide can be easily exfoliated by ultrasonication. We report on the preparation of exfoliated graphene oxide by using sonication method. Ultraviolet-visible spectrometer (UV-Vis) and Fourier-Transform Infrared Spectra Analyzer (FTIR) were used to characterize the exfoliated graphite oxide. Exfoliation of graphite oxide is conducted using water bath sonication. In order to confirm the chemical conformation and structure of the produced graphene oxide, FTIR and UV-Vis spectroscopy were utilized. Both peak of C=O and C-C bond are detected using UV-Vis and the results were confirmed using FTIR. Therefore, from this study, it can be concluded based on FTIR and UV-Vis spectral acquisition that graphene oxide can be produced by exfoliation of graphite oxide using water bath sonication.

  9. Preparation and characterization of solar exfoliated graphene

    SciTech Connect

    M, Sreejesh S, Nagaraja H.; K, Udaya Bhat

    2014-10-15

    Hummer's method was used for the chemical synthesis of graphite oxide from graphite flakes. Simultaneous exfoliation and reduction of graphite oxide to Graphene was achieved through focused solar light irradiation using a convex lens. The morphological characteristics were studied using SEM and TEM. Layered morphology of Graphene was observed through TEM. Raman spectra and FTIR were used for the structural characterization of Graphene. EDAX analysis showed the drop in oxygen content during exfoliation. The method offered a faster, easier and environmental friendly method to produce Graphene for potential applications.

  10. Graphene via sonication assisted liquid-phase exfoliation.

    PubMed

    Ciesielski, Artur; Samorì, Paolo

    2014-01-07

    Graphene, the 2D form of carbon based material existing as a single layer of atoms arranged in a honeycomb lattice, has set the science and technology sectors alight with interest in the last decade in view of its astounding electrical and thermal properties, combined with its mechanical stiffness, strength and elasticity. Two distinct strategies have been undertaken for graphene production, i.e. the bottom-up and the top-down. The former relies on the generation of graphene from suitably designed molecular building blocks undergoing chemical reaction to form covalently linked 2D networks. The latter occurs via exfoliation of graphite into graphene. Bottom-up techniques, based on the organic syntheses starting from small molecular modules, when performed in liquid media, are both size limited, because macromolecules become more and more insoluble with increasing size, and suffer from the occurrence of side reactions with increasing molecular weight. Because of these reasons such a synthesis has been performed more and more on a solid (ideally catalytically active) surface. Substrate-based growth of single layers can be done also by chemical vapor deposition (CVD) or via reduction of silicon carbide, which unfortunately relies on the ability to follow a narrow thermodynamic path. Top-down approaches can be accomplished under different environmental conditions. Alongside the mechanical cleavage based on the scotch tape approach, liquid-phase exfoliation (LPE) methods are becoming more and more interesting because they are extremely versatile, potentially up-scalable, and can be used to deposit graphene in a variety of environments and on different substrates not available using mechanical cleavage or growth methods. Interestingly, LPE can be applied to produce different layered systems exhibiting different compositions such as BN, MoS2, WS2, NbSe2, and TaS2, thereby enabling the tuning of numerous physico-chemical properties of the material. Furthermore, LPE can be

  11. Graphene via Molecule-Assisted Ultrasound-Induced Liquid-Phase Exfoliation: A Supramolecular Approach

    NASA Astrophysics Data System (ADS)

    Eredia, Matilde; Ciesielski, Artur; Samorì, Paolo

    2016-12-01

    Graphene is a two-dimensional (2D) material holding unique optical, mechanical, thermal and electrical properties. The combination of these exceptional characteristics makes graphene an ideal model system for fundamental physical and chemical studies as well as technologically ground breaking material for a large range of applications. Graphene can be produced either following a bottom-up or top-down method. The former is based on the formation of covalent networks suitably engineered molecular building blocks undergoing chemical reaction. The latter takes place through the exfoliation of bulk graphite into individual graphene sheets. Among them, ultrasound-induced liquid-phase exfoliation (UILPE) is an appealing method, being very versatile and applicable to different environments and on various substrate types. In this chapter, we describe the recently reported methods to produce graphene via molecule-assisted UILPE of graphite, aiming at the generation of high-quality graphene. In particular, we will focus on the supramolecular approach, which consists in the use of suitably designed organic molecules during the UILPE of graphite. These molecules act as graphene dispersion-stabilizing agents during the exfoliation. This method relying on the joint effect of a solvent and ad hoc molecules to foster the exfoliation of graphite into graphene in liquid environment represents a promising and modular method toward the improvement of the process of UILPE in terms of the concentration and quality of the exfoliated material. Furthermore, exfoliations in aqueous and organic solutions are presented and discussed separately.

  12. Towards the continuous production of high crystallinity graphene via electrochemical exfoliation with molecular in situ encapsulation

    NASA Astrophysics Data System (ADS)

    Chen, Chia-Hsuan; Yang, Shiou-Wen; Chuang, Min-Chiang; Woon, Wei-Yen; Su, Ching-Yuan

    2015-09-01

    Large-scale production of uniform and high-quality graphene is required for practical applications of graphene. The electrochemical exfoliation method is considered as a promising approach for the practical production of graphene. However, the relatively low production rate of graphene currently hinders its usage. Here, we demonstrate, for the first time, a rapid and high-yield approach to exfoliate graphite into graphene sheets via an electrochemical method with small molecular additives; where in this approach, the use of melamine additives is able to efficiently exfoliate graphite into high-quality graphene sheets. The exfoliation yield can be increased up to 25 wt% with melamine additives compared to electrochemical exfoliation without such additives in the electrolyte. The proposed mechanism for this improvement in the yield is the melamine-induced hydrophilic force from the basal plane; this force facilitates exfoliation and provides in situ protection of the graphene flake surface against further oxidation, leading to high-yield production of graphene of larger crystallite size. The residual melamine can be easily washed away by water after collection of the graphene. The exfoliation with molecular additives exhibits higher uniformity (over 80% is graphene of less than 3 layers), lower oxidation density (C/O ratio of 26.17), and low defect level (D/G < 0.45), which are characteristics superior to those of reduced graphene oxide (rGO) or of a previously reported approach of electrochemical exfoliated graphene (EC-graphene). The continuous films obtained by the purified graphene suspension exhibit a sheet resistance of 13.5 kΩ □-1 at ~95% transmittance. A graphene-based nanocomposite with polyvinyl butyral (PVB) exhibits an electrical conductivity of 3.3 × 10-3 S m-1 for the graphene loading fraction of 0.46 vol%. Moreover, the melamine functionalized graphene sheets are readily dispersed in the aqueous solution during the exfoliation process, allowing for

  13. Simple Synthesis of Fluorinated Graphene: Thermal Exfoliation of Fluorographite.

    PubMed

    Jankovský, Ondřej; Mazánek, Vlastimil; Klímová, Kateřina; Sedmidubský, David; Kosina, Jiří; Pumera, Martin; Sofer, Zdeněk

    2016-12-05

    Fluorinated graphene can be prepared directly by thermal exfoliation of fluorographite. The exfoliation was performed in a dynamic nitrogen atmosphere at various temperatures and the exfoliation products were analysed in detail by GC-MS. The structure and properties of all prepared fluorinated graphenes with various contents of fluorine were characterized by a number of analytical techniques. The results show both the dependence of fluorine concentration on exfoliation temperature and the suitability of this method for the synthesis of graphene with controlled concentration of fluorine. The high-temperature exfoliated fluorographite exhibits a high heterogeneous electron transfer rate and excellent catalytic properties towards the oxygen reduction reaction. These synthetic procedures can open a simple way for the synthesis of fluorinated graphene-based devices with tailored properties.

  14. Heterocyclic aramid nanoparticle-assisted graphene exfoliation for fabrication of pristine graphene-based composite paper

    NASA Astrophysics Data System (ADS)

    Mo, Yao; Liu, Qi; Fan, Jinchen; Shi, Penghui; Min, Yulin; Xu, Qunjie

    2015-07-01

    Mechanically strong, electrically conductive, and flexible pristine graphene-based composite paper was prepared based on heterocyclic aramid nanoparticle-assisted liquid-phase exfoliation of graphite. The macroscopic heterocyclic aramid yarns were split and assembled into heterocyclic aramid nanoparticles with the size of 30 nm by deprotonation in dimethylsulfoxide in the presence of potassium hydroxide. The obtained heterocyclic aramid nanoparticles dimethylsulfoxide dispersion was used as good medium solvent for highly efficiency liquid-phase exfoliation of graphite. The results demonstrated that the concentration of exfoliated graphene can facile reaches 2.72 mg/mL after direct sonication of 7 h with assist of heterocyclic aramid nanoparticles. After exfoliation, the self-assembled pristine graphene-based composite paper was fabricated by vacuum-assisted filtration. Due to the introduction of heterocyclic aramid nanoparticles, the self-assembled pristine graphene/heterocyclic aramid nanoparticles composite paper exhibited good mechanical property with tensile strength of 129.7 MPa, meantime, has a high electrical conductivity of 1.42 × 104 S/m.

  15. Nitroaromatic explosives detection using electrochemically exfoliated graphene

    PubMed Central

    Yew, Ying Teng; Ambrosi, Adriano; Pumera, Martin

    2016-01-01

    Detection of nitroaromatic explosives is of paramount importance from security point of view. Graphene sheets obtained from the electrochemical anodic exfoliation of graphite foil in different electrolytes (LiClO4 and Na2SO4) were compared and tested as electrode material for the electrochemical detection of 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) in seawater. Voltammetry analysis demonstrated the superior electrochemical performance of graphene produced in LiClO4, resulting in higher sensitivity and linearity for the explosives detection and lower limit of detection (LOD) compared to the graphene obtained in Na2SO4. We attribute this to the presence of oxygen functionalities onto the graphene material obtained in LiClO4 which enable charge electrostatic interactions with the –NO2 groups of the analyte, in addition to π-π stacking interactions with the aromatic moiety. Research findings obtained from this study would assist in the development of portable devices for the on-site detection of nitroaromatic explosives. PMID:27633489

  16. Nitroaromatic explosives detection using electrochemically exfoliated graphene.

    PubMed

    Yew, Ying Teng; Ambrosi, Adriano; Pumera, Martin

    2016-09-16

    Detection of nitroaromatic explosives is of paramount importance from security point of view. Graphene sheets obtained from the electrochemical anodic exfoliation of graphite foil in different electrolytes (LiClO4 and Na2SO4) were compared and tested as electrode material for the electrochemical detection of 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) in seawater. Voltammetry analysis demonstrated the superior electrochemical performance of graphene produced in LiClO4, resulting in higher sensitivity and linearity for the explosives detection and lower limit of detection (LOD) compared to the graphene obtained in Na2SO4. We attribute this to the presence of oxygen functionalities onto the graphene material obtained in LiClO4 which enable charge electrostatic interactions with the -NO2 groups of the analyte, in addition to π-π stacking interactions with the aromatic moiety. Research findings obtained from this study would assist in the development of portable devices for the on-site detection of nitroaromatic explosives.

  17. Nitroaromatic explosives detection using electrochemically exfoliated graphene

    NASA Astrophysics Data System (ADS)

    Yew, Ying Teng; Ambrosi, Adriano; Pumera, Martin

    2016-09-01

    Detection of nitroaromatic explosives is of paramount importance from security point of view. Graphene sheets obtained from the electrochemical anodic exfoliation of graphite foil in different electrolytes (LiClO4 and Na2SO4) were compared and tested as electrode material for the electrochemical detection of 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) in seawater. Voltammetry analysis demonstrated the superior electrochemical performance of graphene produced in LiClO4, resulting in higher sensitivity and linearity for the explosives detection and lower limit of detection (LOD) compared to the graphene obtained in Na2SO4. We attribute this to the presence of oxygen functionalities onto the graphene material obtained in LiClO4 which enable charge electrostatic interactions with the –NO2 groups of the analyte, in addition to π-π stacking interactions with the aromatic moiety. Research findings obtained from this study would assist in the development of portable devices for the on-site detection of nitroaromatic explosives.

  18. Thermal Conductive and Mechanical Properties of Polymeric Composites Based on Solution-Exfoliated Boron Nitride and Graphene Nanosheets: A Morphology-Promoted Synergistic Effect.

    PubMed

    Cui, Xieliang; Ding, Peng; Zhuang, Nan; Shi, Liyi; Song, Na; Tang, Shengfu

    2015-09-02

    In this work, we reported a synergistic effect of boron nitride (BN) with graphene nanosheets on the enhancement of thermal conductive and mechanical properties of polymeric composites. Here, few layered BN (s-BN) and graphene (s-GH) were used and obtained by liquid exfoliation method. The polystyrene (PS) and polyamide 6 (PA) composites were obtained via solution blending method and subsequently hot-pressing. The experimental results suggested that the thermal conductivity (TC) of the PS and PA composites increases with additional introduction of s-BN. For example, compared with the composites containing 20 wt % s-GH, additional introduction of only 1.5 wt % s-BN could increase the TC up to 38 and 34% in polystyrene (PS) and polyamide 6 (PA) matrix, respectively. Meanwhile, the mechanical properties of the composites were synchronously enhanced. It was found that s-BN filled in the interspaces of s-GH sheets and formed s-BN/s-GH stacked structure, which were helpful for the synchronously improving TC and mechanical properties of the polymeric materials.

  19. Thermal Exfoliation of Natural Cellulosic Material for Graphene Synthesis

    NASA Astrophysics Data System (ADS)

    Ray, Ajoy Kumar; Chatterjee, Somenath; Singh, Jitendra Kumar; Bapari, Himangshu

    2015-01-01

    Hibiscus flower petals have been used as a cheap natural resource precursor for cost-effective synthesis of high quality graphene by thermal exfoliation process. In order to compare the quality of graphene obtained from the flower petals directly with the flower petals pretreated with nickel(II) chloride, Raman spectroscopic technique has been used as the structural probe. The role of temperature and the effect of nickel on thermal exfoliation process have been examined. It has been observed that graphene obtained via nickel incorporation is of better quality because NI2+ ions that get dispersed in the layered-structured cellulose at elevated temperatures get reduced to the metallic state, which in turn push the graphitic layers during thermal exfoliation to produce good quality graphene. In contrast, no such driving force is present in cellulose and hemi-cellulose of flower petals that contain lignin.

  20. Aqueous Dispersions of Graphene from Electrochemically Exfoliated Graphite.

    PubMed

    Sevilla, Marta; Ferrero, Guillermo A; Fuertes, Antonio B

    2016-11-21

    A facile and environmentally friendly synthetic strategy for the production of stable and easily processable dispersions of graphene in water is presented. This strategy represents an alternative to classical chemical exfoliation methods (for example the Hummers method) that are more complex, harmful, and dangerous. The process is based on the electrochemical exfoliation of graphite and includes three simple steps: 1) the anodic exfoliation of graphite in (NH4 )2 SO4 , 2) sonication to separate the oxidized graphene sheets, and 3) reduction of oxidized graphene to graphene. The procedure makes it possible to convert around 30 wt % of the initial graphite into graphene with short processing times and high yields. The graphene sheets are well dispersed in water, have a carbon/oxygen atomic ratio of 11.7, a lateral size of about 0.5-1 μm, and contain only a few graphene layers, most of which are bilayer sheets. The processability of this type of aqueous dispersion has been demonstrated in the fabrication of macroscopic graphene structures, such as graphene aerogels and graphene films, which have been successfully employed as absorbents or as electrodes in supercapacitors, respectively.

  1. Shear Assisted Electrochemical Exfoliation of Graphite to Graphene.

    PubMed

    Shinde, Dhanraj B; Brenker, Jason; Easton, Christopher D; Tabor, Rico F; Neild, Adrian; Majumder, Mainak

    2016-04-12

    The exfoliation characteristics of graphite as a function of applied anodic potential (1-10 V) in combination with shear field (400-74 400 s(-1)) have been studied in a custom-designed microfluidic reactor. Systematic investigation by atomic force microscopy (AFM) indicates that at higher potentials thicker and more fragmented graphene sheets are obtained, while at potentials as low as 1 V, pronounced exfoliation is triggered by the influence of shear. The shear-assisted electrochemical exfoliation process yields large (∼10 μm) graphene flakes with a high proportion of single, bilayer, and trilayer graphene and small ID/IG ratio (0.21-0.32) with only a small contribution from carbon-oxygen species as demonstrated by X-ray photoelectron spectroscopy measurements. This method comprises intercalation of sulfate ions followed by exfoliation using shear induced by a flowing electrolyte. Our findings on the crucial role of hydrodynamics in accentuating the exfoliation efficiency suggest a safer, greener, and more automated method for production of high quality graphene from graphite.

  2. A facile liquid phase exfoliation method to prepare graphene sheets with different sizes expandable graphite

    SciTech Connect

    Zhou, Keqing; Shi, Yongqian; Jiang, Saihua; Song, Lei; Hu, Yuan; Gui, Zhou

    2013-09-01

    Graphical abstract: - Highlights: • This study presented a novel method for the production of high-quality graphene sheets through the exfoliation of Li-intercalated EG with sonication. • The quality of the graphene sheets produced from different sizes EG was compared for the first time and the formation mechanism was discussed. • The graphene sheets obtained from the small size EG have less layers than the large size EG. - Abstract: In this work, graphene sheets suspension were synthesized directly from expandable graphite (EG) via an intercalation and exfoliation pathway using n-butyl lithium as the intercalating agent, water and N,N-dimethylformamide (DMF) as the exfoliating agent. The quality of the graphene sheets produced from different sizes EG was compared and the formation mechanism was discussed. The formation of the graphene sheets and its formation mechanism were confirmed by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected area electron diffraction (SAED), Raman spectroscopy measurement, inductively coupled plasma atomic emission spectrometry (ICP-AES) and thermogravimetric analysis (TGA). The graphene sheets obtained from the small size EG have less layers than the large size EG.

  3. Organic Radical-Assisted Electrochemical Exfoliation for the Scalable Production of High-Quality Graphene.

    PubMed

    Yang, Sheng; Brüller, Sebastian; Wu, Zhong-Shuai; Liu, Zhaoyang; Parvez, Khaled; Dong, Renhao; Richard, Fanny; Samorì, Paolo; Feng, Xinliang; Müllen, Klaus

    2015-11-04

    Despite the intensive research efforts devoted to graphene fabrication over the past decade, the production of high-quality graphene on a large scale, at an affordable cost, and in a reproducible manner still represents a great challenge. Here, we report a novel method based on the controlled electrochemical exfoliation of graphite in aqueous ammonium sulfate electrolyte to produce graphene in large quantities and with outstanding quality. Because the radicals (e.g., HO(•)) generated from water electrolysis are responsible for defect formation on graphene during electrochemical exfoliation, a series of reducing agents as additives (e.g., (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), ascorbic acid, and sodium borohydride) have been investigated to eliminate these radicals and thus control the exfoliation process. Remarkably, TEMPO-assisted exfoliation results in large graphene sheets (5-10 μm on average), which exhibit outstanding hole mobilities (∼405 cm(2) V(-1) s(-1)), very low Raman I(D)/I(G) ratios (below 0.1), and extremely high carbon to oxygen (C/O) ratios (∼25.3). Moreover, the graphene ink prepared in dimethylformamide can exhibit concentrations as high as 6 mg mL(-1), thus qualifying this material for intriguing applications such as transparent conductive films and flexible supercapacitors. In general, this robust method for electrochemical exfoliation of graphite offers great promise for the preparation of graphene that can be utilized in industrial applications to create integrated nanocomposites, conductive or mechanical additives, as well as energy storage and conversion devices.

  4. Ultrasound exfoliation of inorganic analogues of graphene

    NASA Astrophysics Data System (ADS)

    Štengl, Václav; Henych, Jiří; Slušná, Michaela; Ecorchard, Petra

    2014-04-01

    High-intensity ultrasound exfoliation of a bulk-layered material is an attractive route for large-scale preparation of monolayers. The monolayer slices could potentially be prepared with a high yield (up to 100%) in a few minutes. Exfoliation of natural minerals (such as tungstenite and molybdenite) or bulk synthetic materials (including hexagonal boron nitride (h-BN), hexagonal boron carbon nitride (h-BCN), and graphitic carbon nitride (g-C3N4)) in liquids leads to the breakdown of the 3D graphitic structure into a 2D structure; the efficiency of this process is highly dependent upon the physical effects of the ultrasound. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were employed to verify the quality of the exfoliation. Herein, this new method of exfoliation with ultrasound assistance for application to mono- and bilayered materials in hydrophobic and hydrophilic environments is presented.

  5. One-pot synthesis of fluorescent carbon nanoribbons, nanoparticles, and graphene by the exfoliation of graphite in ionic liquids.

    PubMed

    Lu, Jiong; Yang, Jia-xiang; Wang, Junzhong; Lim, Ailian; Wang, Shuai; Loh, Kian Ping

    2009-08-25

    In this work we demonstrate a facile means to generate fluorescent carbon nanoribbons, nanoparticles, and graphene from graphite electrode using ionic liquid-assisted electrochemical exfoliation. A time-dependence study of products exfoliated from the graphite anode allows the reconstruction of the exfoliation mechanism based on the interplay of anodic oxidation and anion intercalation. We have developed strategies to control the distribution of the exfoliated products. In addition, the fluorescence of these carbon nanomaterials can be tuned from the visible to ultraviolet region by controlling the water content in the ionic liquid electrolyte.

  6. Controlling the number of graphene sheets exfoliated from graphite by designed normal loading and frictional motion

    SciTech Connect

    Lee, Seungjun; Lu, Wei

    2014-07-14

    We use molecular dynamics to study the exfoliation of patterned nanometer-sized graphite under various normal loading conditions for friction-induced exfoliation. Using highly ordered pyrolytic graphite (HOPG) as well as both amorphous and crystalline SiO{sub 2} substrate as example systems, we show that the exfoliation process is attributed to the corrugation of the HOPG surface and the atomistic roughness of the substrate when they contact under normal loading. The critical normal strain, at which the exfoliation occurs, is higher on a crystalline substrate than on an amorphous substrate. This effect is related to the atomistic flatness and stiffness of the crystalline surface. We observe that an increase of the van der Waals interaction between the graphite and the substrate results in a decrease of the critical normal strain for exfoliation. We find that the magnitude of the normal strain can effectively control the number of exfoliated graphene layers. This mechanism suggests a promising approach of applying designed normal loading while sliding to pattern controlled number of graphene layers or other two-dimensional materials on a substrate surface.

  7. Role of Peroxide Ions in Formation of Graphene Nanosheets by Electrochemical Exfoliation of Graphite

    PubMed Central

    Rao, Kodepelly Sanjeeva; Senthilnathan, Jaganathan; Liu, Yung-Fang; Yoshimura, Masahiro

    2014-01-01

    This study demonstrates a facile, mild and environmentally-friendly sustainable (soft processing) approach for the efficient electrochemical exfoliation of graphite using a sodium hydroxide/hydrogen peroxide/water (NaOH/H2O2/H2O) system that can produce high-quality, anodic few-layer graphene nanosheets in 95% yield at ambient reaction conditions. The control experiment conducted using NaOH/H2O revealed the crucial role of H2O2 in the exfoliation of graphite. A possible exfoliation mechanism is proposed. The reaction of H2O2 with hydroxyl ions (HO−) leads to the formation of highly nucleophilic peroxide ions (O22−), which play a crucial role in the exfoliation of graphite via electrochemical-potential-assisted intercalation and strong expansion of graphite sheets. PMID:24577336

  8. Role of Peroxide Ions in Formation of Graphene Nanosheets by Electrochemical Exfoliation of Graphite

    NASA Astrophysics Data System (ADS)

    Rao, Kodepelly Sanjeeva; Senthilnathan, Jaganathan; Liu, Yung-Fang; Yoshimura, Masahiro

    2014-02-01

    This study demonstrates a facile, mild and environmentally-friendly sustainable (soft processing) approach for the efficient electrochemical exfoliation of graphite using a sodium hydroxide/hydrogen peroxide/water (NaOH/H2O2/H2O) system that can produce high-quality, anodic few-layer graphene nanosheets in 95% yield at ambient reaction conditions. The control experiment conducted using NaOH/H2O revealed the crucial role of H2O2 in the exfoliation of graphite. A possible exfoliation mechanism is proposed. The reaction of H2O2 with hydroxyl ions (HO-) leads to the formation of highly nucleophilic peroxide ions (O22-), which play a crucial role in the exfoliation of graphite via electrochemical-potential-assisted intercalation and strong expansion of graphite sheets.

  9. The effect of ultraviolet light on structural properties of exfoliated and CVD graphene

    NASA Astrophysics Data System (ADS)

    Emelianov, A. V.; Kireev, D.; Levin, D. D.; Bobrinetskiy, I. I.

    2016-10-01

    We investigate the effect of UV processing of graphene with different structural properties prepared by mechanical exfoliation and CVD growth. Depending on UV exposure time, we observe different effects like oxidation, doping, and etching. For bi-layered and few-layered graphene flakes, we do not observe significant etching even after 3 h exposure which indicates the high resistance of graphene to reactive oxygen species intercalation between graphene layers. Single-layer CVD-grown graphene is fully etched after 2 h of UV treatment. The crystalline size of exfoliated single layer graphene after UV exposure drops from 45 to 5 nm while for CVD graphene from just 10 to 2 nm. We investigate the effect of UV irradiation on field effect transistors, demonstrating sequential cleaning from polymer residuals, oxidation (doping), and final etching of graphene. After 30 minutes of UV irradiation, we observe the hole mobility of a CVD single layer graphene transistor increasing up to 400 cm2/V.s.

  10. A reliable way of mechanical exfoliation of large scale two dimensional materials with high quality

    NASA Astrophysics Data System (ADS)

    Yuan, Lin; Ge, Jun; Peng, Xianglin; Zhang, Qian; Wu, Zefei; Jian, Yu; Xiong, Xiaolu; Yin, Hongxing; Han, Junfeng

    2016-12-01

    In this work, we have developed a modified way of mechanical exfoliation for making two-dimensional materials by introducing a home-designed exfoliation machine. Optical microscopy was employed to identify the thin-layer (mono- and few-layer) flakes primarily. To testify the high efficiency of our modified exfoliation method, we did a simple statistical work on the exfoliation of graphene and WSe2. Further, we used the Raman spectroscopy and the Atomic Force Microscopy (AFM) to characterize the samples. The results indicated the high quality of the as-fabricated samples. Finally, we developed an exfoliation technique for working with easily oxidizing samples. Our modified exfoliation method would be intriguing and innovative for fabricating two dimensional materials, providing a facile way for making electronic and optoelectronic devices.

  11. Ultrafast carrier kinetics in exfoliated graphene and thin graphite films.

    PubMed

    Newson, Ryan W; Dean, Jesse; Schmidt, Ben; van Driel, Henry M

    2009-02-16

    Time-resolved transmissivity and reflectivity of exfoliated graphene and thin graphite films on a 295 K SiO(2)/Si substrate are measured at 1300 nm following excitation by 150 fs, 800 nm pump pulses. From the extracted transient optical conductivity we identify a fast recovery time constant which increases from approximately 200 to 300 fs and a longer one which increases from 2.5 to 5 ps as the number of atomic layers increases from 1 to approximately 260. We attribute the temporal recovery to carrier cooling and recombination with the layer dependence related to substrate coupling. Results are compared with related measurements for epitaxial, multilayer graphene.

  12. Graphene reflux: improving the yield of liquid-exfoliated nanosheets through repeated separation techniques

    NASA Astrophysics Data System (ADS)

    Rountree, Kyler S.; Shah, Smit A.; Sweeney, Charles B.; Irin, Fahmida; Green, Micah J.

    2016-12-01

    Scalable production of graphene through liquid-phase exfoliation has been plagued by low yields. Although several recent studies have attempted to improve graphene exfoliation technology, the problem of separating colloidal nanosheets from unexfoliated parent material has received far less attention. Here we demonstrate a scalable method for improving nanosheet yield through a facile washing process. By probing the sedimentation of liquid-phase exfoliated slurries of graphene nanosheets and parent material, we found that a portion of exfoliated graphene is entrapped in the sediment, but can be recovered by repeatedly washing the slurry of nanosheet and parent material with additional solvent. We found this process to significantly increase the overall yield of graphene (graphene/parent material) and recover a roughly constant proportion of graphene with each wash. The cumulative amount of graphene recovered is only a function of total solvent volume. Moreover, we found this technique to be applicable to other types of nanosheets such as boron nitride nanosheets.

  13. Synthesis of few layer graphene by direct exfoliation of graphite and a Raman spectroscopic study

    SciTech Connect

    Gayathri, S.; Jayabal, P.; Ramakrishnan, V.; Kottaisamy, M.

    2014-02-15

    The exfoliation of graphene from pristine graphite in a liquid phase was achieved successfully via sonication followed by centrifugation method. Ultraviolet–visible (UV–vis) spectra of the obtained graphene dispersions at different exfoliation time indicated that the concentration of graphene dispersion increased markedly with increasing exfoliation time. The sheet-like morphology of the exfoliated graphene was revealed by Scanning Electron Microscopy (SEM) image. Further, the morphological change in different exfoliation time was investigated by Atomic Force Microscopy (AFM). A complete structural and defect characterization was probed using micro-Raman spectroscopic technique. The shape and position of the 2D band of Raman spectra revealed the formation of bilayer to few layer graphene. Also, Raman mapping confirmed the presence of uniformly distributed bilayer graphene sheets on the substrate.

  14. In Situ Exfoliation of Graphene in Epoxy Resins: A Facile Strategy to Efficient and Large Scale Graphene Nanocomposites.

    PubMed

    Li, Yan; Zhang, Han; Crespo, Maria; Porwal, Harshit; Picot, Olivier; Santagiuliana, Giovanni; Huang, Zhaohui; Barbieri, Ettore; Pugno, Nicola M; Peijs, Ton; Bilotti, Emiliano

    2016-09-14

    Any industrial application aiming at exploiting the exceptional properties of graphene in composites or coatings is currently limited by finding viable production methods for large volumes of good quality and high aspect ratio graphene, few layer graphene (FLG) or graphite nanoplatelets (GNP). Final properties of the resulting composites are inherently related to those of the initial graphitic nanoparticles, which typically depend on time-consuming, resource-demanding and/or low yield liquid exfoliation processes. In addition, efficient dispersion of these nanofillers in polymer matrices, and their interaction, is of paramount importance. Here we show that it is possible to produce graphene/epoxy nanocomposites in situ and with high conversion of graphite to FLG/GNP through the process of three-roll milling (TRM), without the need of any additives, solvents, compatibilisers or chemical treatments. This readily scalable production method allows for more than 5 wt % of natural graphite (NG) to be directly exfoliated into FLG/GNP and dispersed in an epoxy resin. The in situ exfoliated graphitic nanoplatelets, with average aspect ratios of 300-1000 and thicknesses of 5-17 nm, were demonstrated to conferee exceptional enhancements in mechanical and electrical properties to the epoxy resin. The above conclusions are discussed and interpreted in terms of simple analytical models.

  15. Electrochemically Exfoliated Graphene and Graphene Oxide for Energy Storage and Electrochemistry Applications.

    PubMed

    Ambrosi, Adriano; Pumera, Martin

    2016-01-04

    Top-down methods are of key importance for large-scale graphene and graphene oxide preparation. Electrochemical exfoliation of graphite has lately gained much interest because of the simplicity of execution, the short process time, and the good quality of graphene that can be obtained. Here, we test three different electrolytes, that is, H2 SO4 , Na2 SO4 , and LiClO4 , with a common exfoliation procedure to evaluate the difference in structural and chemical properties that result for the graphene. The properties are analyzed by means of scanning transmission electron microscopy (STEM), Raman spectroscopy, and X-ray photoelectron spectroscopy. We then tested the graphene materials for electrochemical applications, measuring the heterogeneous electron transfer (HET) rates with a Fe(CN)6 (3-/4-) redox probe, and their capacitive behavior in alkaline solutions. We correlate the electrochemical features with the presence of structural defects and oxygen functionalities on the graphene materials. In particular, the use of LiClO4 during the electrochemical exfoliation of graphite allowed the formation of highly oxidized graphene with a C/O ratio close to 4.0 and represents a possible avenue for the mass production of graphene oxide as valid alternative to the current laborious and dangerous chemical procedures, which also have limited scalability.

  16. Liquid-Phase Exfoliation of Graphite into Single- and Few-Layer Graphene with α-Functionalized Alkanes.

    PubMed

    Haar, Sébastien; Bruna, Matteo; Lian, Jian Xiang; Tomarchio, Flavia; Olivier, Yoann; Mazzaro, Raffaello; Morandi, Vittorio; Moran, Joseph; Ferrari, Andrea C; Beljonne, David; Ciesielski, Artur; Samorì, Paolo

    2016-07-21

    Graphene has unique physical and chemical properties, making it appealing for a number of applications in optoelectronics, sensing, photonics, composites, and smart coatings, just to cite a few. These require the development of production processes that are inexpensive and up-scalable. These criteria are met in liquid-phase exfoliation (LPE), a technique that can be enhanced when specific organic molecules are used. Here we report the exfoliation of graphite in N-methyl-2-pyrrolidinone, in the presence of heneicosane linear alkanes terminated with different head groups. These molecules act as stabilizing agents during exfoliation. The efficiency of the exfoliation in terms of the concentration of exfoliated single- and few-layer graphene flakes depends on the functional head group determining the strength of the molecular dimerization through dipole-dipole interactions. A thermodynamic analysis is carried out to interpret the impact of the termination group of the alkyl chain on the exfoliation yield. This combines molecular dynamics and molecular mechanics to rationalize the role of functionalized alkanes in the dispersion and stabilization process, which is ultimately attributed to a synergistic effect of the interactions between the molecules, graphene, and the solvent.

  17. Efficient coupling of nanoparticles to electrochemically exfoliated graphene.

    PubMed

    Wei, Wei; Wang, Gang; Yang, Sheng; Feng, Xinliang; Müllen, Klaus

    2015-04-29

    Electrochemically exfoliated graphene (EEG) is a new generation of high-quality graphene that holds great promise for the construction of hybrid materials. However, the assembly of EEG hybrids with well-defined nanostructures has remained a major challenge. In this study, we demonstrate a bottom-up approach toward the assembly of EEG sheets with a series of functional nanoparticles (Si, Fe3O4, and Pt NPs) into two-dimensional sandwich-like hybrid nanostructures. Polyaniline in the emeraldine base form functions as a versatile dopant to couple NPs onto EEG through either electrostatic interactions or hydrogen bonding. This protocol enables processing and assembly of EEG using an economical pathway, for which we further demonstrate the potential application of EEG-Si hybrids as high-performance anode material for lithium storage.

  18. Graphene flakes obtained by local electro-exfoliation of graphite with a STM tip.

    PubMed

    Rubio-Verdú, C; Sáenz-Arce, G; Martinez-Asencio, J; Milan, D C; Moaied, M; Palacios, J J; Caturla, M J; Untiedt, C

    2017-03-15

    Graphite surfaces can be manipulated by several methods to create graphene structures of different shapes and sizes. Scanning tunneling microscopy (STM) can be used to create these structures either through mechanical contact between the tip and the surface or through electro-exfoliation. In the latter, the mechanisms involved in the process of exfoliation at an applied voltage are not fully understood. Here, we show how a graphite surface can be locally exfoliated in a systematic manner by applying an electrostatic force with a STM tip at the edge of a terrace, forming triangular flakes several nanometers in length. We demonstrate, through experiments and simulations, how these flakes are created by a two-step process: first a voltage ramp must be applied at the edge of the terrace, and then the tip must be scanned perpendicular to the edge. Ab initio electrostatic calculations reveal that the presence of charges on the graphite surface weakens the interaction between layers allowing for exfoliation at voltages in the same range as those used experimentally. Molecular dynamics simulations show that a force applied locally on the edge of a step produces triangular flakes such as those observed under STM. Our results provide new insights into surface modification that can be extended to other layered materials.

  19. Polyelectrolyte-induced reduction of exfoliated graphite oxide: a facile route to synthesis of soluble graphene nanosheets.

    PubMed

    Zhang, Sheng; Shao, Yuyan; Liao, Honggang; Engelhard, Mark H; Yin, Geping; Lin, Yuehe

    2011-03-22

    Here we report that poly(diallyldimethylammonium chloride) (PDDA) acts as both a reducing agent and a stabilizer to prepare soluble graphene nanosheets from graphite oxide. The results of transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, and Fourier transform infrared indicated that graphite oxide was successfully reduced to graphene nanosheets which exhibited single-layer structure and high dispersion in various solvents. The reaction mechanism for PDDA-induced reduction of exfoliated graphite oxide was proposed. Furthermore, PDDA facilitated the in situ growth of highly dispersed Pt nanoparticles on the surface of graphene nanosheets to form Pt/graphene nanocomposites, which exhibited excellent catalytic activity toward formic acid oxidation. This work presents a facile and environmentally friendly approach to the synthesis of graphene nanosheets and opens up a new possibility for preparing graphene and graphene-based nanomaterials for large-scale applications.

  20. Polyelectrolyte-Induced Reduction of Exfoliated Graphite Oxide: A Facile Route to Synthesis of Soluble Graphene Nanosheets

    SciTech Connect

    Zhang, Sheng; Shao, Yuyan; Liao, Honggang; Engelhard, Mark H.; Yin, Geping; Lin, Yuehe

    2011-03-22

    Here we report that poly(diallyldimethylammonium chloride) (PDDA) acts as both a reducing agent and a stabilizer to prepare soluble graphene nanosheets from graphite oxide. The results of transmission electron microscopy, X-ray diffraction, X-ray photoeletron spectroscopy, atomic force microscopy, and fourier transform infrared indicated that graphite oxide was successfully reduced to graphene nanosheets which exhibited single-layer structure and high dispersion in various solvents. The reaction mechanism for PDDA-induced reduction of exfoliated graphite oxide was proposed. Furthermore, PDDA facilitated the in-situ growth of highly-dispersed Pt nanoparticles on the surface of graphene nanosheets to form Pt/graphene nanocomposites, which exhibited excellent catalytic activity towards formic acid oxidation. This work presents a facile and environmentally friendly approach to the synthesis of graphene nanosheets, opens up new possibility for preparing graphene and graphene-based nanomaterials for large-scale applications.

  1. Exfoliation and supramolecular functionalization of graphene with an electron donor perylenediimide derivative.

    PubMed

    Martín-Gomis, Luis; Karousis, Nikos; Fernández-Lázaro, Fernando; Petsalakis, Ioannis D; Ohkubo, Kei; Fukuzumi, Shunichi; Tagmatarchis, Nikos; Sastre-Santos, Ángela

    2017-02-06

    The liquid exfoliation of graphite to few layered graphene sheets together with the non-covalent supramolecular functionalization of exfoliated graphene by the synthesized N,N'-di(2-ethylhexyl)-1-(N''''-methylpiperazin-N'''-yl)perylene-3,4,9,10-tetracarboxydiimide (Pip-PDI) is reported. The aromatic Pip-PDI has the ability to non-covalently interact with the exfoliated graphene sheets, stabilizing them and preventing their reassembly. On the other hand, the presence of the piperazine moiety on the bay position of the PDI core makes it an ideal electron donor, nicely coupled with the electron accepting exfoliated graphene, hence, forming a novel donor-acceptor nanoensemble, which was characterized by complementary spectroscopic and microscopy techniques. Theoretical calculations predicted the absence of a meaningful charge-separated state within the Pip-PDI/graphene ensemble, which was also proven by time-resolved fluorescence and transient absorption measurements.

  2. High-quality graphene via microwave reduction of solution-exfoliated graphene oxide

    NASA Astrophysics Data System (ADS)

    Voiry, Damien; Yang, Jieun; Kupferberg, Jacob; Fullon, Raymond; Lee, Calvin; Jeong, Hu Young; Shin, Hyeon Suk; Chhowalla, Manish

    2016-09-01

    Efficient exfoliation of graphite in solutions to obtain high-quality graphene flakes is desirable for printable electronics, catalysis, energy storage, and composites. Graphite oxide with large lateral dimensions has an exfoliation yield of ~100%, but it has not been possible to completely remove the oxygen functional groups so that the reduced form of graphene oxide (GO; reduced form: rGO) remains a highly disordered material. Here we report a simple, rapid method to reduce GO into pristine graphene using 1- to 2-second pulses of microwaves. The desirable structural properties are translated into mobility values of >1000 square centimeters per volt per second in field-effect transistors with microwave-reduced GO (MW-rGO) as the channel material and into particularly high activity for MW-rGO catalyst support toward oxygen evolution reactions.

  3. Challenges in Liquid-Phase Exfoliation, Processing, and Assembly of Pristine Graphene.

    PubMed

    Parviz, Dorsa; Irin, Fahmida; Shah, Smit A; Das, Sriya; Sweeney, Charles B; Green, Micah J

    2016-10-01

    Recent developments in the exfoliation, dispersion, and processing of pristine graphene (i.e., non-oxidized graphene) are described. General metrics are outlined that can be used to assess the quality and processability of various "graphene" products, as well as metrics that determine the potential for industrial scale-up. The pristine graphene production process is categorized from a chemical engineering point of view with three key steps: i) pretreatment, ii) exfoliation, and iii) separation. How pristine graphene colloidal stability is distinct from the exfoliation step and is dependent upon graphene interactions with solvents and dispersants are extensively reviewed. Finally, the challenges and opportunities of using pristine graphene as nanofillers in polymer composites, as well as as building blocks for macrostructure assemblies are summarized in the context of large-scale production.

  4. Adsorption of phenanthrene on multilayer graphene as affected by surfactant and exfoliation.

    PubMed

    Zhao, Jian; Wang, Zhenyu; Zhao, Qing; Xing, Baoshan

    2014-01-01

    Surfactant mediated exfoliation of multilayer graphene and its effects on phenanthrene adsorption were investigated using a passive dosing technique. In the absence of surfactant (sodium cholate, NaC), multilayer graphene had higher adsorption capacity for phenanthrene than carbon nanotube and graphite due to the higher surface area and micropore volume. The observed desorption hysteresis is likely caused by the formation of closed interstitial spaces through folding and rearrangement of graphene sheets. In the presence of NaC (both 100 and 8000 mg/L), phenanthrene adsorption on graphene was decreased due to the direct competition of NaC molecules on the graphene surface. With the aid of sonication, multilayer graphene sheets were exfoliated by NaC, leading to better dispersion. The degree of dispersion depended on the graphene-NaC ratio in aqueous solution rather than critical micelle concentration of NaC, and the good dispersion occurred after reaching adsorption saturation of NaC molecules on graphene sheets. In addition, exfoliation weakened the competition between phenanthrene and NaC and enhanced the adsorption capacity of graphene for phenanthrene due to exposed new sites. The findings on exfoliation of graphene sheets and related adsorption properties highlight not only the potential applications of multilayer graphene as efficient adsorbent but also its possible environmental risk.

  5. Exfoliation of graphene sheets via high energy wet milling of graphite in 2-ethylhexanol and kerosene.

    PubMed

    Al-Sherbini, Al-Sayed; Bakr, Mona; Ghoneim, Iman; Saad, Mohamed

    2017-05-01

    Graphene sheets have been exfoliated from bulk graphite using high energy wet milling in two different solvents that were 2-ethylhexanol and kerosene. The milling process was performed for 60 h using a planetary ball mill. Morphological characteristics were investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). On the other hand, the structural characterization was performed using X-ray diffraction technique (XRD) and Raman spectrometry. The exfoliated graphene sheets have represented good morphological and structural characteristics with a valuable amount of defects and a good graphitic structure. The graphene sheets exfoliated in the presence of 2-ethylhexanol have represented many layers, large crystal size and low level of defects, while the graphene sheets exfoliated in the presence of kerosene have represented fewer number of layers, smaller crystal size and higher level of defects.

  6. BioGraphene: Direct Exfoliation of Graphite in a Kitchen Blender for Enzymology Applications.

    PubMed

    Kumar, C V; Pattammattel, A

    2016-01-01

    A high yielding method for the aqueous exfoliation of graphite crystals to produce high quality graphene nanosheets in a kitchen blender is described here. Bovine serum albumin (BSA), β-lactoglobulin, ovalbumin, lysozyme, and hemoglobin as well as calf serum were used for the exfoliation of graphene. Among these, BSA gave the maximum exfoliation efficiency, exceeding 4mgmL(-1)h(-1) of graphene. Quality of graphene produced was examined by Raman spectroscopy, which indicated 3-5 layer graphene of very high quality and very low levels of defects. Transmission electron microscopy indicated an average size of ~0.5μm flakes. The graphene/BSA dispersions were stable over pH 3.0-11, and at 5°C or 50°C, for more than 2 months. Current approach gave higher rates of BSA/graphene (BioGraphene) in better yields than other methods. Calf serum, when used in place of BSA, also gave high yields of good quality BioGraphene and these preparations may be of direct use for cell culture studies. A simple example of BioGraphene preparation is described that can be adapted in most laboratories, and graphene-adsorbed glucose oxidase is nearly as active as the free enzyme. Current approach may facilitate large-scale production of graphene in most laboratories around the world and it may open new opportunities for biological applications of graphene.

  7. Mechanical graphene

    NASA Astrophysics Data System (ADS)

    Socolar, Joshua E. S.; Lubensky, Tom C.; Kane, Charles L.

    2017-02-01

    We present a model of a mechanical system with a vibrational mode spectrum identical to the spectrum of electronic excitations in a tight-binding model of graphene. The model consists of point masses connected by elastic couplings, called ‘tri-bonds’, that implement certain three-body interactions, which can be tuned by varying parameters that correspond to the relative hopping amplitudes on the different bond directions in graphene. In the mechanical model, this is accomplished by varying the location of a pivot point that determines the allowed rigid rotations of a single tri-bond. The infinite system constitutes a Maxwell lattice, with the number of degrees of freedom equal to the number of constraints imposed by the tri-bonds. We construct the equilibrium and compatibility matrices and analyze the model’s phase diagram, which includes spectra with Weyl points for some placements of the pivot and topologically polarized phases for others. We then discuss the edge modes and associated states of self stress for strips cut from the periodic lattice. Finally, we suggest a physical realization of the tri-bond, which allows access to parameter regimes not available to experiments on (strained) graphene and may be used to create other two-dimensional mechanical metamaterials with different spectral features.

  8. Enhancing the Liquid-Phase Exfoliation of Graphene in Organic Solvents upon Addition of n-Octylbenzene

    PubMed Central

    Haar, Sébastien; El Gemayel, Mirella; Shin, Yuyoung; Melinte, Georgian; Squillaci, Marco A.; Ersen, Ovidiu; Casiraghi, Cinzia; Ciesielski, Artur; Samorì, Paolo

    2015-01-01

    Due to a unique combination of electrical and thermal conductivity, mechanical stiffness, strength and elasticity, graphene became a rising star on the horizon of materials science. This two-dimensional material has found applications in many areas of science ranging from electronics to composites. Making use of different approaches, unfunctionalized and non-oxidized graphene sheets can be produced; among them an inexpensive and scalable method based on liquid-phase exfoliation of graphite (LPE) holds potential for applications in opto-electronics and nanocomposites. Here we have used n-octylbenzene molecules as graphene dispersion-stabilizing agents during the graphite LPE process. We have demonstrated that by tuning the ratio between organic solvents such as N-methyl-2-pyrrolidinone or ortho-dichlorobenzene, and n-octylbenzene molecules, the concentration of exfoliated graphene can be enhanced by 230% as a result of the high affinity of the latter molecules for the basal plane of graphene. The LPE processed graphene dispersions were further deposited onto solid substrates by exploiting a new deposition technique called spin-controlled drop casting, which was shown to produce uniform highly conductive and transparent graphene films. PMID:26573383

  9. Electrochemically exfoliated graphene for electrode films: effect of graphene flake thickness on the sheet resistance and capacitive properties.

    PubMed

    Liu, Jinzhang; Notarianni, Marco; Will, Geoffrey; Tiong, Vincent Tiing; Wang, Hongxia; Motta, Nunzio

    2013-10-29

    We present an electrochemical exfoliation method to produce controlled thickness graphene flakes by ultrasound assistance. Bilayer graphene flakes are dominant in the final product by using sonication during the electrochemical exfoliation process, while without sonication the product contains a larger percentage of four-layer graphene flakes. Graphene sheets prepared by using the two procedures are processed into films to measure their respective sheet resistance and optical transmittance. Solid-state electrolyte supercapacitors are made using the two types of graphene films. Our study reveals that films with a higher content of multilayer graphene flakes are more conductive, and their resistance is more easily reduced by thermal annealing, making them suitable as transparent conducting films. The film with higher content of bilayer graphene flakes shows instead higher capacitance when used as electrode in a supercapacitor.

  10. Environmental Synthesis of Few Layers Graphene Sheets Using Ultrasonic Exfoliation with Enhanced Electrical and Thermal Properties.

    PubMed

    Noroozi, Monir; Zakaria, Azmi; Radiman, Shahidan; Abdul Wahab, Zaidan

    2016-01-01

    In this paper, we report how few layers graphene that can be produced in large quantity with low defect ratio from exfoliation of graphite by using a high intensity probe sonication in water containing liquid hand soap and PVP. It was founded that the graphene powder obtained by this simple exfoliation method after the heat treatment had an excellent exfoliation into a single or layered graphene sheets. The UV-visible spectroscopy, FESEM, TEM, X-ray powder diffraction and Raman spectroscopy was used to analyse the graphene product. The thermal diffusivity of the samples was analysed using a highly accurate thermal-wave cavity photothermal technique. The data obtained showed excellent enhancement in the thermal diffusivity of the graphene dispersion. This well-dispersed graphene was then used to fabricate an electrically conductive polymer-graphene film composite. The results demonstrated that this low cost and environmental friendly technique allowed to the production of high quality layered graphene sheets, improved the thermal and electrical properties. This may find use in the wide range of applications based on graphene.

  11. Environmental Synthesis of Few Layers Graphene Sheets Using Ultrasonic Exfoliation with Enhanced Electrical and Thermal Properties

    PubMed Central

    Noroozi, Monir; Zakaria, Azmi; Radiman, Shahidan; Abdul Wahab, Zaidan

    2016-01-01

    In this paper, we report how few layers graphene that can be produced in large quantity with low defect ratio from exfoliation of graphite by using a high intensity probe sonication in water containing liquid hand soap and PVP. It was founded that the graphene powder obtained by this simple exfoliation method after the heat treatment had an excellent exfoliation into a single or layered graphene sheets. The UV-visible spectroscopy, FESEM, TEM, X-ray powder diffraction and Raman spectroscopy was used to analyse the graphene product. The thermal diffusivity of the samples was analysed using a highly accurate thermal-wave cavity photothermal technique. The data obtained showed excellent enhancement in the thermal diffusivity of the graphene dispersion. This well-dispersed graphene was then used to fabricate an electrically conductive polymer-graphene film composite. The results demonstrated that this low cost and environmental friendly technique allowed to the production of high quality layered graphene sheets, improved the thermal and electrical properties. This may find use in the wide range of applications based on graphene. PMID:27064575

  12. Facile synthesis of graphene nanosheets via Fe reduction of exfoliated graphite oxide.

    PubMed

    Fan, Zhuang-Jun; Kai, Wang; Yan, Jun; Wei, Tong; Zhi, Lin-Jie; Feng, Jing; Ren, Yue-Ming; Song, Li-Ping; Wei, Fei

    2011-01-25

    The synthesis of graphene nanosheets from graphite oxide typically involves harmful chemical reductants that are undesirable for most practical applications of graphene. Here, we demonstrate a green and facile approach to the synthesis of graphene nanosheets based on Fe reduction of exfoliated graphite oxide, resulting in a substantial removal of oxygen functionalities of the graphite oxide. More interestingly, the resulting graphene nanosheets with residual Fe show a high adsorption capacity of 111.62 mg/g for methylene blue at room temperature, as well as easy magnetic separation from the solution. This approach offers a potential for cost-effective, environmentally friendly, and large-scale production of graphene nanosheets.

  13. Exfoliation and Performance Properties of Non-Oxidized Graphene in Water

    NASA Astrophysics Data System (ADS)

    Chen, I.-Wen Peter; Huang, Chun-Yuan; Jhou, Sheng-Hong Saint; Zhang, Yu-Wei

    2014-01-01

    Single-layered graphene has unique electronic, chemical, and electromechanical properties. Recently, graphite exfoliation in N-methylpyrrolidone and molten salt has been demonstrated to generate monolayer exfoliated graphene sheets (EGS). However, these solvents are either high-priced or require special care and have high boiling points and viscosities, making it difficult to deposit the dispersed graphene onto substrates. Here we show a universal principle for the exfoliation of graphite in water to single-layered and several-layered graphene sheets via the direct exfoliation of highly oriented pyrolytic graphite (HOPG) using pyridinium tribromide (Py+Br3-). Electrical conductivity >5100 S/cm was observed for filtered graphene paper, and the EGS exhibited superior performance as a hole transport layer compared to the conventional material N,N-di(naphthalene-1-yl)-N,N-diphenylbenzidine at low voltage. The overall results demonstrate that this method is a scalable process for the preparation of highly conductive graphene for use in the commercial manufacture of high-performance electronic devices.

  14. Influence of pH condition on colloidal suspension of exfoliated graphene oxide by electrostatic repulsion

    SciTech Connect

    Meng, Long-Yue; Park, Soo-Jin

    2012-02-15

    A facile chemical process is described to produce graphene oxide utilizing a zwitterions amino acid intermediate from graphite oxide sheets. 11-aminoundecanoic acid molecules were protonated to intercalate molecules into the graphite oxide sheets to achieve ion exchange, and the carboxyl groups were then ionized in a NaOH solution to exfoliate the graphite oxide sheets. In this way, the produced graphene oxide nanosheets were stably dispersed in water. The delaminated graphene nanosheets were confirmed by XRD, AFM, and TEM. XRD patterns indicated the d{sub 002}-spacing of the graphite greatly increased from 0.380 nm and 0.870 nm. AFM and TEM images showed that the ordered graphite crystal structure of graphene nanosheets was effectively exfoliated by this method. The prepared graphene nanosheets films showed 87.1% transmittance and a sheet resistance of 2.1 Multiplication-Sign 10{sup 3} {Omega}/square. - Graphical abstract: A stable graphene oxide suspension could be quickly prepared by exfoliating a graphite oxide suspension by a host-guest electrostatic repulsion in aqueous solution. Highlights: Black-Right-Pointing-Pointer Graphene nanosheets were prepared by a zwitterions amino acid intermediate from graphite oxide. Black-Right-Pointing-Pointer 11-aminoundecanoic acid was protonated to intercalate molecules into the graphene oxide to achieve ion exchange. Black-Right-Pointing-Pointer The d{sub 002}-spacing of the graphite oxide greatly increased from 0.330 nm to 0.415 nm after 11-aminoundecanoic acid treatment.

  15. Identification and Mapping of Mechanically Exfoliated 1H-MoS2 Flakes for Field-Effect Transistors

    DTIC Science & Technology

    2014-08-01

    Following the discovery of graphene , there has been increased interest in materials that allow for the construction of two- dimensional (2D) devices. In this...project we will focus on 1H-molybdenum disulfide (MoS2), which, like graphene , is a monolayer; unlike graphene , however, it has a band gap. 1H-MoS2...differs from silicon in that its band gap is direct and, like graphene , can be mechanically exfoliated (ME) to isolate it as a single molecular layer

  16. Stable aqueous dispersions of functionalized multi-layer graphene by pulsed underwater plasma exfoliation of graphite

    NASA Astrophysics Data System (ADS)

    Meyer-Plath, Asmus; Beckert, Fabian; Tölle, Folke J.; Sturm, Heinz; Mülhaupt, Rolf

    2016-02-01

    A process was developed for graphite particle exfoliation in water to stably dispersed multi-layer graphene. It uses electrohydraulic shockwaves and the functionalizing effect of solution plasma discharges in water. The discharges were excited by 100 ns high voltage pulsing of graphite particle chains that bridge an electrode gap. The underwater discharges allow simultaneous exfoliation and chemical functionalization of graphite particles to partially oxidized multi-layer graphene. Exfoliation is caused by shockwaves that result from rapid evaporation of carbon and water to plasma-excited gas species. Depending on discharge energy and locus of ignition, the shockwaves cause stirring, erosion, exfoliation and/or expansion of graphite flakes. The process was optimized to produce long-term stable aqueous dispersions of multi-layer graphene from graphite in a single process step without requiring addition of intercalants, surfactants, binders or special solvents. A setup was developed that allows continuous production of aqueous dispersions of flake size-selected multi-layer graphenes. Due to the well-preserved sp2-carbon structure, thin films made from the dispersed graphene exhibited high electrical conductivity. Underwater plasma discharge processing exhibits high innovation potential for morphological and chemical modifications of carbonaceous materials and surfaces, especially for the generation of stable dispersions of two-dimensional, layered materials.

  17. High-yield production of graphene by liquid-phase exfoliation of graphite.

    PubMed

    Hernandez, Yenny; Nicolosi, Valeria; Lotya, Mustafa; Blighe, Fiona M; Sun, Zhenyu; De, Sukanta; McGovern, I T; Holland, Brendan; Byrne, Michele; Gun'Ko, Yurii K; Boland, John J; Niraj, Peter; Duesberg, Georg; Krishnamurthy, Satheesh; Goodhue, Robbie; Hutchison, John; Scardaci, Vittorio; Ferrari, Andrea C; Coleman, Jonathan N

    2008-09-01

    Fully exploiting the properties of graphene will require a method for the mass production of this remarkable material. Two main routes are possible: large-scale growth or large-scale exfoliation. Here, we demonstrate graphene dispersions with concentrations up to approximately 0.01 mg ml(-1), produced by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone. This is possible because the energy required to exfoliate graphene is balanced by the solvent-graphene interaction for solvents whose surface energies match that of graphene. We confirm the presence of individual graphene sheets by Raman spectroscopy, transmission electron microscopy and electron diffraction. Our method results in a monolayer yield of approximately 1 wt%, which could potentially be improved to 7-12 wt% with further processing. The absence of defects or oxides is confirmed by X-ray photoelectron, infrared and Raman spectroscopies. We are able to produce semi-transparent conducting films and conducting composites. Solution processing of graphene opens up a range of potential large-area applications, from device and sensor fabrication to liquid-phase chemistry.

  18. Production of graphene by exfoliation of graphite in a volatile organic solvent.

    PubMed

    Choi, Eun-Young; Choi, Won San; Lee, Young Boo; Noh, Yong-Young

    2011-09-07

    The production of unfunctionalized and nonoxidized graphene by exfoliation of graphite in a volatile solvent, 1-propanol, is reported. A stable homogeneous dispersion of graphene was obtained by mild sonication of graphite powder and subsequent centrifugation. The presence of a graphene monolayer was observed by atomic force microscopy and transmission electron microscopy. The solvent, 1-propanol, from the deposited dispersion was simply and quickly removed by air drying at room temperature, without the help of high temperature annealing or vacuum drying, which shortens production time and does not leave any residue of the solvent in the graphene sheets.

  19. Mechanical exfoliation of graphite in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6) providing graphene nanoplatelets that exhibit enhanced electrocatalysis

    NASA Astrophysics Data System (ADS)

    Hayes, William Ignatius; Lubarsky, Gennady; Li, Meixian; Papakonstantinou, Pagona

    2014-12-01

    A novel production method for graphene nanoplatelets (GPs) with enhanced electrocatalytic behaviour is presented. GPs show improvement in their oxygen reduction reaction (ORR) catalysis after prolonging the grinding of graphite in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6). Nitrogen doping of the GPs has inferred a further increase in ORR. The ORR onset potential, cathodic current magnitude and electron transfer efficiency have all improved as a direct consequence of increasing the graphite grinding duration from 30 min to 4 h. Atomic force microscopy has confirmed a decrease in the GP diameter and height as the grinding increases. Raman spectroscopy indicates a higher level of defects present after prolonging the graphite grinding in BMIM-PF6, most likely a result of the increased edge plane exposure. This increased edge plane appears to promote a higher level of nitrogen incorporation as the graphite grinding duration increases, as confirmed by X-ray photoelectron spectroscopy analysis. The stability of the cathodic current assessed by chronoamperometry analysis is higher for the GP and nitrogen doped graphene nanoplatelet (N-GP) samples than the platinum on carbon black (Pt/C). This study presents a novel process for the production of nitrogen doped graphene nanoplatelets, constituting a strategy for the up-scaled production of electrocatalysts.

  20. Graphene Oxide-Assisted Liquid Phase Exfoliation of Graphite into Graphene for Highly Conductive Film and Electromechanical Sensors.

    PubMed

    Tung, Tran Thanh; Yoo, Jeongha; Alotaibi, Faisal K; Nine, Md J; Karunagaran, Ramesh; Krebsz, Melinda; Nguyen, Giang T; Tran, Diana N H; Feller, Jean-Francois; Losic, Dusan

    2016-06-29

    Here, we report a new method to prepare graphene from graphite by the liquid phase exfoliation process with sonication using graphene oxide (GO) as a dispersant. It was found that GO nanosheets act a as surfactant to the mediated exfoliation of graphite into a GO-adsorbed graphene complex in the aqueous solution, from which graphene was separated by an additional process. The preparation of isolated graphene from a single to a few layers is routinely achieved with an exfoliation yield of up to higher than 40% from the initial graphite material. The prepared graphene sheets showed a high quality (C/O ∼ 21.5), low defect (ID/IG ∼ 0.12), and high conductivity (6.2 × 10(4) S/m). Moreover, the large lateral size ranging from 5 to 10 μm of graphene, which is believed to be due to the shielding effect of GO avoiding damage under ultrasonic jets and cavitation formed by the sonication process. The thin graphene film prepared by the spray-coating technique showed a sheet resistance of 668 Ω/sq with a transmittance of 80% at 550 nm after annealing at 350 °C for 3 h. The transparent electrode was even greater with the resistance only 66.02 Ω when graphene is deposited on an interdigitated electrode (1 mm gap). Finally, a flexible sensor based on a graphene spray-coating polydimethylsiloxane (PDMS) is demonstrated showing excellent performance working under human touch pressure (<10 kPa). The graphene prepared by this method has some distinct properties showing it as a promising material for applications in electronics including thin film coatings, transparent electrodes, wearable electronics, human monitoring sensors, and RFID tags.

  1. A single-stage functionalization and exfoliation method for the production of graphene in water: stepwise construction of 2D-nanostructured composites with iron oxide nanoparticles.

    PubMed

    Ihiawakrim, Dris; Ersen, Ovidiu; Melin, Frédéric; Hellwig, Petra; Janowska, Izabela; Begin, Dominique; Baaziz, Walid; Begin-Colin, Sylvie; Pham-Huu, Cuong; Baati, Rachid

    2013-10-07

    A practically simple top-down process for the exfoliation of graphene (GN) and few-layer graphene (FLG) from graphite is described. We have discovered that a biocompatible amphiphilic pyrene-based hexahistidine peptide is able to exfoliate, functionalize, and dissolve few layer graphene flakes in pure water under exceptionally mild, sustainable and virtually innocuous low intensity cavitation conditions. Large area functionalized graphene flakes with the hexahistidine oligopeptide (His₆-TagGN = His₆@GN) have been produced efficiently at room temperature and characterized by TEM, Raman, and UV spectroscopy. Conductivity experiments carried out on His₆-TagGN samples revealed superior electric performances as compared to reduced graphene oxide (rGO) and non-functionalized graphene, demonstrating the non-invasive features of our non-covalent functionalization process. We postulated a rational exfoliation mechanism based on the intercalation of the peptide amphiphile under cavitational chemistry. We also demonstrated the ability of His6-TagGN nanoassemblies to self-assemble spontaneously with inorganic iron oxide nanoparticles generating magnetic two-dimensional (2D) His₆-TagGN/Fe₃O₄ nanocomposites under mild and non-hydrothermal conditions. The set of original experiments described here open novel perspectives in the facile production of water dispersible high quality GN and FLG sheets that will improve and facilitate the interfacing, processing and manipulation of graphene for promising applications in catalysis, nanocomposite construction, integrated nanoelectronic devices and bionanotechnology.

  2. Percolation scaling in composites of exfoliated MoS2 filled with nanotubes and graphene.

    PubMed

    Cunningham, Graeme; Lotya, Mustafa; McEvoy, Niall; Duesberg, Georg S; van der Schoot, Paul; Coleman, Jonathan N

    2012-10-21

    Applications of films of exfoliated layered compounds in many areas will be limited by their relatively low electrical conductivity. To address this, we have prepared and characterised composites of a nano-conductor (nanotubes or graphene) embedded in a matrix of exfoliated MoS(2) nanosheets. Solvent exfoliation of MoS(2) nanosheets, followed by blending with dispersions of graphene or nanotubes allowed the formation of such composite films by vacuum filtration. This gave spatially uniform mixtures with fully tuneable nano-conductor content. By addition of the nano-conducting phase, it was possible to vary the electrical conductivity of the composite over nine orders of magnitude. For both filler types the conductivity followed percolation scaling laws both above and below the percolation threshold. In the case of SWNT-filled composites, conductivities as high as ~40 S m(-1) were achieved at volume fractions as low as ~4%.

  3. Effect of post-exfoliation treatments on mechanically exfoliated MoS2

    NASA Astrophysics Data System (ADS)

    Budania, P.; Baine, P. T.; Montgomery, J. H.; McNeill, D. W.; Mitchell, S. J. N.; Modreanu, M.; Hurley, P. K.

    2017-02-01

    Post-exfoliation thermal annealing in air and ultrasonic treatments were carried out on mechanically exfoliated MoS2 flakes on oxidized silicon substrates. Ultra-sonication of MoS2 flakes on SiO2 without prior annealing results in almost complete removal of flakes, indicating weak interface bonding. The interface adhesion between MoS2 flakes and the substrate is significantly improved when the samples are annealed at 270 °C as the flakes remain strongly adhered to the substrate during subsequent ultrasonic treatment. We consider that improved adhesion is due to greater contact area between the flakes and the substrate due to effusion of trapped impurities during annealing. Annealing between 75 °C and 175 °C followed by ultrasonic treatment results in small MoS2 fragments on the samples due to breakage and/or partial removal of top layers. It also results in exposing residual adhesive traces on the sample which are caught between the flake and the substrate during repetitive folding of the Scotch® tape during the initial exfoliation. An annealing temperature of 460 °C results in decomposition of MoS2 and formation of MoO3. Optical microscopy, non-contact-mode atomic force microscopy (AFM) and Raman spectroscopy were used for identification of MoS2 fragments and residual traces left on the samples after the post-exfoliation treatments.

  4. Direct exfoliation of graphite to graphene in aqueous media with diazaperopyrenium dications.

    PubMed

    Sampath, Srinivasan; Basuray, Ashish N; Hartlieb, Karel J; Aytun, Taner; Stupp, Samuel I; Stoddart, J Fraser

    2013-05-21

    The 2,9-dimethyldiazaperopyrenium dication can be made from a ubiquitous and inexpensive feedstock in three simple steps as its chloride salt. When mixed with powdered graphite at 23 °C, this behemoth of a molecular compound exfoliates graphite to graphene in water under mild conditions.

  5. Exfoliation of graphene with an industrial dye: teaching an old dog new tricks

    NASA Astrophysics Data System (ADS)

    Schlierf, Andrea; Cha, Kitty; Schwab, Matthias Georg; Samorı, Paolo; Palermo, Vincenzo

    2014-12-01

    We describe the exfoliation, processing and inclusion in polymer composites of few-layers graphene nanoplatelets (GNPs) by using the molecule indanthrone blue sulphonic acid sodium salt (IBS), a very common industrial dyestuff and intermediate for liquid crystal preparation. We show how IBS can be used to successfully exfoliate graphite into few-layers graphene yielding highly stable dispersions in water. To demonstrate that the method is suitable for applications in composites, these graphene-organic hybrids are processed into a commercial commodity polymer (polyvinyl alcohol, PVA), enhancing its electrical bulk conductivity by ten orders of magnitude by adding as few as 3% of GNP. We attribute the good performance of IBS in dispersing GNPs in water to its amphiphilic nature and the tendency to self-assemble through π-π interaction of its large aromatic core with the graphene surface. The molecule studied here, unlike many specialty organic surfactants or solvents commonly known to exfoliate graphene, is already used as a blue pigment dispersant additive in the industrial production of polymers and thus does not need to be removed from the final product.

  6. Preparation of high-quality graphene via electrochemical exfoliation & spark plasma sintering and its applications

    NASA Astrophysics Data System (ADS)

    Gong, Youning; Ping, Yunjie; Li, Delong; Luo, Chengzhi; Ruan, Xuefeng; Fu, Qiang; Pan, Chunxu

    2017-03-01

    In this paper, we report a simple and fast approach for producing high-quality graphene (HQG) by electrochemical exfoliation and spark plasma sintering (SPS). Via a pressureless sintering at 1500 °C for 10 min, the oxygen-containing groups of electrochemically exfoliated graphene can be effectively eliminated and its intrinsic structures and properties are restored. The experimental results show that: 1) the HQG exhibits very low defect density (ID/IG = 0.16), extremely high carbon to oxygen (C/O) ratio of 25.3 and good processability in various solvents; 2) When the HQG is applied to fabricate a free-standing graphene paper (G-paper), its conductivity reaches to as high as 38460 S/m; 3) The G-paper without any binders, which is used as supercapacitor electrodes, delivers a specific capacitance of 129.0 F/g at 1 A/g, and retains 97% capacitance even after 1000 cycles.

  7. Efficient fluorescence quenching in electrochemically exfoliated graphene decorated with gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Hurtado-Morales, M.; Ortiz, M.; Acuña, C.; Nerl, H. C.; Nicolosi, V.; Hernández, Y.

    2016-07-01

    High surface area graphene sheets were obtained by electrochemical exfoliation of graphite in an acid medium under constant potential conditions. Filtration and centrifugation processes played an important role in order to obtain stable dispersions in water. Scanning electron microscopy and transmission electron microscopy imaging revealed highly exfoliated crystalline samples of ∼5 μm. Raman, Fourier transform infrared and x-ray photoelectron spectroscopy further confirmed the high quality of the exfoliated material. The electrochemically exfoliated graphene (EEG) was decorated with gold nanoparticles (AuNPs) using sodium cholate as a buffer layer. This approach allowed for a non-covalent functionalization without altering the desirable electronic properties of the EEG. The AuNP-EEG samples were characterized with various techniques including absorbance and fluorescence spectroscopy. These samples displayed a fluorescence signal using an excitation wavelength of 290 nm. The calculated quantum yield (Φ) for these samples was 40.04%, a high efficiency compared to previous studies using solution processable graphene.

  8. Creating high yield water soluble luminescent graphene quantum dots via exfoliating and disintegrating carbon nanotubes and graphite flakes.

    PubMed

    Lin, Liangxu; Zhang, Shaowei

    2012-10-21

    We have developed an effective method to exfoliate and disintegrate multi-walled carbon nanotubes and graphite flakes. With this technique, high yield production of luminescent graphene quantum dots with high quantum yield and low oxidization can be achieved.

  9. Direct exfoliation of graphene in ionic liquids with aromatic groups

    NASA Astrophysics Data System (ADS)

    Bari, Rozana; Tamas, George; Irin, Fahmida; Aquino, Adelia; Quitevis, Edward; Green, Micah

    2015-03-01

    The imidazolium cation of the designed and synthesized novel ionic liquids (ILs) having aromatic groups interact non-covalently with graphene. The Graphene stabilized by the IL is neither covalently functionalized nor requires the presence of additive stabilizer and such process results in dispersion of pristine graphene. This graphene dispersion is stable against centrifugation and the concentration of the resulting graphene is high as well. It was observed that the ILs are less effective in dispersing graphene if the cation does not have these aromatic groups. The interaction between the cation and the graphene surface plays an important role in the final yield of graphene. The graphene dispersion was characterized by Raman spectroscopy, X-ray Diffraction, and X-ray photoelectron spectroscopy. The experimental observations were compared with the density functional theory (DFT-D3) calculations and the comparison indicated that the experimental observations and the theoretical calculations were in good agreement. These validated theoretical calculations can further be used in future to design and synthesize the ILs in order to optimize the graphene yield without the need for additional experimentation. National Science Foundation under CRIF-MU instrumentation grant CHE-0840493, National Science Foundation under CAREER award CMMI-1253085, Air Force Office of Scientific Research Young Investigator Program (AFOSR FA9550-11-1-0027),

  10. Turbulence-assisted shear exfoliation of graphene using household detergent and a kitchen blender

    NASA Astrophysics Data System (ADS)

    Varrla, Eswaraiah; Paton, Keith R.; Backes, Claudia; Harvey, Andrew; Smith, Ronan J.; McCauley, Joe; Coleman, Jonathan N.

    2014-09-01

    To facilitate progression from the lab to commercial applications, it will be necessary to develop simple, scalable methods to produce high quality graphene. Here we demonstrate the production of large quantities of defect-free graphene using a kitchen blender and household detergent. We have characterised the scaling of both graphene concentration and production rate with the mixing parameters: mixing time, initial graphite concentration, rotor speed and liquid volume. We find the production rate to be invariant with mixing time and to increase strongly with mixing volume, results which are important for scale-up. Even in this simple system, concentrations of up to 1 mg ml-1 and graphene masses of >500 mg can be achieved after a few hours mixing. The maximum production rate was ~0.15 g h-1, much higher than for standard sonication-based exfoliation methods. We demonstrate that graphene production occurs because the mean turbulent shear rate in the blender exceeds the critical shear rate for exfoliation.To facilitate progression from the lab to commercial applications, it will be necessary to develop simple, scalable methods to produce high quality graphene. Here we demonstrate the production of large quantities of defect-free graphene using a kitchen blender and household detergent. We have characterised the scaling of both graphene concentration and production rate with the mixing parameters: mixing time, initial graphite concentration, rotor speed and liquid volume. We find the production rate to be invariant with mixing time and to increase strongly with mixing volume, results which are important for scale-up. Even in this simple system, concentrations of up to 1 mg ml-1 and graphene masses of >500 mg can be achieved after a few hours mixing. The maximum production rate was ~0.15 g h-1, much higher than for standard sonication-based exfoliation methods. We demonstrate that graphene production occurs because the mean turbulent shear rate in the blender exceeds

  11. CVD growth of graphene under exfoliated hexagonal boron nitride for vertical hybrid structures

    SciTech Connect

    Wang, Min; Jang, Sung Kyu; Song, Young Jae; Lee, Sungjoo

    2015-01-15

    Graphical abstract: We have demonstrated a novel yet simple method for fabricating graphene-based vertical hybrid structures by performing the CVD growth of graphene at an h-BN/Cu interface. Our systematic Raman measurements combined with plasma etching process indicate that a graphene film is grown under exfoliated h-BN rather than on its top surface, and that an h-BN/graphene vertical hybrid structure has been fabricated. Electrical transport measurements of this h-BN/graphene, transferred on SiO2, show the carrier mobility up to approximately 2250 cm{sup 2} V{sup −1} s{sup −1}. The developed method would enable the exploration of the possibility of novel hybrid structure integration with two-dimensional material systems. - Abstract: We have demonstrated a novel yet simple method for fabricating graphene-based vertical hybrid structures by performing the CVD growth of graphene at an h-BN/Cu interface. Our systematic Raman measurements combined with plasma etching process indicate that a graphene film is grown under exfoliated h-BN rather than on its top surface, and that an h-BN/graphene vertical hybrid structure has been fabricated. Electrical transport measurements of this h-BN/graphene, transferred on SiO{sub 2}, show the carrier mobility up to approximately 2250 cm{sup 2} V{sup −1} s{sup −1}. The developed method would enable the exploration of the possibility of novel hybrid structure integration with two-dimensional material systems.

  12. Production and stability of mechanochemically exfoliated graphene in water and culture media

    NASA Astrophysics Data System (ADS)

    León, V.; González-Domínguez, J. M.; Fierro, J. L. G.; Prato, M.; Vázquez, E.

    2016-07-01

    The preparation of graphene suspensions in water, without detergents or any other additives is achieved using freeze-dried graphene powders, produced by mechanochemical exfoliation of graphite. These powders of graphene can be safely stored or shipped, and promptly dissolved in aqueous media. The suspensions are relatively stable in terms of time, with a maximum loss of ~25% of the initial concentration at 2 h. This work provides an easy and general access to aqueous graphene suspensions of chemically non-modified graphene samples, an otherwise (almost) impossible task to achieve by other means. A detailed study of the stability of the relative dispersions is also reported.The preparation of graphene suspensions in water, without detergents or any other additives is achieved using freeze-dried graphene powders, produced by mechanochemical exfoliation of graphite. These powders of graphene can be safely stored or shipped, and promptly dissolved in aqueous media. The suspensions are relatively stable in terms of time, with a maximum loss of ~25% of the initial concentration at 2 h. This work provides an easy and general access to aqueous graphene suspensions of chemically non-modified graphene samples, an otherwise (almost) impossible task to achieve by other means. A detailed study of the stability of the relative dispersions is also reported. Electronic supplementary information (ESI) available: A video showing the dispersion process, the N 1s XPS spectrum of BMG, image of the graphite test in CCM, and the characterization of the GO employed. See DOI: 10.1039/c6nr03246j

  13. Performance of Liquid Phase Exfoliated Graphene As Electrochemical Double Layer Capacitors Electrodes

    NASA Astrophysics Data System (ADS)

    Huffstutler, Jacob; Wasala, Milinda; Richie, Julianna; Winchester, Andrew; Ghosh, Sujoy; Kar, Swastik; Talapatra, Saikat

    2014-03-01

    We will present the results of our investigations of electrochemical double layer capacitors (EDLCs) or supercapacitors (SC) fabricated using liquid-phase exfoliated graphene. Several electrolytes, such as aqueous potassium hydroxide KOH (6M), ionic 1-Butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], and ionic 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate[BMP][FAP] were used. These EDLC's show good performance compared to other carbon nanomaterials based EDLC's devices. We found that the liquid phase exfoliated graphene based devices possess specific capacitance values as high as 262 F/g, when used with ionic liquid electrolyte[BMP][FAP], with power densities (~ 454 W/kg) and energy densities (~ 0.38Wh/kg). Further, these devices indicated rapid charge transfer response even without the use of any binders or specially prepared current collectors. A detailed electrochemical impedance spectroscopy analysis in order to understand the phenomenon of charge storage in these materials will be presented.

  14. Direct exfoliation of natural graphite into micrometer size few layers graphene sheets using ionic liquids

    SciTech Connect

    Wang, X.; Fulvio, P. F.; Baker, G. A.; Veith, G. M.; Unocic, R. R.; Mahurin, S., M.; Chi, M.; Dai, S.

    2010-01-01

    Stable high-concentration suspensions (up to 0.95 mg mL-1) of non-oxidized few layer graphene (FLG), five or less sheets, with micrometre-long edges were obtained via direct exfoliation of natural graphite flakes in ionic liquids, such as 1-butyl-3-methyl-imidazolium bis(trifluoro-methane-sulfonyl)imide ([Bmim]-[Tf2N]), by tip ultrasonication.

  15. Direct exfoliation of natural graphite into micrometer size few layers graphene sheets using ionic liquids

    SciTech Connect

    Wang, Xiqing; Fulvio, Pasquale F; Baker, Gary A; Veith, Gabriel M; Unocic, Raymond R; Mahurin, Shannon Mark; Dai, Sheng

    2010-01-01

    Stable high-concentration suspensions (up to 0.95 mg mL{sup -1}) of non-oxidized few layer graphene (FLG), five or less sheets, with micrometre-long edges were obtained via direct exfoliation of natural graphite flakes in ionic liquids, such as 1-butyl-3-methyl-imidazolium bis(trifluoro-methane-sulfonyl)imide ([Bmim]-[Tf{sub 2}N]), by tip ultrasonication.

  16. Dielectric nanosheets made by liquid-phase exfoliation in water and their use in graphene-based electronics

    NASA Astrophysics Data System (ADS)

    Yang, Huafeng; Withers, Freddie; Gebremedhn, Elias; Lewis, Edward; Britnell, Liam; Felten, Alexandre; Palermo, Vincenzo; Haigh, Sarah; Beljonne, David; Casiraghi, Cinzia

    2014-06-01

    One of the challenges associated with the development of next-generation electronics is to find alternatives to silicon oxide caused by the size-reduction constraints of the devices. The dielectric properties of two-dimensional (2D) crystals, added to their excellent chemical stability, mechanical and thermal properties, make them promising dielectrics. Here we show that liquid-phase exfoliation (LPE) in water by using low-cost commercial organic dyes as dispersant agents can efficiently produce defect-free 2D nanosheets, including mono-layers, in suspensions. We further show that these suspensions can be easily incorporated into current practical graphene-based devices. In particular, it is found that boron nitride thin films made by LPE are excellent dielectrics that are highly compatible with graphene-based electronics.

  17. Exfoliation of graphite into graphene in polar solvents mediated by amphiphilic hexa-peri-hexabenzocoronene.

    PubMed

    Kabe, Ryota; Feng, Xinliang; Adachi, Chihaya; Müllen, Klaus

    2014-11-01

    A water-soluble surfactant consisting of hexa-peri-hexabenzocoronene (HBC) as hydrophobic aromatic core and hydrophilic carboxy substituents was synthesized. It exhibited a self-assembled nanofiber structure in the solid state. Profiting from the π interactions between the large aromatic core of HBC and graphene, the surfactant mediated the exfoliation of graphite into graphene in polar solvents, which was further stabilized by the bulky hydrophilic carboxylic groups. A graphene dispersion with a concentration as high as 1.1 mg L(-1) containing 2-6 multilayer nanosheets was obtained. The lateral size of the graphene sheets was in the range of 100-500 nm based on atomic force microscope (AFM) and transmission electron microscope (TEM) measurements.

  18. Reinforcement of poly ether sulphones (PES) with exfoliated graphene oxide for aerospace applications

    NASA Astrophysics Data System (ADS)

    Balasubramanian, K.

    2012-09-01

    Composite materials have been used for aerospace for some time now and have gained virtually 100% acceptance as the materials of choice. Speciality polymers like poly ether sulphones (PES), poly ether ether ketones(PEEK), poly ether imides (PEI) are highly preferred materials as plastic matrix due to their superior temperature performance, excellent wear & friction resistance, excellent dimensional accuracy, high tensile strength, high modulus, precise machinability and chemical resistance. In recent years nanoadditives like single and multiwall carbon nanotubes, graphenes and graphene oxides(GO) are finding huge market potential in aerospace and automobile industries. But manufacture related factors such as particle/ matrix interphases, surface activation, mixing process, particle agglomeration, particle size and shape may lead to different property effects. In this research GO/PES composites were prepared by high shear melt blending technique. GO monolayers were exfoliated from natural graphite flake and dispersed homogeneously in PES matrix for the GO content ranging between 0.5 to 2.0 volume percentage with a high shear twin screw batch mixer. These melt blended nanocomposites were injection moulded for mechanical property validation of tensile strength, flexural modulus and impact resistance. Addition of 0.5 volume percentage of GO enhanced the tensile strength and flexural modulus by 40% and 90% respectively. The results show that addition of GO to PES increase mechanical properties due to the formation of continuous network, good dispersion and strong interfacial interactions. The strong interfacial interactions were accounted for the increase in glass transition temperature. Also there was a significant improvement in the impact resistance of the PES/ GO nanocomposite. The injection moulded samples were tested for stealth performance by measuring the electromagnetic shielding property.

  19. Efficient electrocatalytic performance of thermally exfoliated reduced graphene oxide-Pt hybrid

    SciTech Connect

    Antony, Rajini P. Preethi, L.K.; Gupta, Bhavana; Mathews, Tom Dash, S.; Tyagi, A.K.

    2015-10-15

    Highlights: • Synthesis of Pt–RGO nanohybrids of very high electrochemically active surface area. • Electrocatalytic activity-cum-stability: ∼10 times that of commercial Pt-C catalyst. • TEM confirms narrow size distribution and excellent dispersion of Pt nanoparticles. • SAED and XRD indicate (1 1 1) orientation of Pt nanoparticles. • Methanol oxidation EIS reveal decrease in charge transfer resistance with potential - Abstract: High quality thermally exfoliated reduced graphene oxide (RGO) nanosheets decorated with platinum nanocrystals have been synthesized using a simple environmentally benign process. The electrocatalytic behaviour of the Pt–RGO nanohybrid for methanol oxidation was studied using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. High resolution transmission electron microscopy shows uniform dispersion of Pt nanoparticles of ∼2–4 nm size. X-ray diffraction and selected area diffraction studies reveal (1 1 1) orientation of the platinum nanoparticles. The cyclic voltammetry and chronoamperometry results indicate higher catalytic activity and stability for Pt–RGO compared to commercial Pt-C. The electrochemical active surface area of Pt–RGO (52.16 m{sup 2}/g) is found to be 1.5 times that of commercial Pt-C. Impedance spectroscopy shows different impedance behaviour at different potential regions, indicating change in methanol oxidation reaction mechanism with potential. The reversal of impedance pattern to the second quadrant, at potentials higher than ∼0.40 V, indicates change in the rate determining reaction.

  20. A single-stage functionalization and exfoliation method for the production of graphene in water: stepwise construction of 2D-nanostructured composites with iron oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Ihiawakrim, Dris; Ersen, Ovidiu; Melin, Frédéric; Hellwig, Petra; Janowska, Izabela; Begin, Dominique; Baaziz, Walid; Begin-Colin, Sylvie; Pham-Huu, Cuong; Baati, Rachid

    2013-09-01

    A practically simple top-down process for the exfoliation of graphene (GN) and few-layer graphene (FLG) from graphite is described. We have discovered that a biocompatible amphiphilic pyrene-based hexahistidine peptide is able to exfoliate, functionalize, and dissolve few layer graphene flakes in pure water under exceptionally mild, sustainable and virtually innocuous low intensity cavitation conditions. Large area functionalized graphene flakes with the hexahistidine oligopeptide (His6-TagGN = His6@GN) have been produced efficiently at room temperature and characterized by TEM, Raman, and UV spectroscopy. Conductivity experiments carried out on His6-TagGN samples revealed superior electric performances as compared to reduced graphene oxide (rGO) and non-functionalized graphene, demonstrating the non-invasive features of our non-covalent functionalization process. We postulated a rational exfoliation mechanism based on the intercalation of the peptide amphiphile under cavitational chemistry. We also demonstrated the ability of His6-TagGN nanoassemblies to self-assemble spontaneously with inorganic iron oxide nanoparticles generating magnetic two-dimensional (2D) His6-TagGN/Fe3O4 nanocomposites under mild and non-hydrothermal conditions. The set of original experiments described here open novel perspectives in the facile production of water dispersible high quality GN and FLG sheets that will improve and facilitate the interfacing, processing and manipulation of graphene for promising applications in catalysis, nanocomposite construction, integrated nanoelectronic devices and bionanotechnology.A practically simple top-down process for the exfoliation of graphene (GN) and few-layer graphene (FLG) from graphite is described. We have discovered that a biocompatible amphiphilic pyrene-based hexahistidine peptide is able to exfoliate, functionalize, and dissolve few layer graphene flakes in pure water under exceptionally mild, sustainable and virtually innocuous low

  1. Controllable Edge Oxidation and Bubbling Exfoliation Enable the Fabrication of High Quality Water Dispersible Graphene

    PubMed Central

    Tian, Suyun; Sun, Jing; Yang, Siwei; He, Peng; Wang, Gang; Di, Zengfeng; Ding, Guqiao; Xie, Xiaoming; Jiang, Mianheng

    2016-01-01

    Despite significant progresses made on mass production of chemically exfoliated graphene, the quality, cost and environmental friendliness remain major challenges for its market penetration. Here, we present a fast and green exfoliation strategy for large scale production of high quality water dispersible few layer graphene through a controllable edge oxidation and localized gas bubbling process. Mild edge oxidation guarantees that the pristine sp2 lattice is largely intact and the edges are functionalized with hydrophilic groups, giving rise to high conductivity and good water dispersibility at the same time. The aqueous concentration can be as high as 5.0 mg mL−1, which is an order of magnitude higher than previously reports. The water soluble graphene can be directly spray-coated on various substrates, and the back-gated field effect transistor give hole and electron mobility of ~496 and ~676 cm2 V−1 s−1, respectively. These results achieved are expected to expedite various applications of graphene. PMID:27666869

  2. Controllable Edge Oxidation and Bubbling Exfoliation Enable the Fabrication of High Quality Water Dispersible Graphene

    NASA Astrophysics Data System (ADS)

    Tian, Suyun; Sun, Jing; Yang, Siwei; He, Peng; Wang, Gang; di, Zengfeng; Ding, Guqiao; Xie, Xiaoming; Jiang, Mianheng

    2016-09-01

    Despite significant progresses made on mass production of chemically exfoliated graphene, the quality, cost and environmental friendliness remain major challenges for its market penetration. Here, we present a fast and green exfoliation strategy for large scale production of high quality water dispersible few layer graphene through a controllable edge oxidation and localized gas bubbling process. Mild edge oxidation guarantees that the pristine sp2 lattice is largely intact and the edges are functionalized with hydrophilic groups, giving rise to high conductivity and good water dispersibility at the same time. The aqueous concentration can be as high as 5.0 mg mL‑1, which is an order of magnitude higher than previously reports. The water soluble graphene can be directly spray-coated on various substrates, and the back-gated field effect transistor give hole and electron mobility of ~496 and ~676 cm2 V‑1 s‑1, respectively. These results achieved are expected to expedite various applications of graphene.

  3. In-situ synthesis of vanadium pentoxide nanofibre/exfoliated graphene nanohybrid and its supercapacitor applications

    NASA Astrophysics Data System (ADS)

    Choudhury, Arup; Bonso, Jeliza S.; Wunch, Melissa; Yang, Kap Seung; Ferraris, John P.; Yang, Duck J.

    2015-08-01

    A novel nanohybrid material composed of vanadium pentoxide nanofibres (VNFs) and exfoliated graphene were prepared by in-situ growth of VNFs onto graphene nanosheets, and explicated as electrode material for supercapacitor applications. The existence of non-covalent interactions between VNFs and graphene surfaces was confirmed by Raman and Fourier transform infrared (FTIR) spectroscopes. Morphological analysis of the nanohybrid revealed that the VNF layer uniformly grown on the graphene surfaces, producing high specific surface area and good electronic or ionic conducing path. High crystalline structure with small d-spacing of the VNFs on graphene was observed in X-ray diffraction (XRD) analysis. Compared to pristine VNF, the VNF/graphene nanohybrid exhibited higher specific capacitance of 218 F g-1 at current density of 1 A g-1, higher energy density of 22 Wh kg-1 and power density of 3594 W kg-1. Asymmetric supercapacitor devices were prepared using the Spectracarb 2225 activated carbon cloth and VNF/graphene nanohybrid as positive and negative electrode, respectively. The asymmetric device exhibited capacitance of 279 F g-1 at 1 A g-1, energy density of 37.2 Wh kg-1 and power density of 3743 W kg-1, which are comparable and or superior to reported asymmetric devices consisting of carbon material and metal oxide as electrode components.

  4. Modulation of the exfoliated graphene work function through cycloaddition of nitrile imines.

    PubMed

    Barrejón, Myriam; Gómez-Escalonilla, María J; Fierro, José Luis G; Prieto, Pilar; Carrillo, José R; Rodríguez, Antonio M; Abellán, Gonzalo; López-Escalante, Ma Cruz; Gabás, Mercedes; López-Navarrete, Juan T; Langa, Fernando

    2016-10-26

    After the feasibility of the 1,3-dipolar cycloaddition reaction between nitrile imines and exfoliated graphene by density functional theory calculations was proved, very few-layer graphene was effectively functionalized using this procedure. Hydrazones with different electronic properties were used as precursors for the 1,3-dipoles, and microwave irradiation as an energy source enabled the reaction to be performed in a few minutes. The anchoring of organic addends on the graphene surface was confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis. Ultraviolet photoelectron spectroscopy (UPS) was used to measure the work function and band gap of these new hybrids. Our results demonstrate that it is possible to modulate these important electronic valence band parameters by tailoring the electron richness of the organic addends and/or the degree of functionalization.

  5. Synthesis and Characterization of Microwave-Exfoliated Graphene Oxide-Wrapped Silicon Nanowire via Hydrosilylation.

    PubMed

    Shin, Donghee; Cho, Bomin; Ahn, Jihoon; Kim, Sungsoo; Ko, Young Chun; Sohn, Honglae

    2015-02-01

    Single-crystalline silicon nanowires (SiNWs) were fabricated by using an electroless metal-assisted etching of bulk silicon wafers with silver nanoparticles obtained by wet electroless deposition. The etching of SiNWs is based on sequential treatment in aqueous solutions of silver nitrate followed by hydrofluoric acid and hydrogen peroxide. Free-standing SiNWs were then obtained using ultra-sono method in toluene. Graphene oxide was prepared using the modified Hummers' process. Activated microwave-exfoliated graphite oxide (MEGO) was prepared and used for composition of silicon nanowires and graphene oxide via hydrosilylation. The silicon nanowire-graphene composite materials were characterized using XPS and FE-SEM.

  6. Electrolytic exfoliation of graphite in water with multifunctional electrolytes: en route towards high quality, oxide-free graphene flakes.

    PubMed

    Munuera, J M; Paredes, J I; Villar-Rodil, S; Ayán-Varela, M; Martínez-Alonso, A; Tascón, J M D

    2016-02-07

    Electrolytic--usually referred to as electrochemical--exfoliation of graphite in water under anodic potential holds enormous promise as a simple, green and high-yield method for the mass production of graphene, but currently suffers from several drawbacks that hinder its widespread adoption, one of the most critical being the oxidation and subsequent structural degradation of the carbon lattice that is usually associated with such a production process. To overcome this and other limitations, we introduce and implement the concept of multifunctional electrolytes. The latter are amphiphilic anions (mostly polyaromatic hydrocarbons appended with sulfonate groups) that play different relevant roles as (1) an intercalating electrolyte to trigger exfoliation of graphite into graphene flakes, (2) a dispersant to afford stable aqueous colloidal suspensions of the flakes suitable for further use, (3) a sacrificial agent to prevent graphene oxidation during exfoliation and (4) a linker to promote nanoparticle anchoring on the graphene flakes, yielding functional hybrids. The implementation of this strategy with some selected amphiphiles even furnishes anodically exfoliated graphenes of a quality similar to that of flakes produced by direct, ultrasound- or shear-induced exfoliation of graphite in the liquid phase (i.e., almost oxide- and defect-free). These high quality materials were used for the preparation of catalytically efficient graphene-Pt nanoparticle hybrids, as demonstrated by model reactions (reduction of nitroarenes). The multifunctional performance of these electrolytes is also discussed and rationalized, and a mechanistic picture of their oxidation-preventing ability is proposed. Overall, the present results open the prospect of anodic exfoliation as a competitive method for the production of very high quality graphene flakes.

  7. Large scale production of highly-qualified graphene by ultrasonic exfoliation of expanded graphite under the promotion of (NH4)2CO3 decomposition.

    PubMed

    Wang, Yunwei; Tong, Xili; Guo, Xiaoning; Wang, Yingyong; Jin, Guoqiang; Guo, Xiangyun

    2013-11-29

    Highly-qualified graphene was prepared by the ultrasonic exfoliation of commercial expanded graphite (EG) under the promotion of (NH4)2CO3 decomposition. The yield of graphene from the first exfoliation is 7 wt%, and it can be increased to more than 65 wt% by repeated exfoliations. Atomic force microscopy, x-ray photoelectron spectroscopy and Raman analysis show that the as-prepared graphene only has a few defects or oxides, and more than 95% of the graphene flakes have a thickness of ~1 nm. The electrochemical performance of the as-prepared graphene is comparable to reduced graphene oxide in the determination of dopamine (DA) from the mixed solution of ascorbic acid, uric acid and DA. These results show that the decomposition of (NH4)2CO3 molecules in the EG layers under ultrasonication promotes the exfoliation of graphite and provides a low-priced route for large scale production of highly-quality graphene.

  8. Large scale production of highly-qualified graphene by ultrasonic exfoliation of expanded graphite under the promotion of (NH4)2CO3 decomposition

    NASA Astrophysics Data System (ADS)

    Wang, Yunwei; Tong, Xili; Guo, Xiaoning; Wang, Yingyong; Jin, Guoqiang; Guo, Xiangyun

    2013-11-01

    Highly-qualified graphene was prepared by the ultrasonic exfoliation of commercial expanded graphite (EG) under the promotion of (NH4)2CO3 decomposition. The yield of graphene from the first exfoliation is 7 wt%, and it can be increased to more than 65 wt% by repeated exfoliations. Atomic force microscopy, x-ray photoelectron spectroscopy and Raman analysis show that the as-prepared graphene only has a few defects or oxides, and more than 95% of the graphene flakes have a thickness of ∼1 nm. The electrochemical performance of the as-prepared graphene is comparable to reduced graphene oxide in the determination of dopamine (DA) from the mixed solution of ascorbic acid, uric acid and DA. These results show that the decomposition of (NH4)2CO3 molecules in the EG layers under ultrasonication promotes the exfoliation of graphite and provides a low-priced route for large scale production of highly-quality graphene.

  9. Liquid-phase exfoliation of chemical vapor deposition-grown single layer graphene and its application in solution-processed transparent electrodes for flexible organic light-emitting devices

    SciTech Connect

    Wu, Chaoxing; Li, Fushan E-mail: gtl-fzu@hotmail.com; Wu, Wei; Chen, Wei; Guo, Tailiang E-mail: gtl-fzu@hotmail.com

    2014-12-15

    Efficient and low-cost methods for obtaining high performance flexible transparent electrodes based on chemical vapor deposition (CVD)-grown graphene are highly desirable. In this work, the graphene grown on copper foil was exfoliated into micron-size sheets through controllable ultrasonication. We developed a clean technique by blending the exfoliated single layer graphene sheets with conducting polymer to form graphene-based composite solution, which can be spin-coated on flexible substrate, forming flexible transparent conducting film with high conductivity (∼8 Ω/□), high transmittance (∼81% at 550 nm), and excellent mechanical robustness. In addition, CVD-grown-graphene-based polymer light emitting diodes with excellent bendable performances were demonstrated.

  10. Manganese oxide nanosheets and a 2D hybrid of graphene-manganese oxide nanosheets synthesized by liquid-phase exfoliation

    NASA Astrophysics Data System (ADS)

    Coelho, João; Mendoza-Sánchez, Beatriz; Pettersson, Henrik; Pokle, Anuj; McGuire, Eva K.; Long, Edmund; McKeon, Lorcan; Bell, Alan P.; Nicolosi, Valeria

    2015-06-01

    Manganese oxide nanosheets were synthesized using liquid-phase exfoliation that achieved suspensions in isopropanol (IPA) with concentrations of up to 0.45 mg ml-1. A study of solubility parameters showed that the exfoliation was optimum in N,N-dimethylformamide followed by IPA and diethylene glycol. IPA was the solvent of choice due to its environmentally friendly nature and ease of use for further processing. For the first time, a hybrid of graphene and manganese oxide nanosheets was synthesized using a single-step co-exfoliation process. The two-dimensional (2D) hybrid was synthesized in IPA suspensions with concentrations of up to 0.5 mg ml-1 and demonstrated stability against re-aggregation for up to six months. The co-exfoliation was found to be a energetically favorable process in which both solutes, graphene and manganese oxide nanosheets, exfoliate with an improved yield as compared to the single-solute exfoliation procedure. This work demonstrates the remarkable versatility of liquid-phase exfoliation with respect to the synthesis of hybrids with tailored properties, and it provides proof-of-concept ground work for further future investigation and exploitation of hybrids made of two or more 2D nanomaterials that have key complementary properties for various technological applications.

  11. Salt-assisted direct exfoliation of graphite into high-quality, large-size, few-layer graphene sheets.

    PubMed

    Niu, Liyong; Li, Mingjian; Tao, Xiaoming; Xie, Zhuang; Zhou, Xuechang; Raju, Arun P A; Young, Robert J; Zheng, Zijian

    2013-08-21

    We report a facile and low-cost method to directly exfoliate graphite powders into large-size, high-quality, and solution-dispersible few-layer graphene sheets. In this method, aqueous mixtures of graphite and inorganic salts such as NaCl and CuCl2 are stirred, and subsequently dried by evaporation. Finally, the mixture powders are dispersed into an orthogonal organic solvent solution of the salt by low-power and short-time ultrasonication, which exfoliates graphite into few-layer graphene sheets. We find that the as-made graphene sheets contain little oxygen, and 86% of them are 1-5 layers with lateral sizes as large as 210 μm(2). Importantly, the as-made graphene can be readily dispersed into aqueous solution in the presence of surfactant and thus is compatible with various solution-processing techniques towards graphene-based thin film devices.

  12. Ultrahigh-throughput exfoliation of graphite into pristine 'single-layer' graphene using microwaves and molecularly engineered ionic liquids.

    PubMed

    Matsumoto, Michio; Saito, Yusuke; Park, Chiyoung; Fukushima, Takanori; Aida, Takuzo

    2015-09-01

    Graphene has shown much promise as an organic electronic material but, despite recent achievements in the production of few-layer graphene, the quantitative exfoliation of graphite into pristine single-layer graphene has remained one of the main challenges in developing practical devices. Recently, reduced graphene oxide has been recognized as a non-feasible alternative to graphene owing to variable defect types and levels, and attention is turning towards reliable methods for the high-throughput exfoliation of graphite. Here we report that microwave irradiation of graphite suspended in molecularly engineered oligomeric ionic liquids allows for ultrahigh-efficiency exfoliation (93% yield) with a high selectivity (95%) towards 'single-layer' graphene (that is, with thicknesses <1 nm) in a short processing time (30 minutes). The isolated graphene sheets show negligible structural deterioration. They are also readily redispersible in oligomeric ionic liquids up to ~100 mg ml(-1), and form physical gels in which an anisotropic orientation of graphene sheets, once induced by a magnetic field, is maintained.

  13. Enhanced visible light photocatalytic activity and oxidation ability of porous graphene-like g-C3N4 nanosheets via thermal exfoliation

    NASA Astrophysics Data System (ADS)

    Dong, Fan; Li, Yuhan; Wang, Zhenyu; Ho, Wing-Kei

    2015-12-01

    Graphene-like porous g-C3N4 nanosheets were synthesized via direct pyrolysis of thiourea followed by a thermal exfoliation. With increased exfoliation temperature, the color of the resulting samples gradually became shallow, and the thickness and size of the layers were decreased. A formation mechanism involving layer-by-layer exfoliation coupled with layer splitting was proposed. The band structure of the g-C3N4 nanosheets was continuously tuned because of quantum size effect. Time-resolved decay spectra indicated that the radiative lifetime of charge carriers (τ1 and τ2) increased from 4.13 and 26.23 ns for bulk g-C3N4 to 5.36 and 36.57 ns for graphene-like g-C3N4 nanosheets. The g-C3N4 nanosheet samples were applied for visible light photocatalytic removal of NOx in air. The performance of porous g-C3N4 nanosheets was significantly enhanced with increased exfoliation temperature from 450 to 550 °C. Moreover, photochemical and structural stability was well maintained after multiple reaction cycles. By monitoring the reaction intermediate NO2, it was found that the generation of NO2 was inhibited. The activity enhancement of graphene-like g-C3N4 nanosheets can be predominantly ascribed to the prolonged lifetime and improved photo-oxidation ability of charge carriers arising from the unique electronic structure. As the synthesis method for graphene-like g-C3N4 nanosheets with high a performance is simple, the g-C3N4 nanosheets can be envisioned to be applicable in environmental remediation and solar energy conversion.

  14. Synthesis of graphene sheets with high electrical conductivity and good thermal stability by hydrogen arc discharge exfoliation.

    PubMed

    Wu, Zhong-Shuai; Ren, Wencai; Gao, Libo; Zhao, Jinping; Chen, Zongping; Liu, Bilu; Tang, Daiming; Yu, Bing; Jiang, Chuanbin; Cheng, Hui-Ming

    2009-02-24

    We developed a hydrogen arc discharge exfoliation method for the synthesis of graphene sheets (GSs) with excellent electrical conductivity and good thermal stability from graphite oxide (GO), in combination with solution-phase dispersion and centrifugation techniques. It was found that efficient exfoliation and considerable deoxygenation of GO, and defect elimination and healing of exfoliated graphite can be simultaneously achieved during the hydrogen arc discharge exfoliation process. The GSs obtained by hydrogen arc discharge exfoliation exhibit a high electrical conductivity of approximately 2 x 10(3) S/cm and high thermal stability with oxidization resistance temperature of 601 degrees C, which are much better than those prepared by argon arc discharge exfoliation (approximately 2 x 10(2) S/cm, 525 degrees C) and by conventional thermal exfoliation (approximately 80 S/cm, 507 degrees C) with the same starting GO. These results demonstrate that this hydrogen arc discharge exfoliation method is a good approach for the preparation of GSs with a good quality.

  15. Graphene prepared by thermal reduction–exfoliation of graphite oxide: Effect of raw graphite particle size on the properties of graphite oxide and graphene

    SciTech Connect

    Dao, Trung Dung; Jeong, Han Mo

    2015-10-15

    Highlights: • Effect of raw graphite particle size on properties of GO and graphene is reported. • Size of raw graphite affects oxidation degree and chemical structure of GO. • Highly oxidized GO results in small-sized but well-exfoliated graphene. • GO properties affect reduction degree, structure, and conductivity of graphene. - Abstract: We report the effect of raw graphite size on the properties of graphite oxide and graphene prepared by thermal reduction–exfoliation of graphite oxide. Transmission electron microscope analysis shows that the lateral size of graphene becomes smaller when smaller size graphite is used. X-ray diffraction analysis confirms that graphite with smaller size is more effectively oxidized, resulting in a more effective subsequent exfoliation of the obtained graphite oxide toward graphene. X-ray photoelectron spectroscopy demonstrates that reduction of the graphite oxide derived from smaller size graphite into graphene is more efficient. However, Raman analysis suggests that the average size of the in-plane sp{sup 2}-carbon domains on graphene is smaller when smaller size graphite is used. The enhanced reduction degree and the reduced size of sp{sup 2}-carbon domains contribute contradictively to the electrical conductivity of graphene when the particle size of raw graphite reduces.

  16. Ionic liquid-assisted exfoliation and dispersion: stripping graphene and its two-dimensional layered inorganic counterparts of their inhibitions

    NASA Astrophysics Data System (ADS)

    Ravula, Sudhir; Baker, Sheila N.; Kamath, Ganesh; Baker, Gary A.

    2015-02-01

    Research on graphene--monolayers of carbon atoms arranged in a honeycomb lattice--is proceeding at a relentless pace as scientists of both experimental and theoretical bents seek to explore and exploit its superlative attributes, including giant intrinsic charge mobility, record-setting thermal conductivity, and high fracture strength and Young's modulus. Of course, fully exploiting the remarkable properties of graphene requires reliable, large-scale production methods which are non-oxidative and introduce minimal defects, criteria not fully satisfied by current approaches. A major advance in this direction is ionic liquid-assisted exfoliation and dispersion of graphite, leading to the isolation of few- and single-layered graphene sheets with yields two orders of magnitude higher than the earlier liquid-assisted exfoliation approaches using surface energy-matched solvents such as N-methyl-2-pyrrolidone (NMP). In this Minireview, we discuss the emerging use of ionic liquids for the practical exfoliation, dispersion, and modification of graphene nanosheets. These developments lay the foundation for strategies seeking to overcome the many challenges faced by current liquid-phase exfoliation approaches. Early computational and experimental results clearly indicate that these same approaches can readily be extended to inorganic graphene analogues (e.g., BN, MoX2 (X = S, Se, Te), WS2, TaSe2, NbSe2, NiTe2, and Bi2Te3) as well.

  17. Mechanical cleaning of graphene

    NASA Astrophysics Data System (ADS)

    Goossens, A. M.; Calado, V. E.; Barreiro, A.; Watanabe, K.; Taniguchi, T.; Vandersypen, L. M. K.

    2012-02-01

    Contamination of graphene due to residues from nanofabrication often introduces background doping and reduces electron mobility. For samples of high electronic quality, post-lithography cleaning treatments are therefore needed. We report that mechanical cleaning based on contact mode atomic force microscopy removes residues and significantly improves the electronic properties. A mechanically cleaned dual-gated bilayer graphene transistor with hexagonal boron nitride dielectrics exhibited a mobility of ˜36 000 cm2/Vs at low temperature.

  18. Graphenothermal reduction synthesis of 'exfoliated graphene oxide/iron (II) oxide' composite for anode application in lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Petnikota, Shaikshavali; Marka, Sandeep Kumar; Banerjee, Arkaprabha; Reddy, M. V.; Srikanth, V. V. S. S.; Chowdari, B. V. R.

    2015-10-01

    Graphenothermal Reduction process is used to obtain exfoliated graphene oxide (EG)/iron (II) oxide (FeO) composite prepared at 650 °C for 5 h in argon. Structural and compositional analyses of the sample confirm the formation of EG/FeO composite. This composite shows a reversible capacity of 857 mAh g-1 at a current rate of 50 mA g-1 in the voltage range 0.005-3.0 V versus Li. An excellent capacity retention up to 60 cycles and high coulombic efficiency of 98% are also observed. Characteristic Fe2+/0 redox peaks observed in Cyclic Voltammetry measurement are explained in correlation with lithium storage mechanism. Thermal, electrical and impedance spectroscopy studies of EG/FeO composite are discussed in detail. Comparative electrochemical cycling studies of EG/FeO composite with Fe2O3 and Fe3O4 materials prepared under controlled conditions are also discussed.

  19. Sulfur-doped graphene via thermal exfoliation of graphite oxide in H2S, SO2, or CS2 gas.

    PubMed

    Poh, Hwee Ling; Šimek, Petr; Sofer, Zdeněk; Pumera, Martin

    2013-06-25

    Doping of graphene with heteroatoms is an effective way to tailor its properties. Here we describe a simple and scalable method of doping graphene lattice with sulfur atoms during the thermal exfoliation process of graphite oxides. The graphite oxides were first prepared by Staudenmaier, Hofmann, and Hummers methods followed by treatments in hydrogen sulfide, sulfur dioxide, or carbon disulfide. The doped materials were characterized by scanning electron microscopy, high-resolution X-ray photoelectron spectroscopy, combustible elemental analysis, and Raman spectroscopy. The ζ-potential and conductivity of sulfur-doped graphenes were also investigated in this paper. It was found that the level of doping is more dramatically influenced by the type of graphite oxide used rather than the type of sulfur-containing gas used during exfoliation. Resulting sulfur-doped graphenes act as metal-free electrocatalysts for an oxygen reduction reaction.

  20. Direct Fabrication of the Graphene-Based Composite for Cancer Phototherapy through Graphite Exfoliation with a Photosensitizer.

    PubMed

    Liu, Gang; Qin, Hongmei; Amano, Tsukuru; Murakami, Takashi; Komatsu, Naoki

    2015-10-28

    We report on the application of pristine graphene as a drug carrier for phototherapy (PT). The loading of a photosensitizer, chlorin e6 (Ce6), was achieved simply by sonication of Ce6 and graphite in an aqueous solution. During the loading process, graphite was gradually exfoliated to graphene to give its composite with Ce6 (G-Ce6). This one-step approach is considered to be superior to the graphene oxide (GO)-based composites, which required pretreatment of graphite by strong oxidation. Additionally, the directly exfoliated graphene ensured a high drug loading capacity, 160 wt %, which is about 10 times larger than that of the functionalized GO. Furthermore, the Ce6 concentration for killing cells by G-Ce6 is 6-75 times less than that of the other Ce6 composites including GO-Ce6.

  1. Thermally exfoliated graphene based counter electrode for low cost dye sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Kaniyoor, Adarsh; Ramaprabhu, Sundara

    2011-06-01

    Graphene obtained from thermal exfoliation of graphite oxide are highly wrinkled and have large surface area. Their wrinkled nature is expected to give them excellent catalytic activity. Herein, we demonstrate the use of thermally exfoliated graphene (TEG) as cost effective electrocatalyst for the tri-iodide reduction in dye sensitized solar cells (DSSCs). X-ray diffraction, Raman and Infra red spectroscopy and electron microscopy studies confirm the defective and wrinkled nature of TEG. BET surface area measurement show a large surface area of ˜ 470 m2/g. The counter electrode was fabricated by drop casting a slurry of TEG dispersed in a Nafion:Ethanol solution on fluorine doped tin oxide (FTO) substrates. The use of Nafion prevented film "peel off," thus ensuring a good substrate adhesion. Electrochemical impedance spectroscopy reveals that TEG had a catalytic performance comparable to that of Pt, suggesting its use as counter electrode material. As expected, the DSSC fabricated with Nafion solubilized TEG/FTO as counter electrode shows an efficiency of about 2.8%, comparable to Pt counter electrode based DSSC which has an efficiency of about 3.4%.

  2. Thermally exfoliated graphene based counter electrode for low cost dye sensitized solar cells

    SciTech Connect

    Kaniyoor, Adarsh; Ramaprabhu, Sundara

    2011-06-15

    Graphene obtained from thermal exfoliation of graphite oxide are highly wrinkled and have large surface area. Their wrinkled nature is expected to give them excellent catalytic activity. Herein, we demonstrate the use of thermally exfoliated graphene (TEG) as cost effective electrocatalyst for the tri-iodide reduction in dye sensitized solar cells (DSSCs). X-ray diffraction, Raman and Infra red spectroscopy and electron microscopy studies confirm the defective and wrinkled nature of TEG. BET surface area measurement show a large surface area of {approx} 470 m{sup 2}/g. The counter electrode was fabricated by drop casting a slurry of TEG dispersed in a Nafion:Ethanol solution on fluorine doped tin oxide (FTO) substrates. The use of Nafion prevented film ''peel off,'' thus ensuring a good substrate adhesion. Electrochemical impedance spectroscopy reveals that TEG had a catalytic performance comparable to that of Pt, suggesting its use as counter electrode material. As expected, the DSSC fabricated with Nafion solubilized TEG/FTO as counter electrode shows an efficiency of about 2.8%, comparable to Pt counter electrode based DSSC which has an efficiency of about 3.4%.

  3. The mechanical exfoliation mechanism of black phosphorus to phosphorene: A first-principles study

    NASA Astrophysics Data System (ADS)

    Mu, Yunsheng; Si, M. S.

    2015-11-01

    Today, the renaissance of black phosphorus largely depends on the mechanical exfoliation method, which is accessible to produce few-layer forms from the bulk counterpart. However, the deep understanding of the exfoliation mechanism is missing. To this end, we resolve this issue by simulating the sliding processes of bilayer phosphorene based on first-principles calculations. It is found that the interlayer Coulomb interactions dictate the optimal sliding pathway, leading to the minimal energy barrier as low as ∼60 \\text{meV} , which gives a comparable surface energy of ∼59 \\text{mJ/m}2 in experiment. This means that black phosphorus can be exfoliated by the sliding approach. In addition, considerable bandgap modulations along these sliding pathways are obtained. The study like ours builds up a fundamental understanding of how black phosphorus is exfoliated to few-layer forms, providing a good guide to experimental research.

  4. Synthetic Graphene Grown by Chemical Vapor Deposition on Copper Foils

    DTIC Science & Technology

    2013-04-11

    the intrinsic graphene properties with electronic quality approaching or comparable with exfoliated graphene flakes from graphite . The role of Si–SiO2... electronic applications, graphene also features impressive optical properties arising from massless Dirac fermions. Wavelength independent absorp- tion...interest. Initial studies using mechanically exfoliated graphene unveiled its remarkable electronic , mechanical and thermal properties . There has been a

  5. Enhanced Thermionic Emission and Low 1/f Noise in Exfoliated Graphene/GaN Schottky Barrier Diode.

    PubMed

    Kumar, Ashutosh; Kashid, Ranjit; Ghosh, Arindam; Kumar, Vikram; Singh, Rajendra

    2016-03-01

    Temperature-dependent electrical transport characteristics of exfoliated graphene/GaN Schottky diodes are investigated and compared with conventional Ni/GaN Schottky diodes. The ideality factor of graphene/GaN and Ni/GaN diodes are measured to be 1.33 and 1.51, respectively, which is suggestive of comparatively higher thermionic emission current in graphene/GaN diode. The barrier height values for graphene/GaN diode obtained using thermionic emission model and Richardson plots are found to be 0.60 and 0.72 eV, respectively, which are higher than predicted barrier height ∼0.40 eV as per the Schottky-Mott model. The higher barrier height is attributed to hole doping of graphene due to graphene-Au interaction which shifts the Fermi level in graphene by ∼0.3 eV. The magnitude of flicker noise of graphene/GaN Schottky diode increases up to 175 K followed by its decrease at higher temperatures. This indicates that diffusion currents and barrier inhomogeneities dominate the electronic transport at lower and higher temperatures, respectively. The exfoliated graphene/GaN diode is found to have lower level of barrier inhomogeneities than conventional Ni/GaN diode, as well as earlier reported graphene/GaN diode fabricated using chemical vapor deposited graphene. The lesser barrier inhomogeneities in graphene/GaN diode results in lower flicker noise by 2 orders of magnitude as compared to Ni/GaN diode. Enhanced thermionic emission current, lower level of inhomogeneities, and reduced flicker noise suggests that graphene-GaN Schottky diodes may have the underlying trend for replacing metal-GaN Schottky diodes.

  6. Powder, paper and foam of few-layer graphene prepared in high yield by electrochemical intercalation exfoliation of expanded graphite.

    PubMed

    Wu, Liqiong; Li, Weiwei; Li, Peng; Liao, Shutian; Qiu, Shengqiang; Chen, Mingliang; Guo, Yufen; Li, Qi; Zhu, Chao; Liu, Liwei

    2014-04-09

    A facile and high-yield approach to the preparation of few-layer graphene (FLG) by electrochemical intercalation exfoliation (EIE) of expanded graphite in sulfuric acid electrolyte is reported. Stage-1 H2SO4-graphite intercalation compound is used as a key intermediate in EIE to realize the efficient exfoliation. The yield of the FLG sheets (<7 layers) with large lateral sizes (tens of microns) is more than 75% relative to the total amount of starting expanded graphite. A low degree of oxygen functionalization existing in the prepared FLG flakes enables them to disperse effectively, which contributes to the film-forming characteristics of the FLG flakes. These electrochemically exfoliated FLG flakes are integrated into several kinds of macroscopic graphene structures. Flexible and freestanding graphene papers made of the FLG flakes retain excellent conductivity (≈24,500 S m(-1)). Three-dimensional (3D) graphene foams with light weight are fabricated from the FLG flakes by the use of Ni foams as self-sacrifice templates. Furthermore, 3D graphene/Ni foams without any binders, which are used as supercapacitor electrodes in aqueous electrolyte, provide the specific capacitance of 113.2 F g(-1) at a current density of 0.5 A g(-1), retaining 90% capacitance after 1000 cycles.

  7. Electrolytic exfoliation of graphite in water with multifunctional electrolytes: en route towards high quality, oxide-free graphene flakes

    NASA Astrophysics Data System (ADS)

    Munuera, J. M.; Paredes, J. I.; Villar-Rodil, S.; Ayán-Varela, M.; Martínez-Alonso, A.; Tascón, J. M. D.

    2016-01-01

    Electrolytic - usually referred to as electrochemical - exfoliation of graphite in water under anodic potential holds enormous promise as a simple, green and high-yield method for the mass production of graphene, but currently suffers from several drawbacks that hinder its widespread adoption, one of the most critical being the oxidation and subsequent structural degradation of the carbon lattice that is usually associated with such a production process. To overcome this and other limitations, we introduce and implement the concept of multifunctional electrolytes. The latter are amphiphilic anions (mostly polyaromatic hydrocarbons appended with sulfonate groups) that play different relevant roles as (1) an intercalating electrolyte to trigger exfoliation of graphite into graphene flakes, (2) a dispersant to afford stable aqueous colloidal suspensions of the flakes suitable for further use, (3) a sacrificial agent to prevent graphene oxidation during exfoliation and (4) a linker to promote nanoparticle anchoring on the graphene flakes, yielding functional hybrids. The implementation of this strategy with some selected amphiphiles even furnishes anodically exfoliated graphenes of a quality similar to that of flakes produced by direct, ultrasound- or shear-induced exfoliation of graphite in the liquid phase (i.e., almost oxide- and defect-free). These high quality materials were used for the preparation of catalytically efficient graphene-Pt nanoparticle hybrids, as demonstrated by model reactions (reduction of nitroarenes). The multifunctional performance of these electrolytes is also discussed and rationalized, and a mechanistic picture of their oxidation-preventing ability is proposed. Overall, the present results open the prospect of anodic exfoliation as a competitive method for the production of very high quality graphene flakes.Electrolytic - usually referred to as electrochemical - exfoliation of graphite in water under anodic potential holds enormous promise

  8. Light-enhanced liquid-phase exfoliation and current photoswitching in graphene-azobenzene composites

    NASA Astrophysics Data System (ADS)

    Döbbelin, Markus; Ciesielski, Artur; Haar, Sébastien; Osella, Silvio; Bruna, Matteo; Minoia, Andrea; Grisanti, Luca; Mosciatti, Thomas; Richard, Fanny; Prasetyanto, Eko Adi; de Cola, Luisa; Palermo, Vincenzo; Mazzaro, Raffaello; Morandi, Vittorio; Lazzaroni, Roberto; Ferrari, Andrea C.; Beljonne, David; Samorì, Paolo

    2016-04-01

    Multifunctional materials can be engineered by combining multiple chemical components, each conferring a well-defined function to the ensemble. Graphene is at the centre of an ever-growing research effort due to its combination of unique properties. Here we show that the large conformational change associated with the trans-cis photochemical isomerization of alkyl-substituted azobenzenes can be used to improve the efficiency of liquid-phase exfoliation of graphite, with the photochromic molecules acting as dispersion-stabilizing agents. We also demonstrate reversible photo-modulated current in two-terminal devices based on graphene-azobenzene composites. We assign this tuneable electrical characteristics to the intercalation of the azobenzene between adjacent graphene layers and the resulting increase in the interlayer distance on (photo)switching from the linear trans-form to the bulky cis-form of the photochromes. These findings pave the way to the development of new optically controlled memories for light-assisted programming and high-sensitive photosensors.

  9. Schwinger mechanism and graphene

    SciTech Connect

    Allor, Danielle; Cohen, Thomas D.; McGady, David A.

    2008-11-01

    The Schwinger mechanism, the production of charged particle-antiparticle pairs in a macroscopic external electric field, is derived for 2+1-dimensional theories. The rate of pair production per unit area for four species of massless fermions, with charge q, in a constant electric field E is given by {pi}{sup -2}({Dirac_h}/2{pi}){sup -3/2}c-tilde{sup -1/2}(qE){sup 3/2} where c-tilde is the speed of light for the two-dimensional system. To the extent undoped graphene behaves like the quantum field-theoretic vacuum for massless fermions in 2+1 dimensions, the Schwinger mechanism should be testable experimentally. A possible experimental configuration for this is proposed. Effects due to deviations from this idealized picture of graphene are briefly considered. It is argued that with present day samples of graphene, tests of the Schwinger formula may be possible.

  10. Photocatalytic applications with CdS • block copolymer/exfoliated graphene nanoensembles: hydrogen generation and degradation of Rhodamine B.

    PubMed

    Skaltsas, T; Karousis, N; Pispas, S; Tagmatarchis, N

    2014-11-07

    Amphiphilic block copolymer poly(isoprene-b-acrylic acid) (PI-b-PAA) was used to stabilize exfoliated graphene in water, allowing the immobilization of semiconductor CdS nanoparticles forming CdS • PI-b-PAA/graphene. Characterization using high-resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy proved the success of the preparation method and revealed the presence of spherical CdS. Moreover, UV-Vis and photoluminescence assays suggested that electronic interactions within CdS • PI-b-PAA/graphene exist as evidenced by the significant quenching of the characteristic emission of CdS by exfoliated graphene. Photoillumination of CdS • PI-b-PAA/graphene, in the presence of ammonium formate as a quencher for the photogenerated holes, resulted in the generation of hydrogen by water splitting, monitored by the reduction of 4-nitroaniline to benzene-1,4-diamine (>80 ± 4% at 20 min; 100% at 24 min), much faster and more efficient compared to when reference CdS • PI-b-PAA was used as the photocatalyst (<30 ± 3% at 20 min; 100% at 240 min). Moreover, Rhodamine B was photocatalytically degraded by CdS • PI-b-PAA/graphene, with fast kinetics under visible light illumination in the presence of air. The enhancement of both photocatalytic processes by CdS • PI-b-PAA/graphene was rationalized in terms of effective separation of holes and electrons, contrary to reference CdS • PI-b-PAA, in which rapid recombination of the hole-electron pair is inevitable due to the absence of exfoliated graphene as a suitable electron acceptor.

  11. Photocatalytic applications with CdS • block copolymer/exfoliated graphene nanoensembles: hydrogen generation and degradation of Rhodamine B

    NASA Astrophysics Data System (ADS)

    Skaltsas, T.; Karousis, N.; Pispas, S.; Tagmatarchis, N.

    2014-11-01

    Amphiphilic block copolymer poly(isoprene-b-acrylic acid) (PI-b-PAA) was used to stabilize exfoliated graphene in water, allowing the immobilization of semiconductor CdS nanoparticles forming CdS • PI-b-PAA/graphene. Characterization using high-resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy proved the success of the preparation method and revealed the presence of spherical CdS. Moreover, UV-Vis and photoluminescence assays suggested that electronic interactions within CdS • PI-b-PAA/graphene exist as evidenced by the significant quenching of the characteristic emission of CdS by exfoliated graphene. Photoillumination of CdS • PI-b-PAA/graphene, in the presence of ammonium formate as a quencher for the photogenerated holes, resulted in the generation of hydrogen by water splitting, monitored by the reduction of 4-nitroaniline to benzene-1,4-diamine (>80 ± 4% at 20 min; 100% at 24 min), much faster and more efficient compared to when reference CdS • PI-b-PAA was used as the photocatalyst (<30 ± 3% at 20 min; 100% at 240 min). Moreover, Rhodamine B was photocatalytically degraded by CdS • PI-b-PAA/graphene, with fast kinetics under visible light illumination in the presence of air. The enhancement of both photocatalytic processes by CdS • PI-b-PAA/graphene was rationalized in terms of effective separation of holes and electrons, contrary to reference CdS • PI-b-PAA, in which rapid recombination of the hole-electron pair is inevitable due to the absence of exfoliated graphene as a suitable electron acceptor.

  12. Graphene-analogue carbon nitride: novel exfoliation synthesis and its application in photocatalysis and photoelectrochemical selective detection of trace amount of Cu2+

    NASA Astrophysics Data System (ADS)

    Xu, Hui; Yan, Jia; She, Xiaojie; Xu, Li; Xia, Jiexiang; Xu, Yuanguo; Song, Yanhua; Huang, Liying; Li, Huaming

    2014-01-01

    Graphene-analogue nanostructures defined as a new kind of promising materials with unique electronic, surface and optical properties have received much attention in the fields of catalysis, energy storage, sensing and electronic devices. Due to the distinctive structure characteristics of the graphene-analogue materials, they brought novel and amazing properties. Herein, graphene-analogue carbon nitride (GA-C3N4) was synthesized by high-yield, large-scale thermal exfoliation from the graphitic C3N4-based intercalation compound. Graphene-analogue carbon nitride exhibited 2D thin-layer structure with 6-9 atomic thickness, a high specific surface area of 30.1 m2 g-1, increased photocurrent responses and improved electron transport ability, which could give rise to enhancing the photocatalytic activity and stability. The graphene-analogue carbon nitride had a new features that could make it suitable as a sensor for Cu2+ determination. So GA-C3N4 is a new but promising candidate for heavy metal ions (Cu2+) determination in water environment. The photocatalytic mechanism and photoelectrochemical selective sensing of Cu2+ were also discussed.Graphene-analogue nanostructures defined as a new kind of promising materials with unique electronic, surface and optical properties have received much attention in the fields of catalysis, energy storage, sensing and electronic devices. Due to the distinctive structure characteristics of the graphene-analogue materials, they brought novel and amazing properties. Herein, graphene-analogue carbon nitride (GA-C3N4) was synthesized by high-yield, large-scale thermal exfoliation from the graphitic C3N4-based intercalation compound. Graphene-analogue carbon nitride exhibited 2D thin-layer structure with 6-9 atomic thickness, a high specific surface area of 30.1 m2 g-1, increased photocurrent responses and improved electron transport ability, which could give rise to enhancing the photocatalytic activity and stability. The graphene

  13. Environmentally benign graphite intercalation compound composition for exfoliated graphite, flexible graphite, and nano-scaled graphene platelets

    DOEpatents

    Zhamu, Aruna; Jang, Bor Z.

    2014-06-17

    A carboxylic-intercalated graphite compound composition for the production of exfoliated graphite, flexible graphite, or nano-scaled graphene platelets. The composition comprises a layered graphite with interlayer spaces or interstices and a carboxylic acid residing in at least one of the interstices, wherein the composition is prepared by a chemical oxidation reaction which uses a combination of a carboxylic acid and hydrogen peroxide as an intercalate source. Alternatively, the composition may be prepared by an electrochemical reaction, which uses a carboxylic acid as both an electrolyte and an intercalate source. Exfoliation of the invented composition does not release undesirable chemical contaminants into air or drainage.

  14. Method of producing exfoliated graphite, flexible graphite, and nano-scaled graphene platelets

    DOEpatents

    Zhamu, Aruna; Shi, Jinjun; Guo, Jiusheng; Jang, Bor Z.

    2010-11-02

    The present invention provides a method of exfoliating a layered material (e.g., graphite and graphite oxide) to produce nano-scaled platelets having a thickness smaller than 100 nm, typically smaller than 10 nm. The method comprises (a) dispersing particles of graphite, graphite oxide, or a non-graphite laminar compound in a liquid medium containing therein a surfactant or dispersing agent to obtain a stable suspension or slurry; and (b) exposing the suspension or slurry to ultrasonic waves at an energy level for a sufficient length of time to produce separated nano-scaled platelets. The nano-scaled platelets are candidate reinforcement fillers for polymer nanocomposites. Nano-scaled graphene platelets are much lower-cost alternatives to carbon nano-tubes or carbon nano-fibers.

  15. High Voltage Li-Ion Battery Using Exfoliated Graphite/Graphene Nanosheets Anode.

    PubMed

    Agostini, Marco; Brutti, Sergio; Hassoun, Jusef

    2016-05-04

    The achievement of a new generation of lithium-ion battery, suitable for a continuously growing consumer electronic and sustainable electric vehicle markets, requires the development of new, low-cost, and highly performing materials. Herein, we propose a new and efficient lithium-ion battery obtained by coupling exfoliated graphite/graphene nanosheets (EGNs) anode and high-voltage, spinel-structure cathode. The anode shows a capacity exceeding by 40% that ascribed to commercial graphite in lithium half-cell, at very high C-rate, due to its particular structure and morphology as demonstrated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Li-ion battery reveals excellent efficiency and cycle life, extending up to 150 cycles, as well as an estimated practical energy density of about 260 Wh kg(-1), that is, a value well exceeding the one associated with the present-state Li-ion battery.

  16. Efficient Electrochemical and Photoelectrochemical Water Splitting by a 3D Nanostructured Carbon Supported on Flexible Exfoliated Graphene Foil.

    PubMed

    Hou, Yang; Qiu, Ming; Zhang, Tao; Ma, Ji; Liu, Shaohua; Zhuang, Xiaodong; Yuan, Chris; Feng, Xinliang

    2017-01-01

    A novel 3D Co-Nx |P-complex-doped carbon grown on flexible exfoliated graphene foil is designed and constructed for both electrochemical and photoelectrochemical water splitting. The coordination of Co-Nx active centers hybridized with that of neighboring P atoms enhances the electron transfer and optimizes the charge distribution of the carbon surface, which synergistically promotes reaction kinetics by providing more exposed active sites.

  17. Graphene-analogue carbon nitride: novel exfoliation synthesis and its application in photocatalysis and photoelectrochemical selective detection of trace amount of Cu²⁺.

    PubMed

    Xu, Hui; Yan, Jia; She, Xiaojie; Xu, Li; Xia, Jiexiang; Xu, Yuanguo; Song, Yanhua; Huang, Liying; Li, Huaming

    2014-01-01

    Graphene-analogue nanostructures defined as a new kind of promising materials with unique electronic, surface and optical properties have received much attention in the fields of catalysis, energy storage, sensing and electronic devices. Due to the distinctive structure characteristics of the graphene-analogue materials, they brought novel and amazing properties. Herein, graphene-analogue carbon nitride (GA-C₃N₄) was synthesized by high-yield, large-scale thermal exfoliation from the graphitic C₃N₄-based intercalation compound. Graphene-analogue carbon nitride exhibited 2D thin-layer structure with 6-9 atomic thickness, a high specific surface area of 30.1 m(2) g(-1), increased photocurrent responses and improved electron transport ability, which could give rise to enhancing the photocatalytic activity and stability. The graphene-analogue carbon nitride had a new features that could make it suitable as a sensor for Cu(2+) determination. So GA-C₃N₄ is a new but promising candidate for heavy metal ions (Cu(2+)) determination in water environment. The photocatalytic mechanism and photoelectrochemical selective sensing of Cu(2+) were also discussed.

  18. A mixed-solvent strategy for facile and green preparation of graphene by liquid-phase exfoliation of graphite

    NASA Astrophysics Data System (ADS)

    Yi, Min; Shen, Zhigang; Ma, Shulin; Zhang, Xiaojing

    2012-08-01

    A versatile and scalable mixed-solvent strategy, by which two mediocre solvents could be combined into good solvents for exfoliating graphite, is demonstrated for facile and green preparation of graphene by liquid-phase exfoliation of graphite. Mild sonication of crystal graphite powder in a mixture of water and alcohol could yield graphene nanosheets, which formed a highly stable suspension in the mixed solvents. The graphene yield was estimated as 10 wt%. The optimum mass fraction of ethanol in water-ethanol mixtures and isopropanol in water-isopropanol mixtures was experimentally determined as 40 and 55 % respectively, which could be roughly predicted by the theory of Hansen solubility parameters. Statistics based on atomic force microscopic analysis show that up to 86 % of the prepared nanosheets were less than 10-layer thick with a monolayer fraction of 8 %. High resolution transmission electron microscopy, infrared spectroscopy, X-ray diffraction, and Raman spectrum analysis of the vacuum-filtered films suggest the graphene sheets to be largely free of defects and oxides. The proposed mixed-solvent strategy here extends the scope for liquid-phase processing graphene and gives researchers great freedom in designing ideal solvent systems for specific applications.

  19. Studies on Synthesis of Electrochemically Exfoliated Functionalized Graphene and Polylactic Acid/Ferric Phytate Functionalized Graphene Nanocomposites as New Fire Hazard Suppression Materials.

    PubMed

    Feng, Xiaming; Wang, Xin; Cai, Wei; Qiu, Shuilai; Hu, Yuan; Liew, Kim Meow

    2016-09-28

    Practical application of functionalized graphene in polymeric nanocomposites is hampered by the lack of cost-effective and eco-friendly methods for its production. Here, we reported a facile and green electrochemical approach for preparing ferric phytate functionalized graphene (f-GNS) by simultaneously utilizing biobased phytic acid as electrolyte and modifier for the first time. Due to the presence of phytic acid, electrochemical exfoliation leads to low oxidized graphene sheets (a C/O ratio of 14.8) that are tens of micrometers large. Successful functionalization of graphene was confirmed by the appearance of phosphorus and iron peaks in the X-ray photoelectron spectrum. Further, high-performance polylactic acid/f-GNS nanocomposites are readily fabricated by a convenient masterbatch strategy. Notably, inclusion of well-dispersed f-GNS resulted in dramatic suppression on fire hazards of polylactic acid in terms of reduced peak heat-release rate (decreased by 40%), low CO yield, and formation of a high graphitized protective char layer. Moreover, obviously improvements in crystallization rate and thermal conductivities of polylactic acid nanocomposites were observed, highlighting its promising potential in practical application. This novel strategy toward the simultaneous exfoliation and functionalization for graphene demonstrates a simple yet very effective approach for fabricating graphene-based flame retardants.

  20. Facile and Scalable Synthesis Method for High-Quality Few-Layer Graphene through Solution-Based Exfoliation of Graphite.

    PubMed

    Wee, Boon-Hong; Wu, Tong-Fei; Hong, Jong-Dal

    2017-02-08

    Here we describe a facile and scalable method for preparing defect-free graphene sheets exfoliated from graphite using the positively charged polyelectrolyte precursor poly(p-phenylenevinylene) (PPV-pre) as a stabilizer in an aqueous solution. The graphene exfoliated by PPV-pre was apparently stabilized in the solution as a form of graphene/PPV-pre (denoted to GPPV-pre), which remains in a homogeneous dispersion over a year. The thickness values of 300 selected 76% GPPV-pre flakes ranged from 1 to 10 nm, corresponding to between one and a few layers of graphene in the lateral dimensions of 1 to 2 μm. Furthermore, this approach was expected to yield a marked decrease in the density of defects in the electronic conjugation of graphene compared to that of graphene oxide (GO) obtained by Hummers' method. The positively charged GPPV-pre was employed to fabricate a poly(ethylene terephthalate) (PET) electrode layer-by-layer with negatively charged GO, yielding (GPPV-pre/GO)n film electrode. The PPV-pre and GO in the (GPPV-pre/GO)n films were simultaneously converted using hydroiodic acid vapor to fully conjugated PPV and reduced graphene oxide (RGO), respectively. The electrical conductivity of (GPPV/RGO)23 multilayer films was 483 S/cm, about three times greater than that of the (PPV/RGO)23 multilayer films (166 S/cm) comprising RGO (prepared by Hummers method). Furthermore, the superior electrical properties of GPPV were made evident, when comparing the capacitive performances of two supercapacitor systems; (polyaniline PANi/RGO)30/(GPPV/RGO)23/PET (volumetric capacitance = 216 F/cm(3); energy density = 19 mWh/cm(3); maximum power density = 498 W/cm(3)) and (PANi/RGO)30/(PPV/RGO)23/PET (152 F/cm(3); 9 mWh/cm(3); 80 W/cm(3)).

  1. Low-frequency current fluctuations in "graphene-like" exfoliated thin-films of bismuth selenide topological insulators.

    PubMed

    Hossain, Md Zahid; Rumyantsev, Sergey L; Shahil, Khan M F; Teweldebrhan, Desalegne; Shur, Michael; Balandin, Alexander A

    2011-04-26

    We report on the low-frequency current fluctuations and electronic noise in thin-films made of Bi(2)Se(3) topological insulators. The films were prepared via the "graphene-like" mechanical exfoliation and used as the current conducting channels in the four- and two-contact devices. The thickness of the films ranged from ∼50 to 170 nm to avoid hybridization of the top and bottom electron surface states. Analysis of the resistance dependence on the film thickness indicates that the surface contribution to conductance is dominant in our samples. It was established that the current fluctuations have the noise spectrum close to the pure 1/f in the frequency range from 1 Hz to 10 kHz (f is the frequency). The relative noise amplitude S(I)/I(2) for the examined Bi(2)Se(3) films was increasing from ∼5 × 10(-8) to 5 × 10(-6) (1/Hz) as the resistance of the channels varied from ∼10(3) to 10(5) Ω. The obtained noise data is important for understanding electron transport through the surface and volume of topological insulators, and proposed applications of this class of materials. The results may help to develop a new method of noise reduction in electronic devices via the "scattering immune" transport through the surface states.

  2. Exploring the potential of exfoliated graphene nanoplatelets as the conductive filler in polymeric nanocomposites for bipolar plates

    NASA Astrophysics Data System (ADS)

    Jiang, Xian; Drzal, Lawrence T.

    2012-11-01

    This research explored the potential of using exfoliated graphene nanoplatelets, GNP, as the conductive filler to construct highly conductive polymeric nanocomposites to substitute for conventional metallic and graphite bipolar plates in the polymer electrolyte membrane (PEM) fuel cells. Polyphenylene sulfide (PPS) was selected as the polymer matrix because of its high thermal and chemical tolerance. Solid state ball milling (SSBM) followed by compression molding was then applied to fabricate PPS/GNP nanocomposites. Results showed that PPS/GNP nanocomposites made by this method exhibit excellent mechanical and gas barrier properties but unsatisfied electrical conductivity. However, it was found that the electrical conductivity of these nanocomposites could be substantially enhanced if we combine GNP with second minor conductive filler for a positive synergistic effect and also optimize the processing time of SSBM. Meanwhile, PPS impregnated GNP papers were embedded into these PPS/GNP nanocomposites in order to further improve various properties of the resulting bipolar plates. It is believed that the bipolar plates made from PPS/GNP nanocomposites will allow lighter weight of PEM fuel cells with enhanced performance which is particularly suited for automotive applications.

  3. Production of quasi-2D graphene nanosheets through the solvent exfoliation of pitch-based carbon fiber.

    PubMed

    Yeon, Youngju; Lee, Mi Yeon; Kim, Sang Youl; Lee, Jihoon; Kim, Bongsoo; Park, Byoungnam; In, Insik

    2015-09-18

    Stable dispersion of quasi-2D graphene sheets with a concentration up to 1.27 mg mL(-1) was prepared by sonication-assisted solvent exfoliation of pitch-based carbon fiber in N-methyl pyrrolidone with the mass yield of 2.32%. Prepared quasi-2D graphene sheets have multi-layered 2D plate-like morphology with rich inclusions of graphitic carbons, a low number of structural defects, and high dispersion stability in aprotic polar solvents, and facilitate the utilization of quasi-2D graphene sheets prepared from pitch-based carbon fiber for various electronic and structural applications. Thin films of quasi-2D graphene sheets prepared by vacuum filtration of the dispersion of quasi-2D graphene sheets demonstrated electrical conductivity up to 1.14 × 10(4) Ω/□ even without thermal treatment, which shows that pitch-based carbon fiber might be useful as the source of graphene-related nanomaterials. Because pitch-based carbon fiber could be prepared from petroleum pitch, a very cheap structural material for the pavement of asphalt roads, our approach might be promising for the mass production of quasi-2D graphene nanomaterials.

  4. Production of quasi-2D graphene nanosheets through the solvent exfoliation of pitch-based carbon fiber

    NASA Astrophysics Data System (ADS)

    Yeon, Youngju; Lee, Mi Yeon; Kim, Sang Youl; Lee, Jihoon; Kim, Bongsoo; Park, Byoungnam; In, Insik

    2015-09-01

    Stable dispersion of quasi-2D graphene sheets with a concentration up to 1.27 mg mL-1 was prepared by sonication-assisted solvent exfoliation of pitch-based carbon fiber in N-methyl pyrrolidone with the mass yield of 2.32%. Prepared quasi-2D graphene sheets have multi-layered 2D plate-like morphology with rich inclusions of graphitic carbons, a low number of structural defects, and high dispersion stability in aprotic polar solvents, and facilitate the utilization of quasi-2D graphene sheets prepared from pitch-based carbon fiber for various electronic and structural applications. Thin films of quasi-2D graphene sheets prepared by vacuum filtration of the dispersion of quasi-2D graphene sheets demonstrated electrical conductivity up to 1.14 × 104 Ω/□ even without thermal treatment, which shows that pitch-based carbon fiber might be useful as the source of graphene-related nanomaterials. Because pitch-based carbon fiber could be prepared from petroleum pitch, a very cheap structural material for the pavement of asphalt roads, our approach might be promising for the mass production of quasi-2D graphene nanomaterials.

  5. In Situ Exfoliated, Edge-Rich, Oxygen-Functionalized Graphene from Carbon Fibers for Oxygen Electrocatalysis.

    PubMed

    Liu, Zhijuan; Zhao, Zhenghang; Wang, Yanyong; Dou, Shuo; Yan, Dafeng; Liu, Dongdong; Xia, Zhenhai; Wang, Shuangyin

    2017-03-09

    Metal-free electrocatalysts have been extensively developed to replace noble metal Pt and RuO2 catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in fuel cells or metal-air batteries. These electrocatalysts are usually deposited on a 3D conductive support (e.g., carbon paper or carbon cloth (CC)) to facilitate mass and electron transport. For practical applications, it is desirable to create in situ catalysts on the carbon fiber support to simplify the fabrication process for catalytic electrodes. In this study, the first example of in situ exfoliated, edge-rich, oxygen-functionalized graphene on the surface of carbon fibers using Ar plasma treatment is successfully prepared. Compared to pristine CC, the plasma-etched carbon cloth (P-CC) has a higher specific surface area and an increased number of active sites for OER and ORR. P-CC also displays good intrinsic electron conductivity and excellent mass transport. Theoretical studies show that P-CC has a low overpotential that is comparable to Pt-based catalysts, as a result of both defects and oxygen doping. This study provides a simple and effective approach for producing highly active in situ catalysts on a carbon support for OER and ORR.

  6. Ultrafast and nanoscale plasmonic phenomena in exfoliated graphene revealed by infrared pump-probe nanoscopy.

    PubMed

    Wagner, Martin; Fei, Zhe; McLeod, Alexander S; Rodin, Aleksandr S; Bao, Wenzhong; Iwinski, Eric G; Zhao, Zeng; Goldflam, Michael; Liu, Mengkun; Dominguez, Gerardo; Thiemens, Mark; Fogler, Michael M; Castro Neto, Antonio H; Lau, Chun Ning; Amarie, Sergiu; Keilmann, Fritz; Basov, D N

    2014-02-12

    Pump-probe spectroscopy is central for exploring ultrafast dynamics of fundamental excitations, collective modes, and energy transfer processes. Typically carried out using conventional diffraction-limited optics, pump-probe experiments inherently average over local chemical, compositional, and electronic inhomogeneities. Here, we circumvent this deficiency and introduce pump-probe infrared spectroscopy with ∼ 20 nm spatial resolution, far below the diffraction limit, which is accomplished using a scattering scanning near-field optical microscope (s-SNOM). This technique allows us to investigate exfoliated graphene single-layers on SiO2 at technologically significant mid-infrared (MIR) frequencies where the local optical conductivity becomes experimentally accessible through the excitation of surface plasmons via the s-SNOM tip. Optical pumping at near-infrared (NIR) frequencies prompts distinct changes in the plasmonic behavior on 200 fs time scales. The origin of the pump-induced, enhanced plasmonic response is identified as an increase in the effective electron temperature up to several thousand Kelvin, as deduced directly from the Drude weight associated with the plasmonic resonances.

  7. Ultrafast and Nanoscale Plasmonic Phenomena in Exfoliated Graphene Revealed by Infrared Pump-Probe Nanoscopy

    NASA Astrophysics Data System (ADS)

    Wagner, Martin; Fei, Zhe; McLeod, Alexander S.; Rodin, Aleksandr S.; Bao, Wenzhong; Iwinski, Eric G.; Zhao, Zeng; Goldflam, Michael; Liu, Mengkun; Dominguez, Gerardo; Thiemens, Mark; Fogler, Michael M.; Castro Neto, Antonio H.; Lau, Chun Ning; Amarie, Sergiu; Keilmann, Fritz; Basov, D. N.

    2014-02-01

    Pump-probe spectroscopy is central for exploring ultrafast dynamics of fundamental excitations, collective modes and energy transfer processes. Typically carried out using conventional diffraction-limited optics, pump-probe experiments inherently average over local chemical, compositional, and electronic inhomogeneities. Here we circumvent this deficiency and introduce pump-probe infrared spectroscopy with ~20 nm spatial resolution, far below the diffraction limit, which is accomplished using a scattering scanning near-field optical microscope (s-SNOM). This technique allows us to investigate exfoliated graphene single-layers on SiO2 at technologically significant mid-infrared (MIR) frequencies where the local optical conductivity becomes experimentally accessible through the excitation of surface plasmons via the s-SNOM tip. Optical pumping at near-infrared (NIR) frequencies prompts distinct changes in the plasmonic behavior on 200 femtosecond (fs) time scales. The origin of the pump-induced, enhanced plasmonic response is identified as an increase in the effective electron temperature up to several thousand Kelvin, as deduced directly from the Drude weight associated with the plasmonic resonances.

  8. Electrochemically exfoliated graphene anodes with enhanced biocurrent production in single-chamber air-breathing microbial fuel cells.

    PubMed

    Najafabadi, Amin Taheri; Ng, Norvin; Gyenge, Előd

    2016-07-15

    Microbial fuel cells (MFCs) present promising options for environmentally sustainable power generation especially in conjunction with waste water treatment. However, major challenges remain including low power density, difficult scale-up, and durability of the cell components. This study reports enhanced biocurrent production in a membrane-free MFC, using graphene microsheets (GNs) as anode and MnOx catalyzed air cathode. The GNs are produced by ionic liquid assisted simultaneous anodic and cathodic electrochemical exfoliation of iso-molded graphite electrodes. The GNs produced by anodic exfoliation increase the MFC peak power density by over 300% compared to plain carbon cloth (i.e., 2.85Wm(-2) vs 0.66Wm(-2), respectively), and by 90% compared to conventional carbon black (i.e., Vulcan XC-72) anode. These results exceed previously reported power densities for graphene-containing MFC anodes. The fuel cell polarization results are corroborated by electrochemical impedance spectroscopy indicating three times lower charge transfer resistance for the GN anode. Material characterizations suggest that the best performing GN samples were of relatively smaller size (~500nm), with higher levels of ionic liquid induced surface functionalization during the electrochemical exfoliation process.

  9. In situ growth of capping-free magnetic iron oxide nanoparticles on liquid-phase exfoliated graphene

    NASA Astrophysics Data System (ADS)

    Tsoufis, T.; Syrgiannis, Z.; Akhtar, N.; Prato, M.; Katsaros, F.; Sideratou, Z.; Kouloumpis, A.; Gournis, D.; Rudolf, P.

    2015-05-01

    We report a facile approach for the in situ synthesis of very small iron oxide nanoparticles on the surface of high-quality graphene sheets. Our synthetic strategy involved the direct, liquid-phase exfoliation of highly crystalline graphite (avoiding any oxidation treatment) and the subsequent chemical functionalization of the graphene sheets via the well-established 1,3-dipolar cycloaddition reaction. The resulting graphene derivatives were employed for the immobilization of the nanoparticle precursor (Fe cations) at the introduced organic groups by a modified wet-impregnation method, followed by interaction with acetic acid vapours. The final graphene-iron oxide hybrid material was achieved by heating (calcination) in an inert atmosphere. Characterization by X-ray diffraction, transmission electron and atomic force microscopy, Raman and X-ray photoelectron spectroscopy gave evidence for the formation of rather small (<12 nm), spherical, magnetite-rich nanoparticles which were evenly distributed on the surface of few-layer (<1.2 nm thick) graphene. Due to the presence of the iron oxide nanoparticles, the hybrid material showed a superparamagnetic behaviour at room temperature.We report a facile approach for the in situ synthesis of very small iron oxide nanoparticles on the surface of high-quality graphene sheets. Our synthetic strategy involved the direct, liquid-phase exfoliation of highly crystalline graphite (avoiding any oxidation treatment) and the subsequent chemical functionalization of the graphene sheets via the well-established 1,3-dipolar cycloaddition reaction. The resulting graphene derivatives were employed for the immobilization of the nanoparticle precursor (Fe cations) at the introduced organic groups by a modified wet-impregnation method, followed by interaction with acetic acid vapours. The final graphene-iron oxide hybrid material was achieved by heating (calcination) in an inert atmosphere. Characterization by X-ray diffraction, transmission

  10. Dynamics and Mechanisms of Exfoliated Black Phosphorus Sublimation.

    PubMed

    Fortin-Deschênes, Matthieu; Levesque, Pierre L; Martel, Richard; Moutanabbir, Oussama

    2016-05-05

    We report on real time observations of the sublimation of exfoliated black phosphorus layers throughout annealing using in situ low energy electron microscopy. We found that sublimation manifests itself above 375 ± 20 °C through the nucleation and expansion of asymmetric, faceted holes with the long axis aligned along the [100] direction and sharp tips defined by edges consisting of alternating (10) and (11) steps. This thermally activated process repeats itself via successive sublimation of individual layers. Calculations and simulations using density functional theory and kinetic Monte Carlo allowed to determine the involved atomic pathways. Sublimation is found to occur via detachments of phosphorus dimers rather than single atoms. This behavior and the role of defects is described using an analytical model that captures all essential features. This work establishes an atomistic-level understanding of the thermal stability of exfoliated black phosphorus and defines the temperature window available for material and device processing.

  11. Liquid-phase exfoliated graphene self-assembled films: Low-frequency noise and thermal-electric characterization

    NASA Astrophysics Data System (ADS)

    Tubon Usca, G.; Hernandez-Ambato, J.; Pace, C.; Caputi, L. S.; Tavolaro, A.

    2016-09-01

    In few years, graphene has become a revolutionary material, leading not only to applications in various fields such as electronics, medicine and environment, but also to the production of new types of 2D materials. In this work, Liquid Phase Exfoliation (LPE) was applied to natural graphite by brief sonication or mixer treatment in suitable solvents, in order to produce Few Layers Graphene (FLG) suspensions. Additionally, zeolite 4A (Z4A) was added during the production of FLG flakes-based inks, with the aim of aiding the exfoliation process. Conductive films were obtained by drop casting three types of suspensions over Al2O3 substrates with interdigitated electrodes, with total channel surface of 1.39 mm2. The morphology characterization resulted in the verification of the presence of thin self-assembled flakes. Raman studies gave evidence of 4 to 10 layers graphene flakes. Electrical measurements were performed to state the Low-Frequency Noise and Thermal-Electric characteristics of the samples. We observe interesting relations between sample preparation procedures and electrical properties.

  12. Mechanical properties of graphene papers

    NASA Astrophysics Data System (ADS)

    Liu, Yilun; Xie, Bo; Zhang, Zhong; Zheng, Quanshui; Xu, Zhiping

    2012-04-01

    Graphene-based paper materials attract particular interests recently owing to their outstanding properties, the key of which is their layer-by-layer hierarchical structures similar to many biological materials such as bone, teeth and nacre, combining intralayer strong sp2 bonds and interlayer crosslinks for efficient load transfer. Here we firstly study the mechanical properties of various interlayer and intralayer crosslinks through first-principles calculations, and then perform continuum model analysis for the overall mechanical properties of graphene-based paper materials. We find that there is a characteristic length scale l0, defined as √{Dh0/4G}, where D is the stiffness of the graphene sheet, h0 and G are height of interlayer crosslink and shear modulus respectively. When the size of the graphene sheets exceeds 3l0, the tension-shear (TS) chain model, which is widely used for nanocomposites, fails to predict the overall mechanical properties of the graphene-based papers. Instead we proposed here a deformable tension-shear (DTS) model by considering elastic deformation of graphene sheets, also the interlayer and intralayer crosslinks. The DTS is then applied to predict the mechanical properties of graphene papers under tensile loading. According to the results we thus obtain, optimal design strategies are proposed for graphene papers with ultrahigh stiffness, strength and toughness.

  13. Exfoliation of Graphene Oxide Nanosheets from Pencil Lead and IN SITU Preparation of Gold Nanoparticles on Graphene Oxide Nanosheets

    NASA Astrophysics Data System (ADS)

    Boruah, Sontara Konwar; Boruah, Prabin Kumar; Sarma, Pradyut; Bezbaruah, Bipul; Medhi, Chitrani; Medhi, Okhil Kumar

    2013-01-01

    This work reports the low-cost exfoliation of graphene oxide (GO) from pencil lead using modified Hummer's method. The gold nanoparticles (AuNPs) supported on GO is prepared via an in situ bio reduction of HAuCl4 by polyphenolic biomolecules present in young leaves of tea (Camellia sinensis) extracted in the presence of GO. The UV-Visible absorption spectrum of GO dispersion in water exhibits two bands at 228 nm and a shoulder at 300 nm corresponding to π-π* transitions of aromatic C-C bonds and n-π* transitions of C=O bonds. In photoluminescence (PL) study, GO dispersion in water shows an emission band at 555 nm, when excited at 325 nm. When AuNPs are supported on GO nanosheets the bands at 228 nm and 300 nm of GO disappears and two new UV-Visible bands at 229 nm for π-π* (for C=C) and 550 nm for transverse surface plasmon resonance (TSPR) of AuNPs appears. When AuNPs are supported on GO nanosheets, PL emission band at 555 nm disappears and two new PL emission bands appear at 431 nm and 658 nm. The physical and morphological characterizations are performed by Fourier-transform infrared (FT-IR), X-ray diffraction (XRD), High-resolution-transmission electron microscopy (HR-TEM) and BET surface area measurement. Morphological studies revealed that the GO nanosheets are well dispersed in water and AuNPs are supported on the GO nanosheets.

  14. A study on the physicochemical properties of hydroalcoholic solutions to improve the direct exfoliation of natural graphite down to few-layers graphene

    NASA Astrophysics Data System (ADS)

    Fedi, Filippo; Miglietta, Maria Lucia; Polichetti, Tiziana; Ricciardella, Filiberto; Massera, Ettore; Ninno, Domenico; Di Francia, Girolamo

    2015-03-01

    Straightforward methods to produce pristine graphene flakes in large quantities are based on the liquid-phase exfoliation processes. These one-step physical transformations of graphite into graphene offer many unique advantages. To date, a large number of liquids have been employed as exfoliation media exploiting their thermodynamic and chemical features as compared to those of graphene. Here, we pursued the goal of realizing water based mixtures to exfoliate graphite and disperse graphene without the aid of surfactants. To this aim, aqueous mixtures with suitable values of surface tension and Hansen solubility parameters (HSPs), were specifically designed and used. The very high water surface tension was decreased by the addition of solvents with lower surface tensions such as alcohols, obtaining, in this way, more favourable HSP distances. The specific role of each of these thermodynamic features was finally investigated. The results showed that the designed hydroalcoholic solutions were effective in both the graphite exfoliation and dispersion without the addition of any surfactants or other stabilizing agents. Stable graphene suspensions were obtained at concentration comparable to those produced with low-boiling solvents and water/surfactants.

  15. Efficient exfoliation N-doped graphene from N-containing bamboo-like carbon nanotubes for anode materials of Li-ion battery and Na-ion battery

    NASA Astrophysics Data System (ADS)

    Feng, Jian-Min; Dong, Lei; Han, Yan; Li, Xi-Fei; Li, De-Jun

    2015-08-01

    Nanosize N-doped graphene is prepared from N-containing carbon nanotubes (CNTs) by chemical exfoliation. The CNTs adopted for graphene are characterized by a discontinuous wall that consists of nanosize graphite layers, exhibiting a bamboo-like appearance. Take advantage of this characterization, the most time-consuming process of chemical oxidation that involves intercalation in graphene from CNT has been markedly reduced. The reduction in processing time is attributed to the diffusion distance of chemical oxidation intercalation into nanosize graphite composed of a bamboo-like carbon nanotube (BCNT) wall being far less than that of conventional chemical exfoliation into microsize graphite. The as-prepared nanosize N-doped graphene from BCNTs has shown an excellent electrochemical performance for Li-ion battery and Na-ion battery anode materials.

  16. Ultrasensitive NO2 Sensor Based on Ohmic Metal-Semiconductor Interfaces of Electrolytically Exfoliated Graphene/Flame-Spray-Made SnO2 Nanoparticles Composite Operating at Low Temperatures.

    PubMed

    Tammanoon, Nantikan; Wisitsoraat, Anurat; Sriprachuabwong, Chakrit; Phokharatkul, Ditsayut; Tuantranont, Adisorn; Phanichphant, Sukon; Liewhiran, Chaikarn

    2015-11-04

    In this work, flame-spray-made undoped SnO2 nanoparticles were loaded with 0.1-5 wt % electrolytically exfoliated graphene and systematically studied for NO2 sensing at low working temperatures. Characterizations by X-ray diffraction, transmission/scanning electron microscopy, and Raman and X-ray photoelectron spectroscopy indicated that high-quality multilayer graphene sheets with low oxygen content were widely distributed within spheriodal nanoparticles having polycrystalline tetragonal SnO2 phase. The 10-20 μm thick sensing films fabricated by spin coating on Au/Al2O3 substrates were tested toward NO2 at operating temperatures ranging from 25 to 350 °C in dry air. Gas-sensing results showed that the optimal graphene loading level of 0.5 wt % provided an ultrahigh response of 26,342 toward 5 ppm of NO2 with a short response time of 13 s and good recovery stabilization at a low optimal operating temperature of 150 °C. In addition, the optimal sensor also displayed high sensor response and relatively short response time of 171 and 7 min toward 5 ppm of NO2 at room temperature (25 °C). Furthermore, the sensors displayed very high NO2 selectivity against H2S, NH3, C2H5OH, H2, and H2O. Detailed mechanisms for the drastic NO2 response enhancement by graphene were proposed on the basis of the formation of graphene-undoped SnO2 ohmic metal-semiconductor junctions and accessible interfaces of graphene-SnO2 nanoparticles. Therefore, the electrolytically exfoliated graphene-loaded FSP-made SnO2 sensor is a highly promising candidate for fast, sensitive, and selective detection of NO2 at low operating temperatures.

  17. Spectroscopic metrics allow in situ measurement of mean size and thickness of liquid-exfoliated few-layer graphene nanosheets

    NASA Astrophysics Data System (ADS)

    Backes, Claudia; Paton, Keith R.; Hanlon, Damien; Yuan, Shengjun; Katsnelson, Mikhail I.; Houston, James; Smith, Ronan J.; McCloskey, David; Donegan, John F.; Coleman, Jonathan N.

    2016-02-01

    Liquid phase exfoliation is a powerful and scalable technique to produce defect-free mono- and few-layer graphene. However, samples are typically polydisperse and control over size and thickness is challenging. Notably, high throughput techniques to measure size and thickness are lacking. In this work, we have measured the extinction, absorption, scattering and Raman spectra for liquid phase exfoliated graphene nanosheets of various lateral sizes (90 <= <= 810 nm) and thicknesses (2.7 <= <= 10.4). We found all spectra to show well-defined dependences on nanosheet dimensions. Measurements of extinction and absorption spectra of nanosheet dispersions showed both peak position and spectral shape to vary with nanosheet thickness in a manner consistent with theoretical calculations. This allows the development of empirical metrics to extract the mean thickness of liquid dispersed nanosheets from an extinction (or absorption) spectrum. While the scattering spectra depended on nanosheet length, poor signal to noise ratios made the resultant length metric unreliable. By analyzing Raman spectra measured on graphene nanosheet networks, we found both the D/G intensity ratio and the width of the G-band to scale with mean nanosheet length allowing us to establish quantitative relationships. In addition, we elucidate the variation of 2D/G band intensities and 2D-band shape with the mean nanosheet thickness, allowing us to establish quantitative metrics for mean nanosheet thickness from Raman spectra.Liquid phase exfoliation is a powerful and scalable technique to produce defect-free mono- and few-layer graphene. However, samples are typically polydisperse and control over size and thickness is challenging. Notably, high throughput techniques to measure size and thickness are lacking. In this work, we have measured the extinction, absorption, scattering and Raman spectra for liquid phase exfoliated graphene nanosheets of various lateral sizes (90 <= <= 810 nm) and

  18. Interconnecting Carbon Fibers with the In-situ Electrochemically Exfoliated Graphene as Advanced Binder-free Electrode Materials for Flexible Supercapacitor.

    PubMed

    Zou, Yuqin; Wang, Shuangyin

    2015-07-07

    Flexible energy storage devices are highly demanded for various applications. Carbon cloth (CC) woven by carbon fibers (CFs) is typically used as electrode or current collector for flexible devices. The low surface area of CC and the presence of big gaps (ca. micro-size) between individual CFs lead to poor performance. Herein, we interconnect individual CFs through the in-situ exfoliated graphene with high surface area by the electrochemical intercalation method. The interconnected CFs are used as both current collector and electrode materials for flexible supercapacitors, in which the in-situ exfoliated graphene act as active materials and conductive "binders". The in-situ electrochemical intercalation technique ensures the low contact resistance between electrode (graphene) and current collector (carbon cloth) with enhanced conductivity. The as-prepared electrode materials show significantly improved performance for flexible supercapacitors.

  19. Synthesis of Multimetal-Graphene Composite by Mechanical Milling

    NASA Astrophysics Data System (ADS)

    Saiphaneendra, Bachu; Srivastava, Avi Krishna; Srivastava, Chandan

    2016-10-01

    Multimetal-graphene composites were synthesized using the ball milling technique. To prepare the composite, graphite powder was mixed with Fe, Cr, Co, Cu and Mg powders. This mixture was then mechanically milled for 35 h in toluene medium. After milling, the multimetal-graphite mixture was mixed with sodium lauryl sulfate and sonicated for 2 h. Sonication led to the exfoliation of graphene sheets. Formation of graphene was confirmed from x-ray diffraction and Raman spectroscopy. Transmission electron microscopy-based analysis revealed the formation of multimetal deposits over the graphene surface. Compositional analysis of the multimetal deposits revealed fairly uniform distribution of all the five component metal atoms over the graphene sheet. The average composition of the multimetal deposit was determined to be 11.4 ± 4 at.% Mg, 33.8 ± 19 at.% Cr, 21.8 ± 16 at.% Fe, 9.4 ± 5.7 at.% Co and 23.6 ± 12 at.% Cu.

  20. Rational and practical exfoliation of graphite using well-defined poly(3-hexylthiophene) for the preparation of conductive polymer/graphene composite.

    PubMed

    Iguchi, Hiroki; Higashi, Chisato; Funasaki, Yuichi; Fujita, Keisuke; Mori, Atsunori; Nakasuga, Akira; Maruyama, Tatsuo

    2017-01-06

    Processing and manipulation of highly conductive pristine graphene in large quantities are still major challenges in the practical application of graphene for electric device. In the present study, we report the liquid-phase exfoliation of graphite in toluene using well-defined poly(3-hexylthiophene) (P3HT) to produce a P3HT/graphene composite. We synthesize and use regioregular P3HT with controlled molecular weights as conductive dispersants for graphene. Simple ultrasonication of graphite flakes with the P3HT successfully produces single-layer and few-layer graphene sheets dispersed in toluene. The produced P3HT/graphene composite can be used as conductive graphene ink, indicating that the P3HT/graphene composite has high electrical conductivity owing to the high conductivity of P3HT and graphene. The P3HT/graphene composite also works as an oxidation-resistant and conductive film for a copper substrate, which is due to the high gas-barrier property of graphene.

  1. Rational and practical exfoliation of graphite using well-defined poly(3-hexylthiophene) for the preparation of conductive polymer/graphene composite

    PubMed Central

    Iguchi, Hiroki; Higashi, Chisato; Funasaki, Yuichi; Fujita, Keisuke; Mori, Atsunori; Nakasuga, Akira; Maruyama, Tatsuo

    2017-01-01

    Processing and manipulation of highly conductive pristine graphene in large quantities are still major challenges in the practical application of graphene for electric device. In the present study, we report the liquid-phase exfoliation of graphite in toluene using well-defined poly(3-hexylthiophene) (P3HT) to produce a P3HT/graphene composite. We synthesize and use regioregular P3HT with controlled molecular weights as conductive dispersants for graphene. Simple ultrasonication of graphite flakes with the P3HT successfully produces single-layer and few-layer graphene sheets dispersed in toluene. The produced P3HT/graphene composite can be used as conductive graphene ink, indicating that the P3HT/graphene composite has high electrical conductivity owing to the high conductivity of P3HT and graphene. The P3HT/graphene composite also works as an oxidation-resistant and conductive film for a copper substrate, which is due to the high gas-barrier property of graphene. PMID:28059127

  2. Rational and practical exfoliation of graphite using well-defined poly(3-hexylthiophene) for the preparation of conductive polymer/graphene composite

    NASA Astrophysics Data System (ADS)

    Iguchi, Hiroki; Higashi, Chisato; Funasaki, Yuichi; Fujita, Keisuke; Mori, Atsunori; Nakasuga, Akira; Maruyama, Tatsuo

    2017-01-01

    Processing and manipulation of highly conductive pristine graphene in large quantities are still major challenges in the practical application of graphene for electric device. In the present study, we report the liquid-phase exfoliation of graphite in toluene using well-defined poly(3-hexylthiophene) (P3HT) to produce a P3HT/graphene composite. We synthesize and use regioregular P3HT with controlled molecular weights as conductive dispersants for graphene. Simple ultrasonication of graphite flakes with the P3HT successfully produces single-layer and few-layer graphene sheets dispersed in toluene. The produced P3HT/graphene composite can be used as conductive graphene ink, indicating that the P3HT/graphene composite has high electrical conductivity owing to the high conductivity of P3HT and graphene. The P3HT/graphene composite also works as an oxidation-resistant and conductive film for a copper substrate, which is due to the high gas-barrier property of graphene.

  3. Exfoliation of graphene oxide and its application in improving the electro-optical response of ferroelectric liquid crystal

    SciTech Connect

    Kumar, Veeresh; Kumar, Ajay; Bhandari, Shruti; Biradar, A. M.; Pasricha, Renu E-mail: renu1505@gmail.com; Reddy, G. B.

    2015-09-21

    Near complete exfoliation and reduction of lyophilized graphene oxide (GO) has been carried out at temperature as low as 400 °C. The structural characterizations of the reduced GO have been performed using X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy techniques. The morphological studies were carried out using scanning electron microscopy. The synthesized GO finds an application in improving the switching performance of a liquid crystal (LC) mixture by remarkably modifying the physical properties, such as spontaneous polarization and rotational viscosity of the ferroelectric LC (FLC) material which in turn resulted into faster response of the FLC. The present study explores the possibility of low temperature thermal reduction of GO along with its application in improving the properties of LC based display systems.

  4. Electrolytically exfoliated graphene-loaded flame-made Ni-doped SnO2 composite film for acetone sensing.

    PubMed

    Singkammo, Suparat; Wisitsoraat, Anurat; Sriprachuabwong, Chakrit; Tuantranont, Adisorn; Phanichphant, Sukon; Liewhiran, Chaikarn

    2015-02-11

    In this work, flame-spray-made SnO2 nanoparticles are systematically studied by doping with 0.1-2 wt % nickel (Ni) and loading with 0.1-5 wt % electrolytically exfoliated graphene for acetone-sensing applications. The sensing films (∼12-18 μm in thickness) were prepared by a spin-coating technique on Au/Al2O3 substrates and evaluated for acetone-sensing performances at operating temperatures ranging from 150 to 350 °C in dry air. Characterizations by X-ray diffraction, transmission/scanning electron microscopy, Brunauer-Emmett-Teller analysis, X-ray photoelectron spectroscopy and Raman spectroscopy demonstrated that Ni-doped SnO2 nanostructures had a spheriodal morphology with a polycrystalline tetragonal SnO2 phase, and Ni was confirmed to form a solid solution with SnO2 lattice while graphene in the sensing film after annealing and testing still retained its high-quality nonoxidized form. Gas-sensing results showed that SnO2 sensing film with 0.1 wt % Ni-doping concentration exhibited an optimal response of 54.2 and a short response time of ∼13 s toward 200 ppm acetone at an optimal operating temperature of 350 °C. The additional loading of graphene at 5 wt % into 0.1 wt % Ni-doped SnO2 led to a drastic response enhancement to 169.7 with a very short response time of ∼5.4 s at 200 ppm acetone and 350 °C. The superior gas sensing performances of Ni-doped SnO2 nanoparticles loaded with graphene may be attributed to the large specific surface area of the composite structure, specifically the high interaction rate between acetone vapor and graphene-Ni-doped SnO2 nanoparticles interfaces and high electronic conductivity of graphene. Therefore, the 5 wt % graphene loaded 0.1 wt % Ni-doped SnO2 sensor is a promising candidate for fast, sensitive and selective detection of acetone.

  5. Economical and eco-friendly recycling of used dry batteries for synthesis of graphene oxide by sheer exfoliation in presence of SDS

    NASA Astrophysics Data System (ADS)

    Kochrekar, Sachin; Agharkar, Mahesh; Salgaonkar, Manjunath; Gharge, Mrunal; Hidouri, Slah; Azeez, Musibau A.

    2015-06-01

    Graphene is a two-dimensional form of graphite that has attracted great curiosity for its novel physical properties. A key challenge that has emerged is how to create large amounts of graphene at low cost. The purpose of this Paper is to explore a new method to exfoliate graphite extracted from used dry battery in a small scale blender; in presence of SDS surfactant to synthesize graphene oxide, which can be then reduced to graphene. Quantity of SDS required is extremely less (1/10th) of graphite, and it replaces several steps and chemicals such as KMnO4, H2O2, H2SO4 and NaNO3. In this paper, we present the new process and preliminary characterization of synthesized graphene oxide by Raman and UV-Vis absorbance spectroscopy and ATR-IR spectroscopy.

  6. Direct physical exfoliation of few-layer graphene from graphite grown on a nickel foil using polydimethylsiloxane with tunable elasticity and adhesion

    NASA Astrophysics Data System (ADS)

    Yoo, Kwanghyun; Takei, Yusuke; Kim, Sungjin; Chiashi, Shohei; Maruyama, Shigeo; Matsumoto, Kiyoshi; Shimoyama, Isao

    2013-05-01

    We firstly introduce a facile method for the site-specific direct physical exfoliation of few-layer graphene sheets from cheap and easily enlargeable graphite grown on a Ni foil using an optimized polydimethylsiloxane (PDMS) stamp. By decreasing the PDMS cross-linking time, the PDMS elasticity is reduced to ˜52 kPa, similar to that of a typical gel. As a result of this process, the PDMS becomes more flexible yet remains in a handleable state as a stamp. Furthermore, the PDMS adhesion to a graphite/Ni surface, as measured by the peel strength, increases to ˜5.1 N m-1, which is approximately 17 times greater than that of typical PDMS. These optimized properties allow the PDMS stamp to have improved contact with the graphite/Ni surface, including the graphite wrinkles. This process is verified, and changes in surface morphology are observed using a 3D laser scanning microscope. Under conformal contact, the optimized PDMS stamp demonstrates the site-specific direct physical exfoliation of few-layer graphene sheets including mono- and bi-layer graphene sheets from the graphite/Ni substrate without the use of special equipment, conditions or chemicals. The number of layers of the exfoliated graphene and its high quality are revealed by the measured Raman spectroscopy. The exfoliation method using tunable elasticity and adhesion of the PDMS stamp can be used not only for cost-effective mass production of defect-less few-layer graphene from the graphite substrate for micro/nano device arrays but also for nano-contact printing of various structures, devices and cells.

  7. Direct physical exfoliation of few-layer graphene from graphite grown on a nickel foil using polydimethylsiloxane with tunable elasticity and adhesion.

    PubMed

    Yoo, Kwanghyun; Takei, Yusuke; Kim, Sungjin; Chiashi, Shohei; Maruyama, Shigeo; Matsumoto, Kiyoshi; Shimoyama, Isao

    2013-05-24

    We firstly introduce a facile method for the site-specific direct physical exfoliation of few-layer graphene sheets from cheap and easily enlargeable graphite grown on a Ni foil using an optimized polydimethylsiloxane (PDMS) stamp. By decreasing the PDMS cross-linking time, the PDMS elasticity is reduced to ∼52 kPa, similar to that of a typical gel. As a result of this process, the PDMS becomes more flexible yet remains in a handleable state as a stamp. Furthermore, the PDMS adhesion to a graphite/Ni surface, as measured by the peel strength, increases to ∼5.1 N m⁻¹, which is approximately 17 times greater than that of typical PDMS. These optimized properties allow the PDMS stamp to have improved contact with the graphite/Ni surface, including the graphite wrinkles. This process is verified, and changes in surface morphology are observed using a 3D laser scanning microscope. Under conformal contact, the optimized PDMS stamp demonstrates the site-specific direct physical exfoliation of few-layer graphene sheets including mono- and bi-layer graphene sheets from the graphite/Ni substrate without the use of special equipment, conditions or chemicals. The number of layers of the exfoliated graphene and its high quality are revealed by the measured Raman spectroscopy. The exfoliation method using tunable elasticity and adhesion of the PDMS stamp can be used not only for cost-effective mass production of defect-less few-layer graphene from the graphite substrate for micro/nano device arrays but also for nano-contact printing of various structures, devices and cells.

  8. Synthesis and structure of high quality graphene prepared via solvothermal exfoliation of intercalated graphite flakes

    NASA Astrophysics Data System (ADS)

    Al-Hazmi, Farag S.; Al-Harbi, Ghada H.; Beall, Gary W.; Al-Ghamdi, A. A.; Obaid, A. Y.; Mahmoud, Waleed E.

    2015-10-01

    The large-scale production of graphene via a simple approach is the key factor to be introduced into the industrial applications such as energy conversion, storage materials and optical electronics. In this letter, a rapid and facile approach to synthesize high quality graphene layers with large mass production has been developed. The method depends on the intercalation of graphite flakes with tartaric acid. The treated graphite subjected to a thermal shock at 750 °C for 60 s and followed by solvothermal treatment in the presence of isopropanol at 400 °C for 2 h. The produced graphene layers have an average thickness of 0.53 nm which depicted the production of a monolayer graphene. The FT-IR and Raman spectroscopy confirmed that the produced graphene layers have very low surface defects compared to reported approaches. The XPS spectra revealed that the surface of the produced graphene layers contains only 6 at% oxygen, which is better than the reduced graphene by conventional methods. This novel approach will open a new avenue for a scalable production of high quality graphene monolayer.

  9. Water-soluble polymer exfoliated graphene: as catalyst support and sensor.

    PubMed

    Wang, Haibo; Xia, Baoyu; Yan, Ya; Li, Nan; Wang, Jing-Yuan; Wang, Xin

    2013-05-09

    In this paper, we obtained various water-soluble polymer functionalized graphene in dimethyl sulfoxide under ultrasonication. The atomic force microscope analysis and control experiment shows the water-soluble polymer is the crucial part to help solvent molecules separate interlayer. Such polymer/graphene exhibits high conductivity and tunable surface property, as confirmed by the selected area electron diffraction and Raman and electrochemical impedance spectroscopy. As a result, a catalyst based on polyvinyl pyrrolidone (PVP)/graphene shows better methanol oxidation performance than that based on PVP/reduced graphene oxide. By changing to another polymer, poly(4-vinylpyridine)/graphene shows a stable and reversible response to pH, and demonstrates its potential for sensor application.

  10. High quality NMP exfoliated graphene nanosheet-SnO2 composite anode material for lithium ion battery.

    PubMed

    Ravikumar, Raman; Gopukumar, Sukumaran

    2013-03-21

    A graphene nanosheet-SnO(2) (GNS-SnO(2)) composite is prepared using N-methylpyrrolidone as a solvent to exfoliate graphene from graphite bar with the aid of CTAB by single phase co-precipitation method. The synthesized composites has been characterised physically by powder XRD which confirms the formation of the composite tetragonal SnO(2) crystal system with the low intense broad 002 plane for GNS. The sandwiched morphology of GNS-SnO(2) and the formation of nanosized particles (around 20 nm) have been confirmed by SEM and TEM images. The presence of sp(2) carbon in the GNS is clear by the highly intense G than D band in laser Raman spectroscopy analysis; furthermore, a single chemical shift has been observed at 132.14 ppm from solid-state (13)C NMR analysis. The synthesized composite has been electrochemically characterized using charge-discharge and EIS analysis. The capacity retentions at the end of the first 10 cycles is 57% (100 mA g(-1) rate), the second 10 cycles is 77.83% (200 mA g(-1)), and the final 10 cycles (300 mA g(-1)) is 81.5%. Moreover the impedance analysis clearly explains the low resistance pathway for Li(+) insertion after 30 cycles when compared with the initial cycle. This superior characteristic of GNS-SnO(2) composite suggests that it is a promising candidate for lithium ion battery anode.

  11. Microwave Exfoliation of Graphite Oxides in H2S Plasma for the Synthesis of Sulfur-Doped Graphenes as Oxygen Reduction Catalysts.

    PubMed

    Wong, Colin Hong An; Sofer, Zdeněk; Klímová, Kateřina; Pumera, Martin

    2016-11-23

    Tuning the electronic and chemical properties of graphene can be carried out through heteroatomic doping, enabling its use as an electrocatalyst. Sulfur-doped graphene has been suggested to be a viable alternative to traditional Pt-based catalysts for oxygen reduction under alkaline conditions. Herein we present a fast and efficient route to synthesize S-doped graphenes through the microwave-assisted exfoliation and reduction of three different graphite oxides in the presence of hydrogen sulfide. The materials obtained were characterized using scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, combustion elemental analysis, and voltammetry. These S-doped graphenes were found to have good electrochemical performance and were active in the catalysis of the oxygen reduction reaction.

  12. Functionalized graphene nanomaterials: new insight into direct exfoliation of graphite with supramolecular polymers

    NASA Astrophysics Data System (ADS)

    Cheng, Chih-Chia; Chang, Feng-Chih; Wang, Jui-Hsu; Chen, Jem-Kun; Yen, Ying-Chieh; Lee, Duu-Jong

    2015-12-01

    A novel urea-cytosine end-capped polypropylene glycol (UrCy-PPG) can self-assemble into a long-range ordered lamellar microstructure on the surface of graphene, due to the strong specific interactions between UrCy-PPG and graphene. In addition, the graphene composite produced exhibits a high conductivity (~1093 S m-1) with a dramatic thermo-responsive ON/OFF resistance-switching behavior (10 consecutive cycles).A novel urea-cytosine end-capped polypropylene glycol (UrCy-PPG) can self-assemble into a long-range ordered lamellar microstructure on the surface of graphene, due to the strong specific interactions between UrCy-PPG and graphene. In addition, the graphene composite produced exhibits a high conductivity (~1093 S m-1) with a dramatic thermo-responsive ON/OFF resistance-switching behavior (10 consecutive cycles). Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07076g

  13. The Use of Confocal Raman Spectroscopy to Quantitatively Study the Interactions Between Immersive Water and Graphene/Graphene Oxide Surfaces

    NASA Astrophysics Data System (ADS)

    Narcross, Hannah; Jeon, Byung Ho; Lee, Jong-Won; Ryu, Chang Yeol

    2012-02-01

    The unique mechanical, chemical, optical, and electrical properties of graphene allow for many potential applications in biomaterials. Understanding and quantifying the surface interactions between graphene/graphene oxide and aqueous liquid is essential for the design of such graphene-based nanocomposites. Graphene sheets were produced by the mechanical exfoliation of graphite. We have used depth Confocal Raman Spectroscopy (CRM) profiles to measure graphene wettability using a water immersive objective lens, and demonstrated how surface energy between graphene/graphene oxide and immersive aqueous liquid can be affected to simultaneously measure the depth image profiles. Contact angles were also measured to further investigate the compatibility between graphene/graphene oxide and its environment.

  14. Exfoliating and Dispersing Few-Layered Graphene in Low-Boiling-Point Organic Solvents towards Solution-Processed Optoelectronic Device Applications.

    PubMed

    Zhang, Lu; Miao, Zhongshuo; Hao, Zhen; Liu, Jun

    2016-05-06

    With normal organic surfactants, graphene can only be dispersed in water and cannot be dispersed in low-boiling-point organic solvents, which hampers its application in solution-processed organic optoelectronic devices. Herein, we report the exfoliation of graphite into graphene in low-boiling-point organic solvents, for example, methanol and acetone, by using edge-carboxylated graphene quantum dots (ECGQD) as the surfactant. The great capability of ECGQD for graphene dispersion is due to its ultralarge π-conjugated unit that allows tight adhesion on the graphene surface through strong π-π interactions, its edge-carboxylated structure that diminishes the steric effects of the oxygen-containing functional groups on the basal plane of ECGQD, and its abundance of carboxylic acid groups for solubility. The graphene dispersion in methanol enables the application of graphene:ECGQD as a cathode interlayer in polymer solar cells (PSCs). Moreover, the PSC device performance of graphene:ECGQD is better than that of Ca, the state-of-the-art cathode interlayer material.

  15. Ultrasonic-assisted cathodic electrochemical discharge for graphene synthesis.

    PubMed

    Van Thanh, Dang; Oanh, Phung Phi; Huong, Do Tra; Le, Phuoc Huu

    2017-01-01

    We present a novel and highly efficient method for exfoliating of graphite to produce graphene via the synergistic effects of in-situ plasma induced electrochemical exfoliation with ultrasonic energy, called ultrasonic-assisted cathodic electrochemical discharge. This method can work at moderate temperatures without the need of acidic media or expensive ionic electrolyte. The produced graphene exhibited a large lateral dimension of approximately 6μm and a thickness of 2.5nm, corresponding to approximately seven layers of graphene. An exfoliating mechanism of graphite to produce graphene sheets is also proposed in this study.

  16. Scanning tunneling microscopy of atomically precise graphene nanoribbons exfoliated onto H:Si(100)

    NASA Astrophysics Data System (ADS)

    Radocea, Adrian; Mehdi Pour, Mohammad; Vo, Timothy; Shekhirev, Mikhail; Sinitskii, Alexander; Lyding, Joseph

    Atomically precise graphene nanoribbons (GNRs) are promising materials for next generation transistors due to their well-controlled bandgaps and the high thermal conductivity of graphene. The solution synthesis of graphene nanoribbons offers a pathway towards scalable manufacturing. While scanning tunneling microscopy (STM) can access size scales required for characterization, solvent residue increases experimental difficulty and precludes band-gap determination via scanning tunneling spectroscopy (STS). Our work addresses this challenge through a dry contact transfer method that cleanly transfers solution-synthesized GNRs onto H:Si(100) under UHV using a fiberglass applicator. The semiconducting silicon surface avoids problems with image charge screening enabling intrinsic bandgap measurements. We characterize the nanoribbons using STM and STS. For chevron GNRs, we find a 1.6 eV bandgap, in agreement with computational modeling, and map the electronic structure spatially with detailed spectra lines and current imaging tunneling spectroscopy. Mapping the electronic structure of graphene nanoribbons is an important step towards taking advantage of the ability to form atomically precise nanoribbons and finely tune their properties.

  17. Examination of Humidity Effects on Measured Thickness and Interfacial Phenomena of Exfoliated Graphene on SiO2 via AC-AFM

    NASA Astrophysics Data System (ADS)

    Jinkins, Katherine; Camacho, Jorge; Farina, Lee; Wu, Yan

    2015-03-01

    Tapping (AC) mode Atomic Force Microscopy (AFM) is commonly used to determine the thickness of graphene samples. However, AFM measurements have been shown to be sensitive to environmental conditions such as adsorbed water, in turn dependent on relative humidity (RH). In the present study, AC-AFM is used to measure the thickness and loss tangent of exfoliated graphene on silicon dioxide (SiO2) as RH is increased from 10% to 80%. We show that the measured thickness of graphene is dependent on RH. Loss tangent is an AFM imaging technique that interprets the phase information as a relationship between the stored and dissipated energy in the tip-sample interaction. This study demonstrates the loss tangent of the graphene and oxide regions are both affected by humidity, with generally higher loss tangent for graphene than SiO2. As RH increases, we observe the loss tangent of both materials approaches the same value. We hypothesize that there is a layer of water trapped between the graphene and SiO2 substrate to explain this observation. Using this interpretation, the loss tangent images also indicate movement and change in this trapped water layer as RH increases, which impacts the measured thickness of graphene using AC-AFM.

  18. Examination of humidity effects on measured thickness and interfacial phenomena of exfoliated graphene on silicon dioxide via amplitude modulation atomic force microscopy

    SciTech Connect

    Jinkins, K.; Farina, L.; Wu, Y.; Camacho, J.

    2015-12-14

    The properties of Few-Layer Graphene (FLG) change with the number of layers and Amplitude Modulation (AM) Atomic Force Microscopy (AFM) is commonly used to determine the thickness of FLG. However, AFM measurements have been shown to be sensitive to environmental conditions such as relative humidity (RH). In the present study, AM-AFM is used to measure the thickness and loss tangent of exfoliated graphene on silicon dioxide (SiO{sub 2}) as RH is increased from 10% to 80%. We show that the measured thickness of graphene is dependent on RH. The loss tangent values of the graphene and oxide regions are both affected by humidity, with generally higher loss tangent for graphene than SiO{sub 2}. As RH increases, we observe the loss tangent of both materials approaches the same value. We hypothesize that there is a layer of water trapped between the graphene and SiO{sub 2} substrate to explain this observation. Using this interpretation, the loss tangent images also indicate movement and change in this trapped water layer as RH increases, which impacts the measured thickness of graphene using AM-AFM.

  19. One-Pot Synthesis of Hydrophilic and Hydrophobic N-Doped Graphene Quantum Dots via Exfoliating and Disintegrating Graphite Flakes

    NASA Astrophysics Data System (ADS)

    Kuo, Na-Jung; Chen, Yu-Syuan; Wu, Chien-Wei; Huang, Chun-Yuan; Chan, Yang-Hsiang; Chen, I.-Wen Peter

    2016-07-01

    Graphene quantum dots (GQDs) have drawn tremendous attention on account of their numerous alluring properties and a wide range of application potentials. Here, we report that hydrophilic and hydrophobic N-doped GQDs can be prepared via exfoliating and disintegrating graphite flakes. Various spectroscopic characterizations including TEM, AFM, FTIR, PL, XPS, and Raman spectroscopy demonstrated that the hydrophilic N-doped GQDs (IN-GQDs) and the hydrophobic N-doped GQDs (ON-GQDs) are mono-layered and multi-layered, respectively. In terms of practical aspects, the supercapacitor of an ON-GQDs/SWCNTs composite paper electrode was fabricated and exhibited an areal capacitance of 114 mF/cm2, which is more than 250% higher than the best reported value to date for a GQDs/carbon nanotube hybrid composite. For IN-GQDs applications, bio-memristor devices of IN-GQDs-albumen combination exhibited on/off current ratios in excess of 104 accompanied by stable switching endurance of over 250 cycles. The resistance stability of the high resistance state and the low resistance state could be maintained for over 104 s. Moreover, the IN-GQDs exhibited a superior quantum yield (34%), excellent stability of cellular imaging, and no cytotoxicity. Hence, the solution-based method for synchronized production of IN-GQDs and ON-GQDs is a facile and processable route that will bring GQDs-based electronics and composites closer to actualization.

  20. One-Pot Synthesis of Hydrophilic and Hydrophobic N-Doped Graphene Quantum Dots via Exfoliating and Disintegrating Graphite Flakes

    PubMed Central

    Kuo, Na-Jung; Chen, Yu-Syuan; Wu, Chien-Wei; Huang, Chun-Yuan; Chan, Yang-Hsiang; Chen, I-Wen Peter

    2016-01-01

    Graphene quantum dots (GQDs) have drawn tremendous attention on account of their numerous alluring properties and a wide range of application potentials. Here, we report that hydrophilic and hydrophobic N-doped GQDs can be prepared via exfoliating and disintegrating graphite flakes. Various spectroscopic characterizations including TEM, AFM, FTIR, PL, XPS, and Raman spectroscopy demonstrated that the hydrophilic N-doped GQDs (IN-GQDs) and the hydrophobic N-doped GQDs (ON-GQDs) are mono-layered and multi-layered, respectively. In terms of practical aspects, the supercapacitor of an ON-GQDs/SWCNTs composite paper electrode was fabricated and exhibited an areal capacitance of 114 mF/cm2, which is more than 250% higher than the best reported value to date for a GQDs/carbon nanotube hybrid composite. For IN-GQDs applications, bio-memristor devices of IN-GQDs-albumen combination exhibited on/off current ratios in excess of 104 accompanied by stable switching endurance of over 250 cycles. The resistance stability of the high resistance state and the low resistance state could be maintained for over 104 s. Moreover, the IN-GQDs exhibited a superior quantum yield (34%), excellent stability of cellular imaging, and no cytotoxicity. Hence, the solution-based method for synchronized production of IN-GQDs and ON-GQDs is a facile and processable route that will bring GQDs-based electronics and composites closer to actualization. PMID:27452118

  1. Fabrication of NiCo2-Anchored Graphene Nanosheets by Liquid-Phase Exfoliation for Excellent Microwave Absorbers.

    PubMed

    Yang, Ruilong; Wang, Bochong; Xiang, Jianyong; Mu, Congpu; Zhang, Can; Wen, Fusheng; Wang, Cong; Su, Can; Liu, Zhongyuan

    2017-04-03

    Graphene nanosheets (GNSs) were prepared by an efficient liquid-phase exfoliation method, and then the NiCo2/GNS nanohybrids were fabricated using the single-mode microwave-assisted hydrothermal technique. The NiCo2/GNS composites with different GNS proportions were investigated as microwave absorbers. Morphology investigation suggested that NiCo2 nanocrystals were uniformly anchored on the GNS without aggregation. The electromagnetic parameters of NiCo2/GNS nanohybrids could be artificially adjusted by changing the GNS proportion, which led to an exceptional microwave-absorbing performance. A reflection loss (RL) exceeding -20 dB was obtained in the frequency range of 5.3-16.4 GHz for the absorber thicknesses of 1.2-3.2 mm, while an optimal RL of -30 dB was achieved at 11.7 GHz for a thickness of 1.6 mm. The enhanced microwave-absorbing performance indicated that the NiCo2/10 wt % GNS composite has great potential for use as an excellent microwave absorber.

  2. Cobalt ferrite nanoparticles decorated on exfoliated graphene oxide, application for amperometric determination of NADH and H2O2.

    PubMed

    Ensafi, Ali A; Alinajafi, Hossein A; Jafari-Asl, M; Rezaei, B; Ghazaei, F

    2016-03-01

    Here, cobalt ferrite nanohybrid decorated on exfoliated graphene oxide (CoFe2O4/EGO) was synthesized. The nanohybrid was characterized by different methods such as X-ray diffraction spectroscopy, scanning electron microscopy, energy dispersive X-ray diffraction microanalysis, transmission electron microscopy, FT-IR, Raman spectroscopy and electrochemical methods. The CoFe2O4/EGO nanohybrid was used to modify glassy carbon electrode (GCE). The voltammetric investigations showed that CoFe2O4/EGO nanohybrid has synergetic effect towards the electro-reduction of H2O2 and electro-oxidation of nicotinamide adenine dinucleotide (NADH). Rotating disk chronoamperometry was used for their quantitative analysis. The calibration curves were observed in the range of 0.50 to 100.0 μmol L(-1) NADH and 0.9 to 900.0 μmol L(-1) H2O2 with detections limit of 0.38 and 0.54 μmol L(-1), respectively. The repeatability, reproducibility and selectivity of the electrochemical sensor for analysis of the analytes were studied. The new electrochemical sensor was successfully applied for the determination of NADH and H2O2 in real samples with satisfactory results.

  3. Engineering Graphene Mechanical Systems

    DTIC Science & Technology

    2012-07-05

    Mohiuddin, T. M. G.; Morozov, S. V.; Blake, P.; Halsall, M. P.; Ferrari , A. C.; Boukhvalov, D. W.; Katsnelson, M. I.; Geim, A. K.; Novoselov, K. S. Science...22) Bower, A. F. Linear Elastic Material Behavior. In Applied Mechanics of Solids; CRC Press: Boca Raton, FL, 2010; pp 83−86. (23) Gomez -Navarro, C...Phys. Rev. Lett. 2011, 106, 105505. (26) Ferrari , A. C.; Meyer, J. C.; Scardaci, V.; Casiraghi, C.; Lazzeri, M.; Mauri, F.; Piscanec, S.; Jiang, D

  4. Field emission from few-layer graphene nanosheets produced by liquid phase exfoliation of graphite.

    PubMed

    Dong, Jianhui; Zeng, Baoqing; Lan, Yucheng; Tian, Shikai; Shan, Yun; Liu, Xingchong; Yang, Zhonghai; Wang, Hui; Ren, Z F

    2010-08-01

    Graphene nanosheets have been synthesized from commercial expandable graphite by heating in a microwave oven and dispersing in ethanol by ultrasonication. Scanning and transmission electron microscopy and electron energy-loss spectroscopy and atomic force microscope showed that the nanosheets were about 2 nm in thickness and 10 microm in diameter. The field emission of the graphene sheets has been investigated. An emission current density of 1 mA/cm2 has been achieved at an electric field of 3.7 V/microm with a turn-on field of 1.7 V/microm at 0.01 mA/cm2. The annealing of the samples at 400 degrees C in vacuum greatly improved the field emission performance.

  5. Superior Mechanical Properties of Epoxy Composites Reinforced by 3D Interconnected Graphene Skeleton.

    PubMed

    Ni, Ya; Chen, Lei; Teng, Kunyue; Shi, Jie; Qian, Xiaoming; Xu, Zhiwei; Tian, Xu; Hu, Chuansheng; Ma, Meijun

    2015-06-03

    Epoxy-based composites reinforced by three-dimensional graphene skeleton (3DGS) were fabricated in resin transfer molding method with respect to the difficulty in good dispersion and arrangement of graphene sheets in composites by directly mixing graphene and epoxy. 3DGS was synthesized in the process of self-assembly and reduction with poly(amidoamine) dendrimers. In the formation of 3DGS, graphene sheets were in good dispersion and ordered state, which resulted in exceptional mechanical properties and thermal stability for epoxy composites. For 3DGS/epoxy composites, the tensile and compressive strengths significantly increased by 120.9% and 148.3%, respectively, as well as the glass transition temperature, which increased by a notable 19 °C, unlike the thermal exfoliation graphene/epoxy composites via direct-mixing route, which increased by only 0.20 wt % content of fillers. Relative to the graphene/epoxy composites in direct-mixing method mentioned in literature, the increase in tensile and compressive strengths of 3DGS/epoxy composites was at least twofold and sevenfold, respectively. It can be expected that 3DGS, which comes from preforming graphene sheets orderly and dispersedly, would replace graphene nanosheets in polymer nanocomposite reinforcement and endow composites with unique structure and some unexpected performance.

  6. Synthesizing and Characterizing Graphene via Raman Spectroscopy: An Upper-Level Undergraduate Experiment That Exposes Students to Raman Spectroscopy and a 2D Nanomaterial

    ERIC Educational Resources Information Center

    Parobek, David; Shenoy, Ganesh; Zhou, Feng; Peng, Zhenbo; Ward, Michelle; Liu, Haitao

    2016-01-01

    In this upper-level undergraduate experiment, students utilize micro-Raman spectroscopy to characterize graphene prepared by mechanical exfoliation and chemical vapor deposition (CVD). The mechanically exfoliated samples are prepared by the students while CVD graphene can be purchased or obtained through outside sources. Owing to the intense Raman…

  7. Biomolecule-assisted exfoliation and dispersion of graphene and other two-dimensional materials: a review of recent progress and applications.

    PubMed

    Paredes, J I; Villar-Rodil, S

    2016-08-25

    Direct liquid-phase exfoliation of layered materials by means of ultrasound, shear forces or electrochemical intercalation holds enormous promise as a convenient, cost-effective approach to the mass production of two-dimensional (2D) materials, particularly in the form of colloidal suspensions of high quality and micrometer- and submicrometer-sized flakes. Of special relevance due to environmental and practical reasons is the production of 2D materials in aqueous medium, which generally requires the use of certain additives (surfactants and other types of dispersants) to assist in the exfoliation and colloidal stabilization processes. In this context, biomolecules have received, in recent years, increasing attention as dispersants for 2D materials, as they provide a number of advantages over more conventional, synthetic surfactants. Here, we review research progress in the use of biomolecules as exfoliating and dispersing agents for the production of 2D materials. Although most efforts in this area have focused on graphene, significant advances have also been reported with transition metal dichalcogenides (MoS2, WS2, etc.) or hexagonal boron nitride. Particular emphasis is placed on the specific merits of different types of biomolecules, including proteins and peptides, nucleotides and nucleic acids (RNA, DNA), polysaccharides, plant extracts and bile salts, on their role as efficient colloidal dispersants of 2D materials, as well as on the potential applications that have been explored for such biomolecule-exfoliated materials. These applications are wide-ranging and encompass the fields of biomedicine (photothermal and photodynamic therapy, bioimaging, biosensing, etc.), energy storage (Li- and Na-ion batteries), catalysis (e.g., catalyst supports for the oxygen reduction reaction or electrocatalysts for the hydrogen evolution reaction), or composite materials. As an incipient area of research, a number of knowledge gaps, unresolved issues and novel future

  8. Microwave exfoliated graphene oxide/TiO{sub 2} nanowire hybrid for high performance lithium ion battery

    SciTech Connect

    Ishtiaque Shuvo, Mohammad Arif; Rodriguez, Gerardo; Karim, Hasanul; Lin, Yirong; Islam, Md Tariqul; Noveron, Juan C.; Ramabadran, Navaneet

    2015-09-28

    Lithium ion battery (LIB) is a key solution to the demand of ever-improving, high energy density, clean-alternative energy systems. In LIB, graphite is the most commonly used anode material; however, lithium-ion intercalation in graphite is limited, hindering the battery charge rate and capacity. To date, one of the approaches in LIB performance improvement is by using porous carbon (PC) to replace graphite as anode material. PC's pore structure facilitates ion transport and has been proven to be an excellent anode material candidate in high power density LIBs. In addition, to overcome the limited lithium-ion intercalation obstacle, nanostructured anode assembly has been extensively studied to increase the lithium-ion diffusion rate. Among these approaches, high specific surface area metal oxide nanowires connecting nanostructured carbon materials accumulation have shown promising results for enhanced lithium-ion intercalation. Herein, we demonstrate a hydrothermal approach of growing TiO{sub 2} nanowires (TON) on microwave exfoliated graphene oxide (MEGO) to further improve LIB performance over PC. This MEGO-TON hybrid not only uses the high surface area of MEGO but also increases the specific surface area for electrode–electrolyte interaction. Therefore, this new nanowire/MEGO hybrid anode material enhances both the specific capacity and charge–discharge rate. Scanning electron microscopy and X-ray diffraction were used for materials characterization. Battery analyzer was used for measuring the electrical performance of the battery. The testing results have shown that MEGO-TON hybrid provides up to 80% increment of specific capacity compared to PC anode.

  9. Mechanisms of Sodium Insertion/Extraction on the Surface of Defective Graphenes.

    PubMed

    Pramudita, James C; Rawal, Aditya; Choucair, Mohammad; Pontiroli, Daniele; Magnani, Giacomo; Gaboardi, Mattia; Riccò, Mauro; Sharma, Neeraj

    2017-01-11

    Two chemically synthesized defective graphene materials with distinctly contrasting extended structures and surface chemistry are used to prepare sodium-ion battery electrodes. The difference in electrode performance between the chemically prepared graphene materials is qualified based on correlations with intrinsic structural and chemical dissimilarities. The overall effects of the materials' physical and chemical discrepancies are quantified by measuring the electrode capacities after repeated charge/discharge cycles. Solvothermal synthesized graphene (STSG) electrodes produce capacities of 92 mAh/g in sodium-ion batteries after 50 cycles at 10 mA/g, while thermally exfoliated graphite oxide (TEGO) electrodes produce capacities of 248 mAh/g after 50 cycles at 100 mA/g. Solid-state (23)Na nuclear magnetic resonance spectroscopy is employed to locally probe distinct sodium environments on and between the surface of the graphene layers after charge/discharge cycles that are responsible for the variations in electrode capacities. Multiple distinct sodium environments of which at least 3 are mobile during the charge-discharge cycle are found in both cases, but the majority of Na is predominantly located in an immobile site, assigned to the solid electrolyte interface (SEI) layer. Mechanisms of sodium insertion and extraction on and between the defective graphene surfaces are proposed and discussed in relation to electrode performance. This work provides a direct account of the chemical and structural environments on the surface of graphene that govern the feasibility of graphene materials for use as sodium-ion battery electrodes.

  10. Mechanical stability of substrate-bound graphene in contact with aqueous solutions

    NASA Astrophysics Data System (ADS)

    Velický, Matěj; Cooper, Adam J.; Toth, Peter S.; Patten, Hollie V.; Woods, Colin R.; Novoselov, Konstantin S.; Dryfe, Robert A. W.

    2015-06-01

    We report on the damage caused to mechanically exfoliated monolayer graphene, bound to silicon dioxide substrate, upon contact with liquids. This phenomenon is of significant importance for a wide range of applications where monolayer graphene sheets are used with liquids, especially as an electrode material in electrochemical applications such as energy storage and conversion. Liquid-induced damage to SiO2-bound graphene was previously observed with a range of solvents. A recently developed microdroplet system, used for a detailed examination of this behaviour, reveals that few-layer graphene flakes down to a bi-layer are stable with respect to aqueous electrolyte droplet formation, but the stability of these droplets is significantly reduced on monolayer graphene and irreversible rupture of the underlying graphene flake occurs. This damage, which we attribute to the presence of nanoscale defects and high adhesion between the graphene and the substrate, seems specific to plasma-cleaned SiO2 substrates and is not observed on flakes transferred to other substrates. Furthermore, the introduction of impurities, in the form of both polymer residues and native impurities between the flake and the SiO2 substrate, significantly enhance graphene’s immunity to external strain as shown by optical microscopy, atomic force microscopy, and Raman spectroscopy.

  11. Metal-assisted exfoliation (MAE): green process for transferring graphene to flexible substrates and templating of sub-nanometer plasmonic gaps (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Zaretski, Aliaksandr V.; Marin, Brandon C.; Moetazedi, Herad; Dill, Tyler J.; Jibril, Liban; Kong, Casey; Tao, Andrea R.; Lipomi, Darren J.

    2015-09-01

    This paper describes a new technique, termed "metal-assisted exfoliation," for the scalable transfer of graphene from catalytic copper foils to flexible polymeric supports. The process is amenable to roll-to-roll manufacturing, and the copper substrate can be recycled. We then demonstrate the use of single-layer graphene as a template for the formation of sub-nanometer plasmonic gaps using a scalable fabrication process called "nanoskiving." These gaps are formed between parallel gold nanowires in a process that first produces three-layer thin films with the architecture gold/single-layer graphene/gold, and then sections the composite films with an ultramicrotome. The structures produced can be treated as two gold nanowires separated along their entire lengths by an atomically thin graphene nanoribbon. Oxygen plasma etches the sandwiched graphene to a finite depth; this action produces a sub-nanometer gap near the top surface of the junction between the wires that is capable of supporting highly confined optical fields. The confinement of light is confirmed by surface-enhanced Raman spectroscopy measurements, which indicate that the enhancement of the electric field arises from the junction between the gold nanowires. These experiments demonstrate nanoskiving as a unique and easy-to-implement fabrication technique that is capable of forming sub-nanometer plasmonic gaps between parallel metallic nanostructures over long, macroscopic distances. These structures could be valuable for fundamental investigations as well as applications in plasmonics and molecular electronics.

  12. Solution-Synthesized Chevron Graphene Nanoribbons Exfoliated onto H:Si(100).

    PubMed

    Radocea, Adrian; Sun, Tao; Vo, Timothy H; Sinitskii, Alexander; Aluru, Narayana R; Lyding, Joseph W

    2017-01-11

    There has been tremendous progress in designing and synthesizing graphene nanoribbons (GNRs). The ability to control the width, edge structure, and dopant level with atomic precision has created a large class of accessible electronic landscapes for use in logic applications. One of the major limitations preventing the realization of GNR devices is the difficulty of transferring GNRs onto nonmetallic substrates. In this work, we developed a new approach for clean deposition of solution-synthesized atomically precise chevron GNRs onto H:Si(100) under ultrahigh vacuum. A clean transfer allowed ultrahigh-vacuum scanning tunneling microscopy (STM) to provide high-resolution imaging and spectroscopy and reveal details of the electronic structure of chevron nanoribbons that have not been previously reported. We also demonstrate STM nanomanipulation of GNRs, characterization of multilayer GNR cross-junctions, and STM nanolithography for local depassivation of H:Si(100), which allowed us to probe GNR-Si interactions and revealed a semiconducting-to-metallic transition. The results of STM measurements were shown to be in good agreement with first-principles computational modeling.

  13. The mechanism of caesium intercalation of graphene.

    PubMed

    Petrović, M; Šrut Rakić, I; Runte, S; Busse, C; Sadowski, J T; Lazić, P; Pletikosić, I; Pan, Z-H; Milun, M; Pervan, P; Atodiresei, N; Brako, R; Šokčević, D; Valla, T; Michely, T; Kralj, M

    2013-01-01

    Properties of many layered materials, including copper- and iron-based superconductors, topological insulators, graphite and epitaxial graphene, can be manipulated by the inclusion of different atomic and molecular species between the layers via a process known as intercalation. For example, intercalation in graphite can lead to superconductivity and is crucial in the working cycle of modern batteries and supercapacitors. Intercalation involves complex diffusion processes along and across the layers; however, the microscopic mechanisms and dynamics of these processes are not well understood. Here we report on a novel mechanism for intercalation and entrapment of alkali atoms under epitaxial graphene. We find that the intercalation is adjusted by the van der Waals interaction, with the dynamics governed by defects anchored to graphene wrinkles. Our findings are relevant for the future design and application of graphene-based nano-structures. Similar mechanisms can also have a role for intercalation of layered materials.

  14. Understanding Mechanical Response of Elastomeric Graphene Networks.

    PubMed

    Ni, Na; Barg, Suelen; Garcia-Tunon, Esther; Macul Perez, Felipe; Miranda, Miriam; Lu, Cong; Mattevi, Cecilia; Saiz, Eduardo

    2015-09-08

    Ultra-light porous networks based on nano-carbon materials (such as graphene or carbon nanotubes) have attracted increasing interest owing to their applications in wide fields from bioengineering to electrochemical devices. However, it is often difficult to translate the properties of nanomaterials to bulk three-dimensional networks with a control of their mechanical properties. In this work, we constructed elastomeric graphene porous networks with well-defined structures by freeze casting and thermal reduction, and investigated systematically the effect of key microstructural features. The porous networks made of large reduced graphene oxide flakes (>20 μm) are superelastic and exhibit high energy absorption, showing much enhanced mechanical properties than those with small flakes (<2 μm). A better restoration of the graphitic nature also has a considerable effect. In comparison, microstructural differences, such as the foam architecture or the cell size have smaller or negligible effect on the mechanical response. The recoverability and energy adsorption depend on density with the latter exhibiting a minimum due to the interplay between wall fracture and friction during deformation. These findings suggest that an improvement in the mechanical properties of porous graphene networks significantly depend on the engineering of the graphene flake that controls the property of the cell walls.

  15. Understanding Mechanical Response of Elastomeric Graphene Networks

    PubMed Central

    Ni, Na; Barg, Suelen; Garcia-Tunon, Esther; Macul Perez, Felipe; Miranda, Miriam; Lu, Cong; Mattevi, Cecilia; Saiz, Eduardo

    2015-01-01

    Ultra-light porous networks based on nano-carbon materials (such as graphene or carbon nanotubes) have attracted increasing interest owing to their applications in wide fields from bioengineering to electrochemical devices. However, it is often difficult to translate the properties of nanomaterials to bulk three-dimensional networks with a control of their mechanical properties. In this work, we constructed elastomeric graphene porous networks with well-defined structures by freeze casting and thermal reduction, and investigated systematically the effect of key microstructural features. The porous networks made of large reduced graphene oxide flakes (>20 μm) are superelastic and exhibit high energy absorption, showing much enhanced mechanical properties than those with small flakes (<2 μm). A better restoration of the graphitic nature also has a considerable effect. In comparison, microstructural differences, such as the foam architecture or the cell size have smaller or negligible effect on the mechanical response. The recoverability and energy adsorption depend on density with the latter exhibiting a minimum due to the interplay between wall fracture and friction during deformation. These findings suggest that an improvement in the mechanical properties of porous graphene networks significantly depend on the engineering of the graphene flake that controls the property of the cell walls. PMID:26348898

  16. Understanding Mechanical Response of Elastomeric Graphene Networks

    NASA Astrophysics Data System (ADS)

    Ni, Na; Barg, Suelen; Garcia-Tunon, Esther; Macul Perez, Felipe; Miranda, Miriam; Lu, Cong; Mattevi, Cecilia; Saiz, Eduardo

    2015-09-01

    Ultra-light porous networks based on nano-carbon materials (such as graphene or carbon nanotubes) have attracted increasing interest owing to their applications in wide fields from bioengineering to electrochemical devices. However, it is often difficult to translate the properties of nanomaterials to bulk three-dimensional networks with a control of their mechanical properties. In this work, we constructed elastomeric graphene porous networks with well-defined structures by freeze casting and thermal reduction, and investigated systematically the effect of key microstructural features. The porous networks made of large reduced graphene oxide flakes (>20 μm) are superelastic and exhibit high energy absorption, showing much enhanced mechanical properties than those with small flakes (<2 μm). A better restoration of the graphitic nature also has a considerable effect. In comparison, microstructural differences, such as the foam architecture or the cell size have smaller or negligible effect on the mechanical response. The recoverability and energy adsorption depend on density with the latter exhibiting a minimum due to the interplay between wall fracture and friction during deformation. These findings suggest that an improvement in the mechanical properties of porous graphene networks significantly depend on the engineering of the graphene flake that controls the property of the cell walls.

  17. Mechanisms of nanoclay-enhanced plastic foaming processes: effects of nanoclay intercalation and exfoliation

    NASA Astrophysics Data System (ADS)

    Wong, Anson; Wijnands, Stephan F. L.; Kuboki, Takashi; Park, Chul B.

    2013-08-01

    The foaming behaviors of high-density polypropylene-nanoclay composites with intercalated and exfoliated nanoclay particles blown with carbon dioxide were examined via in situ observation of the foaming processes in a high-temperature/high-pressure view-cell. The intercalated nanoclay particles were 300-600 nm in length and 50-200 nm in thickness, while the exfoliated nanoclay particles were 100-200 nm in length and 1 nm in thickness. Contrary to common belief, it was discovered that intercalated nanoclay yielded higher cell density than exfoliated nanoclay despite its lower particle density. This was attributed to the higher tensile stresses generated around the larger and stiffer intercalated nanoclay particles, which led to increase in supersaturation level for cell nucleation. Also, the coupling agent used to exfoliate nanoclay would increase the affinity between polymer and surface of nanoclay particles. Consequently, the critical work needed for cell nucleation would be increased; pre-existing microvoids, which could act as seeds for cell nucleation, were also less likely to exist. Meanwhile, exfoliated nanoclay had better cell stabilization ability to prevent cell coalescence and cell coarsening. This investigation clarifies the roles of nanoclay in plastic foaming processes and provides guidance for the advancement of polymer nanocomposite foaming technology.

  18. Exfoliated-SnS2 restacked on graphene as a high-capacity, high-rate, and long-cycle life anode for sodium ion batteries

    NASA Astrophysics Data System (ADS)

    Liu, Yongchang; Kang, Hongyan; Jiao, Lifang; Chen, Chengcheng; Cao, Kangzhe; Wang, Yijing; Yuan, Huatang

    2015-01-01

    Designed as a high-capacity, high-rate, and long-cycle life anode for sodium ion batteries, exfoliated-SnS2 restacked on graphene is prepared by the hydrolysis of lithiated SnS2 followed by a facile hydrothermal method. Structural and morphological characterizations demonstrate that ultrasmall SnS2 nanoplates (with a typical size of 20-50 nm) composed of 2-5 layers are homogeneously decorated on the surface of graphene, while the hybrid structure self-assembles into a three-dimensional (3D) network architecture. The obtained SnS2/graphene nanocomposite delivers a remarkable capacity as high as 650 mA h g-1 at a current density of 200 mA g-1. More impressively, the capacity can reach 326 mA h g-1 even at 4000 mA g-1 and remains stable at ~610 mA h g-1 without fading up to 300 cycles when the rate is brought back to 200 mA g-1. The excellent electrochemical performance is attributed to the synergetic effects between the ultrasmall SnS2 and the highly conductive graphene network. The unique structure can simultaneously facilitate Na+ ion diffusion, provide more reaction sites, and suppress aggregation and volume fluctuation of the active materials during prolonged cycling.Designed as a high-capacity, high-rate, and long-cycle life anode for sodium ion batteries, exfoliated-SnS2 restacked on graphene is prepared by the hydrolysis of lithiated SnS2 followed by a facile hydrothermal method. Structural and morphological characterizations demonstrate that ultrasmall SnS2 nanoplates (with a typical size of 20-50 nm) composed of 2-5 layers are homogeneously decorated on the surface of graphene, while the hybrid structure self-assembles into a three-dimensional (3D) network architecture. The obtained SnS2/graphene nanocomposite delivers a remarkable capacity as high as 650 mA h g-1 at a current density of 200 mA g-1. More impressively, the capacity can reach 326 mA h g-1 even at 4000 mA g-1 and remains stable at ~610 mA h g-1 without fading up to 300 cycles when the rate is

  19. Advanced mechanical properties of graphene paper

    NASA Astrophysics Data System (ADS)

    Ranjbartoreh, Ali R.; Wang, Bei; Shen, Xiaoping; Wang, Guoxiu

    2011-01-01

    Graphene paper (GP) has been prepared by flow-directed assembly of graphene nanosheets. The mechanical properties of as-prepared GPs were investigated by tensile, indentation, and bending tests. Heat treated GPs demonstrate superior hardness, ten times that of synthetic graphite, and two times that of carbon steel; besides, their yielding strength is significantly higher than that of carbon steel. GPs show extremely high modulus of elasticity during bending test; in the range of a few terapascal. The high strength and stiffness of GP is ascribed to the interlocking-tile microstructure of individual graphene nanosheets in the paper. These outstanding mechanical properties of GPs could lead to a wide range of engineering applications.

  20. Graphene mechanical oscillators with tunable frequency.

    PubMed

    Chen, Changyao; Lee, Sunwoo; Deshpande, Vikram V; Lee, Gwan-Hyoung; Lekas, Michael; Shepard, Kenneth; Hone, James

    2013-12-01

    Oscillators, which produce continuous periodic signals from direct current power, are central to modern communications systems, with versatile applications including timing references and frequency modulators. However, conventional oscillators typically consist of macroscopic mechanical resonators such as quartz crystals, which require excessive off-chip space. Here, we report oscillators built on micrometre-size, atomically thin graphene nanomechanical resonators, whose frequencies can be electrostatically tuned by as much as 14%. Self-sustaining mechanical motion is generated and transduced at room temperature in these oscillators using simple electrical circuitry. The prototype graphene voltage-controlled oscillators exhibit frequency stability and a modulation bandwidth sufficient for the modulation of radiofrequency carrier signals. As a demonstration, we use a graphene oscillator as the active element for frequency-modulated signal generation and achieve efficient audio signal transmission.

  1. Cytotoxicity of exfoliated transition-metal dichalcogenides (MoS2 , WS2 , and WSe2 ) is lower than that of graphene and its analogues.

    PubMed

    Teo, Wei Zhe; Chng, Elaine Lay Khim; Sofer, Zdeněk; Pumera, Martin

    2014-07-28

    Studies involving transition-metal dichalcogenides (TMDs) have been around for many decades and in recent years, many were focused on using TMDs to synthesize inorganic analogues of carbon nanotubes, fullerene, as well as graphene and its derivatives with the ultimate aim of employing these materials into consumer products. In view of this rising trend, we investigated the cytotoxicity of three common exfoliated TMDs (exTMDs), namely MoS2 , WS2 , and WSe2 , and compared their toxicological effects with graphene oxides and halogenated graphenes to find out whether these inorganic analogues of graphenes and derivatives would show improved biocompatibility. Based on the cell viability assessments using methylthiazolyldiphenyl-tetrazolium bromide (MTT) and water-soluble tetrazolium salt (WST-8) assays on human lung carcinoma epithelial cells (A549) following a 24 h exposure to varying concentrations of the three exTMDs, it was concluded that MoS2 and WS2 nanosheets induced very low cytotoxicity to A549 cells, even at high concentrations. On the other hand, WSe2 exhibited dose-dependent toxicological effects on A549 cells, reducing cell viability to 31.8 % at the maximum concentration of 400 μg mL(-1) ; the higher cytotoxicity displayed by WSe2 might be linked to the identity of the chalcogen. In comparison with graphene oxides and halogenated graphenes, MoS2 and WS2 were much less hazardous, whereas WSe2 showed similar degree of cytotoxicity. Future in-depth studies should be built upon this first work on the in vitro cytotoxicity of MoS2 and WS2 to ensure that they do not pose acute toxicity. Lastly, nanomaterial-induced interference control experiments revealed that exTMDs were capable of reacting with MTT assay viability markers in the absence of cells, but not with WST-8 assay. This suggests that the MTT assay is not suitable for measuring the cytotoxicity of exTMDs because inflated results will be obtained, giving false impressions that the materials are

  2. Deformation of Wrinkled Graphene

    PubMed Central

    2015-01-01

    The deformation of monolayer graphene, produced by chemical vapor deposition (CVD), on a polyester film substrate has been investigated through the use of Raman spectroscopy. It has been found that the microstructure of the CVD graphene consists of a hexagonal array of islands of flat monolayer graphene separated by wrinkled material. During deformation, it was found that the rate of shift of the Raman 2D band wavenumber per unit strain was less than 25% of that of flat flakes of mechanically exfoliated graphene, whereas the rate of band broadening per unit strain was about 75% of that of the exfoliated material. This unusual deformation behavior has been modeled in terms of mechanically isolated graphene islands separated by the graphene wrinkles, with the strain distribution in each graphene island determined using shear lag analysis. The effect of the size and position of the Raman laser beam spot has also been incorporated in the model. The predictions fit well with the behavior observed experimentally for the Raman band shifts and broadening of the wrinkled CVD graphene. The effect of wrinkles upon the efficiency of graphene to reinforce nanocomposites is also discussed. PMID:25765609

  3. Configuration of ripple domains and their topological defects formed under local mechanical stress on hexagonal monolayer graphene

    DOE PAGES

    Park, Yeonggu; Choi, Jin Sik; Choi, Taekjib; ...

    2015-03-24

    Ripples in graphene are extensively investigated because they ensure the mechanical stability of two-dimensional graphene and affect its electronic properties. They arise from spontaneous symmetry breaking and are usually manifested in the form of domains with long-range order. It is expected that topological defects accompany a material exhibiting long-range order, whose functionality depends on characteristics of domains and topological defects. However, there remains a lack of understanding regarding ripple domains and their topological defects formed on monolayer graphene. Here we explore configuration of ripple domains and their topological defects in exfoliated monolayer graphenes on SiO₂/Si substrates using transverse shear microscope.more » We observe three-color domains with three different ripple directions, which meet at a core. Furthermore, the closed domain is surrounded by an even number of cores connected together by domain boundaries, similar to topological vortex and anti-vortex pairs. In addition, we have found that axisymmetric three-color domains can be induced around nanoparticles underneath the graphene. This fascinating configuration of ripple domains may result from the intrinsic hexagonal symmetry of two-dimensional graphene, which is supported by theoretical simulation using molecular dynamics. Our findings are expected to play a key role in understanding of ripple physics in graphene and other two-dimensional materials.« less

  4. Configuration of ripple domains and their topological defects formed under local mechanical stress on hexagonal monolayer graphene

    SciTech Connect

    Park, Yeonggu; Choi, Jin Sik; Choi, Taekjib; Lee, Mi Jung; Jia, Quanxi; Park, Minwoo; Lee, Hoonkyung; Park, Bae Ho

    2015-03-24

    Ripples in graphene are extensively investigated because they ensure the mechanical stability of two-dimensional graphene and affect its electronic properties. They arise from spontaneous symmetry breaking and are usually manifested in the form of domains with long-range order. It is expected that topological defects accompany a material exhibiting long-range order, whose functionality depends on characteristics of domains and topological defects. However, there remains a lack of understanding regarding ripple domains and their topological defects formed on monolayer graphene. Here we explore configuration of ripple domains and their topological defects in exfoliated monolayer graphenes on SiO₂/Si substrates using transverse shear microscope. We observe three-color domains with three different ripple directions, which meet at a core. Furthermore, the closed domain is surrounded by an even number of cores connected together by domain boundaries, similar to topological vortex and anti-vortex pairs. In addition, we have found that axisymmetric three-color domains can be induced around nanoparticles underneath the graphene. This fascinating configuration of ripple domains may result from the intrinsic hexagonal symmetry of two-dimensional graphene, which is supported by theoretical simulation using molecular dynamics. Our findings are expected to play a key role in understanding of ripple physics in graphene and other two-dimensional materials.

  5. Multifunctional polymeric nanocomposites fabricated by incorporation of exfoliated graphene nanoplatelets and their application in bipolar plates for polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Jiang, Xian

    The focus of this research is to investigate the potential of using exfoliated graphene nanoplatelets, GNP, as the multifunctional nano-reinforcement in fabricating polymer/GNP nanocomposites and then explore their prospective applications in bipolar plates for polymer electrolyte membrane (PEM) fuel cells. Firstly, HDPE (high density polyethylene)/GNP nanocomposites were fabricated using the conventional compounding method of melt-extrusion followed by injection molding. The mechanical properties, crystallization behaviors, thermal stability, thermal conductivity, and electrical conductivity of the resulting HDPE/GNP nanocomposites were evaluated as a function of GNP concentration. Results showed that HDPE/GNP nanocomposites exhibit equivalent flexural modulus and strength to HDPE composites filled with other commercial reinforcements but they have superior impact strength. By investigating the crystallization behavior of HDPE/GNP nanocomposites, it was found that GNP is a good nucleating agent at low loading levels and as a result can significantly increase crystallization temperature and crystallinity of HDPE. At high GNP loadings, however, the close proximity of GNP particles retards the crystallization process. The thermal stability and thermal conductivity of HDPE/GNP nanocomposites were significantly enhanced due to the excellent thermal properties of GNP. Meanwhile, results indicated that the percolation threshold of these nanocomposites prepared by the conventional melt-extrusion and injection molding is relatively high at around 10--15 vol% GNP loading. To enhance the electrical conductivity of HDPE/GNP nanocomposites, two special processing methods named solid state ball milling (SSBM) and solid state shear pulverization (SSSP) were studied. The mechanism by which SSBM and SSSP are capable of producing lower percolation or higher electrical conductivity is to coat the polymer surface by GNP platelets which facilitate the formation of conductive networks

  6. Metal-assisted exfoliation (MAE): green, roll-to-roll compatible method for transferring graphene to flexible substrates.

    PubMed

    Zaretski, Aliaksandr V; Moetazedi, Herad; Kong, Casey; Sawyer, Eric J; Savagatrup, Suchol; Valle, Eduardo; O'Connor, Timothy F; Printz, Adam D; Lipomi, Darren J

    2015-01-30

    Graphene is expected to play a significant role in future technologies that span a range from consumer electronics, to devices for the conversion and storage of energy, to conformable biomedical devices for healthcare. To realize these applications, however, a low-cost method of synthesizing large areas of high-quality graphene is required. Currently, the only method to generate large-area single-layer graphene that is compatible with roll-to-roll manufacturing destroys approximately 300 kg of copper foil (thickness = 25 μm) for every 1 g of graphene produced. This paper describes a new environmentally benign and scalable process of transferring graphene to flexible substrates. The process is based on the preferential adhesion of certain thin metallic films to graphene; separation of the graphene from the catalytic copper foil is followed by lamination to a flexible target substrate in a process that is compatible with roll-to-roll manufacturing. The copper substrate is indefinitely reusable and the method is substantially greener than the current process that uses relatively large amounts of corrosive etchants to remove the copper. The sheet resistance of the graphene produced by this new process is unoptimized but should be comparable in principle to that produced by the standard method, given the defects observable by Raman spectroscopy and the presence of process-induced cracks. With further improvements, this green, inexpensive synthesis of single-layer graphene could enable applications in flexible, stretchable, and disposable electronics, low-profile and lightweight barrier materials, and in large-area displays and photovoltaic modules.

  7. Metal-assisted exfoliation (MAE): green, roll-to-roll compatible method for transferring graphene to flexible substrates

    NASA Astrophysics Data System (ADS)

    Zaretski, Aliaksandr V.; Moetazedi, Herad; Kong, Casey; Sawyer, Eric J.; Savagatrup, Suchol; Valle, Eduardo; O'Connor, Timothy F.; Printz, Adam D.; Lipomi, Darren J.

    2015-01-01

    Graphene is expected to play a significant role in future technologies that span a range from consumer electronics, to devices for the conversion and storage of energy, to conformable biomedical devices for healthcare. To realize these applications, however, a low-cost method of synthesizing large areas of high-quality graphene is required. Currently, the only method to generate large-area single-layer graphene that is compatible with roll-to-roll manufacturing destroys approximately 300 kg of copper foil (thickness = 25 μm) for every 1 g of graphene produced. This paper describes a new environmentally benign and scalable process of transferring graphene to flexible substrates. The process is based on the preferential adhesion of certain thin metallic films to graphene; separation of the graphene from the catalytic copper foil is followed by lamination to a flexible target substrate in a process that is compatible with roll-to-roll manufacturing. The copper substrate is indefinitely reusable and the method is substantially greener than the current process that uses relatively large amounts of corrosive etchants to remove the copper. The sheet resistance of the graphene produced by this new process is unoptimized but should be comparable in principle to that produced by the standard method, given the defects observable by Raman spectroscopy and the presence of process-induced cracks. With further improvements, this green, inexpensive synthesis of single-layer graphene could enable applications in flexible, stretchable, and disposable electronics, low-profile and lightweight barrier materials, and in large-area displays and photovoltaic modules.

  8. Graphene on hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Yankowitz, Matthew; Xue, Jiamin; LeRoy, B. J.

    2014-07-01

    The field of graphene research has developed rapidly since its first isolation by mechanical exfoliation in 2004. Due to the relativistic Dirac nature of its charge carriers, graphene is both a promising material for next-generation electronic devices and a convenient low-energy testbed for intrinsically high-energy physical phenomena. Both of these research branches require the facile fabrication of clean graphene devices so as not to obscure its intrinsic physical properties. Hexagonal boron nitride has emerged as a promising substrate for graphene devices as it is insulating, atomically flat and provides a clean charge environment for the graphene. Additionally, the interaction between graphene and boron nitride provides a path for the study of new physical phenomena not present in bare graphene devices. This review focuses on recent advancements in the study of graphene on hexagonal boron nitride devices from the perspective of scanning tunneling microscopy with highlights of some important results from electrical transport measurements.

  9. Enhanced chemical reactivity of graphene induced by mechanical strain.

    PubMed

    Bissett, Mark A; Konabe, Satoru; Okada, Susumu; Tsuji, Masaharu; Ago, Hiroki

    2013-11-26

    Control over chemical reactivity is essential in the field of nanotechnology. Graphene is a two-dimensional atomic sheet of sp(2) hybridized carbon with exceptional properties that can be altered by chemical functionalization. Here, we transferred single-layer graphene onto a flexible substrate and investigated the functionalization using different aryl diazonium molecules while applying mechanical strain. We found that mechanical strain can alter the structure of graphene, and dramatically increase the reaction rate, by a factor of up to 10, as well as increase the final degree of functionalization. Furthermore, we demonstrate that mechanical strain enables functionalization of graphene for both p- and n-type dopants, where unstrained graphene showed negligible reactivity. Theoretical calculations were also performed to support the experimental findings. Our findings offer a simple approach to control the chemical reactivity of graphene through the application of mechanical strain, allowing for a tuning of the properties of graphene.

  10. Elastic properties and mechanical tension of graphene

    NASA Astrophysics Data System (ADS)

    Ramírez, R.; Herrero, C. P.

    2017-01-01

    Room-temperature simulations of graphene have been performed as a function of the mechanical tension of the layer. Finite-size effects are accurately reproduced by an acoustic dispersion law for the out-of-plane vibrations that, in the long-wave limit, behaves as ρ ω2=σ k2+κ k4 . The fluctuation tension σ is finite (˜0.1 N/m) even when the external mechanical tension vanishes. Transverse vibrations imply a duplicity in the definition of the elastic constants of the layer, as observables related to the real area of the surface may differ from those related to the in-plane projected area. This duplicity explains the variability of experimental data on the Young modulus of graphene based on electron spectroscopy, interferometric profilometry, and indentation experiments.

  11. Imaging Mechanical Vibrations in Suspended Graphene Sheets

    NASA Astrophysics Data System (ADS)

    Garcia-Sanchez, D.; van der Zande, A. M.; Paulo, A. San; Lassagne, B.; McEuen, P. L.; Bachtold, A.

    2008-05-01

    We carried out measurements on nanoelectromechanical systems based on multilayer graphene sheets suspended over trenches in silicon oxide. The motion of the suspended sheets was electrostatically driven at resonance using applied radio-frequency voltages. The mechanical vibrations were detected using a novel form of scanning probe microscopy, which allowed identification and spatial imaging of the shape of the mechanical eigenmodes. In as many as half the resonators measured, we observed a new class of exotic nanoscale vibration eigenmodes not predicted by the elastic beam theory, where the amplitude of vibration is maximum at the free edges. By modeling the suspended sheets with the finite element method, these edge eigenmodes are shown to be the result of non-uniform stress with remarkably large magnitudes (up to 1.5 GPa). This non-uniform stress, which arises from the way graphene is prepared by pressing or rubbing bulk graphite against another surface, should be taken into account in future studies on electronic and mechanical properties of graphene.

  12. Electrochemical method of producing nano-scaled graphene platelets

    SciTech Connect

    Zhamu, Aruna; Jang, Joan; Jang, Bor Z.

    2013-09-03

    A method of producing nano-scaled graphene platelets with an average thickness smaller than 30 nm from a layered graphite material. The method comprises (a) forming a carboxylic acid-intercalated graphite compound by an electrochemical reaction; (b) exposing the intercalated graphite compound to a thermal shock to produce exfoliated graphite; and (c) subjecting the exfoliated graphite to a mechanical shearing treatment to produce the nano-scaled graphene platelets. Preferred carboxylic acids are formic acid and acetic acid. The exfoliation step in the instant invention does not involve the evolution of undesirable species, such as NO.sub.x and SO.sub.x, which are common by-products of exfoliating conventional sulfuric or nitric acid-intercalated graphite compounds. The nano-scaled platelets are candidate reinforcement fillers for polymer nanocomposites. Nano-scaled graphene platelets are much lower-cost alternatives to carbon nano-tubes or carbon nano-fibers.

  13. Atomistic mechanisms for bilayer growth of graphene on metal substrates

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Cui, Ping; Zhu, Wenguang; Kaxiras, Efthimios; Gao, Yanfei; Zhang, Zhenyu

    2015-01-01

    Epitaxial growth on metal substrates has been shown to be the most powerful approach in producing large-scale high-quality monolayer graphene, yet it remains a major challenge to realize uniform bilayer graphene growth. Here we carry out a comparative study of the atomistic mechanisms for bilayer graphene growth on the (111) surfaces of Cu and Ni, using multiscale approaches combining first-principles calculations and rate-equation analysis. We first show that the relatively weak graphene-Cu interaction enhances the lateral diffusion and effective nucleation of C atoms underneath the graphene island, thereby making it more feasible to grow bilayer graphene on Cu. In contrast, the stronger graphene-Ni interaction suppresses the lateral mobility and dimerization of C atoms underneath the graphene, making it unlikely to achieve controlled growth of bilayer graphene on Ni. We then determine the critical graphene size beyond which nucleation of the second layer will take place. Intriguingly, the critical size exhibits an effective inverse "Ehrlich-Schwoebel barrier" effect, becoming smaller for faster C migration from the Cu surface to the graphene-Cu interface sites across the graphene edge. These findings allow us to propose a novel alternating growth scheme to realize mass production of bilayer graphene.

  14. Atomistic mechanisms for bilayer growth of graphene on metal substrates

    DOE PAGES

    Chen, Wei; Cui, Ping; Zhu, Wenguang; ...

    2015-01-08

    Epitaxial growth on metal substrates has been shown to be the most powerful approach in producing large-scale high-quality monolayer graphene, yet it remains a major challenge to realize uniform bilayer graphene growth. Here we carry out a comparative study of the atomistic mechanisms for bilayer graphene growth on the (111) surfaces of Cu and Ni, using multiscale approaches combining first-principles calculations and rate-equation analysis. We first show that the relatively weak graphene-Cu interaction enhances the lateral diffusion and effective nucleation of C atoms underneath the graphene island, thereby making it more feasible to grow bilayer graphene on Cu. In contrast,more » the stronger graphene-Ni interaction suppresses the lateral mobility and dimerization of C atoms underneath the graphene, making it unlikely to achieve controlled growth of bilayer graphene on Ni. We then determine the critical graphene size beyond which nucleation of the second layer will take place. Intriguingly, the critical size exhibits an effective inverse "Ehrlich-Schwoebel barrier" effect, becoming smaller for faster C migration from the Cu surface to the graphene-Cu interface sites across the graphene edge. Lastly, these findings allow us to propose a novel alternating growth scheme to realize mass production of bilayer graphene.« less

  15. Atomistic mechanisms for bilayer growth of graphene on metal substrates

    SciTech Connect

    Chen, Wei; Cui, Ping; Zhu, Wenguang; Kaxiras, Efthimios; Gao, Yanfei; Zhang, Zhenyu

    2015-01-08

    Epitaxial growth on metal substrates has been shown to be the most powerful approach in producing large-scale high-quality monolayer graphene, yet it remains a major challenge to realize uniform bilayer graphene growth. Here we carry out a comparative study of the atomistic mechanisms for bilayer graphene growth on the (111) surfaces of Cu and Ni, using multiscale approaches combining first-principles calculations and rate-equation analysis. We first show that the relatively weak graphene-Cu interaction enhances the lateral diffusion and effective nucleation of C atoms underneath the graphene island, thereby making it more feasible to grow bilayer graphene on Cu. In contrast, the stronger graphene-Ni interaction suppresses the lateral mobility and dimerization of C atoms underneath the graphene, making it unlikely to achieve controlled growth of bilayer graphene on Ni. We then determine the critical graphene size beyond which nucleation of the second layer will take place. Intriguingly, the critical size exhibits an effective inverse "Ehrlich-Schwoebel barrier" effect, becoming smaller for faster C migration from the Cu surface to the graphene-Cu interface sites across the graphene edge. Lastly, these findings allow us to propose a novel alternating growth scheme to realize mass production of bilayer graphene.

  16. Highly thermally conductive and mechanically strong graphene fibers

    NASA Astrophysics Data System (ADS)

    Xin, Guoqing; Yao, Tiankai; Sun, Hongtao; Scott, Spencer Michael; Shao, Dali; Wang, Gongkai; Lian, Jie

    2015-09-01

    Graphene, a single layer of carbon atoms bonded in a hexagonal lattice, is the thinnest, strongest, and stiffest known material and an excellent conductor of heat and electricity. However, these superior properties have yet to be realized for graphene-derived macroscopic structures such as graphene fibers. We report the fabrication of graphene fibers with high thermal and electrical conductivity and enhanced mechanical strength. The inner fiber structure consists of large-sized graphene sheets forming a highly ordered arrangement intercalated with small-sized graphene sheets filling the space and microvoids. The graphene fibers exhibit a submicrometer crystallite domain size through high-temperature treatment, achieving an enhanced thermal conductivity up to 1290 watts per meter per kelvin. The tensile strength of the graphene fiber reaches 1080 megapascals.

  17. Layer thinning and etching of mechanically exfoliated MoS2 nanosheets by thermal annealing in air.

    PubMed

    Wu, Jumiati; Li, Hai; Yin, Zongyou; Li, Hong; Liu, Juqing; Cao, Xiehong; Zhang, Qing; Zhang, Hua

    2013-10-11

    A simple thermal annealing method for layer thinning and etching of mechanically exfoliated MoS2 nanosheets in air is reported. Using this method, single-layer (1L) MoS2 nanosheets are achieved after the thinning of MoS2 nanosheets from double-layer (2L) to quadri-layer (4L) at 330 °C. The as-prepared 1L MoS2 nanosheet shows comparable optical and electrical properties with the mechanically exfoliated, pristine one. In addition, for the first time, the MoS2 mesh with high-density of triangular pits is also fabricated at 330 °C, which might arise from the anisotropic etching of the active MoS2 edge sites. As a result of thermal annealing in air, the thinning of MoS2 nanosheet is possible due to its oxidation to form MoO3 . Importantly, the MoO3 fragments on the top of thinned MoS2 layer induces the hole injection, resulting in the p-type channel in fabricated field-effect transistors.

  18. Surfactant-free exfoliation of graphite in aqueous solutions.

    PubMed

    Ricardo, Karen B; Sendecki, Anne; Liu, Haitao

    2014-03-14

    We report an ultrasound exfoliation of graphite in a weakly basic solution to produce multi-layer graphene dispersion. A unique feature of this process is that no surfactant was added to stabilize the exfoliated graphene in water. The concentration of the graphene dispersion prepared by this approach can be up to 0.02 mg mL(-1) and it was stable at room temperature for several months.

  19. A Heterostructure Coupling of Exfoliated Ni-Fe Hydroxide Nanosheet and Defective Graphene as a Bifunctional Electrocatalyst for Overall Water Splitting.

    PubMed

    Jia, Yi; Zhang, Longzhou; Gao, Guoping; Chen, Hua; Wang, Bei; Zhou, Jizhi; Soo, Mun Teng; Hong, Min; Yan, Xuecheng; Qian, Guangren; Zou, Jin; Du, Aijun; Yao, Xiangdong

    2017-03-03

    Herein, the authors demonstrate a heterostructured NiFe LDH-NS@DG10 hybrid catalyst by coupling of exfoliated Ni-Fe layered double hydroxide (LDH) nanosheet (NS) and defective graphene (DG). The catalyst has exhibited extremely high electrocatalytic activity for oxygen evolution reaction (OER) in an alkaline solution with an overpotential of 0.21 V at a current density of 10 mA cm(-2) , which is comparable to the current record (≈0.20 V in Fe-Co-Ni metal-oxide-film system) and superior to all other non-noble metal catalysts. Also, it possesses outstanding kinetics (Tafel slope of 52 mV dec(-1) ) for the reaction. Interestingly, the NiFe LDH-NS@DG10 hybrid has also exhibited the high hydrogen evolution reaction (HER) performance in an alkaline solution (with an overpotential of 115 mV by 2 mg cm(-2) loading at a current density of 20 mA cm(-2) ) in contrast to barely HER activity for NiFe LDH-NS itself. As a result, the bifunctional catalyst the authors developed can achieve a current density of 20 mA cm(-2) by a voltage of only 1.5 V, which is also a record for the overall water splitting. Density functional theory calculation reveals that the synergetic effects of highly exposed 3d transition metal atoms and carbon defects are essential for the bifunctional activity for OER and HER.

  20. Observation of graphene bubbles and effective mass transport under graphene films.

    PubMed

    Stolyarova, E; Stolyarov, D; Bolotin, K; Ryu, S; Liu, L; Rim, K T; Klima, M; Hybertsen, M; Pogorelsky, I; Pavlishin, I; Kusche, K; Hone, J; Kim, P; Stormer, H L; Yakimenko, V; Flynn, G

    2009-01-01

    Mechanically exfoliated graphene mounted on a SiO2/Si substrate was subjected to HF/H(2)O etching or irradiation by energetic protons. In both cases gas was released from the SiO2 and accumulated at the graphene/SiO2 interface resulting in the formation of "bubbles" in the graphene sheet. Formation of these "bubbles" demonstrates the robust nature of single layer graphene membranes, which are capable of containing mesoscopic volumes of gas. In addition, effective mass transport at the graphene/SiO2 interface has been observed.

  1. Exfoliative erythroderma.

    PubMed

    Milavec-Puretić, Visnja; Zorić, Zdenka; Zidanić, Martina; Drcelić, Ada; Stajminger, Gordana

    2007-01-01

    Exfoliative erythroderma refers to the skin that is diffusely red and inflamed with varying degrees and types of scaling. There are many causes of erythroderma, but the most common are exacerbations of an underlying skin disease, drug reactions and underlying malignancies. Erythroderma is a rare, potentially serious skin condition. Protein loss in the form of desquamation and exudation is significant, resulting in hypoproteinemia. Usually more than one skin biopsy should be done. Biopsy analysis is important to rule out cutaneous T-cell lymphoma. Patients should be carefully evaluated for underlying disease. Erythroderma can represent a serious medical threat to the patient, and may require hospitalization. Various forms of exfoliative erythroderma are presented, considering the etiopathogenesis, physical findings, differential diagnosis and treatment.

  2. Nanoparticle-Mediated Physical Exfoliation of Aqueous-Phase Graphene for Fabrication of Three-Dimensionally Structured Hybrid Electrodes

    PubMed Central

    Lee, Younghee; Choi, Hojin; Kim, Min-Sik; Noh, Seonmyeong; Ahn, Ki-Jin; Im, Kyungun; Kwon, Oh Seok; Yoon, Hyeonseok

    2016-01-01

    Monodispersed polypyrrole (PPy) nanospheres were physically incorporated as guest species into stacked graphene layers without significant property degradation, thereby facilitating the formation of unique three-dimensional hybrid nanoarchitecture. The electrochemical properties of the graphene/particulate PPy (GPPy) nanohybrids were dependent on the sizes and contents of the PPy nanospheres. The nanohybrids exhibited optimum electrochemical performance in terms of redox activity, charge-transfer resistance, and specific capacitance at an 8:1 PPy/graphite (graphene precursor) weight ratio. The packing density of the alternately stacked nanohybrid structure varied with the nanosphere content, indicating the potential for high volumetric capacitance. The nanohybrids also exhibited good long-term cycling stability because of a structural synergy effect. Finally, fabricated nanohybrid-based flexible all–solid state capacitor cells exhibited good electrochemical performance in an acidic electrolyte with a maximum energy density of 8.4 Wh kg−1 or 1.9 Wh L−1 at a maximum power density of 3.2 kW kg−1 or 0.7 kW L−1; these performances were based on the mass or packing density of the electrode materials. PMID:26813878

  3. Exfoliative dermatitis.

    PubMed

    Karakayli, G; Beckham, G; Orengo, I; Rosen, T

    1999-02-01

    Exfoliative dermatitis, also known as erythroderma, is an uncommon but serious skin disorder that family physicians must be able to recognize and treat appropriately. Although the etiology is often unknown, exfoliative dermatitis may be the result of a drug reaction or an underlying malignancy. The approach to treatment should include discontinuation of any potentially causative medications and a search for any underlying malignancy. One of the most common malignancies associated with exfoliative dermatitis is cutaneous T-cell lymphoma, which may not manifest for months or even years after the onset of the skin condition. Hospitalization is usually necessary for initial evaluation and treatment. In the hospital, special attention must be given to maintaining temperature control, replacing lost fluids and electrolytes, and preventing and treating infection. The long-term prognosis is good in patients with drug-induced disease, although the course tends to be remitting and relapsing in idiopathic cases. The prognosis of cases associated with malignancy typically depends on the outcome of the underlying malignancy.

  4. Effect of graphene modification on thermo-mechanical and microwave absorption properties of polystyrene/graphene nanocomposites.

    PubMed

    Hatui, Goutam; Das, Chapal Kumar

    2012-10-01

    In the present study the effect of graphene percentage and graphene modification on the microwave absorption properties of the polystyrene/graphene nanocomposites was studied in detail. Acid modified graphene was prepared by the mixed acid route. Polystyrene/graphene nanocomposites with various percentages of graphene and modified graphene were prepared by solution mixing process. The dispersion of graphene sheets in the polystyrene matrix was analyzed by TEM and SEM and found to be uniform for the 1%, 2 wt% of graphene and 1 wt% of modified graphene loading. Microwave absorption of modified graphene containing nanocomposite was found to be superior among the nanocomposites. Incorporation of 1 wt% of ferrite particles enhanced the microwave absorption of the nanocomposite above all the nanocomposites, in the whole range of X-band, due to the effective cancellation of both electrical and magnetic components of the microwave. Incorporation of graphene enhanced the thermal and mechanical properties of the nanocomposites.

  5. Sorption mechanisms of metals to graphene oxide

    NASA Astrophysics Data System (ADS)

    Showalter, Allison R.; Duster, Thomas A.; Szymanowski, Jennifer E. S.; Na, Chongzheng; Fein, Jeremy B.; Bunker, Bruce A.

    2016-05-01

    Environmental toxic metal contamination remediation and prevention is an ongoing issue. Graphene oxide is highly sorptive for many heavy metals over a wide pH range under different ionic strength conditions. We present x-ray absorption fine structure (XAFS) spectroscopy results investigating the binding environment of Pb(II), Cd(II) and U(VI) ions onto multi-layered graphene oxide (MLGO). Analysis indicates that the dominant sorption mechanism of Pb to MLGO changes as a function of pH, with increasing inner sphere contribution as pH increases. In contrast, the sorption mechanism of Cd to MLGO remains constant under the studied pH range. This adsorption mechanism is an electrostatic attraction between the hydrated Cd+2 ion and the MLGO surface. The U(VI), present as the uranyl ion, changes only subtly as a function of pH and is bound to the surface via an inner sphere bond. Knowledge of the binding mechanism for each metal is necessary to help in optimizing environmental remediation or prevention in filtration systems.

  6. Manipulation of Dirac Cones in Mechanical Graphene

    NASA Astrophysics Data System (ADS)

    Kariyado, Toshikaze; Hatsugai, Yasuhiro

    2015-12-01

    Recently, quantum Hall state analogs in classical mechanics attract much attention from topological points of view. Topology is not only for mathematicians but also quite useful in a quantum world. Further it even governs the Newton’s law of motion. One of the advantages of classical systems over solid state materials is its clear controllability. Here we investigate mechanical graphene, which is a spring-mass model with the honeycomb structure as a typical mechanical model with nontrivial topological phenomena. The vibration spectrum of mechanical graphene is characterized by Dirac cones serving as sources of topological nontriviality. We find that the spectrum has dramatic dependence on the spring tension at equilibrium as a natural control parameter, i.e., creation and annihilation of the Dirac particles are realized as the tension increases. Just by rotating the system, the manipulated Dirac particles lead to topological transition, i.e., a jump of the “Chern number” occurs associated with flipping of propagating direction of chiral edge modes. This is a bulk-edge correspondence governed by the Newton’s law. A simple observation that in-gap edge modes exist only at the fixed boundary, but not at the free one, is attributed to the symmetry protection of topological phases.

  7. Manipulation of Dirac Cones in Mechanical Graphene

    PubMed Central

    Kariyado, Toshikaze; Hatsugai, Yasuhiro

    2015-01-01

    Recently, quantum Hall state analogs in classical mechanics attract much attention from topological points of view. Topology is not only for mathematicians but also quite useful in a quantum world. Further it even governs the Newton’s law of motion. One of the advantages of classical systems over solid state materials is its clear controllability. Here we investigate mechanical graphene, which is a spring-mass model with the honeycomb structure as a typical mechanical model with nontrivial topological phenomena. The vibration spectrum of mechanical graphene is characterized by Dirac cones serving as sources of topological nontriviality. We find that the spectrum has dramatic dependence on the spring tension at equilibrium as a natural control parameter, i.e., creation and annihilation of the Dirac particles are realized as the tension increases. Just by rotating the system, the manipulated Dirac particles lead to topological transition, i.e., a jump of the “Chern number” occurs associated with flipping of propagating direction of chiral edge modes. This is a bulk-edge correspondence governed by the Newton’s law. A simple observation that in-gap edge modes exist only at the fixed boundary, but not at the free one, is attributed to the symmetry protection of topological phases. PMID:26667580

  8. Manipulation of Dirac Cones in Mechanical Graphene.

    PubMed

    Kariyado, Toshikaze; Hatsugai, Yasuhiro

    2015-12-15

    Recently, quantum Hall state analogs in classical mechanics attract much attention from topological points of view. Topology is not only for mathematicians but also quite useful in a quantum world. Further it even governs the Newton's law of motion. One of the advantages of classical systems over solid state materials is its clear controllability. Here we investigate mechanical graphene, which is a spring-mass model with the honeycomb structure as a typical mechanical model with nontrivial topological phenomena. The vibration spectrum of mechanical graphene is characterized by Dirac cones serving as sources of topological nontriviality. We find that the spectrum has dramatic dependence on the spring tension at equilibrium as a natural control parameter, i.e., creation and annihilation of the Dirac particles are realized as the tension increases. Just by rotating the system, the manipulated Dirac particles lead to topological transition, i.e., a jump of the "Chern number" occurs associated with flipping of propagating direction of chiral edge modes. This is a bulk-edge correspondence governed by the Newton's law. A simple observation that in-gap edge modes exist only at the fixed boundary, but not at the free one, is attributed to the symmetry protection of topological phases.

  9. Mechanically Robust Polymer-Graphene Aerogels

    NASA Astrophysics Data System (ADS)

    Ha, Heonjoo; Shanmuganathan, Kadhiravan; Ellison, Christopher

    2015-03-01

    Graphene has been intensely studied for the past several years due to its many attractive properties. Graphene oxide (GO) aerogels are particularly interesting due to their light weight and excellent performance in various applications, such as environmental remediation, super-hydrophobic and super-oleophilic materials, energy storage, etc. However, GO aerogels are generally weak and delicate which complicates their handling and potentially limits their application outside the research lab. The focus of this work is to synthesize mechanically stable aerogels that are robust and easy to handle without substantially sacrificing their low density. To overcome this challenge, we found that by intermixing a small amount of readily available and thermally crosslinkable polymer can enhance the mechanical properties without disrupting other characteristic intrinsic properties of the aerogel itself. This method is a simple straight-forward procedure that does not include any tedious chemical reactions or harsh chemicals. Furthermore, we will demonstrate the performance of these materials as a super-absorbent and pressure sensor.

  10. A novel enzyme-free amperometric sensor for hydrogen peroxide based on Nafion/exfoliated graphene oxide-Co3O4 nanocomposite.

    PubMed

    Ensafi, Ali A; Jafari-Asl, M; Rezaei, B

    2013-01-15

    Electrochemical detection of H(2)O(2) was investigated on a Nafion/exfoliated graphene oxide/Co(3)O(4) nanocomposite (Nafion/EGO/Co(3)O(4)) coated glassy carbon electrode. The morphological characterization was examined by scanning electron microscopy, X-ray diffraction, and electrochemical impedance spectroscopy. The modified electrode showed well defined and stable redox couples signal in both alkaline and natural aqueous solutions with excellent electrocatalytic activity for oxidation of hydrogen peroxide. The response of the modified electrode to H(2)O(2) was examined using amperometry (at 0.76 V vs. Ag/AgCl reference electrode) in a phosphate buffer solution (pH 7.4). The detection limit was 0.3 μmol L(-1) with a linearity of up to four orders of magnitude and a sensitivity of 560 μA mmol(-1)Lcm(-2). The response time of the electrode to achieve 95% of the steady-state current was recorded at 4s. The ability of the sensor for routine analyses was demonstrated by the detection of H(2)O(2) presents in milk samples with appreciable recovery values. In addition, the Nafion/EGO/Co(3)O(4)-GCE showed good selectivity for H(2)O(2) detection in the presence of ascorbic acid, uric acid, and glucose. The attractive analytical performances such as remarkable catalytic activity, good reproducibility, long term stability, and facile preparation method made this novel nanocomposite electrode promising for the development of effective H(2)O(2) sensor.

  11. The effect of exfoliated graphite on carbon fiber reinforced composites for cryogenic applications

    NASA Astrophysics Data System (ADS)

    McLaughlin, Adam Michael

    It is desirable to lighten cryogenic fuel tanks through the use of composites for the development of a reusable single stage launch vehicle. Conventional composites fall victim to microcracking due to the cyclic loading and temperature change experienced during launch and re-entry conditions. Also, the strength of a composite is generally limited by the properties of the matrix. The introduction of the nanoplatelet, exfoliated graphite or graphene, to the matrix shows promise of increasing both the microcracking resistivity and the mechanical characteristics. Several carbon fiber composite plates were manufactured with varying concentrations of graphene and tested under both room and cryogenic conditions to characterize graphene's effect on the composite. Results from tensile and fracture testing indicate that the ideal concentration of graphene in our carbon fiber reinforced polymer composites for cryogenic applications is 0.08% mass graphene.

  12. Spin diffusion and non-local spin-valve effect in an exfoliated multilayer graphene with a Co electrode

    NASA Astrophysics Data System (ADS)

    Li, Lijun; Lee, Inyeal; Lim, Dongsuk; Rathi, Servin; Kang, Moonshik; Uemura, Tetsuya; Kim, Gil-Ho

    2016-08-01

    We fabricated a non-local spin valve with a thin layer of graphite with Co transparent electrodes. The spin-valve effect and spin precession were observed at room temperature. The magnitude of the mangetoresistance increases when temperature decreases. The spin-relaxation time, {τ }s, obtained from the fitting of the Hanle curves increases with decreasing temperature with a weak dependence ∼ {T}-0.065 while the spin-diffusion constant D decreases. At room temperature, {τ }s exceeds 100 ps and the spin-diffusion length, {λ }s, is ∼2 μm. The temperature dependence of {λ }s is not monotonic, and it has the largest value at room temperature. Our results show that multilayer graphene is a suitable material for spintronic devices.

  13. Carbon nanosheet-titania nanocrystal composites from reassembling of exfoliated graphene oxide layers with colloidal titania nanoparticles

    SciTech Connect

    Liu Yongjun; Aizawa, Mami; Peng Wenqing; Wang Zhengming; Hirotsu, Takahiro

    2013-01-15

    Nanoporous composites of carbon nanosheets (CNS) and titania nanoparticles (NPs) were synthesized by reassembling of delaminated graphite oxide (GO) layers with titania clear sol (TCS), and their structural and porous properties were examined by various physico-chemical methods such as XRD, TG/DTA, FT-IR, Raman, FE-SEM/TEM, and low temperature N{sub 2} adsorption. It was found that the facile approach, which utilizes the electrostatic attraction between the negatively charged GO layers and the positively charged TCS particles, leads to a well composed CNS and ultrafine TiO{sub 2} NPs material whose titania amount reaches up to 71 wt%. The titania phase in these composite materials is mainly anatase, which is resistible against high temperature calcination, but also contains a little amount of rutile and brookite depending on synthesis condition. The porosity of the composite is improved and partially affected by the size distributions of TiO{sub 2} NPs. The unique structure, better porosity, and compatible surface affinity of these composites bring about an adsorption concentration-promoted photocatalytic effects toward organic dyes by successfully combining both properties of CNS and titania NPs. - Graphical Abstract: Carbon nanosheet-titania nanocrystal composites can be synthesized by a facile delamination-reassembling method from graphene oxide and colloidal titania. Highlights: Black-Right-Pointing-Pointer A facile delamination-reassembling method for graphene oxide-titania nanocomposite. Black-Right-Pointing-Pointer A nanoporous composite containing mixed phase titania nanocrystals. Black-Right-Pointing-Pointer Partition effect of carbon nanosheets preventing TiO{sub 2} nanoparticles from aggregating. Black-Right-Pointing-Pointer Adsorption concentration-promoted photocatalysis.

  14. Graphene-based materials via benzidine-assisted exfoliation and reduction of graphite oxide and their electrochemical properties

    NASA Astrophysics Data System (ADS)

    Vermisoglou, E. C.; Giannakopoulou, T.; Romanos, G.; Boukos, N.; Psycharis, V.; Lei, C.; Lekakou, C.; Petridis, D.; Trapalis, C.

    2017-01-01

    Benzidine, a compound bearing aromatic rings and terminal amino groups, was employed for the intercalation and simultaneous reduction of graphite oxide (GO). The aromatic diamine can be intercalated into GO as follows: (1) by grafting with the epoxy groups of GO, (2) by hydrogen bonding with the oxygen containing groups of GO. Stacking between benzidine aromatic rings and unoxidized domains of GO may occur through π-π interaction. The role of benzidine is influenced by pH conditions and the weight ratio GO/benzidine. Two weight ratios were tested i.e. 1:2 and 1:3. Under strong alkaline conditions through K2CO3 addition (pH ∼10.4-10.6) both intercalation and reduction of GO via amino groups occur, while under strong acidic conditions through HCl addition (pH ∼1.4-2.2) π-π stacking is preferred. When no base or acid is added (pH ∼5.2) and the weight ratio is 1:2, there are indications that reduction and π-π stacking occur, while at a GO/benzidine weight ratio 1:3 intercalation via amino groups and reduction seem to dominate. The aforementioned remarks render benzidine a multifunctional tool towards production of reduced graphene oxide. The effect of pH conditions and the GO/benzidine weight ratio on the quality and the electrochemical properties of the produced graphene-based materials were investigated. Cyclic voltammetry measurements using three-electrode cell and KCl aqueous solution as an electrolyte gave specific capacitance values up to ∼178 F/g. When electric double-layer capacitors (EDLC) were fabricated from these materials, the maximum capacitance in organic electrolyte i.e., tetraethyl ammonium tetrafluoroborate (TEABF4) in polycarbonate (PC) was ∼29 F/g.

  15. Phosphate functionalized graphene with tunable mechanical properties.

    PubMed

    Goods, John B; Sydlik, Stefanie A; Walish, Joseph J; Swager, Timothy M

    2014-02-01

    The synthesis of a covalently modified graphene oxide derivative with exceptional and tunable compressive strength is reported. Treatment of graphene oxide with triethyl phosphite in the presence of LiBr produces monolithic structures comprised of lithium phosphate oligomers tethered to graphene through covalent phosphonate linkages. Variation of the both phosphate content and associated cation produces materials of various compressive strengths and elasticity.

  16. Mechanically and optically controlled graphene valley filter

    SciTech Connect

    Qi, Fenghua; Jin, Guojun

    2014-05-07

    We theoretically investigate the valley-dependent electronic transport through a graphene monolayer modulated simultaneously by a uniform uniaxial strain and linearly polarized light. Within the Floquet formalism, we calculate the transmission probabilities and conductances of the two valleys. It is found that valley polarization can appear only if the two modulations coexist. Under a proper stretching of the sample, the ratio of the light intensity and the light frequency squared is important. If this quantity is small, the electron transport is mainly contributed by the valley-symmetric central band and the conductance is valley unpolarized; but when this quantity is large, the valley-asymmetric sidebands also take part in the transport and the valley polarization of the conductance appears. Furthermore, the degree of the polarization can be tuned by the strain strength, light intensity, and light frequency. It is proposed that the detection of the valley polarization can be realized utilizing the valley beam splitting. Thus, a graphene monolayer can be used as a mechanically and optically controlled valley filter.

  17. Simultaneous Graphite Exfoliation and N Doping in Supercritical Ammonia.

    PubMed

    Sasikala, Suchithra Padmajan; Huang, Kai; Giroire, Baptiste; Prabhakaran, Prem; Henry, Lucile; Penicaud, Alain; Poulin, Philippe; Aymonier, Cyril

    2016-11-16

    We report the exfoliation of graphite and simultaneous N doping of graphene by two methods: supercritical ammonia treatment and liquid-phase exfoliation with NH4OH. While the supercritical ammonia allowed N doping at a level of 6.4 atom % in 2 h, the liquid-phase exfoliation with NH4OH allowed N doping at a level of 2.7 atom % in 6 h. The N doped graphene obtained via the supercritical ammonia route had few layers (<5) and showed large lateral flake size (∼8 μm) and low defect density (ID/IG < 0.6) in spite of their high level of N doping. This work is the first demonstration of supercritical ammonia as an exfoliation agent and N doping precursor for graphene. Notably, the N doped graphene showed electrocatalytic activity toward oxygen reduction reaction with high durability and good methanol tolerance compared to those of commercial Pt/C catalyst.

  18. Bioapplications of graphene constructed functional nanomaterials.

    PubMed

    Gulzar, Arif; Yang, Piaoping; He, Fei; Xu, Jiating; Yang, Dan; Xu, Liangge; Jan, Mohammad Omar

    2017-01-25

    Graphene has distinctive mechanical, electronic, and optical properties, which researchers have applied to develop innovative electronic materials including transparent conductors and ultrafast transistors. Lately, the understanding of various chemical properties of graphene has expedited its application in high-performance devices that generate and store energy. Graphene is now increasing its terrain outside electronic and chemical applications toward biomedical areas such as precise bio sensing through graphene-quenched fluorescence, graphene-enhanced cell differentiation and growth, and graphene-assisted laser desorption/ionization for mass spectrometry. In this Account, we evaluate recent efforts to apply graphene and graphene oxides (GO) to biomedical research and a few different approaches to prepare graphene materials designed for biomedical applications and a brief perspective on their future applications. Because of its outstanding aqueous processability, amphiphilicity, surface functionalizability, surface enhanced Raman scattering (SERS), and fluorescence quenching ability, GO chemically exfoliated from oxidized graphite is considered a promising material for biological applications. In addition, the hydrophobicity and flexibility of large-area graphene synthesized by chemical vapor deposition (CVD) allow this material to play an important role in cell growth and differentiation. Graphene is considered to be an encouraging and smart candidate for numerous biomedical applications such as NIR-responsive cancer therapy and fluorescence bio-imaging and drug delivery. To that end, suitable preparation and unique approaches to utilize graphene-based materials such as graphene oxides (GOs), reduced graphene oxides (rGOs), and graphene quantum dots (GQDs) in biology and medical science are gaining growing interest.

  19. Enhanced mechanical properties of nanocomposites at low graphene content.

    PubMed

    Rafiee, Mohammad A; Rafiee, Javad; Wang, Zhou; Song, Huaihe; Yu, Zhong-Zhen; Koratkar, Nikhil

    2009-12-22

    In this study, the mechanical properties of epoxy nanocomposites with graphene platelets, single-walled carbon nanotubes, and multi-walled carbon nanotube additives were compared at a nanofiller weight fraction of 0.1 +/- 0.002%. The mechanical properties measured were the Young's modulus, ultimate tensile strength, fracture toughness, fracture energy, and the material's resistance to fatigue crack propagation. The results indicate that graphene platelets significantly out-perform carbon nanotube additives. The Young's modulus of the graphene nanocomposite was approximately 31% greater than the pristine epoxy as compared to approximately 3% increase for single-walled carbon nanotubes. The tensile strength of the baseline epoxy was enhanced by approximately 40% with graphene platelets compared to approximately 14% improvement for multi-walled carbon nanotubes. The mode I fracture toughness of the nanocomposite with graphene platelets showed approximately 53% increase over the epoxy compared to approximately 20% improvement for multi-walled carbon nanotubes. The fatigue resistance results also showed significantly different trends. While the fatigue suppression response of nanotube/epoxy composites degrades dramatically as the stress intensity factor amplitude is increased, the reverse effect is seen for graphene-based nanocomposites. The superiority of graphene platelets over carbon nanotubes in terms of mechanical properties enhancement may be related to their high specific surface area, enhanced nanofiller-matrix adhesion/interlocking arising from their wrinkled (rough) surface, as well as the two-dimensional (planar) geometry of graphene platelets.

  20. Graphene NanoElectroMechanical Resonators and Oscillators

    NASA Astrophysics Data System (ADS)

    Chen, Changyao

    Made of only one sheet of carbon atoms, graphene is the thinnest yet strongest material ever exist. Since its discovery in 2004, graphene has attracted tremendous research effort worldwide. Guaranteed by the superior electrical and excellent mechanical properties, graphene is the ideal building block for NanoElectroMechanical Systems (NEMS). In the first parts of the thesis, I will discuss the fabrications and measurements of typical graphene NEMS resonators, including doubly clamped and fully clamped graphene mechanical resonators. I have developed a electrical readout technique by using graphene as frequency mixer, demonstrated resonant frequencies in range from 30 to 200 MHz. Furthermore, I developed the advanced fabrications to achieve local gate structure, which led to the real-time resonant frequency detection under resonant channel transistor (RCT) scheme. Such real-time detection improve the measurement speed by 2 orders of magnitude compared to frequency mixing technique, and is critical for practical applications. Finally, I employed active balanced bridge technique in order to reduce overall electrical parasitics, and demonstrated pure capacitive transduction of graphene NEMS resonators. Characterizations of graphene NEMS resonators properties are followed, including resonant frequency and quality factor (Q) tuning with tension, mass and temperatures. A simple continuum mechanics model was constructed to understand the frequency tuning behavior, and it agrees with experimental data extremely well. In the following parts of the thesis, I will discuss the behavior of graphene mechanical resonators in applied magnetic field, i.e. in Quantum Hall (QH) regime. The couplings between mechanical motion and electronic band structure turned out to be a direct probe for thermodynamic quantities, i.e., chemical potential and compressibility. For a clean graphene resonators, with quality factors of 1 x 104, it underwent resonant frequency oscillations as applied

  1. Knitted graphene-nanoribbon sheet: a mechanically robust structure

    NASA Astrophysics Data System (ADS)

    Wei, Ning; Fan, Zheyong; Xu, Lan-Qing; Zheng, Yong-Ping; Wang, Hui-Qiong; Zheng, Jin-Cheng

    2012-01-01

    In this paper, a new nanostructure is proposed, namely, the knitted graphene-nanoribbon sheet (KGS), which consists of zigzag and/or armchair graphene nanoribbons. The knitting technology is introduced to graphene nanotechnology to produce large area graphene sheets. Compared with pristine graphene, the chirality of a knitted graphene-nanoribbon sheet is much more flexible and can be designed on demand. The mechanical properties of KGSs are investigated by molecular dynamics simulations, including the effect of vacancies. With hydrogen atoms saturating the ribbon edges, the structure (KGS + H) is found to be of significant mechanical robustness, whose fracture does not rely on the critical bonds. The fracture strain of KGS + H remains nearly unchanged as long as there remains a single defect-free graphene nanoribbon in the tensile direction. This graphene nano knitting technique is experimentally feasible, inspired by a recent demonstration by Fournier et al. [Phys. Rev. B, 2011, 84, 035435] of lifting a single molecular wire using a combined frequency-modulated atomic force and tunnelling microscope.

  2. Fabrication of Boron Nitride Nanosheets by Exfoliation.

    PubMed

    Wang, Zifeng; Tang, Zijie; Xue, Qi; Huang, Yan; Huang, Yang; Zhu, Minshen; Pei, Zengxia; Li, Hongfei; Jiang, Hongbo; Fu, Chenxi; Zhi, Chunyi

    2016-06-01

    Nanomaterials with layered structures, with their intriguing properties, are of great research interest nowadays. As one of the primary two-dimensional nanomaterials, the hexagonal boron nitride nanosheet (BNNS, also called white graphene), which is an analogue of graphene, possesses various attractive properties, such as high intrinsic thermal conductivity, excellent chemical and thermal stability, and electrical insulation properties. After being discovered, it has been one of the most intensively studied two-dimensional non-carbon nanomaterials and has been applied in a wide range of applications. To support the exploration of applications of BNNSs, exfoliation, as one of the most promising approaches to realize large-scale production of BNNSs, has been intensively investigated. In this review, methods to yield BNNSs by exfoliation will be summarized and compared with other potential fabrication methods of BNNSs. In addition, the future prospects of the exfoliation of h-BN will also be discussed.

  3. Passively Q-switched Ytterbium doped fiber laser with mechanically exfoliated MoS2 saturable absorber

    NASA Astrophysics Data System (ADS)

    Al-Masoodi, A. H. H.; Ahmed, M. H. M.; Latiff, A. A.; Arof, H.; Harun, S. W.

    2017-01-01

    A passively Q-switched Ytterbium-doped fiber laser (YDFL) based on MoS2 saturable absorber (SA) is demonstrated. A few layers of MoS2 are mechanically exfoliated from a natural MoS2 crystal using a scotch tape and the resulting SA is sandwiched between two fiber ferrules to form a fiber compatible Q-switcher. The saturation intensity, non-saturable intensity, and modulation depth of the MoS2 SA are 23.5 MW/cm2, 23.0, and 11.3%, respectively. By introducing the MoS2 SA into the YDFL cavity, a stable pulse laser is generated at 1070.2 nm wavelength with a threshold pump power of 49.57 mW. The repetition rate of the Q-switched pulses ranges from 3.817 to 25.25 kHz, as the 980 nm pump power increases from 49.57 to 87.2 mW. The highest pulse energy is 295.45 nJ at a pump power of 87.2 mW.

  4. High-efficiency exfoliation of layered materials into 2D nanosheets in switchable CO2/Surfactant/H2O system.

    PubMed

    Wang, Nan; Xu, Qun; Xu, Shanshan; Qi, Yuhang; Chen, Meng; Li, Hongxiang; Han, Buxing

    2015-11-16

    Layered materials present attractive and important properties due to their two-dimensional (2D) structure, allowing potential applications including electronics, optoelectronics, and catalysis. However, fully exploiting the outstanding properties will require a method for their efficient exfoliation. Here we present that a series of layered materials can be successfully exfoliated into single- and few-layer nanosheets using the driving forces coming from the phase inversion, i.e., from micelles to reverse micelles in the emulsion microenvironment built by supercritical carbon dioxide (SC CO2). The effect of variable experimental parameters including CO2 pressure, ethanol/water ratio, and initial concentration of bulk materials on the exfoliation yield have been investigated. Moreover, we demonstrate that the exfoliated 2D nanosheets have their worthwhile applications, for example, graphene can be used to prepare conductive paper, MoS2 can be used as fluorescent label to perform cellular labelling, and BN can effectively reinforce polymers leading to the promising mechanical properties.

  5. High-efficiency exfoliation of layered materials into 2D nanosheets in switchable CO2/Surfactant/H2O system

    NASA Astrophysics Data System (ADS)

    Wang, Nan; Xu, Qun; Xu, Shanshan; Qi, Yuhang; Chen, Meng; Li, Hongxiang; Han, Buxing

    2015-11-01

    Layered materials present attractive and important properties due to their two-dimensional (2D) structure, allowing potential applications including electronics, optoelectronics, and catalysis. However, fully exploiting the outstanding properties will require a method for their efficient exfoliation. Here we present that a series of layered materials can be successfully exfoliated into single- and few-layer nanosheets using the driving forces coming from the phase inversion, i.e., from micelles to reverse micelles in the emulsion microenvironment built by supercritical carbon dioxide (SC CO2). The effect of variable experimental parameters including CO2 pressure, ethanol/water ratio, and initial concentration of bulk materials on the exfoliation yield have been investigated. Moreover, we demonstrate that the exfoliated 2D nanosheets have their worthwhile applications, for example, graphene can be used to prepare conductive paper, MoS2 can be used as fluorescent label to perform cellular labelling, and BN can effectively reinforce polymers leading to the promising mechanical properties.

  6. 7,7,8,8-Tetracyanoquinodimethane-assisted one-step electrochemical exfoliation of graphite and its performance as an electrode material

    NASA Astrophysics Data System (ADS)

    Khanra, Partha; Lee, Chang-No; Kuila, Tapas; Kim, Nam Hoon; Park, Min Jun; Lee, Joong Hee

    2014-04-01

    electrolytes was described. TCNQ is an organic charge-transfer complex with electron accepting and noteworthy electrical properties. The exfoliation of graphite to a few-layer graphene sheets was confirmed by transmission electron microscopy (TEM) and atomic force microscopy (AFM) image analysis. The chemical state, surface functional groups and chemical compositions of bulk graphite as well as TCNQ-functionalized graphene sheets were investigated by Fourier-transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis. Adsorption of TCNQ onto the surface of graphene sheets was confirmed by the appearance of the N1s peak at ~399.4 eV in the XPS of TCNQ-functionalized graphene. Exfoliation of bulk graphite to functionalized graphene sheets was further confirmed by the appearance of a sharp single peak at ~2695 cm-1 along with increased intensity ratios of the D-band to the G-band. Electrochemical performance of a TCNQ-functionalized graphene sheet was investigated using 1 M Na2SO4 and 1 M KOH aqueous solutions. Cyclic voltammetry (CV) and galvanometric charge-discharge experiments revealed that TCNQ-functionalized graphene could be used as a supercapacitor electrode material. The specific capacitance values of TCNQ-modified graphene measured with electrolytes (1 M KOH and 1 M Na2SO4) were 324 and 140 F g-1, respectively, at a current density of 1 A g-1. Impedance spectroscopic analysis revealed that the charge transfer process was dependent on surface functionalization and interaction between the electrode and the electrolyte. Electronic supplementary information (ESI) available: Schematic diagram of the electrochemical exfoliation mechanism, XPS survey spectra of pure graphite, TCNQG1 and TCNQG2, deconvoluted C1s spectra of graphite and comparison of materials preparation and electrochemical performance of TCNQ functionalized graphene sheets with the existing state-of-the-art compounds. See DOI: 10.1039/c3nr05307e

  7. Graphene-based materials: synthesis, characterization, properties, and applications.

    PubMed

    Huang, Xiao; Yin, Zongyou; Wu, Shixin; Qi, Xiaoying; He, Qiyuan; Zhang, Qichun; Yan, Qingyu; Boey, Freddy; Zhang, Hua

    2011-07-18

    Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

  8. Exfoliation/dispersion of low-temperature expandable graphite in nanocellulose matrix by wet co-milling.

    PubMed

    Zhang, Xiaofang; Lu, Zhixing; Zhao, Jiangqi; Li, Qingye; Zhang, Wei; Lu, Canhui

    2017-02-10

    Viability and future of graphene depends, to a great extent, on a methodology that can mass-produce high-quality graphene in an affordable way. In this work, wet co-milling of low-temperature expandable graphite (LTEG) with bamboo cellulose fibers through a grinder was proved to be a scalable and environmentally friendly approach for the exfoliation/dispersion of graphene-like carbon in an aqueous suspension in which the mechanically isolated cellulose nanofibers (CNFs) acted as a "green" dispersant. The exfoliation/dispersion degree of LTEG was studied as a function of passing times through the grinder. Under the assistance of CNFs, stable aqueous dispersions of CNFs/few-layer graphene (FLG) were obtained. Based on the CNFs/FLG dispersions, a series of nanocomposite films with high mechanical strength and excellent flexibility were fabricated. The tensile strength, Young's modulus, and elongation at break of the CNFs/FLG nanocomposite film were enhanced to 59.14MPa, 4.13GPa and 4.17% respectively after 100 passing times through the grinder. However, with the passing time increased, the electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) decreased, in agreement with the good dispersion of FLG in CNFs matrix. The strategy proposed here is simple, highly efficient, and low in cost, exhibiting great potential for producing exfoliated FLG with few defects at an industrial scale.

  9. Functionalized graphene and graphene oxide solution via polyacrylate coating.

    PubMed

    Saha, Arindam; Basiruddin, S K; Ray, S C; Roy, S S; Jana, Nikhil R

    2010-12-01

    Water soluble graphene with various chemical- and biofunctionalities is essential for their different applications. However, exfoliated graphenes are insoluble in water and water soluble graphene oxide precipitate if they are chemically reduced to graphene. We have developed a polyacrylate coating method for graphene oxide and then chemically reduced it into graphene. We found that polyacrylate coating can improve the colloidal stability of both graphene and graphene oxide. The coated graphene has been characterized using XPS, FTIR, XRD and micro-Raman spectroscopy. The primary amine present on the coating backbone has been used to derive glucose functionalized water soluble graphene. Various other functional graphenes can be anticipated from the polyacrylate coated graphene.

  10. Direct optical imaging of graphene in vitro by nonlinear femtosecond laser spectral reshaping.

    PubMed

    Li, Baolei; Cheng, Yingwen; Liu, Jie; Yi, Congwen; Brown, April S; Yuan, Hsiangkuo; Vo-Dinh, Tuan; Fischer, Martin C; Warren, Warren S

    2012-11-14

    Nonlinear optical microscopy, based on femtosecond laser spectral reshaping, characterized and imaged graphene samples made from different methods, both on slides and in a biological environment. This technique clearly discriminates between graphene flakes with different numbers of layers and reveals the distinct nonlinear optical properties of reduced graphene oxide as compared to mechanically exfoliated or chemical vapor deposition grown graphene. The nonlinearity makes it applicable to scattering samples (such as tissue) as opposed to previous methods, such as transmission. This was demonstrated by high-resolution imaging of breast cancer cells incubated with graphene flakes.

  11. Effective elastic mechanical properties of single layer graphene sheets.

    PubMed

    Scarpa, F; Adhikari, S; Srikantha Phani, A

    2009-02-11

    The elastic moduli of single layer graphene sheet (SLGS) have been a subject of intensive research in recent years. Calculations of these effective properties range from molecular dynamic simulations to use of structural mechanical models. On the basis of mathematical models and calculation methods, several different results have been obtained and these are available in the literature. Existing mechanical models employ Euler-Bernoulli beams rigidly jointed to the lattice atoms. In this paper we propose truss-type analytical models and an approach based on cellular material mechanics theory to describe the in-plane linear elastic properties of the single layer graphene sheets. In the cellular material model, the C-C bonds are represented by equivalent mechanical beams having full stretching, hinging, bending and deep shear beam deformation mechanisms. Closed form expressions for Young's modulus, the shear modulus and Poisson's ratio for the graphene sheets are derived in terms of the equivalent mechanical C-C bond properties. The models presented provide not only quantitative information about the mechanical properties of SLGS, but also insight into the equivalent mechanical deformation mechanisms when the SLGS undergoes small strain uniaxial and pure shear loading. The analytical and numerical results from finite element simulations show good agreement with existing numerical values in the open literature. A peculiar marked auxetic behaviour for the C-C bonds is identified for single graphene sheets under pure shear loading.

  12. Production of graphene oxide from pitch-based carbon fiber.

    PubMed

    Lee, Miyeon; Lee, Jihoon; Park, Sung Young; Min, Byunggak; Kim, Bongsoo; In, Insik

    2015-07-09

    Pitch-based graphene oxide (p-GO) whose compositional/structural features are comparable to those of graphene oxide (GO) was firstly produced by chemical exfoliation of pitch-based carbon fiber rather than natural graphite. Incorporation of p-GO as nanofillers into poly(methyl methacrylate) (PMMA) as a matrix polymer resulted in excellent mechanical reinforcement. p-GO/PMMA nanocomposite (1 wt.-% p-GO) demonstrated 800% higher modulus of toughness of neat PMMA.

  13. Production of graphene oxide from pitch-based carbon fiber

    NASA Astrophysics Data System (ADS)

    Lee, Miyeon; Lee, Jihoon; Park, Sung Young; Min, Byunggak; Kim, Bongsoo; in, Insik

    2015-07-01

    Pitch-based graphene oxide (p-GO) whose compositional/structural features are comparable to those of graphene oxide (GO) was firstly produced by chemical exfoliation of pitch-based carbon fiber rather than natural graphite. Incorporation of p-GO as nanofillers into poly(methyl methacrylate) (PMMA) as a matrix polymer resulted in excellent mechanical reinforcement. p-GO/PMMA nanocomposite (1 wt.-% p-GO) demonstrated 800% higher modulus of toughness of neat PMMA.

  14. Production of graphene oxide from pitch-based carbon fiber

    PubMed Central

    Lee, Miyeon; Lee, Jihoon; Park, Sung Young; Min, Byunggak; Kim, Bongsoo; In, Insik

    2015-01-01

    Pitch-based graphene oxide (p-GO) whose compositional/structural features are comparable to those of graphene oxide (GO) was firstly produced by chemical exfoliation of pitch-based carbon fiber rather than natural graphite. Incorporation of p-GO as nanofillers into poly(methyl methacrylate) (PMMA) as a matrix polymer resulted in excellent mechanical reinforcement. p-GO/PMMA nanocomposite (1 wt.-% p-GO) demonstrated 800% higher modulus of toughness of neat PMMA. PMID:26156067

  15. Electromechanical resonators from graphene sheets.

    PubMed

    Bunch, J Scott; van der Zande, Arend M; Verbridge, Scott S; Frank, Ian W; Tanenbaum, David M; Parpia, Jeevak M; Craighead, Harold G; McEuen, Paul L

    2007-01-26

    Nanoelectromechanical systems were fabricated from single- and multilayer graphene sheets by mechanically exfoliating thin sheets from graphite over trenches in silicon oxide. Vibrations with fundamental resonant frequencies in the megahertz range are actuated either optically or electrically and detected optically by interferometry. We demonstrate room-temperature charge sensitivities down to 8 x 10(-4) electrons per root hertz. The thinnest resonator consists of a single suspended layer of atoms and represents the ultimate limit of two-dimensional nanoelectromechanical systems.

  16. Thermal, mechanical and dielectric properties of poly(vinyl alcohol)/graphene oxide composites

    NASA Astrophysics Data System (ADS)

    Rathod, Sunil G.; Bhajantri, R. F.; Ravindrachary, V.; Pujari, P. K.; Sheela, T.; Naik, Jagadish

    2014-04-01

    In this work the composite films of poly(vinyl alcohol) (PVA) doped with functionalized Graphene Oxide (GO) were prepared by solution casting method. The films were characterized using FT-IR, DSC, XRD, mechanical properties and dielectric studies at room temperature. FTIR spectra shows the formation of hydrogen bonds between hydroxyl groups of PVA and the hydroxy groups of GO. The DSC thermograms shows the addition of GO to PVA greatly improves the thermal stability of the composites. XRD patterns shows that the GO exfoliated and uniformly dispersed in PVA matrix. Mechanical properties are significantly improved in PVA/GO composites. The tensile strength increased from 8.2 to 13.7 MPa and the Young's modulus increased from 7.5 to 24.8 MPa for 5 wt% GO doped sample. Dielectric spectroscopy showed a highest dielectric constant for the 5 wt% GO doped PVA films. This work provides a potential design strategy on PVA/GO composite, which would lead to higher-performance, flexible dielectric materials, high charge-storage devices.

  17. Electronic, optical, mechanical and thermoelectric properties of graphene

    NASA Astrophysics Data System (ADS)

    Muley, Sarang Vilas

    Graphene, a two-dimensional allotrope of graphite with sp2 bonded carbon atoms, is arranged in honeycomb structure. Its quasi one-dimensional form is graphene nanoribbon (GNR). Graphene related materials have been found to display excellent electronic, chemical, mechanical properties along with uniquely high thermal conductivity, electrical conductivity and high optical transparency. With excellent electrical characteristics such as high carrier transport properties, quantum Hall effect at room temperature and unusual magnetic properties, graphene has applications in optoelectronic devices. Electronically, graphene is a zero bandgap semiconductor making it essential to tailor its structure for obtaining specific band structure. Narrow GNRs are known to open up bandgap and found to exhibit variations for different chiralities i.e., armchair and zigzag. Doping graphene, with p- or n- type elements, is shown to exhibit bandgap in contrast to pristine graphene. In this study, optical properties including dielectric functions, absorption coefficient, transmittance, and reflectance, as a function of wavelength and incident energy, are studied. Refractive index and extinction coefficient of pristine graphene are presented. A key optical property in the infrared region, emissivity, is studied as a function of wavelength for various multilayered configurations having graphene as one of the constituent layers. Application of such a structure is in the fabrication of a Hot Electron Bolometer (a sensor that operates on the basis of temperature-dependent electrical resistance). Graphene is found to have very high elastic modulus and intrinsic strength. Nanoindentation of graphene sheet is simulated to study the force versus displacement curves. Effects of variation of diameter of indenter, speed of indentation and number of layers of graphene on the mechanical properties are presented. Shrinking size of electronic devices has led to an acute need for thermal management. This

  18. Production of biologically safe and mechanically improved reduced graphene oxide/hydroxyapatite composites

    NASA Astrophysics Data System (ADS)

    Elif, Öztürk; Belma, Özbek; İlkay, Şenel

    2017-01-01

    As research trends included the improvement of the mechanical properties of hydroxyapatite (HA) for biological applications, HA was reinforced with different concentrations of reduced graphene oxide (RGO) in HA. In this context, graphene oxide was synthesized using the chemical exfoliation method and reduced using an environmentally safe and green method. As a green method, RGO was obtained using Melissa officinalis (melisa) extract and used as a second phase combination to the HA structure. RGO-HA composites with different concentrations of RGO in HA (0.25, 0.5, 1.0, 2.0% wt.) were prepared using the liquid precipitation method. Then they were pelleted and sintered. Characterization studies were carried out using UV-vis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), zetasizer (ZS), x-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images. The mechanical properties of the composites were analyzed using a universal testing machine. Compared to pure HA, the compressive strength values of composites were increased significantly with the increase in RGO content. The optimum increase was observed for the RGO-HA (1%) composite, which was 3.2 times higher than the pure HA sample. Therefore, the RGO-HA (1%) composite was chosen as the best composition, and its cytotoxic and proliferative effects were examined using a minimum essential media elution test and a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The results showed that RGO-HA (1%) composites are biocompatible and even though they are proliferative at concentrations lower than 25%.

  19. The Effect of Defects on Mechanical Properties and Failure Mechanisms of Graphene

    NASA Astrophysics Data System (ADS)

    Willman, Jonathan; Gonzalez, Joseph; Perriot, Romain; Oleynik, Ivan

    Recent experiments involving nanoindentation of graphene have demonstrated counterintuitive increasing of Young's modulus with increasing concentrations of point defects in graphene. To fully resolve this controversy we perform large-scale molecular dynamics simulations of graphene nanoindentation. The relaible description of interatomic interactions is achieved by using recently developed screened environment-dependent bond order (SED-REBO) potential. The elastic properties of the defective graphene, the breaking strength and the mechanisms of fracture under indenter are investigated as a function of defect concentration and other factors specific to Atomic Force Microscopy (AFM) nanoindentation experiments.

  20. Nonlinear mechanics of graphene membranes and related systems

    NASA Astrophysics Data System (ADS)

    De Alba, Roberto

    Micro- and nano-mechanical resonators with low mass and high vibrational frequency are often studied for applications in mass and force detection where they can offer unparalleled precision. They are also excellent systems with which to study nonlinear phenomena and fundamental physics due to the numerous routes through which they can couple to each other or to external systems. In this work we study the structural, thermal, and nonlinear properties of various micro-mechanical systems. First, we present a study of graphene-coated silicon nitride membranes; the resulting devices demonstrate the high quality factors of silicon nitride as well as the useful electrical and optical properties of graphene. We then study nonlinear mechanics in pure graphene membranes, where all vibrational eigenmodes are coupled to one another through the membrane tension. This effect enables coherent energy transfer from one mechanical mode to another, in effect creating a graphene mechanics-based frequency mixer. In another experiment, we measure the resonant frequency of a graphene membrane over a wide temperature range, 80K - 550K, to determine whether or not it demonstrates the negative thermal expansion coefficient predicted by prevailing theories; our results indicate that this coefficient is positive at low temperatures - possibly due to polymer contaminants on the graphene surface - and negative above room temperature. Lastly, we study optically-induced self-oscillation in metal-coated silicon nitride nanowires. These structures exhibit self-oscillation at extremely low laser powers ( 1muW incident on the nanowire), and we use this photo-thermal effect to counteract the viscous air-damping that normally inhibits micro-mechanical motion.

  1. Ultrafine nickel oxide quantum dots enbedded with few-layer exfoliative graphene for an asymmetric supercapacitor: Enhanced capacitances by alternating voltage

    NASA Astrophysics Data System (ADS)

    Jing, Mingjun; Wang, Chiwei; Hou, Hongshuai; Wu, Zhibin; Zhu, Yirong; Yang, Yingchang; Jia, Xinnan; Zhang, Yan; Ji, Xiaobo

    2015-12-01

    A green and one-step method of electrochemical alternating voltage has been utilized to form NiO quantum dots/graphene flakes (NiO-dots/Gh) for supercapacitor applications. NiO quantum dots (∼3 nm) are uniformly deposited on few-layer graphene surfaces by oxygen functional groups on graphene surface that is naturally utilized to bridge NiO and graphene through Ni-O-C bands, which exhibits outstanding specific capacitance 1181.1 F g-1 at a current density of 2.1 A g-1 and rate behavior 66.2% at 42 A g-1 as NiO dots can be fleetly wired up to current collector through the underlying graphene two-dimensional layers. The NiO-dots/Gh composite is further undertaken in asymmetric supercapacitors with high energy density (27.3 Wh kg-1 at 1562.6 W kg-1).

  2. Hierarchical graphene nanoribbon assemblies feature unique electronic and mechanical properties

    NASA Astrophysics Data System (ADS)

    Xu, Zhiping; Buehler, Markus J.

    2009-09-01

    Graphene nanoribbons present intriguing electronic properties due to their characteristic size and edge shape, and have been suggested for a wide range of applications from electronics to electromechanical systems. To bridge the scales from their nanostructural geometry—the key for their unique properties—to the requirements critical for large-scale electronics and device applications, here we propose a de novo hierarchical material assembled from functionalized graphene nanoribbons stabilized through hydrogen bonds, mimicking the structure of beta-sheet proteins. By investigating their mechanical and electronic properties through first principles calculations, we demonstrate that hierarchical graphene nanoribbons not only preserve the unique electronic properties of individual graphene nanoribbons in the bulk, but are also energetically and mechanically stable. Specifically, we find that the energy gap of the bulk material shrinks as the width of the constituting graphene nanoribbons increases. The tuning of bulk material properties through controlling the nanostructure enables the synthesis of a broader class of biomimetic multifunctional mechanomutable and electromutable nanomaterials for electromechanical applications.

  3. Graphene doping methods and device applications.

    PubMed

    Oh, Jong Sik; Kim, Kyong Nam; Yeom, Geun Young

    2014-02-01

    Graphene has recently been studied as a promising material to replace and enhance conventional electronic materials in various fields such as electronics, photovoltaics, sensors, etc. However, for the electronic applications of graphene prepared by various techniques such as chemical vapor deposition, chemical exfoliation, mechanical exfoliation, etc., critical limitations are found due to the defects in the graphene in addition to the absence of a semiconducting band gap. For that, many researchers have investigated the doped graphene which is effective to tailor its electronic property and chemical reactivity. This work presents a review of the various graphene doping methods and their device applications. As doping methods, direct synthesis method and post treatment method could be categorized. Because the latter case has been widely investigated and used in various electronic applications, we will focus on the post treatment method. Post treatment method could be further classified into wet and dry doping methods. In the case of wet doping, acid treatment, metal chloride, and organic material coating are the methods used to functionalize graphene by using dip-coating, spin coating, etc. Electron charge transfer achieved from graphene to dopants or from dopants to graphene makes p-type or n-type graphenes, respectively, with sheet resistance reduction effect. In the case of dry doping, it can be further categorized into electrostatic field method, evaporation method, thermal treatment method, plasma treatment method, etc. These doping techniques modify Fermi energy level of graphene and functionalize the property of graphene. Finally, some perspectives and device applications of doped graphene are also briefly discussed.

  4. Graphene Young's modulus: Molecular mechanics and DFT treatments

    NASA Astrophysics Data System (ADS)

    Memarian, F.; Fereidoon, A.; Darvish Ganji, M.

    2015-09-01

    Despite of the numerous theoretical and experimental investigations on the mechanical properties of graphene as a unique nano-structured material, a precious value for this important property has not yet been presented. In the present work, the Young's modulus of single layer graphene sheet has been investigated by using comprehensive classic as well as quantum mechanics (QM) calculations. Molecular mechanics (MM) approach with various well-defined force-fields such as AIREBO, Tresoff and EDIP potentials have been considered. In QM category, several conventional methods (DFTB and DFT-LDA/GGA) have been employed. The results show that EDIP potential method predicts more accurately the graphene Young's modulus value compared to experimental results. Furthermore, despite the various theoretical results reported elsewhere, the EDIP potential calculations result reveals that Young's modulus has the same value at both zigzag and armchair directions. From the results obtained here, we found that among the various MM and QM methods considered here the EDIP method seems to be the most convenient method for evaluation of both structural geometries and mechanical properties of carbon based graphene-like materials. This is because of its less computational costs accompanied with reliable results comparable with the experiments.

  5. Mechanical control over valley magnetotransport in strained graphene

    NASA Astrophysics Data System (ADS)

    Ma, Ning; Zhang, Shengli; Liu, Daqing

    2016-05-01

    Recent experiments report that the graphene exhibits Landau levels (LLs) that form in the presence of a uniform strain pseudomagnetic field with magnitudes up to hundreds of tesla. We further reveal that the strain removes the valley degeneracy in LLs, and leads to a significant valley polarization with inversion symmetry broken. This accordingly gives rise to the well separated valley Hall plateaus and Shubnikov-de Haas oscillations. These effects are absent in strainless graphene, and can be used to generate and detect valley polarization by mechanical means, forming the basis for the new paradigm "valleytronics" applications.

  6. Determination of Young's Modulus of Graphene by Raman Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Ung; Yoon, Duhee; Cheong, Hyeonsik

    2012-02-01

    The mechanical properties of graphene are interesting research subjects because its Young's modulus and strength are extremely high. Values of ˜1 TPa for the Young's modulus have been reported [Lee et al. Science, 321, 385 (2008), Koenig et al. Nat. Nanotech. 6, 543 (2011)]. We made a graphene sample on a SiO2/Si substrate with closed-bottom holes by mechanical exfoliation. A pressure difference across the graphene membrane was applied by putting the sample in a vacuum chamber. This pressure difference makes the graphene membrane bulge upward like a balloon. By measuring the shifts of the Raman G and 2D bands, we estimated the amount of strain on the graphene membrane. By comparing the strain estimated from the Raman measurements with numerical simulations based on the finite element method, we obtained the Young's modulus of graphene.

  7. Mechanical strength of nanoporous graphene as a desalination membrane.

    PubMed

    Cohen-Tanugi, David; Grossman, Jeffrey C

    2014-11-12

    Recent advances in the development of nanoporous graphene (NPG) hold promise for the future of water supply by reverse osmosis (RO) desalination. But while previous studies have highlighted the potential of NPG as an RO membrane, there is less understanding as to whether NPG is strong enough to maintain its mechanical integrity under the high hydraulic pressures inherent to the RO desalination process. Here, we show that an NPG membrane can maintain its mechanical integrity in RO but that the choice of substrate for graphene is critical to this performance. Using molecular dynamics simulations and continuum fracture mechanics, we show that an appropriate substrate with openings smaller than 1 μm would allow NPG to withstand pressures exceeding 57 MPa (570 bar) or ten times more than typical pressures for seawater RO. Furthermore, we demonstrate that NPG membranes exhibit an unusual mechanical behavior in which greater porosity may help the membrane withstand even higher pressures.

  8. Van der Waals epitaxy and characterization of hexagonal boron nitride nanosheets on graphene

    NASA Astrophysics Data System (ADS)

    Song, Yangxi; Zhang, Changrui; Li, Bin; Ding, Guqiao; Jiang, Da; Wang, Haomin; Xie, Xiaoming

    2014-07-01

    Graphene is highly sensitive to environmental influences, and thus, it is worthwhile to deposit protective layers on graphene without impairing its excellent properties. Hexagonal boron nitride (h-BN), a well-known dielectric material, may afford the necessary protection. In this research, we demonstrated the van der Waals epitaxy of h-BN nanosheets on mechanically exfoliated graphene by chemical vapor deposition, using borazine as the precursor to h-BN. The h-BN nanosheets had a triangular morphology on a narrow graphene belt but a polygonal morphology on a larger graphene film. The h-BN nanosheets on graphene were highly crystalline, except for various in-plane lattice orientations. Interestingly, the h-BN nanosheets preferred to grow on graphene than on SiO2/Si under the chosen experimental conditions, and this selective growth spoke of potential promise for application to the preparation of graphene/h-BN superlattice structures fabricated on SiO2/Si.

  9. Van der Waals epitaxy and characterization of hexagonal boron nitride nanosheets on graphene.

    PubMed

    Song, Yangxi; Zhang, Changrui; Li, Bin; Ding, Guqiao; Jiang, Da; Wang, Haomin; Xie, Xiaoming

    2014-01-01

    Graphene is highly sensitive to environmental influences, and thus, it is worthwhile to deposit protective layers on graphene without impairing its excellent properties. Hexagonal boron nitride (h-BN), a well-known dielectric material, may afford the necessary protection. In this research, we demonstrated the van der Waals epitaxy of h-BN nanosheets on mechanically exfoliated graphene by chemical vapor deposition, using borazine as the precursor to h-BN. The h-BN nanosheets had a triangular morphology on a narrow graphene belt but a polygonal morphology on a larger graphene film. The h-BN nanosheets on graphene were highly crystalline, except for various in-plane lattice orientations. Interestingly, the h-BN nanosheets preferred to grow on graphene than on SiO2/Si under the chosen experimental conditions, and this selective growth spoke of potential promise for application to the preparation of graphene/h-BN superlattice structures fabricated on SiO2/Si.

  10. Thermally exfoliated graphite oxide

    NASA Technical Reports Server (NTRS)

    Prud'Homme, Robert K. (Inventor); Aksay, Ilhan A. (Inventor); Abdala, Ahmed (Inventor)

    2011-01-01

    A modified graphite oxide material contains a thermally exfoliated graphite oxide with a surface area of from about 300 sq m/g to 2600 sq m/g, wherein the thermally exfoliated graphite oxide displays no signature of the original graphite and/or graphite oxide, as determined by X-ray diffraction.

  11. Preparation of graphene by jet cavitation.

    PubMed

    Shen, Zhigang; Li, Jinzhi; Yi, Min; Zhang, Xiaojing; Ma, Shulin

    2011-09-07

    Despite its bright prospects, graphene faces challenges including issues concerning mass production. Here we present a totally green approach whereby common crystal graphite can be exfoliated into graphene sheets in aqueous solution by jet cavitation. This is possible mainly because the tensile stress caused by graphite-solution interfacial reflection of compressive waves acts an intensive 'suction disk' on the graphite flakes. We confirm the presence of graphene sheets by diverse characterizations. The graphene yield by our method is estimated as ∼ 4 wt%, which could potentially be improved by further processing. The method, of a mechanical nature, is powerful compared to the traditional low-throughput micromechanical cleavage. Our work here illustrates jet cavitation as a facile, low cost, timesaving and laborsaving route, which can potentially be scaled up to mass production of graphene.

  12. Preparation of graphene by jet cavitation

    NASA Astrophysics Data System (ADS)

    Shen, Zhigang; Li, Jinzhi; Yi, Min; Zhang, Xiaojing; Ma, Shulin

    2011-09-01

    Despite its bright prospects, graphene faces challenges including issues concerning mass production. Here we present a totally green approach whereby common crystal graphite can be exfoliated into graphene sheets in aqueous solution by jet cavitation. This is possible mainly because the tensile stress caused by graphite-solution interfacial reflection of compressive waves acts an intensive 'suction disk' on the graphite flakes. We confirm the presence of graphene sheets by diverse characterizations. The graphene yield by our method is estimated as ~ 4 wt%, which could potentially be improved by further processing. The method, of a mechanical nature, is powerful compared to the traditional low-throughput micromechanical cleavage. Our work here illustrates jet cavitation as a facile, low cost, timesaving and laborsaving route, which can potentially be scaled up to mass production of graphene.

  13. High Yield Chemical Vapor Deposition Growth of High Quality Large-Area AB Stacked Bilayer Graphene

    PubMed Central

    Liu, Lixin; Zhou, Hailong; Cheng, Rui; Yu, Woo Jong; Liu, Yuan; Chen, Yu; Shaw, Jonathan; Zhong, Xing; Huang, Yu; Duan, Xiangfeng

    2012-01-01

    Bernal stacked (AB stacked) bilayer graphene is of significant interest for functional electronic and photonic devices due to the feasibility to continuously tune its band gap with a vertical electrical field. Mechanical exfoliation can be used to produce AB stacked bilayer graphene flakes but typically with the sizes limited to a few micrometers. Chemical vapor deposition (CVD) has been recently explored for the synthesis of bilayer graphene but usually with limited coverage and a mixture of AB and randomly stacked structures. Herein we report a rational approach to produce large-area high quality AB stacked bilayer graphene. We show that the self-limiting effect of graphene growth on Cu foil can be broken by using a high H2/CH4 ratio in a low pressure CVD process to enable the continued growth of bilayer graphene. A high temperature and low pressure nucleation step is found to be critical for the formation of bilayer graphene nuclei with high AB stacking ratio. A rational design of a two-step CVD process is developed for the growth of bilayer graphene with high AB stacking ratio (up to 90 %) and high coverage (up to 99 %). The electrical transport studies demonstrated that devices made of the as-grown bilayer graphene exhibit typical characteristics of AB stacked bilayer graphene with the highest carrier mobility exceeding 4,000 cm2/V·s at room temperature, comparable to that of the exfoliated bilayer graphene. PMID:22906199

  14. Mechanically tunable terahertz graphene plasmonics using soft metasurface

    NASA Astrophysics Data System (ADS)

    Wang, Li; Liu, Xin; Zang, Jianfeng

    2016-12-01

    This letter presents a new approach to continuously tune the resonances of graphene plasmons in terahertz soft metasurface. The continuous tunability of plasmon resonance is either unachievable in conventional plasmonic materials like noble metals or requires gate voltage regulation in graphene. Here we investigate a simplest form of terahertz metasurface, graphene nanoribbon arrays (GNRAs), and demonstrate the graphene plasmon resonance modes can be tailored by mechanical deformation of the elastomeric substrate using finite element method (FEM). By integrating the electric doping with substrate deformation, we have managed to tune the resonance wavelength from 13.7 to 50.6 μm. The 36.9 μm tuning range is nearly doubled compared with that by electric doping regulation only. Moreover, we observe the plasmon coupling effect in GNRAs on waved substrate and its evolution with substrate curvature. A new decoupling mechanism enabled by the out-of-plane separation of the adjacent ribbons is revealed. The out-of-plane setup of plasmonic components extends the fabrication of plasmonic devices into three-dimensional space, which simultaneously increases the nanoribbon density and decreases the coupling strength. Our findings provide an additional degree of freedom to design reconfigurable metasurfaces and metadevices.

  15. Electronic and Mechanical Properties of Hydrogenated Irradiated and Amorphous Graphene

    NASA Astrophysics Data System (ADS)

    Weerasinghe, Asanka; Ramasubramaniam, Ashwin; Maroudas, Dimitrios

    Defect engineering and chemical functionalization of graphene are promising routes for fabrication of carbon nanostructures and 2D metamaterials with unique properties and function. Here, we use hydrogenation of irradiated, including irradiation-induced amorphous, graphene as a means of studying chemical functionalization effects on its electronic structure and mechanical response. We use molecular-dynamics simulations based on a reliable bond-order potential to prepare the hydrogenated configurations and carry out dynamic deformation tests at constant strain rate and temperature. Our mechanical tests show that hydrogenation does not affect the ultimate tensile strength (UTS) of the irradiated graphene sheet if the hydrogenated C atoms remain sp2-hybridized; however, upon inducing sp3 hybridization of these C atoms, UTS decreases by about 10 GPa. Furthermore, the fracture strain of the irradiated structure decreases by up to 30% upon hydrogenation independent of the hybridization type. We also report results for the electronic structure of hydrogenated configurations based on a density-functional tight-binding approach and assess the potential for tuning the electronic properties of these defective, functionalized graphenes.

  16. Graphene Synthesis and Characterization

    DTIC Science & Technology

    2015-04-08

    Carbon source onto copper substrates, and the exfoliation of graphite (chemical and electrochemical ). These methods have a great importance for...by Ching-Yuan Su et al. [12] and involves the electrochemical exfoliation of graphite foil to obtain high quality graphene. The lateral size of the...species, which can be reduced in hydrogen at 450°C. Using the above techniques (CVD and chemical/ electrochemical exfoliation) our goal is to study the

  17. Fabrication of graphene field-effect transistor on top of ferroelectric single-crystal substrate

    NASA Astrophysics Data System (ADS)

    Park, Nahee; Kang, Haeyong; Lee, Yourack; Kim, Jeong-Gyun; Kim, Joong-Gyu; Yun, Yoojoo; Park, Jeongmin; Kim, Taesoo; Kim, Jung Ho; Jin, Youngjo; Shin, Yong Seon; Lee, Young Hee; Suh, Dongseok

    2015-03-01

    In the analysis of Graphene field-effect transistor, the substrate material which has the direct contact with Graphene layer plays an important in the device performance. In this presentation, we have tested PMN-PT(i.e.(1-x)Pb(Mg1/3Nb2/3) O3-xPbTiO3) substrate as a gate dielectric of Graphene field-effect transistor. Unlike the case of previously used substrates such as silicon oxide or hexagonal Boron-Nitride(h-BN), the PMN-PT substrate can induce giant amount of surface charge that is directly injected to the attached Graphene layer due to its ferroelectric property. And the hysteresis of polarization versus electric field of PMN-PT can cause the device to show the ferroelectric nonvolatile memory operation. We had successfully fabricated Graphene field-effect transistor using the mechanically exfoliated Graphene layer transferred on the PMN-PT(001) substrate. Unlike the case of mechanical exfoliation on the surface of silicon-oxide or the Poly(methyl methacrylate) (PMMA), the weak adhesion properties between graphene and PMNPT required the pretreatment on PMMA before the exfoliation process. The device performance is analyzed in terms of the effect of ferro- and piezo-electric effect of PMNPT substrate.

  18. Graphene transfer: key for applications

    NASA Astrophysics Data System (ADS)

    Kang, Junmo; Shin, Dolly; Bae, Sukang; Hong, Byung Hee

    2012-08-01

    The first micrometer-sized graphene flakes extracted from graphite demonstrated outstanding electrical, mechanical and chemical properties, but they were too small for practical applications. However, the recent advances in graphene synthesis and transfer techniques have enabled various macroscopic applications such as transparent electrodes for touch screens and light-emitting diodes (LEDs) and thin-film transistors for flexible electronics in particular. With such exciting potential, a great deal of effort has been put towards producing larger size graphene in the hopes of industrializing graphene production. Little less than a decade after the first discovery, graphene now can be synthesized up to 30 inches in its diagonal size using chemical vapour deposition methods. In making this possible, it was not only the advances in the synthesis techniques but also the transfer methods that deliver graphene onto target substrates without significant mechanical damage. In this article, the recent advancements in transferring graphene to arbitrary substrates will be extensively reviewed. The methods are categorized into mechanical exfoliation, polymer-assisted transfer, continuous transfer by roll-to-roll process, and transfer-free techniques including direct synthesis on insulating substrates.

  19. Chemical vapor deposition of graphene single crystals.

    PubMed

    Yan, Zheng; Peng, Zhiwei; Tour, James M

    2014-04-15

    As a two-dimensional (2D) sp(2)-bonded carbon allotrope, graphene has attracted enormous interest over the past decade due to its unique properties, such as ultrahigh electron mobility, uniform broadband optical absorption and high tensile strength. In the initial research, graphene was isolated from natural graphite, and limited to small sizes and low yields. Recently developed chemical vapor deposition (CVD) techniques have emerged as an important method for the scalable production of large-size and high-quality graphene for various applications. However, CVD-derived graphene is polycrystalline and demonstrates degraded properties induced by grain boundaries. Thus, the next critical step of graphene growth relies on the synthesis of large graphene single crystals. In this Account, we first discuss graphene grain boundaries and their influence on graphene's properties. Mechanical and electrical behaviors of CVD-derived polycrystalline graphene are greatly reduced when compared to that of exfoliated graphene. We then review four representative pathways of pretreating Cu substrates to make millimeter-sized monolayer graphene grains: electrochemical polishing and high-pressure annealing of Cu substrate, adding of additional Cu enclosures, melting and resolidfying Cu substrates, and oxygen-rich Cu substrates. Due to these pretreatments, the nucleation site density on Cu substrates is greatly reduced, resulting in hexagonal-shaped graphene grains that show increased grain domain size and comparable electrical properties as to exfoliated graphene. Also, the properties of graphene can be engineered by its shape, thickness and spatial structure. Thus, we further discuss recently developed methods of making graphene grains with special spatial structures, including snowflakes, six-lobed flowers, pyramids and hexagonal graphene onion rings. The fundamental growth mechanism and practical applications of these well-shaped graphene structures should be interesting topics and

  20. Promising applications of graphene and graphene-based nanostructures

    NASA Astrophysics Data System (ADS)

    Nguyen, Bich Ha; Hieu Nguyen, Van

    2016-06-01

    The present article is a review of research works on promising applications of graphene and graphene-based nanostructures. It contains five main scientific subjects. The first one is the research on graphene-based transparent and flexible conductive films for displays and electrodes: efficient method ensuring uniform and controllable deposition of reduced graphene oxide thin films over large areas, large-scale pattern growth of graphene films for stretchble transparent electrodes, utilization of graphene-based transparent conducting films and graphene oxide-based ones in many photonic and optoelectronic devices and equipments such as the window electrodes of inorganic, organic and dye-sensitized solar cells, organic light-emitting diodes, light-emitting electrochemical cells, touch screens, flexible smart windows, graphene-based saturated absorbers in laser cavities for ultrafast generations, graphene-based flexible, transparent heaters in automobile defogging/deicing systems, heatable smart windows, graphene electrodes for high-performance organic field-effect transistors, flexible and transparent acoustic actuators and nanogenerators etc. The second scientific subject is the research on conductive inks for printed electronics to revolutionize the electronic industry by producing cost-effective electronic circuits and sensors in very large quantities: preparing high mobility printable semiconductors, low sintering temperature conducting inks, graphene-based ink by liquid phase exfoliation of graphite in organic solutions, and developing inkjet printing technique for mass production of high-quality graphene patterns with high resolution and for fabricating a variety of good-performance electronic devices, including transparent conductors, embedded resistors, thin-film transistors and micro supercapacitors. The third scientific subject is the research on graphene-based separation membranes: molecular dynamics simulation study on the mechanisms of the transport of

  1. Mechanism of strength reduction along the graphenization pathway

    PubMed Central

    Gamboa, Antonio; Farbos, Baptiste; Aurel, Philippe; Vignoles, Gérard L.; Leyssale, Jean-Marc

    2015-01-01

    Even though polycrystalline graphene has shown a surprisingly high tensile strength, the influence of inherent grain boundaries on such property remains unclear. We study the fracture properties of a series of polycrystalline graphene models of increasing thermodynamic stability, as obtained from a long molecular dynamics simulation at an elevated temperature. All of the models show the typical and well-documented brittle fracture behavior of polycrystalline graphene; however, a clear decrease in all fracture properties is observed with increasing annealing time. The remarkably high fracture properties obtained for the most disordered (less annealed) structures arise from the formation of many nonpropagating prefracture cracks, significantly retarding failure. The stability of these reversible cracks is due to the nonlocal character of load transfer after a bond rupture in very disordered systems. It results in an insufficient strain level on neighboring bonds to promote fracture propagation. Although polycrystallinity seems to be an unavoidable feature of chemically synthesized graphenes, these results suggest that targeting highly disordered states might be a convenient way to obtain improved mechanical properties. PMID:26702443

  2. Advances in graphene-related technologies: synthesis, devices and outlook.

    PubMed

    Frazier, R M; Hough, W L; Chopra, N; Hathcock, K W

    2012-06-01

    Graphene has been the subject of many scientific investigations since exfoliation methods facilitated isolation of the two-dimensional material. During this time, new synthesis methods have been developed which have opened technological opportunities previously hindered by synthetic constraints. An update on the recent advances in graphene-based technologies, including synthesis and applications into electrical, mechanical and thermal uses will be covered. A special focus on the patent space and commercial landscape will be given in an effort to identify current trends and future commercialization of graphene-related technologies.

  3. Raman Sensitive Degradation and Etching Dynamics of Exfoliated Black Phosphorus

    NASA Astrophysics Data System (ADS)

    Alsaffar, Fadhel; Alodan, Sarah; Alrasheed, Abdul; Alhussain, Abdulrahman; Alrubaiq, Noura; Abbas, Ahmad; Amer, Moh. R.

    2017-03-01

    Layered black phosphorus has drawn much attention due to the existence of a band gap compared to the widely known graphene. However, environmental stability of black phosphorus is still a major issue, which hinders the realization of practical device applications. Here, we spatially Raman map exfoliated black phosphorus using confocal fast-scanning technique at different time intervals. We observe a Raman intensity modulation for , B2g, and modes. This Raman modulation is found to be caused by optical interference, which gives insights into the oxidation mechanism. Finally, we examine the fabrication compatible PMMA coating as a viable passivation layer. Our measurements indicate that PMMA passivated black phosphorus thin film flakes can stay pristine for a period of 19 days when left in a dark environment, allowing sufficient time for further nanofabrication processing. Our results shed light on black phosphorus degradation which can aid future passivation methods.

  4. Raman Sensitive Degradation and Etching Dynamics of Exfoliated Black Phosphorus

    PubMed Central

    Alsaffar, Fadhel; Alodan, Sarah; Alrasheed, Abdul; Alhussain, Abdulrahman; Alrubaiq, Noura; Abbas, Ahmad; Amer, Moh. R.

    2017-01-01

    Layered black phosphorus has drawn much attention due to the existence of a band gap compared to the widely known graphene. However, environmental stability of black phosphorus is still a major issue, which hinders the realization of practical device applications. Here, we spatially Raman map exfoliated black phosphorus using confocal fast-scanning technique at different time intervals. We observe a Raman intensity modulation for , B2g, and modes. This Raman modulation is found to be caused by optical interference, which gives insights into the oxidation mechanism. Finally, we examine the fabrication compatible PMMA coating as a viable passivation layer. Our measurements indicate that PMMA passivated black phosphorus thin film flakes can stay pristine for a period of 19 days when left in a dark environment, allowing sufficient time for further nanofabrication processing. Our results shed light on black phosphorus degradation which can aid future passivation methods. PMID:28317834

  5. Raman Sensitive Degradation and Etching Dynamics of Exfoliated Black Phosphorus.

    PubMed

    Alsaffar, Fadhel; Alodan, Sarah; Alrasheed, Abdul; Alhussain, Abdulrahman; Alrubaiq, Noura; Abbas, Ahmad; Amer, Moh R

    2017-03-20

    Layered black phosphorus has drawn much attention due to the existence of a band gap compared to the widely known graphene. However, environmental stability of black phosphorus is still a major issue, which hinders the realization of practical device applications. Here, we spatially Raman map exfoliated black phosphorus using confocal fast-scanning technique at different time intervals. We observe a Raman intensity modulation for , B2g, and modes. This Raman modulation is found to be caused by optical interference, which gives insights into the oxidation mechanism. Finally, we examine the fabrication compatible PMMA coating as a viable passivation layer. Our measurements indicate that PMMA passivated black phosphorus thin film flakes can stay pristine for a period of 19 days when left in a dark environment, allowing sufficient time for further nanofabrication processing. Our results shed light on black phosphorus degradation which can aid future passivation methods.

  6. Oxidative Stress and Mitochondrial Activation as the Main Mechanisms Underlying Graphene Toxicity against Human Cancer Cells

    PubMed Central

    Jarosz, Anna; Skoda, Marta; Dudek, Ilona; Szukiewicz, Dariusz

    2016-01-01

    Due to the development of nanotechnology graphene and graphene-based nanomaterials have attracted the most attention owing to their unique physical, chemical, and mechanical properties. Graphene can be applied in many fields among which biomedical applications especially diagnostics, cancer therapy, and drug delivery have been arousing a lot of interest. Therefore it is essential to understand better the graphene-cell interactions, especially toxicity and underlying mechanisms for proper use and development. This review presents the recent knowledge concerning graphene cytotoxicity and influence on different cancer cell lines. PMID:26649139

  7. Facile solvothermal synthesis of graphene-MnOOH nanocomposites

    SciTech Connect

    Chen Sheng; Zhu Junwu; Huang Huajie; Zeng Guiyu; Nie Fude; Wang Xin

    2010-11-15

    In this paper, we report a facile solvothermal route capable of aligning MnOOH nanocrystals on graphene. X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations indicate that the exfoliated graphene sheets are decorated randomly by MnOOH nanocrystals, forming well-dispersed graphene-MnOOH nanocomposites. Dissolution-crystallization and oriented attachment are speculated to be the vital mechanisms in the synthetic process. The attachment of additives, such as MnOOH nanoparticles, are found to be beneficial for the exfoliation of GO as well as preventing the restack of graphene sheets. Moreover, cyclic voltammetry (CV) analyses suggest that the electrochemical reversibility is improved by anchoring MnOOH on graphene. Notably, the as-fabricated nanocomposites reveal unusual catalytic performance for the thermal decomposition of ammonium perchlorate (AP) due to the concerted effects of graphene and MnOOH. This template-free method is easy to reproduce, and the process proceeds at a low temperature and can be readily extended to prepare other graphene-based nanocomposites. - Graphical abstract: Manganese oxyhydroxide nanocrystals have been successfully attached onto the graphene sheets via an oriented attachment and dissolution-crystallization process, forming a nanocomposite with unusual catalytic capabilities. Display Omitted

  8. Effect of Surface Morphology on Adhesion of Graphene

    NASA Astrophysics Data System (ADS)

    Lee, Changgu; Cho, Dae-Hyun; Kim, Jin-Seon; Jin, Taiyu; Kang, Jinyoung; Liu, Renlong; Kim, Youngchan; Wang, Lei; Lee, Gwan-Hyoung; Hone, James

    2013-03-01

    The friction of graphene on various substrates, such as SiO2, h-BN, graphite, and mica, was investigated to characterize the adhesion level between graphene and the underlying surface. The friction of graphene on SiO2 decreased with increasing thickness and converged around the penta-layers due to incomplete contact between the two surfaces. However, the friction of graphene on an atomically flat substrate, such as h-BN and graphite, was low and comparable to that of bulk-like graphene. In contrast, the friction of graphene folded onto graphite was indistinguishable with that of mono-layer graphene on SiO2 despite the ultra-smoothness of the graphite. The characterization of the graphene's roughness before and after folding showed that the corrugation of graphene induced by SiO2 morphology was preserved even after it was folded onto an atomically flat substrate. In addition, graphene deposited on mica, when folded, preserved the same corrugation level as before the folding event. We found that graphene, once exfoliated from the bulk crystal, tends to maintain its corrugation level even after it is folded onto an atomically flat substrate and that ultraflatness in both graphene and the substrate is required to achieve the intimate contact necessary for strong adhesion. School of Mechanical Engineering, SKKU Advanced Institute of Nanotechnology

  9. High-yield chemical vapor deposition growth of high-quality large-area AB-stacked bilayer graphene.

    PubMed

    Liu, Lixin; Zhou, Hailong; Cheng, Rui; Yu, Woo Jong; Liu, Yuan; Chen, Yu; Shaw, Jonathan; Zhong, Xing; Huang, Yu; Duan, Xiangfeng

    2012-09-25

    Bernal-stacked (AB-stacked) bilayer graphene is of significant interest for functional electronic and photonic devices due to the feasibility to continuously tune its band gap with a vertical electric field. Mechanical exfoliation can be used to produce AB-stacked bilayer graphene flakes but typically with the sizes limited to a few micrometers. Chemical vapor deposition (CVD) has been recently explored for the synthesis of bilayer graphene but usually with limited coverage and a mixture of AB- and randomly stacked structures. Herein we report a rational approach to produce large-area high-quality AB-stacked bilayer graphene. We show that the self-limiting effect of graphene growth on Cu foil can be broken by using a high H(2)/CH(4) ratio in a low-pressure CVD process to enable the continued growth of bilayer graphene. A high-temperature and low-pressure nucleation step is found to be critical for the formation of bilayer graphene nuclei with high AB stacking ratio. A rational design of a two-step CVD process is developed for the growth of bilayer graphene with high AB stacking ratio (up to 90%) and high coverage (up to 99%). The electrical transport studies demonstrate that devices made of the as-grown bilayer graphene exhibit typical characteristics of AB-stacked bilayer graphene with the highest carrier mobility exceeding 4000 cm(2)/V · s at room temperature, comparable to that of the exfoliated bilayer graphene.

  10. Anomalous Enhancement of Mechanical Properties in the Ammonia Adsorbed Defective Graphene

    PubMed Central

    Ma, Fengxian; Jiao, Yalong; Gu, Yuantong; Bilic, Ante; Chen, Ying; Chen, Zhongfang; Du, Aijun

    2016-01-01

    Pure graphene is known as the strongest material ever discovered. However, the unavoidable defect formation in the fabrication process renders the strength of defective graphene much lower (~14%) than that of its perfect counterpart. By means of density functional theory computations, we systematically explored the effect of gas molecules (H2, N2, NH3, CO, CO2 and O2) adsorption on the mechanical strength of perfect/defective graphene. The NH3 molecule is found to play a dominant role in enhancing the strength of defective graphene by up to ~15.6%, while other gas molecules decrease the strength of graphene with varying degrees. The remarkable strength enhancement can be interpreted by the decomposition of NH3, which saturates the dangling bond and leads to charge redistribution at the defect site. The present work provides basic information for the mechanical failure of gas-adsorbed graphene and guidance for manufacturing graphene-based electromechanical devices. PMID:27667709

  11. Mechanical and electromechanical properties of graphene and their potential application in MEMS

    NASA Astrophysics Data System (ADS)

    Khan, Zulfiqar H.; Kermany, Atieh R.; Öchsner, Andreas; Iacopi, Francesca

    2017-02-01

    Graphene-based micro-electromechanical systems (MEMS) are very promising candidates for next generation miniaturized, lightweight, and ultra-sensitive devices. In this review, we review the progress to date of the assessment of the mechanical, electromechanical, and thermomechanical properties of graphene for application in graphene-based MEMS. Graphene possesses a plethora of outstanding properties—such as a 1 TPa Young’s modulus, exceptionally high 2D failure strength that stems from its sp2 hybridization, and strong sigma bonding between carbon atoms. Such exceptional mechanical properties can enable, for example, graphene-based sound sources capable of generating sound beyond the audible range. The recently engineered piezoelectric properties of atomic force microscope tip-pressed graphene membranes or supported graphene on SiO2 substrates, have paved the way in fabricating graphene-based nano-generators and actuators. On the other hand, graphene’s piezoresistive properties have enabled miniaturized pressure and strain sensors. 2D graphene nano-mechanical resonators can potentially measure ultralow forces, charges and potentially detect single atomic masses. The exceptional tribology of graphene can play a significant role in achieving superlubricity. In addition, the highest reported thermal conductivity of graphene is amenable for use in chips and providing better performing MEMS, as heat is efficiently dissipated. On top of that, graphene membranes could be nano-perforated to realize specialized applications like DNA translocation and desalination. Finally, to ensure stability and reliability of the graphene-based MEMS, adhesion is an important mechanical property that should be considered. In general, graphene could be used as a structural material in resonators, sensors, actuators and nano-generators with better performance and sensitivity than conventional MEMS.

  12. Enhancement mechanisms of graphene in nano-58S bioactive glass scaffold: mechanical and biological performance

    PubMed Central

    Gao, Chengde; Liu, Tingting; Shuai, Cijun; Peng, Shuping

    2014-01-01

    Graphene is a novel material and currently popular as an enabler for the next-generation nanocomposites. Here, we report the use of graphene to improve the mechanical properties of nano-58S bioactive glass for bone repair and regeneration. And the composite scaffolds were fabricated by a homemade selective laser sintering system. Qualitative and quantitative analysis demonstrated the successful incorporation of graphene into the scaffold without obvious structural damage and weight loss. The optimum compressive strength and fracture toughness reached 48.65 ± 3.19 MPa and 1.94 ± 0.10 MPa·m1/2 with graphene content of 0.5 wt%, indicating significant improvements by 105% and 38% respectively. The mechanisms of pull-out, crack bridging, crack deflection and crack tip shielding were found to be responsible for the mechanical enhancement. Simulated body fluid and cell culture tests indicated favorable bioactivity and biocompatibility of the composite scaffold. The results suggest a great potential of graphene/nano-58S composite scaffold for bone tissue engineering applications. PMID:24736662

  13. Two-dimensional Clay and Graphene Nanosheets for Polymer Nanocomposites and Energy Storage Applications

    NASA Astrophysics Data System (ADS)

    Qian, Yuqiang

    Clay and graphene nanosheets are attractive to materials scientists due to their unique structural and physical properties and potentially low cost. This thesis focuses on the surface modification and structure design of clay and graphene nanosheets, targeting special requirements in polymer nanocomposites and energy storage applications. The high aspect ratio and stiffness of clay and graphene nanosheets make them promising candidates to reinforce polymers. However, it is challenging to achieve a good dispersion of the nanosheets in a polymer matrix. It is demonstrated in this study that organic modifications of clay and graphene nanosheets lead to better filler dispersion in polymer matrices. A prepolymer route was developed to achieve clay exfoliation in a polyurethane-vermiculite system. However, the phase-separated structure of the polyurethane matrix was disrupted. Intragallery catalysis was adopted to promote the clay exfoliation during polymerization. With both catalytic and reactive groups on the clay modifier, the polyurethane-vermiculite nanocomposites showed a significant increase in modulus and improved barrier performance, compared to neat polyurethane. The toughening effect of graphene on thermosetting epoxies and unsaturated polyesters (UPs) was also investigated. Various types of graphene with different structures and surface functionalities were incorporated into the thermosetting resin by in situ polymerization. The toughening effect was observed for epoxy nanocomposites at loading levels of less than 0.1 wt%, and a peak of fracture toughness was observed at 0.02 or 0.04 wt% of graphene loadings for all epoxy-graphene systems. A microcrack-crazing mechanism was proposed to explain the fracture behavior of epoxy-graphene systems based on fractography observations. Similar peak behavior of fracture toughness was not observed in UP system. UP nanocomposites with modified graphene oxide showed better mechanical performance than those with unmodified

  14. Lubrication mechanisms of graphene for DLC films scratched by a diamond tip

    NASA Astrophysics Data System (ADS)

    Bai, Lichun; Srikanth, Narasimalu; Zhao, Bo; Liu, Bo; Liu, Zishun; Zhou, Kun

    2016-12-01

    The lubrication behavior of graphene for diamond-like carbon (DLC) films scratched by a diamond tip is investigated by molecular dynamics (MD) simulations. Graphene can efficiently lubricate the DLC film, and its lubrication performance can be improved by the increase of its layer number but be degraded by its defects and large size. The friction mechanisms of graphene during its lubrication highly depend on normal force, F N. Under a small F N, a superlow friction force, F f, is obtained which represents the super-lubrication of graphene. Under a large F N, the F f increases due to the tribochemical reactions of graphene. Such reactions happen before the rupture of the graphene, which indicates the limitations of the super-lubrication of graphene in realistic situations.

  15. Facile solvothermal synthesis of graphene-MnOOH nanocomposites

    NASA Astrophysics Data System (ADS)

    Chen, Sheng; Zhu, Junwu; Huang, Huajie; Zeng, Guiyu; Nie, Fude; Wang, Xin

    2010-11-01

    In this paper, we report a facile solvothermal route capable of aligning MnOOH nanocrystals on graphene. X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations indicate that the exfoliated graphene sheets are decorated randomly by MnOOH nanocrystals, forming well-dispersed graphene-MnOOH nanocomposites. Dissolution-crystallization and oriented attachment are speculated to be the vital mechanisms in the synthetic process. The attachment of additives, such as MnOOH nanoparticles, are found to be beneficial for the exfoliation of GO as well as preventing the restack of graphene sheets. Moreover, cyclic voltammetry (CV) analyses suggest that the electrochemical reversibility is improved by anchoring MnOOH on graphene. Notably, the as-fabricated nanocomposites reveal unusual catalytic performance for the thermal decomposition of ammonium perchlorate (AP) due to the concerted effects of graphene and MnOOH. This template-free method is easy to reproduce, and the process proceeds at a low temperature and can be readily extended to prepare other graphene-based nanocomposites.

  16. Study of nanotribological properties of multilayer graphene by calibrated atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Peng, Yitian; Wang, Zhuoqiong; Li, Cong

    2014-08-01

    The nanotribological properties of multilayer graphene oxide (MGO), multilayer reduced graphene oxide (MRGO), and mechanically exfoliated multilayer graphene (MEMG) deposited on SiO2 substrate were comparatively investigated via calibrated atomic force microscopy in ambient conditions. Friction as a function of the applied normal load and sliding velocity was studied. Results show that all three types of multilayer graphene films exhibit good adhesion and friction reduction properties. MEMG exhibits the lowest friction and adhesive force because of its perfect planar lattice. A logarithmic increase in friction was observed at low sliding velocities for all measured graphene films. Friction decreases on MGO and bare SiO2 substrate, whereas it remains approximately constant on MEMG and MRGO, when the sliding velocity exceeds their critical velocities. The possible mechanisms for the experimental results were discussed. Our studies provide a good opportunity to use different types of multilayer graphene films for promising lubricant applications in nanodevices.

  17. Grain size control for CVD-grown single crystal mono- and bi-layer graphene

    NASA Astrophysics Data System (ADS)

    Luo, Zhengtang

    2015-03-01

    By suppressing the nucleation density during Chemical Vapor Deposition (CVD) growth, we demonstrate that the large-size single crystal monolayer and bilayer graphene can be synthesized by this method. For single layer, single crystals with diameter up to 5.9 mm, have been successfully obtained by adjusting degree of oxidation during surface treatment step and hydrogen annealing duration during growth, thereby allow us to control nucleation density and consequently to control graphene grains sizes. For bilayer growth, our main strategy is to maximize the duration that is controlled by the absorption-diffusion mechanism. With this method, sub-millimeter size single crystal bilayer graphene is also obtained. Electron transport measurement on those produced graphene has shown carrier mobility that is comparable with that of mechanical exfoliated graphene, indicating the high quality of our graphene sample. This project is supported by the Research Grant Council of Hong Kong SAR (Project Number 623512 and DAG12EG05).

  18. Thermal, Mechanical, and Electrical Properties of Graphene Nanoplatelet/Graphene Oxide/ Polyurethane Hybrid Nanocomposite.

    PubMed

    Pokharel, Pashupati; Lee, Sang Hyub; Lee, Dai Soo

    2015-01-01

    Hybrid nanocomposites of polyurethane (PU) were prepared by in-situ polymerization of 4,4'- diphenyl methane diisocyanate (MDI) with mixture of graphene oxide (GO) and graphene nanoplatelet (GNP) dispersed in a poly(tetramethylene ether glycol) (PTMEG). Effects of the fillers, GO and GNP, on the thermal, mechanical, and electrical properties of the nanocomposites of PU were investigated. Sonication of the hybrid of GNP and GO with PTMEG enabled effective dispersion of the fillers in the solution than the sonication of GNP alone. The addition of PTMEG in the solution prevented the GNPs from the restacking during the drying process. It was observed that the electrical conductivity and mechanical property of the nanocomposites based on the hybrid of GO and GNP were superior to the nanocomposite based on GNP alone at the same loading of the filler. At the loading of the 3 wt% hybrid filler in PU, we observed the improvement of Young's modulus -200% and the surface resistivity of 10(9.5) ohm/sq without sacrificing the elongation at break.

  19. Surface Tension Components Based Selection of Cosolvents for Efficient Liquid Phase Exfoliation of 2D Materials.

    PubMed

    Shen, Jianfeng; Wu, Jingjie; Wang, Man; Dong, Pei; Xu, Jingxuan; Li, Xiaoguang; Zhang, Xiang; Yuan, Junhua; Wang, Xifan; Ye, Mingxin; Vajtai, Robert; Lou, Jun; Ajayan, Pulickel M

    2016-05-01

    A proper design of direct liquid phase exfoliation (LPE) for 2D materials as graphene, MoS2 , WS2 , h-BN, Bi2 Se3 , MoSe2 , SnS2 , and TaS2 with common cosolvents is carried out based on considering the polar and dispersive components of surface tensions of various cosolvents and 2D materials. It has been found that the exfoliation efficiency is enhanced by matching the ratio of surface tension components of cosolvents to that of the targeted 2D materials, based on which common cosolvents composed of IPA/water, THF/water, and acetone/water can be designed for sufficient LPE process. In this context, the library of low-toxic and low-cost solvents with low boiling points for LPE is infinitely enlarged when extending to common cosolvents. Polymer-based composites reinforced with a series of different 2D materials are compared with each other. It is demonstrated that the incorporation of cosolvents-exfoliated 2D materials can substantially improve the mechanical and thermal properties of polymer matrices. Typically, with the addition of 0.5 wt% of such 2D material as MoS2 nanosheets, the tensile strength and Young's modulus increased up to 74.85% and 136.97%, respectively. The different enhancement effect of 2D materials is corresponded to the intrinsic properties and LPE capacity of 2D materials.

  20. Preparation and mechanical properties of graphene oxide: cement nanocomposites.

    PubMed

    Babak, Fakhim; Abolfazl, Hassani; Alimorad, Rashidi; Parviz, Ghodousi

    2014-01-01

    We investigate the performance of graphene oxide (GO) in improving mechanical properties of cement composites. A polycarboxylate superplasticizer was used to improve the dispersion of GO flakes in the cement. The mechanical strength of graphene-cement nanocomposites containing 0.1-2 wt% GO and 0.5 wt% superplasticizer was measured and compared with that of cement prepared without GO. We found that the tensile strength of the cement mortar increased with GO content, reaching 1.5%, a 48% increase in tensile strength. Ultra high-resolution field emission scanning electron microscopy (FE-SEM) used to observe the fracture surface of samples containing 1.5 wt% GO indicated that the nano-GO flakes were well dispersed in the matrix, and no aggregates were observed. FE-SEM observation also revealed good bonding between the GO surfaces and the surrounding cement matrix. In addition, XRD diffraction data showed growth of the calcium silicate hydrates (C-S-H) gels in GO cement mortar compared with the normal cement mortar.

  1. Graphene mechanics: I. Efficient first principles based Morse potential.

    PubMed

    Costescu, Bogdan I; Baldus, Ilona B; Gräter, Frauke

    2014-06-28

    We present a computationally efficient pairwise potential for use in molecular dynamics simulations of large graphene or carbon nanotube systems, in particular, for those under mechanical deformation, and also for mixed systems including biomolecules. Based on the Morse potential, it is only slightly more complex and computationally expensive than a harmonic bond potential, allowing such large or mixed simulations to reach experimentally relevant time scales. By fitting to data obtained from quantum mechanics (QM) calculations to represent bond breaking in graphene patches, we obtain a dissociation energy of 805 kJ mol(-1) which reflects the steepness of the QM potential up to the inflection point. A distinctive feature of our potential is its truncation at the inflection point, allowing a realistic treatment of ruptured C-C bonds without relying on a bond order model. The results obtained from equilibrium MD simulations using our potential compare favorably with results obtained from experiments and from similar simulations with more complex and computationally expensive potentials.

  2. Preparation and Mechanical Properties of Graphene Oxide: Cement Nanocomposites

    PubMed Central

    Babak, Fakhim; Abolfazl, Hassani; Alimorad, Rashidi; Parviz, Ghodousi

    2014-01-01

    We investigate the performance of graphene oxide (GO) in improving mechanical properties of cement composites. A polycarboxylate superplasticizer was used to improve the dispersion of GO flakes in the cement. The mechanical strength of graphene-cement nanocomposites containing 0.1–2 wt% GO and 0.5 wt% superplasticizer was measured and compared with that of cement prepared without GO. We found that the tensile strength of the cement mortar increased with GO content, reaching 1.5%, a 48% increase in tensile strength. Ultra high-resolution field emission scanning electron microscopy (FE-SEM) used to observe the fracture surface of samples containing 1.5 wt% GO indicated that the nano-GO flakes were well dispersed in the matrix, and no aggregates were observed. FE-SEM observation also revealed good bonding between the GO surfaces and the surrounding cement matrix. In addition, XRD diffraction data showed growth of the calcium silicate hydrates (C-S-H) gels in GO cement mortar compared with the normal cement mortar. PMID:24574878

  3. High broad-band photoresponsivity of mechanically formed InSe-graphene van der Waals heterostructures.

    PubMed

    Mudd, Garry W; Svatek, Simon A; Hague, Lee; Makarovsky, Oleg; Kudrynskyi, Zakhar R; Mellor, Christopher J; Beton, Peter H; Eaves, Laurence; Novoselov, Kostya S; Kovalyuk, Zakhar D; Vdovin, Evgeny E; Marsden, Alex J; Wilson, Neil R; Patanè, Amalia

    2015-07-01

    High broad-band photoresponsivity of mechanically formed InSe-graphene van der Waals heterostructures is achieved by exploiting the broad-band transparency of graphene, the direct bandgap of InSe, and the favorable band line up of InSe with graphene. The photoresponsivity exceeds that for other van der Waals heterostructures and the spectral response extends from the near-infrared to the visible spectrum.

  4. Strong and electrically conductive graphene-based composite fibers and laminates

    SciTech Connect

    Vlassiouk, Ivan V.; Polyzos, Georgios; Cooper, Ryan C.; Ivanov, Ilia N.; Keum, Jong Kahk; Paulauskas, Felix L.; Datskos, Panos G.; Smirnov, Sergei

    2015-04-28

    In this study, graphene is an ideal candidate for lightweight, high-strength composite materials given its superior mechanical properties (specific strength of 130 GPa and stiffness of 1 TPa). To date, easily scalable graphene-like materials in a form of separated flakes (exfoliated graphene, graphene oxide, and reduced graphene oxide) have been investigated as candidates for large-scale applications such as material reinforcement. These graphene-like materials do not fully exhibit all the capabilities of graphene in composite materials. In this study, we show that macro (2 inch × 2 inch) graphene laminates and fibers can be produced using large continuous sheets of single-layer graphene grown by chemical vapor deposition. The resulting composite structures have potential to outperform the current state-of-the-art composite materials in both mechanical properties and electrical conductivities (>8 S/cm with only 0.13% volumetric graphene loading and 5 × 103 S/cm for pure graphene fibers) with estimated graphene contributions of >10 GPa in strength and 1 TPa in stiffness.

  5. Strong and electrically conductive graphene-based composite fibers and laminates

    DOE PAGES

    Vlassiouk, Ivan V.; Polyzos, Georgios; Cooper, Ryan C.; ...

    2015-04-28

    In this study, graphene is an ideal candidate for lightweight, high-strength composite materials given its superior mechanical properties (specific strength of 130 GPa and stiffness of 1 TPa). To date, easily scalable graphene-like materials in a form of separated flakes (exfoliated graphene, graphene oxide, and reduced graphene oxide) have been investigated as candidates for large-scale applications such as material reinforcement. These graphene-like materials do not fully exhibit all the capabilities of graphene in composite materials. In this study, we show that macro (2 inch × 2 inch) graphene laminates and fibers can be produced using large continuous sheets of single-layermore » graphene grown by chemical vapor deposition. The resulting composite structures have potential to outperform the current state-of-the-art composite materials in both mechanical properties and electrical conductivities (>8 S/cm with only 0.13% volumetric graphene loading and 5 × 103 S/cm for pure graphene fibers) with estimated graphene contributions of >10 GPa in strength and 1 TPa in stiffness.« less

  6. Determining the Mechanism of Low Temperature Graphene Growth

    DTIC Science & Technology

    2014-05-27

    and cheaper production of large area conductive and transparent electrodes. 15. SUBJECT TERMS Graphene, nanoscience & Technology, nano...conductive and transparent electrodes. 15. SUBJECT TERMS Graphene, nanoscience & Technology, nano materials 16. SECURITY CLASSIFICATION OF: 17

  7. Selective mechanical transfer of graphene from seed copper foil using rate effects.

    PubMed

    Na, Seung Ryul; Suk, Ji Won; Tao, Li; Akinwande, Deji; Ruoff, Rodney S; Huang, Rui; Liechti, Kenneth M

    2015-02-24

    A very fast, dry transfer process based on mechanical delamination successfully effected the transfer of large-area, CVD grown graphene on copper foil to silicon. This has been achieved by bonding silicon backing layers to both sides of the graphene-coated copper foil with epoxy and applying a suitably high separation rate to the backing layers. At the highest separation rate considered (254.0 μm/s), monolayer graphene was completely transferred from the copper foil to the target silicon substrate. On the other hand, the lowest rate (25.4 μm/s) caused the epoxy to be completely separated from the graphene. Fracture mechanics analyses were used to determine the adhesion energy between graphene and its seed copper foil (6.0 J/m(2)) and between graphene and the epoxy (3.4 J/m(2)) at the respective loading rates. Control experiments for the epoxy/silicon interface established a rate dependent adhesion, which supports the hypothesis that the adhesion of the graphene/epoxy interface was higher than that of the graphene/copper interface at the higher separation rate, thereby providing a controllable mechanism for selective transfer of graphene in future nanofabrication systems such as roll-to-roll transfer.

  8. Interfacial Mechanical Properties of Graphene on Self-Assembled Monolayers: Experiments and Simulations.

    PubMed

    Tu, Qing; Kim, Ho Shin; Oweida, Thomas J; Parlak, Zehra; Yingling, Yaroslava G; Zauscher, Stefan

    2017-03-22

    Self-assembled monolayers (SAMs) have been widely used to engineer the electronic properties of substrate-supported graphene devices. However, little is known about how the surface chemistry of SAMs affects the interfacial mechanical properties of graphene supported on SAMs. Fluctuations and changes in these properties affect the stress transfer between substrate and the supported graphene and thus the performance of graphene-based devices. The changes in interfacial mechanical properties can be characterized by measuring the out-of-plane elastic properties. Combining contact resonance atomic force microcopy experiments with molecular dynamics simulations, we show that the head group chemistry of a SAM, which affects the interfacial interactions, can have a significant effect on the out-of-plane elastic modulus of the graphene-SAM heterostructure. Graphene supported on hydrophobic SAMs leads to heterostructures stiffer than those of graphene supported on hydrophilic SAMs, which is largely due to fewer water molecules present at the graphene-SAM interface. Our results provide an important, and often overlooked, insight into the mechanical properties of substrate-supported graphene electronics.

  9. Nitrogen-tuned bonding mechanism of Li and Ti adatom embedded graphene

    SciTech Connect

    Lee, Sangho; Chung, Yong-Chae

    2013-09-15

    The effects of nitrogen defects on the bonding mechanism and resultant binding energy between the metal and graphene layer were investigated using density functional theory (DFT) calculations. For the graphitic N-doped graphene, Li adatom exhibited ionic bonding character, while Ti adatom showed features of covalent bonding similar to that of pristine graphene. However, in the cases of pyridinic and pyrrolic structures, partially covalent bonding characteristic occurred around N atoms in the process of binding with metals, and this particular bond formation enhanced the bond strength of metal on the graphene layer as much as it exceeded the cohesive energy of the metal bulk. Thus, Li and Ti metals are expected to be dispersed with atomic accuracy on the pyridinic and pyrrolic N-doped graphene layers. These results demonstrate that the bonding mechanism of metal–graphene complex can change according to the type of N defect, and this also affects the binding results. - Graphical abstract: Display Omitted - Highlights: • Nitrogen defects changed the bonding mechanism between metal and graphene. • Bonding character and binding results were investigated using DFT calculations. • Covalent bonding character occurred around pyridinic and pyrrolic N-doped graphene. • Pyridinic and pyrrolic N atoms are effective for metal dispersion on the graphene.

  10. Exfoliation corrosion susceptibility and mechanisms of Al -- Li 2060 T8E30 aluminum lithium alloy in acidic media

    NASA Astrophysics Data System (ADS)

    Karayan, Ahmad Ivan

    The Al - Li 2060 aluminum lithium alloy was first launched in 2011. This alloy is a potential candidate for the use at wing/fuselage forgings, lower wing, and fuselage/pressure cabin. However, since its first launching, the corrosion properties of this alloy has not been extensively explored. There are three common laboratory tests for assessing the exfoliation corrosion (EFC) susceptibility of aluminum alloy 2XXX, namely EFC test in EXCO, modified EXCO and MASTMAASIS media. The objectives of this work is to study the susceptibility and mecahnism of corrosion of this alloy in EXCO, modified EXCO and MATSMAASIS media. These three media are acid. In the EXCO solution, this alloy suffers EFC after a 96-hour EFC test. The pH dramatically increases in the first 11 hours from 0.25 to 0.30. The pH then slightly increases and tends to remain constant at pH of 3.45 after 96 hours. The cyclic potentiodynamic polarization (CPP) test results show the presence of negative hysteresis and one breakdwon potential. This negative hysteresis suggests the absence of pitting corrosion due to the breakdown of passive film. The potentiostatic tests at potentials below and above the breakdown potential show an abrupt increase in potential in the first minutes and the presence of current transients. The scanning electron microscopy (SEM)-energy dispersive x-ray spectroscopy (EDS) examination confirms that the Al 20Cu2Mn3 particles preferentially dissolve, leaving the pitting after a potentiostatic test below the breakdown potential. From the potentiostatic test at a potential above the breakdown potential and an SEM examination after this potentiostatic test, intergranular corrosion (IGC) was observed. The electrochemical impedance spectroscopy (EIS) test and mathematical modeling indicates that the adsorption of intermediates in reduction of hydrogen ions is dominant in the first hours of immersion. The two time constants are observed when EFC occurs. The video capture microscopy

  11. Graphene field-effect transistors for label-free chemical and biological sensors

    NASA Astrophysics Data System (ADS)

    Ohno, Yasuhide; Maehashi, Kenzo; Matsumoto, Kazuhiko

    2011-06-01

    Electrical detection of solution pH, protein adsorption and specific biomolecules were demonstrated by using graphene field-effect transistors (G-FETs). The monolayer graphene flakes were used as channel, which were obtained by conventional mechanical exfoliation from bulk graphite. The transport characteristics shifted to the positive voltage direction with increasing solution pH. The drain current changed by desorption of the charged protein. Moreover, we immobilized aptamers on the graphene surface. As a result, specific immunoglobulin sensing can be carried out using aptamer-modified G-FETs. These results strongly suggested that the G-FETs have high potentials for chemical and biological sensors.

  12. Characterization of reduced graphene oxide field-effect transistor and its application to biosensor

    NASA Astrophysics Data System (ADS)

    Hasegawa, Masaki; Hirayama, Yuki; Ohno, Yasuhide; Maehashi, Kenzo; Matsumoto, Kazuhiko

    2014-01-01

    We confirmed the specific detection of immunoglobulin E (IgE) using an aptamer-immobilized reduced graphene oxide (rGO) field effect transistor (FET). The detection limit and dynamic range were estimated to be 8.1 ng/ml and 104, respectively. These characteristics are comparable with these of current fluorescent markers. Although the mobility of rGO-FET was around 6 cm2 V-1 s-1, which is two to three orders lower than that of mechanically exfoliated pristine graphene FET, its sensitivity to IgE was only one order lower than that of pristine graphene FET.

  13. Nitrogen doping and vacancy effects on the mechanical properties of graphene: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Mortazavi, Bohayra; Ahzi, Said; Toniazzo, Valérie; Rémond, Yves

    2012-02-01

    In this Letter, we used classical Molecular Dynamics (MD) simulations to investigate the tensile behavior of graphene. The validity of the proposed MD architecture is verified by comparing the simulation results with the available experimental results. By performing uniaxial tension simulations, we studied the effects of strain rate, chirality, nanoribbons width and number of atomic planes on the mechanical properties of graphene. We particularly investigated the effects of doped nitrogen atoms and point vacancies concentrations on the Young's modulus and tensile strength of graphene. By plotting the deformation process of graphene at various strain levels, the failure behavior is discussed.

  14. The different adsorption mechanism of methane molecule onto a boron nitride and a graphene flakes

    SciTech Connect

    Seyed-Talebi, Seyedeh Mozhgan; Neek-Amal, M.

    2014-10-21

    Graphene and single layer hexagonal boron-nitride are two newly discovered 2D materials with wonderful physical properties. Using density functional theory, we study the adsorption mechanism of a methane molecule over a hexagonal flake of single layer hexagonal boron-nitride (h-BN) and compare the results with those of graphene. We found that independent of the used functional in our ab-initio calculations, the adsorption energy in the h-BN flake is larger than that for graphene. Despite of the adsorption energy profile of methane over a graphene flake, we show that there is a long range behavior beyond minimum energy in the adsorption energy of methane over h-BN flake. This result reveals the higher sensitivity of h-BN sheet to the adsorption of a typical closed shell molecule with respect to graphene. The latter gives insight in the recent experiments of graphene over hexagonal boron nitride.

  15. Non-Hookean statistical mechanics of clamped graphene ribbons

    NASA Astrophysics Data System (ADS)

    Bowick, Mark J.; Košmrlj, Andrej; Nelson, David R.; Sknepnek, Rastko

    2017-03-01

    Thermally fluctuating sheets and ribbons provide an intriguing forum in which to investigate strong violations of Hooke's Law: Large distance elastic parameters are in fact not constant but instead depend on the macroscopic dimensions. Inspired by recent experiments on free-standing graphene cantilevers, we combine the statistical mechanics of thin elastic plates and large-scale numerical simulations to investigate the thermal renormalization of the bending rigidity of graphene ribbons clamped at one end. For ribbons of dimensions W ×L (with L ≥W ), the macroscopic bending rigidity κR determined from cantilever deformations is independent of the width when W <ℓth , where ℓth is a thermal length scale, as expected. When W >ℓth , however, this thermally renormalized bending rigidity begins to systematically increase, in agreement with the scaling theory, although in our simulations we were not quite able to reach the system sizes necessary to determine the fully developed power law dependence on W . When the ribbon length L >ℓp , where ℓp is the W -dependent thermally renormalized ribbon persistence length, we observe a scaling collapse and the beginnings of large scale random walk behavior.

  16. Surface-Plasmon-Mediated Gradient Force Enhancement and Mechanical State Transitions of Graphene Sheets

    SciTech Connect

    Zhang, Peng; Shen, Nian-Hai; Koschny, Thomas; Soukoulis, Costas M.

    2016-12-16

    Graphene, a two-dimensional material possessing extraordinary properties in electronics as well as mechanics, provides a great platform for various optoelectronic and opto-mechanical devices. Here in this article, we theoretically study the optical gradient force arising from the coupling of surface plasmon modes on parallel graphene sheets, which can be several orders stronger than that between regular dielectric waveguides. Furthermore, with an energy functional optimization model, possible force-induced deformation of graphene sheets is calculated. We show that the significantly enhanced optical gradient force may lead to mechanical state transitions of graphene sheets, which are accompanied by abrupt changes in reflection and transmission spectra of the system. Our demonstrations illustrate the potential for a broader graphene-related applications such as force sensors and actuators.

  17. Surface-Plasmon-Mediated Gradient Force Enhancement and Mechanical State Transitions of Graphene Sheets

    DOE PAGES

    Zhang, Peng; Shen, Nian-Hai; Koschny, Thomas; ...

    2016-12-16

    Graphene, a two-dimensional material possessing extraordinary properties in electronics as well as mechanics, provides a great platform for various optoelectronic and opto-mechanical devices. Here in this article, we theoretically study the optical gradient force arising from the coupling of surface plasmon modes on parallel graphene sheets, which can be several orders stronger than that between regular dielectric waveguides. Furthermore, with an energy functional optimization model, possible force-induced deformation of graphene sheets is calculated. We show that the significantly enhanced optical gradient force may lead to mechanical state transitions of graphene sheets, which are accompanied by abrupt changes in reflection andmore » transmission spectra of the system. Our demonstrations illustrate the potential for a broader graphene-related applications such as force sensors and actuators.« less

  18. The influence of tilt grain boundaries on the mechanical properties of bicrystalline graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Xu, Na; Guo, Jian-Gang; Cui, Zhen

    2016-10-01

    The mechanical properties of bicrystalline graphene nanoribbons with various tilt grain boundaries (GBs) which typically consist of repeating pentagon-heptagon ring defects are investigated based on the method of molecular structural mechanics. The GB models are constructed via the theory of disclinations in crystals, and the elastic properties and ultimate strength of bicrystalline graphene nanoribbons are calculated under uniaxial tensile loads in perpendicular and parallel directions to grain boundaries. The dependence of mechanical properties is analyzed on the chirality and misorientation angles of graphene nanoribbons, and the experimental phenomena that Young's modulus and ultimate strength of bicrystalline graphene nanoribbons can either increase or decrease with the grain boundary angles are further verified and discussed. In addition, the influence of GB on the size effects of graphene Young's modulus is also analyzed.

  19. Fragmentation and exfoliation of 2-dimensional materials: a statistical approach

    NASA Astrophysics Data System (ADS)

    Kouroupis-Agalou, Konstantinos; Liscio, Andrea; Treossi, Emanuele; Ortolani, Luca; Morandi, Vittorio; Pugno, Nicola Maria; Palermo, Vincenzo

    2014-05-01

    The main advantage for applications of graphene and related 2D materials is that they can be produced on large scales by liquid phase exfoliation. The exfoliation process shall be considered as a particular fragmentation process, where the 2D character of the exfoliated objects will influence significantly fragmentation dynamics as compared to standard materials. Here, we used automatized image processing of Atomic Force Microscopy (AFM) data to measure, one by one, the exact shape and size of thousands of nanosheets obtained by exfoliation of an important 2D-material, boron nitride, and used different statistical functions to model the asymmetric distribution of nanosheet sizes typically obtained. Being the resolution of AFM much larger than the average sheet size, analysis could be performed directly at the nanoscale and at the single sheet level. We find that the size distribution of the sheets at a given time follows a log-normal distribution, indicating that the exfoliation process has a ``typical'' scale length that changes with time and that exfoliation proceeds through the formation of a distribution of random cracks that follow Poisson statistics. The validity of this model implies that the size distribution does not depend on the different preparation methods used, but is a common feature in the exfoliation of this material and thus probably for other 2D materials.The main advantage for applications of graphene and related 2D materials is that they can be produced on large scales by liquid phase exfoliation. The exfoliation process shall be considered as a particular fragmentation process, where the 2D character of the exfoliated objects will influence significantly fragmentation dynamics as compared to standard materials. Here, we used automatized image processing of Atomic Force Microscopy (AFM) data to measure, one by one, the exact shape and size of thousands of nanosheets obtained by exfoliation of an important 2D-material, boron nitride, and used

  20. Graphene-SnO2 nanocomposites decorated with quantum tunneling junctions: preparation strategies, microstructures and formation mechanism.

    PubMed

    Wang, Qingxiu; Wu, Xianzheng; Wang, Lijun; Chen, Zhiwen; Wang, Shilong

    2014-09-28

    Tin dioxide (SnO2) and graphene are versatile materials that are vitally important for creating new functional and smart materials. A facile, simple and efficient ultrasonic-assisted hydrothermal synthesis approach has been developed to prepare graphene-SnO2 nanocomposites (GSNCs), including three samples with graphene/Sn weight ratios = 1 : 2 (GSNC-2), 1 : 1 (GSNC-1), and graphene oxide/Sn weight ratio = 1 : 1 (GOSNC-1). Low-magnification electron microscopy analysis indicated that graphene was exfoliated and adorned with SnO2 nanoparticles, which were dispersed uniformly on both the sides of the graphene nanosheets. High-magnification electron microscopy analysis confirmed that the graphene-SnO2 nanocomposites presented network tunneling frameworks, which were decorated with the SnO2 quantum tunneling junctions. The size distribution of SnO2 nanoparticles was estimated to range from 3 to 5.5 nm. Comparing GSNC-2, GSNC-1, and GOSNC-1, GOSNC-1 was found to exhibit a significantly better the homogeneous distribution and a considerably smaller size distribution of SnO2 nanoparticles, which indicated that it was better to use graphene oxide as a supporting material and SnCl4·5H2O as a precursor to synthesize hybrid graphene-SnO2 nanocomposites. Experimental results suggest that the graphene-SnO2 nanocomposites with interesting SnO2 quantum tunneling junctions may be a promising material to facilitate the improvement of the future design of micro/nanodevices.

  1. Enhanced Mechanical Properties of Graphene (Reduced Graphene Oxide)/Aluminum Composites with a Bioinspired Nanolaminated Structure.

    PubMed

    Li, Zan; Guo, Qiang; Li, Zhiqiang; Fan, Genlian; Xiong, Ding-Bang; Su, Yishi; Zhang, Jie; Zhang, Di

    2015-12-09

    Bulk graphene (reduced graphene oxide)-reinforced Al matrix composites with a bioinspired nanolaminated microstructure were fabricated via a composite powder assembly approach. Compared with the unreinforced Al matrix, these composites were shown to possess significantly improved stiffness and tensile strength, and a similar or even slightly higher total elongation. These observations were interpreted by the facilitated load transfer between graphene and the Al matrix, and the extrinsic toughening effect as a result of the nanolaminated microstructure.

  2. Polymer reinforcement using liquid-exfoliated boron nitride nanosheets

    NASA Astrophysics Data System (ADS)

    Khan, Umar; May, Peter; O'Neill, Arlene; Bell, Alan P.; Boussac, Elodie; Martin, Arnaud; Semple, James; Coleman, Jonathan N.

    2012-12-01

    We have exfoliated hexagonal boron nitride by ultrasonication in solutions of polyvinylalcohol in water. The resultant nanosheets are sterically stabilised by adsorbed polymer chains. Centrifugation-based size-selection was used to give dispersions of nanosheets with aspect ratio (length/thickness) of ~1400. Such dispersions can be used to produce polyvinylalcohol-BN composite films. Helium ion microscopy of fracture surfaces shows the nanosheets to be well dispersed and the composites to fail by pull-out. We find both modulus, Y, and strength, σB, of these composites to increase linearly with volume fraction, Vf, up to Vf ~ 0.1 vol% BN before falling off. The rates of increase are extremely high; dY/dVf = 670 GPa and dσB/dVf = 47 GPa. The former value matches theory based on continuum mechanics while the latter value is consistent with remarkably high polymer-filler interfacial strength. However, because the mechanical properties increase over such a narrow volume fraction range, the maximum values of both modulus and strength are only ~40% higher than the pure polymer. This phenomenon has also been observed for graphene-filled composites and represents a serious hurdle to the production of high performance polymer-nanosheet composites.We have exfoliated hexagonal boron nitride by ultrasonication in solutions of polyvinylalcohol in water. The resultant nanosheets are sterically stabilised by adsorbed polymer chains. Centrifugation-based size-selection was used to give dispersions of nanosheets with aspect ratio (length/thickness) of ~1400. Such dispersions can be used to produce polyvinylalcohol-BN composite films. Helium ion microscopy of fracture surfaces shows the nanosheets to be well dispersed and the composites to fail by pull-out. We find both modulus, Y, and strength, σB, of these composites to increase linearly with volume fraction, Vf, up to Vf ~ 0.1 vol% BN before falling off. The rates of increase are extremely high; dY/dVf = 670 GPa and d

  3. The effect of intrinsic crumpling on the mechanics of free-standing graphene

    SciTech Connect

    Nicholl, Ryan J. T.; Conley, Hiram J.; Lavrik, Nickolay V.; Vlassiouk, Ivan; Puzyrev, Yevgeniy S.; Sreenivas, Vijayashree Parsi; Pantelides, Sokrates T.; Bolotin, Kirill I.

    2015-11-06

    Free-standing graphene is inherently crumpled in the out-of-plane direction due to dynamic flexural phonons and static wrinkling. We explore the consequences of this crumpling on the effective mechanical constants of graphene. We develop a sensitive experimental approach to probe stretching of graphene membranes under low applied stress at cryogenic to room temperatures. We find that the in-plane stiffness of graphene is 20–100 N m–1 at room temperature, much smaller than 340 N m–1 (the value expected for flat graphene). Moreover, while the in-plane stiffness only increases moderately when the devices are cooled down to 10 K, it approaches 300 N m–1 when the aspect ratio of graphene membranes is increased. Finally, these results indicate that softening of graphene at temperatures <400 K is caused by static wrinkling, with only a small contribution due to flexural phonons. Altogether, these results explain the large variation in reported mechanical constants of graphene devices and pave the way towards controlling their mechanical properties.

  4. The effect of intrinsic crumpling on the mechanics of free-standing graphene

    DOE PAGES

    Nicholl, Ryan J. T.; Conley, Hiram J.; Lavrik, Nickolay V.; ...

    2015-11-06

    Free-standing graphene is inherently crumpled in the out-of-plane direction due to dynamic flexural phonons and static wrinkling. We explore the consequences of this crumpling on the effective mechanical constants of graphene. We develop a sensitive experimental approach to probe stretching of graphene membranes under low applied stress at cryogenic to room temperatures. We find that the in-plane stiffness of graphene is 20–100 N m–1 at room temperature, much smaller than 340 N m–1 (the value expected for flat graphene). Moreover, while the in-plane stiffness only increases moderately when the devices are cooled down to 10 K, it approaches 300 Nmore » m–1 when the aspect ratio of graphene membranes is increased. Finally, these results indicate that softening of graphene at temperatures <400 K is caused by static wrinkling, with only a small contribution due to flexural phonons. Altogether, these results explain the large variation in reported mechanical constants of graphene devices and pave the way towards controlling their mechanical properties.« less

  5. The effect of intrinsic crumpling on the mechanics of free-standing graphene

    PubMed Central

    Nicholl, Ryan J.T.; Conley, Hiram J.; Lavrik, Nickolay V.; Vlassiouk, Ivan; Puzyrev, Yevgeniy S.; Sreenivas, Vijayashree Parsi; Pantelides, Sokrates T.; Bolotin, Kirill I.

    2015-01-01

    Free-standing graphene is inherently crumpled in the out-of-plane direction due to dynamic flexural phonons and static wrinkling. We explore the consequences of this crumpling on the effective mechanical constants of graphene. We develop a sensitive experimental approach to probe stretching of graphene membranes under low applied stress at cryogenic to room temperatures. We find that the in-plane stiffness of graphene is 20–100 N m−1 at room temperature, much smaller than 340 N m−1 (the value expected for flat graphene). Moreover, while the in-plane stiffness only increases moderately when the devices are cooled down to 10 K, it approaches 300 N m−1 when the aspect ratio of graphene membranes is increased. These results indicate that softening of graphene at temperatures <400 K is caused by static wrinkling, with only a small contribution due to flexural phonons. Together, these results explain the large variation in reported mechanical constants of graphene devices and pave the way towards controlling their mechanical properties. PMID:26541811

  6. Mechanical properties and failure behaviors of the interface of hybrid graphene/hexagonal boron nitride sheets

    PubMed Central

    Ding, Ning; Chen, Xiangfeng; Wu, Chi-Man Lawrence

    2016-01-01

    Hybrid graphene/h-BN sheet has been fabricated recently and verified to possess unusual physical properties. During the growth process, defects such as vacancies are unavoidably present at the interface between graphene and h-BN. In the present work, typical vacancy defects, which were located at the interface between graphene and h-BN, were studied by density functional theory. The interface structure, mechanical and electronic properties, and failure behavior of the hybrid graphene/h-BN sheet were investigated and compared. The results showed that the formation energy of the defective graphene/h-BN interface basically increased with increasing inflection angles. However, Young’s modulus for all graphene/h-BN systems studied decreased with the increase in inflection angles. The intrinsic strength of the hybrid graphene/h-BN sheets was affected not only by the inflection angles, but also by the type of interface connection and the type of defects. The energy band structure of the hybrid interface could be tuned by applying mechanical strain to the systems. These results demonstrated that vacancies introduced significant effects on the mechanical and electronic properties of the hybrid graphene/h-BN sheet. PMID:27527371

  7. Synthesis of soluble graphite and graphene.

    PubMed

    Kelly, K F; Billups, W E

    2013-01-15

    Because of graphene's anticipated applications in electronics and its thermal, mechanical, and optical properties, many scientists and engineers are interested in this material. Graphene is an isolated layer of the π-stacked hexagonal allotrope of carbon known as graphite. The interlayer cohesive energy of graphite, or exfoliation energy, that results from van der Waals attractions over the interlayer spacing distance of 3.34 Å (61 meV/C atom) is many times weaker than the intralayer covalent bonding. Since graphene itself does not occur naturally, scientists and engineers are still learning how to isolate and manipulate individual layers of graphene. Some researchers have relied on the physical separation of the sheets, a process that can sometimes be as simple as peeling of sheets from crystalline graphite using Scotch tape. Other researchers have taken an ensemble approach, where they exploit the chemical conversion of graphite to the individual layers. The typical intermediary state is graphite oxide, which is often produced using strong oxidants under acidic conditions. Structurally, researchers hypothesize that acidic functional groups functionalize the oxidized material at the edges and a network of epoxy groups cover the sp(2)-bonded carbon network. The exfoliated material formed under these conditions can be used to form dispersions that are usually unstable. However, more importantly, irreversible defects form in the basal plane during oxidation and remain even after reduction of graphite oxide back to graphene-like material. As part of our interest in the dissolution of carbon nanomaterials, we have explored the derivatization of graphite following the same procedures that preserve the sp(2) bonding and the associated unique physical and electronic properties in the chemical processing of single-walled carbon nanotubes. In this Account, we describe efficient routes to exfoliate graphite either into graphitic nanoparticles or into graphene without

  8. Graphene coating for anti-corrosion and the investigation of failure mechanism

    NASA Astrophysics Data System (ADS)

    Zhu, Y. X.; Duan, C. Y.; Liu, H. Y.; Chen, Y. F.; Wang, Y.

    2017-03-01

    Graphene produced by chemical vapor deposition (CVD) methods has been considered as a promising corrosion prevention layer because of its exceptional structure and impermeability. However, the anti-corrosion performance and the failure mechanism are still controversial. In this study, graphene layers with different quality levels, crystallite sizes, and layer numbers were prepared on the surface of Cu by a CVD process. The effects of grain boundaries (GBs) on the failure of graphene layers to provide adequate protection were investigated in detail by combining graphene transfer techniques, computation, and anti-corrosion measurements. Our results reveal that corrosion rates decrease marginally upon the increase of graphene layer number, and this rather weak dependence on thickness likely arises from the aligned nature of the GBs in CVD-grown few-layer graphene. This problem can potentially be overcome by layer-by-layer graphene transfer technique, in which corrosion is found to be arrested locally when transferred graphene is present on top of the as-grown graphene. However, this advantage is not reflected in corrosion studies performed on large-scale samples, where cracks or imperfect interfaces could offset the advantages of GB misalignment. With improvements in technology, the layer-by-layer assembly technique could be used to develop an effective anti-corrosion barrier.

  9. Experimental and modeling study on charge storage/transfer mechanism of graphene-based supercapacitors

    NASA Astrophysics Data System (ADS)

    Ban, Shuai; Jing, Xie; Zhou, Hongjun; Zhang, Lei; Zhang, Jiujun

    2014-12-01

    A symmetrical graphene-based supercapacitor is constructed for studying the charge-transfer mechanism within the graphene-based electrodes using both experiment measurements and molecular simulation. The in-house synthesized graphene is characterized by XRD, SEM and BET measurements for morphology and surface area. It is observed that the electric capacity of graphene electrode can be reduced by both high internal resistance and limited mass transfer. Computer modeling is conducted at the molecular level to characterize the diffusion behavior of electrolyte ions to the interior of electrode with emphasis on the unique 2D confinement imposed by graphene layers. Although graphene powder poses a moderate internal surface of 400 m2 g-1, the capacitance performance of graphene electrode can be as good as that of commercial activated carbon which has an overwhelming surface area of 1700 m2 g-1. An explanation to this abnormal correlation is that graphene material has an intrinsic capability of adaptively reorganizing its microporous structure in response to intercalation of ions and immergence of electrolyte solvent. The accessible surface of graphene is believed to be dramatically enlarged for ion adsorption during the charging process of capacitor.

  10. Charge transport mechanisms of graphene/semiconductor Schottky barriers: A theoretical and experimental study

    SciTech Connect

    Zhong, Haijian; Liu, Zhenghui; Xu, Gengzhao; Shi, Lin; Fan, Yingmin; Yang, Hui; Xu, Ke Wang, Jianfeng; Ren, Guoqiang

    2014-01-07

    Graphene has been proposed as a material for semiconductor electronic and optoelectronic devices. Understanding the charge transport mechanisms of graphene/semiconductor Schottky barriers will be crucial for future applications. Here, we report a theoretical model to describe the transport mechanisms at the interface of graphene and semiconductors based on conventional semiconductor Schottky theory and a floating Fermi level of graphene. The contact barrier heights can be estimated through this model and be close to the values obtained from the experiments, which are lower than those of the metal/semiconductor contacts. A detailed analysis reveals that the barrier heights are as the function of the interface separations and dielectric constants, and are influenced by the interfacial states of semiconductors. Our calculations show how this behavior of lowering barrier heights arises from the Fermi level shift of graphene induced by the charge transfer owing to the unique linear electronic structure.

  11. In situ thermally reduced graphene oxide/epoxy composites: thermal and mechanical properties

    NASA Astrophysics Data System (ADS)

    Olowojoba, Ganiu B.; Eslava, Salvador; Gutierrez, Eduardo S.; Kinloch, Anthony J.; Mattevi, Cecilia; Rocha, Victoria G.; Taylor, Ambrose C.

    2016-10-01

    Graphene has excellent mechanical, thermal, optical and electrical properties and this has made it a prime target for use as a filler material in the development of multifunctional polymeric composites. However, several challenges need to be overcome to take full advantage of the aforementioned properties of graphene. These include achieving good dispersion and interfacial properties between the graphene filler and the polymeric matrix. In the present work, we report the thermal and mechanical properties of reduced graphene oxide/epoxy composites prepared via a facile, scalable and commercially viable method. Electron micrographs of the composites demonstrate that the reduced graphene oxide (rGO) is well dispersed throughout the composite. Although no improvements in glass transition temperature, tensile strength and thermal stability in air of the composites were observed, good improvements in thermal conductivity (about 36 %), tensile and storage moduli (more than 13 %) were recorded with the addition of 2 wt% of rGO.

  12. Functionalized graphene and graphene oxide solution via polyacrylate coating

    NASA Astrophysics Data System (ADS)

    Saha, Arindam; Basiruddin, Sk; Ray, S. C.; Roy, S. S.; Jana, Nikhil R.

    2010-12-01

    Water soluble graphene with various chemical- and biofunctionalities is essential for their different applications. However, exfoliated graphenes are insoluble in water and water soluble graphene oxide precipitate if they are chemically reduced to graphene. We have developed a polyacrylate coating method for graphene oxide and then chemically reduced it into graphene. We found that polyacrylate coating can improve the colloidal stability of both graphene and graphene oxide. The coated graphene has been characterized using XPS, FTIR, XRD and micro-Raman spectroscopy. The primary amine present on the coating backbone has been used to derive glucose functionalized water soluble graphene. Various other functional graphenes can be anticipated from the polyacrylate coated graphene.Water soluble graphene with various chemical- and biofunctionalities is essential for their different applications. However, exfoliated graphenes are insoluble in water and water soluble graphene oxide precipitate if they are chemically reduced to graphene. We have developed a polyacrylate coating method for graphene oxide and then chemically reduced it into graphene. We found that polyacrylate coating can improve the colloidal stability of both graphene and graphene oxide. The coated graphene has been characterized using XPS, FTIR, XRD and micro-Raman spectroscopy. The primary amine present on the coating backbone has been used to derive glucose functionalized water soluble graphene. Various other functional graphenes can be anticipated from the polyacrylate coated graphene. Electronic supplementary information (ESI) available: Details of XPS, XRD, AFM and FTIR of polymer coated GO and G and results of fluorescence quenching experiments. See DOI: 10.1039/c0nr00376j

  13. Mechanism of Transition-Metal Nanoparticle Catalytic Graphene Cutting.

    PubMed

    Ma, Liang; Wang, Jinlan; Yip, Joanne; Ding, Feng

    2014-04-03

    Catalytic cutting by transition-metal (TM) particles is a promising method for the synthesizing of high-quality graphene quantum dots and nanoribbons with smooth edges. Experimentally, it is observed that the cutting always results in channels with zigzag (ZZ) or armchair (AC) edges. However, the driving force that is responsible for such a cutting behavior remains a puzzle. Here, by calculating the interfacial formation energies of the TM-graphene edges with ab initio method, we show that the surface of a catalyst particle tends to be aligned along either AC or ZZ direction of the graphene lattice, and thus the cutting of graphene is guided as such. The different cutting behaviors of various catalysts are well-explained based on the competition between TM-passivated graphene edges and the etching-agent-terminated ones. Furthermore, the kinetics of graphene catalytic cutting along ZZ and AC directions, respectively, are explored at the atomic level.

  14. Adsorption of Ar on individual carbon nanotubes, graphene, and graphite

    NASA Astrophysics Data System (ADS)

    Dzyubenko, Boris; Kahn, Joshua; Vilches, Oscar; Cobden, David

    2015-03-01

    We compare and contrast results of adsorption measurements of Ar on single-walled carbon nanotubes, graphene, and graphite. Adsorption isotherms on individual suspended nanotubes were obtained using both the mechanical resonance frequency shift (sensitive to mass adsorption) and the electrical conductance. Isotherms on graphene mounted on hexagonal boron nitride were obtained using only the conductance. New volumetric adsorption isotherms on bulk exfoliated graphite were also obtained, paying special attention to the very low coverage region (less than 2% of a monolayer). This allowed us to compare the degree of heterogeneity on the three substrate types, the binding energies, and the van der Waals 2D parameters. Research supported by NSF DMR 1206208.

  15. Mechanical and Electrochemical Performance of Graphene-Based Flexible Supercapacitors

    DTIC Science & Technology

    2014-08-01

    metal film on Kapton current collectors. After printing, the graphene oxide was thermally reduced to produce conductive graphene electrodes. These...substrate, it must be reduced to the conductive graphene form, which we do with a thermal anneal. Previously, we reported good capacitor performance...electrodes are assembled with an intervening frame of FEP-coated Kapton, c) electrodes are heat sealed face to face on three sides, d) the polypropylene

  16. Control and Characterization of Individual Grains and Grain Boundaries in Graphene Grown by Chemical Vapour Deposition

    DTIC Science & Technology

    2011-06-01

    active investigation, both experimentally25–28 and theoretically29–31. For example, exfoliated monolayer graphene flakes can show both zigzag and...crystalsmade of eithermultilayer or monolayer CVD graphene as well as transferred exfoliated graphene /graphite. Seeds made from multilayer CVD graphene ...synthesis of graphene by chemical vapour deposition and its application in hydrogen sensing. Sens. Actuat. B 150, 296–300 (2010). 21. Li, X. S., Cai, W. W

  17. Penta-graphene: A new carbon allotrope

    SciTech Connect

    Zhang, Shunhong; Zhou, Jian; Wang, Qian; Chen, Xiaoshuang; Kawazoe, Yoshiyuki; Jena, Puru

    2015-02-02

    A 2D metastable carbon allotrope, penta-graphene, composed entirely of carbon pentagons and resembling the Cairo pentagonal tiling, is proposed in this paper. State-of-the-art theoretical calculations confirm that the new carbon polymorph is not only dynamically and mechanically stable, but also can withstand temperatures as high as 1000 K. Due to its unique atomic configuration, penta-graphene has an unusual negative Poisson’s ratio and ultrahigh ideal strength that can even outperform graphene. Furthermore, unlike graphene that needs to be functionalized for opening a band gap, penta-graphene possesses an intrinsic quasi-direct band gap as large as 3.25 eV, close to that of ZnO and GaN. Equally important, penta-graphene can be exfoliated from T12-carbon. When rolled up, it can form pentagon-based nanotubes which are semiconducting, regardless of their chirality. When stacked in different patterns, stable 3D twin structures of T12-carbon are generated with band gaps even larger than that of T12-carbon. Finally, the versatility of penta-graphene and its derivatives are expected to have broad applications in nanoelectronics and nanomechanics.

  18. Penta-graphene: A new carbon allotrope

    DOE PAGES

    Zhang, Shunhong; Zhou, Jian; Wang, Qian; ...

    2015-02-02

    A 2D metastable carbon allotrope, penta-graphene, composed entirely of carbon pentagons and resembling the Cairo pentagonal tiling, is proposed in this paper. State-of-the-art theoretical calculations confirm that the new carbon polymorph is not only dynamically and mechanically stable, but also can withstand temperatures as high as 1000 K. Due to its unique atomic configuration, penta-graphene has an unusual negative Poisson’s ratio and ultrahigh ideal strength that can even outperform graphene. Furthermore, unlike graphene that needs to be functionalized for opening a band gap, penta-graphene possesses an intrinsic quasi-direct band gap as large as 3.25 eV, close to that of ZnOmore » and GaN. Equally important, penta-graphene can be exfoliated from T12-carbon. When rolled up, it can form pentagon-based nanotubes which are semiconducting, regardless of their chirality. When stacked in different patterns, stable 3D twin structures of T12-carbon are generated with band gaps even larger than that of T12-carbon. Finally, the versatility of penta-graphene and its derivatives are expected to have broad applications in nanoelectronics and nanomechanics.« less

  19. Penta-graphene: A new carbon allotrope

    PubMed Central

    Zhang, Shunhong; Zhou, Jian; Wang, Qian; Chen, Xiaoshuang; Kawazoe, Yoshiyuki; Jena, Puru

    2015-01-01

    A 2D metastable carbon allotrope, penta-graphene, composed entirely of carbon pentagons and resembling the Cairo pentagonal tiling, is proposed. State-of-the-art theoretical calculations confirm that the new carbon polymorph is not only dynamically and mechanically stable, but also can withstand temperatures as high as 1000 K. Due to its unique atomic configuration, penta-graphene has an unusual negative Poisson’s ratio and ultrahigh ideal strength that can even outperform graphene. Furthermore, unlike graphene that needs to be functionalized for opening a band gap, penta-graphene possesses an intrinsic quasi-direct band gap as large as 3.25 eV, close to that of ZnO and GaN. Equally important, penta-graphene can be exfoliated from T12-carbon. When rolled up, it can form pentagon-based nanotubes which are semiconducting, regardless of their chirality. When stacked in different patterns, stable 3D twin structures of T12-carbon are generated with band gaps even larger than that of T12-carbon. The versatility of penta-graphene and its derivatives are expected to have broad applications in nanoelectronics and nanomechanics. PMID:25646451

  20. Evaluation of Nanoclay Exfoliation Strategies for Thermoset Polyimide Nanocomposite Systems

    NASA Technical Reports Server (NTRS)

    Ginter, Michael J.; Jana, Sadhan C.; Miller, Sandi G.

    2007-01-01

    Prior works show exfoliated layered silicate reinforcement improves polymer composite properties. However, achieving full clay exfoliation in high performance thermoset polyimides remains a challenge. This study explores a new method of clay exfoliation, which includes clay intercalation by lower molecular weight PMR monomer under conditions of low and high shear and sonication, clay treatments by aliphatic and aromatic surfactants, and clay dispersion in primary, higher molecular weight PMR resin. Clay spacing, thermal, and mechanical properties were evaluated and compared with the best results available in literature for PMR polyimide systems.

  1. Strain and morphology of graphene membranes on responsive microhydrogel patterns

    SciTech Connect

    Shaina, P. R.; Jaiswal, Manu

    2014-11-10

    We study the configuration of atomically-thin graphene membranes on tunable microhydrogel patterns. The polyethylene oxide microhydrogel structures patterned by electron-beam lithography show increase in height, with a persistent swelling ratio up to ∼10, upon exposure to vapors of an organic solvent. We demonstrate that modifying the height fluctuations of the microhydrogel affects the strain and morphology of ultrathin graphene membrane over-layer. Raman spectroscopic investigations indicate that small lattice strains can be switched on in mechanically exfoliated few-layer graphene membranes that span these microhydrogel structures. In case of chemical-vapor deposited single-layer graphene, we observe Raman signatures of local depinning of the membranes upon swelling of microhydrogel pillars. We attribute this depinning transition to the competition between membrane-substrate adhesion energy and membrane strain energy, where the latter is tuned by hydrogel swelling.

  2. High-efficiency exfoliation of layered materials into 2D nanosheets in switchable CO2/Surfactant/H2O system

    PubMed Central

    Wang, Nan; Xu, Qun; Xu, Shanshan; Qi, Yuhang; Chen, Meng; Li, Hongxiang; Han, Buxing

    2015-01-01

    Layered materials present attractive and important properties due to their two-dimensional (2D) structure, allowing potential applications including electronics, optoelectronics, and catalysis. However, fully exploiting the outstanding properties will require a method for their efficient exfoliation. Here we present that a series of layered materials can be successfully exfoliated into single- and few-layer nanosheets using the driving forces coming from the phase inversion, i.e., from micelles to reverse micelles in the emulsion microenvironment built by supercritical carbon dioxide (SC CO2). The effect of variable experimental parameters including CO2 pressure, ethanol/water ratio, and initial concentration of bulk materials on the exfoliation yield have been investigated. Moreover, we demonstrate that the exfoliated 2D nanosheets have their worthwhile applications, for example, graphene can be used to prepare conductive paper, MoS2 can be used as fluorescent label to perform cellular labelling, and BN can effectively reinforce polymers leading to the promising mechanical properties. PMID:26568039

  3. Electronic and mechanical properties of graphene-germanium interfaces grown by chemical vapor deposition

    SciTech Connect

    Kiraly, Brian T.; Jacobberger, Robert M.; Mannix, Andrew J.; Campbell, Gavin P.; Bedzyk, Michael J.; Arnold, Michael S.; Hersam, Mark C.; Guisinger, Nathan P.

    2015-10-27

    Epitaxially oriented wafer-scale graphene grown directly on semiconducting Ge substrates is of high interest for both fundamental science and electronic device applications. To date, however, this material system remains relatively unexplored structurally and electronically, particularly at the atomic scale. To further understand the nature of the interface between graphene and Ge, we utilize ultrahigh vacuum scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) along with Raman and X-ray photoelectron spectroscopy to probe interfacial atomic structure and chemistry. STS reveals significant differences in electronic interactions between graphene and Ge(110)/Ge(111), which is consistent with a model of stronger interaction on Ge(110) leading to epitaxial growth. Raman spectra indicate that the graphene is considerably strained after growth, with more point-to-point variation on Ge(111). Furthermore, this native strain influences the atomic structure of the interface by inducing metastable and previously unobserved Ge surface reconstructions following annealing. These nonequilibrium reconstructions cover >90% of the surface and, in turn, modify both the electronic and mechanical properties of the graphene overlayer. Finally, graphene on Ge(001) represents the extreme strain case, where graphene drives the reorganization of the Ge surface into [107] facets. From this study, it is clear that the interaction between graphene and the underlying Ge is not only dependent on the substrate crystallographic orientation, but is also tunable and strongly related to the atomic reconfiguration of the graphene–Ge interface.

  4. Direct coupling between charge current and spin polarization by extrinsic mechanisms in graphene

    NASA Astrophysics Data System (ADS)

    Huang, Chunli; Chong, Y. D.; Cazalilla, Miguel A.

    2016-08-01

    Spintronics—the all-electrical control of the electron spin for quantum or classical information storage and processing—is one of the most promising applications of the two-dimensional material graphene. Although pristine graphene has negligible spin-orbit coupling (SOC), both theory and experiment suggest that SOC in graphene can be enhanced by extrinsic means, such as functionalization by adatom impurities. We present a theory of transport in graphene that accounts for the spin-coherent dynamics of the carriers, including hitherto-neglected spin precession processes taking place during resonant scattering in the dilute impurity limit. We uncover an "anisotropic spin precession" (ASP) scattering process in graphene, which contributes a large current-induced spin polarization and modifies the standard spin Hall effect. ASP scattering arises from two dimensionality and extrinsic SOC, and apart from graphene, it can be present in other 2D materials or in the surface states of 3D materials with a fluctuating SOC. Our theory also yields a comprehensive description of the spin relaxation mechanisms present in adatom-decorated graphene, including Elliot-Yafet and D'yakonov-Perel relaxation rates, the latter of which can become an amplification process in a certain parameter regime of the SOC disorder potential. Our work provides theoretical foundations for designing future graphene-based integrated spintronic devices.

  5. Electronic and mechanical properties of graphene-germanium interfaces grown by chemical vapor deposition

    DOE PAGES

    Kiraly, Brian T.; Jacobberger, Robert M.; Mannix, Andrew J.; ...

    2015-10-27

    Epitaxially oriented wafer-scale graphene grown directly on semiconducting Ge substrates is of high interest for both fundamental science and electronic device applications. To date, however, this material system remains relatively unexplored structurally and electronically, particularly at the atomic scale. To further understand the nature of the interface between graphene and Ge, we utilize ultrahigh vacuum scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) along with Raman and X-ray photoelectron spectroscopy to probe interfacial atomic structure and chemistry. STS reveals significant differences in electronic interactions between graphene and Ge(110)/Ge(111), which is consistent with a model of stronger interaction on Ge(110)more » leading to epitaxial growth. Raman spectra indicate that the graphene is considerably strained after growth, with more point-to-point variation on Ge(111). Furthermore, this native strain influences the atomic structure of the interface by inducing metastable and previously unobserved Ge surface reconstructions following annealing. These nonequilibrium reconstructions cover >90% of the surface and, in turn, modify both the electronic and mechanical properties of the graphene overlayer. Finally, graphene on Ge(001) represents the extreme strain case, where graphene drives the reorganization of the Ge surface into [107] facets. From this study, it is clear that the interaction between graphene and the underlying Ge is not only dependent on the substrate crystallographic orientation, but is also tunable and strongly related to the atomic reconfiguration of the graphene–Ge interface.« less

  6. Single-Nanowire Electrochemical Probe Detection for Internally Optimized Mechanism of Porous Graphene in Electrochemical Devices.

    PubMed

    Hu, Ping; Yan, Mengyu; Wang, Xuanpeng; Han, Chunhua; He, Liang; Wei, Xiujuan; Niu, Chaojiang; Zhao, Kangning; Tian, Xiaocong; Wei, Qiulong; Li, Zijia; Mai, Liqiang

    2016-03-09

    Graphene has been widely used to enhance the performance of energy storage devices due to its high conductivity, large surface area, and excellent mechanical flexibility. However, it is still unclear how graphene influences the electrochemical performance and reaction mechanisms of electrode materials. The single-nanowire electrochemical probe is an effective tool to explore the intrinsic mechanisms of the electrochemical reactions in situ. Here, pure MnO2 nanowires, reduced graphene oxide/MnO2 wire-in-scroll nanowires, and porous graphene oxide/MnO2 wire-in-scroll nanowires are employed to investigate the capacitance, ion diffusion coefficient, and charge storage mechanisms in single-nanowire electrochemical devices. The porous graphene oxide/MnO2 wire-in-scroll nanowire delivers an areal capacitance of 104 nF/μm(2), which is 4.0 and 2.8 times as high as those of reduced graphene oxide/MnO2 wire-in-scroll nanowire and MnO2 nanowire, respectively, at a scan rate of 20 mV/s. It is demonstrated that the reduced graphene oxide wrapping around the MnO2 nanowire greatly increases the electronic conductivity of the active materials, but decreases the ion diffusion coefficient because of the shielding effect of graphene. By creating pores in the graphene, the ion diffusion coefficient is recovered without degradation of the electron transport rate, which significantly improves the capacitance. Such single-nanowire electrochemical probes, which can detect electrochemical processes and behavior in situ, can also be fabricated with other active materials for energy storage and other applications in related fields.

  7. Study of antibacterial mechanism of graphene oxide using Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Nanda, Sitansu Sekhar; Yi, Dong Kee; Kim, Kwangmeyung

    2016-06-01

    Graphene oxide (GO) is extensively proposed as an effective antibacterial agent in commercial product packaging and for various biomedical applications. However, the antibacterial mode of action of GO is yet hypothetical and unclear. Here we developed a new and sensitive fingerprint approach to study the antibacterial activity of GO and underlying mechanism, using Raman spectroscopy. Spectroscopic signatures obtained from biomolecules such as Adenine and proteins from bacterial cultures with different concentrations of GO, allowed us to probe the antibacterial activity of GO with its mechanism at the molecular level. Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) were used as model micro-organisms for all the experiments performed. The observation of higher intensity Raman peaks from Adenine and proteins in GO treated E. coli and E. faecalis; correlated with induced death, confirmed by Scanning electron Microscopy (SEM) and Biological Atomic Force Microscopy (Bio-AFM). Our findings open the way for future investigations of the antibacterial properties of different nanomaterial/GO composites using Raman spectroscopy.

  8. Study of antibacterial mechanism of graphene oxide using Raman spectroscopy

    PubMed Central

    Nanda, Sitansu Sekhar; Yi, Dong Kee; Kim, Kwangmeyung

    2016-01-01

    Graphene oxide (GO) is extensively proposed as an effective antibacterial agent in commercial product packaging and for various biomedical applications. However, the antibacterial mode of action of GO is yet hypothetical and unclear. Here we developed a new and sensitive fingerprint approach to study the antibacterial activity of GO and underlying mechanism, using Raman spectroscopy. Spectroscopic signatures obtained from biomolecules such as Adenine and proteins from bacterial cultures with different concentrations of GO, allowed us to probe the antibacterial activity of GO with its mechanism at the molecular level. Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) were used as model micro-organisms for all the experiments performed. The observation of higher intensity Raman peaks from Adenine and proteins in GO treated E. coli and E. faecalis; correlated with induced death, confirmed by Scanning electron Microscopy (SEM) and Biological Atomic Force Microscopy (Bio-AFM). Our findings open the way for future investigations of the antibacterial properties of different nanomaterial/GO composites using Raman spectroscopy. PMID:27324288

  9. Exfoliative toxins of Staphylococcus aureus.

    PubMed

    Bukowski, Michal; Wladyka, Benedykt; Dubin, Grzegorz

    2010-05-01

    Staphylococcus aureus is an important pathogen of humans and livestock. It causes a diverse array of diseases, ranging from relatively harmless localized skin infections to life-threatening systemic conditions. Among multiple virulence factors, staphylococci secrete several exotoxins directly associated with particular disease symptoms. These include toxic shock syndrome toxin 1 (TSST-1), enterotoxins, and exfoliative toxins (ETs). The latter are particularly interesting as the sole agents responsible for staphylococcal scalded skin syndrome (SSSS), a disease predominantly affecting infants and characterized by the loss of superficial skin layers, dehydration, and secondary infections. The molecular basis of the clinical symptoms of SSSS is well understood. ETs are serine proteases with high substrate specificity, which selectively recognize and hydrolyze desmosomal proteins in the skin. The fascinating road leading to the discovery of ETs as the agents responsible for SSSS and the characterization of the molecular mechanism of their action, including recent advances in the field, are reviewed in this article.

  10. Plasticity and ductility in graphene oxide through a mechanochemically induced damage tolerance mechanism

    PubMed Central

    Wei, Xiaoding; Mao, Lily; Soler-Crespo, Rafael A.; Paci, Jeffrey T.; Espinosa, Horacio D.

    2015-01-01

    The ability to bias chemical reaction pathways is a fundamental goal for chemists and material scientists to produce innovative materials. Recently, two-dimensional materials have emerged as potential platforms for exploring novel mechanically activated chemical reactions. Here we report a mechanochemical phenomenon in graphene oxide membranes, covalent epoxide-to-ether functional group transformations that deviate from epoxide ring-opening reactions, discovered through nanomechanical experiments and density functional-based tight binding calculations. These mechanochemical transformations in a two-dimensional system are directionally dependent, and confer pronounced plasticity and damage tolerance to graphene oxide monolayers. Additional experiments on chemically modified graphene oxide membranes, with ring-opened epoxide groups, verify this unique deformation mechanism. These studies establish graphene oxide as a two-dimensional building block with highly tuneable mechanical properties for the design of high-performance nanocomposites, and stimulate the discovery of new bond-selective chemical transformations in two-dimensional materials. PMID:26289729

  11. Hydrogen Implants for Layer Exfoliation

    NASA Astrophysics Data System (ADS)

    Cherekdjian, S.; Couillard, J. G.; Wilcox, C.

    2011-01-01

    Researchers at Corning Incorporated have developed a process whereby single crystal silicon thin films are transferred onto a flat panel display glass substrate using hydrogen ion implantation. The energy of the implant controls the effective exfoliation thickness, agreeing well with SRIM calculations, while the hydrogen ion dose controls the size of the platelets formed. The ion dose was found to influence the final void defect count in exfoliated films. Finally, the ion beam and ion implant end-station cooling characteristics were investigated. These parameters control the effective implant heat load generated during ion beam processing. The temperature at which exfoliation occurs during an exfoliation heat cycle was found to be inversely proportional to the hydrogen ion dose when the temperature during ion implantation is <100 °C. The most sensitive exfoliation temperature to ion dose dependence was observed for cooler implants, i.e. <35 °C. Data indicates that at the minimum exfoliation dose the exfoliation temperature is reduced significantly by increasing the implant heat generated during ion beam processing. Higher hydrogen doses than the minimum required for exfoliation exhibit only a small exfoliation temperature variation with ion dose. By optimizing the implant heat load generated during ion beam processing it is observed that the efficiency of the exfoliation process is also enhanced. Implant temperatures of 150 to 160 °C were found to further reduce the minimum implant dose required for exfoliation by an additional 5%, as verified by calorimetric measurements. These results enable us to further conclude that hydrogen out-diffusion is not significant in this process.

  12. Modulation of mechanical resonance by chemical potential oscillation in graphene

    NASA Astrophysics Data System (ADS)

    Chen, Changyao; Deshpande, Vikram V.; Koshino, Mikito; Lee, Sunwoo; Gondarenko, Alexander; MacDonald, Allan H.; Kim, Philip; Hone, James

    2016-03-01

    The classical picture of the force on a capacitor assumes a large density of electronic states, such that the electrochemical potential of charges added to the capacitor is given by the external electrostatic potential and the capacitance is determined purely by geometry. Here we consider capacitively driven motion of a nano-mechanical resonator with a low density of states, in which these assumptions can break down. We find three leading-order corrections to the classical picture: the first of which is a modulation in the static force due to variation in the internal chemical potential; the second and third are changes in the static force and dynamic spring constant due to the rate of change of chemical potential, expressed as the quantum (density of states) capacitance. As a demonstration, we study capacitively driven graphene mechanical resonators, where the chemical potential is modulated independently of the gate voltage using an applied magnetic field to manipulate the energy of electrons residing in discrete Landau levels. In these devices, we observe large periodic frequency shifts consistent with the three corrections to the classical picture. In devices with extremely low strain and disorder, the first correction term dominates and the resonant frequency closely follows the chemical potential. The theoretical model fits the data with only one adjustable parameter representing disorder-broadening of the Landau levels. The underlying electromechanical coupling mechanism is not limited by the particular choice of material, geometry, or mechanism for variation in the chemical potential, and can thus be extended to other low-dimensional systems.

  13. Modeling the mechanics of graphene-based polymer composite film measured by the bulge test

    NASA Astrophysics Data System (ADS)

    Zhang, Jian-Jun; Sun, You-yi; Li, Dian-sen; Cao, Yang; Wang, Zuo; Ma, Jing; Zhao, Gui-Zhe

    2015-10-01

    Graphene-based polymer composite films have wide-ranging potential applications, such as in sensors, electromagnetic shielding, absorbing materials, corrosion resistance and so on. In addition, the practical applications of graphene-based polymer composite films are closely related to their mechanical properties. However, the mechanical properties of graphene-based polymer composite films are difficult to characterize with tensile tests. In this paper, the bugle test was used to investigate the mechanical properties of graphene-based polymer composite films. The experimental results show that the Young’s modulus of polymer composite films increases non-linearly with an increase in the doping content of graphene, and viscoelastic deformation is induced under cyclic loading conditions. Moreover, in order to describe their mechanical behavior, an ‘Arruda-Boyce’ finite-strain constitutive model (modified BPA model), based on the strain amplification hypothesis, and a traditional ‘Arruda-Boyce’ model was proposed, which incorporated many of the features of previous theories. The numerical treatment of the modified BPA model associated with finite element analysis is also discussed. This new model is shown to be able to predict the experimentally observed mechanical behavior of graphene based polymer composite films measured by the bugle test effectively.

  14. Polymer reinforcement using liquid-exfoliated boron nitride nanosheets.

    PubMed

    Khan, Umar; May, Peter; O'Neill, Arlene; Bell, Alan P; Boussac, Elodie; Martin, Arnaud; Semple, James; Coleman, Jonathan N

    2013-01-21

    We have exfoliated hexagonal boron nitride by ultrasonication in solutions of polyvinylalcohol in water. The resultant nanosheets are sterically stabilised by adsorbed polymer chains. Centrifugation-based size-selection was used to give dispersions of nanosheets with aspect ratio (length/thickness) of ∼1400. Such dispersions can be used to produce polyvinylalcohol-BN composite films. Helium ion microscopy of fracture surfaces shows the nanosheets to be well dispersed and the composites to fail by pull-out. We find both modulus, Y, and strength, σ(B), of these composites to increase linearly with volume fraction, V(f), up to V(f)∼ 0.1 vol% BN before falling off. The rates of increase are extremely high; dY/dV(f) = 670 GPa and dσ(B)/dV(f) = 47 GPa. The former value matches theory based on continuum mechanics while the latter value is consistent with remarkably high polymer-filler interfacial strength. However, because the mechanical properties increase over such a narrow volume fraction range, the maximum values of both modulus and strength are only ∼40% higher than the pure polymer. This phenomenon has also been observed for graphene-filled composites and represents a serious hurdle to the production of high performance polymer-nanosheet composites.

  15. First-principles study of the mechanism of wettability transition of defective graphene

    NASA Astrophysics Data System (ADS)

    Błoński, Piotr; Otyepka, Michal

    2017-02-01

    Hydrophobicity of graphene limits its application potential in polar media, therefore modifications of graphene wettability have been in an area of active research for many years. Recently, a reversible wettability transition of graphene has been reported (Xu et al 2014 Sci. Rep. 4 6450). The presence of undercoordinated carbon atoms in otherwise hydrophobic graphene is believed to trigger the hydrophobic to hydrophilic transition, but the underlying mechanism, especially of the reverse process, remained unclear. Using density functional theory with range-separated hybrid functional HSE06, we investigate the dissociative adsorption of up to two water molecules on the defective graphene layer containing odd number of missing lattice atoms. We show, that depending on the defect type either a full dissociation of the water molecule or a partial splitting of H2O to OH and H takes place leading to the saturation of graphene dangling bonds due to the formation of oxiranes or by hydroxyls, respectively. The dissociation barriers are significantly lower for the water dimer than for the single molecule. Our findings providing detailed insights into the remarkable differences between the reactivity of vacancy defects with water shed new light on the wettability-transition mechanism of defective graphene.

  16. Fabrication, Characterization, and Applications of Graphene-based Flexible Films

    NASA Astrophysics Data System (ADS)

    Naik, Gautam

    Scientific interest in the field of nanotechnology has increased multifold since the discovery of multi-walled carbon nanotubes in the early 1990s. This further received a tremendous boost with the isolation of graphene, a single layer of sp2-hybridized carbon atoms, in 2004. Graphene has exceptional mechanical and electrical properties, which makes it an attractive candidate for electronics and composites. In order to realize the implementation of graphene for such applications, scalable production of graphene-based materials needs to be accomplished. Graphene oxide, the product of oxidation and exfoliation of graphite, is a promising precursor for bulk-production of graphene and graphene-like materials. The oxidation of graphite to synthesize graphene oxide results in the decoration of the basal plane of graphene with oxygen-containing functional groups. The presence of these functional groups makes graphene oxide strongly hydrophilic, making it soluble in water and a good candidate for solution-based processing. This hydrophilic nature of graphene oxide can also be utilized to fabricate highly sensitive and flexible humidity sensors, the results of which are included in this research. The fabricated humidity sensors show high sensitivity and a fast response time. A difference in response is observed at low and high humidity, with hysteresis observed at high humidity levels. A method to "reset" the sensor and a mechanism to explain the response is also proposed. Although the hydrophilic nature of graphene oxide makes it suitable for bulk processing, the presence of functional groups makes it defective and insulating. Graphene oxide needs to be reduced to make it electrically active. Numerous methodologies proposed for reduction of graphene oxide result in the simultaneous reduction and exfoliation of graphene oxide films. But for instances where flexible graphene films are required for certain applications, a method for reduction of graphene oxide flexible films

  17. One-Pot Exfoliation of Graphite and Synthesis of Nanographene/Dimesitylporphyrin Hybrids

    PubMed Central

    Bernal, M. Mar; Pérez, Emilio M.

    2015-01-01

    A simple one-pot process to exfoliate graphite and synthesize nanographene-dimesitylporphyrin hybrids has been developed. Despite the bulky mesityl groups, which are expected to hinder the efficient π–π stacking between the porphyrin core and graphene, the liquid-phase exfoliation of graphite is significantly favored by the presence of the porphyrins. Metallation of the porphyrin further enhances this effect. The resulting graphene/porphyrin hybrids were characterized by spectroscopy (UV-visible, fluorescence, and Raman) and microscopy (STEM, scanning transmission electron microscopy). PMID:25984598

  18. One-pot exfoliation of graphite and synthesis of nanographene/dimesitylporphyrin hybrids.

    PubMed

    Bernal, M Mar; Pérez, Emilio M

    2015-05-12

    A simple one-pot process to exfoliate graphite and synthesize nanographene-dimesitylporphyrin hybrids has been developed. Despite the bulky mesityl groups, which are expected to hinder the efficient π-π stacking between the porphyrin core and graphene, the liquid-phase exfoliation of graphite is significantly favored by the presence of the porphyrins. Metallation of the porphyrin further enhances this effect. The resulting graphene/porphyrin hybrids were characterized by spectroscopy (UV-visible, fluorescence, and Raman) and microscopy (STEM, scanning transmission electron microscopy).

  19. Explosive thermal reduction of graphene oxide-based materials: mechanism and safety implications.

    PubMed

    Qiu, Yang; Guo, Fei; Hurt, Robert; Külaots, Indrek

    2014-06-01

    Thermal reduction of graphene oxide or graphite oxide (GO) is an important processing step in the fabrication of many graphene-based materials and devices. Here we show that some bulk solid GO samples can undergo explosive decomposition when small samples are heated slowly in inert gas environments, while others do not. These micro-explosions can occur for samples as small as few milligrams and are sufficiently energetic to cause laboratory equipment damage. Thermochemical analysis methods are used to understand the factors that lead to the explosive reduction mode. The studies show that the explosive mode of reduction is caused by the exothermicity of GO reduction coupled with a threshold sample mass/size that causes heat and mass transfer limitations leading to local temperature rise and a thermal runaway reaction. The explosive mode of reduction is not caused or promoted by interstitial water, and its onset temperature can be lowered by immersion in potassium hydroxide solution. By allowing early release of internal gas pressure, the explosive mode reduces the extent of surface area development in GO exfoliation from an optimum value of 1470 m(2)g(-1) obtained under non-explosive reduction conditions. Explosive reduction of bulk GO poses industrial safety hazards during large-scale storage, handling, and processing.

  20. Explosive thermal reduction of graphene oxide-based materials: mechanism and safety implications

    PubMed Central

    Qiu, Yang; Guo, Fei; Hurt, Robert; Külaots, Indrek

    2014-01-01

    Thermal reduction of graphene oxide or graphite oxide (GO) is an important processing step in the fabrication of many graphene-based materials and devices. Here we show that some bulk solid GO samples can undergo explosive decomposition when small samples are heated slowly in inert gas environments, while others do not. These micro-explosions can occur for samples as small as few milligrams and are sufficiently energetic to cause laboratory equipment damage. Thermochemical analysis methods are used to understand the factors that lead to the explosive reduction mode. The studies show that the explosive mode of reduction is caused by the exothermicity of GO reduction coupled with a threshold sample mass/size that causes heat and mass transfer limitations leading to local temperature rise and a thermal runaway reaction. The explosive mode of reduction is not caused or promoted by interstitial water, and its onset temperature can be lowered by immersion in potassium hydroxide solution. By allowing early release of internal gas pressure, the explosive mode reduces the extent of surface area development in GO exfoliation from an optimum value of 1470 m2g−1 obtained under non-explosive reduction conditions. Explosive reduction of bulk GO poses industrial safety hazards during large-scale storage, handling, and processing. PMID:25018560

  1. Growth mechanism of graphene on platinum: Surface catalysis and carbon segregation

    SciTech Connect

    Sun, Jie Lindvall, Niclas; Yurgens, August; Nam, Youngwoo; Cole, Matthew T.; Teo, Kenneth B. K.; Woo Park, Yung

    2014-04-14

    A model of the graphene growth mechanism of chemical vapor deposition on platinum is proposed and verified by experiments. Surface catalysis and carbon segregation occur, respectively, at high and low temperatures in the process, representing the so-called balance and segregation regimes. Catalysis leads to self-limiting formation of large area monolayer graphene, whereas segregation results in multilayers, which evidently “grow from below.” By controlling kinetic factors, dominantly monolayer graphene whose high quality has been confirmed by quantum Hall measurement can be deposited on platinum with hydrogen-rich environment, quench cooling, tiny but continuous methane flow and about 1000 °C growth temperature.

  2. Growth mechanism of graphene on platinum: Surface catalysis and carbon segregation

    NASA Astrophysics Data System (ADS)

    Sun, Jie; Nam, Youngwoo; Lindvall, Niclas; Cole, Matthew T.; Teo, Kenneth B. K.; Woo Park, Yung; Yurgens, August

    2014-04-01

    A model of the graphene growth mechanism of chemical vapor deposition on platinum is proposed and verified by experiments. Surface catalysis and carbon segregation occur, respectively, at high and low temperatures in the process, representing the so-called balance and segregation regimes. Catalysis leads to self-limiting formation of large area monolayer graphene, whereas segregation results in multilayers, which evidently "grow from below." By controlling kinetic factors, dominantly monolayer graphene whose high quality has been confirmed by quantum Hall measurement can be deposited on platinum with hydrogen-rich environment, quench cooling, tiny but continuous methane flow and about 1000 °C growth temperature.

  3. Mechanical strain induced valley-dependent quantum magnetotransport of Dirac particles in graphene

    NASA Astrophysics Data System (ADS)

    Ma, Ning; Zhang, Shengli; Liu, Daqing; Wang, Vei

    2015-12-01

    We have explored the mechanical strain effects on the magnetotransport in graphene with a 1D electrostatic periodic potential in the presence of a perpendicular magnetic field. We find that, in a strong magnetic field regime, the conductivity exhibits a superposition of the Shubnikov-de Haas and Weiss oscillations in each valley due to the electrical modulation. Especially, the strain removes the valley degeneracy of Landau levels in inversion symmetric Dirac cones. Accordingly, this causes the valley-dependence of the conductivity. These phenomena, absent in a freestanding graphene, are a consequence of the anomalous spectrum of carriers in a fully stained graphene.

  4. Geometry, mechanics, and electronics of singular structures and wrinkles in graphene.

    PubMed

    Pereira, Vitor M; Castro Neto, A H; Liang, H Y; Mahadevan, L

    2010-10-08

    As the thinnest atomic membrane, graphene presents an opportunity to combine geometry, elasticity, and electronics at the limits of their validity. We describe the transport and electronic structure in the neighborhood of conical singularities, the elementary excitations of the ubiquitous wrinkled and crumpled graphene. We use a combination of atomistic mechanical simulations, analytical geometry, and transport calculations in curved graphene, and exact diagonalization of the electronic spectrum to calculate the effects of geometry on electronic structure, transport, and mobility in suspended samples, and how the geometry-generated pseudomagnetic and pseudoelectric fields might disrupt Landau quantization.

  5. The effect of graphene content and sliding speed on the wear mechanism of nickel-graphene nanocomposites

    NASA Astrophysics Data System (ADS)

    Algul, H.; Tokur, M.; Ozcan, S.; Uysal, M.; Cetinkaya, T.; Akbulut, H.; Alp, A.

    2015-12-01

    Nickel-graphene metal matrix composite coatings were fabricated by pulse electrodeposition technique from a Watt's type electrolyte. Effect of the graphene concentration in the electrolyte on the microstructure, microhardness, tribological features of nanocomposite coatings were evaluated in details. Microhardness of the composite coating was measured using a Vicker's microhardness indenter. The surfaces of the samples were characterized by scanning electron microscopy (SEM). Raman spectroscopy, EDS and XRD analysis were used to determine chemical composition and structure of composite coatings. The tribological behavior of the resultant composite coating was tested by a reciprocating ball-on disk method at constant load but varying sliding speeds for determination the wear loss and friction coefficient features against a counterface. The wear and friction variations of the electrodeposited nickel graphene nanocomposite coatings sliding against an M50 steel balls were carried out on a CSM Instrument. The friction and wear properties of the coatings were examined without any lubrication at room temperature in the ambient air. The change in wear mechanisms by changing graphene nanosheets content was also comprehensively studied.

  6. Recompressed exfoliated graphite articles

    DOEpatents

    Zhamu, Aruna; Shi, Jinjun; Guo, Jiusheng; Jang, Bor Z

    2013-08-06

    This invention provides an electrically conductive, less anisotropic, recompressed exfoliated graphite article comprising a mixture of (a) expanded or exfoliated graphite flakes; and (b) particles of non-expandable graphite or carbon, wherein the non-expandable graphite or carbon particles are in the amount of between about 3% and about 70% by weight based on the total weight of the particles and the expanded graphite flakes combined; wherein the mixture is compressed to form the article having an apparent bulk density of from about 0.1 g/cm.sup.3 to about 2.0 g/cm.sup.3. The article exhibits a thickness-direction conductivity typically greater than 50 S/cm, more typically greater than 100 S/cm, and most typically greater than 200 S/cm. The article, when used in a thin foil or sheet form, can be a useful component in a sheet molding compound plate used as a fuel cell separator or flow field plate. The article may also be used as a current collector for a battery, supercapacitor, or any other electrochemical cell.

  7. Metallic Nanoislands on Graphene as Highly Sensitive Transducers of Mechanical, Biological, and Optical Signals

    PubMed Central

    2016-01-01

    This article describes an effect based on the wetting transparency of graphene; the morphology of a metallic film (≤20 nm) when deposited on graphene by evaporation depends strongly on the identity of the substrate supporting the graphene. This control permits the formation of a range of geometries, such as tightly packed nanospheres, nanocrystals, and island-like formations with controllable gaps down to 3 nm. These graphene-supported structures can be transferred to any surface and function as ultrasensitive mechanical signal transducers with high sensitivity and range (at least 4 orders of magnitude of strain) for applications in structural health monitoring, electronic skin, measurement of the contractions of cardiomyocytes, and substrates for surface-enhanced Raman scattering (SERS, including on the tips of optical fibers). These composite films can thus be treated as a platform technology for multimodal sensing. Moreover, they are low profile, mechanically robust, semitransparent and have the potential for reproducible manufacturing over large areas. PMID:26765039

  8. Metallic Nanoislands on Graphene as Highly Sensitive Transducers of Mechanical, Biological, and Optical Signals.

    PubMed

    Zaretski, Aliaksandr V; Root, Samuel E; Savchenko, Alex; Molokanova, Elena; Printz, Adam D; Jibril, Liban; Arya, Gaurav; Mercola, Mark; Lipomi, Darren J

    2016-02-10

    This article describes an effect based on the wetting transparency of graphene; the morphology of a metallic film (≤20 nm) when deposited on graphene by evaporation depends strongly on the identity of the substrate supporting the graphene. This control permits the formation of a range of geometries, such as tightly packed nanospheres, nanocrystals, and island-like formations with controllable gaps down to 3 nm. These graphene-supported structures can be transferred to any surface and function as ultrasensitive mechanical signal transducers with high sensitivity and range (at least 4 orders of magnitude of strain) for applications in structural health monitoring, electronic skin, measurement of the contractions of cardiomyocytes, and substrates for surface-enhanced Raman scattering (SERS, including on the tips of optical fibers). These composite films can thus be treated as a platform technology for multimodal sensing. Moreover, they are low profile, mechanically robust, semitransparent and have the potential for reproducible manufacturing over large areas.

  9. Doping mechanisms in graphene-MoS{sub 2} hybrids

    SciTech Connect

    Sachs, B. Lichtenstein, A. I.; Britnell, L.; Eckmann, A.; Novoselov, K. S.; Wehling, T. O.; Jalil, R.; Belle, B. D.; Katsnelson, M. I.

    2013-12-16

    We present a joint theoretical and experimental investigation of charge doping and electronic potential landscapes in hybrid structures composed of graphene and semiconducting single layer molybdenum disulfide (MoS{sub 2}). From first-principles simulations, we find electron doping of graphene due to the presence of rhenium impurities in MoS{sub 2}. Furthermore, we show that MoS{sub 2} edges give rise to charge reordering and a potential shift in graphene, which can be controlled through external gate voltages. The interplay of edge and impurity effects allows the use of the graphene-MoS{sub 2} hybrid as a photodetector. Spatially resolved photocurrent signals can be used to resolve potential gradients and local doping levels in the sample.

  10. Excitonic recombinations in h-BN: From bulk to exfoliated layers

    NASA Astrophysics Data System (ADS)

    Pierret, A.; Loayza, J.; Berini, B.; Betz, A.; Plaçais, B.; Ducastelle, F.; Barjon, J.; Loiseau, A.

    2014-01-01

    Hexagonal boron nitride (h-BN) and graphite are structurally similar but with very different properties. Their combination in graphene-based devices is now of intense research focus, and it becomes particularly important to evaluate the role played by crystalline defects on their properties. In this paper, the cathodoluminescence (CL) properties of hexagonal boron nitride crystallites are reported and compared to those of nanosheets mechanically exfoliated from them. First, the link between the presence of structural defects and the recombination intensity of trapped excitons, the so-called D series, is confirmed. Low defective h-BN regions are further evidenced by CL spectral mapping (hyperspectral imaging), allowing us to observe new features in the near-band-edge region, tentatively attributed to phonon replicas of exciton recombinations. Second, the h-BN thickness was reduced down to six atomic layers, using mechanical exfoliation, as evidenced by atomic force microscopy. Even at these low thicknesses, the luminescence remains intense and exciton recombination energies are not strongly modified with respect to the bulk, as expected from theoretical calculations, indicating extremely compact excitons in h-BN.

  11. Understanding the growth mechanism of graphene on Ge/Si(001) surfaces

    PubMed Central

    Dabrowski, J.; Lippert, G.; Avila, J.; Baringhaus, J.; Colambo, I.; Dedkov, Yu S.; Herziger, F.; Lupina, G.; Maultzsch, J.; Schaffus, T.; Schroeder, T.; Kot, M.; Tegenkamp, C.; Vignaud, D.; Asensio, M.-C.

    2016-01-01

    The practical difficulties to use graphene in microelectronics and optoelectronics is that the available methods to grow graphene are not easily integrated in the mainstream technologies. A growth method that could overcome at least some of these problems is chemical vapour deposition (CVD) of graphene directly on semiconducting (Si or Ge) substrates. Here we report on the comparison of the CVD and molecular beam epitaxy (MBE) growth of graphene on the technologically relevant Ge(001)/Si(001) substrate from ethene (C2H4) precursor and describe the physical properties of the films as well as we discuss the surface reaction and diffusion processes that may be responsible for the observed behavior. Using nano angle resolved photoemission (nanoARPES) complemented by transport studies and Raman spectroscopy as well as density functional theory (DFT) calculations, we report the direct observation of massless Dirac particles in monolayer graphene, providing a comprehensive mapping of their low-hole doped Dirac electron bands. The micrometric graphene flakes are oriented along two predominant directions rotated by 30° with respect to each other. The growth mode is attributed to the mechanism when small graphene “molecules” nucleate on the Ge(001) surface and it is found that hydrogen plays a significant role in this process. PMID:27531322

  12. Failure mechanism of monolayer graphene under hypervelocity impact of spherical projectile

    NASA Astrophysics Data System (ADS)

    Xia, Kang; Zhan, Haifei; Hu, De’An; Gu, Yuantong

    2016-09-01

    The excellent mechanical properties of graphene have enabled it as appealing candidate in the field of impact protection or protective shield. By considering a monolayer graphene membrane, in this work, we assessed its deformation mechanisms under hypervelocity impact (from 2 to 6 km/s), based on a serial of in silico studies. It is found that the cracks are formed preferentially in the zigzag directions which are consistent with that observed from tensile deformation. Specifically, the boundary condition is found to exert an obvious influence on the stress distribution and transmission during the impact process, which eventually influences the penetration energy and crack growth. For similar sample size, the circular shape graphene possesses the best impact resistance, followed by hexagonal graphene membrane. Moreover, it is found the failure shape of graphene membrane has a strong relationship with the initial kinetic energy of the projectile. The higher kinetic energy, the more number the cracks. This study provides a fundamental understanding of the deformation mechanisms of monolayer graphene under impact, which is crucial in order to facilitate their emerging future applications for impact protection, such as protective shield from orbital debris for spacecraft.

  13. Failure mechanism of monolayer graphene under hypervelocity impact of spherical projectile.

    PubMed

    Xia, Kang; Zhan, Haifei; Hu, De'an; Gu, Yuantong

    2016-09-13

    The excellent mechanical properties of graphene have enabled it as appealing candidate in the field of impact protection or protective shield. By considering a monolayer graphene membrane, in this work, we assessed its deformation mechanisms under hypervelocity impact (from 2 to 6 km/s), based on a serial of in silico studies. It is found that the cracks are formed preferentially in the zigzag directions which are consistent with that observed from tensile deformation. Specifically, the boundary condition is found to exert an obvious influence on the stress distribution and transmission during the impact process, which eventually influences the penetration energy and crack growth. For similar sample size, the circular shape graphene possesses the best impact resistance, followed by hexagonal graphene membrane. Moreover, it is found the failure shape of graphene membrane has a strong relationship with the initial kinetic energy of the projectile. The higher kinetic energy, the more number the cracks. This study provides a fundamental understanding of the deformation mechanisms of monolayer graphene under impact, which is crucial in order to facilitate their emerging future applications for impact protection, such as protective shield from orbital debris for spacecraft.

  14. Failure mechanism of monolayer graphene under hypervelocity impact of spherical projectile

    PubMed Central

    Xia, Kang; Zhan, Haifei; Hu, De’an; Gu, Yuantong

    2016-01-01

    The excellent mechanical properties of graphene have enabled it as appealing candidate in the field of impact protection or protective shield. By considering a monolayer graphene membrane, in this work, we assessed its deformation mechanisms under hypervelocity impact (from 2 to 6 km/s), based on a serial of in silico studies. It is found that the cracks are formed preferentially in the zigzag directions which are consistent with that observed from tensile deformation. Specifically, the boundary condition is found to exert an obvious influence on the stress distribution and transmission during the impact process, which eventually influences the penetration energy and crack growth. For similar sample size, the circular shape graphene possesses the best impact resistance, followed by hexagonal graphene membrane. Moreover, it is found the failure shape of graphene membrane has a strong relationship with the initial kinetic energy of the projectile. The higher kinetic energy, the more number the cracks. This study provides a fundamental understanding of the deformation mechanisms of monolayer graphene under impact, which is crucial in order to facilitate their emerging future applications for impact protection, such as protective shield from orbital debris for spacecraft. PMID:27618989

  15. Investigating photoresponse in graphene by light polarization

    NASA Astrophysics Data System (ADS)

    Eginligil, M.; Cao, B. C.; Wang, Z. L.; Soci, C.; Yu, T.

    2014-03-01

    We report our photocurrent studies on single layer graphene (SLG), bilayer graphene (BLG) and trilayer graphene (TLG) by exciting with circularly polarized light. In addition to p-n junctions based on gated graphene field-effect-transistor (g-FET), it was recently demonstrated that in the graphene/metal interface large photocurrent (PC) can be generated and this PC can be manipulated by backgate voltage in a simple g-FET. In this work we fabricated g-FETs from mechanically exfoliated graphene and explored backgate voltage dependence of photon drag effect (PDE), linear and circular photogalvanic effect (CPGE) of SLG, BLG and TLG. In BLG, we noticed a cos θ dependence of the measured PC, where θ is the angle of incident light polarization, in addition to PDE and CPGE effects which have cos4 θ and sin2 θ dependence, respectively. This cos θ dependence is attributed to the Berry curvature related valley PC, which can be induced as a result of broken inversion symmetry and asymmetry in the two low energy valleys of BLG. The latter is absent in SLG and peculiar for ABA stacked TLG. By varying backgate voltage we distinguish all helicity dependent PC contributions. Our data show good agreement with the theory. Supported by the National Research Foundation of Singapore under Award No. NRF-RF2010-07 and MOE Tier 2 MOE2012-T2-2-049.

  16. Stability and exfoliation of germanane: a germanium graphane analogue.

    PubMed

    Bianco, Elisabeth; Butler, Sheneve; Jiang, Shishi; Restrepo, Oscar D; Windl, Wolfgang; Goldberger, Joshua E

    2013-05-28

    Graphene's success has shown not only that it is possible to create stable, single-atom-thick sheets from a crystalline solid but that these materials have fundamentally different properties than the parent material. We have synthesized for the first time, millimeter-scale crystals of a hydrogen-terminated germanium multilayered graphane analogue (germanane, GeH) from the topochemical deintercalation of CaGe2. This layered van der Waals solid is analogous to multilayered graphane (CH). The surface layer of GeH only slowly oxidizes in air over the span of 5 months, while the underlying layers are resilient to oxidation based on X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy measurements. The GeH is thermally stable up to 75 °C; however, above this temperature amorphization and dehydrogenation begin to occur. These sheets can be mechanically exfoliated as single and few layers onto SiO2/Si surfaces. This material represents a new class of covalently terminated graphane analogues and has great potential for a wide range of optoelectronic and sensing applications, especially since theory predicts a direct band gap of 1.53 eV and an electron mobility ca. five times higher than that of bulk Ge.

  17. Lignin-assisted exfoliation of molybdenum disulfide in aqueous media and its application in lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Liu, Wanshuang; Zhao, Chenyang; Zhou, Rui; Zhou, Dan; Liu, Zhaolin; Lu, Xuehong

    2015-05-01

    In this article, alkali lignin (AL)-assisted direct exfoliation of MoS2 mineral into single-layer and few-layer nanosheets in water is reported for the first time. Under optimized conditions, the concentration of MoS2 nanosheets in the obtained dispersion can be as high as 1.75 +/- 0.08 mg mL-1, which is much higher than the typical reported concentrations (<1.0 mg mL-1) using synthetic polymers or compounds as surfactants. The stabilizing mechanism primarily lies in the electrostatic repulsion between negative charged AL, as suggested by zeta-potential measurements. When the exfoliated MoS2 nanosheets are applied as electrode materials for lithium ion batteries, they show much improved electrochemical performance compared with the pristine MoS2 mineral because of the enhanced ion and electron transfer kinetics. This facile, scalable and eco-friendly aqueous-based process in combination with renewable and ultra-low-cost lignin opens up possibilities for large-scale fabrication of MoS2-based nanocomposites and devices. Moreover, herein we demonstrate that AL is also an excellent surfactant for exfoliation of many other types of layered materials, including graphene, tungsten disulfide and boron nitride, in water, providing rich opportunities for a wider range of applications.In this article, alkali lignin (AL)-assisted direct exfoliation of MoS2 mineral into single-layer and few-layer nanosheets in water is reported for the first time. Under optimized conditions, the concentration of MoS2 nanosheets in the obtained dispersion can be as high as 1.75 +/- 0.08 mg mL-1, which is much higher than the typical reported concentrations (<1.0 mg mL-1) using synthetic polymers or compounds as surfactants. The stabilizing mechanism primarily lies in the electrostatic repulsion between negative charged AL, as suggested by zeta-potential measurements. When the exfoliated MoS2 nanosheets are applied as electrode materials for lithium ion batteries, they show much improved

  18. One-step preparation of fluorographene: a highly efficient, low-cost, and large-scale approach of exfoliating fluorographite.

    PubMed

    Yang, Yang; Lu, Guolin; Li, Yongjun; Liu, Zhanzhan; Huang, Xiaoyu

    2013-12-26

    Fluorographene, a cousin of graphene, not only inherits the excellent mechanical properties of graphene but also has great unique application potential in high-performance devices and materials, such as lubricating agents, digital transistors, nanocomposites, and energy-storage devices. However, large-scale preparation of fluorographene remains a great challenge. Herein, an easy-operating, highly scalable, and low-cost approach was reported for the preparation of fluorographene using commercially available fluorographite as the starting material. In this procedure, fluorographite turned into few-layer fluorographene through a rapid exfoliation process with Na2O2 and HSO3Cl as exfoliating agents. The whole preparation process was performed in air and without heating, sonication, and protective gas. The obtained fluorographene was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, (19)F nuclear magnetic resonance spectroscopy, X-ray diffraction, thermogravimetric analysis, atomic force microscopy, and transmission electron microscopy, and it possesses a hexagonal polycrystalline structure. Fluorographene and fluorographite were employed as cathode materials of the primary lithium battery, and it was found that the specific discharge capacity of the battery using fluorographene was improved remarkably compared to that using fluorographite. Cyclic voltammetry results also showed that specific capacitances of fluorographene were dozens of times higher than that of fluorographite. It is clear that electrochemical properties of fluorographene are significantly improved against fluorographite.

  19. Preparation of g-C3N4/Graphene Composite for Detecting NO2 at Room Temperature

    PubMed Central

    Zhang, Shaolin; Hang, Nguyen Thuy; Zhang, Zhijun; Yue, Hongyan; Yang, Woochul

    2017-01-01

    Graphitic carbon nitride (g-C3N4) nanosheets were exfoliated from bulk g-C3N4 and utilized to improve the sensing performance of a pure graphene sensor for the first time. The role of hydrochloric acid treatment on the exfoliation result was carefully examined. The exfoliated products were characterized by X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis spectroscopy. The exfoliated g-C3N4 nanosheets exhibited a uniform thickness of about 3–5 nm and a lateral size of about 1–2 µm. A g-C3N4/graphene nanocomposite was prepared via a self-assembly process and was demonstrated to be a promising sensing material for detecting nitrogen dioxide gas at room temperature. The nanocomposite sensor exhibited better recovery as well as two-times the response compared to pure graphene sensor. The detailed sensing mechanism was then proposed. PMID:28336846

  20. Functionalized graphene nanoplatelets for enhanced mechanical and thermal properties of polyurethane nanocomposites

    NASA Astrophysics Data System (ADS)

    Yadav, Santosh Kumar; Cho, Jae Whan

    2013-02-01

    In the evolution of high performance graphene-based polymer nanocomposites, homogeneous dispersion of graphene nanoplatelets in the polymer matrix and exact interface control are difficult to achieve due to the potent interlayer cohesive energy and surface inactiveness of the nanocomposites. Herein, we present an effective way to fabricate high performance polyurethane (PU) nanocomposites via the incorporation of functionalized graphene nanoplatelets (f-GNP) during in situ polymerization. The f-GNP/PU nanocomposites exhibited a significant improvement in terms of their mechanical, thermal, and shape recovery properties. The modulus of the f-GNP/PU nanocomposites at 2 wt% graphene nanoplatelets loading is ten times greater than that of the pure PU sample. The breaking stress and shape recovery showed a highly improving trend with increasing wt% of f-GNP. An unprecedented enhancement of thermal stability at 30 °C compared to the pure PU is also found at 2 wt% loading of f-GNP via in situ polymerization.

  1. Physisorption mechanism in graphene/noble metal (111)/Ni(111) heterostructures: An ab-initio study

    NASA Astrophysics Data System (ADS)

    Moaddeli, Mohammad; Salehi, Hamdollah; Amiri, Peiman

    2016-08-01

    The 3D stacking of various 2D systems is an intelligent way of aiming to overcome the limitations usually faced by 2D systems. We study the adsorption of graphene on noble metal monolayers upon Ni (111) substrate, using density functional theory. The bonding mechanism at noble metal-graphene and noble metal-Ni interfaces is found to be physisorption and chemisorption, respectively. The bonding of graphene to Cu, Ag, and Au (111) monolayers is so weak that the conical shape of the Dirac point is preserved. The doping effects of a substrate lead to a small opening gap for gr/Cu/Ni and gr/Ag/Ni systems. These predictions are in agreement with experimental results. The intercalation of a noble metal monolayer between graphene and Ni (111) substrate changes the magnetic response from Ni surface and causes the formation of a ferrimagnetic system.

  2. Paper-like graphene-Ag composite films with enhanced mechanical and electrical properties

    PubMed Central

    2013-01-01

    In this paper, we have reported that paper-like graphene-Ag composite films could be prepared by a facile and novel chemical reduction method at a large scale. Using ascorbic acid as a reducing agent, graphene oxide films dipped in Ag+ aqueous solutions can be easily reduced along with the decoration of different sizes of Ag particles distributed uniformly. The results reveal that the obtained films exhibit improved mechanical properties with the enhancement of tensile strength and Young's modulus by as high as 82% and 136%, respectively. The electrical properties of graphene-Ag composite films were studied as well, with the sheet resistance of which reaching lower than approximately 600 Ω/□. The graphene-Ag composite films can be expected to find interesting applications in the area of nanoelectronics, sensors, transparent electrodes, supercapacitors, and nanocomposites. PMID:23324465

  3. Unraveling the formation mechanism of graphitic nitrogen-doping in thermally treated graphene with ammonia

    PubMed Central

    Li, Xiao-Fei; Lian, Ke-Yan; Liu, Lingling; Wu, Yingchao; Qiu, Qi; Jiang, Jun; Deng, Mingsen; Luo, Yi

    2016-01-01

    Nitrogen-doped graphene (N-graphene) has attractive properties that has been widely studied over the years. However, its possible formation process still remains unclear. Here, we propose a highly feasible formation mechanism of the graphitic-N doing in thermally treated graphene with ammonia by performing ab initio molecular dynamic simulations at experimental conditions. Results show that among the commonly native point defects in graphene, only the single vacancy 5–9 and divacancy 555–777 have the desirable electronic structures to trap N-containing groups and to mediate the subsequent dehydrogenation processes. The local structure of the defective graphene in combining with the thermodynamic and kinetic effect plays a crucial role in dominating the complex atomic rearrangement to form graphitic-N which heals the corresponding defect perfectly. The importance of the symmetry, the localized force field, the interaction of multiple trapped N-containing groups, as well as the catalytic effect of the temporarily formed bridge-N are emphasized, and the predicted doping configuration agrees well with the experimental observation. Hence, the revealed mechanism will be helpful for realizing the targeted synthesis of N-graphene with reduced defects and desired properties. PMID:27002190

  4. Complex transport behaviors of rectangular graphene quantum dots subject to mechanical vibrations

    NASA Astrophysics Data System (ADS)

    Xu, Mengke; Wang, Yisen; Bao, Rui; Huang, Liang; Lai, Ying-Cheng

    2016-05-01

    Graphene-based mechanical resonators have attracted much attention due to their superior elastic properties and extremely low mass density. We investigate the effects of mechanical vibrations on electronic transport through graphene quantum dots, under the physically reasonable assumption that the time scale associated with electronic transport is much shorter than that with mechanical vibration so that, at any given time, an electron “sees” a static but deformed graphene sheet. We find that, besides periodic oscillation in the quantum transmission at the same frequency as that of mechanical vibrations, structures at finer scales can emerge as an intermediate state, which may lead to spurious higher-frequency components in the current through the device.

  5. Growth Mechanism for Low Temperature PVD Graphene Synthesis on Copper Using Amorphous Carbon

    NASA Astrophysics Data System (ADS)

    Narula, Udit; Tan, Cher Ming; Lai, Chao Sung

    2017-03-01

    Growth mechanism for synthesizing PVD based Graphene using Amorphous Carbon, catalyzed by Copper is investigated in this work. Different experiments with respect to Amorphous Carbon film thickness, annealing time and temperature are performed for the investigation. Copper film stress and its effect on hydrogen diffusion through the film grain boundaries are found to be the key factors for the growth mechanism, and supported by our Finite Element Modeling. Low temperature growth of Graphene is achieved and the proposed growth mechanism is found to remain valid at low temperatures.

  6. Strain engineering for mechanical properties in graphene nanoribbons revisited: The warping edge effect

    NASA Astrophysics Data System (ADS)

    Jiang, Jin-Wu

    2016-06-01

    We investigate the strain engineering and the edge effect for mechanical properties in graphene nanoribbons. The free edges of the graphene nanoribbons are warped due to compressive edge stresses. There is a structural transformation for the free edges from the three-dimensional warping configuration to the two-dimensional planar structure at the critical strain ɛc = 0.7%, at which the applied mechanical stress is equal to the intrinsic compressive edge stress. This structural transformation leads to step-like changes in several mechanical properties studied in the present work, including the Young's modulus, the Poisson's ratio, the quality factor of nanomechanical resonators, and the phonon edge mode.

  7. Growth Mechanism for Low Temperature PVD Graphene Synthesis on Copper Using Amorphous Carbon

    PubMed Central

    Narula, Udit; Tan, Cher Ming; Lai, Chao Sung

    2017-01-01

    Growth mechanism for synthesizing PVD based Graphene using Amorphous Carbon, catalyzed by Copper is investigated in this work. Different experiments with respect to Amorphous Carbon film thickness, annealing time and temperature are performed for the investigation. Copper film stress and its effect on hydrogen diffusion through the film grain boundaries are found to be the key factors for the growth mechanism, and supported by our Finite Element Modeling. Low temperature growth of Graphene is achieved and the proposed growth mechanism is found to remain valid at low temperatures. PMID:28276475

  8. Graphene nonvolatile memory prototype based on charge-transfer mechanism

    NASA Astrophysics Data System (ADS)

    Lv, Hongming; Wu, Huaqiang; Huang, Can; Wang, Yuda; Qian, He

    2014-04-01

    A graphene nonvolatile memory (GNVM) prototype based on charge transfer between the graphene layer and the NH2(CH2)3Si(OEt)3 (APTES) self-assembled monolayer (SAM) is demonstrated. Graphene was transferred to an APTES-SAM-engineered SiO2 substrate and patterned into bottom-gate transistors. Owing to the charge trapping/detrapping property of the nitrogen atoms in APTES, a significant and reproducible transfer curve hysteresis is observed. Memory performance metrics, including retention and endurance, are reported. Comparisons between vacuum and ambient environment test results indicate air absorbates’ detrimental effect. Loss of nonvolatile storage is explained on the basis of a two-layer tunneling junction model, which sheds light on further device improvement through aminosilane molecule structure optimization.

  9. An efficient and environment-friendly method of removing graphene oxide in wastewater and its degradation mechanisms.

    PubMed

    Zhang, Chao-Zhi; Li, Ting; Yuan, Yang; Xu, Jianqiang

    2016-06-01

    Graphene and graphene oxide (GO) have already existed in air, water and soil due to their popular application in functional materials. However, degradation of graphene and GO in wastewater has not been reported. Degradation of GO plays a key role in the elimination of graphene and GO in wastewater due to graphene being easily oxidized to GO. In this paper, GO was completely degraded to give CO2 by Photo-Fenton. The degradation intermediates were determined by UV-vis absorption spectra, elemental analysis (EA), fourier transform infrared (FT-IR) and liquid chromatography-mass spectrometry (LC-MS). Experimental results showed that graphene oxide was completely degraded to give CO2 after 28 days. Based on UV, FT-IR, LC-MS spectra and EA data of these degradation intermediates, the degradation mechanisms of GO were supposed. This paper suggests an efficient and environment-friendly method to degrade GO and graphene.

  10. Towards the Intrinsic Limit in As-Exfoliated MoS2

    NASA Astrophysics Data System (ADS)

    Sutton, Erin; George, Edward; Whapham, Emily; Burch, Kenneth; Burch Group Team

    In recent years, two-dimensional transition metal dichalcogenide (TMDC) semiconductors have been intensively studied as exciting non-zero band gap analogs to graphene. For example, molybdenum disulfide (MoS2), a TMDC, is a van der Waals material which can be thinned down to single atomic layers less than a nanometer thick via micro-mechanical cleavage. In this regime, quantum confinement effects give rise to properties not seen in the bulk crystal. The attractive properties of ultrathin MoS2 have inspired myriad applications, including spin- and valley-tronics, and LED and photo-detecting devices. As the performance of these devices is optimized, a method of modulating these properties is strongly desired. Through exfoliating MoS2 on various substrates in an inert glovebox environment, we have produced as-exfoliated MoS2 doped at the intrinsic level. We study the changes in the MoS2 via Raman and photoluminescence spectra and see shifts in excitonic behavior. The ability to create intrinsic MoS2 without the need for chemical doping or gating has exciting implications for optical studies of the material in addition to device applications such as photovoltaic, photocatalytic, and LED devices.

  11. The Origin of Hierarchical Structure in Self-Assembled Graphene Oxide Papers and the Effect on Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Nandy, Krishanu

    The quest for new materials with ever improving properties has motivated interest in bulk nanostructured materials. Graphene, a two-dimensional sheet of hexagonally arranged carbon atoms, has been of particular interest given its exceptional mechanical, thermal, optical and electrical properties. Graphene oxide is a chemically modified form of graphene in which the honeycomb lattice of carbon atoms is decorated with oxygen bearing functional groups. Graphene oxide represents a facile route for the production of large quantities of graphene based materials, is stable in aqueous and polar organic solvents and has the potential for further chemical modification. In this dissertation, the origin and influence of hierarchical structure on the mechanical properties of graphene oxide paper and graphene oxide paper based materials has been investigated. Free-standing papers derived from graphene oxide are of interest as structural materials due to their impressive mechanical properties. While studies have investigated the mechanical properties of graphene oxide papers, little is known about the formation mechanism. Using a series of flash-freezing experiments on graphene oxide papers undergoing formation, a stop-motion animation of the fabrication process was obtained. The results explain the origin of the hierarchical nature of graphene oxide papers and provide a method for the tailoring of graphene oxide based materials. An in depth study of fusion of graphene oxide papers demonstrates a simple single-step route for the fabrication of practical materials derived from graphene oxide papers. Fused papers retain the properties of constituent papers allowing for the fabrication of mechanical heterostructures that replicate the hierarchical nature of natural materials. The contribution of the hierarchical nature of graphene oxide papers to the mechanical properties was examined by comparing papers formed by two different mechanisms. The intermediate length scale structures

  12. Thermo-mechanical behavior of graphene oxide hydrogel

    NASA Astrophysics Data System (ADS)

    Ghosh, Rituparna; Deka Boruah, Buddha; Misra, Abha

    2017-02-01

    Graphene oxide hydrogel with encapsulated water presents a unique structural characteristic similar to open cell foam. It is demonstrated that the encapsulated water plays a vital role in tailoring compressive behavior of graphene oxide hydrogel under varying thermal conditions. The present study is focused on systematically evaluating both the temperature and frequency dependence on compressive behavior of hydrogel to elucidate the evolution of stiffness in a wider temperature range. The stiffness of the hydrogel is further tailored through encapsulation of nanoparticles to achieve an extraordinary enhancement in storage modulus. It is concluded that the change in phase of water provides a large gradient in the stiffness of the hydrogel.

  13. The mechanics and design of a lightweight three-dimensional graphene assembly

    PubMed Central

    Qin, Zhao; Jung, Gang Seob; Kang, Min Jeong; Buehler, Markus J.

    2017-01-01

    Recent advances in three-dimensional (3D) graphene assembly have shown how we can make solid porous materials that are lighter than air. It is plausible that these solid materials can be mechanically strong enough for applications under extreme conditions, such as being a substitute for helium in filling up an unpowered flight balloon. However, knowledge of the elastic modulus and strength of the porous graphene assembly as functions of its structure has not been available, preventing evaluation of its feasibility. We combine bottom-up computational modeling with experiments based on 3D-printed models to investigate the mechanics of porous 3D graphene materials, resulting in new designs of carbon materials. Our study reveals that although the 3D graphene assembly has an exceptionally high strength at relatively high density (given the fact that it has a density of 4.6% that of mild steel and is 10 times as strong as mild steel), its mechanical properties decrease with density much faster than those of polymer foams. Our results provide critical densities below which the 3D graphene assembly starts to lose its mechanical advantage over most polymeric cellular materials. PMID:28070559

  14. The mechanics and design of a lightweight three-dimensional graphene assembly.

    PubMed

    Qin, Zhao; Jung, Gang Seob; Kang, Min Jeong; Buehler, Markus J

    2017-01-01

    Recent advances in three-dimensional (3D) graphene assembly have shown how we can make solid porous materials that are lighter than air. It is plausible that these solid materials can be mechanically strong enough for applications under extreme conditions, such as being a substitute for helium in filling up an unpowered flight balloon. However, knowledge of the elastic modulus and strength of the porous graphene assembly as functions of its structure has not been available, preventing evaluation of its feasibility. We combine bottom-up computational modeling with experiments based on 3D-printed models to investigate the mechanics of porous 3D graphene materials, resulting in new designs of carbon materials. Our study reveals that although the 3D graphene assembly has an exceptionally high strength at relatively high density (given the fact that it has a density of 4.6% that of mild steel and is 10 times as strong as mild steel), its mechanical properties decrease with density much faster than those of polymer foams. Our results provide critical densities below which the 3D graphene assembly starts to lose its mechanical advantage over most polymeric cellular materials.

  15. Directed Therapy for Exfoliation Syndrome

    PubMed Central

    Angelilli, Allison; Ritch, Robert

    2009-01-01

    Exfoliation syndrome (XFS) is an age-related disorder of the extracellular matrix that leads the production of abnormal fibrillar material that leads to elevated intraocular pressure and a relatively severe glaucoma. Exfoliation material is deposited in numerous ocular tissues and extraocular organs. XFS is associated with ocular ischemia, cerebrovascular disease, neurodegenerative disease and cardiovascular disease. Current modalities of treatment include intraocular pressure lowering with topical antihypertensives, laser trabeculoplasty and filtration surgery. The disease paradigm for XFS should be expanded to include directed therapy designed specifically to target the underlying disease process. Potential targets include preventing the formation or promoting the depolymerization of exfoliation material. Novel therapies targeting trabecular meshwork may prove particularly useful in the care of exfoliative glaucoma. The systemic and ocular associations of XFS underscore the need for a comprehensive search for neuroprotective agents in its treatment. PMID:19888433

  16. Electric field effects in graphene/LaAlO{sub 3}/SrTiO{sub 3} heterostructures and nanostructures

    SciTech Connect

    Huang, Mengchen; Jnawali, Giriraj; Hsu, Jen-Feng; Dhingra, Shonali; Bi, Feng; Chen, Lu; D’Urso, Brian; Irvin, Patrick; Levy, Jeremy; Lee, Hyungwoo; Ryu, Sangwoo; Eom, Chang-Beom; Ghahari, Fereshte; Ravichandran, Jayakanth; Kim, Philip

    2015-06-01

    We report the development and characterization of graphene/LaAlO{sub 3}/SrTiO{sub 3} heterostructures. Complex-oxide heterostructures are created by pulsed laser deposition and are integrated with graphene using both mechanical exfoliation and transfer from chemical-vapor deposition on ultraflat copper substrates. Nanoscale control of the metal-insulator transition at the LaAlO{sub 3}/SrTiO{sub 3} interface, achieved using conductive atomic force microscope lithography, is demonstrated to be possible through the graphene layer. LaAlO{sub 3}/SrTiO{sub 3}-based electric field effects using a graphene top gate are also demonstrated. The ability to create functional field-effect devices provides the potential of graphene-complex-oxide heterostructures for scientific and technological advancement.

  17. Molecular Dynamics Simulation of Water Transport Mechanisms through Nanoporous Boron Nitride and Graphene Multilayers.

    PubMed

    Shahbabaei, Majid; Kim, Daejoong

    2017-03-23

    In this study, molecular dynamics simulations are used to investigate water transport mechanisms through hourglass-shaped pore structure in nanoporous boron nitride (BN) and graphene multilayers. An increase in water flux is evidenced as the gap between the layers increases, reaching a maximum of 41 and 43 at d=6 Å in BN and graphene multilayers, respectively. Moreover, the BN multilayer exhibits less flux compared to graphene due to large friction force and energy barrier. In BN, the friction force dramatically increases when the layers are strongly stacked (d=3.5 Å), whereas it would be independent of the layer separation when the layers are sufficiently spaced (d≥5 Å). In contrast, it was shown that the friction force is independent of the layer spacing in graphene. On the other hand, water molecules across the BN exhibits larger energy barriers compared to graphene when the layers are highly spaced at d=8 Å. In consistent with the result reported for the flux, the axial diffusion coefficient of water molecules in graphene increases with layer spacing, reaching a maximum of when the layers are spaced at d=6 Å.

  18. Electronic and Mechanical Properties of Graphene-Germanium Interfaces Grown by Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Kiraly, Brian; Jacobberger, Robert; Mannix, Andrew; Campbell, Gavin; Bedzyk, Michael; Arnold, Michael; Hersam, Mark; Guisinger, Nathan

    Epitaxial graphene grown directly on semiconducting Ge wafers holds potential for fundamental science and electronics applications. However, since the initial demonstration, little work has been done on the structural and electronic properties of this system. To gain insight into the interface between graphene and Ge, we performed ultra-high vacuum scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) along with Raman and X-ray photoelectron spectroscopy experiments to probe the atomic structure and chemistry at the interface. STS confirms stronger interfacial interaction on Ge(110), consistent with models of epitaxial growth. Raman spectroscopy shows that strain is highly prevalent after growth. Furthermore, the native strain modifies the atomic structure of the Germanium, inducing new and metastable Ge surface reconstructions following annealing. These reconstructions, in turn, modify both the electronic and mechanical properties of the graphene. Finally, graphene/Ge(001) represents the extremely strained case. Here graphene forces restructuring of the Ge surface into [107] facets. From this work, we see that the interaction between graphene and Ge is both dependent on the substrate crystallographic orientation and tunable.

  19. Energy efficient reduced graphene oxide additives: Mechanism of effective lubrication and antiwear properties.

    PubMed

    Gupta, Bhavana; Kumar, N; Panda, Kalpataru; Dash, S; Tyagi, A K

    2016-01-04

    Optimized concentration of reduced graphene oxide (rGO) in the lube is one of the important factors for effective lubrication of solid body contacts. At sufficiently lower concentration, the lubrication is ineffective and friction/wear is dominated by base oil. In contrast, at sufficiently higher concentration, the rGO sheets aggregates in the oil and weak interlayer sliding characteristic of graphene sheets is no more active for providing lubrication. However, at optimized concentration, friction coefficient and wear is remarkably reduced to 70% and 50%, respectively, as compared to neat oil. Traditionally, such lubrication is described by graphene/graphite particle deposited in contact surfaces that provides lower shear strength of boundary tribofilm. In the present investigation, graphene/graphite tribofilm was absent and existing traditional lubrication mechanism for the reduction of friction and wear is ruled out. It is demonstrated that effective lubrication is possible, if rGO is chemically linked with PEG molecules through hydrogen bonding and PEG intercalated graphene sheets provide sufficiently lower shear strength of freely suspended composite tribofilm under the contact pressure. The work revealed that physical deposition and adsorption of the graphene sheets in the metallic contacts is not necessary for the lubrication.

  20. Energy efficient reduced graphene oxide additives: Mechanism of effective lubrication and antiwear properties

    PubMed Central

    Gupta, Bhavana; Kumar, N.; Panda, Kalpataru; Dash, S.; Tyagi, A. K.

    2016-01-01

    Optimized concentration of reduced graphene oxide (rGO) in the lube is one of the important factors for effective lubrication of solid body contacts. At sufficiently lower concentration, the lubrication is ineffective and friction/wear is dominated by base oil. In contrast, at sufficiently higher concentration, the rGO sheets aggregates in the oil and weak interlayer sliding characteristic of graphene sheets is no more active for providing lubrication. However, at optimized concentration, friction coefficient and wear is remarkably reduced to 70% and 50%, respectively, as compared to neat oil. Traditionally, such lubrication is described by graphene/graphite particle deposited in contact surfaces that provides lower shear strength of boundary tribofilm. In the present investigation, graphene/graphite tribofilm was absent and existing traditional lubrication mechanism for the reduction of friction and wear is ruled out. It is demonstrated that effective lubrication is possible, if rGO is chemically linked with PEG molecules through hydrogen bonding and PEG intercalated graphene sheets provide sufficiently lower shear strength of freely suspended composite tribofilm under the contact pressure. The work revealed that physical deposition and adsorption of the graphene sheets in the metallic contacts is not necessary for the lubrication. PMID:26725334

  1. Equilibrium at the edge and atomistic mechanisms of graphene growth

    PubMed Central

    Artyukhov, Vasilii I.; Liu, Yuanyue; Yakobson, Boris I.

    2012-01-01

    The morphology of graphene is crucial for its applications, yet an adequate theory of its growth is lacking: It is either simplified to a phenomenological-continuum level or is overly detailed in atomistic simulations, which are often intractable. Here we put forward a comprehensive picture dubbed nanoreactor, which draws from ideas of step-flow crystal growth augmented by detailed first-principles calculations. As the carbon atoms migrate from the feedstock to catalyst to final graphene lattice, they go through a sequence of states whose energy levels can be computed and arranged into a step-by-step map. Analysis begins with the structure and energies of arbitrary edges to yield equilibrium island shapes. Then, it elucidates how the atoms dock at the edges and how they avoid forming defects. The sequence of atomic row assembly determines the kinetic anisotropy of growth, and consequently, graphene island morphology, explaining a number of experimental facts and suggesting how the growth product can further be improved. Finally, this analysis adds a useful perspective on the synthesis of carbon nanotubes and its essential distinction from graphene. PMID:22949702

  2. Aqueous dispersions of few-layer-thick chemically modified magnesium diboride nanosheets by ultrasonication assisted exfoliation.

    PubMed

    Das, Saroj Kumar; Bedar, Amita; Kannan, Aadithya; Jasuja, Kabeer

    2015-06-04

    The discovery of graphene has led to a rising interest in seeking quasi two-dimensional allotropes of several elements and inorganic compounds. Boron, carbon's neighbour in the periodic table, presents a curious case in its ability to be structured as graphene. Although it cannot independently constitute a honeycomb planar structure, it forms a graphenic arrangement in association with electron-donor elements. This is exemplified in magnesium diboride (MgB2): an inorganic layered compound comprising boron honeycomb planes alternated by Mg atoms. Till date, MgB2 has been primarily researched for its superconducting properties; it hasn't been explored for the possibility of its exfoliation. Here we show that ultrasonication of MgB2 in water results in its exfoliation to yield few-layer-thick Mg-deficient hydroxyl-functionalized nanosheets. The hydroxyl groups enable an electrostatically stabilized aqueous dispersion and create a heterogeneity leading to an excitation wavelength dependent photoluminescence. These chemically modified MgB2 nanosheets exhibit an extremely small absorption coefficient of 2.9 ml mg(-1) cm(-1) compared to graphene and its analogs. This ability to exfoliate MgB2 to yield nanosheets with a chemically modified lattice and properties distinct from the parent material presents a fundamentally new perspective to the science of MgB2 and forms a first foundational step towards exfoliating metal borides.

  3. Aqueous dispersions of few-layer-thick chemically modified magnesium diboride nanosheets by ultrasonication assisted exfoliation

    PubMed Central

    Das, Saroj Kumar; Bedar, Amita; Kannan, Aadithya; Jasuja, Kabeer

    2015-01-01

    The discovery of graphene has led to a rising interest in seeking quasi two-dimensional allotropes of several elements and inorganic compounds. Boron, carbon’s neighbour in the periodic table, presents a curious case in its ability to be structured as graphene. Although it cannot independently constitute a honeycomb planar structure, it forms a graphenic arrangement in association with electron-donor elements. This is exemplified in magnesium diboride (MgB2): an inorganic layered compound comprising boron honeycomb planes alternated by Mg atoms. Till date, MgB2 has been primarily researched for its superconducting properties; it hasn’t been explored for the possibility of its exfoliation. Here we show that ultrasonication of MgB2 in water results in its exfoliation to yield few-layer-thick Mg-deficient hydroxyl-functionalized nanosheets. The hydroxyl groups enable an electrostatically stabilized aqueous dispersion and create a heterogeneity leading to an excitation wavelength dependent photoluminescence. These chemically modified MgB2 nanosheets exhibit an extremely small absorption coefficient of 2.9 ml mg−1 cm−1 compared to graphene and its analogs. This ability to exfoliate MgB2 to yield nanosheets with a chemically modified lattice and properties distinct from the parent material presents a fundamentally new perspective to the science of MgB2 and forms a first foundational step towards exfoliating metal borides. PMID:26041686

  4. Synthesis of graphene nanoribbons from amyloid templates by gallium vapor-assisted solid-phase graphitization

    SciTech Connect

    Murakami, Katsuhisa Dong, Tianchen; Kajiwara, Yuya; Takahashi, Teppei; Fujita, Jun-ichi; Hiyama, Takaki; Takai, Eisuke; Ohashi, Gai; Shiraki, Kentaro

    2014-06-16

    Single- and double-layer graphene nanoribbons (GNRs) with widths of around 10 nm were synthesized directly onto an insulating substrate by solid-phase graphitization using a gallium vapor catalyst and carbon templates made of amyloid fibrils. Subsequent investigation revealed that the crystallinity, conductivity, and carrier mobility were all improved by increasing the temperature of synthesis. The carrier mobility of the GNR synthesized at 1050 °C was 0.83 cm{sup 2}/V s, which is lower than that of mechanically exfoliated graphene. This is considered to be most likely due to electron scattering by the defects and edges of the GNRs.

  5. Reduction of graphene oxide to graphene, A study of changes in the atomic structure

    NASA Astrophysics Data System (ADS)

    Mittal, A.; Wagner, A.; Mattevi, C.; Chov, A.; Liao, K.; Macosko, C.; Chhowalla, M.; Mkhoyan, K. A.

    2012-02-01

    An economic method for large scale production of graphene is based on exfoliation of graphite into 1-atom thick sheets by oxidation, creating graphene oxide (GO) and subsequent reduction of GO into graphene. Reduced GO sheets approach the highly desired properties of graphene, such as electrical conductivity and mechanical strength, to various degrees, but not completely. To understand why, we must understand the nanostructure of the sheets. Different methods of reduction result in products that are similar to graphene, but these products retain some oxidized areas or contain regions with sp^3 bonded carbon. The concentration and distribution of these defects on the reduced GO sheet affect the properties of the 2D material. Here, we have characterized the atomic structure of GO and reduced GO via high resolution transmission electron microscopy, electron diffraction, and electron energy loss spectroscopy. Spectroscopic data taken during thermal reduction of GO shows changes in the fine structure of carbon K-edge as the carbon changes from an oxidized form to elemental amorphous carbon to graphite like form, clearly delineating the process of reduction of GO to graphene. Products of several other reduction methods are also characterized revealing information on electronic environment surrounding carbon atoms, distribution of crystalline areas, and oxygen removal from GO.

  6. CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES: Mechanical Properties of Ni-Coated Single Graphene Sheet and Their Embedded Aluminum Matrix Composites

    NASA Astrophysics Data System (ADS)

    Song, Hai-Yang; Zha, Xin-Wei

    2010-07-01

    The effects of Ni coating on the mechanical behaviors of single graphene sheet and their embedded Al matrix composites under axial tension are investigated using molecular dynamics (MD) simulation method. The results show that the Young's moduli and tensile strength of graphene obviously decrease after Ni coating. The results also show that the mechanical properties of Al matrix can be obviously increased by embedding a single graphene sheet. From the simulation, we also find that the Young's modulus and tensile strength of the Ni-coated graphene/Al composite is obviously larger than those of the uncoated graphene/Al composite. The increased magnitude of the Young's modulus and tensile strength of graphene/Al composite are 52.27% and 32.32% at 0.01 K, respectively, due to Ni coating. By exploring the effects of temperature on the mechanical properties of single graphene sheet and their embedded Al matrix composites, it is found that the higher temperature leads to the lower critical strain and tensile strength.

  7. In-situ growth of graphene/polyaniline for synergistic improvement of extracellular electron transfer in bioelectrochemical systems.

    PubMed

    Sun, De-Zhen; Yu, Yang-Yang; Xie, Rong-Rong; Zhang, Chun-Lian; Yang, Yuan; Zhai, Dan-Dan; Yang, Guodong; Liu, Lei; Yong, Yang-Chun

    2017-01-15

    Graphene composite has been widely used in various bioelectrochemical systems (BES). However, it is suffered from tedious fabrication procedure and ambiguous mechanism for its effect on BES. Here, a one-step and in-situ strategy for simultaneously graphene exfoliation and aniline polymerization was developed for fabrication of graphene/PANI composite electrode (GO/PANIOS). This GO/PANIOS outperformed graphite paper (GP), GP with PANI (GP/PANI) and GP with electrochemical exfoliated graphene (GOH2SO4) in Shewanella oneidensis MR-1 inoculated BES (improved the power density output, i.e., 24, 3.4 and 5.7 times of GP , GP/PANI and GOH2SO4, respectively). Further analysis revealed a synergistic improvement on both direct and mediated extracellular electron transfer of S. oneidensis MR-1 by GO/PANIOS contributed to its performance enhancement in BES. This work not only provided a simple strategy for graphene composite fabrication, but also unveiled the underlying mechanism for its stimulation on BES, which promises new opportunity of graphene composite application in various biosystems.

  8. Revealing the toughening mechanism of graphene-polymer nanocomposite through molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Liu, Jun; Shen, Jianxiang; Zheng, Zijian; Wu, Youping; Zhang, Liqun

    2015-07-01

    By employing united atom molecular dynamics simulation, we have investigated the effects of polymer-graphene interaction {\\varepsilon }np, volume fraction of graphene φ , thermodynamics of polymer matrix (rubbery versus glassy), interfacial interaction in the case of the same dispersion state, shape of nanoparticles (NPs) such as {{{C}}}60, CNT and graphene at the same loading on the toughening efficiency of polymer nanocomposites. By beginning with the pure polymer, we observe that a plateau stress occurs at long chain length because entangled polymer chains in fibrils cannot become broken. We find that the work needed to dissipate during the failure increases with the increase of {\\varepsilon }np and φ , and the yield point in the stress-strain behavior occurs at a smaller strain for an attractive NPs filled system compared to the pure case, attributed to the more mechanically heterogeneous environment. The thermodynamics of the polymer matrix (below and above Tg) seems to have a significant effect on the toughening efficiency of graphene sheets. In the case of the same dispersion state, stronger interfacial interaction always induces long and highly orientated polymer fibrils along the deformation direction, with graphene sheets being encapsulated in these fiber-like bundles. By characterizing the interaction energy between polymer-polymer and polymer-graphene as a function of the strain, we find that the separation of polymer chains from the graphene sheets cease immediately after the yield point, followed by the continuous propagation of the cavities by excluding surrounded polymer chains and graphene sheets together. We also find that at the same attractive interfacial interaction and same loading, the toughening efficiency exhibits the following order: graphene > CNT > {{{C}}}60. Generally, the toughening mechanism of graphene sheets results from the formation of long and highly orientated polymer fibrils to prevent the occurrence of the rupture, which

  9. Stacking order dependent mechanical properties of graphene/MoS{sub 2} bilayer and trilayer heterostructures

    SciTech Connect

    Elder, Robert M. E-mail: mahesh.neupane.ctr@mail.mil; Neupane, Mahesh R. E-mail: mahesh.neupane.ctr@mail.mil; Chantawansri, Tanya L.

    2015-08-17

    Transition metal dichalcogenides (TMDC) such as molybdenum disulfide (MoS{sub 2}) are two-dimensional materials that show promise for flexible electronics and piezoelectric applications, but their weak mechanical strength is a barrier to practical use. In this work, we perform nanoindentation simulations using atomistic molecular dynamics to study the mechanical properties of heterostructures formed by combining MoS{sub 2} with graphene. We consider both bi- and tri-layer heterostructures formed with MoS{sub 2} either supported or encapsulated by graphene. Mechanical properties, such as Young's modulus, bending modulus, ultimate tensile strength, and fracture strain, are extracted from nanoindentation simulations and compared to the monolayer and homogeneous bilayer systems. We observed that the heterostructures, regardless of the stacking order, are mechanically more robust than the mono- and bi-layer MoS{sub 2}, mainly due to the mechanical reinforcement provided by the graphene layer. The magnitudes of ultimate strength and fracture strain are similar for both the bi- and tri-layer heterostructures, but substantially larger than either the mono- and bi-layer MoS{sub 2}. Our results demonstrate the potential of graphene-based heterostructures to improve the mechanical properties of TMDC materials.

  10. CMOS integration of inkjet-printed graphene for humidity sensing

    PubMed Central

    Santra, S.; Hu, G.; Howe, R. C. T.; De Luca, A.; Ali, S. Z.; Udrea, F.; Gardner, J. W.; Ray, S. K.; Guha, P. K.; Hasan, T.

    2015-01-01

    We report on the integration of inkjet-printed graphene with a CMOS micro-electro-mechanical-system (MEMS) microhotplate for humidity sensing. The graphene ink is produced via ultrasonic assisted liquid phase exfoliation in isopropyl alcohol (IPA) using polyvinyl pyrrolidone (PVP) polymer as the stabilizer. We formulate inks with different graphene concentrations, which are then deposited through inkjet printing over predefined interdigitated gold electrodes on a CMOS microhotplate. The graphene flakes form a percolating network to render the resultant graphene-PVP thin film conductive, which varies in presence of humidity due to swelling of the hygroscopic PVP host. When the sensors are exposed to relative humidity ranging from 10–80%, we observe significant changes in resistance with increasing sensitivity from the amount of graphene in the inks. Our sensors show excellent repeatability and stability, over a period of several weeks. The location specific deposition of functional graphene ink onto a low cost CMOS platform has the potential for high volume, economic manufacturing and application as a new generation of miniature, low power humidity sensors for the internet of things. PMID:26616216

  11. Two-Dimensional Fluorinated Graphene: Synthesis, Structures, Properties and Applications.

    PubMed

    Feng, Wei; Long, Peng; Feng, Yiyu; Li, Yu

    2016-07-01

    Fluorinated graphene, an up-rising member of the graphene family, combines a two-dimensional layer-structure, a wide bandgap, and high stability and attracts significant attention because of its unique nanostructure and carbon-fluorine bonds. Here, we give an extensive review of recent progress on synthetic methods and C-F bonding; additionally, we present the optical, electrical and electronic properties of fluorinated graphene and its electrochemical/biological applications. Fluorinated graphene exhibits various types of C-F bonds (covalent, semi-ionic, and ionic bonds), tunable F/C ratios, and different configurations controlled by synthetic methods including direct fluorination and exfoliation methods. The relationship between the types/amounts of C-F bonds and specific properties, such as opened bandgap, high thermal and chemical stability, dispersibility, semiconducting/insulating nature, magnetic, self-lubricating and mechanical properties and thermal conductivity, is discussed comprehensively. By optimizing the C-F bonding character and F/C ratios, fluorinated graphene can be utilized for energy conversion and storage devices, bioapplications, electrochemical sensors and amphiphobicity. Based on current progress, we propose potential problems of fluorinated graphene as well as the future challenge on the synthetic methods and C-F bonding character. This review will provide guidance for controlling C-F bonds, developing fluorine-related effects and promoting the application of fluorinated graphene.

  12. Two‐Dimensional Fluorinated Graphene: Synthesis, Structures, Properties and Applications

    PubMed Central

    Long, Peng; Feng, Yiyu; Li, Yu

    2016-01-01

    Fluorinated graphene, an up‐rising member of the graphene family, combines a two‐dimensional layer‐structure, a wide bandgap, and high stability and attracts significant attention because of its unique nanostructure and carbon–fluorine bonds. Here, we give an extensive review of recent progress on synthetic methods and C–F bonding; additionally, we present the optical, electrical and electronic properties of fluorinated graphene and its electrochemical/biological applications. Fluorinated graphene exhibits various types of C–F bonds (covalent, semi‐ionic, and ionic bonds), tunable F/C ratios, and different configurations controlled by synthetic methods including direct fluorination and exfoliation methods. The relationship between the types/amounts of C–F bonds and specific properties, such as opened bandgap, high thermal and chemical stability, dispersibility, semiconducting/insulating nature, magnetic, self‐lubricating and mechanical properties and thermal conductivity, is discussed comprehensively. By optimizing the C–F bonding character and F/C ratios, fluorinated graphene can be utilized for energy conversion and storage devices, bioapplications, electrochemical sensors and amphiphobicity. Based on current progress, we propose potential problems of fluorinated graphene as well as the future challenge on the synthetic methods and C‐F bonding character. This review will provide guidance for controlling C–F bonds, developing fluorine‐related effects and promoting the application of fluorinated graphene. PMID:27981018

  13. CMOS integration of inkjet-printed graphene for humidity sensing.

    PubMed

    Santra, S; Hu, G; Howe, R C T; De Luca, A; Ali, S Z; Udrea, F; Gardner, J W; Ray, S K; Guha, P K; Hasan, T

    2015-11-30

    We report on the integration of inkjet-printed graphene with a CMOS micro-electro-mechanical-system (MEMS) microhotplate for humidity sensing. The graphene ink is produced via ultrasonic assisted liquid phase exfoliation in isopropyl alcohol (IPA) using polyvinyl pyrrolidone (PVP) polymer as the stabilizer. We formulate inks with different graphene concentrations, which are then deposited through inkjet printing over predefined interdigitated gold electrodes on a CMOS microhotplate. The graphene flakes form a percolating network to render the resultant graphene-PVP thin film conductive, which varies in presence of humidity due to swelling of the hygroscopic PVP host. When the sensors are exposed to relative humidity ranging from 10-80%, we observe significant changes in resistance with increasing sensitivity from the amount of graphene in the inks. Our sensors show excellent repeatability and stability, over a period of several weeks. The location specific deposition of functional graphene ink onto a low cost CMOS platform has the potential for high volume, economic manufacturing and application as a new generation of miniature, low power humidity sensors for the internet of things.

  14. Nonlinear damping in mechanical resonators made from carbon nanotubes and graphene

    NASA Astrophysics Data System (ADS)

    Eichler, A.; Moser, J.; Chaste, J.; Zdrojek, M.; Wilson-Rae, I.; Bachtold, A.

    2011-06-01

    The theory of damping is discussed in Newton's Principia and has been tested in objects as diverse as the Foucault pendulum, the mirrors in gravitational-wave detectors and submicrometre mechanical resonators. In general, the damping observed in these systems can be described by a linear damping force. Advances in nanofabrication mean that it is now possible to explore damping in systems with one or more atomic-scale dimensions. Here we study the damping of mechanical resonators based on carbon nanotubes and graphene sheets. The damping is found to strongly depend on the amplitude of motion, and can be described by a nonlinear rather than a linear damping force. We exploit the nonlinear nature of damping in these systems to improve the figures of merit for both nanotube and graphene resonators. For instance, we achieve a quality factor of 100,000 for a graphene resonator.

  15. Nonlinear damping in mechanical resonators made from carbon nanotubes and graphene.

    PubMed

    Eichler, A; Moser, J; Chaste, J; Zdrojek, M; Wilson-Rae, I; Bachtold, A

    2011-05-15

    The theory of damping is discussed in Newton's Principia and has been tested in objects as diverse as the Foucault pendulum, the mirrors in gravitational-wave detectors and submicrometre mechanical resonators. In general, the damping observed in these systems can be described by a linear damping force. Advances in nanofabrication mean that it is now possible to explore damping in systems with one or more atomic-scale dimensions. Here we study the damping of mechanical resonators based on carbon nanotubes and graphene sheets. The damping is found to strongly depend on the amplitude of motion, and can be described by a nonlinear rather than a linear damping force. We exploit the nonlinear nature of damping in these systems to improve the figures of merit for both nanotube and graphene resonators. For instance, we achieve a quality factor of 100,000 for a graphene resonator.

  16. A structural mechanics approach for the phonon dispersion analysis of graphene

    NASA Astrophysics Data System (ADS)

    Hou, X. H.; Deng, Z. C.; Zhang, K.

    2017-04-01

    A molecular structural mechanics model for the numerical simulation of phonon dispersion relations of graphene is developed by relating the C-C bond molecular potential energy to the strain energy of the equivalent beam-truss space frame. With the stiffness matrix known and further based on the periodic structure characteristics, the Bloch theorem is introduced to develop the dispersion relation of graphene sheet. Being different from the existing structural mechanics model, interactions between the fourth-nearest neighbor atoms are further simulated with beam elements to compensate the reduced stretching stiffness, where as a result not only the dispersion relations in the low frequency field are accurately achieved, but results in the high frequency field are also reasonably obtained. This work is expected to provide new opportunities for the dynamic properties analysis of graphene and future application in the engineering sector.

  17. Finite temperature effect on mechanical properties of graphene sheets with various grain boundaries

    NASA Astrophysics Data System (ADS)

    Yong, Ge; Hong-Xiang, Sun; Yi-Jun, Guan; Gan-He, Zeng

    2016-06-01

    The mechanical properties of graphene sheets with various grain boundaries are studied by molecular dynamics method at finite temperatures. The finite temperature reduces the ultimate strengths of the graphenes with different types of grain boundaries. More interestingly, at high temperatures, the ultimate strengths of the graphene with the zigzag-orientation grain boundaries at low tilt angles exhibit different behaviors from those at lower temperatures, which is determined by inner initial stress in grain boundaries. The results indicate that the finite temperature, especially the high one, has a significant effect on the ultimate strength of graphene with grain boundaries, which gives a more in-depth understanding of their mechanical properties and could be useful for potential graphene applications. Project supported by the Nation Natural Science Foundation of China (Grant Nos. 11347219 and 11404147), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20140519), the Training Project of Young Backbone Teacher of Jiangsu University, the Advanced Talents of Jiangsu University, China (Grant No. 11JDG118), the Practice Innovation Training Program Projects for Industrial Center of Jiangsu University, China, and the State Key Laboratory of Acoustics, Chinese Academy of Sciences (Grant No. SKLOA201308).

  18. Exfoliated YBCO filaments for second-generation superconducting cable

    NASA Astrophysics Data System (ADS)

    Solovyov, Vyacheslav; Farrell, Paul

    2017-01-01

    The second-generation high temperature superconductor (2G HTS) wire is the most promising conductor for high-field magnets such as accelerator dipoles and compact fusion devices. The key element of the wire is a thin Y1Ba2Cu3O7 (YBCO) layer deposited on a flexible metal substrate. The substrate, which becomes incorporated in the 2G conductor, reduces the electrical and mechanical performance of the wire. This is a process that exfoliates the YBCO layer from the substrate while retaining the critical current density of the superconductor. Ten-centimeter long coupons of exfoliated YBCO layers were manufactured, and detailed structural, electrical, and mechanical characterization were reported. After exfoliation, the YBCO layer was supported by a 75 μm thick stainless steel foil, which makes for a compact, mechanically stronger, and inexpensive conductor. The critical current density of the filaments was measured at both 77 K and 4.2 K. The exfoliated YBCO retained 90% of the original critical current. Similarly, tests in an external magnetic field at 4.2 K confirmed that the pinning strength of the YBCO layer was also retained following exfoliation.

  19. Facile synthesis and photoluminescence mechanism of graphene quantum dots

    SciTech Connect

    Yang, Ping; Zhou, Ligang; Zhang, Shenli; Pan, Wei Shen, Wenzhong; Wan, Neng

    2014-12-28

    We report a facile hydrothermal synthesis of intrinsic fluorescent graphene quantum dots (GQDs) with two-dimensional morphology. This synthesis uses glucose, concentrate sulfuric acid, and deionized water as reagents. Concentrated sulfuric acid is found to play a key role in controlling the transformation of as-prepared hydrothermal products from amorphous carbon nanodots to well-crystallized GQDs. These GQDs show typical absorption characteristic for graphene, and have nearly excitation-independent ultraviolet and blue intrinsic emissions. Temperature-dependent PL measurements have demonstrated strong electron-electron scattering and electron-phonon interactions, suggesting a similar temperature behavior of GQDs to inorganic semiconductor quantum dots. According to optical studies, the ultraviolet emission is found to originate from the recombination of electron-hole pairs localized in the C=C bonds, while the blue emission is from the electron transition of sp{sup 2} domains.

  20. Negative Differential Resistance in Boron Nitride Graphene Heterostructures: Physical Mechanisms and Size Scaling Analysis

    PubMed Central

    Zhao, Y.; Wan, Z.; Xu, X.; Patil, S. R.; Hetmaniuk, U.; Anantram, M. P.

    2015-01-01

    Hexagonal boron nitride (hBN) is drawing increasing attention as an insulator and substrate material to develop next generation graphene-based electronic devices. In this paper, we investigate the quantum transport in heterostructures consisting of a few atomic layers thick hBN film sandwiched between graphene nanoribbon electrodes. We show a gate-controllable vertical transistor exhibiting strong negative differential resistance (NDR) effect with multiple resonant peaks, which stay pronounced for various device dimensions. We find two distinct mechanisms that are responsible for NDR, depending on the gate and applied biases, in the same device. The origin of first mechanism is a Fabry-Pérot like interference and that of the second mechanism is an in-plane wave vector matching when the Dirac points of the electrodes align. The hBN layers can induce an asymmetry in the current-voltage characteristics which can be further modulated by an applied bias. We find that the electron-phonon scattering suppresses the first mechanism whereas the second mechanism remains relatively unaffected. We also show that the NDR features are tunable by varying device dimensions. The NDR feature with multiple resonant peaks, combined with ultrafast tunneling speed provides prospect for the graphene-hBN-graphene heterostructure in the high-performance electronics. PMID:25991076

  1. Mechanism for excitation-dependent photoluminescence from graphene quantum dots and other graphene oxide derivates: consensus, debates and challenges

    NASA Astrophysics Data System (ADS)

    Gan, Zhixing; Xu, Hao; Hao, Yanling

    2016-04-01

    Luminescent nanomaterials, with wide applications in biosensing, bioimaging, illumination and display techniques, have been consistently garnering enormous research attention. In particular, those with wavelength-controllable emissions could be highly beneficial. Carbon nanostructures, including graphene quantum dots (GQDs) and other graphene oxide derivates (GODs), with excitation-dependent photoluminescence (PL), which means their fluorescence color could be tuned simply by changing the excitation wavelength, have attracted lots of interest. However the intrinsic mechanism for the excitation-dependent PL is still obscure and fiercely debated presently. In this review, we attempt to summarize the latest efforts to explore the mechanism, including the quantum confinement effect, surface traps model, giant red-edge effect, edge states model and electronegativity of heteroatom model, as well as the newly developed synergistic model, to seek some clues to unravel the mechanism. Meanwhile the controversial difficulties for each model are further discussed. Besides this, the challenges and potential influences of the synthetic methodology and development of the materials are illustrated extensively to elicit more thought and constructive attempts toward their application.

  2. Exfoliation and Dispersion of 2-Dimensional Materials by Elevating Temperature

    NASA Astrophysics Data System (ADS)

    Kwon, Sanghyuk; Kim, Jinseon; Kwon, Hyukjoon; Lee, Changgu; Graphene Engneering Lab Team

    It is known that graphene and other 2-dimensional materials are hard to dissolve in water without using chemicals or surfactants. Here, we present a facile method to exfoliate and disperse those materials in water by simply controlling temperature. Graphene, when sonicated in water at high temperature (60°C), was edge-functionalized due to the extremely high temperature and pressure locally induced by ultrasonic cavitation, and dissolved in water stably even for longer than 1 month. However, it was not dispersed at low temperature(30°C) because of less cavitation and reduced sonochemical reaction. Other 2-dimensional materials, such as h-BN, MoS2, and other layered metal chalcogenides, were also well dissolved in water as graphene, but even at low temperature. Their stable solution is from the electric double layer because their relatively high insulating property. Also elevated storage temperature (60°C) improved the long-term dispersion stability compared to lower storage temperature (20°C) Exfoliation and Dispersion of 2-Dimensional Materials by Elevating Temperature.

  3. Investigating the mechanism of hysteresis effect in graphene electrical field device fabricated on SiO₂ substrates using Raman spectroscopy.

    PubMed

    Xu, Hua; Chen, Yabin; Zhang, Jin; Zhang, Haoli

    2012-09-24

    The hysteresis effect is a common problem in graphene field-effect transistors (FETs). Usually, the external doping to graphene is considered to be responsible for the hysteresis behavior, but is not yet clearly understood. By monitoring the doping of graphene and the hysteresis in graphene FETs under different atmospheres using in situ Raman spectroscopy, it is confirmed that the electrochemical doping of O(2) /H(2) O redox couple to graphene is responsible for the hysteresis effect. In addition, Raman spectra of graphene on SiO(2) substrate show stronger doping than that suspended, which indicates that SiO(2) substrate plays an important role in the doping of graphene. Herein it is proposed that the doping species (H(2) O and O(2) ) are bounded at the interface of graphene/SiO(2) substrate by hydrogen-bonds with the silanol groups on SiO(2) substrate. The dynamic equilibrium process of the charge-transfer between H(2) O/O(2) redox couple and graphene under electrical field modulation is carefully analyzed using Marcus-Gerischer theory. This work provides a clear view to the mechanism of the hysteresis effect, and is of benefit to a reliable design to suppress the hysteresis in graphene FETs.

  4. Microscopic mechanisms of graphene electrolytic delamination from metal substrates

    NASA Astrophysics Data System (ADS)

    Fisichella, G.; Di Franco, S.; Roccaforte, F.; Ravesi, S.; Giannazzo, F.

    2014-06-01

    In this paper, hydrogen bubbling delamination of graphene (Gr) from copper using a strong electrolyte (KOH) water solution was performed, focusing on the effect of the KOH concentration (CKOH) on the Gr delamination rate. A factor of ˜10 decrease in the time required for the complete Gr delamination from Cu cathodes with the same geometry was found increasing CKOH from ˜0.05 M to ˜0.60 M. After transfer of the separated Gr membranes to SiO2 substrates by a highly reproducible thermo-compression printing method, an accurate atomic force microscopy investigation of the changes in Gr morphology as a function of CKOH was performed. Supported by these analyses, a microscopic model of the delamination process has been proposed, where a key role is played by graphene wrinkles acting as nucleation sites for H2 bubbles at the cathode perimeter. With this approach, the H2 supersaturation generated at the electrode for different electrolyte concentrations was estimated and the inverse dependence of td on CKOH was quantitatively explained. Although developed in the case of Cu, this analysis is generally valid and can be applied to describe the electrolytic delamination of graphene from several metal substrates.

  5. Fe-catalyzed etching of graphene layers

    NASA Astrophysics Data System (ADS)

    Cheng, Guangjun; Calizo, Irene; Hight Walker, Angela; PML, NIST Team

    We investigate the Fe-catalyzed etching of graphene layers in forming gas. Fe thin films are deposited by sputtering onto mechanically exfoliated graphene, few-layer graphene (FLG), and graphite flakes on a Si/SiO2 substrate. When the sample is rapidly annealed in forming gas, particles are produced due to the dewetting of the Fe thin film and those particles catalyze the etching of graphene layers. Monolayer graphene and FLG regions are severely damaged and that the particles catalytically etch channels in graphite. No etching is observed on graphite for the Fe thin film annealed in nitrogen. The critical role of hydrogen indicates that this graphite etching process is catalyzed by Fe particles through the carbon hydrogenation reaction. By comparing with the etched monolayer and FLG observed for the Fe film annealed in nitrogen, our Raman spectroscopy measurements identify that, in forming gas, the catalytic etching of monolayer and FLG is through carbon hydrogenation. During this process, Fe particles are catalytically active in the dissociation of hydrogen into hydrogen atoms and in the production of hydrogenated amorphous carbon through hydrogen spillover.

  6. Electrical conductivity of PFPA functionalized graphene

    NASA Astrophysics Data System (ADS)

    Plachinda, P.; Evans, D.; Solanki, R.

    2013-01-01

    Chemical modification of graphene by covalently functionalizing its surface potentially allows a wider flexibility in engineering electronic structure, in particular the local density of states of the carbon atoms bound to the modifier that can result in opening of the band gap. Such binding can involve covalent hydrogenation of graphene to modify hybridization of carbon atoms from sp2 to sp3 geometry [1-3]. Methods have also been developed to functionalize graphene covalently with molecular species [4-8]. Among these, perfluorophenylazide (PFPA) functionalization of graphene is well-developed using a nitrene intermediate. Films of this molecule also act as adhesion layers that allow production of long ribbons of exfoliated graphene [7-9]. We have developed a theory to predict electrical properties of PFPA functionalized graphene and compared it to experimental results. Conductivity of these PFPA functionalized ribbons of exfoliated graphene show good agreement with our theory.

  7. Self-Assembly and Relaxation Behavior of Graphene Containing Acrylic Triblock Copolymer Gels

    NASA Astrophysics Data System (ADS)

    Zabet, Mahla; Hashemnejad, Seyedmeysam; Kundu, Santanu

    2015-03-01

    Investigation of gel mechanical properties as a function of their structure is a significant research interest. This study presents the effect of graphene (or few-layer graphene) on the self-assembly and the relaxation behavior of a thermoreversible gel consists of a physically cross-linked poly (methyl methacrylate)-poly (n-butyl acrylate)-poly (methyl methacrylate) [PMMA-PnBA-PMMA] triblock copolymer in 2-ethyl-1-hexanol, a midblock selective solvent. Graphene was obtained by sonicating exfoliated graphite in 2-ethyl-1-hexanol at various concentrations. Filtration technique and spectrophotometry were utilized to measure the graphene concentration in the dispersions. The dispersed graphene was then incorporated in a series of gels and the effect of graphene on mechanical properties, including the relaxation behavior were studied. Small angle X-ray scattering (SAXS) was used to investigate the microstructure of these gels at room temperature. SAXS data were analyzed to estimate the number of end blocks per junction zone, the average spacing between the junctions, and the change of these properties as a function of graphene concentration. The results indicate that the presence of graphene affects the self-assembly process.

  8. Multichannel and repeatable self-healing of mechanical enhanced graphene-thermoplastic polyurethane composites.

    PubMed

    Huang, Lu; Yi, Ningbo; Wu, Yingpeng; Zhang, Yi; Zhang, Qian; Huang, Yi; Ma, Yanfeng; Chen, Yongsheng

    2013-04-18

    A novel self-healing material, which was fabricated using few-layered graphene (FG) and thermoplastic polyurethane (TPU) via a facile method, not only exhibits a mechanical enhanced property, but also can be repeatedly healed by various methods including infrared (IR) light, electricity and electromagnetic wave with healing efficiencies higher than 98%.

  9. Resonant Scattering off Magnetic Impurities in Graphene: Mechanism for Ultrafast Spin Relaxation

    NASA Astrophysics Data System (ADS)

    Kochan, D.; Gmitra, M.; Fabian, J.

    We give a tutorial account of our recently proposed mechanism for spin relaxation based on spin-flip resonant scattering off local magnetic moments. The mechanism is rather general, working in any material with a resonant local moment, but we believe that its particular niche is graphene, whose measured spin relaxation time is 100-1000 ps. Conventional spin-orbit coupling based mechanisms (Elliott-Yafet or Dyakonov-Perel) would require large concentrations (1000 ppm) of impurities to explain this. Our mechanism needs only 1 ppm of resonant local moments, as these act as local spin hot spots: the resonant scatterers do not appear to substantially affect graphene's measured resistivity, but are dominating spin relaxation. In principle, the local moments can come from a variety of sources. Most likely would be organic molecule adsorbants or metallic adatoms. As the representative model, particularly suited for a tutorial, we consider hydrogen adatoms which are theoretically and experimentally demonstrated to yield local magnetic moments when chemisorbed on graphene. We introduce the scattering formalism and apply it to graphene, to obtain the T-matrix and spin-flip scattering rates using the generalized Fermi golden rule.

  10. Tensile mechanical properties of nano-layered copper/graphene composite

    NASA Astrophysics Data System (ADS)

    He, Yezeng; Huang, Feng; Li, Hui; Sui, Yanwei; Wei, Fuxiang; Meng, Qingkun; Yang, Weiming; Qi, Jiqiu

    2017-03-01

    The solidification of two-dimensional liquid copper confined to graphene layers has been studied using molecular dynamics simulations. The results clearly show that the liquid copper undergoes an obvious transition to a crystal film with the decrease of temperature, accompanied by dramatic change in potential energy and radial distribution function. Moreover, five different simulation models are used to investigate the effects of the number of graphene layers on the mechanical properties of the composites. It is found that the strength and plasticity of the composites have been improved significantly.

  11. Continuous production of nitrogen-functionalized graphene nanosheets for catalysis applications

    NASA Astrophysics Data System (ADS)

    Sanjeeva Rao, Kodepelly; Senthilnathan, Jaganathan; Ting, Jyh-Ming; Yoshimura, Masahiro

    2014-10-01

    This study reports the ``continuous production'' of high-quality, few-layer nitrogen-functionalized graphene nanosheets in aqueous solutions directly from graphite via a two-step method. The initial step utilizes our recently developed peroxide-mediated soft and green electrochemical exfoliation approach for the production of few-layer graphene nanosheets. The subsequent step, developed here, produces nitrogen-functionalized graphene nanosheets via selective alkylation/basic hydrolysis reactions using rather a simple nitrogen precursor bromoacetonitrile, which was never reported in the literature. A possible reaction mechanism of the nitrogen-functionalized graphene formation is proposed. The proposed method allows the quantification of the phenolic and hydroxyl functional groups of anodic few-layer graphene via the derivatization chemistry approach. Additionally, a nitrogen-functionalized graphene-gold nanocrystal hybrid is prepared using gold nanocrystals obtained via the microwave irradiation of H[AuCl4] and trisodium citrate solution. A systematic investigation demonstrates that the nitrogen-functionalized graphene-gold nanocrystal hybrid shows enhanced catalytic reduction of carbonyl compounds such as benzaldehyde.This study reports the ``continuous production'' of high-quality, few-layer nitrogen-functionalized graphene nanosheets in aqueous solutions directly from graphite via a two-step method. The initial step utilizes our recently developed peroxide-mediated soft and green electrochemical exfoliation approach for the production of few-layer graphene nanosheets. The subsequent step, developed here, produces nitrogen-functionalized graphene nanosheets via selective alkylation/basic hydrolysis reactions using rather a simple nitrogen precursor bromoacetonitrile, which was never reported in the literature. A possible reaction mechanism of the nitrogen-functionalized graphene formation is proposed. The proposed method allows the quantification of the phenolic

  12. Adsorption by design: Tuning atom-graphene van der Waals interactions via mechanical strain

    NASA Astrophysics Data System (ADS)

    Nichols, Nathan S.; Del Maestro, Adrian; Wexler, Carlos; Kotov, Valeri N.

    2016-05-01

    We aim to understand how the van der Waals force between neutral adatoms and a graphene layer is modified by uniaxial strain and electron correlation effects. A detailed analysis is presented for three atoms (He, H, and Na) and graphene strain ranging from weak to moderately strong. We show that the van der Waals potential can be significantly enhanced by strain, and present applications of our results to the problem of elastic scattering of atoms from graphene. In particular, we find that quantum reflection can be significantly suppressed by strain, meaning that dissipative inelastic effects near the surface become of increased importance. Furthermore, we introduce a method to independently estimate the Lennard-Jones parameters used in an effective model of He interacting with graphene, and determine how they depend on strain. At short distances, we find that strain tends to reduce the interaction strength by pushing the location of the adsorption potential minima to higher distances above the deformed graphene sheet. This opens up the exciting possibility of mechanically engineering an adsorption potential, with implications for the formation and observation of anisotropic low-dimensional superfluid phases.

  13. The electro-mechanical responses of suspended graphene ribbons for electrostatic discharge applications

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Ma, Rui; Chen, Qi; Xia, Ming; Ng, Jimmy; Wang, Albert; Xie, Ya-Hong

    2016-04-01

    This work presents a suspended graphene ribbon device for electrostatic discharge (ESD) applications. The device structure was proposed and fabricated after careful design considerations. Compared to the conventional ESD devices such as diodes, bipolar junction transistors, and metal-oxide-semiconductor field effect transistors, the proposed device structure is believed to render several advantages including zero leakage, low parasitic effects, fast response, and high critical current density. A process flow was developed for higher yield and reliability of the suspended graphene ribbons. Direct current (DC) and transmission-line pulse (TLP) measurements were carried out to investigate the switching behavior of the device, which is crucial for ESD operation. DC measurements with a different configuration were used to assess the mechanical shape evolution of the graphene ribbon upon biasing. Finite Element Simulations were conducted and agreed well with the experimental results. Furthermore, the current carrying capability of non-suspended graphene ribbons was tested using TLP. It was found that the critical current density of graphene is higher than that of copper wires widely used as interconnects in integrated circuits (ICs).

  14. On the failure load and mechanism of polycrystalline graphene by nanoindentation.

    PubMed

    Sha, Z D; Wan, Q; Pei, Q X; Quek, S S; Liu, Z S; Zhang, Y W; Shenoy, V B

    2014-12-11

    Nanoindentation has been recently used to measure the mechanical properties of polycrystalline graphene. However, the measured failure loads are found to be scattered widely and vary from lab to lab. We perform molecular dynamics simulations of nanoindentation on polycrystalline graphene at different sites including grain center, grain boundary (GB), GB triple junction, and holes. Depending on the relative position between the indenter tip and defects, significant scattering in failure load is observed. This scattering is found to arise from a combination of the non-uniform stress state, varied and weakened strengths of different defects, and the relative location between the indenter tip and the defects in polycrystalline graphene. Consequently, the failure behavior of polycrystalline graphene by nanoindentation is critically dependent on the indentation site, and is thus distinct from uniaxial tensile loading. Our work highlights the importance of the interaction between the indentation tip and defects, and the need to explicitly consider the defect characteristics at and near the indentation site in polycrystalline graphene during nanoindentation.

  15. Structural, electronic, mechanical, and dynamical properties of graphene oxides: A first principles study

    SciTech Connect

    Dabhi, Shweta D.; Gupta, Sanjay D.; Jha, Prafulla K.

    2014-05-28

    We report the results of a theoretical study on the structural, electronic, mechanical, and vibrational properties of some graphene oxide models (GDO, a-GMO, z-GMO, ep-GMO and mix-GMO) at ambient pressure. The calculations are based on the ab-initio plane-wave pseudo potential density functional theory, within the generalized gradient approximations for the exchange and correlation functional. The calculated values of lattice parameters, bulk modulus, and its first order pressure derivative are in good agreement with other reports. A linear response approach to the density functional theory is used to derive the phonon frequencies. We discuss the contribution of the phonons in the dynamical stability of graphene oxides and detailed analysis of zone centre phonon modes in all the above mentioned models. Our study demonstrates a wide range of energy gap available in the considered models of graphene oxide and hence the possibility of their use in nanodevices.

  16. Structural, electronic, mechanical, and dynamical properties of graphene oxides: A first principles study

    NASA Astrophysics Data System (ADS)

    Dabhi, Shweta D.; Gupta, Sanjay D.; Jha, Prafulla K.

    2014-05-01

    We report the results of a theoretical study on the structural, electronic, mechanical, and vibrational properties of some graphene oxide models (GDO, a-GMO, z-GMO, ep-GMO and mix-GMO) at ambient pressure. The calculations are based on the ab-initio plane-wave pseudo potential density functional theory, within the generalized gradient approximations for the exchange and correlation functional. The calculated values of lattice parameters, bulk modulus, and its first order pressure derivative are in good agreement with other reports. A linear response approach to the density functional theory is used to derive the phonon frequencies. We discuss the contribution of the phonons in the dynamical stability of graphene oxides and detailed analysis of zone centre phonon modes in all the above mentioned models. Our study demonstrates a wide range of energy gap available in the considered models of graphene oxide and hence the possibility of their use in nanodevices.

  17. Enhancing the mass sensitivity of graphene nanoresonators via nonlinear oscillations: the effective strain mechanism.

    PubMed

    Jiang, Jin-Wu; Park, Harold S; Rabczuk, Timon

    2012-11-30

    We perform classical molecular dynamics simulations to investigate the enhancement of the mass sensitivity and resonant frequency of graphene nanomechanical resonators that is achieved by driving them into the nonlinear oscillation regime. The mass sensitivity as measured by the resonant frequency shift is found to triple if the actuation energy is about 2.5 times the initial kinetic energy of the nanoresonator. The mechanism underlying the enhanced mass sensitivity is found to be the effective strain that is induced in the nanoresonator due to the nonlinear oscillations, where we obtain an analytic relationship between the induced effective strain and the actuation energy that is applied to the graphene nanoresonator. An important implication of this work is that there is no need for experimentalists to apply tensile strain to the resonators before actuation in order to enhance the mass sensitivity. Instead, enhanced mass sensitivity can be obtained by the far simpler technique of actuating nonlinear oscillations of an existing graphene nanoresonator.

  18. Incorporation of graphene nanosheets into cellulose aerogels: enhanced mechanical, thermal, and oil adsorption properties

    NASA Astrophysics Data System (ADS)

    Wan, Caichao; Li, Jian

    2016-02-01

    In this paper, novel graphene/cellulose (GC) aerogels were prepared based on a green NaOH/PEG solution. Scanning electron microscope observation indicates that the three-dimensional network skeleton structure of cellulose aerogels is tightly covered by the compact sheet structure. X-ray diffraction and Raman spectroscopy analyses demonstrate that the graphene nanosheets have been successfully synthesized and embedded in the cellulose aerogels. The incorporation of graphene nanosheets gives rise to the significant improvement in the specific surface area and pore volume, thermal stability, mechanical strength, and oil adsorption efficiency of GC aerogels. Therefore, the green hybrid GC aerogels have more advantages over the pure cellulose aerogels in treating oil-containing wastewater or oil spills under the harsh environment.

  19. Bio-inspired mechanics of highly sensitive stretchable graphene strain sensors

    NASA Astrophysics Data System (ADS)

    Wang, Wen; Yang, Tingting; Zhu, Hongwei; Zheng, Quanshui

    2015-04-01

    Graphene woven fabrics (GWFs) can sense large strain up to 10% with the highest gauge factors (105) thus far reported. This result promises key applications particularly in sensing strains of soft materials such as biological tissues, but the mechanism of such super gauge factor (SGF) property was not very clear. Through a bio-inspired Voronoi polycrystalline micromechanics model together with experimental validations, we show that the successive cracking, the "fish-scale" like network structure of GWFs, and the superlubricity between overlapped graphene flakes play crucial roles resulting in the SGF property. We also reveal the influences of overlapping width, graphene strip size, Poisson's ratio of the substrate material, size effect, interfacial resistance, and network size to the SGF property. These results can guide the design of GWFs with desired sensing performance.

  20. Quantum resistance metrology using graphene.

    PubMed

    Janssen, T J B M; Tzalenchuk, A; Lara-Avila, S; Kubatkin, S; Fal'ko, V I

    2013-10-01

    In this paper, we review the recent extraordinary progress in the development of a new quantum standard for resistance based on graphene. We discuss the unique properties of this material system relating to resistance metrology and discuss results of the recent highest-ever precision direct comparison of the Hall resistance between graphene and traditional GaAs. We mainly focus our review on graphene expitaxially grown on SiC, a system which so far resulted in the best results. We also briefly discuss progress in the two other graphene material systems, exfoliated graphene and chemical vapour deposition graphene, and make a critical comparison with SiC graphene. Finally, we discuss other possible applications of graphene in metrology.

  1. Fabrication of biocompatible and mechanically reinforced graphene oxide-chitosan nanocomposite films

    PubMed Central

    2013-01-01

    Background Graphene oxide (GO)can be dispersed through functionalization, or chemically converted to make different graphene-based nanocomposites with excellent mechanical and thermal properties. Chitosan, a partially deacetylated derivative of chitin, is extensively used for food packaging, biosensors, water treatment, and drug delivery. GO can be evenly dispersed in chitosan matrix through the formation of amide linkages between them, which is different from previous reports focusing on preparing GO/chitosan nanocomposites through physical mixing. Results In this study, free-standing graphene oxide-chitosan (GO-chitosan) nanocomposite films have been prepared. The GO-chitosan films are biologically compatible and mechanically reinforced. Through the formation of amide linkages between GO’s carboxylic acid groups and chitosan's amine groups, GO could be evenly dispersed within the chitosan matrix. We also characterized the GO-chitosan composite films using element analysis, Fourier transform infrared spectroscopy, X-ray photo electron spectroscopy, differential scanning calorimetry, and thermo gravimetric analysis. Compared to pristine chitosan film, the tensile strength of GO-chitosan film is improved by 2.5 folds and Young’s modulus increases by nearly 4.6 folds. The glass transition temperature of GO-chitosan composite film shifts from 118°C to 158°C compared to the pristine chitosan, indicating its enhanced thermal stability. GO-chitosan composite film was also evaluated for its biocompatibility with C3H10T1/2 cells by in vitro fluorescent staining. The graphene oxide-reinforced chitosan composite films could have applications in functional biomaterials. Conclusion The present study describes a useful and simple method to chemically attach biocompatible chitosan onto graphene oxide. We envision that the GO-chitosan film will open avenues for next-generation graphene applications in the realm of functional biomaterial. PMID:23442350

  2. Quantum mechanics of graphene with a one-dimensional potential

    SciTech Connect

    Miserev, D. S.; Entin, M. V.

    2012-10-15

    Electron states in graphene with a one-dimensional potential have been studied. An approximate solution has been obtained for a small angle between vectors of the incident electron momentum and potential gradient. Exactly solvable problems with a potential of the smoothened step type U(x) Utanh(x/a) and a potential with a singularity U(x) = -U/(|x| + d) are considered. The transmission/reflection coefficients and phases for various potential barriers are determined. A quasi-classical solution is obtained.

  3. Production of ultra-thin nano-scaled graphene platelets from meso-carbon micro-beads

    DOEpatents

    Zhamu, Aruna; Guo, Jiusheng; Jang, Bor Z

    2014-11-11

    A method of producing nano-scaled graphene platelets (NGPs) having an average thickness no greater than 50 nm, typically less than 2 nm, and, in many cases, no greater than 1 nm. The method comprises (a) intercalating a supply of meso-carbon microbeads (MCMBs) to produce intercalated MCMBs; and (b) exfoliating the intercalated MCMBs at a temperature and a pressure for a sufficient period of time to produce the desired NGPs. Optionally, the exfoliated product may be subjected to a mechanical shearing treatment, such as air milling, air jet milling, ball milling, pressurized fluid milling, rotating-blade grinding, or ultrasonicating. The NGPs are excellent reinforcement fillers for a range of matrix materials to produce nanocomposites. Nano-scaled graphene platelets are much lower-cost alternatives to carbon nano-tubes or carbon nano-fibers.

  4. Verification of electron doping in single-layer graphene due to H2 exposure with thermoelectric power

    NASA Astrophysics Data System (ADS)

    Hong, Sung Ju; Park, Min; Kang, Hojin; Lee, Minwoo; Soler-Delgado, David; Shin, Dong Seok; Kim, Kyung Ho; Kubatkin, Sergey; Jeong, Dae Hong; Park, Yung Woo; Kim, Byung Hoon

    2015-04-01

    We report the electron doping of single-layer graphene (SLG) grown by chemical vapor deposition (CVD) by means of dissociative hydrogen adsorption. The transfer characteristic showed n-type doping behavior similar to that of mechanically exfoliated graphene. Furthermore, we studied the thermoelectric power (TEP) of CVD-grown SLG before and after exposure to high-pressure H2 molecules. From the TEP results, which indicate the intrinsic electrical properties, we observed that the CVD-grown SLG is n-type doped without degradation of the quality after hydrogen adsorption. Finally, the electron doping was also verified by Raman spectroscopy.

  5. Verification of electron doping in single-layer graphene due to H{sub 2} exposure with thermoelectric power

    SciTech Connect

    Hong, Sung Ju; Kang, Hojin; Soler-Delgado, David; Kim, Kyung Ho; Park, Yung Woo E-mail: kbh37@incheon.ac.kr; Park, Min; Lee, Minwoo; Jeong, Dae Hong; Shin, Dong Seok; Kim, Byung Hoon E-mail: kbh37@incheon.ac.kr; Kubatkin, Sergey

    2015-04-06

    We report the electron doping of single-layer graphene (SLG) grown by chemical vapor deposition (CVD) by means of dissociative hydrogen adsorption. The transfer characteristic showed n-type doping behavior similar to that of mechanically exfoliated graphene. Furthermore, we studied the thermoelectric power (TEP) of CVD-grown SLG before and after exposure to high-pressure H{sub 2} molecules. From the TEP results, which indicate the intrinsic electrical properties, we observed that the CVD-grown SLG is n-type doped without degradation of the quality after hydrogen adsorption. Finally, the electron doping was also verified by Raman spectroscopy.

  6. How to Exfoliate Safely and Give Your Skin a Healthy Glow

    MedlinePlus

    ... home. Dead skin can be removed with a mechanical tool, such as a brush, scrub or sponge. ... thicker skin may prefer stronger chemical treatments or mechanical exfoliation. Those with darker skin may not respond ...

  7. Graphene Oxide and Thermally Exfoliated Graphene Cyanate Ester Resin Composites

    DTIC Science & Technology

    2013-05-01

    30 minutes under reduced pressure (300 mm Hg). To prepare cured samples for TMA, silicone molds made from R2364A silicone from Silpak Inc. (mixed at...cyclotrimerization cure exotherm. Dynamic DSCs of LECy-GO mixtures reflect this effect to a small extent. The peaks in figure 5 are the...10:1 by weight with R2364B platinum-based curing agent) were made by de-gassing for 60 minutes at 95 °C and 300 mm Hg, cured overnight at room

  8. Large-Scale Production of Nanographite by Tube-Shear Exfoliation in Water

    PubMed Central

    Engström, Ann-Christine; Hummelgård, Magnus; Andres, Britta; Forsberg, Sven; Olin, Håkan

    2016-01-01

    The number of applications based on graphene, few-layer graphene, and nanographite is rapidly increasing. A large-scale process for production of these materials is critically needed to achieve cost-effective commercial products. Here, we present a novel process to mechanically exfoliate industrial quantities of nanographite from graphite in an aqueous environment with low energy consumption and at controlled shear conditions. This process, based on hydrodynamic tube shearing, produced nanometer-thick and micrometer-wide flakes of nanographite with a production rate exceeding 500 gh-1 with an energy consumption about 10 Whg-1. In addition, to facilitate large-area coating, we show that the nanographite can be mixed with nanofibrillated cellulose in the process to form highly conductive, robust and environmentally friendly composites. This composite has a sheet resistance below 1.75 Ω/sq and an electrical resistivity of 1.39×10-4 Ωm and may find use in several applications, from supercapacitors and batteries to printed electronics and solar cells. A batch of 100 liter was processed in less than 4 hours. The design of the process allow scaling to even larger volumes and the low energy consumption indicates a low-cost process. PMID:27128841

  9. DNA-Assisted Exfoliation of Tungsten Dichalcogenides and Their Antibacterial Effect.

    PubMed

    Bang, Gyeong Sook; Cho, Suhyung; Son, Narae; Shim, Gi Woong; Cho, Byung-Kwan; Choi, Sung-Yool

    2016-01-27

    This study reports a method for the facile and high-yield exfoliation of WX2 (X = S, Se) by sonication under aqueous conditions using single-stranded DNA (abbreviated as ssDNA) of high molecular weight. The ssDNA provided a high degree of stabilization and prevented reaggregation, and it enhanced the exfoliation efficiency of WX2 nanosheets due to adsorption on the WX2 surface and the electrostatic repulsion of sugars in the ssDNA backbone. The exfoliation yield was higher with ssDNA (80%-90%) than without (2%-4%); the yield with ssDNA was also higher than the value previously reported for aqueous exfoliation (∼10%). Given that two-dimensional nanomaterials have potential health and environmental applications, we investigated antibacterial activity of exfoliated WX2-ssDNA nanosheets, relative to graphene oxide (GO), and found that WSe2-ssDNA nanosheets had higher antibacterial activity against Escherichia coli K-12 MG1655 cells than GO. Our method enables large-scale exfoliation in an aqueous environment in a single step with a short reaction time and under ambient conditions, and it can be used to produce surface-active or catalytic materials that have broad applications in biomedicine and other areas.

  10. Preparation and mechanical characterization of polycaprolactone/graphene oxide biocomposite nanofibers

    NASA Astrophysics Data System (ADS)

    Lopresti, Francesco; Maio, Andrea; Botta, Luigi; Scaffaro, Roberto

    2016-05-01

    Biocomposite nanofiber scaffolds of polycaprolactone (PCL) filled with graphene oxide (GO) were prepared using electrospinning technology. Morphological and mechanical properties of the scaffolds were characterized in dry and wet environment. The results showed that the successful incorporation of GO nanosheets into PCL polymer nanofibers improved their mechanical properties. Furthermore it was demonstrated the higher performance achieved when GO is filled at low concentration in the nanofibers.

  11. Prediction of structural and mechanical properties of atom-decorated porous graphene via density functional calculations

    NASA Astrophysics Data System (ADS)

    Ansari, Reza; Ajori, Shahram; Malakpour, Sina

    2016-04-01

    The considerable demand for novel materials with specific properties has motivated the researchers to synthesize supramolecular nanostructures through different methods. Porous graphene is the first two-dimensional hydrocarbon synthesized quite recently. This investigation is aimed at studying the mechanical properties of atom-decorated (functionalized) porous graphene by employing density functional theory (DFT) calculation within both local density approximations (LDA) and generalized gradient approximations (GGA). The atoms are selected from period 3 of periodic table as well as Li and O atom from period 2. The results reveal that metallic atoms and noble gases are adsorbed physically on porous graphene and nonmetallic ones form chemical bonds with carbon atom in porous graphene structure. Also, it is shown that, in general, atom decoration reduces the values of mechanical properties such as Young's, bulk and shear moduli as well as Poisson's ratio, and this reduction is more considerable in the case of nonmetallic atoms (chemical adsorption), especially oxygen atoms, as compared to metallic atoms and noble gases (physical adsorption).

  12. Synthesis and structural characterization of separate graphene oxide and reduced graphene oxide nanosheets

    NASA Astrophysics Data System (ADS)

    Aslam, M.; Kalyar, M. A.; Raza, Z. A.

    2016-10-01

    Graphene, being a unique carbon allotrope with a structure that is one atom thick, is known as a mysterious material in the current era due to its strange nature. It has attained global attention due to its amazing mechanical, electrical, thermal and optical properties. Recent progress has revealed that materials built with graphene can have a limitless impact on nanocomposites, electronic, optoelectronic and energy storage devices as well as chemical sensors. In the present study, graphite flakes were chemically oxidized in graphite oxide via the modified Hummers’ method, i.e. without adding sodium nitrate. The graphite oxide was exfoliated in distilled water by using an ultrasonic bath to fabricate graphene oxide nanosheets. The graphene was acquired through an inexpensive and large-scale production route to eliminate functional groups containing oxygen by using hydrazine monohydrate as a reducing agent. The reduced graphene oxide obtained through this route contained residual oxygen-functional groups which can act as active sites for gas molecular interaction and be used in a variety of applications like gas sensing. The prepared samples were analyzed using the dynamic light scattering technique, UV-visible spectroscopy, Fourier transform infrared spectroscopy, x-ray diffraction, scanning electron microscopy and atomic force microscopy.

  13. Reduced graphene oxide-induced recrystallization of NiS nanorods to nanosheets and the improved Na-storage properties.

    PubMed

    Pan, Qin; Xie, Jian; Zhu, Tiejun; Cao, Gaoshao; Zhao, Xinbing; Zhang, Shichao

    2014-04-07

    Preparation of two-dimensional (2D) graphene-like materials is currently an emerging field in materials science since the discovery of single-atom-thick graphene prepared by mechanical cleavage. In this work, we proposed a new method to prepare 2D NiS, where reduced graphene oxide (rGO) was found to induce the recrystallization of NiS from nanorods to nanosheets in a hydrothermal process. The process and mechanism of recrystallization have been clarified by various characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) mapping, and X-ray photoelectron spectroscopy (XPS). The characterization of ex situ NiS/rGO products by SEM and EDS mapping indicates that the recrystallization of NiS from nanorods to nanosheets is realized actually through an exfoliation process, while the characterization of in situ NiS/rGO products by SEM, TEM, and EDS mapping reveals the exfoliation process. The XPS result demonstrates that hydrothermally assisted chemical bonding occurs between NiS and rGO, which induces the exfoliation of NiS nanorods into nanosheets. The obtained NiS/rGO composite shows promising Na-storage properties.

  14. Strategy and mechanism for controlling the direction of defect evolution in graphene: preparation of high quality defect healed and hierarchically porous graphene

    NASA Astrophysics Data System (ADS)

    Cao, Kecheng; Tian, Yin; Zhang, Yongzhi; Yang, Xiaodan; Bai, Chiyao; Luo, Yue; Zhao, Xiaosheng; Ma, Lijian; Li, Shoujian

    2014-10-01

    In this paper, a novel approach for controlling the direction of defect evolution in graphene through intercalation of organic small molecules into graphite oxide (GO) combined with a one-pot microwave-assisted reaction is reported. By using ethanol as intercalator, the bulk production of high quality graphene with its defects being satisfactorily healed is achieved. The repair of defects using extraneous carbon atoms and the hybrid state of these carbon atoms are definitely demonstrated using isotopic tracing studies with 13C-labeled ethanol combined with 13C solid-state NMR. The defect healed graphene shows excellent crystallinity, extremely low oxygen content (C : O ratio of 23.8) and has the highest sheet conductivity (61 500 S m-1) compared to all other reported graphene products derived from GO. By using methanol or benzene as intercalators, hierarchically porous graphene with a self-supported 3-dimensional framework (~917 m2 g-1) containing both macropores and mesopores (2-5 nm) is obtained. This graphene possesses a distinctive amorphous carbon structure around the edge of the nanopores, which could be conducive to enhancing the lithium storage performance (up to 580 mA h g-1 after 300 cycles) when tested as an anode of lithium ion batteries, and might have promising applications in the field of electrode materials, catalysis, and separation, and so on. The mechanism involved for the controlled defect evolution is also proposed. The simple, ultrafast and unified strategy developed in this research provides a practical and effective approach to harness structural defects in graphene-based materials, which could also be expanded for designing and preparing other ordered carbon materials with specific structures.In this paper, a novel approach for controlling the direction of defect evolution in graphene through intercalation of organic small molecules into graphite oxide (GO) combined with a one-pot microwave-assisted reaction is reported. By using ethanol as

  15. Graphene field-effect transistors

    NASA Astrophysics Data System (ADS)

    Reddy, Dharmendar; Register, Leonard F.; Carpenter, Gary D.; Banerjee, Sanjay K.

    2011-08-01

    Owing in part to scaling challenges for metal oxide semiconductor field-effect transistors (MOSFETs) and complementary metal oxide semiconductor (CMOS) logic, the semiconductor industry is placing an increased emphasis on emerging materials and devices that may provide improved MOSFET performance beyond the 22 nm node, or provide novel functionality for, e.g. 'beyond CMOS' devices. Graphene, with its novel and electron-hole symmetric band structure and its high carrier mobilities and thermal velocities, is one such material that has garnered a great deal of interest for both purposes. Single and few layer carbon sheets have been fabricated by a variety of techniques including mechanical exfoliation and chemical vapour deposition, and field-effect transistors have been demonstrated with room-temperature mobilities as high as 10 000 cm2 V-1 s-1. But graphene is a gapless semiconductor and gate control of current is challenging, off-state leakage currents are high, and current does not readily saturate with drain voltage. However, various ways to overcome, adapt to, or even embrace this property are now being considered for device applications. In this work we explore through illustrative examples the potential of and challenges to graphene use for conventional and novel device applications.

  16. Why edge effects are important on the intrinsic loss mechanisms of graphene nanoresonators

    NASA Astrophysics Data System (ADS)

    Jiang, Jin-Wu; Wang, Jian-Sheng

    2012-03-01

    Molecular dynamics simulations are performed to investigate edge effects on the quality factor of graphene nanoresonators with different edge configurations and of various sizes. If the periodic boundary condition is applied, very high quality factors (3 × 105) are obtained for all kinds of graphene nanoresonators. However, if the free boundary condition is applied, quality factors will be greatly reduced by two effects resulting from free edges: the imaginary edge vibration effect and the artificial effect. Imaginary edge vibrations will flip between a pair of doubly degenerate warping states during the mechanical oscillation of nanoresonators. The flipping process breaks the coherence of the mechanical oscillation of the nanoresonator, which is the dominant mechanism for extremely low quality factors. There is an artificial effect if the mechanical oscillation of the graphene nanoresonator is actuated according to an artificial vibration (non-natural vibration of the system), which slightly reduces the quality factor. The artificial effect can be eliminated by actuating the mechanical oscillation according to a natural vibration of the nanoresonator. Our simulations provide an explanation for the recent experiment, where the measured quality factor is low and varies between identical samples with free edges.

  17. Polycrystallinity and stacking in CVD graphene.

    PubMed

    Tsen, Adam W; Brown, Lola; Havener, Robin W; Park, Jiwoong

    2013-10-15

    Graphene, a truly two-dimensional hexagonal lattice of carbon atoms, possesses remarkable properties not seen in any other material, including ultrahigh electron mobility, high tensile strength, and uniform broadband optical absorption. While scientists initially studied its intrinsic properties with small, mechanically exfoliated graphene crystals found randomly, applying this knowledge would require growing large-area films with uniform structural and physical properties. The science of graphene has recently experienced revolutionary change, mainly due to the development of several large-scale growth methods. In particular, graphene synthesis by chemical vapor deposition (CVD) on copper is a reliable method to obtain films with mostly monolayer coverage. These films are also polycrystalline, consisting of multiple graphene crystals joined by grain boundaries. In addition, portions of these graphene films contain more than one layer, and each layer can possess a different crystal orientation and stacking order. In this Account, we review the structural and physical properties that originate from polycrystallinity and stacking in CVD graphene. To begin, we introduce dark-field transmission electron microscopy (DF-TEM), a technique which allows rapid and accurate imaging of key structural properties, including the orientation of individual domains and relative stacking configurations. Using DF-TEM, one can easily identify "lateral junctions," or grain boundaries between adjacent domains, as well as "vertical junctions" from the stacking of graphene multilayers. With this technique, we can distinguish between oriented (Bernal or rhombohedral) and misoriented (twisted) configurations. The structure of lateral junctions in CVD graphene is sensitive to growth conditions and is reflected in the material's electrical and mechanical properties. In particular, grain boundaries in graphene grown under faster reactant flow conditions have no gaps or overlaps, unlike more

  18. Growing vertical ZnO nanorod arrays within graphite: efficient isolation of large size and high quality single-layer graphene.

    PubMed

    Ding, Ling; E, Yifeng; Fan, Louzhen; Yang, Shihe

    2013-07-18

    We report a unique strategy for efficiently exfoliating large size and high quality single-layer graphene directly from graphite into DMF dispersions by growing ZnO nanorod arrays between the graphene layers in graphite.

  19. Manganese ion-assisted assembly of superparamagnetic graphene oxide microbowls

    NASA Astrophysics Data System (ADS)

    Tian, Zhengshan; Xu, Chunxiang; Li, Jitao; Zhu, Gangyi; Xu, Xiaoyong; Dai, Jun; Shi, Zengliang; Lin, Yi

    2014-03-01

    A facile manganese ion Mn(II)-assisted assembly has been designed to fabricate microbowls by using graphene oxide nanosheets as basic building blocks, which were exfoliated ultrasonically from the oxidized soot powders in deionized water. From the morphology evolution observations of transmission electron microscope and scanning electron microscope, a coordinating-tiling-collapsing manner is proposed to interpret the assembly mechanism based on attractive Van der Waals forces, π-π stacking, and capillary action. It is interesting to note that the as-prepared microbowls present a room temperature superparamagnetic behavior.

  20. Characterization of SiO{sub 2}/SiN{sub x} gate insulators for graphene based nanoelectromechanical systems

    SciTech Connect

    Tóvári, E.; Csontos, M. Kriváchy, T.; Csonka, S.; Fürjes, P.

    2014-09-22

    The structural and magnetotransport characterization of graphene nanodevices exfoliated onto Si/SiO{sub 2}/SiN{sub x} heterostructures are presented. Improved visibility of the deposited flakes is achieved by optimal tuning of the dielectric film thicknesses. The conductance of single layer graphene Hall-bar nanostructures utilizing SiO{sub 2}/SiN{sub x} gate dielectrics were characterized in the quantum Hall regime. Our results highlight that, while exhibiting better mechanical and chemical stability, the effect of non-stoichiometric SiN{sub x} on the charge carrier mobility of graphene is comparable to that of SiO{sub 2}, demonstrating the merits of SiN{sub x} as an ideal material platform for graphene based nanoelectromechanical applications.

  1. Beyond Graphene: Electronic and Mechanical Properties of Defective 2-D Materials

    NASA Astrophysics Data System (ADS)

    Terrones, Humberto

    One of the challenges in the production of 2-D materials is the synthesis of defect free systems which can achieve the desired properties for novel applications. However, the reality so far indicates that we need to deal with defective systems and understand their main features in order to perform defect engineering in such a way that we can engineer a new material. In this talk I discuss first, the introduction of defects in a hierarchic way starting from 2-D graphene to form giant Schwarzites or graphene foams, which also can exhibit further defects, thus we can have several levels of defectiveness. In this context, it will be shown that giant Schwarzites, depending on their symmetry, can exhibit Dirac-Fermion behavior and further, possess protected topological states as shown by other authors. Regarding the mechanical properties of these systems, it is possible to tune the Poisson Ratio by the addition of defects, thus shedding light to the explanation of the almost zero Poisson ratios in experimentally obtained graphene foams. Second, the idea of Haeckelites, a planar sp2 graphene-like structure with heptagons and pentagons, can be extended to transition metal dichalcogenides (TMDs) with square and octagonal-like defects, finding semi-metallic behaviors with Dirac-Fermions, and even topological insulating properties. National Science Foundation (EFRI-1433311).

  2. Viscoelastic properties of graphene-based epoxy resins

    NASA Astrophysics Data System (ADS)

    Nobile, Maria Rossella; Fierro, Annalisa; Rosolia, Salvatore; Raimondo, Marialuigia; Lafdi, Khalid; Guadagno, Liberata

    2015-12-01

    In this paper the viscoelastic properties of an epoxy resin filled with graphene-based nanoparticles have been investigated in the liquid state, before curing, by means of a rotational rheometer equipped with a parallel plate geometry. Exfoliated graphite was prepared using traditional acid intercalation followed by a sudden treatment at high temperature (900°C). The percentage of exfoliated graphite was found to be 56%. The epoxy matrix was prepared by mixing a tetrafunctional precursor with a reactive diluent which produces a significant decrease in the viscosity of the epoxy precursor so that the dispersion step of nanofillers in the matrix can easily occur. The hardener agent, the 4,4-diaminodiphenyl sulfone (DDS), was added at a stoichiometric concentration with respect to all the epoxy rings. The inclusion of the partially exfoliated graphite (pEG) in the formulated epoxy mixture significantly modifies the rheological behaviour of the mixture itself. The epoxy mixture, indeed, shows a Newtonian behaviour while, at 3 wt % pEG content, the complex viscosity of the nanocomposite clearly shows a shear thinning behaviour with η* values much higher at the lower frequencies. The increase in complex viscosity with the increasing of the partially exfoliated graphite content was mostly caused by a dramatic increase in the storage modulus. All the graphene-based epoxy mixtures were cured by a two-stage curing cycles: a first isothermal stage was carried out at the lower temperature of 125°C for 1 hour while the second isothermal stage was performed at the higher temperature of 200°C for 3 hours. The mechanical properties of the cured nanocomposites show high values in the storage modulus and glass transition temperature.

  3. Preparation and retention mechanism study of graphene and graphene oxide bonded silica microspheres as stationary phases for high performance liquid chromatography.

    PubMed

    Zhang, Xiaoqiong; Chen, Sha; Han, Qiang; Ding, Mingyu

    2013-09-13

    Graphene oxide (GO) bonded stationary phase for high performance liquid chromatography (HPLC) was fabricated by coating GO sheets onto aminosilica microspheres via covalent coupling. Graphene (G) functionalized HPLC stationary phase was then prepared through hydrazine reduction of GO bonded silica (GO@SiO2) composite, which was the first example of using graphene as stationary-phase component for HPLC. Effective separations of the tested neutral and polar compounds on both GO@SiO2 and graphene bonded silica (G@SiO2) columns were achieved under the optimal experimental conditions. Compared with commercial C18 column, the different chromatographic performances of GO and graphene bonded columns were ascribed to their unique retention mechanisms. The polyaromatic scaffold of GO and graphene gives π-π stacking property and hydrophobic effect, and other retention mechanisms, such as π-π electron-donor-acceptor (EDA) interaction for the separation of nitroaromatic compounds and hydrogen bonding for hydroxyl and amino compounds, may also be taken into consideration. Experimental results indicated that the mixed-mode retention mechanism can facilitate the separation of analytes with similar hydrophobicity, which is a unique property compared with C18 column. Additionally, G@SiO2 showed higher affinity to aromatic analytes in contrast with GO@SiO2 and its retention mechanism was not consistent with the typical reversed phase behavior. The separation of aromatic compounds on G@SiO2 column relies primarily on the π-π stacking interaction and then the hydrophobicity, while the two interactions have equal shares on GO@SiO2 column.

  4. Effects of annealing on the ripple texture and mechanical properties of suspended bilayer graphene

    NASA Astrophysics Data System (ADS)

    Annamalai, M.; Mathew, S.; Jamali, M.; Zhan, D.; Palaniapan, M.

    2013-04-01

    Periodic ripples of amplitude ˜15 nm were formed in suspended bilayer graphene after nanoindentation with incremental forces up to 600 nN. The structure was annealed at ˜620 K in high vacuum and the corresponding modifications in the mechanical properties and surface morphology were investigated. The pre-tension of the pristine sample was found to be 1.46 N m-1 and after annealing it was reduced to 0.72 N m-1. The nanometre-sized ripples induced by mechanical excitation were found to be flattened after annealing. Tailoring surface corrugations in bilayer graphene through nanoindentation and thermal engineering of these ripples thus provides an innovative fabrication route for flexible electronic devices and strain sensors.

  5. Nanoarchitectured materials composed of fullerene-like spheroids and disordered graphene layers with tunable mechanical properties.

    PubMed

    Zhao, Zhisheng; Wang, Erik F; Yan, Hongping; Kono, Yoshio; Wen, Bin; Bai, Ligang; Shi, Feng; Zhang, Junfeng; Kenney-Benson, Curtis; Park, Changyong; Wang, Yanbin; Shen, Guoyin

    2015-02-04

    Type-II glass-like carbon is a widely used material with a unique combination of properties including low density, high strength, extreme impermeability to gas and liquid and resistance to chemical corrosion. It can be considered as a carbon-based nanoarchitectured material, consisting of a disordered multilayer graphene matrix encasing numerous randomly distributed nanosized fullerene-like spheroids. Here we show that under both hydrostatic compression and triaxial deformation, this high-strength material is highly compressible and exhibits a superelastic ability to recover from large strains. Under hydrostatic compression, bulk, shear and Young's moduli decrease anomalously with pressure, reaching minima around 1-2 GPa, where Poisson's ratio approaches zero, and then revert to normal behaviour with positive pressure dependences. Controlling the concentration, size and shape of fullerene-like spheroids with tailored topological connectivity to graphene layers is expected to yield exceptional and tunable mechanical properties, similar to mechanical metamaterials, with potentially wide applications.

  6. Extremely Efficient Liquid Exfoliation and Dispersion of Layered Materials by Unusual Acoustic Cavitation

    PubMed Central

    Han, Joong Tark; Jang, Jeong In; Kim, Haena; Hwang, Jun Yeon; Yoo, Hyung Keun; Woo, Jong Seok; Choi, Sua; Kim, Ho Young; Jeong, Hee Jin; Jeong, Seung Yol; Baeg, Kang-Jun; Cho, Kilwon; Lee, Geon-Woong

    2014-01-01

    Layered materials must be exfoliated and dispersed in solvents for diverse applications. Usually, highly energetic probe sonication may be considered to be an unfavourable method for the less defective exfoliation and dispersion of layered materials. Here we show that judicious use of ultrasonic cavitation can produce exfoliated transition metal dichalcogenide nanosheets extraordinarily dispersed in non-toxic solvent by minimising the sonolysis of solvent molecules. Our method can also lead to produce less defective, large graphene oxide nanosheets from graphite oxide in a short time (within 10 min), which show high electrical conductivity (>20,000 S m−1) of the printed film. This was achieved by adjusting the ultrasonic probe depth to the liquid surface to generate less energetic cavitation (delivered power ~6 W), while maintaining sufficient acoustic shearing (0.73 m s−1) and generating additional microbubbling by aeration at the liquid surface. PMID:24875584

  7. Microwave Assisted 2D Materials Exfoliation

    NASA Astrophysics Data System (ADS)

    Wang, Yanbin

    Two-dimensional materials have emerged as extremely important materials with applications ranging from energy and environmental science to electronics and biology. Here we report our discovery of a universal, ultrafast, green, solvo-thermal technology for producing excellent-quality, few-layered nanosheets in liquid phase from well-known 2D materials such as such hexagonal boron nitride (h-BN), graphite, and MoS2. We start by mixing the uniform bulk-layered material with a common organic solvent that matches its surface energy to reduce the van der Waals attractive interactions between the layers; next, the solutions are heated in a commercial microwave oven to overcome the energy barrier between bulk and few-layers states. We discovered the minutes-long rapid exfoliation process is highly temperature dependent, which requires precise thermal management to obtain high-quality inks. We hypothesize a possible mechanism of this proposed solvo-thermal process; our theory confirms the basis of this novel technique for exfoliation of high-quality, layered 2D materials by using an as yet unknown role of the solvent.

  8. Functional hybrid systems based on large-area high-quality graphene.

    PubMed

    Coraux, Johann; Marty, Laëtitia; Bendiab, Nedjma; Bouchiat, Vincent

    2013-10-15

    The properties of sp² carbon allotropes can be tuned and enriched by their interaction with other materials. The large interface to the outside world in these forms of carbon is ideally suited for combining in an optimal manner several functionalities thanks to this interaction. A wide range of novel materials holding strong promise in energy, optoelectronics, microelectronics, mechanics, or medical applications have been designed accordingly. Graphene, the last representative of this family of sp² carbon materials, has already yielded a wealth of hybrid systems. A new class of these hybrids is emerging, which allows researchers to exploit the properties of truly single-layer graphene. These systems rely on high-quality graphene. In this Account, we describe our recent efforts to develop hybrid systems through various approaches and with various scopes. Depending on the interaction between graphene and molecules, metal clusters, layers, and substrates, either graphene may essentially preserve the electronic properties that make it a unique platform for electronic transport, or new organization and properties in the materials may arise due to the graphene contact at the expense of deep modification of graphene's properties. We prepare our graphene samples by both mechanical exfoliation of graphite and chemical vapor deposition on metals. We use this to study graphene in contact with various species, which either decorate graphene or are intercalated between it and its substrate. We first address the electronic and magnetic properties in systems where graphene is in epitaxy with a metal and discuss the potential to manipulate the properties of both materials, highlighting graphene's role as a protective capping layer in magnetic functional systems. We then present graphene/metal dot hybrids, which can utilize the two-dimensional gas properties of Dirac fermions in graphene. These hybrids allow one to tune the coupling between clusters hosting electronically ordered

  9. Quantum mechanical properties of graphene nano-flakes and quantum dots.

    PubMed

    Shi, Hongqing; Barnard, Amanda S; Snook, Ian K

    2012-11-07

    In recent years considerable attention has been given to methods for modifying and controlling the electronic and quantum mechanical properties of graphene quantum dots. However, as these types of properties are indirect consequences of the wavefunction of the material, a more efficient way of determining properties may be to engineer the wavefunction directly. One way of doing this may be via deliberate structural modifications, such as producing graphene nanostructures with specific sizes and shapes. In this paper we use quantum mechanical simulations to determine whether the wavefunction, quantified via the distribution of the highest occupied molecular orbital, has a direct and reliable relationship to the physical structure, and whether structural modifications can be useful for wavefunction engineering. We find that the wavefunction of small molecular graphene structures can be different from those of larger nanoscale counterparts, and the distribution of the highest occupied molecular orbital is strongly affected by the geometric shape (but only weakly by edge and corner terminations). This indicates that both size and shape may be more useful parameters in determining quantum mechanical and electronic properties, which should then be reasonably robust against variations in the chemical passivation or functionalisation around the circumference.

  10. Strategy and mechanism for controlling the direction of defect evolution in graphene: preparation of high quality defect healed and hierarchically porous graphene.

    PubMed

    Cao, Kecheng; Tian, Yin; Zhang, Yongzhi; Yang, Xiaodan; Bai, Chiyao; Luo, Yue; Zhao, Xiaosheng; Ma, Lijian; Li, Shoujian

    2014-11-21

    In this paper, a novel approach for controlling the direction of defect evolution in graphene through intercalation of organic small molecules into graphite oxide (GO) combined with a one-pot microwave-assisted reaction is reported. By using ethanol as intercalator, the bulk production of high quality graphene with its defects being satisfactorily healed is achieved. The repair of defects using extraneous carbon atoms and the hybrid state of these carbon atoms are definitely demonstrated using isotopic tracing studies with (13)C-labeled ethanol combined with (13)C solid-state NMR. The defect healed graphene shows excellent crystallinity, extremely low oxygen content (C : O ratio of 23.8) and has the highest sheet conductivity (61 500 S m(-1)) compared to all other reported graphene products derived from GO. By using methanol or benzene as intercalators, hierarchically porous graphene with a self-supported 3-dimensional framework (∼917 m(2) g(-1)) containing both macropores and mesopores (2-5 nm) is obtained. This graphene possesses a distinctive amorphous carbon structure around the edge of the nanopores, which could be conducive to enhancing the lithium storage performance (up to 580 mA h g(-1) after 300 cycles) when tested as an anode of lithium ion batteries, and might have promising applications in the field of electrode materials, catalysis, and separation, and so on. The mechanism involved for the controlled defect evolution is also proposed. The simple, ultrafast and unified strategy developed in this research provides a practical and effective approach to harness structural defects in graphene-based materials, which could also be expanded for designing and preparing other ordered carbon materials with specific structures.

  11. Review on mechanism of directly fabricating wafer-scale graphene on dielectric substrates by chemical vapor deposition.

    PubMed

    Ning, Jing; Wang, Dong; Chai, Yang; Feng, Xin; Mu, Meishan; Guo, Lixin; Zhang, Jincheng; Hao, Yue

    2017-04-07

    To date, although the chemical vapor deposition with a catalytic transition metal is a potential way to achieve low cost, high quality and uniform wafer-scale graphene. But the annoying underneath catalytic metals removing and transferring process can also bring large amounts of uncertain facts for the performance deterioration of graphene,such as the pollution of surface polymeric residues, unmentioned doping and structural damages. Thus, to develop a technique of directly fabricating graphene on dielectric substrates is quite meaningful. In this review, we will present specific methods of catalyst- or transfer-free techniques for graphene growth and discuss the diversity of growth mechanisms.

  12. An experimental investigation on the mechanical properties of the interface between large-sized graphene and a flexible substrate

    SciTech Connect

    Xu, Chaochen; Guo, Jiangang Song, Haibin; Xie, Haimei; Xue, Tao; Qin, Qinghua; Wu, Sen

    2015-04-28

    In this paper, the interfacial mechanical properties of large-sized monolayer graphene attached to a flexible polyethylene terephthalate (PET) substrate are investigated. Using a micro-tensile test and Raman spectroscopy, in situ measurements are taken to obtain the full-field deformation of graphene subjected to a uniaxial tensile loading and unloading cycle. The results of the full-field deformation are subsequently used to identify the status of the interface between the graphene and the substrate as one of perfect adhesion, one showing slide or partial debonding, and one that is fully debonded. The interfacial stress/strain transfer and the evolution of the interface from one status to another during the loading and unloading processes are discussed and the mechanical parameters, such as interfacial strength and interfacial shear strength, are obtained quantitatively demonstrating a relatively weak interface between large-sized graphene and PET.

  13. An experimental investigation on the mechanical properties of the interface between large-sized graphene and a flexible substrate

    NASA Astrophysics Data System (ADS)

    Xu, Chaochen; Xue, Tao; Guo, Jiangang; Qin, Qinghua; Wu, Sen; Song, Haibin; Xie, Haimei

    2015-04-01

    In this paper, the interfacial mechanical properties of large-sized monolayer graphene attached to a flexible polyethylene terephthalate (PET) substrate are investigated. Using a micro-tensile test and Raman spectroscopy, in situ measurements are taken to obtain the full-field deformation of graphene subjected to a uniaxial tensile loading and unloading cycle. The results of the full-field deformation are subsequently used to identify the status of the interface between the graphene and the substrate as one of perfect adhesion, one showing slide or partial debonding, and one that is fully debonded. The interfacial stress/strain transfer and the evolution of the interface from one status to another during the loading and unloading processes are discussed and the mechanical parameters, such as interfacial strength and interfacial shear strength, are obtained quantitatively demonstrating a relatively weak interface between large-sized graphene and PET.

  14. Insight into the Mechanism of Graphene Oxide Degradation via the Photo-Fenton Reaction.

    PubMed

    Bai, Hao; Jiang, Wentao; Kotchey, Gregg P; Saidi, Wissam A; Bythell, Benjamin J; Jarvis, Jacqueline M; Marshall, Alan G; Robinson, Renã A S; Star, Alexander

    2014-05-15

    Graphene represents an attractive two-dimensional carbon-based nanomaterial that holds great promise for applications such as electronics, batteries, sensors, and composite materials. Recent work has demonstrated that carbon-based nanomaterials are degradable/biodegradable, but little work has been expended to identify products formed during the degradation process. As these products may have toxicological implications that could leach into the environment or the human body, insight into the mechanism and structural elucidation remain important as carbon-based nanomaterials become commercialized. We provide insight into a potential mechanism of graphene oxide degradation via the photo-Fenton reaction. We have determined that after 1 day of treatment intermediate oxidation products (with MW 150-1000 Da) were generated. Upon longer reaction times (i.e., days 2 and 3), these products were no longer present in high abundance, and the system was dominated by graphene quantum dots (GQDs). On the basis of FTIR, MS, and NMR data, potential structures for these oxidation products, which consist of oxidized polycyclic aromatic hydrocarbons, are proposed.

  15. STM observation of a box-shaped graphene nanostructure appeared after mechanical cleavage of pyrolytic graphite

    NASA Astrophysics Data System (ADS)

    Lapshin, Rostislav V.

    2016-01-01

    A description is given of a three-dimensional box-shaped graphene (BSG) nanostructure formed/uncovered by mechanical cleavage of highly oriented pyrolytic graphite (HOPG). The discovered nanostructure is a multilayer system of parallel hollow channels located along the surface and having quadrangular cross-section. The thickness of the channel walls/facets is approximately equal to 1 nm. The typical width of channel facets makes about 25 nm, the channel length is 390 nm and more. The investigation of the found nanostructure by means of a scanning tunneling microscope (STM) allows us to draw a conclusion that it is possible to make spatial constructions of graphene similar to the discovered one by mechanical compression, bending, splitting, and shifting graphite surface layers. The distinctive features of such constructions are the following: simplicity of the preparation method, small contact area between graphene planes and a substrate, large surface area, nanometer cross-sectional sizes of the channels, large aspect ratio. Potential fields of application include: ultra-sensitive detectors, high-performance catalytic cells, nanochannels for DNA manipulation, nanomechanical resonators, electron multiplication channels, high-capacity sorbents for hydrogen storage.

  16. Line defects in graphene: How doping affects the electronic and mechanical properties

    NASA Astrophysics Data System (ADS)

    Berger, Daniel; Ratsch, Christian

    2016-06-01

    Graphene and carbon nanotubes have extraordinary mechanical and electronic properties. Intrinsic line defects such as local nonhexagonal reconstructions or grain boundaries, however, significantly reduce the tensile strength, but feature exciting electronic properties. Here, we address the properties of line defects in graphene from first principles on the level of full-potential density-functional theory, and assess doping as one strategy to strengthen such materials. We carefully disentangle the global and local effect of doping by comparing results from the virtual crystal approximation with those from local substitution of chemical species, in order to gain a detailed understanding of the breaking and stabilization mechanisms. We find that doping primarily affects the occupation of the frontier orbitals. Occupation through n -type doping or local substitution with nitrogen increases the ultimate tensile strength significantly. In particular, it can stabilize the defects beyond the ultimate tensile strength of the pristine material. We therefore propose this as a key strategy to strengthen graphenic materials. Furthermore, we find that doping and/or applying external stress lead to tunable and technologically interesting metal/semiconductor transitions.

  17. Insight into the Mechanism of Graphene Oxide Degradation via the Photo-Fenton Reaction

    PubMed Central

    2015-01-01

    Graphene represents an attractive two-dimensional carbon-based nanomaterial that holds great promise for applications such as electronics, batteries, sensors, and composite materials. Recent work has demonstrated that carbon-based nanomaterials are degradable/biodegradable, but little work has been expended to identify products formed during the degradation process. As these products may have toxicological implications that could leach into the environment or the human body, insight into the mechanism and structural elucidation remain important as carbon-based nanomaterials become commercialized. We provide insight into a potential mechanism of graphene oxide degradation via the photo-Fenton reaction. We have determined that after 1 day of treatment intermediate oxidation products (with MW 150–1000 Da) were generated. Upon longer reaction times (i.e., days 2 and 3), these products were no longer present in high abundance, and the system was dominated by graphene quantum dots (GQDs). On the basis of FTIR, MS, and NMR data, potential structures for these oxidation products, which consist of oxidized polycyclic aromatic hydrocarbons, are proposed. PMID:24860637

  18. Preparation of reduced graphene oxide/gelatin composite films with reinforced mechanical strength

    SciTech Connect

    Wang, Wenchao; Wang, Zhipeng; Liu, Yu; Li, Nan; Wang, Wei; Gao, Jianping

    2012-09-15

    Highlights: ► We used and compared different proportion of gelatin and chitosan as reducing agents. ► The mechanical properties of the films are investigated, especially the wet films. ► The cell toxicity of the composite films as biomaterial is carried out. ► The water absorption capabilities of the composite films also studied. -- Abstract: Graphene oxide (GO) was reduced by chitosan/gelatin solution and added to gelatin (Gel) to fabricate reduced graphene oxide/gelatin (RGO/Gel) films by a solvent-casting method using genipin as cross-linking agent. The structure and properties of the films were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and UV–vis spectroscopy. The addition of RGO increased the tensile strength of the RGO/Gel films in both dry and wet states, but decreased their elongation at break. The incorperation of RGO also decreased the swelling ability of the films in water. Cell cultures were carried out in order to test the cytotoxicity of the films. The cells grew and reproduced well on the RGO/Gel films, indicating that the addition of RGO has no negative effect on the compatibility of the gelatin. Therefore, the reduced graphene oxide/gelatin composite is a promising biomaterial with excellent mechanical properties and good cell compatibility.

  19. Graphene immobilized enzyme/polyethersulfone mixed matrix membrane: Enhanced antibacterial, permeable and mechanical properties

    NASA Astrophysics Data System (ADS)

    Duan, Linlin; Wang, Yuanming; Zhang, Yatao; Liu, Jindun

    2015-11-01

    Enzyme immobilization has been developed to address lots of issues of free enzyme, such as instability, low activity and difficult to retain. In this study, graphene was used as an ideal carrier for lysozyme immobilization, including graphene oxide (GO) immobilized lysozyme (GO-Ly) and chemically reduced graphene oxide (CRGO) immobilized lysozyme (CRGO-Ly). Herein, lysozyme as a bio-antibacterial agent has excellent antibacterial performance and the products of its catalysis are safety and nontoxic. Then the immobilized lysozyme materials were blended into polyethersulfone (PES) casting solution to prepare PES ultrafiltration membrane via phase inversion method. GO and CRGO were characterized by Fourier transform infrared spectroscopy (FTIR), Ultraviolet-visible spectrum (UV), X-ray diffraction (XRD), and transmission electron microscopy (TEM) and the immobilized lysozyme composites were observed by fluorescent microscopy. The results revealed that GO and CRGO were successfully synthesized and lysozyme was immobilized on their surfaces. The morphology, hydrophilicity, mechanical properties, separation properties and antibacterial activity of the hybrid membranes were characterized in detail. The hydrophilicity, water flux and mechanical strength of the hybrid membranes were significantly enhanced after adding the immobilized lysozyme. In the antibacterial experiment, the hybrid membranes exhibited an effective antibacterial performance against Escherichia coli (E. coli).

  20. Reduced silanized graphene oxide/epoxy-polyurethane composites with enhanced thermal and mechanical properties

    NASA Astrophysics Data System (ADS)

    Lin, Jing; Zhang, Peipei; Zheng, Cheng; Wu, Xu; Mao, Taoyan; Zhu, Mingning; Wang, Huaquan; Feng, Danyan; Qian, Shuxuan; Cai, Xianfang

    2014-10-01

    This paper describes the synthesis of reduced silanized graphene oxide/epoxy-polyurethane (EPUAs/R-Si-GEO) composites with enhanced thermal and mechanical properties. Graphene oxide (GEO), prepared from natural graphite flakes, was modified with methacryloxypropyltrimethoxysilane to prepare silanized GEO (Si-GEO), and was then reduced by NaHSO3 to prepare R-Si-GEO (partially reduced Si-GEO). EPAc/R-Si-GEO (R-Si-GEO/epoxy acrylate copolymers) was synthesized via an in situ polymerization of R-Si-GEO and epoxy acrylic monomers. EPUAs/R-Si-GEO was obtained by curing reaction between EPAc/R-Si-GEO and an isocyanate curing agent. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were used to characterize the surface and crystal structure of the modified graphene and EPUAs/R-Si-GEO. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize their morphology. Thermal gravimetric analysis (TGA), tensile strength, elongation at break, and cross-linking density measurements showed that the thermal stability and mechanical properties of EPUAs/R-Si-GEO were greatly enhanced by the addition of R-Si-GEO.

  1. Lightweight, Superelastic, and Mechanically Flexible Graphene/Polyimide Nanocomposite Foam for Strain Sensor Application.

    PubMed

    Qin, Yuyang; Peng, Qingyu; Ding, Yujie; Lin, Zaishan; Wang, Chunhui; Li, Ying; Xu, Fan; Li, Jianjun; Yuan, Ye; He, Xiaodong; Li, Yibin

    2015-09-22

    The creation of superelastic, flexible three-dimensional (3D) graphene-based architectures is still a great challenge due to structure collapse or significant plastic deformation. Herein, we report a facile approach of transforming the mechanically fragile reduced graphene oxide (rGO) aerogel into superflexible 3D architectures by introducing water-soluble polyimide (PI). The rGO/PI nanocomposites are fabricated using strategies of freeze casting and thermal annealing. The resulting monoliths exhibit low density, excellent flexibility, superelasticity with high recovery rate, and extraordinary reversible compressibility. The synergistic effect between rGO and PI endows the elastomer with desirable electrical conductivity, remarkable compression sensitivity, and excellent durable stability. The rGO/PI nanocomposites show potential applications in multifunctional strain sensors under the deformations of compression, bending, stretching, and torsion.

  2. Quantum-mechanical interference in charge exchange between hydrogen and graphene-like surfaces.

    PubMed

    Romero, M; Iglesias-García, A; Goldberg, E C

    2012-02-01

    The neutral to negative charge fluctuation of a hydrogen atom in front of a graphene surface is calculated by using the Anderson model within an infinite intra atomic Coulomb repulsion approximation. We perform an ab initio calculation of the Anderson hybridization function that allows investigation of the effect of quantum-mechanical interference related to the Berry phase inherent to the graphene band structure. We find that consideration of the interaction of hydrogen on top of many C atoms leads to a marked asymmetry of the imaginary part of the hybridization function with respect to the Fermi level. Consequently, Fano factors larger than one and strongly dependent on the energy around the Fermi level are predicted. Moreover, the suppression of the hybridization for energies above the Fermi level can explain the unexpected large negative ion formation measured in the scattering of protons by graphite-like surfaces.

  3. Boron nitride colloidal solutions, ultralight aerogels and freestanding membranes through one-step exfoliation and functionalization

    NASA Astrophysics Data System (ADS)

    Lei, Weiwei; Mochalin, Vadym N.; Liu, Dan; Qin, Si; Gogotsi, Yury; Chen, Ying

    2015-11-01

    Manufacturing of aerogels and membranes from hexagonal boron nitride (h-BN) is much more difficult than from graphene or graphene oxides because of the poor dispersibility of h-BN in water, which limits its exfoliation and preparation of colloidal solutions. Here, a simple, one-step mechano-chemical process to exfoliate and functionalize h-BN into highly water-dispersible, few-layer h-BN containing amino groups is presented. The colloidal solutions of few-layer h-BN can have unprecedentedly high concentrations, up to 30 mg ml-1, and are stable for up to several months. They can be used to produce ultralight aerogels with a density of 1.4 mg cm-3, which is ~1,500 times less than bulk h-BN, and freestanding membranes simply by cryodrying and filtration, respectively. The material shows strong blue light emission under ultraviolet excitation, in both dispersed and dry state.

  4. Granite Exfoliation, Cosumnes River Watershed, Somerset, California

    NASA Astrophysics Data System (ADS)

    Crockett, I. Q.; Neiss-Cortez, M.

    2015-12-01

    In the Sierra Nevada foothills of California there are many exposed granite plutons within the greater Sierra Nevada batholith. As with most exposed parts of the batholith, these granite slabs exfoliate. It is important to understand exfoliation for issues of public safety as it can cause rock slides near homes, roads, and recreation areas. Through observation, measuring, and mapping we characterize exfoliation in our Cosumnes River watershed community.

  5. Few layer graphene-polypropylene nanocomposites: the role of flake diameter.

    PubMed

    Vallés, Cristina; Abdelkader, Amr M; Young, Robert J; Kinloch, Ian A

    2014-01-01

    Graphene shows excellent potential as a structural reinforcement in polymer nanocomposites due to its exceptional mechanical properties. We have shown previously that graphene composites can be analysed using conventional composite theory with the graphene flakes acting as short fillers which have a critical length of ∼3 μm which is required for good reinforcement. Herein, polypropylene (PP) nanocomposites were prepared using electrochemically-exfoliated few layer graphene (FLG) with two different flake diameters (5 μm and 20 μm). The crystallization temperature and degree of crystallinity of the PP were found to increase with the loading of FLG, which suggests that the flakes acted as crystallisation nucleation sites. Mechanical testing showed that the 5 μm flakes behaved as short fillers and reinforced the PP matrix poorly. The modulus of the 20 μm flake composites, however, increased linearly with loading up to 20 wt%, without any of the detrimental aggregation effects seen in other graphene systems. The mechanical data were compared with our previous work on other graphene composite systems and the apparent need to balance the degree of functionalization to improve matrix compatibility whilst not encouraging aggregation is discussed.

  6. Aromatic graphene

    NASA Astrophysics Data System (ADS)

    Das, D. K.; Sahoo, S.

    2016-04-01

    In recent years graphene attracts the scientific and engineering communities due to its outstanding electronic, thermal, mechanical and optical properties and many potential applications. Recently, Popov et al. [1] have studied the properties of graphene and proved that it is aromatic but without fragrance. In this paper, we present a theory to prepare graphene with fragrance. This can be used as scented pencils, perfumes, room and car fresheners, cosmetics and many other useful household substances.

  7. Synthesis and characterization of electrically conductive polyethylene-supported graphene films

    PubMed Central

    2014-01-01

    We describe a simple mechanical approach for low-density polyethylene film coating by multilayer graphene. The technique is based on the exfoliation of nanocrystalline graphite (few-layer graphene) by application of shear stress and allows to obtain thin graphene layers on the plastic substrate. We report on the temperature dependence of electrical resistance behaviors in films of different thickness. The experimental results suggest that the semiconducting behavior observed at low temperature can be described in the framework of the Efros-Shklovskii variable-range-hopping model. The obtained films exhibit good electrical conductivity and transparency in the visible spectral region. PACS 72.80.Vp; 78.67.Wj; 78.66.Qn; 85.40.Hp PMID:25288910

  8. Mode-locked thulium-bismuth codoped fiber laser using graphene saturable absorber in ring cavity.

    PubMed

    Zen, D I M; Saidin, N; Damanhuri, S S A; Harun, S W; Ahmad, H; Ismail, M A; Dimyati, K; Halder, A; Paul, M C; Das, S; Pal, M; Bhadra, S K

    2013-02-20

    We demonstrate mode locking of a thulium-bismuth codoped fiber laser (TBFL) operating at 1901.6 nm, using a graphene-based saturable absorber (SA). In this work, a single layer graphene is mechanically exfoliated using the scotch tape method and directly transferred onto the surface of a fiber pigtail to fabricate the SA. The obtained Raman spectrum characteristic indicates that the graphene on the core surface has a single layer. At 1552 nm pump power of 869 mW, the mode-locked TBFL self starts to generate an optical pulse train with a repetition rate of 16.7 MHz and pulse width of 0.37 ps. This is a simple, low-cost, stable, and convenient laser oscillator for applications where eye-safe and low-photon-energy light sources are required, such as sensing and biomedical diagnostics.

  9. Exfoliative cytology for diagnosing oral cancer.

    PubMed

    Pérez-Sayánsm, M; Somoza-Martín, J M; Barros-Angueira, F; Reboiras-López, M D; Gándara-Vila, P; Gándara Rey, J M; García-García, A

    2010-04-28

    Exfoliative cytology is a minimally invasive technique for obtaining oral cell specimens from patients for diagnostic purposes. Classical applications of oral cytology studies, such as oral candidiasis, have been extended to include oral precancerous and cancerous lesions. A number of analytical methods are available for studying cytology specimens. The development of molecular analysis techniques, the oral cancer etiopathogenic process, and improvements in liquid-based exfoliative cytology are leading to renewed interest in exfoliative cytology. Results sometimes are disputed, so the aim of our review was to clarify the applicability of exfoliative cytology to the diagnosis of oral precancerous and cancerous lesions.

  10. Role of different scattering mechanisms on the temperature dependence of transport in graphene

    PubMed Central

    Sarkar, Suman; Amin, Kazi Rafsanjani; Modak, Ranjan; Singh, Amandeep; Mukerjee, Subroto; Bid, Aveek

    2015-01-01

    Detailed experimental and theoretical studies of the temperature dependence of the effect of different scattering mechanisms on electrical transport properties of graphene devices are presented. We find that for high mobility devices the transport properties are mainly governed by completely screened short range impurity scattering. On the other hand, for the low mobility devices transport properties are determined by both types of scattering potentials - long range due to ionized impurities and short range due to completely screened charged impurities. The results could be explained in the framework of Boltzmann transport equations involving the two independent scattering mechanisms. PMID:26608479

  11. Triangular Black Phosphorus Atomic Layers by Liquid Exfoliation

    PubMed Central

    Seo, Soonjoo; Lee, Hyun Uk; Lee, Soon Chang; Kim, Yooseok; Kim, Hyeran; Bang, Junhyeok; Won, Jonghan; Kim, Youngjun; Park, Byoungnam; Lee, Jouhahn

    2016-01-01

    Few-layer black phosphorus (BP) is the most promising material among the two-dimensional materials due to its layered structure and the excellent semiconductor properties. Currently, thin BP atomic layers are obtained mostly by mechanical exfoliation of bulk BP, which limits applications in thin-film based electronics due to a scaling process. Here we report highly crystalline few-layer black phosphorus thin films produced by liquid exfoliation. We demonstrate that the liquid-exfoliated BP forms a triangular crystalline structure on SiO2/Si (001) and amorphous carbon. The highly crystalline BP layers are faceted with a preferred orientation of the (010) plane on the sharp edge, which is an energetically most favorable facet according to the density functional theory calculations. Our results can be useful in understanding the triangular BP structure for large-area applications in electronic devices using two-dimensional materials. The sensitivity and selectivity of liquid-exfoliated BP to gas vapor demonstrate great potential for practical applications as sensors. PMID:27026070

  12. Intrinsic device-to-device variation in graphene field-effect transistors on a Si/SiO{sub 2} substrate as a platform for discriminative gas sensing

    SciTech Connect

    Lipatov, Alexey; Varezhnikov, Alexey; Sysoev, Victor; Augustin, Martin; Sommer, Martin; Bruns, Michael; Kolmakov, Andrei; Sinitskii, Alexander

    2014-01-06

    Arrays of nearly identical graphene devices on Si/SiO{sub 2} exhibit a substantial device-to-device variation, even in case of a high-quality chemical vapor deposition (CVD) or mechanically exfoliated graphene. We propose that such device-to-device variation could provide a platform for highly selective multisensor electronic olfactory systems. We fabricated a multielectrode array of CVD graphene devices on a Si/SiO{sub 2} substrate and demonstrated that the diversity of these devices is sufficient to reliably discriminate different short-chain alcohols: methanol, ethanol, and isopropanol. The diversity of graphene devices on Si/SiO{sub 2} could possibly be used to construct similar multisensor systems trained to recognize other analytes as well.

  13. Solvothermal-assisted liquid-phase exfoliation of graphite in a mixed solvent of toluene and oleylamine.

    PubMed

    Dang, Dinh Khoi; Kim, Eui Jung

    2015-12-01

    We report an effective method for producing graphene sheets using solvothermal-assisted exfoliation of graphite in a mixed solvent of toluene and oleylamine. The mixed solvent of toluene and oleylamine produces higher yield of graphene than its constituents, oleylamine and toluene. The oleylamine molecules with its long chain enwrap the graphene sheets efficiently, while toluene helps the oleylamine molecules become more flexible and easily intercalate into the edge of graphite. The prepared graphene sheets have a high quality, and the concentration of graphene in the dispersion is as high as 0.128 mg mL(-1). The high-quality graphene sheets obtained in this work make them suitable for application in many fields such as energy-storage materials and polymer composites.

  14. Failure processes in embedded monolayer graphene under axial compression.

    PubMed

    Androulidakis, Charalampos; Koukaras, Emmanuel N; Frank, Otakar; Tsoukleri, Georgia; Sfyris, Dimitris; Parthenios, John; Pugno, Nicola; Papagelis, Konstantinos; Novoselov, Kostya S; Galiotis, Costas

    2014-06-12

    Exfoliated monolayer graphene flakes were embedded in a polymer matrix and loaded under axial compression. By monitoring the shifts of the 2D Raman phonons of rectangular flakes of various sizes under load, the critical strain to failure was determined. Prior to loading care was taken for the examined area of the flake to be free of residual stresses. The critical strain values for first failure were found to be independent of flake size at a mean value of -0.60% corresponding to a yield stress up to -6 GPa. By combining Euler mechanics with a Winkler approach, we show that unlike buckling in air, the presence of the polymer constraint results in graphene buckling at a fixed value of strain with an estimated wrinkle wavelength of the order of 1-2 nm. These results were compared with DFT computations performed on analogue coronene/PMMA oligomers and a reasonable agreement was obtained.

  15. Commercialization of graphene-based technologies: a critical insight.

    PubMed

    Ciriminna, Rosaria; Zhang, Nan; Yang, Min-Quan; Meneguzzo, Francesco; Xu, Yi-Jun; Pagliaro, Mario

    2015-04-28

    Carbon in its single layer atomic morphology has exceptional thermal, optical, electronic and mechanical properties, which may form the basis for several functional products and enhanced technologies that go from electricity storage to polymer nanocomposites of so far unsurpassed characteristics. Due to the high cost, however, the current global production of graphene does not exceed 120 tonnes. New chemical and physical methods to exfoliate graphite, however, were recently engineered and commercialized, which open the route to massive adoption of graphene as the "enabler" of numerous important technologies, including enhanced electricity storage. This feature article presents an updated, critical overview that will be useful to nanochemistry and nanotechnology research practitioners and to entrepreneurs in advanced materials.

  16. Failure Processes in Embedded Monolayer Graphene under Axial Compression

    PubMed Central

    Androulidakis, Charalampos; Koukaras, Emmanuel N.; Frank, Otakar; Tsoukleri, Georgia; Sfyris, Dimitris; Parthenios, John; Pugno, Nicola; Papagelis, Konstantinos; Novoselov, Kostya S.; Galiotis, Costas

    2014-01-01

    Exfoliated monolayer graphene flakes were embedded in a polymer matrix and loaded under axial compression. By monitoring the shifts of the 2D Raman phonons of rectangular flakes of various sizes under load, the critical strain to failure was determined. Prior to loading care was taken for the examined area of the flake to be free of residual stresses. The critical strain values for first failure were found to be independent of flake size at a mean value of –0.60% corresponding to a yield stress up to -6 GPa. By combining Euler mechanics with a Winkler approach, we show that unlike buckling in air, the presence of the polymer constraint results in graphene buckling at a fixed value of strain with an estimated wrinkle wavelength of the order of 1–2 nm. These results were compared with DFT computations performed on analogue coronene/PMMA oligomers and a reasonable agreement was obtained. PMID:24920340

  17. The effect of interlayer adhesion on the mechanical behaviors of macroscopic graphene oxide papers.

    PubMed

    Gao, Yun; Liu, Lu-Qi; Zu, Sheng-Zhen; Peng, Ke; Zhou, Ding; Han, Bao-Hang; Zhang, Zhong

    2011-03-22

    High mechanical performances of macroscopic graphene oxide (GO) papers are attracting great interest owing to their merits of lightweight and multiple functionalities. However, the loading role of individual nanosheets and its effect on the mechanical properties of the macroscopic GO papers are not yet well understood. Herein, we effectively tailored the interlayer adhesions of the GO papers by introducing small molecules, that is, glutaraldehyde (GA) and water molecules, into the gallery regions. With the help of in situ Raman spectroscopy, we compared the varied load-reinforcing roles of nanosheets, and further predicted the Young's moduli of the GO papers. Systematic mechanical tests have proven that the enhancement of the tensile modulus and strength of the GA-treated GO paper arose from the improved load-bearing capability of the nanosheets. On the basis of Raman and macroscopic mechanical tests, the influences of interlayer adhesions on the fracture mechanisms of the strained GO papers were inferred.

  18. Mechanical Properties of Graphene Nanoplatelet Carbon Fiber Epoxy Hybrid Composites: Multiscale Modeling and Experiments

    NASA Technical Reports Server (NTRS)

    Hadden, Cameron M.; Klimek-McDonald, Danielle R.; Pineda, Evan J.; King, Julie A.; Reichanadter, Alex M.; Miskioglu, Ibrahim; Gowtham, S.; Odegard, Gregory M.

    2015-01-01

    Because of the relatively high specific mechanical properties of carbon fiber/epoxy composite materials, they are often used as structural components in aerospace applications. Graphene nanoplatelets (GNPs) can be added to the epoxy matrix to improve the overall mechanical properties of the composite. The resulting GNP/carbon fiber/epoxy hybrid composites have been studied using multiscale modeling to determine the influence of GNP volume fraction, epoxy crosslink density, and GNP dispersion on the mechanical performance. The hierarchical multiscale modeling approach developed herein includes Molecular Dynamics (MD) and micromechanical modeling, and it is validated with experimental testing of the same hybrid composite material system. The results indicate that the multiscale modeling approach is accurate and provides physical insight into the composite mechanical behavior. Also, the results quantify the substantial impact of GNP volume fraction and dispersion on the transverse mechanical properties of the hybrid composite, while the effect on the axial properties is shown to be insignificant.

  19. Mechanical Properties of Graphene Nanoplatelet/Carbon Fiber/Epoxy Hybrid Composites: Multiscale Modeling and Experiments

    NASA Technical Reports Server (NTRS)

    Hadden, C. M.; Klimek-McDonald, D. R.; Pineda, E. J.; King, J. A.; Reichanadter, A. M.; Miskioglu, I.; Gowtham, S.; Odegard, G. M.

    2015-01-01

    Because of the relatively high specific mechanical properties of carbon fiber/epoxy composite materials, they are often used as structural components in aerospace applications. Graphene nanoplatelets (GNPs) can be added to the epoxy matrix to improve the overall mechanical properties of the composite. The resulting GNP/carbon fiber/epoxy hybrid composites have been studied using multiscale modeling to determine the influence of GNP volume fraction, epoxy crosslink density, and GNP dispersion on the mechanical performance. The hierarchical multiscale modeling approach developed herein includes Molecular Dynamics (MD) and micromechanical modeling, and it is validated with experimental testing of the same hybrid composite material system. The results indicate that the multiscale modeling approach is accurate and provides physical insight into the composite mechanical behavior. Also, the results quantify the substantial impact of GNP volume fraction and dispersion on the transverse mechanical properties of the hybrid composite while the effect on the axial properties is shown to be insignificant.

  20. Mechanical Properties of Graphene Nanoplatelet/Carbon Fiber/Epoxy Hybrid Composites: Multiscale Modeling and Experiments

    NASA Technical Reports Server (NTRS)

    Hadden, C. M.; Klimek-McDonald, D. R.; Pineda, E. J.; King, J. A.; Reichanadter, A. M.; Miskioglu, I.; Gowtham, S.; Odegard, G. M.

    2015-01-01

    Because of the relatively high specific mechanical properties of carbon fiber/epoxy composite materials, they are often used as structural components in aerospace applications. Graphene nanoplatelets (GNPs) can be added to the epoxy matrix to improve the overall mechanical properties of the composite. The resulting GNP/carbon fiber/epoxy hybrid composites have been studied using multiscale modeling to determine the influence of GNP volume fraction, epoxy crosslink density, and GNP dispersion on the mechanical performance. The hierarchical multiscale modeling approach developed herein includes Molecular Dynamics (MD) and micromechanical modeling, and it is validated with experimental testing of the same hybrid composite material system. The results indicate that the multiscale modeling approach is accurate and provides physical insight into the composite mechanical behavior. Also, the results quantify the substantial impact of GNP volume fraction and dispersion on the transverse mechanical properties of the hybrid composite, while the effect on the axial properties is shown to be insignificant.

  1. Graphene-based nafion nanocomposite membranes: enhanced proton transport and water retention by novel organo-functionalized graphene oxide nanosheets.

    PubMed

    Enotiadis, Apostolos; Angjeli, Kristina; Baldino, Noemi; Nicotera, Isabella; Gournis, Dimitrios

    2012-11-05

    Novel nanostructured organo-modified layered materials based on graphene oxide carrying various hydrophilic functional groups (-NH(2), -OH, -SO(3)H) are prepared and tested as nanofillers for the creation of innovative graphene-based Nafion nanocomposites. The hybrid membranes are characterized by a combination of analytical techniques, which show that highly homogeneous exfoliated nanocomposites are created. The pulsed field gradient NMR technique is used to measure the water self-diffusion coefficients. Remarkable behavior at temperatures up to 140 °C is observed for some composite membranes, thereby verifying the exceptional water retention property of these materials. Dynamic mechanical analysis shows that hybrid membranes are much stiffer and can withstand higher temperatures than pure Nafion.

  2. Confocal microscopy and exfoliative cytology

    PubMed Central

    Reddy, Shyam Prasad; Ramani, Pratibha; Nainani, Purshotam

    2013-01-01

    Context: Early detection of potentially malignant lesions and invasive squamous-cell carcinoma in the oral cavity could be greatly improved through techniques that permit visualization of subtle cellular changes indicative of the neoplastic transformation process. One such technique is confocal microscopy. Combining rapidity with reliability, an innovative idea has been put forward using confocal microscope in exfoliative cytology. Aims: The main objective of this study was to assess confocal microscopy for cytological diagnosis and the results were compared with that of the standard PAP stain. Settings and Design: Confocal microscope, acridine orange (AO) stain, PAP (Papanicolaou) stain. The study was designed to assess confocal microscopy for cytological diagnosis. In the process, smears of patients with (clinically diagnosed and/or suspected) oral squamous cell carcinoma as well as those of controls (normal people) were stained with acridine orange and observed under confocal microscope. The results were compared with those of the standard PAP method. Materials and Methods: Samples of buccal mucosa smears from normal patients and squamous cell carcinoma patients were made, fixed in 100% alcohol, followed by AO staining. The corresponding set of smears was stained with PAP stain using rapid PAP stain kit. The results obtained were compared with those obtained with AO confocal microscopy. Results: The study had shown nuclear changes (malignant cells) in the smears of squamous cell carcinoma patients as increased intensity of fluorescence of the nucleus, when observed under confocal microscope. Acridine orange confocal microscopy showed good amount of sensitivity and specificity (93%) in identifying malignant cells in exfoliative cytological smears. Conclusion: Confocal microscopy was found to have good sensitivity in the identification of cancer (malignant) cells in exfoliative cytology, at par with the PAP method. The rapidity of processing and screening a

  3. Electronic Properties of Large-scale Graphene Chemical Vapor Synthesized on Nickel and on Sapphire

    NASA Astrophysics Data System (ADS)

    Cao, Helin; Zhang, Liyuan; Chen, Yong; Yu, Qingkai; Li, Hao

    2009-03-01

    We have studied the electronic transport properties of large area few-layer graphene/graphitic films grown by two different chemical vapor based methods. The first type of samples (metal-transfer graphene) is synthesized by carbon segregation from Ni, then transferred to SiO2/Si substrates. The second type of samples is synthesized by direct chemical vapor deposition (CVD) on sapphire. We measured these samples under variable temperatures (from 2K to 300 K) and transverse magnet fields (from 0 to 7 T). For both types of samples, we found a negative magnetoresistance at low field, and carrier mobilities on the order of several hundreds of cm^2/V-s. For metal-transfer graphene in particular, we were able to measure a moderate field effect response, using the highly doped Si substrate as back gate. The observed magnetoresistance shows characteristic features of weak localization, from which we extract various carrier scattering lengths in the metal-transfer graphene samples. Comparison with those measured in mechanically exfoliated graphene suggests possibly different carrier scattering mechanisms for graphene materials prepared with different methods.

  4. Soliton-dependent plasmon reflection at bilayer graphene domain walls.

    PubMed

    Jiang, Lili; Shi, Zhiwen; Zeng, Bo; Wang, Sheng; Kang, Ji-Hun; Joshi, Trinity; Jin, Chenhao; Ju, Long; Kim, Jonghwan; Lyu, Tairu; Shen, Yuen-Ron; Crommie, Michael; Gao, Hong-Jun; Wang, Feng

    2016-08-01

    Layer-stacking domain walls in bilayer graphene are emerging as a fascinating one-dimensional system that features stacking solitons structurally and quantum valley Hall boundary states electronically. The interactions between electrons in the 2D graphene domains and the one-dimensional domain-wall solitons can lead to further new quantum phenomena. Domain-wall solitons of varied local structures exist along different crystallographic orientations, which can exhibit distinct electrical, mechanical and optical properties. Here we report soliton-dependent 2D graphene plasmon reflection at different 1D domain-wall solitons in bilayer graphene using near-field infrared nanoscopy. We observe various domain-wall structures in mechanically exfoliated graphene bilayers, including network-forming triangular lattices, individual straight or bent lines, and even closed circles. The near-field infrared contrast of domain-wall solitons arises from plasmon reflection at domain walls, and exhibits markedly different behaviours at the tensile- and shear-type domain-wall solitons. In addition, the plasmon reflection at domain walls exhibits a peculiar dependence on electrostatic gating. Our study demonstrates the unusual and tunable coupling between 2D graphene plasmons and domain-wall solitons.

  5. Mechanical, Thermal and Dynamic Mechanical Properties of PP/GF/xGnP Nanocomposites

    NASA Astrophysics Data System (ADS)

    Ashenai Ghasemi, F.; Ghorbani, A.; Ghasemi, I.

    2017-03-01

    The mechanical, thermal, and dynamic mechanical properties of ternary nanocomposites based on polypropylene, short glass fibers, and exfoliated graphene nanoplatelets were studied. To investigate the mechanical properties, uniaxial tensile and Charpy impact tests were carried out. To study the crystallinity of the compositions, a DSC test was performed. A dynamic mechanical analysis was used to characterize the storage modulus and loss factor (tan δ). The morphology of the composites was studied by a scanning electron microscope (SEM). The results obtained are presented in tables and graphics.

  6. The formation mechanism of multiple vacancies and amorphous graphene under electron irradiation

    NASA Astrophysics Data System (ADS)

    Zhao, Ruiqi; Zhuang, Jianing; Liang, Zilin; Yan, Tianying; Ding, Feng

    2015-04-01

    The evolution of multiple vacancies (Vns) in graphene under electron irradiation (EI) was explored systematically by long time non-equilibrium molecular dynamics simulations, with n varying from 4 to 40. The simulations showed that the Vns form haeckelites in the case with small n, while forming holes as n increases. The scale of the haeckelites, characterized by the number of pentagon-heptagon pairs, grows linearly with n. Such a linear relationship can be interpreted as a consequence of compensating the missing area, caused by the Vns, in order to maintain the area of the perfect sp2 network by self-healing. Beyond that, the scale of the haeckelite vs. the density of missing atoms is predicted to be Sh ~ 6Dn, where Sh and Dn are the percentage of non-hexagonal rings and missing atoms, respectively. This study provides an intuitive picture of the formation of amorphous graphene under EI and the quantitative understanding of the mechanism.The evolution of multiple vacancies (Vns) in graphene under electron irradiation (EI) was explored systematically by long time non-equilibrium molecular dynamics simulations, with n varying from 4 to 40. The simulations showed that the Vns form haeckelites in the case with small n, while forming holes as n increases. The scale of the haeckelites, characterized by the number of pentagon-heptagon pairs, grows linearly with n. Such a linear relationship can be interpreted as a consequence of compensating the missing area, caused by the Vns, in order to maintain the area of the perfect sp2 network by self-healing. Beyond that, the scale of the haeckelite vs. the density of missing atoms is predicted to be Sh ~ 6Dn, where Sh and Dn are the percentage of non-hexagonal rings and missing atoms, respectively. This study provides an intuitive picture of the formation of amorphous graphene under EI and the quantitative understanding of the mechanism. Electronic supplementary information (ESI) available: Efs of certain haeckelites observed in

  7. Assisted deposition of nano-hydroxyapatite onto exfoliated carbon nanotube oxide scaffolds

    NASA Astrophysics Data System (ADS)

    Zanin, H.; Rosa, C. M. R.; Eliaz, N.; May, P. W.; Marciano, F. R.; Lobo, A. O.

    2015-05-01

    Electrodeposited nano-hydroxyapatite (nHAp) is more similar to biological apatite in terms of microstructure and dimension than apatites prepared by other processes. Reinforcement with carbon nanotubes (CNTs) enhances its mechanical properties and increases adhesion of osteoblasts. Here, we carefully studied nHAp deposited onto vertically aligned multi-walled CNT (VAMWCNT) scaffolds by electrodeposition and soaking in a simulated body fluid (SBF). VAMWCNTs are porous biocompatible scaffolds with nanometric porosity and exceptional mechanical and chemical properties. The VAMWCNT films were prepared on a Ti substrate by a microwave plasma chemical vapour deposition method, and then oxidized and exfoliated by oxygen plasma etching (OPE) to produce graphene oxide (GO) at the VAMWCNT tips. The attachment of oxygen functional groups was found to be crucial for nHAp nucleation during electrodeposition. A thin layer of plate-like and needle-like nHAp with high crystallinity was formed without any need for thermal treatment. This composite (henceforth referred to as nHAp-VAMWCNT-GO) served as the scaffold for in vitro biomineralization when soaked in the SBF, resulting in the formation of both carbonate-rich and carbonate-poor globular-like nHAp. Different steps in the deposition of biological apatite onto VAMWCNT-GO and during the short-term biomineralization process were analysed. Due to their unique structure and properties, such nano-bio-composites may become useful in accelerating in vivo bone regeneration processes.

  8. Efavirenz-induced exfoliative dermatitis.

    PubMed

    Zhang, Jiu-Cong; Sun, Yong-Tao

    2013-01-01

    Individuals with a human immunodeficiency virus (HIV) infection are at higher risk of developing adverse drug reactions. Multiple drugs are usually prescribed to patients with HIV infection for preventing the replication of HIV and for the treatment of the associated opportunistic infections. We report here the first case of an HIV-1-infected patient who developed an exfoliative dermatitis induced by efavirenz, a non-nucleoside reverse transcriptase inhibitor. Physicians should be aware of the possible occurrence of efavirenz-induced skin eruptions from the start of antiviral treatment of HIV infection.

  9. [Exfoliative esophagitis while taking dabigatran].

    PubMed

    Scheppach, Wolfgang; Meesmann, Malte

    2015-04-01

    History | A 77-year-old woman was admitted with severe chest pain, heartburn, dysphagia and odynophagia. She had been on dabigatran for 13 months due to atrial fibrillation and arterial hypertension. Investigations and findings | Endoscopy of the esophagus revealed sloughing of mucosal casts, predominantly in the upper half of the organ. Treatment and course | The patient was placed on pantoprazol, local anaesthetic antacid and i. v. fluids. Dabigatran was discontinued. The symptoms disappeared within 3 days. Control endoscopy after 12 days showed complete healing of the esophageal mucosa. Conclusion | The intake of dabigatran was associated with exfoliative esophagitis, possibly due to caustic tissue damage by prolonged drug contact.

  10. Dynamical strong coupling and parametric amplification of mechanical modes of graphene drums

    NASA Astrophysics Data System (ADS)

    Mathew, John P.; Patel, Raj N.; Borah, Abhinandan; Vijay, R.; Deshmukh, Mandar M.

    2016-09-01

    Mechanical resonators are ubiquitous in modern information technology. With the possibility of coupling them to electromagnetic and plasmonic modes, they hold promise as the key building blocks in future quantum information technology. Graphene-based resonators are of interest for technological applications due to their high resonant frequencies, multiple mechanical modes and low mass. The tension-mediated nonlinear coupling between various modes of the resonator can be excited in a controllable manner. Here we engineer a graphene resonator with large frequency tunability at low temperatures, resulting in a large intermodal coupling strength. We observe the emergence of new eigenmodes and amplification of the coupled modes using red and blue parametric excitation, respectively. We demonstrate that the dynamical intermodal coupling is tunable. A cooperativity of 60 between two resonant modes of ∼100 MHz is achieved in the strong coupling regime. The ability to dynamically control the coupling between the high-frequency eigenmodes of a mechanical system opens up the possibility of quantum mechanical experiments at low temperatures.

  11. Tuning the mechanical properties of vertical graphene sheets through atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Davami, Keivan; Jiang, Yijie; Cortes, John; Lin, Chen; Shaygan, Mehrdad; Turner, Kevin T.; Bargatin, Igor

    2016-04-01

    We report the fabrication and characterization of graphene nanostructures with mechanical properties that are tuned by conformal deposition of alumina. Vertical graphene (VG) sheets, also called carbon nanowalls (CNWs), were grown on copper foil substrates using a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique and conformally coated with different thicknesses of alumina (Al2O3) using atomic layer deposition (ALD). Nanoindentation was used to characterize the mechanical properties of pristine and alumina-coated VG sheets. Results show a significant increase in the effective Young’s modulus of the VG sheets with increasing thickness of deposited alumina. Deposition of only a 5 nm thick alumina layer on the VG sheets nearly triples the effective Young’s modulus of the VG structures. Both energy absorption and strain recovery were lower in VG sheets coated with alumina than in pure VG sheets (for the same peak force). This may be attributed to the increase in bending stiffness of the VG sheets and the creation of connection