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Sample records for adjacent graphene layers

  1. Temperature variations at nano-scale level in phase transformed nanocrystalline NiTi shape memory alloys adjacent to graphene layers.

    PubMed

    Amini, Abbas; Cheng, Chun; Naebe, Minoo; Church, Jeffrey S; Hameed, Nishar; Asgari, Alireza; Will, Frank

    2013-07-21

    The detection and control of the temperature variation at the nano-scale level of thermo-mechanical materials during a compression process have been challenging issues. In this paper, an empirical method is proposed to predict the temperature at the nano-scale level during the solid-state phase transition phenomenon in NiTi shape memory alloys. Isothermal data was used as a reference to determine the temperature change at different loading rates. The temperature of the phase transformed zone underneath the tip increased by ∼3 to 40 °C as the loading rate increased. The temperature approached a constant with further increase in indentation depth. A few layers of graphene were used to enhance the cooling process at different loading rates. Due to the presence of graphene layers the temperature beneath the tip decreased by a further ∼3 to 10 °C depending on the loading rate. Compared with highly polished NiTi, deeper indentation depths were also observed during the solid-state phase transition, especially at the rate dependent zones. Larger superelastic deformations confirmed that the latent heat transfer through the deposited graphene layers allowed a larger phase transition volume and, therefore, more stress relaxation and penetration depth. PMID:23744099

  2. Temperature variations at nano-scale level in phase transformed nanocrystalline NiTi shape memory alloys adjacent to graphene layers

    NASA Astrophysics Data System (ADS)

    Amini, Abbas; Cheng, Chun; Naebe, Minoo; Church, Jeffrey S.; Hameed, Nishar; Asgari, Alireza; Will, Frank

    2013-06-01

    The detection and control of the temperature variation at the nano-scale level of thermo-mechanical materials during a compression process have been challenging issues. In this paper, an empirical method is proposed to predict the temperature at the nano-scale level during the solid-state phase transition phenomenon in NiTi shape memory alloys. Isothermal data was used as a reference to determine the temperature change at different loading rates. The temperature of the phase transformed zone underneath the tip increased by ~3 to 40 °C as the loading rate increased. The temperature approached a constant with further increase in indentation depth. A few layers of graphene were used to enhance the cooling process at different loading rates. Due to the presence of graphene layers the temperature beneath the tip decreased by a further ~3 to 10 °C depending on the loading rate. Compared with highly polished NiTi, deeper indentation depths were also observed during the solid-state phase transition, especially at the rate dependent zones. Larger superelastic deformations confirmed that the latent heat transfer through the deposited graphene layers allowed a larger phase transition volume and, therefore, more stress relaxation and penetration depth.

  3. Temperature variations at nano-scale level in phase transformed nanocrystalline NiTi shape memory alloys adjacent to graphene layers.

    PubMed

    Amini, Abbas; Cheng, Chun; Naebe, Minoo; Church, Jeffrey S; Hameed, Nishar; Asgari, Alireza; Will, Frank

    2013-07-21

    The detection and control of the temperature variation at the nano-scale level of thermo-mechanical materials during a compression process have been challenging issues. In this paper, an empirical method is proposed to predict the temperature at the nano-scale level during the solid-state phase transition phenomenon in NiTi shape memory alloys. Isothermal data was used as a reference to determine the temperature change at different loading rates. The temperature of the phase transformed zone underneath the tip increased by ∼3 to 40 °C as the loading rate increased. The temperature approached a constant with further increase in indentation depth. A few layers of graphene were used to enhance the cooling process at different loading rates. Due to the presence of graphene layers the temperature beneath the tip decreased by a further ∼3 to 10 °C depending on the loading rate. Compared with highly polished NiTi, deeper indentation depths were also observed during the solid-state phase transition, especially at the rate dependent zones. Larger superelastic deformations confirmed that the latent heat transfer through the deposited graphene layers allowed a larger phase transition volume and, therefore, more stress relaxation and penetration depth.

  4. Boundary Layers of Air Adjacent to Cylinders

    PubMed Central

    Nobel, Park S.

    1974-01-01

    Using existing heat transfer data, a relatively simple expression was developed for estimating the effective thickness of the boundary layer of air surrounding cylinders. For wind velocities from 10 to 1000 cm/second, the calculated boundary-layer thickness agreed with that determined for water vapor diffusion from a moistened cylindrical surface 2 cm in diameter. It correctly predicted the resistance for water vapor movement across the boundary layers adjacent to the (cylindrical) inflorescence stems of Xanthorrhoea australis R. Br. and Scirpus validus Vahl and the leaves of Allium cepa L. The boundary-layer thickness decreased as the turbulence intensity increased. For a turbulence intensity representative of field conditions (0.5) and for νwindd between 200 and 30,000 cm2/second (where νwind is the mean wind velocity and d is the cylinder diameter), the effective boundary-layer thickness in centimeters was equal to [Formula: see text]. PMID:16658855

  5. Burning Graphene Layer-by-Layer.

    PubMed

    Ermakov, Victor A; Alaferdov, Andrei V; Vaz, Alfredo R; Perim, Eric; Autreto, Pedro A S; Paupitz, Ricardo; Galvao, Douglas S; Moshkalev, Stanislav A

    2015-01-01

    Graphene, in single layer or multi-layer forms, holds great promise for future electronics and high-temperature applications. Resistance to oxidation, an important property for high-temperature applications, has not yet been extensively investigated. Controlled thinning of multi-layer graphene (MLG), e.g., by plasma or laser processing is another challenge, since the existing methods produce non-uniform thinning or introduce undesirable defects in the basal plane. We report here that heating to extremely high temperatures (exceeding 2000 K) and controllable layer-by-layer burning (thinning) can be achieved by low-power laser processing of suspended high-quality MLG in air in "cold-wall" reactor configuration. In contrast, localized laser heating of supported samples results in non-uniform graphene burning at much higher rates. Fully atomistic molecular dynamics simulations were also performed to reveal details of oxidation mechanisms leading to uniform layer-by-layer graphene gasification. The extraordinary resistance of MLG to oxidation paves the way to novel high-temperature applications as continuum light source or scaffolding material.

  6. Burning Graphene Layer-by-Layer.

    PubMed

    Ermakov, Victor A; Alaferdov, Andrei V; Vaz, Alfredo R; Perim, Eric; Autreto, Pedro A S; Paupitz, Ricardo; Galvao, Douglas S; Moshkalev, Stanislav A

    2015-01-01

    Graphene, in single layer or multi-layer forms, holds great promise for future electronics and high-temperature applications. Resistance to oxidation, an important property for high-temperature applications, has not yet been extensively investigated. Controlled thinning of multi-layer graphene (MLG), e.g., by plasma or laser processing is another challenge, since the existing methods produce non-uniform thinning or introduce undesirable defects in the basal plane. We report here that heating to extremely high temperatures (exceeding 2000 K) and controllable layer-by-layer burning (thinning) can be achieved by low-power laser processing of suspended high-quality MLG in air in "cold-wall" reactor configuration. In contrast, localized laser heating of supported samples results in non-uniform graphene burning at much higher rates. Fully atomistic molecular dynamics simulations were also performed to reveal details of oxidation mechanisms leading to uniform layer-by-layer graphene gasification. The extraordinary resistance of MLG to oxidation paves the way to novel high-temperature applications as continuum light source or scaffolding material. PMID:26100466

  7. Layer-by-layer assembly of vertically conducting graphene devices.

    PubMed

    Chen, Jing-Jing; Meng, Jie; Zhou, Yang-Bo; Wu, Han-Chun; Bie, Ya-Qing; Liao, Zhi-Min; Yu, Da-Peng

    2013-01-01

    Graphene has various potential applications owing to its unique electronic, optical, mechanical and chemical properties, which are primarily based on its two-dimensional nature. Graphene-based vertical devices can extend the investigations and potential applications range to three dimensions, while interfacial properties are crucial for the function and performance of such graphene vertical devices. Here we report a general method to construct graphene vertical devices with controllable functions via choosing different interfaces between graphene and other materials. Two types of vertically conducting devices are demonstrated: graphene stacks sandwiched between two Au micro-strips, and between two Co layers. The Au|graphene|Au junctions exhibit large magnetoresistance with ratios up to 400% at room temperature, which have potential applications in magnetic field sensors. The Co|graphene|Co junctions display a robust spin valve effect at room temperature. The layer-by-layer assembly of graphene offers a new route for graphene vertical structures. PMID:23715280

  8. Structured Water Layers Adjacent to Biological Membranes

    PubMed Central

    Higgins, Michael J.; Polcik, Martin; Fukuma, Takeshi; Sader, John E.; Nakayama, Yoshikazu; Jarvis, Suzanne P.

    2006-01-01

    Water amid the restricted space of crowded biological macromolecules and at membrane interfaces is essential for cell function, though the structure and function of this “biological water” itself remains poorly defined. The force required to remove strongly bound water is referred to as the hydration force and due to its widespread importance, it has been studied in numerous systems. Here, by using a highly sensitive dynamic atomic force microscope technique in conjunction with a carbon nanotube probe, we reveal a hydration force with an oscillatory profile that reflects the removal of up to five structured water layers from between the probe and biological membrane surface. Further, we find that the hydration force can be modified by changing the membrane fluidity. For 1,2-dipalmitoyl-sn-glycero-3-phosphocholine gel (Lβ) phase bilayers, each oscillation in the force profile indicates the force required to displace a single layer of water molecules from between the probe and bilayer. In contrast, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine fluid (Lα) phase bilayers at 60°C and 1,2-dioleoyl-sn-glycero-3-phosphocholine fluid (Lα) phase bilayers at 24°C seriously disrupt the molecular ordering of the water and result predominantly in a monotonic force profile. PMID:16798815

  9. Cleaning graphene with a titanium sacrificial layer

    SciTech Connect

    Joiner, C. A. Roy, T.; Hesabi, Z. R.; Vogel, E. M.; Chakrabarti, B.

    2014-06-02

    Graphene is a promising material for future electronic applications and chemical vapor deposition of graphene on copper is a promising method for synthesizing graphene on the wafer scale. The processing of such graphene films into electronic devices introduces a variety of contaminants which can be difficult to remove. An approach to cleaning residues from the graphene channel is presented in which a thin layer of titanium is deposited via thermal e-beam evaporation and immediately removed. This procedure does not damage the graphene as evidenced by Raman spectroscopy, greatly enhances the electrical performance of the fabricated graphene field effect transistors, and completely removes the chemical residues from the surface of the graphene channel as evidenced by x-ray photoelectron spectroscopy.

  10. Counting graphene layers with very slow electrons

    SciTech Connect

    Frank, Ludĕk; Mikmeková, Eliška; Müllerová, Ilona; Lejeune, Michaël

    2015-01-05

    The study aimed at collection of data regarding the transmissivity of freestanding graphene for electrons across their full energy scale down to the lowest energies. Here, we show that the electron transmissivity of graphene drops with the decreasing energy of the electrons and remains below 10% for energies below 30 eV, and that the slow electron transmissivity value is suitable for reliable determination of the number of graphene layers. Moreover, electrons incident below 50 eV release adsorbed hydrocarbon molecules and effectively clean graphene in contrast to faster electrons that decompose these molecules and create carbonaceous contamination.

  11. Graphene/ferroelectrics/graphene hybrid structure: Asymmetric doping of graphene layers

    SciTech Connect

    Duong, Dinh Loc; Lee, Si Young; Kim, Seong Kyu; Lee, Young Hee

    2015-06-15

    We report graphene/ferroelectric/graphene hybrid structure to demonstrate an asymmetrical doping in two graphene layers, one side with electrons and another side with holes. Two ferroelectrics, a poly(vinylidenefluoride) (PVDF) and a hydrofluorinated graphene, were used to demonstrate the concept with density functional calculations, revealing the Fermi level shift of 0.35 and 0.75 eV, respectively. This concept was confirmed by Raman spectroscopy using graphene/poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE))/graphene hybrid, which can easily form β-phase close to our simulation model. G-band peak position was downshifted for electron doping and upshifted for hole doping. This hybrid structure opens an opportunity to study bilayer graphene system with a controllable thickness for a wide range of high carrier concentration.

  12. 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.

  13. Additional waves in the graphene layered medium.

    PubMed

    Chern, Ruey-Lin; Han, Dezhuan; Zhang, Z Q; Chan, C T

    2014-12-29

    We investigate the features of additional waves that arise in the graphene layered medium, within the framework of nonlocal effective medium model. The additional wave is manifest on the biquadratic dispersion relation of the medium and represents as a distinctive nonlocal character at long wavelength. In particular, the reflection and transmission coefficients for the nonlocal medium are underdetermined by Maxwell's boundary conditions. An additional boundary condition based on modal expansions is proposed to derive the generalized Fresnel equations, based on which the additional wave in the graphene layered medium is determined. The additional wave tends to be significant near the effective plasma frequency, near which the graphene plasmons are excited inside the medium. PMID:25607138

  14. Selective exfoliation of single-layer graphene from non-uniform graphene grown on Cu

    NASA Astrophysics Data System (ADS)

    Lim, Jae-Young; Lee, Jae-Hyun; Jang, Hyeon-Sik; Joo, Won-Jae; Hwang, SungWoo; Whang, Dongmok

    2015-11-01

    Graphene growth on a copper surface via metal-catalyzed chemical vapor deposition has several advantages in terms of providing high-quality graphene with the potential for scale-up, but the product is usually inhomogeneous due to the inability to control the graphene layer growth. The non-uniform regions strongly affect the reliability of the graphene in practical electronic applications. Herein, we report a novel graphene transfer method that allows for the selective exfoliation of single-layer graphene from non-uniform graphene grown on a Cu foil. Differences in the interlayer bonding energy are exploited to mechanically separate only the top single-layer graphene and transfer this to an arbitrary substrate. The dry-transferred single-layer graphene showed electrical characteristics that were more uniform than those of graphene transferred using conventional wet-etching transfer steps.

  15. The Thermomagnetic Instability in Superconducting Films with Adjacent Metal Layer

    NASA Astrophysics Data System (ADS)

    Vestgården, J. I.; Galperin, Y. M.; Johansen, T. H.

    2013-12-01

    Dendritic flux avalanches is a frequently encountered consequence of the thermomagnetic instability in type-II superconducting films. The avalanches, which are potentially harmful for superconductor-based devices, can be suppressed by an adjacent normal metal layer, even when the two layers are not in thermal contact. The suppression of the avalanches in this case is due to so-called magnetic braking, caused by eddy currents generated in the metal layer by propagating magnetic flux. We develop a theory of magnetic braking by analyzing coupled electrodynamics and heat flow in a superconductor-normal metal bilayer. The equations are solved by linearization and by numerical simulation of the avalanche dynamics. We find that in an uncoated superconductor, even a uniform thermomagnetic instability can develop into a dendritic flux avalanche. The mechanism is that a small non-uniformity caused by the electromagnetic non-locality induces a flux-flow hot spot at a random position. The hot spot quickly develops into a finger, which at high speeds penetrates into the superconductor, forming a branching structure. Magnetic braking slows the avalanches, and if the normal metal conductivity is sufficiently high, it can suppress the formation of the dendritic structure. During avalanches, the braking by the normal metal layer prevents the temperature from exceeding the transition temperature of the superconductor. Analytical criteria for the instability threshold are developed using the linear stability analysis. The criteria are found to match quantitatively the instability onsets obtained in simulations.

  16. Layer resolved capacitive probing of graphene bilayers

    NASA Astrophysics Data System (ADS)

    Zibrov, Alexander; Parmentier, François; Li, Jia; Wang, Lei; Hunt, Benjamin; Dean, Cory; Hone, James; Taniguchi, Takashi; Watanabe, Kenji; Young, Andrea

    Compared to single layer graphene, graphene bilayers have an additional ``which-layer'' degree of freedom that can be controlled by an external electric field in a dual-gated device geometry. We describe capacitance measurements capable of directly probing this degree of freedom. By performing top gate, bottom gate, and penetration field capacitance measurements, we directly extract layer polarization of both Bernal and twisted bilayers. We will present measurements of hBN encapsulated bilayers at both zero and high magnetic field, focusing on the physics of the highly degenerate zero-energy Landau level in the high magnetic field limit where spin, valley, and layer degeneracy are all lifted by electronic interactions.

  17. Symmetry Breaking in Few Layer Graphene Films

    SciTech Connect

    Bostwick, A.; Ohta, T.; McChesney, J.L.; Emtsev, K.; Seyller,Th.; Horn, K.; Rotenberg, E.

    2007-05-25

    Recently, it was demonstrated that the quasiparticledynamics, the layer-dependent charge and potential, and the c-axisscreening coefficient could be extracted from measurements of thespectral function of few layer graphene films grown epitaxially on SiCusing angle-resolved photoemission spectroscopy (ARPES). In this articlewe review these findings, and present detailed methodology for extractingsuch parameters from ARPES. We also present detailed arguments againstthe possibility of an energy gap at the Dirac crossing ED.

  18. Selective growth of graphene in layer-by-layer via chemical vapor deposition.

    PubMed

    Park, Jaehyun; An, Hyosub; Choi, Dong-Chul; Hussain, Sajjad; Song, Wooseok; An, Ki-Seok; Lee, Won-Jun; Lee, Naesung; Lee, Wan-Gyu; Jung, Jongwan

    2016-08-14

    Selective and precise control of the layer number of graphene remains a critical issue for the practical applications of graphene. First, it is highly challenging to grow a continuous and uniform few-layer graphene since once the monolayer graphene fully covers a copper (Cu) surface, the growth of the second layer stops, resulting in mostly nonhomogeneous films. Second, from the selective adlayer growth point of view, there is no clear pathway for achieving this. We have developed the selective growth of a graphene adlayer in layer-by-layer via chemical vapor deposition (CVD) which makes it possible to stack graphene on a specific position. The key idea is to deposit a thin Cu layer (∼40 nm thick) on pre-grown monolayer graphene and to apply additional growth. The thin Cu atop the graphene/Cu substrate acts as a catalyst to decompose methane (CH4) gas during the additional growth. The adlayer is grown selectively on the pre-grown graphene, and the thin Cu is removed through evaporation during CVD, eventually forming large-area and uniform double layer graphene. With this technology, highly uniform graphene films with precise thicknesses of 1 to 5 layers and graphene check patterns with 1 to 3 layers were successfully demonstrated. This method provides precise LBL growth for a uniform graphene film and a technique for the design of new graphene devices. PMID:27436358

  19. Benchmarking the penetration-resistance efficiency of multilayer graphene sheets due to spacing the graphene layers

    NASA Astrophysics Data System (ADS)

    Sadeghzadeh, S.

    2016-07-01

    In this paper, the penetration-resistance efficiency of single-layer and multilayer graphene sheets has been investigated by means of the multiscale approach. The employed multiscale approach has been implemented by establishing a direct correlation between the finite element method and the molecular dynamics approach and validated by comparing its results with those of the existing experimental works. Since by using numerous techniques, a new class of graphene sheets can be fabricated in which the graphene layers are spaced farther apart (more than the usual distance between layers), this paper has concentrated on the optimal spacing between graphene layers with the goal of improving the impact properties of graphene sheets as important candidates for novel impact-resistant panels. For this purpose, the relative protection (protection with respect to weight) values of graphene sheets were obtained, and it was observed that the relative protection of a single-layer graphene sheet is about 3.64 times that of a 20-layer graphene sheet. This study also showed that a spaced multilayer graphene sheet, with its inter-layer distance being 20 times the usual spacing between ordinary graphene layers, has an impact resistance which is about 20 % higher than that of an ordinary 20-layer graphene sheet. The findings of this paper can be appropriately used in the design and fabrication of future-generation impact-resistant protective panels.

  20. Strengthening effect of single-atomic-layer graphene in metal-graphene nanolayered composites.

    PubMed

    Kim, Youbin; Lee, Jinsup; Yeom, Min Sun; Shin, Jae Won; Kim, Hyungjun; Cui, Yi; Kysar, Jeffrey W; Hone, James; Jung, Yousung; Jeon, Seokwoo; Han, Seung Min

    2013-01-01

    Graphene is a single-atomic-layer material with excellent mechanical properties and has the potential to enhance the strength of composites. Its two-dimensional geometry, high intrinsic strength and modulus can effectively constrain dislocation motion, resulting in the significant strengthening of metals. Here we demonstrate a new material design in the form of a nanolayered composite consisting of alternating layers of metal (copper or nickel) and monolayer graphene that has ultra-high strengths of 1.5 and 4.0 GPa for copper-graphene with 70-nm repeat layer spacing and nickel-graphene with 100-nm repeat layer spacing, respectively. The ultra-high strengths of these metal-graphene nanolayered structures indicate the effectiveness of graphene in blocking dislocation propagation across the metal-graphene interface. Ex situ and in situ transmission electron microscopy compression tests and molecular dynamics simulations confirm a build-up of dislocations at the graphene interface. PMID:23820590

  1. Optical and Electrical Characteristics of Graphene Double Layer Formed by a Double Transfer of Graphene Single Layers.

    PubMed

    Kim, Young Jun; Bae, Gi Yoon; Chun, Sungwoo; Park, Wanjun

    2016-03-01

    We demonstrate formation of double layer graphene by means of a double transfer using two single graphene layers grown by a chemical vapor deposition method. It is observed that shiftiness and broadness in the double-resonance of Raman scattering are much weaker than those of bilayer graphene formed naturally. Transport characteristics examined from transmission line measurements and field effect transistors show the similar behavior with those of single layer graphene. It indicates that interlayer separation, in electrical view, is large enough to avoid correlation between layers for the double layer structure. It is also observed from a transistor with the double layer graphene that molecules adsorpted on two inner graphene surfaces in the double layered structure are isolated and conserved from ambient environment. PMID:27455706

  2. Optical and Electrical Characteristics of Graphene Double Layer Formed by a Double Transfer of Graphene Single Layers.

    PubMed

    Kim, Young Jun; Bae, Gi Yoon; Chun, Sungwoo; Park, Wanjun

    2016-03-01

    We demonstrate formation of double layer graphene by means of a double transfer using two single graphene layers grown by a chemical vapor deposition method. It is observed that shiftiness and broadness in the double-resonance of Raman scattering are much weaker than those of bilayer graphene formed naturally. Transport characteristics examined from transmission line measurements and field effect transistors show the similar behavior with those of single layer graphene. It indicates that interlayer separation, in electrical view, is large enough to avoid correlation between layers for the double layer structure. It is also observed from a transistor with the double layer graphene that molecules adsorpted on two inner graphene surfaces in the double layered structure are isolated and conserved from ambient environment.

  3. Improving the electrical properties of graphene layers by chemical doping

    NASA Astrophysics Data System (ADS)

    Farooq Khan, Muhammad; Zahir Iqbal, Muhammad; Waqas Iqbal, Muhammad; Eom, Jonghwa

    2014-10-01

    Although the electronic properties of graphene layers can be modulated by various doping techniques, most of doping methods cost degradation of structural uniqueness or electrical mobility. It is matter of huge concern to develop a technique to improve the electrical properties of graphene while sustaining its superior properties. Here, we report the modification of electrical properties of single- bi- and trilayer graphene by chemical reaction with potassium nitrate (KNO3) solution. Raman spectroscopy and electrical transport measurements showed the n-doping effect of graphene by KNO3. The effect was most dominant in single layer graphene, and the mobility of single layer graphene was improved by the factor of more than 3. The chemical doping by using KNO3 provides a facile approach to improve the electrical properties of graphene layers sustaining their unique characteristics.

  4. Twisted bi-layer graphene: microscopic rainbows.

    PubMed

    Campos-Delgado, J; Algara-Siller, G; Santos, C N; Kaiser, U; Raskin, J-P

    2013-10-11

    Blue, pink, and yellow colorations appear from twisted bi-layer graphene (tBLG) when transferred to a SiO2 /Si substrate (SiO2 = 100 nm-thick). Raman and electron microscope studies reveal that these colorations appear for twist angles in the 9-15° range. Optical contrast simulations confirm that the observed colorations are related to the angle-dependent electronic properties of tBLG combined with the reflection that results from the layered structure tBLG/100 nm-thick SiO2 /Si. PMID:23606323

  5. Characterization of few-layered graphene grown by carbon implantation

    SciTech Connect

    Lee, Kin Kiong; McCallum, Jeffrey C.; Jamieson, David N.

    2014-02-21

    Graphene is considered to be a very promising material for applications in nanotechnology. The properties of graphene are strongly dependent on defects that occur during growth and processing. These defects can be either detrimental or beneficial to device performance depending on defect type, location and device application. Here we present experimental results on formation of few-layered graphene by carbon ion implantation into nickel films and characteristics of graphene devices formed by graphene transfer and lithographic patterning. Micro-Raman spectroscopy was used to determine the number of graphene layers formed and identify defects arising from the device processing. The graphene films were cleaned by annealing in vacuum. Transport properties of cleaned graphene films were investigated by fabrication of back-gated field-effect transistors, which exhibited high hole and electron mobility of 1935 and 1905 cm2/Vs, respectively.

  6. Electrochemistry at Edge of Single Graphene Layer in a Nanopore

    PubMed Central

    Banerjee, Shouvik; Shim, Jiwook; Rivera, Jose; Jin, Xiaozhong; Estrada, David; Solovyeva, Vita; You, Xiuque; Pak, James; Pop, Eric; Aluru, Narayana; Bashir, Rashid

    2013-01-01

    We study the electrochemistry of single layer graphene edges using a nanopore-based structure consisting of stacked graphene and Al2O3 dielectric layers. Nanopores, with diameters ranging from 5 to 20 nm, are formed by an electron beam sculpting process on the stacked layers. This leads to unique edge structure which, along with the atomically thin nature of the embedded graphene electrode, demonstrates electrochemical current densities as high as 1.2 × 104 A/cm2. The graphene edge embedded structure offers a unique capability to study the electrochemical exchange at an individual graphene edge, isolated from the basal plane electrochemical activity. We also report ionic current modulation in the nanopore by biasing the embedded graphene terminal with respect to the electrodes in the fluid. The high electrochemical specific current density for a graphene nanopore-based device can have many applications in sensitive chemical and biological sensing, and energy storage devices. PMID:23249127

  7. Substrate-induced magnetism in epitaxial graphene buffer layers.

    PubMed

    Ramasubramaniam, A; Medhekar, N V; Shenoy, V B

    2009-07-01

    Magnetism in graphene is of fundamental as well as technological interest, with potential applications in molecular magnets and spintronic devices. While defects and/or adsorbates in freestanding graphene nanoribbons and graphene sheets have been shown to cause itinerant magnetism, controlling the density and distribution of defects and adsorbates is in general difficult. We show from first principles calculations that graphene buffer layers on SiC(0001) can also show intrinsic magnetism. The formation of graphene-substrate chemical bonds disrupts the graphene pi-bonds and causes localization of graphene states near the Fermi level. Exchange interactions between these states lead to itinerant magnetism in the graphene buffer layer. We demonstrate the occurrence of magnetism in graphene buffer layers on both bulk-terminated as well as more realistic adatom-terminated SiC(0001) surfaces. Our calculations show that adatom density has a profound effect on the spin distribution in the graphene buffer layer, thereby providing a means of engineering magnetism in epitaxial graphene.

  8. Detection of interlayer interaction in few-layer graphene

    NASA Astrophysics Data System (ADS)

    Wu, Zefei; Han, Yu; Lin, Jiangxiazi; Zhu, Wei; He, Mingquan; Xu, Shuigang; Chen, Xiaolong; Lu, Huanhuan; Ye, Weiguang; Han, Tianyi; Wu, Yingying; Long, Gen; Shen, Junying; Huang, Rui; Wang, Lin; He, Yuheng; Cai, Yuan; Lortz, Rolf; Su, Dangsheng; Wang, Ning

    2015-08-01

    Bernal-stacked few-layer graphene has been investigated by analyzing its Landau-level spectra through quantum capacitance measurements. We find that surface relaxation, which is insignificant in trilayer graphene, starts to manifest in Bernal-stacked tetralayer graphene. In trilayer graphene, the interlayer interaction parameters are generally similar to those of graphite. However, in tetralayer graphene, the hopping parameters of the two bulk layers are quite different from those of the two outer layers. This represents direct evidence of the surface relaxation phenomenon. Traditionally, the van der Waals interaction between the carbon layers is thought to be insignificant. However, we suggest that the interlayer interaction is an important factor in explaining the observed results, and the symmetry-breaking effects in graphene sublattice are not negligible.

  9. Graphene Layer Growth: Collision of Migrating Five-MemberRings

    SciTech Connect

    Whitesides, Russell; Kollias, Alexander C.; Domin, Dominik; Lester Jr., William A.; Frenklach, Michael

    2005-12-02

    A reaction pathway is explored in which two cyclopenta groups combine on the zigzag edge of a graphene layer. The process is initiated by H addition to a five-membered ring, followed by opening of that ring and the formation of a six-membered ring adjacent to another five-membered ring. The elementary steps of the migration pathway are analyzed using density functional theory to examine the region of the potential energy surface associated with the pathway. The calculations are performed on a substrate modeled by the zigzag edge of tetracene. Based on the obtained energetics, the dynamics of the system are analyzed by solving the energy transfer master equations. The results indicate energetic and reaction-rate similarity between the cyclopenta combination and migration reactions. Also examined in the present study are desorption rates of migrating cyclopenta rings which are found to be comparable to cyclopenta ring migration.

  10. Confined water between two graphene layers

    NASA Astrophysics Data System (ADS)

    Peeters, Francois; Sobrino Fernandez, Mario; Neek-Amal, Mehdi; Condensed Matter Theory Team

    Water confined between two layers with a separation of a few Angstrom forms a layered two- dimensional ice structure. Using large scale molecular dynamics simulations with the adoptable ReaxFF interatomic potential we found that monolayer ice with a rhombic-square structure nucleates between graphene layers which is non-polar and non-ferroelectric. We provide different energetic considerations and H-bonding results that explain the inter-layer and intra-layer properties of two-dimensional ice. The controversional AA-stacking found experimentally is consistent with our minimum energy crystal structure of bilayer ice. Furthermore, we predict that odd-number of layers of ice has the same lattice structure as monolayer ice, while even number of ice layers exhibit the square ice AA-stacking of bilayer ice.We predict that an inplane electric field polarizes the water molecules resulting in distinct-ferroelectricity. Electrical hysteresis in the response of the total dipole moment of monolayer ice is found

  11. Selective growth of graphene in layer-by-layer via chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Park, Jaehyun; An, Hyosub; Choi, Dong-Chul; Hussain, Sajjad; Song, Wooseok; An, Ki-Seok; Lee, Won-Jun; Lee, Naesung; Lee, Wan-Gyu; Jung, Jongwan

    2016-07-01

    Selective and precise control of the layer number of graphene remains a critical issue for the practical applications of graphene. First, it is highly challenging to grow a continuous and uniform few-layer graphene since once the monolayer graphene fully covers a copper (Cu) surface, the growth of the second layer stops, resulting in mostly nonhomogeneous films. Second, from the selective adlayer growth point of view, there is no clear pathway for achieving this. We have developed the selective growth of a graphene adlayer in layer-by-layer via chemical vapor deposition (CVD) which makes it possible to stack graphene on a specific position. The key idea is to deposit a thin Cu layer (~40 nm thick) on pre-grown monolayer graphene and to apply additional growth. The thin Cu atop the graphene/Cu substrate acts as a catalyst to decompose methane (CH4) gas during the additional growth. The adlayer is grown selectively on the pre-grown graphene, and the thin Cu is removed through evaporation during CVD, eventually forming large-area and uniform double layer graphene. With this technology, highly uniform graphene films with precise thicknesses of 1 to 5 layers and graphene check patterns with 1 to 3 layers were successfully demonstrated. This method provides precise LBL growth for a uniform graphene film and a technique for the design of new graphene devices.Selective and precise control of the layer number of graphene remains a critical issue for the practical applications of graphene. First, it is highly challenging to grow a continuous and uniform few-layer graphene since once the monolayer graphene fully covers a copper (Cu) surface, the growth of the second layer stops, resulting in mostly nonhomogeneous films. Second, from the selective adlayer growth point of view, there is no clear pathway for achieving this. We have developed the selective growth of a graphene adlayer in layer-by-layer via chemical vapor deposition (CVD) which makes it possible to stack graphene

  12. Controlling Edge Morphology in Graphene Layers Using Electron Irradiation: From Sharp Atomic Edges to Coalesced Layers Forming Loops

    SciTech Connect

    Cruz-Silva, E.; Botello-Mendez, A.R.; Barnett, Zachary M; Jia, Xiaoting; Dresselhaus, M; Terrones, H.; Terrones, M.; Sumpter, Bobby G; Meunier, Vincent

    2010-01-01

    Recent experimental reports indicate that Joule heating can atomically sharpen the edges of chemical vapor deposition grown graphitic nanoribbons. The absence or presence of loops between adjacent layers in the annealed materials is the topic of a growing debate that this Letter aims to put to rest. We offer a rationale explaining why loops do form if Joule heating is used alone, and why adjacent nanoribbon layers do not coalesce when Joule heating is applied after high-energy electrons first irradiate the sample. Our work, based on large-scale quantum molecular dynamics and electronic-transport calculations, shows that vacancies on adjacent graphene sheets, created by electron irradiation, inhibit the formation of edge loops.

  13. Nanoscale imaging of freestanding nitrogen doped single layer graphene.

    PubMed

    Iyer, Ganjigunte R S; Wang, Jian; Wells, Garth; Bradley, Michael P; Borondics, Ferenc

    2015-02-14

    Graphene can be p-type or n-type doped by introduction of specific species. Doping can modulate the electronic properties of graphene, but opening a sizable-well-tuned bandgap is essential for graphene-based tunable electronic devices. N-doped graphene is widely used for device applications and is mostly achieved by introducing ammonia into the synthesis gas during the chemical vapor deposition (CVD) process. Post synthesis treatment studies to fine-tune the electron hole doping in graphene are limited. In this work realization of N-doping in large area freestanding single layer graphene (LFG) is achieved by post treatment in nitrogen plasma. The changes in the chemical and electronic properties of graphene are followed with Raman microscopy and mapped via synchrotron based scanning transmission X-ray microscopy (STXM) at the nanoscale.

  14. In situ imaging and control of layer-by-layer femtosecond laser thinning of graphene.

    PubMed

    Li, D W; Zhou, Y S; Huang, X; Jiang, L; Silvain, J-F; Lu, Y F

    2015-02-28

    Although existing methods (chemical vapor deposition, mechanical exfoliation, etc.) are available to produce graphene, the lack of thickness control limits further graphene applications. In this study, we demonstrate an approach to precisely thin graphene films to a specific thickness using femtosecond (fs) laser raster scanning. By using appropriate laser fluence and scanning times, graphene thinning with an atomic layer precision, namely layer-by-layer graphene removal, has been realized. The fs laser used was configured in a four-wave mixing (FWM) system which can be used to distinguish graphene layer thickness and count the number of layers using the linear relationship between the FWM signal intensity and the graphene thickness. Furthermore, FWM imaging has been successfully applied to achieve in situ, real-time monitoring of the fs laser graphene thinning process. This method can not only realize the large-scale thinning of graphene with atomic layer precision, but also provide in situ, rapid imaging capability of graphene for an accurate assessment of the number of layers.

  15. Nanoscale imaging of freestanding nitrogen doped single layer graphene

    NASA Astrophysics Data System (ADS)

    Iyer, Ganjigunte R. S.; Wang, Jian; Wells, Garth; Bradley, Michael P.; Borondics, Ferenc

    2015-01-01

    Graphene can be p-type or n-type doped by introduction of specific species. Doping can modulate the electronic properties of graphene, but opening a sizable-well-tuned bandgap is essential for graphene-based tunable electronic devices. N-doped graphene is widely used for device applications and is mostly achieved by introducing ammonia into the synthesis gas during the chemical vapor deposition (CVD) process. Post synthesis treatment studies to fine-tune the electron hole doping in graphene are limited. In this work realization of N-doping in large area freestanding single layer graphene (LFG) is achieved by post treatment in nitrogen plasma. The changes in the chemical and electronic properties of graphene are followed with Raman microscopy and mapped via synchrotron based scanning transmission X-ray microscopy (STXM) at the nanoscale.Graphene can be p-type or n-type doped by introduction of specific species. Doping can modulate the electronic properties of graphene, but opening a sizable-well-tuned bandgap is essential for graphene-based tunable electronic devices. N-doped graphene is widely used for device applications and is mostly achieved by introducing ammonia into the synthesis gas during the chemical vapor deposition (CVD) process. Post synthesis treatment studies to fine-tune the electron hole doping in graphene are limited. In this work realization of N-doping in large area freestanding single layer graphene (LFG) is achieved by post treatment in nitrogen plasma. The changes in the chemical and electronic properties of graphene are followed with Raman microscopy and mapped via synchrotron based scanning transmission X-ray microscopy (STXM) at the nanoscale. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05385k

  16. Damage evaluation in graphene underlying atomic layer deposition dielectrics

    PubMed Central

    Tang, Xiaohui; Reckinger, Nicolas; Poncelet, Olivier; Louette, Pierre; Ureña, Ferran; Idrissi, Hosni; Turner, Stuart; Cabosart, Damien; Colomer, Jean-François; Raskin, Jean-Pierre; Hackens, Benoit; Francis, Laurent A.

    2015-01-01

    Based on micro-Raman spectroscopy (μRS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, μRS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors. PMID:26311131

  17. Damage evaluation in graphene underlying atomic layer deposition dielectrics.

    PubMed

    Tang, Xiaohui; Reckinger, Nicolas; Poncelet, Olivier; Louette, Pierre; Ureña, Ferran; Idrissi, Hosni; Turner, Stuart; Cabosart, Damien; Colomer, Jean-François; Raskin, Jean-Pierre; Hackens, Benoit; Francis, Laurent A

    2015-08-27

    Based on micro-Raman spectroscopy (μRS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, μRS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors.

  18. Plasmon modes of circular cylindrical double-layer graphene.

    PubMed

    Zhao, Tao; Hu, Min; Zhong, Renbin; Chen, Xiaoxing; Zhang, Ping; Gong, Sen; Zhang, Chao; Liu, Shenggang

    2016-09-01

    In this paper, a theoretical investigation on plasmon modes in a circular cylindrical double-layer graphene structure is presented. Due to the interlayer electromagnetic interaction, there exist two branches of plasmon modes, the optical plasmon mode and the acoustic plasmon mode. The characteristics of these two modes, such as mode pattern, effective mode index and propagation loss, are analyzed. The modal behaviors can be effectively tuned by changing the distance between two graphene layers, the chemical potential of graphene and the permittivity of interlayer dielectric. Importantly, the breakup of tradeoff between mode confinement and propagation loss is discovered in the distance-dependent modal behavior, which originates from the unique dispersion properties of a double-layer graphene system. As a consequence, both strong mode confinement and longer propagation length can be achieved. Our results may provide good opportunities for developing applications based on graphene plasmonics in circular cylindrical structure. PMID:27607651

  19. Plasmon modes of circular cylindrical double-layer graphene.

    PubMed

    Zhao, Tao; Hu, Min; Zhong, Renbin; Chen, Xiaoxing; Zhang, Ping; Gong, Sen; Zhang, Chao; Liu, Shenggang

    2016-09-01

    In this paper, a theoretical investigation on plasmon modes in a circular cylindrical double-layer graphene structure is presented. Due to the interlayer electromagnetic interaction, there exist two branches of plasmon modes, the optical plasmon mode and the acoustic plasmon mode. The characteristics of these two modes, such as mode pattern, effective mode index and propagation loss, are analyzed. The modal behaviors can be effectively tuned by changing the distance between two graphene layers, the chemical potential of graphene and the permittivity of interlayer dielectric. Importantly, the breakup of tradeoff between mode confinement and propagation loss is discovered in the distance-dependent modal behavior, which originates from the unique dispersion properties of a double-layer graphene system. As a consequence, both strong mode confinement and longer propagation length can be achieved. Our results may provide good opportunities for developing applications based on graphene plasmonics in circular cylindrical structure.

  20. Surface stress of graphene layers supported on soft substrate

    PubMed Central

    Du, Feng; Huang, Jianyong; Duan, Huiling; Xiong, Chunyang; Wang, Jianxiang

    2016-01-01

    We obtain the surface stress of a single layer and multilayers of graphene supported on silicone substrates by measuring the deformation of the graphene-covered substrates induced by the surface tension of liquid droplets together with the Neumann’s triangle concept. We find that the surface stress of the graphene-covered substrate is significant larger than that of the bare substrate, and it increases with increasing graphene layers, and finally reaches a constant value of about 120 mN/m on three and more layers of graphene. This work demonstrates that the apparent surface stress of graphene-substrate systems can be tuned by the substrate and the graphene layers. The surface stress and the tuning effect of the substrate on it may have applications in design and characterization of graphene-based ultra-sensitive sensors and other devices. Moreover, the method may also be used to measure the surface stress of other ultrathin films supported on soft substrates. PMID:27166087

  1. Understanding Graphene Coatings: Characterization of Solvent Exfoliated Few-Layer Graphene by Raman Scattering

    NASA Astrophysics Data System (ADS)

    Camacho, Jorge; Lampert, Lester; Arifin, Willson; Flaig, Robby; Rue, Timothy; Krisko, Tyler; Hamilton, James

    2011-03-01

    Graphene has unique properties like its ballistic transport at room temperature combined with chemical and mechanical stability and these properties can be extended to few-layer of graphene. Potential large-area applications that include transparent conductive coatings and fuel cell electrodes require dispersing graphene in a fluid phase. Graphene nano-platelets can be synthesized by dispersion and exfoliation of graphite in organic solvents such N-methyl-pyrrolidine (NMP) and cyclohexylpyrrolidone (CHP). However, liquid-phase exfoliation produces graphene with defects that can disrupt the electronic properties. One of the remaining questions is whether the defects created during synthesis can be minimized. We report a Raman spectroscopic study showing that defects in few-layer graphene produced by liquid-phase exfoliation of graphite can be controlled by the type or mixture of solvents used.

  2. Remote catalyzation for direct formation of graphene layers on oxides.

    PubMed

    Teng, Po-Yuan; Lu, Chun-Chieh; Akiyama-Hasegawa, Kotone; Lin, Yung-Chang; Yeh, Chao-Hui; Suenaga, Kazu; Chiu, Po-Wen

    2012-03-14

    Direct deposition of high-quality graphene layers on insulating substrates such as SiO(2) paves the way toward the development of graphene-based high-speed electronics. Here, we describe a novel growth technique that enables the direct deposition of graphene layers on SiO(2) with crystalline quality potentially comparable to graphene grown on Cu foils using chemical vapor deposition (CVD). Rather than using Cu foils as substrates, our approach uses them to provide subliming Cu atoms in the CVD process. The prime feature of the proposed technique is remote catalyzation using floating Cu and H atoms for the decomposition of hydrocarbons. This allows for the direct graphitization of carbon radicals on oxide surfaces, forming isolated low-defect graphene layers without the need for postgrowth etching or evaporation of the metal catalyst. The defect density of the resulting graphene layers can be significantly reduced by tuning growth parameters such as the gas ratios, Cu surface areas, and substrate-to-Cu distance. Under optimized conditions, graphene layers with nondiscernible Raman D peaks can be obtained when predeposited graphite flakes are used as seeds for extended growth. PMID:22332771

  3. Ultraviolet laser deposition of graphene thin films without catalytic layers

    NASA Astrophysics Data System (ADS)

    Sarath Kumar, S. R.; Alshareef, H. N.

    2013-01-01

    In this letter, the formation of nanostructured graphene by ultraviolet laser ablation of a highly ordered pyrolytic graphite target under optimized conditions is demonstrated, without a catalytic layer, and a model for the growth process is proposed. Previously, graphene film deposition by low-energy laser (2.3 eV) was explained by photo-thermal models, which implied that graphene films cannot be deposited by laser energies higher than the C-C bond energy in highly ordered pyrolytic graphite (3.7 eV). Here, we show that nanostructured graphene films can in fact be deposited using ultraviolet laser (5 eV) directly over different substrates, without a catalytic layer. The formation of graphene is explained by bond-breaking assisted by photoelectronic excitation leading to formation of carbon clusters at the target and annealing out of defects at the substrate.

  4. Ballistic electron propagation through periodic few-layer graphene nanostructures

    NASA Astrophysics Data System (ADS)

    Dragoman, Daniela; Mihalache, Iulia

    2016-10-01

    We have studied electron propagation in periodic structures containing mono- and few-layer graphene regions and/or semiconducting stripes. The calculation of the transmission coefficient in all cases has been performed using transfer matrices inside regions with the same material/potential energy, as well as interface matrices between regions in which the evolution laws of charge carriers differ. Numerical simulations of the transmission coefficient, as well as of the low-temperature conductance, suggest that different periodic structures modulate differently the electrical current. The obtained results can be used to model ballistic transport in all-graphene devices, in particular in few-layer graphene structures.

  5. Addressing Raman features of individual layers in isotopically labeled Bernal stacked bilayer graphene

    NASA Astrophysics Data System (ADS)

    Costa, Sara D.; Weis, Johan Ek; Frank, Otakar; Fridrichová, Michaela; Kalbac, Martin

    2016-06-01

    In this report important Raman modes for the evaluation of strain in graphene (the 2D and 2D‧) are analyzed. The isotope labeling is used to disentangle contribution of individual graphene layers of graphene bilayer to the studied Raman modes. It is shown that for Bernal-stacked bilayers, the 2D and the 2D‧ Raman modes have three distinct components that can be assigned to processes originating solely from the top graphene layer, bottom graphene layer, and from a combination of processes originating both from the top and bottom layers. The reported results thus enable addressing the properties of individual graphene layers in graphene bilayer by Raman spectroscopy.

  6. Geomechanical analysis of a welding salt layer and its effects on adjacent sediments

    NASA Astrophysics Data System (ADS)

    Heidari, Mahdi; Nikolinakou, Maria A.; Hudec, Michael R.; Flemings, Peter B.

    2016-06-01

    We simulate welding of the source layer of a salt diapir with a forward finite-element model and study stresses and deformation in the salt layer and the diapir, as well as in their adjacent sediments. Welded salt layers are abundant in mature salt basins, where most or all of the salt has withdrawn into diapirs. However, there is little understanding of the stress field in these layers and their adjacent sediments. We show that salt flow along the source layer leads to significant stress anomalies inside the layer and in adjacent sediments. In the source layer, salt pressure becomes higher than overburden stress in nearly welded areas and becomes lower than overburden stress in adjacent thicker areas. When the source layer welds, stresses increase significantly in sediments near the weld tip, which helps compaction of these sediments and possibly their fracturing and faulting. Our model illustrates that all sediments overlying the weld experience this stress increase and the associated material changes as the weld tip propagates along the weld. We present natural examples fitting our predictions and discuss the importance of our results for the exploration, characterization, and production of reservoirs near welded salt layers.

  7. Layered graphene structure of a hexagonal carbon

    NASA Astrophysics Data System (ADS)

    Zhang, Bin

    2013-06-01

    Experiments show that there is a novel hexagonal carbon polymorph restricted to the space group of P-62c, but the detailed atomic structure is not determined. Here we set carbon atoms occupying P-62c 4f or P-62c 2c and 2d Wyckoff positions, and calculate the total energy of the different cell structures changing the internal parameter by first-principles calculations, which demonstrates that the stable structures in energy (at local minima) are hexagonal carbon (P-62c 2c and 2d) and hexagonal diamond (P-62c 4f, z=1/16). The calculated bulk modulus 437±16 GPa and interlayer distance 2.062 Å of the layered graphene structure P-62c 2c and 2d are in good agreement with those of the proposed new carbon, which indicates that P-62c 2c and 2d is a possible precursor or intermediate hard phase during the structural transformation of carbon.

  8. Interfacial Atomic Structure of Twisted Few-Layer Graphene.

    PubMed

    Ishikawa, Ryo; Lugg, Nathan R; Inoue, Kazutoshi; Sawada, Hidetaka; Taniguchi, Takashi; Shibata, Naoya; Ikuhara, Yuichi

    2016-02-18

    A twist in bi- or few-layer graphene breaks the local symmetry, introducing a number of intriguing physical properties such as opening new bandgaps. Therefore, determining the twisted atomic structure is critical to understanding and controlling the functional properties of graphene. Combining low-angle annular dark-field electron microscopy with image simulations, we directly determine the atomic structure of twisted few-layer graphene in terms of a moiré superstructure which is parameterized by a single twist angle and lattice constant. This method is shown to be a powerful tool for accurately determining the atomic structure of two-dimensional materials such as graphene, even in the presence of experimental errors. Using coincidence-site-lattice and displacement-shift-complete theories, we show that the in-plane translation state between layers is not a significant structure parameter, explaining why the present method is adequate not only for bilayer graphene but also a few-layered twisted graphene.

  9. Interfacial Atomic Structure of Twisted Few-Layer Graphene

    PubMed Central

    Ishikawa, Ryo; Lugg, Nathan R.; Inoue, Kazutoshi; Sawada, Hidetaka; Taniguchi, Takashi; Shibata, Naoya; Ikuhara, Yuichi

    2016-01-01

    A twist in bi- or few-layer graphene breaks the local symmetry, introducing a number of intriguing physical properties such as opening new bandgaps. Therefore, determining the twisted atomic structure is critical to understanding and controlling the functional properties of graphene. Combining low-angle annular dark-field electron microscopy with image simulations, we directly determine the atomic structure of twisted few-layer graphene in terms of a moiré superstructure which is parameterized by a single twist angle and lattice constant. This method is shown to be a powerful tool for accurately determining the atomic structure of two-dimensional materials such as graphene, even in the presence of experimental errors. Using coincidence-site-lattice and displacement-shift-complete theories, we show that the in-plane translation state between layers is not a significant structure parameter, explaining why the present method is adequate not only for bilayer graphene but also a few-layered twisted graphene. PMID:26888259

  10. Molecular dynamics simulation for interlayer interactions of graphene nanoribbons with multiple layers

    NASA Astrophysics Data System (ADS)

    Nazemnezhad, Reza; Zare, Mojtaba; Hosseini-Hashemi, Shahrokh; Shokrollahi, Hassan

    2016-10-01

    A new study is conducted with the aid of molecular dynamics (MD) simulation to investigate the effect of shear modulus value of the interlayer van der Waals (vdWs) interactions on free vibration of cantilever multi-layer graphene nanoribbons (MLGNRs). The corresponding calibrated nonlocal parameters of the nonlocal model are obtained accordingly. The vdWs interactions are treated as the cores between every two adjacent graphene layers and their equivalent shear modulus is calculated using MD simulation. The obtained resonant frequencies via the nonlocal sandwich model are compared to the MD simulation results to calibrate the nonlocal parameter. Results reveal a strong conclusion that the calibrated nonlocal parameter is dependent on the values of interlayer shear modulus.

  11. Single-layer graphene on silicon nitride micromembrane resonators

    SciTech Connect

    Schmid, Silvan; Guillermo Villanueva, Luis; Amato, Bartolo; Boisen, Anja; Bagci, Tolga; Zeuthen, Emil; Sørensen, Anders S.; Usami, Koji; Polzik, Eugene S.; Taylor, Jacob M.; Marcus, Charles M.; Cheol Shin, Yong; Kong, Jing

    2014-02-07

    Due to their low mass, high quality factor, and good optical properties, silicon nitride (SiN) micromembrane resonators are widely used in force and mass sensing applications, particularly in optomechanics. The metallization of such membranes would enable an electronic integration with the prospect for exciting new devices, such as optoelectromechanical transducers. Here, we add a single-layer graphene on SiN micromembranes and compare electromechanical coupling and mechanical properties to bare dielectric membranes and to membranes metallized with an aluminium layer. The electrostatic coupling of graphene covered membranes is found to be equal to a perfectly conductive membrane, without significantly adding mass, decreasing the superior mechanical quality factor or affecting the optical properties of pure SiN micromembranes. The concept of graphene-SiN resonators allows a broad range of new experiments both in applied physics and fundamental basic research, e.g., for the mechanical, electrical, or optical characterization of graphene.

  12. Nonlocal thermal transport across embedded few-layer graphene sheets

    SciTech Connect

    Liu, Ying; Huxtable, Scott T.; Yang, Bao; Sumpter, Bobby G.; Qiao, Rui

    2014-11-13

    Thermal transport across the interfaces between few-layer graphene sheets and soft materials exhibits intriguing anomalies when interpreted using the classical Kapitza model, e.g., the conductance of the same interface differs greatly for different modes of interfacial thermal transport. Using atomistic simulations, we show that such thermal transport follows a nonlocal flux-temperature drop constitutive law and is characterized jointly by a quasi-local conductance and a nonlocal conductance instead of the classical Kapitza conductance. Lastly, the nonlocal model enables rationalization of many anomalies of the thermal transport across embedded few-layer graphene sheets and should be used in studies of interfacial thermal transport involving few-layer graphene sheets or other ultra-thin layered materials.

  13. Nonlocal thermal transport across embedded few-layer graphene sheets

    DOE PAGES

    Liu, Ying; Huxtable, Scott T.; Yang, Bao; Sumpter, Bobby G.; Qiao, Rui

    2014-11-13

    Thermal transport across the interfaces between few-layer graphene sheets and soft materials exhibits intriguing anomalies when interpreted using the classical Kapitza model, e.g., the conductance of the same interface differs greatly for different modes of interfacial thermal transport. Using atomistic simulations, we show that such thermal transport follows a nonlocal flux-temperature drop constitutive law and is characterized jointly by a quasi-local conductance and a nonlocal conductance instead of the classical Kapitza conductance. Lastly, the nonlocal model enables rationalization of many anomalies of the thermal transport across embedded few-layer graphene sheets and should be used in studies of interfacial thermal transportmore » involving few-layer graphene sheets or other ultra-thin layered materials.« less

  14. Metal-doped graphene layers composed with boron nitride-graphene as an insulator: a nano-capacitor.

    PubMed

    Monajjemi, Majid

    2014-11-01

    A model of a nanoscale dielectric capacitor composed of a few dopants has been investigated in this study. This capacitor includes metallic graphene layers which are separated by an insulating medium containing a few h-BN layers. It has been observed that the elements from group IIIA of the periodic table are more suitable as dopants for hetero-structures of the {metallic graphene/hBN/metallic graphene} capacitors compared to those from groups IA or IIA. In this study, we have specifically focused on the dielectric properties of different graphene/h-BN/graphene including their hetero-structure counterparts, i.e., Boron-graphene/h-BN/Boron-graphene, Al-graphene/h-BN/Al-graphene, Mg-graphene/h-BN/Mg-graphene, and Be-graphene/h-BN/Be-graphene stacks for monolayer form of dielectrics. Moreover, we studied the multi dielectric properties of different (h-BN)n/graphene hetero-structures of Boron-graphene/(h-BN)n/Boron-graphene. PMID:25359456

  15. Compression behavior of single-layer graphenes.

    PubMed

    Frank, Otakar; Tsoukleri, Georgia; Parthenios, John; Papagelis, Konstantinos; Riaz, Ibtsam; Jalil, Rashid; Novoselov, Kostya S; Galiotis, Costas

    2010-06-22

    Central to most applications involving monolayer graphenes is its mechanical response under various stress states. To date most of the work reported is of theoretical nature and refers to tension and compression loading of model graphenes. Most of the experimental work is indeed limited to the bending of single flakes in air and the stretching of flakes up to typically approximately 1% using plastic substrates. Recently we have shown that by employing a cantilever beam we can subject single graphenes to various degrees of axial compression. Here we extend this work much further by measuring in detail both stress uptake and compression buckling strain in single flakes of different geometries. In all cases the mechanical response is monitored by simultaneous Raman measurements through the shift of either the G or 2D phonons of graphene. Despite the infinitely small thickness of the monolayers, the results show that graphenes embedded in plastic beams exhibit remarkable compression buckling strains. For large length (l)-to-width (w) ratios (> or =0.2) the buckling strain is of the order of -0.5% to -0.6%. However, for l/w < 0.2 no failure is observed for strains even higher than -1%. Calculations based on classical Euler analysis show that the buckling strain enhancement provided by the polymer lateral support is more than 6 orders of magnitude compared to that of suspended graphene in air. PMID:20496881

  16. The Electronic Structure of Single-Layer Graphene

    NASA Astrophysics Data System (ADS)

    Siegel, David Alan

    Single-layer graphene has been widely researched in recent years due to its perceived technological applicability and its scientific importance as a unique model system with relativistic Dirac Fermions. Because of its unique geometric and electronic structure, the properties of graphene can be tuned or manipulated in several ways. This tunability is important for technological applications in its own right, and it also allows us to study the fundamental properties of Dirac Fermions, including unique many-body interactions and the nature of the quasiparticles at half-filling. This thesis is a detailed examination of the electronic and structural properties of graphene, studied with angle-resolved photoemission spectroscopy (ARPES) and other surface science techniques like low-energy electron microscopy and diffraction. This thesis is organized as follows. Chapter 1 gives an introduction to the electronic and structural properties of single-layer graphene. It provides a brief historical overview of major theoretical and experimental milestones and sets the stage for the important theoretical and experimental questions that this thesis addresses. Chapters 2 and 3 describe the experimental setup. Chapter 2 discusses the experimental techniques used in this thesis with particular focus on the mechanics of ARPES. Chapter 3 discusses the different graphene growth techniques that were used to create our sample with particular focus on our characterization of epitaxial graphene on SiC(0001). Chapters 4 and 5 form the meat of this thesis: they provide a thorough discussion of the electronic properties of graphene as studied by ARPES. Chapter 4 describes how various perturbations can result in the manipulation of the bare electronic band structure, including the deposition of atomic or molecular species on top of an epitaxial graphene sheet as well as the interactions between graphene and its substrate. Chapter 5 describes the many-body physics in single-layer graphene. It

  17. Significantly reduced thermal diffusivity of free-standing two-layer graphene in graphene foam.

    PubMed

    Lin, Huan; Xu, Shen; Wang, Xinwei; Mei, Ning

    2013-10-18

    We report on a thermal diffusivity study of suspended graphene foam (GF) using the transient electro-thermal technique. Our Raman study confirms the GF is composed of two-layer graphene. By measuring GF of different lengths, we are able to exclude the radiation effect. Using Schuetz's model, the intrinsic thermal diffusivity of the free-standing two-layer graphene is determined with a high accuracy without using knowledge of the porosity of the GF. The intrinsic thermal diffusivity of the two-layer graphene is determined at 1.16-2.22 × 10(-4) m(2) s(-1). The corresponding intrinsic thermal conductivity is 182-349 W m(-1) K(-1), about one order of magnitude lower than those reported for single-layer graphene. Extensive surface impurity defects, wrinkles and rough edges are observed under a scanning electron microscope for the studied GF. These structural defects induce substantial phonon scattering and explain the observed significant thermal conductivity reduction. Our thermal diffusivity characterization of GF provides an advanced way to look into the thermal transport capacity of free-standing graphene with high accuracy and ease of experimental implementation. PMID:24060813

  18. Significantly reduced thermal diffusivity of free-standing two-layer graphene in graphene foam

    NASA Astrophysics Data System (ADS)

    Lin, Huan; Xu, Shen; Wang, Xinwei; Mei, Ning

    2013-10-01

    We report on a thermal diffusivity study of suspended graphene foam (GF) using the transient electro-thermal technique. Our Raman study confirms the GF is composed of two-layer graphene. By measuring GF of different lengths, we are able to exclude the radiation effect. Using Schuetz’s model, the intrinsic thermal diffusivity of the free-standing two-layer graphene is determined with a high accuracy without using knowledge of the porosity of the GF. The intrinsic thermal diffusivity of the two-layer graphene is determined at 1.16-2.22 × 10-4 m2 s-1. The corresponding intrinsic thermal conductivity is 182-349 W m-1 K-1, about one order of magnitude lower than those reported for single-layer graphene. Extensive surface impurity defects, wrinkles and rough edges are observed under a scanning electron microscope for the studied GF. These structural defects induce substantial phonon scattering and explain the observed significant thermal conductivity reduction. Our thermal diffusivity characterization of GF provides an advanced way to look into the thermal transport capacity of free-standing graphene with high accuracy and ease of experimental implementation.

  19. Significantly reduced thermal diffusivity of free-standing two-layer graphene in graphene foam.

    PubMed

    Lin, Huan; Xu, Shen; Wang, Xinwei; Mei, Ning

    2013-10-18

    We report on a thermal diffusivity study of suspended graphene foam (GF) using the transient electro-thermal technique. Our Raman study confirms the GF is composed of two-layer graphene. By measuring GF of different lengths, we are able to exclude the radiation effect. Using Schuetz's model, the intrinsic thermal diffusivity of the free-standing two-layer graphene is determined with a high accuracy without using knowledge of the porosity of the GF. The intrinsic thermal diffusivity of the two-layer graphene is determined at 1.16-2.22 × 10(-4) m(2) s(-1). The corresponding intrinsic thermal conductivity is 182-349 W m(-1) K(-1), about one order of magnitude lower than those reported for single-layer graphene. Extensive surface impurity defects, wrinkles and rough edges are observed under a scanning electron microscope for the studied GF. These structural defects induce substantial phonon scattering and explain the observed significant thermal conductivity reduction. Our thermal diffusivity characterization of GF provides an advanced way to look into the thermal transport capacity of free-standing graphene with high accuracy and ease of experimental implementation.

  20. Functionalization of graphene and few-layer graphene with aqueous solution of hydrofluoric acid

    NASA Astrophysics Data System (ADS)

    Nebogatikova, N. A.; Antonova, I. V.; Volodin, V. A.; Prinz, V. Ya.

    2013-08-01

    In the present study, conditions suitable for efficient modification of graphene and few-layer graphene (FLG) films with aqueous solutions of hydrofluoric acid (HF) and for local protection of the graphene against such modification in isopropyl alcohol were identified. A combination of the two treatments gives one a key to nanodesign of graphene-based 2D devices. It was found that a few-minute treatment of graphene or FLG in HF aqueous solutions (∼1 min for graphene and ∼5 min for FLG films about 5 nm thick) leads to strong changes in the structural and electrical properties of graphene involving a step-like increase in resistivity (up to 1011 Ω/□). Two types of materials were obtained after different times of treatment: (i) promising for electronic applications of the material due to a combination of high carrier mobility, high conductivity, and strong current modulation by gate voltage (up to four orders of magnitude); (ii) a material with insulating properties and graphene quantum dots embedded in an insulating matrix.

  1. Broadband single-layered graphene absorber using periodic arrays of graphene ribbons with gradient width

    NASA Astrophysics Data System (ADS)

    Zhihong, Zhu; Chucai, Guo; Jianfa, Zhang; Ken, Liu; Xiaodong, Yuan; Shiqiao, Qin

    2015-01-01

    We demonstrate that a broadband single-layered graphene absorber can be obtained in the THz range using periodic arrays of chemically doped graphene ribbons with gradient width, supported on a dielectric film placed on a thick piece of metal. The working bandwidth of 90% absorption for this structure is as high as 1.3 THz with a central frequency of 3 THz. The broadband operation mechanism is a result of the varying continuous plasmon resonances occurring in graphene ribbons with gradient width. The operation wavelength can be expanded to the far-infrared range.

  2. Fingerprints of Multiple Electron Scatterings in Single-Layer Graphene

    PubMed Central

    Jung, Minbok; Sohn, So-Dam; Park, Jonghyun; Lee, Keun-U; Shin, Hyung-Joon

    2016-01-01

    The electrons in graphene exhibit unusual behaviours, which can be described by massless Dirac quasiparticles. Understanding electron scattering in graphene has been of significant importance for its future application in electronic devices because electron scattering determines electrical properties such as resistivity and electron transport. There are two types of electron scatterings in graphene: intervalley scattering and intravalley scattering. In single-layer graphene, to date, it has been difficult to observe intravalley scattering because of the suppression of backscattering resulting from the chiral nature of the electrons in graphene. Here, we report the multiple electron scattering behaviours in single-layer graphene on a metallic substrate. By applying one- and two-dimensional Fourier transforms to maps of the local density of states, we can distinguish individual scattering processes from complex interference patterns. These techniques enable us to provide direct evidence of intravalley scattering, revealing a linear dispersion relation with a Fermi velocity of ~7.4 × 105 m/s. PMID:26936521

  3. Fabrication of graphene/polyaniline composite multilayer films by electrostatic layer-by-layer assembly

    SciTech Connect

    Cong, Jiaojiao; Chen, Yuze; Luo, Jing Liu, Xiaoya

    2014-10-15

    A novel graphene/polyaniline composite multilayer film was fabricated by electrostatic interactions induced layer-by-layer self-assembly technique, using water dispersible and negatively charged chemically converted graphene (CCG) and positively charged polyaniline (PANI) as building blocks. CCG was achieved through partly reduced graphene oxide, which remained carboxyl group on its surface. The remaining carboxyl groups not only retain the dispersibility of CCG, but also allow the growth of the multilayer films via electrostatic interactions between graphene and PANI. The structure and morphology of the obtained CCG/PANI multilayer film are characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, Ultraviolet–visible absorption spectrum (UV–vis), scanning electron microscopy (SEM), Raman spectroscopy and X-Ray Diffraction (XRD). The electrochemical properties of the resulting film are studied using cyclic voltammetry (CV), which showed that the resulting CCG/PANI multilayer film kept electroactivity in neutral solution and showed outstanding cyclic stability up to 100 cycles. Furthermore, the composite film exhibited good electrocatalytic ability toward ascorbic acid (AA) with a linear response from 1×10{sup −4} to 1.2×10{sup −3} M with the detect limit of 5×10{sup −6} M. This study provides a facile and effective strategy to fabricate graphene/PANI nanocomposite film with good electrochemical property, which may find potential applications in electronic devices such as electrochemical sensor. - Graphical abstract: A novel graphene/polyaniline (CCG/PANI) film was prepared by layer-by-layer assembly. - Highlights: • A novel graphene/polyaniline (CCG/PANI) film was prepared by layer-by-layer assembly. • The water dispersible and negatively charged graphene (CCG) was used as building block. • CCG was achieved through partly reduced graphene oxide with carboxyl group on its surface. • CCG/PANI film kept

  4. Organic solar cells with graphene electrodes and vapor printed poly(3,4-ethylenedioxythiophene) as the hole transporting layers.

    PubMed

    Park, Hyesung; Howden, Rachel M; Barr, Miles C; Bulović, Vladimir; Gleason, Karen; Kong, Jing

    2012-07-24

    For the successful integration of graphene as a transparent conducting electrode in organic solar cells, proper energy level alignment at the interface between the graphene and the adjacent organic layer is critical. The role of a hole transporting layer (HTL) thus becomes more significant due to the generally lower work function of graphene compared to ITO. A commonly used HTL material with ITO anodes is poly(3,4-ethylenedioxythiophene) (PEDOT) with poly(styrenesulfonate) (PSS) as the solid-state dopant. However, graphene's hydrophobic surface renders uniform coverage of PEDOT:PSS (aqueous solution) by spin-casting very challenging. Here, we introduce a novel, yet simple, vapor printing method for creating patterned HTL PEDOT layers directly onto the graphene surface. Vapor printing represents the implementation of shadow masking in combination with oxidative chemical vapor deposition (oCVD). The oCVD method was developed for the formation of blanket (i.e., unpatterened) layers of pure PEDOT (i.e., no PSS) with systematically variable work function. In the unmasked regions, vapor printing produces complete, uniform, smooth layers of pure PEDOT over graphene. Graphene electrodes were synthesized under low-pressure chemical vapor deposition (LPCVD) using a copper catalyst. The use of another electron donor material, tetraphenyldibenzoperiflanthene, instead of copper phthalocyanine in the organic solar cells also improves the power conversion efficiency. With the vapor printed HTL, the devices using graphene electrodes yield comparable performances to the ITO reference devices (η(p,LPCVD) = 3.01%, and η(p,ITO) = 3.20%). PMID:22724887

  5. High quality reduced graphene oxide through repairing with multi-layered graphene ball nanostructures

    PubMed Central

    Kim, Kyoung Hwan; Yang, MinHo; Cho, Kyeong Min; Jun, Young-Si; Lee, Sang Bok; Jung, Hee-Tae

    2013-01-01

    We present a simple and up-scalable method to produce highly repaired graphene oxide with a large surface area, by introducing spherical multi-layered graphene balls with empty interiors. These graphene balls are prepared via chemical vapor deposition (CVD) of Ni particles on the surface of the graphene oxides (GO). Transmission electron microscopy and Raman spectroscopy results reveal that defects in the GO surfaces are well repaired during the CVD process, with the help of nickel nanoparticles attached to the functional groups of the GO surface, further resulting in a high electrical conductivity of 18,620 S/m. In addition, the graphene balls on the GO surface effectively prevent restacking of the GO layers, thus providing a large surface area of 527 m2/g. Two electrode supercapacitor cells using this highly conductive graphene material demonstrate ideal electrical double layer capacitive behavior, due to the effective use of the outstanding electric conductivity and the large surface area. PMID:24248235

  6. AA-stacked bilayer square ice between graphene layers

    NASA Astrophysics Data System (ADS)

    Sobrino Fernandez Mario, M.; Neek-Amal, M.; Peeters, F. M.

    2015-12-01

    Water confined between two graphene layers with a separation of a few Å forms a layered two-dimensional ice structure. Using large scale molecular dynamics simulations with the adoptable ReaxFF interatomic potential we found that flat monolayer ice with a rhombic-square structure nucleates between the graphene layers which is nonpolar and nonferroelectric. We provide different energetic considerations and H-bonding results that explain the interlayer and intralayer properties of two-dimensional ice. The controversial AA stacking found experimentally [Algara-Siller et al., Nature (London) 519, 443 (2015), 10.1038/nature14295] is consistent with our minimum-energy crystal structure of bilayer ice. Furthermore, we predict that an odd number of layers of ice has the same lattice structure as monolayer ice, while an even number of ice layers exhibits the square ice AA stacking of bilayer ice.

  7. A graphene superficial layer for the advanced electroforming process

    NASA Astrophysics Data System (ADS)

    Rho, Hokyun; Park, Mina; Lee, Seungmin; Bae, Sukang; Kim, Tae-Wook; Ha, Jun-Seok; Lee, Sang Hyun

    2016-06-01

    Advances in electroplating technology facilitate the progress of modern electronic devices, including computers, microprocessors and other microelectronic devices. Metal layers with high electrical and thermal conductivities are essential for high speed and high power devices. In this paper, we report an effective route to fabricate free-standing metal films using graphene as a superficial layer in the electroforming process. Chemical vapor deposition (CVD) graphene grown on a Cu foil was used as a template, which provides high electrical conductivity and low adhesive force with the template, thus enabling an effective electroforming process. The required force for delamination of the electroplated Cu layer from graphene is more than one order smaller than the force required for removing graphene from the Cu foil. We also demonstrated that the electroformed free-standing Cu thin films could be utilized for patterning microstructures and incorporated onto a flexible substrate for LEDs. This innovative process could be beneficial for the advancement of flexible electronics and optoelectronics, which require a wide range of mechanical and physical properties.Advances in electroplating technology facilitate the progress of modern electronic devices, including computers, microprocessors and other microelectronic devices. Metal layers with high electrical and thermal conductivities are essential for high speed and high power devices. In this paper, we report an effective route to fabricate free-standing metal films using graphene as a superficial layer in the electroforming process. Chemical vapor deposition (CVD) graphene grown on a Cu foil was used as a template, which provides high electrical conductivity and low adhesive force with the template, thus enabling an effective electroforming process. The required force for delamination of the electroplated Cu layer from graphene is more than one order smaller than the force required for removing graphene from the Cu foil

  8. Mode dependent lattice thermal conductivity of single layer graphene

    SciTech Connect

    Wei, Zhiyong; Yang, Juekuan; Bi, Kedong; Chen, Yunfei

    2014-10-21

    Molecular dynamics simulation is performed to extract the phonon dispersion and phonon lifetime of single layer graphene. The mode dependent thermal conductivity is calculated from the phonon kinetic theory. The predicted thermal conductivity at room temperature exhibits important quantum effects due to the high Debye temperature of graphene. But the quantum effects are reduced significantly when the simulated temperature is as high as 1000 K. Our calculations show that out-of-plane modes contribute about 41.1% to the total thermal conductivity at room temperature. The relative contribution of out-of-plane modes has a little decrease with the increase of temperature. Contact with substrate can reduce both the total thermal conductivity of graphene and the relative contribution of out-of-plane modes, in agreement with previous experiments and theories. Increasing the coupling strength between graphene and substrate can further reduce the relative contribution of out-of-plane modes. The present investigations also show that the relative contribution of different mode phonons is not sensitive to the grain size of graphene. The obtained phonon relaxation time provides useful insight for understanding the phonon mean free path and the size effects in graphene.

  9. Tunneling Plasmonics in Bilayer Graphene.

    PubMed

    Fei, Z; Iwinski, E G; Ni, G X; Zhang, L M; Bao, W; Rodin, A S; Lee, Y; Wagner, M; Liu, M K; Dai, S; Goldflam, M D; Thiemens, M; Keilmann, F; Lau, C N; Castro-Neto, A H; Fogler, M M; Basov, D N

    2015-08-12

    We report experimental signatures of plasmonic effects due to electron tunneling between adjacent graphene layers. At subnanometer separation, such layers can form either a strongly coupled bilayer graphene with a Bernal stacking or a weakly coupled double-layer graphene with a random stacking order. Effects due to interlayer tunneling dominate in the former case but are negligible in the latter. We found through infrared nanoimaging that bilayer graphene supports plasmons with a higher degree of confinement compared to single- and double-layer graphene, a direct consequence of interlayer tunneling. Moreover, we were able to shut off plasmons in bilayer graphene through gating within a wide voltage range. Theoretical modeling indicates that such a plasmon-off region is directly linked to a gapped insulating state of bilayer graphene, yet another implication of interlayer tunneling. Our work uncovers essential plasmonic properties in bilayer graphene and suggests a possibility to achieve novel plasmonic functionalities in graphene few-layers.

  10. Electron transport in molecular junctions with graphene as protecting layer

    SciTech Connect

    Hüser, Falco; Solomon, Gemma C.

    2015-12-07

    We present ab initio transport calculations for molecular junctions that include graphene as a protecting layer between a single molecule and gold electrodes. This vertical setup has recently gained significant interest in experiment for the design of particularly stable and reproducible devices. We observe that the signals from the molecule in the electronic transmission are overlayed by the signatures of the graphene sheet, thus raising the need for a reinterpretation of the transmission. On the other hand, we see that our results are stable with respect to various defects in the graphene. For weakly physiosorbed molecules, no signs of interaction with the graphene are evident, so the transport properties are determined by offresonant tunnelling between the gold leads across an extended structure that includes the molecule itself and the additional graphene layer. Compared with pure gold electrodes, calculated conductances are about one order of magnitude lower due to the increased tunnelling distance. Relative differences upon changing the end group and the length of the molecule on the other hand, are similar.

  11. Electron transport in molecular junctions with graphene as protecting layer

    NASA Astrophysics Data System (ADS)

    Hüser, Falco; Solomon, Gemma C.

    2015-12-01

    We present ab initio transport calculations for molecular junctions that include graphene as a protecting layer between a single molecule and gold electrodes. This vertical setup has recently gained significant interest in experiment for the design of particularly stable and reproducible devices. We observe that the signals from the molecule in the electronic transmission are overlayed by the signatures of the graphene sheet, thus raising the need for a reinterpretation of the transmission. On the other hand, we see that our results are stable with respect to various defects in the graphene. For weakly physiosorbed molecules, no signs of interaction with the graphene are evident, so the transport properties are determined by offresonant tunnelling between the gold leads across an extended structure that includes the molecule itself and the additional graphene layer. Compared with pure gold electrodes, calculated conductances are about one order of magnitude lower due to the increased tunnelling distance. Relative differences upon changing the end group and the length of the molecule on the other hand, are similar.

  12. Precise Control of the Number of Layers of Graphene by Picosecond Laser Thinning.

    PubMed

    Lin, Zhe; Ye, Xiaohui; Han, Jinpeng; Chen, Qiao; Fan, Peixun; Zhang, Hongjun; Xie, Dan; Zhu, Hongwei; Zhong, Minlin

    2015-06-26

    The properties of graphene can vary as a function of the number of layers (NOL). Controlling the NOL in large area graphene is still challenging. In this work, we demonstrate a picosecond (ps) laser thinning removal of graphene layers from multi-layered graphene to obtain desired NOL when appropriate pulse threshold energy is adopted. The thinning process is conducted in atmosphere without any coating and it is applicable for graphene films on arbitrary substrates. This method provides many advantages such as one-step process, non-contact operation, substrate and environment-friendly, and patternable, which will enable its potential applications in the manufacturing of graphene-based electronic devices.

  13. Self assembled multi-layer nanocomposite of graphene and metal oxide materials

    DOEpatents

    Liu, Jun; Aksay, Ilhan A; Choi, Daiwon; Kou, Rong; Nie, Zimin; Wang, Donghai; Yang, Zhenguo

    2015-04-28

    Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochemical or energy storage device.

  14. Self assembled multi-layer nanocomposite of graphene and metal oxide materials

    SciTech Connect

    Liu, Jun; Choi, Daiwon; Kou, Rong; Nie, Zimin; Wang, Donghai; Yang, Zhenguo

    2014-09-16

    Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochemical or energy storage device.

  15. Self assembled multi-layer nanocomposite of graphene and metal oxide materials

    SciTech Connect

    Liu, Jun; Aksay, Ilhan A; Choi, Daiwon; Kou, Rong; Nie, Zimin; Wang, Donghai; Yang, Zhenguo

    2013-10-22

    Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochemical or energy storage device.

  16. One-step transfer and integration of multifunctionality in CVD graphene by TiO₂/graphene oxide hybrid layer.

    PubMed

    Jeong, Hee Jin; Kim, Ho Young; Jeong, Hyun; Han, Joong Tark; Jeong, Seung Yol; Baeg, Kang-Jun; Jeong, Mun Seok; Lee, Geon-Woong

    2014-05-28

    We present a straightforward method for simultaneously enhancing the electrical conductivity, environmental stability, and photocatalytic properties of graphene films through one-step transfer of CVD graphene and integration by introducing TiO2/graphene oxide layer. A highly durable and flexible TiO2 layer is successfully used as a supporting layer for graphene transfer instead of the commonly used PMMA. Transferred graphene/TiO2 film is directly used for measuring the carrier transport and optoelectronic properties without an extra TiO2 removal and following deposition steps for multifunctional integration into devices because the thin TiO2 layer is optically transparent and electrically semiconducting. Moreover, the TiO2 layer induces charge screening by electrostatically interacting with the residual oxygen moieties on graphene, which are charge scattering centers, resulting in a reduced current hysteresis. Adsorption of water and other chemical molecules onto the graphene surface is also prevented by the passivating TiO2 layer, resulting in the long term environmental stability of the graphene under high temperature and humidity. In addition, the graphene/TiO2 film shows effectively enhanced photocatalytic properties because of the increase in the transport efficiency of the photogenerated electrons due to the decrease in the injection barrier formed at the interface between the F-doped tin oxide and TiO2 layers. PMID:24578338

  17. Extreme ultraviolet induced defects on few-layer graphene

    NASA Astrophysics Data System (ADS)

    Gao, A.; Rizo, P. J.; Zoethout, E.; Scaccabarozzi, L.; Lee, C. J.; Banine, V.; Bijkerk, F.

    2013-07-01

    We use Raman spectroscopy to show that exposing few-layer graphene to extreme ultraviolet (EUV, 13.5 nm) radiation, i.e., relatively low photon energy, results in an increasing density of defects. Furthermore, exposure to EUV radiation in a H2 background increases the graphene dosage sensitivity, due to reactions caused by the EUV induced hydrogen plasma. X-ray photoelectron spectroscopy results show that the sp2 bonded carbon fraction decreases while the sp3 bonded carbon and oxide fraction increases with exposure dose. Our experimental results confirm that even in reducing environment oxidation is still one of the main source of inducing defects.

  18. Electrochemical double-layer capacitors based on functionalized graphene

    NASA Astrophysics Data System (ADS)

    Pope, Michael Allan

    Graphene is a promising electrode material for electrochemical double-layer capacitors (EDLCs) used for energy storage due to its high electrical conductivity and theoretical specific surface area. However, the intrinsic capacitance of graphene is known to be low and governed by the electronic side of the interface. Furthermore, graphene tends to aggregate and stack together when processed into thick electrode films. This significantly lowers the ion-accessible specific surface area (SSA). Maximizing both the SSA and the intrinsic capacitance are the main problems addressed in this thesis in an effort to improve the specific capacitance and energy density of EDLCs. In contrast to pristine graphene, functionalized graphene produced by the thermal exfoliation of graphite oxide contains residual functional groups and lattice defects. To study how these properties affect the double-layer capacitance, a model electrode system capable of measuring the intrinsic electrochemical properties of functionalized graphene was developed. To prevent artifacts and uncertainties related to measurements on porous electrodes, the functionalized graphene sheets (FGSs) were assembled as densely tiled monolayers using a Langmuir-Blodgett technique. In this way, charging can be studied in a well-defined 2D geometry. The possibility of measuring and isolating the intrinsic electrochemical properties of FGS monolayers was first demonstrated by comparing capacitance and redox probe measurements carried out on coatings deposited on passivated gold and single crystal graphite substrates. This monolayer system was then used to follow the double-layer capacitance of the FGS/electrolyte interface as the structure and chemistry of graphene was varied by thermal treatments ranging from 300 °C to 2100 °C. Elemental analysis and Raman spectroscopy were used to determine the resulting chemical and structural transformation upon heat treatment. It was demonstrated that intrinsically defective

  19. Intrinsic Negative Poisson's Ratio for Single-Layer Graphene.

    PubMed

    Jiang, Jin-Wu; Chang, Tienchong; Guo, Xingming; Park, Harold S

    2016-08-10

    Negative Poisson's ratio (NPR) materials have drawn significant interest because the enhanced toughness, shear resistance, and vibration absorption that typically are seen in auxetic materials may enable a range of novel applications. In this work, we report that single-layer graphene exhibits an intrinsic NPR, which is robust and independent of its size and temperature. The NPR arises due to the interplay between two intrinsic deformation pathways (one with positive Poisson's ratio, the other with NPR), which correspond to the bond stretching and angle bending interactions in graphene. We propose an energy-based deformation pathway criteria, which predicts that the pathway with NPR has lower energy and thus becomes the dominant deformation mode when graphene is stretched by a strain above 6%, resulting in the NPR phenomenon. PMID:27408994

  20. Graphene and graphene-like layered transition metal dichalcogenides in energy conversion and storage.

    PubMed

    Wang, Hua; Feng, Hongbin; Li, Jinghong

    2014-06-12

    Being confronted with the energy crisis and environmental problems, the exploration of clean and renewable energy materials as well as their devices are urgently demanded. Two-dimensional (2D) atomically-thick materials, graphene and grpahene-like layered transition metal dichalcogenides (TMDs), have showed vast potential as novel energy materials due to their unique physicochemical properties. In this Review, we outline the typical application of graphene and grpahene-like TMDs in energy conversion and storage fields, and hope to promote the development of 2D TMDs in this field through the analysis and comparisons with the relatively natural graphene. First, a brief introduction of electronic structures and basic properties of graphene and TMDs are presented. Then, we summarize the exciting progress of these materials made in both energy conversion and storage field including solar cells, electrocatalysis, supercapacitors and lithium ions batteries. Finally, the prospects and further developments in these exciting fields of graphene and graphene-like TMDs materials are also suggested.

  1. Plasmons in spatially separated double-layer graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Bagheri, Mehran; Bahrami, Mousa

    2014-05-01

    Motivated by innovative progresses in designing multi-layer graphene nanostructured materials in the laboratory, we theoretically investigate the Dirac plasmon modes of a spatially separated double-layer graphene nanoribbon system, made up of a vertically offset armchair and metallic graphene nanoribbon pair. We find striking features of the collective excitations in this novel Coulomb correlated system, where both nanoribbons are supposed to be either intrinsic (undoped/ungated) or extrinsic (doped/gated). In the former, it is shown the low-energy acoustical and the high-energy optical plasmon modes are tunable only by the inter-ribbon charge separation. In the later, the aforementioned plasmon branches are modified by the added doping factor. As a result, our model could be useful to examine the existence of a linear Landau-undamped low-energy acoustical plasmon mode tuned via the inter-ribbon charge separation as well as doping. This study might also be utilized for devising novel quantum optical waveguides based on the Coulomb coupled graphene nanoribbons.

  2. Plasmons in spatially separated double-layer graphene nanoribbons

    SciTech Connect

    Bagheri, Mehran; Bahrami, Mousa

    2014-05-07

    Motivated by innovative progresses in designing multi-layer graphene nanostructured materials in the laboratory, we theoretically investigate the Dirac plasmon modes of a spatially separated double-layer graphene nanoribbon system, made up of a vertically offset armchair and metallic graphene nanoribbon pair. We find striking features of the collective excitations in this novel Coulomb correlated system, where both nanoribbons are supposed to be either intrinsic (undoped/ungated) or extrinsic (doped/gated). In the former, it is shown the low-energy acoustical and the high-energy optical plasmon modes are tunable only by the inter-ribbon charge separation. In the later, the aforementioned plasmon branches are modified by the added doping factor. As a result, our model could be useful to examine the existence of a linear Landau-undamped low-energy acoustical plasmon mode tuned via the inter-ribbon charge separation as well as doping. This study might also be utilized for devising novel quantum optical waveguides based on the Coulomb coupled graphene nanoribbons.

  3. Touch stimulated pulse generation in biomimetic single-layer graphene

    NASA Astrophysics Data System (ADS)

    Sul, Onejae; Chun, Hyunsuk; Choi, Eunseok; Choi, Jungbong; Cho, Kyeongwon; Jang, Dongpyo; Chun, Sungwoo; Park, Wanjun; Lee, Seung-Beck

    2016-02-01

    Detecting variation in contact pressure is a separate sensing mode in the human somatosensory system that differs from the detection of pressure magnitude. If pressure magnitude and variation sensing can be achieved simultaneously, an advanced biomimetic tactile system that better emulates human senses may be developed. We report on a novel single-layer graphene based artificial mechanoreceptor that generates a resistance pulse as the contact stimulus passes a specific threshold pressure, mimicking the generation of action potentials in a biological fast-adapting mechanoreceptor. The electric field from a flexible membrane gate electrode placed above a graphene channel raises the Fermi level from the valence band as pressure deflects the membrane. The threshold pressure is reached when the Fermi level crosses the Dirac point in the graphene energy band, which generates a sharp peak in the measured resistance. We found that by changing the gate potential it was possible to modulate the threshold pressure and using a series of graphene channels, a train of pulses were generated during a transient pressurizing stimulus demonstrating biomimetic behaviour.Detecting variation in contact pressure is a separate sensing mode in the human somatosensory system that differs from the detection of pressure magnitude. If pressure magnitude and variation sensing can be achieved simultaneously, an advanced biomimetic tactile system that better emulates human senses may be developed. We report on a novel single-layer graphene based artificial mechanoreceptor that generates a resistance pulse as the contact stimulus passes a specific threshold pressure, mimicking the generation of action potentials in a biological fast-adapting mechanoreceptor. The electric field from a flexible membrane gate electrode placed above a graphene channel raises the Fermi level from the valence band as pressure deflects the membrane. The threshold pressure is reached when the Fermi level crosses the Dirac

  4. Fabrication of a single layer graphene by copper intercalation on a SiC(0001) surface

    SciTech Connect

    Yagyu, Kazuma; Tochihara, Hiroshi; Tomokage, Hajime; Suzuki, Takayuki; Tajiri, Takayuki; Kohno, Atsushi; Takahashi, Kazutoshi

    2014-02-03

    Cu atoms deposited on a zero layer graphene grown on a SiC(0001) substrate, intercalate between the zero layer graphene and the SiC substrate after the thermal annealing above 600 °C, forming a Cu-intercalated single layer graphene. On the Cu-intercalated single layer graphene, a graphene lattice with superstructure due to moiré pattern is observed by scanning tunneling microscopy, and specific linear dispersion at the K{sup ¯} point as well as a characteristic peak in a C{sub 1s} core level spectrum, which is originated from a free-standing graphene, is confirmed by photoemission spectroscopy. The Cu-intercalated single layer graphene is found to be n-doped.

  5. Spatiotemporal morphometry of adjacent tissue layers with application to the study of sulcal formation.

    PubMed

    Rajagopalan, Vidya; Scott, Julia; Habas, Piotr A; Kim, Kio; Rousseau, François; Glenn, Orit A; Barkovich, A James; Studholme, Colin

    2011-01-01

    The process of brain growth involves the expansion of tissue at different rates at different points within the brain. As the layers within the developing brain evolve they can thicken or increase in area as the brain surface begins to fold. In this work we propose a new spatiotemporal formulation of tensor based volume morphometry that is derived in relation to tissue boundaries. This allows the study of the directional properties of tissue growth by separately characterizing the changes in area and thickness of the adjacent layers. The approach uses temporally weighted, local regression across a population of anatomies with different ages to model changes in components of the growth radial and tangential to the boundary between tissue layers. The formulation is applied to the study of sulcal formation from in-utero MR imaging of human fetal brain anatomy. Results show that the method detects differential growth of tissue layers adjacent to the cortical surface, particularly at sulcal locations, as early as 22 gestational weeks. PMID:21995063

  6. Graphene oxide monolayers as atomically thin seeding layers for atomic layer deposition of metal oxides

    NASA Astrophysics Data System (ADS)

    Nourbakhsh, Amirhasan; Adelmann, Christoph; Song, Yi; Lee, Chang Seung; Asselberghs, Inge; Huyghebaert, Cedric; Brizzi, Simone; Tallarida, Massimo; Schmeißer, Dieter; van Elshocht, Sven; Heyns, Marc; Kong, Jing; Palacios, Tomás; de Gendt, Stefan

    2015-06-01

    Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the capacitive properties of GO with its electronic structure. Capacitance-voltage measurements showed that the capacitive behavior of Al2O3/GO depends on the oxidation level of GO. Finally, GO was successfully used as an ALD seed layer for the deposition of Al2O3 on chemically inert single layer graphene, resulting in high performance top-gated field-effect transistors.Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the

  7. Self-organized arrays of graphene and few-layer graphene quantum dots in fluorographene matrix: Charge transient spectroscopy

    SciTech Connect

    Antonova, Irina V.; Nebogatikova, Nadezhda A.; Prinz, Victor Ya.

    2014-05-12

    Arrays of graphene or few-layer graphene quantum dots (QDs) embedded in a partially fluorinated graphene matrix were created by chemical functionalization of layers. Charge transient spectroscopy employed for investigation of obtained QD systems (size 20–70 nm) has allowed us to examine the QD energy spectra and the time of carrier emission (or charge relaxation) from QDs as a function of film thickness. It was found that the characteristic time of carrier emission from QDs decreased markedly (by about four orders of magnitude) on increasing the QD thickness from one graphene monolayer to 3 nm. Daylight-assisted measurements also demonstrate a strong decrease of the carrier emission time.

  8. Low-energy phase change memory with graphene confined layer

    NASA Astrophysics Data System (ADS)

    Zhu, Chengqiu; Ma, Jun; Ge, Xiaoming; Rao, Feng; Ding, Keyuan; Lv, Shilong; Wu, Liangcai; Song, Zhitang

    2016-06-01

    How to reduce the Reset operation energy is the key scientific and technological problem in the field of phase change memory (PCM). Here, we show in the Ge2Sb2Te5 based PCM cell, inserting an additional graphene monolayer in the Ge2Sb2Te5 layer can remarkably decrease both the Reset current and energy. Because of the small out-of-plane electrical and thermal conductivities of such monolayer graphene, the Set resistance and the heat dissipation towards top TiN electrode of the modified PCM cell are significantly increased and decreased, respectively. The mushroom-typed larger active phase transition volume thus can be confined inside the underlying thinner GST layer, resulting in the lower power consumption.

  9. Physisorption of Fullerenes in Graphene layers and carbon Nanoribbons

    NASA Astrophysics Data System (ADS)

    Pacheco, Monica; Orellana, Pedro; Correa, Julian

    2015-03-01

    The study of nanostructures based on carbon allotropes has captured the interest of the scientific community in the last two decades, due to its great versatility. In such structures a simple change of geometry leads to important changes in their physicochemical properties. In this context it has been studied different carbon allotropes complexes in particular for the development of photovoltaic systems. In this paper we show a study of opto-electronic properties of fullerenes physisorbed on graphene nanoribbons. Our calculations are carried out within the framework of density functional theory (DFT) using the SIESTA package. Our results show that effectively the fullerenes bind both to the layer of graphene as well as to the nanoribbons, with binding energies of about 0.5EV. We find that when the complex is formed, the physical properties of fullerenes, graphene and nanoribbons are preserved and when graphene is functionalized with various fullerenes the electronic spectrum is composed of bands of energy which increases the intensity of the optical absorption spectrum of the complex. Conicyt ACT 1204, USM 11.14.68.

  10. Layer-by-layer assembly of thin films containing exfoliated pristine graphene nanosheets and polyethyleneimine.

    PubMed

    Sham, Alison Y W; Notley, Shannon M

    2014-03-11

    A method for the modification of surface properties through the deposition of stabilized graphene nanosheets is described. Here, the thickness of the film is controlled through the use of the layer-by-layer technique, where the sequential adsorption of the cationic polyethyleneimine (PEI) is followed by the adsorption of anionic graphene sheets modified with layers of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) surfactants. The graphene particles were prepared using the surfactant-assisted liquid-phase exfoliation technique, with the low residual negative charge arising from edge defects. The buildup of the multilayer assembly through electrostatic interactions was strongly influenced by the solution conditions, including pH, ionic strength, and ionic species. Thereby, not only could the thickness of the film be tailored through the choice of the number of bilayers deposited but the viscoelastic properties of the film could also be modified by changing solution conditions at which the different species were deposited. The quartz crystal microbalance was used to measure the mass of graphene and polyelectrolyte immobilized at the interface as well as to probe the energy dissipated in the adsorbed layer.

  11. Graphene oxide monolayers as atomically thin seeding layers for atomic layer deposition of metal oxides.

    PubMed

    Nourbakhsh, Amirhasan; Adelmann, Christoph; Song, Yi; Lee, Chang Seung; Asselberghs, Inge; Huyghebaert, Cedric; Brizzi, Simone; Tallarida, Massimo; Schmeisser, Dieter; Van Elshocht, Sven; Heyns, Marc; Kong, Jing; Palacios, Tomás; De Gendt, Stefan

    2015-06-28

    Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the capacitive properties of GO with its electronic structure. Capacitance-voltage measurements showed that the capacitive behavior of Al2O3/GO depends on the oxidation level of GO. Finally, GO was successfully used as an ALD seed layer for the deposition of Al2O3 on chemically inert single layer graphene, resulting in high performance top-gated field-effect transistors.

  12. Fabrication of graphene/polyaniline composite multilayer films by electrostatic layer-by-layer assembly

    NASA Astrophysics Data System (ADS)

    Cong, Jiaojiao; Chen, Yuze; Luo, Jing; Liu, Xiaoya

    2014-10-01

    A novel graphene/polyaniline composite multilayer film was fabricated by electrostatic interactions induced layer-by-layer self-assembly technique, using water dispersible and negatively charged chemically converted graphene (CCG) and positively charged polyaniline (PANI) as building blocks. CCG was achieved through partly reduced graphene oxide, which remained carboxyl group on its surface. The remaining carboxyl groups not only retain the dispersibility of CCG, but also allow the growth of the multilayer films via electrostatic interactions between graphene and PANI. The structure and morphology of the obtained CCG/PANI multilayer film are characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, Ultraviolet-visible absorption spectrum (UV-vis), scanning electron microscopy (SEM), Raman spectroscopy and X-Ray Diffraction (XRD). The electrochemical properties of the resulting film are studied using cyclic voltammetry (CV), which showed that the resulting CCG/PANI multilayer film kept electroactivity in neutral solution and showed outstanding cyclic stability up to 100 cycles. Furthermore, the composite film exhibited good electrocatalytic ability toward ascorbic acid (AA) with a linear response from 1×10-4 to 1.2×10-3 M with the detect limit of 5×10-6 M. This study provides a facile and effective strategy to fabricate graphene/PANI nanocomposite film with good electrochemical property, which may find potential applications in electronic devices such as electrochemical sensor.

  13. Water desalination using nanoporous single-layer graphene.

    PubMed

    Surwade, Sumedh P; Smirnov, Sergei N; Vlassiouk, Ivan V; Unocic, Raymond R; Veith, Gabriel M; Dai, Sheng; Mahurin, Shannon M

    2015-05-01

    By creating nanoscale pores in a layer of graphene, it could be used as an effective separation membrane due to its chemical and mechanical stability, its flexibility and, most importantly, its one-atom thickness. Theoretical studies have indicated that the performance of such membranes should be superior to state-of-the-art polymer-based filtration membranes, and experimental studies have recently begun to explore their potential. Here, we show that single-layer porous graphene can be used as a desalination membrane. Nanometre-sized pores are created in a graphene monolayer using an oxygen plasma etching process, which allows the size of the pores to be tuned. The resulting membranes exhibit a salt rejection rate of nearly 100% and rapid water transport. In particular, water fluxes of up to 10(6) g m(-2) s(-1) at 40 °C were measured using pressure difference as a driving force, while water fluxes measured using osmotic pressure as a driving force did not exceed 70 g m(-2) s(-1) atm(-1).

  14. Water desalination using nanoporous single-layer graphene

    NASA Astrophysics Data System (ADS)

    Surwade, Sumedh P.; Smirnov, Sergei N.; Vlassiouk, Ivan V.; Unocic, Raymond R.; Veith, Gabriel M.; Dai, Sheng; Mahurin, Shannon M.

    2015-05-01

    By creating nanoscale pores in a layer of graphene, it could be used as an effective separation membrane due to its chemical and mechanical stability, its flexibility and, most importantly, its one-atom thickness. Theoretical studies have indicated that the performance of such membranes should be superior to state-of-the-art polymer-based filtration membranes, and experimental studies have recently begun to explore their potential. Here, we show that single-layer porous graphene can be used as a desalination membrane. Nanometre-sized pores are created in a graphene monolayer using an oxygen plasma etching process, which allows the size of the pores to be tuned. The resulting membranes exhibit a salt rejection rate of nearly 100% and rapid water transport. In particular, water fluxes of up to 106 g m-2 s-1 at 40 °C were measured using pressure difference as a driving force, while water fluxes measured using osmotic pressure as a driving force did not exceed 70 g m-2 s-1 atm-1.

  15. Aqueous proton transfer across single-layer graphene

    DOE PAGES

    Achtyl, Jennifer L.; Unocic, Raymond R.; Xu, Lijun; Cai, Yu; Raju, Muralikrishna; Zhang, Weiwei; Sacci, Robert L.; Vlassiouk, Ivan V.; Fulvio, Pasquale F.; Ganesh, Panchapakesan; et al

    2015-03-17

    Proton transfer across single-layer graphene proceeds with large computed energy barriers and is thought to be unfavourable at room temperature unless nanoscale holes or dopants are introduced, or a potential bias is applied. Here we subject single-layer graphene supported on fused ​silica to cycles of high and low pH, and show that protons transfer reversibly from the aqueous phase through the graphene to the other side where they undergo acid–base chemistry with the silica hydroxyl groups. After ruling out diffusion through macroscopic pinholes, the protons are found to transfer through rare, naturally occurring atomic defects. Computer simulations reveal low energymore » barriers of 0.61–0.75 eV for aqueous proton transfer across hydroxyl-terminated atomic defects that participate in a Grotthuss-type relay, while ​pyrylium-like ether terminations shut down proton exchange. In conclusion, unfavourable energy barriers to helium and ​hydrogen transfer indicate the process is selective for aqueous protons.« less

  16. Aqueous proton transfer across single-layer graphene

    PubMed Central

    Achtyl, Jennifer L.; Unocic, Raymond R.; Xu, Lijun; Cai, Yu; Raju, Muralikrishna; Zhang, Weiwei; Sacci, Robert L.; Vlassiouk, Ivan V.; Fulvio, Pasquale F.; Ganesh, Panchapakesan; Wesolowski, David J.; Dai, Sheng; van Duin, Adri C. T.; Neurock, Matthew; Geiger, Franz M.

    2015-01-01

    Proton transfer across single-layer graphene proceeds with large computed energy barriers and is therefore thought to be unfavourable at room temperature unless nanoscale holes or dopants are introduced, or a potential bias is applied. Here we subject single-layer graphene supported on fused silica to cycles of high and low pH, and show that protons transfer reversibly from the aqueous phase through the graphene to the other side where they undergo acid–base chemistry with the silica hydroxyl groups. After ruling out diffusion through macroscopic pinholes, the protons are found to transfer through rare, naturally occurring atomic defects. Computer simulations reveal low energy barriers of 0.61–0.75 eV for aqueous proton transfer across hydroxyl-terminated atomic defects that participate in a Grotthuss-type relay, while pyrylium-like ether terminations shut down proton exchange. Unfavourable energy barriers to helium and hydrogen transfer indicate the process is selective for aqueous protons. PMID:25781149

  17. Aqueous proton transfer across single-layer graphene

    SciTech Connect

    Achtyl, Jennifer L.; Unocic, Raymond R.; Xu, Lijun; Cai, Yu; Raju, Muralikrishna; Zhang, Weiwei; Sacci, Robert L.; Vlassiouk, Ivan V.; Fulvio, Pasquale F.; Ganesh, Panchapakesan; Wesolowski, David J.; Dai, Sheng; van Duin, Adri C. T.; Neurock, Matthew; Geiger, Franz M.

    2015-03-17

    Proton transfer across single-layer graphene proceeds with large computed energy barriers and is thought to be unfavourable at room temperature unless nanoscale holes or dopants are introduced, or a potential bias is applied. Here we subject single-layer graphene supported on fused ​silica to cycles of high and low pH, and show that protons transfer reversibly from the aqueous phase through the graphene to the other side where they undergo acid–base chemistry with the silica hydroxyl groups. After ruling out diffusion through macroscopic pinholes, the protons are found to transfer through rare, naturally occurring atomic defects. Computer simulations reveal low energy barriers of 0.61–0.75 eV for aqueous proton transfer across hydroxyl-terminated atomic defects that participate in a Grotthuss-type relay, while ​pyrylium-like ether terminations shut down proton exchange. In conclusion, unfavourable energy barriers to helium and ​hydrogen transfer indicate the process is selective for aqueous protons.

  18. Structural distortions in few-layer graphene creases.

    PubMed

    Robertson, Alex W; Bachmatiuk, Alicja; Wu, Yimin A; Schäffel, Franziska; Büchner, Bernd; Rümmeli, Mark H; Warner, Jamie H

    2011-12-27

    Folds and creases are frequently found in graphene grown by chemical vapor deposition (CVD), due to the differing thermal expansion coefficients of graphene from the growth catalyst and the flexibility of the sheet during transfer from the catalyst. The structure of a few-layer graphene (FLG) crease is examined by aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM). A study of 2D fast Fourier transforms (FFTs) taken about the region of the crease allowed for the crystal stacking structure of the system to be elucidated. It was found that strain-induced stacking faults were created in the AB Bernal-stacked FLG bulk around the region proximal to the crease termination; this is of interest as the stacking order of FLG is known to have an effect on its electronic properties and thus should be considered when transferring CVD-grown FLG to alternate substrates for electronic device fabrication. The FFTs, along with analysis of the real space images, were used to determine the configuration of the layers in the crease itself and were corroborated by multislice atomistic TEM simulations. The termination of the crease part way through the FLG sheet is also examined and is found to show strong out of plane distortions in the area about it. PMID:22122696

  19. Aqueous proton transfer across single-layer graphene

    NASA Astrophysics Data System (ADS)

    Achtyl, Jennifer L.; Unocic, Raymond R.; Xu, Lijun; Cai, Yu; Raju, Muralikrishna; Zhang, Weiwei; Sacci, Robert L.; Vlassiouk, Ivan V.; Fulvio, Pasquale F.; Ganesh, Panchapakesan; Wesolowski, David J.; Dai, Sheng; van Duin, Adri C. T.; Neurock, Matthew; Geiger, Franz M.

    2015-03-01

    Proton transfer across single-layer graphene proceeds with large computed energy barriers and is therefore thought to be unfavourable at room temperature unless nanoscale holes or dopants are introduced, or a potential bias is applied. Here we subject single-layer graphene supported on fused silica to cycles of high and low pH, and show that protons transfer reversibly from the aqueous phase through the graphene to the other side where they undergo acid-base chemistry with the silica hydroxyl groups. After ruling out diffusion through macroscopic pinholes, the protons are found to transfer through rare, naturally occurring atomic defects. Computer simulations reveal low energy barriers of 0.61-0.75 eV for aqueous proton transfer across hydroxyl-terminated atomic defects that participate in a Grotthuss-type relay, while pyrylium-like ether terminations shut down proton exchange. Unfavourable energy barriers to helium and hydrogen transfer indicate the process is selective for aqueous protons.

  20. Formation of Silica/Graphene Oxide Hybrid Nano Films by Layer-by-Layer Self-Assembly and Biomimetic Silicification.

    PubMed

    Yang, Sung Ho

    2015-02-01

    Silica/graphene oxide hybrid thin films were formed by layer-by-layer self-assembly and biomimetic silicification, and the thickness and structure of hybrid thin films were finely controlled at the nanometer scale, by tuning number of the layer-by-layer process. The physical properties of thin films were characterized by infrared spectroscopy, atomic force microscopy, and scanning electron microscopy. In addition, silica/graphene oxide hybrid thin films were successfully utilized for cell culture platforms.

  1. Graphene as an efficient interfacial layer for electrochromic devices.

    PubMed

    Lin, Feng; Bult, Justin B; Nanayakkara, Sanjini; Dillon, Anne C; Richards, Ryan M; Blackburn, Jeffrey L; Engtrakul, Chaiwat

    2015-06-01

    This study presents an interfacial modification strategy to improve the performance of electrochromic films that were fabricated by a magnetron sputtering technique. High-quality graphene sheets, synthesized by chemical vapor deposition, were used to modify fluorine-doped tin oxide substrates, followed by the deposition of high-performance nanocomposite nickel oxide electrochromic films. Electrochromic cycling results revealed that a near-complete monolayer graphene interfacial layer improves the electrochromic performance in terms of switching kinetics, activation period, coloration efficiency, and bleached-state transparency, while maintaining ∼100% charge reversibility. The present study offers an alternative route for improving the interfacial properties between electrochromic and transparent conducting oxide films without relying on conventional methods such as nanostructuring or thin film composition control. PMID:25950270

  2. Extreme ultraviolet induced defects on few-layer graphene

    SciTech Connect

    Gao, A.; Zoethout, E.; Lee, C. J.; Rizo, P. J.; Scaccabarozzi, L.; Banine, V.; Bijkerk, F.

    2013-07-28

    We use Raman spectroscopy to show that exposing few-layer graphene to extreme ultraviolet (EUV, 13.5 nm) radiation, i.e., relatively low photon energy, results in an increasing density of defects. Furthermore, exposure to EUV radiation in a H{sub 2} background increases the graphene dosage sensitivity, due to reactions caused by the EUV induced hydrogen plasma. X-ray photoelectron spectroscopy results show that the sp{sup 2} bonded carbon fraction decreases while the sp{sup 3} bonded carbon and oxide fraction increases with exposure dose. Our experimental results confirm that even in reducing environment oxidation is still one of the main source of inducing defects.

  3. Graphene Layer Growth Chemistry: Five-Six-Ring Flip Reaction

    SciTech Connect

    Whitesides, R.; Domin, D.; Salomon-Ferrer, R.; Lester Jr., W.A.; Frenklach, M.

    2007-12-01

    Reaction pathways are presented for hydrogen-mediated isomerization of a five and six member carbon ring complex on the zigzag edge of a graphene layer. A new reaction sequence that reverses orientation of the ring complex, or 'flips' it, was identified. Competition between the flip reaction and 'ring separation' was examined. Ring separation is the reverse of the five and six member ring complex formation reaction, previously reported as 'ring collision'. The elementary steps of the pathways were analyzed using density-functional theory (DFT). Rate coefficients were obtained by solution of the energy master equation and classical transition state theory utilizing the DFT energies, frequencies, and geometries. The results indicate that the flip reaction pathway dominates the separation reaction and should be competitive with other pathways important to the graphene zigzag edge growth in high temperature environments.

  4. Mode manipulation and near-THz absorptions in binary grating-graphene layer structures

    PubMed Central

    2014-01-01

    The excitation and absorption properties of grating coupled graphene surface plasmons were studied. It was found that whether a mode can be excited is mainly determined by the frequency of incident light and the duty ratio of gratings. In the structure consisting graphene bilayer, a blueshift of the excitation frequency existed when the distance between neighbor graphene layer were decreased gradually. In graphene-grating multilayer structures, a strong absorption (approximately 90% at maximum) was found in near-THz range. PMID:24559407

  5. Thermal conductivity of giant mono- to few-layered CVD graphene supported on an organic substrate.

    PubMed

    Liu, Jing; Wang, Tianyu; Xu, Shen; Yuan, Pengyu; Xu, Xu; Wang, Xinwei

    2016-05-21

    The thermal conductivity (k) of supported graphene is a critical property that reflects the graphene-substrate interaction, graphene structure quality, and is needed for thermal design of a graphene device. Yet the related k measurement has never been a trivial work and very few studies are reported to date, only at the μm level. In this work, for the first time, the k of giant chemical vapor decomposition (CVD) graphene supported on poly(methyl methacrylate) (PMMA) is characterized using our transient electro-thermal technique based on a differential concept. Our graphene size is ∼mm, far above the samples studied in the past. This giant graphene measurement eliminates the thermal contact resistance problems and edge phonon scattering encountered in μm-scale graphene k measurement. Such mm-scale measurement is critical for device/system-level thermal design since it reflects the effect of abundant grains in graphene. The k of 1.33-layered, 1.53-layered, 2.74-layered and 5.2-layered supported graphene is measured as 365 W m(-1) K(-1), 359 W m(-1) K(-1), 273 W m(-1) K(-1) and 33.5 W m(-1) K(-1), respectively. These values are significantly lower than the k of supported graphene on SiO2, and are about one order of magnitude lower than the k of suspended graphene. We speculate that the abundant C atoms in the PMMA promote more ready energy and momentum exchange with the supported graphene, and give rise to more phonon scattering than the SiO2 substrate. This leads to a lower k of CVD graphene on PMMA than that on SiO2. We attribute the existence of disorder in the sp(2) domain, graphene oxide (GO) and stratification in the 5.2-layered graphene to its more k reduction. The Raman linewidth (G peak) of the 5.2-layered graphene is also twice larger than that of the other three kinds of graphene, indicating the much more phonon scattering and shorter phonon lifetime in it. Also the electrical conductivity of the 5.2-layered graphene is about one-fifth of that for the

  6. Thermal conductivity of giant mono- to few-layered CVD graphene supported on an organic substrate

    NASA Astrophysics Data System (ADS)

    Liu, Jing; Wang, Tianyu; Xu, Shen; Yuan, Pengyu; Xu, Xu; Wang, Xinwei

    2016-05-01

    The thermal conductivity (k) of supported graphene is a critical property that reflects the graphene-substrate interaction, graphene structure quality, and is needed for thermal design of a graphene device. Yet the related k measurement has never been a trivial work and very few studies are reported to date, only at the μm level. In this work, for the first time, the k of giant chemical vapor decomposition (CVD) graphene supported on poly(methyl methacrylate) (PMMA) is characterized using our transient electro-thermal technique based on a differential concept. Our graphene size is ~mm, far above the samples studied in the past. This giant graphene measurement eliminates the thermal contact resistance problems and edge phonon scattering encountered in μm-scale graphene k measurement. Such mm-scale measurement is critical for device/system-level thermal design since it reflects the effect of abundant grains in graphene. The k of 1.33-layered, 1.53-layered, 2.74-layered and 5.2-layered supported graphene is measured as 365 W m-1 K-1, 359 W m-1 K-1, 273 W m-1 K-1 and 33.5 W m-1 K-1, respectively. These values are significantly lower than the k of supported graphene on SiO2, and are about one order of magnitude lower than the k of suspended graphene. We speculate that the abundant C atoms in the PMMA promote more ready energy and momentum exchange with the supported graphene, and give rise to more phonon scattering than the SiO2 substrate. This leads to a lower k of CVD graphene on PMMA than that on SiO2. We attribute the existence of disorder in the sp2 domain, graphene oxide (GO) and stratification in the 5.2-layered graphene to its more k reduction. The Raman linewidth (G peak) of the 5.2-layered graphene is also twice larger than that of the other three kinds of graphene, indicating the much more phonon scattering and shorter phonon lifetime in it. Also the electrical conductivity of the 5.2-layered graphene is about one-fifth of that for the other three. This

  7. A novel mechanical cleavage method for synthesizing few-layer graphenes

    PubMed Central

    2011-01-01

    A novel method to synthesize few layer graphene from bulk graphite by mechanical cleavage is presented here. The method involves the use of an ultrasharp single crystal diamond wedge to cleave a highly ordered pyrolytic graphite sample to generate the graphene layers. Cleaving is aided by the use of ultrasonic oscillations along the wedge. Characterization of the obtained layers shows that the process is able to synthesize graphene layers with an area of a few micrometers. Application of oscillation enhances the quality of the layers produced with the layers having a reduced crystallite size as determined from the Raman spectrum. Interesting edge structures are observed that needs further investigation. PMID:21711598

  8. Direct growth of multilayer graphene by precipitation using W capping layer

    NASA Astrophysics Data System (ADS)

    Yamada, Jumpei; Ueda, Yuki; Maruyama, Takahiro; Naritsuka, Shigeya

    2016-10-01

    In this study, the direct growth of multilayer graphene from amorphous carbon on a sapphire (0001) substrate by precipitation using a nickel catalyst layer and a tungsten capping layer was examined. The findings revealed that a tungsten carbide layer was formed on top of the catalyst, and this suppressed the diffusion of carbon atoms upwards towards the surface. This caused the graphene layer to precipitate below the catalyst layer rather than above it. Under optimized growth conditions, Raman spectroscopy indicated that a high-quality graphene layer was formed with a low D/G peak intensity ratio of 0.10.

  9. Graphene as transparent conducting electrodes in organic photovoltaics: studies in graphene morphology, hole transporting layers, and counter electrodes.

    PubMed

    Park, Hyesung; Brown, Patrick R; Bulović, Vladimir; Kong, Jing

    2012-01-11

    In this work, organic photovoltaics (OPV) with graphene electrodes are constructed where the effect of graphene morphology, hole transporting layers (HTL), and counter electrodes are presented. Instead of the conventional poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) PEDOT:PSS HTL, an alternative transition metal oxide HTL (molybdenum oxide (MoO(3))) is investigated to address the issue of surface immiscibility between graphene and PEDOT:PSS. Graphene films considered here are synthesized via low-pressure chemical vapor deposition (LPCVD) using a copper catalyst and experimental issues concerning the transfer of synthesized graphene onto the substrates of OPV are discussed. The morphology of the graphene electrode and HTL wettability on the graphene surface are shown to play important roles in the successful integration of graphene films into the OPV devices. The effect of various cathodes on the device performance is also studied. These factors (i.e., suitable HTL, graphene surface morphology and residues, and the choice of well-matching counter electrodes) will provide better understanding in utilizing graphene films as transparent conducting electrodes in future solar cell applications. PMID:22107487

  10. Temperature-activated layer-breathing vibrations in few-layer graphene.

    PubMed

    Lui, Chun Hung; Ye, Zhipeng; Keiser, Courtney; Xiao, Xun; He, Rui

    2014-08-13

    We investigated the low-frequency Raman spectra of freestanding few-layer graphene (FLG) at varying temperatures (400-900 K) controlled by laser heating. At high temperature, we observed the fundamental Raman mode for the lowest-frequency branch of rigid-plane layer-breathing mode (LBM) vibration. The mode frequency redshifts dramatically from 81 cm(-1) for bilayer to 23 cm(-1) for 8-layer. The thickness dependence is well described by a simple model of coupled oscillators. Notably, the LBM Raman response is unobservable at room temperature, and it is turned on at higher temperature (>600 K) with a steep increase of Raman intensity. The observation suggests that the LBM vibration is strongly suppressed by molecules adsorbed on the graphene surface but is activated as desorption occurs at high temperature.

  11. Electronic Raman scattering in graphite and single-layer and few-layer graphene

    NASA Astrophysics Data System (ADS)

    Ponosov, Yu. S.; Ushakov, A. V.; Streltsov, S. V.

    2015-05-01

    We investigated polarization-resolved electronic Raman scattering in different graphitic structures, including bulk graphite and single-layer and few-layer graphene. For all investigated samples, the broad continua of interband electronic transitions were detected at an energy ˜0.35 eV, while they were expected to be at ˜6 eV [Phys. Rev. B 88, 085416 (2013), 10.1103/PhysRevB.88.085416]. The symmetry of the observed excitations corresponds to the A2 g irreducible representation. A quasilinear behavior of the Raman response is observed at low energies in all cases at room temperature, in agreement with performed tight-binding calculations. High-energy features at ˜0.8 eV are detected in the spectra of graphite and few-layer graphene. They are attributed to interband transitions in the vicinity of the K point, which involve electronic bands split by interlayer interaction. The effects of the substrate type, defect amount, and doping on the continuum line shape and symmetry are discovered. The silent layer-breathing mode is observed in a single-layer graphene. The results evidence that the electronic light scattering in graphitic structures without an external magnetic field is a powerful tool, which provides a variety of data on the structure and symmetry of low-energy electronic excitations.

  12. Fluorinated graphene and hexagonal boron nitride as ALD seed layers for graphene-based van der Waals heterostructures

    NASA Astrophysics Data System (ADS)

    Guo, Hongwei; Liu, Yunlong; Xu, Yang; Meng, Nan; Wang, Hongtao; Hasan, Tawfique; Wang, Xinran; Luo, Jikui; Yu, Bin

    2014-09-01

    Ultrathin dielectric materials prepared by atomic-layer-deposition (ALD) technology are commonly used in graphene electronics. Using the first-principles density functional theory calculations with van der Waals (vdW) interactions included, we demonstrate that single-side fluorinated graphene (SFG) and hexagonal boron nitride (h-BN) exhibit large physical adsorption energy and strong electrostatic interactions with H2O-based ALD precursors, indicating their potential as the ALD seed layer for dielectric growth on graphene. In graphene-SFG vdW heterostructures, graphene is n-doped after ALD precursor adsorption on the SFG surface caused by vertical intrinsic polarization of SFG. However, graphene-h-BN vdW heterostructures help preserving the intrinsic characteristics of the underlying graphene due to in-plane intrinsic polarization of h-BN. By choosing SFG or BN as the ALD seed layer on the basis of actual device design needs, the graphene vdW heterostructures may find applications in low-dimensional electronics.

  13. Fluorinated graphene and hexagonal boron nitride as ALD seed layers for graphene-based van der Waals heterostructures.

    PubMed

    Guo, Hongwei; Liu, Yunlong; Xu, Yang; Meng, Nan; Wang, Hongtao; Hasan, Tawfique; Wang, Xinran; Luo, Jikui; Yu, Bin

    2014-09-01

    Ultrathin dielectric materials prepared by atomic-layer-deposition (ALD) technology are commonly used in graphene electronics. Using the first-principles density functional theory calculations with van der Waals (vdW) interactions included, we demonstrate that single-side fluorinated graphene (SFG) and hexagonal boron nitride (h-BN) exhibit large physical adsorption energy and strong electrostatic interactions with H2O-based ALD precursors, indicating their potential as the ALD seed layer for dielectric growth on graphene. In graphene-SFG vdW heterostructures, graphene is n-doped after ALD precursor adsorption on the SFG surface caused by vertical intrinsic polarization of SFG. However, graphene-h-BN vdW heterostructures help preserving the intrinsic characteristics of the underlying graphene due to in-plane intrinsic polarization of h-BN. By choosing SFG or BN as the ALD seed layer on the basis of actual device design needs, the graphene vdW heterostructures may find applications in low-dimensional electronics. PMID:25116064

  14. Fluorinated graphene and hexagonal boron nitride as ALD seed layers for graphene-based van der Waals heterostructures.

    PubMed

    Guo, Hongwei; Liu, Yunlong; Xu, Yang; Meng, Nan; Wang, Hongtao; Hasan, Tawfique; Wang, Xinran; Luo, Jikui; Yu, Bin

    2014-09-01

    Ultrathin dielectric materials prepared by atomic-layer-deposition (ALD) technology are commonly used in graphene electronics. Using the first-principles density functional theory calculations with van der Waals (vdW) interactions included, we demonstrate that single-side fluorinated graphene (SFG) and hexagonal boron nitride (h-BN) exhibit large physical adsorption energy and strong electrostatic interactions with H2O-based ALD precursors, indicating their potential as the ALD seed layer for dielectric growth on graphene. In graphene-SFG vdW heterostructures, graphene is n-doped after ALD precursor adsorption on the SFG surface caused by vertical intrinsic polarization of SFG. However, graphene-h-BN vdW heterostructures help preserving the intrinsic characteristics of the underlying graphene due to in-plane intrinsic polarization of h-BN. By choosing SFG or BN as the ALD seed layer on the basis of actual device design needs, the graphene vdW heterostructures may find applications in low-dimensional electronics.

  15. Benzocyclobutene (BCB) Polymer as Amphibious Buffer Layer for Graphene Field-Effect Transistor.

    PubMed

    Wu, Yun; Zou, Jianjun; Huo, Shuai; Lu, Haiyan; Kong, Yuecan; Chen, Tangshen; Wu, Wei; Xu, Jingxia

    2015-08-01

    Owing to the scattering and trapping effects, the interfaces of dielectric/graphene or substrate/graphene can tailor the performance of field-effect transistor (FET). In this letter, the polymer of benzocyclobutene (BCB) was used as an amphibious buffer layer and located at between the layers of substrate and graphene and between the layers of dielectric and graphene. Interestingly, with the help of nonpolar and hydrophobic BCB buffer layer, the large-scale top-gated, chemical vapor deposited (CVD) graphene transistors was prepared on Si/SiO2 substrate, its cutoff frequency (fT) and the maximum cutoff frequency (fmax) of the graphene field-effect transistor (GFET) can be reached at 12 GHz and 11 GHz, respectively. PMID:26369142

  16. Protecting nickel with graphene spin-filtering membranes: A single layer is enough

    SciTech Connect

    Martin, M.-B.; Dlubak, B.; Piquemal-Banci, M.; Collin, S.; Petroff, F.; Anane, A.; Fert, A.; Seneor, P.; Yang, H.; Blume, R.; Schloegl, R.

    2015-07-06

    We report on the demonstration of ferromagnetic spin injectors for spintronics which are protected against oxidation through passivation by a single layer of graphene. The graphene monolayer is directly grown by catalytic chemical vapor deposition on pre-patterned nickel electrodes. X-ray photoelectron spectroscopy reveals that even with its monoatomic thickness, monolayer graphene still efficiently protects spin sources against oxidation in ambient air. The resulting single layer passivated electrodes are integrated into spin valves and demonstrated to act as spin polarizers. Strikingly, the atom-thick graphene layer is shown to be sufficient to induce a characteristic spin filtering effect evidenced through the sign reversal of the measured magnetoresistance.

  17. Protecting nickel with graphene spin-filtering membranes: A single layer is enough

    NASA Astrophysics Data System (ADS)

    Martin, M.-B.; Dlubak, B.; Weatherup, R. S.; Piquemal-Banci, M.; Yang, H.; Blume, R.; Schloegl, R.; Collin, S.; Petroff, F.; Hofmann, S.; Robertson, J.; Anane, A.; Fert, A.; Seneor, P.

    2015-07-01

    We report on the demonstration of ferromagnetic spin injectors for spintronics which are protected against oxidation through passivation by a single layer of graphene. The graphene monolayer is directly grown by catalytic chemical vapor deposition on pre-patterned nickel electrodes. X-ray photoelectron spectroscopy reveals that even with its monoatomic thickness, monolayer graphene still efficiently protects spin sources against oxidation in ambient air. The resulting single layer passivated electrodes are integrated into spin valves and demonstrated to act as spin polarizers. Strikingly, the atom-thick graphene layer is shown to be sufficient to induce a characteristic spin filtering effect evidenced through the sign reversal of the measured magnetoresistance.

  18. Long Spin Diffusion Length in Few-Layer Graphene Flakes

    NASA Astrophysics Data System (ADS)

    Yan, W.; Phillips, L. C.; Barbone, M.; Hämäläinen, S. J.; Lombardo, A.; Ghidini, M.; Moya, X.; Maccherozzi, F.; van Dijken, S.; Dhesi, S. S.; Ferrari, A. C.; Mathur, N. D.

    2016-09-01

    We report a spin valve with a few-layer graphene flake bridging highly spin-polarized La0.67Sr0.33MnO3 electrodes, whose surfaces are kept clean during lithographic definition. Sharp magnetic switching is verified using photoemission electron microscopy with x-ray magnetic circular dichroism contrast. A naturally occurring high interfacial resistance ˜12 M Ω facilitates spin injection, and a large resistive switching (0.8 M Ω at 10 K) implies a 70 - 130 μ m spin diffusion length that exceeds previous values obtained with sharp-switching electrodes.

  19. Plasma resonant terahertz photomixers based on double graphene layer structures

    NASA Astrophysics Data System (ADS)

    Ryzhii, Maxim; Shur, Michael S.; Mitin, Vladimir; Satou, Akira; Ryzhii, Victor; Otsuji, Taiichi

    2014-03-01

    We propose terahertz (THz) photomixers based on double graphene layer (DGL) structures, utilizing the interband absorption of modulated optical radiation, tunneling or thermionic inter-GL transitions, and resonant excitation of plasma oscillations. Using the developed device model, we substantiate the operation of the photomixers and calculate their characteristics. We demonstrate that the output frequency-dependent power of THz radiation exhibits pronounced resonant peaks at the plasmonic resonant frequencies. The proposed THz photomixer can surpass the pertinent devices based on the standard heterostructures.

  20. Monolayer and/or few-layer graphene on metal or metal-coated substrates

    DOEpatents

    Sutter, Peter Werner; Sutter, Eli Anguelova

    2015-04-14

    Disclosed is monolayer and/or few-layer graphene on metal or metal-coated substrates. Embodiments include graphene mirrors. In an example, a mirror includes a substrate that has a surface exhibiting a curvature operable to focus an incident beam onto a focal plane. A graphene layer conformally adheres to the substrate, and is operable to protect the substrate surface from degradation due to the incident beam and an ambient environment.

  1. Biomass derived solvents for the scalable production of single layered graphene from graphite.

    PubMed

    Sharma, Mukesh; Mondal, Dibyendu; Singh, Nripat; Prasad, Kamalesh

    2016-07-12

    Among four different biomass derived green and sustainable solvents namely levulinic acid (LA), ethyl lactate (EL), γ-valerolactone (GVL) and formic acid (FA) only LA was found to exfoliate graphite to single and few layered graphene sheets. During exfoliation, the formation of LA crystals embedded with single layered graphene sheets was observed. The process is scalable and the solvent can be recovered and reused in five subsequent cycles of exfoliation for the large scale production of graphene sheets.

  2. Investigation of energy transfer mechanisms between two adjacent phosphorescent emission layers

    NASA Astrophysics Data System (ADS)

    Diez, Carola; Reusch, Thilo C. G.; Seidel, Stefan; Brütting, Wolfgang

    2012-06-01

    The investigation of energy transfer mechanisms between two adjacent phosphorescent emission layers comprising the green emitter molecule fac-tris(2-phenly-pyridin)iridium (Ir(ppy)3) and the red emitter molecule iridium(III)bis(2-methyldibenzo[f,h]quinoxaline(acetylacetonate) (Ir(MDQ)2(acac)) is presented. We show that the performance can be enhanced by a variation of the emission layer thickness and the emitter concentration. By inserting different interlayer materials between the emission units, we demonstrate that triplet excitons are formed on the Ir(ppy)3 and subsequently transferred to the Ir(MDQ)2(acac) molecules via the hole transporting host material N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine of the red emission layer. The variation of the interlayer thickness shows that the triplet diffusion length is several tens of nanometers. After optimization of the guest-host system an efficiency enhancement by 15% was achieved and the lifetime of the red-green emissive unit could be enhanced by 55%. Additionally, it is shown that this improved red-green unit can be combined with a fluorescent blue emitter in a state-of-the-art stacked white emissive organic light emitting diode.

  3. Development of the layer-by-layer biosensor using graphene films: application for cholesterol determination

    NASA Astrophysics Data System (ADS)

    Binh Nguyen, Hai; Chuc Nguyen, Van; Nguyen, Van Tu; Doan Le, Huu; Quynh Nguyen, Van; Thanh Tam Ngo, Thi; Phuc Do, Quan; Nghia Nguyen, Xuan; Phan, Ngoc Minh; Tran, Dai Lam

    2013-03-01

    The preparation and characterization of graphene films for cholesterol determination are described. The graphene films were synthesized by thermal chemical vapor deposition (CVD) method. Methane gas (CH4) and copper tape were used as carbon source and catalyst in the graphene growth process, respectively. The intergrated array was fabricated by using micro-electro-mechanical systems (MEMS) technology in which Fe3O4-doped polyaniline (PANi) film was electropolymerized on Pt/Gr electrodes. The properties of the Pt/Gr/PANi/Fe3O4 films were investigated by field-emission scanning electron microscopy (FE-SEM), Raman spectroscopy and electrochemical techniques. Cholesterol oxidase (ChOx) has been immobilized onto the working electrode with glutaraldehyde agent. The cholesterol electrochemical biosensor shows high sensitivity (74 μA mM-1 cm-2) and fast response time (<5 s). A linear calibration plot was obtained in the wide cholesterol concentration range from 2 to 20 mM and correlation coefficient square (R2) of 0.9986. This new layer-by-layer biosensor based on graphene films promises many practical applications.

  4. Atomic layer deposition of HfO2 on graphene through controlled ion beam treatment

    NASA Astrophysics Data System (ADS)

    Kim, Ki Seok; Oh, Il-Kwon; Jung, Hanearl; Kim, Hyungjun; Yeom, Geun Young; Kim, Kyong Nam

    2016-05-01

    The polymer residue generated during the graphene transfer process to the substrate tends to cause problems (e.g., a decrease in electron mobility, unwanted doping, and non-uniform deposition of the dielectric material). In this study, by using a controllable low-energy Ar+ ion beam, we cleaned the polymer residue without damaging the graphene network. HfO2 grown by atomic layer deposition on graphene cleaned using an Ar+ ion beam showed a dense uniform structure, whereas that grown on the transferred graphene (before Ar+ ion cleaning) showed a non-uniform structure. A graphene-HfO2-metal capacitor fabricated by growing 20-nm thick HfO2 on graphene exhibited a very low leakage current (<10-11 A/cm2) for Ar+ ion-cleaned graphene, whereas a similar capacitor grown using the transferred graphene showed high leakage current.

  5. Filler-depletion layer adjacent to interface impacts performance of thermal interface material

    NASA Astrophysics Data System (ADS)

    Yada, Susumu; Oyake, Takafumi; Sakata, Masanori; Shiomi, Junichiro

    2016-01-01

    When installing thermal interface material (TIM) between heat source and sink to reduce contact thermal resistance, the interfacial thermal resistance (ITR) between the TIM and heat source/sink may become important, especially when the TIM thickness becomes smaller in the next-generation device integration. To this end, we have investigated ITR between TIM and aluminum surface by using the time-domain thermoreflectance method. The measurements reveal large ITR attributed to the depletion of filler particles in TIM adjacent to the aluminum surface. The thickness of the depletion layer is estimated to be about 100 nm. As a consequence, the fraction of ITR to the total contact thermal resistance becomes about 20% when the TIM thickness is about 50 μm (current thickness), and it exceeds 50% when the thickness is smaller than 10 μm (next-generation thickness).

  6. Growth of high quality GaN layer on carbon nanotube-graphene network structure as intermediate layer

    NASA Astrophysics Data System (ADS)

    Seo, Taeo Hoon; Park, Ah Hyun; Park, Sungchan; Kim, Myung Jong; Suh, Eun-Kyung

    2015-03-01

    In general, high-quality GaN layers are synthesized on low-temperature (LT) GaN buffer layer on a single crystal sapphire substrate. However, large differences in fundamental properties such as lattice constants and thermal expansion coefficients between GaN layer and sapphire substrate generate high density of threading dislocation (TD) that leads to deterioration of optical and structural properties. Graphene has been attracting much attention due to its excellent physical properties However, direct epitaxial growth of GaN film onto graphene layer on substrates is not easily accessible due to the lack of chemical reactivity on graphene which consisted of C-C bond of sp2 hexagonally arranged carbon atoms with no dangling bonds. In this work, an intermediate layer for the GaN growth on sapphire substrate was constructed by inserting carbon nanotubes and graphene hybrid structure (CGH) Optical and structural properties of GaN layer grown on CGH were compared with those of GaN layer directly grown on sapphire CNTs act as nucleation sites and play a crucial role in the growth of single crystal high-quality GaN on graphene layer. Also, graphene film acts as a mask for epitaxial lateral overgrowth of GaN layer, which can effectively reduce TD density. A grant from the Korea Institute of Science and Technology (KIST) institutional program.

  7. Property transformation of graphene with Al2O3 films deposited directly by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Zheng, Li; Cheng, Xinhong; Cao, Duo; Wang, Zhongjian; Xia, Chao; Yu, Yuehui; Shen, Dashen

    2014-01-01

    Al2O3 films are deposited directly onto graphene by H2O-based atomic layer deposition (ALD), and the films are pinhole-free and continuously cover the graphene surface. The growth process of Al2O3 films does not introduce any detective defects in graphene, suppresses the hysteresis effect and tunes the graphene doping to n-type. The self-cleaning of ALD growth process, together with the physically absorbed H2O and oxygen-deficient ALD environment consumes OH- bonds, suppresses the p-doping of graphene, shifts Dirac point to negative gate bias and enhances the electron mobility.

  8. Few-layer graphene shells and nonmagnetic encapsulates: a versatile and nontoxic carbon nanomaterial.

    PubMed

    Bachmatiuk, Alicja; Mendes, Rafael G; Hirsch, Cordula; Jähne, Carsten; Lohe, Martin R; Grothe, Julia; Kaskel, Stefan; Fu, Lei; Klingeler, Rüdiger; Eckert, Jürgen; Wick, Peter; Rümmeli, Mark H

    2013-12-23

    In this work a simple and scalable approach to coat nonmagnetic nanoparticles with few-layer graphene is presented. In addition, the easy processing of such nanoparticles to remove their core, leaving only the 3D graphene nanoshell, is demonstrated. The samples are comprehensively characterized, as are their versatility in terms of functionalization and as a material for electrochemical storage. Indeed, these 3D graphene nanostructures are easily functionalized much as is found with carbon nanotubes and planar graphene. Electrochemical investigations indicate these nanostructures are promising for stable long-life battery applications. Finally, initial toxicological investigations suggest no acute health risk from these 3D graphene nanostructures.

  9. Precise Control of the Number of Layers of Graphene by Picosecond Laser Thinning

    PubMed Central

    Lin, Zhe; Ye, Xiaohui; Han, Jinpeng; Chen, Qiao; Fan, Peixun; Zhang, Hongjun; Xie, Dan; Zhu, Hongwei; Zhong, Minlin

    2015-01-01

    The properties of graphene can vary as a function of the number of layers (NOL). Controlling the NOL in large area graphene is still challenging. In this work, we demonstrate a picosecond (ps) laser thinning removal of graphene layers from multi-layered graphene to obtain desired NOL when appropriate pulse threshold energy is adopted. The thinning process is conducted in atmosphere without any coating and it is applicable for graphene films on arbitrary substrates. This method provides many advantages such as one-step process, non-contact operation, substrate and environment-friendly, and patternable, which will enable its potential applications in the manufacturing of graphene-based electronic devices. PMID:26111758

  10. Synthesis and characterization of intercalated few-layer graphenes

    NASA Astrophysics Data System (ADS)

    Sato, Shogo; Ichikawa, Hiroaki; Iwata, Nobuyuki; Yamamoto, Hiroshi

    2014-02-01

    Toward achieving room-temperature superconductivity, FeCl3-intercalated few-layer graphenes (FeCl3-FLGs) and Ca-intercalated few-layer graphenes (Ca-FLGs) were synthesized. FeCl3-FLGs were synthesized by the two-zone method and Ca-FLGs were synthesized using Ca-Li alloy. The Raman spectra of the FeCl3-FLGs showed a lower-intensity peak at 1607 cm-1 than that of the corresponding bare G. The peak at 1607 cm-1 suggested that the sample was stage 4-5 FeCl3-FLGs. The room-temperature electrical resistivity of FeCl3-FLGs was 2.65 × 10-5 Ω·m, which linearly decreased with decreasing temperature with a marked change occurring at approximately 200 K. From a XRD pattern of Ca-FLGs, we concluded that Ca is intercalated in FLGs. The room-temperature resistivity of Ca-FLGs was 3.45 × 10-5 Ω·m, which increased with decreasing temperature.

  11. Reversible Loss of Bernal Stacking during the Deformation of Few-Layer Graphene in Nanocomposites

    PubMed Central

    2013-01-01

    The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (∼0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed. PMID:23899378

  12. Reversible loss of Bernal stacking during the deformation of few-layer graphene in nanocomposites.

    PubMed

    Gong, Lei; Young, Robert J; Kinloch, Ian A; Haigh, Sarah J; Warner, Jamie H; Hinks, Jonathan A; Xu, Ziwei; Li, Li; Ding, Feng; Riaz, Ibtsam; Jalil, Rashid; Novoselov, Kostya S

    2013-08-27

    The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (~0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed. PMID:23899378

  13. Excitonic Effects in Tungsten Disulfide Monolayers on Two-Layer Graphene.

    PubMed

    Giusca, Cristina E; Rungger, Ivan; Panchal, Vishal; Melios, Christos; Lin, Zhong; Lin, Yu-Chuan; Kahn, Ethan; Elías, Ana Laura; Robinson, Joshua A; Terrones, Mauricio; Kazakova, Olga

    2016-08-23

    Light emission in atomically thin heterostructures is known to depend on the type of materials and the number and stacking sequence of the constituent layers. Here we show that the thickness of a two-dimensional substrate can be crucial in modulating the light emission. We study the layer-dependent charge transfer in vertical heterostructures built from monolayer tungsten disulfide (WS2) on one- and two-layer epitaxial graphene, unravelling the effect that the interlayer electronic coupling has on the excitonic properties of such heterostructures. We bring evidence that the excitonic properties of WS2 can be effectively tuned by the number of supporting graphene layers. Integrating WS2 monolayers with two-layer graphene leads to a significant enhancement of the photoluminescence response, up to 1 order of magnitude higher compared to WS2 supported on one-layer graphene. Our findings highlight the importance of substrate engineering when constructing atomically thin-layered heterostructures. PMID:27434813

  14. Nonlinear dynamics of bi-layered graphene sheet, double-walled carbon nanotube and nanotube bundle

    NASA Astrophysics Data System (ADS)

    Gajbhiye, Sachin O.; Singh, S. P.

    2016-05-01

    Due to strong van der Waals (vdW) interactions, the graphene sheets and nanotubes stick to each other and form clusters of these corresponding nanostructures, viz. bi-layered graphene sheet (BLGS), double-walled carbon nanotube (DWCNT) and nanotube bundle (NB) or ropes. This research work is concerned with the study of nonlinear dynamics of BLGS, DWCNT and NB due to nonlinear interlayer vdW forces using multiscale atomistic finite element method. The energy between two adjacent carbon atoms is represented by the multibody interatomic Tersoff-Brenner potential, whereas the nonlinear interlayer vdW forces are represented by Lennard-Jones 6-12 potential function. The equivalent nonlinear material model of carbon-carbon bond is used to model it based on its force-deflection relation. Newmark's algorithm is used to solve the nonlinear matrix equation governing the motion of the BLGS, DWCNT and NB. An impulse and harmonic excitations are used to excite these nanostructures under cantilevered, bridged and clamped boundary conditions. The frequency responses of these nanostructures are computed, and the dominant resonant frequencies are identified. Along with the forced vibration of these structures, the eigenvalue extraction problem of armchair and zigzag NB is also considered. The natural frequencies and corresponding mode shapes are extracted for the different length and boundary conditions of the nanotube bundle.

  15. Inhomogeneous longitudinal distribution of Ni atoms on graphene induced by layer-number-dependent internal diffusion

    NASA Astrophysics Data System (ADS)

    Hasegawa, M.; Tashima, K.; Kotsugi, M.; Ohkochi, T.; Suemitsu, M.; Fukidome, H.

    2016-09-01

    The intrinsic transport properties, such as carrier mobility and saturation velocity, of graphene are the highest among materials owing to its linear band dispersion and weak backscattering. However, the reported field-effect mobility of transistors using graphene as a channel is much lower than the intrinsic channel mobility. One of the reasons for this low mobility is the high contact resistance between graphene and metals used for the source and drain electrodes, which results from the interfacial roughness. Even Ni, which is a promising contact metal for many materials because of its high adhesion and lower contact resistance, does not meet the requirement as a contact metal for graphene. Noticing that the interfacial roughness between the a metal and graphene is strongly related to the onset of the contact resistance, we performed transmission electron microscopy and photoemission electron microscopy measurements to evaluate the microscopic lateral and longitudinal distributions of Ni atoms at the Ni/graphene interface formed on epitaxial graphene (EG) on 4H-SiC(0001). Our data revealed that the deposited Ni atoms diffused into the EG layers, but they did not reach the EG/SiC interface, and the diffusion was stronger on bilayered graphene than on monolayered graphene. We thus ascribe the layer-number-dependent internal diffusion of Ni atoms in EG as a cause of the microscopic interfacial roughness between graphene and the metal. Ensuring homogeneous distribution of the number of EG layers should be key to lowering the contact resistance.

  16. Direct Synthesis of Few-Layer Graphene on NaCl Crystals.

    PubMed

    Shi, Liurong; Chen, Ke; Du, Ran; Bachmatiuk, Alicja; Rümmeli, Mark Hermann; Priydarshi, Manish Kumar; Zhang, Yanfeng; Manivannan, Ayyakkannu; Liu, Zhongfan

    2015-12-16

    Chemical vapor deposition is used to synthesize few-layer graphene on micro crystalline sodium chloride (NaCl) powder. The water-soluble nature of NaCl makes it convenient to produce free standing graphene layers via a facile and low-cost approach. Unlike traditional metal-catalyzed or oxygen-aided growth, the micron-size NaCl crystal planes play an important role in the nucleation and growth of few-layer graphene. Moreover, the possibility of synthesizing cuboidal graphene is also demonstrated in the present approach for the first time. Raman spectroscopy, optical microscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy are used to evaluate the quality and structure of the few-layer graphene along with cuboidal graphene obtained in this process. The few-layer graphene synthesized using the present method has an adsorption ability for anionic and cationic dye molecules in water. The present synthesis method may pave a facile way for manufacturing few-layer graphene on a large scale. PMID:26524105

  17. Graphene coated with controllable N-doped carbon layer by molecular layer deposition as electrode materials for supercapacitors

    NASA Astrophysics Data System (ADS)

    Chen, Yao; Gao, Zhe; Zhang, Bin; Zhao, Shichao; Qin, Yong

    2016-05-01

    In this work, graphene is coated with nitrogen-doped carbon layer, which is produced by a carbonization process of aromatic polyimide (PI) films deposited on the surfaces of graphene by molecular layer deposition (MLD). The utilization of MLD not only allows uniform coating of PI layers on the surfaces of pristine graphene without any surface treatment, but also enables homogenous dispersion of doped nitrogen atoms in the carbonized products. The as-prepared N-doped carbon layer coated graphene (NC-G) exhibited remarkable capacitance performance as electrode materials for supercapacitor, showing a high specific capacitance of 290.2 F g-1 at current density of 1 A g-1 in 6 M KOH aqueous electrolyte, meanwhile maintaining good rate performance and stable cycle capability. The NC-G synthesized by this way represents an alternative promising candidate as electrode material for supercapacitors.

  18. Electron dynamics of the buffer layer and bilayer graphene on SiC

    NASA Astrophysics Data System (ADS)

    Shearer, Alex J.; Johns, James E.; Caplins, Benjamin W.; Suich, David E.; Hersam, Mark C.; Harris, Charles B.

    2014-06-01

    Angle- and time-resolved two-photon photoemission (TPPE) was used to investigate electronic states in the buffer layer of 4H-SiC(0001). An image potential state (IPS) series was observed on this strongly surface-bound buffer layer, and dispersion measurements indicated free-electron-like behavior for all states in this series. These results were compared with TPPE taken on bilayer graphene, which also show the existence of a free-electron-like IPS series. Lifetimes for the n = 2, and n = 3 states were obtained from time-resolved TPPE; slightly increased lifetimes were observed in the bilayer graphene sample for the n = 2 the n = 3 states. Despite the large band gap of graphene at the center of the Brillouin zone, the lifetime results demonstrate that the graphene layers do not behave as a simple tunneling barrier, suggesting that the buffer layer and graphene overlayers play a direct role in the decay of IPS electrons.

  19. Electrical Double Layer Capacitance in a Graphene-embedded Al2O3 Gate Dielectric

    PubMed Central

    Ki Min, Bok; Kim, Seong K.; Jun Kim, Seong; Ho Kim, Sung; Kang, Min-A; Park, Chong-Yun; Song, Wooseok; Myung, Sung; Lim, Jongsun; An, Ki-Seok

    2015-01-01

    Graphene heterostructures are of considerable interest as a new class of electronic devices with exceptional performance in a broad range of applications has been realized. Here, we propose a graphene-embedded Al2O3 gate dielectric with a relatively high dielectric constant of 15.5, which is about 2 times that of Al2O3, having a low leakage current with insertion of tri-layer graphene. In this system, the enhanced capacitance of the hybrid structure can be understood by the formation of a space charge layer at the graphene/Al2O3 interface. The electrical properties of the interface can be further explained by the electrical double layer (EDL) model dominated by the diffuse layer. PMID:26530817

  20. Enhanced ultra-low-frequency interlayer shear modes in folded graphene layers

    NASA Astrophysics Data System (ADS)

    Cong, Chunxiao; Yu, Ting

    2014-08-01

    Few-layer graphene has attracted tremendous attention owing to its exceptional electronic properties inherited from single-layer graphene and new features led by introducing extra freedoms such as interlayer stacking sequences or rotations. Effectively probing interlayer shear modes are critical for unravelling mechanical and electrical properties of few-layer graphene and further developing its practical potential. Unfortunately, shear modes are extremely weak and almost fully blocked by a Rayleigh rejecter in Raman measurements. This greatly hinders investigations of shear modes in few-layer graphene. Here, we demonstrate enhancing of shear modes by properly folding few-layer graphene. As a direct benefit of the strong signal, enhancement mechanism, vibrational symmetry, anharmonicity and electron-phonon coupling of the shear modes are uncovered through studies of Raman mapping, polarization- and temperature-dependent Raman spectroscopy. This work complements Raman studies of graphene layers, and paves an efficient way to exploit low-frequency shear modes of few-layer graphene and other two-dimensional layered materials.

  1. Spin and valley resolved Landau level crossing in tri-layer ABA stacked graphene

    NASA Astrophysics Data System (ADS)

    Datta, Biswajit; Gupta, Vishakha; Borah, Abhinandan; Watanabe, Kenji; Taniguchi, Takashi; Deshmukh, Mandar

    We present quantum Hall measurements on a high quality encapsulated tri-layer graphene device. Low temperature field effect mobility of this device is around 500,000 cm2/Vs and we see SdH oscillations at a magnetic field as low as 0.3 T. Quantum Hall measurements confirm that the chosen tri layer graphene is Bernal (ABA) stacked. Due to the presence of both mass-less monolayer like Dirac fermions and massive bi-layer like Dirac fermions in Bernal stacked tri-layer graphene, there are Landau level crossings between monolayer and bi-layer bands in quantum Hall regime. Although most of the Landau Level crossings are predominantly present on the electron sides, we also observe signatures of the crossings on the hole side. This behaviour is consistent with the asymmetry of electron and hole in ABA tri-layer graphene. We observe a series of crossings of the spin and valley resolved Landau Levels.

  2. Resistance and rupture analysis of single- and few-layer graphene nanosheets impacted by various projectiles

    NASA Astrophysics Data System (ADS)

    Sadeghzadeh, Sadegh; Liu, Ling

    2016-09-01

    In this paper, a quasi-classical model for the collision of various nanoparticles with single- and few-layer graphene nanosheets was introduced as a multi-scale approach that couples non-equilibrium molecular dynamics with the Finite Element Method. As a resistance criterion, it was observed that the coefficient of restitution and the induced stresses depend on the impact velocity of projectile. These parameters were evaluated computationally, and it was revealed that certain resulting behaviors differ from behaviors at the macro scale. By obtaining an out-of-plane yield stress limit of 1.0 TPa for graphene, the stress analysis of single- and multi-layer graphene sheets revealed that the limit projectile velocity needed for the yielding of graphene sheets increases with the increase in the number of layers. For aluminum nanoparticles, this increase is almost linear, and for other metals, it slightly deviates from the linear trend. It was also observed that the graphene sheets have a different rupture form when impacted by gaseous molecules than by metal particles. Considering the very high momentum of gas molecules and their shock-like behavior during high-speed collisions with a graphene sheet, pores with a size of one carbon atom can be created in graphene sheets. Since a single-layer graphene sheet can withstand a projectile which is 3.64 times larger than a projectile impacting a 20-layer graphene sheet, spaced graphene sheets seem to be more effective in absorbing the impact energy of projectiles than conventional few-layer graphene sheets.

  3. Observing the Heterogeneous Electro-redox of Individual Single-Layer Graphene Sheets.

    PubMed

    Chen, Tao; Zhang, Yuwei; Xu, Weilin

    2016-09-27

    Electro-redox-induced heterogeneous fluorescence of an individual single-layer graphene sheet was observed in real time by a total internal reflection fluorescence microscope. It was found that the fluorescence intensity of an individual sheet can be tuned reversibly by applying periodic voltages to control the redox degree of graphene sheets. Accordingly, the oxidation and reduction kinetics of an individual single-layer graphene sheet was studied at different voltages. The electro-redox-induced reversible variation of fluorescence intensity of individual sheets indicates a reversible band gap tuning strategy. Furthermore, correlation analysis of redox rate constants on individual graphene sheets revealed a redox-induced spatiotemporal heterogeneity or dynamics of graphene sheets. The observed controllable redox kinetics can rationally guide the precise band gap tuning of individual graphene sheets and then help their extensive applications in optoelectronics and devices for renewable energy.

  4. Selective growth of Pb islands on graphene/SiC buffer layers

    SciTech Connect

    Liu, X. T.; Miao, Y. P.; Ma, D. Y.; Hu, T. W.; Ma, F. E-mail: kwxu@mail.xjtu.edu.cn; Chu, Paul K.; Xu, K. W. E-mail: kwxu@mail.xjtu.edu.cn

    2015-02-14

    Graphene is fabricated by thermal decomposition of silicon carbide (SiC) and Pb islands are deposited by Pb flux in molecular beam epitaxy chamber. It is found that graphene domains and SiC buffer layer coexist. Selective growth of Pb islands on SiC buffer layer rather than on graphene domains is observed. It can be ascribed to the higher adsorption energy of Pb atoms on the 6√(3) reconstruction of SiC. However, once Pb islands nucleate on graphene domains, they will grow very large owing to the lower diffusion barrier of Pb atoms on graphene. The results are consistent with first-principle calculations. Since Pb atoms on graphene are nearly free-standing, Pb islands grow in even-number mode.

  5. Robust adhesion of flower-like few-layer graphene nanoclusters.

    PubMed

    Tian, Shibing; Li, Lin; Sun, Wangning; Xia, Xiaoxiang; Han, Dong; Li, Junjie; Gu, Changzhi

    2012-01-01

    Nanostructured surface possessing ultrahigh adhesion like "gecko foot" or "rose petal" can offer more opportunities for bionic application. We grow flower-like few-layer graphene on silicon nanocone arrays to form graphene nanoclusters, showing robust adhesion. Their contact angle (CA) is 164° with a hysteresis CA of 155° and adhesive force for a 5 μL water droplet is about 254 μN that is far larger than present reported results. We bring experimental evidences that this great adhesion depends on large-area plentiful edges of graphene nanosheets tuned by conical nanostructure and intrinsic wetting features of graphene. Such new hierarchical few-layer graphene nanostructure provides a feasible strategy to understand the ultra-adhesive mechanism of the "gecko effect" or "rose effect" and enhance the wettability of graphene for many practical applications.

  6. Multi-layer graphene on Co(0001) by ethanol chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Kazi, H.; Cao, Y.; Tanabe, I.; Driver, M. S.; Dowben, P. A.; Kelber, J. A.

    2014-09-01

    N layer (1 ⩽ N ⩽ 10) monolayer films of graphene were formed by the chemical vapor deposition of ethanol on either clean or oxidized Co(0001) substrates at 1000 K, with no evidence of either interfacial oxide formation or graphene/substrate charge transfer. Low energy electron diffraction data indicate that the graphene layers or domains are azimuthally rotated, but otherwise show the characteristics of graphene with a Raman spectra D/G intensity ratio of 0.25 or less, and a C 1s binding energy of 284.5 eV with an observable π → π* transition. Magneto optic Kerr effect spectra indicate only the ferromagnetic hysteresis with high remanence, with no evidence of Co/graphene exchange bias. This is very different from the negligible remanent magnetization of graphene/Co3O4/Co trilayer structures.

  7. Few-layer graphene characterization by near-field scanning microwave microscopy.

    PubMed

    Talanov, Vladimir V; Del Barga, Christopher; Wickey, Lee; Kalichava, Irakli; Gonzales, Edward; Shaner, Eric A; Gin, Aaron V; Kalugin, Nikolai G

    2010-07-27

    Near-field scanning microwave microscopy is employed for quantitative imaging at 4 GHz of the local impedance for monolayer and few-layer graphene. The microwave response of graphene is found to be thickness dependent and determined by the local sheet resistance of the graphene flake. Calibration of the measurement system and knowledge of the probe geometry allows evaluation of the AC impedance for monolayer and few-layer graphene, which is found to be predominantly active. The use of localized evanescent electromagnetic field in our experiment provides a promising tool for investigations of plasma waves in graphene with wave numbers determined by the spatial spectrum of the near-field. By using near-field microwave microscopy one can perform simultaneous imaging of location, geometry, thickness, and distribution of electrical properties of graphene without a need for device fabrication. PMID:20536187

  8. Robust adhesion of flower-like few-layer graphene nanoclusters

    NASA Astrophysics Data System (ADS)

    Tian, Shibing; Li, Lin; Sun, Wangning; Xia, Xiaoxiang; Han, Dong; Li, Junjie; Gu, Changzhi

    2012-07-01

    Nanostructured surface possessing ultrahigh adhesion like ``gecko foot'' or ``rose petal'' can offer more opportunities for bionic application. We grow flower-like few-layer graphene on silicon nanocone arrays to form graphene nanoclusters, showing robust adhesion. Their contact angle (CA) is 164° with a hysteresis CA of 155° and adhesive force for a 5 μL water droplet is about 254 μN that is far larger than present reported results. We bring experimental evidences that this great adhesion depends on large-area plentiful edges of graphene nanosheets tuned by conical nanostructure and intrinsic wetting features of graphene. Such new hierarchical few-layer graphene nanostructure provides a feasible strategy to understand the ultra-adhesive mechanism of the ``gecko effect'' or ``rose effect'' and enhance the wettability of graphene for many practical applications.

  9. Thermoacoustic and photoacoustic characterizations of few-layer graphene by pulsed excitations

    NASA Astrophysics Data System (ADS)

    Wang, Xiong; Witte, Russell S.; Xin, Hao

    2016-04-01

    We characterized the thermoacoustic and photoacoustic properties of large-area, few-layer graphene by pulsed microwave and optical excitations. Due to its high electric conductivity and low heat capacity per unit area, graphene lends itself to excellent microwave and optical energy absorption and acoustic signal emanation due to the thermoacoustic effect. When exposed to pulsed microwave or optical radiation, distinct thermoacoustic and photoacoustic signals generated by the few-layer graphene are obtained due to microwave and laser absorption of the graphene, respectively. Clear thermoacoustic and photoacoustic images of large-area graphene sample are achieved. A numerical model is developed and the simulated results are in good accordance with the measured ones. This characterization work may find applications in ultrasound generator and detectors for microwave and optical radiation. It may also become an alternative characterization approach for graphene and other types of two-dimensional materials.

  10. Graphene-silicon layered structures on single-crystalline Ir(111) thin films

    SciTech Connect

    Que, Yande D.; Tao, Jing; Zhang, Yong; Wang, Yeliang L.; Wu, Lijun J.; Zhu, Yimei M.; Kim, Kisslinger; Weinl, Michael; Schreck, Matthias; Shen, Chengmin M.; Du, Shixuan X.; Liu, Yunqi Q.; Gao, H. -J.; Huang, Li; Xu, Wenyan Y.

    2015-01-20

    Epitaxial growth of graphene on transition metal crystals, such as Ru,⁽¹⁻³⁾ Ir,⁽⁴⁻⁶⁾ and Ni,⁽⁷⁾ provides large-area, uniform graphene layers with controllable defect density, which is crucial for practical applications in future devices. To decrease the high cost of single-crystalline metal bulks, single-crystalline metal films are strongly suggested as the substrates for epitaxial growth large-scale high-quality graphene.⁽⁸⁻¹⁰⁾ Moreover, in order to weaken the interactions of graphene with its metal host, which may result in a suppression of the intrinsic properties of graphene,⁽¹¹ ¹²⁾ the method of element intercalation of semiconductors at the interface between an epitaxial graphene layer and a transition metal substrate has been successfully realized.⁽¹³⁻¹⁶⁾

  11. Graphene-silicon layered structures on single-crystalline Ir(111) thin films

    DOE PAGES

    Que, Yande D.; Tao, Jing; Zhang, Yong; Wang, Yeliang L.; Wu, Lijun J.; Zhu, Yimei M.; Kim, Kisslinger; Weinl, Michael; Schreck, Matthias; Shen, Chengmin M.; et al

    2015-01-20

    Epitaxial growth of graphene on transition metal crystals, such as Ru,⁽¹⁻³⁾ Ir,⁽⁴⁻⁶⁾ and Ni,⁽⁷⁾ provides large-area, uniform graphene layers with controllable defect density, which is crucial for practical applications in future devices. To decrease the high cost of single-crystalline metal bulks, single-crystalline metal films are strongly suggested as the substrates for epitaxial growth large-scale high-quality graphene.⁽⁸⁻¹⁰⁾ Moreover, in order to weaken the interactions of graphene with its metal host, which may result in a suppression of the intrinsic properties of graphene,⁽¹¹ ¹²⁾ the method of element intercalation of semiconductors at the interface between an epitaxial graphene layer and a transitionmore » metal substrate has been successfully realized.⁽¹³⁻¹⁶⁾« less

  12. Observing the Heterogeneous Electro-redox of Individual Single-Layer Graphene Sheets.

    PubMed

    Chen, Tao; Zhang, Yuwei; Xu, Weilin

    2016-09-27

    Electro-redox-induced heterogeneous fluorescence of an individual single-layer graphene sheet was observed in real time by a total internal reflection fluorescence microscope. It was found that the fluorescence intensity of an individual sheet can be tuned reversibly by applying periodic voltages to control the redox degree of graphene sheets. Accordingly, the oxidation and reduction kinetics of an individual single-layer graphene sheet was studied at different voltages. The electro-redox-induced reversible variation of fluorescence intensity of individual sheets indicates a reversible band gap tuning strategy. Furthermore, correlation analysis of redox rate constants on individual graphene sheets revealed a redox-induced spatiotemporal heterogeneity or dynamics of graphene sheets. The observed controllable redox kinetics can rationally guide the precise band gap tuning of individual graphene sheets and then help their extensive applications in optoelectronics and devices for renewable energy. PMID:27552441

  13. Imaging layer number and stacking order through formulating Raman fingerprints obtained from hexagonal single crystals of few layer graphene

    NASA Astrophysics Data System (ADS)

    Hwang, Jih-Shang; Lin, Yu-Hsiang; Hwang, Jeong-Yuan; Chang, Railing; Chattopadhyay, Surojit; Chen, Chang-Jiang; Chen, Peilin; Chiang, Hai-Pang; Tsai, Tsong-Ru; Chen, Li-Chyong; Chen, Kuei-Hsien

    2013-01-01

    Quantitative mapping of layer number and stacking order for CVD-grown graphene layers is realized by formulating Raman fingerprints obtained on two stepwise stacked graphene single-crystal domains with AB Bernal and turbostratic stacking (with ˜30°interlayer rotation), respectively. The integrated peak area ratio of the G band to the Si band, AG/ASi, is proven to be a good fingerprint for layer number determination, while the area ratio of the 2D and G bands, A2D/AG, is shown to differentiate effectively between the two different stacking orders. The two fingerprints are well formulated and resolve, quantitatively, the layer number and stacking type of various graphene domains that used to rely on tedious transmission electron microscopy for structural analysis. The approach is also noticeable in easy discrimination of the turbostratic graphene region (˜30° rotation), the structure of which resembles the well known high-mobility graphene R30/R2± fault pairs found on the vacuum-annealed C-face SiC and suggests an electron mobility reaching 14 700 cm3 V-1 s-1. The methodology may shed light on monitoring and control of high-quality graphene growth, and thereby facilitate future mass production of potential high-speed graphene applications.

  14. Layer-by-layer assembly of functionalized reduced graphene oxide for direct electrochemistry and glucose detection.

    PubMed

    Mascagni, Daniela Branco Tavares; Miyazaki, Celina Massumi; da Cruz, Nilson Cristino; de Moraes, Marli Leite; Riul, Antonio; Ferreira, Marystela

    2016-11-01

    We report an electrochemical glucose biosensor made with layer-by-layer (LbL) films of functionalized reduced graphene oxide (rGO) and glucose oxidase (GOx). The LbL assembly using positively and negatively charged rGO multilayers represents a simple approach to develop enzymatic biosensors. The electron transport properties of graphene were combined with the specificity provided by the enzyme. rGO was obtained and functionalized using chemical methods, being positively charged with poly(diallyldimethylammonium chloride) to form GPDDA, and negatively charged with poly(styrene sulfonate) to form GPSS. Stable aqueous dispersions of GPDDA and GPSS are easily obtained, enabling the growth of LbL films on various solid supports. The use of graphene in the immobilization of GOx promoted Direct Electron Transfer, which was evaluated by Cyclic Voltammetry. Amperometric measurements indicated a detection limit of 13.4μmol·L(-1) and sensitivity of 2.47μA·cm(-2)·mmol(-1)·L for glucose with the (GPDDA/GPSS)1/(GPDDA/GOx)2 architecture, whose thickness was 19.80±0.28nm, as determined by Surface Plasmon Resonance (SPR). The sensor may be useful for clinical analysis since glucose could be detected even in the presence of typical interfering agents and in real samples of a lactose-free milk and an electrolyte solution to prevent dehydration. PMID:27524075

  15. Sprayable, Paintable Layer-by-Layer Polyaniline Nanofiber/Graphene Electrodes for Electrochemical Energy Storage

    NASA Astrophysics Data System (ADS)

    Kwon, Se Ra; Jeon, Ju-Won; Lutkenhus, Jodie

    2015-03-01

    Sprayable batteries are growing in interest for applications in structural energy storage and power or flexible power. Spray-assisted layer-by-layer (LbL) assembly, in which complementary species are alternately sprayed onto a surface, is particularly amenable toward this application. Here, we report on the fabrication of composite films containing polyaniline nanofibers (PANI NF) and graphene oxide (GO) sheets fabricated via spray-assisted LbL assembly. The resulting films are electrochemical reduced to yield PANI NF/electrochemically reduced graphene (ERGO) electrodes for use as a cathode in non-aqueous energy storage systems. Through the spray-assisted LbL process, the hybrid electrodes could be fabricated 74 times faster than competing dip-assisted LbL assembly. The resulting electrodes are highly porous (0.72 void fraction), and are comprised of 67 wt% PANI NF and 33 wt% ERGO. The sprayed electrodes showed better rate capability, higher specific power, as well as more stable cycle life than dip-assisted LbL electrodes. It is shown here that the spray-assisted LbL approach is well-suited towards the fabrication of paintable electrodes containing polyaniline nanofibers and electrochemically reduced graphene oxide sheets.

  16. Highly ordered ultralong magnetic nanowires wrapped in stacked graphene layers

    PubMed Central

    El Mel, Abdel-Aziz; Duvail, Jean-Luc; Gautron, Eric; Xu, Wei; Choi, Chang-Hwan; Angleraud, Benoit; Granier, Agnès

    2012-01-01

    Summary We report on the synthesis and magnetic characterization of ultralong (1 cm) arrays of highly ordered coaxial nanowires with nickel cores and graphene stacking shells (also known as metal-filled carbon nanotubes). Carbon-containing nickel nanowires are first grown on a nanograted surface by magnetron sputtering. Then, a post-annealing treatment favors the metal-catalyzed crystallization of carbon into stacked graphene layers rolled around the nickel cores. The observed uniaxial magnetic anisotropy field oriented along the nanowire axis is an indication that the shape anisotropy dominates the dipolar coupling between the wires. We further show that the thermal treatment induces a decrease in the coercivity of the nanowire arrays. This reflects an enhancement of the quality of the nickel nanowires after annealing attributed to a decrease of the roughness of the nickel surface and to a reduction of the defect density. This new type of graphene–ferromagnetic-metal nanowire appears to be an interesting building block for spintronic applications. PMID:23365798

  17. Large scale atomistic simulation of single-layer graphene growth on Ni(111) surface: molecular dynamics simulation based on a new generation of carbon-metal potential

    NASA Astrophysics Data System (ADS)

    Xu, Ziwei; Yan, Tianying; Liu, Guiwu; Qiao, Guanjun; Ding, Feng

    2015-12-01

    To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results.To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are

  18. Synthesis of layer-tunable graphene: A combined kinetic implantation and thermal ejection approach

    SciTech Connect

    Wang, Gang; Zhang, Miao; Liu, Su; Xie, Xiaoming; Ding, Guqiao; Wang, Yongqiang; Chu, Paul K.; Gao, Heng; Ren, Wei; Yuan, Qinghong; Zhang, Peihong; Wang, Xi; Di, Zengfeng

    2015-05-04

    Layer-tunable graphene has attracted broad interest for its potentials in nanoelectronics applications. However, synthesis of layer-tunable graphene by using traditional chemical vapor deposition (CVD) method still remains a great challenge due to the complex experimental parameters and the carbon precipitation process. Herein, by performing ion implantation into a Ni/Cu bilayer substrate, the number of graphene layers, especially single or double layer, can be controlled precisely by adjusting the carbon ion implant fluence. The growth mechanism of the layer-tunable graphene is revealed by monitoring the growth process is observed that the entire implanted carbon atoms can be expelled towards the substrate surface and thus graphene with designed layer number can be obtained. Such a growth mechanism is further confirmed by theoretical calculations. The proposed approach for the synthesis of layer-tunable graphene offers more flexibility in the experimental conditions. Being a core technology in microelectronics processing, ion implantation can be readily implemented in production lines and is expected to expedite the application of graphene to nanoelectronics.

  19. Synthesis of layer-tunable graphene: A combined kinetic implantation and thermal ejection approach

    DOE PAGES

    Wang, Gang; Zhang, Miao; Liu, Su; Xie, Xiaoming; Ding, Guqiao; Wang, Yongqiang; Chu, Paul K.; Gao, Heng; Ren, Wei; Yuan, Qinghong; et al

    2015-05-04

    Layer-tunable graphene has attracted broad interest for its potentials in nanoelectronics applications. However, synthesis of layer-tunable graphene by using traditional chemical vapor deposition (CVD) method still remains a great challenge due to the complex experimental parameters and the carbon precipitation process. Herein, by performing ion implantation into a Ni/Cu bilayer substrate, the number of graphene layers, especially single or double layer, can be controlled precisely by adjusting the carbon ion implant fluence. The growth mechanism of the layer-tunable graphene is revealed by monitoring the growth process is observed that the entire implanted carbon atoms can be expelled towards the substratemore » surface and thus graphene with designed layer number can be obtained. Such a growth mechanism is further confirmed by theoretical calculations. The proposed approach for the synthesis of layer-tunable graphene offers more flexibility in the experimental conditions. Being a core technology in microelectronics processing, ion implantation can be readily implemented in production lines and is expected to expedite the application of graphene to nanoelectronics.« less

  20. Numerical simulation of multi-layer graphene structures based on quantum-chemical model

    NASA Astrophysics Data System (ADS)

    Kasper, Y.; Tuchin, A.; Bokova, A.; Bityutskaya, L.

    2016-08-01

    The electronic structure of the multi-layer graphene has been studied using the density functional theory (DFT). The dependence of the average interlayer distance on the number of layers (n = 2 ÷ 6) has been determined. The analysis of the charge redistribution and the electron density of the bi- and three-layer graphene under the external pressure up to 50 GPa has been performed. The model of the interlayer conductivity of compressed multigraphene was offered

  1. Room temperature broadband terahertz gains in graphene heterostructures based on inter-layer radiative transitions

    SciTech Connect

    Tang, Linlong; Du, Jinglei; Shi, Haofei Wei, Dongshan; Du, Chunlei

    2014-10-15

    We exploit inter-layer radiative transitions to provide gains to amplify terahertz waves in graphene heterostructures. This is achieved by properly doping graphene sheets and aligning their energy bands so that the processes of stimulated emissions can overwhelm absorptions. We derive an expression for the gain estimation and show the gain is insensitive to temperature variation. Moreover, the gain is broadband and can be strong enough to compensate the free carrier loss, indicating graphene based room temperature terahertz lasers are feasible.

  2. Multi-layer graphene membrane based memory cell

    NASA Astrophysics Data System (ADS)

    Siahlo, Andrei I.; Popov, Andrey M.; Poklonski, Nikolai A.; Lozovik, Yurii E.; Vyrko, Sergey A.; Ratkevich, Sergey V.

    2016-10-01

    The scheme and operational principles of the nanoelectromechanical memory cell based on the bending of a multi-layer graphene membrane by the electrostatic force are proposed. An analysis of the memory cell total energy as a function of the memory cell sizes is used to determine the sizes corresponding to a bistable memory cell with the conducting ON and non-conducting OFF states and to calculate the switching voltage between the OFF and ON states. It is shown that a potential barrier between the OFF and ON states is huge for practically all sizes of a bistable memory cell which excludes spontaneous switching and allows the proposed memory cell to be used for long-term archival storage.

  3. Graphene Layer Growth Chemistry: Five-Six-Ring Flip Reaction

    SciTech Connect

    Whitesides, Russell; Domin, Dominik; Lester Jr., William A.; Frenklach, Michael

    2007-03-24

    A theoretical study revealed a new reaction pathway, in which a fused five and six-membered ring complex on the zigzag edge of a graphene layer isomerizes to reverse its orientation, or 'flips,' after activation by a gaseous hydrogen atom. The process is initiated by hydrogen addition to or abstraction from the surface complex. The elementary steps of the migration pathway were analyzed using density-functional theory (DFT) calculations to examine the region of the potential energy surface associated with the pathway. The DFT calculations were performed on substrates modeled by the zigzag edges of tetracene and pentacene. Rate constants for the flip reaction were obtained by the solution of energy master equation utilizing the DFT energies, frequencies, and geometries. The results indicate that this reaction pathway is competitive with other pathways important to the edge evolution of aromatic species in high temperature environments.

  4. Electrochemically Produced Graphene for Microporous Layers in Fuel Cells.

    PubMed

    Najafabadi, Amin Taheri; Leeuwner, Magrieta J; Wilkinson, David P; Gyenge, Előd L

    2016-07-01

    The microporous layer (MPL) is a key cathodic component in proton exchange membrane fuel cells owing to its beneficial influence on two-phase mass transfer. However, its performance is highly dependent on material properties such as morphology, porous structure, and electrical resistance. To improve water management and performance, electrochemically exfoliated graphene (EGN) microsheets are considered as an alternative to the conventional carbon black (CB) MPLs. The EGN-based MPLs decrease the kinetic overpotential and the Ohmic potential loss, whereas the addition of CB to form a composite EGN+CB MPL improves the mass-transport limiting current density drastically. This is reflected by increases of approximately 30 and 70 % in peak power densities at 100 % relative humidity (RH) compared with those for CB- and EGN-only MPLs, respectively. The composite EGN+CB MPL also retains the superior performance at a cathode RH of 20 %, whereas the CB MPL shows significant performance loss. PMID:27254459

  5. 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. PMID:27064575

  6. 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.

  7. 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

  8. Facile Large Scale Production of Few-Layer Graphene Sheets by Shear Exfoliation in Volatile Solvent.

    PubMed

    Akhtar, M Wasim; Park, Chan Woo; Kim, Youn Sop; Kim, Jong Seok

    2015-12-01

    Few layer graphene sheets were synthesized from natural graphite through mechanical shear mixer in 1-butanol as solvent. The liquid phase exfoliation of graphite through the shear mixer generated incising forces for 20 minutes which changed the large amount of graphite's flake into few layer graphene. The removal of solvent from the deposited dispersion was performed immediately by keeping at the room temperature. The deposited graphene thin films were characterized by AFM, HR-TEM, XRD, FT-IR and Raman Spectroscopy. The HR-TEM results showed the formation of few layers and well dispersed graphene. The Raman spectroscopy and XRD characterization confirmed the good quality and non-oxidized state of graphene. PMID:26682388

  9. Direct Growth Properties of Graphene Layers on Sapphire Substrate by Alcohol-Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Nakamura, Atsushi; Miyasaka, Yuta; Temmyo, Jiro

    2012-04-01

    Few nanometers thick graphene layers were directly grown on a-plane (11bar 20) sapphire substrates by alcohol-chemical vapor deposition (alcohol-CVD) using ethanol as a carbon source and without any catalytic metal on the substrate surface. The growth relationship between the graphene layer and substrate was analyzed using a transmission electron microscope (TEM). The growth rate of graphene layers with different growth temperatures revealed that the Al atom act as a catalyst for synthesizing a graphitic material during the decomposition of ethanol. An optical transmittance and a sheet resistance of the graphene sheet directly grown on sapphire substrate were observed. SiO2/Si and n-6H-SiC substrates were also examined for graphene direct growth to discuss the catalytic behavior of Si atoms compared with Al atoms.

  10. Raman Scattering from few-layer Graphene Films

    NASA Astrophysics Data System (ADS)

    Gupta, A.; Joshi, P.; Srinivas, T.; Eklund, Peter

    2006-03-01

    Few layer-graphene sheet (nGL's) films, where n is the number of graphene layers, are new two-dimensional sp^2 carbon systems that have been shown to produce exciting Fractional Quantum Hall phenomena. We report here on the first Raman scattering (RS) results of nGLs. nGLs with lateral dimensions of ˜1-3 μm were prepared by chemical delamination of graphite flake or HOPG and then transferred from solution onto substrates (mica, pyrex,In/pyrex and Au/pyrex). RS spectra have been collected on nGL's with n=1, 2, 3 and compared with the graphite. Graphite exhibits two E2g interlayer modes at 42 cm-1 and 1582 cm-1. The Raman spectra of (n=1-3) nGLs were found to exhibit peaks at 1350 cm-1 and 1620 cm-1, i.e., near frequencies associated with high phonon density of states. The high frequency E2g band is found to split into two bands when the nGL is supported on metallic substrates (In,Au). In both these cases, we observe bands at 1583 cm-1, ˜1592 cm-1 rather than one band at 1581 cm-1 when the nGL is on insulating pyrex. The splitting of the interlayer band when on metallic substrates is identified with charge transfer between the nGL and the substrate. The phonon density of states scattering observed does not appear to be due to disorder in the basal plane.

  11. Design of graphene sheets-supported Pt catalyst layer in PEM fuel cells

    SciTech Connect

    Park, Seh K.; Shao, Yuyan; Wan, Haiying; Rieke, Peter C.; Viswanathan, Vilayanur V.; Towne, Silas A.; Saraf, Laxmikant V.; Liu, Jun; Lin, Yuehe; Wang, Yong

    2011-03-01

    A series of cathodes using Pt supported onto graphene sheets with different contents of carbon black in the catalyst layer were prepared and characterized. Carbon black was added as a spacer between two-dimensional graphene sheets in the catalyst layer to study its effect on the performances of proton exchange membrane fuel cell. Electrochemical properties and surface morphology of the cathodes with and without carbon black were characterized using cyclic voltammetry, ac-impedance spectroscopy, electrochemical polarization technique, and scanning electron microscopy. The results indicated that carbon black effectively modifies the array of graphene supports, resulting in more Pt nanoparticles available for electrochemical reaction and better mass transport in the catalyst layer.

  12. Electronic band structure imaging of three layer twisted graphene on single crystal Cu(111)

    SciTech Connect

    Marquez Velasco, J.; Kelaidis, N.; Xenogiannopoulou, E.; Tsoutsou, D.; Tsipas, P.; Speliotis, Th.; Pilatos, G.; Likodimos, V.; Falaras, P.; Dimoulas, A.; Raptis, Y. S.

    2013-11-18

    Few layer graphene (FLG) is grown on single crystal Cu(111) by Chemical Vapor Deposition, and the electronic valence band structure is imaged by Angle-Resolved Photo-Emission Spectroscopy. It is found that graphene essentially grows polycrystalline. Three nearly ideal Dirac cones are observed along the Cu Γ{sup ¯}K{sup ¯} direction in k-space, attributed to the presence of ∼4° twisted three layer graphene with negligible interlayer coupling. The number of layers and the stacking order are compatible with Raman data analysis demonstrating the complementarity of the two techniques for a more accurate characterization of FLG.

  13. Contribution of Dielectric Screening to the Total Capacitance of Few-Layer Graphene Electrodes.

    PubMed

    Zhan, Cheng; Jiang, De-en

    2016-03-01

    We apply joint density functional theory (JDFT), which treats the electrode/electrolyte interface self-consistently, to an electric double-layer capacitor (EDLC) based on few-layer graphene electrodes. The JDFT approach allows us to quantify a third contribution to the total capacitance beyond quantum capacitance (CQ) and EDL capacitance (CEDL). This contribution arises from the dielectric screening of the electric field by the surface of the few-layer graphene electrode, and we therefore term it the dielectric capacitance (CDielec). We find that CDielec becomes significant in affecting the total capacitance when the number of graphene layers in the electrode is more than three. Our investigation sheds new light on the significance of the electrode dielectric screening on the capacitance of few-layer graphene electrodes. PMID:26884129

  14. Contribution of dielectric screening to the total capacitance of few-layer graphene electrodes

    DOE PAGES

    Zhan, Cheng; Jiang, De-en

    2016-02-17

    We apply joint density functional theory (JDFT), which treats the electrode/electrolyte interface self-consistently, to an electric double-layer capacitor (EDLC) based on few-layer graphene electrodes. The JDFT approach allows us to quantify a third contribution to the total capacitance beyond quantum capacitance (CQ) and EDL capacitance (CEDL). This contribution arises from the dielectric screening of the electric field by the surface of the few-layer graphene electrode, and we therefore term it the dielectric capacitance (CDielec). We find that CDielec becomes significant in affecting the total capacitance when the number of graphene layers in the electrode is more than three. In conclusion,more » our investigation sheds new light on the significance of the electrode dielectric screening on the capacitance of few-layer graphene electrodes.« less

  15. Synthesis of few layer graphene by non-transferred arc plasma system.

    PubMed

    Baek, Jong-Jun; Kim, Tae-Hee; Park, Dong-Wha

    2013-11-01

    Graphene has recently been the focus of a great deal of attention owing to its outstanding properties, which include high mobility, high thermal conductivity and high structural stability. In this study, a few layer graphene was successfully synthesized from methane gas using a non-transferred direct current arc plasma system. Non-transferred thermal plasma offers high temperature, steep temperature gradient and high enthalpy to enhance the reaction kinetics of graphene synthesis. In order to prepare high quality few layer graphene, graphene products synthesized under several conditions was analyzed comparatively. Effects of gap distance between the plasma torch and graphite substrate, the flow rate of additional reactant gas, and different types of plasma forming gas on the synthesis of few layer graphene were investigated. Methane gas was injected into the plasma jet as a carbon source for the synthesis of graphene and a thermal plasma jet was generated by pure argon or a mixture of argon-hydrogen. The results revealed that hydrogen gas improved the quality of few layer graphene by inducing surface etching and increasing plasma power. PMID:24245266

  16. Synthesis of few layer graphene by non-transferred arc plasma system.

    PubMed

    Baek, Jong-Jun; Kim, Tae-Hee; Park, Dong-Wha

    2013-11-01

    Graphene has recently been the focus of a great deal of attention owing to its outstanding properties, which include high mobility, high thermal conductivity and high structural stability. In this study, a few layer graphene was successfully synthesized from methane gas using a non-transferred direct current arc plasma system. Non-transferred thermal plasma offers high temperature, steep temperature gradient and high enthalpy to enhance the reaction kinetics of graphene synthesis. In order to prepare high quality few layer graphene, graphene products synthesized under several conditions was analyzed comparatively. Effects of gap distance between the plasma torch and graphite substrate, the flow rate of additional reactant gas, and different types of plasma forming gas on the synthesis of few layer graphene were investigated. Methane gas was injected into the plasma jet as a carbon source for the synthesis of graphene and a thermal plasma jet was generated by pure argon or a mixture of argon-hydrogen. The results revealed that hydrogen gas improved the quality of few layer graphene by inducing surface etching and increasing plasma power.

  17. A theoretical study of symmetry-breaking organic overlayers on single- and bi-layer graphene

    NASA Astrophysics Data System (ADS)

    Morales-Cifuentes, Josue; Einstein, T. L.

    2013-03-01

    An ``overlayer'' of molecules that breaks the AB symmetry of graphene can produce (modify) a band gap in single- (bi-) layer graphene.[2] Since the triangular shaped trimesic acid (TMA) molecule forms two familiar symmetry breaking configurations, we are motivated to model TMA physisorption on graphene surfaces in conjunction with experiments by Groce et al. at UMD. Using VASP, with ab initio van der Waals density functionals (vdW-DF), we simulate adsorption of TMA onto a graphene surface in several symmetry-breaking arrangements in order to predict/understand the effect of TMA adsorption on experimental observables. Supported by NSF-MRSEC Grant DMR 05-20471.

  18. Structural Analysis and Direct Imaging of Rotational Stacking Faults in Few-Layer Graphene Synthesized from Solid Botanical Precursor

    NASA Astrophysics Data System (ADS)

    Kalita, Golap; Wakita, Koichi; Umeno, Masayoshi

    2011-07-01

    Here, we report the structural analysis and rotational stacking faults of few-layer graphene sheets derived by the controlled pyrolysis of the solid botanical derivative camphor (C10H16O). The second-order Raman spectra of the sheets show that the graphene layers are more than one single layer, and the numbers of layers can be controlled by adjusting the amount of camphor pyrolyzed. Transmission electron microscopy images show a minimum of 3 layers for thinner graphene sheets and a maximum of 12 layers for thicker graphene sheets. Low-voltage aberration-corrected high-resolution transmission electron microscopy is also carried out to gain insight into the hexagonal structure and stacking of graphene layers. The transmission electron microscopy study showed the presence of moiré patterns with a relative rotation between graphene layers.

  19. Designed nitrogen doping of few-layer graphene functionalized by selective oxygenic groups

    PubMed Central

    2014-01-01

    Few-layer nitrogen doped graphene was synthesized originating from graphene oxide functionalized by selective oxygenic functional groups (hydroxyl, carbonyl, carboxyl etc.) under hydrothermal conditions, respectively. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observation evidenced few-layer feature of the graphene oxide. X-ray diffraction (XRD) pattern confirmed phase structure of the graphene oxide and reduced graphene oxide. Nitrogen doping content and bonding configuration of the graphene was determined by X-ray photoelectron spectroscopy (XPS), which indicated that different oxygenic functional groups were evidently different in affecting the nitrogen doping process. Compared with other oxygenic groups, carboxyl group played a crucial role in the initial stage of nitrogen doping while hydroxyls exhibited more evident contribution to the doping process in the late stage of the reaction. Formation of graphitic-like nitrogen species was controlled by a synergistic effect of the involved oxygenic groups (e.g., -COOH, -OH, C-O-C, etc.). The doping mechanism of nitrogen in the graphene was scrutinized. The research in this work may not only contribute to the fundamental understandings of nitrogen doping within graphene but promote the development of producing novel graphene-based devices with designed surface functionalization. PMID:25520594

  20. Investigating change of properties in gallium ion irradiation patterned single-layer graphene

    NASA Astrophysics Data System (ADS)

    Wang, Quan; Dong, Jinyao; Bai, Bing; Xie, Guoxin

    2016-10-01

    Besides its excellent physical properties, graphene promises to play a significant role in electronics with superior properties, which requires patterning of graphene for device integration. Here, we presented the changes in properties of single-layer graphene before and after patterning using gallium ion beam. Combined with Raman spectra of graphene, the scanning capacitance microscopy (SCM) image confirmed that a metal-insulator transition occurred after large doses of gallium ion irradiation. The changes in work function and Raman spectra of graphene indicated that the defect density increased as increasing the dose and a structural transition occurred during gallium ion irradiation. The patterning width of graphene presented an increasing trend due to the scattering influence of the impurities and the substrate.

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    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.

  2. Synthesis of Few-Layer Graphene Using DC PE-CVD

    NASA Astrophysics Data System (ADS)

    Kim, Jeong Hyuk; Castro, Edward Joseph D.; Hwang, Yong Gyoo; Lee, Choong Hun

    2011-12-01

    Few layer graphene (FLG) had been successfully grown on polycrystalline Ni films or foils on a large scale using DC Plasma Enhanced Chemical Vapor Deposition (DC PE-CVD) as a result of the Raman spectra drawn out of the sample. The size of graphene films is dependent on the area of the Ni film as well as the DC PE-CVD chamber size. Synthesis time has an effect on the quality of graphene produced. However, further analysis and experiments must be pursued to further identify the optimum settings and conditions of producing better quality graphene. Applied plasma voltage on the other hand, had an influence on the minimization of defects in the graphene grown. It has also presented a method of producing a free standing PMMA/graphene membrane on a FeCl3(aq) solution which could then be transferred to a desired substrate.

  3. Design and comparative study of lateral and vertical LEDs with graphene as current spreading layer

    NASA Astrophysics Data System (ADS)

    Palakurthy, Shivani; Singh, Sumitra; Pal, Suchandan; Dhanavantri, Chenna

    2015-10-01

    This study analyzes the current spreading effect of graphene on lateral and vertical light emitting diodes (LEDs). We observe an improvement in uniformity of current distribution, light output power and wall-plug efficiency in lateral LEDs (L-LEDs) with graphene current spreading layer (CSL) as compared to those with indium tin oxide (ITO) CSL. From the results we conclude that graphene CSL may be better alternative to ITO CSL. We further carried out a comparative study of lateral and vertical LEDs with graphene CSL. We observe 17% higher light output power, 16% higher wall-plug efficiency and 62% lower series resistance in the case of V-LEDs with graphene CSL when compared to that of L-LEDs with a graphene CSL. Reasons behind these results have been discussed.

  4. AA stacking, tribological and electronic properties of double-layer graphene with krypton spacer.

    PubMed

    Popov, Andrey M; Lebedeva, Irina V; Knizhnik, Andrey A; Lozovik, Yurii E; Potapkin, Boris V; Poklonski, Nikolai A; Siahlo, Andrei I; Vyrko, Sergey A

    2013-10-21

    Structural, energetic, and tribological characteristics of double-layer graphene with commensurate and incommensurate krypton spacers of nearly monolayer coverage are studied within the van der Waals-corrected density functional theory. It is shown that when the spacer is in the commensurate phase, the graphene layers have the AA stacking. For this phase, the barriers to relative in-plane translational and rotational motion and the shear mode frequency of the graphene layers are calculated. For the incommensurate phase, both of the barriers are found to be negligibly small. A considerable change of tunneling conductance between the graphene layers separated by the commensurate krypton spacer at their relative subangstrom displacement is revealed by the use of the Bardeen method. The possibility of nanoelectromechanical systems based on the studied tribological and electronic properties of the considered heterostructures is discussed.

  5. Interactions between C and Cu atoms in single-layer graphene: direct observation and modelling.

    PubMed

    Kano, Emi; Hashimoto, Ayako; Kaneko, Tomoaki; Tajima, Nobuo; Ohno, Takahisa; Takeguchi, Masaki

    2016-01-01

    Metal doping into the graphene lattice has been studied recently to develop novel nanoelectronic devices and to gain an understanding of the catalytic activities of metals in nanocarbon structures. Here we report the direct observation of interactions between Cu atoms and single-layer graphene by transmission electron microscopy. We document stable configurations of Cu atoms in the graphene sheet and unique transformations of graphene promoted by Cu atoms. First-principles calculations based on density functional theory reveal a reduction of energy barrier that caused rotation of C-C bonds near Cu atoms. We discuss two driving forces, electron irradiation and in situ heating, and conclude that the observed transformations were mainly promoted by electron irradiation. Our results suggest that individual Cu atoms can promote reconstruction of single-layer graphene.

  6. Roller-style electrostatic printing of prepatterned few-layer-graphenes

    NASA Astrophysics Data System (ADS)

    Liang, Xiaogan; Giacometti, Valentina; Ismach, Ariel; Harteneck, Bruce D.; Olynick, Deirdre L.; Cabrini, Stefano

    2010-01-01

    Electrostatic exfoliation of patterned few-layer-graphenes was demonstrated using a method compatible with high throughput roll-to-roll manufacturing. A patterned graphite template was placed on a roller and used to exfoliate patterned graphene on a planar substrate. The exfoliated graphene features were subsequently characterized by Raman spectroscopy. In comparison with previously demonstrated planar electrostatic exfoliation approach, the roller-style method can create a narrower distribution of thickness of few-layer-graphenes, which is attributed to the combinational action of tangential rolling friction and electrostatic forces. This roller-style electrostatic printing technique could be applied for roll-to-roll manufacturing of graphene-based devices in the future.

  7. Comparison of graphene oxide with reduced graphene oxide as hole extraction layer in organic photovoltaic cells.

    PubMed

    Choi, Kyoung Soon; Park, Yensil; Kim, Soo Young

    2013-05-01

    A comparison was performed between the use of graphene oxide (GO) and reduced graphene oxide (rGO) as a hole extraction layer (HEL) in organic photovoltaic (OPV) cells with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester. Hydrazine hydrate (HYD) and the thermal method (Thermal) were adopted to change the GO to rGO. The GO HEL was deposited on an indium tin oxide electrode by spin coating, followed by the reduction process to form the rGO HELs. The success of the reduction processes was confirmed by X-ray diffraction, Raman spectroscopy, X-ray photoemission spectroscopy, transmittance, and 2-point probe method. The OPV cell with the GO (-3 nm) HEL exhibits an increased power conversion efficiency (PCE) as high as 2.5% under 100 mW/cm2 illumination under air mass conditions, which is higher than that of the OPV cell without HEL, viz. 1.78%. However, the PCE of the OPV cell with rGO HEL is not high as the values of 1.8% for the HYD-rGO and 1.9% for the Thermal-rGO. The ultraviolet photoemission spectroscopy results showed that the work function of GO was 4.7 eV, but those of HYD-rGO and Thermal-rGO were 4.2 eV and 4.5 eV, respectively. Therefore, it is considered that GO is adequate to extract the holes from the active layer, but HYD-rGO and Thermal-rGO are not appropriate to use as HELs in OPV cells from the viewpoint of the energy alignment.

  8. Layer-by-layer assembly of 3D tissue constructs with functionalized graphene

    PubMed Central

    Shin, Su Ryon; Aghaei-Ghareh-Bolagh, Behnaz; Gao, Xiguang; Nikkhah, Mehdi; Jung, Sung Mi; Dolatshahi-Pirouz, Alireza; Kim, Sang Bok; Kim, Sun Min; Dokmeci, Mehmet R.; Tang, Xiaowu (Shirley); Khademhosseini, Ali

    2014-01-01

    Carbon-based nanomaterials have been considered as promising candidates to mimic certain structure and function of native extracellular matrix materials for tissue engineering. Significant progress has been made in fabricating carbon nanoparticle-incorporated cell culture substrates, but limited studies have been reported on the development of three-dimensional (3D) tissue constructs using these nanomaterials. Here, we present a novel approach to engineer 3D multi-layered constructs using layer-by-layer (LbL) assembly of cells separated with self-assembled graphene oxide (GO)-based thin films. The GO-based structures are shown to serve as cell adhesive sheets that effectively facilitate the formation of multi-layer cell constructs with interlayer connectivity. By controlling the amount of GO deposited in forming the thin films, the thickness of the multi-layer tissue constructs could be tuned with high cell viability. Specifically, this approach could be useful for creating dense and tightly connected cardiac tissues through the co-culture of cardiomyocytes and other cell types. In this work, we demonstrated the fabrication of stand-alone multi-layer cardiac tissues with strong spontaneous beating behavior and programmable pumping properties. Therefore, this LbL-based cell construct fabrication approach, utilizing GO thin films formed directly on cell surfaces, has great potential in engineering 3D tissue structures with improved organization, electrophysiological function, and mechanical integrity. PMID:25419209

  9. Interactions between C and Cu atoms in single-layer graphene: direct observation and modelling

    NASA Astrophysics Data System (ADS)

    Kano, Emi; Hashimoto, Ayako; Kaneko, Tomoaki; Tajima, Nobuo; Ohno, Takahisa; Takeguchi, Masaki

    2015-12-01

    Metal doping into the graphene lattice has been studied recently to develop novel nanoelectronic devices and to gain an understanding of the catalytic activities of metals in nanocarbon structures. Here we report the direct observation of interactions between Cu atoms and single-layer graphene by transmission electron microscopy. We document stable configurations of Cu atoms in the graphene sheet and unique transformations of graphene promoted by Cu atoms. First-principles calculations based on density functional theory reveal a reduction of energy barrier that caused rotation of C-C bonds near Cu atoms. We discuss two driving forces, electron irradiation and in situ heating, and conclude that the observed transformations were mainly promoted by electron irradiation. Our results suggest that individual Cu atoms can promote reconstruction of single-layer graphene.Metal doping into the graphene lattice has been studied recently to develop novel nanoelectronic devices and to gain an understanding of the catalytic activities of metals in nanocarbon structures. Here we report the direct observation of interactions between Cu atoms and single-layer graphene by transmission electron microscopy. We document stable configurations of Cu atoms in the graphene sheet and unique transformations of graphene promoted by Cu atoms. First-principles calculations based on density functional theory reveal a reduction of energy barrier that caused rotation of C-C bonds near Cu atoms. We discuss two driving forces, electron irradiation and in situ heating, and conclude that the observed transformations were mainly promoted by electron irradiation. Our results suggest that individual Cu atoms can promote reconstruction of single-layer graphene. Electronic supplementary information (ESI) available: Three TEM movies, additional TEM data corresponding to movies, calculated models, and lifetime results. See DOI: 10.1039/c5nr05913e

  10. Switchable graphene-substrate coupling through formation/dissolution of an intercalated Ni-carbide layer

    PubMed Central

    Africh, Cristina; Cepek, Cinzia; Patera, Laerte L.; Zamborlini, Giovanni; Genoni, Pietro; Menteş, Tevfik O.; Sala, Alessandro; Locatelli, Andrea; Comelli, Giovanni

    2016-01-01

    Control over the film-substrate interaction is key to the exploitation of graphene’s unique electronic properties. Typically, a buffer layer is irreversibly intercalated “from above” to ensure decoupling. For graphene/Ni(111) we instead tune the film interaction “from below”. By temperature controlling the formation/dissolution of a carbide layer under rotated graphene domains, we reversibly switch graphene’s electronic structure from semi-metallic to metallic. Our results are relevant for the design of controllable graphene/metal interfaces in functional devices. PMID:26804138

  11. Magnetic properties of cobalt single layer added on graphene: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Afshar, M.; Doosti, H.

    2015-01-01

    In this paper, we have demonstrated magnetic ordering of single cobalt layer added on graphene using relativistic density functional theory at the level of generalized gradient approximation. We have shown that the single Co layer added on graphene show ferromagnetic ordering with perpendicular alignment to the graphene sheet. In the presence of spin-orbit coupling, a spin-polarization degree of about 92% was found for this quasi-two-dimensional magnetic system where it is shown a nearly half-metallic feature.

  12. Stacking sequence and interlayer coupling in few-layer graphene revealed by in situ imaging

    PubMed Central

    Wang, Zhu-Jun; Dong, Jichen; Cui, Yi; Eres, Gyula; Timpe, Olaf; Fu, Qiang; Ding, Feng; Schloegl, R.; Willinger, Marc-Georg

    2016-01-01

    In the transition from graphene to graphite, the addition of each individual graphene layer modifies the electronic structure and produces a different material with unique properties. Controlled growth of few-layer graphene is therefore of fundamental interest and will provide access to materials with engineered electronic structure. Here we combine isothermal growth and etching experiments with in situ scanning electron microscopy to reveal the stacking sequence and interlayer coupling strength in few-layer graphene. The observed layer-dependent etching rates reveal the relative strength of the graphene–graphene and graphene–substrate interaction and the resulting mode of adlayer growth. Scanning tunnelling microscopy and density functional theory calculations confirm a strong coupling between graphene edge atoms and platinum. Simulated etching confirms that etching can be viewed as reversed growth. This work demonstrates that real-time imaging under controlled atmosphere is a powerful method for designing synthesis protocols for sp2 carbon nanostructures in between graphene and graphite. PMID:27759024

  13. Large scale atomistic simulation of single-layer graphene growth on Ni(111) surface: molecular dynamics simulation based on a new generation of carbon-metal potential.

    PubMed

    Xu, Ziwei; Yan, Tianying; Liu, Guiwu; Qiao, Guanjun; Ding, Feng

    2016-01-14

    To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results.

  14. Large scale atomistic simulation of single-layer graphene growth on Ni(111) surface: molecular dynamics simulation based on a new generation of carbon-metal potential.

    PubMed

    Xu, Ziwei; Yan, Tianying; Liu, Guiwu; Qiao, Guanjun; Ding, Feng

    2016-01-14

    To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results. PMID:26658834

  15. PREFACE: Ultrathin layers of graphene, h-BN and other honeycomb structures Ultrathin layers of graphene, h-BN and other honeycomb structures

    NASA Astrophysics Data System (ADS)

    Geber, Thomas; Oshima, Chuhei

    2012-08-01

    Since ancient times, pure carbon materials have been familiar in human society—not only diamonds in jewellery and graphite in pencils, but also charcoal and coal which have been used for centuries as fuel for living and industry. Carbon fibers are stronger, tougher and lighter than steel and increase material efficiency because of their lower weight. Today, carbon fibers and related composite materials are used to make the frames of bicycles, cars and even airplane parts. The two-dimensional allotrope, now called graphene, is just a single layer of carbon atoms, locked together in a strongly bonded honeycomb lattice. In plane, graphene is stiffer than diamond, but out-of-plane it is soft, like rubber. It is virtually invisible, may conduct electricity (heat) better than copper and weighs next to nothing. Carbon compounds with two carbon atoms as a base, such as graphene, graphite or diamond, have isoelectronic sister compounds made of boron-nitrogen pairs: hexagonal and cubic boron nitride, with almost the same lattice constant. Although the two 2D sisters, graphene and h-BN, have the same number of valence electrons, their electronic properties are very different: freestanding h-BN is an insulator, while charge carriers in graphene are highly mobile. The past ten years have seen a great expansion in studies of single-layer and few-layer graphene. This activity has been concerned with the π electron transport in graphene, in electric and magnetic fields. More than 30 years ago, however, single-layer graphene and h-BN on solid surfaces were widely investigated. It was noted that they drastically changed the chemical reactivity of surfaces, and they were known to 'poison' heterogeneous catalysts, to passivate surfaces, to prevent oxidation of surfaces and to act as surfactants. Also, it was realized that the controlled growth of h-BN and graphene on substrates yields the formation of mismatch driven superstructures with peculiar template functionality on the

  16. Hexagonal single crystal domains of few-layer graphene on copper foils.

    PubMed

    Robertson, Alex W; Warner, Jamie H

    2011-03-01

    Hexagonal-shaped single crystal domains of few layer graphene (FLG) are synthesized on copper foils using atmospheric pressure chemical vapor deposition with a high methane flow. Scanning electron microscopy reveals that the graphene domains have a hexagonal shape and are randomly orientated on the copper foil. However, the sites of graphene nucleation exhibit some correlation by forming linear rows. Transmission electron microscopy is used to examine the folded edges of individual domains and reveals they are few-layer graphene consisting of approximately 5-10 layers in the central region and thinning out toward the edges of the domain. Selected area electron diffraction of individual isolated domains reveals they are single crystals with AB Bernal stacking and free from the intrinsic rotational stacking faults that are associated with turbostratic graphite. We study the time-dependent growth dynamics of the domains and show that the final continuous FLG film is polycrystalline, consisting of randomly connected single crystal domains.

  17. Absorption of THz electromagnetic wave in two mono-layers of graphene

    NASA Astrophysics Data System (ADS)

    Reynolds, Cole B.; Shoufie Ukhtary, M.; Saito, Riichiro

    2016-05-01

    Nearly 100% absorption of an electromagnetic (EM) wave in terahertz (THz) frequency is proposed for a system consisting of two mono-layers of graphene. Here, we demonstrate that the system can almost perfectly absorb an EM wave with frequency of 2 THz, even though we have a low electron mobility of roughly 1000 cm2  Vs‑1. The absorption probability is calculated by using the transfer matrix method. We show that the two mono-layers of the graphene system is needed to obtain nearly 100% absorption when the graphene has a relatively low Fermi energy. The absorption dependence on the distance between the graphene layers is also discussed.

  18. Deformation sensor based on polymer-supported discontinuous graphene multi-layer coatings

    NASA Astrophysics Data System (ADS)

    Carotenuto, G.; Schiavo, L.; Romeo, V.; Nicolais, L.

    2014-05-01

    Graphene can be conveniently used in the modification of polymer surfaces. Graphene macromolecules are perfectly transparent to the visible light and electrically conductive, consequently these two properties can be simultaneously provided to polymeric substrates by surface coating with thin graphene layers. In addition, such coating process provides the substrates of: water-repellence, higher surface hardness, low-friction, self-lubrication, gas-barrier properties, and many other functionalities. Polyolefins have a non-polar nature and therefore graphene strongly sticks on their surface. Nano-crystalline graphite can be used as graphene precursor in some chemical processes (e.g., graphite oxide synthesis by the Hummer method), in addition it can be directly applied to the surface of a polyolefin substrate (e.g., polyethylene) to cover it by a thin graphene multilayer. In particular, the nano-crystalline graphite perfectly exfoliate under the application of a combination of shear and friction forces and the produced graphene single-layers perfectly spread and adhere on the polyethylene substrate surface. Such polymeric materials can be used as ITO (indium-tin oxide) substitute and in the fabrication of different electronic devices. Here the fabrication of transparent resistive deformation sensors based on low-density polyethylene films coated by graphene multilayers is described. Such devices are very sensible and show a high reversible and reproducible behavior.

  19. Deformation sensor based on polymer-supported discontinuous graphene multi-layer coatings

    SciTech Connect

    Carotenuto, G.; Schiavo, L.; Romeo, V.; Nicolais, L.

    2014-05-15

    Graphene can be conveniently used in the modification of polymer surfaces. Graphene macromolecules are perfectly transparent to the visible light and electrically conductive, consequently these two properties can be simultaneously provided to polymeric substrates by surface coating with thin graphene layers. In addition, such coating process provides the substrates of: water-repellence, higher surface hardness, low-friction, self-lubrication, gas-barrier properties, and many other functionalities. Polyolefins have a non-polar nature and therefore graphene strongly sticks on their surface. Nano-crystalline graphite can be used as graphene precursor in some chemical processes (e.g., graphite oxide synthesis by the Hummer method), in addition it can be directly applied to the surface of a polyolefin substrate (e.g., polyethylene) to cover it by a thin graphene multilayer. In particular, the nano-crystalline graphite perfectly exfoliate under the application of a combination of shear and friction forces and the produced graphene single-layers perfectly spread and adhere on the polyethylene substrate surface. Such polymeric materials can be used as ITO (indium-tin oxide) substitute and in the fabrication of different electronic devices. Here the fabrication of transparent resistive deformation sensors based on low-density polyethylene films coated by graphene multilayers is described. Such devices are very sensible and show a high reversible and reproducible behavior.

  20. A further comparison of graphene and thin metal layers for plasmonics.

    PubMed

    He, Xiaoyong; Gao, Pingqi; Shi, Wangzhou

    2016-05-21

    Which one is much more suitable for plasmonic materials, graphene or metal? To address this problem well, the plasmonic properties of thin metal sheets at different thicknesses have been investigated and compared with a graphene layer. As demonstration examples, the propagation properties of insulator-metal-insulator and metamaterials (MMs) structures are also shown. The results manifest that the plasmonic properties of the graphene layer are comparable to that of thin metal sheets with the thickness of tens of nanometers. For the graphene MMs structure, by using the periodic stack structure in the active region, the resonant transmission strength significantly improves. At the optimum period number, 3-5 periods of graphene/SiO2, the graphene MMs structure manifests good frequency and amplitude tunable properties simultaneously, and the resonant strength is also strong with large values of the Q-factor. Therefore, graphene is a good tunable plasmonic material. The results are very helpful to develop novel graphene plasmonic devices, such as modulators, antenna and filters.

  1. A further comparison of graphene and thin metal layers for plasmonics

    NASA Astrophysics Data System (ADS)

    He, Xiaoyong; Gao, Pingqi; Shi, Wangzhou

    2016-05-01

    Which one is much more suitable for plasmonic materials, graphene or metal? To address this problem well, the plasmonic properties of thin metal sheets at different thicknesses have been investigated and compared with a graphene layer. As demonstration examples, the propagation properties of insulator-metal-insulator and metamaterials (MMs) structures are also shown. The results manifest that the plasmonic properties of the graphene layer are comparable to that of thin metal sheets with the thickness of tens of nanometers. For the graphene MMs structure, by using the periodic stack structure in the active region, the resonant transmission strength significantly improves. At the optimum period number, 3-5 periods of graphene/SiO2, the graphene MMs structure manifests good frequency and amplitude tunable properties simultaneously, and the resonant strength is also strong with large values of the Q-factor. Therefore, graphene is a good tunable plasmonic material. The results are very helpful to develop novel graphene plasmonic devices, such as modulators, antenna and filters.

  2. High-yield synthesis of few-layer graphene flakes through electrochemical expansion of graphite in propylene carbonate electrolyte.

    PubMed

    Wang, Junzhong; Manga, Kiran Kumar; Bao, Qiaoliang; Loh, Kian Ping

    2011-06-15

    High-yield production of few-layer graphene flakes from graphite is important for the scalable synthesis and industrial application of graphene. However, high-yield exfoliation of graphite to form graphene sheets without using any oxidation process or super-strong acid is challenging. Here we demonstrate a solution route inspired by the lithium rechargeable battery for the high-yield (>70%) exfoliation of graphite into highly conductive few-layer graphene flakes (average thickness <5 layers). A negative graphite electrode can be electrochemically charged and expanded in an electrolyte of Li salts and organic solvents under high current density and exfoliated efficiently into few-layer graphene sheets with the aid of sonication. The dispersible graphene can be ink-brushed to form highly conformal coatings of conductive films (15 ohm/square at a graphene loading of <1 mg/cm(2)) on commercial paper. PMID:21557613

  3. Thermal vibration of a rectangular single-layered graphene sheet with quantum effects

    SciTech Connect

    Wang, Lifeng Hu, Haiyan

    2014-06-21

    The thermal vibration of a rectangular single-layered graphene sheet is investigated by using a rectangular nonlocal elastic plate model with quantum effects taken into account when the law of energy equipartition is unreliable. The relation between the temperature and the Root of Mean Squared (RMS) amplitude of vibration at any point of the rectangular single-layered graphene sheet in simply supported case is derived first from the rectangular nonlocal elastic plate model with the strain gradient of the second order taken into consideration so as to characterize the effect of microstructure of the graphene sheet. Then, the RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet simply supported on an elastic foundation is derived. The study shows that the RMS amplitude of the rectangular single-layered graphene sheet predicted from the quantum theory is lower than that predicted from the law of energy equipartition. The maximal relative difference of RMS amplitude of thermal vibration appears at the sheet corners. The microstructure of the graphene sheet has a little effect on the thermal vibrations of lower modes, but exhibits an obvious effect on the thermal vibrations of higher modes. The quantum effect is more important for the thermal vibration of higher modes in the case of smaller sides and lower temperature. The relative difference of maximal RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet decreases monotonically with an increase of temperature. The absolute difference of maximal RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet increases slowly with the rising of Winkler foundation modulus.

  4. Power Enhancement of Lithium-Ion Batteries by a Graphene Interfacial Layer.

    PubMed

    Song, Young Il; An, Ja Hwa; Kim, Tae Yoo; Lee, Jung Woo; Yoo, Young Zo; Suh, Su Jeong; Kim, Sung-Soo

    2015-11-01

    We achieved a method for power enhancement of heavy-duty lithium-ion batteries (LIBs) by synthesizing a graphene interfacial layer onto the anode copper current collector (ACCC). We tested fabricated coin cells, which used either 35-μm-thick rolled pristine copper foil or graphene synthesized onto the pristine copper foil for power output estimation of the LIBs. We observed the copper surface morphology with a scanning electron microscope (SEM). Raman spectroscopy was used to measure the bonding characteristics and estimate the layers of graphene films. In addition, transmittance and electrical resistance were measured by ultra-violet visible near-infrared spectroscopy (UV-Vis IR) and 4 point probe surface resistance measurement. The graphene films on polyethylene terephthalate (PET) substrate obtained a transmittance of 97.5% and sheet resistance of 429 Ω/square. Power enhancement performances was evaluated using LIB coin cells. After 5C current discharge rate of -1.7 A/g reversible capacity of 293 mAh/g and 326 mAh/g were obtained for pristine and synthesized graphene anode current collectors, respectively. The graphene synthesized onto the ACCC showed superior power performance. The results presented herein demonstrate a power enhancement of LIBs by a decrease in electron flow resistivity between active materials and the ACCC and removal of the native oxide layer on the anode copper surface using high quality graphene synthesized onto the ACCC. PMID:26726638

  5. Morphology Control of Zinc Oxide Nanostructure on Single Layer Graphene.

    PubMed

    Ahn, Seungbae; Vijayarangamuthu, K; Jeon, Ki-Jeon

    2016-05-01

    Various morphologies of zinc oxide (ZnO) nanostructures on single layer graphene were synthesized by electrodeposition method. The current density was utilized to control the morphology of the ZnO. The Scanning Electron Microscope (SEM) was used to examine the surface morphology of the samples. SEM analysis shows morphology changes to nanorod, flower, and flakes with increase in the current density from 0.1, 0.2, and 0.3 mA/cm(-1) respectively. The XRD, XPS, and Raman spectroscopy were adopted to characterize the ZnO nanostructure and to understand the formation of various morphologies. The Raman result clearly shows extra modes due to for flakes structure caused by c-axis orientation along the substrate direction. Further, XPS data also supports formation of ZnO without any other intermediate compound such as Zn(OH)2. The formation of various morphologies was correlated to the formation different ratio of Zn2+ and OH- ions and the change in growth direction due to various current densities. PMID:27483766

  6. Growth of bi- and tri-layered graphene on silicon carbide substrate via molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Min, Tjun Kit; Lim, Thong Leng; Yoon, Tiem Leong

    2015-04-01

    Molecular dynamics (MD) simulation with simulated annealing method is used to study the growth process of bi- and tri-layered graphene on a 6H-SiC (0001) substrate via molecular dynamics simulation. Tersoff-Albe-Erhart (TEA) potential is used to describe the inter-atomic interactions among the atoms in the system. The formation temperature, averaged carbon-carbon bond length, pair correlation function, binding energy and the distance between the graphene formed and the SiC substrate are quantified. The growth mechanism, graphitization of graphene on the SiC substrate and characteristics of the surface morphology of the graphene sheet obtained in our MD simulation compare well to that observed in epitaxially grown graphene experiments and other simulation works.

  7. 1-nm-thick graphene tri-layer as the ultimate copper diffusion barrier

    SciTech Connect

    Nguyen, Ba-Son; Lin, Jen-Fin

    2014-02-24

    We demonstrate the thinnest ever reported Cu diffusion barrier, a 1-nm-thick graphene tri-layer. X-ray diffraction patterns and Raman spectra show that the graphene is thermally stable at up to 750 °C against Cu diffusion. Transmission electron microscopy images show that there was no inter-diffusion in the Cu/graphene/Si structure. Raman analyses indicate that the graphene may have degraded into a nanocrystalline structure at 750 °C. At 800 °C, the perfect carbon structure was damaged, and thus the barrier failed. The results of this study suggest that graphene could be the ultimate Cu interconnect diffusion barrier.

  8. Growth of bi- and tri-layered graphene on silicon carbide substrate via molecular dynamics simulation

    SciTech Connect

    Min, Tjun Kit; Yoon, Tiem Leong; Lim, Thong Leng

    2015-04-24

    Molecular dynamics (MD) simulation with simulated annealing method is used to study the growth process of bi- and tri-layered graphene on a 6H-SiC (0001) substrate via molecular dynamics simulation. Tersoff-Albe-Erhart (TEA) potential is used to describe the inter-atomic interactions among the atoms in the system. The formation temperature, averaged carbon-carbon bond length, pair correlation function, binding energy and the distance between the graphene formed and the SiC substrate are quantified. The growth mechanism, graphitization of graphene on the SiC substrate and characteristics of the surface morphology of the graphene sheet obtained in our MD simulation compare well to that observed in epitaxially grown graphene experiments and other simulation works.

  9. Tuning inter-dot tunnel coupling of an etched graphene double quantum dot by adjacent metal gates

    PubMed Central

    Wei, Da; Li, Hai-Ou; Cao, Gang; Luo, Gang; Zheng, Zhi-Xiong; Tu, Tao; Xiao, Ming; Guo, Guang-Can; Jiang, Hong-Wen; Guo, Guo-Ping

    2013-01-01

    Graphene double quantum dots (DQDs) open to use charge or spin degrees of freedom for storing and manipulating quantum information in this new electronic material. However, impurities and edge disorders in etched graphene nano-structures hinder the ability to control the inter-dot tunnel coupling, tC, the most important property of the artificial molecule. Here we report measurements of tC in an all-metal-side-gated graphene DQD. We find that tC can be controlled continuously about a factor of four by employing a single gate. Furthermore, tC, can be changed monotonically about another factor of four as electrons are gate-pumped into the dot one by one. The results suggest that the strength of tunnel coupling in etched graphene DQDs can be varied in a rather broad range and in a controllable manner, which improves the outlook to use graphene as a base material for qubit applications. PMID:24213723

  10. Multilayer films of cationic graphene-polyelectrolytes and anionic graphene-polyelectrolytes fabricated using layer-by-layer self-assembly

    NASA Astrophysics Data System (ADS)

    Rani, Adila; Oh, Kyoung Ah; Koo, Hyeyoung; Lee, Hyung jung; Park, Min

    2011-03-01

    Extremely thin sheets of carbon atoms called graphene have been predicted to possess excellent thermal properties, electrical conductivity, and mechanical stiffness. To harness such properties in composite materials for multifunctional applications, one would require the incorporation of graphene. In this study, new thin film composites were created using layer-by-layer (LBL) assembly of polymer-coated graphitic nanoplatelets. The positive and negative polyelectrolytes used to cover graphene sheets were poly allylamine hydrochloride (PAH) and poly sodium 4-styrenesulfonate (PSS). The synthesized poly allylamine hydrochloride-graphene (PAH-G) and poly sodium 4-styrenesulfonate-gaphene (PSS-G) were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and thermo gravimetric analysis (TGA). The multilayer films created by spontaneous sequential adsorption of PAH-G and PSS-G were characterized by ultra violet spectroscopy (UV-vis), scanning electron microscopy (SEM), and AFM. The electrical conductivity of the graphene/polyelectrolyte multilayer film composites measured by the four-point probe method was 0.2 S cm -1, which was sufficient for the construction of advanced electro-optical devices and sensors.

  11. Strong piezoelectricity in single-layer graphene deposited on SiO2 grating substrates.

    PubMed

    da Cunha Rodrigues, Gonçalo; Zelenovskiy, Pavel; Romanyuk, Konstantin; Luchkin, Sergey; Kopelevich, Yakov; Kholkin, Andrei

    2015-06-25

    Electromechanical response of materials is a key property for various applications ranging from actuators to sophisticated nanoelectromechanical systems. Here electromechanical properties of the single-layer graphene transferred onto SiO2 calibration grating substrates is studied via piezoresponse force microscopy and confocal Raman spectroscopy. The correlation of mechanical strains in graphene layer with the substrate morphology is established via Raman mapping. Apparent vertical piezoresponse from the single-layer graphene supported by underlying SiO2 structure is observed by piezoresponse force microscopy. The calculated vertical piezocoefficient is about 1.4 nm V(-1), that is, much higher than that of the conventional piezoelectric materials such as lead zirconate titanate and comparable to that of relaxor single crystals. The observed piezoresponse and achieved strain in graphene are associated with the chemical interaction of graphene's carbon atoms with the oxygen from underlying SiO2. The results provide a basis for future applications of graphene layers for sensing, actuating and energy harvesting.

  12. Controlling single and few-layer graphene crystals growth in a solid carbon source based chemical vapor deposition

    SciTech Connect

    Papon, Remi; Sharma, Subash; Shinde, Sachin M.; Vishwakarma, Riteshkumar; Tanemura, Masaki; Kalita, Golap

    2014-09-29

    Here, we reveal the growth process of single and few-layer graphene crystals in the solid carbon source based chemical vapor deposition (CVD) technique. Nucleation and growth of graphene crystals on a polycrystalline Cu foil are significantly affected by the injection of carbon atoms with pyrolysis rate of the carbon source. We observe micron length ribbons like growth front as well as saturated growth edges of graphene crystals depending on growth conditions. Controlling the pyrolysis rate of carbon source, monolayer and few-layer crystals and corresponding continuous films are obtained. In a controlled process, we observed growth of large monolayer graphene crystals, which interconnect and merge together to form a continuous film. On the other hand, adlayer growth is observed with an increased pyrolysis rate, resulting few-layer graphene crystal structure and merged continuous film. The understanding of monolayer and few-layer crystals growth in the developed CVD process can be significant to grow graphene with controlled layer numbers.

  13. First-principles study of graphene under c-HfO2(111) layers: Electronic structures and transport properties

    NASA Astrophysics Data System (ADS)

    Kaneko, Tomoaki; Ohno, Takahisa

    2016-08-01

    We investigated the electronic properties, stability, and transport of graphene under c-HfO2(111) layers by performing first-principles calculations with special attention to the chemical bonding between graphene and HfO2 surfaces. When the interface of HfO2/graphene is terminated by an O layer, the linear dispersion of graphene is preserved and the degradation of transport is suppressed. For other interface structures, HfO2 is tightly adsorbed on graphene and the transport is strictly limited. In terms of the stability of the interface structures, an O-terminated interface is preferable, which is achieved under an O-deficient condition.

  14. Few layers isolated graphene domains grown on copper foils by microwave surface wave plasma CVD using camphor as a precursor

    NASA Astrophysics Data System (ADS)

    Ram Aryal, Hare; Adhikari, Sudip; Uchida, Hideo; Wakita, Koichi; Umeno, Masayoshi

    2016-03-01

    Few layers isolated graphene domains were grown by microwave surface wave plasma CVD technique using camphor at low temperature. Graphene nucleation centers were suppressed on pre-annealed copper foils by supplying low dissociation energy. Scanning electron microscopy study of time dependent growth reveals that graphene nucleation centers were preciously suppressed, which indicates the possibility of controlled growth of large area single crystal graphene domains by plasma processing. Raman spectroscopy revealed that the graphene domains are few layered which consist of relatively low defects.

  15. Mechanical Deformation of Single- and Few- Layer Graphene on Micro-Scale-Grooved PDMS

    NASA Astrophysics Data System (ADS)

    Rocklin, David; Scharfenberg, Scott; Chialvo, Cesar; Weaver, Richard; Goldbart, Paul; Mason, Nadya

    2009-11-01

    The physical properties of the material graphene are currently of wide interest. To explore their mechanical aspects, we placed graphene flakes, of thicknesses ranging from one to seven layers, on a rubbery PDMS (polydimethylsiloxane) substrate containing microgrooves. We used Atomic Force Microscopy (AFM) imaging techniques to study the resulting deformations of the surface, and found that the graphene adhered to the sample and substantially flattened the profile of the grooves. We have examined this flattening effect within a model based on linear elasticity theory. Thus, we have been able to identify, at least tentatively, the point at which shear stress breaks the interlayer coupling and causes the graphene layers to slide against each other.

  16. Water Desalination Using Nanoporous Single-Layer Graphene with Tunable Pore Size

    SciTech Connect

    Surwade, Sumedh P.; Smirnov, Sergei N.; Vlassiouk, Ivan V.; Unocic, Raymond R.; Veith, Gabriel M.; Dai, Sheng; Mahurin, Shannon Mark

    2015-03-23

    Graphene has great potential to serve as a separation membrane due to its unique properties such as chemical and mechanical stability, flexibility and most importantly its one-atom thickness. In this study, we demonstrate first experimental evidence of the use of single-layer porous graphene as a desalination membrane. Nanometer-sized pores are introduced into single layer graphene using a convenient oxygen plasma etching process that permits tuning of the pore size. The resulting porous graphene membrane exhibited high rejection of salt ions and rapid water transport, thus functioning as an efficient water desalination membrane. Salt rejection selectivity of nearly 100% and exceptionally high water fluxes exceeding 105 g m-2 s-1 at 40 C were measured using saturated water vapor as a driving force.

  17. Water Desalination Using Nanoporous Single-Layer Graphene with Tunable Pore Size

    DOE PAGES

    Surwade, Sumedh P.; Smirnov, Sergei N.; Vlassiouk, Ivan V.; Unocic, Raymond R.; Veith, Gabriel M.; Dai, Sheng; Mahurin, Shannon Mark

    2015-03-23

    Graphene has great potential to serve as a separation membrane due to its unique properties such as chemical and mechanical stability, flexibility and most importantly its one-atom thickness. In this study, we demonstrate first experimental evidence of the use of single-layer porous graphene as a desalination membrane. Nanometer-sized pores are introduced into single layer graphene using a convenient oxygen plasma etching process that permits tuning of the pore size. The resulting porous graphene membrane exhibited high rejection of salt ions and rapid water transport, thus functioning as an efficient water desalination membrane. Salt rejection selectivity of nearly 100% and exceptionallymore » high water fluxes exceeding 105 g m-2 s-1 at 40 C were measured using saturated water vapor as a driving force.« less

  18. A highly sensitive pressure sensor using a double-layered graphene structure for tactile sensing.

    PubMed

    Chun, Sungwoo; Kim, Youngjun; Oh, Hyeong-Sik; Bae, Giyeol; Park, Wanjun

    2015-07-21

    In this paper, we propose a graphene sensor using two separated single-layered graphenes on a flexible substrate for use as a pressure sensor, such as for soft electronics. The working pressure corresponds to the range in which human perception recognizes surface morphologies. A specific design of the sensor structure drives the piezoresistive character due to the contact resistance between two graphene layers and the electromechanical properties of graphene itself. Accordingly, sensitivity in resistance change is given by two modes for low pressure (-0.24 kPa(-1)) and high pressure (0.039 kPa(-1)) with a crossover pressure (700 Pa). This sensor can detect infinitesimal pressure as low as 0.3 Pa with uniformly applied vertical force. With the attachment of the artificial fingerprint structure (AFPS) on the sensor, the detection ability for both the locally generated shear force and actual human touch confirms recognition of the surface morphology constructed by periodic structures. PMID:26098064

  19. The effect of spin-orbit coupling in band structure of few-layer graphene

    SciTech Connect

    Sahdan, Muhammad Fauzi Darma, Yudi

    2014-03-24

    Topological insulators are electronic materials that have a bulk band gap like an ordinary insulator but have protected conducting states on their edge or surface. This can be happened due to spin-orbit coupling and time-reversal symmetry. Moreover, the edge current flows through their edge or surface depends on its spin orientation and also it is robust against non-magnetic impurities. Therefore, topological insulators are predicted to be useful ranging from spintronics to quantum computation. Graphene was first predicted to be the precursor of topological insulator by Kane-Mele. They developed a Hamiltonian model to describe the gap opening in graphene. In this work, we investigate the band structure of few-layer graphene by using this model with analytical approach. The results of our calculations show that the gap opening occurs at K and K’ point, not only in single layer, but also in bilayer and trilayer graphene.

  20. A highly sensitive pressure sensor using a double-layered graphene structure for tactile sensing.

    PubMed

    Chun, Sungwoo; Kim, Youngjun; Oh, Hyeong-Sik; Bae, Giyeol; Park, Wanjun

    2015-07-21

    In this paper, we propose a graphene sensor using two separated single-layered graphenes on a flexible substrate for use as a pressure sensor, such as for soft electronics. The working pressure corresponds to the range in which human perception recognizes surface morphologies. A specific design of the sensor structure drives the piezoresistive character due to the contact resistance between two graphene layers and the electromechanical properties of graphene itself. Accordingly, sensitivity in resistance change is given by two modes for low pressure (-0.24 kPa(-1)) and high pressure (0.039 kPa(-1)) with a crossover pressure (700 Pa). This sensor can detect infinitesimal pressure as low as 0.3 Pa with uniformly applied vertical force. With the attachment of the artificial fingerprint structure (AFPS) on the sensor, the detection ability for both the locally generated shear force and actual human touch confirms recognition of the surface morphology constructed by periodic structures.

  1. Nanosecond spin relaxation times in single layer graphene spin valves with hexagonal boron nitride tunnel barriers

    NASA Astrophysics Data System (ADS)

    Singh, Simranjeet; Katoch, Jyoti; Xu, Jinsong; Tan, Cheng; Zhu, Tiancong; Amamou, Walid; Hone, James; Kawakami, Roland

    2016-09-01

    We present an experimental study of spin transport in single layer graphene using atomic sheets of hexagonal boron nitride (h-BN) as a tunnel barrier for spin injection. While h-BN is expected to be favorable for spin injection, previous experimental studies have been unable to achieve spin relaxation times in the nanosecond regime, suggesting potential problems originating from the contacts. Here, we investigate spin relaxation in graphene spin valves with h-BN barriers and observe room temperature spin lifetimes in excess of a nanosecond, which provides experimental confirmation that h-BN is indeed a good barrier material for spin injection into graphene. By carrying out measurements with different thicknesses of h-BN, we show that few layer h-BN is a better choice than monolayer for achieving high non-local spin signals and longer spin relaxation times in graphene.

  2. Silicon Layer Intercalation and Interface Properties between Graphene and Metal hosts

    NASA Astrophysics Data System (ADS)

    Wang, Yeliang; Mao, Jinhai; Meng, Lei; Gao, Hongjun; Junfeng He Collaboration; Shixuan Du Collaboration; Xingjiang Zhou Collaboration; A. H. Castro Neto Collaboration

    2013-03-01

    Graphene is being considered as a contender as the reference material with extraordinary properties for a post-CMOS technology. The availability of high quality and large scale single crystal graphene is fundamental for it to fulfill its promise in electronic applications. Graphene is usually grown on a metallic substrate from which it has to be transferred before it can be used. However, uncontrolled shear and strain, associated with the transfer and the presence of extended domains, lead to unavoidable tearing, rendering it useless for scalable production. We propose a way to overcome this bottleneck and produce high quality, free standing graphene by intercalating Si in graphene epitaxially grown on metals, like Ru(0001) & Ir(111). This G/Si/metal architecture, produced by the silicon-layer intercalation approach (SIA), was characterized by STM/STS, Raman, and angle resolved electron photoemission spectroscopy (ARPES) and proves the high structural and electronic qualities of the new composite. The SIA eliminates the need for the graphene transfer and also allows for an atomic control of the distance between the graphene and the metal. Graphene Research Center, Singapore National University.

  3. Driving Forces of Conformational Changes in Single-Layer Graphene Oxide

    PubMed Central

    2012-01-01

    The extensive oxygen-group functionality of single-layer graphene oxide proffers useful anchor sites for chemical functionalization in the controlled formation of graphene architecture and composites. However, the physicochemical environment of graphene oxide and its single-atom thickness facilitate its ability to undergo conformational changes due to responses to its environment, whether pH, salinity, or temperature. Here, we report experimental and molecular simulations confirming the conformational changes of single-layer graphene oxide sheets from the wet or dry state. MD, PM6, and ab initio simulations of dry SLG and dry and wetted SLGO and electron microscopy imaging show marked differences in the properties of the materials that can explain variations in previously observed results for the pH dependent behavior of SLGO and electrical conductivity of chemically modified graphene-polymer composites. Understanding the physicochemical responses of graphene and graphene oxide architecture and performing selected chemistry will ultimately facilitate greater tunability of their performance. PMID:22494387

  4. In situ formation of graphene layers on graphite surfaces for efficient anodes of microbial fuel cells.

    PubMed

    Tang, Jiahuan; Chen, Shanshan; Yuan, Yong; Cai, Xixi; Zhou, Shungui

    2015-09-15

    Graphene can be used to improve the performance of the anode in a microbial fuel cell (MFC) due to its good biocompatibility, high electrical conductivity and large surface area. However, the chemical production and modification of the graphene on the anode are environmentally hazardous because of the use of various harmful chemicals. This study reports a novel method based on the electrochemical exfoliation of a graphite plate (GP) for the in situ formation of graphene layers on the surface of a graphite electrode. When the resultant graphene-layer-based graphite plate electrode (GL/GP) was used as an anode in an MFC, a maximum power density of 0.67 ± 0.034 W/m(2) was achieved. This value corresponds to 1.72-, 1.56- and 1.26-times the maximum power densities of the original GP, exfoliated-graphene-modified GP (EG/GP) and chemically-reduced-graphene-modified GP (rGO/GP) anodes, respectively. Electrochemical measurements revealed that the high performance of the GL/GP anode was attributable to its macroporous structure, improved electron transfer and high electrochemical capacitance. The results demonstrated that the proposed method is a facile and environmentally friendly synthesis technique for the fabrication of high-performance graphene-based electrodes for use in microbial energy harvesting. PMID:25950933

  5. Basics of quantum field theory of electromagnetic interaction processes in single-layer graphene

    NASA Astrophysics Data System (ADS)

    Hieu Nguyen, Van

    2016-09-01

    The content of this work is the study of electromagnetic interaction in single-layer graphene by means of the perturbation theory. The interaction of electromagnetic field with Dirac fermions in single-layer graphene has a peculiarity: Dirac fermions in graphene interact not only with the electromagnetic wave propagating within the graphene sheet, but also with electromagnetic field propagating from a location outside the graphene sheet and illuminating this sheet. The interaction Hamiltonian of the system comprising electromagnetic field and Dirac fermions fields contains the limits at graphene plane of electromagnetic field vector and scalar potentials which can be shortly called boundary electromagnetic field. The study of S-matrix requires knowing the limits at graphene plane of 2-point Green functions of electromagnetic field which also can be shortly called boundary 2-point Green functions of electromagnetic field. As the first example of the application of perturbation theory, the second order terms in the perturbative expansions of boundary 2-point Green functions of electromagnetic field as well as of 2-point Green functions of Dirac fermion fields are explicitly derived. Further extension of the application of perturbation theory is also discussed.

  6. Hydrothermal synthesis of highly nitrogen-doped few-layer graphene via solid–gas reaction

    SciTech Connect

    Liang, Xianqing; Zhong, Jun; Shi, Yalin; Guo, Jin; Huang, Guolong; Hong, Caihao; Zhao, Yidong

    2015-01-15

    Highlights: • A novel approach to synthesis of N-doped few-layer graphene has been developed. • The high doping levels of N in products are achieved. • XPS and XANES results reveal a thermal transformation of N bonding configurations. • The developed method is cost-effective and eco-friendly. - Abstract: Nitrogen-doped (N-doped) graphene sheets with high doping concentration were facilely synthesized through solid–gas reaction of graphene oxide (GO) with ammonia vapor in a self-designed hydrothermal system. The morphology, surface chemistry and electronic structure of N-doped graphene sheets were investigated by TEM, AFM, XRD, XPS, XANES and Raman characterizations. Upon hydrothermal treatment, up to 13.22 at% of nitrogen could be introduced into the crumpled few-layer graphene sheets. Both XPS and XANES analysis reveal that the reaction between oxygen functional groups in GO and ammonia vapor produces amide and amine species in hydrothermally treated GO (HTGO). Subsequent thermal annealing of the resultant HTGO introduces a gradual transformation of nitrogen bonding configurations in graphene sheets from amine N to pyridinic and graphitic N with the increase of annealing temperature. This study provides a simple but cost-effective and eco-friendly method to prepare N-doped graphene materials in large-scale for potential applications.

  7. In situ formation of graphene layers on graphite surfaces for efficient anodes of microbial fuel cells.

    PubMed

    Tang, Jiahuan; Chen, Shanshan; Yuan, Yong; Cai, Xixi; Zhou, Shungui

    2015-09-15

    Graphene can be used to improve the performance of the anode in a microbial fuel cell (MFC) due to its good biocompatibility, high electrical conductivity and large surface area. However, the chemical production and modification of the graphene on the anode are environmentally hazardous because of the use of various harmful chemicals. This study reports a novel method based on the electrochemical exfoliation of a graphite plate (GP) for the in situ formation of graphene layers on the surface of a graphite electrode. When the resultant graphene-layer-based graphite plate electrode (GL/GP) was used as an anode in an MFC, a maximum power density of 0.67 ± 0.034 W/m(2) was achieved. This value corresponds to 1.72-, 1.56- and 1.26-times the maximum power densities of the original GP, exfoliated-graphene-modified GP (EG/GP) and chemically-reduced-graphene-modified GP (rGO/GP) anodes, respectively. Electrochemical measurements revealed that the high performance of the GL/GP anode was attributable to its macroporous structure, improved electron transfer and high electrochemical capacitance. The results demonstrated that the proposed method is a facile and environmentally friendly synthesis technique for the fabrication of high-performance graphene-based electrodes for use in microbial energy harvesting.

  8. Suppressing Manganese Dissolution from Lithium Manganese Oxide Spinel Cathodes with Single-Layer Graphene

    SciTech Connect

    Jaber-Ansari, Laila; Puntambekar, Kanan P.; Kim, Soo; Aykol, Muratahan; Luo, Langli; Wu, Jinsong; Myers, Benjamin D.; Iddir, Hakim; Russell, John T.; Saldana, Spencer J.; Kumar, Rajan; Thackeray, Michael M.; Curtiss, Larry A.; Dravid, Vinayak P.; Wolverton, Christopher M.; Hersam, Mark C.

    2015-06-24

    Spinel-structured LiMn 2 O 4 (LMO) is a desirable cathode material for Li-ion batteries due to its low cost, abundance, and high power capability. However, LMO suffers from limited cycle life that is triggered by manganese dissolution into the electrolyte during electrochemical cycling. Here, it is shown that single-layer graphene coatings suppress manganese dissolution, thus enhancing the performance and lifetime of LMO cathodes. Relative to lithium cells with uncoated LMO cathodes, cells with graphene-coated LMO cathodes provide improved capacity retention with enhanced cycling stability. X-ray photoelectron spectroscopy reveals that graphene coatings inhibit manganese depletion from the LMO surface. Additionally, transmission electron microscopy demonstrates that a stable solid electrolyte interphase is formed on graphene, which screens the LMO from direct contact with the electrolyte. Density functional theory calculations provide two mechanisms for the role of graphene in the suppression of manganese dissolution. First, common defects in single-layer graphene are found to allow the transport of lithium while concurrently acting as barriers for manganese diffusion. Second, graphene can chemically interact with Mn 3+ at the LMO electrode surface, promoting an oxidation state change to Mn 4+ , which suppresses dissolution.

  9. Quantitative secondary electron imaging for work function extraction at atomic level and layer identification of graphene

    PubMed Central

    Zhou, Yangbo; Fox, Daniel S; Maguire, Pierce; O’Connell, Robert; Masters, Robert; Rodenburg, Cornelia; Wu, Hanchun; Dapor, Maurizio; Chen, Ying; Zhang, Hongzhou

    2016-01-01

    Two-dimensional (2D) materials usually have a layer-dependent work function, which require fast and accurate detection for the evaluation of their device performance. A detection technique with high throughput and high spatial resolution has not yet been explored. Using a scanning electron microscope, we have developed and implemented a quantitative analytical technique which allows effective extraction of the work function of graphene. This technique uses the secondary electron contrast and has nanometre-resolved layer information. The measurement of few-layer graphene flakes shows the variation of work function between graphene layers with a precision of less than 10 meV. It is expected that this technique will prove extremely useful for researchers in a broad range of fields due to its revolutionary throughput and accuracy. PMID:26878907

  10. A graphene meta-interface for enhancing the stretchability of brittle oxide layers.

    PubMed

    Won, Sejeong; Jang, Jae-Won; Choi, Hyung-Jin; Kim, Chang-Hyun; Lee, Sang Bong; Hwangbo, Yun; Kim, Kwang-Seop; Yoon, Soon-Gil; Lee, Hak-Joo; Kim, Jae-Hyun; Lee, Soon-Bok

    2016-03-01

    Oxide materials have recently attracted much research attention for applications in flexible and stretchable electronics due to their excellent electrical properties and their compatibility with established silicon semiconductor processes. Their widespread uptake has been hindered, however, by the intrinsic brittleness and low stretchability. Here we investigate the use of a graphene meta-interface to enhance the electromechanical stretchability of fragile oxide layers. Electromechanical tensile tests of indium tin oxide (ITO) layers on polymer substrates were carried out with in situ observations using an optical microscope. It was found that the graphene meta-interface reduced the strain transfer between the ITO layer and the substrate, and this behavior was well described using a shear lag model. The graphene meta-interface provides a novel pathway for realizing flexible and stretchable electronic applications based on oxide layers. PMID:26540317

  11. Tunable and Sizable Band Gap of Single Layer Graphene Sandwiched between Hexagonal Boron Nitride

    NASA Astrophysics Data System (ADS)

    Zheng, Jiaxin; Qu, Heruge; Liu, Qihang; Qin, Rui; Zhou, Jing; Yu, Dapeng; Gao, Zhengxiang; Lu, Jing; Luo, Guangfu; Nagase, Shigeru; Mei, Wai-Ning

    2012-02-01

    It is a big challenge to open a tunable and sizable band gap of single layer graphene without big loss in structural integrity and carrier mobility. By using density functional theory calculations, we show that the band gap of single layer graphene can be opened to 0.16 (without electrical field) and 0.34 eV (with a strong electrical field) when sandwiched between two hexagonal boron nitride single layers in a proper way. The zero-field band gaps are increased by about 50% when many-body effects are included. Ab initio quantum transport simulation of a dual-gated FET out of such a sandwich structure further confirms an electrical field-enhanced transport gap. The tunable and sizeable band gap and structural integrity render this sandwich structure a promising candidate for high-performance single layer graphene field effect transistors.

  12. Controllable synthesis of graphene sheets with different numbers of layers and effect of the number of graphene layers on the specific capacity of anode material in lithium-ion batteries

    SciTech Connect

    Tong, Xin; Wang, Hui; Wang, Gang; Wan, Lijuan; Ren, Zhaoyu; Bai, Jintao; Bai, Jinbo

    2011-05-15

    High quality graphene sheets are synthesized through efficient oxidation process followed by rapid thermal expansion and reduction by H{sub 2}. The number of graphene layers is controlled by tuning the oxidation degree of GOs. The higher the oxidation degree of GOs is getting, the fewer the numbers of graphene layers can be obtained. The material is characterized by elemental analysis, thermo-gravimetric analysis, scanning electron microscopy, atomic force microscopy, transmission electron microscopy and Fourier transform infrared spectroscopies. The obtained graphene sheets with single, triple and quintuplicate layers as anode materials exhibit a high reversible capacity of 1175, 1007, and 842 mA h g{sup -1}, respectively, which show that the graphene sheets with fewer layers have higher reversible capacity. -- Graphical abstract: The typical TEM images of the graphene sheets derived from GO3(a), GO2(b) and GO1(c). Display Omitted Highlights: {yields} With the oxidation degree of GO increasing, the numbers of graphene layers decreased. {yields} With the numbers of graphene layers decreasing, the reversible capacity improved. {yields} Graphene sheets with single-layer exhibit the best electrochemical performances.

  13. Giant enhancement of the third harmonic in graphene integrated in a layered structure

    NASA Astrophysics Data System (ADS)

    Savostianova, N. A.; Mikhailov, S. A.

    2015-11-01

    Graphene was shown to have strongly nonlinear electrodynamic properties. In particular, being irradiated by an electromagnetic wave with the frequency ω, it can efficiently generate higher frequency harmonics. Here, we predict that in a specially designed structure "graphene— dielectric—metal" the third-harmonic ( 3 ω ) intensity can be increased by more than two orders of magnitude as compared to an isolated graphene layer.

  14. Molecular dynamics calculation of the thermal conductivity coefficient of single-layer and multilayer graphene sheets

    NASA Astrophysics Data System (ADS)

    Selezenev, A. A.; Aleinikov, A. Yu.; Ganchuk, N. S.; Ganchuk, S. N.; Jones, R. E.; Zimmerman, J. A.

    2013-04-01

    The thermal conductivity coefficients of single-layer and multilayer graphene sheets have been calculated using the molecular dynamics simulation. Calculations have been performed for graphene sheets with lengths in the range 20-130 nm and at average temperatures in the range 230-630 K. The results obtained have been compared with the experimental data and results of calculations carried out in other works.

  15. Chemical vapour deposition growth and Raman characterization of graphene layers and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Lai, Y.-C.; Rafailov, P. M.; Vlaikova, E.; Marinova, V.; Lin, S. H.; Yu, P.; Yu, S.-C.; Chi, G. C.; Dimitrov, D.; Sveshtarov, P.; Mehandjiev, V.; Gospodinov, M. M.

    2016-02-01

    Single-layer graphene films were grown by chemical vapour deposition (CVD) on Cu foil. The CVD process was complemented by plasma enhancement to grow also vertically aligned multiwalled carbon nanotubes using Ni nanoparticles as catalyst. The obtained samples were characterized by Raman spectroscopy analysis. Nature of defects in the samples and optimal growth conditions leading to achieve high quality of graphene and carbon nanotubes are discussed.

  16. Overview of the Use of Graphene in Electric Double Layer Capacitors

    NASA Astrophysics Data System (ADS)

    Coleman, Arthur

    2012-10-01

    Advances in the manufacture and optimization of Electric Double Layer Capacitors or ultra-capacitors may make them a good alternative to batteries. Using graphene in the EDLC layers seems to limit the high self-discharge and voltage loss on discharge that plagues ultra-capacitors.

  17. Role of metallic substrate on the plasmon modes in double-layer graphene structures

    NASA Astrophysics Data System (ADS)

    Cruz, G. Gonzalez de la

    2015-07-01

    Novel heterostructures combining different layered materials offer new opportunities for applications and fundamental studies of collective excitations driven by interlayer Coulomb interactions. In this work, we have investigated the influence of the metallic-like substrate on the plasmon spectrum of a double layer graphene system and a structure consisting of conventional two-dimensional electron gas (2DEG) immersed in a semiconductor quantum well and a graphene sheet with an interlayer separation of d. Long-range Coulomb interactions between substrate and graphene layered systems lead a new set of spectrum plasmons. At long wavelengths (q→0) the acoustic modes (ω~q) depend, besides on the carrier density in each layer, on the distance between the first carrier layer and the substrate in both structures. Furthermore, in the relativistic/nonrelativistic layered structure an undamped acoustic mode emerges for a certain interlayer critical distance dc. On the other hand, the optical plasmon modes emerging from the coupling of the double-layer systems and the substrate, both start at finite frequency at q=0 in contrast to the collective excitation spectrum ω~q1/2 reported in the literature for double-layer graphene structures.

  18. A graphene meta-interface for enhancing the stretchability of brittle oxide layers

    NASA Astrophysics Data System (ADS)

    Won, Sejeong; Jang, Jae-Won; Choi, Hyung-Jin; Kim, Chang-Hyun; Lee, Sang Bong; Hwangbo, Yun; Kim, Kwang-Seop; Yoon, Soon-Gil; Lee, Hak-Joo; Kim, Jae-Hyun; Lee, Soon-Bok

    2016-02-01

    Oxide materials have recently attracted much research attention for applications in flexible and stretchable electronics due to their excellent electrical properties and their compatibility with established silicon semiconductor processes. Their widespread uptake has been hindered, however, by the intrinsic brittleness and low stretchability. Here we investigate the use of a graphene meta-interface to enhance the electromechanical stretchability of fragile oxide layers. Electromechanical tensile tests of indium tin oxide (ITO) layers on polymer substrates were carried out with in situ observations using an optical microscope. It was found that the graphene meta-interface reduced the strain transfer between the ITO layer and the substrate, and this behavior was well described using a shear lag model. The graphene meta-interface provides a novel pathway for realizing flexible and stretchable electronic applications based on oxide layers.Oxide materials have recently attracted much research attention for applications in flexible and stretchable electronics due to their excellent electrical properties and their compatibility with established silicon semiconductor processes. Their widespread uptake has been hindered, however, by the intrinsic brittleness and low stretchability. Here we investigate the use of a graphene meta-interface to enhance the electromechanical stretchability of fragile oxide layers. Electromechanical tensile tests of indium tin oxide (ITO) layers on polymer substrates were carried out with in situ observations using an optical microscope. It was found that the graphene meta-interface reduced the strain transfer between the ITO layer and the substrate, and this behavior was well described using a shear lag model. The graphene meta-interface provides a novel pathway for realizing flexible and stretchable electronic applications based on oxide layers. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05412e

  19. 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.

  20. Femtosecond laser induced periodic surface structures on multi-layer graphene

    SciTech Connect

    Beltaos, Angela Kovačević, Aleksander G.; Matković, Aleksandar; Ralević, Uroš; Savić-Šević, Svetlana; Jovanović, Djordje; Jelenković, Branislav M.; Gajić, Radoš

    2014-11-28

    In this work, we present an observation of laser induced periodic surface structures (LIPSS) on graphene. LIPSS on other materials have been observed for nearly 50 years, but until now, not on graphene. Our findings for LIPSS on multi-layer graphene were consistent with previous reports of LIPSS on other materials, thus classifying them as high spatial frequency LIPSS. LIPSS on multi-layer graphene were generated in an air environment by a linearly polarized femtosecond laser with excitation wavelength λ of 840 nm, pulse duration τ of ∼150 fs, and a fluence F of ∼4.3–4.4 mJ/cm{sup 2}. The observed LIPSS were perpendicular to the laser polarization and had dimensions of width w of ∼30–40 nm and length l of ∼0.5–1.5 μm, and spatial periods Λ of ∼70–100 nm (∼λ/8–λ/12), amongst the smallest of spatial periods reported for LIPSS on other materials. The spatial period and width of the LIPSS were shown to decrease for an increased number of laser shots. The experimental results support the leading theory behind high spatial frequency LIPSS formation, implying the involvement of surface plasmon polaritons. This work demonstrates a new way to pattern multi-layer graphene in a controllable manner, promising for a variety of emerging graphene/LIPSS applications.

  1. Li Storage Properties of Disordered Single- and Bi-Layer Graphene

    NASA Astrophysics Data System (ADS)

    Yildirim, H.; Kinaci, Alper; Zhao, Zhi-Jian; Chan, Maria; Greeley, Jeffrey P.

    2015-03-01

    Due to the limited capacity of the traditional intercalation-type graphite materials (373 mAh/g, LiC6) , much effort has been made to explore new anode materials to meet the increasing demand for batteries of high energy density. Among them, graphene has much attracted attention as an ideal platform for higher Li storage capacity, and for obtaining fundamental understanding of Li-C interaction. In this respect, we performed extensive first-principles calculations to model Li adsorption and intercalation in single- and bi-layer graphene, which are activated by defects for Li adsorption. For a wide range of Li coverages, the calculations predict that defect-free single layer graphene is not thermodynamically favorable compared to bulk metallic Li. However, graphene activated by defects are generally found to bind Li more strongly, and the interaction strength is sensitive to both the nature of defects and their densities. A rigorous thermodynamic analysis establishes the theoretical Li storage capacities of the defected graphene, and in some cases, these capacities are found to approach, although not exceed, those of bulk graphite. We will provide a performance comparison between defected single- and bi-layer graphene and bulk-graphite for Li storage capacities. A detailed analysis of the effect of the van der Walls (vdW) interactions will also be presented.

  2. Optical reflectivity and Raman scattering in few-layer-thick graphene highly doped by K and Rb.

    PubMed

    Jung, Naeyoung; Kim, Bumjung; Crowther, Andrew C; Kim, Namdong; Nuckolls, Colin; Brus, Louis

    2011-07-26

    We report the optical reflectivity and Raman scattering of few layer (L) graphene exposed to K and Rb vapors. Samples many tens of layers thick show the reflectivity and Raman spectra of the stage 1 bulk alkali intercalation compounds (GICs) KC(8) and RbC(8). However, these bulk optical and Raman properties only begin to appear in samples more than about 15 graphene layers thick. The 1 L to 4 L alkali exposed graphene Raman spectra are profoundly different than the Breit-Wigner-Fano (BWF) spectra of the bulk stage 1 compounds. Samples less than 10 layers thick show Drude-like plasma edge reflectivity dip in the visible; alkali exposed few layer graphenes are significantly more transparent than intrinsic graphene. Simulations show the in-plane free electron density is lower than in the bulk stage 1 GICs. In few layer graphenes, alkalis both intercalate between layers and adsorb on the graphene surfaces. Charge transfer electrically dopes the graphene sheets to densities near and above 10(+14) electrons/cm(2). New intrinsic Raman modes at 1128 and 1264 cm(-1) are activated by in-plane graphene zone folding caused by strongly interacting, locally crystalline alkali adlayers. The K Raman spectra are independent of thickness for L = 1-4, indicating that charge transfer from adsorbed and intercalated K layers are similar. The Raman G mode is downshifted and significantly broadened from intrinsic graphene. In contrast, the Rb spectra vary strongly with L and show increased doping by intercalated alkali as L increases. Rb adlayers appear to be disordered liquids, while intercalated layers are locally crystalline solids. A significant intramolecular G mode electronic resonance Raman enhancement is observed in K exposed graphene, as compared with intrinsic graphene. PMID:21682332

  3. PREFACE: Ultrathin layers of graphene, h-BN and other honeycomb structures Ultrathin layers of graphene, h-BN and other honeycomb structures

    NASA Astrophysics Data System (ADS)

    Geber, Thomas; Oshima, Chuhei

    2012-08-01

    Since ancient times, pure carbon materials have been familiar in human society—not only diamonds in jewellery and graphite in pencils, but also charcoal and coal which have been used for centuries as fuel for living and industry. Carbon fibers are stronger, tougher and lighter than steel and increase material efficiency because of their lower weight. Today, carbon fibers and related composite materials are used to make the frames of bicycles, cars and even airplane parts. The two-dimensional allotrope, now called graphene, is just a single layer of carbon atoms, locked together in a strongly bonded honeycomb lattice. In plane, graphene is stiffer than diamond, but out-of-plane it is soft, like rubber. It is virtually invisible, may conduct electricity (heat) better than copper and weighs next to nothing. Carbon compounds with two carbon atoms as a base, such as graphene, graphite or diamond, have isoelectronic sister compounds made of boron-nitrogen pairs: hexagonal and cubic boron nitride, with almost the same lattice constant. Although the two 2D sisters, graphene and h-BN, have the same number of valence electrons, their electronic properties are very different: freestanding h-BN is an insulator, while charge carriers in graphene are highly mobile. The past ten years have seen a great expansion in studies of single-layer and few-layer graphene. This activity has been concerned with the π electron transport in graphene, in electric and magnetic fields. More than 30 years ago, however, single-layer graphene and h-BN on solid surfaces were widely investigated. It was noted that they drastically changed the chemical reactivity of surfaces, and they were known to 'poison' heterogeneous catalysts, to passivate surfaces, to prevent oxidation of surfaces and to act as surfactants. Also, it was realized that the controlled growth of h-BN and graphene on substrates yields the formation of mismatch driven superstructures with peculiar template functionality on the

  4. Synthesis of few-layered graphene by H{sub 2}O{sub 2} plasma etching of graphite

    SciTech Connect

    Zhao Guixia; Shao Dadong; Chen Changlun; Wang Xiangke

    2011-05-02

    Herein, we reported an approach to synthesize few-layered graphene by etching of the graphite using H{sub 2}O{sub 2} plasma technique. The synthesized few-layered graphene was characterized by scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS). The analysis showed that few-layered graphene was formed in high quality level. The XPS analysis suggested that H{sub 2}O{sub 2} plasma etching of graphite could oxidize graphene and generated -C-OH and >C=O groups on the graphene surfaces. The H{sub 2}O{sub 2} plasma technique is an easy and environmental friendly method to synthesize few-layered graphene from the graphite.

  5. 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.

  6. Controlling Interfacial Reactions and Intermetallic Compound Growth at the Interface of a Lead-free Solder Joint with Layer-by-Layer Transferred Graphene.

    PubMed

    Ko, Yong-Ho; Lee, Jong-Dae; Yoon, Taeshik; Lee, Chang-Woo; Kim, Taek-Soo

    2016-03-01

    The immoderate growth of intermetallic compounds (IMCs) formed at the interface of a solder metal and the substrate during soldering can degrade the mechanical properties and reliability of a solder joint in electronic packaging. Therefore, it is critical to control IMC growth at the solder joints between the solder and the substrate. In this study, we investigated the control of interfacial reactions and IMC growth by the layer-by-layer transfer of graphene during the reflow process at the interface between Sn-3.0Ag-0.5Cu (in wt %) lead-free solder and Cu. As the number of graphene layers transferred onto the surface of the Cu substrate increased, the thickness of the total IMC (Cu6Sn5 and Cu3Sn) layer decreased. After 10 repetitions of the reflow process for 50 s above 217 °C, the melting temperature of Sn-3.0Ag-0.5Cu, with a peak temperature of 250 °C, the increase in thickness of the total IMC layer at the interface with multiple layers of graphene was decreased by more than 20% compared to that at the interface of bare Cu without graphene. Furthermore, the average diameter of the Cu6Sn5 scallops at the interface with multiple layers of graphene was smaller than that at the interface without graphene. Despite 10 repetitions of the reflow process, the growth of Cu3Sn at the interface with multiple layers of graphene was suppressed by more than 20% compared with that at the interface without graphene. The multiple layers of graphene at the interface between the solder metal and the Cu substrate hindered the diffusion of Cu atoms from the Cu substrate and suppressed the reactions between Cu and Sn in the solder. Thus, the multiple layers of graphene transferred at the interface between dissimilar metals can control the interfacial reaction and IMC growth occurring at the joining interface. PMID:26856638

  7. On the hydrogen-graphene layers interactions, relevance to the onboard storage problem.

    PubMed

    Nechaev, Y S; Ochsner, A

    2012-10-01

    Empirical evaluations of fundamental characteristics of the physical and chemical interaction of hydrogen with graphene layers in different kinds of graphite and novel carbonaceous nanomaterials of graphene layer structure have been carried out. This was done by using the approaches of the thermodynamics of reversible and irreversible processes for analysis of the adsorption, absorption, diffusion, the temperature-programmed desorption (TPD) and other experimental data and comparing such analytical results with first-principles calculations. Such an analysis of a number of the known experimental and theoretical data has shown a real possibility of the multilayer specific adsorption (intercalation) of hydrogen between graphene layers in novel carbonaceous nanomaterials. This is of relevance for solving the bottle-neck problem of the hydrogen on-board storage in fuel-cell-powered vehicles, and other technical applications. PMID:23421196

  8. SrO(001) on graphene: a universal buffer layer for integration of complex oxides

    NASA Astrophysics Data System (ADS)

    Ahmed, Adam; Wen, Hua; Pinchuk, Igor; Zhu, Tiancong; Kawakami, Roland

    2015-03-01

    We report the successful growth of high-quality crystalline SrO on highly-ordered pyrolytic graphite (HOPG) and single layer graphene by molecular beam epitaxy. The epitaxial SrO layers have (001) orientation as confirmed by x-ray diffraction (XRD), and atomic force microscopy measurements show rms surface roughness of optimal films to be 1.2 Å. Transport measurements of exfoliated graphene after SrO deposition show a strong dependence between the Dirac point and Sr oxidation. To show the utility of SrO as a buffer layer for complex oxide integration, we grew perovskite crystal SrTiO3 on SrO, and it was also confirmed to have (001) orientation from x-ray diffraction. This materials advancement opens the door to integration of many other complex oxides to explore novel correlated electron physics in graphene.

  9. On the hydrogen-graphene layers interactions, relevance to the onboard storage problem.

    PubMed

    Nechaev, Y S; Ochsner, A

    2012-10-01

    Empirical evaluations of fundamental characteristics of the physical and chemical interaction of hydrogen with graphene layers in different kinds of graphite and novel carbonaceous nanomaterials of graphene layer structure have been carried out. This was done by using the approaches of the thermodynamics of reversible and irreversible processes for analysis of the adsorption, absorption, diffusion, the temperature-programmed desorption (TPD) and other experimental data and comparing such analytical results with first-principles calculations. Such an analysis of a number of the known experimental and theoretical data has shown a real possibility of the multilayer specific adsorption (intercalation) of hydrogen between graphene layers in novel carbonaceous nanomaterials. This is of relevance for solving the bottle-neck problem of the hydrogen on-board storage in fuel-cell-powered vehicles, and other technical applications.

  10. Few layered graphene Sheet decorated by ZnO Nanoparticles for anti-bacterial application

    NASA Astrophysics Data System (ADS)

    Bykkam, Satish; Narsingam, Sowmya; Ahmadipour, Mohsen; Dayakar, T.; Venkateswara Rao, K.; Shilpa Chakra, Ch.; Kalakotla, Shanker

    2015-07-01

    A widely soluble few layered graphene (FLG) sheets decorated by ZnO nano particles were prepared through hydrothermal method using ethylene glycol as a solvent and a reducing agent. The obtained FLG/ZnO composite material was characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Raman spectroscopy. The anti-bacterial properties of ZnO nano particles decorated few layered graphenes were tested against Escherichia coli and Salmonella typhi by using well diffusion method. The results confirmed that FLG/ZnO has significant antibacterial activity more against S. typhi than E. coli. The obtained results from the current research work conclusively states that the ZnO nano particles which were decorated by few layered graphene possess a significant anti-bacterial activity.

  11. Electron dynamics of the buffer layer and bilayer graphene on SiC

    SciTech Connect

    Shearer, Alex J.; Caplins, Benjamin W.; Suich, David E.; Harris, Charles B.; Johns, James E.; Hersam, Mark C.

    2014-06-09

    Angle- and time-resolved two-photon photoemission (TPPE) was used to investigate electronic states in the buffer layer of 4H-SiC(0001). An image potential state (IPS) series was observed on this strongly surface-bound buffer layer, and dispersion measurements indicated free-electron-like behavior for all states in this series. These results were compared with TPPE taken on bilayer graphene, which also show the existence of a free-electron-like IPS series. Lifetimes for the n = 2, and n = 3 states were obtained from time-resolved TPPE; slightly increased lifetimes were observed in the bilayer graphene sample for the n = 2 the n = 3 states. Despite the large band gap of graphene at the center of the Brillouin zone, the lifetime results demonstrate that the graphene layers do not behave as a simple tunneling barrier, suggesting that the buffer layer and graphene overlayers play a direct role in the decay of IPS electrons.

  12. Graphene on a metal surface with an h-BN buffer layer: gap opening and N-doping

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Lu, Yunhao; Feng, Y. P.

    2016-04-01

    Graphene grown on a metal surface, Cu(111), with a boron-nitride (h-BN) buffer layer is studied. Our first-principles calculations reveal that charge is transferred from the copper substrate to graphene through the h-BN buffer layer which results in n-doped graphene in the absence of a gate voltage. More importantly, a gap of 0.2 eV, which is comparable to that of a typical narrow gap semiconductor, opens just 0.5 eV below the Fermi level at the Dirac point. The Fermi level can be easily shifted inside this gap to make graphene a semiconductor, which is crucial for graphene-based electronic devices. A graphene-based p-n junction can be realized with graphene eptaxially grown on a metal surface.

  13. Synthesis of transparent vertically aligned TiO2 nanotubes on a few-layer graphene (FLG) film.

    PubMed

    Cottineau, Thomas; Albrecht, Arnaud; Janowska, Izabela; Macher, Nicolas; Bégin, Dominique; Ledoux, Marc Jacques; Pronkin, Sergey; Savinova, Elena; Keller, Nicolas; Keller, Valérie; Pham-Huu, Cuong

    2012-01-30

    Novel transparent 1D-TiO(2)/few-layer graphene electrodes are realised by the anodic growth of vertically aligned TiO(2) nano-tubes on a few-layer graphene film coated on a glass substrate. PMID:22057023

  14. Graphene as a transparent conducting and surface field layer in planar Si solar cells.

    PubMed

    Kumar, Rakesh; Mehta, Bodh R; Bhatnagar, Mehar; S, Ravi; Mahapatra, Silika; Salkalachen, Saji; Jhawar, Pratha

    2014-01-01

    This work presents an experimental and finite difference time domain (FDTD) simulation-based study on the application of graphene as a transparent conducting layer on a planar and untextured crystalline p-n silicon solar cell. A high-quality monolayer graphene with 97% transparency and 350 Ω/□ sheet resistance grown by atmospheric pressure chemical vapor deposition method was transferred onto planar Si cells. An increase in efficiency from 5.38% to 7.85% was observed upon deposition of graphene onto Si cells, which further increases to 8.94% upon SiO2 deposition onto the graphene/Si structure. A large increase in photon conversion efficiency as a result of graphene deposition shows that the electronic interaction and the presence of an electric field at the graphene/Si interface together play an important role in this improvement and additionally lead to a reduction in series resistance due to the conducting nature of graphene. PMID:25114642

  15. Towards wafer-size graphene layers by atmospheric pressure graphitization of silicon carbide.

    PubMed

    Emtsev, Konstantin V; Bostwick, Aaron; Horn, Karsten; Jobst, Johannes; Kellogg, Gary L; Ley, Lothar; McChesney, Jessica L; Ohta, Taisuke; Reshanov, Sergey A; Röhrl, Jonas; Rotenberg, Eli; Schmid, Andreas K; Waldmann, Daniel; Weber, Heiko B; Seyller, Thomas

    2009-03-01

    Graphene, a single monolayer of graphite, has recently attracted considerable interest owing to its novel magneto-transport properties, high carrier mobility and ballistic transport up to room temperature. It has the potential for technological applications as a successor of silicon in the post Moore's law era, as a single-molecule gas sensor, in spintronics, in quantum computing or as a terahertz oscillator. For such applications, uniform ordered growth of graphene on an insulating substrate is necessary. The growth of graphene on insulating silicon carbide (SiC) surfaces by high-temperature annealing in vacuum was previously proposed to open a route for large-scale production of graphene-based devices. However, vacuum decomposition of SiC yields graphene layers with small grains (30-200 nm; refs 14-16). Here, we show that the ex situ graphitization of Si-terminated SiC(0001) in an argon atmosphere of about 1 bar produces monolayer graphene films with much larger domain sizes than previously attainable. Raman spectroscopy and Hall measurements confirm the improved quality of the films thus obtained. High electronic mobilities were found, which reach mu=2,000 cm (2) V(-1) s(-1) at T=27 K. The new growth process introduced here establishes a method for the synthesis of graphene films on a technologically viable basis.

  16. Substrate effect modulates adhesion and proliferation of fibroblast on graphene layer.

    PubMed

    Lin, Feng; Du, Feng; Huang, Jianyong; Chau, Alicia; Zhou, Yongsheng; Duan, Huiling; Wang, Jianxiang; Xiong, Chunyang

    2016-10-01

    Graphene is an emerging candidate for biomedical applications, including biosensor, drug delivery and scaffold biomaterials. Cellular functions and behaviors on different graphene-coated substrates, however, still remain elusive to a great extent. This paper explored the functional responses of cells such as adhesion and proliferation, to different kinds of substrates including coverslips, silicone, polydimethylsiloxane (PDMS) with different curing ratios, PDMS treated with oxygen plasma, and their counterparts coated with single layer graphene (SLG). Specifically, adherent cell number, spreading area and cytoskeleton configuration were exploited to characterize cell-substrate adhesion ability, while MTT assay was employed to test the proliferation capability of fibroblasts. Experimental outcome demonstrated graphene coating had excellent cytocompatibility, which could lead to an increase in early adhesion, spreading, proliferation, and remodeling of cytoskeletons of fibroblast cells. Notably, it was found that the underlying substrate effect, e.g., stiffness of substrate materials, could essentially regulate the adhesion and proliferation of cells cultured on graphene. The stiffer the substrates were, the stronger the abilities of adhesion and proliferation of fibroblasts were. This study not only deepens our understanding of substrate-modulated interfacial interactions between live cells and graphene, but also provides a valuable guidance for the design and application of graphene-based biomaterials in biomedical engineering. PMID:27451366

  17. Graphene as a transparent conducting and surface field layer in planar Si solar cells

    PubMed Central

    2014-01-01

    This work presents an experimental and finite difference time domain (FDTD) simulation-based study on the application of graphene as a transparent conducting layer on a planar and untextured crystalline p-n silicon solar cell. A high-quality monolayer graphene with 97% transparency and 350 Ω/□ sheet resistance grown by atmospheric pressure chemical vapor deposition method was transferred onto planar Si cells. An increase in efficiency from 5.38% to 7.85% was observed upon deposition of graphene onto Si cells, which further increases to 8.94% upon SiO2 deposition onto the graphene/Si structure. A large increase in photon conversion efficiency as a result of graphene deposition shows that the electronic interaction and the presence of an electric field at the graphene/Si interface together play an important role in this improvement and additionally lead to a reduction in series resistance due to the conducting nature of graphene. PMID:25114642

  18. Thermal transport across graphene and single layer hexagonal boron nitride

    SciTech Connect

    Zhang, Jingchao E-mail: yyue@whu.edu.cn; Hong, Yang; Yue, Yanan E-mail: yyue@whu.edu.cn

    2015-04-07

    As the dimensions of nanocircuits and nanoelectronics shrink, thermal energies are being generated in more confined spaces, making it extremely important and urgent to explore for efficient heat dissipation pathways. In this work, the phonon energy transport across graphene and hexagonal boron-nitride (h-BN) interface is studied using classic molecular dynamics simulations. Effects of temperature, interatomic bond strength, heat flux direction, and functionalization on interfacial thermal transport are investigated. It is found out that by hydrogenating graphene in the hybrid structure, the interfacial thermal resistance (R) between graphene and h-BN can be reduced by 76.3%, indicating an effective approach to manipulate the interfacial thermal transport. Improved in-plane/out-of-plane phonon couplings and broadened phonon channels are observed in the hydrogenated graphene system by analyzing its phonon power spectra. The reported R results monotonically decrease with temperature and interatomic bond strengths. No thermal rectification phenomenon is observed in this interfacial thermal transport. Results reported in this work give the fundamental knowledge on graphene and h-BN thermal transport and provide rational guidelines for next generation thermal interface material designs.

  19. Band gap engineering for single-layer graphene by using slow Li(+) ions.

    PubMed

    Ryu, Mintae; Lee, Paengro; Kim, Jingul; Park, Heemin; Chung, Jinwook

    2016-08-01

    In order to utilize the superb electronic properties of graphene in future electronic nano-devices, a dependable means of controlling the transport properties of its Dirac electrons has to be devised by forming a tunable band gap. We report on the ion-induced modification of the electronic properties of single-layer graphene (SLG) grown on a SiC(0001) substrate by doping low-energy (5 eV) Li(+) ions. We find the opening of a sizable and tunable band gap up to 0.85 eV, which depends on the Li(+) ion dose as well as the following thermal treatment, and is the largest band gap in the π-band of SLG by any means reported so far. Our Li 1s core-level data together with the valence band suggest that Li(+) ions do not intercalate below the topmost graphene layer, but cause a significant charge asymmetry between the carbon sublattices of SLG to drive the opening of the band gap. We thus provide a route to producing a tunable graphene band gap by doping Li(+) ions, which may play a pivotal role in the utilization of graphene in future graphene-based electronic nano-devices. PMID:27345294

  20. Theory of photon-electron interaction in single-layer graphene sheet

    NASA Astrophysics Data System (ADS)

    Nguyen, Bich Ha; Hieu Nguyen, Van; Bui, Dinh Hoi; Thu Phuong Le, Thi

    2015-12-01

    The purpose of this work is to elaborate the quantum theory of photon-electron interaction in a single-layer graphene sheet. Since the light source must be located outside the extremely thin graphene sheet, the problem must be formulated and solved in the three-dimensional physical space, in which the graphene sheet is a thin plane layer. It is convenient to use the orthogonal coordinate system in which the xOy coordinate plane is located in the middle of the plane graphene sheet and therefore the Oz axis is perpendicular to this plane. For the simplicity we assume that the quantum motions of electron in the directions parallel to the coordinate plane xOy and that along the direction of the Oz axis are independent. Then we have a relatively simple formula for the overall Hamiltonian of the electron gas in the graphene sheet. The explicit expressions of the wave functions of the charge carriers are easily derived. The electron-hole formalism is introduced, and the Hamiltonian of the interaction of some external quantum electromagnetic field with the charge carriers in the graphene sheet is established. From the expression of this interaction Hamiltonian it is straightforward to derive the matrix elements of photons with the Dirac fermion-Dirac hole pairs as well as with the electrons in the quantum well along the direction of the Oz axis.

  1. Band gap engineering for single-layer graphene by using slow Li+ ions

    NASA Astrophysics Data System (ADS)

    Ryu, Mintae; Lee, Paengro; Kim, Jingul; Park, Heemin; Chung, Jinwook

    2016-08-01

    In order to utilize the superb electronic properties of graphene in future electronic nano-devices, a dependable means of controlling the transport properties of its Dirac electrons has to be devised by forming a tunable band gap. We report on the ion-induced modification of the electronic properties of single-layer graphene (SLG) grown on a SiC(0001) substrate by doping low-energy (5 eV) Li+ ions. We find the opening of a sizable and tunable band gap up to 0.85 eV, which depends on the Li+ ion dose as well as the following thermal treatment, and is the largest band gap in the π-band of SLG by any means reported so far. Our Li 1s core-level data together with the valence band suggest that Li+ ions do not intercalate below the topmost graphene layer, but cause a significant charge asymmetry between the carbon sublattices of SLG to drive the opening of the band gap. We thus provide a route to producing a tunable graphene band gap by doping Li+ ions, which may play a pivotal role in the utilization of graphene in future graphene-based electronic nano-devices.

  2. Magneto-transport properties of a random distribution of few-layer graphene patches

    NASA Astrophysics Data System (ADS)

    Iacovella, Fabrice; Trinsoutrot, Pierre; Mitioglu, Anatolie; Conédéra, Véronique; Pierre, Mathieu; Raquet, Bertrand; Goiran, Michel; Vergnes, Hugues; Caussat, Brigitte; Plochocka, Paulina; Escoffier, Walter

    2014-11-01

    In this study, we address the electronic properties of conducting films constituted of an array of randomly distributed few layer graphene patches and investigate on their most salient galvanometric features in the moderate and extreme disordered limit. We demonstrate that, in annealed devices, the ambipolar behaviour and the onset of Landau level quantization in high magnetic field constitute robust hallmarks of few-layer graphene films. In the strong disorder limit, however, the magneto-transport properties are best described by a variable-range hopping behaviour. A large negative magneto-conductance is observed at the charge neutrality point, in consistency with localized transport regime.

  3. Quantifying defects in N-layer graphene via a phenomenological model of Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Giro, Ronaldo; Archanjo, Braulio S.; Martins Ferreira, Erlon H.; Capaz, Rodrigo B.; Jorio, Ado; Achete, Carlos A.

    2014-01-01

    We construct a model to obtain the density of point defects in N-layer graphene by combining Raman spectroscopy and the TRIM (Transport Range of Ions in Matter) simulation package. The model relates the intensity (or area) ratio of graphene's D and G bands to the defect density on each layer due to Ar+ bombardment. Our method is effective for ion fluences ranging from 1011 to ∼1014 Ar+/cm-2 and it should be in principle extendable to any kind of ion and energy.

  4. Nanoscale mapping of intrinsic defects in single-layer graphene using tip-enhanced Raman spectroscopy.

    PubMed

    Su, Weitao; Kumar, Naresh; Dai, Ning; Roy, Debdulal

    2016-07-01

    Non-gap mode tip-enhanced Raman spectroscopy (TERS) is used for the first time to successfully map the intrinsic defects in single-layer graphene with 20 nm spatial resolution. The nanoscale Raman mapping is enabled by an unprecedented near-field to far-field signal contrast of 8.5 at the Ag-coated TERS tip-apex. These results demonstrate the potential of TERS for characterisation of defects in single-layer graphene-based devices at the nanometre length-scale. PMID:27279142

  5. Surface diffusion coefficient of Au atoms on single layer graphene grown on Cu

    SciTech Connect

    Ruffino, F. Cacciato, G.; Grimaldi, M. G.

    2014-02-28

    A 5 nm thick Au film was deposited on single layer graphene sheets grown on Cu. By thermal processes, the dewetting phenomenon of the Au film on the graphene was induced so to form Au nanoparticles. The mean radius, surface-to-surface distance, and surface density evolution of the nanoparticles on the graphene sheets as a function of the annealing temperature were quantified by scanning electron microscopy analyses. These quantitative data were analyzed within the classical mean-field nucleation theory so to obtain the temperature-dependent Au atoms surface diffusion coefficient on graphene: D{sub S}(T)=[(8.2±0.6)×10{sup −8}]exp[−(0.31±0.02(eV)/(at) )/kT] cm{sup 2}/s.

  6. Bimodal behaviour of charge carriers in graphene induced by electric double layer

    NASA Astrophysics Data System (ADS)

    Tsai, Sing-Jyun; Yang, Ruey-Jen

    2016-07-01

    A theoretical investigation is performed into the electronic properties of graphene in the presence of liquid as a function of the contact area ratio. It is shown that the electric double layer (EDL) formed at the interface of the graphene and the liquid causes an overlap of the conduction bands and valance bands and increases the density of state (DOS) at the Fermi energy (EF). In other words, a greater number of charge carriers are induced for transport and the graphene changes from a semiconductor to a semimetal. In addition, it is shown that the dependence of the DOS at EF on the contact area ratio has a bimodal distribution which responses to the experimental observation, a pinnacle curve. The maximum number of induced carriers is expected to occur at contact area ratios of 40% and 60%. In general, the present results indicate that modulating the EDL provides an effective means of tuning the electronic properties of graphene in the presence of liquid.

  7. An iron-based green approach to 1-h production of single-layer graphene oxide

    NASA Astrophysics Data System (ADS)

    Peng, Li; Xu, Zhen; Liu, Zheng; Wei, Yangyang; Sun, Haiyan; Li, Zheng; Zhao, Xiaoli; Gao, Chao

    2015-01-01

    As a reliable and scalable precursor of graphene, graphene oxide (GO) is of great importance. However, the environmentally hazardous heavy metals and poisonous gases, explosion risk and long reaction times involved in the current synthesis methods of GO increase the production costs and hinder its real applications. Here we report an iron-based green strategy for the production of single-layer GO in 1 h. Using the strong oxidant K2FeO4, our approach not only avoids the introduction of polluting heavy metals and toxic gases in preparation and products but also enables the recycling of sulphuric acid, eliminating pollution. Our dried GO powder is highly soluble in water, in which it forms liquid crystals capable of being processed into macroscopic graphene fibres, films and aerogels. This green, safe, highly efficient and ultralow-cost approach paves the way to large-scale commercial applications of graphene.

  8. Direct growth of single-layer graphene on Ni surface manipulated by Si barrier

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Li, Jinhua; Chen, Da; Zheng, Li; Zheng, Xiaohu; Guo, Qinglei; Wei, Xing; Ding, Guqiao; Zhang, Miao; Di, Zengfeng; Liu, Su

    2014-05-01

    Pure Ni film is the first metal catalyst that can generate graphene with small domains and variable thickness across the film. The lack of control over layer number is attributed to the high carbon solubility of Ni. We designed a combinatorial Ni/Si system, which enables the direct growth of monolayer graphene via chemical vapor deposition method. In this system, Si was introduced as the carbon diffusion barriers to prevent carbon diffusing into Ni film. The designed system fully overcomes the fundamental limitations of Ni and provides a facile and effective strategy to yield homogenous monolayer graphene over large area. The field effect transistors were fabricated and characterized to determine the electrical properties of the synthesized graphene film. Furthermore, this technique can utilize standard equipments available in semiconductor technology.

  9. Optical limiting properties and mechanisms of single-layer graphene dispersions in heavy-atom solvents.

    PubMed

    Yan, Lihe; Xiong, Yaobing; Si, Jinhai; Sun, Xuehui; Yi, Wenhui; Hou, Xun

    2014-12-29

    The optical limiting (OL) properties of single-layer graphene dispersions in different solvents were studied using a nanosecond pulse laser. The graphene dispersions, especially in heavy-atom solvents, showed much better OL properties compared with referenced C60-toluene solution. The dependences of OL thresholds and nonlinear scattering (NLS) intensities on the solvent surface tensions indicated that, NLS effect played an important role in the OL process of graphene dispersions, while nonlinear absorption (NLA) effect might also contribute in solvents with heavy atoms. The NLA measurements further demonstrated the contribution of NLA effect to the excellent OL property of graphene dispersions in heavy-atom solvents. PMID:25607151

  10. An iron-based green approach to 1-h production of single-layer graphene oxide

    PubMed Central

    Peng, Li; Xu, Zhen; Liu, Zheng; Wei, Yangyang; Sun, Haiyan; Li, Zheng; Zhao, Xiaoli; Gao, Chao

    2015-01-01

    As a reliable and scalable precursor of graphene, graphene oxide (GO) is of great importance. However, the environmentally hazardous heavy metals and poisonous gases, explosion risk and long reaction times involved in the current synthesis methods of GO increase the production costs and hinder its real applications. Here we report an iron-based green strategy for the production of single-layer GO in 1 h. Using the strong oxidant K2FeO4, our approach not only avoids the introduction of polluting heavy metals and toxic gases in preparation and products but also enables the recycling of sulphuric acid, eliminating pollution. Our dried GO powder is highly soluble in water, in which it forms liquid crystals capable of being processed into macroscopic graphene fibres, films and aerogels. This green, safe, highly efficient and ultralow-cost approach paves the way to large-scale commercial applications of graphene. PMID:25607686

  11. Use of Double Layer of Acellular Dermal Matrix and Modified Tunnel Technique to Treat Multiple Adjacent Gingival Recession Defects.

    PubMed

    Mahn, Douglas H

    2016-09-01

    The goal of connective tissue grafting is to cover exposed root surfaces with gingival tissues that are stable and have a natural appearance. The use of an acellular dermal matrix (ADM) has been shown to be a successful alternative to the palatal connective tissue graft. Use of a double layer of an ADM has been shown to have stable results for 1 year. Tunnel grafting techniques can yield root coverage with a natural appearing soft-tissue architecture. The purpose of this case report is to demonstrate the use of a modified tunnel technique and a double layer of ADM in the treatment of multiple adjacent gingival recession defects. Treated teeth were found to have root coverage and natural soft-tissue contours that were stable at 20 months. PMID:27606567

  12. Single adatom dynamics at monatomic steps of free-standing few-layer reduced graphene

    PubMed Central

    Chang, Haixin; Saito, Mitsuhiro; Nagai, Takuro; Liang, Yunye; Kawazoe, Yoshiyuki; Wang, Zhongchang; Wu, Hongkai; Kimoto, Koji; Ikuhara, Yuichi

    2014-01-01

    Steps and their associated adatoms extensively exist and play prominent roles in affecting surface properties of materials. Such impacts should be especially pronounced in two-dimensional, atomically-thin membranes like graphene. However, how single adatom behaves at monatomic steps of few-layer graphene is still illusive. Here, we report dynamics of individual adatom at monatomic steps of free-standing few-layer reduced graphene under the electron beam radiations, and demonstrate the prevalent existence of monatomic steps even down to unexpectedly ultrasmall lateral size of a circular diameter of ~5 Å. Single adatom prefers to stay at the edges of the atomic steps of few-layer reduced graphene and evolve with the steps. Moreover, we also find that how the single adatom behaves at atomic step edges can be remarkably influenced by the type of adatoms and step edges. Such single adatoms at monatomic steps and ultrasmall atomic steps open up a new window for surface physics and chemistry for graphene-based as well as other two-dimensional materials. PMID:25113125

  13. Single-layer and bilayer graphene superlattices: collimation, additional Dirac points and Dirac lines.

    PubMed

    Barbier, Michaël; Vasilopoulos, Panagiotis; Peeters, François M

    2010-12-13

    We review the energy spectrum and transport properties of several types of one-dimensional superlattices (SLs) on single-layer and bilayer graphene. In single-layer graphene, for certain SL parameters an electron beam incident on an SL is highly collimated. On the other hand, there are extra Dirac points generated for other SL parameters. Using rectangular barriers allows us to find analytical expressions for the location of new Dirac points in the spectrum and for the renormalization of the electron velocities. The influence of these extra Dirac points on the conductivity is investigated. In the limit of δ-function barriers, the transmission T through and conductance G of a finite number of barriers as well as the energy spectra of SLs are periodic functions of the dimensionless strength P of the barriers, Pδ(x) = V(x)/ħv(F), with v(F) the Fermi velocity. For a Kronig-Penney SL with alternating sign of the height of the barriers, the Dirac point becomes a Dirac line for P = π/2+nπ with n an integer. In bilayer graphene, with an appropriate bias applied to the barriers and wells, we show that several new types of SLs are produced and two of them are similar to type I and type II semiconductor SLs. Similar to single-layer graphene SLs, extra 'Dirac' points are found in bilayer graphene SLs. Non-ballistic transport is also considered. PMID:21041227

  14. Plasmon Excitations of Multi-layer Graphene on a Conducting Substrate

    PubMed Central

    Gumbs, Godfrey; Iurov, Andrii; Wu, Jhao-Ying; Lin, M. F.; Fekete, Paula

    2016-01-01

    We predict the existence of low-frequency nonlocal plasmons at the vacuum-surface interface of a superlattice of N graphene layers interacting with conducting substrate. We derive a dispersion function that incorporates the polarization function of both the graphene monolayers and the semi-infinite electron liquid at whose surface the electrons scatter specularly. We find a surface plasmon-polariton that is not damped by particle-hole excitations or the bulk modes and which separates below the continuum mini-band of bulk plasmon modes. The surface plasmon frequency of the hybrid structure always lies below , the surface plasmon frequency of the conducting substrate. The intensity of this mode depends on the distance of the graphene layers from the conductor’s surface, the energy band gap between valence and conduction bands of graphene monolayer and, most importantly, on the number of two-dimensional layers. For a sufficiently large number of layers the hybrid structure has no surface plasmon. The existence of plasmons with different dispersion relations indicates that quasiparticles with different group velocity may coexist for various ranges of wavelengths determined by the number of layers in the superlattice. PMID:26883086

  15. Plasmon Excitations of Multi-layer Graphene on a Conducting Substrate.

    PubMed

    Gumbs, Godfrey; Iurov, Andrii; Wu, Jhao-Ying; Lin, M F; Fekete, Paula

    2016-02-17

    We predict the existence of low-frequency nonlocal plasmons at the vacuum-surface interface of a superlattice of N graphene layers interacting with conducting substrate. We derive a dispersion function that incorporates the polarization function of both the graphene monolayers and the semi-infinite electron liquid at whose surface the electrons scatter specularly. We find a surface plasmon-polariton that is not damped by particle-hole excitations or the bulk modes and which separates below the continuum mini-band of bulk plasmon modes. The surface plasmon frequency of the hybrid structure always lies below ωs = ωp/√2, the surface plasmon frequency of the conducting substrate. The intensity of this mode depends on the distance of the graphene layers from the conductor's surface, the energy band gap between valence and conduction bands of graphene monolayer and, most importantly, on the number of two-dimensional layers. For a sufficiently large number of layers (N ≥ 7) the hybrid structure has no surface plasmon. The existence of plasmons with different dispersion relations indicates that quasiparticles with different group velocity may coexist for various ranges of wavelengths determined by the number of layers in the superlattice.

  16. How water layers on graphene affect folding and adsorption of TrpZip2.

    PubMed

    Peter, Emanuel K; Agarwal, Mrigya; Kim, BongKeun; Pivkin, Igor V; Shea, Joan-Emma

    2014-12-14

    We present a computational study of the folding of the Trp-rich β-hairpin TrpZip2 near graphene, a surface of interest as a platform for biosensors. The protein adsorbs to the surface, populating a new bound, folded state, coexisting with extended, adsorbed conformations. Adsorption and folding are modulated by direct interactions between the indole rings of TrpZip2 and the rings on the graphene surface, as well as by indirect water-mediated interactions. In particular, we observe strong layering of water near graphene, ice-like water configurations, and the formation of short lived hydrogen-bonds between water and protein. In order to study the effect of this layering in more detail, we modified the interactions between graphene and water to obtain two extreme cases: (1) enhanced layering of water that prevents the peptide from penetrating the water layer thereby enabling it to fold to a bulk-like structure, and (2) disruption of the water layer leading to adsorption and unfolding of the protein on the surface. These studies illuminate the roles of direct and solvent mediated interactions in modulating adsorption and folding of proteins on surfaces. PMID:25494782

  17. Growth and optical characteristics of high-quality ZnO thin films on graphene layers

    SciTech Connect

    Park, Suk In; Tchoe, Youngbin; Baek, Hyeonjun; Hyun, Jerome K.; Yi, Gyu-Chul E-mail: gcyi@snu.ac.kr; Heo, Jaehyuk; Jo, Janghyun; Kim, Miyoung; Kim, Nam-Jung E-mail: gcyi@snu.ac.kr

    2015-01-01

    We report the growth of high-quality, smooth, and flat ZnO thin films on graphene layers and their photoluminescence (PL) characteristics. For the growth of high-quality ZnO thin films on graphene layers, ZnO nanowalls were grown using metal-organic vapor-phase epitaxy on oxygen-plasma treated graphene layers as an intermediate layer. PL measurements were conducted at low temperatures to examine strong near-band-edge emission peaks. The full-width-at-half-maximum value of the dominant PL emission peak was as narrow as 4 meV at T = 11 K, comparable to that of the best-quality films reported previously. Furthermore, the stimulated emission of ZnO thin films on the graphene layers was observed at the low excitation energy of 180 kW/cm{sup 2} at room temperature. Their structural and optical characteristics were investigated using X-ray diffraction, transmission electron microscopy, and PL spectroscopy.

  18. Electronic Structure and Morphology of Graphene Layers on SiC

    NASA Astrophysics Data System (ADS)

    Ohta, Taisuke

    2008-03-01

    Recent years have witnessed the discovery and the unique electronic properties of graphene, a sheet of carbon atoms arranged in a honeycomb lattice. The unique linear dispersion relation of charge carriers near the Fermi level (``Dirac Fermions'') lead to exciting transport properties, such as an unusual quantum Hall effect, and have aroused scientific and technological interests. On the way towards graphene-based electronics, a knowledge of the electronic band structure and the morphology of epitaxial graphene films on silicon carbide substrates is imperative. We have studied the evolution of the occupied band structure and the morphology of graphene layers on silicon carbide by systematically increasing the layer thickness. Using angle-resolved photoemission spectroscopy (ARPES), we examine this unique 2D system in its development from single layer to multilayers, by characteristic changes in the π band, the highest occupied state, and the dispersion relation in the out-of-plane electron wave vector in particular. The evolution of the film morphology is evaluated by the combination of low-energy electron microscopy and ARPES. By exploiting the sensitivity of graphene's electronic states to the charge carrier concentration, changes in the on-site Coulomb potential leading to a change of π and π* bands can be examined using ARPES. We demonstrate that, in a graphene bilayer, the gap between π and π* bands can be controlled by selectively adjusting relative carrier concentrations, which suggests a possible application of the graphene bilayer for switching functions in electronic devices. This work was done in collaboration with A. Bostwick, J. L. McChesney, and E. Rotenberg at Advanced Light Source, Lawrence Berkeley National Laboratory, K. Horn at Fritz-Haber-Institut, K. V. Emtsev and Th. Seyller at Lehrstuhl für Technische Physik, Universität Erlangen-Nürnberg, and F. El Gabaly and A. K. Schmid at National Center for Electron Microscopy, Lawrence Berkeley

  19. Edge field emission of large-area single layer graphene

    NASA Astrophysics Data System (ADS)

    Kleshch, Victor I.; Bandurin, Denis A.; Orekhov, Anton S.; Purcell, Stephen T.; Obraztsov, Alexander N.

    2015-12-01

    Field electron emission from the edges of large-area (∼1 cm × 1 cm) graphene films deposited onto quartz wafers was studied. The graphene was previously grown by chemical vapour deposition on copper. An extreme enhancement of electrostatic field at the edge of the films with macroscopically large lateral dimensions and with single atom thickness was achieved. This resulted in the creation of a blade type electron emitter, providing stable field emission at low-voltage with linear current density up to 0.5 mA/cm. A strong hysteresis in current-voltage characteristics and a step-like increase of the emission current during voltage ramp up were observed. These effects were explained by the local mechanical peeling of the graphene edge from the quartz substrate by the ponderomotive force during the field emission process. Specific field emission phenomena exhibited in the experimental study are explained by a unique combination of structural, electronic and mechanical properties of graphene. Various potential applications ranging from linear electron beam sources to microelectromechanical systems are discussed.

  20. One-step formation of a single atomic-layer transistor by the selective fluorination of a graphene film.

    PubMed

    Ho, Kuan-I; Liao, Jia-Hong; Huang, Chi-Hsien; Hsu, Chang-Lung; Zhang, Wenjing; Lu, Ang-Yu; Li, Lain-Jong; Lai, Chao-Sung; Su, Ching-Yuan

    2014-03-12

    In this study, the scalable and one-step fabrication of single atomic-layer transistors is demonstrated by the selective fluorination of graphene using a low-damage CF4 plasma treatment, where the generated F-radicals preferentially fluorinated the graphene at low temperature (<200 °C) while defect formation was suppressed by screening out the effect of ion damage. The chemical structure of the C-F bonds is well correlated with their optical and electrical properties in fluorinated graphene, as determined by X-ray photoelectron spectroscopy, Raman spectroscopy, and optical and electrical characterizations. The electrical conductivity of the resultant fluorinated graphene (F-graphene) was demonstrated to be in the range between 1.6 kΩ/sq and 1 MΩ/sq by adjusting the stoichiometric ratio of C/F in the range between 27.4 and 5.6, respectively. Moreover, a unique heterojunction structure of semi-metal/semiconductor/insulator can be directly formed in a single layer of graphene using a one-step fluorination process by introducing a Au thin-film as a buffer layer. With this heterojunction structure, it would be possible to fabricate transistors in a single graphene film via a one-step fluorination process, in which pristine graphene, partial F-graphene, and highly F-graphene serve as the source/drain contacts, the channel, and the channel isolation in a transistor, respectively. The demonstrated graphene transistor exhibits an on-off ratio above 10, which is 3-fold higher than that of devices made from pristine graphene. This efficient transistor fabrication method produces electrical heterojunctions of graphene over a large area and with selective patterning, providing the potential for the integration of electronics down to the single atomic-layer scale.

  1. The Assembling of Poly (3-Octyl-Thiophene) on CVD Grown Single Layer Graphene

    PubMed Central

    Jiang, Yanqiu; Yang, Ling; Guo, Zongxia; Lei, Shengbin

    2015-01-01

    The interface between organic semiconductor and graphene electrode, especially the structure of the first few molecular layers at the interface, is crucial for the device properties such as the charge transport in organic field effect transistors. In this work, we have used scanning tunneling microscopy to investigate the poly (3-octyl-thiophene) (P3OT)-graphene interface. Our results reveal the dynamic assembling of P3OT on single layer graphene. As on other substrates the epitaxial effect plays a role in determining the orientation of the P3OT assembling, however, the inter-thiophene distance along the backbone is consistent with that optimized in vaccum, no compression was observed. Adsorption of P3OT on ripples is weaker due to local curvature, which has been verified both by scanning tunneling microscopy and density functional theory simulation. Scanning tunneling microscopy also reveals that P3OT tends to form hairpin folds when meets a ripple. PMID:26634648

  2. A 3D insight on the catalytic nanostructuration of few-layer graphene

    PubMed Central

    Melinte, G.; Florea, I.; Moldovan, S.; Janowska, I.; Baaziz, W.; Arenal, R.; Wisnet, A.; Scheu, C.; Begin-Colin, S.; Begin, D.; Pham-Huu, C.; Ersen, O.

    2014-01-01

    The catalytic cutting of few-layer graphene is nowadays a hot topic in materials research due to its potential applications in the catalysis field and the graphene nanoribbons fabrication. We show here a 3D analysis of the nanostructuration of few-layer graphene by iron-based nanoparticles under hydrogen flow. The nanoparticles located at the edges or attached to the steps on the FLG sheets create trenches and tunnels with orientations, lengths and morphologies defined by the crystallography and the topography of the carbon substrate. The cross-sectional analysis of the 3D volumes highlights the role of the active nanoparticle identity on the trench size and shape, with emphasis on the topographical stability of the basal planes within the resulting trenches and channels, no matter the obstacle encountered. The actual study gives a deep insight on the impact of nanoparticles morphology and support topography on the 3D character of nanostructures built up by catalytic cutting. PMID:24916201

  3. Evolution of the Raman spectra from single-, few-, and many-layer graphene with increasing disorder

    SciTech Connect

    Martins Ferreira, E. H.; Stavale, F.; Moutinho, Marcus V. O.; Lucchese, M. M.; Capaz, Rodrigo B.; Achete, C. A.; Jorio, A.

    2010-09-15

    We report on the micro-Raman spectroscopy of monolayer, bilayer, trilayer, and many layers of graphene (graphite) bombarded by low-energy argon ions with different doses. The evolution of peak frequencies, intensities, linewidths, and areas of the main Raman bands of graphene is analyzed as function of the distance between defects and number of layers. We describe the disorder-induced frequency shifts and the increase in the linewidth of the Raman bands by means of a spatial-correlation model. Also, the evolution of the relative areas A{sub D}/A{sub G}, A{sub D}{sup '}/A{sub G}, and A{sub G}{sup '}/A{sub G} is described by a phenomenological model. The present results can be used to fully characterize disorder in graphene systems.

  4. Plasmon-drag-assisted terahertz generation in a graphene layer incorporating an asymmetric plasmon nanostructure

    NASA Astrophysics Data System (ADS)

    Raeis-Zadeh, S. Mohsen; Semnani, Behrooz; Safavi-Naeini, Safieddin

    2016-09-01

    This Rapid Communication presents a structure and full theoretical analysis to exploit the photon drag effect for THz signal generation in a graphene layer integrated with a plasmonic structure. The plasmonic structure is composed of a periodic array of asymmetric nanoparticles patterned over a graphene layer. The nanoparticles are designed to accomplish two goals: field localization due to the plasmonic resonance and manipulating the phase of the near field to effectively drag the quasiparticles in graphene. Combining the asymmetry with the plasmon resonances of nanoparticles, we show that an enhancement as large as three orders of magnitude is attainable in the power of the generated THz wave. This level of unprecedented enhancement mostly stems from the phase manipulation of the near field caused by asymmetric nanoparticles. Using the achieved enhancement, it is demonstrated that an ultra-wideband THz signal carrying the power of 1 μ W can be generated using a commercially available femtosecond pulsed laser.

  5. Influence of Metal Contacts on Graphene Transport Characteristics and Its Removal with Nano-carbon Interfacial Layer

    NASA Astrophysics Data System (ADS)

    Kanda, Akinobu; Ito, Yu; Katakura, Kenta; Sonoda, Hiroki; Higuchi, Shoma; Tomori, Hikari; Ootuka, Youiti

    Graphene is a promising candidate for the next-generation electronic material. While considerable effort has been devoted to achieve higher mobility in graphene films, relatively little attention has been paid to the effect of metal contacts, which are indispensable to the electric devices. At a graphene/metal interface, mainly due to the difference in work functions, carriers are injected from the metal to graphene. The resulting shift of local Dirac point is not limited at the graphene/metal interface but extends into the graphene channel. This carrier doping affects more significantly the performance of graphene field effect devices with shorter channel, as well as may conceal Dirac physics at the graphene/metal interface. Here, we experimentally investigate the channel length dependence of graphene transport properties in a wide gate-voltage range and extract the effect of metal contact. Several metal species are investigated. We reveal the origin of electron-hole asymmetry and the effect of the chemical interaction between graphene and metal, and derive the effective work function of graphene (4.93 eV). Furthermore, we succeed in reducing the influence of metal contact by inserting a thin nano-carbon layer (amorphous carbon or multilayer graphene (MLG)) at the interface.

  6. Selective ionic transport through tunable subnanometer pores in single-layer graphene membranes.

    PubMed

    O'Hern, Sean C; Boutilier, Michael S H; Idrobo, Juan-Carlos; Song, Yi; Kong, Jing; Laoui, Tahar; Atieh, Muataz; Karnik, Rohit

    2014-03-12

    We report selective ionic transport through controlled, high-density, subnanometer diameter pores in macroscopic single-layer graphene membranes. Isolated, reactive defects were first introduced into the graphene lattice through ion bombardment and subsequently enlarged by oxidative etching into permeable pores with diameters of 0.40 ± 0.24 nm and densities exceeding 10(12) cm(-2), while retaining structural integrity of the graphene. Transport measurements across ion-irradiated graphene membranes subjected to in situ etching revealed that the created pores were cation-selective at short oxidation times, consistent with electrostatic repulsion from negatively charged functional groups terminating the pore edges. At longer oxidation times, the pores allowed transport of salt but prevented the transport of a larger organic molecule, indicative of steric size exclusion. The ability to tune the selectivity of graphene through controlled generation of subnanometer pores addresses a significant challenge in the development of advanced nanoporous graphene membranes for nanofiltration, desalination, gas separation, and other applications.

  7. 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.

  8. Examining the impact of multi-layer graphene using cellular and amphibian models

    NASA Astrophysics Data System (ADS)

    Muzi, Laura; Mouchet, Florence; Cadarsi, Stéphanie; Janowska, Izabela; Russier, Julie; Ménard-Moyon, Cécilia; Risuleo, Gianfranco; Soula, Brigitte; Galibert, Anne-Marie; Flahaut, Emmanuel; Pinelli, Eric; Gauthier, Laury; Bianco, Alberto

    2016-06-01

    In the last few years, graphene has been defined as the revolutionary material showing an incredible expansion in industrial applications. Different graphene forms have been applied in several contexts, spreading from energy technologies and electronics to food and agriculture technologies. Graphene showed promises also in the biomedical field. Hopeful results have been already obtained in diagnostic, drug delivery, tissue regeneration and photothermal cancer ablation. In view of the enormous development of graphene-based technologies, a careful assessment of its impact on health and environment is demanded. It is evident how investigating the graphene toxicity is of fundamental importance in the context of medical purposes. On the other hand, the nanomaterial present in the environment, likely to be generated all along the industrial life-cycle, may have harmful effects on living organisms. In the present work, an important contribution on the impact of multi-layer graphene (MLG) on health and environment is given by using a multifaceted approach. For the first purpose, the effect of the material on two mammalian cell models was assessed. Key cytotoxicity parameters were considered such as cell viability and inflammatory response induction. This was combined with an evaluation of MLG toxicity towards Xenopus laevis, used as both in vivo and environmental model organism.

  9. Giant enhancement in vertical conductivity of stacked CVD graphene sheets by self-assembled molecular layers.

    PubMed

    Liu, Yanpeng; Yuan, Li; Yang, Ming; Zheng, Yi; Li, Linjun; Gao, Libo; Nerngchamnong, Nisachol; Nai, Chang Tai; Sangeeth, C S Suchand; Feng, Yuan Ping; Nijhuis, Christian A; Loh, Kian Ping

    2014-11-20

    Layer-by-layer-stacked chemical vapour deposition (CVD) graphene films find applications as transparent and conductive electrodes in solar cells, organic light-emitting diodes and touch panels. Common to lamellar-type systems with anisotropic electron delocalization, the plane-to-plane (vertical) conductivity in such systems is several orders lower than its in-plane conductivity. The poor electronic coupling between the planes is due to the presence of transfer process organic residues and trapped air pocket in wrinkles. Here we show the plane-to-plane tunnelling conductivity of stacked CVD graphene layers can be improved significantly by inserting 1-pyrenebutyric acid N-hydroxysuccinimide ester between the graphene layers. The six orders of magnitude increase in plane-to-plane conductivity is due to hole doping, orbital hybridization, planarization and the exclusion of polymer residues. Our results highlight the importance of interfacial modification for enhancing the performance of LBL-stacked CVD graphene films, which should be applicable to other types of stacked two-dimensional films.

  10. Wavevector filtering through single-layer and bilayer graphene with magnetic barrier structures

    NASA Astrophysics Data System (ADS)

    Masir, M. Ramezani; Vasilopoulos, P.; Peeters, F. M.

    2008-12-01

    We show that the angular range of the transmission through magnetic barrier structures can be efficiently controlled in single-layer and bilayer graphenes and this renders the structure's efficient wavevector filters. As the number of magnetic barriers increases, this range shrinks, the gaps in the transmission versus energy become wider, and the conductance oscillates with the Fermi energy.

  11. Giant enhancement in vertical conductivity of stacked CVD graphene sheets by self-assembled molecular layers.

    PubMed

    Liu, Yanpeng; Yuan, Li; Yang, Ming; Zheng, Yi; Li, Linjun; Gao, Libo; Nerngchamnong, Nisachol; Nai, Chang Tai; Sangeeth, C S Suchand; Feng, Yuan Ping; Nijhuis, Christian A; Loh, Kian Ping

    2014-01-01

    Layer-by-layer-stacked chemical vapour deposition (CVD) graphene films find applications as transparent and conductive electrodes in solar cells, organic light-emitting diodes and touch panels. Common to lamellar-type systems with anisotropic electron delocalization, the plane-to-plane (vertical) conductivity in such systems is several orders lower than its in-plane conductivity. The poor electronic coupling between the planes is due to the presence of transfer process organic residues and trapped air pocket in wrinkles. Here we show the plane-to-plane tunnelling conductivity of stacked CVD graphene layers can be improved significantly by inserting 1-pyrenebutyric acid N-hydroxysuccinimide ester between the graphene layers. The six orders of magnitude increase in plane-to-plane conductivity is due to hole doping, orbital hybridization, planarization and the exclusion of polymer residues. Our results highlight the importance of interfacial modification for enhancing the performance of LBL-stacked CVD graphene films, which should be applicable to other types of stacked two-dimensional films. PMID:25410480

  12. Surface-Engineered Graphene Quantum Dots Incorporated into Polymer Layers for High Performance Organic Photovoltaics

    PubMed Central

    Kim, Jung Kyu; Kim, Sang Jin; Park, Myung Jin; Bae, Sukang; Cho, Sung-Pyo; Du, Qing Guo; Wang, Dong Hwan; Park, Jong Hyeok; Hong, Byung Hee

    2015-01-01

    Graphene quantum dots (GQDs), a newly emerging 0-dimensional graphene based material, have been widely exploited in optoelectronic devices due to their tunable optical and electronic properties depending on their functional groups. Moreover, the dispersibility of GQDs in common solvents depending on hydrophobicity or hydrophilicity can be controlled by chemical functionalization, which is particularly important for homogeneous incorporation into various polymer layers. Here we report that a surface-engineered GQD-incorporated polymer photovoltaic device shows enhanced power conversion efficiency (PCE), where the oxygen-related functionalization of GQDs enabled good dispersity in a PEDOT:PSS hole extraction layer, leading to significantly improved short circuit current density (Jsc) value. To maximize the PCE of the device, hydrophobic GQDs that are hydrothermally reduced (rGQD) were additionally incorporated in a bulk-heterojunction layer, which is found to promote a synergistic effect with the GQD-incorporated hole extraction layer. PMID:26392211

  13. Reflection electron energy loss spectrum of single layer graphene measured on a graphite substrate

    NASA Astrophysics Data System (ADS)

    Werner, Wolfgang S. M.; Bellissimo, Alessandra; Leber, Roland; Ashraf, Afshan; Segui, Silvina

    2015-05-01

    Reflection electron energy loss spectra (REELS) have been measured on a highly oriented pyrolytic graphite (HOPG) sample. Two spectra were measured for different energies, 1600 eV, being more sensitive to the bulk and 500 eV being more sensitive to the surface. The energy loss distributions for a single surface and bulk excitation were extracted from the two spectra using a simple decomposition procedure. These single scattering loss distributions correspond to electron trajectories with significantly different penetration depths and agree with energy loss spectra measured on free standing single layer graphene and multilayer graphene (i.e. graphite). This result implies that for a layered electron gas (LEG) material, the number of layers which responds in a correlated fashion to an external perturbation is determined by the depth range penetrated by the external perturbation, and not by the number of layers actually present in the specimen.

  14. Perfluorodecyltrichlorosilane-based seed-layer for improved chemical vapour deposition of ultrathin hafnium dioxide films on graphene.

    PubMed

    Kitzmann, Julia; Göritz, Alexander; Fraschke, Mirko; Lukosius, Mindaugas; Wenger, Christian; Wolff, Andre; Lupina, Grzegorz

    2016-07-06

    We investigate the use of perfluorodecyltrichlorosilane-based self-assembled monolayer as seeding layer for chemical vapour deposition of HfO2 on large area CVD graphene. The deposition and evolution of the FDTS-based seed layer is investigated by X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy. Crystalline quality of graphene transferred from Cu is monitored during formation of the seed layer as well as the HfO2 growth using Raman spectroscopy. We demonstrate that FDTS-based seed layer significantly improves nucleation of HfO2 layers so that graphene can be coated in a conformal way with HfO2 layers as thin as 10 nm. Proof-of-concept experiments on 200 mm wafers presented here validate applicability of the proposed approach to wafer scale graphene device fabrication.

  15. Perfluorodecyltrichlorosilane-based seed-layer for improved chemical vapour deposition of ultrathin hafnium dioxide films on graphene

    PubMed Central

    Kitzmann, Julia; Göritz, Alexander; Fraschke, Mirko; Lukosius, Mindaugas; Wenger, Christian; Wolff, Andre; Lupina, Grzegorz

    2016-01-01

    We investigate the use of perfluorodecyltrichlorosilane-based self-assembled monolayer as seeding layer for chemical vapour deposition of HfO2 on large area CVD graphene. The deposition and evolution of the FDTS-based seed layer is investigated by X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy. Crystalline quality of graphene transferred from Cu is monitored during formation of the seed layer as well as the HfO2 growth using Raman spectroscopy. We demonstrate that FDTS-based seed layer significantly improves nucleation of HfO2 layers so that graphene can be coated in a conformal way with HfO2 layers as thin as 10 nm. Proof-of-concept experiments on 200 mm wafers presented here validate applicability of the proposed approach to wafer scale graphene device fabrication. PMID:27381715

  16. Perfluorodecyltrichlorosilane-based seed-layer for improved chemical vapour deposition of ultrathin hafnium dioxide films on graphene

    NASA Astrophysics Data System (ADS)

    Kitzmann, Julia; Göritz, Alexander; Fraschke, Mirko; Lukosius, Mindaugas; Wenger, Christian; Wolff, Andre; Lupina, Grzegorz

    2016-07-01

    We investigate the use of perfluorodecyltrichlorosilane-based self-assembled monolayer as seeding layer for chemical vapour deposition of HfO2 on large area CVD graphene. The deposition and evolution of the FDTS-based seed layer is investigated by X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy. Crystalline quality of graphene transferred from Cu is monitored during formation of the seed layer as well as the HfO2 growth using Raman spectroscopy. We demonstrate that FDTS-based seed layer significantly improves nucleation of HfO2 layers so that graphene can be coated in a conformal way with HfO2 layers as thin as 10 nm. Proof-of-concept experiments on 200 mm wafers presented here validate applicability of the proposed approach to wafer scale graphene device fabrication.

  17. Perfluorodecyltrichlorosilane-based seed-layer for improved chemical vapour deposition of ultrathin hafnium dioxide films on graphene.

    PubMed

    Kitzmann, Julia; Göritz, Alexander; Fraschke, Mirko; Lukosius, Mindaugas; Wenger, Christian; Wolff, Andre; Lupina, Grzegorz

    2016-01-01

    We investigate the use of perfluorodecyltrichlorosilane-based self-assembled monolayer as seeding layer for chemical vapour deposition of HfO2 on large area CVD graphene. The deposition and evolution of the FDTS-based seed layer is investigated by X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy. Crystalline quality of graphene transferred from Cu is monitored during formation of the seed layer as well as the HfO2 growth using Raman spectroscopy. We demonstrate that FDTS-based seed layer significantly improves nucleation of HfO2 layers so that graphene can be coated in a conformal way with HfO2 layers as thin as 10 nm. Proof-of-concept experiments on 200 mm wafers presented here validate applicability of the proposed approach to wafer scale graphene device fabrication. PMID:27381715

  18. Long-Term Passivation of Strongly Interacting Metals with Single-Layer Graphene.

    PubMed

    Weatherup, Robert S; D'Arsié, Lorenzo; Cabrero-Vilatela, Andrea; Caneva, Sabina; Blume, Raoul; Robertson, John; Schloegl, Robert; Hofmann, Stephan

    2015-11-18

    The long-term (>18 months) protection of Ni surfaces against oxidation under atmospheric conditions is demonstrated by coverage with single-layer graphene, formed by chemical vapor deposition. In situ, depth-resolved X-ray photoelectron spectroscopy of various graphene-coated transition metals reveals that a strong graphene-metal interaction is of key importance in achieving this long-term protection. This strong interaction prevents the rapid intercalation of oxidizing species at the graphene-metal interface and thus suppresses oxidation of the substrate surface. Furthermore, the ability of the substrate to locally form a passivating oxide close to defects or damaged regions in the graphene overlayer is critical in plugging these defects and preventing oxidation from proceeding through the bulk of the substrate. We thus provide a clear rationale for understanding the extent to which two-dimensional materials can protect different substrates and highlight the key implications for applications of these materials as barrier layers to prevent oxidation. PMID:26499041

  19. Atomic-scale friction modulated by potential corrugation in multi-layered graphene materials

    NASA Astrophysics Data System (ADS)

    Zhuang, Chunqiang; Liu, Lei

    2015-03-01

    Friction is an important issue that has to be carefully treated for the fabrication of graphene-based nano-scale devices. So far, the friction mechanism of graphene materials on the atomic scale has not yet been clearly presented. Here, first-principles calculations were employed to unveil the friction behaviors and their atomic-scale mechanism. We found that potential corrugations on sliding surfaces dominate the friction force and the friction anisotropy of graphene materials. Higher friction forces correspond to larger corrugations of potential energy, which are tuned by the number of graphene layers. The friction anisotropy is determined by the regular distributions of potential energy. The sliding along a fold-line path (hollow-atop-hollow) has a relatively small potential energy barrier. Thus, the linear sliding observed in macroscopic friction experiments may probably be attributed to the fold-line sliding mode on the atomic scale. These findings can also be extended to other layer-structure materials, such as molybdenum disulfide (MoS2) and graphene-like BN sheets.

  20. Atomic-scale friction modulated by potential corrugation in multi-layered graphene materials

    SciTech Connect

    Zhuang, Chunqiang; Liu, Lei

    2015-03-21

    Friction is an important issue that has to be carefully treated for the fabrication of graphene-based nano-scale devices. So far, the friction mechanism of graphene materials on the atomic scale has not yet been clearly presented. Here, first-principles calculations were employed to unveil the friction behaviors and their atomic-scale mechanism. We found that potential corrugations on sliding surfaces dominate the friction force and the friction anisotropy of graphene materials. Higher friction forces correspond to larger corrugations of potential energy, which are tuned by the number of graphene layers. The friction anisotropy is determined by the regular distributions of potential energy. The sliding along a fold-line path (hollow-atop-hollow) has a relatively small potential energy barrier. Thus, the linear sliding observed in macroscopic friction experiments may probably be attributed to the fold-line sliding mode on the atomic scale. These findings can also be extended to other layer-structure materials, such as molybdenum disulfide (MoS{sub 2}) and graphene-like BN sheets.

  1. Self-healing of vacancy defects in single-layer graphene and silicene

    NASA Astrophysics Data System (ADS)

    Özçelik, V. Ongun; Gurel, H. Hakan; Ciraci, S.

    2013-07-01

    Self-healing mechanisms of vacancy defects in graphene and silicene are studied using first-principles calculations. We investigated host adatom adsorption, diffusion, vacancy formation, and revealed atomistic mechanisms in the healing of single, double, and triple vacancies of single-layer graphene and silicene. Silicon adatom, which is adsorbed to silicene at the top site forms a dumbbell-like structure by pushing one Si atom underneath. The asymmetric reconstruction of the single vacancy in graphene is induced by the magnetization through the rebonding of two dangling bonds and acquiring a significant magnetic moment through the remaining unsaturated dangling bond. In silicene, three twofold coordinated atoms surrounding the single vacancy become fourfold coordinated and nonmagnetic through rebonding. The energy gained through new bond formation becomes the driving force for the reconstruction. Under the external supply of host atoms, while the vacancy defects of graphene heal perfectly, the Stone-Wales defect can form in the course of healing of silicene vacancy. The electronic and magnetic properties of suspended, single-layer graphene and silicene are modified by reconstructed vacancy defects.

  2. Self Healing of Vacancy Defects in Single Layer Graphene and Silicene

    NASA Astrophysics Data System (ADS)

    Ozcelik, V. Ongun; Gurel, Hakan; Ciraci, Salim

    2014-03-01

    Self healing mechanisms of vacancy defects in graphene and silicene are studied using first principles calculations. We investigated host adatom adsorption, diffusion, vacancy formation and revealed atomistic mechanisms in the healing of single, double and triple vacancies of single layer graphene and silicene. Silicon adatom, which is adsorbed to silicene at the top site forms a dumbbell like structure by pushing one Si atom underneath. The asymmetric reconstruction of the single vacancy in graphene is induced by the magnetization through the rebonding of two dangling bonds and acquiring a significant magnetic moment through remaining unsaturated dangling bond. In silicene, three two-fold coordinated atoms surrounding the single vacancy become four-fold coordinated and nonmagnetic through rebonding. The energy gained through new bond formation becomes the driving force for the reconstruction. Under the external supply of host atoms, while the vacancy defects of graphene heal perfectly, Stone-Wales defect can form in the course of healing of silicene vacancy. The electronic and magnetic properties of suspended, single layer graphene and silicene are modified by reconstructed vacancy defects.

  3. Nanoindentation experiments for single-layer rectangular graphene films: a molecular dynamics study

    PubMed Central

    2014-01-01

    A molecular dynamics study on nanoindentation experiments is carried out for some single-layer rectangular graphene films with four edges clamped. Typical load–displacement curves are obtained, and the effects of various factors including indenter radii, loading speeds, and aspect ratios of the graphene film on the simulation results are discussed. A formula describing the relationship between the load and indentation depth is obtained according to the molecular dynamics simulation results. Young’s modulus and the strength of the single-layer graphene film are measured as about 1.0 TPa and 200 GPa, respectively. It is found that the graphene film ruptured in the central point at a critical indentation depth. The deformation mechanisms and dislocation activities are discussed in detail during the loading-unloading-reloading process. It is observed from the simulation results that once the loading speed is larger than the critical loading speed, the maximum force exerted on the graphene film increases and the critical indentation depth decreases with the increase of the loading speed. PMID:24447765

  4. Atomistic finite element model for axial buckling and vibration analysis of single-layered graphene sheets

    NASA Astrophysics Data System (ADS)

    Rouhi, S.; Ansari, R.

    2012-01-01

    In this article, an atomistic model is developed to study the buckling and vibration characteristics of single-layered graphene sheets (SLGSs). By treating SLGSs as space-frame structures, in which the discrete nature of graphene sheets is preserved, they are modeled using three-dimensional elastic beam elements for the bonds. The elastic moduli of the beam elements are determined via a linkage between molecular mechanics and structural mechanics. Based on this model, the critical compressive forces and fundamental natural frequencies of single-layered graphene sheets with different boundary conditions and geometries are obtained and then compared. It is indicated that the compressive buckling force decreases when the graphene sheet aspect ratio increases. At low aspect ratios, the increase of aspect ratios will result in a significant decrease in the critical buckling load. It is also indicated that increasing aspect ratio at a given side length results in the convergence of buckling envelops associated with armchair and zigzag graphene sheets. The influence of boundary conditions will be studied for different geometries. It will be shown that the influence of boundary conditions is not significant for sufficiently large SLGSs.

  5. Controlled surface oxidation of multi-layered graphene anode to increase hole injection efficiency in organic electronic devices

    NASA Astrophysics Data System (ADS)

    Han, Tae-Hee; Kwon, Sung-Joo; Seo, Hong-Kyu; Lee, Tae-Woo

    2016-03-01

    Ultraviolet ozone (UVO) surface treatment of graphene changes its sp2-hybridized carbons to sp3-bonded carbons, and introduces oxygen-containing components. Oxidized graphene has a finite energy band gap, so UVO modification of the surface of a four-layered graphene anode increases its surface ionization potential up to ∼5.2 eV and improves the hole injection efficiency (η) in organic electronic devices by reducing the energy barrier between the graphene anode and overlying organic layers. By controlling the conditions of the UVO treatment, the electrical properties of the graphene can be tuned to improve η. This controlled surface modification of the graphene will provide a way to achieve efficient and stable flexible displays and solid-state lighting.

  6. Tribological characteristics of few-layer graphene over Ni grain and interface boundaries

    NASA Astrophysics Data System (ADS)

    Tripathi, Manoj; Awaja, Firas; Paolicelli, Guido; Bartali, Ruben; Iacob, Erica; Valeri, Sergio; Ryu, Seunghwa; Signetti, Stefano; Speranza, Giorgio; Pugno, Nicola Maria

    2016-03-01

    The tribological properties of metal-supported few-layered graphene depend strongly on the grain topology of the metal substrate. Inhomogeneous distribution of graphene layers at such regions led to variable landscapes with distinguishable roughness. This discrepancy in morphology significantly affects the frictional and wetting characteristics of the FLG system. We discretely measured friction characteristics of FLG covering grains and interfacial grain boundaries of polycrystalline Ni metal substrate via an atomic force microscopy (AFM) probe. The friction coefficient of FLG covered at interfacial grain boundaries is found to be lower than that on grains in vacuum (at 10-5 Torr pressure) and similar results were obtained in air condition. Sliding history with AFM cantilever, static and dynamic pull-in and pull-off adhesion forces were addressed in the course of friction measurements to explain the role of the out-of-plane deformation of graphene layer(s). Finite element simulations showed good agreement with experiments and led to a rationalization of the observations. Thus, with interfacial grain boundaries the FLG tribology can be effectively tuned.The tribological properties of metal-supported few-layered graphene depend strongly on the grain topology of the metal substrate. Inhomogeneous distribution of graphene layers at such regions led to variable landscapes with distinguishable roughness. This discrepancy in morphology significantly affects the frictional and wetting characteristics of the FLG system. We discretely measured friction characteristics of FLG covering grains and interfacial grain boundaries of polycrystalline Ni metal substrate via an atomic force microscopy (AFM) probe. The friction coefficient of FLG covered at interfacial grain boundaries is found to be lower than that on grains in vacuum (at 10-5 Torr pressure) and similar results were obtained in air condition. Sliding history with AFM cantilever, static and dynamic pull-in and pull

  7. Significant thickness dependence of the thermal resistance between few-layer graphenes

    NASA Astrophysics Data System (ADS)

    Ni, Yuxiang; Chalopin, Yann; Volz, Sebastian

    2013-08-01

    The inter-layer resistance in few layer graphene (FLG) is an unknown intrinsic property that affects the heat removal efficiency of FLG-based thermal devices. Here we present data that demonstrates the layer number dependence of the resistance between FLGs, by using molecular dynamics simulations. The resistance was found to decrease as the layer number increases. FLGs with larger thicknesses are proposed to be advantageous in heat spreading owing to their lower contact resistances. The observed properties do not depend on temperature, which is crucial for FLG based structures to retain a stable heat removal efficiency while working at a large temperature range.

  8. Fabricating Large-Area Sheets of Single-Layer Graphene by CVD

    NASA Technical Reports Server (NTRS)

    Bronikowski, Michael; Manohara, Harish

    2008-01-01

    This innovation consists of a set of methodologies for preparing large area (greater than 1 cm(exp 2)) domains of single-atomic-layer graphite, also called graphene, in single (two-dimensional) crystal form. To fabricate a single graphene layer using chemical vapor deposition (CVD), the process begins with an atomically flat surface of an appropriate substrate and an appropriate precursor molecule containing carbon atoms attached to substituent atoms or groups. These molecules will be brought into contact with the substrate surface by being flowed over, or sprayed onto, the substrate, under CVD conditions of low pressure and elevated temperature. Upon contact with the surface, the precursor molecules will decompose. The substituent groups detach from the carbon atoms and form gas-phase species, leaving the unfunctionalized carbon atoms attached to the substrate surface. These carbon atoms will diffuse upon this surface and encounter and bond to other carbon atoms. If conditions are chosen carefully, the surface carbon atoms will arrange to form the lowest energy single-layer structure available, which is the graphene lattice that is sought. Another method for creating the graphene lattice includes metal-catalyzed CVD, in which the decomposition of the precursor molecules is initiated by the catalytic action of a catalytic metal upon the substrate surface. Another type of metal-catalyzed CVD has the entire substrate composed of catalytic metal, or other material, either as a bulk crystal or as a think layer of catalyst deposited upon another surface. In this case, the precursor molecules decompose directly upon contact with the substrate, releasing their atoms and forming the graphene sheet. Atomic layer deposition (ALD) can also be used. In this method, a substrate surface at low temperature is covered with exactly one monolayer of precursor molecules (which may be of more than one type). This is heated up so that the precursor molecules decompose and form one

  9. Enhanced photocurrent density in graphene/Si based solar cell (GSSC) by optimizing active layer thickness

    SciTech Connect

    Rosikhin, Ahmad Hidayat, Aulia Fikri; Syuhada, Ibnu; Winata, Toto

    2015-12-29

    Thickness dependent photocurrent density in active layer of graphene/Si based solar cell has been investigated via analytical – simulation study. This report is a preliminary comparison of experimental and analytical investigation of graphene/Si based solar cell. Graphene sheet was interfaced with Si thin film forming heterojunction solar cell that was treated as a device model for photocurrent generator. Such current can be enhanced by optimizing active layer thickness and involving metal oxide as supporting layer to shift photons absorption. In this case there are two type of devices model with and without TiO{sub 2} in which the silicon thickness varied at 20 – 100 nm. All of them have examined and also compared with each other to obtain an optimum value. From this calculation it found that generated currents almost linear with thickness but there are saturated conditions that no more enhancements will be achieved. Furthermore TiO{sub 2} layer is effectively increases photon absorption but reducing device stability, maximum current is fluctuates enough. This may caused by the disturbance of excitons diffusion and resistivity inside each layer. Finally by controlling active layer thickness, it is quite useful to estimate optimization in order to develop the next solar cell devices.

  10. Numerical Study of Transmission Loss Through a Slow Gas Layer Adjacent to a Plate

    NASA Technical Reports Server (NTRS)

    Schiller, Noah H.; Beck, Benjamin S.; Slagle, Adam C.

    2013-01-01

    This paper describes a systematic numerical investigation of the sound transmission loss through a multilayer system consisting of a bagged gas and lightweight panel. The goal of the study is to better understand the effect of the gas on transmission loss and determine whether a gas with a slow speed of sound is beneficial for noise control applications. As part of the study, the density and speed of sound of the gas are varied independently to assess the impact of each on transmission loss. Results show that near grazing incidence the plane wave transmission loss through the multilayer system is more sensitive to the speed of sound than the density of the gas. In addition, it was found that a slow wave speed in the bagged gas provides more low-frequency transmission loss benefit than a fast wave speed. At low angles of incidence, close to the plate normal, the benefit is due to the reduction of the characteristic impedance of the gas. At high angles of incidence, the benefit is attributed to the fact that the incident waves at the air/gas interface are bent towards the surface normal. Since transmission loss is angle dependent, refraction in the slow gas layer results in a significant improvement in the transmission loss at high angles of incidence.

  11. Laser sintered thin layer graphene and cubic boron nitride reinforced nickel matrix nanocomposites

    NASA Astrophysics Data System (ADS)

    Hu, Zengrong; Tong, Guoquan

    2015-10-01

    Laser sintered thin layer graphene (Gr)-cubic boron nitride (CBN)-Ni nanocomposites were fabricated on AISI 4140 plate substrate. The composites fabricating process, composites microstructure and mechanical properties were studied. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy were employed to study the micro structures and composition of the composites. XRD and Raman tests proved that graphene and CBN were dispersed in the nanocomposites. Nanoindentation test results indicate the significant improvements were achieved in the composites mechanical properties.

  12. A highly sensitive pressure sensor using a double-layered graphene structure for tactile sensing

    NASA Astrophysics Data System (ADS)

    Chun, Sungwoo; Kim, Youngjun; Oh, Hyeong-Sik; Bae, Giyeol; Park, Wanjun

    2015-07-01

    In this paper, we propose a graphene sensor using two separated single-layered graphenes on a flexible substrate for use as a pressure sensor, such as for soft electronics. The working pressure corresponds to the range in which human perception recognizes surface morphologies. A specific design of the sensor structure drives the piezoresistive character due to the contact resistance between two graphene layers and the electromechanical properties of graphene itself. Accordingly, sensitivity in resistance change is given by two modes for low pressure (-0.24 kPa-1) and high pressure (0.039 kPa-1) with a crossover pressure (700 Pa). This sensor can detect infinitesimal pressure as low as 0.3 Pa with uniformly applied vertical force. With the attachment of the artificial fingerprint structure (AFPS) on the sensor, the detection ability for both the locally generated shear force and actual human touch confirms recognition of the surface morphology constructed by periodic structures.In this paper, we propose a graphene sensor using two separated single-layered graphenes on a flexible substrate for use as a pressure sensor, such as for soft electronics. The working pressure corresponds to the range in which human perception recognizes surface morphologies. A specific design of the sensor structure drives the piezoresistive character due to the contact resistance between two graphene layers and the electromechanical properties of graphene itself. Accordingly, sensitivity in resistance change is given by two modes for low pressure (-0.24 kPa-1) and high pressure (0.039 kPa-1) with a crossover pressure (700 Pa). This sensor can detect infinitesimal pressure as low as 0.3 Pa with uniformly applied vertical force. With the attachment of the artificial fingerprint structure (AFPS) on the sensor, the detection ability for both the locally generated shear force and actual human touch confirms recognition of the surface morphology constructed by periodic structures. Electronic

  13. Tunable surface plasmon-polaritons in a gyroelectric slab sandwiched between two graphene layers

    NASA Astrophysics Data System (ADS)

    Xu, Guoding; Cao, Ming; Liu, Chang; Sun, Jian; Pan, Tao

    2016-05-01

    We study numerically the properties of surface plasmon-polaritons (SPPs) in a gyroelectric slab sandwiched between two graphene layers, where the external static magnetic field is applied in the Voigt geometry. It is shown that the dispersion characteristics and propagation lenghts of the SPPs for both the optical and the acoustic branches can be tuned flexibly by the external magnetic field and graphene's chemical potential, and that the nonreciprocal properties of the SPPs caused by the external magnetic field are rather obvious. The results provide a method for adjusting and improving the dispersion and propagation properties of the SPPs, which might be helpful for the design of the related plasmonic devices.

  14. Formation of graphene layers by vacuum sublimation of silicon carbide using a scanning heat source

    SciTech Connect

    Dmitriev, A. N.; Cherednichenko, D. I.

    2011-12-15

    The kinetics of surface graphitization during dissociative vacuum evaporation of silicon carbide, under the effect of a scanning heat source, is studied. A model of the process is developed. The model provides a means for theoretically treating the dynamics of formation and the number of residual carbon atomic layers. The vapor stoichiometric coefficient which ensures the minimization of the number of structural defects in graphene, is optimized at the sublimation temperature: {theta} = 1/{eta}(T{sub max}). The proposed method can be used as a basis for graphene production technology.

  15. Foundry-compatible SOI waveguides with a graphene top layer for wideband wavelength conversion

    NASA Astrophysics Data System (ADS)

    Vermeulen, N.; Cheng, J. L.; Sipe, J. E.; Thienpont, H.

    2016-05-01

    The tremendous progress in the fabrication of highly confining silicon-on-insulator (SOI) waveguides has been very beneficial for four-wave-mixing (FWM)-based wavelength conversion applications. Nevertheless, to establish power-efficient and wideband FWM wavelength conversion, one typically requires long (cm-scale) SOI waveguides with dispersion-engineered cross-sections that do not comply with the fabrication constraints of multiproject- wafer-oriented silicon photonics foundries. In this paper, we numerically examine the opportunities for wideband wavelength conversion through FWM in a foundry-compatible SOI waveguide covered with the highly nonlinear two-dimensional material of graphene. When combining subwatt level pump powers with a short waveguide length of only a few hundreds of microns, perfectly phase-matched conversion with significant efficiencies close to 20 dB can be obtained over a more than 40 THz-wide signal band adjacent to the pump frequency. Because of the tunability of the graphene properties, it is also possible to obtain quasi-phase matched FWM conversion through a periodic sign reversal of the graphene third-order nonlinearity along the waveguide. Conversion efficiencies exceeding 30 dB can be achieved over a 3.4 THz-wide signal band that is situated as much as 58 THz away from the pump frequency. Finally, the graphene tunability also allows for switching between the perfectly phase-matched and quasi-phase-matched operation modes.

  16. 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. PMID:23824229

  17. 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.

  18. Orbital-dependent Electron-Hole Interaction in Graphene and Associated Multi-Layer Structures.

    PubMed

    Deng, Tianqi; Su, Haibin

    2015-01-01

    We develop an orbital-dependent potential to describe electron-hole interaction in materials with structural 2D character, i.e. quasi-2D materials. The modulated orbital-dependent potentials are also constructed with non-local screening, multi-layer screening, and finite gap due to the coupling with substrates. We apply the excitonic Hamiltonian in coordinate-space with developed effective electron-hole interacting potentials to compute excitons' binding strength at M (π band) and Γ (σ band) points in graphene and its associated multi-layer forms. The orbital-dependent potential provides a range-separated property for regulating both long- and short-range interactions. This accounts for the existence of the resonant π exciton in single- and bi-layer graphenes. The remarkable strong electron-hole interaction in σ orbitals plays a decisive role in the existence of σ exciton in graphene stack at room temperature. The interplay between gap-opening and screening from substrates shed a light on the weak dependence of σ exciton binding energy on the thickness of graphene stacks. Moreover, the analysis of non-hydrogenic exciton spectrum in quasi-2D systems clearly demonstrates the remarkable comparable contribution of orbital dependent potential with respect to non-local screening process. The understanding of orbital-dependent potential developed in this work is potentially applicable for a wide range of materials with low dimension. PMID:26610715

  19. Few-layer graphene as a support film for transmission electron microscopy imaging of nanoparticles.

    PubMed

    McBride, James R; Lupini, Andrew R; Schreuder, Michael A; Smith, Nathanael J; Pennycook, Stephen J; Rosenthal, Sandra J

    2009-12-01

    One consistent limitation for high-resolution imaging of small nanoparticles is the high background signal from the amorphous carbon support film. With interest growing for smaller and smaller nanostructures, state of the art electron microscopes are becoming necessary for rudimentary tasks, such as nanoparticle sizing. As a monolayer of carbon, free-standing graphene represents the ultimate support film for nanoparticle imaging. In this work, conventional high-resolution transmission electron microscopy (HRTEM) and aberration-corrected scanning transmission electron microscopy (STEM) were used to assess the benefits and feasibility of few-layer graphene support films. Suspensions of few-layer graphene to produce the support films were prepared by simple sonication of exfoliated graphite. The greatest benefit was observed for conventional HRTEM, where lattice resolved imaging of sub 2 nm CdSe nanocrystals was achieved. The few-layer graphene films were also used as a support film for C(s)-corrected STEM and electron energy loss spectroscopy of CuInSe(2) nanocrystals. PMID:20356171

  20. Graphene-layered steps and their fields visualized by 4D electron microscopy

    PubMed Central

    Park, Sang Tae; Yurtsever, Aycan; Baskin, John Spencer; Zewail, Ahmed H.

    2013-01-01

    Enhanced image contrast has been seen at graphene-layered steps a few nanometers in height by means of photon-induced near-field electron microscopy (PINEM) using synchronous femtosecond pulses of light and electrons. The observed steps are formed by the edges of graphene strips lying on the surface of a graphene substrate, where the strips are hundreds of nanometers in width and many micrometers in length. PINEM measurements reflect the interaction of imaging electrons and induced (near) electric fields at the steps, and this leads to a much higher contrast than that achieved in bright-field transmission electron microscopy imaging of the same strips. Theory and numerical simulations support the experimental PINEM findings and elucidate the nature of the electric field at the steps formed by the graphene layers. These results extend the range of applications of the experimental PINEM methodology, which has previously been demonstrated for spherical, cylindrical, and triangular nanostructures, to shapes of high aspect ratio (rectangular strips), as well as into the regime of atomic layer thicknesses. PMID:23690572

  1. Orbital-dependent Electron-Hole Interaction in Graphene and Associated Multi-Layer Structures

    PubMed Central

    Deng, Tianqi; Su, Haibin

    2015-01-01

    We develop an orbital-dependent potential to describe electron-hole interaction in materials with structural 2D character, i.e. quasi-2D materials. The modulated orbital-dependent potentials are also constructed with non-local screening, multi-layer screening, and finite gap due to the coupling with substrates. We apply the excitonic Hamiltonian in coordinate-space with developed effective electron-hole interacting potentials to compute excitons’ binding strength at M (π band) and Γ (σ band) points in graphene and its associated multi-layer forms. The orbital-dependent potential provides a range-separated property for regulating both long- and short-range interactions. This accounts for the existence of the resonant π exciton in single- and bi-layer graphenes. The remarkable strong electron-hole interaction in σ orbitals plays a decisive role in the existence of σ exciton in graphene stack at room temperature. The interplay between gap-opening and screening from substrates shed a light on the weak dependence of σ exciton binding energy on the thickness of graphene stacks. Moreover, the analysis of non-hydrogenic exciton spectrum in quasi-2D systems clearly demonstrates the remarkable comparable contribution of orbital dependent potential with respect to non-local screening process. The understanding of orbital-dependent potential developed in this work is potentially applicable for a wide range of materials with low dimension. PMID:26610715

  2. Calculation of the superconducting transition temperature of a graphene layer doped with titanium and palladium

    NASA Astrophysics Data System (ADS)

    Vazquez, Gerardo; Magana, Fernando; Salas-Torres, Osiris

    We explore the structural interactions between graphene and transition metals such as palladium (Pd) and titanium (Ti) and the possibility of inducing superconductivity in a graphene sheet in two cases, one by doping its surface with palladium atoms sit on the center of the hexagons of the graphene layer and other by covering the graphene layer with two layers of titanium metal atoms. The results here were obtained from first-principles density functional theory in the local density approximation. The Quantum-Espresso package was used with norm conserving pseudopotentials. All of the structures considered were relaxed to their minimum energy configuration. Phonon frequencies were calculated using the linear-response technique on several phonon wave-vector mesh. The electron-phonon coupling parameter was calculated with several electron momentum k-mesh. The superconducting critical temperature was estimated using the Allen-Dynes formula with μ* = 0.1 - 0.15. We note that palladium and titanium are good candidate materials to show a metal-to-superconductor transition. We thank Dirección General de Asuntos del Personal Académico de la Universidad Nacional Autónoma de México, partial financial support by Grant IN-106514 and we also thank Miztli Super-Computing center the technical assistance.

  3. Local, global, and nonlinear screening in twisted double-layer graphene

    NASA Astrophysics Data System (ADS)

    Lu, Chih-Pin; Rodriguez-Vega, Martin; Li, Guohong; Luican-Mayer, Adina; Watanabe, Kenji; Taniguchi, Takashi; Rossi, Enrico; Andrei, Eva Y.

    2016-06-01

    One-atom-thick crystalline layers and their vertical heterostructures carry the promise of designer electronic materials that are unattainable by standard growth techniques. To realize their potential it is necessary to isolate them from environmental disturbances, in particular those introduced by the substrate. However, finding and characterizing suitable substrates, and minimizing the random potential fluctuations they introduce, has been a persistent challenge in this emerging field. Here we show that Landau-level (LL) spectroscopy offers the unique capability to quantify both the reduction of the quasiparticles’ lifetime and the long-range inhomogeneity due to random potential fluctuations. Harnessing this technique together with direct scanning tunneling microscopy and numerical simulations we demonstrate that the insertion of a graphene buffer layer with a large twist angle is a very effective method to shield a 2D system from substrate interference that has the additional desirable property of preserving the electronic structure of the system under study. We further show that owing to its remarkable nonlinear screening capability a single graphene buffer layer provides better shielding than either increasing the distance to the substrate or doubling the carrier density and reduces the amplitude of the potential fluctuations in graphene to values even lower than the ones in AB-stacked bilayer graphene.

  4. Single-Layer Graphene Enhances the Osteogenic Differentiation of Human Mesenchymal Stem Cells In Vitro and In Vivo.

    PubMed

    Liu, Yunsong; Chen, Tong; Du, Feng; Gu, Ming; Zhang, Ping; Zhang, Xiao; Liu, Jianzhang; Lv, Longwei; Xiong, Chunyang; Zhou, Yongsheng

    2016-06-01

    In recent years, although several studies have demonstrated the potential of graphene-coated substrates in promoting attachment, proliferation and differentiation of osteoblasts and mesenchymal stem cells (MSCs), the effects of single-layer graphene on the osteogenic differentiation of human MSCs (hMSCs) remains unclear, especially in vivo. In this study, we transferred chemical vapor deposition (CVD) grown single-layer graphene to glass slides and observed its effects on adhesion, proliferation and osteogenic differentiation of human adipose-derived stem cells (hASCs) and human bone marrow mesenchymal stem cells (hBMMSCs) in vitro. Then, in vivo, we incubated hASCs and hBMMSCs on single-layer graphene-coated smooth titanium (Ti) disks before implanting them into the back subcutaneous area of nude mice. We found that single-layer graphene accelerated cell adhesion to the substrate without influencing cell proliferation of hMSCs. Moreover, we present the first study that explores the epigenetic role of single-layer graphene in determining stem cell fate. By utilizing epigenetic approaches, we reveal that single-layer graphene promotes osteogenic differentiation of hMSCs both in vitro and in vivo, potentially by upregulating methylation of H3K4 at the promoter regions of osteogenesis-associated genes. Overall, our results highlight the potential of this material in implants and injured tissues in clinical applications.

  5. Single-Layer Graphene Enhances the Osteogenic Differentiation of Human Mesenchymal Stem Cells In Vitro and In Vivo.

    PubMed

    Liu, Yunsong; Chen, Tong; Du, Feng; Gu, Ming; Zhang, Ping; Zhang, Xiao; Liu, Jianzhang; Lv, Longwei; Xiong, Chunyang; Zhou, Yongsheng

    2016-06-01

    In recent years, although several studies have demonstrated the potential of graphene-coated substrates in promoting attachment, proliferation and differentiation of osteoblasts and mesenchymal stem cells (MSCs), the effects of single-layer graphene on the osteogenic differentiation of human MSCs (hMSCs) remains unclear, especially in vivo. In this study, we transferred chemical vapor deposition (CVD) grown single-layer graphene to glass slides and observed its effects on adhesion, proliferation and osteogenic differentiation of human adipose-derived stem cells (hASCs) and human bone marrow mesenchymal stem cells (hBMMSCs) in vitro. Then, in vivo, we incubated hASCs and hBMMSCs on single-layer graphene-coated smooth titanium (Ti) disks before implanting them into the back subcutaneous area of nude mice. We found that single-layer graphene accelerated cell adhesion to the substrate without influencing cell proliferation of hMSCs. Moreover, we present the first study that explores the epigenetic role of single-layer graphene in determining stem cell fate. By utilizing epigenetic approaches, we reveal that single-layer graphene promotes osteogenic differentiation of hMSCs both in vitro and in vivo, potentially by upregulating methylation of H3K4 at the promoter regions of osteogenesis-associated genes. Overall, our results highlight the potential of this material in implants and injured tissues in clinical applications. PMID:27319220

  6. Few-layer graphene growth from polystyrene as solid carbon source utilizing simple APCVD method

    NASA Astrophysics Data System (ADS)

    Ahmadi, Shahrokh; Afzalzadeh, Reza

    2016-07-01

    This research article presents development of an economical, simple, immune and environment friendly process to grow few-layer graphene by controlling evaporation rate of polystyrene on copper foil as catalyst and substrate utilizing atmospheric pressure chemical vapor deposition (APCVD) method. Evaporation rate of polystyrene depends on molecular structure, amount of used material and temperature. We have found controlling rate of evaporation of polystyrene by controlling the source temperature is easier than controlling the material weight. Atomic force microscopy (AFM) as well as Raman Spectroscopy has been used for characterization of the layers. The frequency of G‧ to G band ratio intensity in some samples varied between 0.8 and 1.6 corresponding to few-layer graphene. Topography characterization by atomic force microscopy confirmed Raman results.

  7. Nitrogen-incorporated ultrananocrystalline diamond and multi-layer-graphene-like hybrid carbon films

    PubMed Central

    Tzeng, Yonhua; Yeh, Shoupu; Fang, Wei Cheng; Chu, Yuehchieh

    2014-01-01

    Nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) and multi-layer-graphene-like hybrid carbon films have been synthesized by microwave plasma enhanced chemical vapor deposition (MPECVD) on oxidized silicon which is pre-seeded with diamond nanoparticles. MPECVD of N-UNCD on nanodiamond seeds produces a base layer, from which carbon structures nucleate and grow perpendicularly to form standing carbon platelets. High-resolution transmission electron microscopy and Raman scattering measurements reveal that these carbon platelets are comprised of ultrananocrystalline diamond embedded in multilayer-graphene-like carbon structures. The hybrid carbon films are of low electrical resistivity. UNCD grains in the N-UNCD base layer and the hybrid carbon platelets serve as high-density diamond nuclei for the deposition of an electrically insulating UNCD film on it. Biocompatible carbon-based heaters made of low-resistivity hybrid carbon heaters encapsulated by insulating UNCD for possible electrosurgical applications have been demonstrated. PMID:24681781

  8. Atomically Thin Heterostructures Based on Single-Layer Tungsten Diselenide and Graphene [Plus Supplemental Information

    SciTech Connect

    Lin, Yu-Chuan; Chang, Chih-Yuan S.; Ghosh, Ram Krishna; Li, Jie; Zhu, Hui; Addou, Rafik; Diaconescu, Bogdan; Ohta, Taisuke; Peng, Xin; Lu, Ning; Kim, Moon J.; Robinson, Jeremy T.; Wallace, Robert M.; Mayer, Theresa S.; Datta, Suman; Li, Lain-Jong; Robinson, Joshua A.

    2014-11-10

    Heterogeneous engineering of two-dimensional layered materials, including metallic graphene and semiconducting transition metal dichalcogenides, presents an exciting opportunity to produce highly tunable electronic and optoelectronic systems. We report the direct growth of highly crystalline, monolayer tungsten diselenide (WSe2) on epitaxial graphene (EG). Raman spectroscopy and photoluminescence confirms high-quality WSe2 monolayers; while transmission electron microscopy shows an atomically sharp interface and low energy electron diffraction confirms near perfect orientation between WSe2 and EG. Vertical transport measurements across the WSe2/EG heterostructure provides evidence that a tunnel barrier exists due to the van der Waals gap, and is supported by density functional theory that predicts a 1.6 eV barrier for transport from WSe2 to graphene.

  9. High sensitive formaldehyde graphene gas sensor modified by atomic layer deposition zinc oxide films

    SciTech Connect

    Mu, Haichuan; Zhang, Zhiqiang; Wang, Keke; Xie, Haifen; Zhao, Xiaojing; Liu, Feng

    2014-07-21

    Zinc oxide (ZnO) thin films with various thicknesses were fabricated by Atomic Layer Deposition on Chemical Vapor Deposition grown graphene films and their response to formaldehyde has been investigated. It was found that 0.5 nm ZnO films modified graphene sensors showed high response to formaldehyde with the resistance change up to 52% at the concentration of 9 parts-per-million (ppm) at room temperature. Meanwhile, the detection limit could reach 180 parts-per-billion (ppb) and fast response of 36 s was also obtained. The high sensitivity could be attributed to the combining effect from the highly reactive, top mounted ZnO thin films, and high conductive graphene base network. The dependence of ZnO films surface morphology and its sensitivity on the ZnO films thickness was also investigated.

  10. Atomically Thin Heterostructures Based on Single-Layer Tungsten Diselenide and Graphene [Plus Supplemental Information

    DOE PAGES

    Lin, Yu-Chuan; Chang, Chih-Yuan S.; Ghosh, Ram Krishna; Li, Jie; Zhu, Hui; Addou, Rafik; Diaconescu, Bogdan; Ohta, Taisuke; Peng, Xin; Lu, Ning; et al

    2014-11-10

    Heterogeneous engineering of two-dimensional layered materials, including metallic graphene and semiconducting transition metal dichalcogenides, presents an exciting opportunity to produce highly tunable electronic and optoelectronic systems. We report the direct growth of highly crystalline, monolayer tungsten diselenide (WSe2) on epitaxial graphene (EG). Raman spectroscopy and photoluminescence confirms high-quality WSe2 monolayers; while transmission electron microscopy shows an atomically sharp interface and low energy electron diffraction confirms near perfect orientation between WSe2 and EG. Vertical transport measurements across the WSe2/EG heterostructure provides evidence that a tunnel barrier exists due to the van der Waals gap, and is supported by density functional theorymore » that predicts a 1.6 eV barrier for transport from WSe2 to graphene.« less

  11. High sensitive formaldehyde graphene gas sensor modified by atomic layer deposition zinc oxide films

    NASA Astrophysics Data System (ADS)

    Mu, Haichuan; Zhang, Zhiqiang; Zhao, Xiaojing; Liu, Feng; Wang, Keke; Xie, Haifen

    2014-07-01

    Zinc oxide (ZnO) thin films with various thicknesses were fabricated by Atomic Layer Deposition on Chemical Vapor Deposition grown graphene films and their response to formaldehyde has been investigated. It was found that 0.5 nm ZnO films modified graphene sensors showed high response to formaldehyde with the resistance change up to 52% at the concentration of 9 parts-per-million (ppm) at room temperature. Meanwhile, the detection limit could reach 180 parts-per-billion (ppb) and fast response of 36 s was also obtained. The high sensitivity could be attributed to the combining effect from the highly reactive, top mounted ZnO thin films, and high conductive graphene base network. The dependence of ZnO films surface morphology and its sensitivity on the ZnO films thickness was also investigated.

  12. A multiple-resonator approach for broadband light absorption in a single layer of nanostructured graphene.

    PubMed

    Yi, Soongyu; Zhou, Ming; Shi, Xi; Gan, Qiaoqiang; Zi, Jian; Yu, Zongfu

    2015-04-20

    The interaction between two-dimensional (2D) materials and light is rather weak due to their ultrathin thickness. In order for these emerging 2D materials to achieve performances that are comparable to those of conventional optoelectronic devices, the light-material interaction must be significantly enhanced. An effective way to enhance the interaction is to use optical resonances. Efficient light absorption has been demonstrated in a single layer of graphene based on a variety of resonators. However, the bandwidth of the absorption enhancement is always narrow, which limits its application for optoelectronic devices. In order to broaden the enhancement of light-material interaction, here we propose a multiple-resonator approach based on nanostructured graphene. These nanostructures having different geometry support resonances at different frequencies. Owing to their deep subwavelength sizes, graphene resonators can be closely packed in space, resulting in a high optical density of states, which enables the broadband light absorption.

  13. Structural and optical properties of cobalt slanted nanopillars conformally coated with few-layer graphene

    SciTech Connect

    Wilson, Peter M.; Lipatov, Alexey; Schmidt, Daniel; Schubert, Eva; Schubert, Mathias; Hofmann, Tino E-mail: thofmann@engr.unl.edu; Sinitskii, Alexander E-mail: thofmann@engr.unl.edu

    2015-06-08

    Optical characterization of anisotropic multicomponent nanostructures is generally not a trivial task, since the relation between a material's structural properties and its permittivity tensor is nonlinear. In this regard, an array of slanted cobalt nanopillars that are conformally coated with few-layer graphene is a particularly challenging object for optical characterization, as it has a complex anisotropic geometry and comprises several materials with different topologies and filling fractions. Normally, a detailed characterization of such complex nanostructures would require a combination of several microscopic and spectroscopic techniques. In this letter, we demonstrate that the important structural parameters of these graphene-coated sculptured thin films can be determined using a fast and simple generalized spectroscopic ellipsometry test combined with an anisotropic Bruggeman effective medium approximation. The graphene coverage as well as structural parameters of nanostructured thin films agree excellently with electron microscopy and Raman spectroscopy observations. The demonstrated optical approach may also be applied to the characterization of other nanostructured materials.

  14. Direct observation of electrically induced Pauli paramagnetism in single-layer graphene using ESR spectroscopy

    NASA Astrophysics Data System (ADS)

    Fujita, Naohiro; Matsumoto, Daisuke; Sakurai, Yuki; Kawahara, Kenji; Ago, Hiroki; Takenobu, Taishi; Marumoto, Kazuhiro

    2016-10-01

    Graphene has been actively investigated as an electronic material owing to many excellent physical properties, such as high charge mobility and quantum Hall effect, due to the characteristics of a linear band structure and an ideal two-dimensional electron system. However, the correlations between the transport characteristics and the spin states of charge carriers or atomic vacancies in graphene have not yet been fully elucidated. Here, we show the spin states of single-layer graphene to clarify the correlations using electron spin resonance (ESR) spectroscopy as a function of accumulated charge density using transistor structures. Two different electrically induced ESR signals were observed. One is originated from a Fermi-degenerate two-dimensional electron system, demonstrating the first observation of electrically induced Pauli paramagnetism from a microscopic viewpoint, showing a clear contrast to no ESR observation of Pauli paramagnetism in carbon nanotubes (CNTs) due to a one-dimensional electron system. The other is originated from the electrically induced ambipolar spin vanishments due to atomic vacancies in graphene, showing a universal phenomenon for carbon materials including CNTs. The degenerate electron system with the ambipolar spin vanishments would contribute to high charge mobility due to the decrease in spin scatterings in graphene.

  15. Direct observation of electrically induced Pauli paramagnetism in single-layer graphene using ESR spectroscopy

    PubMed Central

    Fujita, Naohiro; Matsumoto, Daisuke; Sakurai, Yuki; Kawahara, Kenji; Ago, Hiroki; Takenobu, Taishi; Marumoto, Kazuhiro

    2016-01-01

    Graphene has been actively investigated as an electronic material owing to many excellent physical properties, such as high charge mobility and quantum Hall effect, due to the characteristics of a linear band structure and an ideal two-dimensional electron system. However, the correlations between the transport characteristics and the spin states of charge carriers or atomic vacancies in graphene have not yet been fully elucidated. Here, we show the spin states of single-layer graphene to clarify the correlations using electron spin resonance (ESR) spectroscopy as a function of accumulated charge density using transistor structures. Two different electrically induced ESR signals were observed. One is originated from a Fermi-degenerate two-dimensional electron system, demonstrating the first observation of electrically induced Pauli paramagnetism from a microscopic viewpoint, showing a clear contrast to no ESR observation of Pauli paramagnetism in carbon nanotubes (CNTs) due to a one-dimensional electron system. The other is originated from the electrically induced ambipolar spin vanishments due to atomic vacancies in graphene, showing a universal phenomenon for carbon materials including CNTs. The degenerate electron system with the ambipolar spin vanishments would contribute to high charge mobility due to the decrease in spin scatterings in graphene. PMID:27731338

  16. Polarized Raman spectroscopy with differing angles of laser incidence on single-layer graphene

    NASA Astrophysics Data System (ADS)

    Heo, Gaeun; Kim, Yong Seung; Chun, Seung-Hyun; Seong, Maeng-Je

    2015-02-01

    Chemical vapor deposition (CVD)-grown single-layer graphene samples, transferred onto a transmission electron microscope (TEM) grid and onto a quartz plate, were studied using polarized Raman spectroscopy with differing angles of laser incidence ( θ). Two different polarization configurations are used. In an in-plane configuration, the polarization direction of both incident and scattered light is parallel to the graphene plane. In an out-of-plane configuration, the angle between the polarization vector and the graphene plane is the same as the angle of laser incidence ( θ). The normalized Raman intensity of the G-band measured in the out-of-plane configuration, with respect to that in the in-plane configuration, was analyzed as a function of θ. The normalized Raman intensity showed approximately cos2 θ-dependence up to θ = 70°, which can be explained by the fact that only the electric field component of the incident and the scattered photon in the out-of-plane configuration projected onto the graphene plane can contribute to the Raman scattering process because of the perfect confinement of the electrons to the graphene plane.

  17. Chemical Vapor Deposited Few-Layer Graphene as an Electron Field Emitter.

    PubMed

    Behural, Sanjay K; Nayak, Sasmita; Yang, Qiaoqin; Hirose, Akira; Janil, Omkar

    2016-01-01

    Chemical vapor deposition (CVD) growth of graphene on polycrystalline copper (Cu) foil in a low pressure conditions has been presented, aiming to achieve the highest quality with large-scale fabrications, which requires comprehensive understanding and effective controlling of the growth process. Herein, few-layer graphene (FLG) films with large-domain sizes were grown on Cu metal catalyst substrates using a vertical mass-flow hot-filament CVD reactor, with the intention of large scale production, by optimizing the CVD system and three of the process parameters: (i) gas flow compositions, (ii) substrate annealing time and (iii) graphene deposition time. The detailed scanning electron microscope and Raman spectroscopy analysis indicate that all the above mentioned process parameters affect growth of FLG film on Cu substrate. The presence of two intense peaks, G and 2D-band at 1583.6 and 2702.6 cm⁻¹ for synthesized sample at optimized conditions (H₂/CH₄ ratio of 50:1 at graphene deposition time of 10 minutes and substrate annealed time for 20 minutes) revealed the formation of FLG films with large domain size. These graphene films on Cu have shown the room temperature field electron emission characteristics, hence appears to be prospective candidate for vacuum nanoelectronics. PMID:27398456

  18. Multi-layer and multi-component intercalation at the graphene/Ir(111) interface

    NASA Astrophysics Data System (ADS)

    Bazarnik, Maciej; Decker, Régis; Brede, Jens; Wiesendanger, Roland

    2015-09-01

    We present a scanning tunneling microscopy study of Fe and Co intercalated at the graphene-Ir(111) interface. In the case of Fe, we investigate the morphology of the surface with respect to the annealing temperature, which activates the intercalation, and as a function of coverage. By increasing the coverage we show that it is possible to intercalate multilayers at the interface. Finally, we demonstrate that the successive intercalation of Co and Fe for the same sample leads to distinct adjacent intercalation areas.

  19. Single-Layer Graphene as a Barrier Layer for Intense UV Laser-Induced Damages for Silver Nanowire Network.

    PubMed

    Das, Suprem R; Nian, Qiong; Saei, Mojib; Jin, Shengyu; Back, Doosan; Kumar, Prashant; Janes, David B; Alam, Muhammad A; Cheng, Gary J

    2015-11-24

    Single-layer graphene (SLG) has been proposed as the thinnest protective/barrier layer for wide applications involving resistance to oxidation, corrosion, atomic/molecular diffusion, electromagnetic interference, and bacterial contamination. Functional metallic nanostructures have lower thermal stability than their bulk forms and are therefore susceptible to high energy photons. Here, we demonstrate that SLG can shield metallic nanostructures from intense laser radiation that would otherwise ablate them. By irradiation via a UV laser beam with nanosecond pulse width and a range of laser intensities (in millions of watt per cm(2)) onto a silver nanowire network, and conformally wrapping SLG on top of the nanowire network, we demonstrate that graphene "extracts and spreads" most of the thermal energy away from nanowire, thereby keeping it damage-free. Without graphene wrapping, the radiation would fragment the wires into smaller pieces and even decompose them into droplets. A systematic molecular dynamics simulation confirms the mechanism of SLG shielding. Consequently, particular damage-free and ablation-free laser-based nanomanufacturing of hybrid nanostructures might be sparked off by application of SLG on functional surfaces and nanofeatures. PMID:26447828

  20. The role of electron confinement in Pd films for the oscillatory magnetic anisotropy in an adjacent Co layer.

    PubMed

    Manna, Sujit; Przybylski, M; Sander, D; Kirschner, J

    2016-11-16

    We demonstrate the interplay between quantum well states in Pd and the magnetic anisotropy in Pd/Co/Cu (0 0 1) by combined scanning tunneling spectroscopy (STS) and magneto optical Kerr effect (MOKE) measurements. Low temperature scanning tunneling spectroscopy reveals occupied and unoccupied quantum well states (QWS) in atomically flat Pd films on Co/Cu (0 0 1). These states give rise to sharp peaks in the differential conductance spectra. A quantitative analysis of the spectra reveals the electronic dispersion of the Pd (0 0 1) d-band ([Formula: see text]-type) along the [Formula: see text]-X direction. In situ MOKE experiments on Pd/Co/Cu (1, 1, 13) uncover a periodic variation of the in-plane uniaxial magnetic anisotropy as a function of Pd thickness with a period of 6 atomic layers Pd. STS shows that QWS in Pd cross the Fermi level with the same periodicity of 6 atomic layers. Backed by previous theoretical work we ascribe the variation of the magnetic anisotropy in Co to QWS in the Pd overlayer. Our results suggest a novel venue towards tailoring uniaxial magnetic anisotropy of ferromagnetic films by exploiting QWS in an adjacent material with large spin-orbit coupling. PMID:27609044

  1. The role of electron confinement in Pd films for the oscillatory magnetic anisotropy in an adjacent Co layer

    NASA Astrophysics Data System (ADS)

    Manna, Sujit; Przybylski, M.; Sander, D.; Kirschner, J.

    2016-11-01

    We demonstrate the interplay between quantum well states in Pd and the magnetic anisotropy in Pd/Co/Cu (0 0 1) by combined scanning tunneling spectroscopy (STS) and magneto optical Kerr effect (MOKE) measurements. Low temperature scanning tunneling spectroscopy reveals occupied and unoccupied quantum well states (QWS) in atomically flat Pd films on Co/Cu (0 0 1). These states give rise to sharp peaks in the differential conductance spectra. A quantitative analysis of the spectra reveals the electronic dispersion of the Pd (0 0 1) d-band ({{ Δ }5} -type) along the Γ -X direction. In situ MOKE experiments on Pd/Co/Cu (1, 1, 13) uncover a periodic variation of the in-plane uniaxial magnetic anisotropy as a function of Pd thickness with a period of 6 atomic layers Pd. STS shows that QWS in Pd cross the Fermi level with the same periodicity of 6 atomic layers. Backed by previous theoretical work we ascribe the variation of the magnetic anisotropy in Co to QWS in the Pd overlayer. Our results suggest a novel venue towards tailoring uniaxial magnetic anisotropy of ferromagnetic films by exploiting QWS in an adjacent material with large spin-orbit coupling.

  2. Separation and electrical properties of self-organized graphene/graphite layers

    NASA Astrophysics Data System (ADS)

    Mailian, Manuel R.; Mailian, Aram R.

    2015-02-01

    Intrinsic layered structure of graphite is the source of ongoing and expanding search of ways of obtaining low-cost and promising graphite thin layers. We report on a novel method of obtaing and seperating rubbed graphite sheets by using water soluble NaCl substrate. The electrical behavior of sheets was characterized by current-voltage measurements. An in-plane electrical anisotropy depending on rubbing direction is discovered. Optical microscopy observations combined with discovered non-linear electrical behavior revealed that friction leads to the formation of sheet makeup which contain an optically transparent lamina of self-organized few-layer graphene.

  3. Modified TM and TE waveguide modes and reflectivity by graphene layer in coupled-graphene-metal multilayer structure in sub-terahertz frequency

    NASA Astrophysics Data System (ADS)

    Shkerdin, Gennady; Alkorre, Hameda; Stiens, Johan; Vounckx, Roger

    2015-05-01

    In this paper we focus on the dispersion characteristics of TM and TE waveguide modes and the reflectivity of plane waves, incident on the four-layer structure consisting of air/graphene monolayer/dielectric buffer layer/metal substrate. The TM waveguide modes split up into two branches for small frequencies, one of the branches (cutoff waveguide branch) undergoes cutoff at a certain cutoff buffer thicknesses. There is no splitting of TE waveguide modes. However, these modes can be converted into short-range waves for smaller buffer thickness with subsequent modes cutoff depending on frequency and graphene electron concentration. Reflection coefficients of the TM polarized incident electromagnetic waves from air on the multi-layer structure vanish in the vicinity of cutoff buffer thicknesses. It is demonstrated that waveguide mode propagation constants and reflectivity in the multilayer structure can be considerably influenced by the presence of a graphene layer in the vicinity of the cutoff thicknesses of the waveguide modes.

  4. Few layer graphene synthesis via SiC decomposition at low temperature and low vacuum

    NASA Astrophysics Data System (ADS)

    Kayali, Emre; Mercan, Elif; Emre Oren, Ersin; Cambaz Buke, Goknur

    2016-04-01

    Based on the large-scale availability and good electrical properties, the epitaxial graphene (EG) on SiC exhibits a big potential for future electronic devices. However, it is still necessary to work continuously on lowering the formation temperature and vacuum values of EG while improving the quality and increasing the lateral size to fabricate high-performance electronic devices at reduced processing costs. In this study, we investigated the effect of the presence of Mo plate and hydrogen atmosphere as well as the vacuum annealing durations on SiC decomposition. Our studies showed that the graphene layers can be produced at lower annealing temperatures (1200 °C) and vacuum values (10-4 Torr) in the presence of Mo plate and hydrogen. For high quality continuous graphene formation, Mo plate should be in contact with SiC. If there is a gap between Mo and SiC, non-wetting oxide droplets on few layer graphene (FLG) are recorded. Moreover, it is found that the morphology of these islands can be controlled by changing the annealing time and atmosphere conditions, and applying external disturbances such as vibration.

  5. Atomic layer deposition of dielectrics on graphene using reversibly physisorbed ozone.

    PubMed

    Jandhyala, Srikar; Mordi, Greg; Lee, Bongki; Lee, Geunsik; Floresca, Carlo; Cha, Pil-Ryung; Ahn, Jinho; Wallace, Robert M; Chabal, Yves J; Kim, Moon J; Colombo, Luigi; Cho, Kyeongjae; Kim, Jiyoung

    2012-03-27

    Integration of graphene field-effect transistors (GFETs) requires the ability to grow or deposit high-quality, ultrathin dielectric insulators on graphene to modulate the channel potential. Here, we study a novel and facile approach based on atomic layer deposition through ozone functionalization to deposit high-κ dielectrics (such as Al(2)O(3)) without breaking vacuum. The underlying mechanisms of functionalization have been studied theoretically using ab initio calculations and experimentally using in situ monitoring of transport properties. It is found that ozone molecules are physisorbed on the surface of graphene, which act as nucleation sites for dielectric deposition. The physisorbed ozone molecules eventually react with the metal precursor, trimethylaluminum to form Al(2)O(3). Additionally, we successfully demonstrate the performance of dual-gated GFETs with Al(2)O(3) of sub-5 nm physical thickness as a gate dielectric. Back-gated GFETs with mobilities of ~19,000 cm(2)/(V·s) are also achieved after Al(2)O(3) deposition. These results indicate that ozone functionalization is a promising pathway to achieve scaled gate dielectrics on graphene without leaving a residual nucleation layer.

  6. Interlayer catalytic exfoliation realizing scalable production of large-size pristine few-layer graphene.

    PubMed

    Geng, Xiumei; Guo, Yufen; Li, Dongfang; Li, Weiwei; Zhu, Chao; Wei, Xiangfei; Chen, Mingliang; Gao, Song; Qiu, Shengqiang; Gong, Youpin; Wu, Liqiong; Long, Mingsheng; Sun, Mengtao; Pan, Gebo; Liu, Liwei

    2013-01-01

    Mass production of reduced graphene oxide and graphene nanoplatelets has recently been achieved. However, a great challenge still remains in realizing large-quantity and high-quality production of large-size thin few-layer graphene (FLG). Here, we create a novel route to solve the issue by employing one-time-only interlayer catalytic exfoliation (ICE) of salt-intercalated graphite. The typical FLG with a large lateral size of tens of microns and a thickness less than 2 nm have been obtained by a mild and durative ICE. The high-quality graphene layers preserve intact basal crystal planes owing to avoidance of the degradation reaction during both intercalation and ICE. Furthermore, we reveal that the high-quality FLG ensures a remarkable lithium-storage stability (>1,000 cycles) and a large reversible specific capacity (>600 mAh g(-1)). This simple and scalable technique acquiring high-quality FLG offers considerable potential for future realistic applications.

  7. Dynamical screening of the van der Waals interaction between graphene layers.

    PubMed

    Dappe, Y J; Bolcatto, P G; Ortega, J; Flores, F

    2012-10-24

    The interaction between graphene layers is analyzed combining local orbital DFT and second order perturbation theory. For this purpose we use the linear combination of atomic orbitals-orbital occupancy (LCAO-OO) formalism, that allows us to separate the interaction energy as the sum of a weak chemical interaction between graphene layers plus the van der Waals interaction (Dappe et al 2006 Phys. Rev. B 74 205434). In this work, the weak chemical interaction is calculated by means of corrected-LDA calculations using an atomic-like sp(3)d(5) basis set. The van der Waals interaction is calculated by means of second order perturbation theory using an atom-atom interaction approximation and the atomic-like-orbital occupancies. We also analyze the effect of dynamical screening in the van der Waals interaction using a simple model. We find that this dynamical screening reduces by 40% the van der Waals interaction. Taking this effect into account, we obtain a graphene-graphene interaction energy of 70 ± 5 meV/atom in reasonable agreement with the experimental evidence.

  8. Interlayer catalytic exfoliation realizing scalable production of large-size pristine few-layer graphene

    NASA Astrophysics Data System (ADS)

    Geng, Xiumei; Guo, Yufen; Li, Dongfang; Li, Weiwei; Zhu, Chao; Wei, Xiangfei; Chen, Mingliang; Gao, Song; Qiu, Shengqiang; Gong, Youpin; Wu, Liqiong; Long, Mingsheng; Sun, Mengtao; Pan, Gebo; Liu, Liwei

    2013-01-01

    Mass production of reduced graphene oxide and graphene nanoplatelets has recently been achieved. However, a great challenge still remains in realizing large-quantity and high-quality production of large-size thin few-layer graphene (FLG). Here, we create a novel route to solve the issue by employing one-time-only interlayer catalytic exfoliation (ICE) of salt-intercalated graphite. The typical FLG with a large lateral size of tens of microns and a thickness less than 2 nm have been obtained by a mild and durative ICE. The high-quality graphene layers preserve intact basal crystal planes owing to avoidance of the degradation reaction during both intercalation and ICE. Furthermore, we reveal that the high-quality FLG ensures a remarkable lithium-storage stability (>1,000 cycles) and a large reversible specific capacity (>600 mAh g-1). This simple and scalable technique acquiring high-quality FLG offers considerable potential for future realistic applications.

  9. Interface Coupling in Twisted Multilayer Graphene by Resonant Raman Spectroscopy of Layer Breathing Modes.

    PubMed

    Wu, Jiang-Bin; Hu, Zhi-Xin; Zhang, Xin; Han, Wen-Peng; Lu, Yan; Shi, Wei; Qiao, Xiao-Fen; Ijiäs, Mari; Milana, Silvia; Ji, Wei; Ferrari, Andrea C; Tan, Ping-Heng

    2015-07-28

    Raman spectroscopy is the prime nondestructive characterization tool for graphene and related layered materials. The shear (C) and layer breathing modes (LBMs) are due to relative motions of the planes, either perpendicular or parallel to their normal. This allows one to directly probe the interlayer interactions in multilayer samples. Graphene and other two-dimensional (2d) crystals can be combined to form various hybrids and heterostructures, creating materials on demand with properties determined by the interlayer interaction. This is the case even for a single material, where multilayer stacks with different relative orientations have different optical and electronic properties. In twisted multilayer graphene there is a significant enhancement of the C modes due to resonance with new optically allowed electronic transitions, determined by the relative orientation of the layers. Here we show that this applies also to the LBMs, which can be now directly measured at room temperature. We find that twisting has a small effect on LBMs, quite different from the case of the C modes. This implies that the periodicity mismatch between two twisted layers mostly affects shear interactions. Our work shows that ultralow-frequency Raman spectroscopy is an ideal tool to uncover the interface coupling of 2d hybrids and heterostructures.

  10. Tribological characteristics of few-layer graphene over Ni grain and interface boundaries.

    PubMed

    Tripathi, Manoj; Awaja, Firas; Paolicelli, Guido; Bartali, Ruben; Iacob, Erica; Valeri, Sergio; Ryu, Seunghwa; Signetti, Stefano; Speranza, Giorgio; Pugno, Nicola Maria

    2016-03-28

    The tribological properties of metal-supported few-layered graphene depend strongly on the grain topology of the metal substrate. Inhomogeneous distribution of graphene layers at such regions led to variable landscapes with distinguishable roughness. This discrepancy in morphology significantly affects the frictional and wetting characteristics of the FLG system. We discretely measured friction characteristics of FLG covering grains and interfacial grain boundaries of polycrystalline Ni metal substrate via an atomic force microscopy (AFM) probe. The friction coefficient of FLG covered at interfacial grain boundaries is found to be lower than that on grains in vacuum (at 10(-5) Torr pressure) and similar results were obtained in air condition. Sliding history with AFM cantilever, static and dynamic pull-in and pull-off adhesion forces were addressed in the course of friction measurements to explain the role of the out-of-plane deformation of graphene layer(s). Finite element simulations showed good agreement with experiments and led to a rationalization of the observations. Thus, with interfacial grain boundaries the FLG tribology can be effectively tuned. PMID:26948836

  11. 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.

  12. Thinning segregated graphene layers on high carbon solubility substrates of rhodium foils by tuning the quenching process.

    PubMed

    Liu, Mengxi; Zhang, Yanfeng; Chen, Yubin; Gao, Yabo; Gao, Teng; Ma, Donglin; Ji, Qingqing; Zhang, Yu; Li, Cong; Liu, Zhongfan

    2012-12-21

    We report the synthesis of large-scale uniform graphene films on high carbon solubility substrates of Rh foils for the first time using an ambient-pressure chemical vapor deposition method. We find that, by increasing the cooling rate in the growth process, the thickness of graphene can be tuned from multilayer to monolayer, resulting from the different segregation amount of carbon atoms from bulk to surface. The growth feature was characterized with scanning electron microscopy, Raman spectra, transmission electron microscopy, and scanning tunneling microscopy. We also find that bilayer or few-layer graphene prefers to stack deviating from the Bernal stacking geometry, with the formation of versatile moiré patterns. On the basis of these results, we put forward a segregation growth mechanism for graphene growth on Rh foils. Of particular importance, we propose that this randomly stacked few-layer graphene can be a model system for exploring some fantastic physical properties such as van Hove singularities.

  13. Chemistry and physics of a single atomic layer: strategies and challenges for functionalization of graphene and graphene-based materials.

    PubMed

    Yan, Liang; Zheng, Yue Bing; Zhao, Feng; Li, Shoujian; Gao, Xingfa; Xu, Bingqian; Weiss, Paul S; Zhao, Yuliang

    2012-01-01

    Graphene has attracted great interest for its superior physical, chemical, mechanical, and electrical properties that enable a wide range of applications from electronics to nanoelectromechanical systems. Functionalization is among the significant vectors that drive graphene towards technological applications. While the physical properties of graphene have been at the center of attention, we still lack the knowledge framework for targeted graphene functionalization. In this critical review, we describe some of the important chemical and physical processes for graphene functionalization. We also identify six major challenges in graphene research and give perspectives and practical strategies for both fundamental studies and applications of graphene (315 references).

  14. Layer Number Dependence of Li(+) Intercalation on Few-Layer Graphene and Electrochemical Imaging of Its Solid-Electrolyte Interphase Evolution.

    PubMed

    Hui, Jingshu; Burgess, Mark; Zhang, Jiarui; Rodríguez-López, Joaquín

    2016-04-26

    A fundamental question facing electrodes made out of few layers of graphene (FLG) is if they display chemical properties that are different to their bulk graphite counterpart. Here, we show evidence that suggests that lithium ion intercalation on FLG, as measured via stationary voltammetry, shows a strong dependence on the number of layers of graphene that compose the electrode. Despite its extreme thinness and turbostratic structure, Li ion intercalation into FLG still proceeds through a staging process, albeit with different signatures than bulk graphite or multilayer graphene. Single-layer graphene does not show any evidence of ion intercalation, while FLG with four graphene layers displays limited staging peaks, which broaden and increase in number as the layer number increases to six. Despite these mechanistic differences on ion intercalation, the formation of a solid-electrolyte interphase (SEI) was observed on all electrodes. Scanning electrochemical microscopy (SECM) in the feedback mode was used to demonstrate changes in the surface conductivity of FLG during SEI evolution. Observation of ion intercalation on large area FLG was conditioned to the fabrication of "ionic channels" on the electrode. SECM measurements using a recently developed Li-ion sensitive imaging technique evidenced the role of these channels in enabling Li-ion intercalation through localized flux measurements. This work highlights the impact of nanostructure and microstructure on macroscopic electrochemical behavior and provides guidance to the mechanistic control of ion intercalation using graphene, an atomically thin interface where surface and bulk reactivity converge. PMID:26943950

  15. The impact of the thermal conductivity of a dielectric layer on the self-heating effect of a graphene transistor.

    PubMed

    Pan, T S; Gao, M; Huang, Z L; Zhang, Y; Feng, Xue; Lin, Y

    2015-08-28

    The self-heating effect of a graphene transistor on the transport properties was studied. Different dielectric layers, SiO2 and AlN, which have different thermal conductivities, were used to tune the thermal dissipation of the graphene transistor. An obvious change in channel resistance and a shift of charge neutrality point were observed during the operation of the transistor with SiO2, while the change is slight when AlN is the dielectric layer. This observation is considered to be related to the temperature determined desorption rate of p-type dopants in graphene.

  16. CVD synthesis of mono- and few-layer graphene using alcohols at low hydrogen concentration and atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Campos-Delgado, Jessica; Botello-Méndez, Andrés R.; Algara-Siller, Gerardo; Hackens, Benoit; Pardoen, Thomas; Kaiser, Ute; Dresselhaus, Mildred S.; Charlier, Jean-Christophe; Raskin, Jean-Pierre

    2013-10-01

    An original and easy route to produce mono-, bi- and tri-layer graphene is proposed using the chemical vapor deposition technique. The synthesis is carried out at atmospheric pressure using liquid precursors, copper as catalyst, and a single gas injection line consisting of a very diluted mixture of H2 in Argon (H2: 5%). Two different alcohols are investigated as possible sources of carbon: 2-phenylethanol and ethanol. The characterization of the samples with SEM, TEM and Raman spectroscopy confirms the presence of graphene on top of copper, and yields a detailed picture of the structure of the produced graphene layers.

  17. On the Quantum Hall Effect in mono(bi)-layer graphene

    NASA Astrophysics Data System (ADS)

    Cheremisin, M. V.

    2014-11-01

    Based on a thermodynamic approach, we have calculated the specific resistivity of mono(bi)-layer graphene assumed dissipationless in quantizing magnetic field. The resistivity arises from combination of Peltier and Seebeck effects. The current I causes heating (cooling) at the first (second) sample contacts, due to the Peltier effect. The voltage measured across the sample is equal to the Seebeck thermoemf, and thus provides finite resistivity as I→0. The resistivity is a universal function of the magnetic field, e-h plasma density and temperature, expressed in fundamental units h/e2. At fixed magnetic field the magneto-transport problem is resolved in the vicinity of the Dirac point taking into account the splitting of zeroth Landau level. For mono(bi)- layer graphene the B-dependent splitting of zeroth Landau level is recovered from experimental data.

  18. Electrostatically transparent graphene quantum-dot trap layers for efficient nonvolatile memory

    SciTech Connect

    Kim, Young Rae; Jo, Yong Eun; Sung, Yeo Hyun; Won, Ui Yeon; Shin, Yong Seon; Kang, Won Tae; Yu, Woo Jong E-mail: micco21@skku.edu; Lee, Young Hee E-mail: micco21@skku.edu

    2015-03-09

    In this study, we have demonstrated nonvolatile memory devices using graphene quantum-dots (GQDs) trap layers with indium zinc oxide (IZO) semiconductor channel. The Fermi-level of GQD was effectively modulated by tunneling electrons near the Dirac point because of limited density of states and weak electrostatic screening in monolayer graphene. As a result, large gate modulation was driven in IZO channel to achieve a subthreshold swing of 5.21 V/dec (300 nm SiO{sub 2} gate insulator), while Au quantum-dots memory shows 15.52 V/dec because of strong electrostatic screening in metal quantum-dots. Together, discrete charge traps of GQDs enable stable performance in the endurance test beyond 800 cycles of programming and erasing. Our study suggests the exciting potential of GQD trap layers to be used for a highly promising material in non-volatile memory devices.

  19. High temperature and current density induced degradation of multi-layer graphene

    SciTech Connect

    Wang, Baoming; Haque, M. A.; Mag-isa, Alexander E.; Kim, Jae-Hyun; Lee, Hak-Joo

    2015-10-19

    We present evidence of moderate current density, when accompanied with high temperature, promoting migration of foreign atoms on the surface of multi-layer graphene. Our in situ transmission electron microscope experiments show migration of silicon atoms at temperatures above 800 °C and current density around 4.2 × 10{sup 7} A/cm{sup 2}. Originating from the micro-machined silicon structures that clamp the freestanding specimen, the atoms are observed to react with the carbon atoms in the multi-layer graphene to produce silicon carbide at temperatures of 900–1000 °C. In the absence of electrical current, there is no migration of silicon and only pyrolysis of polymeric residue is observed.

  20. 11-GHz waveguide Nd:YAG laser CW mode-locked with single-layer graphene

    PubMed Central

    Okhrimchuk, Andrey G.; Obraztsov, Petr A.

    2015-01-01

    We report stable, passive, continuous-wave (CW) mode-locking of a compact diode-pumped waveguide Nd:YAG laser with a single-layer graphene saturable absorber. The depressed cladding waveguide in the Nd:YAG crystal is fabricated with an ultrafast laser inscription method. The saturable absorber is formed by direct deposition of CVD single-layer graphene on the output coupler. The few millimeter-long cavity provides generation of 16-ps pulses with repetition rates in the GHz range (up to 11.3 GHz) and 12 mW average power. Stable CW mode-locking operation is achieved by controlling the group delay dispersion in the laser cavity with a Gires–Tournois interferometer. PMID:26052678

  1. Single layered flexible photo-detector based on perylene/graphene composite through printed technology

    NASA Astrophysics Data System (ADS)

    Ali, Shawkat; Bae, Jinho; Lee, Chong Hyun

    2015-07-01

    In this paper, a single layered passive photo sensor based on perylene/graphene composite is proposed, which is deposited in comb type silver electrodes separated as 50 μm spacing. To increase an electrical conductivity of the proposed sensor, perylene and graphene are blended. Photo sensing layer (120nm thick) and Silver electrodes (50 μm width, 350 nm thick) are deposited on poly(ethylene terephthalate) (PET) substrate through electro-hydrodynamic (EHD) system. The proposed photo sensor detects a terminal resistance inversely varied by an incident light in the range between 78 GΩ in dark and 25 GΩ at light intensity of 400lux. The device response is maximum at 465 nm ~ 535 nm wavelength range at blue light. The device exhibited bendability up to 4mm diameter for 1000 endurance cycles. The surface morphology analysis is carried out with FE-SEM and microscope.

  2. Carrier lifetime in exfoliated few-layer graphene determined from intersubband optical transitions.

    PubMed

    Limmer, Thomas; Feldmann, Jochen; Da Como, Enrico

    2013-05-24

    We report a femtosecond transient spectroscopy study in the near to middle infrared range, 0.8-0.35 eV photon energy, on graphene and few layer graphene single flakes. The spectra show an evolving structure of photoinduced absorption bands superimposed on the bleaching caused by Pauli blocking of the interband optically coupled states. Supported by tight-binding model calculations, we assign the photoinduced absorption features to intersubband transitions as the number of layers is increased. Interestingly, the intersubband photoinduced resonances show a longer dynamics than the interband bleaching, because of their independence from the absolute energy of the carriers with respect to the Dirac point. The dynamic of these intersubband transitions reflects the lifetime of the hot carriers and provides an elegant method to access it in this important class of semimetals.

  3. Carrier Lifetime in Exfoliated Few-Layer Graphene Determined from Intersubband Optical Transitions

    NASA Astrophysics Data System (ADS)

    Limmer, Thomas; Feldmann, Jochen; Da Como, Enrico

    2013-05-01

    We report a femtosecond transient spectroscopy study in the near to middle infrared range, 0.8-0.35 eV photon energy, on graphene and few layer graphene single flakes. The spectra show an evolving structure of photoinduced absorption bands superimposed on the bleaching caused by Pauli blocking of the interband optically coupled states. Supported by tight-binding model calculations, we assign the photoinduced absorption features to intersubband transitions as the number of layers is increased. Interestingly, the intersubband photoinduced resonances show a longer dynamics than the interband bleaching, because of their independence from the absolute energy of the carriers with respect to the Dirac point. The dynamic of these intersubband transitions reflects the lifetime of the hot carriers and provides an elegant method to access it in this important class of semimetals.

  4. Tunable plasmons in few-layer nitrogen-doped graphene nanostructures: A time-dependent density functional theory study

    NASA Astrophysics Data System (ADS)

    Shu, Xiao-qin; Zhang, Hong; Cheng, Xin-lu; Miyamoto, Yoshiyuki

    2016-05-01

    Compared with conventional metal plasmonic materials, surface plasmons in graphene are advantageous in terms of higher confinement, relative low loss, flexible featuring, and good tunability. However, the working frequencies of the pristine graphene (undoped graphene) surface plasmons are located in the terahertz and infrared regions, which limit their applications. Here we show high-frequency plasmons in nitrogen (N)-doped graphene nanostructures investigated by time-dependent density functional theory. We found the optical absorption strength of systems containing two layers to be more than twofold stronger than that of systems with monolayers. The optical absorption strength increases as the interlayer distance increases, and the absorption spectra are red-shifted for impulse excitations polarized in the armchair edge direction (x axis). For microstructures of more than two layers, the optical absorption strength increases as number of layers of the N-doped graphene nanostructures increases. In addition, when the number of layers becomes elevated at low-energy resonances, the absorption spectra are seen to blue-shift. The plasmon energy resonance points are located in the visible and ultraviolet regions. The N-doped graphene provides an effective strategy for nanoscale plasmon devices in the visible and ultraviolet regions, despite their weaker absorption intensities when compared with the pristine graphene.

  5. Layer-by-layer evolution of structure, strain, and activity for the oxygen evolution reaction in graphene-templated Pt monolayers.

    PubMed

    Abdelhafiz, Ali; Vitale, Adam; Joiner, Corey; Vogel, Eric; Alamgir, Faisal M

    2015-03-25

    In this study, we explore the dimensional aspect of structure-driven surface properties of metal monolayers grown on a graphene/Au template. Here, surface limited redox replacement (SLRR) is used to provide precise layer-by-layer growth of Pt monolayers on graphene. We find that after a few iterations of SLRR, fully wetted 4-5 monolayer Pt films can be grown on graphene. Incorporating graphene at the Pt-Au interface modifies the growth mechanism, charge transfers, equilibrium interatomic distances, and associated strain of the synthesized Pt monolayers. We find that a single layer of sandwiched graphene is able to induce a 3.5% compressive strain on the Pt adlayer grown on it, and as a result, catalytic activity is increased due to a greater areal density of the Pt layers beyond face-centered-cubic close packing. At the same time, the sandwiched graphene does not obstruct vicinity effects of near-surface electron exchange between the substrate Au and adlayers Pt. X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) techniques are used to examine charge mediation across the Pt-graphene-Au junction and the local atomic arrangement as a function of the Pt adlayer dimension. Cyclic voltammetry (CV) and the oxygen reduction reaction (ORR) are used as probes to examine the electrochemically active area of Pt monolayers and catalyst activity, respectively. Results show that the inserted graphene monolayer results in increased activity for the Pt due to a graphene-induced compressive strain, as well as a higher resistance against loss of the catalytically active Pt surface.

  6. Ion transport in complex layered graphene-based membranes with tuneable interlayer spacing

    PubMed Central

    Cheng, Chi; Jiang, Gengping; Garvey, Christopher J.; Wang, Yuanyuan; Simon, George P.; Liu, Jefferson Z.; Li, Dan

    2016-01-01

    Investigation of the transport properties of ions confined in nanoporous carbon is generally difficult because of the stochastic nature and distribution of multiscale complex and imperfect pore structures within the bulk material. We demonstrate a combined approach of experiment and simulation to describe the structure of complex layered graphene-based membranes, which allows their use as a unique porous platform to gain unprecedented insights into nanoconfined transport phenomena across the entire sub–10-nm scales. By correlation of experimental results with simulation of concentration-driven ion diffusion through the cascading layered graphene structure with sub–10-nm tuneable interlayer spacing, we are able to construct a robust, representative structural model that allows the establishment of a quantitative relationship among the nanoconfined ion transport properties in relation to the complex nanoporous structure of the layered membrane. This correlation reveals the remarkable effect of the structural imperfections of the membranes on ion transport and particularly the scaling behaviors of both diffusive and electrokinetic ion transport in graphene-based cascading nanochannels as a function of channel size from 10 nm down to subnanometer. Our analysis shows that the range of ion transport effects previously observed in simple one-dimensional nanofluidic systems will translate themselves into bulk, complex nanoslit porous systems in a very different manner, and the complex cascading porous circuities can enable new transport phenomena that are unattainable in simple fluidic systems. PMID:26933689

  7. Dynamically tunable plasmonically induced transparency in sinusoidally curved and planar graphene layers.

    PubMed

    Xia, Sheng-Xuan; Zhai, Xiang; Wang, Ling-Ling; Sun, Bin; Liu, Jian-Qiang; Wen, Shuang-Chun

    2016-08-01

    To achieve plasmonically induced transparency (PIT), general near-field plasmonic systems based on couplings between localized plasmon resonances of nanostructures rely heavily on the well-designed interantenna separations. However, the implementation of such devices and techniques encounters great difficulties mainly to due to very small sized dimensions of the nanostructures and gaps between them. Here, we propose and numerically demonstrate that PIT can be achieved by using two graphene layers that are composed of a upper sinusoidally curved layer and a lower planar layer, avoiding any pattern of the graphene sheets. Both the analytical fitting and the Akaike Information Criterion (AIC) method are employed efficiently to distinguish the induced window, which is found to be more likely caused by Autler-Townes splitting (ATS) instead of electromagnetically induced transparency (EIT). Besides, our results show that the resonant modes cannot only be tuned dramatically by geometrically changing the grating amplitude and the interlayer spacing, but also by dynamically varying the Fermi energy of the graphene sheets. Potential applications of the proposed system could be expected on various photonic functional devices, including optical switches, plasmonic sensors. PMID:27505756

  8. Transport gap in vertical devices made of incommensurately misoriented graphene layers

    NASA Astrophysics Data System (ADS)

    Nguyen, V. Hung; Dollfus, P.

    2016-02-01

    By means of atomistic tight-binding calculations, we investigate the transport properties of vertical devices made of two incommensurately misoriented graphene layers. For a given transport direction (Ox-axis), we define two classes of rotated graphene lattice distinguished by difference in lattice symmetry and, hence, in Brillouin zone. In particular, these two classes correspond to two different cases where the position of their Dirac cones in the k y -axis is determined differently, i.e. Ky\\prime={{K}y}=0 or Ky\\prime=-{{K}y}=2π /3{{L}y} (L y is the periodic length along the Oy axis). As a consequence, in devices made of two layers of different lattice classes, the misalignment of Dirac cones between the left and right graphene sections opens a finite energy-gap of conductance that can reach a few hundreds of meV. We also show that strain engineering can be used to further enlarge the transport gap and to diminish the sensitivity of the gap on the twist angle and on the commensurateness of the layer stack.

  9. Electrostatic force microscopy and electrical isolation of etched few-layer graphene nano-domains

    SciTech Connect

    Hunley, D. Patrick; Sundararajan, Abhishek; Boland, Mathias J.; Strachan, Douglas R.

    2014-12-15

    Nanostructured bi-layer graphene samples formed through catalytic etching are investigated with electrostatic force microscopy. The measurements and supporting computations show a variation in the microscopy signal for different nano-domains that are indicative of changes in capacitive coupling related to their small sizes. Abrupt capacitance variations detected across etch tracks indicates that the nano-domains have strong electrical isolation between them. Comparison of the measurements to a resistor-capacitor model indicates that the resistance between two bi-layer graphene regions separated by an approximately 10 nm wide etch track is greater than about 1×10{sup 12} Ω with a corresponding gap resistivity greater than about 3×10{sup 14} Ω⋅nm. This extremely large gap resistivity suggests that catalytic etch tracks within few-layer graphene samples are sufficient for providing electrical isolation between separate nano-domains that could permit their use in constructing atomically thin nanogap electrodes, interconnects, and nanoribbons.

  10. Effects of Electrode Layer Band Structure on the Performance of Multilayer Graphene-hBN-Graphene Interlayer Tunnel Field Effect Transistors.

    PubMed

    Kang, Sangwoo; Prasad, Nitin; Movva, Hema C P; Rai, Amritesh; Kim, Kyounghwan; Mou, Xuehao; Taniguchi, Takashi; Watanabe, Kenji; Register, Leonard F; Tutuc, Emanuel; Banerjee, Sanjay K

    2016-08-10

    Interlayer tunnel field-effect transistors based on graphene and hexagonal boron nitride (hBN) have recently attracted much interest for their potential as beyond-CMOS devices. Using a recently developed method for fabricating rotationally aligned two-dimensional heterostructures, we show experimental results for devices with varying thicknesses and stacking order of the graphene electrode layers and also model the current-voltage behavior. We show that an increase in the graphene layer thickness results in narrower resonance. However, due to a simultaneous increase in the number of sub-bands and decrease of sub-band separation with an increase in thickness, the negative differential resistance peaks becomes less prominent and do not appear for certain conditions at room temperature. Also, we show that due to the unique band structure of odd number of layer Bernal-stacked graphene, the number of closely spaced resonance conditions increase, causing interference between neighboring resonance peaks. Although this can be avoided with even number of layer graphene, we find that in this case the bandgap opening present at high biases tend to broaden the resonance peaks. PMID:27416362

  11. First-principles study of hydrogen adsorption on titanium-decorated single-layer and bilayer graphenes

    NASA Astrophysics Data System (ADS)

    Pan, Hong-Zhe; Wang, Yong-Long; He, Kai-Hua; Wei, Ming-Zhen; Ouyang, Yu; Chen, Li

    2013-06-01

    The adsorption of hydrogen molecules on titanium-decorated (Ti-decorated) single-layer and bilayer graphenes is studied using density functional theory (DFT) with the relativistic effect. Both the local density approximation (LDA) and the generalized gradient approximation (GGA) are used for obtaining the region of the adsorption energy of H2 molecules on Ti-decorated graphene. We find that a graphene layer with titanium (Ti) atoms adsorbed on both sides can store hydrogen up to 9.51 wt% with average adsorption energy in a range from -0.170 eV to -0.518 eV. Based on the adsorption energy criterion, we find that chemisorption is predominant for H2 molecules when the concentration of H2 molecules absorbed is low while physisorption is predominant when the concentration is high. The computation results for the bilayer graphene decorated with Ti atoms show that the lower carbon layer makes no contribution to hydrogen adsorption.

  12. Magnetotransport properties of a few-layer graphene-ferromagnetic metal junctions in vertical spin valve devices

    SciTech Connect

    Entani, Shiro Naramoto, Hiroshi; Sakai, Seiji

    2015-05-07

    Magnetotransport properties were studied for the vertical spin valve devices with two junctions of permalloy electrodes and a few-layer graphene interlayer. The graphene layer was directly grown on the bottom electrode by chemical vapor deposition. X-ray photoelectron spectroscopy showed that the permalloy surface fully covered with a few-layer graphene is kept free from oxidation and contamination even after dispensing and removing photoresist. This enabled fabrication of the current perpendicular to plane spin valve devices with a well-defined interface between graphene and permalloy. Spin-dependent electron transport measurements revealed a distinct spin valve effect in the devices. The magnetotransport ratio was 0.8% at room temperature and increased to 1.75% at 50 K. Linear current-voltage characteristics and resistance increase with temperature indicated that ohmic contacts are realized at the relevant interfaces.

  13. Heterogeneous fluorescence intermittency in single layer reduced graphene oxide

    NASA Astrophysics Data System (ADS)

    Si, Jixin; Volkan-Kacso, Sandor; Eltom, Ahmed; Morozov, Yurii; McDonald, Matthew P.; Ruth, Anthony; Kuno, Masaru; Janko, Boldizsar

    Fluorescence intermittency, or blinking, has been observed in a wide range of systems, including quantum dots, nanorods, and nanowires. Striking similarities have been documented in the optical response of these nanoscale emitters. However, the mechanism behind blinking still remains elusive. For the first time, blinking has been observed in a two-dimensional system in recent experiments on reduced graphene oxide (rGO). Here we reveal the power spectral density (PSD) of the blinking in rGO shares the same 1/f-like behavior of previously known blinking systems; meanwhile, the heterogeneous dynamic evolution and spatial correlation make rGO a unique blinking system. To investigate the origin of blinking, we self-consistently explain the evolution of rGO blinking using the phenomenological multiple recombination center (MRC) model that captures common features of nanoscale blinking. Furthermore, tight binding method and ab-initio method calculations of carbon nanodots are utilized to look for the microscopic structure corresponding to the RCs in the MRC model. M. K. thanks the American Chemical Society Petroleum Research Fund, the Army Research Office (W911NF-12-1-0578) for support. B.J. was supported in part by the U. S. DOE, Office of Science, Office of Basic Energy Sciences, under Contract W-31-109-Eng-38.

  14. Hydrogen intercalation of single and multiple layer graphene synthesized on Si-terminated SiC(0001) surface

    SciTech Connect

    Sołtys, Jakub; Piechota, Jacek; Ptasinska, Maria; Krukowski, Stanisław

    2014-08-28

    Ab initio density functional theory simulations were used to investigate the influence of hydrogen intercalation on the electronic properties of single and multiple graphene layers deposited on the SiC(0001) surface (Si-face). It is shown that single carbon layer, known as a buffer layer, covalently bound to the SiC substrate, is liberated after hydrogen intercalation, showing characteristic Dirac cones in the band structure. This is in agreement with the results of angle resolved photoelectron spectroscopy measurements of hydrogen intercalation of SiC-graphene samples. In contrast to that hydrogen intercalation has limited impact on the multiple sheet graphene, deposited on Si-terminated SiC surface. The covalently bound buffer layer is liberated attaining its graphene like structure and dispersion relation typical for multilayer graphene. Nevertheless, before and after intercalation, the four layer graphene preserved the following dispersion relations in the vicinity of K point: linear for (AAAA) stacking, direct parabolic for Bernal (ABAB) stacking and “wizard hat” parabolic for rhombohedral (ABCA) stacking.

  15. Bimodal behaviour of charge carriers in graphene induced by electric double layer

    PubMed Central

    Tsai, Sing-Jyun; Yang, Ruey-Jen

    2016-01-01

    A theoretical investigation is performed into the electronic properties of graphene in the presence of liquid as a function of the contact area ratio. It is shown that the electric double layer (EDL) formed at the interface of the graphene and the liquid causes an overlap of the conduction bands and valance bands and increases the density of state (DOS) at the Fermi energy (EF). In other words, a greater number of charge carriers are induced for transport and the graphene changes from a semiconductor to a semimetal. In addition, it is shown that the dependence of the DOS at EF on the contact area ratio has a bimodal distribution which responses to the experimental observation, a pinnacle curve. The maximum number of induced carriers is expected to occur at contact area ratios of 40% and 60%. In general, the present results indicate that modulating the EDL provides an effective means of tuning the electronic properties of graphene in the presence of liquid. PMID:27464986

  16. Spatially resolved electrical characterisation of graphene layers by an evanescent field microwave microscope

    NASA Astrophysics Data System (ADS)

    Gregory, Andrew; Hao, Ling; Klein, Norbert; Gallop, John; Mattevi, Cecilia; Shaforost, Olena; Lees, Kevin; Clarke, Bob

    2014-02-01

    An evanescent field microwave microscope has been developed at the National Physical Laboratory. This instrument has multiple applications and has been developed to allow traceable measurements of local complex permittivity, unlike most other microwave scanning microscopes. In this paper we describe basic operation of the microscope and show measurements on graphene samples produced at Imperial College. The microscope obtains images by raster scanning of a wire probe in ‘contact mode’. Of particular interest to the graphene community is the possibility of being able to scan over large areas (up to 4×4 mm2), and to be able to measure actual values of surface resistance without a requirement for metal contacts. As an ultrathin semimetal, a graphene layer being placed in the evanescent field of the probe is expected to behave like a lossy dielectric material, its microwave loss tangent is proportional to its conductivity. Employing a high Q dual mode re-entrant cavity as host resonator and a spherical metal probe of 180 μm diameter, we found that spatial variations of the conductivity of graphene can be clearly resolved.

  17. Reduced graphene oxide with ultrahigh conductivity as carbon coating layer for high performance sulfur@reduced graphene oxide cathode

    NASA Astrophysics Data System (ADS)

    Zhao, Hongbin; Peng, Zhenhuan; Wang, Wenjun; Chen, Xikun; Fang, Jianhui; Xu, Jiaqiang

    2014-01-01

    We developed hydrogen iodide (HI) reduction of rGO and surfactant-assisted chemical reaction- deposition method to form hybrid material of sulfur (S) encapsulated in reduced graphene oxide (rGO) sheets for rechargeable lithium batteries. The surfactant-assisted chemical reaction-deposition method strategy provides intimate contact between the S and graphene oxide. Chemical reduced rGO with high conductivity as carbon coating layer prevented the dissolution of polysulfide ions and improved the electron transfer. This novel core-shell structured S@rGO composites with high S content showed high reversible capacity, good discharge capacity retention and enhanced rate capability used as cathodes in rechargeable Li/S cells. We demonstrated here that an electrode prepared from a S@rGO with up to 85 wt% S maintains a stable discharge capacity of about 980 mAh g-1 at 0.05 C and 570 mAh g-1 at 1C after 200 cycles charge/discharge. These results emphasize the importance of rGO with high electrical conductivity after HI-reduced rGO homogeneously coating on the surface of S, therefore, effectively alleviating the shuttle phenomenon of polysulfides in organic electrolyte. Our surfactant-assisted chemical reaction-HI reduction approach should offer a new technique for the design and synthesis of battery electrodes based on highly conducting carbon materials.

  18. Applications of single-layered graphene sheets as mass sensors and atomistic dust detectors

    NASA Astrophysics Data System (ADS)

    Sakhaee-Pour, A.; Ahmadian, M. T.; Vafai, A.

    2008-01-01

    Molecular structural mechanics is implemented to model the vibrational behavior of defect-free single-layered graphene sheets (SLGSs) at constant temperature. To mimic these two-dimensional layers, zigzag and armchair models with cantilever and bridge boundary conditions are adopted. Fundamental frequencies of these nanostructures are calculated, and it is perceived that they are independent of the chirality and aspect ratio. The effects of point mass and atomistic dust on the fundamental frequencies are also considered in order to investigate the possibility of using SLGSs as sensors. The results show that the principal frequencies are highly sensitive to an added mass of the order of 10-6 fg.

  19. Polymer solar cells with gold nanoclusters decorated multi-layer graphene as transparent electrode

    NASA Astrophysics Data System (ADS)

    Zhang, Di; Choy, Wallace C. H.; Wang, Charlie C. D.; Li, Xiao; Fan, Lili; Wang, Kunlin; Zhu, Hongwei

    2011-11-01

    A thin layer of ultraviolet-ozone (UVO) treated gold (Au) is introduced on multi-layer graphene (MLG) to enable the MLG as an effective anode for polymer solar cells (PSCs). By optimizing the Au thickness and the durations of the UVO treatments at different stages, MLG PSCs with enhanced fill factor and power conversion efficiency are obtained, exhibiting better performance compared with MLG devices directly modified with UVO and poly(3,4-ethylenedioythiophene):poly(styrenesulfonate). Further analysis shows that UVO treated Au provides favorable band alignment at the MLG/polymer interface. Moreover, the improved interfacial contact and shortened UVO durations reduce the series resistance of PSCs significantly.

  20. Microscopic theoretical model study of band gap opening in AA-stacked bi-layer graphene

    NASA Astrophysics Data System (ADS)

    Sahu, Sivabrata; Parashar, S. K. S.; Rout, G. C.

    2016-05-01

    We address here a tight-binding theoretical model calculation for AA-stacked bi-layer graphene taking into account of a biased potential between two layers to study the density of states and the band dispersion within the total Brillouin zone. We have calculated the electronic Green's function for electron operator corresponding to A and B sub lattices by Zubarev's Green's function technique from which the electronic density of states and the electron band energy dispersion are calculated. The numerically computed density of states and band energy dispersions are investigated by tuning the biased potential to exhibit the band gap by varying the different physical parameters.

  1. Quantitative Assessment of Friction Characteristics of Single-Layer MoS2 and Graphene Using Atomic Force Microscopy.

    PubMed

    Khac, Bien-cuong tran; Chung, Koo-hyun

    2016-05-01

    Atomically thin layered materials such as MoS2 and graphene have attracted a lot of interest as protective coating layers for micro- and nano-electromechanical devices based on their superior mechanical properties and chemical inertness. In this work, the frictional characteristics of single layer MoS2 and graphene prepared by the mechanical exfoliation method were quantitatively investigated using atomic force microscopy. The results showed that both MoS2 and graphene exhibited relatively low friction forces of 1-3 nN under normal forces ranging from 1 to 30 nN. However, a higher increase in the friction force as the normal force increased was observed in the case of MoS2. The differences in the adhesion characteristics and mechanical properties of atomically thin layered materials may influence the puckering of the layer, which in turn influences the frictional behavior. PMID:27483768

  2. Enhanced opto-electrical properties of graphene electrode InGaN/GaN LEDs with a NiOx inter-layer

    NASA Astrophysics Data System (ADS)

    Wu, Caichuan; Liu, Fengyuan; Liu, Bin; Zhuang, Zhe; Dai, Jiangping; Tao, Tao; Zhang, Guogang; Xie, Zili; Wang, Xinran; Zhang, Rong

    2015-07-01

    We report the fabrication of gallium nitride (GaN)-based light-emitting diode (LED) with uniform and monolayer graphene as transparent current spreading layer. Two-dimensional graphene successfully provides efficient current spreading and hole injection into the active layers of the LEDs for light emission. To further reduce the ohmic contact resistance between p-GaN and graphene film, ultrathin NiOx inter-layer is introduced in the device, improving its electrical and optical performance.

  3. Effect of radical fluorination on mono- and bi-layer graphene in Ar/F{sub 2} plasma

    SciTech Connect

    Tahara, K.; Iwasaki, T.; Hatano, M.; Matsutani, A.

    2012-10-15

    Fluorinated graphene has the possibility to achieve unique properties and functions in graphene. We propose a highly controlled fluorination method utilizing fluorine radicals in Ar/F{sub 2} plasma. To suppress ion bombardments and improve the reaction with fluorine radicals on graphene, the substrate was placed 'face down' in the plasma chamber. Although monolayer graphene was more reactive than bilayer, fluorination of bilayer reached the level of I{sub D}/I{sub G} {approx} 0.5 in Raman D peak intensity at 532 nm excitation. Annealing fluorinated samples proved reversibility of radical fluorination for both mono- and bi-layer graphenes. X-ray photoelectron spectroscopy showed the existence of carbon-fluorine bonding.

  4. Property transformation of graphene with Al{sub 2}O{sub 3} films deposited directly by atomic layer deposition

    SciTech Connect

    Zheng, Li; Cao, Duo; Wang, Zhongjian; Xia, Chao; Cheng, Xinhong Yu, Yuehui; Shen, Dashen

    2014-01-13

    Al{sub 2}O{sub 3} films are deposited directly onto graphene by H{sub 2}O-based atomic layer deposition (ALD), and the films are pinhole-free and continuously cover the graphene surface. The growth process of Al{sub 2}O{sub 3} films does not introduce any detective defects in graphene, suppresses the hysteresis effect and tunes the graphene doping to n-type. The self-cleaning of ALD growth process, together with the physically absorbed H{sub 2}O and oxygen-deficient ALD environment consumes OH{sup −} bonds, suppresses the p-doping of graphene, shifts Dirac point to negative gate bias and enhances the electron mobility.

  5. Rational design of a binary metal alloy for chemical vapour deposition growth of uniform single-layer graphene.

    PubMed

    Dai, Boya; Fu, Lei; Zou, Zhiyu; Wang, Min; Xu, Haitao; Wang, Sheng; Liu, Zhongfan

    2011-01-01

    Controlled growth of high-quality graphene is still the bottleneck of practical applications. The widely used chemical vapour deposition process generally suffers from an uncontrollable carbon precipitation effect that leads to inhomogeneous growth and strong correlation to the growth conditions. Here we report the rational design of a binary metal alloy that effectively suppresses the carbon precipitation process and activates a self-limited growth mechanism for homogeneous monolayer graphene. As demonstrated by an Ni-Mo alloy, the designed binary alloy contains an active catalyst component for carbon source decomposition and graphene growth and a black hole counterpart for trapping the dissolved carbons and forming stable metal carbides. This type of process engineering has been used to grow strictly single-layer graphene with 100% surface coverage and excellent tolerance to variations in growth conditions. With simplicity, scalability and a very large growth window, the presented approach may facilitate graphene research and industrial applications. PMID:22045001

  6. Direct Preparation of Few Layer Graphene Epoxy Nanocomposites from Untreated Flake Graphite.

    PubMed

    Throckmorton, James; Palmese, Giuseppe

    2015-07-15

    The natural availability of flake graphite and the exceptional properties of graphene and graphene-polymer composites create a demand for simple, cost-effective, and scalable methods for top-down graphite exfoliation. This work presents a novel method of few layer graphite nanocomposite preparation directly from untreated flake graphite using a room temperature ionic liquid and laminar shear processing regimen. The ionic liquid serves both as a solvent and initiator for epoxy polymerization and is incorporated chemically into the matrix. This nanocomposite shows low electrical percolation (0.005 v/v) and low thickness (1-3 layers) graphite/graphene flakes by TEM. Additionally, the effect of processing conditions by rheometry and comparison with solvent-free conditions reveal the interactions between processing and matrix properties and provide insight into the theory of the chemical and physical exfoliation of graphite crystals and the resulting polymer matrix dispersion. An interaction model that correlates the interlayer shear physics of graphite flakes and processing parameters is proposed and tested.

  7. Effect of radial stretch on vibration characteristics of single-layered circular graphene sheets

    NASA Astrophysics Data System (ADS)

    Pahlani, Gunjan; Verma, Deepti; Gupta, Shakti

    Vibrations of single-layered circular graphene sheets are studied using molecular mechanics (MM) simulations. Interactions between bonded and non-bonded atoms are prescribed using MM3 potential. Frequencies of different modes of vibration are computed from the eigenvalues and eigen vectors of mass weighted Hessian of the system. This study is performed on graphene sheets of various diameters. A linear continuum membrane model for predicting vibrational frequencies is studied using finite element (FE) method. Frequencies for several modes computed from continuum and molecular model matched well for moderate values of radial stretch, however, with increased stretch those deviated from each other significantly. In particular for higher values of stretch the MM simulations predict considerably lower values of frequencies compared to that found from FE simulations. Also, at higher values of stretch the frequency vs. stretch curve obtained from MM simulations showed a hardening behavior which could not be captured by the linear continuum model. We have also found a similar behavior in two-layered graphene sheets using MM simulations.

  8. Long-Term Passivation of Strongly Interacting Metals with Single-Layer Graphene

    PubMed Central

    2015-01-01

    The long-term (>18 months) protection of Ni surfaces against oxidation under atmospheric conditions is demonstrated by coverage with single-layer graphene, formed by chemical vapor deposition. In situ, depth-resolved X-ray photoelectron spectroscopy of various graphene-coated transition metals reveals that a strong graphene–metal interaction is of key importance in achieving this long-term protection. This strong interaction prevents the rapid intercalation of oxidizing species at the graphene–metal interface and thus suppresses oxidation of the substrate surface. Furthermore, the ability of the substrate to locally form a passivating oxide close to defects or damaged regions in the graphene overlayer is critical in plugging these defects and preventing oxidation from proceeding through the bulk of the substrate. We thus provide a clear rationale for understanding the extent to which two-dimensional materials can protect different substrates and highlight the key implications for applications of these materials as barrier layers to prevent oxidation. PMID:26499041

  9. Single layer nano graphene platelets derived from graphite nanofibres

    NASA Astrophysics Data System (ADS)

    Huang, Kai; Delport, Géraud; Orcin-Chaix, Lucile; Drummond, Carlos; Lauret, Jean-Sebastien; Penicaud, Alain

    2016-04-01

    Solutions of calibrated nanographenides (negatively charged nanographenes) are obtained by dissolution of graphite nanofibre intercalation compounds (GNFICs). Deposits show homogeneous unfolded nanographene platelets of 1 to 2 layers thickness and 10 nm lateral size, evidenced by atomic force microscopy and Raman spectroscopy. Upon oxidation, nanographenide solutions exhibit strong photoluminescence.Solutions of calibrated nanographenides (negatively charged nanographenes) are obtained by dissolution of graphite nanofibre intercalation compounds (GNFICs). Deposits show homogeneous unfolded nanographene platelets of 1 to 2 layers thickness and 10 nm lateral size, evidenced by atomic force microscopy and Raman spectroscopy. Upon oxidation, nanographenide solutions exhibit strong photoluminescence. Electronic supplementary information (ESI) available: Raman, SEM, TEM and XPS characterization of the raw nanofibres, detailed XPS spectra analysis of deposits from GNFIC/THF and GNFIC/NMP solutions, Raman and AFM characterization of fresh and aged solutions of nanofibres obtained from 3 different suppliers. See DOI: 10.1039/c6nr01512c

  10. Micrometer-Thick Graphene Oxide-Layered Double Hydroxide Nacre-Inspired Coatings and Their Properties.

    PubMed

    Yan, You-Xian; Yao, Hong-Bin; Mao, Li-Bo; Asiri, Abdullah M; Alamry, Khalid A; Marwani, Hadi M; Yu, Shu-Hong

    2016-02-10

    Robust, functional, and flame retardant coatings are attractive in various fields such as building construction, food packaging, electronics encapsulation, and so on. Here, strong, colorful, and fire-retardant micrometer-thick hybrid coatings are reported, which can be constructed via an enhanced layer-by-layer assembly of graphene oxide (GO) nanosheets and layered double hydroxide (LDH) nanoplatelets. The fabricated GO-LDH hybrid coatings show uniform nacre-like layered structures that endow them good mechanic properties with Young's modulus of ≈ 18 GPa and hardness of ≈ 0.68 GPa. In addition, the GO-LDH hybrid coatings exhibit nacre-like iridescence and attractive flame retardancy as well due to their well-defined 2D microstructures. This kind of nacre-inspired GO-LDH hybrid thick coatings will be applied in various fields in future due to their high strength and multifunctionalities.

  11. Microstructure and Functional Mechanism of Friction Layer in Ni3Al Matrix Composites with Graphene Nanoplatelets

    NASA Astrophysics Data System (ADS)

    Xue, Bing; Zhu, Qingshuai; Shi, Xiaoliang; Zhai, Wenzheng; Yang, Kang; Huang, Yuchun

    2016-08-01

    Microstructure and functional mechanism of friction layer need to be further researched. In the present work, the friction coefficients and wear rates are analyzed through response surface methodology to obtain an empirical model for the best response. Fitting results show that the tribological performance of Ni3Al matrix composites (NMCs) with graphene nanoplatelets (GNPs) is better than that of NMCs without GNPs, especially at high sliding velocities and high loads. Further research suggests that the formation of integrated friction layer, which consists of a soft microfilm on a hard coating, is the major reason to cause the differences. Of which, the wear debris layer (WDL) with a low shear strength can reduce the shear force. The ultrafine layer (UL), which is much harder and finer, can effectively avoid fracture and improve the load support capacity. Moreover, the GNPs in WDL and UL can be easily sheared and help to withstand the loads, trending to be parallel to the direction of shear force.

  12. Microstructure and Functional Mechanism of Friction Layer in Ni3Al Matrix Composites with Graphene Nanoplatelets

    NASA Astrophysics Data System (ADS)

    Xue, Bing; Zhu, Qingshuai; Shi, Xiaoliang; Zhai, Wenzheng; Yang, Kang; Huang, Yuchun

    2016-10-01

    Microstructure and functional mechanism of friction layer need to be further researched. In the present work, the friction coefficients and wear rates are analyzed through response surface methodology to obtain an empirical model for the best response. Fitting results show that the tribological performance of Ni3Al matrix composites (NMCs) with graphene nanoplatelets (GNPs) is better than that of NMCs without GNPs, especially at high sliding velocities and high loads. Further research suggests that the formation of integrated friction layer, which consists of a soft microfilm on a hard coating, is the major reason to cause the differences. Of which, the wear debris layer (WDL) with a low shear strength can reduce the shear force. The ultrafine layer (UL), which is much harder and finer, can effectively avoid fracture and improve the load support capacity. Moreover, the GNPs in WDL and UL can be easily sheared and help to withstand the loads, trending to be parallel to the direction of shear force.

  13. Graphene oxide-based carbon interconnecting layer for polymer tandem solar cells.

    PubMed

    Chen, Yonghua; Lin, Wei-Chun; Liu, Jun; Dai, Liming

    2014-03-12

    Tandem polymer solar cells (PSCs), consisting of more than one (normally two) subcells connected by a charge recombination layer (i.e., interconnecting layer), hold great promise for enhancing the performance of PSCs. For an ideal tandem solar cell, the open circuit voltage (Voc) equals to the sum of those of the subcells while keeping the short circuit current the same as the lower one, leading to an increased overall power conversion efficiency. The interconnecting layer plays an important role in regulating the tandem device performance. Here, we report that graphene oxide (GO)/GO-Cs (cesium neutralized GO) bilayer modified with ultrathin Al and MoO3 can act as an efficient interconnecting layer in tandem PSCs to achieve a significantly increased Voc, reaching almost 100% of the sum of the subcell V(oc)s under standard AM 1.5 conditions. PMID:24521516

  14. Micrometer-Thick Graphene Oxide-Layered Double Hydroxide Nacre-Inspired Coatings and Their Properties.

    PubMed

    Yan, You-Xian; Yao, Hong-Bin; Mao, Li-Bo; Asiri, Abdullah M; Alamry, Khalid A; Marwani, Hadi M; Yu, Shu-Hong

    2016-02-10

    Robust, functional, and flame retardant coatings are attractive in various fields such as building construction, food packaging, electronics encapsulation, and so on. Here, strong, colorful, and fire-retardant micrometer-thick hybrid coatings are reported, which can be constructed via an enhanced layer-by-layer assembly of graphene oxide (GO) nanosheets and layered double hydroxide (LDH) nanoplatelets. The fabricated GO-LDH hybrid coatings show uniform nacre-like layered structures that endow them good mechanic properties with Young's modulus of ≈ 18 GPa and hardness of ≈ 0.68 GPa. In addition, the GO-LDH hybrid coatings exhibit nacre-like iridescence and attractive flame retardancy as well due to their well-defined 2D microstructures. This kind of nacre-inspired GO-LDH hybrid thick coatings will be applied in various fields in future due to their high strength and multifunctionalities. PMID:26682698

  15. Ultraviolet protection cotton fabric achieved via layer-by-layer self-assembly of graphene oxide and chitosan

    NASA Astrophysics Data System (ADS)

    Tian, Mingwei; Hu, Xili; Qu, Lijun; Du, Minzhi; Zhu, Shifeng; Sun, Yaning; Han, Guangting

    2016-07-01

    Cotton fabrics with robust ultraviolet protective property can be facilely prepared by depositing graphene oxide (GO) and chitosan (CS) upon fabric substrate via the electrostatic layer-by-layer self-assembly approach. The structure and morphology of the resultant fabrics were characterized by SEM, AFM, FTIR, XPS and dyeing color depth (K/S value), and the ultraviolet (UV) blocking properties were also further investigated. As expected, the UV protection ability was evaluated with Ultraviolet Protection Factor (UPF), and the cotton fabrics deposited with GO and CS showed more than 40-fold increase with a UPF value of 452 than that of control cotton (UPF rating at 9.37). Moreover, the LbL deposited fabric showed excellent washing durability even after 10 times water laundering.

  16. 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.

  17. 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

    2015-01-01

    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. PMID:25648723

  18. Laser Writing Block Copolymer Self-Assembly on Graphene Light-Absorbing Layer.

    PubMed

    Jin, Hyeong Min; Lee, Seung Hyun; Kim, Ju Young; Son, Seung-Woo; Kim, Bong Hoon; Lee, Hwan Keon; Mun, Jeong Ho; Cha, Seung Keun; Kim, Jun Soo; Nealey, Paul F; Lee, Keon Jae; Kim, Sang Ouk

    2016-03-22

    Recent advance of high-power laser processing allows for rapid, continuous, area-selective material fabrication, typically represented by laser crystallization of silicon or oxides for display applications. Two-dimensional materials such as graphene exhibit remarkable physical properties and are under intensive development for the manufacture of flexible devices. Here we demonstrate an area-selective ultrafast nanofabrication method using low intensity infrared or visible laser irradiation to direct the self-assembly of block copolymer films into highly ordered manufacturing-relevant architectures at the scale below 12 nm. The fundamental principles underlying this light-induced nanofabrication mechanism include the self-assembly of block copolymers to proceed across the disorder-order transition under large thermal gradients, and the use of chemically modified graphene films as a flexible and conformal light-absorbing layers for transparent, nonplanar, and mechanically flexible surfaces. PMID:26871736

  19. Layered and scrolled nanocomposites with aligned semi-infinite graphene inclusions at the platelet limit.

    PubMed

    Liu, Pingwei; Jin, Zhong; Katsukis, Georgios; Drahushuk, Lee William; Shimizu, Steven; Shih, Chih-Jen; Wetzel, Eric D; Taggart-Scarff, Joshua K; Qing, Bo; Van Vliet, Krystyn J; Li, Richard; Wardle, Brian L; Strano, Michael S

    2016-07-22

    Two-dimensional (2D) materials can uniquely span the physical dimensions of a surrounding composite matrix in the limit of maximum reinforcement. However, the alignment and assembly of continuous 2D components at high volume fraction remain challenging. We use a stacking and folding method to generate aligned graphene/polycarbonate composites with as many as 320 parallel layers spanning 0.032 to 0.11 millimeters in thickness that significantly increases the effective elastic modulus and strength at exceptionally low volume fractions of only 0.082%. An analogous transverse shear scrolling method generates Archimedean spiral fibers that demonstrate exotic, telescoping elongation at break of 110%, or 30 times greater than Kevlar. Both composites retain anisotropic electrical conduction along the graphene planar axis and transparency. These composites promise substantial mechanical reinforcement, electrical, and optical properties at highly reduced volume fraction.

  20. Thermal transport in three-dimensional foam architectures of few-layer graphene and ultrathin graphite.

    PubMed

    Pettes, Michael Thompson; Ji, Hengxing; Ruoff, Rodney S; Shi, Li

    2012-06-13

    At a very low solid concentration of 0.45 ± 0.09 vol %, the room-temperature thermal conductivity (κ(GF)) of freestanding graphene-based foams (GF), comprised of few-layer graphene (FLG) and ultrathin graphite (UG) synthesized through the use of methane chemical vapor deposition on reticulated nickel foams, was increased from 0.26 to 1.7 W m(-1) K(-1) after the etchant for the sacrificial nickel support was changed from an aggressive hydrochloric acid solution to a slow ammonium persulfate etchant. In addition, κ(GF) showed a quadratic dependence on temperature between 11 and 75 K and peaked at about 150 K, where the solid thermal conductivity (κ(G)) of the FLG and UG constituents reached about 1600 W m(-1) K(-1), revealing the benefit of eliminating internal contact thermal resistance in the continuous GF structure.

  1. Laser Writing Block Copolymer Self-Assembly on Graphene Light-Absorbing Layer.

    PubMed

    Jin, Hyeong Min; Lee, Seung Hyun; Kim, Ju Young; Son, Seung-Woo; Kim, Bong Hoon; Lee, Hwan Keon; Mun, Jeong Ho; Cha, Seung Keun; Kim, Jun Soo; Nealey, Paul F; Lee, Keon Jae; Kim, Sang Ouk

    2016-03-22

    Recent advance of high-power laser processing allows for rapid, continuous, area-selective material fabrication, typically represented by laser crystallization of silicon or oxides for display applications. Two-dimensional materials such as graphene exhibit remarkable physical properties and are under intensive development for the manufacture of flexible devices. Here we demonstrate an area-selective ultrafast nanofabrication method using low intensity infrared or visible laser irradiation to direct the self-assembly of block copolymer films into highly ordered manufacturing-relevant architectures at the scale below 12 nm. The fundamental principles underlying this light-induced nanofabrication mechanism include the self-assembly of block copolymers to proceed across the disorder-order transition under large thermal gradients, and the use of chemically modified graphene films as a flexible and conformal light-absorbing layers for transparent, nonplanar, and mechanically flexible surfaces.

  2. Layered and scrolled nanocomposites with aligned semi-infinite graphene inclusions at the platelet limit.

    PubMed

    Liu, Pingwei; Jin, Zhong; Katsukis, Georgios; Drahushuk, Lee William; Shimizu, Steven; Shih, Chih-Jen; Wetzel, Eric D; Taggart-Scarff, Joshua K; Qing, Bo; Van Vliet, Krystyn J; Li, Richard; Wardle, Brian L; Strano, Michael S

    2016-07-22

    Two-dimensional (2D) materials can uniquely span the physical dimensions of a surrounding composite matrix in the limit of maximum reinforcement. However, the alignment and assembly of continuous 2D components at high volume fraction remain challenging. We use a stacking and folding method to generate aligned graphene/polycarbonate composites with as many as 320 parallel layers spanning 0.032 to 0.11 millimeters in thickness that significantly increases the effective elastic modulus and strength at exceptionally low volume fractions of only 0.082%. An analogous transverse shear scrolling method generates Archimedean spiral fibers that demonstrate exotic, telescoping elongation at break of 110%, or 30 times greater than Kevlar. Both composites retain anisotropic electrical conduction along the graphene planar axis and transparency. These composites promise substantial mechanical reinforcement, electrical, and optical properties at highly reduced volume fraction. PMID:27463667

  3. Polarized dependence of nonlinear susceptibility in a single layer graphene system in infrared region

    NASA Astrophysics Data System (ADS)

    Solookinejad, G.

    2016-09-01

    In this study, the linear and nonlinear susceptibility of a single-layer graphene nanostructure driven by a weak probe light and an elliptical polarized coupling field is discussed theoretically. The Landau levels of graphene can be separated in infrared or terahertz regions under the strong magnetic field. Therefore, by using the density matrix formalism in quantum optic, the linear and nonlinear susceptibility of the medium can be derived. It is demonstrated that by adjusting the elliptical parameter, one can manipulate the linear and nonlinear absorption as well as Kerr nonlinearity of the medium. It is realized that the enhanced Kerr nonlinearity can be possible with zero linear absorption and nonlinear amplification at some values of elliptical parameter. Our results may be having potential applications in quantum information science based on Nano scales devices.

  4. Graphene-like single-layered covalent organic frameworks: synthesis strategies and application prospects.

    PubMed

    Liu, Xuan-He; Guan, Cui-Zhong; Wang, Dong; Wan, Li-Jun

    2014-10-29

    Two-dimensional (2D) nanomaterials, such as graphene and transition metal chalcogenides, show many interesting dimension-related materials properties. Inspired by the development of 2D inorganic nanomaterials, single-layered covalent organic frameworks (sCOFs), featuring atom-thick sheets and crystalline extended organic structures with covalently bonded building blocks, have attracted great attention in recent years. With their unique graphene-like topological structure and the merit of structural diversity, sCOFs promise to possess novel and designable properties. However, the synthesis of sCOFs with well-defined structures remains a great challenge. Herein, the recent development of the bottom-up synthesis methods of 2D sCOFs, such as thermodynamic equilibrium control methods, growth-kinetics control methods, and surface-assisted covalent polymerization methods, are reviewed. Finally, some of the critical properties and application prospects of these materials are outlined.

  5. Nanoscale mass sensing based on vibration of single-layered graphene sheet in thermal environments

    NASA Astrophysics Data System (ADS)

    Fazelzadeh, S. Ahmad; Ghavanloo, Esmaeal

    2014-02-01

    Based on vibration analysis, single-layered graphene sheet (SLGS) with multiple attached nanoparticles is developed as nanoscale mass sensor in thermal environments. Graphene sensors are assumed to be in simply-supported configuration. Based on the nonlocal plate theory which incorporates size effects into the classical theory, closed-form expressions for the frequencies and relative frequency shifts of SLGS-based mass sensor are derived using the Galerkin method. The suggested model is justified by a good agreement between the results given by the present model and available data in literature. The effects of temperature difference, nonlocal parameter, the location of the nanoparticle and the number of nanoparticles on the relative frequency shift of the mass sensor are also elucidated. The obtained results show that the sensitivity of the SLGS-based mass sensor increases with increasing temperature difference. [Figure not available: see fulltext.

  6. Layered and scrolled nanocomposites with aligned semi-infinite graphene inclusions at the platelet limit

    NASA Astrophysics Data System (ADS)

    Liu, Pingwei; Jin, Zhong; Katsukis, Georgios; Drahushuk, Lee William; Shimizu, Steven; Shih, Chih-Jen; Wetzel, Eric D.; Taggart-Scarff, Joshua K.; Qing, Bo; Van Vliet, Krystyn J.; Li, Richard; Wardle, Brian L.; Strano, Michael S.

    2016-07-01

    Two-dimensional (2D) materials can uniquely span the physical dimensions of a surrounding composite matrix in the limit of maximum reinforcement. However, the alignment and assembly of continuous 2D components at high volume fraction remain challenging. We use a stacking and folding method to generate aligned graphene/polycarbonate composites with as many as 320 parallel layers spanning 0.032 to 0.11 millimeters in thickness that significantly increases the effective elastic modulus and strength at exceptionally low volume fractions of only 0.082%. An analogous transverse shear scrolling method generates Archimedean spiral fibers that demonstrate exotic, telescoping elongation at break of 110%, or 30 times greater than Kevlar. Both composites retain anisotropic electrical conduction along the graphene planar axis and transparency. These composites promise substantial mechanical reinforcement, electrical, and optical properties at highly reduced volume fraction.

  7. High-power thulium fiber laser Q switched with single-layer graphene.

    PubMed

    Tang, Yulong; Yu, Xuechao; Li, Xiaohui; Yan, Zhiyu; Wang, Qi Jie

    2014-02-01

    We report high-power 2 μm Tm3+ fiber lasers passively Q switched by double-piece single-layer graphene transferred onto a glass plate. Through manipulating intracavity laser beam size and increasing pump ratios, an average power of 5.2 W is directly achieved from the laser oscillator with an optical-to-optical slope efficiency of 26%. The laser pulse energy can be as high as ∼18  μJ, comparable to that from actively Q-switched fiber lasers. The narrowest pulse width is 320 ns, and the pulse repetition rate can be tuned from tens of kilohertz to 280 kHz by changing the pump power. To the best of our knowledge, this is the highest average power and pulse energy, as well as the narrowest pulse width, from graphene-based Q-switched 2 μm fiber lasers.

  8. Negative magnetoresistance in a vertical single-layer graphene spin valve at room temperature.

    PubMed

    Singh, Arun Kumar; Eom, Jonghwa

    2014-02-26

    Single-layer graphene (SLG) is an ideal material for spintronics because of its high charge-carrier mobility, long spin lifetime resulting from the small spin-orbit coupling, and hyperfine interactions of carbon atoms. Here, we report a vertical spin valve with SLG with device configuration Co/SLG/Al2O3/Ni. We observed negative magnetoresistance (-0.4%) for the Co/SLG/Al2O3/Ni junction at room temperature. However, the Co/Al2O3/Ni junction, which is without graphene, shows positive magnetoresistance. The current-voltage (I-V) characteristics of both Co/SLG/Al2O3/Ni and Co/Al2O3/Ni junctions are nonlinear, and this reveals that charge transport occurs by a tunneling mechanism. We have also explained the reason for negative magnetoresistance for the Co/SLG/Al2O3/Ni junction. PMID:24495123

  9. Hydrogen storage in a chemical bond stabilized Co9S8-graphene layered structure

    NASA Astrophysics Data System (ADS)

    Qin, Wei; Han, Lu; Bi, Hai; Jian, Jiahuang; Wu, Xiaohong; Gao, Peng

    2015-11-01

    With the high energy ball milling method, a Co9S8-decorated reduced graphene oxide (RGO) composite, which shows excellent hydrogen storage capacity, has been successfully fabricated with a well-organized layered structure. Moreover, the stabilized mechanism of the well-organized layered structure is investigated and attributed to the strong interactions between Co9S8 and defective RGO. The C-S bond interaction is identified and the hydrogen storage process is also studied with different analysis methods. Finally, an optimized Co9S8 to RGO weight ratio of 6 : 1 shows excellent electrochemical performances in terms of the excellent cycling stability and competitive hydrogen storage capacity of 4.86 wt%.With the high energy ball milling method, a Co9S8-decorated reduced graphene oxide (RGO) composite, which shows excellent hydrogen storage capacity, has been successfully fabricated with a well-organized layered structure. Moreover, the stabilized mechanism of the well-organized layered structure is investigated and attributed to the strong interactions between Co9S8 and defective RGO. The C-S bond interaction is identified and the hydrogen storage process is also studied with different analysis methods. Finally, an optimized Co9S8 to RGO weight ratio of 6 : 1 shows excellent electrochemical performances in terms of the excellent cycling stability and competitive hydrogen storage capacity of 4.86 wt%. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06116d

  10. Charge transfer at junctions of a single layer of graphene and a metallic single walled carbon nanotube.

    PubMed

    Paulus, Geraldine L C; Wang, Qing Hua; Ulissi, Zachary W; McNicholas, Thomas P; Vijayaraghavan, Aravind; Shih, Chih-Jen; Jin, Zhong; Strano, Michael S

    2013-06-10

    Junctions between a single walled carbon nanotube (SWNT) and a monolayer of graphene are fabricated and studied for the first time. A single layer graphene (SLG) sheet grown by chemical vapor deposition (CVD) is transferred onto a SiO₂/Si wafer with aligned CVD-grown SWNTs. Raman spectroscopy is used to identify metallic-SWNT/SLG junctions, and a method for spectroscopic deconvolution of the overlapping G peaks of the SWNT and the SLG is reported, making use of the polarization dependence of the SWNT. A comparison of the Raman peak positions and intensities of the individual SWNT and graphene to those of the SWNT-graphene junction indicates an electron transfer of 1.12 × 10¹³ cm⁻² from the SWNT to the graphene. This direction of charge transfer is in agreement with the work functions of the SWNT and graphene. The compression of the SWNT by the graphene increases the broadening of the radial breathing mode (RBM) peak from 3.6 ± 0.3 to 4.6 ± 0.5 cm⁻¹ and of the G peak from 13 ± 1 to 18 ± 1 cm⁻¹, in reasonable agreement with molecular dynamics simulations. However, the RBM and G peak position shifts are primarily due to charge transfer with minimal contributions from strain. With this method, the ability to dope graphene with nanometer resolution is demonstrated. PMID:23281165

  11. Tunable Electrical and Optical Characteristics in Monolayer Graphene and Few-Layer MoS2 Heterostructure Devices.

    PubMed

    Rathi, Servin; Lee, Inyeal; Lim, Dongsuk; Wang, Jianwei; Ochiai, Yuichi; Aoki, Nobuyuki; Watanabe, Kenji; Taniguchi, Takashi; Lee, Gwan-Hyoung; Yu, Young-Jun; Kim, Philip; Kim, Gil-Ho

    2015-08-12

    Lateral and vertical two-dimensional heterostructure devices, in particular graphene-MoS2, have attracted profound interest as they offer additional functionalities over normal two-dimensional devices. Here, we have carried out electrical and optical characterization of graphene-MoS2 heterostructure. The few-layer MoS2 devices with metal electrode at one end and monolayer graphene electrode at the other end show nonlinearity in drain current with drain voltage sweep due to asymmetrical Schottky barrier height at the contacts and can be modulated with an external gate field. The doping effect of MoS2 on graphene was observed as double Dirac points in the transfer characteristics of the graphene field-effect transistor (FET) with a few-layer MoS2 overlapping the middle part of the channel, whereas the underlapping of graphene have negligible effect on MoS2 FET characteristics, which showed typical n-type behavior. The heterostructure also exhibits a strongest optical response for 520 nm wavelength, which decreases with higher wavelengths. Another distinct feature observed in the heterostructure is the peak in the photocurrent around zero gate voltage. This peak is distinguished from conventional MoS2 FETs, which show a continuous increase in photocurrent with back-gate voltage. These results offer significant insight and further enhance the understanding of the graphene-MoS2 heterostructure.

  12. Layer-by-layer assembly of graphene oxide nanosheets on polyamide membranes for durable reverse-osmosis applications.

    PubMed

    Choi, Wansuk; Choi, Jungkyu; Bang, Joona; Lee, Jung-Hyun

    2013-12-11

    Improving membrane durability associated with fouling and chlorine resistance remains one of the major challenges in desalination membrane technology. Here, we demonstrate that attractive features of graphene oxide (GO) nanosheets such as high hydrophilicity, chemical robustness, and ultrafast water permeation can be harnessed for a dual-action barrier coating layer that enhances resistance to both fouling and chlorine-induced degradation of polyamide (PA) thin-film composite (TFC) membranes while preserving their separation performance. GO multilayers were coated on the PA-TFC membrane surfaces via layer-by-layer (LbL) deposition of oppositely charged GO nanosheets. Consequently, it was shown that the conformal GO coating layer can increase the surface hydrophilicity and reduce the surface roughness, leading to the significantly improved antifouling performance against a protein foulant. It was also demonstrated that the chemically inert nature of GO nanosheets enables the GO coating layer to act as a chlorine barrier for the underlying PA membrane, resulting in a profound suppression of the membrane degradation in salt rejection upon chlorine exposure.

  13. Layer-by-layer assembly of graphene oxide nanosheets on polyamide membranes for durable reverse-osmosis applications.

    PubMed

    Choi, Wansuk; Choi, Jungkyu; Bang, Joona; Lee, Jung-Hyun

    2013-12-11

    Improving membrane durability associated with fouling and chlorine resistance remains one of the major challenges in desalination membrane technology. Here, we demonstrate that attractive features of graphene oxide (GO) nanosheets such as high hydrophilicity, chemical robustness, and ultrafast water permeation can be harnessed for a dual-action barrier coating layer that enhances resistance to both fouling and chlorine-induced degradation of polyamide (PA) thin-film composite (TFC) membranes while preserving their separation performance. GO multilayers were coated on the PA-TFC membrane surfaces via layer-by-layer (LbL) deposition of oppositely charged GO nanosheets. Consequently, it was shown that the conformal GO coating layer can increase the surface hydrophilicity and reduce the surface roughness, leading to the significantly improved antifouling performance against a protein foulant. It was also demonstrated that the chemically inert nature of GO nanosheets enables the GO coating layer to act as a chlorine barrier for the underlying PA membrane, resulting in a profound suppression of the membrane degradation in salt rejection upon chlorine exposure. PMID:24219033

  14. Fabrication of hybrid graphene oxide/polyelectrolyte capsules by means of layer-by-layer assembly on erythrocyte cell templates.

    PubMed

    Irigoyen, Joseba; Politakos, Nikolaos; Diamanti, Eleftheria; Rojas, Elena; Marradi, Marco; Ledezma, Raquel; Arizmendi, Layza; Rodríguez, J Alberto; Ziolo, Ronald F; Moya, Sergio E

    2015-01-01

    A novel and facile method was developed to produce hybrid graphene oxide (GO)-polyelectrolyte (PE) capsules using erythrocyte cells as templates. The capsules are easily produced through the layer-by-layer technique using alternating polyelectrolyte layers and GO sheets. The amount of GO and therefore its coverage in the resulting capsules can be tuned by adjusting the concentration of the GO dispersion during the assembly. The capsules retain the approximate shape and size of the erythrocyte template after the latter is totally removed by oxidation with NaOCl in water. The PE/GO capsules maintain their integrity and can be placed or located on other surfaces such as in a device. When the capsules are dried in air, they collapse to form a film that is approximately twice the thickness of the capsule membrane. AFM images in the present study suggest a film thickness of approx. 30 nm for the capsules in the collapsed state implying a thickness of approx. 15 nm for the layers in the collapsed capsule membrane. The polyelectrolytes used in the present study were polyallylamine hydrochloride (PAH) and polystyrenesulfonate sodium salt (PSS). Capsules where characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS) and Raman microscopy, the constituent layers by zeta potential and GO by TEM, XRD, and Raman and FTIR spectroscopies.

  15. Fabrication of hybrid graphene oxide/polyelectrolyte capsules by means of layer-by-layer assembly on erythrocyte cell templates

    PubMed Central

    Irigoyen, Joseba; Politakos, Nikolaos; Diamanti, Eleftheria; Rojas, Elena; Marradi, Marco; Ledezma, Raquel; Arizmendi, Layza; Rodríguez, J Alberto; Ziolo, Ronald F

    2015-01-01

    Summary A novel and facile method was developed to produce hybrid graphene oxide (GO)–polyelectrolyte (PE) capsules using erythrocyte cells as templates. The capsules are easily produced through the layer-by-layer technique using alternating polyelectrolyte layers and GO sheets. The amount of GO and therefore its coverage in the resulting capsules can be tuned by adjusting the concentration of the GO dispersion during the assembly. The capsules retain the approximate shape and size of the erythrocyte template after the latter is totally removed by oxidation with NaOCl in water. The PE/GO capsules maintain their integrity and can be placed or located on other surfaces such as in a device. When the capsules are dried in air, they collapse to form a film that is approximately twice the thickness of the capsule membrane. AFM images in the present study suggest a film thickness of approx. 30 nm for the capsules in the collapsed state implying a thickness of approx. 15 nm for the layers in the collapsed capsule membrane. The polyelectrolytes used in the present study were polyallylamine hydrochloride (PAH) and polystyrenesulfonate sodium salt (PSS). Capsules where characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS) and Raman microscopy, the constituent layers by zeta potential and GO by TEM, XRD, and Raman and FTIR spectroscopies. PMID:26734521

  16. Fabrication of hybrid graphene oxide/polyelectrolyte capsules by means of layer-by-layer assembly on erythrocyte cell templates.

    PubMed

    Irigoyen, Joseba; Politakos, Nikolaos; Diamanti, Eleftheria; Rojas, Elena; Marradi, Marco; Ledezma, Raquel; Arizmendi, Layza; Rodríguez, J Alberto; Ziolo, Ronald F; Moya, Sergio E

    2015-01-01

    A novel and facile method was developed to produce hybrid graphene oxide (GO)-polyelectrolyte (PE) capsules using erythrocyte cells as templates. The capsules are easily produced through the layer-by-layer technique using alternating polyelectrolyte layers and GO sheets. The amount of GO and therefore its coverage in the resulting capsules can be tuned by adjusting the concentration of the GO dispersion during the assembly. The capsules retain the approximate shape and size of the erythrocyte template after the latter is totally removed by oxidation with NaOCl in water. The PE/GO capsules maintain their integrity and can be placed or located on other surfaces such as in a device. When the capsules are dried in air, they collapse to form a film that is approximately twice the thickness of the capsule membrane. AFM images in the present study suggest a film thickness of approx. 30 nm for the capsules in the collapsed state implying a thickness of approx. 15 nm for the layers in the collapsed capsule membrane. The polyelectrolytes used in the present study were polyallylamine hydrochloride (PAH) and polystyrenesulfonate sodium salt (PSS). Capsules where characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS) and Raman microscopy, the constituent layers by zeta potential and GO by TEM, XRD, and Raman and FTIR spectroscopies. PMID:26734521

  17. Intrinsic carrier mobility of a single-layer graphene covalently bonded with single-walled carbon nanotubes

    SciTech Connect

    Li, Dian; Shao, Zhi-Gang; Hao, Qing; Zhao, Hongbo

    2014-06-21

    We report intrinsic carrier mobility calculations of a two-dimensional nanostructure that consists of porous single layer graphene covalently bonded with single-walled carbon nanotubes on both sides. We used first-principles calculation and found that the deformation potential of such system is about 25% of that of graphene, and the carrier mobility is about 5 × 10{sup 4} cm{sup 2} V{sup −1} s{sup −1} for both electrons and holes, about one order of magnitude lower than that of graphene. This nanostructure and its three-dimensional stacking could serve as novel organic electronic materials.

  18. A comparative density functional study on electrical properties of layered penta-graphene

    SciTech Connect

    Yu, Zhi Gen Zhang, Yong-Wei

    2015-10-28

    We present a comparative study of the influence of the number of layers, the biaxial strain in the range of −3% to 3%, and the stacking misalignments on the electronic properties of a new 2D carbon allotrope, penta-graphene (PG), based on hybrid-functional method within the density functional theory (DFT). In comparison with local exchange-correlation approximation in the DFT, the hybrid-functional provides an accurate description on the degree of p{sub z} orbitals localization and bandgap. Importantly, the predicted bandgap of few-layer PG has a weak layer dependence. The bandgap of monolayer PG is 3.27 eV, approximately equal to those of GaN and ZnO; and the bandgap of few-layer PG decreases slowly with the number of layers (N) and converge to 2.57 eV when N ≥ 4. Our calculations using HSE06 functional on few-layer PG reveal that bandgap engineering by stacking misalignment can further tune the bandgap down to 1.37 eV. Importantly, there is no direct-to-indirect bandgap transition in PG by varying strain, layer number, and stacking misalignment. Owing to its tunable, robustly direct, and wide bandgap characteristics, few-layer PG is promising for optoelectronic and photovoltaic applications.

  19. A comparative density functional study on electrical properties of layered penta-graphene

    NASA Astrophysics Data System (ADS)

    Yu, Zhi Gen; Zhang, Yong-Wei

    2015-10-01

    We present a comparative study of the influence of the number of layers, the biaxial strain in the range of -3% to 3%, and the stacking misalignments on the electronic properties of a new 2D carbon allotrope, penta-graphene (PG), based on hybrid-functional method within the density functional theory (DFT). In comparison with local exchange-correlation approximation in the DFT, the hybrid-functional provides an accurate description on the degree of pz orbitals localization and bandgap. Importantly, the predicted bandgap of few-layer PG has a weak layer dependence. The bandgap of monolayer PG is 3.27 eV, approximately equal to those of GaN and ZnO; and the bandgap of few-layer PG decreases slowly with the number of layers (N) and converge to 2.57 eV when N ≥ 4. Our calculations using HSE06 functional on few-layer PG reveal that bandgap engineering by stacking misalignment can further tune the bandgap down to 1.37 eV. Importantly, there is no direct-to-indirect bandgap transition in PG by varying strain, layer number, and stacking misalignment. Owing to its tunable, robustly direct, and wide bandgap characteristics, few-layer PG is promising for optoelectronic and photovoltaic applications.

  20. Microwave-Assisted Synthesis of Highly-Crumpled, Few-Layered Graphene and Nitrogen-Doped Graphene for Use as High-Performance Electrodes in Capacitive Deionization

    PubMed Central

    Amiri, Ahmad; Ahmadi, Goodarz; Shanbedi, Mehdi; Savari, Maryam; Kazi, S. N.; Chew, B. T.

    2015-01-01

    Capacitive deionization (CDI) is a promising procedure for removing various charged ionic species from brackish water. The performance of graphene-based material in capacitive deionization is lower than the expectation of the industry, so highly-crumpled, few-layered graphene (HCG) and highly-crumpled nitrogen-doped graphene (HCNDG) with high surface area have been introduced as promising candidates for CDI electrodes. Thus, HCG and HCNDG were prepared by exfoliation of graphite in the presence of liquid-phase, microwave-assisted methods. An industrially-scalable, cost-effective, and simple approach was employed to synthesize HCG and HCNDG, resulting in few-layered graphene and nitrogen-doped graphene with large specific surface area. Then, HCG and HCNDG were utilized for manufacturing a new class of carbon nanostructure-based electrodes for use in large-scale CDI equipment. The electrosorption results indicated that both the HCG and HCNDG have fairly large specific surface areas, indicating their huge potential for capacitive deionization applications. PMID:26643279

  1. Gold nanoparticle-embedded porous graphene thin films fabricated via layer-by-layer self-assembly and subsequent thermal annealing for electrochemical sensing.

    PubMed

    Xi, Qian; Chen, Xu; Evans, David G; Yang, Wensheng

    2012-06-26

    A uniform three-dimensional (3D) gold nanoparticle (AuNP)-embedded porous graphene (AuEPG) thin film has been fabricated by electrostatic layer-by-layer assembly of AuNPs and graphene nanosheets functionalized with bovine serum albumin and subsequent thermal annealing in air at 340 °C for 2 h. Scanning electron microscopy (SEM) investigations for the AuEPG film indicate that an AuNP was embedded in every pore of the porous graphene film, something that was difficult to achieve with previously reported methods. The mechanism of formation of the AuEPG film was initially explored. Application of the AuEPG film in electrochemical sensing was further demonstrated by use of H(2)O(2) as a model analyte. The AuEPG film-modified electrode showed improved electrochemical performance in H(2)O(2) detection compared with nonporous graphene-AuNP composite film-modified electrodes, which is mainly attributed to the porous structure of the AuEPG film. This work opens up a new and facile way for direct preparation of metal or metal oxide nanoparticle-embedded porous graphene composite films, which will enable exciting opportunities in highly sensitive electrochemical sensors and other advanced applications based on graphene-metal composites.

  2. Incorporating nanoporous polyaniline into layer-by-layer ionic liquid-carbon nanotube-graphene paper: towards freestanding flexible electrodes with improved supercapacitive performance

    NASA Astrophysics Data System (ADS)

    Sun, Yimin; Fang, Zheng; Wang, Chenxu; Zhou, Aijun; Duan, Hongwei

    2015-09-01

    The growing demand for lightweight and flexible supercapacitor devices necessitates innovation in electrode materials and electrode configuration. We have developed a new type of three-dimensional (3D) flexible nanohybrid electrode by incorporating nanoporous polyaniline (PANI) into layer-by-layer ionic liquid (IL) functionalized carbon nanotube (CNT)-graphene paper (GP), and explored its practical application as a freestanding flexible electrode in a supercapacitor. Our results have demonstrated that the surface modification of graphene nanosheets and CNTs by hydrophilic IL molecules makes graphene and CNTs well-dispersed in aqueous solution, and also improves the hydrophility of the assembled graphene-based paper. Furthermore, the integration of highly conductive one-dimensional (1D) CNTs with two-dimensional (2D) graphene nanosheets leads to 3D sandwich-structured nanohybrid paper with abundant interconnected pores, which is preferred for fast mass and electron transport kinetics. For in situ electropolymerization of PANI on paper electrodes, the IL functionalized CNT-GP (IL-CNT-GP) offers large surface area and interlayer spacing and the unique π surface of graphene and CNTs for efficient and stable loading of PANI. A key finding is that the structural integration of multiple components in this 3D freestanding flexible sheet electrode gives rise to a synergic effect, leading to a high capacitance of 725.6 F g-1 at a current density of 1 A g-1 and good cycling stability by retaining 90% of the initial specific capacitance after 5000 cycles.

  3. Photodetection in Hybrid Single-Layer Graphene/Fully Coherent Germanium Island Nanostructures Selectively Grown on Silicon Nanotip Patterns.

    PubMed

    Niu, Gang; Capellini, Giovanni; Lupina, Grzegorz; Niermann, Tore; Salvalaglio, Marco; Marzegalli, Anna; Schubert, Markus Andreas; Zaumseil, Peter; Krause, Hans-Michael; Skibitzki, Oliver; Lehmann, Michael; Montalenti, Francesco; Xie, Ya-Hong; Schroeder, Thomas

    2016-01-27

    Dislocation networks are one of the most principle sources deteriorating the performances of devices based on lattice-mismatched heteroepitaxial systems. We demonstrate here a technique enabling fully coherent germanium (Ge) islands selectively grown on nanotip-patterned Si(001) substrates. The silicon (Si)-tip-patterned substrate, fabricated by complementary metal oxide semiconductor compatible nanotechnology, features ∼50-nm-wide Si areas emerging from a SiO2 matrix and arranged in an ordered lattice. Molecular beam epitaxy growths result in Ge nanoislands with high selectivity and having homogeneous shape and size. The ∼850 °C growth temperature required for ensuring selective growth has been shown to lead to the formation of Ge islands of high crystalline quality without extensive Si intermixing (with 91 atom % Ge). Nanotip-patterned wafers result in geometric, kinetic-diffusion-barrier intermixing hindrance, confining the major intermixing to the pedestal region of Ge islands, where kinetic diffusion barriers are, however, high. Theoretical calculations suggest that the thin Si/Ge layer at the interface plays, nevertheless, a significant role in realizing our fully coherent Ge nanoislands free from extended defects especially dislocations. Single-layer graphene/Ge/Si-tip Schottky junctions were fabricated, and thanks to the absence of extended defects in Ge islands, they demonstrate high-performance photodetection characteristics with responsivity of ∼45 mA W(-1) and an Ion/Ioff ratio of ∼10(3). PMID:26709534

  4. Electromagnetic properties of a double-layer graphene system with electron-hole pairing

    NASA Astrophysics Data System (ADS)

    Germash, K. V.; Fil, D. V.

    2016-05-01

    We study electromagnetic properties of a double-layer graphene system in which electrons from one layer are coupled with holes from the other layer. The gauge invariant linear response functions are obtained. The frequency dependences of the transmission, reflection, and absorption coefficients are computed. We predict a peak in the reflection and absorption at the frequency equal to the gap in the quasiparticle spectrum. It is shown that the electron-hole pairing results in an essential modification of the spectrum of surface TM plasmons. We find that the optical TM mode splits into a low frequency undamped branch and a high frequency damped branch. At zero temperature the lower branch disappears. It is established that the pairing does not influence the acoustic TM mode. It is also shown that the pairing opens the frequency window in the subgap range for the surface TE wave.

  5. Experimental investigation of metallic thin film modification of nickel substrates for chemical vapor deposition growth of single layer graphene at low temperature

    NASA Astrophysics Data System (ADS)

    Aminalragia Giamini, Sigiava; Marquez-Velasco, Jose; Sakellis, Ilias; Tsipas, Polychronis; Kelaidis, Nikolaos; Tsoutsou, Dimitra; Boukos, Nikolaos; Kantarelou, Vasiliki; Xenogiannopoulou, Evangelia; Speliotis, Thanassis; Aretouli, Kleopatra; Kordas, George; Dimoulas, Athanasios

    2016-11-01

    Lowering the growth temperature of single layer graphene by chemical vapor deposition (CVD) is important for its real-life application and mass production. Doing this without compromising quality requires advances in catalytic substrates. It is shown in this work that deposition of Zn and Bi metals modify the surface of nickel suppressing the uncontrollable growth of multiple layers of graphene. As a result, single layer graphene is obtained by CVD at 600 °C with minimum amount of defects, showing substantial improvement over bare Ni. In contrast, Cu, and Mo suppress graphene growth. We also show that graphene grown with our method has a defect density that is strongly dependent on the roughness of the original nickel foil. Good quality or highly defective holey single layer graphene can be grown at will by selecting a smooth or rough foil substrate respectively.

  6. Seeding Atomic Layer Deposition of High-k Dielectrics on Epitaxial Graphene with Organic Self-assembled Monolayers

    SciTech Connect

    Alaboson, Justice M. P.; Wang, Qing Hua; Emery, Jonathan D.; Lipson, Albert L.; Bedzyk, Michael J.; Elam, Jeffrey W.; Pellin, Michael J.; Hersam, Mark C.

    2011-06-28

    The development of high-performance graphene-based nanoelectronics requires the integration of ultrathin and pinhole-free high-k dielectric films with graphene at the wafer scale. Here, we demonstrate that self-assembled monolayers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) act as effective organic seeding layers for atomic layer deposition (ALD) of HfO₂ and Al₂O₃ on epitaxial graphene on SiC(0001). The PTCDA is deposited via sublimation in ultrahigh vacuum and shown to be highly ordered with low defect density by molecular-resolution scanning tunneling microscopy. Whereas identical ALD conditions lead to incomplete and rough dielectric deposition on bare graphene, the chemical functionality provided by the PTCDA seeding layer yields highly uniform and conformal films. The morphology and chemistry of the dielectric films are characterized by atomic force microscopy, ellipsometry, cross-sectional scanning electron microscopy, and X-ray photoelectron spectroscopy, while high-resolution X-ray reflectivity measurements indicate that the underlying graphene remains intact following ALD. Using the PTCDA seeding layer, metal-oxide-graphene capacitors fabricated with a 3 nm Al₂O₃ and 10 nm HfO₂ dielectric stack show high capacitance values of ~700 nF/cm² and low leakage currents of ~5 × 10{sup –9} A/cm² at 1 V applied bias. These results demonstrate the viability of sublimated organic self-assembled monolayers as seeding layers for high-k dielectric films in graphene-based nanoelectronics.

  7. Large-Area Growth of Turbostratic Graphene on Ni(111) via Physical Vapor Deposition

    DOE PAGES

    Garlow, Joseph A.; Barrett, Lawrence K.; Wu, Lijun; Kisslinger, Kim; Zhu, Yimei; Pulecio, Javier F.

    2016-01-29

    Single-layer graphene has demonstrated remarkable electronic properties that are strongly influenced by interfacial bonding and break down for the lowest energy configuration of stacked graphene layers (AB Bernal). Multilayer graphene with relative rotations between carbon layers, known as turbostratic graphene, can effectively decouple the electronic states of adjacent layers, preserving properties similar to that of SLG. While the growth of AB Bernal graphene through chemical vapor deposition has been widely reported, we investigate the growth of turbostratic graphene on heteroepitaxial Ni(111) thin films utilizing physical vapor deposition. By varying the carbon deposition temperature between 800–1100°C, we report an increase inmore » the graphene quality concomitant with a transition in the size of uniform thickness graphene, ranging from nanocrystallites to thousands of square microns. Combination Raman modes of as-grown graphene within the frequency range of 1650 cm₋1 to 2300 cm₋1, along with features of the Raman 2D mode, were employed as signatures of turbostratic graphene. Bilayer and multilayer graphene were directly identified from areas that exhibited Raman characteristics of turbostratic graphene using high-resolution TEM imaging. Lastly, Raman maps of the pertinent modes reveal large regions of turbostratic graphene on Ni(111) thin films at a deposition temperature of 1100°C.« less

  8. Large-Area Growth of Turbostratic Graphene on Ni(111) via Physical Vapor Deposition

    PubMed Central

    Garlow, Joseph A.; Barrett, Lawrence K.; Wu, Lijun; Kisslinger, Kim; Zhu, Yimei; Pulecio, Javier F.

    2016-01-01

    Single-layer graphene has demonstrated remarkable electronic properties that are strongly influenced by interfacial bonding and break down for the lowest energy configuration of stacked graphene layers (AB Bernal). Multilayer graphene with relative rotations between carbon layers, known as turbostratic graphene, can effectively decouple the electronic states of adjacent layers, preserving properties similar to that of SLG. While the growth of AB Bernal graphene through chemical vapor deposition has been widely reported, we investigate the growth of turbostratic graphene on heteroepitaxial Ni(111) thin films utilizing physical vapor deposition. By varying the carbon deposition temperature between 800 –1100 °C, we report an increase in the graphene quality concomitant with a transition in the size of uniform thickness graphene, ranging from nanocrystallites to thousands of square microns. Combination Raman modes of as-grown graphene within the frequency range of 1650 cm−1 to 2300 cm−1, along with features of the Raman 2D mode, were employed as signatures of turbostratic graphene. Bilayer and multilayer graphene were directly identified from areas that exhibited Raman characteristics of turbostratic graphene using high-resolution TEM imaging. Raman maps of the pertinent modes reveal large regions of turbostratic graphene on Ni(111) thin films at a deposition temperature of 1100 °C. PMID:26821604

  9. Layered Chalcogenides beyond Graphene: from Electronic Structure Evolution to the Spin Transport

    NASA Astrophysics Data System (ADS)

    Yuan, Hongtao

    2014-03-01

    Recent efforts on graphene-like atomic layer materials, aiming at novel electronic properties and quantum phenomena beyond graphene, have attracted much attention for potential electronics/spintronics applications. Compared to the weak spin-orbit-interaction (SOI) in graphene, metal chalcogenides MX2 have heavy 4d/5d elements with strong atomic SOI, providing a unique way for generating spin polarization based on valleytronics physics. Indeed, such a spin-polarized band structure has been demonstrated theoretically and supported by optical investigations. However, despite these exciting progresses, following two important issues in MX2 community remain elusive: 1. the quantitative band structure of MX2 compounds (where are the valleys -band maxima/minima- locating in the BZ) have not been experimentally confirmed. Especially for those cleaved ultrathin mono- and bi-layer flakes hosting most of recently-reported exotic phenomena at the 2D limit, the direct detection for band dispersion becomes of great importance for valleytronics. 2. Spin transports have seldom been reported even though such a strong SOI system can serve as an ideal platform for the spin polarization and spin transport. In this work, we started from the basic electronic structures of representative MX2, obtained by ARPES, and investigated both the band variation between these compounds and their band evolution from bulk to the monolayer limit. After having a systematic understanding on band structures, we reported a giant Zeeman-type spin-polarization generated and modulated by an external electric field in WSe2 electric-double-layer transistors. The non-magnetic approach for realizing such an intriguing spin splitting not only keeps the system time-reversally invariant but also suggests a new paradigm for manipulating the spin-degrees of freedom of electrons. Acknowledge the support from DoE, BES, Division of MSE under contract DE-AC02-76SF00515.

  10. Study on the high spectral intensity at the Dirac energy of single-layer graphene on an SiC substrate

    NASA Astrophysics Data System (ADS)

    Hwang, Jinwoong; Hwang, Choongyu

    2016-04-01

    We have investigated electron band structure of epitaxially grown graphene on an SiC(0001) substrate using angle-resolved photoemission spectroscopy. In single-layer graphene, abnormal high spectral intensity is observed at the Dirac energy whose origin has been questioned between in-gap states induced by the buffer layer and plasmaron bands induced by electron–plasmon interactions. With the formation of double-layer graphene, the Dirac energy does not show the high spectral intensity any longer different from the single-layer case. The inconsistency between the two systems suggests that the main ingredient of the high spectral intensity at the Dirac energy of single-layer graphene is the electronic states originating from the coupling of the graphene π bands to the localized π states of the buffer layer, consistent with the theoretical prediction on the presence of in-gap states.

  11. Tuning the mechanical properties of vertical graphene sheets through atomic layer deposition.

    PubMed

    Davami, Keivan; Jiang, Yijie; Cortes, John; Lin, Chen; Shaygan, Mehrdad; Turner, Kevin T; Bargatin, Igor

    2016-04-15

    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 connections between the sheets after ALD deposition. These results demonstrate that the mechanical properties of VG sheets can be tuned over a wide range through conformal atomic layer deposition, facilitating the use of VG sheets in applications where specific mechanical properties are needed. PMID:26926386

  12. 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 connections between the sheets after ALD deposition. These results demonstrate that the mechanical properties of VG sheets can be tuned over a wide range through conformal atomic layer deposition, facilitating the use of VG sheets in applications where specific mechanical properties are needed.

  13. Tuning the mechanical properties of vertical graphene sheets through atomic layer deposition.

    PubMed

    Davami, Keivan; Jiang, Yijie; Cortes, John; Lin, Chen; Shaygan, Mehrdad; Turner, Kevin T; Bargatin, Igor

    2016-04-15

    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 connections between the sheets after ALD deposition. These results demonstrate that the mechanical properties of VG sheets can be tuned over a wide range through conformal atomic layer deposition, facilitating the use of VG sheets in applications where specific mechanical properties are needed.

  14. Quantum transport simulation of exciton condensate transport physics in a double-layer graphene system

    NASA Astrophysics Data System (ADS)

    Mou, Xuehao; Register, Leonard F.; MacDonald, Allan H.; Banerjee, Sanjay K.

    2015-12-01

    Spatially indirect electron-hole exciton condensates stabilized by interlayer Fock exchange interactions have been predicted in systems containing a pair of two-dimensional semiconductor or semimetal layers separated by a thin tunnel dielectric. The layer degree of freedom in these systems can be described as a pseudospin. Condensation is then analogous to ferromagnetism, and the interplay between collective and quasiparticle contributions to transport is analogous to phenomena that are heavily studied in spintronics. These phenomena are the basis for pseudospintronic device proposals based on possible low-voltage switching between high (nearly shorted) and low interlayer conductance states and on near-perfect Coulomb drag-counterflow current along the layers. In this work, a quantum transport simulator incorporating a nonlocal Fock exchange interaction is presented, and used to model the essential transport physics in, for specificity, a graphene-dielectric-graphene system. Finite-size effects, Coulomb drag-counterflow current, critical interlayer currents beyond which interlayer dc conductance collapses at subthermal voltages, nonlocal coupling between interlayer critical currents in multiple lead devices, and an Andreev-like reflection process are illustrated.

  15. MgO-decorated few-layered graphene as an anode for li-ion batteries.

    PubMed

    Petnikota, Shaikshavali; Rotte, Naresh K; Reddy, M V; Srikanth, Vadali V S S; Chowdari, B V R

    2015-02-01

    Combustion of magnesium in dry ice and a simple subsequent acid treatment step resulted in a MgO-decorated few-layered graphene (FLG) composite that has a specific surface area of 393 m(2)/g and an average pore volume of 0.9 cm(3)/g. As an anode material in Li-ion batteries, the composite exhibited high reversible capacity and excellent cyclic performance in spite of high first-cycle irreversible capacity loss. A reversible capacity as high as 1052 mAh/g was measured during the first cycle. Even at the end of the 60th cycle, more than 83% of the capacity could be retained. Cyclic voltammetry results indicated pseudocapacitance behavior due to electrochemical absorption and desorption of lithium ions onto graphene. An increase in the capacity has been observed during long-term cycling owing to electrochemical exfoliation of graphene sheets. Owing to its good thermal stability and superior cyclic performance with high reversible capacities, MgO-decked FLG can be an excellent alternative to graphite as an anode material in Li-ion batteries, after suitable modifications. PMID:25559260

  16. Wafer-scale synthesis of multi-layer graphene by high-temperature carbon ion implantation

    SciTech Connect

    Kim, Janghyuk; Lee, Geonyeop; Kim, Jihyun

    2015-07-20

    We report on the synthesis of wafer-scale (4 in. in diameter) high-quality multi-layer graphene using high-temperature carbon ion implantation on thin Ni films on a substrate of SiO{sub 2}/Si. Carbon ions were bombarded at 20 keV and a dose of 1 × 10{sup 15 }cm{sup −2} onto the surface of the Ni/SiO{sub 2}/Si substrate at a temperature of 500 °C. This was followed by high-temperature activation annealing (600–900 °C) to form a sp{sup 2}-bonded honeycomb structure. The effects of post-implantation activation annealing conditions were systematically investigated by micro-Raman spectroscopy and transmission electron microscopy. Carbon ion implantation at elevated temperatures allowed a lower activation annealing temperature for fabricating large-area graphene. Our results indicate that carbon-ion implantation provides a facile and direct route for integrating graphene with Si microelectronics.

  17. Enhanced memory effect with embedded graphene nanoplatelets in ZnO charge trapping layer

    SciTech Connect

    El-Atab, Nazek; Nayfeh, Ammar; Cimen, Furkan; Alkis, Sabri; Okyay, Ali K.

    2014-07-21

    A charge trapping memory with graphene nanoplatelets embedded in atomic layer deposited ZnO (GNIZ) is demonstrated. The memory shows a large threshold voltage V{sub t} shift (4 V) at low operating voltage (6/−6 V), good retention (>10 yr), and good endurance characteristic (>10{sup 4} cycles). This memory performance is compared to control devices with graphene nanoplatelets (or ZnO) and a thicker tunnel oxide. These structures showed a reduced V{sub t} shift and retention characteristic. The GNIZ structure allows for scaling down the tunnel oxide thickness along with improving the memory window and retention of data. The larger V{sub t} shift indicates that the ZnO adds available trap states and enhances the emission and retention of charges. The charge emission mechanism in the memory structures with graphene nanoplatelets at an electric field E ≥ 5.57 MV/cm is found to be based on Fowler-Nordheim tunneling. The fabrication of this memory device is compatible with current semiconductor processing, therefore, has great potential in low-cost nano-memory applications.

  18. Single layer graphene band hybridization with silver nanoplates: Interplay between doping and plasmonic enhancement

    NASA Astrophysics Data System (ADS)

    Syed, Salmaan R.; Lim, Guh-Hwan; Flanders, Stuart J.; Taylor, Adam B.; Lim, Byungkwon; Chon, James W. M.

    2016-09-01

    In this paper, we report single layer graphene (SLG) hybridized with silver nanoplates, in which nanoplates act as either a charge doping or a field enhancement source for the SLG Raman spectrum. Surprisingly, the stiffening of both G and 2D peaks of more than 10 cm-1 was observed with no plasmonic enhancement of peaks, indicating that p-doping from nanoplates on SLG is occurring. Such observation is explained in terms of the contact separation distance between the graphene and the silver nanoplates being enough (˜4 Å) to cause a Fermi level shift in graphene to allow p-doping. When nanoplates were modified in shape with laser irradiation by either photothermal plasmon printing or laser induced ablation, the charge doping was lifted and the strong plasmonic enhancement of Raman signals was observed, indicating that the separation distance is increased. Further, when the nanoplates are oxidized, the two effects on the Raman bands of SLG are turned off, returning the Raman signals back to the original SLG state.

  19. Identifying active functionalities on few-layered graphene catalysts for oxidative dehydrogenation of isobutane.

    PubMed

    Dathar, Gopi Krishna Phani; Tsai, Yu-Tung; Gierszal, Kamil; Xu, Ye; Liang, Chengdu; Rondinone, Adam J; Overbury, Steven H; Schwartz, Viviane

    2014-02-01

    The general consensus in the studies of nanostructured carbon catalysts for oxidative dehydrogenation (ODH) of alkanes to olefins is that the oxygen functionalities generated during synthesis and reaction are responsible for the catalytic activity of these nanostructured carbons. Identification of the highly active oxygen functionalities would enable engineering of nanocarbons for ODH of alkanes. Few-layered graphenes were used as model catalysts in experiments to synthesize reduced graphene oxide samples with varying oxygen concentrations, to characterize oxygen functionalities, and to measure the activation energies for ODH of isobutane. Periodic density functional theory calculations were performed on graphene nanoribbon models with a variety of oxygen functionalities at the edges to calculate their thermal stability and to model reaction mechanisms for ODH of isobutane. Comparing measured and calculated thermal stability and activation energies leads to the conclusion that dicarbonyls at the zigzag edges and quinones at armchair edges are appropriately balanced for high activity, relative to other model functionalities considered herein. In the ODH of isobutane, both dehydrogenation and regeneration of catalytic sites are relevant at the dicarbonyls, whereas regeneration is facile compared with dehydrogenation at quinones. The catalytic mechanism involves weakly adsorbed isobutane reducing functional oxygen and leaving as isobutene, and O2 in the feed, weakly adsorbed on the hydrogenated functionality, reacting with that hydrogen and regenerating the catalytic sites.

  20. MgO-decorated few-layered graphene as an anode for li-ion batteries.

    PubMed

    Petnikota, Shaikshavali; Rotte, Naresh K; Reddy, M V; Srikanth, Vadali V S S; Chowdari, B V R

    2015-02-01

    Combustion of magnesium in dry ice and a simple subsequent acid treatment step resulted in a MgO-decorated few-layered graphene (FLG) composite that has a specific surface area of 393 m(2)/g and an average pore volume of 0.9 cm(3)/g. As an anode material in Li-ion batteries, the composite exhibited high reversible capacity and excellent cyclic performance in spite of high first-cycle irreversible capacity loss. A reversible capacity as high as 1052 mAh/g was measured during the first cycle. Even at the end of the 60th cycle, more than 83% of the capacity could be retained. Cyclic voltammetry results indicated pseudocapacitance behavior due to electrochemical absorption and desorption of lithium ions onto graphene. An increase in the capacity has been observed during long-term cycling owing to electrochemical exfoliation of graphene sheets. Owing to its good thermal stability and superior cyclic performance with high reversible capacities, MgO-decked FLG can be an excellent alternative to graphite as an anode material in Li-ion batteries, after suitable modifications.

  1. Density Functional Theory Study of Atomic Layer Deposition of Zinc Oxide on Graphene

    NASA Astrophysics Data System (ADS)

    Ali, Amgad Ahmed; Hashim, Abdul Manaf

    2015-07-01

    The dissociation of zinc ions (Zn2+) from vapor-phase zinc acetylacetonate, Zn(C5H7O2)2, or Zn(acac)2 and its adsorption onto graphene oxide via atomic layer deposition (ALD) were studied using a quantum mechanics approach. Density functional theory (DFT) was used to obtain an approximate solution to the Schrödinger equation. The graphene oxide cluster model was used to represent the surface of the graphene film after pre-oxidation. In this study, the geometries of reactants, transition states, and products were optimized using the B3LYB/6-31G** level of theory or higher. Furthermore, the relative energies of the various intermediates and products in the gas-phase radical mechanism were calculated at the B3LYP/6-311++G** and MP2/6-311 + G(2df,2p) levels of theory. Additionally, a molecular orbital (MO) analysis was performed for the products of the decomposition of the Zn(acac)2 complex to investigate the dissociation of Zn2+ and the subsequent adsorption of H atoms on the C5H7O2 cluster to form acetylacetonate enol. The reaction energies were calculated, and the reaction mechanism was accordingly proposed. A simulation of infrared (IR) properties was performed using the same approach to support the proposed mechanism via a complete explanation of bond forming and breaking during each reaction step.

  2. Observation of spin-charge conversion in chemical-vapor-deposition-grown single-layer graphene

    SciTech Connect

    Ohshima, Ryo; Sakai, Atsushi; Ando, Yuichiro; Shiraishi, Masashi; Shinjo, Teruya; Kawahara, Kenji; Ago, Hiroki

    2014-10-20

    Conversion of pure spin current to charge current in single-layer graphene (SLG) is investigated by using spin pumping. Large-area SLG grown by chemical vapor deposition is used for the conversion. Efficient spin accumulation in SLG by spin pumping enables observing an electromotive force produced by the inverse spin Hall effect (ISHE) of SLG. The spin Hall angle of SLG is estimated to be 6.1 × 10{sup −7}. The observed ISHE in SLG is ascribed to its non-negligible spin-orbit interaction in SLG.

  3. Influence of irradiation upon few-layered graphene using electron-beams and gamma-rays

    SciTech Connect

    Wang, Yuqing; Feng, Yi Mo, Fei; Qian, Gang; Chen, Yangming; Yu, Dongbo; Wang, Yang; Zhang, Xuebin

    2014-07-14

    Few-layered graphene (FLG) is irradiated by electron beams and gamma rays. After 100 keV electron irradiation, the edges of FLG start bending, shrinking, and finally generate gaps and carbon onions due to sputtering and knock-on damage mechanism. When the electron beam energy is increased further to 200 keV, FLG suffers rapid and catastrophic destruction. Unlike electron irradiation, Compton effect is the dominant damage mechanism in gamma irradiation. The irradiation results indicate the crystallinity of FLG decreases first, then restores as increasing irradiation doses, additionally, the ratio (O/C) of FLG surface and the relative content of oxygen groups increases after irradiation.

  4. Electron-hole asymmetry of spin injection and transport in single-layer graphene.

    PubMed

    Han, Wei; Wang, W H; Pi, K; McCreary, K M; Bao, W; Li, Yan; Miao, F; Lau, C N; Kawakami, R K

    2009-04-01

    Spin-dependent properties of single-layer graphene (SLG) have been studied by nonlocal spin valve measurements at room temperature. Gate voltage dependence shows that the nonlocal magnetoresistance (MR) is proportional to the conductivity of the SLG, which is the predicted behavior for transparent ferromagnetic-nonmagnetic contacts. While the electron and hole bands in SLG are symmetric, gate voltage and bias dependence of the nonlocal MR reveal an electron-hole asymmetry in which the nonlocal MR is roughly independent of bias for electrons, but varies significantly with bias for holes. PMID:19392401

  5. On the charge transfer in the "single-sheet graphene-intercalated metal layer-SiC substrate" system

    NASA Astrophysics Data System (ADS)

    Davydov, S. Yu.

    2014-02-01

    The proposed scheme for the consideration of charge transfer in the three-layer Gr/Me/SiC system (where Gr is a single-sheet graphene, Me is an intercalated metal layer, and SiC is a substrate) contains three stages. At the first stage, a metal monolayer adsorbed on silicon carbide is considered and the charge of adatoms in this monolayer is calculated. At the second stage, the shift of the Dirac point of free-standing single-layer graphene in an electrostatic field induced by charged adatoms of the monolayer is estimated. At the third stage, a weak interaction between Me/SiC and free-standing graphene is included, which allows electrons to tunnel but does not significantly distort the density of states of free-standing graphene. Estimations are performed for n- and p-type 6 H-SiC(0001) substrates and Cu, Ag, and Au layers. The charge state of the graphene sheet and the shift of the Dirac point with respect to the Fermi level of the system are calculated. A comparison with the available experimental and theoretical results shows that the proposed scheme works quite satisfactorily.

  6. Sulfur-infiltrated graphene-based layered porous carbon cathodes for high-performance lithium-sulfur batteries.

    PubMed

    Yang, Xi; Zhang, Long; Zhang, Fan; Huang, Yi; Chen, Yongsheng

    2014-05-27

    Because of advantages such as excellent electronic conductivity, high theoretical specific surface area, and good mechanical flexibility, graphene is receiving increasing attention as an additive to improve the conductivity of sulfur cathodes in lithium-sulfur (Li-S) batteries. However, graphene is not an effective substrate material to confine the polysulfides in cathodes and stable the cycling. Here, we designed and synthesized a graphene-based layered porous carbon material for the impregnation of sulfur as cathode for Li-S battery. In this composite, a thin layer of porous carbon uniformly covers both surfaces of the graphene and sulfur is highly dispersed in its pores. The high specific surface area and pore volume of the porous carbon layers not only can achieve a high sulfur loading in highly dispersed amorphous state, but also can act as polysulfide reservoirs to alleviate the shuttle effect. When used as the cathode material in Li-S batteries, with the help of the thin porous carbon layers, the as-prepared materials demonstrate a better electrochemical performance and cycle stability compared with those of graphene/sulfur composites.

  7. Spectroscopic ellipsometry on Si/SiO{sub 2}/graphene tri-layer system exposed to downstream hydrogen plasma: Effects of hydrogenation and chemical sputtering

    SciTech Connect

    Eren, Baran; Fu, Wangyang; Marot, Laurent Calame, Michel; Steiner, Roland; Meyer, Ernst

    2015-01-05

    In this work, the optical response of graphene to hydrogen plasma treatment is investigated with spectroscopic ellipsometry measurements. Although the electronic transport properties and Raman spectrum of graphene change after plasma hydrogenation, ellipsometric parameters of the Si/SiO2/graphene tri-layer system do not change. This is attributed to plasma hydrogenated graphene still being electrically conductive, since the light absorption of conducting 2D materials does not depend on the electronic band structure. A change in the light transmission can only be observed when higher energy hydrogen ions (30 eV) are employed, which chemically sputter the graphene layer. An optical contrast is still apparent after sputtering due to the remaining traces of graphene and hydrocarbons on the surface. In brief, plasma treatment does not change the light transmission of graphene; and when it does, this is actually due to plasma damage rather than plasma hydrogenation.

  8. Self-screened high performance multi-layer MoS2 transistor formed by using a bottom graphene electrode

    NASA Astrophysics Data System (ADS)

    Qu, Deshun; Liu, Xiaochi; Ahmed, Faisal; Lee, Daeyeong; Yoo, Won Jong

    2015-11-01

    We investigated the carrier transport in multi-layer MoS2 with consideration of the contact resistance (Rc) and interlayer resistance (Rint). A bottom graphene contact was suggested to overcome the degradation of Id modulation in a back gated multi-layer MoS2 field effect transistor (FET) due to the accumulated Rint and increased Rc with increasing thickness. As a result, non-degraded drain current (Id) modulation with increasing flake thickness was achieved due to the non-cumulative Rint. Benefiting from the low Rc induced by the negligible Schottky barrier at the graphene/MoS2 interface, the intrinsic carrier transport properties immune to Rc were investigated in the multi-layer MoS2 FET. ~2 times the enhanced carrier mobility was attained from the self-screened channel in the bottom graphene contacted device, compared to those with top metal contacts.We investigated the carrier transport in multi-layer MoS2 with consideration of the contact resistance (Rc) and interlayer resistance (Rint). A bottom graphene contact was suggested to overcome the degradation of Id modulation in a back gated multi-layer MoS2 field effect transistor (FET) due to the accumulated Rint and increased Rc with increasing thickness. As a result, non-degraded drain current (Id) modulation with increasing flake thickness was achieved due to the non-cumulative Rint. Benefiting from the low Rc induced by the negligible Schottky barrier at the graphene/MoS2 interface, the intrinsic carrier transport properties immune to Rc were investigated in the multi-layer MoS2 FET. ~2 times the enhanced carrier mobility was attained from the self-screened channel in the bottom graphene contacted device, compared to those with top metal contacts. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06076a

  9. The influence of few-layer graphene on the gas permeability of the high-free-volume polymer PIM-1

    PubMed Central

    Althumayri, Khalid; Harrison, Wayne J.; Shin, Yuyoung; Gardiner, John M.; Casiraghi, Cinzia; Bernardo, Paola; Clarizia, Gabriele

    2016-01-01

    Gas permeability data are presented for mixed matrix membranes (MMMs) of few-layer graphene in the polymer of intrinsic microporosity PIM-1, and the results compared with previously reported data for two other nanofillers in PIM-1: multiwalled carbon nanotubes functionalized with poly(ethylene glycol) (f-MWCNTs) and fused silica. For few-layer graphene, a significant enhancement in permeability is observed at very low graphene content (0.05 vol.%), which may be attributed to the effect of the nanofiller on the packing of the polymer chains. At higher graphene content permeability decreases, as expected for the addition of an impermeable filler. Other nanofillers, reported in the literature, also give rise to enhancements in permeability, but at substantially higher loadings, the highest measured permeabilities being at 1 vol.% for f-MWCNTs and 24 vol.% for fused silica. These results are consistent with the hypothesis that packing of the polymer chains is influenced by the curvature of the nanofiller surface at the nanoscale, with an increasingly pronounced effect on moving from a more-or-less spherical nanoparticle morphology (fused silica) to a cylindrical morphology (f-MWCNT) to a planar morphology (graphene). While the permeability of a high-free-volume polymer such as PIM-1 decreases over time through physical ageing, for the PIM-1/graphene MMMs a significant permeability enhancement was retained after eight months storage. PMID:26712643

  10. The influence of few-layer graphene on the gas permeability of the high-free-volume polymer PIM-1.

    PubMed

    Althumayri, Khalid; Harrison, Wayne J; Shin, Yuyoung; Gardiner, John M; Casiraghi, Cinzia; Budd, Peter M; Bernardo, Paola; Clarizia, Gabriele; Jansen, Johannes C

    2016-02-13

    Gas permeability data are presented for mixed matrix membranes (MMMs) of few-layer graphene in the polymer of intrinsic microporosity PIM-1, and the results compared with previously reported data for two other nanofillers in PIM-1: multiwalled carbon nanotubes functionalized with poly(ethylene glycol) (f-MWCNTs) and fused silica. For few-layer graphene, a significant enhancement in permeability is observed at very low graphene content (0.05 vol.%), which may be attributed to the effect of the nanofiller on the packing of the polymer chains. At higher graphene content permeability decreases, as expected for the addition of an impermeable filler. Other nanofillers, reported in the literature, also give rise to enhancements in permeability, but at substantially higher loadings, the highest measured permeabilities being at 1 vol.% for f-MWCNTs and 24 vol.% for fused silica. These results are consistent with the hypothesis that packing of the polymer chains is influenced by the curvature of the nanofiller surface at the nanoscale, with an increasingly pronounced effect on moving from a more-or-less spherical nanoparticle morphology (fused silica) to a cylindrical morphology (f-MWCNT) to a planar morphology (graphene). While the permeability of a high-free-volume polymer such as PIM-1 decreases over time through physical ageing, for the PIM-1/graphene MMMs a significant permeability enhancement was retained after eight months storage. PMID:26712643

  11. Phase transitions and kinetic properties of gold nanoparticles confined between two-layer graphene nanosheets

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Wu, Nanhua; Chen, Jionghua; Wang, Jinjian; Shao, Jingling; Zhu, Xiaolei; Lu, Xiaohua; Guo, Lucun

    2016-11-01

    The thermodynamic and kinetic behaviors of gold nanoparticles confined between two-layer graphene nanosheets (two-layer-GNSs) are examined and investigated during heating and cooling processes via molecular dynamics (MD) simulation technique. An EAM potential is applied to represent the gold-gold interactions while a Lennard-Jones (L-J) potential is used to describe the gold-GNS interactions. The MD melting temperature of 1345 K for bulk gold is close to the experimental value (1337 K), confirming that the EAM potential used to describe gold-gold interactions is reliable. On the other hand, the melting temperatures of gold clusters supported on graphite bilayer are corrected to the corresponding experimental values by adjusting the εAu-C value. Therefore, the subsequent results from current work are reliable. The gold nanoparticles confined within two-layer GNSs exhibit face center cubic structures, which is similar to those of free gold clusters and bulk gold. The melting points, heats of fusion, and heat capacities of the confined gold nanoparticles are predicted based on the plots of total energies against temperature. The density distribution perpendicular to GNS suggests that the freezing of confined gold nanoparticles starts from outermost layers. The confined gold clusters exhibit layering phenomenon even in liquid state. The transition of order-disorder in each layer is an essential characteristic in structure for the freezing phase transition of the confined gold clusters. Additionally, some vital kinetic data are obtained in terms of classical nucleation theory.

  12. Anode modification of polymer light-emitting diode using graphene oxide interfacial layer: The role of ultraviolet-ozone treatment

    NASA Astrophysics Data System (ADS)

    Jiang, Xiao-Chen; Li, Yan-Qing; Deng, Yan-Hong; Zhuo, Qi-Qi; Lee, Shuit-Tong; Tang, Jian-Xin

    2013-08-01

    A simple and efficient method has been developed to modify the anode interface of polymer light-emitting diode by incorporating solution-processable graphene oxide as hole transport layer. Interface engineering of ultraviolet-ozone treatment on graphene oxide is demonstrated to dramatically enhance the electrical properties, leading to 15% increase in efficiency compared to that with a traditionally used poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) layer. As determined by photoelectron spectroscopy and impedance spectroscopy, an optimized ultraviolet-ozone treatment results in a more favorable energy level alignment and a decrease in series resistance, which can subsequently facilitate charge injection at the anodic interface.

  13. Phase Conjugated and Transparent Wavelength Conversions of Nyquist 16-QAM Signals Employing a Single-Layer Graphene Coated Fiber Device.

    PubMed

    Hu, Xiao; Zeng, Mengqi; Long, Yun; Liu, Jun; Zhu, Yixiao; Zou, Kaiheng; Zhang, Fan; Fu, Lei; Wang, Jian

    2016-03-02

    We fabricate a nonlinear optical device based on a fiber pigtail cross-section coated with a single-layer graphene grown by chemical vapor deposition (CVD) method. Using the fabricated graphene-assisted nonlinear optical device and employing Nyquist 16-ary quadrature amplitude modulation (16-QAM) signal, we experimentally demonstrate phase conjugated wavelength conversion by degenerate four-wave mixing (FWM) and transparent wavelength conversion by non-degenerate FWM in graphene. We study the conversion efficiency as functions of the pump power and pump wavelength and evaluate the bit-error rate (BER) performance. We also compare the time-varying symbol sequence for graphene-assisted phase conjugated and transparent wavelength conversions of Nyquist 16-QAM signal.

  14. Phase Conjugated and Transparent Wavelength Conversions of Nyquist 16-QAM Signals Employing a Single-Layer Graphene Coated Fiber Device

    PubMed Central

    Hu, Xiao; Zeng, Mengqi; Long, Yun; Liu, Jun; Zhu, Yixiao; Zou, Kaiheng; Zhang, Fan; Fu, Lei; Wang, Jian

    2016-01-01

    We fabricate a nonlinear optical device based on a fiber pigtail cross-section coated with a single-layer graphene grown by chemical vapor deposition (CVD) method. Using the fabricated graphene-assisted nonlinear optical device and employing Nyquist 16-ary quadrature amplitude modulation (16-QAM) signal, we experimentally demonstrate phase conjugated wavelength conversion by degenerate four-wave mixing (FWM) and transparent wavelength conversion by non-degenerate FWM in graphene. We study the conversion efficiency as functions of the pump power and pump wavelength and evaluate the bit-error rate (BER) performance. We also compare the time-varying symbol sequence for graphene-assisted phase conjugated and transparent wavelength conversions of Nyquist 16-QAM signal. PMID:26932470

  15. Fabrication of positively charged nanofiltration membrane via the layer-by-layer assembly of graphene oxide and polyethylenimine for desalination

    NASA Astrophysics Data System (ADS)

    Nan, Qian; Li, Pei; Cao, Bing

    2016-11-01

    Highly positively charged nanofiltration (NF) membranes have been prepared via a layer-by-layer (LbL) self-assembly technique using graphene oxide (GO) and polyethyleneimine (PEI). The high aspect ratio and unique 2D structure of GO nanosheets enabled them to be easily assembled on the membrane surface, and the intrinsic low resistant channels within the GO nanosheets resulted in a high water flux of the membrane. By assembled a PEI layer on the membrane outer surface, the composite membrane exhibited high positive charge and resulted in the high rejections to multivalent ions. The effects of deposition time, PEI and GO concentrations on separation performance of the NF membranes were detailed studied. The best performance among all the membranes was achieved with salt rejections of 93.9% and 38.1% for Mg2+ and Na+, and a water flux of 4.2 L/m2 h bar at 30 °C and 0.5 MPa. The attractive performance of these NF membranes showed a great potential in the industrial application of water softening.

  16. Topography, complex refractive index, and conductivity of graphene layers measured by correlation of optical interference contrast, atomic force, and back scattered electron microscopy

    SciTech Connect

    Vaupel, Matthias Dutschke, Anke; Wurstbauer, Ulrich; Pasupathy, Abhay; Hitzel, Frank

    2013-11-14

    The optical phase shift by reflection on graphene is measured by interference contrast microscopy. The height profile across graphene layers on 300 nm thick SiO{sub 2} on silicon is derived from the phase profile. The complex refractive index and conductivity of graphene layers on silicon with 2 nm thin SiO{sub 2} are evaluated from a phase profile, while the height profile of the layers is measured by atomic force microscopy. It is observed that the conductivity measured on thin SiO{sub 2} is significantly greater than on thick SiO{sub 2}. Back scattered electron contrast of graphene layers is correlated to the height of graphene layers.

  17. Effect of interfacial interactions on the thermal conductivity and interfacial thermal conductance in tungsten–graphene layered structure

    SciTech Connect

    Jagannadham, K.

    2014-09-01

    Graphene film was deposited by microwave plasma assisted deposition on polished oxygen free high conductivity copper foils. Tungsten–graphene layered film was formed by deposition of tungsten film by magnetron sputtering on the graphene covered copper foils. Tungsten film was also deposited directly on copper foil without graphene as the intermediate film. The tungsten–graphene–copper samples were heated at different temperatures up to 900 °C in argon atmosphere to form an interfacial tungsten carbide film. Tungsten film deposited on thicker graphene platelets dispersed on silicon wafer was also heated at 900 °C to identify the formation of tungsten carbide film by reaction of tungsten with graphene platelets. The films were characterized by scanning electron microscopy, Raman spectroscopy, and x-ray diffraction. It was found that tungsten carbide film formed at the interface upon heating only above 650 °C. Transient thermoreflectance signal from the tungsten film surface on the samples was collected and modeled using one-dimensional heat equation. The experimental and modeled results showed that the presence of graphene at the interface reduced the cross-plane effective thermal conductivity and the interfacial thermal conductance of the layer structure. Heating at 650 and 900 °C in argon further reduced the cross-plane thermal conductivity and interface thermal conductance as a result of formation nanocrystalline tungsten carbide at the interface leading to separation and formation of voids. The present results emphasize that interfacial interactions between graphene and carbide forming bcc and hcp elements will reduce the cross-plane effective thermal conductivity in composites.

  18. Detecting single graphene layer by using fluorescence from high-speed Ar^7+ ion

    NASA Astrophysics Data System (ADS)

    Miyamoto, Yoshiyuki; Zhang, Hong

    2008-03-01

    A highly-charged-ion interacting with graphite causes structural change in nano-scales [1]. While when the ion's kinetic energy reaches few MeVs, the induced is not the structural change but electronic excitation. An experiment [2] showed fluorescence from Ar^7+ ions penetrating through carbon foil with kinetic energy of 2 MeV. Motivated by this experiment, we tested interaction between an Ar^7+ ion and a graphene sheet by the time-dependent density functional approach, and found that the electronic excitation in the Ar^ 7+ ion is also the case even when the incident kinetic energy is 500 KeV and the target thickness is only mono-atomic layer. This simulation suggests the possibility of detecting a suspended mono-atomic layer of graphene [3] by monitoring fluorescence from the penetrated Ar^7+ ions. We will discuss its importance for analyzing bombardment of solids by highly charged, high-speed ions and possible experiments according to the present result. References: [1] T. Meguro, et al., Appl. Phys. Lett 79, 3866 (2001). [2] S. Bashkin, H. Oona, E. Veje, Phys, Rev. A25, 417 (1982). [3] J. Mayer et al., Nature (London), 446, 60 (2007).

  19. Graphene-like two-dimensional layered nanomaterials: applications in biosensors and nanomedicine

    NASA Astrophysics Data System (ADS)

    Yang, Guohai; Zhu, Chengzhou; Du, Dan; Zhu, Junjie; Lin, Yuehe

    2015-08-01

    The development of nanotechnology provides promising opportunities for various important applications. The recent discovery of atomically-thick two-dimensional (2D) nanomaterials can offer manifold perspectives to construct versatile devices with high-performance to satisfy multiple requirements. Many studies directed at graphene have stimulated renewed interest on graphene-like 2D layered nanomaterials (GLNs). GLNs including boron nitride nanosheets, graphitic-carbon nitride nanosheets and transition metal dichalcogenides (e.g. MoS2 and WS2) have attracted significant interest in numerous research fields from physics and chemistry to biology and engineering, which has led to numerous interdisciplinary advances in nano science. Benefiting from the unique physical and chemical properties (e.g. strong mechanical strength, high surface area, unparalleled thermal conductivity, remarkable biocompatibility and ease of functionalization), these 2D layered nanomaterials have shown great potential in biochemistry and biomedicine. This review summarizes recent advances of GLNs in applications of biosensors and nanomedicine, including electrochemical biosensors, optical biosensors, bioimaging, drug delivery and cancer therapy. Current challenges and future perspectives in these rapidly developing areas are also outlined. It is expected that they will have great practical foundation in biomedical applications with future efforts.

  20. Synthesis and characterization of hexagonal boron nitride film as a dielectric layer for graphene devices.

    PubMed

    Kim, Ki Kang; Hsu, Allen; Jia, Xiaoting; Kim, Soo Min; Shi, Yumeng; Dresselhaus, Mildred; Palacios, Tomas; Kong, Jing

    2012-10-23

    Hexagonal boron nitride (h-BN) is a promising material as a dielectric layer or substrate for two-dimensional electronic devices. In this work, we report the synthesis of large-area h-BN film using atmospheric pressure chemical vapor deposition on a copper foil, followed by Cu etching and transfer to a target substrate. The growth rate of h-BN film at a constant temperature is strongly affected by the concentration of borazine as a precursor and the ambient gas condition such as the ratio of hydrogen and nitrogen. h-BN films with different thicknesses can be achieved by controlling the growth time or tuning the growth conditions. Transmission electron microscope characterization reveals that these h-BN films are polycrystalline, and the c-axis of the crystallites points to different directions. The stoichiometry ratio of boron and nitrogen is close to 1:1, obtained by electron energy loss spectroscopy. The dielectric constant of h-BN film obtained by parallel capacitance measurements (25 μm(2) large areas) is 2-4. These CVD-grown h-BN films were integrated as a dielectric layer in top-gated CVD graphene devices, and the mobility of the CVD graphene device (in the few thousands cm(2)/(V·s) range) remains the same before and after device integration. PMID:22970651

  1. Coherent commensurate electronic states at the interface between misoriented graphene layers

    NASA Astrophysics Data System (ADS)

    Koren, Elad; Leven, Itai; Lörtscher, Emanuel; Knoll, Armin; Hod, Oded; Duerig, Urs

    2016-09-01

    Graphene and layered materials in general exhibit rich physics and application potential owing to their exceptional electronic properties, which arise from the intricate π-orbital coupling and the symmetry breaking in twisted bilayer systems. Here, we report room-temperature experiments to study electrical transport across a bilayer graphene interface with a well-defined rotation angle between the layers that is controllable in situ. This twisted interface is artificially created in mesoscopic pillars made of highly oriented pyrolytic graphite by mechanical actuation. The overall measured angular dependence of the conductivity is consistent with a phonon-assisted transport mechanism that preserves the electron momentum of conduction electrons passing the interface. The most intriguing observations are sharp conductivity peaks at interlayer rotation angles of 21.8° and 38.2°. These angles correspond to a commensurate crystalline superstructure leading to a coherent two-dimensional (2D) electronic interface state. Such states, predicted by theory, form the basis for a new class of 2D weakly coupled bilayer systems with hitherto unexplored properties and applications.

  2. Indirect optical transitions in hybrid spheres with alternating layers of titania and graphene oxide nanosheets.

    PubMed

    Bao, Shanshan; Hua, Zheng; Wang, Xiaoyong; Zhou, Yong; Zhang, Chunfeng; Tu, Wenguang; Zou, Zhigang; Xiao, Min

    2012-12-17

    In this report, we studied the optical properties of hybrid spherical structures consisting of alternating nanosheets of titania (TiO(2)) and graphene oxide (GO) prepared by a layer-by-layer self-assembly technique. Compared to samples with only TiO(2) spheres or GO nanosheets, a blue-to-red light emission band emerges and persists in this novel composite material even after it was further reduced through microwave irradiation. From detailed time-resolved measurements and energy-level structure modeling, this unexpected fluorescent feature was attributed to the indirect optical transitions between TiO(2) and the localized sp(2) domains of GO in a charge-separated configuration.

  3. Hydrogen storage in a chemical bond stabilized Co9S8-graphene layered structure.

    PubMed

    Qin, Wei; Han, Lu; Bi, Hai; Jian, Jiahuang; Wu, Xiaohong; Gao, Peng

    2015-12-21

    With the high energy ball milling method, a Co9S8-decorated reduced graphene oxide (RGO) composite, which shows excellent hydrogen storage capacity, has been successfully fabricated with a well-organized layered structure. Moreover, the stabilized mechanism of the well-organized layered structure is investigated and attributed to the strong interactions between Co9S8 and defective RGO. The C-S bond interaction is identified and the hydrogen storage process is also studied with different analysis methods. Finally, an optimized Co9S8 to RGO weight ratio of 6:1 shows excellent electrochemical performances in terms of the excellent cycling stability and competitive hydrogen storage capacity of 4.86 wt%.

  4. Oriented 2D covalent organic framework thin films on single-layer graphene.

    PubMed

    Colson, John W; Woll, Arthur R; Mukherjee, Arnab; Levendorf, Mark P; Spitler, Eric L; Shields, Virgil B; Spencer, Michael G; Park, Jiwoong; Dichtel, William R

    2011-04-01

    Covalent organic frameworks (COFs), in which molecular building blocks form robust microporous networks, are usually synthesized as insoluble and unprocessable powders. We have grown two-dimensional (2D) COF films on single-layer graphene (SLG) under operationally simple solvothermal conditions. The layered films stack normal to the SLG surface and show improved crystallinity compared with COF powders. We used SLG surfaces supported on copper, silicon carbide, and transparent fused silica (SiO(2)) substrates, enabling optical spectroscopy of COFs in transmission mode. Three chemically distinct COF films grown on SLG exhibit similar vertical alignment and long-range order, and two of these are of interest for organic electronic devices for which thin-film formation is a prerequisite for characterizing their optoelectronic properties.

  5. Effect of current stress during thermal CVD of multilayer graphene on cobalt catalytic layer

    NASA Astrophysics Data System (ADS)

    Ueno, Kazuyoshi; Ichikawa, Hiroyasu; Uchida, Takaki

    2016-04-01

    To improve the crystallinity of multilayer graphene (MLG) by CVD at a low temperature, the effect of current stress during thermal CVD on a cobalt (Co) catalytic layer was investigated. The crystallinity of MLG obtained by CVD with current was higher than that without current at the same temperature. This indicates that current has effects besides the Joule heating effect. The current effects on the Co catalytic layer and the MLG growth reaction were investigated, and it was found that current had small effects on the grain size and crystal structure of the Co catalyst and large effects on the MLG growth reaction such as large grain growth and a low activation energy of 0.49 eV, which is close to the value reported for carbon surface diffusion on Co. It is considered that the enhancement of MLG growth reaction by current leads to the improved crystallinity of MLG at a relatively low temperature.

  6. Strong composite films with layered structures prepared by casting silk fibroin-graphene oxide hydrogels.

    PubMed

    Huang, Liang; Li, Chun; Yuan, Wenjing; Shi, Gaoquan

    2013-05-01

    Composite films of graphene oxide (GO) sheets and silk fibroin (SF) with layered structures have been prepared by facile solution casting of SF-GO hydrogels. The as-prepared composite film containing 15% (by weight, wt%) of SF shows a high tensile strength of 221 ± 16 MPa and a failure strain of 1.8 ± 0.4%, which partially surpass those of natural nacre. Particularly, this composite film also has a high modulus of 17.2 ± 1.9 GPa. The high mechanical properties of this composite film can be attributed to its high content of GO (85 wt%), compact layered structure and the strong hydrogen bonding interaction between SF chains and GO sheets. PMID:23538717

  7. Effect of the intra-layer potential distributions and spatial currents on the performance of graphene SymFETs

    SciTech Connect

    Hasan, Mehdi; Sensale-Rodriguez, Berardi

    2015-09-15

    In this paper, a two-dimensional (2-D) model for a graphene symmetric field effect transistor (SymFET), which considers (a) the intra-graphene layer potential distributions and (b) the internal current flows through the device, is presented and discussed. The local voltages along the graphene electrodes as well as the current-voltage characteristics of the device are numerically calculated based on a single-particle tunneling model. Our numerical results show that: (i) when the tunneling current is small, due to either a large tunneling thickness (≥ 2 atomic layers of BN) or a small coherence length, the voltage distributions along the graphene electrodes have almost zero variations upon including these distributed effects, (ii) when the tunnel current is large, due to either a small tunneling thickness (∼ 1 atomic layer of BN) or due to a large coherence length, the local voltage distributions along the graphene electrodes become appreciable and the device behavior deviates from that predicted by a 1-D approximation. These effects, which are not captured in one-dimensional SymFET models, can provide a better understanding about the electron dynamics in the device and might indicate potential novel applications for this proposed device.

  8. Strong composite films with layered structures prepared by casting silk fibroin-graphene oxide hydrogels

    NASA Astrophysics Data System (ADS)

    Huang, Liang; Li, Chun; Yuan, Wenjing; Shi, Gaoquan

    2013-04-01

    Composite films of graphene oxide (GO) sheets and silk fibroin (SF) with layered structures have been prepared by facile solution casting of SF-GO hydrogels. The as-prepared composite film containing 15% (by weight, wt%) of SF shows a high tensile strength of 221 +/- 16 MPa and a failure strain of 1.8 +/- 0.4%, which partially surpass those of natural nacre. Particularly, this composite film also has a high modulus of 17.2 +/- 1.9 GPa. The high mechanical properties of this composite film can be attributed to its high content of GO (85 wt%), compact layered structure and the strong hydrogen bonding interaction between SF chains and GO sheets.Composite films of graphene oxide (GO) sheets and silk fibroin (SF) with layered structures have been prepared by facile solution casting of SF-GO hydrogels. The as-prepared composite film containing 15% (by weight, wt%) of SF shows a high tensile strength of 221 +/- 16 MPa and a failure strain of 1.8 +/- 0.4%, which partially surpass those of natural nacre. Particularly, this composite film also has a high modulus of 17.2 +/- 1.9 GPa. The high mechanical properties of this composite film can be attributed to its high content of GO (85 wt%), compact layered structure and the strong hydrogen bonding interaction between SF chains and GO sheets. Electronic supplementary information (ESI) available: XPS spectrum of the SF-GO hybrid film, SEM images of lyophilized GO dispersion and the failure surface of GO film. See DOI: 10.1039/c3nr00196b

  9. Suppressing thermal conductivity of suspended tri-layer graphene by gold deposition.

    PubMed

    Wang, Jiayi; Zhu, Liyan; Chen, Jie; Li, Baowen; Thong, John T L

    2013-12-17

    A simple and general strategy for suppressing the thermal conductivity in graphene is shown. The strategy uses gold nano-particles physically deposited on graphene to continuously reduce the thermal conductivity of graphene with increasing coverage, which demonstrates the potential for practical development of graphene-based devices with tunable thermal conductivity for thermal management.

  10. Interactions between fluorescence of atomically layered graphene oxide and metallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Li, Shao-Sian; Yeh, Yun-Chieh; Yu, Chen-Chieh; Chen, Hsuen-Li; Li, Feng-Chieh; Chang, Yu-Ming; Chen, Chun-Wei

    2013-01-01

    Graphene oxide (GO) demonstrates interesting photoluminescence (PL) because of its unique heterogeneous atomic structure, which consists of variable sp2- and sp3-bonded carbons. In this study, we report the interaction between the luminescence of GO ranging from a single atomic layer to few-layered thin films and localized surface plasmon resonance (LSPR) from silver nanoparticles (Ag NPs). The photoluminescence of GO in the vicinity of the Ag NPs is enhanced significantly due to the near-field plasmonic effect by coupling electron-hole pairs of GO with oscillating electrons in Ag NPs, leading to an increased PL intensity and a decreased PL decay lifetime. The maxima 30-fold enhancement in PL intensity is obtained with an optimized film thickness of GO, and the luminescence image from a single atomic layer GO sheet is successfully observed with the assistance of the LSPR effect. The results provide an ideal platform for exploring the interactions between the fluorescence of two-dimensional layered materials and the LSPR effect.Graphene oxide (GO) demonstrates interesting photoluminescence (PL) because of its unique heterogeneous atomic structure, which consists of variable sp2- and sp3-bonded carbons. In this study, we report the interaction between the luminescence of GO ranging from a single atomic layer to few-layered thin films and localized surface plasmon resonance (LSPR) from silver nanoparticles (Ag NPs). The photoluminescence of GO in the vicinity of the Ag NPs is enhanced significantly due to the near-field plasmonic effect by coupling electron-hole pairs of GO with oscillating electrons in Ag NPs, leading to an increased PL intensity and a decreased PL decay lifetime. The maxima 30-fold enhancement in PL intensity is obtained with an optimized film thickness of GO, and the luminescence image from a single atomic layer GO sheet is successfully observed with the assistance of the LSPR effect. The results provide an ideal platform for exploring the

  11. Graphene Quantum Dot Layers with Energy-Down-Shift Effect on Crystalline-Silicon Solar Cells.

    PubMed

    Lee, Kyung D; Park, Myung J; Kim, Do-Yeon; Kim, Soo M; Kang, Byungjun; Kim, Seongtak; Kim, Hyunho; Lee, Hae-Seok; Kang, Yoonmook; Yoon, Sam S; Hong, Byung H; Kim, Donghwan

    2015-09-01

    Graphene quantum dot (GQD) layers were deposited as an energy-down-shift layer on crystalline-silicon solar cell surfaces by kinetic spraying of GQD suspensions. A supersonic air jet was used to accelerate the GQDs onto the surfaces. Here, we report the coating results on a silicon substrate and the GQDs' application as an energy-down-shift layer in crystalline-silicon solar cells, which enhanced the power conversion efficiency (PCE). GQD layers deposited at nozzle scan speeds of 40, 30, 20, and 10 mm/s were evaluated after they were used to fabricate crystalline-silicon solar cells; the results indicate that GQDs play an important role in increasing the optical absorptivity of the cells. The short-circuit current density was enhanced by about 2.94% (0.9 mA/cm(2)) at 30 mm/s. Compared to a reference device without a GQD energy-down-shift layer, the PCE of p-type silicon solar cells was improved by 2.7% (0.4 percentage points).

  12. Single-layer graphene as a stable and transparent electrode for nonaqueous radical annihilation electrogenerated chemiluminescence.

    PubMed

    Cristarella, Teresa C; Chinderle, Adam J; Hui, Jingshu; Rodríguez-López, Joaquín

    2015-04-01

    We explored the use of single-layer graphene (SLG) obtained by chemical vapor deposition, and transferred to a glass substrate, as a transparent electrode material for use in coupled electrochemical and spectroscopic experiments in nonaqueous media through electrogenerated chemiluminescence (ECL). SLG was used with classical ECL luminophores, rubrene and 9,10-diphenylanthracene, in an inert environment to generate stable electrochemical responses and measure light emission through it. As an electrode material, SLG displayed excellent stability during electrochemical potential stepping and voltammetry in a window that spanned at least from ca. -2.4 to +1.8 V versus SCE in acetonitrile and acetonitrile/benzene. Although the peak splitting between forward and reverse sweeps in voltammetry was larger in comparison to metal electrodes due to in-plane resistance, SLG displayed sufficiently facile electron transfer properties to yield stable voltammetric cycling and ECL. SLG electrodes patterned with poly tetrafluoroethylene permitted the stable generation of radical ions on an SLG microelectrode to be studied through scanning electrochemical microscopy in the generation/collection mode. SLG was able to stably collect radical ions produced by a 50 μm gold tip with up to 96% collection efficiency. The transparency of graphene was used to obtain accurate spectral responses in ECL. While inner filter effects are known to cause a shift in peak emission wavelength of spectroelectrochemical studies, the use of SLG electrodes with detection through the graphene window reduced apparent peak shifts by up to 10 nm in peak wavelength. This work introduces SLG as a virtually transparent, electrochemically active, and chemically stable platform for studying ECL in the radical annihilation mode, where large electrode polarizations could compromise the chemical stability of other existing transparent electrodes. PMID:25780938

  13. Graphene oxide as a highly selective substrate to synthesize a layered MoS2 hybrid electrocatalyst.

    PubMed

    Firmiano, Edney G S; Cordeiro, Marcos A L; Rabelo, Adriano C; Dalmaschio, Cleocir J; Pinheiro, Antonio N; Pereira, Ernesto C; Leite, Edson R

    2012-08-11

    We merged the microwave synthesis approach with an extension of the nonhydrolytic sol-gel method to induce highly selective crystallization of MoS(2) layers over graphene sheets. This hybrid material showed superior electrocatalytic activity in hydrogen evolution reactions.

  14. Molecular Dynamics Simulations Reveal that Water Diffusion between Graphene Oxide Layers is Slow.

    PubMed

    Devanathan, Ram; Chase-Woods, Dylan; Shin, Yongsoon; Gotthold, David W

    2016-07-08

    Membranes made of stacked layers of graphene oxide (GO) hold the tantalizing promise of revolutionizing desalination and water filtration if selective transport of molecules can be controlled. We present the findings of an integrated study that combines experiment and molecular dynamics simulation of water intercalated between GO layers. We simulated a range of hydration levels from 1 wt.% to 23.3 wt.% water. The interlayer spacing increased upon hydration from 0.8 nm to 1.1 nm. We also synthesized GO membranes that showed an increase in layer spacing from about 0.7 nm to 0.8 nm and an increase in mass of about 15% on hydration. Water diffusion through GO layers is an order of magnitude slower than that in bulk water, because of strong hydrogen bonded interactions. Most of the water molecules are bound to OH groups even at the highest hydration level. We observed large water clusters that could span graphitic regions, oxidized regions and holes that have been experimentally observed in GO. Slow interlayer diffusion can be consistent with experimentally observed water transport in GO if holes lead to a shorter path length than previously assumed and sorption serves as a key rate-limiting step.

  15. Molecular Dynamics Simulations Reveal that Water Diffusion between Graphene Oxide Layers is Slow

    PubMed Central

    Devanathan, Ram; Chase-Woods, Dylan; Shin, Yongsoon; Gotthold, David W.

    2016-01-01

    Membranes made of stacked layers of graphene oxide (GO) hold the tantalizing promise of revolutionizing desalination and water filtration if selective transport of molecules can be controlled. We present the findings of an integrated study that combines experiment and molecular dynamics simulation of water intercalated between GO layers. We simulated a range of hydration levels from 1 wt.% to 23.3 wt.% water. The interlayer spacing increased upon hydration from 0.8 nm to 1.1 nm. We also synthesized GO membranes that showed an increase in layer spacing from about 0.7 nm to 0.8 nm and an increase in mass of about 15% on hydration. Water diffusion through GO layers is an order of magnitude slower than that in bulk water, because of strong hydrogen bonded interactions. Most of the water molecules are bound to OH groups even at the highest hydration level. We observed large water clusters that could span graphitic regions, oxidized regions and holes that have been experimentally observed in GO. Slow interlayer diffusion can be consistent with experimentally observed water transport in GO if holes lead to a shorter path length than previously assumed and sorption serves as a key rate-limiting step. PMID:27388562

  16. Interactions between fluorescence of atomically layered graphene oxide and metallic nanoparticles.

    PubMed

    Wang, Yu; Li, Shao-Sian; Yeh, Yun-Chieh; Yu, Chen-Chieh; Chen, Hsuen-Li; Li, Feng-Chieh; Chang, Yu-Ming; Chen, Chun-Wei

    2013-02-21

    Graphene oxide (GO) demonstrates interesting photoluminescence (PL) because of its unique heterogeneous atomic structure, which consists of variable sp(2)- and sp(3)-bonded carbons. In this study, we report the interaction between the luminescence of GO ranging from a single atomic layer to few-layered thin films and localized surface plasmon resonance (LSPR) from silver nanoparticles (Ag NPs). The photoluminescence of GO in the vicinity of the Ag NPs is enhanced significantly due to the near-field plasmonic effect by coupling electron-hole pairs of GO with oscillating electrons in Ag NPs, leading to an increased PL intensity and a decreased PL decay lifetime. The maxima 30-fold enhancement in PL intensity is obtained with an optimized film thickness of GO, and the luminescence image from a single atomic layer GO sheet is successfully observed with the assistance of the LSPR effect. The results provide an ideal platform for exploring the interactions between the fluorescence of two-dimensional layered materials and the LSPR effect. PMID:23340692

  17. Molecular Dynamics Simulations Reveal that Water Diffusion between Graphene Oxide Layers is Slow

    NASA Astrophysics Data System (ADS)

    Devanathan, Ram; Chase-Woods, Dylan; Shin, Yongsoon; Gotthold, David W.

    2016-07-01

    Membranes made of stacked layers of graphene oxide (GO) hold the tantalizing promise of revolutionizing desalination and water filtration if selective transport of molecules can be controlled. We present the findings of an integrated study that combines experiment and molecular dynamics simulation of water intercalated between GO layers. We simulated a range of hydration levels from 1 wt.% to 23.3 wt.% water. The interlayer spacing increased upon hydration from 0.8 nm to 1.1 nm. We also synthesized GO membranes that showed an increase in layer spacing from about 0.7 nm to 0.8 nm and an increase in mass of about 15% on hydration. Water diffusion through GO layers is an order of magnitude slower than that in bulk water, because of strong hydrogen bonded interactions. Most of the water molecules are bound to OH groups even at the highest hydration level. We observed large water clusters that could span graphitic regions, oxidized regions and holes that have been experimentally observed in GO. Slow interlayer diffusion can be consistent with experimentally observed water transport in GO if holes lead to a shorter path length than previously assumed and sorption serves as a key rate-limiting step.

  18. Molecular Dynamics Simulations Reveal that Water Diffusion between Graphene Oxide Layers is Slow.

    PubMed

    Devanathan, Ram; Chase-Woods, Dylan; Shin, Yongsoon; Gotthold, David W

    2016-01-01

    Membranes made of stacked layers of graphene oxide (GO) hold the tantalizing promise of revolutionizing desalination and water filtration if selective transport of molecules can be controlled. We present the findings of an integrated study that combines experiment and molecular dynamics simulation of water intercalated between GO layers. We simulated a range of hydration levels from 1 wt.% to 23.3 wt.% water. The interlayer spacing increased upon hydration from 0.8 nm to 1.1 nm. We also synthesized GO membranes that showed an increase in layer spacing from about 0.7 nm to 0.8 nm and an increase in mass of about 15% on hydration. Water diffusion through GO layers is an order of magnitude slower than that in bulk water, because of strong hydrogen bonded interactions. Most of the water molecules are bound to OH groups even at the highest hydration level. We observed large water clusters that could span graphitic regions, oxidized regions and holes that have been experimentally observed in GO. Slow interlayer diffusion can be consistent with experimentally observed water transport in GO if holes lead to a shorter path length than previously assumed and sorption serves as a key rate-limiting step. PMID:27388562

  19. In situ nitrogenated graphene-few-layer WS2 composites for fast and reversible Li+ storage.

    PubMed

    Chen, Dongyun; Ji, Ge; Ding, Bo; Ma, Yue; Qu, Baihua; Chen, Weixiang; Lee, Jim Yang

    2013-09-01

    Two-dimensional nanosheets can leverage on their open architecture to support facile insertion and removal of Li(+) as lithium-ion battery electrode materials. In this study, two two-dimensional nanosheets with complementary functions, namely nitrogen-doped graphene and few-layer WS2, were integrated via a facile surfactant-assisted synthesis under hydrothermal conditions. The layer structure and morphology of the composites were confirmed by X-ray diffraction, scanning electron microscopy and high-resolution transmission microscopy. The effects of surfactant amount on the WS2 layer number were investigated and the performance of the layered composites as high energy density lithium-ion battery anodes was evaluated. The composite formed with a surfactant : tungsten precursor ratio of 1 : 1 delivered the best cyclability (average of only 0.08% capacity fade per cycle for 100 cycles) and good rate performance (80% capacity retention with a 50-fold increase in current density from 100 mA g(-1) to 5000 mA g(-1)), and may find uses in power-oriented applications.

  20. Vibrational characteristics of graphene sheets elucidated using an elastic network model.

    PubMed

    Kim, Min Hyeok; Kim, Daejoong; Choi, Jae Boong; Kim, Moon Ki

    2014-08-01

    Recent studies of graphene have demonstrated its great potential for highly sensitive resonators. In order to capture the intrinsic vibrational characteristics of graphene, we propose an atomistic modeling method called the elastic network model (ENM), in which a graphene sheet is modeled as a mass-spring network of adjacent atoms connected by various linear springs with specific bond ratios. Normal mode analysis (NMA) reveals the various vibrational features of bi-layer graphene sheets (BLGSs) clamped at two edges. We also propose a coarse-graining (CG) method to extend our graphene study into the meso- and macroscales, at which experimental measurements and synthesis of graphene become practical. The simulation results show good agreement with experimental observations. Therefore, the proposed ENM approach will not only shed light on the theoretical study of graphene mechanics, but also play an important role in the design of highly-sensitive graphene-based resonators.

  1. 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

    2014-04-01

    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.

  2. Surface-enhanced Raman scattering studies of few-layer graphene on silver substrate with 514 nm excitation

    NASA Astrophysics Data System (ADS)

    Ouyang, Yu; Chen, Li

    2011-04-01

    Few-layer graphene was prepared by deoxidizing graphite oxide. Surface-enhanced Raman scattering (SERS) spectrum of graphene on Ag substrate was presented with 514 nm excitation. More than nine Raman lines are shown in the 100-3200 cm -1. The intensities of all lines are enhanced. Besides D mode at 1347 cm -1, G peak at 1581 cm -1, G ∗ band at ˜2458 cm -1, and G' band at ˜2691 cm -1, there are two features in low frequency area at about 239 cm -1 and 992 cm -1 separately, one line in high frequency area at about 2900 cm -1 with a shoulder appearing at ˜2860 cm -1. According to SERS, the structure of graphene was analyzed. Furthermore, the increase of D/G intensity ratio in SERS shows the SERS has much potential to be applied in controlling synthesis quality of graphene. In addition, low frequency Raman lines presented in SERS show application potential in analyzing the layer number, stacked style and edge of graphene.

  3. An acetylcholinesterase biosensor based on graphene-gold nanocomposite and calcined layered double hydroxide.

    PubMed

    Zhai, Chen; Guo, Yemin; Sun, Xia; Zheng, Yuhe; Wang, Xiangyou

    2014-05-10

    In this study, a novel acetylcholinesterase-based biosensor was fabricated. Acetylcholinesterase (AChE) was immobilized onto a glassy carbon electrode (GCE) with the aid of Cu-Mg-Al calcined layered double hydroxide (CLDH). CLDH can provide a bigger effective surface area for AChE loading, which could improve the precision and stability of AChE biosensor. However, the poor electroconductibility of CLDHs could lead to the low sensitivity of AChE biosensor. In order to effectively compensate the disadvantages of CLDHs, graphene-gold nanocomposites were used for improving the electron transfer rate. Thus, the graphene-gold nanocomposite (GN-AuNPs) was firstly modified onto the GCE, and then the prepared CLDH-AChE composite was immobilized onto the modified GCE to construct a sensitive AChE biosensor for pesticides detection. Relevant parameters were studied in detail and optimized, including the pH of the acetylthiocholine chloride (ATCl) solution, the amount of AChE immobilized on the biosensor and the inhibition time governing the analytical performance of the biosensor. The biosensor detected chlorpyrifos at concentrations ranging from 0.05 to 150μg/L. The detection limit for chlorpyrifos was 0.05μg/L.

  4. Oil lubricant tribological behaviour improvement through dispersion of few layer graphene oxide.

    PubMed

    Sarno, Maria; Senatore, Adolfo; Cirillo, Claudia; Petrone, Vincenzo; Ciambelli, Paolo

    2014-07-01

    Few layer graphene oxide (GO) nanosheets were prepared by a very fast modified Hummers method and widely characterized. Avoiding further chemical reactions, trying to take advantage of the easy exfoliation of GO favoring the formation of a tribofilm, and using a methodology well known to the lubricant industry, they were added to a mineral oil by the help of a dispersant. The tribological behaviour of GO in mineral oil was investigated under a wide spectrum of conditions, from boundary and mixed lubrication to elastohydrodynamic regimes. A ball on disc setup tribometer has been used to verify the friction reduction due to nanosheets dispersed in mineral oil. Their good friction and anti-wear properties may possibly be attributed to the small and extremely thin laminated structure, which offer lower shear stress and prevent interaction between metal interfaces. Furthermore, the results clearly prove that graphene platelets in oil easily form a protective film to prevent the direct contact between steel surfaces and, thereby, improving the frictional behaviour of the base oil. This evidence is also related to the frictional coefficient trend in boundary regime.

  5. Stacking Structures of Few-Layer Graphene Revealed by Phase-Sensitive Infrared Nanoscopy.

    PubMed

    Kim, Deok-Soo; Kwon, Hyuksang; Nikitin, Alexey Yu; Ahn, Seongjin; Martín-Moreno, Luis; García-Vidal, Francisco J; Ryu, Sunmin; Min, Hongki; Kim, Zee Hwan

    2015-07-28

    The stacking orders in few-layer graphene (FLG) strongly influences the electronic properties of the material. To explore the stacking-specific properties of FLG in detail, one needs powerful microscopy techniques that visualize stacking domains with sufficient spatial resolution. We demonstrate that infrared (IR) scattering scanning near-field optical microscopy (sSNOM) directly maps out the stacking domains of FLG with a nanometric resolution, based on the stacking-specific IR conductivities of FLG. The intensity and phase contrasts of sSNOM are compared with the sSNOM contrast model, which is based on the dipolar tip-sample coupling and the theoretical conductivity spectra of FLG, allowing a clear assignment of each FLG domain as Bernal, rhombohedral, or intermediate stacks for tri-, tetra-, and pentalayer graphene. The method offers 10-100 times better spatial resolution than the far-field Raman and infrared spectroscopic methods, yet it allows far more experimental flexibility than the scanning tunneling microscopy and electron microscopy.

  6. Josephson coupling between superconducting islands on single- and bi-layer graphene

    NASA Astrophysics Data System (ADS)

    Mancarella, Francesco; Fransson, Jonas; Balatsky, Alexander

    2016-05-01

    We study the Josephson coupling of superconducting (SC) islands through the surface of single-layer graphene (SLG) and bilayer graphene (BLG) in the long-junction regime, as a function of the distance between the grains, temperature, chemical potential and external (transverse) gate-voltage. For SLG, we provide a comparison with existing literature. The proximity effect is analyzed through a Matsubara Green’s function approach. This represents the first step in a discussion of the conditions for the onset of a granular superconductivity within the film, made possible by Josephson currents flowing between superconductors. To ensure phase coherence over the 2D sample, a random spatial distribution can be assumed for the SC islands on the SLG sheet (or intercalating the BLG sheets). The tunable gate-voltage-induced band gap of BLG affects the asymptotic decay of the Josephson coupling-distance characteristic for each pair of SC islands in the sample, which results in a qualitatively strong field dependence of the relation between Berezinskii–Kosterlitz–Thouless transition critical temperature and gate voltage.

  7. Frequency stabilization of single layer graphene oscillators through optical injection locking

    NASA Astrophysics Data System (ADS)

    Houri, Samer; Cartamil Bueno, Santiago; Venstra, Warner

    Single layer graphene (SLG) drum resonators offer exciting prospects as experimental testbeds for nonlinear dynamics. Recently, photo-thermal induced feedback effects leading to self-oscillations in graphene have been demonstrated. In this paper we examine the phase jitter of self-oscillating SLG, and the means to improve the frequency stability through optical injection locking. The resonator consists of an SLG on top of a 10 micron diameter circular cavity with a cavity depth of 750 nm. By shining a 10 mW He-Ne laser the drum enters a regime of photo-thermally induced self-oscillation. The oscillating SLG suffers from a significant phase noise that can be directly observed in the time domain as random walk of the oscillation period. By applying a lock tone to the oscillator through the application of a modulated blue laser (405 nm), the SLG motion is then phase locked to the applied tone with more than an order of magnitude improvement in its coherence time. The injection locking is also studied as a function of lock signal detuning and power. Presenting author.

  8. Josephson coupling between superconducting islands on single- and bi-layer graphene

    NASA Astrophysics Data System (ADS)

    Mancarella, Francesco; Fransson, Jonas; Balatsky, Alexander

    2016-05-01

    We study the Josephson coupling of superconducting (SC) islands through the surface of single-layer graphene (SLG) and bilayer graphene (BLG) in the long-junction regime, as a function of the distance between the grains, temperature, chemical potential and external (transverse) gate-voltage. For SLG, we provide a comparison with existing literature. The proximity effect is analyzed through a Matsubara Green’s function approach. This represents the first step in a discussion of the conditions for the onset of a granular superconductivity within the film, made possible by Josephson currents flowing between superconductors. To ensure phase coherence over the 2D sample, a random spatial distribution can be assumed for the SC islands on the SLG sheet (or intercalating the BLG sheets). The tunable gate-voltage-induced band gap of BLG affects the asymptotic decay of the Josephson coupling-distance characteristic for each pair of SC islands in the sample, which results in a qualitatively strong field dependence of the relation between Berezinskii-Kosterlitz-Thouless transition critical temperature and gate voltage.

  9. Graphene device and method of using graphene device

    SciTech Connect

    Bouchiat, Vincent; Girit, Caglar; Kessler, Brian; Zettl, Alexander K.

    2015-08-11

    An embodiment of a graphene device includes a layered structure, first and second electrodes, and a dopant island. The layered structure includes a conductive layer, an insulating layer, and a graphene layer. The electrodes are coupled to the graphene layer. The dopant island is coupled to an exposed surface of the graphene layer between the electrodes. An embodiment of a method of using a graphene device includes providing the graphene device. A voltage is applied to the conductive layer of the graphene device. Another embodiment of a method of using a graphene device includes providing the graphene device without the dopant island. A dopant island is placed on an exposed surface of the graphene layer between the electrodes. A voltage is applied to the conductive layer of the graphene device. A response of the dopant island to the voltage is observed.

  10. Bottom-gate coplanar graphene transistors with enhanced graphene adhesion on atomic layer deposition Al{sub 2}O{sub 3}

    SciTech Connect

    Park, Dong-Wook; Mikael, Solomon; Chang, Tzu-Hsuan; Ma, Zhenqiang; Gong, Shaoqin

    2015-03-09

    A graphene transistor with a bottom-gate coplanar structure and an atomic layer deposition (ALD) aluminum oxide (Al{sub 2}O{sub 3}) gate dielectric is demonstrated. Wetting properties of ALD Al{sub 2}O{sub 3} under different deposition conditions are investigated by measuring the surface contact angle. It is observed that the relatively hydrophobic surface is suitable for adhesion between graphene and ALD Al{sub 2}O{sub 3}. To achieve hydrophobic surface of ALD Al{sub 2}O{sub 3}, a methyl group (CH{sub 3})-terminated deposition method has been developed and compared with a hydroxyl group (OH)-terminated deposition. Based on this approach, bottom-gate coplanar graphene field-effect transistors are fabricated and characterized. A post-thermal annealing process improves the performance of the transistors by enhancing the contacts between the source/drain metal and graphene. The fabricated transistor shows an I{sub on}/I{sub off} ratio, maximum transconductance, and field-effect mobility of 4.04, 20.1 μS at V{sub D} = 0.1 V, and 249.5 cm{sup 2}/V·s, respectively.

  11. 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.

  12. The most stable mono-layers of (111)-Pt (fcc) on Graphene: A first-principles GGA study

    NASA Astrophysics Data System (ADS)

    Otalora-Acevedo, J.; Rodríguez Martínez, J. A.; Moreno-Armenta, G.; Vera, E.; Takeuchi Tan, N.

    2016-08-01

    We investigate monolayers of planes (111) of Pt in the FCC structure located on graphene. The energy of formation showed that the most stable structure is √3×√3 — Pt on 2 × 2 — graphene. This system has a mismatch in the lattice constant of 0.45. The layers are completely flat, and its band structure shows that the new structure is metallic and the Dirac's cones are displaced 0.6eV above of the Fermi level. In this work we present the dependence of the enthalpy of formation of these structures and we calculated all structural parameters of their relaxation.

  13. Few layers graphene as thermally activated optical modulator in the visible-near IR spectral range.

    PubMed

    Benítez, J L; Hernández-Cordero, Juan; Muhl, S; Mendoza, D

    2016-01-01

    We report the temperature modulation of the optical transmittance of a few layers of graphene (FLG). The FLG was heated either by the Joule effect of the current flowing between coplanar electrodes or by the absorption of a continuous-wave 532 nm laser. The optical signals used to evaluate the modulation of the FLG were at 633, 975, and 1550 nm; the last wavelengths are commonly used in optical communications. We also evaluated the effect of the substrate on the modulation effect by comparing the performance of a freely suspended FLG sample with one mounted on a glass substrate. Our results show that the modulation of the optical transmittance of FLG can be from millihertz to kilohertz. PMID:26696185

  14. Graphene oxide hole transport layers for large area, high efficiency organic solar cells

    SciTech Connect

    Smith, Chris T. G.; Rhodes, Rhys W.; Beliatis, Michail J.; Imalka Jayawardena, K. D. G.; Rozanski, Lynn J.; Mills, Christopher A.; Silva, S. Ravi P.

    2014-08-18

    Graphene oxide (GO) is becoming increasingly popular for organic electronic applications. We present large active area (0.64 cm{sup 2}), solution processable, poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1, 3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]:[6,6]-Phenyl C{sub 71} butyric acid methyl ester (PCDTBT:PC{sub 70}BM) organic photovoltaic (OPV) solar cells, incorporating GO hole transport layers (HTL). The power conversion efficiency (PCE) of ∼5% is the highest reported for OPV using this architecture. A comparative study of solution-processable devices has been undertaken to benchmark GO OPV performance with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) HTL devices, confirming the viability of GO devices, with comparable PCEs, suitable as high chemical and thermal stability replacements for PEDOT:PSS in OPV.

  15. Fabrication of nanoelectrode ensembles by electrodepositon of Au nanoparticles on single-layer graphene oxide sheets.

    PubMed

    Wang, Zhijuan; Zhang, Juan; Yin, Zongyou; Wu, Shixin; Mandler, Daniel; Zhang, Hua

    2012-04-21

    Nanoelectrode ensembles (NEEs) have been fabricated by the electrodeposition of Au nanoparticles (AuNPs) on single-layer graphene oxide (GO) sheets coated on a glassy carbon electrode (GCE). The fabricated NEEs show a typical sigmoidal shaped voltammetric profile, arising from the low coverage density of AuNPs on GCE and large distance among them, which can be easily controlled by varying the electrodeposition time. As a proof of concept, after the probe HS-DNA is immobilized on the NEEs through the Au-S bonding, the target DNA is detected with the methylene blue intercalator. Our results show that the target DNA can be detected as low as 100 fM, i.e. 0.5 amol DNA in 5 μL solution.

  16. Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

    PubMed Central

    Sun, Shuhui; Zhang, Gaixia; Gauquelin, Nicolas; Chen, Ning; Zhou, Jigang; Yang, Songlan; Chen, Weifeng; Meng, Xiangbo; Geng, Dongsheng; Banis, Mohammad N.; Li, Ruying; Ye, Siyu; Knights, Shanna; Botton, Gianluigi A.; Sham, Tsun-Kong; Sun, Xueliang

    2013-01-01

    Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

  17. Imprinted nonoxidized graphene sheets as an efficient hole transport layer in polymer light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Huang, Chun-Yuan; Peter Chen, I.-Wen; Chen, Chih-Jung; Chiang, Ray-Kuang; Vu, Hoang-Tuan

    2014-02-01

    Nonoxidized graphene sheets (NGSs) with single- and multilayered structures were generated by direct exfoliation of highly oriented pyrolytic graphite in a water-ethanol mixture with the assistances of pyridinium salt (Py+Br3-) and sonication. Raman spectrum exhibited a low intensity ratio (0.055) of D and G bands, indicating that the NGSs were nearly defect-free. Their application for the fabrication of polymer light-emitting diodes (PLEDs) was also demonstrated. The PLEDs that used an imprinted NGS film as a hole transport layer show a luminance exceeding 13000 cd/m2, which was comparable to that of devices using the typical hole transport material: poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid.

  18. Graphene oxide hole transport layers for large area, high efficiency organic solar cells

    NASA Astrophysics Data System (ADS)

    Smith, Chris T. G.; Rhodes, Rhys W.; Beliatis, Michail J.; Imalka Jayawardena, K. D. G.; Rozanski, Lynn J.; Mills, Christopher A.; P. Silva, S. Ravi

    2014-08-01

    Graphene oxide (GO) is becoming increasingly popular for organic electronic applications. We present large active area (0.64 cm2), solution processable, poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]:[6,6]-Phenyl C71 butyric acid methyl ester (PCDTBT:PC70BM) organic photovoltaic (OPV) solar cells, incorporating GO hole transport layers (HTL). The power conversion efficiency (PCE) of ˜5% is the highest reported for OPV using this architecture. A comparative study of solution-processable devices has been undertaken to benchmark GO OPV performance with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) HTL devices, confirming the viability of GO devices, with comparable PCEs, suitable as high chemical and thermal stability replacements for PEDOT:PSS in OPV.

  19. Nonlocal transient thermal analysis of a single-layered graphene sheet embedded in viscoelastic medium

    NASA Astrophysics Data System (ADS)

    Zenkour, Ashraf M.

    2016-05-01

    The transient thermal analysis of a single-layered graphene sheet (SLGS) embedded in viscoelastic medium is presented by using the nonlocal elasticity theory. The elastic medium, which characterized by the linear Winkler's modulus and Pasternak's (shear) foundation modulus, is changed to a viscoelastic one by including the viscous damping term. The governing dynamical equation is obtained and solved for simply-supported SLGSs. Firstly; the effect of the nonlocal parameter is discussed carefully for the vibration and bending problems. Secondly, the effects of other parameter like aspect ratio, thickness-to-length ratio, Winkler-Pasternak's foundation, viscous damping coefficient on bending field quantities of the SLGSs are investigated in detail. The present results are compared with the corresponding available in the literature. Additional results for thermal local and nonlocal deflections and stresses are presented to investigate the thermal visco-Pasternak's parameters for future comparisons.

  20. Field emission properties of hybrid few-layer graphene-carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Lei Qi, Jun; Zhang, Fu; Xia Zhang, Li; Cao, Jian; Cai Feng, Ji

    2014-04-01

    Few-layer graphene (FLG) and carbon nanotube (CNT) hybrid is prepared by in situ growth of FLG on the walls of CNTs, using PECVD, without catalyst. The amount and size of FLG can be controlled by total gas pressure and growth time. The field emission (FE) characteristics of CNTs coated with different-density FLG were studied, and an FE phenomenon schematic and electrostatic field equipotential model of these FLG-CNTs were proposed. These results show that the geometrical morphology of FLG plays an important role in the FE property of hybrid FLG-CNTs. The medium-density FLG on the CNTs exhibits excellent FE properties, with a low turn-on electric field and threshold field, as well as large field enhancement factor, which are much better than those of the as-grown CNTs. The excellent FE properties of the FLG-CNT hybrids make them promising candidates for high-performance FE emitters.