Science.gov

Sample records for aba-stacked trilayer graphene

  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. Optical conductivity of ABA stacked graphene trilayer: mid-IR resonance due to band nesting

    NASA Astrophysics Data System (ADS)

    Rashidian, Zeinab; Bludov, Yuliy V.; Ribeiro, Ricardo M.; Peres, N. M. R.; Vasilevskiy, Mikhail I.

    2014-10-01

    The band structure and the optical conductivity of an ABA (Bernal-type) stacked graphene trilayer are calculated. It is shown that, under appropriate doping, a strong resonant peak develops in the optical conductivity, located at the frequency corresponding to approximately 1.4 times the interlayer hopping energy and caused by the ‘nesting’ of two nearly parabolic bands in the electronic spectrum. The intensity of this resonant absorption can be controlled by adjusting the gate voltage. The effect is robust with respect to increasing temperature.

  3. Optical absorption in trilayer graphene

    NASA Astrophysics Data System (ADS)

    Li, Xiao; Zhang, Fan; Niu, Qian

    2013-03-01

    We use a low energy effective model to analyze the optical responses of trilayer graphene samples. We first show that optical absorption of the ABA-stacked trilayer has strong dependence on both the Fermi energy and optical frequency, which is in sharp contrast to that of ABC-stacked trilayer graphene. Secondly, we are able to determine the possible existence of trigonal warping effects in the bandstructure of ABC-stacked trilayer graphene by a divergence in the absorption spectra at around 10 meV. In addition, we can partially distinguish the vairious broken symmetry states driven by electron-electron interactions in ABC-stacked trilayer graphene. In particular, the quantum anomalous Hall (QAH) state is sensitive to the polarization of the incident light, giving a way to detect its possible existence.

  4. Electronic spectrum of trilayer graphene

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Ajay

    2014-08-01

    Present work deals with the analysis of the single particle electronic spectral function in trilayer (ABC-, ABA- and AAA-stacked) graphene. Tight binding Hamiltonian containing intralayer nearest-neighbor and next-nearest neighbor hopping along-with the interlayer coupling parameter within two triangular sub-lattice approach for trilayer graphene has been employed. The expression of single particle spectral functions A(kw) is obtained within mean-field Green's function equations of motion approach. Spectral function at Γ, M and K points of the Brillouin zone has been numerically computed. It is pointed out that the nature of electronic states at different points of Brillouin zone is found to be influenced by stacking order and Coulomb interactions. At Γ and M points, a trilayer splitting is predicted while at K point a bilayer splitting effect is observed due to crossing of two bands (at K point). Interlayer coupling ( t_{ bot } ) is found to be responsible for the splitting of quasi-particle peaks at each point of Brillouin zone. The influence of t_{ bot } in trilayer graphene is prominent for AAA-stacking compared to ABC- and ABA-stacking. On the other hand, onsite Coulomb interaction reduces the trilayer splitting effect into bilayer splitting at Γ and M points of Brillouin zone and bilayer splitting into single peak spectral function at K point with a shifting of the peak away from Fermi level.

  5. Electronic structure and quantum transport properties of trilayers formed from graphene and boron nitride.

    PubMed

    Zhong, Xiaoliang; Amorim, Rodrigo G; Scheicher, Ralph H; Pandey, Ravindra; Karna, Shashi P

    2012-09-07

    We report the results of a theoretical study of graphene/BN/graphene and BN/graphene/BN trilayers using the van-der-Waals-corrected density functional theory in conjunction with the non-equilibrium Green's Function method. These trilayer systems formed from graphene and BN exhibit distinct stacking-dependent features in their ground state electronic structure and response to an applied electric field perpendicular to the trilayer planes. The graphene/BN/graphene system shows a negligible gap in the electronic band structure that increases for the AAA and ABA stackings under an external electric field, while the zero-field band gap of BN/graphene/BN remains unaffected by the electric field. When both types of trilayer systems are contacted with gold electrodes, a metal-like conduction is predicted in the low-field regime, which changes to a p-type conduction with an increase in the applied perpendicular bias field.

  6. Magneto-optical properties of ABC-stacked trilayer graphene.

    PubMed

    Lin, Yi-Ping; Lin, Chiun-Yan; Ho, Yen-Hung; Do, Thi-Nga; Lin, Ming-Fa

    2015-06-28

    The generalized tight-binding model is developed to investigate the magneto-optical absorption spectra of ABC-stacked trilayer graphene. The absorption peaks can be classified into nine categories of inter-Landau-level optical excitations, including three intra-group and six inter-group ones. Most of them belong to the twin-peak structures because of the asymmetric Landau level spectrum. The threshold absorption peak alone comes from a certain excitation channel, and its frequency is associated with a specific interlayer atomic interaction. The Landau-level anticrossings cause extra absorption peaks. Moreover, a simple relationship between the absorption frequency and the field strength is absent. The magneto-optical properties of ABC-stacked trilayer graphene are totally different from those of AAA- and ABA-stacked ones, such as the number, intensity and frequency of absorption peaks.

  7. First-principles studies of electric field effects on the electronic structure of trilayer graphene

    NASA Astrophysics Data System (ADS)

    Wang, Yun-Peng; Li, Xiang-Guo; Fry, James N.; Cheng, Hai-Ping

    2016-10-01

    A gate electric field is a powerful way to manipulate the physical properties of nanojunctions made of two-dimensional crystals. To simulate field effects on the electronic structure of trilayer graphene, we used density functional theory in combination with the effective screening medium method, which enables us to understand the field-dependent layer-layer interactions and the fundamental physics underlying band gap variations and the resulting band modifications. Two different graphene stacking orders, Bernal (or ABC) and rhombohedral (or ABA), were considered. In addition to confirming the experimentally observed band gap opening in ABC-stacked and the band overlap in ABA-stacked trilayer systems, our results reveal rich physics in these fascinating systems, where layer-layer couplings are present but some characteristics features of single-layer graphene are partially preserved. For ABC stacking, the electric-field-induced band gap size can be tuned by charge doping, while for ABA band the tunable quantity is the band overlap. Our calculations show that the electronic structures of the two stacking orders respond very differently to charge doping. We find that in the ABA stacking hole doping can reopen a band gap in the band-overlapping region, a phenomenon distinctly different from electron doping. The physical origins of the observed behaviors were fully analyzed, and we conclude that the dual-gate configuration greatly enhances the tunability of the trilayer systems.

  8. Stacking-dependent electronic property of trilayer graphene epitaxially grown on Ru(0001)

    SciTech Connect

    Que, Yande; Xiao, Wende E-mail: hjgao@iphy.ac.cn; Chen, Hui; Wang, Dongfei; Du, Shixuan; Gao, Hong-Jun E-mail: hjgao@iphy.ac.cn

    2015-12-28

    The growth, atomic structure, and electronic property of trilayer graphene (TLG) on Ru(0001) were studied by low temperature scanning tunneling microscopy and spectroscopy in combined with tight-binding approximation (TBA) calculations. TLG on Ru(0001) shows a flat surface with a hexagonal lattice due to the screening effect of the bottom two layers and the AB-stacking in the top two layers. The coexistence of AA- and AB-stacking in the bottom two layers leads to three different stacking orders of TLG, namely, ABA-, ABC-, and ABB-stacking. STS measurements combined with TBA calculations reveal that the density of states of TLG with ABC- and ABB-stacking is characterized by one and two sharp peaks near to the Fermi level, respectively, in contrast to the V-shaped feature of TLG with ABA-stacking. Our work demonstrates that TLG on Ru(0001) might be an ideal platform for exploring stacking-dependent electronic properties of graphene.

  9. Edge magnetization in Bernal-stacked trilayer zigzag graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Pérez, Juan Antonio Casao

    2016-06-01

    We have used a tight-binding Hamiltonian of an ABA-stacked trilayer zigzag graphene nanoribbon with β-alignment edges to study the edge magnetizations. Our model includes the effect of the intralayer next-nearest-neighbor hopping, the interlayer hopping responsible for the trigonal warping and the interaction between electrons, which is considered by a single band Hubbard model in the mean field approximation. Firstly, in the neutral system we analyzed the two magnetic states in which both edge magnetizations reach their maximum value; the first one is characterized by an intralayer ferromagnetic coupling between the magnetizations at opposite edges, whereas in the second state that coupling is antiferromagnetic. The band structure, the location of the edge-state bands and the local density of states resolved in spin are calculated in order to understand the origins of the edge magnetizations. We have also introduced an electron doping so that the number of electrons in the ribbon unit cell is higher than in neutral case. As a consequence, we have obtained magnetization steps and charge accumulation at the edges of the sample, which are caused by the edge-state flat bands.

  10. Transport in bilayer and trilayer graphene: band gap engineering and band structure tuning

    NASA Astrophysics Data System (ADS)

    Zhu, Jun

    2014-03-01

    Controlling the stacking order of atomically thin 2D materials offers a powerful tool to control their properties. Linearly dispersed bands become hyperbolic in Bernal (AB) stacked bilayer graphene (BLG). Both Bernal (ABA) and rhombohedral (ABC) stacking occur in trilayer graphene (TLG), producing distinct band structures and electronic properties. A symmetry-breaking electric field perpendicular to the sample plane can further modify the band structures of BLG and TLG. In this talk, I will describe our experimental effort in these directions using dual-gated devices. Using thin HfO2 film deposited by ALD as gate dielectric, we are able to apply large displacement fields D > 6 V/nm and observe the opening and saturation of the field-induced band gap Eg in bilayer and ABC-stacked trilayer graphene, where the conduction in the mid gap changes by more than six decades. Its field and temperature dependence highlights the crucial role played by Coulomb disorder in facilitating hopping conduction and suppressing the effect of Eg in the tens of meV regime. In contrast, mid-gap conduction decreases with increasing D much more rapidly in clean h-BN dual-gated devices. Our studies also show the evolution of the band structure in ABA-stacked TLG, in particular the splitting of the Dirac-like bands in large D field and the signatures of two-band transport at high carrier densities. Comparison to theory reveals the need for more sophisticated treatment of electronic screening beyond self-consistent Hartree calculations to accurately predict the band structures of trilayer graphene and graphenic materials in general.

  11. Integer Quantum Hall Effect in Trilayer Graphene

    NASA Astrophysics Data System (ADS)

    Kumar, A.; Escoffier, W.; Poumirol, J. M.; Faugeras, C.; Arovas, D. P.; Fogler, M. M.; Guinea, F.; Roche, S.; Goiran, M.; Raquet, B.

    2011-09-01

    By using high-magnetic fields (up to 60 T), we observe compelling evidence of the integer quantum Hall effect in trilayer graphene. The magnetotransport fingerprints are similar to those of the graphene monolayer, except for the absence of a plateau at a filling factor of ν=2. At a very low filling factor, the Hall resistance vanishes due to the presence of mixed electron and hole carriers induced by disorder. The measured Hall resistivity plateaus are well reproduced theoretically, using a self-consistent Hartree calculations of the Landau levels and assuming an ABC stacking order of the three layers.

  12. Magnetic oscillation of optical phonon in ABA- and ABC-stacked trilayer graphene

    NASA Astrophysics Data System (ADS)

    Cong, Chunxiao; Jung, Jeil; Cao, Bingchen; Qiu, Caiyu; Shen, Xiaonan; Ferreira, Aires; Adam, Shaffique; Yu, Ting

    2015-06-01

    We present a comparative measurement of the G -peak oscillations of phonon frequency, Raman intensity, and linewidth in the magneto-Raman scattering of optical E2 g phonons in mechanically exfoliated ABA- and ABC-stacked trilayer graphene (TLG). Whereas in ABA-stacked TLG, we observe magnetophonon oscillations consistent with single-bilayer chiral band doublets, the features are flat for ABC-stacked TLG up to magnetic fields of 9 T. This suppression can be attributed to the enhancement of band chirality that compactifies the spectrum of Landau levels and modifies the magnetophonon resonance properties. The drastically different coupling behavior between the electronic excitations and the E2 g phonons in ABA- and ABC-stacked TLG reflects their different electronic band structures and the electronic Landau level transitions and thus can be another way to determine the stacking orders and to probe the stacking-order-dependent electronic structures. In addition, the sensitivity of the magneto-Raman scattering to the particular stacking order in few-layer graphene highlights the important role of interlayer coupling in modifying the optical response properties in van der Waals layered materials.

  13. Atomic and electronic structure of trilayer graphene/SiC(0001): Evidence of Strong Dependence on Stacking Sequence and charge transfer

    NASA Astrophysics Data System (ADS)

    Pierucci, Debora; Brumme, Thomas; Girard, Jean-Christophe; Calandra, Matteo; Silly, Mathieu G.; Sirotti, Fausto; Barbier, Antoine; Mauri, Francesco; Ouerghi, Abdelkarim

    2016-09-01

    The transport properties of few-layer graphene are the directly result of a peculiar band structure near the Dirac point. Here, for epitaxial graphene grown on SiC, we determine the effect of charge transfer from the SiC substrate on the local density of states (LDOS) of trilayer graphene using scaning tunneling microscopy/spectroscopy and angle resolved photoemission spectroscopy (ARPES). Different spectra are observed and are attributed to the existence of two stable polytypes of trilayer: Bernal (ABA) and rhomboedreal (ABC) staking. Their electronic properties strongly depend on the charge transfer from the substrate. We show that the LDOS of ABC stacking shows an additional peak located above the Dirac point in comparison with the LDOS of ABA stacking. The observed LDOS features, reflecting the underlying symmetry of the two polytypes, were reproduced by explicit calculations within density functional theory (DFT) including the charge transfer from the substrate. These findings demonstrate the pronounced effect of stacking order and charge transfer on the electronic structure of trilayer or few layer graphene. Our approach represents a significant step toward understand the electronic properties of graphene layer under electrical field.

  14. Atomic and electronic structure of trilayer graphene/SiC(0001): Evidence of Strong Dependence on Stacking Sequence and charge transfer

    PubMed Central

    Pierucci, Debora; Brumme, Thomas; Girard, Jean-Christophe; Calandra, Matteo; Silly, Mathieu G.; Sirotti, Fausto; Barbier, Antoine; Mauri, Francesco; Ouerghi, Abdelkarim

    2016-01-01

    The transport properties of few-layer graphene are the directly result of a peculiar band structure near the Dirac point. Here, for epitaxial graphene grown on SiC, we determine the effect of charge transfer from the SiC substrate on the local density of states (LDOS) of trilayer graphene using scaning tunneling microscopy/spectroscopy and angle resolved photoemission spectroscopy (ARPES). Different spectra are observed and are attributed to the existence of two stable polytypes of trilayer: Bernal (ABA) and rhomboedreal (ABC) staking. Their electronic properties strongly depend on the charge transfer from the substrate. We show that the LDOS of ABC stacking shows an additional peak located above the Dirac point in comparison with the LDOS of ABA stacking. The observed LDOS features, reflecting the underlying symmetry of the two polytypes, were reproduced by explicit calculations within density functional theory (DFT) including the charge transfer from the substrate. These findings demonstrate the pronounced effect of stacking order and charge transfer on the electronic structure of trilayer or few layer graphene. Our approach represents a significant step toward understand the electronic properties of graphene layer under electrical field. PMID:27629702

  15. Embedded trilayer graphene flakes under tensile and compressive loading

    NASA Astrophysics Data System (ADS)

    Tsoukleri, G.; Parthenios, J.; Galiotis, C.; Papagelis, K.

    2015-06-01

    The mechanical response of embedded ABA trilayer graphene flakes loaded in tension and compression on polymer beams is monitored by simultaneous Raman measurements through the strain sensitivity of the G or 2D peaks. A characteristic peculiarity of the investigated flake is that it contains a trilayer and bilayer part. The Bernal stacked bilayer was used as a strain sensor aiming to assess the efficiency of the load transfer from the polymer matrix through shear to the individual graphene layers. For the trilayer graphene in tension, both peaks are redshifted and splitting of the G peak is reported for the first time. In compression, the studied sample was an almost isolated trilayer, in which both peaks are blue-shifted up to a critical compressive strain. This critical strain is found to be one fourth of the value found in the case of single layer graphene despite the higher bending rigidity that trilayer exhibits over the much thinner monolayer.

  16. Field-induced stacking transition of biofunctionalized trilayer graphene

    NASA Astrophysics Data System (ADS)

    Masato Nakano, C.; Sajib, Md Symon Jahan; Samieegohar, Mohammadreza; Wei, Tao

    2016-02-01

    Trilayer graphene (TLG) is attracting a lot of attention as their stacking structures (i.e., rhombohedral vs. Bernal) drastically affect electronic and optical properties. Based on full-atom molecular dynamics simulations, we here predict electric field-induced rhombohedral-to-Bernal transition of TLG tethered with proteins. Furthermore, our simulations show that protein's electrophoretic mobility and diffusivity are enhanced on TLG surface. This phenomenon of controllable TLG stacking transition will contribute to various applications including biosensing.

  17. Interfacial Properties of Bilayer and Trilayer Graphene on Metal Substrates

    PubMed Central

    Zheng, Jiaxin; Wang, Yangyang; Wang, Lu; Quhe, Ruge; Ni, Zeyuan; Mei, Wai-Ning; Gao, Zhengxiang; Yu, Dapeng; Shi, Junjie; Lu, Jing

    2013-01-01

    One popular approach to prepare graphene is to grow them on transition metal substrates via chemical vapor deposition. By using the density functional theory with dispersion correction, we systematically investigate for the first time the interfacial properties of bilayer (BLG) and trilayer graphene (TLG) on metal substrates. Three categories of interfacial structures are revealed. The adsorption of B(T)LG on Al, Ag, Cu, Au, and Pt substrates is a weak physisorption, but a band gap can be opened. The adsorption of B(T)LG on Ti, Ni, and Co substrates is a strong chemisorption, and a stacking-insensitive band gap is opened for the two uncontacted layers of TLG. The adsorption of B(T)LG on Pd substrate is a weaker chemisorption, with a band gap opened for the uncontacted layers. This fundamental study also helps for B(T)LG device study due to inevitable graphene/metal contact. PMID:23803738

  18. Flower-Shaped Domains and Wrinkles in Trilayer Epitaxial Graphene on Silicon Carbide

    PubMed Central

    Lalmi, B.; Girard, J. C.; Pallecchi, E.; Silly, M.; David, C.; Latil, S.; Sirotti, F.; Ouerghi, A.

    2014-01-01

    Trilayer graphene is of particular interest to the 2D materials community because of its unique tunable electronic structure. However, to date, there is a lack of fundamental understanding of the properties of epitaxial trilayer graphene on silicon carbide. Here, following successful synthesis of large-area uniform trilayer graphene, atomic force microscopy (AFM) showed that the trilayer graphene on 6H-SiC(0001) was uniform over a large scale. Additionally, distinct defects, identified as flower-shaped domains and isolated wrinkle structures, were observed randomly on the surface using scanning tunneling microscopy and spectroscopy (STM/STS). These carbon nanostructures formed during growth, has different structural and electronic properties when compared with the adjacent flat regions of the graphene. Finally, using low temperature STM/STS at 4K, we found that the isolated wrinkles showed an irreversible rotational motion between two 60° configurations at different densities of states. PMID:24513669

  19. Stacking-Dependent Electronic Structure of Trilayer Graphene Resolved by Nanospot Angle-Resolved Photoemission Spectroscopy.

    PubMed

    Bao, Changhua; Yao, Wei; Wang, Eryin; Chen, Chaoyu; Avila, José; Asensio, Maria C; Zhou, Shuyun

    2017-03-08

    The crystallographic stacking order in multilayer graphene plays an important role in determining its electronic structure. In trilayer graphene, rhombohedral stacking (ABC) is particularly intriguing, exhibiting a flat band with an electric-field tunable band gap. Such electronic structure is distinct from simple hexagonal stacking (AAA) or typical Bernal stacking (ABA) and is promising for nanoscale electronics and optoelectronics applications. So far clean experimental electronic spectra on the first two stackings are missing because the samples are usually too small in size (μm or nm scale) to be resolved by conventional angle-resolved photoemission spectroscopy (ARPES). Here, by using ARPES with a nanospot beam size (NanoARPES), we provide direct experimental evidence for the coexistence of three different stackings of trilayer graphene and reveal their distinctive electronic structures directly. By fitting the experimental data, we provide important experimental band parameters for describing the electronic structure of trilayer graphene with different stackings.

  20. First-principles studies of the electric-field effect on the band structure of trilayer graphenes

    NASA Astrophysics Data System (ADS)

    Wang, Yun-Peng; Li, Xiang-Guo; Cheng, Hai-Ping

    Electric-field effects on the electronic structure of trilayer graphene are investigated using the density functional theory in the generalized gradient approximation. Two different stacking orders, namely Bernal and rhombohedral, of trilayer graphene are considered. Our calculations reproduce the experimentally data on band gap opening in Bernal stacking and band overlap in rhombohedral trilayer graphene. In addition, we studied effects of charge doping using dual gate configurations. The size of band gap opening in Bernal trilayer graphene can be tuned by charge doping, and charge doping also causes an electron-hole asymmetry in the density of states. Furthermore, hole-doping can reopen a band gap in the band overlapping region of rhombohedral trilayer grapheme induced by electric fields, which contributes to an extra peak in the optical conductivity spectra. This work is supported by DOE # DE-FG02-02ER45995.

  1. High Electron Mobility in Epitaxial Trilayer Graphene on Off-axis SiC(0001).

    PubMed

    Hajlaoui, Mahdi; Sediri, Haikel; Pierucci, Debora; Henck, Hugo; Phuphachong, Thanyanan; Silly, Mathieu G; de Vaulchier, Louis-Anne; Sirotti, Fausto; Guldner, Yves; Belkhou, Rachid; Ouerghi, Abdelkarim

    2016-01-07

    The van de Waals heterostructure formed by an epitaxial trilayer graphene is of particular interest due to its unique tunable electronic band structure and stacking sequence. However, to date, there has been a lack in the fundamental understanding of the electronic properties of epitaxial trilayer graphene. Here, we investigate the electronic properties of large-area epitaxial trilayer graphene on a 4° off-axis SiC(0001) substrate. Micro-Raman mappings and atomic force microscopy (AFM) confirmed predominantly trilayer on the sample obtained under optimized conditions. We used angle-resolved photoemission spectroscopy (ARPES) and Density Functional Theory (DFT) calculations to study in detail the structure of valence electronic states, in particular the dispersion of π bands in reciprocal space and the exact determination of the number of graphene layers. Using far-infrared magneto-transmission (FIR-MT), we demonstrate, that the electron cyclotron resonance (CR) occurs between Landau levels with a (B)(1/2) dependence. The CR line-width is consistent with a high Dirac fermions mobility of ~3000 cm(2)·V(-1)·s(-1) at 4 K.

  2. High Electron Mobility in Epitaxial Trilayer Graphene on Off-axis SiC(0001)

    PubMed Central

    Hajlaoui, Mahdi; Sediri, Haikel; Pierucci, Debora; Henck, Hugo; Phuphachong, Thanyanan; Silly, Mathieu G.; de Vaulchier, Louis-Anne; Sirotti, Fausto; Guldner, Yves; Belkhou, Rachid; Ouerghi, Abdelkarim

    2016-01-01

    The van de Waals heterostructure formed by an epitaxial trilayer graphene is of particular interest due to its unique tunable electronic band structure and stacking sequence. However, to date, there has been a lack in the fundamental understanding of the electronic properties of epitaxial trilayer graphene. Here, we investigate the electronic properties of large-area epitaxial trilayer graphene on a 4° off-axis SiC(0001) substrate. Micro-Raman mappings and atomic force microscopy (AFM) confirmed predominantly trilayer on the sample obtained under optimized conditions. We used angle-resolved photoemission spectroscopy (ARPES) and Density Functional Theory (DFT) calculations to study in detail the structure of valence electronic states, in particular the dispersion of π bands in reciprocal space and the exact determination of the number of graphene layers. Using far-infrared magneto-transmission (FIR-MT), we demonstrate, that the electron cyclotron resonance (CR) occurs between Landau levels with a (B)1/2 dependence. The CR line-width is consistent with a high Dirac fermions mobility of ~3000 cm2·V−1·s−1 at 4 K. PMID:26739366

  3. Strong electronic interaction and multiple quantum Hall ferromagnetic phases in trilayer graphene

    NASA Astrophysics Data System (ADS)

    Datta, Biswajit; Dey, Santanu; Samanta, Abhisek; Agarwal, Hitesh; Borah, Abhinandan; Watanabe, Kenji; Taniguchi, Takashi; Sensarma, Rajdeep; Deshmukh, Mandar M.

    2017-02-01

    Quantum Hall effect provides a simple way to study the competition between single particle physics and electronic interaction. However, electronic interaction becomes important only in very clean graphene samples and so far the trilayer graphene experiments are understood within non-interacting electron picture. Here, we report evidence of strong electronic interactions and quantum Hall ferromagnetism seen in Bernal-stacked trilayer graphene. Due to high mobility ~500,000 cm2 V-1 s-1 in our device compared to previous studies, we find all symmetry broken states and that Landau-level gaps are enhanced by interactions; an aspect explained by our self-consistent Hartree-Fock calculations. Moreover, we observe hysteresis as a function of filling factor and spikes in the longitudinal resistance which, together, signal the formation of quantum Hall ferromagnetic states at low magnetic field.

  4. Strong electronic interaction and multiple quantum Hall ferromagnetic phases in trilayer graphene.

    PubMed

    Datta, Biswajit; Dey, Santanu; Samanta, Abhisek; Agarwal, Hitesh; Borah, Abhinandan; Watanabe, Kenji; Taniguchi, Takashi; Sensarma, Rajdeep; Deshmukh, Mandar M

    2017-02-20

    Quantum Hall effect provides a simple way to study the competition between single particle physics and electronic interaction. However, electronic interaction becomes important only in very clean graphene samples and so far the trilayer graphene experiments are understood within non-interacting electron picture. Here, we report evidence of strong electronic interactions and quantum Hall ferromagnetism seen in Bernal-stacked trilayer graphene. Due to high mobility ∼500,000 cm(2 )V(-1 )s(-1) in our device compared to previous studies, we find all symmetry broken states and that Landau-level gaps are enhanced by interactions; an aspect explained by our self-consistent Hartree-Fock calculations. Moreover, we observe hysteresis as a function of filling factor and spikes in the longitudinal resistance which, together, signal the formation of quantum Hall ferromagnetic states at low magnetic field.

  5. Strong electronic interaction and multiple quantum Hall ferromagnetic phases in trilayer graphene

    PubMed Central

    Datta, Biswajit; Dey, Santanu; Samanta, Abhisek; Agarwal, Hitesh; Borah, Abhinandan; Watanabe, Kenji; Taniguchi, Takashi; Sensarma, Rajdeep; Deshmukh, Mandar M.

    2017-01-01

    Quantum Hall effect provides a simple way to study the competition between single particle physics and electronic interaction. However, electronic interaction becomes important only in very clean graphene samples and so far the trilayer graphene experiments are understood within non-interacting electron picture. Here, we report evidence of strong electronic interactions and quantum Hall ferromagnetism seen in Bernal-stacked trilayer graphene. Due to high mobility ∼500,000 cm2 V−1 s−1 in our device compared to previous studies, we find all symmetry broken states and that Landau-level gaps are enhanced by interactions; an aspect explained by our self-consistent Hartree–Fock calculations. Moreover, we observe hysteresis as a function of filling factor and spikes in the longitudinal resistance which, together, signal the formation of quantum Hall ferromagnetic states at low magnetic field. PMID:28216666

  6. Analytical modeling of trilayer graphene nanoribbon Schottky-barrier FET for high-speed switching applications.

    PubMed

    Rahmani, Meisam; Ahmadi, Mohammad Taghi; Abadi, Hediyeh Karimi Feiz; Saeidmanesh, Mehdi; Akbari, Elnaz; Ismail, Razali

    2013-01-30

    Recent development of trilayer graphene nanoribbon Schottky-barrier field-effect transistors (FETs) will be governed by transistor electrostatics and quantum effects that impose scaling limits like those of Si metal-oxide-semiconductor field-effect transistors. The current-voltage characteristic of a Schottky-barrier FET has been studied as a function of physical parameters such as effective mass, graphene nanoribbon length, gate insulator thickness, and electrical parameters such as Schottky barrier height and applied bias voltage. In this paper, the scaling behaviors of a Schottky-barrier FET using trilayer graphene nanoribbon are studied and analytically modeled. A novel analytical method is also presented for describing a switch in a Schottky-contact double-gate trilayer graphene nanoribbon FET. In the proposed model, different stacking arrangements of trilayer graphene nanoribbon are assumed as metal and semiconductor contacts to form a Schottky transistor. Based on this assumption, an analytical model and numerical solution of the junction current-voltage are presented in which the applied bias voltage and channel length dependence characteristics are highlighted. The model is then compared with other types of transistors. The developed model can assist in comprehending experiments involving graphene nanoribbon Schottky-barrier FETs. It is demonstrated that the proposed structure exhibits negligible short-channel effects, an improved on-current, realistic threshold voltage, and opposite subthreshold slope and meets the International Technology Roadmap for Semiconductors near-term guidelines. Finally, the results showed that there is a fast transient between on-off states. In other words, the suggested model can be used as a high-speed switch where the value of subthreshold slope is small and thus leads to less power consumption.

  7. Trilayer graphene is a semimetal with a gate-tunable band overlap.

    PubMed

    Craciun, M F; Russo, S; Yamamoto, M; Oostinga, J B; Morpurgo, A F; Tarucha, S

    2009-06-01

    Graphene-based materials are promising candidates for nanoelectronic devices because very high carrier mobilities can be achieved without the use of sophisticated material preparation techniques. However, the carrier mobilities reported for single-layer and bilayer graphene are still less than those reported for graphite crystals at low temperatures, and the optimum number of graphene layers for any given application is currently unclear, because the charge transport properties of samples containing three or more graphene layers have not yet been investigated systematically. Here, we study charge transport through trilayer graphene as a function of carrier density, temperature, and perpendicular electric field. We find that trilayer graphene is a semimetal with a resistivity that decreases with increasing electric field, a behaviour that is markedly different from that of single-layer and bilayer graphene. We show that the phenomenon originates from an overlap between the conduction and valence bands that can be controlled by an electric field, a property that had never previously been observed in any other semimetal. We also determine the effective mass of the charge carriers, and show that it accounts for a large part of the variation in the carrier mobility as the number of layers in the sample is varied.

  8. 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.

  9. 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.

  10. Landau quantization in graphene monolayer, Bernal bilayer, and Bernal trilayer on graphite surface

    NASA Astrophysics Data System (ADS)

    Yin, Long-Jing; Li, Si-Yu; Qiao, Jia-Bin; Nie, Jia-Cai; He, Lin

    2015-03-01

    Electronic properties of surface areas decoupled from graphite are studied using scanning tunneling microscopy and spectroscopy. We show that it is possible to identify the decoupled graphene monolayer, the Bernal bilayer, and the Bernal trilayer on a graphite substrate according to their tunneling spectra in a high magnetic field. The decoupled monolayer and bilayer exhibit Landau quantization of massless and massive Dirac fermions, respectively. The substrate generates a sizable band gap ˜35 meV in the Bernal bilayer, therefore, the eightfold degenerate Landau level at the charge neutrality point is split into two valley-polarized quartets polarized on each layer. In the decoupled Bernal trilayer, we find that both massless and massive Dirac fermions coexist and its low-energy band structure can be described quite well by taking into account only the nearest-neighbor intra- and interlayer hopping parameters. A strong correlation between the Fermi velocity of the massless Dirac fermions and the effective mass of the massive Dirac fermions is observed in the graphene trilayer. Our result demonstrates that the surface of graphite provides a natural ideal platform to probe the electronic spectra of graphene layers.

  11. Electric field control of soliton motion and stacking in trilayer graphene

    NASA Astrophysics Data System (ADS)

    Yankowitz, Matthew; Wang, Joel I.-Jan; Birdwell, A. Glen; Chen, Yu-An; Watanabe, K.; Taniguchi, T.; Jacquod, Philippe; San-Jose, Pablo; Jarillo-Herrero, Pablo; Leroy, Brian J.

    2014-08-01

    The crystal structure of a material plays an important role in determining its electronic properties. Changing from one crystal structure to another involves a phase transition that is usually controlled by a state variable such as temperature or pressure. In the case of trilayer graphene, there are two common stacking configurations (Bernal and rhombohedral) that exhibit very different electronic properties. In graphene flakes with both stacking configurations, the region between them consists of a localized strain soliton where the carbon atoms of one graphene layer shift by the carbon-carbon bond distance. Here we show the ability to move this strain soliton with a perpendicular electric field and hence control the stacking configuration of trilayer graphene with only an external voltage. Moreover, we find that the free-energy difference between the two stacking configurations scales quadratically with electric field, and thus rhombohedral stacking is favoured as the electric field increases. This ability to control the stacking order in graphene opens the way to new devices that combine structural and electrical properties.

  12. Stacking order dependent mechanical properties of graphene/MoS{sub 2} bilayer and trilayer heterostructures

    SciTech Connect

    Elder, Robert M. E-mail: mahesh.neupane.ctr@mail.mil; Neupane, Mahesh R. E-mail: mahesh.neupane.ctr@mail.mil; Chantawansri, Tanya L.

    2015-08-17

    Transition metal dichalcogenides (TMDC) such as molybdenum disulfide (MoS{sub 2}) are two-dimensional materials that show promise for flexible electronics and piezoelectric applications, but their weak mechanical strength is a barrier to practical use. In this work, we perform nanoindentation simulations using atomistic molecular dynamics to study the mechanical properties of heterostructures formed by combining MoS{sub 2} with graphene. We consider both bi- and tri-layer heterostructures formed with MoS{sub 2} either supported or encapsulated by graphene. Mechanical properties, such as Young's modulus, bending modulus, ultimate tensile strength, and fracture strain, are extracted from nanoindentation simulations and compared to the monolayer and homogeneous bilayer systems. We observed that the heterostructures, regardless of the stacking order, are mechanically more robust than the mono- and bi-layer MoS{sub 2}, mainly due to the mechanical reinforcement provided by the graphene layer. The magnitudes of ultimate strength and fracture strain are similar for both the bi- and tri-layer heterostructures, but substantially larger than either the mono- and bi-layer MoS{sub 2}. Our results demonstrate the potential of graphene-based heterostructures to improve the mechanical properties of TMDC materials.

  13. In-plane chiral tunneling and out-of-plane valley-polarized quantum tunneling in twisted graphene trilayer

    NASA Astrophysics Data System (ADS)

    Qiao, Jia-Bin; He, Lin

    2014-08-01

    Here we show that a twisted graphene trilayer made by misoriented stacking of a graphene monolayer on top of a Bernal graphene bilayer can exhibit rich and tailored electronic properties. For the case that the graphene monolayer and bilayer are strongly coupled, both the massless Dirac fermions and massive chiral fermions coexist in the twisted trilayer, leading to unique in-plane chiral tunneling. For a weak coupling between the two graphene systems, the distinct chiralities and pseudospin textures of quasiparticles in monolayer and bilayer enable vertical valley-polarized quantum tunneling between them. Intriguingly, the polarity of the valley polarization can be inverted simply by either controlling the rotational angles between the two systems or tuning the Fermi levels of the two systems. Our result implies that layered van der Waals structures assembled from individual atomic planes can create materials that harbor unusual properties and alternative functionalities depending on the stacking configuration of the crystalline layers.

  14. Structure stability and high-temperature distortion resistance of trilayer complexes formed from graphenes and boron nitride nanosheets.

    PubMed

    Yuan, Jianhui; Liew, K M

    2014-01-07

    The molecular dynamics was employed to study the structure stability and high-temperature distortion resistance of a trilayer complex formed by a monolayer graphene sandwiched in bilayer boron nitride nanosheets (BN-G-BN) and graphenes (G-G-G). The investigation shows that the optimal interlayer distances are about 0.347 nm for BN-G-BN and 0.341 nm for G-G-G. Analysis and comparison of the binding energy, van der Waals interactions between layers and radial distribution function (RDF) revealed that the BN-G-BN achieves a more stable combined structure than G-G-G. The interlayer graphene in the trilayer complex nanosheets, especially the graphene in BN-G-BN, is more integrated than monolayer graphenes in a crystal structure. The structures at high temperature of 1500 K show that the BN-G-BN exhibits less distortion than G-G-G; especially, fixing the atomic positions on up-down layers can obviously further reduce structural deformation of interlayer graphene. The result further indicates that the high-temperature distortion resistance of interlayer graphene in the trilayer complex is related to both material type and conditions of constraints at the up-down layers.

  15. Bound state properties of ABC-stacked trilayer graphene quantum dots.

    PubMed

    Xiong, Haonan; Jiang, Wentao; Song, Yipu; Duan, Luming

    2017-04-03

    The few-layer graphene quantum dot provides a promising platform for quantum computing with both spin and valley degrees of freedom. Gate-defined quantum dots in particular can avoid noise from edge disorders. In connection with the recent experimental efforts [Y. Song et al., Nano Lett. 16, 6245 (2016)], we investigate the bound state properties of trilayer graphene (TLG) quantum dots (QDs) through numerical simulations. We show that the valley degeneracy can be lifted by breaking the time reversal symmetry through the application of a perpendicular magnetic field. The spectrum under such a potential exhibits a transition from one group of Landau levels to the other group, which can be understood analytically through perturbation theory. Our results provide insight to the transport property of TLG QDs, with possible applications to study of spin qubits and valleytronics in TLG QDs.

  16. Optical study of nonuniform quantum-Hall ferromagnetic states in bilayer and trilayer graphene

    NASA Astrophysics Data System (ADS)

    Barrette, Manuel; Côté, René

    2015-03-01

    The chiral two-dimensional electron gas in the N = 0 Landau level of a Bernal-stacked bilayer graphene is host to a variety of broken-symmetry ground states that can be described as layer, spin, or orbital quantum Hall ferromagnets (QHFs). At filling factors ν = 1 , 3 , an externally applied electric field between the two layers can induce a transition from uniform to nonuniform orbital QHF states with an helical or skyrmionic texture of electric dipoles. A similar skyrmionic texture can also arise in the N = 0 Landau level of an ABC-stacked trilayer graphene. In this talk, we discuss the optical properties of these textured ground states. We compute their electromagnetic absorption as well as the Kerr and Faraday rotations induced by their collective excitations and show that each textured phase has a distinct optical signature.

  17. Multicomponent Quantum Hall Ferromagnetism and Landau Level Crossing in Rhombohedral Trilayer Graphene.

    PubMed

    Lee, Y; Tran, D; Myhro, K; Velasco, J; Gillgren, N; Poumirol, J M; Smirnov, D; Barlas, Y; Lau, C N

    2016-01-13

    Using transport measurements, we investigate multicomponent quantum Hall (QH) ferromagnetism in dual-gated rhombohedral trilayer graphene (r-TLG) in which the real spin, orbital pseudospin, and layer pseudospins of the lowest Landau level form spontaneous ordering. We observe intermediate QH plateaus, indicating a complete lifting of the degeneracy of the zeroth Landau level (LL) in the hole-doped regime. In charge neutral r-TLG, the orbital degeneracy is broken first, and the layer degeneracy is broken last and only in the presence of an interlayer potential U⊥. In the phase space of U⊥ and filling factor ν, we observe an intriguing "hexagon" pattern, which is accounted for by a model based on crossings between symmetry-broken LLs.

  18. Stacking-dependent interlayer coupling in trilayer MoS2 with broken inversion symmetry

    DOE PAGES

    Yan, Jiaxu; Wang, Xingli; Tay, Beng Kang; ...

    2015-11-13

    The stacking configuration in few-layer two-dimensional (2D) materials results in different structural symmetries and layer-to-layer interactions, and hence it provides a very useful parameter for tuning their electronic properties. For example, ABA-stacking trilayer graphene remains semimetallic similar to that of monolayer, while ABC-stacking is predicted to be a tunable band gap semiconductor under an external electric field. Such stacking dependence resulting from many-body interactions has recently been the focus of intense research activities. Here we demonstrate that few-layer MoS2 samples grown by chemical vapor deposition with different stacking configurations (AA, AB for bilayer; AAB, ABB, ABA, AAA for trilayer) exhibitmore » distinct coupling phenomena in both photoluminescence and Raman spectra. By means of ultralow-frequency (ULF) Raman spectroscopy, we demonstrate that the evolution of interlayer interaction with various stacking configurations correlates strongly with layer-breathing mode (LBM) vibrations. Our ab initio calculations reveal that the layer-dependent properties arise from both the spin–orbit coupling (SOC) and interlayer coupling in different structural symmetries. Lastly, such detailed understanding provides useful guidance for future spintronics fabrication using various stacked few-layer MoS2 blocks.« less

  19. Landau Level Splittings, Phase Transitions, and Nonuniform Charge Distribution in Trilayer Graphene.

    PubMed

    Campos, Leonardo C; Taychatanapat, Thiti; Serbyn, Maksym; Surakitbovorn, Kawin; Watanabe, Kenji; Taniguchi, Takashi; Abanin, Dmitry A; Jarillo-Herrero, Pablo

    2016-08-05

    We report on magnetotransport studies of dual-gated, Bernal-stacked trilayer graphene (TLG) encapsulated in boron nitride crystals. We observe a quantum Hall effect staircase which indicates a complete lifting of the 12-fold degeneracy of the zeroth Landau level. As a function of perpendicular electric field, our data exhibit a sequence of phase transitions between all integer quantum Hall states in the filling factor interval -8<ν<0. We develop a theoretical model and argue that, in contrast to monolayer and bilayer graphene, the observed Landau level splittings and quantum Hall phase transitions can be understood within a single-particle picture, but imply the presence of a charge density imbalance between the inner and outer layers of TLG, even at charge neutrality and zero transverse electric field. Our results indicate the importance of a previously unaccounted band structure parameter which, together with a more accurate estimate of the other tight-binding parameters, results in a significantly improved determination of the electronic and Landau level structure of TLG.

  20. Ab initio quasiparticle bandstructure of ABA and ABC-stacked graphene trilayers

    NASA Astrophysics Data System (ADS)

    Menezes, Marcos; Capaz, Rodrigo; Louie, Steven

    2013-03-01

    We obtain the quasiparticle band structure of ABA and ABC-stacked graphene trilayers through ab initio density functional theory (DFT) and many-body quasiparticle calculations within the GW approximation. To interpret our results, we fit the DFT and GW π bands to a low energy tight-binding model, which is found to reproduce very well the observed features near the K point. The values of the extracted hopping parameters are reported and compared with available theoretical and experimental data. For both stackings, the quasiparticle corrections lead to a renormalization of the Fermi velocity, an effect also observed in previous calculations on monolayer graphene. They also increase the separation between the higher energy bands, which is proportional to the nearest neighbor interlayer hopping parameter γ1. Both features are brought to closer agreement with experiment through the quasiparticle corrections. Finally, other effects, such as trigonal warping, electron-hole assymetry and energy gaps are discussed in terms of the associated parameters. This work was supported by the Brazilian funding agencies: CAPES, CNPq, FAPERJ and INCT-Nanomateriais de Carbono. It was also supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231.

  1. Energy levels of ABC-stacked trilayer graphene quantum dots with infinite-mass boundary conditions

    NASA Astrophysics Data System (ADS)

    Mirzakhani, M.; Zarenia, M.; da Costa, D. R.; Ketabi, S. A.; Peeters, F. M.

    2016-10-01

    Using the continuum model, we investigate the confined states and the corresponding wave functions of ABC-stacked trilayer graphene (TLG) quantum dots (QDs). First, a general infinite-mass boundary condition is derived and applied to calculate the electron and hole energy levels of a circular QD in both the absence and presence of a perpendicular magnetic field. Our analytical results for the energy spectra agree with those obtained by using the tight-binding model, where a TLG QD is surrounded by a staggered potential. Our findings show that (i ) the energy spectrum exhibits intervalley symmetry EKe(m ) =-EK'h(m ) for the electron (e) and hole (h) states, where m is the angular momentum quantum number, (i i ) the zero-energy Landau level (LL) is formed by the magnetic states with m ⩽0 for both Dirac valleys, that is different from monolayer and bilayer graphene QD with infinite-mass potential in which only one of the cones contributes, and (i i i ) groups of three quantum Hall edge states in the tight-binding magnetic spectrum approach the zero LL, which results from the layer symmetry in TLG QDs.

  2. Observation of chirality transition of quasiparticles at stacking solitons in trilayer graphene

    NASA Astrophysics Data System (ADS)

    Yin, Long-Jing; Wang, Wen-Xiao; Zhang, Yu; Ou, Yang-Yang; Zhang, Hao-Ting; Shen, Cai-Yun; He, Lin

    2017-02-01

    Trilayer graphene (TLG) exhibits rich, alternative electronic properties and extraordinary quantum Hall phenomena owing to enhanced electronic interactions and tunable chirality of its quasiparticles. Here, we report direct observation of chirality transition of quasiparticles at stacking solitons of TLG via spatial-resolved Landau level spectroscopy. The one-dimensional stacking solitons with width of the order of 10 nm separate adjacent Bernal-stacked TLG and rhombohedral-stacked TLG. By using high-field tunneling spectra from scanning tunneling microscopy, we measured Landau quantization in both the Bernal-stacked TLG and the rhombohedral-stacked TLG and, importantly, we observed evolution of quasiparticles between the chiral degree l =1 and 2 and l =3 across the stacking domain-wall solitons. Our experiment indicates that such a chirality transition occurs smoothly, accompanying the transition of the stacking orders of TLG, around the domain-wall solitons. This result demonstrates the important relationship between the crystallographic stacking order and the chirality of quasiparticles in graphene systems.

  3. Landau Level Splittings, Phase Transitions, and Nonuniform Charge Distribution in Trilayer Graphene

    NASA Astrophysics Data System (ADS)

    Campos, Leonardo C.; Taychatanapat, Thiti; Serbyn, Maksym; Surakitbovorn, Kawin; Watanabe, Kenji; Taniguchi, Takashi; Abanin, Dmitry A.; Jarillo-Herrero, Pablo

    2016-08-01

    We report on magnetotransport studies of dual-gated, Bernal-stacked trilayer graphene (TLG) encapsulated in boron nitride crystals. We observe a quantum Hall effect staircase which indicates a complete lifting of the 12-fold degeneracy of the zeroth Landau level. As a function of perpendicular electric field, our data exhibit a sequence of phase transitions between all integer quantum Hall states in the filling factor interval -8 <ν <0 . We develop a theoretical model and argue that, in contrast to monolayer and bilayer graphene, the observed Landau level splittings and quantum Hall phase transitions can be understood within a single-particle picture, but imply the presence of a charge density imbalance between the inner and outer layers of TLG, even at charge neutrality and zero transverse electric field. Our results indicate the importance of a previously unaccounted band structure parameter which, together with a more accurate estimate of the other tight-binding parameters, results in a significantly improved determination of the electronic and Landau level structure of TLG.

  4. Stacking-dependent interlayer coupling in trilayer MoS2 with broken inversion symmetry

    SciTech Connect

    Yan, Jiaxu; Wang, Xingli; Tay, Beng Kang; Zhou, Wu; Liu, Zheng; Shen, Ze Xiang; Xia, Juan; Liu, Lei; Kuo, Jer -Lai; Chen, Shoushun

    2015-11-13

    The stacking configuration in few-layer two-dimensional (2D) materials results in different structural symmetries and layer-to-layer interactions, and hence it provides a very useful parameter for tuning their electronic properties. For example, ABA-stacking trilayer graphene remains semimetallic similar to that of monolayer, while ABC-stacking is predicted to be a tunable band gap semiconductor under an external electric field. Such stacking dependence resulting from many-body interactions has recently been the focus of intense research activities. Here we demonstrate that few-layer MoS2 samples grown by chemical vapor deposition with different stacking configurations (AA, AB for bilayer; AAB, ABB, ABA, AAA for trilayer) exhibit distinct coupling phenomena in both photoluminescence and Raman spectra. By means of ultralow-frequency (ULF) Raman spectroscopy, we demonstrate that the evolution of interlayer interaction with various stacking configurations correlates strongly with layer-breathing mode (LBM) vibrations. Our ab initio calculations reveal that the layer-dependent properties arise from both the spin–orbit coupling (SOC) and interlayer coupling in different structural symmetries. Lastly, such detailed understanding provides useful guidance for future spintronics fabrication using various stacked few-layer MoS2 blocks.

  5. Atmospheric pressure route to epitaxial nitrogen-doped trilayer graphene on 4H-SiC (0001) substrate

    SciTech Connect

    Boutchich, M.; Arezki, H.; Alamarguy, D.; Güneş, F.; Alvarez, J.; Kleider, J. P.; Ho, K.-I.; Lai, C. S.; Sediri, H.; Ouerghi, A.

    2014-12-08

    Large-area graphene film doped with nitrogen is of great interest for a wide spectrum of nanoelectronics applications, such as field effect devices, super capacitors, and fuel cells among many others. Here, we report on the structural and electronic properties of nitrogen doped trilayer graphene on 4H-SiC (0001) grown under atmospheric pressure. The trilayer nature of the growth is evidenced by scanning transmission electron microscopy. X-ray photoelectron spectroscopy shows the incorporation of 1.2% of nitrogen distributed in pyrrolic-N, and pyridinic-N configurations as well as a graphitic-N contribution. This incorporation causes an increase in the D band on the Raman signature indicating that the nitrogen is creating defects. Ultraviolet photoelectron spectroscopy shows a decrease of the work function of 0.3 eV due to the N-type doping of the nitrogen atoms in the carbon lattice and the edge defects. A top gate field effect transistor device has been fabricated and exhibits carrier mobilities up to 1300 cm{sup 2}/V s for holes and 850 cm{sup 2}/V s for electrons at room temperature.

  6. Investigating photoresponse in graphene by light polarization

    NASA Astrophysics Data System (ADS)

    Eginligil, M.; Cao, B. C.; Wang, Z. L.; Soci, C.; Yu, T.

    2014-03-01

    We report our photocurrent studies on single layer graphene (SLG), bilayer graphene (BLG) and trilayer graphene (TLG) by exciting with circularly polarized light. In addition to p-n junctions based on gated graphene field-effect-transistor (g-FET), it was recently demonstrated that in the graphene/metal interface large photocurrent (PC) can be generated and this PC can be manipulated by backgate voltage in a simple g-FET. In this work we fabricated g-FETs from mechanically exfoliated graphene and explored backgate voltage dependence of photon drag effect (PDE), linear and circular photogalvanic effect (CPGE) of SLG, BLG and TLG. In BLG, we noticed a cos θ dependence of the measured PC, where θ is the angle of incident light polarization, in addition to PDE and CPGE effects which have cos4 θ and sin2 θ dependence, respectively. This cos θ dependence is attributed to the Berry curvature related valley PC, which can be induced as a result of broken inversion symmetry and asymmetry in the two low energy valleys of BLG. The latter is absent in SLG and peculiar for ABA stacked TLG. By varying backgate voltage we distinguish all helicity dependent PC contributions. Our data show good agreement with the theory. Supported by the National Research Foundation of Singapore under Award No. NRF-RF2010-07 and MOE Tier 2 MOE2012-T2-2-049.

  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. Rhombohedral Multilayer Graphene: A Magneto-Raman Scattering Study.

    PubMed

    Henni, Younes; Ojeda Collado, Hector Pablo; Nogajewski, Karol; Molas, Maciej R; Usaj, Gonzalo; Balseiro, Carlos A; Orlita, Milan; Potemski, Marek; Faugeras, Clement

    2016-06-08

    Graphene layers are known to stack in two stable configurations, namely, ABA or ABC stacking, with drastically distinct electronic properties. Unlike the ABA stacking, little has been done to experimentally investigate the electronic properties of ABC graphene multilayers. Here, we report on the first magneto optical study of a large ABC domain in a graphene multilayer flake, with ABC sequences exceeding 17 graphene sheets. ABC-stacked multilayers can be fingerprinted with a characteristic electronic Raman scattering response, which persists even at room temperatures. Tracing the magnetic field evolution of the inter Landau level excitations from this domain gives strong evidence for the existence of a dispersionless electronic band near the Fermi level, characteristic of such stacking. Our findings present a simple yet powerful approach to probe ABC stacking in graphene multilayer flakes, where this highly degenerated band appears as an appealing candidate to host strongly correlated states.

  9. How graphene slides: measurement and theory of strain-dependent frictional forces between graphene and SiO2.

    PubMed

    Kitt, Alexander L; Qi, Zenan; Rémi, Sebastian; Park, Harold S; Swan, Anna K; Goldberg, Bennett B

    2013-06-12

    Strain, bending rigidity, and adhesion are interwoven in determining how graphene responds when pulled across a substrate. Using Raman spectroscopy of circular, graphene-sealed microchambers under variable external pressure, we demonstrate that graphene is not firmly anchored to the substrate when pulled. Instead, as the suspended graphene is pushed into the chamber under pressure, the supported graphene outside the microchamber is stretched and slides, pulling in an annulus. Analyzing Raman G band line scans with a continuum model extended to include sliding, we extract the pressure dependent sliding friction between the SiO2 substrate and mono-, bi-, and trilayer graphene. The sliding friction for trilayer graphene is directly proportional to the applied load, but the friction for monolayer and bilayer graphene is inversely proportional to the strain in the graphene, which is in violation of Amontons' law. We attribute this behavior to the high surface conformation enabled by the low bending rigidity and strong adhesion of few layer graphene.

  10. A trilayer separator with dual function for high performance lithium-sulfur batteries

    NASA Astrophysics Data System (ADS)

    Song, Rensheng; Fang, Ruopian; Wen, Lei; Shi, Ying; Wang, Shaogang; Li, Feng

    2016-01-01

    In this article, we propose a trilayer graphene/polypropylene/Al2O3 (GPA) separator with dual function for high performance lithium-sulfur (Li-S) batteries. Graphene is coated on one side of polypropylene (PP) separator, which functions as a conductive layer and an electrolyte reservoir that allows for rapid electron and ion transport. Then Al2O3 particles are coated on the other side to further enhance thermal stability and safety of the graphene coated polypropylene (GCP) separator, which are touched with lithium metal anode in the Li-S battery. The GPA separator shows good thermal stability after heating at 157 °C for 10 min while both GCP and PP separators showing an obvious shrinkage about 10%. The initial discharge specific capacity of Li-S coin cell with a GPA separator could reach 1067.7 mAh g-1 at 0.2C. After 100 discharge/charge cycles, it can still deliver a reversible capacity of as high as 804.4 mAh g-1 with 75% capacity retention. The pouch cells further confirm that the trilayer design has great promise towards practical applications.

  11. Graphene folding on flat substrates

    SciTech Connect

    Chen, Xiaoming; Zhao, Yadong; Ke, Changhong; Zhang, Liuyang; Wang, Xianqiao

    2014-10-28

    We present a combined experimental-theoretical study of graphene folding on flat substrates. The structure and deformation of the folded graphene sheet are experimentally characterized by atomic force microscopy. The local graphene folding behaviors are interpreted based on nonlinear continuum mechanics modeling and molecular dynamics simulations. Our study on self-folding of a trilayer graphene sheet reports a bending stiffness of about 6.57 eV, which is about four times the reported values for monolayer graphene. Our results reveal that an intriguing free sliding phenomenon occurs at the interlayer van der Waals interfaces during the graphene folding process. This work demonstrates that it is a plausible venue to quantify the bending stiffness of graphene based on its self-folding conformation on flat substrates. The findings reported in this work are useful to a better understanding of the mechanical properties of graphene and in the pursuit of its applications.

  12. Understanding and Controlling the Electronic Properties of Graphene Using Scanning Probe Microscopy

    DTIC Science & Technology

    2014-07-21

    crystal structure of a material determines its electrical properties. Trilayer graphene comes in two inequivalent stacking configurations, ABA (Bernal) or...ABC (Rhombohedral). These configurations are nearly degenerate in energy and both are found in naturally occurring graphite. The ABA structure is...able to open a band gap. Furthermore, the dispersion relations of the two different stacking orders are different. ABA trilayer graphene resembles

  13. A trilayer architecture for polymer photoconductors

    NASA Astrophysics Data System (ADS)

    Jin, Zhiwen; Wang, Jizheng

    2013-02-01

    A trilayer architecture is designed for polymer photoconductors. In such a structure, photogenerated electrons in poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid ethyl ester (P3HT:PCBM) blend film will flow into a TiOx layer beneath and then diffuse into a underlying PCBM layer. Photogenerated holes and electrons are thus efficiently separated by the spacer TiOx, and, respectively, transport in P3HT and PCBM films, carrier recombination is thereby greatly suppressed. As a result, photocurrent of the PCBM/TiOx/P3HT:PCBM trilayer structure increases more than 200 times over that of the conventional P3HT:PCBM single layer device.

  14. Electrohydrodynamic instabilities in thin liquid trilayer films

    DOE PAGES

    Roberts, Scott A.; Kumar, Satish

    2010-12-09

    Experiments by Dickey and Leach show that novel pillar shapes can be generated from electrohydrodynamic instabilities at the interfaces of thin polymer/polymer/air trilayer films. In this paper, we use linear stability analysis to investigate the effect of free charge and ac electric fields on the stability of trilayer systems. Our work is also motivated by our recent theoretical study which demonstrates how ac electric fields can be used to increase control over the pillar formation process in thin liquid bilayer films. For perfect dielectric films, the effect of an AC electric field can be understood by considering an equivalent DCmore » field. Leaky dielectric films yield pillar configurations that are drastically different from perfect dielectric films, and AC fields can be used to control the location of free charge within the trilayer system. This can alter the pillar instability modes and generate smaller diameter pillars when conductivities are mismatched. The results presented may be of interest for the creation of complex topographical patterns on polymer coatings and in microelectronics.« less

  15. Electrohydrodynamic instabilities in thin liquid trilayer films

    SciTech Connect

    Roberts, Scott A.; Kumar, Satish

    2010-12-09

    Experiments by Dickey and Leach show that novel pillar shapes can be generated from electrohydrodynamic instabilities at the interfaces of thin polymer/polymer/air trilayer films. In this paper, we use linear stability analysis to investigate the effect of free charge and ac electric fields on the stability of trilayer systems. Our work is also motivated by our recent theoretical study which demonstrates how ac electric fields can be used to increase control over the pillar formation process in thin liquid bilayer films. For perfect dielectric films, the effect of an AC electric field can be understood by considering an equivalent DC field. Leaky dielectric films yield pillar configurations that are drastically different from perfect dielectric films, and AC fields can be used to control the location of free charge within the trilayer system. This can alter the pillar instability modes and generate smaller diameter pillars when conductivities are mismatched. The results presented may be of interest for the creation of complex topographical patterns on polymer coatings and in microelectronics.

  16. Electronic structure of few-layer epitaxial graphene on Ru(0001).

    PubMed

    Sutter, P; Hybertsen, M S; Sadowski, J T; Sutter, E

    2009-07-01

    The electronic structure of epitaxial monolayer, bilayer, and trilayer graphene on Ru(0001) was determined by selected-area angle-resolved photoelectron spectroscopy (micro-ARPES). Micro-ARPES band maps provide evidence for a strong electronic coupling between monolayer graphene and the adjacent metal, which causes the complete disruption of the graphene pi-bands near the Fermi energy. However, the perturbation by the metal decreases rapidly with the addition of further graphene sheets, and already an epitaxial graphene bilayer on Ru recovers the characteristic Dirac cones of isolated monolayer graphene. A graphene trilayer on Ru behaves like free-standing bilayer graphene. Density-functional theory based calculations show that this decoupling is due to the efficient passivation of metal d-states by the interfacial graphene layer.

  17. 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.

  18. Tailored magnetic anisotropy in an amorphous trilayer

    NASA Astrophysics Data System (ADS)

    Fu, Yu; Barsukov, I.; Raanaei, H.; Spasova, M.; Lindner, J.; Meckenstock, R.; Farle, M.; Hjörvarsson, B.

    2011-06-01

    An amorphous Co68Fe24Zr8(3 nm)/Al70Zr30(3 nm)/Co68Fe24Zr8(3 nm) trilayer system has been investigated using in-plane and out-of-plane angular dependent ferromagnetic resonance at different frequencies. The in-plane magnetic anisotropy is uniaxial, retaining its value of (2.9 ± 0.1) × 103 J/m3 for each magnetic layer, whereas its direction was tailored independently in an arbitrary manner by applying an external magnetic field during the film deposition. The perpendicular anisotropy constant, supposed to reflect the interface quality, is nearly identical for both layers. Furthermore, the magnetic layers act independently upon each other due to the absence of interlayer coupling.

  19. Trilayer TMDC Heterostructures for MOSFETs and Nanobiosensors

    NASA Astrophysics Data System (ADS)

    Datta, Kanak; Shadman, Abir; Rahman, Ehsanur; Khosru, Quazi D. M.

    2017-02-01

    Two dimensional materials such as transition metal dichalcogenides (TMDC) and their bi-layer/tri-layer heterostructures have become the focus of intense research and investigation in recent years due to their promising applications in electronics and optoelectronics. In this work, we have explored device level performance of trilayer TMDC heterostructure (MoS2/MX2/MoS2; M = Mo or, W and X = S or, Se) metal oxide semiconductor field effect transistors (MOSFETs) in the quantum ballistic regime. Our simulation shows that device `on' current can be improved by inserting a WS2 monolayer between two MoS2 monolayers. Application of biaxial tensile strain reveals a reduction in drain current which can be attributed to the lowering of carrier effective mass with increased tensile strain. In addition, it is found that gate underlap geometry improves electrostatic device performance by improving sub-threshold swing. However, increase in channel resistance reduces drain current. Besides exploring the prospect of these materials in device performance, novel trilayer TMDC heterostructure double gate field effect transistors (FETs) are proposed for sensing Nano biomolecules as well as for pH sensing. Bottom gate operation ensures these FETs operating beyond Nernst limit of 59 mV/pH. Simulation results found in this work reveal that scaling of bottom gate oxide results in better sensitivity while top oxide scaling exhibits an opposite trend. It is also found that, for identical operating conditions, proposed TMDC FET pH sensors show super-Nernst sensitivity indicating these materials as potential candidates in implementing such sensor. Besides pH sensing, all these materials show high sensitivity in the sub-threshold region as a channel material in nanobiosensor while MoS2/WS2/MoS2 FET shows the least sensitivity among them.

  20. The application of polypyrrole trilayer actuators in microfluidics and robotics

    NASA Astrophysics Data System (ADS)

    Kiefer, Rudolf; Mandviwalla, Xerxes; Archer, Rosalind; Tjahyono, Sungkono Surya; Wang, Han; MacDonald, Bruce; Bowmaker, Graham A.; Kilmartin, Paul A.; Travas-Sejdic, Jadranka

    2008-03-01

    Trilayer actuators were constructed using polypyrrole (PPy) films doped with dodecylbenzene sulfonate (DBS). Identical 5-20 μm PPy/DBS films were grown on either side of a 110 μm poly(vinylidene fluoride) (PVDF) membrane to serve as working and counter electrodes with respect to each other. The performance of the trilayer actuator was tested using potential step experiments between -0.8 and +0.8 V at different frequencies (0.03 to 10 Hz) and trilayer lengths (1 to 2.5 cm), and the extent of deflection was measured using a CCD camera. Satisfactory deflections in the range of 1-3 mm were observed for 10 μm thick PPy layers on trilayers 1.5 to 2.5 cm in length when operated at 1-5 Hz for over 40,000 cycles. The trilayer actuators were examined in a fluidics channels, and mathematical modelling using finite element analysis was used to predict overall fluid movement and flow rates. The trilayers were also used to construct a 'fish-tail' positioned at the back of a self-driven robotic fish.

  1. Twinning and twisting of tri- and bilayer graphene.

    PubMed

    Brown, Lola; Hovden, Robert; Huang, Pinshane; Wojcik, Michal; Muller, David A; Park, Jiwoong

    2012-03-14

    The electronic, optical, and mechanical properties of bilayer and trilayer graphene vary with their structure, including the stacking order and relative twist, providing novel ways to realize useful characteristics not available to single layer graphene. However, developing controlled growth of bilayer and trilayer graphene requires efficient large-scale characterization of multilayer graphene structures. Here, we use dark-field transmission electron microscopy for rapid and accurate determination of key structural parameters (twist angle, stacking order, and interlayer spacing) of few-layer CVD graphene. We image the long-range atomic registry for oriented bilayer and trilayer graphene, find that it conforms exclusively to either Bernal or rhombohedral stacking, and determine their relative abundances. In contrast, our data on twisted multilayers suggest the absence of such long-range atomic registry. The atomic registry and its absence are consistent with the two different strain-induced deformations we observe; by tilting the samples to break mirror symmetry, we find a high density of twinned domains in oriented multilayer graphene, where multiple domains of two different stacking configurations coexist, connected by discrete twin boundaries. In contrast, individual layers in twisted regions continuously stretch and shear independently, forming elaborate Moiré patterns. These results, and the twist angle distribution in our CVD graphene, can be understood in terms of an angle-dependent interlayer potential model.

  2. Wettability of graphene.

    PubMed

    Raj, Rishi; Maroo, Shalabh C; Wang, Evelyn N

    2013-04-10

    Graphene, an atomically thin two-dimensional material, has received significant attention due to its extraordinary electronic, optical, and mechanical properties. Studies focused on understanding the wettability of graphene for thermo-fluidic and surface-coating applications, however, have been sparse. Meanwhile, wettability results reported in literature via static contact angle measurement experiments have been contradictory and highlight the lack of clear understanding of the underlying physics that dictates wetting behavior. In this work, dynamic contact angle measurements and detailed graphene surface characterizations were performed to demonstrate that the defects present in CVD grown and transferred graphene coatings result in unusually high contact angle hysteresis (16-37°) on these otherwise smooth surfaces. Hence, understanding the effect of the underlying substrate based on static contact angle measurements as reported in literature is insufficient. The advancing contact angle measurements on mono-, bi-, and trilayer graphene sheets on copper, thermally grown silica (SiO2), and glass substrates were observed to be independent of the number of layers of graphene and in good agreement with corresponding molecular dynamics simulations and theoretical calculations. Irrespective of the number of graphene layers, the advancing contact angle values were also in good agreement with the advancing contact angle on highly ordered pyrolytic graphite (HOPG), reaffirming the negligible effect of the underlying substrate. These results suggest that the advancing contact angle is a true representation of a graphene-coated surface while the receding contact angle is significantly influenced by intrinsic defects introduced during the growth and transfer processes. These observations, where the underlying substrates do not affect the wettability of graphene coatings, is shown to be due to the large interlayer spacing resulting from the loose interlamellar coupling between

  3. Multilayer Graphene with Chemical Modification as Transparent Conducting Electrodes in Organic Light-Emitting Diode.

    PubMed

    Xu, Yilin; Yu, Haojian; Wang, Cong; Cao, Jin; Chen, Yigang; Ma, Zhongquan; You, Ying; Wan, Jixiang; Fang, Xiaohong; Chen, Xiaoyuan

    2017-12-01

    Graphene is a promising candidate for the replacement of the typical transparent electrode indium tin oxide in optoelectronic devices. Currently, the application of polycrystalline graphene films grown by chemical vapor deposition is limited for their low electrical conductivity due to the poor transfer technique. In this work, we developed a new method of preparing tri-layer graphene films with chemical modification and explored the influence of doping and patterning process on the performance of the graphene films as transparent electrodes. In order to demonstrate the application of the tri-layer graphene films in optoelectronics, we fabricated the organic light-emitting diodes (OLEDs) based on them and found that plasma etching is feasible with certain influence on the quality of the graphene films and the performance of the OLEDs.

  4. Torque engineering in trilayer spin-hall system

    NASA Astrophysics Data System (ADS)

    Gupta, Gaurav; Jalil, Mansoor Bin Abdul; Liang, Gengchiau

    2016-02-01

    A trilayer system with perpendicularly magnetized metallic (FMM) free-layer, heavy metal (HM) with strong spin-hall effect and ferromagnetic insulating (FMI) substrate has been proposed to significantly enhance the torque acting on FMM. Its magnitude can be engineered by configuring the magnetization of the FMI. The analytical solution has been developed for four stable magnetization states (non-magnetic and magnetization along three Cartesian axes) of FMI to comprehensively appraise the anti-damping torque on FMM and the Gain factor. It is shown that the proposed system has much larger gain and torque compared to a bilayer system (or a trilayer system with non-magnetic substrate). The performance improvement may be extremely large for system with a thin HM. Device optimization is shown to be non-trivial and various constraints have been explained. These results would enable design of more efficient spin-orbit torque memories and logic with faster switching at yet lower current.

  5. Fabrication of magnetic trilayer stripes using interference lithography

    NASA Astrophysics Data System (ADS)

    Zhu, Meng; MacArthur, James; McMichael, Robert

    2009-03-01

    Both theoretical (PRB, 74, 024424, 2006) and experimental (APL, 90, 232504, 2007) studies of a single layer magnetic film edge have shown that the edge-mode of magnetization precession detected by ferromagnetic resonance (FMR) is an effective tool to probe magnetic properties of thin film edges. To extend the measurement technique to realistic devices such as spin-valves or tunnel junctions, magnetic multilayer stripes have to be fabricated. Here, we present the fabrication of Py/Cu/Co magnetic trilayer stripes by interference lithography. A resist stack consisting of positive photoresist 1805 and WIDE-B anti-reflective coating (ARC) is exposed by a blue laser at 405nm using Lloyd's mirror interferometer. Optimal soft-baking temperature of ARC results in an undercut during the development of the photoresist. This undercut facilitates the lift-off process after the evaporation of Py/Cu/Co trilayer. A uniform array of trilayer stripes with a period of ˜620nm was obtained. This work has been supported in part by the NIST-CNST/UMD-NanoCenter Cooperative Agreement and NIST CNST-NSF REU #DMR-0754115.

  6. Tri-layered elastomeric scaffolds for engineering heart valve leaflets

    PubMed Central

    Masoumi, Nafiseh; Annabi, Nasim; Assmann, Alexander; Larson, Benjamin L.; Hjortnaes, Jesper; Alemdar, Neslihan; Kharaziha, Mahshid; Manning, Keefe B.; Mayer, John E.; Khademhosseini, Ali

    2014-01-01

    Tissue engineered heart valves (TEHVs) that can grow and remodel have the potential to serve as permanent replacements of the current non-viable prosthetic valves particularly for pediatric patients. A major challenge in designing functional TEHVs is to mimic both structural and anisotropic mechanical characteristics of the native valve leaflets. To establish a more biomimetic model of TEHV, we fabricated tri-layered scaffolds by combining electrospinning and microfabrication techniques. These constructs were fabricated by assembling microfabricated poly(glycerol sebacate) (PGS) and fibrous PGS/poly(-caprolactone) (PCL) electrospun sheets to develop elastic scaffolds with tunable anisotropic mechanical properties similar to the mechanical characteristics of the native heart valves. The engineered scaffolds supported valvular interstitial cells (VICs) and mesenchymal stem cells (MSCs) growth within the 3D structure and promoted the deposition of heart valve extracellular matrix (ECM). MSCs were also organized and aligned along the anisotropic axes of the engineered tri-layered scaffolds. In addition, the fabricated constructs opened and closed properly in an ex vivo model of porcine heart valve leaflet tissue replacement. The engineered tri-layered scaffolds have the potential for successful translation towards TEHV replacements. PMID:24947233

  7. Highly Efficient and Anomalous Charge Transfer in van der Waals Trilayer Semiconductors.

    PubMed

    Ceballos, Frank; Ju, Ming-Gang; Lane, Samuel D; Zeng, Xiao Cheng; Zhao, Hui

    2017-03-08

    Two-dimensional materials, such as graphene and monolayer transition metal dichalcogenides, allow the fabrication of multilayer structures without lattice matching restriction. A central issue in developing such artificial materials is to understand and control the interlayer electron transfer process, which plays a key role in harnessing their emergent properties. Recent photoluminescence and transient absorption measurements revealed that the electron transfer in heterobilayers occurs on ultrafast time scales. However, there is still a lack of fundamental understanding on how this process can be so efficient at van der Waals interfaces. Here we show evidence suggesting the coherent nature of such interlayer electron transfer. In a trilayer of MoS2-WS2-MoSe2, electrons excited in MoSe2 transfer to MoS2 in about one picosecond. Surprisingly, these electrons do not populate the middle WS2 layer during this process. Calculations showed the coherent nature of the charge transfer and reproduced the measured electron transfer time. The hole transfer from MoS2 to MoSe2 is also found to be efficient and ultrafast. The separation of electrons and holes extends their lifetimes to more than one nanosecond, suggesting potential applications of such multilayer structures in optoelectronics.

  8. Band gap tunning in BN-doped graphene systems with high carrier mobility

    SciTech Connect

    Kaloni, T. P.; Schwingenschlögl, U.; Joshi, R. P.; Adhikari, N. P.

    2014-02-17

    Using density functional theory, we present a comparative study of the electronic properties of BN-doped graphene monolayer, bilayer, trilayer, and multilayer systems. In addition, we address a superlattice of pristine and BN-doped graphene. Five doping levels between 12.5% and 75% are considered, for which we obtain band gaps from 0.02 eV to 2.43 eV. We demonstrate a low effective mass of the charge carriers.

  9. Investigations of the mechanical properties of bi-layer and trilayer fiber reinforced composites

    NASA Astrophysics Data System (ADS)

    Jayakrishna, K.; Balasubramani, K.; Sultan, M. T. H.; Karthikeyan, S.

    2016-10-01

    Natural fibers are renewable raw materials with an environmental-friendly properties and they are recyclable. The mechanical properties of bi-layer and tri-layer thermoset polymer composites have been analyzed. The bi-layer composite consists of basalt and jute mats, while the tri-layer composite consists of basalt fiber, jute fiber and glass fiber mats. In both cases, the epoxy resin was used as the matrix and PTFE as a filler in the composites. The developed trilayer natural fiber composite can be used in various industrial applications such as automobile parts, construction and manufacturing. Furthermore, it also can be adopted in aircraft interior decoration and designed body parts. Flexural, impact, tensile, compression, shear and hardness tests, together with density measurement, were conducted to study the mechanical properties of both bi-layer and tri-layer composites. From the comparison, the tri-layer composite was found to perform in a better way in all tests.

  10. Phase transitions of monolayers on graphene

    NASA Astrophysics Data System (ADS)

    Kahn, Joshua; Dzyubenko, Boris; Vilches, Oscar; Cobden, David

    We have studied physisorbed layers of monatomic and diatomic gases on graphene. We used devices in which few-layer graphene, ranging from monolayer to trilayer, is suspended across a trench between two platinum contacts and are cleaned by thermal and current annealing. We found that the density of adsorbates is revealed by the conductance, similar to the case with nanotubes. The conductance change for a monolayer can be large. On trilayer graphene the adsorbed gases can be seen to exhibit transitions between two-dimensional phases identical to those on bulk graphite, including incommensurate and commensurate solid, fluid and vapor and multiple layers. New features appear in the conductance at the boundaries of the commensurate phase of Kr. We are able to measure single-particle binding energies very accurately and see how it depends on thickness; investigate the effects of changing disorder by gradually current annealing; and search for new phases in the case of monolayer graphene where atoms adsorbed on both sides can interact. We can map out the 2d phase diagrams very quickly by ohmic heating, which gives nearly instantaneous control of the temperature.

  11. Engineering the interlayer exchange coupling in magnetic trilayers

    PubMed Central

    Chang, Ching-Hao; Dou, Kun-Peng; Chen, Ying-Chin; Hong, Tzay-Ming; Kaun, Chao-Cheng

    2015-01-01

    When the thickness of metal film approaches the nanoscale, itinerant carriers resonate between its boundaries and form quantum well states (QWSs), which are crucial to account for the film’s electrical, transport and magnetic properties. Besides the classic origin of particle-in-a-box, the QWSs are also susceptible to the crystal structures that affect the quantum resonance. Here we investigate the QWSs and the magnetic interlayer exchange coupling (IEC) in the Fe/Ag/Fe (001) trilayer from first-principles calculations. We find that the carriers at the Brillouin-zone center (belly) and edge (neck) separately form electron- and hole-like QWSs that give rise to an oscillatory feature for the IEC as a function of the Ag-layer thickness with long and short periods. Since the QWS formation sensitively depends on boundary conditions, one can switch between these two IEC periods by changing the Fe-layer thickness. These features, which also occur in the magnetic trilayers with other noble-metal spacers, open a new degree of freedom to engineer the IEC in magnetoresistance devices. PMID:26596253

  12. Superconducting magnetoresistance in ferromagnet/superconductor/ferromagnet trilayers.

    PubMed

    Stamopoulos, D; Aristomenopoulou, E

    2015-08-26

    Magnetoresistance is a multifaceted effect reflecting the diverse transport mechanisms exhibited by different kinds of plain materials and hybrid nanostructures; among other, giant, colossal, and extraordinary magnetoresistance versions exist, with the notation indicative of the intensity. Here we report on the superconducting magnetoresistance observed in ferromagnet/superconductor/ferromagnet trilayers, namely Co/Nb/Co trilayers, subjected to a parallel external magnetic field equal to the coercive field. By manipulating the transverse stray dipolar fields that originate from the out-of-plane magnetic domains of the outer layers that develop at coercivity, we can suppress the supercurrent of the interlayer. We experimentally demonstrate a scaling of the magnetoresistance magnitude that we reproduce with a closed-form phenomenological formula that incorporates relevant macroscopic parameters and microscopic length scales of the superconducting and ferromagnetic structural units. The generic approach introduced here can be used to design novel cryogenic devices that completely switch the supercurrent 'on' and 'off', thus exhibiting the ultimate magnetoresistance magnitude 100% on a regular basis.

  13. Engineering the interlayer exchange coupling in magnetic trilayers

    NASA Astrophysics Data System (ADS)

    Chang, Ching-Hao; Dou, Kun-Peng; Chen, Ying-Chin; Hong, Tzay-Ming; Kaun, Chao-Cheng

    2015-11-01

    When the thickness of metal film approaches the nanoscale, itinerant carriers resonate between its boundaries and form quantum well states (QWSs), which are crucial to account for the film’s electrical, transport and magnetic properties. Besides the classic origin of particle-in-a-box, the QWSs are also susceptible to the crystal structures that affect the quantum resonance. Here we investigate the QWSs and the magnetic interlayer exchange coupling (IEC) in the Fe/Ag/Fe (001) trilayer from first-principles calculations. We find that the carriers at the Brillouin-zone center (belly) and edge (neck) separately form electron- and hole-like QWSs that give rise to an oscillatory feature for the IEC as a function of the Ag-layer thickness with long and short periods. Since the QWS formation sensitively depends on boundary conditions, one can switch between these two IEC periods by changing the Fe-layer thickness. These features, which also occur in the magnetic trilayers with other noble-metal spacers, open a new degree of freedom to engineer the IEC in magnetoresistance devices.

  14. THERMAL RESIDUAL STRESSES IN BILAYERED, TRILAYERED AND GRADED DENTAL CERAMICS

    PubMed Central

    Fabris, Douglas; Souza, Júlio C.M.; Silva, Filipe S.; Fredel, Márcio; Mesquita-Guimarães, Joana; Zhang, Yu; Henriques, Bruno

    2017-01-01

    Layered ceramic systems are usually hit by residual thermal stresses created during cooling from high processing temperature. The purpose of this study was to determine the thermal residual stresses at different ceramic multi-layered systems and evaluate their influence on the bending stress distribution. Finite elements method was used to evaluate the residual stresses in zirconia-porcelain and alumina-porcelain multi-layered discs and to simulate the ‘piston-on-ring’ test. Temperature-dependent material properties were used. Three different multi-layered designs were simulated: a conventional bilayered design; a trilayered design, with an intermediate composite layer with constant composition; and a graded design, with an intermediate layer with gradation of properties. Parameters such as the interlayer thickness and composition profiles were varied in the study. Alumina-porcelain discs present smaller residual stress than the zirconia-porcelain discs, regardless of the type of design. The homogeneous interlayer can yield a reduction of ~40% in thermal stress relative to bilayered systems. Thinner interlayers favoured the formation of lower thermal stresses. The graded discs showed the lowest thermal stresses for a gradation profile given by power law function with p=2. The bending stresses were significantly affected by the thermal stresses in the discs. The risk of failure for all-ceramic dental restorative systems can be significantly reduced by using trilayered systems (homogenous or graded interlayer) with the proper design. PMID:28163345

  15. Engineering the interlayer exchange coupling in magnetic trilayers.

    PubMed

    Chang, Ching-Hao; Dou, Kun-Peng; Chen, Ying-Chin; Hong, Tzay-Ming; Kaun, Chao-Cheng

    2015-11-24

    When the thickness of metal film approaches the nanoscale, itinerant carriers resonate between its boundaries and form quantum well states (QWSs), which are crucial to account for the film's electrical, transport and magnetic properties. Besides the classic origin of particle-in-a-box, the QWSs are also susceptible to the crystal structures that affect the quantum resonance. Here we investigate the QWSs and the magnetic interlayer exchange coupling (IEC) in the Fe/Ag/Fe (001) trilayer from first-principles calculations. We find that the carriers at the Brillouin-zone center (belly) and edge (neck) separately form electron- and hole-like QWSs that give rise to an oscillatory feature for the IEC as a function of the Ag-layer thickness with long and short periods. Since the QWS formation sensitively depends on boundary conditions, one can switch between these two IEC periods by changing the Fe-layer thickness. These features, which also occur in the magnetic trilayers with other noble-metal spacers, open a new degree of freedom to engineer the IEC in magnetoresistance devices.

  16. Single-crystalline monolayer and multilayer graphene nano switches

    SciTech Connect

    Li, Peng; Cui, Tianhong; Jing, Gaoshan; Zhang, Bo; Sando, Shota

    2014-03-17

    Growth of monolayer, bi-layer, and tri-layer single-crystalline graphene (SCG) using chemical vapor deposition method is reported. SCG's mechanical properties and single-crystalline nature were characterized and verified by atomic force microscope and Raman spectroscopy. Electro-mechanical switches based on mono- and bi-layer SCG were fabricated, and the superb properties of SCG enable the switches to operate at pull-in voltage as low as 1 V, and high switching speed about 100 ns. These devices exhibit lifetime without a breakdown of over 5000 cycles, far more durable than any other graphene nanoelectromechanical system switches reported.

  17. Harvesting energy from water flow over graphene?

    PubMed

    Yin, Jun; Zhang, Zhuhua; Li, Xuemei; Zhou, Jianxin; Guo, Wanlin

    2012-03-14

    It is reported excitingly in a previous letter (Nano Lett. 2011, 11, 3123) that a small piece of graphene sheet about 30 × 16 μm(2) immersed in flowing water with 0.6 M hydrochloric acid can produce voltage ~20 mV. Here we find that no measurable voltage can be induced by the flow over mono-, bi- and trilayered graphene samples of ~1 × 1.5 cm(2) in size in the same solution once the electrodes on graphene are isolated from interacting with the solution, mainly because the H(3)O(+) cations in the water adsorb onto graphene by strong covalent bonds as revealed by our first-principles calculations. When both the graphene and its metal electrodes are exposed to the solution as in the previous work, water flow over the graphene-electrode system can induce voltages from a few to over a hundred millivolts. In this situation, the graphene mainly behaves as a load connecting between the electrodes. Therefore, the harvested energy is not from the immersed carbon nanomaterials themselves in ionic water flow but dominated by the exposed electrodes.

  18. Infrared spectra of giant magnetoresistance Fe/Cr/Fe trilayers

    SciTech Connect

    Uran, S.; Grimsditch, M.; Fullerton, E.E.; Bader, S.D.

    1998-02-01

    Magnetic-field-induced changes in infrared transmission and reflection from Fe/Cr/Fe trilayers are reported. Changes as large as {approx}1{percent} (compared with 4{endash}5{percent} changes in resistivity) are observed around 2000cm{sup {minus}1}, and the magnitude of the effect decreases monotonically to zero at {approx}5000cm{sup {minus}1}. The field dependence mimics that of the resistivity, and saturates at the same field at which the magnetization of the two Fe layers align parallel to each other. A simple model, which estimates the frequency dependence of the resistivity and includes the frequency dependence of the skin depth, produces semiquantitative agreement with experiment. {copyright} {ital 1998} {ital The American Physical Society}

  19. Interaction-induced insulating state in thick multilayer graphene

    NASA Astrophysics Data System (ADS)

    Nam, Youngwoo; Ki, Dong-Keun; Koshino, Mikito; McCann, Edward; Morpurgo, Alberto F.

    2016-12-01

    Close to charge neutrality, the low-energy properties of high-quality suspended devices based on atomically thin graphene layers are determined by electron-electron interactions. Bernal-stacked layers, in particular, have shown a remarkable even-odd effect with mono- and tri-layers remaining gapless conductors, and bi- and tetra-layers becoming gapped insulators. These observations—at odds with the established notion that (Bernal) trilayers and thicker multilayers are semi-metals—have resulted in the proposal of a physical scenario leading to a surprising prediction, namely that even-layered graphene multilayers remain insulating irrespective of their thickness. Here, we present data from two devices that conform ideally to this hypothesis, exhibiting the behavior expected for Bernal-stacked hexa- and octa-layer graphene. Despite their large thickness, these multilayers are insulating for carrier density |n| < 2-3 × 1010 cm-2, possess an energy gap of approximately 1.5 meV at charge neutrality—in virtually perfect agreement with what is observed in bi- and tetra-layer graphene—and exhibit the expected integer quantum Hall effect. These findings indicate the soundness of our basic insights on the effect of electron interactions in Bernal graphene multilayers, show that graphene multilayers exhibit unusual and interesting physics that remains to be understood, and pose ever more pressing questions as to the microscopic mechanisms behind the semimetallic behavior of bulk graphite.

  20. Chemical bath deposition of cadmium sulfide on graphene-coated flexible glass substrate

    SciTech Connect

    Seo, Won-Oh; Jung, Younghun; Kim, Jihyun; Kim, Jiwan; Kim, Donghwan

    2014-03-31

    We demonstrate a flexible structure of cadmium sulfide (CdS) on graphene-coated glass substrate, where CdS was deposited by the chemical bath deposition method on defective tri-layer graphene. The defects in graphene, confirmed by micro-Raman spectroscopy, were created by a ultra-violet treatment with varying exposure time from 10 to 60 min. The number of defect sites in the graphene as a seed layer was related to the quality of the CdS thin films determined from the results from X-ray diffraction, optical transmittance, scanning electron microscopy, and room temperature micro-photoluminescence. Our film-on-substrate structure of CdS-graphene-on-glass was maintained up to a tensile strain of 0.3%, where graphene with a high failure strain was employed as a transparent conductive layer.

  1. Band structure mapping of bilayer graphene via quasiparticle scattering

    NASA Astrophysics Data System (ADS)

    Yankowitz, Matthew; Wang, Joel I.-Jan; Li, Suchun; Birdwell, A. Glen; Chen, Yu-An; Watanabe, Kenji; Taniguchi, Takashi; Quek, Su Ying; Jarillo-Herrero, Pablo; LeRoy, Brian J.

    2014-09-01

    A perpendicular electric field breaks the layer symmetry of Bernal-stacked bilayer graphene, resulting in the opening of a band gap and a modification of the effective mass of the charge carriers. Using scanning tunneling microscopy and spectroscopy, we examine standing waves in the local density of states of bilayer graphene formed by scattering from a bilayer/trilayer boundary. The quasiparticle interference properties are controlled by the bilayer graphene band structure, allowing a direct local probe of the evolution of the band structure of bilayer graphene as a function of electric field. We extract the Slonczewski-Weiss-McClure model tight binding parameters as γ0 = 3.1 eV, γ1 = 0.39 eV, and γ4 = 0.22 eV.

  2. Computation of the binding free energy of peptides to graphene in explicit water.

    PubMed

    Welch, Corrinne M; Camden, Aerial N; Barr, Stephen A; Leuty, Gary M; Kedziora, Gary S; Berry, Rajiv J

    2015-07-28

    The characteristic properties of graphene make it useful in an assortment of applications. One particular application--the use of graphene in biosensors--requires a thorough understanding of graphene-peptide interactions. In this study, the binding of glycine (G) capped amino acid residues (termed GXG tripeptides) to trilayer graphene surfaces in aqueous solution was examined and compared to results previously obtained for peptide binding to single-layer free-standing graphene [A. N. Camden, S. A. Barr, and R. J. Berry, J. Phys. Chem. B 117, 10691-10697 (2013)]. In order to understand the interactions between the peptides and the surface, binding enthalpy and free energy values were calculated for each GXG system, where X cycled through the typical 20 amino acids. When the GXG tripeptides were bound to the surface, distinct conformations were observed, each with a different binding enthalpy. Analysis of the binding energy showed the binding of peptides to trilayer graphene was dominated by van der Waals interactions, unlike the free-standing graphene systems, where the binding was predominantly electrostatic in nature. These results demonstrate the utility of computational materials science in the mechanistic explanation of surface-biomolecule interactions which could be applied to a wide range of systems.

  3. Raman spectra of epitaxial graphene on SiC and of epitaxial graphene transferred to SiO2.

    PubMed

    Lee, Dong Su; Riedl, Christian; Krauss, Benjamin; von Klitzing, Klaus; Starke, Ulrich; Smet, Jurgen H

    2008-12-01

    Raman spectra were measured for mono-, bi-, and trilayer graphene grown on SiC by solid state graphitization, whereby the number of layers was preassigned by angle-resolved ultraviolet photoemission spectroscopy. It was found that the only unambiguous fingerprint in Raman spectroscopy to identify the number of layers for graphene on SiC(0001) is the line width of the 2D (or D*) peak. The Raman spectra of epitaxial graphene show significant differences as compared to micromechanically cleaved graphene obtained from highly oriented pyrolytic graphite crystals. The G peak is found to be blue-shifted. The 2D peak does not exhibit any obvious shoulder structures, but it is much broader and almost resembles a single-peak even for multilayers. Flakes of epitaxial graphene were transferred from SiC onto SiO2 for further Raman studies. A comparison of the Raman data obtained for graphene on SiC with data for epitaxial graphene transferred to SiO2 reveals that the G peak blue-shift is clearly due to the SiC substrate. The broadened 2D peak however stems from the graphene structure itself and not from the substrate.

  4. Measuring the Complex Optical Conductivity of Graphene by Fabry-Pérot Reflectance Spectroscopy

    PubMed Central

    Ghamsari, Behnood G.; Tosado, Jacob; Yamamoto, Mahito; Fuhrer, Michael S.; Anlage, Steven M.

    2016-01-01

    We have experimentally studied the dispersion of optical conductivity in few-layer graphene through reflection spectroscopy at visible wavelengths. A laser scanning microscope (LSM) with a supercontinuum laser source measured the frequency dependence of the reflectance of exfoliated graphene flakes, including monolayer, bilayer and trilayer graphene, loaded on a Si/SiO2 Fabry-Pérot resonator in the 545–700 nm range. The complex refractive index of few-layer graphene, n − ik, was extracted from the reflectance contrast to the bare substrate. It was found that each few-layer graphene possesses a unique dispersionless optical index. This feature indicates that the optical conductivity does not simply scale with the number of layers, and that inter-layer electrodynamics are significant at visible energies. PMID:27682974

  5. 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

  6. Low vacuum annealing of cellulose acetate on nickel towards transparent conductive CNT-graphene hybrid films.

    PubMed

    Nguyen, Duc Dung; Tiwari, Rajanish N; Matsuoka, Yuki; Hashimoto, Goh; Rokuta, Eiji; Chen, Yu-Ze; Chueh, Yu-Lun; Yoshimura, Masamichi

    2014-06-25

    We report a versatile method based on low vacuum annealing of cellulose acetate on nickel (Ni) surface for rapid fabrication of graphene and carbon nanotube (CNT)-graphene hybrid films with tunable properties. Uniform films mainly composed of tri-layer graphene can be achieved via a surface precipitation of dissociated carbon at 800 °C for 30 seconds under vacuum conditions of ∼0.6 Pa. The surface precipitation process is further found to be efficient for joining the precipitated graphene with pre-coated CNTs on the Ni surface, consequently, generating the hybrid films. As expected, the hybrid films exhibit substantial opto-electrical and field electron emission properties superior to their individual counterparts. The finding suggests a promising route to hybridize the graphene with diverse nanomaterials for constructing novel hybrid materials with improved performances.

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

    PubMed

    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

    2015-11-04

    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.

  8. Effective optical constants and effective optical properties of ultrathin trilayer structures

    NASA Astrophysics Data System (ADS)

    Haija, A. J.; Larry Freeman, W.; Umbel, Rachel

    2011-01-01

    This work presents an extension of the characteristic effective medium approximation (CEMA) to ultrathin trilayer systems. The extension has been carried out analytically and is supported by corresponding calculations of the effective optical constants of Cu-Au-Cu and Ag-SiO-Ag trilayer systems using the CEMA approximation. This work is in essence a generalization of the characteristic effective medium approximation introduced earlier for ultrathin bilayer structures. This method is used to derive the effective optical constants of a trilayer system, consisting of three thin layers with each constituent layer of thickness much less than the wavelength of the incident radiation. Within this regime a trilayer system is viewed as one effective layer referred to as an effective stack (ES) with well defined effective optical constants, which can be used to calculate the optical properties of the trilayer stack within a specified wavelength range. The CEMA based calculations of the effective optical constants are applied to two trilayer systems with a total of five stacks. Three are Cu-Au-Cu and two are Ag-SiO-Ag stacks. The thicknesses of the parent layers in the Cu-Au-Cu stack range from 3 to 30 nm for Cu and 4 to 40 nm for Au; in the Ag-SiO-Ag stack the constituent layers are 6 nm for Ag, but range from 5 to 10 nm for SiO. This study is for normal or near normal incidence spectroscopy in a wavelength range that extends from visible to near infrared. The agreement between CEMA based ES stack results and those of the standard CMT technique is very satisfactory.

  9. Development of new Si-contained hardmask for tri-layer process

    NASA Astrophysics Data System (ADS)

    Nakajima, Makoto; Kanno, Yuta; Shibayama, Wataru; Takeda, Satoshi; Kato, Masakazu; Matsumoto, Takashi

    2011-04-01

    In the advanced semiconductor lithography process, the tri-layer process have been used for the essential technique{photoresist/ silicon contained hard mask (Si-HM) / spin on carbon hard mask (SOC)}(Figure 1). Tri-layer process was introduced and applied to the L/S and C/H patterning in the ArF dry and ArF immersion lithography process. Therefore, Si-HM should have the wider compatibility with different photoresist. In this paper, we investigate the interface behavior between photoresist and Si-HM in detail and get the new Si-HM to have the wider compatibility with different photoresist.

  10. Characterization and dynamic charge dependent modeling of conducting polymer trilayer bending

    NASA Astrophysics Data System (ADS)

    Farajollahi, Meisam; Sassani, Farrokh; Naserifar, Naser; Fannir, Adelyne; Plesse, Cédric; Nguyen, Giao T. M.; Vidal, Frédéric; Madden, John D. W.

    2016-11-01

    Trilayer bending actuators are charge driven devices that have the ability to function in air and provide large mechanical amplification. The electronic and mechanical properties of these actuators are known to be functions of their charge state making prediction of their responses more difficult when they operate over their full range of deformation. In this work, a combination of state space representation and a two-dimensional RC transmission line model are used to implement a nonlinear time variant model for conducting polymer-based trilayer actuators. Electrical conductivity and Young’s modulus of electromechanically active PEDOT conducting polymer containing films as a function of applied voltage were measured and incorporated into the model. A 16% drop in Young’s modulus and 24 times increase in conductivity are observed by oxidizing the PEDOT. A closed form formulation for radius of curvature of trilayer actuators considering asymmetric and location dependent Young’s modulus and conductivity in the conducting polymer layers is derived and implemented in the model. The nonlinear model shows the capability to predict the radius of curvature as a function of time and position with reasonable consistency (within 4%). The formulation is useful for general trilayer configurations to calculate the radius of curvature as a function of time. The proposed electrochemical modeling approach may also be useful for modeling energy storage devices.

  11. Properties of Superconducting Mo, Mo2n and Trilayer Mo2n-Mo-Mo2n Thin Films

    NASA Technical Reports Server (NTRS)

    Barrentine, E. M.; Stevenson, T. R.; Brown, A. D.; Lowitz, A. E.; Noroozian, O.; U-Yen, K.; Eshan, N.; Hsieh, W. T.; Moseley, S. H.; Wollack, E. J.

    2014-01-01

    We present measurements of the properties of thin film superconducting Mo, Mo2N and Mo2N/Mo/Mo2N trilayers of interest for microwave kinetic inductance detector (MKID) applications. Using microwave resonator devices, we investigate the transition temperature, energy gaps, kinetic inductance, and internal quality factors of these materials. We present an Usadel-based interpretation of the trilayer transition temperature as a function of trilayer thicknesses, and a 2-gap interpretation to understand the change in kinetic inductance and internal resonance quality factor (Q) as a function of temperature.

  12. Resonant tunneling and intrinsic bistability in twisted graphene structures

    NASA Astrophysics Data System (ADS)

    Rodriguez-Nieva, J. F.; Dresselhaus, M. S.; Levitov, L. S.

    2016-08-01

    We predict that vertical transport in heterostructures formed by twisted graphene layers can exhibit a unique bistability mechanism. Intrinsically bistable I -V characteristics arise from resonant tunneling and interlayer charge coupling, enabling multiple stable states in the sequential tunneling regime. We consider a simple trilayer architecture, with the outer layers acting as the source and drain and the middle layer floating. Under bias, the middle layer can be either resonant or nonresonant with the source and drain layers. The bistability is controlled by geometric device parameters easily tunable in experiments. The nanoscale architecture can enable uniquely fast switching times.

  13. 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.

  14. Contribution of individual interfaces in the MgO/Co/Pd trilayer to perpendicular magnetic anisotropy upon annealing

    SciTech Connect

    Kim, Minseok; Kim, Sanghoon; Ko, Jungho; Hong, Jongill

    2015-03-09

    The contribution of each interface of the MgO/Co/Pd trilayer to the perpendicular magnetic anisotropy (PMA) was studied by changing chemical and crystalline structures through annealing. We found that volumetric anisotropy in the MgO/Co/Pd trilayer was significantly increased due to enhanced magnetoelastic anisotropy caused by stress built up most likely at the MgO/Co interface during annealing. When the trilayer was annealed at 400 °C, the alloy formation at the Co/Pd interface additionally increased the volumetric anisotropy. Our x-ray magnetic circular dichroism study supported that those structural modifications led to an increase in the orbital moment through spin-orbit coupling (SOC) along the film normal two times larger than that of the as-deposited trilayer, thereby enhancing PMA greatly. Our experimental results prove that the Co/Pd interface, rather than the MgO/Co interface, plays an essential role in inducing strong PMA in the trilayer. The precise investigation of annealing effect on both volumetric and interfacial anisotropies can provide a methodological solution to improve the SOC of the trilayer that can serve as the core unit of spintronic devices.

  15. Magnetic depth profiles of complex oxide F/S/F trilayers.

    NASA Astrophysics Data System (ADS)

    Visani, C.; Sefrioui, Z.; Leon, C.; Santamaria, J.; Te Velthuis, S. G. E.; Hoffmann, A.; Nemes, Norbert M.; Garcia-Hernandez, M.; Fitzsimmons, M. R.; Kirby, B. J.

    2008-03-01

    The origin of the large magnetoresitance in epitaxial F/S/F trilayers composed of highly spin polarized ferromagnetic La0.7Ca0.3MnO3 and high-Tc superconducting YBa2Cu3O7-δ (YBCO) is investigated by characterizing the magnetic structure. Polarized neutron reflectometry experiments have determined the detailed magnetization depth profiles in trilayers with varying YBCO layer thicknesses. In addition to inhomogeneous magnetization profiles, rotation of the magnetization during the magnetization reversal for the films with thick (>= 17.7 nm) YBCO layers has been observed. The results are consistent with the presence of an (in plane) easy-axis tilted away from the (100) direction.

  16. NiCo-lead zirconium titanate-NiCo trilayered magnetoelectric composites prepared by electroless deposition

    SciTech Connect

    Zhou, M. H.; Wang, Y. G.; Bi, K.; Fan, H. P.; Zhao, Z. S.

    2015-04-15

    The NiCo layers with various Ni/Co atomic ratio have been successfully electroless deposited on PZT layers by varying the bath composition. As the cobalt atomic ratio in the deposited layer increases from 17.2 to 54.8 wt%, the magnetostrictive coefficient decreases. The magnetoelectric effect depends strongly on the magnetostrictive properties of magnetostrictive phase. The magnetoelectric coefficient of NiCo/PZT/NiCo trilayers increases with Ni/Co atomic ratio of the deposited NiCo layers increasing from 45:55 to 83:17. A maximum ME voltage coefficient of α{sub E,31} = 2.8 V ⋅ cm{sup −1} ⋅ Oe{sup −1} is obtained at a frequency of about 88 kHz, which makes these trilayers suitable for applications in actuators, transducers and sensors.

  17. Preparation of gold/silver/titania trilayered nanorods and their photocatalytic activities.

    PubMed

    Horiguchi, Yoshimasa; Kanda, Takashi; Torigoe, Kanjiro; Sakai, Hideki; Abe, Masahiko

    2014-01-28

    Gold/silver/titania trilayered nanorods have been prepared by the successive deposition of silver and titania layers on gold nanorod cores, and their photocatalytic activities were investigated under visible-light illumination (λ > 420 nm). The photocatalytic activity of the trilayered nanorods in the oxidation of 2-propanol depends on both the Au/Ag composition and the thickness of the TiO2 shell. It increases with increasing Ag content up to [Au]/[Ag] = 1:5 (molar ratio) and then decreases with further increasing Ag content. The photocatalytic activity also increases with increasing TiO2 shell thickness up to 10 nm and then decreases with further increases in the shell thickness. These effects were explained by electron-transfer and energy-transfer mechanisms.

  18. Polycrystallinity and stacking in CVD graphene.

    PubMed

    Tsen, Adam W; Brown, Lola; Havener, Robin W; Park, Jiwoong

    2013-10-15

    slowly grown films. These structural differences can affect the material's electrical properties: for example, better-connected grain boundaries are more electrically conductive. However, grain boundaries in general are mechanically weaker than pristine graphene, which is an order of magnitude stronger than CVD graphene based on indentation measurements performed with an atomic force microscope. Vertical junctions in multilayer CVD graphene have two key structural features. First, bilayer graphene (BLG) with Bernal stacking exists in two mirrored configurations (AB or AC) that also form isolated domains. Similarly, oriented trilayer graphene also has alternating ABA and ABC stacked layers. Second, in twisted multilayer graphene, stacked layers lack long-range atomic registry and can move freely relative to each other, which generates unique optical properties. In particular, an interlayer optical excitation produces strong Raman and absorption peaks, dependent on the twist angle. A better understanding of the structural and physical properties of grain boundaries and multilayers in CVD graphene is central to realizing the full potential of graphene in large-scale applications. In addition, these studies provide a model for characterizing other layered materials, such as hexagonal boron nitride and MoS2, where similar polycrystallinity and stacking are expected when grown in large areas.

  19. Experimental investigations of superconductivity in quasi-two-dimensional epitaxial copper oxide superlattices and trilayers

    SciTech Connect

    Lowndes, D.H.; Norton, D.P.

    1993-06-01

    Epitaxial trilayer and superlattice structures grown by pulsed laser ablation have been used to study the superconducting-to-normal transition of ultrathin (one and two c-axis unit cells) YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} layers. The normalized flux-flow resistances for several epitaxial structures containing two-cell-thick YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} films collapse onto the ``universal`` curve of the Ginzburg-Landau Coulomb Gas (GLCG) model. Analysis of normalized resistance data for a series of superlattices containing one-cell-thick YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} layers also is consistent with the behavior expected for quasi-two-dimensional layers in a highly anisotropic, layered three-dimensional superconductor. Current-voltage measurements for one of the trilayer structures also are consistent with the normalized resistance data, and with the GLCG model. Scanning tunneling microscopy, transmission electron microscopy, and electrical transport studies show that growth-related steps in ultrathin YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} layers affect electrical continuity over macroscopic distances, acting as weak links. However , the perturbation of the superconducting order parameter can be minimized by utilizing hole-doped buffer and cap layers, on both sides of the YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} layer, in trilayers and superlattices. These results demonstrate the usefulness of epitaxial trilayer and superlattice structures as tools for systematic, fundamental studies of high-temperature superconductivity.

  20. Polarizing properties of embedded symmetric trilayer stacks under conditions of frustrated total internal reflection.

    PubMed

    Azzam, Rasheed M A; Perla, Siva R

    2006-03-01

    An all-transparent symmetric trilayer structure, which consists of a high-index center layer coated on both sides by a low-index film and embedded in a high-index prism, can function as an efficient polarizer or polarizing beam splitter under conditions of frustrated total internal reflection over a wide range of incidence angles. For a given set of refractive indices, all possible solutions for the thicknesses of the layers that suppress the reflection of either the p or s polarization at a specified angle, as well as the reflectance of the system for the orthogonal polarization, are determined. A 633 nm design that uses a MgF2-ZnS-MgF2 trilayer embedded in a ZnS prism achieves an extinction ratio (ER) > 40 dB from 50 degrees to 80 degrees in reflection and an ER > 20 dB from 58 degrees to 80 degrees in transmission. IR polarizers that use CaF2-Ge-CaF2 trilayers embedded in a ZnS prism are also considered.

  1. Graphene aerogels

    DOEpatents

    Pauzauskie, Peter J; Worsley, Marcus A; Baumann, Theodore F; Satcher, Jr., Joe H; Biener, Juergen

    2015-03-31

    Graphene aerogels with high conductivity and surface areas including a method for making a graphene aerogel, including the following steps: (1) preparing a reaction mixture comprising a graphene oxide suspension and at least one catalyst; (2) curing the reaction mixture to produce a wet gel; (3) drying the wet gel to produce a dry gel; and (4) pyrolyzing the dry gel to produce a graphene aerogel. Applications include electrical energy storage including batteries and supercapacitors.

  2. In-situ observation of graphene growth on Ni(111)

    NASA Astrophysics Data System (ADS)

    Odahara, Genki; Otani, Shigeki; Oshima, Chuhei; Suzuki, Masahiko; Yasue, Tsuneo; Koshikawa, Takanori

    2011-06-01

    Graphene growth of mono-, bi- and tri-layers on Ni(111) through surface segregation was observed in situ by low energy electron microscopy. The carbon segregation was controlled by adjusting substrate temperature from 1200 K to 1050 K. After the completion of the first layer at 1125 K, the second layer grew at the interface between the first-layer and the substrate at 1050 K. The third layer also started to grow at the same temperature, 1050 K. All the layers exhibited a 1 × 1 atomic structure. The edges of the first-layer islands were straight lines, reflecting the hexagonal atomic structure. On the other hand, the shapes of the second-layer islands were dendritic. The edges of the third-layer islands were again straight lines similar to those of the first-layer islands. The phenomena presumably originate from the changes of interfacial-bond strength of the graphene to Ni substrate depending on the graphene thickness. No nucleation site of graphene layers was directly observed. All the layers expanded out of the field of view and covered the surface. The number of nucleation sites is extremely small on Ni(111) surface. This finding might open the way to grow the high quality, single-domain graphene crystals.

  3. Observation of resistively detected hole spin resonance and zero-field pseudo-spin splitting in epitaxial graphene

    PubMed Central

    Mani, Ramesh G.; Hankinson, John; Berger, Claire; de Heer, Walter A.

    2012-01-01

    Electronic carriers in graphene show a high carrier mobility at room temperature. Thus, this system is widely viewed as a potential future charge-based high-speed electronic material to complement–or replace–silicon. At the same time, the spin properties of graphene have suggested improved capability for spin-based electronics or spintronics and spin-based quantum computing. As a result, the detection, characterization and transport of spin have become topics of interest in graphene. Here we report a microwave photo-excited transport study of monolayer and trilayer graphene that reveals an unexpectedly strong microwave-induced electrical response and dual microwave-induced resonances in the dc resistance. The results suggest the resistive detection of spin resonance, and provide a measurement of the g-factor, the spin relaxation time and the sub-lattice degeneracy splitting at zero magnetic field. PMID:22871815

  4. PREFACE: Graphene Graphene

    NASA Astrophysics Data System (ADS)

    Singleton, John; Ferry, David K.

    2009-08-01

    As is now well known, graphene was made in 2004 by the 'simple' expedient of cleaving a single atomic layer from a sample of graphite using a piece of sticky tape [1, 2]. This discovery stimulated a whirlwind of activity; at last, predictions about the unique behaviour of band electrons in a two-dimensional honeycomb lattice made as early as the 1940s could be verified experimentally [1, 2]. Perhaps the most influential result has been the confirmation that the charge carriers in graphene behave in many ways as 'Dirac fermions', mimicing the dynamics of hyper-relativistic electrons, but with 1/300th of the velocity. Another important pairing of prediction and result has been the observation of carrier mobilities that have an unusual (in)dependence on impurity concentration, suggesting applications in high-speed ballistic transistors and even the eventual part replacement of silicon by graphene as the devices on chips become ever smaller [1, 2]. As a result of the considerable and rapid activity in this field, reviews of the properties of graphene have appeared; a good introduction to the early work at a level appropriate to students is given in [1], whilst [2] covers more recent progress at a more advanced level. However, the field is progressing so rapidly that even good reviews become dated by the time they appear in print, and new work and studies are appearing daily. In this issue, we have tried to pull together a group of papers which examine some of these new areas of work in graphene; these range from low-temperature physics to high electric field transport at room temperature [3]. Given the postulated future use of graphene in ultra-small devices, it is no surprise that quantum dots and wires feature heavily in the articles by Peres et al [4], Huang et al [5] and Sun and Xie [6]. Moreover, applications will inevitably involve graphene in contact with other materials and chemical systems, resulting in modifications to its electronic properties. For example

  5. Graphene spintronics.

    PubMed

    Han, Wei; Kawakami, Roland K; Gmitra, Martin; Fabian, Jaroslav

    2014-10-01

    The isolation of graphene has triggered an avalanche of studies into the spin-dependent physical properties of this material and of graphene-based spintronic devices. Here, we review the experimental and theoretical state-of-art concerning spin injection and transport, defect-induced magnetic moments, spin-orbit coupling and spin relaxation in graphene. Future research in graphene spintronics will need to address the development of applications such as spin transistors and spin logic devices, as well as exotic physical properties including topological states and proximity-induced phenomena in graphene and other two-dimensional materials.

  6. Synthesis of an air-working trilayer artificial muscle using a conductive cassava starch biofilm (manihot esculenta, cranz) and polypyrrole (PPy)

    NASA Astrophysics Data System (ADS)

    Núñez D, Y. E.; Arrieta A, Á. A.; Segura B, J. A.; Bertel H, S. D.

    2016-02-01

    In this study, a methodology for obtaining a conductive cassava starch biofilm doped with lithium perchlorate (LiClO4) is shown, as well as the electrochemical technique for the synthesis of polypyrrole films, which are used for developing the trilayer artificial muscle PPy/Biopolymer/PPy designed to operate in air. Furthermore, results from the trilayer movement using chronoamperometric techniques are shown.

  7. Graphene transistors.

    PubMed

    Schwierz, Frank

    2010-07-01

    Graphene has changed from being the exclusive domain of condensed-matter physicists to being explored by those in the electron-device community. In particular, graphene-based transistors have developed rapidly and are now considered an option for post-silicon electronics. However, many details about the potential performance of graphene transistors in real applications remain unclear. Here I review the properties of graphene that are relevant to electron devices, discuss the trade-offs among these properties and examine their effects on the performance of graphene transistors in both logic and radiofrequency applications. I conclude that the excellent mobility of graphene may not, as is often assumed, be its most compelling feature from a device perspective. Rather, it may be the possibility of making devices with channels that are extremely thin that will allow graphene field-effect transistors to be scaled to shorter channel lengths and higher speeds without encountering the adverse short-channel effects that restrict the performance of existing devices. Outstanding challenges for graphene transistors include opening a sizeable and well-defined bandgap in graphene, making large-area graphene transistors that operate in the current-saturation regime and fabricating graphene nanoribbons with well-defined widths and clean edges.

  8. 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.

  9. High quality ZnS/Au/ZnS transparent conductive tri-layer films deposited by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Wang, Caifeng; Li, Qingshan; Wang, Jisuo; Zhang, Lichun; Zhao, Fengzhou; Dong, Fangying

    2016-07-01

    ZnS/Au/ZnS tri-layer films were deposited on quartz glass substrates by pulsed laser deposition. The influence of Au layer thickness on optical and electrical properties of the tri-layer ZnS/Au/ZnS was studied. X-ray diffractometer (XRD) and scanning electron microscope were employed to characterize the crystalline structure and surface morphology of the tri-layer films. Hall measurements, ultraviolet and visible spectrophotometer, four-point probe were used to explore the optoelectronic properties of the ZnS/Au/ZnS. The increase of Au layer thickness resulted in the decreased resistivity, the increased carrier concentration, and the declined transmittance in the visible light region.

  10. Ferromagnetic resonance studies of exchange coupled ultrathin Py/Cr/Py trilayers

    NASA Astrophysics Data System (ADS)

    Topkaya, R.; Erkovan, M.; Öztürk, A.; Öztürk, O.; Aktaş, B.; Özdemir, M.

    2010-07-01

    Magnetic properties of ultrathin Py/Cr/Py trilayers have been investigated as a function of Cr spacer layer thickness by using ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques. The Cr spacer layer thickness was increased from 4 to 40 Å with 1 Å steps to determine the dependence of interlayer exchange coupling between ferromagnetic layers on the spacer layer thickness. Two strong and well resolved peaks were observed which correspond to a strong (acoustic) and weak (optic) modes of magnetization precession in the effective dc field due to the exciting external microwave field as the external dc field orientation comes close to the film normal. The separation of the two modes in the field axis depends on the thickness of Cr spacer layer. An interchange in the relative positions of the acoustic and optic modes has been observed for a particular thickness of Cr spacer layer as well. A computer program for magnetically exchange coupled N magnetic layers was written to simulate the experimental FMR spectra and to obtain the magnetic parameters of ultrathin Py/Cr/Py trilayers. FMR data have been analyzed from every aspect by using this program and interlayer exchange coupling constant was calculated for the prepared structures. It was found that the relative position of the peaks depends on the nature (sign) of the interlayer exchange coupling between ferromagnetic layers through Cr spacer layer. In Py/Cr/Py trilayers, strength of the interlayer exchange coupling constant oscillates and changes its sign with Cr spacer layer thickness with a period of about 11 Å.

  11. Cyclic chlorine trap-doping for transparent, conductive, thermally stable and damage-free graphene.

    PubMed

    Pham, Viet Phuong; Kim, Kyong Nam; Jeon, Min Hwan; Kim, Ki Seok; Yeom, Geun Young

    2014-12-21

    We propose a novel doping method of graphene using the cyclic trap-doping method with low energy chlorine adsorption. Low energy chlorine adsorption for graphene chlorination avoided defect (D-band) formation during the doping by maintaining the π-bonding of the graphene, which affects conductivity. In addition, by trapping chlorine dopants between the graphene layers, the sheet resistance could be decreased by ∼ 88% under optimized conditions. Among the reported doping methods, including chemical, plasma, and photochemical methods, the proposed doping method is believed to be the most promising for producing graphene with extremely high transmittance, low sheet resistance, high thermal stability, and high flexibility for use in various flexible electronic devices. The results of Raman spectroscopy and sheet resistance showed that this method is also non-destructive and controllable. The sheet resistance of the doped tri-layer graphene was 70 Ω per sq. at transmittance of 94%, and which was maintained for more than 100 h in a vacuum at 230 °C. Moreover, the defect intensity of graphene was not increased during the cyclic trap-doping.

  12. Interplay between magnetic anisotropy and interlayer coupling in nanosecond magnetization reversal of spin-valve trilayers

    NASA Astrophysics Data System (ADS)

    Vogel, J.; Kuch, W.; Camarero, J.; Fukumoto, K.; Pennec, Y.; Pizzini, S.; Bonfim, M.; Petroff, F.; Fontaine, A.; Kirschner, J.

    2005-02-01

    The influence of magnetic anisotropy on nanosecond magnetization reversal in coupled FeNi/Cu/Co trilayers was studied using a photoelectron emission microscope combined with x-ray magnetic circular dicroism. In quasi-isotropic samples the reversal of the soft FeNi layer is determined by domain-wall pinning that leads to the formation of small and irregular domains. In samples with uniaxial magnetic anisotropy, the domains are larger and the influence of local interlayer coupling dominates the domain structure and the reversal of the FeNi layer.

  13. Fabrication of Planar, Layered Nanoparticles Using Tri-layer Resist Templates

    PubMed Central

    Hu, Wei; Zhang, Mingliang; Wilson, Robert J.; Koh, Ai Leen; Wi, Jung-Sub; Tang, Mary; Sinclair, Robert; Wang, Shan X.

    2011-01-01

    A simple and universal pathway to produce free multilayer synthetic nanoparticles is developed based on lithography, vapor phase deposition and a tri-layer resist lift off and release process. The fabrication method presented in this work is ideal for production of a broad range of nanoparticles, either free in solution or still attached to an intact release layer, with unique magnetic, optical, radioactive, electronic and catalytic properties. Multi-modal capabilities are implicit in the layered architecture. As an example, directly fabricated magnetic nanoparticles are evaluated to illustrate the structural integrity of thin internal multilayers and the nanoparticle stability in aggressive biological environments, which is highly desired for biomedical applications. PMID:21415483

  14. Surface-plasmon-induced optical magnetic response in perforated trilayer metamaterial.

    PubMed

    Li, T; Liu, H; Wang, F M; Li, J Q; Zhu, Y Y; Zhu, S N

    2007-07-01

    Surface plasmon excitations and the associated optical transmission properties in perforated metal/dielectric/metal trilayer structures are numerically investigated. Pronounced magnetic modes are observed in the antisymmetric and asymmetric modes of surface plasmon polaritons (SPPs). The influence of substrates on the magnetic response is studied in detail. Quite different from the conventional LC-circuit resonance, these magnetic excitations arise from the nonlocalized SPPs in the perforated layered structure, which may considerably enrich the electromagnetic properties of such metamaterials, especially the artificial magnetism at optical frequency.

  15. Nonlinear motion of coupled magnetic vortices in ferromagnetic/non-magnetic/ferromagnetic trilayer

    SciTech Connect

    Jun, Su-Hyeong; Shim, Je-Ho; Oh, Suhk-Kun; Yu, Seong-Cho; Kim, Dong-Hyun; Mesler, Brooke; Fischer, Peter

    2009-07-05

    We have investigated a coupled motion of two vortex cores in ferromagnetic/nonmagnetic/ferromagnetic trilayer cynliders by means of micromagnetic simulation. Dynamic motion of two vortex with parallel and antiparallel relative chiralities of curling spins around the vortex cores have been examined after excitation by 1-ns pulsed external field. With systematic variation in non-magnetic spacer layer thickness from 0 to 20 nm, the coupling between two cores becomes significant as the spacer becomes thinner. Significant coupling leads to a nonlinear chaotic coupled motion of two vortex cores for the parallel chiralities and a faster coupled gyrotropic oscillation for the antiparallel chiralities.

  16. Enhancement of thermoelectric efficiency by quantum interference effects in trilayer silicene flakes

    NASA Astrophysics Data System (ADS)

    Cortés, Natalia; Rosales, L.; Chico, Leonor; Pacheco, M.; Orellana, P. A.

    2017-01-01

    In recent years, the enhancement of thermoelectric efficiencies has been accomplished in nanoscale systems by making use of quantum effects. We exploit the presence of quantum interference phenomena such as bound states in the continuum and Fano antiresonances in trilayer silicene flakes to produce sharp changes in the electronic transmission of the system. By applying symmetric gate voltages the thermoelectric properties can be tuned and, for particular flake lengths, a great enhancement of the figure of merit can be achieved. We show that the most favorable configurations are those in which the electronic transmission is dominated by the coupling of bound states to the continuum, tuned by an external gate.

  17. Spin-current-induced magnetoresistance in trilayer structure with nonmagnetic metallic interlayer

    NASA Astrophysics Data System (ADS)

    Iguchi, Ryo; Sato, Koji; Uchida, Ken-ichi; Saitoh, Eiji

    2017-04-01

    We have theoretically investigated the spin Hall magnetoresistance (SMR) and Rashba–Edelstein magnetoresistance (REMR), mediated by spin currents, in a ferrimagnetic insulator/nonmagnetic metal/heavy metal system in the diffusive regime. The magnitude of both SMR and REMR decreases with increasing thickness of the interlayer because of the current shunting effect and the reduction in spin accumulation across the interlayer. The latter contribution is due to driving a spin current and persists even in the absence of spin relaxation, which is essential for understanding the magnetoresistance ratio in trilayer structures.

  18. Electric field and dewetting induced hierarchical structure formation in polymer/polymer/air trilayers.

    PubMed

    Leach, K Amanda; Gupta, Suresh; Dickey, Michael D; Willson, C Grant; Russell, Thomas P

    2005-12-01

    Electrohydrodynamics were studied in a trilayer thin film system consisting of two different polymeric layers and air. A polymer with a higher dielectric constant, poly(methyl methacrylate), was sandwiched between air and a lower dielectric constant polymer, polystyrene. An electric field was applied normal to the interfaces. Along with electrostatic forces, dewetting forces were significant at two of the interfaces, namely, the polystyrene/silicon wafer and the polystyrene/poly(methyl methacrylate) interfaces. These two combined forces produce novel closed-cell structures that are difficult to produce by other existing techniques.

  19. Compression Limit of Two-Dimensional Water Constrained in Graphene Nanocapillaries.

    PubMed

    Zhu, YinBo; Wang, FengChao; Bai, Jaeil; Zeng, Xiao Cheng; Wu, HengAn

    2015-12-22

    Evaluation of the tensile/compression limit of a solid under conditions of tension or compression is often performed to provide mechanical properties that are critical for structure design and assessment. Algara-Siller et al. recently demonstrated that when water is constrained between two sheets of graphene, it becomes a two-dimensional (2D) liquid and then is turned into an intriguing monolayer solid with a square pattern under high lateral pressure [ Nature , 2015 , 519 , 443 - 445 ]. From a mechanics point of view, this liquid-to-solid transformation characterizes the compression limit (or metastability limit) of the 2D monolayer water. Here, we perform a simulation study of the compression limit of 2D monolayer, bilayer, and trilayer water constrained in graphene nanocapillaries. At 300 K, a myriad of 2D ice polymorphs (both crystalline-like and amorphous) are formed from the liquid water at different widths of the nanocapillaries, ranging from 6.0 to11.6 Å. For monolayer water, the compression limit is typically a few hundred MPa, while for the bilayer and trilayer water, the compression limit is 1.5 GPa or higher, reflecting the ultrahigh van der Waals pressure within the graphene nanocapillaries. The compression-limit (phase) diagram is obtained at the nanocapillary width versus pressure (h-P) plane, based on the comprehensive molecular dynamics simulations at numerous thermodynamic states as well as on the Clapeyron equation. Interestingly, the compression-limit curves exhibit multiple local minima.

  20. Square ice in graphene nanocapillaries.

    PubMed

    Algara-Siller, G; Lehtinen, O; Wang, F C; Nair, R R; Kaiser, U; Wu, H A; Geim, A K; Grigorieva, I V

    2015-03-26

    Bulk water exists in many forms, including liquid, vapour and numerous crystalline and amorphous phases of ice, with hexagonal ice being responsible for the fascinating variety of snowflakes. Much less noticeable but equally ubiquitous is water adsorbed at interfaces and confined in microscopic pores. Such low-dimensional water determines aspects of various phenomena in materials science, geology, biology, tribology and nanotechnology. Theory suggests many possible phases for adsorbed and confined water, but it has proved challenging to assess its crystal structure experimentally. Here we report high-resolution electron microscopy imaging of water locked between two graphene sheets, an archetypal example of hydrophobic confinement. The observations show that the nanoconfined water at room temperature forms 'square ice'--a phase having symmetry qualitatively different from the conventional tetrahedral geometry of hydrogen bonding between water molecules. Square ice has a high packing density with a lattice constant of 2.83 Å and can assemble in bilayer and trilayer crystallites. Molecular dynamics simulations indicate that square ice should be present inside hydrophobic nanochannels independently of their exact atomic nature.

  1. Structural and electronic properties of multilayer graphene on monolayer hexagonal boron nitride/nickel (111) interface system: A van der Waals density functional study

    NASA Astrophysics Data System (ADS)

    Yelgel, Celal

    2016-02-01

    The structural and electronic properties of multilayer graphene adsorbed on monolayer hexagonal boron nitride (h-BN)/Ni(111) interface system are investigated using the density functional theory with a recently developed non-local van der Waals density functional (rvv10). The most energetically favourable configuration for a monolayer h-BN/Ni(111) interface is found to be N atom atop the Ni atoms and B atom in fcc site with the interlayer distance of 2.04 Å and adsorption energy of 302 meV/BN. Our results show that increasing graphene layers on a monolayer h-BN/Ni(111) interface leads to a weakening of the interfacial interaction between the monolayer h-BN and Ni(111) surface. The adsorption energy of graphene layers on the h-BN/Ni(111) interface is found to be in the range of the 50-120 meV/C atom as the vertical distance from h-BN to the bottommost graphene layers decreases. With the adsorption of a multilayer graphene on the monolayer h-BN/Ni(111) interface system, the band gap of 0.12 eV and 0.25 eV opening in monolayer graphene and bilayer graphene near the K point is found with an upward shifting of the Fermi level. However, a stacking-sensitive band gap is opened in trilayer graphene. We obtain the band gap of 0.35 eV close to the K point with forming a Mexican hat band structure for ABC-stacked trilayer graphene.

  2. Aromatic graphene

    NASA Astrophysics Data System (ADS)

    Das, D. K.; Sahoo, S.

    2016-04-01

    In recent years graphene attracts the scientific and engineering communities due to its outstanding electronic, thermal, mechanical and optical properties and many potential applications. Recently, Popov et al. [1] have studied the properties of graphene and proved that it is aromatic but without fragrance. In this paper, we present a theory to prepare graphene with fragrance. This can be used as scented pencils, perfumes, room and car fresheners, cosmetics and many other useful household substances.

  3. Shear Assisted Electrochemical Exfoliation of Graphite to Graphene.

    PubMed

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

    2016-04-12

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

  4. Oxidative pit formation in pristine, hydrogenated and dehydrogenated graphene

    NASA Astrophysics Data System (ADS)

    Jones, J. D.; Morris, C. F.; Verbeck, G. F.; Perez, J. M.

    2013-01-01

    We study oxidative pit formation in pristine, hydrogenated, and dehydrogenated monolayer graphene (MLG), bilayer graphene (BLG) and trilayer graphene (TLG). Graphene samples are produced by mechanical exfoliation of highly oriented pyrolytic graphite (HOPG) onto SiO2 substrates. Etching is carried out by exposing samples to O2 gas at 450-700 °C. Using atomic force microscopy, we observe that pre-heating pristine MLG in vacuum at 590 °C increases the onset temperature for pit formation to values comparable to those in HOPG. We attribute this decrease in reactivity to an increase in adhesion between the MLG and substrate. In hydrogenated MLG and BLG, we observe a significant decrease in the onset temperature for pit formation. Dehydrogenation of these materials results in a decrease in the density of pits. We attribute the decrease in onset temperature to H-related defects in their sp3-bonded structure. In contrast, hydrogenated TLG and thicker-layer samples show no significant change in pit formation. We propose that this is because they are not transformed into an sp3-bonded structure by hydrogenation.

  5. Origin of perpendicular magnetic anisotropy in epitaxial Pd /Co /Pd (111 ) trilayers

    NASA Astrophysics Data System (ADS)

    Davydenko, A. V.; Kozlov, A. G.; Ognev, A. V.; Stebliy, M. E.; Samardak, A. S.; Ermakov, K. S.; Kolesnikov, A. G.; Chebotkevich, L. A.

    2017-02-01

    Perpendicular magnetic anisotropy in epitaxial Pd /Co /Pd (111 ) trilayered films grown on Si(111) substrate was investigated. Contributions to perpendicular magnetic anisotropy from the bottom and top Co/Pd interfaces were deduced by replacement of Pd layers by Cu layers and comparative analysis of the magnetic anisotropy in the samples. Perpendicular magnetic anisotropy in Pd/Co/Pd films was induced both by interface electronic effects and by stress caused by lattice mismatch between Pd and Co. Due to asymmetry of the stress in the Co film, the contribution to magnetic anisotropy induced by the bottom Co/Pd interface was stronger than that induced by the top Pd/Co interface. The energy of the perpendicular magnetic anisotropy and asymmetrical contributions from the bottom Co/Pd and top Pd/Co interfaces to anisotropy in Pd/Co/Pd trilayers strongly depend on the thickness of the bottom and top Pd layers and may be precisely controlled. The roughness of the interfaces does not have a large influence on the energy of perpendicular magnetic anisotropy in this system.

  6. Quantitative analysis of spin Hall magnetoresistance in ferrimagnetic insulator/Cu/normal metal trilayer structure

    NASA Astrophysics Data System (ADS)

    Iguchi, Ryo; Hirobe, Daichi; Uchida, Kenichi; Saitoh, Eiji

    2014-03-01

    A spin current, a flow of spin angular momentum without a charge current, has been attracted much attention in spintronics. As recently demonstrated, a spin current gives rise to a new magnetoresistance effect called spin Hall magnetoresistance (SMR) owing to the interaction between charge and spin currents via the direct and inverse spin Hall effects. SMR has been intensely studied in the ferrimagnetic insulator(FI)/normal metal (NM) bilayer structure both experimentally and theoretically. In contrast, it is not quantitatively investigated in the FI/Cu/NM trilayer structure. The insertion of a Cu layer, which has a long spin diffusion length, between the FI and NM layers is useful for avoiding the possible appearance of an extrinsic proximity effect in NM close to the Stoner ferromagnetic instability such as Pd and Pt. Thus, the quantitative analysis of the FI/Cu/NM system helps to clarify the origin of magnetoresistive behavior observed in the FI/NM system. We studied SMR in the trilayer structure based on the spin diffusion equation and the spin circuit theory, and found that the reported experimental results are well reproduced by our calculation.

  7. High-Si content BARC for dual-BARC systems such as trilayer patterning

    NASA Astrophysics Data System (ADS)

    Kennedy, Joseph; Xie, Song-Yuan; Wu, Ze-Yu; Katsanes, Ron; Flanigan, Kyle; Lee, Kevin; Slezak, Mark; Liu, Zhi; Lin, Shang-Ho

    2009-03-01

    This work discusses the requirements and performance of Honeywell's middle layer material, UVAS, for tri-layer patterning. UVAS is a high Si content polymer synthesized directly from Si containing starting monomer components. The monomers are selected to produce a film that meets the requirements as a middle layer for tri-layer patterning (TLP) and gives us a level of flexibility to adjust the properties of the film to meet the customer's specific photoresist and patterning requirements. Results of simulations of the substrate reflectance versus numerical aperture, UVAS thickness, and under layer film are presented. ArF photoresist line profiles and process latitude versus UVAS bake at temperatures as low as 150ºC are presented and discussed. Immersion lithographic patterning of ArF photoresist line space and contact hole features will be presented. A sequence of SEM images detailing the plasma etch transfer of line space photoresist features through the middle and under layer films comprising the TLP film stack will be presented. Excellent etch selectivity between the UVAS and the organic under layer film exists as no edge erosion or faceting is observed as a result of the etch process. A detailed study of the impact of a PGMEA solvent photoresist rework process on the lithographic process window of a TLP film stack was performed with the results indicating that no degradation to the UVAS film occurs.

  8. Influence of Interlayer Design on Residual Thermal Stresses in Trilayered and Graded All-Ceramic Restorations

    PubMed Central

    Henriques, Bruno; Fabris, Douglas; Souza, Júlio C. M.; Silva, Filipe S.; Mesquita-Guimarães, Joana; Zhang, Yu; Fredel, Márcio

    2017-01-01

    Residual thermal stresses are formed in dental restorations during cooling from high temperature processing. The aim of this study was to evaluate the influence of constructive design variables (composition and interlayer thickness) on residual stresses in alumina- and zirconia-graded restorations. Restorations' real-like cooling conditions were simulated using finite elements method and temperature-dependent material properties were used. Three different designs were evaluated: a bilayered restoration (sharp transition between materials); a trilayered restoration with a homogenous interlayer between core and veneer; and a trilayered restoration with a graded interlayer. The interlayer thickness and composition were varied. Zirconia restorations presented overall higher thermal stress values than alumina ones. Thermal stresses were significantly reduced by the presence of a homogeneous interlayer. The composition of the interlayer showed great influence on the thermal stresses, with the best results for homogeneous interlayers being observed for porcelain contents in the composite ranging between 30%-50% (vol.%), for both alumina and zirconia restorations. The interlayer's thickness showed a minor contribution in the thermal stress reduction. The graded interlayer showed an optimized reduction in restorations' thermal stresses. The use of graded interlayer, favoring enhanced thermal stress distributions and lower magnitude is expected to reduce the risk of catastrophic failure. PMID:27987657

  9. Electrochemomechanical deformation (ECMD) of PPyDBS in free standing film formation and trilayer designs

    NASA Astrophysics Data System (ADS)

    Aydemir, Nihan; Tamm, Tarmo; Travas-Sejdic, Jadranka; Kilmartin, Paul A.; Aabloo, Alvo; Kiefer, Rudolf

    2014-03-01

    An investigation is reported into the electrochemomechanical deformation (ECMD) of polypyrrole (PPy) doped with dodecylbenzenesulfonate (DBS) in the form of freestanding films and deposited onto conductive substrates (chemically fixed poly-3,4-(ethylenedioxythiophene, PEDOT) based on PVdF (poly(vinylidenefluoride)). Linear actuation has been achieved starting from a trilayer bending actuator design with a stretchable middle layer. To allow evaluation of the proposed design, commercially available PVdF membranes were chosen as model material. For bending trilayer functionality, electronic separation of both electrode layers is essential, but in order to obtain linear actuation, the CP layers on either side are connected to form a single working electrode. The PPyDBS free standing films and PPyDBS deposited on PEDOT-PVdF-PEDOT were investigated by electrochemical methods (cyclic voltammetry, square wave potentials) in a 4-methyl-1,3-dioxolan-2-one (propylene carbonate, PC) solution of tetrabutylammonium trifluoromethanesulfonate (TBACF3SO3). This study also presents a novel method of utilizing scanning ion-conductance microscopy (SICM) to accurately examine the electrochemical redox behavior of the surface layer of the linear actuator using a micropipette tip.

  10. Magnetic patterning of Fe/Cr/Fe(001) trilayers by Ga{sup +} ion irradiation

    SciTech Connect

    Blomeier, S.; Hillebrands, B.; Demidov, V.E.; Demokritov, S.O.; Reuscher, B.; Brodyanski, A.; Kopnarski, M.

    2005-11-01

    Magnetic patterning of antiferromagnetically coupled epitaxial Fe (10 nm)/Cr (0.7 nm)/Fe (10 nm) (001) trilayers by irradiation with 30 keV Ga{sup +} ions was studied by means of atomic force microscopy, magnetic force microscopy, and Kerr magnetometry. It was found that within a fluence range of (1.25-5)x10{sup 16} ions/cm{sup 2} a complete transition from antiferromagnetic to ferromagnetic coupling between the two Fe layers can be achieved. The magnetization reversal processes of the nonirradiated, antiferromagnetically coupled areas situated close to the irradiated areas were studied with lateral resolution. Evidence for a lateral coupling mechanism between the magnetic moments of the irradiated and nonirradiated areas was found. Special attention was paid to preserve the flatness of the irradiated samples. Depending on the fluence, topographic steps ranging from +1.5 to -2 nm between the nonirradiated and irradiated areas were observed. At lower fluences the irradiation causes an increase of the surface height, while for higher fluences the height decreases. It was found that for the particular fluence of 2.7x10{sup 16} ions/cm{sup 2} no height difference between the irradiated and nonirradiated areas occurs. The results suggest that the irradiation of Fe/Cr/Fe trilayers with midenergy ions is an innovative method for magnetic patterning, preserving the initial smoothness of the sample.

  11. Fabrication and adhesion of conjugated polymer trilayer structures for soft, flexible micromanipulators

    NASA Astrophysics Data System (ADS)

    Khaldi, Alexandre; Falk, Daniel; Maziz, Ali; Jager, Edwin W. H.

    2016-04-01

    We are developing soft, flexible micromanipulators such as micro- tweezers for the handling and manipulation of biological species including cells and surgical tools for minimal invasive surgery. Our aim is to produce tools with minimal dimensions of 100 μm to 1 mm in size, which is 1-2 orders of magnitude smaller than existing technology. However, the displacement of the current developed micromanipulator remains limited due to the low ionic conductivity of the materials. Here, we present developed methods for the fabrication of conjugated polymer trilayer structure which exhibit potential to high stretchability/flexibility as well as a good adhesion between the three different layers. The outcomes of this study contribute to the realisation of low-foot print devices articulated with electroactive polymer actuators for which the physical interface with the power source has been a significant challenge limiting their application. Here, we present a new flexible trilayer structure, which will allow the fabrication of metal-free soft microactuators.

  12. Highly strained graphene samples of varying thickness and comparison of their behaviour.

    PubMed

    Pérez-Garza, Héctor Hugo; Kievit, Eric Walter; Schneider, Grégory F; Staufer, Urs

    2014-11-21

    Mechanically straining graphene opens the possibility to exploit new properties linked to the stressed lattice of this two-dimensional material. In particular, theoretical analyses have forecast that straining graphene by more than 10% is a requirement for many novel applications that have not yet been experimentally demonstrated. Recently, we reported having achieved 12.5% strain in a trilayer graphene sample (3LG) in a controlled, reversible and non-destructive way. In this paper, we explore our method by straining samples of varying thicknesses and comparing their behavior, where strains of 14% and 11% were achieved for monolayer and four-layer graphene (4LG), respectively. For the analysis, optical tracking and the correspondent Raman spectra were taken. While doing so, we observed slippage between two layers in a bilayer sample of which one layer was clamped on one side only. The obtained results when stretching different samples to extreme strains demonstrated the exceptional elasticity of graphene, which might be essential for practical applications. Hysteretic effects observed in the partially clamped layer hints at small energy losses during slippage. This may shed new light on the superlubricity property of graphene that has been reported in the literature.

  13. Highly strained graphene samples of varying thickness and comparison of their behaviour

    NASA Astrophysics Data System (ADS)

    Pérez-Garza, Héctor Hugo; Kievit, Eric Walter; Schneider, Grégory F.; Staufer, Urs

    2014-11-01

    Mechanically straining graphene opens the possibility to exploit new properties linked to the stressed lattice of this two-dimensional material. In particular, theoretical analyses have forecast that straining graphene by more than 10% is a requirement for many novel applications that have not yet been experimentally demonstrated. Recently, we reported having achieved 12.5% strain in a trilayer graphene sample (3LG) in a controlled, reversible and non-destructive way. In this paper, we explore our method by straining samples of varying thicknesses and comparing their behavior, where strains of 14% and 11% were achieved for monolayer and four-layer graphene (4LG), respectively. For the analysis, optical tracking and the correspondent Raman spectra were taken. While doing so, we observed slippage between two layers in a bilayer sample of which one layer was clamped on one side only. The obtained results when stretching different samples to extreme strains demonstrated the exceptional elasticity of graphene, which might be essential for practical applications. Hysteretic effects observed in the partially clamped layer hints at small energy losses during slippage. This may shed new light on the superlubricity property of graphene that has been reported in the literature.

  14. Enhanced photovoltaic performances of graphene/Si solar cells by insertion of a MoS₂ thin film.

    PubMed

    Tsuboi, Yuka; Wang, Feijiu; Kozawa, Daichi; Funahashi, Kazuma; Mouri, Shinichiro; Miyauchi, Yuhei; Takenobu, Taishi; Matsuda, Kazunari

    2015-09-14

    Transition-metal dichalcogenides exhibit great potential as active materials in optoelectronic devices because of their characteristic band structure. Here, we demonstrated that the photovoltaic performances of graphene/Si Schottky junction solar cells were significantly improved by inserting a chemical vapor deposition (CVD)-grown, large MoS2 thin-film layer. This layer functions as an effective electron-blocking/hole-transporting layer. We also demonstrated that the photovoltaic properties are enhanced with the increasing number of graphene layers and the decreasing thickness of the MoS2 layer. A high photovoltaic conversion efficiency of 11.1% was achieved with the optimized trilayer-graphene/MoS2/n-Si solar cell.

  15. Graphene Kirigami

    NASA Astrophysics Data System (ADS)

    Blees, Melina; Rose, Peter; Barnard, Arthur; Roberts, Samantha; McEuen, Paul L.

    2014-03-01

    We have developed a powerful new approach to working with graphene by applying the principles of kirigami, the sculptural art of paper cutting. We have release graphene from the surface, allowing us to treat it like a sheet of atom-thick paper. Working in water, we can pull the graphene along the surface or peel it up entirely. Combining this technique with lithographic patterning, we have created a variety of graphene kirigami devices including three-dimensional structures and resilient, atomically-thin hinges. We have also created soft in-plane springs by patterning a series of cuts into the graphene. The spring constants of these devices depend on the pattern of cuts, so the patterned graphene becomes an adjustable mechanical metamaterial. With possible spring constants ranging from 1 N/m to 10-9 N/m, these springs could be used as sensitive force measurement devices. Such kirigami patterning techniques could also be applied to flexible and stretchable electronics, including soft electrodes for biological experiments. This unusual way of interacting with graphene opens up a world of potential applications that we are just beginning to explore.

  16. In-plane Isotropic Microwave Performance of CoZr Trilayer in GHz Range

    PubMed Central

    Pan, Lulu; Wang, Fenglong; Wang, Wenfeng; Chai, Guozhi; Xue, Desheng

    2016-01-01

    In this paper, we investigate the high frequency performance of Co90Zr10/SiO2/Co90Zr10 trilayers. It is demonstrated that the in-plane isotropic microwave performance is theoretically derived from the solution of the Landau-Lifshitz-Gilbert equation and experimentally achieved in that sandwich structured film. The valuable isotropic behavior comes from the superposition of two uncouple ferromagnetic layers in which the uniaxial magnetic anisotropic fields are equivalent but mutually orthogonal. Moreover, the isotropic microwave performance can be tuned to higher resonance frequency up to 5.3 GHz by employing the oblique deposition technique. It offers a convenient and effective way to achieve an unusual in-plane isotropic microwave performance with high permeability in GHz, holding promising applications for the magnetic devices in the high frequency information technology. PMID:26883790

  17. Effect of spacer layer on the magnetization dynamics of permalloy/rare-earth/permalloy trilayers

    SciTech Connect

    Luo, Chen Yin, Yuli; Zhang, Dong; Jiang, Sheng; Yue, Jinjin; Zhai, Ya; Du, Jun; Zhai, Hongru

    2015-05-07

    The permalloy/rare-earth/permalloy trilayers with different types (Gd and Nd) and thicknesses of spacer layer are investigated using frequency dependence of ferromagnetic resonance (FMR) measurements at room temperature, which shows different behaviors with different rare earth spacer layers. By fitting the frequency dependence of the FMR resonance field and linewidth, we find that the in-plane uniaxial anisotropy retains its value for all samples, the perpendicular anisotropy remains almost unchanged for different thickness of Gd layer but the values are tailored by different thicknesses of Nd layer. The Gilbert damping is almost unchanged with different thicknesses of Gd; however, the Gilbert damping is significantly enhanced from 8.4×10{sup −3} to 20.1×10{sup −3} with 6 nm of Nd and then flatten out when the Nd thickness rises above 6 nm.

  18. Mössbauer study 57Fe in ultrathin trilayer films with sharp and rough interfaces

    NASA Astrophysics Data System (ADS)

    Pogorily, A. N.; Bondarkova, G. V.; Razumov, O. N.; Shypil, E. V.

    2011-04-01

    Trilayer thin films Py/57Fe/Gd and Gd/57Fe/Py (Py: Fe20Ni80 permalloy) have been prepared by electron-beam evaporation and investigated using conversion-electron Mössbauer spectroscopy (CEMS), scanning tunneling microscopy (STM), polar magneto-optical Kerr effect (PMOKE), and ferromagnetic resonance (FMR). It was shown that the films deposited in the same vacuum and temperature runs but with the reverse order of the layers gave a different quality of interfaces: sharp (Py/57Fe/Gd) and rough (Gd/57Fe/Py). Different distribution of atoms in sharp and rough interfaces results in different magnetic properties: the Mössbauer spectra, FMR, and PMOKE data show the appearance of perpendicular magnetic anisotropy (PMA) and enhancement of magnetization in the samples with the rough Gd/Py interface.

  19. Evidence for a π-junction in Nb/F/Nb' trilayers from superfluid density measurements

    NASA Astrophysics Data System (ADS)

    Lemberger, Thomas; Hinton, Michael; Steers, Stanley; Peters, Bryan; Yang, Fengyuan

    Two-coil measurements of the sheet superfluid density of Nb/NiV/Nb' trilayers reveal the transition temperatures and volume superfluid densities of both Nb layers, as functions of the thickness, dF, of the intervening ferromagnetic (F) Ni0.96V0.04 layer. The upper transition occurs when the thicker Nb layer goes superconducting and superfluid first appears. Fitting the high-temperature superfluid density to an appropriate functional form reveals the presence of a lower ``transition'' where additional superfluid appears. This event is really a crossover, but the difference is irrelevant here. There is a surprising minimum in superfluid densities of both Nb layers at dF ~ 30 Å, followed by a slow rise. This behavior suggests that a π phase difference between the Nb layers develops at dF ~ 30 Å and continues to larger F thickness. Supported in part by NSF Grant DMR-0805227.

  20. Establishment of a biomimetic device based on tri-layer polymer actuators--propulsion fins.

    PubMed

    Alici, Gursel; Spinks, Geoffrey; Huynh, Nam N; Sarmadi, Laleh; Minato, Rick

    2007-06-01

    We propose to use bending type tri-layer polymer actuators as propulsion fins for a biomimetic device consisting of a rigid body, like a box fish having a carapace, and paired fins running through the rigid body, like a fish having pectoral fins. The fins or polymer bending actuators can be considered as individually controlled flexible membranes. Each fin is activated with sinusoidal inputs such that there is a phase lag between the movements of successive fins to create enough thrust force for propulsion. Eight fins with 0.125 aspect ratio have been used along both sides of the rigid body to move the device in the direction perpendicular to the longitudinal axis of the body. The designed device with the paired fins was successfully tested, moving in an organic solution consisting of solvent, propylene carbonate (PC), and electrolyte. The design procedure outlined in this study is offered as a guide to making functional devices based on polymer actuators and sensors.

  1. Asymmetric magnetic proximity effect in a Pd/Co/Pd trilayer system

    PubMed Central

    Kim, Dong-Ok; Song, Kyung Mee; Choi, Yongseong; Min, Byoung-Chul; Kim, Jae-Sung; Choi, Jun Woo; Lee, Dong Ryeol

    2016-01-01

    In spintronic devices consisting of ferromagnetic/nonmagnetic systems, the ferromagnet-induced magnetic moment in the adjacent nonmagnetic material significantly influences the spin transport properties. In this study, such magnetic proximity effect in a Pd/Co/Pd trilayer system is investigated by x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity, which enables magnetic characterizations with element and depth resolution. We observe that the total Pd magnetic moments induced at the top Co/Pd interface are significantly larger than the Pd moments at the bottom Pd/Co interface, whereas transmission electron microscopy and reflectivity analysis indicate the two interfaces are nearly identical structurally. Such asymmetry in magnetic proximity effects could be important for understanding spin transport characteristics in ferromagnetic/nonmagnetic systems and its potential application to spin devices. PMID:27151368

  2. Analysis of oxygen induced anisotropy crossover in Pt/Co/MOx trilayers

    NASA Astrophysics Data System (ADS)

    Manchon, A.; Ducruet, C.; Lombard, L.; Auffret, S.; Rodmacq, B.; Dieny, B.; Pizzini, S.; Vogel, J.; Uhlíř, V.; Hochstrasser, M.; Panaccione, G.

    2008-08-01

    Extraordinary Hall effect and x-ray spectroscopy measurements have been performed on a series of Pt/Co/MOx trilayers (M =Al, Mg, Ta, etc.) in order to investigate the role of oxidation in the onset of perpendicular magnetic anisotropy at the Co/MOx interface. It is observed that varying the plasma oxidation time modifies the magnetic properties of the Co layer, inducing a magnetic anisotropy crossover from in plane to out of plane. We focused on the influence of plasma oxidation on Pt/Co/AlOx perpendicular magnetic anisotropy. The interfacial electronic structure is analyzed via x-ray photoelectron spectroscopy measurements. It is shown that the maximum of out-of-plane magnetic anisotropy corresponds to the appearance of a significant density of Co-O bondings at the Co/AlOx interface.

  3. Asymmetric magnetic proximity effect in a Pd/Co/Pd trilayer system

    DOE PAGES

    Kim, Dong -Ok; Song, Kyung Mee; Choi, Yongseong; ...

    2016-05-06

    In spintronic devices consisting of ferromagnetic/nonmagnetic systems, the ferromagnet-induced magnetic moment in the adjacent nonmagnetic material significantly influences the spin transport properties. In this study, such magnetic proximity effect in a Pd/Co/Pd trilayer system is investigated by x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity, which enables magnetic characterizations with element and depth resolution. We observe that the total Pd magnetic moments induced at the top Co/Pd interface are significantly larger than the Pd moments at the bottom Pd/Co interface, whereas transmission electron microscopy and reflectivity analysis indicate the two interfaces are nearly identical structurally. Furthermore, such asymmetry inmore » magnetic proximity effects could be important for understanding spin transport characteristics in ferromagnetic/nonmagnetic systems and its potential application to spin devices.« less

  4. Asymmetric magnetic proximity effect in a Pd/Co/Pd trilayer system

    SciTech Connect

    Kim, Dong -Ok; Song, Kyung Mee; Choi, Yongseong; Min, Byoung -Chul; Kim, Jae -Sung; Choi, Jun Woo; Lee, Dong Ryeol

    2016-05-06

    In spintronic devices consisting of ferromagnetic/nonmagnetic systems, the ferromagnet-induced magnetic moment in the adjacent nonmagnetic material significantly influences the spin transport properties. In this study, such magnetic proximity effect in a Pd/Co/Pd trilayer system is investigated by x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity, which enables magnetic characterizations with element and depth resolution. We observe that the total Pd magnetic moments induced at the top Co/Pd interface are significantly larger than the Pd moments at the bottom Pd/Co interface, whereas transmission electron microscopy and reflectivity analysis indicate the two interfaces are nearly identical structurally. Furthermore, such asymmetry in magnetic proximity effects could be important for understanding spin transport characteristics in ferromagnetic/nonmagnetic systems and its potential application to spin devices.

  5. Two-dimensional iron oxide bi-and trilayer structures on Pd(100)

    NASA Astrophysics Data System (ADS)

    Kuhness, D.; Pomp, S.; Mankad, V.; Barcaro, G.; Sementa, L.; Fortunelli, A.; Netzer, F. P.; Surnev, S.

    2016-03-01

    The growth morphology and structure of iron oxide films, prepared by postoxidation of Fe monolayers on a Pd(100) surface, have been investigated in a multitechnique study, using scanning tunneling microscopy (STM), low energy electron diffraction (LEED), high-resolution x-ray photoelectron spectroscopy (HR-XPS) and x-ray absorption spectroscopy (XAS), both using synchrotron radiation, and comprehensive density functional theory (DFT) analysis. A two-dimensional (2-D) hexagonal O-Fe-O trilayer phase has been generated at submonolayer Fe coverages, which converges into two different 2-D hexagonal Fe-O bilayer structures at one monolayer. One phase exhibits a c(8 × 2) coincidence structure and is associated with a stoichiometric FeO(111) bilayer. The second phase displays a superstructure of triangular loops, which is understood from DFT modeling as excess O ad-atoms in the terminating oxygen layer, thus corresponding to a FeO bilayer with a formal FeO1.125 stoichiometry. Annealing the latter in ultrahigh vacuum to 770 K results in the pure c(8 × 2) wetting layer. The thermodynamic stability of the O-Fe-O trilayer and FeO bilayer phases is analyzed in the DFT framework and is found to be in good agreement with the experiment. The absence of a c(4 × 2)-Fe3O4 phase in the experimental phase diagram, which is found to be stable by DFT and is experimentally encountered for other transition metal oxide films, such as Ni-, Co-, and Mn-oxide on Pd(100), is ascribed to kinetic reasons.

  6. Stable and sensitive silver surface plasmon resonance imaging sensor using trilayered metallic structures.

    PubMed

    Wang, Zhiyou; Cheng, Zhiqiang; Singh, Vikramjeet; Zheng, Zheng; Wang, Yanmei; Li, Shaopeng; Song, Lusheng; Zhu, Jinsong

    2014-02-04

    The silver surface plasmon resonance (SPR) sensor has long been explored due to its intrinsic sensitivity enhancement over the conventional single-layered gold SPR sensor. However, the silver SPR sensor has not been exploited for practical applications because of pronounced instability problems. We propose a novel gold-silver-gold trilayered SPR sensor chip, in which an extra buffer layer of gold is added between the silver and substrate adhesion layer (i.e., chromium) compared to the previously reported silver-gold bilayered SPR sensors. Subjected to prolonged agitation in phosphate-buffered saline (PBS) solution, the new chip exhibited high integrity according to both optical and atomic force microscopy (AFM) analysis. Having undergone repeated cycles of calibration, binding, and regeneration in various chemical solutions, 25 regions of interest (ROIs) over a 14 mm ×14 mm area were chosen and monitored by large detection area SPR microscopy; the new sensor chip exhibited stability comparable to the single gold layered SPR chip. In terms of sensing performances, over 50% increases in sensitivity and signal-to-noise ratio (S/N) than those of the single gold layered SPR chip were determined by SPR microscopy at 660 nm. Protein arrays of protein A and bovine serum albumin (BSA) on both the new chip and single-layered gold SPR chip were fabricated and underwent biomolecular interactions with human IgG, for the purpose of consistency, comparison on kinetics parameters, values from the microarray trilayered chip showed reasonable consistency with those from the single gold layered SPR chip. This study suggests that the new chip is a viable alternative to the conventional single gold layered SPR chip with improved sensing performances.

  7. Stacked charge stripes in the quasi-2D trilayer nickelate La4Ni3O8

    NASA Astrophysics Data System (ADS)

    Zhang, Junjie; Chen, Yu-Sheng; Phelan, D.; Zheng, Hong; Norman, M. R.; Mitchell, J. F.

    2016-08-01

    The quasi-2D nickelate La4Ni3O8 (La-438), consisting of trilayer networks of square planar Ni ions, is a member of the so-called T' family, which is derived from the Ruddlesden-Popper (R-P) parent compound La4Ni3O10-x by removing two oxygen atoms and rearranging the rock salt layers to fluorite-type layers. Although previous studies on polycrystalline samples have identified a 105-K phase transition with a pronounced electronic and magnetic response but weak lattice character, no consensus on the origin of this transition has been reached. Here, we show using synchrotron X-ray diffraction on high-pO2 floating zone-grown single crystals that this transition is associated with a real space ordering of charge into a quasi-2D charge stripe ground state. The charge stripe superlattice propagation vector, q = (2/3, 0, 1), corresponds with that found in the related 1/3-hole doped single-layer R-P nickelate, La5/3Sr1/3NiO4 (LSNO-1/3; Ni2.33+), with orientation at 45° to the Ni-O bonds. The charge stripes in La-438 are weakly correlated along c to form a staggered ABAB stacking that reduces the Coulomb repulsion among the stripes. Surprisingly, however, we find that the charge stripes within each trilayer of La-438 are stacked in phase from one layer to the next, at odds with any simple Coulomb repulsion argument.

  8. Stacked charge stripes in the quasi-2D trilayer nickelate La4Ni3O8

    PubMed Central

    Zhang, Junjie; Chen, Yu-Sheng; Phelan, D.; Zheng, Hong; Norman, M. R.; Mitchell, J. F.

    2016-01-01

    The quasi-2D nickelate La4Ni3O8 (La-438), consisting of trilayer networks of square planar Ni ions, is a member of the so-called T′ family, which is derived from the Ruddlesden–Popper (R-P) parent compound La4Ni3O10−x by removing two oxygen atoms and rearranging the rock salt layers to fluorite-type layers. Although previous studies on polycrystalline samples have identified a 105-K phase transition with a pronounced electronic and magnetic response but weak lattice character, no consensus on the origin of this transition has been reached. Here, we show using synchrotron X-ray diffraction on high-pO2 floating zone-grown single crystals that this transition is associated with a real space ordering of charge into a quasi-2D charge stripe ground state. The charge stripe superlattice propagation vector, q = (2/3, 0, 1), corresponds with that found in the related 1/3-hole doped single-layer R-P nickelate, La5/3Sr1/3NiO4 (LSNO-1/3; Ni2.33+), with orientation at 45° to the Ni-O bonds. The charge stripes in La-438 are weakly correlated along c to form a staggered ABAB stacking that reduces the Coulomb repulsion among the stripes. Surprisingly, however, we find that the charge stripes within each trilayer of La-438 are stacked in phase from one layer to the next, at odds with any simple Coulomb repulsion argument. PMID:27462109

  9. Ion irradiation induced evolution of nanostructure in a graded multi-trilayer system

    NASA Astrophysics Data System (ADS)

    Roy, Sumalay; Ghatak, J.; Dev, B. N.

    2012-02-01

    Nanostructural modifications in a double-graded Pt/Ni/C multi-trilayer, due to irradiation by an energetic ion-beam, have been analyzed using X-ray reflectivity (XRR), X-ray standing wave (XSW) and cross-sectional transmission electron microscopy (X-TEM) techniques. 2 MeV Au2+ ions were rastered on Pt/Ni/C multi-trilayer samples producing a uniformly irradiated area at ion-fluences ranging from 1 × 1014 ions/cm2 to 2 × 1015 ions/cm2. Ion irradiation induced modifications of microstructural parameters, e.g., layer thicknesses and electron densities of individual layers and interface roughnesses have been obtained from XRR analysis. Pt- and Ni-fluorescence yield from the as-deposited sample under the XSW condition show the distinct existence of Pt and Ni layers. The almost indistinguishable Pt- and Ni-fluorescence data over the first order Bragg peak from the sample irradiated at the highest ion-fluence, suggest complete mixing of Pt and Ni. Strong mixing between Pt and Ni in the ion irradiated samples is also corroborated by XRR results. X-TEM studies reveal the individual layer structure in the as-deposited sample. This layer structure is lost in the sample irradiated at the highest ion fluence indicating a complete mixing between Pt and Ni layers and nanoscale grain growth of Pt-Ni alloys. Additionally, formation of Pt-Ni alloy nano-clusters in the C-layers is observed. The results are understood in the light of the positive heat of mixing between Pt and C, and Ni and C and the negative heat of mixing between Pt and Ni. The effect of heat of mixing becomes dominant at high fluence irradiation.

  10. Stacking nature and band gap opening of graphene: Perspective for optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Ullah, Naeem; Zhang, R. Q.; Murtaza, G.; Yar, Abdullah; Mahmood, Asif

    2016-11-01

    Using first principles density functional theory calculations, we have performed geometrical and electronic structure calculations of two-dimensional graphene(G) sheet on the hexagonal boron nitride (h-BN) with different stacking orders. We found that AB stacking appears as the ground state while AA-stacking is a local minima. Band gap opening in the hybrid G/h-BN is sensitive to the interlayer distance and stacking arrangement. Charge redistribution in the graphene sheet determined the band gap opening where the onsite energy difference between carbon lattice atoms of G-sheet takes place. Similar behavior can be observed for the proposed h-BN/G/h-BN tri-layer system. Stacking resolved calculations of the absorptive part of complex dielectric function and optical conductivity revealed the importance of the proposed hybrid systems in the optoelectronics.

  11. Electronic Structure of ABC-stacked Multilayer Graphene and Trigonal Warping:A First Principles Calculation

    NASA Astrophysics Data System (ADS)

    Yelgel, Celal

    2016-04-01

    We present an extensive density functional theory (DFT) based investigation of the electronic structures of ABC-stacked N-layer graphene. It is found that for such systems the dispersion relations of the highest valence and the lowest conduction bands near the K point in the Brillouin zone are characterised by a mixture of cubic, parabolic, and linear behaviours. When the number of graphene layers is increased to more than three, the separation between the valence and conduction bands decreases up until they touch each other. For five and six layer samples these bands show flat behaviour close to the K point. We note that all states in the vicinity of the Fermi energy are surface states originated from the top and/or bottom surface of all the systems considered. For the trilayer system, N = 3, pronounced trigonal warping of the bands slightly above the Fermi level is directly obtained from DFT calculations.

  12. Graphene kirigami

    NASA Astrophysics Data System (ADS)

    Blees, Melina K.; Barnard, Arthur W.; Rose, Peter A.; Roberts, Samantha P.; McGill, Kathryn L.; Huang, Pinshane Y.; Ruyack, Alexander R.; Kevek, Joshua W.; Kobrin, Bryce; Muller, David A.; McEuen, Paul L.

    2015-08-01

    For centuries, practitioners of origami (`ori', fold; `kami', paper) and kirigami (`kiru', cut) have fashioned sheets of paper into beautiful and complex three-dimensional structures. Both techniques are scalable, and scientists and engineers are adapting them to different two-dimensional starting materials to create structures from the macro- to the microscale. Here we show that graphene is well suited for kirigami, allowing us to build robust microscale structures with tunable mechanical properties. The material parameter crucial for kirigami is the Föppl-von Kármán number γ: an indication of the ratio between in-plane stiffness and out-of-plane bending stiffness, with high numbers corresponding to membranes that more easily bend and crumple than they stretch and shear. To determine γ, we measure the bending stiffness of graphene monolayers that are 10-100 micrometres in size and obtain a value that is thousands of times higher than the predicted atomic-scale bending stiffness. Interferometric imaging attributes this finding to ripples in the membrane that stiffen the graphene sheets considerably, to the extent that γ is comparable to that of a standard piece of paper. We may therefore apply ideas from kirigami to graphene sheets to build mechanical metamaterials such as stretchable electrodes, springs, and hinges. These results establish graphene kirigami as a simple yet powerful and customizable approach for fashioning one-atom-thick graphene sheets into resilient and movable parts with microscale dimensions.

  13. Graphene kirigami.

    PubMed

    Blees, Melina K; Barnard, Arthur W; Rose, Peter A; Roberts, Samantha P; McGill, Kathryn L; Huang, Pinshane Y; Ruyack, Alexander R; Kevek, Joshua W; Kobrin, Bryce; Muller, David A; McEuen, Paul L

    2015-08-13

    For centuries, practitioners of origami ('ori', fold; 'kami', paper) and kirigami ('kiru', cut) have fashioned sheets of paper into beautiful and complex three-dimensional structures. Both techniques are scalable, and scientists and engineers are adapting them to different two-dimensional starting materials to create structures from the macro- to the microscale. Here we show that graphene is well suited for kirigami, allowing us to build robust microscale structures with tunable mechanical properties. The material parameter crucial for kirigami is the Föppl-von Kármán number γ: an indication of the ratio between in-plane stiffness and out-of-plane bending stiffness, with high numbers corresponding to membranes that more easily bend and crumple than they stretch and shear. To determine γ, we measure the bending stiffness of graphene monolayers that are 10-100 micrometres in size and obtain a value that is thousands of times higher than the predicted atomic-scale bending stiffness. Interferometric imaging attributes this finding to ripples in the membrane that stiffen the graphene sheets considerably, to the extent that γ is comparable to that of a standard piece of paper. We may therefore apply ideas from kirigami to graphene sheets to build mechanical metamaterials such as stretchable electrodes, springs, and hinges. These results establish graphene kirigami as a simple yet powerful and customizable approach for fashioning one-atom-thick graphene sheets into resilient and movable parts with microscale dimensions.

  14. Rebar graphene.

    PubMed

    Yan, Zheng; Peng, Zhiwei; Casillas, Gilberto; Lin, Jian; Xiang, Changsheng; Zhou, Haiqing; Yang, Yang; Ruan, Gedeng; Raji, Abdul-Rahman O; Samuel, Errol L G; Hauge, Robert H; Yacaman, Miguel Jose; Tour, James M

    2014-05-27

    As the cylindrical sp(2)-bonded carbon allotrope, carbon nanotubes (CNTs) have been widely used to reinforce bulk materials such as polymers, ceramics, and metals. However, both the concept demonstration and the fundamental understanding on how 1D CNTs reinforce atomically thin 2D layered materials, such as graphene, are still absent. Here, we demonstrate the successful synthesis of CNT-toughened graphene by simply annealing functionalized CNTs on Cu foils without needing to introduce extraneous carbon sources. The CNTs act as reinforcing bar (rebar), toughening the graphene through both π-π stacking domains and covalent bonding where the CNTs partially unzip and form a seamless 2D conjoined hybrid as revealed by aberration-corrected scanning transmission electron microscopy analysis. This is termed rebar graphene. Rebar graphene can be free-standing on water and transferred onto target substrates without needing a polymer-coating due to the rebar effects of the CNTs. The utility of rebar graphene sheets as flexible all-carbon transparent electrodes is demonstrated. The in-plane marriage of 1D nanotubes and 2D layered materials might herald an electrical and mechanical union that extends beyond carbon chemistry.

  15. Beam focusing from double subwavelength slits surrounded by Ag/SiO2/Ag tri-layer gratings

    NASA Astrophysics Data System (ADS)

    Su, Wei; Zhou, Chong; Zheng, Gaige; Li, Xiangyin

    2016-12-01

    A silver(Ag)/SiO2/Ag tri-layer grating structure with double slits for beam focusing has been proposed. Compared with the metal/dielectric double-layer grating-based structure, the focusing efficiency of our proposed structure can be greatly enhanced. Numerical simulations using the finite-different time-domain (FDTD) method verify that the focal length and deflection angle can be controlled by adjusting the refractive indexes of dielectric mediums in the two slits.

  16. High-Performance Li-O2 Batteries with Trilayered Pd/MnO x /Pd Nanomembranes.

    PubMed

    Lu, Xueyi; Deng, Junwen; Si, Wenping; Sun, Xiaolei; Liu, Xianghong; Liu, Bo; Liu, Lifeng; Oswald, Steffen; Baunack, Stefan; Grafe, Hans Joachim; Yan, Chenglin; Schmidt, Oliver G

    2015-09-01

    Trilayered Pd/MnO x /Pd nanomembranes are fabricated as the cathode catalysts for Li-O2 batteries. The combination of Pd and MnO x facilitates the transport of electrons, lithium ions, and oxygen-containing intermediates, thus effectively decomposing the discharge product Li2O2 and significantly lowering the charge overpotential and enhancing the power efficiency. This is promising for future environmentally friendly applications.

  17. Modulated exchange bias in NiFe/CoO/α-Fe2O3 trilayers and NiFe/CoO bilayers

    NASA Astrophysics Data System (ADS)

    Li, X.; Lin, K.-W.; Yeh, W.-C.; Desautels, R. D.; van Lierop, J.; Pong, Philip W. T.

    2017-02-01

    While the exchange bias in ferromagnetic/antiferromagnetic (FM/AF) bilayer and FM1/AF/FM2 trilayer configurations has been widely investigated, the role of an AF2 layer in FM/AF1/AF2 trilayer configurations is still not well understood. In this work, the magnetic properties of NiFe/CoO, NiFe/α-Fe2O3 bilayers, and NiFe/CoO/α-Fe2O3 trilayer were studied comparatively. The microstructure and chemical composition were characterized. Temperature dependent magnetometry reveals increased irreversibility temperature in NiFe/CoO/α-Fe2O3 trilayer compared with NiFe/CoO bilayer. The magnetic hysteresis loops show that the exchange bias (Hex) and coercivity (Hc) depend strongly on the anisotropy of AF layer (CoO, α-Fe2O3 and CoO/α-Fe2O3). Our work shows that the AF1/AF2 interfacial interactions can be used effectively for tuning the exchange bias in FM/AF1/AF2 trilayers.

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

    PubMed

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

    2010-12-01

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

  19. Optical melting of the transverse Josephson plasmon: A comparison between bilayer and trilayer cuprates

    NASA Astrophysics Data System (ADS)

    Hu, W.; Nicoletti, D.; Boris, A. V.; Keimer, B.; Cavalleri, A.

    2017-03-01

    We report on an investigation of the redistribution of interlayer coherence in the trilayer cuprate B i2S r2C a2C u3O10 . The experiment is performed under the same apical-oxygen phonon excitation discussed in the past for the bilayer cuprate YB a2C u3O6.5 . In B i2S r2C a2C u3O10 , we observe a similar spectral weight loss at the transverse plasma mode resonance as that seen in YB a2C u3O6.5 . However, this feature is not accompanied by the light-enhanced interlayer coherence that was found in YB a2C u3O6 +x , for which the transverse plasma mode is observed at equilibrium even in the normal state. These new observations offer an experimental perspective in the context of the physics of light-enhanced interlayer coupling in various cuprates.

  20. Spin pumping in magnetic trilayer structures with an MgO barrier

    NASA Astrophysics Data System (ADS)

    Baker, A. A.; Figueroa, A. I.; Pingstone, D.; Lazarov, V. K.; van der Laan, G.; Hesjedal, T.

    2016-10-01

    We present a study of the interaction mechanisms in magnetic trilayer structures with an MgO barrier grown by molecular beam epitaxy. The interlayer exchange coupling, Aex, is determined using SQUID magnetometry and ferromagnetic resonance (FMR), displaying an unexpected oscillatory behaviour as the thickness, tMgO, is increased from 1 to 4 nm. Transmission electron microscopy confirms the continuity and quality of the tunnelling barrier, eliminating the prospect of exchange arising from direct contact between the two ferromagnetic layers. The Gilbert damping is found to be almost independent of the MgO thickness, suggesting the suppression of spin pumping. The element-specific technique of x-ray detected FMR reveals a small dynamic exchange interaction, acting in concert with the static interaction to induce coupled precession across the multilayer stack. These results highlight the potential of spin pumping and spin transfer torque for device applications in magnetic tunnel junctions relying on commonly used MgO barriers.

  1. Spin pumping in magnetic trilayer structures with an MgO barrier.

    PubMed

    Baker, A A; Figueroa, A I; Pingstone, D; Lazarov, V K; van der Laan, G; Hesjedal, T

    2016-10-18

    We present a study of the interaction mechanisms in magnetic trilayer structures with an MgO barrier grown by molecular beam epitaxy. The interlayer exchange coupling, Aex, is determined using SQUID magnetometry and ferromagnetic resonance (FMR), displaying an unexpected oscillatory behaviour as the thickness, tMgO, is increased from 1 to 4 nm. Transmission electron microscopy confirms the continuity and quality of the tunnelling barrier, eliminating the prospect of exchange arising from direct contact between the two ferromagnetic layers. The Gilbert damping is found to be almost independent of the MgO thickness, suggesting the suppression of spin pumping. The element-specific technique of x-ray detected FMR reveals a small dynamic exchange interaction, acting in concert with the static interaction to induce coupled precession across the multilayer stack. These results highlight the potential of spin pumping and spin transfer torque for device applications in magnetic tunnel junctions relying on commonly used MgO barriers.

  2. Spin pumping in magnetic trilayer structures with an MgO barrier

    PubMed Central

    Baker, A. A.; Figueroa, A. I.; Pingstone, D.; Lazarov, V. K.; van der Laan, G.; Hesjedal, T.

    2016-01-01

    We present a study of the interaction mechanisms in magnetic trilayer structures with an MgO barrier grown by molecular beam epitaxy. The interlayer exchange coupling, Aex, is determined using SQUID magnetometry and ferromagnetic resonance (FMR), displaying an unexpected oscillatory behaviour as the thickness, tMgO, is increased from 1 to 4 nm. Transmission electron microscopy confirms the continuity and quality of the tunnelling barrier, eliminating the prospect of exchange arising from direct contact between the two ferromagnetic layers. The Gilbert damping is found to be almost independent of the MgO thickness, suggesting the suppression of spin pumping. The element-specific technique of x-ray detected FMR reveals a small dynamic exchange interaction, acting in concert with the static interaction to induce coupled precession across the multilayer stack. These results highlight the potential of spin pumping and spin transfer torque for device applications in magnetic tunnel junctions relying on commonly used MgO barriers. PMID:27752117

  3. Broken symmetry, excitons, gapless modes, and topological excitations in trilayer quantum Hall systems

    NASA Astrophysics Data System (ADS)

    Ye, Jinwu

    2005-03-01

    We study the interlayer coherent incompressible phase in trilayer quantum Hall systems (TLQH) at total filling factor νT=1 from three approaches: Mutual composite fermion (MCF), composite boson (CB), and wave function approach. Just like in bilayer quantum Hall system, CB approach is superior than MCF approach in studying TLQH with broken symmetry. The Hall and Hall drag resistivities are found to be quantized at h/e2 . Two neutral gapless modes with linear dispersion relations are identified and the ratio of the two velocities is close to 3 . The excitation spectra are classified into two classes, charge neutral bosonic two-body bound states and charge ±1 fermionic three-body bound states. In general, there are two two-body Kosterlize-Thouless (KT) transition temperatures and one three-body KT transition. The charge ±1 three-body fermionic bound states may be the main dissipation source of transport measurements. The broken symmetry in terms of SU (3) algebra is studied. The structure of excitons and their flowing patterns are given. The coupling between the two Goldstone modes will lead to the broadening in the zero-bias peak in the interlayer correlated tunnelings of the TLQH. Several interesting features unique to TLQH are outlined. Limitations of the CB approach are also pointed out.

  4. Force control of a tri-layer conducting polymer actuator using optimized fuzzy logic control

    NASA Astrophysics Data System (ADS)

    Itik, Mehmet; Sabetghadam, Mohammadreza; Alici, Gursel

    2014-12-01

    Conducting polymers actuators (CPAs) are potential candidates for replacing conventional actuators in various fields, such as robotics and biomedical engineering, due to their advantageous properties, which includes their low cost, light weight, low actuation voltage and biocompatibility. As these actuators are very suitable for use in micro-nano manipulation and in injection devices in which the magnitude of the force applied to the target is of crucial importance, the force generated by CPAs needs to be accurately controlled. In this paper, a fuzzy logic (FL) controller with a Mamdani inference system is designed to control the blocking force of a trilayer CPA with polypyrrole electrodes, which operates in air. The particle swarm optimization (PSO) method is employed to optimize the controller’s membership function parameters and therefore enhance the performance of the FL controller. An adaptive neuro-fuzzy inference system model, which can capture the nonlinear dynamics of the actuator, is utilized in the optimization process. The optimized Mamdani FL controller is then implemented on the CPA experimentally, and its performance is compared with a non-optimized fuzzy controller as well as with those obtained from a conventional PID controller. The results presented indicate that the blocking force at the tip of the CPA can be effectively controlled by the optimized FL controller, which shows excellent transient and steady state characteristics but increases the control voltage compared to the non-optimized fuzzy controllers.

  5. Exponentially decaying magnetic coupling in sputtered thin film FeNi/Cu/FeCo trilayers

    NASA Astrophysics Data System (ADS)

    Wei, Yajun; Akansel, Serkan; Thersleff, Thomas; Harward, Ian; Brucas, Rimantas; Ranjbar, Mojtaba; Jana, Somnath; Lansaker, Pia; Pogoryelov, Yevgen; Dumas, Randy K.; Leifer, Klaus; Karis, Olof; Åkerman, Johan; Celinski, Zbigniew; Svedlindh, Peter

    2015-01-01

    Magnetic coupling in trilayer films of FeNi/Cu/FeCo deposited on Si/SiO2 substrates have been studied. While the thicknesses of the FeNi and FeCo layers were kept constant at 100 Å, the thickness of the Cu spacer was varied from 5 to 50 Å. Both hysteresis loop and ferromagnetic resonance results indicate that all films are ferromagnetically coupled. Micromagnetic simulations well reproduce the ferromagnetic resonance mode positions measured by experiments, enabling the extraction of the coupling constants. Films with a thin Cu spacer are found to be strongly coupled, with an effective coupling constant of 3 erg/cm2 for the sample with a 5 Å Cu spacer. The strong coupling strength is qualitatively understood within the framework of a combined effect of Ruderman-Kittel-Kasuya-Yosida and pinhole coupling, which is evidenced by transmission electron microscopy analysis. The magnetic coupling constant surprisingly decreases exponentially with increasing Cu spacer thickness, without showing an oscillatory thickness dependence. This is partially connected to the substantial interfacial roughness that washes away the oscillation. The results have implications on the design of multilayers for spintronic applications.

  6. Exponentially decaying magnetic coupling in sputtered thin film FeNi/Cu/FeCo trilayers

    SciTech Connect

    Wei, Yajun Akansel, Serkan; Thersleff, Thomas; Brucas, Rimantas; Lansaker, Pia; Leifer, Klaus; Svedlindh, Peter; Harward, Ian; Celinski, Zbigniew; Ranjbar, Mojtaba; Dumas, Randy K.; Jana, Somnath; Pogoryelov, Yevgen; Karis, Olof; Åkerman, Johan

    2015-01-26

    Magnetic coupling in trilayer films of FeNi/Cu/FeCo deposited on Si/SiO{sub 2} substrates have been studied. While the thicknesses of the FeNi and FeCo layers were kept constant at 100 Å, the thickness of the Cu spacer was varied from 5 to 50 Å. Both hysteresis loop and ferromagnetic resonance results indicate that all films are ferromagnetically coupled. Micromagnetic simulations well reproduce the ferromagnetic resonance mode positions measured by experiments, enabling the extraction of the coupling constants. Films with a thin Cu spacer are found to be strongly coupled, with an effective coupling constant of 3 erg/cm{sup 2} for the sample with a 5 Å Cu spacer. The strong coupling strength is qualitatively understood within the framework of a combined effect of Ruderman-Kittel-Kasuya-Yosida and pinhole coupling, which is evidenced by transmission electron microscopy analysis. The magnetic coupling constant surprisingly decreases exponentially with increasing Cu spacer thickness, without showing an oscillatory thickness dependence. This is partially connected to the substantial interfacial roughness that washes away the oscillation. The results have implications on the design of multilayers for spintronic applications.

  7. Role of spin polarization in FM/Al/FM trilayer film at low temperature

    NASA Astrophysics Data System (ADS)

    Lu, Ning; Webb, Richard

    2014-03-01

    Measurements of electronic transport in diffusive FM/normal metal/FM trilayer film are performed at temperature ranging from 2K to 300K to determine the behavior of the spin polarized current in normal metal under the influence of quantum phase coherence and spin-orbital interaction. Ten samples of Hall bar with length of 200 micron and width of 20 micron are fabricated through e-beam lithography followed by e-gun evaporation of Ni0.8Fe0.2, aluminum and Ni0.8Fe0.2 with different thickness (5nm to 45nm) in vacuum. At low temperature of 4.2K, coherent backscattering, Rashba spin-orbital interaction and spin flip scattering of conduction electrons contribute to magnetoresistance at low field. Quantitative analysis of magnetoresistance shows transition between weak localization and weak anti-localization for samples with different thickness ratio, which indicates the spin polarization actually affects the phase coherence length and spin-orbital scattering length. However, at temperature between 50K and 300K, only the spin polarization dominates the magnetoresistance.

  8. Medical data sheet in safe havens - A tri-layer cryptic solution.

    PubMed

    Praveenkumar, Padmapriya; Amirtharajan, Rengarajan; Thenmozhi, K; Balaguru Rayappan, John Bosco

    2015-07-01

    Secured sharing of the diagnostic reports and scan images of patients among doctors with complementary expertise for collaborative treatment will help to provide maximum care through faster and decisive decisions. In this context, a tri-layer cryptic solution has been proposed and implemented on Digital Imaging and Communications in Medicine (DICOM) images to establish a secured communication for effective referrals among peers without compromising the privacy of patients. In this approach, a blend of three cryptic schemes, namely Latin square image cipher (LSIC), discrete Gould transform (DGT) and Rubik׳s encryption, has been adopted. Among them, LSIC provides better substitution, confusion and shuffling of the image blocks; DGT incorporates tamper proofing with authentication; and Rubik renders a permutation of DICOM image pixels. The developed algorithm has been successfully implemented and tested in both the software (MATLAB 7) and hardware Universal Software Radio Peripheral (USRP) environments. Specifically, the encrypted data were tested by transmitting them through an additive white Gaussian noise (AWGN) channel model. Furthermore, the sternness of the implemented algorithm was validated by employing standard metrics such as the unified average changing intensity (UACI), number of pixels change rate (NPCR), correlation values and histograms. The estimated metrics have also been compared with the existing methods and dominate in terms of large key space to defy brute force attack, cropping attack, strong key sensitivity and uniform pixel value distribution on encryption.

  9. Transmission line circuit model of a PPy based trilayer mechanical sensor

    NASA Astrophysics Data System (ADS)

    Khalili, Nazanin; Naguib, Hani E.; Kwon, Roy H.

    2015-04-01

    Many efforts have been devoted to modeling the diffusive impedance of conjugated polymer (CP) based actuators using their equivalent electrical circuits. Employing the same methodology, CP based mechanical sensors can also be treated by an equivalent transmission line circuit and their overall impedance can be modeled, correspondingly. Due to the large number of resources to study the electrical circuits, this technique is a practical tool. Therefore, in this study, an equivalent RC-circuit model including electrochemical parameters is determined to obtain a better perception of the sensing mechanism of these mechanical sensors. Conjugated polymers are capable of generating an output current or voltage upon an induced mechanical deformation or force. This observed behavior in polymer based mechanical sensors is considered as the reverse actuation process. Many outstanding properties of the conjugated polymer actuators including their light weight and biocompatibility are still retained by these sensors. Sensors with a trilayer configuration are capable of operating in air in response to a mechanically induced bending deformation. However, due to their nonlinear behavior and multivariable characteristics, it is required to propose a systematic approach in order to optimize their performance and gain the optimal values of their constituent decision variable. Therefore, the proposed mathematical model is used to define the output voltage of the PPy based mechanical sensor along with the sensitivity of the model to the applied frequency of the induced deformation. Applying a multiobjective optimization algorithm, the optimization problem was solved and the tracking ability of the proposed model was then verified.

  10. Predicting origami-inspired programmable self-folding of hydrogel trilayers

    NASA Astrophysics Data System (ADS)

    An, Ning; Li, Meie; Zhou, Jinxiong

    2016-11-01

    Imitating origami principles in active or programmable materials opens the door for development of origami-inspired self-folding structures for not only aesthetic but also functional purposes. A variety of programmable materials enabled self-folding structures have been demonstrated across various fields and scales. These folding structures have finite thickness and the mechanical properties of the active materials dictate the folding process. Yet formalizing the use of origami rules for use in computer modeling has been challenging, owing to the zero-thickness theory and the exclusion of mechanical properties in current models. Here, we describe a physics-based finite element simulation scheme to predict programmable self-folding of temperature-sensitive hydrogel trilayers. Patterning crease and assigning mountain or valley folds are highlighted for complex origami such as folding of the Randlett’s flapping bird and the crane. Our efforts enhance the understanding and facilitate the design of origami-inspired self-folding structures, broadening the realization and application of reconfigurable structures.

  11. Antiferromagnet-induced perpendicular magnetic anisotropy in ferromagnetic/antiferromagnetic/ferromagnetic trilayers

    NASA Astrophysics Data System (ADS)

    Wang, Bo-Yao; Lin, Po-Han; Tsai, Ming-Shian; Shih, Chun-Wei; Lee, Meng-Ju; Huang, Chun-Wei; Jih, Nae-Yeou; Wei, Der-Hsin

    2016-08-01

    This study demonstrates the effect of antiferromagnet-induced perpendicular magnetic anisotropy (PMA) on ferromagnetic/antiferromagnetic/ferromagnetic (FM/AFM/FM) trilayers and reveals its interplay with a long-range interlayer coupling between separated FM layers. In epitaxially grown 12 monolayer (ML) Ni/Co/Mn/5 ML Co/Cu(001) films, magnetic hysteresis loops and element-resolved magnetic domain imaging showed that the magnetization direction of the top layers of 12 ML Ni/Co films could be changed from the in-plane direction to the perpendicular direction, when the thickness of the Mn films (tMn) was greater than a critical value close to the thickness threshold associated with the onset of AFM ordering (tMn=3.5 ML). The top FM layers exhibited a significantly enhanced PMA when tMn increased further, and this enhancement can be attributed to a strengthened AFM ordering of the volume moments of the Mn films, as evidenced by the presence of induced domain frustration. By contrast, the long-range interlayer coupling presented clear effects only when tMn was at a lower coverage.

  12. Non-linear dynamics of viscoelastic liquid trilayers subjected to an electric field

    NASA Astrophysics Data System (ADS)

    Karapetsas, George; Bontozoglou, Vasilis

    2014-11-01

    The scope of this work is to investigate the non-linear dynamics of the electro-hydrodynamic instability of a trilayer of immiscible liquids. We consider the case of a polymer film which is separated from the top electrode by two viscous fluids. We develop a computational model and carry out 2D numerical simulations fully accounting for the flow and electric field in all phases. For the numerical solution of the governing equations we employ the mixed finite element method combined with a quasi-elliptic mesh generation scheme which is capable of following the large deformations of the liquid-liquid interface. We model the viscoelastic behavior using the Phan-Thien and Tanner (PTT) constitutive equation taking fully into account the non-linear elastic effects as well as a varying shear and extensional viscosity. We perform a thorough parametric study and investigate the influence of the electric properties of fluids, applied voltage and various rheological parameters. The authors acknowledge the support by the General Secretariat of Research and Technology of Greece under the action ``Supporting Postdoctoral Researchers'' (Grant Number PE8/906), co-funded by the European Social Fund and National Resources.

  13. Graphene-Dielectric Integration for Graphene Transistors

    PubMed Central

    Liao, Lei; Duan, Xiangfeng

    2010-01-01

    Graphene is emerging as an interesting electronic material for future electronics due to its exceptionally high carrier mobility and single-atomic thickness. Graphene-dielectric integration is of critical importance for the development of graphene transistors and a new generation of graphene based electronics. Deposition of dielectric materials onto graphene is of significant challenge due to the intrinsic material incompatibility between pristine graphene and dielectric oxide materials. Here we review various strategies being researched for graphene-dielectric integration. Physical vapor deposition (PVD) can be used to directly deposit dielectric materials on graphene, but often introduces significant defects into the monolayer of carbon lattice; Atomic layer deposition (ALD) process has also been explored to to deposit high-κ dielectrics on graphene, which however requires functionalization of graphene surface with reactive groups, inevitably leading to a significant degradation in carrier mobilities; Using naturally oxidized thin aluminum or polymer as buffer layer for dielectric deposition can mitigate the damages to graphene lattice and improve the carrier mobility of the resulted top-gated transistors; Lastly, a physical assembly approach has recently been explored to integrate dielectric nanostructures with graphene without introducing any appreciable defects, and enabled top-gated graphene transistors with the highest carrier mobility reported to date. We will conclude with a brief summary and perspective on future opportunities. PMID:21278913

  14. Growth of single and bilayer graphene by filtered cathodic vacuum arc technique

    SciTech Connect

    Kesarwani, A. K.; Panwar, O. S. Bisht, Atul; Dhakate, S. R.; Rakshit, R. K.; Singh, V. N.; Kumar, Ashish

    2016-03-15

    The authors present a viable process to grow the high quality graphene films with control over number of layers by the filtered cathodic vacuum arc (FCVA) technique. In the FCVA process, the different carbon concentrations can be controlled by precisely tuning the arc time (1–4 s). The arc generated carbon was deposited on the nickel catalyst at 800 °C, annealed for 10 min, and cooled down to room temperature in the presence of hydrogen gas, resulting in the graphene films with control over number of layers. Prior to arcing, hydrogen etching of nickel was carried out to clean the surface of the substrate. A growth model to prepare the high quality graphene has also been proposed. The as-grown graphene films were transferred to different substrates and are characterized by Raman spectroscopy, optical microscopy, high resolution transmission electron microscopy, and atomic force microscopy to determine the number of layers present in these films. Raman spectra of the prepared graphene films exhibit change in the G peak position from 1582.4 to 1578.1 cm{sup −1}, two-dimensional (2D) peak shifts from 2688.5 to 2703.8 cm{sup −1}, the value of I{sub 2D}/I{sub G} increased from 0.38 to 3.82, and the full width at half maxima of 2D peak changed from 41 to 70 cm{sup −1}, for different layers of graphene films. The high resolution transmission electron microscopy image revealed that the graphene films prepared for 1 and 2 s arc times have single and bi- or trilayered structures, respectively.

  15. Enhancement of the transverse magneto-optical Kerr effect via resonant tunneling in Au/Ce:YIG/Au trilayers and its application

    NASA Astrophysics Data System (ADS)

    Li, Jie; Tang, Tingting; Zhang, Yanfen; Luo, Li

    2017-02-01

    We propose a new structure to enhance the transverse magneto-optical Kerr effect (TMOKE) via resonant photon tunneling. In trilayer structures with a magnetic dielectric layer sandwiched between non-magnetic metal layers, an enhanced TMOKE can be observed. The TMOKE in Au/Ce:YIG/Au trilayers with different widths of magnetic dielectric layers are calculated using a 4  ×  4 transfer-matrix method, in which the maximum absolute value reaches 0.7. Based on the enhanced TMOKE, we apply the structure proposed above in magnetic field sensing, and TMOKE values are calculated when the external magnetic field intensity is increasing. Compared with other magnetic field sensing methods, the Au/Ce:YIG/Au trilayer possesses a very simple structure and shows high sensitivity to magnetic field variation, which is promising as a highly integrated and sensitive magneto-optical device.

  16. Influence of Interface and Polarization on Magnetoelectric Coupling in Ni-LEAD Zirconium TITANATE-Ni Trilayers Derived by Electroless Deposition

    NASA Astrophysics Data System (ADS)

    Bi, K.; Wang, Y. G.

    2012-06-01

    Magnetoelectric (ME) coupling in layered structures of magnetostrictive and piezoelectric phases are mediated by mechanical deformation and depends strongly on the interface conditions. Ni-lead zirconium titanate-Ni trilayers with neither electrodes nor bonding layers have been derived by electroless deposition. The structure of the electroless deposited Ni layer was characterized by X-ray diffraction. The cross-section of the Ni/PZT layers was investigated using scanning electron microscopy. The value of ME voltage coefficient (αE,31) increases as the interface roughness increases. The maximum of αE,31 for the Ni/PZT/Ni trilayers polarized after electroless deposition is higher than that for the Ni/PZT/Ni trilayers polarized before electroless deposition. It is essential to optimize the interface and the polarization to obtain higher ME voltage coefficient.

  17. Spectroscopic characterization of charge carrier anisotropic motion in twisted few-layer graphene

    PubMed Central

    Kandyba, Viktor; Yablonskikh, Mikhail; Barinov, Alexei

    2015-01-01

    Graphene, a layer of carbon atoms in a honeycomb lattice, captures enormous interest as probably the most promising component of future electronics thanks to its mechanical robustness, flexibility, and unique charge carrier quasiparticles propagating like massless high energy Dirac fermions. If several graphene layers form a stack, the interaction between them is, on the one hand, weak, allowing realization of various registries between the layers and, on the other hand, strong enough for a wide range tuning of the electronic properties. Here we grow few layer graphene with various number of layers and twist configurations and address the electronic properties of individual atomic layers in single microscopic domains using angle-resolved photoelectron spectromicroscopy. The dependence of the interlayer coupling on the twist angle is analyzed and, in the domains with tri-layers and more, if different rotations are present, the electrons in weaker coupled adjacent layers are shown to have different properties manifested by coexisting van Hove singularities, moiré superlattices with corresponding superlattice Dirac points, and charge carrier group velocity renormalizations. Moreover, pronounced anisotropy in the charge carrier motion, opening a possibility to transform strongly coupled graphene bilayers into quasi one-dimensional conductors, is observed. PMID:26548567

  18. Modification of magnetic properties of Pt/Co/Pt trilayers driven by nanosecond pulses of extreme ultraviolet irradiation

    NASA Astrophysics Data System (ADS)

    Sveklo, I.; Kurant, Z.; Bartnik, A.; Klinger, D.; Sobierajski, R.; Wawro, A.; Kisielewski, J.; Tekielak, M.; Maziewski, A.

    2017-01-01

    An irreversible rotation of magnetization from in-plane to an out-of-plane direction was induced in Pt/Co/Pt epitaxial trilayers by single and multiple pulses of extreme ultraviolet (EUV) irradiations. The radial dependence of remanence, coercivity and saturation fields across the irradiated spots was studied with the help of magneto-optical techniques for the samples with various Co and Pt buffer layer thicknesses. The sample surface and magnetic ordering were investigated using atomic force and magnetic force microscopies. Based on magnetic and morphological changes, the residual stress after thermoplastic deformation in the spot area is discussed as a reason for the observed transformation.

  19. Mechanical graphene

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  20. The Management of Diabetic Foot Ulcers with Porcine Small Intestine Submucosa Tri-Layer Matrix: A Randomized Controlled Trial

    PubMed Central

    Cazzell, Shawn M.; Lange, Darrell L.; Dickerson, Jaime E.; Slade, Herbert B.

    2015-01-01

    Objective: This study demonstrates that superior outcomes are possible when diabetic foot ulcers (DFU) are managed with tri-layer porcine small intestine submucosa (SIS). Approach: Patients with DFU from 11 centers participated in this prospective randomized controlled trial. Qualified subjects were randomized (1:1) to either SIS or standard care (SC) selected at the discretion of the Investigator and followed for 12 weeks or complete ulcer closure. Results: Eighty-two subjects (41 in each group) were evaluable in the intent-to-treat analysis. Ulcers managed with SIS had a significantly greater proportion closed by 12 weeks than for the Control group (54% vs. 32%, p=0.021) and this proportion was numerically higher at all visits. Time to closure for ulcers achieving closure was 2 weeks earlier for the SIS group than for SC. Median reduction in ulcer area was significantly greater for SIS at each weekly visit (all p values<0.05). Review of reported adverse events found no safety concerns. Innovation: These data support the use of tri-layer SIS for the effective management of DFU. Conclusion: In this randomized controlled trial, SIS was found to be associated with more rapid improvement, and a higher likelihood of achieving complete ulcer closure than those ulcers treated with SC. PMID:26634183

  1. Analytical modeling of demagnetizing effect in magnetoelectric ferrite/PZT/ferrite trilayers taking into account a mechanical coupling

    NASA Astrophysics Data System (ADS)

    Loyau, V.; Aubert, A.; LoBue, M.; Mazaleyrat, F.

    2017-03-01

    In this paper, we investigate the demagnetizing effect in ferrite/PZT/ferrite magnetoelectric (ME) trilayer composites consisting of commercial PZT discs bonded by epoxy layers to Ni-Co-Zn ferrite discs made by a reactive Spark Plasma Sintering (SPS) technique. ME voltage coefficients (transversal mode) were measured on ferrite/PZT/ferrite trilayer ME samples with different thicknesses or phase volume ratio in order to highlight the influence of the magnetic field penetration governed by these geometrical parameters. Experimental ME coefficients and voltages were compared to analytical calculations using a quasi-static model. Theoretical demagnetizing factors of two magnetic discs that interact together in parallel magnetic structures were derived from an analytical calculation based on a superposition method. These factors were introduced in ME voltage calculations which take account of the demagnetizing effect. To fit the experimental results, a mechanical coupling factor was also introduced in the theoretical formula. This reflects the differential strain that exists in the ferrite and PZT layers due to shear effects near the edge of the ME samples and within the bonding epoxy layers. From this study, an optimization in magnitude of the ME voltage is obtained. Lastly, an analytical calculation of demagnetizing effect was conducted for layered ME composites containing higher numbers of alternated layers (n ≥ 5). The advantage of such a structure is then discussed.

  2. Preparation and characterization of inorganic-organic trilayer core-shell polysilsesquioxane/polyacrylate/polydimethylsiloxane hybrid latex particles

    NASA Astrophysics Data System (ADS)

    Bai, Ruiqin; Qiu, Teng; Han, Feng; He, Lifan; Li, Xiaoyu

    2012-07-01

    The inorganic-organic trilayer core-shell polysilsesquioxane/polyacrylate/polydimethylsiloxane hybrid latex particles have been successfully prepared via seeded emulsion polymerization of acrylate monomers and octamethylcyclotetrasiloxane (D4) gradually, using functional polymethacryloxypropylsilsesquioxane (PSQ) latex particles with reactive methacryloxypropyl groups synthesized by the hydrolysis and polycondensation of (3-methacryloxypropyl)trimethoxysilane in the presence of mixed emulsifiers as seeds. The FTIR spectra show that acrylate monomers and D4 are effectively involved in the emulsion copolymerization and formed the polydimethylsiloxane-containing hybrid latex particles. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) confirm that the resultant hybrid latex particles have evident trilayer core-shell structure and a narrow size distribution. XPS analysis also indicates that polysilsesquioxane/polyacrylate/polydimethylsiloxane hybrid latex particles have been successfully prepared and PDMS is rich in the surface of the hybrid latex film. Additionally, compared with the hybrid latex film without PDMS, the hybrid latex film containing PDMS shows higher hydrophobicity (water contact angle) and lower water absorption.

  3. Design, Fabrication, and Testing of a TiN/Ti/TiN Trilayer KID Array for 3 mm CMB Observations

    NASA Astrophysics Data System (ADS)

    Lowitz, A. E.; Brown, A. D.; Mikula, V.; Stevenson, T. R.; Timbie, P. T.; Wollack, E. J.

    2016-08-01

    Kinetic inductance detectors (KIDs) are a promising technology for astronomical observations over a wide range of wavelengths in the mm and sub-mm regime. Simple fabrication, in as little as one lithographic layer, and passive frequency-domain multiplexing, with readout of up to ˜ 1000 pixels on a single line with a single cold amplifier, make KIDs an attractive solution for high-pixel-count detector arrays. We are developing an array that optimizes KIDs for optical frequencies near 100 GHz to expand their usefulness in mm-wave applications, with a particular focus on CMB B-mode measurement efforts in association with the QUBIC telescope. We have designed, fabricated, and tested a 20-pixel prototype array using a simple quasi-lumped microstrip design and pulsed DC reactive magnetron-sputtered TiN/Ti/TiN trilayer resonators, optimized for detecting 100 GHz (3 mm) signals. Here we present a discussion of design considerations for the array, as well as preliminary detector characterization measurements and results from a study of TiN trilayer properties.

  4. Observation of magnon-mediated current drag in Pt/yttrium iron garnet/Pt(Ta) trilayers

    SciTech Connect

    Li, Junxue; Xu, Yadong; Aldosary, Mohammed; Tang, Chi; Lin, Zhisheng; Zhang, Shufeng; Lake, Roger; Shi, Jing

    2016-03-02

    Pure spin current, a flow of spin angular momentum without flow of any accompanying net charge, is generated in two common ways. One makes use of the spin Hall effect in normal metals (NM) with strong spin–orbit coupling, such as Pt or Ta. The other utilizes the collective motion of magnetic moments or spin waves with the quasi-particle excitations called magnons. A popular material for the latter is yttrium iron garnet, a magnetic insulator (MI). Here we demonstrate in NM/MI/NM trilayers that these two types of spin currents are interconvertible across the interfaces, predicated as the magnon-mediated current drag phenomenon. The transmitted signal scales linearly with the driving current without a threshold and follows the power-law Tn with n ranging from 1.5 to 2.5. Lastly, our results indicate that the NM/MI/NM trilayer structure can serve as a scalable pure spin current valve device which is an essential ingredient in spintronics.

  5. Observation of magnon-mediated current drag in Pt/yttrium iron garnet/Pt(Ta) trilayers

    DOE PAGES

    Li, Junxue; Xu, Yadong; Aldosary, Mohammed; ...

    2016-03-02

    Pure spin current, a flow of spin angular momentum without flow of any accompanying net charge, is generated in two common ways. One makes use of the spin Hall effect in normal metals (NM) with strong spin–orbit coupling, such as Pt or Ta. The other utilizes the collective motion of magnetic moments or spin waves with the quasi-particle excitations called magnons. A popular material for the latter is yttrium iron garnet, a magnetic insulator (MI). Here we demonstrate in NM/MI/NM trilayers that these two types of spin currents are interconvertible across the interfaces, predicated as the magnon-mediated current drag phenomenon.more » The transmitted signal scales linearly with the driving current without a threshold and follows the power-law Tn with n ranging from 1.5 to 2.5. Lastly, our results indicate that the NM/MI/NM trilayer structure can serve as a scalable pure spin current valve device which is an essential ingredient in spintronics.« less

  6. Observation of magnon-mediated current drag in Pt/yttrium iron garnet/Pt(Ta) trilayers

    PubMed Central

    Li, Junxue; Xu, Yadong; Aldosary, Mohammed; Tang, Chi; Lin, Zhisheng; Zhang, Shufeng; Lake, Roger; Shi, Jing

    2016-01-01

    Pure spin current, a flow of spin angular momentum without flow of any accompanying net charge, is generated in two common ways. One makes use of the spin Hall effect in normal metals (NM) with strong spin–orbit coupling, such as Pt or Ta. The other utilizes the collective motion of magnetic moments or spin waves with the quasi-particle excitations called magnons. A popular material for the latter is yttrium iron garnet, a magnetic insulator (MI). Here we demonstrate in NM/MI/NM trilayers that these two types of spin currents are interconvertible across the interfaces, predicated as the magnon-mediated current drag phenomenon. The transmitted signal scales linearly with the driving current without a threshold and follows the power-law Tn with n ranging from 1.5 to 2.5. Our results indicate that the NM/MI/NM trilayer structure can serve as a scalable pure spin current valve device which is an essential ingredient in spintronics. PMID:26932316

  7. Effect of diffusion and alloying on the magnetic and transport properties of Fe/V/Fe trilayers

    NASA Astrophysics Data System (ADS)

    Iuşan, Diana; Alouani, M.; Bengone, O.; Eriksson, O.

    2007-01-01

    The magnetic and transport properties of the Fe/V/Fe(001) trilayers were studied using the self-consistent Green’s function technique based on the tight-binding linear muffin-tin orbital method in the atomic-sphere approximation. The coherent potential approximation was used to describe the effects of interdiffusion and alloying at the interfaces on the properties of the semi-infinite bcc Fe(001)/mFe/nV/mFe/Fe(001) trilayers. The electric conductance was calculated using the Kubo-Landauer formalism, in the current-perpendicular-to-plane geometry. It is shown that a dipole moment is created at the Fe/V interface due to the charge transfer from vanadium to iron, and a small induced magnetic moment is present in the first vanadium layer and is antiparallel to that of iron. The interlayer exchange coupling shows rapid oscillations for small spacer thicknesses, and the interdiffusion and alloying at the interface stabilize the ferromagnetic coupling. Moreover, the interdiffusion reduces the vanadium-induced magnetic moment and increases the iron magnetic moment at the interface. The giant magnetoresistance (GMR) ratio presents damped oscillations as a function of the vanadium spacer thickness. The interdiffusion and the presence of Mn impurities at the interface reduce considerably the GMR ratio and produce results that are in agreement with experimental data.

  8. Graphene-based composites.

    PubMed

    Huang, Xiao; Qi, Xiaoying; Boey, Freddy; Zhang, Hua

    2012-01-21

    Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), offers a wide range of possibilities to synthesize graphene-based functional materials for various applications. This critical review presents and discusses the current development of graphene-based composites. After introduction of the synthesis methods for graphene and its derivatives as well as their properties, we focus on the description of various methods to synthesize graphene-based composites, especially those with functional polymers and inorganic nanostructures. Particular emphasis is placed on strategies for the optimization of composite properties. Lastly, the advantages of graphene-based composites in applications such as the Li-ion batteries, supercapacitors, fuel cells, photovoltaic devices, photocatalysis, as well as Raman enhancement are described (279 references).

  9. Evidence for a π junction in Nb/Ni 0.96V0.04/Nb trilayers revealed by superfluid density measurements

    NASA Astrophysics Data System (ADS)

    Hinton, M. J.; Steers, Stanley; Peters, Bryan; Yang, F. Y.; Lemberger, T. R.

    2016-07-01

    We report measurements of the superfluid density, λ-2(T ) , in ferromagnet-on-superconductor (F/S) bilayers and S/F/S' trilayers comprising Nb with Ni, Py, CoFe, and NiV ferromagnets. Bilayers provide information about F/S interface transparency and the T dependence of λ-2 that inform interpretation of trilayer data. The Houzet-Meyer theory accounts well for the measured dependence of λ-2(0 ) and Tc of F/S bilayers on thickness of F layer, dF, except that λ-2(0 ) is slightly under expectations for CoFe/Nb bilayers. For Nb/F/Nb' trilayers, we are able to extract Tc and and λ-2 for both Nb layers when F is thick enough to weaken interlayer coupling. The lower "Tc" is actually a crossover identified by onset of superfluid in the lower-Tc Nb layer. For Nb/NiV/Nb' trilayers, λ-2(0 ) versus dF for both Nb layers has a minimum followed by a recovery, suggestive of a π junction.

  10. Nanoscale measurements of unoccupied band dispersion in few-layer graphene

    PubMed Central

    Jobst, Johannes; Kautz, Jaap; Geelen, Daniël; Tromp, Rudolf M.; van der Molen, Sense Jan

    2015-01-01

    The properties of any material are fundamentally determined by its electronic band structure. Each band represents a series of allowed states inside a material, relating electron energy and momentum. The occupied bands, that is, the filled electron states below the Fermi level, can be routinely measured. However, it is remarkably difficult to characterize the empty part of the band structure experimentally. Here, we present direct measurements of unoccupied bands of monolayer, bilayer and trilayer graphene. To obtain these, we introduce a technique based on low-energy electron microscopy. It relies on the dependence of the electron reflectivity on incidence angle and energy and has a spatial resolution ∼10 nm. The method can be easily applied to other nanomaterials such as van der Waals structures that are available in small crystals only. PMID:26608712

  11. Nanoscale measurements of unoccupied band dispersion in few-layer graphene

    NASA Astrophysics Data System (ADS)

    Jobst, Johannes; Kautz, Jaap; Geelen, Daniël; Tromp, Rudolf M.; van der Molen, Sense Jan

    2015-11-01

    The properties of any material are fundamentally determined by its electronic band structure. Each band represents a series of allowed states inside a material, relating electron energy and momentum. The occupied bands, that is, the filled electron states below the Fermi level, can be routinely measured. However, it is remarkably difficult to characterize the empty part of the band structure experimentally. Here, we present direct measurements of unoccupied bands of monolayer, bilayer and trilayer graphene. To obtain these, we introduce a technique based on low-energy electron microscopy. It relies on the dependence of the electron reflectivity on incidence angle and energy and has a spatial resolution ~10 nm. The method can be easily applied to other nanomaterials such as van der Waals structures that are available in small crystals only.

  12. Epitaxial Graphene Quantum Electronics

    DTIC Science & Technology

    2014-05-19

    ferromagnetism with spintronics potential. * We have achieved the highest operational frequency in graphene transistors. Epitaxial graphene; quantum transport...important discovery with implications for spintronics . * We have found that ballistic transport most likely involves non-conventional charge carriers

  13. EDITORIAL: Focus on Graphene

    NASA Astrophysics Data System (ADS)

    Peres, N. M. R.; Ribeiro, Ricardo M.

    2009-09-01

    Graphene physics is currently one of the most active research areas in condensed matter physics. Countless theoretical and experimental studies have already been performed, targeting electronic, magnetic, thermal, optical, structural and vibrational properties. Also, studies that modify pristine graphene, aiming at finding new physics and possible new applications, have been considered. These include patterning nanoribbons and quantum dots, exposing graphene's surface to different chemical species, studying multilayer systems, and inducing strain and curvature (modifying in this way graphene's electronic properties). This focus issue includes many of the latest developments on graphene research. Focus on Graphene Contents Electronic properties of graphene and graphene nanoribbons with 'pseudo-Rashba' spin-orbit coupling Tobias Stauber and John Schliemann Strained graphene: tight-binding and density functional calculations R M Ribeiro, Vitor M Pereira, N M R Peres, P R Briddon and A H Castro Neto The effect of sublattice symmetry breaking on the electronic properties of doped graphene A Qaiumzadeh and R Asgari Interfaces within graphene nanoribbons J Wurm, M Wimmer, I Adagideli, K Richter and H U Baranger Weak localization and transport gap in graphene antidot lattices J Eroms and D Weiss Electronic properties of graphene antidot lattices J A Fürst, J G Pedersen, C Flindt, N A Mortensen, M Brandbyge, T G Pedersen and A-P Jauho Splitting of critical energies in the n=0 Landau level of graphene Ana L C Pereira Double-gated graphene-based devices S Russo, M F Craciun, M Yamamoto, S Tarucha and A F Morpurgo Pinning and switching of magnetic moments in bilayer graphene Eduardo V Castro, M P López-Sancho and M A H Vozmediano Electronic transport properties of graphene nanoribbons Katsunori Wakabayashi, Yositake Takane, Masayuki Yamamoto and Manfred Sigrist Many-body effects on out-of-plane phonons in graphene J González and E Perfetto Graphene zigzag ribbons, square

  14. Study of perpendicular anisotropy L1{sub 0}-FePt pseudo spin valves using a micromagnetic trilayer model

    SciTech Connect

    Ho, Pin; Evans, Richard F. L.; Chantrell, Roy W.; Han, Guchang; Chow, Gan-Moog; Chen, Jingsheng

    2015-06-07

    A trilayer micromagnetic model based on the Landau-Lifshitz-Bloch equation of motion is utilized to study the properties of L1{sub 0}-FePt/TiN/L1{sub 0}-FePt pseudo spin valves (PSVs) in direct comparison with experiment. Theoretical studies give an insight on the crystallographic texture, magnetic properties, reversal behavior, interlayer coupling effects, and magneto-transport properties of the PSVs, in particular, with varying thickness of the top L1{sub 0}-FePt and TiN spacer. We show that morphological changes in the FePt layers, induced by varying the FePt layer thickness, lead to different hysteresis behaviors of the samples, caused by changes in the interlayer and intralayer exchange couplings. Such effects are important for the optimization of the PSVs due to the relationship between the magnetic properties, domain structures, and the magnetoresistance of the device.

  15. A theoretical investigation of Ferromagnetic Resonance Linewidth and damping constants in coupled trilayer and spin valve systems

    SciTech Connect

    Layadi, A.

    2015-05-15

    The ferromagnetic resonance intrinsic field linewidth ΔH is investigated for a multilayer system such as a coupled trilayer and a spin valve structure. The magnetic coupling between two ferromagnetic layers separated by a nonmagnetic interlayer will be described by the bilinear J{sub 1} and biquadratic J{sub 2} coupling parameters. The interaction at the interface of the first ferromagnetic layer with the antiferromagnetic one is account for by the exchange anisotropy field, H{sub E}. A general formula is derived for the intrinsic linewidth ΔH. The explicit dependence of ΔH with H{sub E}, J{sub 1} and J{sub 2} will be highlighted. Analytical expressions for each mode field linewidth are found in special cases. Equivalent damping constants will be discussed.

  16. Graphene Synthesis & Graphene/Polymer Nanocomposites

    NASA Astrophysics Data System (ADS)

    Liao, Ken-Hsuan

    We successfully developed a novel, fast, hydrazine-free, high-yield method for producing single-layered graphene. Graphene sheets were formed from graphite oxide by reduction with de-ionized water at 130 ºC. Over 65% of the sheets are single graphene layers. A dehydration reaction of exfoliated graphene oxide was utilized to reduce oxygen and transform C-C bonds from sp3 to sp2. The reduction appears to occur in large uniform interconnected oxygen-free patches so that despite the presence of residual oxygen the sp2 carbon bonds formed on the sheets are sufficient to provide electronic properties comparable to reduced graphene sheets obtained using other methods. Cytotoxicity of aqueous graphene was investigated with Dr. Yu-Shen Lin by measuring mitochondrial activity in adherent human skin fibroblasts using two assays. The methyl-thiazolyl-diphenyl-tetrazolium bromide (MTT) assay, a typical nanotoxicity assay, fails to predict the toxicity of graphene oxide and graphene toxicity because of the spontaneous reduction of MTT by graphene and graphene oxide, resulting in a false positive signal. An appropriate alternate assessment, using the water soluble tetrazolium salt (WST-8) assay, reveals that the compacted graphene sheets are more damaging to mammalian fibroblasts than the less densely packed graphene oxide. Clearly, the toxicity of graphene and graphene oxide depends on the exposure environment (i.e. whether or not aggregation occurs) and mode of interaction with cells (i.e. suspension versus adherent cell types). Ultralow percolation concentration of 0.15 wt% graphene, as determined by surface resistance and modulus, was observed from in situ polymerized thermally reduced graphene (TRG)/ poly-urethane-acrylate (PUA) nanocomposite. A homogeneous dispersion of TRG in PUA was revealed by TEM images. The aspect ratio of dispersed TRG, calculated from percolation concentration and modulus, was found to be equivalent to the reported aspect ratio of single

  17. A graphene electron lens

    NASA Astrophysics Data System (ADS)

    Gerhard, L.; Moyen, E.; Balashov, T.; Ozerov, I.; Portail, M.; Sahaf, H.; Masson, L.; Wulfhekel, W.; Hanbücken, M.

    2012-04-01

    An epitaxial layer of graphene was grown on a pre patterned 6H-SiC(0001) crystal. The graphene smoothly covers the hexagonal nano-holes in the substrate without the introduction of small angle grain boundaries or dislocations. This is achieved by an elastic deformation of the graphene by ≈0.3% in accordance to its large elastic strain limit. This elastic stretching of the graphene leads to a modification of the band structure and to a local lowering of the electron group velocity of the graphene. We propose to use this effect to focus two-dimensional electrons in analogy to simple optical lenses.

  18. Plasmonic graphene transparent conductors.

    PubMed

    Xu, Guowei; Liu, Jianwei; Wang, Qian; Hui, Rongqing; Chen, Zhijun; Maroni, Victor A; Wu, Judy

    2012-03-08

    Plasmonic graphene is fabricated using thermally assisted self-assembly of silver nanoparticles on graphene. The localized surface-plasmonic effect is demonstrated with the resonance frequency shifting from 446 to 495 nm when the lateral dimension of the Ag nanoparticles increases from about 50 to 150 nm. Finite-difference time-domain simulations are employed to confirm the experimentally observed light-scattering enhancement in the solar spectrum in plasmonic graphene and the decrease of both the plasmonic resonance frequency and amplitude with increasing graphene thickness. In addition, plasmonic graphene shows much-improved electrical conductance by a factor of 2-4 as compared to the original graphene, making the plasmonic graphene a promising advanced transparent conductor with enhanced light scattering for thin-film optoelectronic devices.

  19. Functionalized graphene and graphene oxide solution via polyacrylate coating

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Water soluble graphene with various chemical- and biofunctionalities is essential for their different applications. However, exfoliated graphenes are insoluble in water and water soluble graphene oxide precipitate if they are chemically reduced to graphene. We have developed a polyacrylate coating method for graphene oxide and then chemically reduced it into graphene. We found that polyacrylate coating can improve the colloidal stability of both graphene and graphene oxide. The coated graphene has been characterized using XPS, FTIR, XRD and micro-Raman spectroscopy. The primary amine present on the coating backbone has been used to derive glucose functionalized water soluble graphene. Various other functional graphenes can be anticipated from the polyacrylate coated graphene.Water soluble graphene with various chemical- and biofunctionalities is essential for their different applications. However, exfoliated graphenes are insoluble in water and water soluble graphene oxide precipitate if they are chemically reduced to graphene. We have developed a polyacrylate coating method for graphene oxide and then chemically reduced it into graphene. We found that polyacrylate coating can improve the colloidal stability of both graphene and graphene oxide. The coated graphene has been characterized using XPS, FTIR, XRD and micro-Raman spectroscopy. The primary amine present on the coating backbone has been used to derive glucose functionalized water soluble graphene. Various other functional graphenes can be anticipated from the polyacrylate coated graphene. Electronic supplementary information (ESI) available: Details of XPS, XRD, AFM and FTIR of polymer coated GO and G and results of fluorescence quenching experiments. See DOI: 10.1039/c0nr00376j

  20. All-epitaxial Co{sub 2}FeSi/Ge/Co{sub 2}FeSi trilayers fabricated by Sn-induced low-temperature epitaxy

    SciTech Connect

    Kawano, M.; Ikawa, M.; Arima, K.; Yamada, S.; Kanashima, T.; Hamaya, K.

    2016-01-28

    We demonstrate low-temperature growth of all-epitaxial Co{sub 2}FeSi/Ge/Co{sub 2}FeSi trilayer structures by developing Sn-induced surfactant-mediated molecular beam epitaxy (SMBE) of Ge on Co{sub 2}FeSi. Despite the growth of a semiconductor on a metal, we verify that the inserted Sn monolayers between Ge and Co{sub 2}FeSi enable to promote the 2D epitaxial growth of Ge up to 5 nm at a T{sub G} of 250 °C. An understanding of the mechanism of the Sn-induced SMBE leads to the achievement of all-epitaxial Co{sub 2}FeSi/Ge/Co{sub 2}FeSi trilayer structures with spin-valve-like magnetization reversals. This study will open a way for vertical-type and high-performance Ge-based spintronics devices.

  1. My Spring with Graphene

    SciTech Connect

    O'Leary, Timothy Sean

    2015-06-08

    Graphene is a two-dimensional structure, one atom thick, with many uses in the world of technology. It has many useful electrical properties, is a very strong and durable material, and can be used to protect different types of substances. The world would be able to use these properties to further the strength of cars, protect metals from oxidation, increase computer speeds, use to improve superconductors, and whatever future uses that scientist invent or discover. We sought to optimize the growth and transfer of graphene. We grew graphene on copper foils by heating the foil in a furnace, and having various gases flow through a tube, where the copper foil was placed. We varied some of the concentrations of gases, along with having different times for heating the copper foil, different times for graphene growth, or a combination of the two. The focus of our experiment was to specifically grow monolayer single crystal graphene, which means that we do not want multiplayers of graphene, and do not want multiple crystals growing to form a bigger crystal. Our goal was to grow large single crystals from the growth experiment. We used a few different types of transfer methods that ranged from: using heat and pressure to press the graphene on different materials, using a polymer to cover the graphene with a method to destroy the copper, but leave the graphene and polymer intact, and using a type of heat tape with a combination of varying pressures to transfer the graphene, and then destroy the copper foil. To discover if we grew graphene we used different techniques involving lasers and microscopes to take different types of measurements. Discovering the best way of growing and transferring graphene will help with managing the cost of the future uses of graphene.

  2. Graphene device and method of using graphene device

    DOEpatents

    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.

  3. Halogenated graphenes: rapidly growing family of graphene derivatives.

    PubMed

    Karlický, František; Kumara Ramanatha Datta, Kasibhatta; Otyepka, Michal; Zbořil, Radek

    2013-08-27

    Graphene derivatives containing covalently bound halogens (graphene halides) represent promising two-dimensional systems having interesting physical and chemical properties. The attachment of halogen atoms to sp(2) carbons changes the hybridization state to sp(3), which has a principal impact on electronic properties and local structure of the material. The fully fluorinated graphene derivative, fluorographene (graphene fluoride, C1F1), is the thinnest insulator and the only stable stoichiometric graphene halide (C1X1). In this review, we discuss structural properties, syntheses, chemistry, stabilities, and electronic properties of fluorographene and other partially fluorinated, chlorinated, and brominated graphenes. Remarkable optical, mechanical, vibrational, thermodynamic, and conductivity properties of graphene halides are also explored as well as the properties of rare structures including multilayered fluorinated graphenes, iodine-doped graphene, and mixed graphene halides. Finally, patterned halogenation is presented as an interesting approach for generating materials with applications in the field of graphene-based electronic devices.

  4. Towards the Synthesis of Graphene Azide from Graphene Oxide.

    PubMed

    Halbig, Christian E; Rietsch, Philipp; Eigler, Siegfried

    2015-11-26

    In the last decades, organic azides haven proven to be very useful precursors in organic chemistry, for example in 1,3-dipolar cycloaddition reactions (click-chemistry). Likewise, azides can be introduced into graphene oxide with an almost intact carbon framework, namely oxo-functionalized graphene (oxo-G₁), which is a highly oxidized graphene derivative and a powerful precursor for graphene that is suitable for electronic devices. The synthesis of a graphene derivative with exclusively azide groups (graphene azide) is however still a challenge. In comparison also hydrogenated graphene, called graphene or halogenated graphene remain challenging to synthesize. A route to graphene azide would be the desoxygenation of azide functionalized oxo-G₁. Here we show how treatment of azide functionalized oxo-G₁ with HCl enlarges the π-system and removes strongly adsorbed water and some oxo-functional groups. This development reflects one step towards graphene azide.

  5. Erratum: "Influence of heavy metal materials on magnetic properties of Pt/Co/heavy metal tri-layered structures" [Appl. Phys. Lett. 110, 012405 (2017)

    NASA Astrophysics Data System (ADS)

    Zhang, Boyu; Cao, Anni; Qiao, Junfeng; Tang, Minghong; Cao, Kaihua; Zhao, Xiaoxuan; Eimer, Sylvain; Si, Zhizhong; Lei, Na; Wang, Zhaohao; Lin, Xiaoyang; Zhang, Zongzhi; Wu, Mingzhong; Zhao, Weisheng

    2017-03-01

    Pt/Co/heavy metal (HM) tri-layered structures with interfacial perpendicular magnetic anisotropy (PMA) are currently under intensive research for several emerging spintronic effects, such as spinorbit torque, domain wall motion, and room temperature skyrmions. HM materials are used as capping layers to generate the structural asymmetry and enhance the interfacial effects. For instance, the Pt/Co/Ta structure attracts a lot of attention as it may exhibit large Dzyaloshinskii-Moriya interaction. However, the dependence of magnetic properties on different capping materials has not been systematically investigated. In this paper, we experimentally show the interfacial PMA and damping constant for Pt/Co/HM tri-layered structures through time-resolved magneto-optical Kerr effect measurements as well as magnetometry measurements, where the capping HM materials are W, Ta, and Pd. We found that the Co/HM interface plays an important role on the magnetic properties. In particular, the magnetic multilayers with a W capping layer features the lowest effective damping value, which may be attributed to the different spin-orbit coupling and interfacial hybridization between Co and HM materials. Our findings allow a deep understanding of the Pt/Co/HM tri-layered structures. Such structures could lead to a better era of data storage and processing devices.

  6. XAS and XMCD studies of magnetic properties modifications of Pt/Co/Au and Pt/Co/Pt trilayers induced by Ga⁺ ions irradiation.

    PubMed

    Mazalski, Piotr; Sveklo, Iosif; Kurant, Zbigniew; Ollefs, Katharina; Rogalev, Andrei; Wilhelm, Fabrice; Fassbender, Juergen; Baczewski, Lech Tomasz; Wawro, Andrzej; Maziewski, Andrzej

    2015-05-01

    Magnetic and magneto-optical properties of Pt/Co/Au and Pt/Co/Pt trilayers subjected to 30 keV Ga(+) ion irradiation are compared. In two-dimensional maps of these properties as a function of cobalt thickness and ion fluence, two branches with perpendicular magnetic anisotropy (PMA) for Pt/Co/Pt trilayers are well distinguished. The replacement of the Pt capping layer with Au results in the two branches still being visible but the in-plane anisotropy for the low-fluence branch is suppressed whereas the high-fluence branch displays PMA. The X-ray absorption spectra and X-ray magnetic circular dichroism (XMCD) spectra are discussed and compared with non-irradiated reference samples. The changes of their shapes and peak amplitude, particularly for the high-fluence branch, are related to the modifications of the local environment of Co(Pt) atoms and the etching effects induced by ion irradiation. Additionally, in irradiated trilayers the XMCD measurements at the Pt L2,3-edge reveal an increase of the magnetic moment induced in Pt atoms.

  7. Perpendicular Magnetic Anisotropy in CoSiB/Pd/CoSiB Trilayer Thin Films with Varying Pd-Layer Thicknesses.

    PubMed

    Jung, Sol; Kim, Taewan; Yim, Haein

    2015-11-01

    We investigate the magnetic properties of CoSiB (1 5-Å-thickness)/Pd (Pd thickness = 8, 11, 14, 17, 20, 24, 27, 29 and 33 Å)/CoSiB (15-Å-thickness) trilayer thin films. The CoSiB-layer thickness was fixed to 15 Å, while the Pd-layer thickness was varied from 8-33 Å. In this paper, we present a new type of thin film containing amorphous Co75Si15B10 and Pd. We investigate the magnetic properties of a fabricated CoSiB/Pd/CoSiB trilayer thin film with perpendicular magnetic anisotropy, and determine the correlation between the magnetic properties and the nonmagnetic Pd-layer thickness. With increasing Pd-layer thickness, both the coercivity and the saturation magnetization decreased. Furthermore, the maximum values of the magnetic anisotropy were calculated as 0.3 x 10(6) erg/cc. In order to examine the difference between the in-plane magnetic anisotropy and perpendicular magnetic anisotropy, magnetic force microscopy images of the CoSiB (15-Å-thickness)/Pd (Pd thickness = 8 and 14 Å)/CoSiB (15-Å-thickness) trilayer thin films were obtained.

  8. All-Graphene Photodetectors

    PubMed Central

    2013-01-01

    We investigate the optoelectronic properties of novel graphene/FeCl3-intercalated few-layer graphene (FeCl3–FLG, dubbed graphexeter) heterostructures using photovoltage spectroscopy. We observe a prominent photovoltage signal generated at the graphene/FeCl3–FLG and graphene/Au interfaces, whereas the photovoltage at the FeCl3–FLG/Au interface is negligible. The sign of the photovoltage changes upon sweeping the chemical potential of the pristine graphene through the charge neutrality point, and we show that this is due to the photothermoelectric effect. Our results are a first step toward all-graphene-based photodetectors and photovoltaics. PMID:23597182

  9. Enabling graphene nanoelectronics.

    SciTech Connect

    Pan, Wei; Ohta, Taisuke; Biedermann, Laura Butler; Gutierrez, Carlos; Nolen, C. M.; Howell, Stephen Wayne; Beechem Iii, Thomas Edwin; McCarty, Kevin F.; Ross, Anthony Joseph, III

    2011-09-01

    Recent work has shown that graphene, a 2D electronic material amenable to the planar semiconductor fabrication processing, possesses tunable electronic material properties potentially far superior to metals and other standard semiconductors. Despite its phenomenal electronic properties, focused research is still required to develop techniques for depositing and synthesizing graphene over large areas, thereby enabling the reproducible mass-fabrication of graphene-based devices. To address these issues, we combined an array of growth approaches and characterization resources to investigate several innovative and synergistic approaches for the synthesis of high quality graphene films on technologically relevant substrate (SiC and metals). Our work focused on developing the fundamental scientific understanding necessary to generate large-area graphene films that exhibit highly uniform electronic properties and record carrier mobility, as well as developing techniques to transfer graphene onto other substrates.

  10. Trifluoromethylation of graphene

    SciTech Connect

    Zhou, Lin; Zhou, Lushan; Wang, Xi; Yu, Jingwen; Yang, Mingmei; Wang, Jianbo; Peng, Hailin E-mail: hlpeng@pku.edu.cn; Liu, Zhongfan E-mail: hlpeng@pku.edu.cn

    2014-09-01

    We demonstrate trifluoromethylation of graphene by copper-catalyzed free radical reaction. The covalent addition of CF{sub 3} to graphene, which changes the carbon atom hybridization from sp{sup 2} to sp{sup 3}, and modifies graphene in a homogeneous and nondestructive manner, was verified with Raman spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. X-ray photoelectron spectroscopy reveals that CF{sub 3} groups are grafted to the basal plane of graphene, with about 4 at. % CF{sub 3} coverage. After trifluoromethylation, the average resistance increases by nearly one order of magnitude, and an energy gap of about 98 meV appears. The noninvasive and mild reaction to synthesize trifluoromethylated graphene paves the way for graphene's applications in electronics and biomedical areas.

  11. Spin transport in graphene

    NASA Astrophysics Data System (ADS)

    Özyilmaz, Barbaros

    2012-02-01

    Conventional electronic transistors involve the control of electronic charge at the nanoscale to realize memory, logic and communication functions. All these electronic charges, however, also carry a spin that remains unutilized in present commercial devices. This has motivated the search for new materials that propagate spin-polarized currents over large distances. Among the most promising materials for spintronics has been graphene. Micron-scale spin relaxation lengths have been previously demonstrated in single-layer graphene. Recently, we showed that bilayer graphene is a far more interesting candidate for spintronics. By fabricating spin valves on bilayer graphene we have achieved at room temperature spin relaxation times up to 2 nanoseconds, which are an order of magnitude higher than for single layer graphene [1]. Furthermore, the spin-relaxation time scales inversely with the mobility of BLG sample. This indicates the importance of D'yakonov-Perel' spin scattering in BLG. Last not but least, the presence of an electric field tunable band gap in bilayer graphene makes it particularly appealing. Our work provides fundamental insight into the unique properties of bilayer graphene for spintronic applications. Remarkably, a similar difference between single layer and bilayer graphene is also observed in large area graphene grown by the CVD method on copper. These results demonstrate the potential of CVD graphene in realistic spintronics devices [2]. [4pt] [1] T - Y. Yang et al., Observation of Long Spin-Relaxation Times in Bilayer Graphene at Room Temperature, PRL (2011). [0pt] [2] A. Avsar et al., Towards Wafer Scale Fabrication of Graphene Based Spin Valve Devices, Nano Lett. (2011).

  12. Fourier optics on graphene

    NASA Astrophysics Data System (ADS)

    Vakil, Ashkan; Engheta, Nader

    2012-02-01

    Using numerical simulations, here, we demonstrate that a single sheet of graphene with properly designed inhomogeneous, nonuniform conductivity distributions can act as a convex lens for focusing and collimating the transverse-magnetic (TM) surface plasmon polariton (SPP) surface waves propagating along the graphene. Consequently, we show that the graphene can act as a platform for obtaining spatial Fourier transform of infrared (IR) SPP signals. This may lead to rebirth of the field of Fourier optics on a 1-atom-thick structure.

  13. Suspended graphene variable capacitor

    NASA Astrophysics Data System (ADS)

    AbdelGhany, M.; Mahvash, F.; Mukhopadhyay, M.; Favron, A.; Martel, R.; Siaj, M.; Szkopek, T.

    2016-12-01

    Electromechanical variable capacitors, or varactors, find a wide range of applications including sensing applications and the tuning of electrical circuit resonance. We demonstrate a nano-electromechanical graphene varactor, a variable capacitor wherein the capacitance is tuned by voltage controlled deflection of a dense array of suspended graphene membranes. The low flexural rigidity of graphene monolayers is exploited to achieve low actuation voltage and high tunable capacitance density in an ultra-thin structure. Large arrays comprising thousands of suspensions were fabricated to give a tunable capacitance of over 10 pF mm-2. This capacitance density suggests that graphene offers a potential solution to the challenge of reducing the size of micro-electromechanical systems (MEMS). A capacitance tuning of 55% was achieved with a 10 V actuating voltage, exceeding the 50% tuning limit of Hookean parallel plate pull-in without the use of complex mechanical schemes that occupy substrate area. Capacitor behavior was investigated experimentally, and described by a simple theoretical model. Mechanical properties of the graphene membranes were measured independently using atomic force microscopy. We present a comparison of state-of-the-art MEMS and graphene varactors. The quality factor of graphene varactors is limited by graphene sheet resistance, pull-in voltage can be improved with more aggressive scaling, while the power handling and cycling stability of graphene varactors remains unknown.

  14. Deformation of Wrinkled Graphene

    PubMed Central

    2015-01-01

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

  15. Graphene monolayer rotation on Ni(111) facilitates bilayer graphene growth

    NASA Astrophysics Data System (ADS)

    Dahal, Arjun; Addou, Rafik; Sutter, Peter; Batzill, Matthias

    2012-06-01

    Synthesis of bilayer graphene by chemical vapor deposition is of importance for graphene-based field effect devices. Here, we demonstrate that bilayer graphene preferentially grows by carbon-segregation under graphene sheets that are rotated relative to a Ni(111) substrate. Rotated graphene monolayer films can be synthesized at growth temperatures above 650 °C on a Ni(111) thin-film. The segregated second graphene layer is in registry with the Ni(111) substrate and this suppresses further C-segregation, effectively self-limiting graphene formation to two layers.

  16. Graphene Monolayer Rotation on Ni(111) Facilities Bilayer Graphene Growth

    SciTech Connect

    Batzill M.; Sutter P.; Dahal, A.; Addou, R.

    2012-06-11

    Synthesis of bilayer graphene by chemical vapor deposition is of importance for graphene-based field effect devices. Here, we demonstrate that bilayer graphene preferentially grows by carbon-segregation under graphene sheets that are rotated relative to a Ni(111) substrate. Rotated graphene monolayer films can be synthesized at growth temperatures above 650 C on a Ni(111) thin-film. The segregated second graphene layer is in registry with the Ni(111) substrate and this suppresses further C-segregation, effectively self-limiting graphene formation to two layers.

  17. Toward high performance graphene fibers.

    PubMed

    Chen, Li; He, Yuling; Chai, Songgang; Qiang, Hong; Chen, Feng; Fu, Qiang

    2013-07-07

    Two-dimensional graphene and graphene-based materials have attracted tremendous interest, hence much attention has been drawn to exploring and applying their exceptional characteristics and properties. Integration of graphene sheets into macroscopic fibers is a very important way for their application and has received increasing interest. In this study, neat and macroscopic graphene fibers were continuously spun from graphene oxide (GO) suspensions followed by chemical reduction. By varying wet-spinning conditions, a series of graphene fibers were prepared, then, the structural features, mechanical and electrical performances of the fibers were investigated. We found the orientation of graphene sheets, the interaction between inter-fiber graphene sheets and the defects in the fibers have a pronounced effect on the properties of the fibers. Graphene fibers with excellent mechanical and electrical properties will yield great advances in high-tech applications. These findings provide guidance for the future production of high performance graphene fibers.

  18. X-ray diffraction studies of trilayer oscillations in the preferred thickness of In films on Si(111)

    NASA Astrophysics Data System (ADS)

    Gray, A.; Liu, Y.; Hong, Hawoong; Chiang, T.-C.

    2013-05-01

    We report a surface x-ray diffraction study of the structure of In films grown on Si(111)-(7×7) and Si(111)-(3×3)-In substrates at a low temperature (135 K). The (7×7) reconstruction of the clean Si(111) surface is found to persist upon burial by the In. X-ray reflectivity measurements yield patterns that deviate strongly from the ideal case; the results suggest a complex In film structure, possibly distorted by the corrugated interfacial reconstruction. By contrast, In films grown on the Si(111)-(3×3)-In surface exhibit reflectivity data that are much closer to the ideal case. The films are found to grow approximately layer by layer, resulting in a relatively small roughness. Upon annealing, the films develop preferred thicknesses at 10, 13, and 16 monolayers (MLs). Previous photoemission studies revealed preferred thicknesses at 4 and 7 MLs. Putting these results together, the preferred thickness sequence, 4, 7, 10, 13, and 16 ML, establishes a trilayer oscillation period. This period is expected from the known electronic structure of In, and arises from quantum confinement of the In valence electrons. This is the second example, after the well-known bilayer period in Pb, which shows quantum oscillations over a wide range of film thickness.

  19. Interface roughness induced asymmetric magnetic property in sputter-deposited Co/CoO/Co exchange coupled trilayers

    SciTech Connect

    Wang, J.; Sannomiya, T.; Shi, J.; Nakamura, Y.

    2012-04-01

    The effect of interface roughness on magnetic properties of exchange coupled polycrystalline Co/CoO(t{sub AF})/Co trilayers has been investigated by varying antiferromagnetic layer (CoO) thickness. It has been found that the upper CoO/Co interface becomes rougher with increasing CoO layer thickness, resulting in stronger exchange bias of the upper interface than the lower one. The interfacial exchange coupling is strengthened by the increase of defect-generated uncompensated antiferromagnetic spins; such spins form coupling with spins in the Co layer at the interface. As a result, the CoO layer thickness dependence of exchange bias is much enhanced for the upper Co layer. The transition from anisotropic magnetoresistance to isotropic magnetoresistance for the top Co layer has also been found. This could be attributed to the defects, probably partial thin oxide layers, between Co grains in the top Co layer that leads a switch from spin-orbit scattering related magnetoresistance to spin-dependent electron scattering dominated magnetoresistance.

  20. Equivalent circuit model of converse magnetoelectric effect for the tri-layer magnetoelectric laminates with thermal and stress loadings

    NASA Astrophysics Data System (ADS)

    Zhou, Hao-Miao; Li, Meng-Han; Liu, Hui; Cui, Xiao-Le

    2015-12-01

    For the converse magnetoelectric coupling effect of the piezoelectric/magnetostrictive/piezoelectric tri-layer symmetric magnetoelectric laminates, based on the nonlinear thermo-magneto-mechanical constitutive equations of the giant magnetostrictive materials and the thermo-electro-mechanical constitutive equations of the piezoelectric materials, according to Newton's second law and the magnetic circuit theorem, an equivalent circuit is established. Then an expression of the converse magnetoelectric coefficient describing nonlinear thermo-magneto-electro-mechanical coupling is established. The curve of the nonlinear converse magnetoelectric coefficient versus the bias magnetic field, is predicted effectively by the expression, and the predictions are in good agreement with the experimental result both qualitatively and quantitatively. Furthermore, the model can predict the complex influences of the bias magnetic field, the stress and the ambient temperature on the converse magnetoelectric coefficient. It can be found from these predictions that the converse magnetoelectric coefficient decreases with the increasing temperature and increases with the increasing tensile stress. Under the common effect of the ambient temperature and the stress, it is also found that the converse magnetoelectric coefficient changes sharply with the ambient temperature when the tensile stress is applied on the laminates, but it has a good stability of temperature when a large compressive stress is applied. Therefore, this work contributes to the researches on the giant converse magnetoelectric coefficient and the designs of magnetoelectric devices based on the converse magnetoelectric coupling.

  1. Solid state synthesis of Mn5Ge3 in Ge/Ag/Mn trilayers: Structural and magnetic studies

    NASA Astrophysics Data System (ADS)

    Myagkov, V. G.; Bykova, L. E.; Matsynin, A. A.; Volochaev, M. N.; Zhigalov, V. S.; Tambasov, I. A.; Mikhlin, Yu L.; Velikanov, D. A.; Bondarenko, G. N.

    2017-02-01

    The thin-film solid-state reaction between elemental Ge and Mn across chemically inert Ag layers with thicknesses of (0, 0.3, 1 and 2.2 μm) in Ge/Ag/Mn trilayers was studied for the first time. The initial samples were annealed at temperatures between 50 and 500 °C at 50 °C intervals for 1 h. The initiation temperature of the reaction for Ge/Mn (without a Ag barrier layer) was 120 °C and increased slightly up to 250 °C when the Ag barrier layer thickness increased up to 2.2 μm. In spite of the Ag layer, only the ferromagnetic Mn5Ge3 compound and the Nowotny phase were observed in the initial stage of the reaction after annealing at 500 °C. The cross-sectional studies show that during Mn5Ge3 formation the Ge is the sole diffusing species. The magnetic and cross-sectional transmission electron microscopy (TEM) studies show an almost complete transfer of Ge atoms from the Ge film, via a 2.2 μm Ag barrier layer, into the Mn layer. We attribute the driving force of the long-range transfer to the long-range chemical interactions between reacting Mn and Ge atoms.

  2. Charge transport in ion-gated mono-, bi-, and trilayer MoS2 field effect transistors

    PubMed Central

    Chu, Leiqiang; Schmidt, Hennrik; Pu, Jiang; Wang, Shunfeng; Özyilmaz, Barbaros; Takenobu, Taishi; Eda, Goki

    2014-01-01

    Charge transport in MoS2 in the low carrier density regime is dominated by trap states and band edge disorder. The intrinsic transport properties of MoS2 emerge in the high density regime where conduction occurs via extended states. Here, we investigate the transport properties of mechanically exfoliated mono-, bi-, and trilayer MoS2 sheets over a wide range of carrier densities realized by a combination of ion gel top gate and SiO2 back gate, which allows us to achieve high charge carrier (>1013 cm−2) densities. We discuss the gating properties of the devices as a function of layer thickness and demonstrate resistivities as low as 1 kΩ for monolayer and 420 Ω for bilayer devices at 10 K. We show that from the capacitive coupling of the two gates, quantum capacitance can be roughly estimated to be on the order of 1 μF/cm2 for all devices studied. The temperature dependence of the carrier mobility in the high density regime indicates that short-range scatterers limit charge transport at low temperatures. PMID:25465059

  3. Largely enhanced energy density in epitaxial SmCo5/Fe/SmCo5 exchange spring trilayers

    NASA Astrophysics Data System (ADS)

    Sawatzki, S.; Heller, R.; Mickel, Ch.; Seifert, M.; Schultz, L.; Neu, V.

    2011-06-01

    In order to enhance the energy density (BH)max as a key property for permanent magnet applications, exchanged-coupled trilayers of SmCo5/Fe/SmCo5 with fixed SmCo5 layer thicknesses (25 nm) and varying soft magnetic Fe film thickness have been epitaxially grown by pulsed laser deposition on Cr buffered MgO(110) substrates. The effect of the increasing soft layer thickness on the reversal mechanism and improved remanence due to the higher Fe-volume fraction was investigated by vibrating sample magnetometry in external fields up to 9 T. As the energy density strongly depends on the volume of the samples, emphasis is put on multilayer architecture investigation and reliable thickness determination. Concerning the latter all applied analysis methods as energy dispersive x-ray analysis, Rutherford backscattering spectroscopy and transmission electron microscopy confirm energy densities with maximum values of 312 kJ/m3 (39 MGOe) for a soft layer thickness of 12.6 nm.

  4. Quantum spin Hall insulators in centrosymmetric thin films composed from topologically trivial BiTeI trilayers

    PubMed Central

    Nechaev, I. A.; Eremeev, S. V.; Krasovskii, E. E.; Echenique, P. M.; Chulkov, E. V.

    2017-01-01

    The quantum spin Hall insulators predicted ten years ago and now experimentally observed are instrumental for a break- through in nanoelectronics due to non-dissipative spin-polarized electron transport through their edges. For this transport to persist at normal conditions, the insulators should possess a sufficiently large band gap in a stable topological phase. Here, we theoretically show that quantum spin Hall insulators can be realized in ultra-thin films constructed from a trivial band insulator with strong spin-orbit coupling. The thinnest film with an inverted gap large enough for practical applications is a centrosymmetric sextuple layer built out of two inversely stacked non-centrosymmetric BiTeI trilayers. This nontrivial sextuple layer turns out to be the structure element of an artificially designed strong three-dimensional topological insulator Bi2Te2I2. We reveal general principles of how a topological insulator can be composed from the structure elements of the BiTeX family (X = I, Br, Cl), which opens new perspectives towards engineering of topological phases. PMID:28252656

  5. Quantum spin Hall insulators in centrosymmetric thin films composed from topologically trivial BiTeI trilayers

    NASA Astrophysics Data System (ADS)

    Nechaev, I. A.; Eremeev, S. V.; Krasovskii, E. E.; Echenique, P. M.; Chulkov, E. V.

    2017-03-01

    The quantum spin Hall insulators predicted ten years ago and now experimentally observed are instrumental for a break- through in nanoelectronics due to non-dissipative spin-polarized electron transport through their edges. For this transport to persist at normal conditions, the insulators should possess a sufficiently large band gap in a stable topological phase. Here, we theoretically show that quantum spin Hall insulators can be realized in ultra-thin films constructed from a trivial band insulator with strong spin-orbit coupling. The thinnest film with an inverted gap large enough for practical applications is a centrosymmetric sextuple layer built out of two inversely stacked non-centrosymmetric BiTeI trilayers. This nontrivial sextuple layer turns out to be the structure element of an artificially designed strong three-dimensional topological insulator Bi2Te2I2. We reveal general principles of how a topological insulator can be composed from the structure elements of the BiTeX family (X = I, Br, Cl), which opens new perspectives towards engineering of topological phases.

  6. Quantum spin Hall insulators in centrosymmetric thin films composed from topologically trivial BiTeI trilayers.

    PubMed

    Nechaev, I A; Eremeev, S V; Krasovskii, E E; Echenique, P M; Chulkov, E V

    2017-03-02

    The quantum spin Hall insulators predicted ten years ago and now experimentally observed are instrumental for a break- through in nanoelectronics due to non-dissipative spin-polarized electron transport through their edges. For this transport to persist at normal conditions, the insulators should possess a sufficiently large band gap in a stable topological phase. Here, we theoretically show that quantum spin Hall insulators can be realized in ultra-thin films constructed from a trivial band insulator with strong spin-orbit coupling. The thinnest film with an inverted gap large enough for practical applications is a centrosymmetric sextuple layer built out of two inversely stacked non-centrosymmetric BiTeI trilayers. This nontrivial sextuple layer turns out to be the structure element of an artificially designed strong three-dimensional topological insulator Bi2Te2I2. We reveal general principles of how a topological insulator can be composed from the structure elements of the BiTeX family (X = I, Br, Cl), which opens new perspectives towards engineering of topological phases.

  7. High performance solid oxide fuel cells based on tri-layer yttria-stabilized zirconia by low temperature sintering process

    NASA Astrophysics Data System (ADS)

    Liu, Ze; Zheng, Zi-wei; Han, Min-fang; Liu, Mei-lin

    Performance of solid oxide fuel cells (SOFCs) depends critically on the composition and microstructure of the electrodes. It is fabricated a dense yttria-stabilized zirconia (YSZ) electrolyte layer sandwiched between two porous YSZ layers at low temperature. The advantages of this structure include excellent structural stability and unique flexibility for evaluation of new electrode materials for SOFC applications, which would be difficult or impossible to be evaluated using conventional cell fabrication techniques because of incompatibility with YSZ under processing conditions. The porosity of porous YSZ increases from 65.8% to 68.6% as the firing temperature decreased from 1350 to 1200 °C. The open cell voltages of the cells based on the tri-layers of YSZ, co-fired using a two-step sintering at 1200 °C, are above 1.0 V at 700-800 °C, and the peak power densities of cells infiltrated LSCF and Pd-SDC electrodes are about 525, 733, and 935 mW cm -2 at 700, 750, and 800 °C, respectively.

  8. Quasistatic computer simulation study of the shear behavior of Bi- and trilayer water films confined between model hydrophilic surfaces.

    PubMed

    Pertsin, Alexander; Grunze, Michael

    2008-05-06

    In this paper, our previous simulations of the shear behavior of confined water monolayers (Pertsin, A.; Grunze, M. Langmuir 2008, 24, 135) are extended to water films two and three monolayers thick. The shear response of the films is studied in the quasistatic regime corresponding to the infinitely low shear rate. In certain ranges of wall-to-wall separations, bilayer films are found to be capable of sustaining shear stress, as is characteristic of solids, while remaining fluidlike in respect of the lateral order and molecular mobility. The relation between the solidlike and fluidlike properties of the films is dependent on the relative alignment of the walls and on the period of the wall lattice. The films become more fluid when the walls are moved out of alignment and when the wall lattice is uniformly compressed or stretched with respect to the "optimum" lattice that favors crystal-like packing. Trilayer films do not sustain shear stress in the whole range of wall-to-wall separations where these films are formed.

  9. Van Hove singularities in doped twisted graphene bilayers studied by scanning tunneling spectroscopy

    NASA Astrophysics Data System (ADS)

    Cherkez, V.; de Laissardière, G. Trambly; Mallet, P.; Veuillen, J.-Y.

    2015-04-01

    The effect of electron doping on the van Hove singularities (vHs) which develop in twisted graphene bilayers (tBLs) is studied for a broad range of rotation angles θ (1 .5∘<θ <15∘) by means of scanning tunneling microscopy and spectroscopy. Bilayer and trilayer graphene islands were grown on the 6H-SiC(000-1) (3 ×3 ) surface, which results in tBLs doped in the 1012cm-2 range by charge transfer from the substrate. For large angles, doping manifests in a strong asymmetry of the positions of the upper (in empty states) and lower (in occupied states) vHs with respect to the Fermi level. The splitting of these vHs energies is found essentially independent of doping for the whole range of θ values, but the center of theses vHs shifts towards negative energies with increasing electron doping. Consequently, the upper vHs crosses the Fermi level for smaller angles (around 3∘ ). The analysis of the data performed using tight-binding calculations and simple electrostatic considerations shows that the interlayer bias remains small (<100 mV ) for the doping level resulting from the interfacial charge transfer (≃5 ×1012cm-2) .

  10. Insulating state in tetralayers reveals an even-odd interaction effect in multilayer graphene

    NASA Astrophysics Data System (ADS)

    Grushina, Anya L.; Ki, Dong-Keun; Koshino, Mikito; Nicolet, Aurelien A. L.; Faugeras, Clément; McCann, Edward; Potemski, Marek; Morpurgo, Alberto F.

    2015-03-01

    Close to charge neutrality, the electronic properties of graphene and its multilayers are sensitive to electron-electron interactions. In bilayers, for instance, interactions are predicted to open a gap between valence and conduction bands, turning the system into an insulator. In mono and (Bernal-stacked) trilayers, which remain conducting at low temperature, interactions do not have equally drastic consequences. It is expected that interaction effects become weaker for thicker multilayers, whose behaviour should converge to that of graphite. Here we show that this expectation does not correspond to reality by revealing the occurrence of an insulating state close to charge neutrality in Bernal-stacked tetralayer graphene. The phenomenology—incompatible with the behaviour expected from the single-particle band structure—resembles that observed in bilayers, but the insulating state in tetralayers is visible at higher temperature. We explain our findings, and the systematic even-odd effect of interactions in Bernal-stacked layers of different thickness that emerges from experiments, in terms of a generalization of the interaction-driven, symmetry-broken states proposed for bilayers.

  11. Ultrathin Planar Graphene Supercapacitors

    SciTech Connect

    Huang, Jingsong; Meunier, Vincent; Sumpter, Bobby G; Ajayan, Pullikel M; Yoo, Jung Joon; Balakrishnan, Kaushik; Srivastava, Anchal; Conway, Michelle; Reddy, Arava Leela Mohan; Yu, Jin; Vajtai, Robert

    2011-01-01

    With the advent of atomically thin and flat layers of conducting materials such as graphene, new designs for thin film energy storage devices with good performance have become possible. Here, we report an in-plane fabrication approach for ultrathin supercapacitors based on electrodes comprised of pristine graphene and multi-layer reduced graphene oxide. The in-plane design is straightforward to implement and exploits efficiently the surface of each graphene layer for energy storage. The open architecture and the effect of graphene edges enable even the thinnest of devices, made from as grown 1-2 graphene layers, to reach specific capacities up to 80 Fcm-2. While, much higher (394 Fcm-2) specific capacities are observed in case of multi-layered graphene oxide electrodes, owing to the better utilization of the available electrochemical surface area. The performances of devices with pristine as well as thicker graphene based structures are examined using a combination of experiments and model calculations. The demonstrated all solid-state supercapacitors provide a prototype for a broad range of thin-film based energy storage devices.

  12. Quantum Complexity in Graphene

    NASA Astrophysics Data System (ADS)

    Baskaran, G.

    Carbon has a unique position among elements in the periodic table. It produces an allotrope, graphene, a mechanically robust two dimensional semimetal. The multifarious properties that graphene exhibits has few parallels among elemental metals. From simplicity, namely carbon atoms connected by pure sp2 bonds, a wealth of novel quantum properties emerge. In classical complex systems such as a spin glass or a finance market, several competing agents or elements are responsible for unanticipated and difficult to predict emergent properties. The complex (sic) structure of quantum mechanics is responsbile for an unanticipated set of emergent properties in graphene. We call this quantum complexity. In fact, most quantum systems, phenomena and modern quantum field theory could be viewed as examples of quantum complexity. After giving a brief introduction to the quantum complexity we focus on our own work, which indicates the breadth in the type of quantum phenomena that graphene could support. We review our theoretical suggestions of, (i) spin-1 collective mode in netural graphene, (ii) relativistic type of phenomena in crossed electric and magnetic fields, (iii) room temperature superconductivity in doped graphene and (iv) composite Fermi sea in neutral graphene in uniform magnetic field and (v) two-channel Kondo effect. Except for the relativistic type of phenomena, the rest depend in a fundamental way on a weak electron correlation that exists in the broad two-dimensional band of graphene.

  13. Quantum Complexity in Graphene

    NASA Astrophysics Data System (ADS)

    Baskaran, G.

    Carbon has a unique position among elements in the periodic table. It produces an allotrope, graphene, a mechanically robust two dimensional semimetal. The multifarious properties that graphene exhibits has few parallels among elemental metals. From simplicity, namely carbon atoms connected by pure sp2 bonds, a wealth of novel quantum properties emerge. In classical complex systems such as a spin glass or a finance market, several competing agents or elements are responsible for unanticipated and difficult to predict emergent properties. The complex (sic) structure of quantum mechanics is responsbile for an unanticipated set of emergent properties in graphene. We call this quantum complexity. Infact, most quantum systems, phenomena and modern quantum field theory could be viewed as examples of quantum complexity. After giving a brief introduction to the quantum complexity we focus on our own work, which indicates the breadth in the type of quantum phenomena that graphene could support. We review our theoretical suggestions of, (i) spin-1 collective mode in netural graphene, (ii) relativistic type of phenomena in crossed electric and magnetic fields, (iii) room temperature superconductivity in doped graphene and (iv) composite Fermi sea in neutral graphene in uniform magnetic field and (v) 2-channel Kondo effect. Except for the relativistic type of phenomena and Kondo effect, the rest depend in a fundamental way on a weak electron correlations that exist in graphene.

  14. Multifunctional graphene woven fabrics

    PubMed Central

    Li, Xiao; Sun, Pengzhan; Fan, Lili; Zhu, Miao; Wang, Kunlin; Zhong, Minlin; Wei, Jinquan; Wu, Dehai; Cheng, Yao; Zhu, Hongwei

    2012-01-01

    Tailoring and assembling graphene into functional macrostructures with well-defined configuration are key for many promising applications. We report on a graphene-based woven fabric (GWF) prepared by interlacing two sets of graphene micron-ribbons where the ribbons pass each other essentially at right angles. By using a woven copper mesh as the template, the GWF grown from chemical vapour deposition retains the network configuration of the copper mesh. Embedded into polymer matrices, it has significant flexibility and strength gains compared with CVD grown graphene films. The GWFs display both good dimensional stability in both the warp and the weft directions and the combination of film transparency and conductivity could be optimized by tuning the ribbon packing density. The GWF creates a platform to integrate a large variety of applications, e.g., composites, strain sensors and solar cells, by taking advantages of the special structure and properties of graphene. PMID:22563524

  15. Waving potential in graphene.

    PubMed

    Yin, Jun; Zhang, Zhuhua; Li, Xuemei; Yu, Jin; Zhou, Jianxin; Chen, Yaqing; Guo, Wanlin

    2014-05-06

    Nanoscale materials offer much promise in the pursuit of high-efficient energy conversion technology owing to their exceptional sensitivity to external stimulus. In particular, experiments have demonstrated that flowing water over carbon nanotubes can generate electric voltages. However, the reported flow-induced voltages are in wide discrepancy and the proposed mechanisms remain conflictive. Here we find that moving a liquid-gas boundary along a piece of graphene can induce a waving potential of up to 0.1 V. The potential is proportional to the moving velocity and the graphene length inserted into ionic solutions, but sharply decreases with increasing graphene layers and vanishes in other materials. This waving potential arises from charge transfer in graphene driven by a moving boundary of an electric double layer between graphene and ionic solutions. The results reveal a unique electrokinetic phenomenon and open prospects for functional sensors, such as tsunami monitors.

  16. Vacancies in epitaxial graphene

    SciTech Connect

    Davydov, S. Yu.

    2015-08-15

    The coherent-potential method is used to consider the problem of the influence of a finite concentration of randomly arranged vacancies on the density of states of epitaxial graphene. To describe the density of states of the substrate, simple models (the Anderson model, Haldane-Anderson model, and parabolic model) are used. The electronic spectrum of free single-sheet graphene is considered in the low-energy approximation. Charge transfer in the graphene-substrate system is discussed. It is shown that, in all cases, the density of states of epitaxial graphene decreases proportionally to the vacancy concentration. At the same time, the average charge transferred from graphene to the substrate increases.

  17. Biocompatibility of Graphene Oxide

    NASA Astrophysics Data System (ADS)

    Wang, Kan; Ruan, Jing; Song, Hua; Zhang, Jiali; Wo, Yan; Guo, Shouwu; Cui, Daxiang

    2011-12-01

    Herein, we report the effects of graphene oxides on human fibroblast cells and mice with the aim of investigating graphene oxides' biocompatibility. The graphene oxides were prepared by the modified Hummers method and characterized by high-resolution transmission electron microscope and atomic force microscopy. The human fibroblast cells were cultured with different doses of graphene oxides for day 1 to day 5. Thirty mice divided into three test groups (low, middle, high dose) and one control group were injected with 0.1, 0.25, and 0.4 mg graphene oxides, respectively, and were raised for 1 day, 7 days, and 30 days, respectively. Results showed that the water-soluble graphene oxides were successfully prepared; graphene oxides with dose less than 20 μg/mL did not exhibit toxicity to human fibroblast cells, and the dose of more than 50 μg/mL exhibits obvious cytotoxicity such as decreasing cell adhesion, inducing cell apoptosis, entering into lysosomes, mitochondrion, endoplasm, and cell nucleus. Graphene oxides under low dose (0.1 mg) and middle dose (0.25 mg) did not exhibit obvious toxicity to mice and under high dose (0.4 mg) exhibited chronic toxicity, such as 4/9 mice death and lung granuloma formation, mainly located in lung, liver, spleen, and kidney, almost could not be cleaned by kidney. In conclusion, graphene oxides exhibit dose-dependent toxicity to cells and animals, such as inducing cell apoptosis and lung granuloma formation, and cannot be cleaned by kidney. When graphene oxides are explored for in vivo applications in animal or human body, its biocompatibility must be considered.

  18. Graphene and Graphene Oxide: Biofunctionalization and Applications in Biotechnology

    SciTech Connect

    Wang, Ying; Li, Zhaohui; Wang, Jun; Li, Jinghong; Lin, Yuehe

    2011-05-01

    Graphene is the basic building block of zero-dimensional fullerene, 1D carbon nanotubes, and 3D graphite. Graphene has a unique planar structure as well as novel electronic properties, which have attracted great interest from scientists. This review selectively analyzes current advances in the field of graphene bioapplications. In particular, the functionalization of graphene for biological applications, FRET-based biosensor development by using graphene-based nanomaterials, and the investigation of graphene for living cell studies have been summarized in more details. Future perspectives and possible challenges in this rapidly developing area are also discussed.

  19. New routes to graphene, graphene oxide and their related applications.

    PubMed

    Zhu, Yu; James, Dustin K; Tour, James M

    2012-09-18

    Recent research has focused upon the growth of the graphene, with a concentration on the synthesis of graphene and related materials using both solution processes and high temperature chemical vapor and solid growth methods. Protocols to prepare high aspect ratio graphene nanoribbons from multi-walled carbon nanotubes have been developed as well as techniques to grow high quality graphene for electronics and other applications where high quality is needed. Graphene materials have been manipulated and modified for use in applications such as transparent electrodes, field effect transistors, thin film transistors and energy storage devices. This review summarizes the development of graphene and related materials.

  20. 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.

  1. Tunneling Plasmonics in Bilayer Graphene

    NASA Astrophysics Data System (ADS)

    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.

    2015-08-01

    We report experimental signatures of plasmonic effects due to electron tunneling between adjacent graphene layers. At sub-nanometer 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 nano-imaging 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.

  2. Stabilization of graphene nanopore

    PubMed Central

    Lee, Jaekwang; Yang, Zhiqing; Zhou, Wu; Pennycook, Stephen J.; Pantelides, Sokrates T.; Chisholm, Matthew F.

    2014-01-01

    Graphene is an ultrathin, impervious membrane. The controlled introduction of nanoscale pores in graphene would lead to applications that involve water purification, chemical separation, and DNA sequencing. However, graphene nanopores are unstable against filling by carbon adatoms. Here, using aberration-corrected scanning transmission electron microscopy and density-functional calculations, we report that Si atoms stabilize graphene nanopores by bridging the dangling bonds around the perimeter of the hole. Si‐passivated pores remain intact even under intense electron beam irradiation, and they were observed several months after the sample fabrication, demonstrating that these structures are intrinsically robust and stable against carbon filling. Theoretical calculations reveal the underlying mechanism for this stabilization effect: Si atoms bond strongly to the graphene edge, and their preference for tetrahedral coordination forces C adatoms to form dendrites sticking out of the graphene plane, instead of filling the nanopore. Our results provide a novel way to develop stable nanopores, which is a major step toward reliable graphene-based molecular translocation devices. PMID:24821802

  3. Industrial graphene metrology.

    PubMed

    Kyle, Jennifer Reiber; Ozkan, Cengiz S; Ozkan, Mihrimah

    2012-07-07

    Graphene is an allotrope of carbon whose structure is based on one-atom-thick planar sheets of carbon atoms that are densely packed in a honeycomb crystal lattice. Its unique electrical and optical properties raised worldwide interest towards the design and fabrication of future electronic and optical devices with unmatched performance. At the moment, extensive efforts are underway to evaluate the reliability and performance of a number of such devices. With the recent advances in synthesizing large-area graphene sheets, engineers have begun investigating viable methodologies for conducting graphene metrology and quality control at industrial scales to understand a variety of reliability issues including defects, patternability, electrical, and physical properties. This review summarizes the current state of industrial graphene metrology and provides an overview of graphene metrology techniques. In addition, a recently developed large-area graphene metrology technique based on fluorescence quenching is introduced. For each metrology technique, the industrial metrics it measures are identified--layer thickness, edge structure, defects, Fermi level, and thermal conductivity--and a detailed description is provided as to how the measurements are performed. Additionally, the potential advantages of each technique for industrial use are identified, including throughput, scalability, sensitivity to substrate/environment, and on their demonstrated ability to achieve quantified results. The recently developed fluorescence-quenching metrology technique is shown to meet all the necessary criteria for industrial applications, rendering it the first industry-ready graphene metrology technique.

  4. How Water Meets Graphene

    NASA Astrophysics Data System (ADS)

    Zhou, Hua; Fenter, Paul; McDonough, Jake; Presser, Volker; Gogotsi, Yuri; Wander, Matthew; Shuford, Kevin

    2011-03-01

    The interactions of electrolyte fluids with solids control many complex interfacial processes encountered in electrochemical energy storage systems. In this talk, we will demonstrate how to develop a fundamental atomic-scale understanding of interfacial structures at the water-graphene interface, a model fluid-solid interface combination. We have performed systematic measurements of high resolution X-ray reflectivity from epitaxial graphene films in contact with electrolytes including deionized water and aqueous salt solutions. The electron density profiles and structural models from the fully analyzed data reveal the intrinsic interfacial structures. It is noted that the interfacial water structure above the first graphene layer exhibits remarkable differences with those of subsequent graphene layers. The latter one, resembling water on freestanding graphene, is well predicted by parallel computational simulations. Moreover, the pH of aqueous solutions was found to have a subtle influence on the interfacial water structure above the first graphene layer. This may well be an indication of the interfacial structural distortions that might exist in this layer, and which may play an important role in controlling the chemical activity of monolayer epitaxial graphene.

  5. Buckling resistant graphene nanocomposites

    NASA Astrophysics Data System (ADS)

    Rafiee, M. A.; Rafiee, J.; Yu, Z.-Z.; Koratkar, N.

    2009-11-01

    An experimental study on buckling of graphene/epoxy nanocomposite beam structures is presented. Significant increase (up to 52%) in critical buckling load is observed with addition of only 0.1% weight fraction of graphene platelets into the epoxy matrix. Based on the classical Euler-buckling model, the buckling load is predicted to increase by ˜32%. The over 50% increase in buckling load observed in our testing suggests a significant enhancement in load transfer effectiveness between the matrix and the graphene platelets under compressive load. Such nanocomposites with high buckling stability show potential as lightweight and buckling-resistant structural elements in aeronautical and space applications.

  6. The chemistry of graphene oxide.

    PubMed

    Dreyer, Daniel R; Park, Sungjin; Bielawski, Christopher W; Ruoff, Rodney S

    2010-01-01

    The chemistry of graphene oxide is discussed in this critical review. Particular emphasis is directed toward the synthesis of graphene oxide, as well as its structure. Graphene oxide as a substrate for a variety of chemical transformations, including its reduction to graphene-like materials, is also discussed. This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material (91 references).

  7. Graphene for Biomedical Implants

    NASA Astrophysics Data System (ADS)

    Moore, Thomas; Podila, Ramakrishna; Alexis, Frank; Rao, Apparao; Clemson Bioengineering Team; Clemson Physics Team

    2013-03-01

    In this study, we used graphene, a one-atom thick sheet of carbon atoms, to modify the surfaces of existing implant materials to enhance both bio- and hemo-compatibility. This novel effort meets all functional criteria for a biomedical implant coating as it is chemically inert, atomically smooth and highly durable, with the potential for greatly enhancing the effectiveness of such implants. Specifically, graphene coatings on nitinol, a widely used implant and stent material, showed that graphene coated nitinol (Gr-NiTi) supports excellent smooth muscle and endothelial cell growth leading to better cell proliferation. We further determined that the serum albumin adsorption on Gr-NiTi is greater than that of fibrinogen, an important and well understood criterion for promoting a lower thrombosis rate. These hemo-and biocompatible properties and associated charge transfer mechanisms, along with high strength, chemical inertness and durability give graphene an edge over most antithrombogenic coatings for biomedical implants and devices.

  8. Transformation optics using graphene.

    PubMed

    Vakil, Ashkan; Engheta, Nader

    2011-06-10

    Metamaterials and transformation optics play substantial roles in various branches of optical science and engineering by providing schemes to tailor electromagnetic fields into desired spatial patterns. We report a theoretical study showing that by designing and manipulating spatially inhomogeneous, nonuniform conductivity patterns across a flake of graphene, one can have this material as a one-atom-thick platform for infrared metamaterials and transformation optical devices. Varying the graphene chemical potential by using static electric field yields a way to tune the graphene conductivity in the terahertz and infrared frequencies. Such degree of freedom provides the prospect of having different "patches" with different conductivities on a single flake of graphene. Numerous photonic functions and metamaterial concepts can be expected to follow from such a platform.

  9. Graphene gas osmometers

    NASA Astrophysics Data System (ADS)

    Dolleman, Robin J.; Cartamil-Bueno, Santiago J.; van der Zant, Herre S. J.; Steeneken, Peter G.

    2017-03-01

    We show that graphene membranes that separate two gases at identical pressure are deflected by osmotic pressure. The osmotic pressure is a consequence of differences in gas permeation rates into a few-layer graphene enclosed cavity. The deflection of the membrane is detected by measuring the tension-induced resonance frequency with an interferometric technique. Using a calibration measurement of the relation between resonance frequency and pressure, the time dependent osmotic pressure on the graphene is extracted. The time dependent osmotic pressure for different combinations of gases shows large differences that can be accounted for by a model based on the different gas permeation rates. In this way, a graphene-membrane based gas osmometer with a responsivity of ˜60 kHz mbar-1 and nanoscale dimensions is demonstrated.

  10. Crumpled graphene nanoreactors

    NASA Astrophysics Data System (ADS)

    Wang, Zhongying; Lv, Xiaoshu; Chen, Yantao; Liu, Dan; Xu, Xinhua; Palmore, G. Tayhas R.; Hurt, Robert H.

    2015-05-01

    Nanoreactors are material structures that provide engineered internal cavities that create unique confined nanoscale environments for chemical reactions. Crumpled graphene nanoparticles or ``nanosacks'' may serve as nanoreactors when filled with reactive or catalytic particles and engineered for a specific chemical function. This article explores the behavior of crumpled graphene nanoreactors containing nanoscale ZnO, Ag, Ni, Cu, Fe, or TiO2 particles, either alone or in combination, in a series of case studies designed to reveal their fundamental behaviors. The first case study shows that ZnO nanoparticles undergo rapid dissolution inside the nanoreactor cavity accompanied by diffusive release of soluble products to surrounding aqueous media through the irregular folded shell. This behavior demonstrates the open nature of the sack structure, which facilitates rapid small-molecule exchange between inside and outside that is a requirement for nanoreactor function. In a case study on copper and silver nanoparticles, encapsulation in graphene nanoreactors is shown in some cases to enhance their oxidation rate in aqueous media, which is attributed to electron transfer from the metal core to graphene that bypasses surface oxides and allows reduction of molecular oxygen on the high-area graphene shell. Nanoreactors also allow particle-particle electron transfer interactions that are mediated by the connecting conductive graphene, which give rise to novel behaviors such as galvanic protection of Ag nanoparticles in Ag/Ni-filled nanoreactors, and the photochemical control of Ag-ion release in Ag/TiO2-filled nanoreactors. It is also shown that internal graphene structures within the sacks provide pockets that reduce particle mobility and inhibit particle sintering during thermal treatment. Finally, these novel behaviors are used to suggest and demonstrate several potential applications for graphene nanoreactors in catalysts, controlled release, and environmental remediation

  11. Cytotoxicity of halogenated graphenes

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Graphene and its family of derivatives possess unique and remarkable physicochemical properties which make them valuable materials for applications in many areas like electronics, energy storage and biomedicine. In response to the possibility of its large-scale manufacturing as commercial products in the future, an investigation was conducted to determine the cytotoxicity of one particular family of graphene derivatives, the halogenated graphenes, for the first time. Halogenated graphenes were prepared through thermal exfoliation of graphite oxide in gaseous chlorine, bromine or iodine atmospheres to yield chlorine- (TRGO-Cl), bromine- (TRGO-Br) and iodine-doped graphene (TRGO-I) respectively. 24 h exposure of human lung carcinoma epithelial cells (A549) to the three halogenated graphenes and subsequent cell viability assessments using methylthiazolyldiphenyl-tetrazolium bromide (MTT) and water-soluble tetrazolium salt (WST-8) assays revealed that all the halogenated graphenes examined are rather cytotoxic at the concentrations tested (3.125 μg mL-1 to 200 μg mL-1) and the effects are dose-dependent, with TRGO-Cl reducing the cell viability to as low as 25.7% at the maximum concentration of 200 μg mL-1. Their levels of cytotoxicity can be arranged in the order of TRGO-Cl > TRGO-Br > TRGO-I, and it is suggested that the amount of halogen present in the graphene material is the determining factor for the observed trend. Control experiments were carried out to test for possible nanomaterial-induced interference as a consequence of reaction between the halogenated graphenes and the viability markers (MTT/WST-8 reagent) or binding of the formazan products under cell-free conditions. The data obtained eliminate the probability of significant influence by these interferents as the change in the normalized percentage of formazan formed is relatively small and thorough washings were performed prior to the viability assessments to reduce the amount of halogenated

  12. Mechanical cleaning of graphene

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  13. Graphene for future electronics

    NASA Astrophysics Data System (ADS)

    Pasanen, Pirjo; Voutilainen, Martti; Helle, Meri; Song, Xuefeng; Hakonen, Pertti J.

    2012-01-01

    We discuss some aspects of how graphene could be used in mainstream electronic devices. The main focus is on signal processing applications in high-volume, industrially manufactured battery-powered devices, e.g. mobile phones and laptop computers, but we will also discuss applicability to other components like interconnects, wireless communication antennae and camera sensors, as well as novel types of signal processing devices, based on the unique physical properties of graphene.

  14. Graphene Electrostatic Microphone

    NASA Astrophysics Data System (ADS)

    Zhou, Qin; Onishi, Seita; Zettl, A.

    2015-03-01

    We demonstrate a wideband electrostatic graphene microphone displaying flat frequency response over the entire human audible region as well as into the ultrasonic regime. Using the microphone, low-level ultrasonic bat calls are successfully recorded. The microphone can be paired with a similarly constructed electrostatic graphene loudspeaker to create a wideband ultrasonic radio. Materials Sciences Division, Lawrence Berkeley National Laboratory Kavli Energy NanoSciences Institute at the University of California - Berkeley.

  15. Crumpled graphene nanoreactors.

    PubMed

    Wang, Zhongying; Lv, Xiaoshu; Chen, Yantao; Liu, Dan; Xu, Xinhua; Palmore, G Tayhas R; Hurt, Robert H

    2015-06-14

    Nanoreactors are material structures that provide engineered internal cavities that create unique confined nanoscale environments for chemical reactions. Crumpled graphene nanoparticles or "nanosacks" may serve as nanoreactors when filled with reactive or catalytic particles and engineered for a specific chemical function. This article explores the behavior of crumpled graphene nanoreactors containing nanoscale ZnO, Ag, Ni, Cu, Fe, or TiO2 particles, either alone or in combination, in a series of case studies designed to reveal their fundamental behaviors. The first case study shows that ZnO nanoparticles undergo rapid dissolution inside the nanoreactor cavity accompanied by diffusive release of soluble products to surrounding aqueous media through the irregular folded shell. This behavior demonstrates the open nature of the sack structure, which facilitates rapid small-molecule exchange between inside and outside that is a requirement for nanoreactor function. In a case study on copper and silver nanoparticles, encapsulation in graphene nanoreactors is shown in some cases to enhance their oxidation rate in aqueous media, which is attributed to electron transfer from the metal core to graphene that bypasses surface oxides and allows reduction of molecular oxygen on the high-area graphene shell. Nanoreactors also allow particle-particle electron transfer interactions that are mediated by the connecting conductive graphene, which give rise to novel behaviors such as galvanic protection of Ag nanoparticles in Ag/Ni-filled nanoreactors, and the photochemical control of Ag-ion release in Ag/TiO2-filled nanoreactors. It is also shown that internal graphene structures within the sacks provide pockets that reduce particle mobility and inhibit particle sintering during thermal treatment. Finally, these novel behaviors are used to suggest and demonstrate several potential applications for graphene nanoreactors in catalysts, controlled release, and environmental remediation.

  16. Thermodynamics of graphene

    NASA Astrophysics Data System (ADS)

    Rusanov, A. I.

    2014-12-01

    The 21st century has brought a lot of new results related to graphene. Apparently, graphene has been characterized from all points of view except surface science and, especially, surface thermodynamics. This report aims to close this gap. Since graphene is the first real two-dimensional solid, a general formulation of the thermodynamics of two-dimensional solid bodies is given. The two-dimensional chemical potential tensor coupled with stress tensor is introduced, and fundamental equations are derived for energy, free energy, grand thermodynamic potential (in the classical and hybrid forms), enthalpy, and Gibbs energy. The fundamentals of linear boundary phenomena are formulated with explaining the concept of a dividing line, the mechanical and thermodynamic line tensions, line energy and other linear properties with necessary thermodynamic equations. The one-dimensional analogs of the Gibbs adsorption equation and Shuttleworth-Herring relation are presented. The general thermodynamic relationships are illustrated with calculations based on molecular theory. To make the reader sensible of the harmony of chemical and van der Waals forces in graphene, the remake of the classical graphite theory is presented with additional variable combinations of graphene sheets. The calculation of the line energy of graphene is exhibited including contributions both from chemical bonds and van der Waals forces (expectedly, the latter are considerably smaller than the former). The problem of graphene holes originating from migrating vacancies is discussed on the basis of the Gibbs-Curie principle. An important aspect of line tension is the planar sheet/nanotube transition where line tension acts as a driving force. Using the bending stiffness of graphene, the possible radius range is estimated for achiral (zigzag and armchair) nanotubes.

  17. Electrostatic Graphene Loudspeaker

    DTIC Science & Technology

    2013-06-01

    protective SiO2 layer is deposited on the electrodes to pre- vent the graphene from accidentally shorting to the electro - des at very large drive...on damping requirements, see supplementary material7). To fabricate the EDGS structure the graphene is first attached to a suspension frame (Figure 2(a...In fact, the power efficiency of an electro - static speaker can be exceedingly high (close to 1) because the power dissipation path is almost pure

  18. Colloquium: Graphene spectroscopy

    NASA Astrophysics Data System (ADS)

    Basov, D. N.; Fogler, M. M.; Lanzara, A.; Wang, Feng; Zhang, Yuanbo

    2014-07-01

    Spectroscopic studies of electronic phenomena in graphene are reviewed. A variety of methods and techniques are surveyed, from quasiparticle spectroscopies (tunneling, photoemission) to methods probing density and current response (infrared optics, Raman) to scanning probe nanoscopy and ultrafast pump-probe experiments. Vast complimentary information derived from these investigations is shown to highlight unusual properties of Dirac quasiparticles and many-body interaction effects in the physics of graphene.

  19. Wettability of partially suspended graphene

    PubMed Central

    Ondarçuhu, Thierry; Thomas, Vincent; Nuñez, Marc; Dujardin, Erik; Rahman, Atikur; Black, Charles T.; Checco, Antonio

    2016-01-01

    The dependence of the wettability of graphene on the nature of the underlying substrate remains only partially understood. Here, we systematically investigate the role of liquid-substrate interactions on the wettability of graphene by varying the area fraction of suspended graphene from 0 to 95% by means of nanotextured substrates. We find that completely suspended graphene exhibits the highest water contact angle (85° ± 5°) compared to partially suspended or supported graphene, regardless of the hydrophobicity (hydrophilicity) of the substrate. Further, 80% of the long-range water-substrate interactions are screened by the graphene monolayer, the wettability of which is primarily determined by short-range graphene-liquid interactions. By its well-defined chemical and geometrical properties, supported graphene therefore provides a model system to elucidate the relative contribution of short and long range interactions to the macroscopic contact angle. PMID:27072195

  20. Quantum resistance metrology using graphene.

    PubMed

    Janssen, T J B M; Tzalenchuk, A; Lara-Avila, S; Kubatkin, S; Fal'ko, V I

    2013-10-01

    In this paper, we review the recent extraordinary progress in the development of a new quantum standard for resistance based on graphene. We discuss the unique properties of this material system relating to resistance metrology and discuss results of the recent highest-ever precision direct comparison of the Hall resistance between graphene and traditional GaAs. We mainly focus our review on graphene expitaxially grown on SiC, a system which so far resulted in the best results. We also briefly discuss progress in the two other graphene material systems, exfoliated graphene and chemical vapour deposition graphene, and make a critical comparison with SiC graphene. Finally, we discuss other possible applications of graphene in metrology.

  1. Wettability of partially suspended graphene

    DOE PAGES

    Ondarçuhu, Thierry; Thomas, Vincent; Nuñez, Marc; ...

    2016-04-13

    Dependence on the wettability of graphene on the nature of the underlying substrate remains only partially understood. We systematically investigate the role of liquid-substrate interactions on the wettability of graphene by varying the area fraction of suspended graphene from 0 to 95% by means of nanotextured substrates. We find that completely suspended graphene exhibits the highest water contact angle (85° ± 5°) compared to partially suspended or supported graphene, regardless of the hydrophobicity (hydrophilicity) of the substrate. Moreover, 80% of the long-range water-substrate interactions are screened by the graphene monolayer, the wettability of which is primarily determined by short-range graphene-liquidmore » interactions. By its well-defined chemical and geometrical properties, supported graphene therefore provides a model system to elucidate the relative contribution of short and long range interactions to the macroscopic contact angle.« less

  2. Wettability of partially suspended graphene

    SciTech Connect

    Ondarçuhu, Thierry; Thomas, Vincent; Nuñez, Marc; Dujardin, Erik; Rahman, Atikur; Black, Charles T.; Checco, Antonio

    2016-04-13

    Dependence on the wettability of graphene on the nature of the underlying substrate remains only partially understood. We systematically investigate the role of liquid-substrate interactions on the wettability of graphene by varying the area fraction of suspended graphene from 0 to 95% by means of nanotextured substrates. We find that completely suspended graphene exhibits the highest water contact angle (85° ± 5°) compared to partially suspended or supported graphene, regardless of the hydrophobicity (hydrophilicity) of the substrate. Moreover, 80% of the long-range water-substrate interactions are screened by the graphene monolayer, the wettability of which is primarily determined by short-range graphene-liquid interactions. By its well-defined chemical and geometrical properties, supported graphene therefore provides a model system to elucidate the relative contribution of short and long range interactions to the macroscopic contact angle.

  3. Graphene on hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  4. Vibrational stability of graphene

    NASA Astrophysics Data System (ADS)

    Hu, Yangfan; Wang, Biao

    2013-05-01

    The mechanical stability of graphene as temperature rises is analyzed based on three different self-consistent phonon (SCP) models. Compared with three-dimensional (3-D) materials, the critical temperature Ti at which instability occurs for graphene is much closer to its melting temperature Tm obtained from Monte Carlo simulation (Ti ≃ 2Tm, K. V. Zakharchenko, A. Fasolino, J. H. Los, and M. I. Katsnelson, J. Phys. Condens. Matter 23, 202202). This suggests that thermal vibration plays a significant role in melting of graphene while melting for 3-D materials is often dominated by topologic defects. This peculiar property of graphene derives from its high structural anisotropy, which is characterized by the vibrational anisotropic coefficient (VAC), defined upon its Lindermann ratios in different directions. For any carbon based material with a graphene-like structure, the VAC value must be smaller than 5.4 to maintain its stability. It is also found that the high VAC value of graphene is responsible for its negative thermal expansion coefficient at low temperature range. We believe that the VAC can be regarded as a new criterion concerning the vibrational stability of any low-dimensional (low-D) materials.

  5. Wetting transparency of graphene.

    PubMed

    Rafiee, Javad; Mi, Xi; Gullapalli, Hemtej; Thomas, Abhay V; Yavari, Fazel; Shi, Yunfeng; Ajayan, Pulickel M; Koratkar, Nikhil A

    2012-01-22

    We report that graphene coatings do not significantly disrupt the intrinsic wetting behaviour of surfaces for which surface-water interactions are dominated by van der Waals forces. Our contact angle measurements indicate that a graphene monolayer is wetting-transparent to copper, gold or silicon, but not glass, for which the wettability is dominated by short-range chemical bonding. With increasing number of graphene layers, the contact angle of water on copper gradually transitions towards the bulk graphite value, which is reached for ~6 graphene layers. Molecular dynamics simulations and theoretical predictions confirm our measurements and indicate that graphene's wetting transparency is related to its extreme thinness. We also show a 30-40% increase in condensation heat transfer on copper, as a result of the ability of the graphene coating to suppress copper oxidation without disrupting the intrinsic wettability of the surface. Such an ability to independently tune the properties of surfaces without disrupting their wetting response could have important implications in the design of conducting, conformal and impermeable surface coatings.

  6. Synthesis of water soluble graphene.

    PubMed

    Si, Yongchao; Samulski, Edward T

    2008-06-01

    A facile and scalable preparation of aqueous solutions of isolated, sparingly sulfonated graphene is reported. (13)C NMR and FTIR spectra indicate that the bulk of the oxygen-containing functional groups was removed from graphene oxide. The electrical conductivity of thin evaporated films of graphene (1250 S/m) relative to similarly prepared graphite (6120 S/m) implies that an extended conjugated sp (2) network is restored in the water soluble graphene.

  7. Optimization of ultra-soft CoZrTa/SiO2/CoZrTa trilayer elements for integrated inductor structures

    NASA Astrophysics Data System (ADS)

    Cheng, Cheng; Davies, Ryan; Sturcken, Noah; Shepard, Kenneth; Bailey, William E.

    2013-05-01

    We show the optimization of magnetic properties of ferromagnetic (FM)/SiO2/FM trilayer structures as potential candidates for the magnetic core in toroidal integrated inductors, with FM materials Co91.5Zr4.0Ta4.5 (CZT) and Ni80Fe20 (Py). In the single-layer parent films, we found a monotonic reduction of easy-axis coercivity (Hc down to 0.17 Oe in CZT, 0.4 Oe in Py) with increasing dc magnetron sputtering voltage. In the trilayer rectangular structures, with induced easy-axis in the short lateral dimension, we found proof of dipolar coupling between the two FM layers from BH loop measurements in the CZT system, showing linear response with minimal hysteresis loss when the external field is applied in the long axis. Py elements did not show this optimized property. Further investigation of domain configurations using scanning transmission x-ray microscopy suggests an insufficient induced anisotropy in Py compared with the shape anisotropy to realize the antiparallel-coupled state.

  8. Interfacial Characterization of Dissimilar Joints Between Al/Mg/Al-Trilayered Clad Sheet to High-Strength Low-Alloy Steel

    NASA Astrophysics Data System (ADS)

    Macwan, A.; Jiang, X. Q.; Chen, D. L.

    2015-07-01

    Magnesium (Mg) alloys are increasingly used in the automotive and aerospace sectors to reduce vehicle weight. Al/Mg/Al tri-layered clad sheets are deemed as a promising alternative to improve the corrosion resistance and formability of Mg alloys. The structural application of Al/Mg/Al tri-layered clad sheets inevitably involves welding and joining in the multi-material vehicle body manufacturing. This study aimed to characterize the bonding interface microstructure of the Al/Mg/Al-clad sheet to high-strength low-alloy steel with and without Zn coating using ultrasonic spot welding at different levels of welding energy. It was observed that the presence of Zn coating improved the bonding at the interface due to the formation of Al-Zn eutectic structure via enhanced diffusion. At a higher level of welding energy, characteristic flow patterns of Zn into Al-clad layer were observed with an extensive penetration mainly along some high angle grain boundaries. The dissimilar joints without Zn coating made at a high welding energy of 800 J failed partially from the Al/Fe weld interface and partially from the Al/Mg clad interface, while the joints with Zn coating failed from the Al/Mg clad interface due to the presence of brittle Al12Mg17 phase.

  9. Interlayer exchange coupling, dipolar coupling and magnetoresistance in Fe/MgO/Fe trilayers with a subnanometer MgO barrier

    NASA Astrophysics Data System (ADS)

    Kozioł-Rachwał, A.; Skowroński, W.; Frankowski, M.; Chęciński, J.; Ziętek, S.; Rzeszut, P.; Ślęzak, M.; Matlak, K.; Ślęzak, T.; Stobiecki, T.; Korecki, J.

    2017-02-01

    Fe/MgO/Fe trilayers with a subnanometer MgO tunnel barrier were grown by molecular beam epitaxy. Longitudinal magnetooptic Kerr effect measurements confirmed the existence of the antiferromagnetic interlayer exchange coupling (IEC) between the Fe layers for 2 Åtrilayer grown on a homoepitaxial MgO buffer layer, and its IEC constant was estimated to be -3.3 erg/cm2 at a MgO thickness of 2.7 Å. After magnetic characterization, the sample was patterned into circular-shaped pillars with diameters ranging from 200 nm to 520 nm. We showed that the dipolar coupling that appeared after the nanofabrication process modified the effective coupling between layers, and we determined dependence of the dipolar coupling on the pillar diameter. Finally, magnetoresistance (MR) was measured as a function of MgO thickness (dMgO), and a non-zero MR was found for the MgO as thin as 3.4 Å. Extrapolation of the MR (dMgO) dependence to MR=0 allowed us to determine the length of the pinholes in our sample, which was estimated to be (3.2±0.5) Å.

  10. Design, Fabrication, and Testing of a TiN Ti TiN Trilayer KID Array for 3mm CMB Observations

    NASA Technical Reports Server (NTRS)

    Lowitz, A. E.; Brown, A. D.; Mikula, V.; Stevenson, T. R.; Timbie, P. T.; Wollack, E. J.

    2016-01-01

    Kinetic inductance detectors (KIDs) are a promising technology for astronomical observations over a wide range of wavelengths in the mm and sub-mm regime. Simple fabrication, in as little as one lithographic layer, and passive frequency-domain multiplexing, with readout of up to 1000 pixels on a single line with a single cold amplifier, make KIDs an attractive solution for high-pixel-count detector arrays. We are developing an array that optimizes KIDs for optical frequencies near 100GHz to expand their usefulness in mm-wave applications, with a particular focus on CMBB-mode measurement efforts in association with the QUBIC telescope. We have designed, fabricated, and tested a 20-pixel prototype array using a simple quasi lumped microstrip design and pulsed DC reactive magnetron-sputtered TiNTiTiN trilayer resonators, optimized for detecting 100GHz (3mm) signals. Here we present a discussion of design considerations for the array, as well as preliminary detector characterization measurements and results from a study of TiN trilayer properties.

  11. The Enhancement of spin Hall torque efficiency and Reduction of Gilbert damping in spin Hall metal/normal metal/ferromagnetic trilayers

    NASA Astrophysics Data System (ADS)

    Nguyen, Minh-Hai; Pai, Chi-Feng; Ralph, Daniel C.; Buhrman, Robert A.

    2015-03-01

    The spin Hall effect (SHE) in ferromagnet/heavy metal bilayer structures has been demonstrated to be a powerful means for producing pure spin currents and for exerting spin-orbit damping-like and field-like torques on the ferromagnetic layer. Large spin Hall (SH) angles have been reported for Pt, beta-Ta and beta-W films and have been utilized to achieve magnetic switching of in-plane and out-of-plane magnetized nanomagnets, spin torque auto-oscillators, and the control of high velocity domain wall motion. For many of the proposed applications of the SHE it is also important to achieve an effective Gilbert damping parameter that is as low as possible. In general the spin orbit torques and the effective damping are predicted to depend directly on the spin-mixing conductance of the SH metal/ferromagnet interface. This opens up the possibility of tuning these properties with the insertion of a very thin layer of another metal between the SH metal and the ferromagnet. Here we will report on experiments with such trilayer structures in which we have observed both a large enhancement of the spin Hall torque efficiency and a significant reduction in the effective Gilbert damping. Our results indicate that there is considerable opportunity to optimize the effectiveness and energy efficiency of the damping-like torque through engineering of such trilayer structures. Supported in part by NSF and Samsung Electronics Corporation.

  12. Promising applications of graphene and graphene-based nanostructures

    NASA Astrophysics Data System (ADS)

    Nguyen, Bich Ha; Hieu Nguyen, Van

    2016-06-01

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

  13. Probing graphene defects and estimating graphene quality with optical microscopy

    SciTech Connect

    Lai, Shen; Kyu Jang, Sung; Jae Song, Young; Lee, Sungjoo

    2014-01-27

    We report a simple and accurate method for detecting graphene defects that utilizes the mild, dry annealing of graphene/Cu films in air. In contrast to previously reported techniques, our simple approach with optical microscopy can determine the density and degree of dislocation of defects in a graphene film without inducing water-related damage or functionalization. Scanning electron microscopy, confocal Raman and atomic force microscopy, and X-ray photoelectron spectroscopy analysis were performed to demonstrate that our nondestructive approach to characterizing graphene defects with optimized thermal annealing provides rapid and comprehensive determinations of graphene quality.

  14. Fluorescent biosensors enabled by graphene and graphene oxide.

    PubMed

    Zhang, Huan; Zhang, Honglu; Aldalbahi, Ali; Zuo, Xiaolei; Fan, Chunhai; Mi, Xianqiang

    2017-03-15

    During the past few years, graphene and graphene oxide (GO) have attracted numerous attentions for the potential applications in various fields from energy technology, biosensing to biomedical diagnosis and therapy due to their various functionalization, high volume surface ratio, unique physical and electrical properties. Among which, graphene and graphene oxide based fluorescent biosensors enabled by their fluorescence-quenching properties have attracted great interests. The fluorescence of fluorophore or dye labeled on probes (such as molecular beacon, aptamer, DNAzymes and so on) was quenched after adsorbed on to the surface of graphene. While in the present of the targets, due to the strong interactions between probes and targets, the probes were detached from the surface of graphene, generating dramatic fluorescence, which could be used as signals for detection of the targets. This strategy was simple and economy, together with great programmable abilities of probes; we could realize detection of different kinds of species. In this review, we first briefly introduced the history of graphene and graphene oxide, and then summarized the fluorescent biosensors enabled by graphene and GO, with a detailed account of the design mechanism and comparison with other nanomaterials (e.g. carbon nanotubes and gold nanoparticles). Following that, different sensing platforms for detection of DNAs, ions, biomolecules and pathogens or cells as well as the cytotoxicity issue of graphene and GO based in vivo biosensing were further discussed. We hope that this review would do some help to researchers who are interested in graphene related biosening research work.

  15. Graphene Based Flexible Gas Sensors

    NASA Astrophysics Data System (ADS)

    Yi, Congwen

    Graphene is a novel carbon material with great promise for a range of applications due to its electronic and mechanical properties. Its two-dimensional nature translates to a high sensitivity to surface chemical interactions thereby making it an ideal platform for sensors. Graphene's electronic properties are not degraded due to mechanical flexing or strain (Kim, K. S., et al. nature 07719, 2009) offering another advantage for flexible sensors integrated into numerous systems including fabrics, etc. We have demonstrated a graphene NO2 sensor on a solid substrate (100nm SiO2/heavily doped silicon). Three different methods were used to synthesize graphene and the sensor fabrication process was optimized accordingly. Water is used as a controllable p-type dopant in graphene to study the relationship between doping and graphene's response to NO2 . Experimental results show that interface water between graphene and the supporting SiO2 substrate induces higher p-doping in graphene, leading to a higher sensitivity to NO2, consistent with theoretical predications (Zhang, Y. et al., Nanotechnology 20(2009) 185504). We have also demonstrated a flexible and stretchable graphene-based sensor. Few layer graphene, grown on a Ni substrate, is etched and transferred to a highly stretchable polymer substrate (VHB from 3M) with preloaded stress, followed by metal contact formation to construct a flexible, stretchable sensor. With up to 500% deformation caused by compressive stress, graphene still shows stable electrical response to NO2. Our results suggest that higher compressive stress results in smaller sheet resistance and higher sensitivity to NO2. A possible molecular detection sensor utilizing Surface Enhanced Raman Spectrum (SERS) based on a graphene/gallium nanoparticles platform is also studied. By correlating the enhancement of the graphene Raman modes with metal coverage, we propose that the Ga transfers electrons to the graphene creating local regions of enhanced

  16. Graphene: Substrate preparation and introduction.

    PubMed

    Pantelic, Radosav S; Suk, Ji Won; Magnuson, Carl W; Meyer, Jannik C; Wachsmuth, Philipp; Kaiser, Ute; Ruoff, Rodney S; Stahlberg, Henning

    2011-04-01

    This technical note describes the transfer of continuous, single-layer, pristine graphene to standard Quantifoil TEM grids. We compare the transmission properties of pristine graphene substrates to those of graphene oxide and thin amorphous carbon substrates. Positively stained DNA imaged across amorphous carbon is typically indiscernible and requires metal shadowing for sufficient contrast. However, in a practical illustration of the new substrates properties, positively stained DNA is imaged across pristine graphene in striking contrast without the need of metal shadowing. We go onto discuss technical considerations and the potential applications of pristine graphene substrates as well as their ongoing development.

  17. Graphene-based structure, method of suspending graphene membrane, and method of depositing material onto graphene membrane

    DOEpatents

    Zettl, Alexander K.; Meyer, Jannik Christian

    2013-04-02

    An embodiment of a method of suspending a graphene membrane across a gap in a support structure includes attaching graphene to a substrate. A pre-fabricated support structure having the gap is attached to the graphene. The graphene and the pre-fabricated support structure are then separated from the substrate which leaves the graphene membrane suspended across the gap in the pre-fabricated support structure. An embodiment of a method of depositing material includes placing a support structure having a graphene membrane suspended across a gap under vacuum. A precursor is adsorbed to a surface of the graphene membrane. A portion of the graphene membrane is exposed to a focused electron beam which deposits a material from the precursor onto the graphene membrane. An embodiment of a graphene-based structure includes a support structure having a gap, a graphene membrane suspended across the gap, and a material deposited in a pattern on the graphene membrane.

  18. Engineering epitaxial graphene with oxygen

    NASA Astrophysics Data System (ADS)

    Kimouche, Amina; Martin, Sylvain; Winkelmann, Clemens; Fruchart, Olivier; Courtois, Hervé; Coraux, Johann; Hybrid system at low dimension Team

    2013-03-01

    Almost free-standing graphene can be obtained on metals by decoupling graphene from its substrate, for instance by intercalation of atoms beneath graphene, as it was shown with oxygen atoms. We show that the interaction of oxygen with epitaxial graphene on iridium leads to the formation of an ultrathin crystalline oxide extending between graphene and the metallic substrate via the graphene wrinkles. Graphene studied in this work was prepared under ultra-high vacuum by CVD. The samples were studied by combining scanning probe microscopy (STM, AFM) and spatially resolved spectroscopy (Raman, STS). The ultrathin oxide forms a decoupling barrier layer between graphene and Ir, yielding truly free-standing graphene whose hybridization and charge transfers with the substrate have been quenched. Our work presents novel types of graphene-based nanostructures, and opens the route to the transfer-free preparation of graphene directly onto an insulating support contacted to the metallic substrate which could serve as a gate electrode. Work supported by the EU-NMP GRENADA project

  19. Integrating functional oxides with graphene

    NASA Astrophysics Data System (ADS)

    Hong, X.; Zou, K.; DaSilva, A. M.; Ahn, C. H.; Zhu, J.

    2012-08-01

    Graphene-oxide hybrid structures offer the opportunity to combine the versatile functionalities of oxides with the excellent electronic transport in graphene. Understanding and controlling how the dielectric environment affects the intrinsic properties of graphene is also critical to fundamental studies and technological development of graphene. Here we review our recent effort on understanding the transport properties of graphene interfaced with ferroelectric Pb(Zr,Ti)O3 (PZT) and high-κ HfO2. Graphene field effect devices prepared on high-quality single crystal PZT substrates exhibit up to tenfold increases in mobility compared to SiO2-gated devices. An unusual and robust resistance hysteresis is observed in these samples, which is attributed to the complex surface chemistry of the ferroelectric. Surface polar optical phonons of oxides in graphene transistors play an important role in the device performance. We review their effects on mobility and the high source-drain bias saturation current of graphene, which are crucial for developing graphene-based room temperature high-speed amplifiers. Oxides also introduce scattering sources that limit the low temperature electron mobility in graphene. We present a comprehensive study of the transport and quantum scattering times to differentiate various scattering scenarios and quantitatively evaluate the density and distribution of charged impurities and the effect of dielectric screening. Our results can facilitate the design of multifunctional nano-devices utilizing graphene-oxide hybrid structures.

  20. Graphene: corrosion-inhibiting coating.

    PubMed

    Prasai, Dhiraj; Tuberquia, Juan Carlos; Harl, Robert R; Jennings, G Kane; Rogers, Bridget R; Bolotin, Kirill I

    2012-02-28

    We report the use of atomically thin layers of graphene as a protective coating that inhibits corrosion of underlying metals. Here, we employ electrochemical methods to study the corrosion inhibition of copper and nickel by either growing graphene on these metals, or by mechanically transferring multilayer graphene onto them. Cyclic voltammetry measurements reveal that the graphene coating effectively suppresses metal oxidation and oxygen reduction. Electrochemical impedance spectroscopy measurements suggest that while graphene itself is not damaged, the metal under it is corroded at cracks in the graphene film. Finally, we use Tafel analysis to quantify the corrosion rates of samples with and without graphene coatings. These results indicate that copper films coated with graphene grown via chemical vapor deposition are corroded 7 times slower in an aerated Na(2)SO(4) solution as compared to the corrosion rate of bare copper. Tafel analysis reveals that nickel with a multilayer graphene film grown on it corrodes 20 times slower while nickel surfaces coated with four layers of mechanically transferred graphene corrode 4 times slower than bare nickel. These findings establish graphene as the thinnest known corrosion-protecting coating.

  1. Electron Interactions in Graphene

    NASA Astrophysics Data System (ADS)

    Kim, Philip

    2011-03-01

    Electrons confined in two dimensions (2D) can exhibit strongly correlated states. Recent experimental discovery of integer and fractional quantum Hall effect in graphene amplified interest in correlated 2D electronic systems, owning to presence of the unusual topological phase associated with zero effective mass of charge carriers. In this talk, we will discuss the role of the many-body effects due to the electron-electron interaction in graphene manifested in electron transport phenomena. In particular, we will discuss the nature unusual spontaneous symmetry breaking Landau levels graphene under the extreme quantum condition, the appearance of unique low density insulating states and fractional quantum Hall states. Employing extremely high quality samples obtained by suspending graphene and graphene on atomically flat defect free insulating substrate such as hexa-bron nitride, we now investigate various broken symmetry states under high magnetic field. The nature of these broken symmetry state can be explained generally considering underlying SU(4) symmetry in the single particle level of the Landau levels.

  2. Graphene mobility mapping

    NASA Astrophysics Data System (ADS)

    Buron, Jonas D.; Pizzocchero, Filippo; Jepsen, Peter U.; Petersen, Dirch H.; Caridad, José M.; Jessen, Bjarke S.; Booth, Timothy J.; Bøggild, Peter

    2015-07-01

    Carrier mobility and chemical doping level are essential figures of merit for graphene, and large-scale characterization of these properties and their uniformity is a prerequisite for commercialization of graphene for electronics and electrodes. However, existing mapping techniques cannot directly assess these vital parameters in a non-destructive way. By deconvoluting carrier mobility and density from non-contact terahertz spectroscopic measurements of conductance in graphene samples with terahertz-transparent backgates, we are able to present maps of the spatial variation of both quantities over large areas. The demonstrated non-contact approach provides a drastically more efficient alternative to measurements in contacted devices, with potential for aggressive scaling towards wafers/minute. The observed linear relation between conductance and carrier density in chemical vapour deposition graphene indicates dominance by charged scatterers. Unexpectedly, significant variations in mobility rather than doping are the cause of large conductance inhomogeneities, highlighting the importance of statistical approaches when assessing large-area graphene transport properties.

  3. Transition metal contacts to graphene

    SciTech Connect

    Politou, Maria De Gendt, Stefan; Heyns, Marc; Asselberghs, Inge; Radu, Iuliana; Conard, Thierry; Richard, Olivier; Martens, Koen; Huyghebaert, Cedric; Tokei, Zsolt; Lee, Chang Seung; Sayan, Safak

    2015-10-12

    Achieving low resistance contacts to graphene is a common concern for graphene device performance and hybrid graphene/metal interconnects. In this work, we have used the circular Transfer Length Method (cTLM) to electrically characterize Ag, Au, Ni, Ti, and Pd as contact metals to graphene. The consistency of the obtained results was verified with the characterization of up to 72 cTLM structures per metal. Within our study, the noble metals Au, Ag and Pd, which form a weaker bond with graphene, are shown to result in lower contact resistance (Rc) values compared to the more reactive Ni and Ti. X-ray Photo Electron Spectroscopy and Transmission Electron Microscopy characterization for the latter have shown the formation of Ti and Ni carbides. Graphene/Pd contacts show a distinct intermediate behavior. The weak carbide formation signature and the low Rc values measured agree with theoretical predictions of an intermediate state of weak chemisorption of Pd on graphene.

  4. Quasiparticle dynamics in graphene

    NASA Astrophysics Data System (ADS)

    Bostwick, Aaron; Ohta, Taisuke; Seyller, Thomas; Horn, Karsten; Rotenberg, Eli

    2007-01-01

    The effectively massless, relativistic behaviour of graphene's charge carriers-known as Dirac fermions-is a result of its unique electronic structure, characterized by conical valence and conduction bands that meet at a single point in momentum space (at the Dirac crossing energy). The study of many-body interactions amongst the charge carriers in graphene and related systems such as carbon nanotubes, fullerenes and graphite is of interest owing to their contribution to superconductivity and other exotic ground states in these systems. Here we show, using angle-resolved photoemission spectroscopy, that electron-plasmon coupling plays an unusually strong role in renormalizing the bands around the Dirac crossing energy-analogous to mass renormalization by electron-boson coupling in ordinary metals. Our results show that electron-electron, electron-plasmon and electron-phonon coupling must be considered on an equal footing in attempts to understand the dynamics of quasiparticles in graphene and related systems.

  5. Crumpling Damaged Graphene

    PubMed Central

    Giordanelli, I.; Mendoza, M.; Andrade Jr., J. S.; Gomes, M. A. F.; Herrmann, H. J.

    2016-01-01

    Through molecular mechanics we find that non-covalent interactions modify the fractality of crumpled damaged graphene. Pristine graphene membranes are damaged by adding random vacancies and carbon-hydrogen bonds. Crumpled membranes exhibit a fractal dimension of 2.71 ± 0.02 when all interactions between carbon atoms are considered, and 2.30 ± 0.05 when non-covalent interactions are suppressed. The transition between these two values, obtained by switching on/off the non-covalent interactions of equilibrium configurations, is shown to be reversible and independent on thermalisation. In order to explain this transition, we propose a theoretical model that is compatible with our numerical findings. Finally, we also compare damaged graphene membranes with other crumpled structures, as for instance polymerised membranes and paper sheets, that share similar scaling properties. PMID:27173442

  6. Acoustoelectric photoresponse in graphene

    SciTech Connect

    Poole, T.; Bandhu, L.; Nash, G. R.

    2015-03-30

    The acoustoelectric current in graphene has been investigated as a function of illumination, using blue (450 nm) and red (735 nm) light-emitting diodes (LEDs), and surface acoustic wave (SAW) intensity and frequency. The measured acoustoelectric current increases with illumination, more than the measured change in the conductivity of the graphene, whilst retaining a linear dependence on the SAW intensity. The latter is consistent with the interaction between the carriers and SAWs being described by a relatively simple classical relaxation model suggesting that the change in the acoustoelectric current is caused by the effect of the illumination on the electronic properties of the graphene. The increase in the acoustoelectric current is greatest under illumination with the blue LED, consistent with the creation of a hot electron distribution.

  7. Inorganic Graphene Analogs

    NASA Astrophysics Data System (ADS)

    Rao, C. N. R.; Maitra, Urmimala

    2015-07-01

    In the last four to five years, there has been a great resurgence of research on two-dimensional inorganic materials, partly because of the impetus received from graphene research. Unlike graphene, which is a gap-less material, most inorganic layered materials are semiconductors or insulators. Some of them, as exemplified by MoS2, exhibit unexpected properties, not unlike graphene, with possible applications. Thus, layered metal chalcogenides are being explored intensely, and MoS2 is emerging as a wonder material. In this article, we present the synthesis and properties of nanosheets composing single or few layers of these fascinating materials. Besides metal chalcogenides, boron nitride, borocarbonitrides (BxCyNz), metal oxides, and metal-organic frameworks are also discussed.

  8. Hyperelastic tension of graphene

    NASA Astrophysics Data System (ADS)

    Saavedra Flores, E. I.; Ajaj, R. M.; Adhikari, S.; Dayyani, I.; Friswell, M. I.; Castro-Triguero, Rafael

    2015-02-01

    In this paper, we investigate the hyperelastic tensile behaviour of single layer graphene sheets (SLGSs). A one-term incompressible Ogden-type hyperelastic model is chosen to describe the mechanical response of C-C bonds. By establishing equality between the Ogden strain-energy and the variation of the Tersoff-Brenner interatomic potential, three different geometries of SLGSs are studied under tensile loading. We compute the Young's modulus, the finite-deformation Poisson's ratio, ultimate strains, total reactions, and the variation of the potential energy per carbon atom for large strains. Numerical simulations are compared with results obtained by molecular mechanics and molecular dynamics simulations, finite elements, continuum mechanics theory, and experiments. Our predictions are validated, revealing the potential predictive capabilities of the present hyperelastic framework for the analysis of graphene in the context of infinitesimal and large deformations. The good agreement found between our calculations and the published data suggests that graphene may be described as a hyperelastic material.

  9. Graphene in turbine blades

    NASA Astrophysics Data System (ADS)

    Das, D. K.; Swain, P. K.; Sahoo, S.

    2016-07-01

    Graphene, the two-dimensional (2D) nanomaterial, draws interest of several researchers due to its many superior properties. It has extensive applications in numerous fields. A turbine is a hydraulic machine which extracts energy from a fluid and converts it into useful work. Recently, Gudukeya and Madanhire have tried to increase the efficiency of Pelton turbine. Beucher et al. have also tried the same by reducing friction between fluid and turbine blades. In this paper, we study the advantages of using graphene as a coating on Pelton turbine blades. It is found that the efficiency of turbines increases, running and maintenance cost is reduced with more power output. By the application of graphene in pipes, cavitation will be reduced, durability of pipes will increase, operation and maintenance cost of water power plants will be less.

  10. Schwinger mechanism and graphene

    SciTech Connect

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

    2008-11-01

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

  11. Helically Coiled Graphene Nanoribbons.

    PubMed

    Daigle, Maxime; Miao, Dandan; Lucotti, Andrea; Tommasini, Matteo; Morin, Jean-François

    2017-03-07

    Graphene is a zero-gap, semiconducting 2D material that exhibits outstanding charge-transport properties. One way to open a band gap and make graphene useful as a semiconducting material is to confine the electron delocalization in one dimension through the preparation of graphene nanoribbons (GNR). Although several methods have been reported so far, solution-phase, bottom-up synthesis is the most promising in terms of structural precision and large-scale production. Herein, we report the synthesis of a well-defined, helically coiled GNR from a polychlorinated poly(m-phenylene) through a regioselective photochemical cyclodehydrochlorination (CDHC) reaction. The structure of the helical GNR was confirmed by (1) H NMR, FT-IR, XPS, TEM, and Raman spectroscopy. This Riemann surface-like GNR has a band gap of 2.15 eV and is highly emissive in the visible region, both in solution and the solid state.

  12. Acoustoelectric photoresponse in graphene

    NASA Astrophysics Data System (ADS)

    Poole, T.; Bandhu, L.; Nash, G. R.

    2015-03-01

    The acoustoelectric current in graphene has been investigated as a function of illumination, using blue (450 nm) and red (735 nm) light-emitting diodes (LEDs), and surface acoustic wave (SAW) intensity and frequency. The measured acoustoelectric current increases with illumination, more than the measured change in the conductivity of the graphene, whilst retaining a linear dependence on the SAW intensity. The latter is consistent with the interaction between the carriers and SAWs being described by a relatively simple classical relaxation model suggesting that the change in the acoustoelectric current is caused by the effect of the illumination on the electronic properties of the graphene. The increase in the acoustoelectric current is greatest under illumination with the blue LED, consistent with the creation of a hot electron distribution.

  13. Hyperelastic tension of graphene

    SciTech Connect

    Saavedra Flores, E. I.; Ajaj, R. M.; Adhikari, S.; Dayyani, I.; Friswell, M. I.; Castro-Triguero, Rafael

    2015-02-09

    In this paper, we investigate the hyperelastic tensile behaviour of single layer graphene sheets (SLGSs). A one-term incompressible Ogden-type hyperelastic model is chosen to describe the mechanical response of C-C bonds. By establishing equality between the Ogden strain-energy and the variation of the Tersoff-Brenner interatomic potential, three different geometries of SLGSs are studied under tensile loading. We compute the Young's modulus, the finite-deformation Poisson's ratio, ultimate strains, total reactions, and the variation of the potential energy per carbon atom for large strains. Numerical simulations are compared with results obtained by molecular mechanics and molecular dynamics simulations, finite elements, continuum mechanics theory, and experiments. Our predictions are validated, revealing the potential predictive capabilities of the present hyperelastic framework for the analysis of graphene in the context of infinitesimal and large deformations. The good agreement found between our calculations and the published data suggests that graphene may be described as a hyperelastic material.

  14. Water tribology on graphene.

    PubMed

    N'guessan, Hartmann E; Leh, Aisha; Cox, Paris; Bahadur, Prashant; Tadmor, Rafael; Patra, Prabir; Vajtai, Robert; Ajayan, Pulickel M; Wasnik, Priyanka

    2012-01-01

    Classical experiments show that the force required to slide liquid drops on surfaces increases with the resting time of the drop, t(rest), and reaches a plateau typically after several minutes. Here we use the centrifugal adhesion balance to show that the lateral force required to slide a water drop on a graphene surface is practically invariant with t(rest). In addition, the drop's three-phase contact line adopts a peculiar micrometric serrated form. These observations agree well with current theories that relate the time effect to deformation and molecular re-orientation of the substrate surface. Such molecular re-orientation is non-existent on graphene, which is chemically homogenous. Hence, graphene appears to provide a unique tribological surface test bed for a variety of liquid drop-surface interactions.

  15. Graphene-graphene oxide floating gate transistor memory.

    PubMed

    Jang, Sukjae; Hwang, Euyheon; Lee, Jung Heon; Park, Ho Seok; Cho, Jeong Ho

    2015-01-21

    A novel transparent, flexible, graphene channel floating-gate transistor memory (FGTM) device is fabricated using a graphene oxide (GO) charge trapping layer on a plastic substrate. The GO layer, which bears ammonium groups (NH3+), is prepared at the interface between the crosslinked PVP (cPVP) tunneling dielectric and the Al2 O3 blocking dielectric layers. Important design rules are proposed for a high-performance graphene memory device: (i) precise doping of the graphene channel, and (ii) chemical functionalization of the GO charge trapping layer. How to control memory characteristics by graphene doping is systematically explained, and the optimal conditions for the best performance of the memory devices are found. Note that precise control over the doping of the graphene channel maximizes the conductance difference at a zero gate voltage, which reduces the device power consumption. The proposed optimization via graphene doping can be applied to any graphene channel transistor-type memory device. Additionally, the positively charged GO (GO-NH3+) interacts electrostatically with hydroxyl groups of both UV-treated Al2 O3 and PVP layers, which enhances the interfacial adhesion, and thus the mechanical stability of the device during bending. The resulting graphene-graphene oxide FGTMs exhibit excellent memory characteristics, including a large memory window (11.7 V), fast switching speed (1 μs), cyclic endurance (200 cycles), stable retention (10(5) s), and good mechanical stability (1000 cycles).

  16. 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.

  17. Confining crack propagation in defective graphene.

    PubMed

    López-Polín, Guillermo; Gómez-Herrero, Julio; Gómez-Navarro, Cristina

    2015-03-11

    Crack propagation in graphene is essential to understand mechanical failure in 2D materials. We report a systematic study of crack propagation in graphene as a function of defect content. Nanoindentations and subsequent images of graphene membranes with controlled induced defects show that while tears in pristine graphene span microns length, crack propagation is strongly reduced in the presence of defects. Accordingly, graphene oxide exhibits minor crack propagation. Our work suggests controlled defect creation as an approach to avoid catastrophic failure in graphene.

  18. Electrostatic graphene loudspeaker

    NASA Astrophysics Data System (ADS)

    Zhou, Qin; Zettl, A.

    2013-06-01

    Graphene has extremely low mass density and high mechanical strength, and key qualities for efficient wide-frequency-response electrostatic audio speaker design. Low mass ensures good high frequency response, while high strength allows for relatively large free-standing diaphragms necessary for effective low frequency response. Here, we report on construction and testing of a miniaturized graphene-based electrostatic audio transducer. The speaker/earphone is straightforward in design and operation and has excellent frequency response across the entire audio frequency range (20 Hz-20 kHz), with performance matching or surpassing commercially available audio earphones.

  19. Vertical spin transport in Al with Pd/Al/Ni80Fe20 trilayer films at room temperature by spin pumping

    PubMed Central

    Kitamura, Yuta; Shikoh, Eiji; Ando, Yuichiro; Shinjo, Teruya; Shiraishi, Masashi

    2013-01-01

    Spin pumping enables the vertical transport of pure spin current through Al in a Pd/Al/Ni80Fe20(Py) trilayer film, in which the Py acts as a spin battery. The spin current injected into the Al flows through the Al to reach the Pd, resulting in the generation of electromotive forces due to the inverse spin Hall effect in the Pd. The electromotive forces decreased with increasing thickness of the Al layer. A simple model based on the theory by Tserkovnyak et al., allows an estimation of the spin coherence of the vertical spin transport in the Al of 61 nm. This comparatively short coherence is attributed to a reduction in spin pumping efficiency because of the roughness of the Al/Py interface.

  20. High-Quality Crystal Growth and Characteristics of AlGaN-Based Solar-Blind Distributed Bragg Reflectors with a Tri-layer Period Structure.

    PubMed

    Chang, Jianjun; Chen, Dunjun; Yang, Lianhong; Liu, Yanli; Dong, Kexiu; Lu, Hai; Zhang, Rong; Zheng, Youdou

    2016-07-06

    To realize AlGaN-based solar-blind ultraviolet distributed Bragg reflectors (DBRs), a novel tri-layer AlGaN/AlInN/AlInGaN periodical structure that differs from the traditional periodically alternating layers of high- and low-refractive-index materials was proposed and grown on an Al0.5Ga0.5N template via metal-organic chemical vapour deposition. Because of the intentional design of the AlInGaN strain transition layer, a state-of-the-art DBR structure with atomic-level-flatness interfaces was achieved using an AlGaN template. The fabricated DBR exhibits a peak reflectivity of 86% at the centre wavelength of 274 nm and a stopband with a full-width at half-maximum of 16 nm.

  1. ZnO/(Hf,Zr)O2/ZnO-trilayered nanowire capacitor structure fabricated solely by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Fujisawa, Hironori; Kuwamoto, Kei; Nakashima, Seiji; Shimizu, Masaru

    2016-02-01

    HfO2-based thin films are one of the key dielectric and ferroelectric materials in Si-CMOS LSIs as well as in oxide electronic nanodevices. In this study, we demonstrated the fabrication of a ZnO/(Hf,Zr)O2/ZnO-trilayered nanowire (NW) capacitor structure solely by metalorganic chemical vapor deposition (MOCVD). 15-nm-thick dielectric (Hf,Zr)O2 and 40-nm-thick top ZnO electrode layers were uniformly grown by MOCVD on a ZnO NW template with average diameter, length, and aspect ratio of 110 nm, 10 µm, and ˜90, respectively. The diameter and aspect ratio of the resultant trilayerd NWs are 200-300 nm and above 30, respectively. The crystalline phase of HfO2 and stacked the structure are also discussed.

  2. High-Quality Crystal Growth and Characteristics of AlGaN-Based Solar-Blind Distributed Bragg Reflectors with a Tri-layer Period Structure

    NASA Astrophysics Data System (ADS)

    Chang, Jianjun; Chen, Dunjun; Yang, Lianhong; Liu, Yanli; Dong, Kexiu; Lu, Hai; Zhang, Rong; Zheng, Youdou

    2016-07-01

    To realize AlGaN-based solar-blind ultraviolet distributed Bragg reflectors (DBRs), a novel tri-layer AlGaN/AlInN/AlInGaN periodical structure that differs from the traditional periodically alternating layers of high- and low-refractive-index materials was proposed and grown on an Al0.5Ga0.5N template via metal-organic chemical vapour deposition. Because of the intentional design of the AlInGaN strain transition layer, a state-of-the-art DBR structure with atomic-level-flatness interfaces was achieved using an AlGaN template. The fabricated DBR exhibits a peak reflectivity of 86% at the centre wavelength of 274 nm and a stopband with a full-width at half-maximum of 16 nm.

  3. Spacer-thickness dependence of interlayer exchange coupling in GaMnAs/InGaAs/GaMnAs trilayers grown on ZnCdSe buffers

    NASA Astrophysics Data System (ADS)

    Tivakornsasithorn, Kritsanu; Yoo, Taehee; Lee, Hakjoon; Choi, Seonghoon; Lee, Sanghoon; Liu, Xinyu; Dobrowolska, M.; Furdyna, Jacek K.

    2017-03-01

    Interlayer exchange coupling (IEC) between GaMnAs layers in GaMnAs/InGaAs/GaMnAs tri-layers was studied by magnetization measurements. Minor hysteresis loops are observed to shift in a direction indicating the presence of ferromagnetic (FM) IEC in the structures. The strength of the FM IEC clearly exhibits an exponential decrease with respect to nonmagnetic InGaAs spacer thickness. The fitting of the spacer thickness dependence of the FM IEC to an exponential decay function provides a decay length of 3.3±0.3 nm, which is relatively large compared to metallic multilayers, indicating a long ranged IEC in systems based on GaMnAs.

  4. Tri-layered composite plasmonic structure with a nanohole array for multiband enhanced absorption at visible to NIR frequencies: plasmonic and metamaterial resonances

    NASA Astrophysics Data System (ADS)

    Behera, Gangadhar; Ramakrishna, S. Anantha

    2016-02-01

    A tri-layered composite structure of gold/ZnS/gold, with the top gold layer patterned into a periodic array of circular holes, was fabricated by laser interference lithography and lift-off processes. This plasmonic composite absorbing structure showed a series of enhanced absorption peaks across the visible to NIR frequencies with an peak absorption exceeding 95% at 0.52 μm wavelength. These absorption peaks were reproduced in electromagnetic simulations of the structures. The peaks are shown to arise from the various resonances of the system: the localized surface plasmon resonances of the holes, the surface plasmon polaritons on the various interfaces and the shape dependent electromagnetic resonances of the holes. The measured angular dispersion of the absorption peaks indicated the SPP origin of the resonances while the computer simulations of the electromagnetic fields could be used to understand the nature of the localized resonances.

  5. Large exchange bias enhancement in (Pt(or Pd)/Co)/IrMn/Co trilayers with ultrathin IrMn thanks to interfacial Cu dusting

    SciTech Connect

    Vinai, G.; Moritz, J.; Bandiera, S.; Prejbeanu, I. L.; Dieny, B.

    2014-04-21

    The magnitude of exchange bias (H{sub ex}) at room temperature can be significantly enhanced in IrMn/Co and (Pt(or Pd)/Co)/IrMn/Co structures thanks to the insertion of an ultrathin Cu dusting layer at the IrMn/Co interface. The combination of trilayer structure and interfacial Cu dusting leads to a three-fold increase in H{sub ex} as compared to the conventional IrMn/Co bilayer structure, with an increased blocking temperature (T{sub B}) and a concave curvature of the temperature dependence H{sub ex}(T), ideal for improved Thermally Assisted-Magnetic Random Access Memory storage layer. This exchange bias enhancement is ascribed to a reduction of the spin frustration at the IrMn/Co interface thanks to interfacial Cu addition.

  6. Vertical spin transport in Al with Pd/Al/Ni80Fe20 trilayer films at room temperature by spin pumping

    NASA Astrophysics Data System (ADS)

    Kitamura, Yuta; Shikoh, Eiji; Ando, Yuichiro; Shinjo, Teruya; Shiraishi, Masashi

    2013-04-01

    Spin pumping enables the vertical transport of pure spin current through Al in a Pd/Al/Ni80Fe20(Py) trilayer film, in which the Py acts as a spin battery. The spin current injected into the Al flows through the Al to reach the Pd, resulting in the generation of electromotive forces due to the inverse spin Hall effect in the Pd. The electromotive forces decreased with increasing thickness of the Al layer. A simple model based on the theory by Tserkovnyak et al., allows an estimation of the spin coherence of the vertical spin transport in the Al of 61 nm. This comparatively short coherence is attributed to a reduction in spin pumping efficiency because of the roughness of the Al/Py interface.

  7. High-Quality Crystal Growth and Characteristics of AlGaN-Based Solar-Blind Distributed Bragg Reflectors with a Tri-layer Period Structure

    PubMed Central

    Chang, Jianjun; Chen, Dunjun; Yang, Lianhong; Liu, Yanli; Dong, Kexiu; Lu, Hai; Zhang, Rong; Zheng, Youdou

    2016-01-01

    To realize AlGaN-based solar-blind ultraviolet distributed Bragg reflectors (DBRs), a novel tri-layer AlGaN/AlInN/AlInGaN periodical structure that differs from the traditional periodically alternating layers of high- and low-refractive-index materials was proposed and grown on an Al0.5Ga0.5N template via metal-organic chemical vapour deposition. Because of the intentional design of the AlInGaN strain transition layer, a state-of-the-art DBR structure with atomic-level-flatness interfaces was achieved using an AlGaN template. The fabricated DBR exhibits a peak reflectivity of 86% at the centre wavelength of 274 nm and a stopband with a full-width at half-maximum of 16 nm. PMID:27381651

  8. Growth of Fe3Si/Ge/Fe3Si trilayers on GaAs(001) using solid-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Gaucher, S.; Jenichen, B.; Kalt, J.; Jahn, U.; Trampert, A.; Herfort, J.

    2017-03-01

    Ferromagnetic Heusler alloys can be used in combination with semiconductors to create spintronic devices. The materials have cubic crystal structures, making it possible to grow lattice-matched heterojunctions by molecular beam epitaxy. However, the development of devices is limited by the difficulty of growing epitaxial semiconductors over metallic surfaces while preventing chemical reactions, a requirement to obtain abrupt interfaces and achieve efficient spin-injection by tunneling. We used a solid-phase epitaxy approach to grow crystalline thin film stacks on GaAs(001) substrates, while preventing interfacial reactions. The crystallized Ge layer forms superlattice regions, which are caused by the migration of Fe and Si atoms into the film. X-ray diffraction and transmission electron microscopy indicate that the trilayers are fully crystalline, lattice-matched, and have ideal interface quality over extended areas.

  9. Very large domain wall velocities in Pt/Co/GdOx and Pt/Co/Gd trilayers with Dzyaloshinskii-Moriya interaction

    NASA Astrophysics Data System (ADS)

    Pham, Thai Ha; Vogel, J.; Sampaio, J.; Vaňatka, M.; Rojas-Sánchez, J.-C.; Bonfim, M.; Chaves, D. S.; Choueikani, F.; Ohresser, P.; Otero, E.; Thiaville, A.; Pizzini, S.

    2016-03-01

    We carried out measurements of domain wall (DW) velocities driven by magnetic-field pulses in symmetric Pt/Co/Pt and asymmetric Pt/Co/AlOx, Pt/Co/GdOx and Pt/Co/Gd trilayers with ultrathin Co layers and perpendicular magnetic anisotropy. The maximum observed velocity is much larger in the asymmetric samples, where the interfacial Dzyaloshinskii-Moriya interaction (DMI) stabilises chiral Néel walls. In quantitative agreement with analytical models, in all samples the maximum observed DW speed scales as D/Ms , where D is the strength of the DMI and Ms the spontaneous magnetisation. In Pt/Co/Gd, where the anti-parallel coupling between the magnetic moments of Gd and Co leads to a decrease of the total magnetisation, very large DW speeds (up to 700 m/s) are obtained.

  10. Graphene: from functionalization to devices

    NASA Astrophysics Data System (ADS)

    Tejeda, Antonio; Soukiassian, Patrick G.

    2014-03-01

    The year 2014 marks the first decade of the rise of graphene. Graphene, a single atomic layer of carbon atoms in sp2 bonding configuration having a honeycomb structure, has now become a well-known and well-established material. Among some of its many outstanding fundamental properties, one can mention a very high carrier mobility, a very large spin diffusion length, unsurpassed mechanical properties as graphene is the strongest material ever measured and an exceptional thermal conductivity scaling more than one order of magnitude above that of copper. After the first years of the graphene rush, graphene growth is now well controlled using various methods like epitaxial growth on silicon carbide substrate, chemical vapour deposition (CVD) or plasma techniques on metal, insulator or semiconductor substrates. More applied research is now taking over the initial studies on graphene production. Indeed, graphene is a promising material for many advanced applications such as, but not limited to, electronic, spintronics, sensors, photonics, micro/nano-electromechanical (MEMS/NEMS) systems, super-capacitors or touch-screen technologies. In this context, this Special Issue of the Journal of Physics D: Applied Physics on graphene reviews some of the recent achievements, progress and prospects in this field. It includes a collection of seventeen invited articles covering the current status and future prospects of some selected topics of strong current interest. This Special Issue is organized in four sections. The first section is dedicated to graphene devices, and opens with an article by de Heer et al on an investigation of integrating graphene devices with silicon complementary metal-oxide-semiconductor (CMOS) technology. Then, a study by Svintsov et al proposes a lateral all-graphene tunnel field-effect transistor (FET) with a high on/off current switching ratio. Next, Tsukagoshi et al present how a band-gap opening occurs in a graphene bilayer by using a perpendicular

  11. Giant magnetoelectric coupling interaction in BaTiO{sub 3}/BiFeO{sub 3}/BaTiO{sub 3} trilayer multiferroic heterostructures

    SciTech Connect

    Kotnala, R. K. E-mail: rkkotnala@gmail.com; Gupta, Rekha; Chaudhary, Sujeet

    2015-08-24

    Multiferroic trilayer thin films of BaTiO{sub 3}/BiFeO{sub 3}/BaTiO{sub 3} were prepared by RF-magnetron sputtering technique at different thicknesses of BiFeO{sub 3} layer. A pure phase polycrystalline growth of thin films was confirmed from X-ray diffraction results. The film showed maximum remnant electric polarization (2P{sub r}) of 13.5 μC/cm{sup 2} and saturation magnetization (M{sub s}) of 61 emu/cc at room temperature. Thermally activated charge transport dominated via oxygen vacancies as calculated by their activation energy, which was consistent with current–voltage characteristics. Magnetic field induced large change in resistance and capacitance of grain, and grain boundary was modeled by combined impedance and modulus spectroscopy in the presence of varied magnetic fields. Presence of large intrinsic magnetoelectric coupling was established by a maximum 20% increase in grain capacitance (C{sub g}) with applied magnetic field (2 kG) on trilayer having 20 nm BiFeO{sub 3} layer. Substantially higher magnetoelectric coupling in thinner films has been observed due to bonding between Fe and Ti atoms at interface via oxygen atoms. Room temperature magnetoelectric coupling was confirmed by dynamic magnetoelectric coupling, and maximum longitudinal magnetoelectric coupling of 515 mV/cm-Oe was observed at 20 nm thickness of BiFeO{sub 3}. The observed magnetoelectric properties are potentially useful for novel room temperature magnetoelectric and spintronic device applications for obtaining higher voltage at lower applied magnetic field.

  12. Surface phononic graphene

    NASA Astrophysics Data System (ADS)

    Yu, Si-Yuan; Sun, Xiao-Chen; Ni, Xu; Wang, Qing; Yan, Xue-Jun; He, Cheng; Liu, Xiao-Ping; Feng, Liang; Lu, Ming-Hui; Chen, Yan-Feng

    2016-12-01

    Strategic manipulation of wave and particle transport in various media is the key driving force for modern information processing and communication. In a strongly scattering medium, waves and particles exhibit versatile transport characteristics such as localization, tunnelling with exponential decay, ballistic, and diffusion behaviours due to dynamical multiple scattering from strong scatters or impurities. Recent investigations of graphene have offered a unique approach, from a quantum point of view, to design the dispersion of electrons on demand, enabling relativistic massless Dirac quasiparticles, and thus inducing low-loss transport either ballistically or diffusively. Here, we report an experimental demonstration of an artificial phononic graphene tailored for surface phonons on a LiNbO3 integrated platform. The system exhibits Dirac quasiparticle-like transport, that is, pseudo-diffusion at the Dirac point, which gives rise to a thickness-independent temporal beating for transmitted pulses, an analogue of Zitterbewegung effects. The demonstrated fully integrated artificial phononic graphene platform here constitutes a step towards on-chip quantum simulators of graphene and unique monolithic electro-acoustic integrated circuits.

  13. Graphene nanophotonic sensors

    NASA Astrophysics Data System (ADS)

    Zhu, Alexander Y.; Cubukcu, Ertugrul

    2015-09-01

    Graphene is known to possess a host of remarkable properties such as a zero bandgap at its Dirac point, broadband saturable optical absorption, ballistic carrier transport at room temperature, as well as extremely high stiffness and thermal conductivity. This has in turn made it a material of interest for many applications, ranging from fundamental physics studies to electronic devices. From a photonics perspective, graphene’s ability to support surface plasmon-polaritons with extremely small mode volumes in the infrared spectral regime and beyond renders it an ideal platform for strongly enhanced light-matter interactions at deeply subwavelength size scales. Together with its large bandwidth of operation, as well as intrinsic chemical stability and affinity to organic molecules, graphene serves as a natural candidate for numerous optics-based sensing applications. This article reviews recent works that highlight the various advantages of graphene in an optical sensing context. Specifically, it focuses on how the passive functionalization of graphene can improve the performance of existing optical sensors, and how its use as an active signal transduction element could lead to various novel or hybrid devices that extend the functionalities of traditional sensors.

  14. The rise of graphene

    NASA Astrophysics Data System (ADS)

    Geim, A. K.; Novoselov, K. S.

    2007-03-01

    Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

  15. Crown ethers in graphene

    DOE PAGES

    Guo, Junjie; Lee, Jaekwang; Contescu, Cristian I.; ...

    2014-11-13

    Crown ethers, introduced by Pedersen1, are at their most basic level neutral rings constructed of oxygen atoms linked by two- or three-carbon chains. They have attracted special attention for their ability to selectively incorporate various atoms2 or molecules within the cavity formed by the ring3-6. This property has led to the use of crown ethers and their compounds in a wide range of chemical and biological applications7,8. However, crown ethers are typically highly flexible, frustrating efforts to rigidify them for many uses that demand higher binding affinity and selectivity9,10. In this Letter, we report atomic-resolution images of the same basicmore » structures of the original crown ethers embedded in graphene. This arrangement constrains the crown ethers to be rigid and planar and thus uniquely suited for the many applications that crown ethers are known for. First-principles calculations show that the close similarity of the structures seen in graphene with those of crown ether molecules also extends to their selectivity towards specific metal cations depending on the ring size. Atoms (or molecules) incorporated within the crown ethers in graphene offer a simple environment that can be easily and systematically probed and modeled. Thus, we expect that this discovery will introduce a new wave of investigations and applications of chemically functionalized graphene.« less

  16. Crown ethers in graphene

    SciTech Connect

    Guo, Junjie; Lee, Jaekwang; Contescu, Cristian I.; Gallego, Nidia C.; Pantelides, Sokrates T.; Pennycook, Stephen J.; Moyer, Bruce A.; Chisholm, Matthew F.

    2014-11-13

    Crown ethers, introduced by Pedersen1, are at their most basic level neutral rings constructed of oxygen atoms linked by two- or three-carbon chains. They have attracted special attention for their ability to selectively incorporate various atoms2 or molecules within the cavity formed by the ring3-6. This property has led to the use of crown ethers and their compounds in a wide range of chemical and biological applications7,8. However, crown ethers are typically highly flexible, frustrating efforts to rigidify them for many uses that demand higher binding affinity and selectivity9,10. In this Letter, we report atomic-resolution images of the same basic structures of the original crown ethers embedded in graphene. This arrangement constrains the crown ethers to be rigid and planar and thus uniquely suited for the many applications that crown ethers are known for. First-principles calculations show that the close similarity of the structures seen in graphene with those of crown ether molecules also extends to their selectivity towards specific metal cations depending on the ring size. Atoms (or molecules) incorporated within the crown ethers in graphene offer a simple environment that can be easily and systematically probed and modeled. Thus, we expect that this discovery will introduce a new wave of investigations and applications of chemically functionalized graphene.

  17. Surface phononic graphene.

    PubMed

    Yu, Si-Yuan; Sun, Xiao-Chen; Ni, Xu; Wang, Qing; Yan, Xue-Jun; He, Cheng; Liu, Xiao-Ping; Feng, Liang; Lu, Ming-Hui; Chen, Yan-Feng

    2016-12-01

    Strategic manipulation of wave and particle transport in various media is the key driving force for modern information processing and communication. In a strongly scattering medium, waves and particles exhibit versatile transport characteristics such as localization, tunnelling with exponential decay, ballistic, and diffusion behaviours due to dynamical multiple scattering from strong scatters or impurities. Recent investigations of graphene have offered a unique approach, from a quantum point of view, to design the dispersion of electrons on demand, enabling relativistic massless Dirac quasiparticles, and thus inducing low-loss transport either ballistically or diffusively. Here, we report an experimental demonstration of an artificial phononic graphene tailored for surface phonons on a LiNbO3 integrated platform. The system exhibits Dirac quasiparticle-like transport, that is, pseudo-diffusion at the Dirac point, which gives rise to a thickness-independent temporal beating for transmitted pulses, an analogue of Zitterbewegung effects. The demonstrated fully integrated artificial phononic graphene platform here constitutes a step towards on-chip quantum simulators of graphene and unique monolithic electro-acoustic integrated circuits.

  18. Quasiparticle properties in graphene

    NASA Astrophysics Data System (ADS)

    Hwang, Euyheon

    2012-02-01

    The quasiparticle properties in both single layer and bilayer graphene are presented. We study the electron self-energy as well as the quasiparticle spectral function in graphene, taking into account electron-electron interaction in the leading order dynamically screened Coulomb coupling and electron-impurity interaction associated with quenched disorder. Our calculation of the self-energy provides the basis for calculating all one-electron properties of graphene. We provide analytical and numerical results for quasiparticle renormalization in graphene. Comparison with existing angle-resolved photoemission spectroscopy measurements shows broad qualitative and semiquantitative agreement between theory and experiment, for both the momentum-distribution and energy-distribution curves in the measured spectra. We also present the inelastic quasiparticle scattering rate and the carrier mean free path for energetic hot electrons as a function of carrier energy, density, and temperature, including both electron-electron and electron-phonon interactions. Our results are directly applicable to device structures where ballistic transport is relevant with inelastic scattering dominating over elastic scattering.[4pt] S. Das Sarma, S. Adam, E. H. Hwang, and E. Rossi, Rev. Mod. Phys. 83, 407 (2011). [0pt] E. H. Hwang, Ben Yu-Kuang Hu, and S. Das Sarma Phys. Rev. B 76, 115434 (2007). [0pt] E. H. Hwang and S. Das Sarma Phys. Rev. B 77, 081412 (2008). [0pt] Rajdeep Sensarma, E. H. Hwang, and S. Das Sarma, Phys. Rev. B 84, 041408(R) (2011).

  19. Graphene and graphene-based materials for energy storage applications.

    PubMed

    Zhu, Jixin; Yang, Dan; Yin, Zongyou; Yan, Qingyu; Zhang, Hua

    2014-09-10

    With the increased demand in energy resources, great efforts have been devoted to developing advanced energy storage and conversion systems. Graphene and graphene-based materials have attracted great attention owing to their unique properties of high mechanical flexibility, large surface area, chemical stability, superior electric and thermal conductivities that render them great choices as alternative electrode materials for electrochemical energy storage systems. This Review summarizes the recent progress in graphene and graphene-based materials for four energy storage systems, i.e., lithium-ion batteries, supercapacitors, lithium-sulfur batteries and lithium-air batteries.

  20. Programmable hydrogenation of graphene for novel nanocages

    NASA Astrophysics Data System (ADS)

    Zhang, Liuyang; Zeng, Xiaowei; Wang, Xianqiao

    2013-11-01

    Folded graphene has exhibited novel electrical and mechanical properties unmatched by pristine graphene, which implies that morphology of graphene adds the dimensionality of design space to tailor its properties. However, how to overcome the energy barrier of the folding process to fold the graphene with the specific morphology remains unexplored. Here we propose a programmable chemical functionalization by doping a pristine graphene sheet in a certain pattern with hydrogen atoms to precisely control its folding morphology. Molecular dynamics simulation has been performed to create a cross-shaped cubic graphene nanocage encapsulating a biomolecule by warping the top graphene layer downward and the bottom graphene layer upward to mimic the drug delivery vehicle. Such a paradigm, programmable enabled graphene nanocage, opens up a new avenue to control the 3D architecture of folded graphene and therefore provides a feasible way to exploit and fabricate the graphene-based unconventional nanomaterials and nanodevices for drug delivery.

  1. Tunable superconductivity in decorated graphene

    NASA Astrophysics Data System (ADS)

    Han, Zheng; Allain, Adrien; Marty, Laetitia; Bendiab, Nedjma; Toulemonde, Pierre; Strobel, Pierre; Coraux, Johann; Bouchiat, Vincent

    2013-03-01

    Graphene offers an exposed bidimensional gas of high mobility charge carriers with gate tunable density. Its chemical inertness offers an outstanding platform to explore exotic 2D superconductivity. Superconductivity can be induced in graphene by means of proximity effect (by depositing a set of superconducting metal clusters such as lead or tin nanoparticles). The influence of decoration material, density or particles and disorder of graphene will be discussed. In the case of disordered graphene, Tin decoration leads to a gate-tunable superconducting-to-insulator quantum phase transition. Superconductivity in graphene is also expected to occur under strong charge doping (induced either by gating or under chemical decoration, in analogy with graphite intercalated compounds). I will also show preliminary results showing the influence of Calcium intercalation of few layer graphene and progress toward the demonstration of intrinsic superconductivity in such systems. Work supported by EU GRANT FP7-NMP GRENADA.

  2. Graphene nanodevices for DNA sequencing

    NASA Astrophysics Data System (ADS)

    Heerema, Stephanie J.; Dekker, Cees

    2016-02-01

    Fast, cheap, and reliable DNA sequencing could be one of the most disruptive innovations of this decade, as it will pave the way for personalized medicine. In pursuit of such technology, a variety of nanotechnology-based approaches have been explored and established, including sequencing with nanopores. Owing to its unique structure and properties, graphene provides interesting opportunities for the development of a new sequencing technology. In recent years, a wide range of creative ideas for graphene sequencers have been theoretically proposed and the first experimental demonstrations have begun to appear. Here, we review the different approaches to using graphene nanodevices for DNA sequencing, which involve DNA passing through graphene nanopores, nanogaps, and nanoribbons, and the physisorption of DNA on graphene nanostructures. We discuss the advantages and problems of each of these key techniques, and provide a perspective on the use of graphene in future DNA sequencing technology.

  3. Electromechanical oscillations in bilayer graphene.

    PubMed

    Benameur, Muhammed M; Gargiulo, Fernando; Manzeli, Sajedeh; Autès, Gabriel; Tosun, Mahmut; Yazyev, Oleg V; Kis, Andras

    2015-10-20

    Nanoelectromechanical systems constitute a class of devices lying at the interface between fundamental research and technological applications. Realizing nanoelectromechanical devices based on novel materials such as graphene allows studying their mechanical and electromechanical characteristics at the nanoscale and addressing fundamental questions such as electron-phonon interaction and bandgap engineering. In this work, we realize electromechanical devices using single and bilayer graphene and probe the interplay between their mechanical and electrical properties. We show that the deflection of monolayer graphene nanoribbons results in a linear increase in their electrical resistance. Surprisingly, we observe oscillations in the electromechanical response of bilayer graphene. The proposed theoretical model suggests that these oscillations arise from quantum mechanical interference in the transition region induced by sliding of individual graphene layers with respect to each other. Our work shows that bilayer graphene conceals unexpectedly rich and novel physics with promising potential in applications based on nanoelectromechanical systems.

  4. Electromechanical oscillations in bilayer graphene

    NASA Astrophysics Data System (ADS)

    Benameur, Muhammed M.; Gargiulo, Fernando; Manzeli, Sajedeh; Autès, Gabriel; Tosun, Mahmut; Yazyev, Oleg V.; Kis, Andras

    2015-10-01

    Nanoelectromechanical systems constitute a class of devices lying at the interface between fundamental research and technological applications. Realizing nanoelectromechanical devices based on novel materials such as graphene allows studying their mechanical and electromechanical characteristics at the nanoscale and addressing fundamental questions such as electron-phonon interaction and bandgap engineering. In this work, we realize electromechanical devices using single and bilayer graphene and probe the interplay between their mechanical and electrical properties. We show that the deflection of monolayer graphene nanoribbons results in a linear increase in their electrical resistance. Surprisingly, we observe oscillations in the electromechanical response of bilayer graphene. The proposed theoretical model suggests that these oscillations arise from quantum mechanical interference in the transition region induced by sliding of individual graphene layers with respect to each other. Our work shows that bilayer graphene conceals unexpectedly rich and novel physics with promising potential in applications based on nanoelectromechanical systems.

  5. Hydrogenated Graphene as a Homoepitaxial Tunnel Barrier for Spin and Charge Transport in Graphene.

    PubMed

    Friedman, Adam L; van 't Erve, Olaf M J; Robinson, Jeremy T; Whitener, Keith E; Jonker, Berend T

    2015-07-28

    We demonstrate that hydrogenated graphene performs as a homoepitaxial tunnel barrier on a graphene charge/spin channel. We examine the tunneling behavior through measuring the IV curves and zero bias resistance. We also fabricate hydrogenated graphene/graphene nonlocal spin valves and measure the spin lifetimes using the Hanle effect, with spintronic nonlocal spin valve operation demonstrated up to room temperature. We show that while hydrogenated graphene indeed allows for spin transport in graphene and has many advantages over oxide tunnel barriers, it does not perform as well as similar fluorinated graphene/graphene devices, possibly due to the presence of magnetic moments in the hydrogenated graphene that act as spin scatterers.

  6. Graphene-ionic liquid composites

    DOEpatents

    Aksay, Ilhan A.; Korkut, Sibel; Pope, Michael; Punckt, Christian

    2016-11-01

    Method of making a graphene-ionic liquid composite. The composite can be used to make elec-trodes for energy storage devices, such as batteries and supercapacitors. Dis-closed and claimed herein is method of making a graphene-ionic liquid com-posite, comprising combining a graphene source with at least one ionic liquid and heating the combination at a temperature of at least about 130 .degree. C.

  7. Model Development for Graphene Spintronics

    DTIC Science & Technology

    2015-09-21

    to be considered. It is important to clarify three concepts in graphene: the electrostatic (Galvani) potential, ES, the electrochemical potential... electrochemical potential in graphene is defined as the energy per electron at the Fermi level. Under bias, it may be above or below the Dirac point, and...density in graphene, CS is the capacitance of the SiO2 dielectric per unit area, VG is the electrochemical or electrostatic potential at the gate, and

  8. Graphene: Atomically thin protective coating

    NASA Astrophysics Data System (ADS)

    Prasai, Dhiraj; Bolotin, Kirill; Tuberquia, Juan; Harl, Robert; Jennings, Kane

    2011-03-01

    We explore the properties of graphene as a cathodic coating to protect copper substrates from oxidation and further corrosion. High-quality and large area graphene films are grown on copper substrates by chemical vapor deposition. Samples were thermally oxidized in an oxygen-rich environment. X-ray photoelectron spectroscopy (XPS) characterization of a Graphene/copper and bare copper samples reveals the absence of oxidized copper at the graphene/copper interface indicating that the graphene monolayer protects the underlying copper. We also determine the protective properties of graphene in aqueous media using electrochemical characterization techniques. First, we use Electrochemical Impedance Spectroscopy (EIS) to show that graphene coated substrates lower frequencies (1Hz) exhibit impedance values 2 orders of magnitude higher compared to bare Cu substrates. Cyclic voltammetry also shows that a monolayer of graphene significantly reduces the oxygen reduction, thus exhibiting little charge transfer at the solid-liquid interface. Finally, we use Tafel analysis to estimate that the corrosion rate exhibited by Graphene/Cu is ~ 7 times lower than that of bare Cu substrates.

  9. Graphene: Nanostructure engineering and applications

    NASA Astrophysics Data System (ADS)

    Zhang, Tingting; Wu, Shuang; Yang, Rong; Zhang, Guangyu

    2017-02-01

    Graphene has attracted extensive research interest in recent years because of its fascinating physical properties and its potential for various applications. The band structure or electronic properties of graphene are very sensitive to its geometry, size, and edge structures, especially when the size of graphene is below the quantum confinement limit. Graphene nanoribbons (GNRs) can be used as a model system to investigate such structure-sensitive parameters. In this review, we examine the fabrication of GNRs via both top-down and bottom-up approaches. The edge-related electronic and transport properties of GNRs are also discussed.

  10. Dry-cleaning of graphene

    SciTech Connect

    Algara-Siller, Gerardo; Lehtinen, Ossi; Kaiser, Ute; Turchanin, Andrey

    2014-04-14

    Studies of the structural and electronic properties of graphene in its pristine state are hindered by hydrocarbon contamination on the surfaces. Also, in many applications, contamination reduces the performance of graphene. Contamination is introduced during sample preparation and is adsorbed also directly from air. Here, we report on the development of a simple dry-cleaning method for producing large atomically clean areas in free-standing graphene. The cleanness of graphene is proven using aberration-corrected high-resolution transmission electron microscopy and electron spectroscopy.

  11. Collective superlubricity of graphene flakes

    NASA Astrophysics Data System (ADS)

    van Wijk, Merel M.; de Wijn, Astrid S.; Fasolino, Annalisa

    2016-04-01

    We investigate solid lubrication of graphene and graphene flakes using atomistic molecular-dynamics simulations. We find that graphene flakes yield lower friction than graphene as a result of a collective mechanism that emerges from the independent behaviour of the flakes. By freezing out different degrees of freedom of the flakes, we are able to attribute the low friction to non-simultaneous slipping of the individual flakes. We also compare the results of the atomistic simulations to those of a simplified two-dimensional model and find that the behaviour of the latter is strongly dependent on parameters, which emerge naturally from the atomistic simulations.

  12. Collective superlubricity of graphene flakes.

    PubMed

    van Wijk, Merel M; de Wijn, Astrid S; Fasolino, Annalisa

    2016-04-06

    We investigate solid lubrication of graphene and graphene flakes using atomistic molecular-dynamics simulations. We find that graphene flakes yield lower friction than graphene as a result of a collective mechanism that emerges from the independent behaviour of the flakes. By freezing out different degrees of freedom of the flakes, we are able to attribute the low friction to non-simultaneous slipping of the individual flakes. We also compare the results of the atomistic simulations to those of a simplified two-dimensional model and find that the behaviour of the latter is strongly dependent on parameters, which emerge naturally from the atomistic simulations.

  13. Volume Fraction of Graphene Platelets in Copper-Graphene Composites

    NASA Astrophysics Data System (ADS)

    Jagannadham, K.

    2013-01-01

    Copper-graphene composite films were deposited on copper foil using electrochemical deposition. Four electrolyte solutions that each consist of 250 mL of graphene oxide suspension in distilled water and increasing volume of 0.2 M solution of CuSO4 in steps of 250 mL were used to deposit the composite films with and without a magnetic stirrer. Graphene oxide in the films was reduced to graphene by hydrogen treatment for 6 hours at 673 K (400 °C). The samples were characterized by X-ray diffraction for identification of phases, scanning electron microscopy for distribution of graphene, energy dispersive spectrometry for evaluation of elemental composition, electrical resistivity and temperature coefficient of electrical resistance and thermal conductivity. Effective mean field analysis (EMA) was used to determine the volume fraction and electrical conductivity of graphene and interfacial thermal conductance between graphene and copper. The electrical resistivity was reduced from 2.031 to 1.966 μΩ cm and the thermal conductivity was improved from 3.8 to 5.0 W/cm K upon addition of graphene platelets to electrolytic copper. The use of stirrer during deposition of the films increased the average size and the thickness of the graphene platelets and as a result the improvement in electrical conductivity was lower compared to the values obtained without the stirrer. Using the EMA, the volume fraction of graphene platelets that was responsible for the improvement in the electrical conductivity was found to be lower than that for the improvement in the thermal conductivity. The results of the analysis are used to determine the volume fraction of the thinner and the thicker graphene platelets in the composite films.

  14. Photochemical Transformation of Graphene Oxide in Sunlight

    EPA Science Inventory

    Graphene oxide (GO) is a graphene derivative that is more easily manufactured in large scale and used to synthesize reduced graphene oxide (rGO) with properties analogous to graphene. In this study, we investigate the photochemical fate of GO under sunlight conditions. The resu...

  15. Graphene-porphyrin single-molecule transistors.

    PubMed

    Mol, Jan A; Lau, Chit Siong; Lewis, Wilfred J M; Sadeghi, Hatef; Roche, Cecile; Cnossen, Arjen; Warner, Jamie H; Lambert, Colin J; Anderson, Harry L; Briggs, G Andrew D

    2015-08-21

    We demonstrate a robust graphene-molecule-graphene transistor architecture. We observe remarkably reproducible single electron charging, which we attribute to insensitivity of the molecular junction to the atomic configuration of the graphene electrodes. The stability of the graphene electrodes allow for high-bias transport spectroscopy and the observation of multiple redox states at room-temperature.

  16. Graphene and Graphene-like Molecules: Prospects in Solar Cells.

    PubMed

    Loh, Kian Ping; Tong, Shi Wun; Wu, Jishan

    2016-02-03

    Graphene is constantly hyped as a game-changer for flexible transparent displays. However, to date, no solar cell fabricated on graphene electrodes has out-performed indium tin oxide in power conversion efficiency (PCE). This Perspective covers the enabling roles that graphene can play in solar cells because of its unique properties. Compared to transparent and conducting metal oxides, graphene may not have competitive advantages in terms of its electrical conductivity. The unique strength of graphene lies in its ability to perform various enabling roles in solar cell architectures, leading to overall improvement in PCE. Graphene can serve as an ultrathin and transparent diffusion barrier in solar cell contacts, as an intermediate layer in tandem solar cells, as an electron acceptor, etc. Inspired by the properties of graphene, chemists are also designing graphene-like molecules in which the topology of π-electron array, donor-acceptor structures, and conformation can be tuned to offer a new class of light-harvesting materials.

  17. Thermoelectric effects in graphene nanostructures

    NASA Astrophysics Data System (ADS)

    Dollfus, Philippe; Nguyen, Viet Hung; Saint-Martin, Jérôme

    2015-04-01

    The thermoelectric properties of graphene and graphene nanostructures have recently attracted significant attention from the physics and engineering communities. In fundamental physics, the analysis of Seebeck and Nernst effects is very useful in elucidating some details of the electronic band structure of graphene that cannot be probed by conductance measurements alone, due in particular to the ambipolar nature of this gapless material. For applications in thermoelectric energy conversion, graphene has two major disadvantages. It is gapless, which leads to a small Seebeck coefficient due to the opposite contributions of electrons and holes, and it is an excellent thermal conductor. The thermoelectric figure of merit ZT of a two-dimensional (2D) graphene sheet is thus very limited. However, many works have demonstrated recently that appropriate nanostructuring and bandgap engineering of graphene can concomitantly strongly reduce the lattice thermal conductance and enhance the Seebeck coefficient without dramatically degrading the electronic conductance. Hence, in various graphene nanostructures, ZT has been predicted to be high enough to make them attractive for energy conversion. In this article, we review the main results obtained experimentally and theoretically on the thermoelectric properties of graphene and its nanostructures, emphasizing the physical effects that govern these properties. Beyond pure graphene structures, we discuss also the thermoelectric properties of some hybrid graphene structures, as graphane, layered carbon allotropes such as graphynes and graphdiynes, and graphene/hexagonal boron nitride heterostructures which offer new opportunities. Finally, we briefly review the recent activities on other atomically thin 2D semiconductors with finite bandgap, i.e. dichalcogenides and phosphorene, which have attracted great attention for various kinds of applications, including thermoelectrics.

  18. Chemical Functionalization of Graphene Family Members

    NASA Astrophysics Data System (ADS)

    Vacchi, Isabella Anna; Ménard-Moyon, Cécilia; Bianco, Alberto

    2017-01-01

    Thanks to their outstanding physicochemical properties, graphene and its derivatives are interesting nanomaterials with a high potential in several fields. Graphene, graphene oxide, and reduced graphene oxide, however, differ partially in their characteristics due to their diverse surface composition. Those differences influence the chemical reactivity of these materials. In the following chapter the reactivity and main functionalization reactions performed on graphene, graphene oxide, and reduced graphene oxide are discussed. A part is also dedicated to the main analytical techniques used for characterization of these materials. Functionalization of graphene and its derivatives is highly important to modulate their characteristics and design graphene-based conjugates with novel properties. Functionalization can be covalent by forming strong and stable bonds with the graphene surface, or non-covalent via π-π, electrostatic, hydrophobic, and/or van der Waals interactions. Both types of functionalization are currently exploited.

  19. A New Member of the Graphene Family: Graphene Acid.

    PubMed

    Jankovský, Ondřej; Nováček, Michal; Luxa, Jan; Sedmidubský, David; Fila, Vlastimil; Pumera, Martin; Sofer, Zdeněk

    2016-11-21

    A new member of the family of graphene derivatives, namely, graphene acid with a composition close to C1 (COOH)1 , was prepared by oxidation of graphene oxide. The synthetic procedure is based on repeated oxidation of graphite with potassium permanganate in an acidic environment. The oxidation process was studied in detail after each step. The multiple oxidations led to oxidative removal of other oxygen functional groups formed in the first oxidation step. Detailed chemical analysis showed only a minor amount of other oxygen-containing functional groups such as hydroxyl and the dominant presence of carboxyl groups in a concentration of about 30 wt %. Further oxidation led to complete decomposition of graphene acid. The obtained material exhibits unique sorption capacity towards metal ions and carbon dioxide. The highly hydrophilic nature of graphene acid allowed the assembly of ultrathin free-standing membranes with high transparency.

  20. Reducing agent free synthesis of graphene from graphene oxide

    NASA Astrophysics Data System (ADS)

    Kumar, R. Naresh; Shaikshavali, P.; Srikanth, Vadali V. S. S.; Sankara Rao, K. Bhanu

    2013-06-01

    Graphene is synthesized by microwave irradiation (MWI) of graphene oxide (GO) and subsequent sonication. MWI of GO is carried in a household microwave oven without using any reducing agents. Sonication of microwave irradiated GO is carried out in distilled water using a probe type sonicator. This method does not evolve any unsafe by-product gases which is otherwise the case when reducing agents are used in the reduction of GO to graphene. Moreover, due to its intrinsic nature, the method is scalable and cost effective. The synthesized product has been characterized as graphene using micro Raman scattering, x-ray diffraction and electron diffraction. Diffraction results show that the synthesized graphene is highly oriented.

  1. Broadband graphene polarizer

    NASA Astrophysics Data System (ADS)

    Bao, Qiaoliang; Zhang, Han; Wang, Bing; Ni, Zhenhua; Lim, Candy Haley Yi Xuan; Wang, Yu; Tang, Ding Yuan; Loh, Kian Ping

    2011-07-01

    Conventional polarizers can be classified into three main modes of operation: sheet polarizer using anisotropic absorption media, prism polarizer by refraction and Brewster-angle polarizer by reflection. These polarizing components are not easily integrated with photonic circuits. The in-line fibre polarizer, which relies on polarization-selective coupling between the evanescent field and birefringent crystal or metal, is a promising alternative because of its compatibility with most fibre-optic systems. Here, we demonstrate the operation of a broadband fibre polarizer based on graphene, an ultrathin two-dimensional carbon material. The out-coupled light in the telecommunication band shows a strong s-polarization effect with an extinction ratio of 27 dB. Unlike polarizers made from thin metal film, a graphene polarizer can support transverse-electric-mode surface wave propagation due to its linear dispersion of Dirac electrons.

  2. Irradiated bilayer graphene

    NASA Astrophysics Data System (ADS)

    Abergel, D. S. L.; Chakraborty, Tapash

    2011-01-01

    We describe the gated bilayer graphene system when it is subjected to intense terahertz frequency electromagnetic radiation. We examine the electron band structure and density of states via exact diagonalization methods within Floquet theory. We find that dynamical states are induced which lead to modification of the band structure. We first examine the situation where there is no external magnetic field. In the unbiased case, dynamical gaps appear in the spectrum which manifest as dips in the density of states. For finite inter-layer bias (where a static gap is present in the band structure of unirradiated bilayer graphene), dynamical states may be induced in the static gap. These states can show a high degree of valley polarization. When the system is placed in a strong magnetic field, the radiation induces coupling between the Landau levels which allows dynamical levels to exist. For strong fields, this means the Landau levels are smeared to form a near-continuum of states.

  3. Graphene based gene transfection

    NASA Astrophysics Data System (ADS)

    Feng, Liangzhu; Zhang, Shuai; Liu, Zhuang

    2011-03-01

    Graphene as a star in materials research has been attracting tremendous attentions in the past few years in various fields including biomedicine. In this work, for the first time we successfully use graphene as a non-toxic nano-vehicle for efficient gene transfection. Graphene oxide (GO) is bound with cationic polymers, polyethyleneimine (PEI) with two different molecular weights at 1.2 kDa and 10 kDa, forming GO-PEI-1.2k and GO-PEG-10k complexes, respectively, both of which are stable in physiological solutions. Cellular toxicity tests reveal that our GO-PEI-10k complex exhibits significantly reduced toxicity to the treated cells compared to the bare PEI-10k polymer. The positively charged GO-PEI complexes are able to further bind with plasmid DNA (pDNA) for intracellular transfection of the enhanced green fluorescence protein (EGFP) gene in HeLa cells. While EGFP transfection with PEI-1.2k appears to be ineffective, high EGFP expression is observed using the corresponding GO-PEI-1.2k as the transfection agent. On the other hand, GO-PEI-10k shows similar EGFP transfection efficiency but lower toxicity compared with PEI-10k. Our results suggest graphene to be a novel gene delivery nano-vector with low cytotoxicity and high transfection efficiency, promising for future applications in non-viral based gene therapy.Graphene as a star in materials research has been attracting tremendous attentions in the past few years in various fields including biomedicine. In this work, for the first time we successfully use graphene as a non-toxic nano-vehicle for efficient gene transfection. Graphene oxide (GO) is bound with cationic polymers, polyethyleneimine (PEI) with two different molecular weights at 1.2 kDa and 10 kDa, forming GO-PEI-1.2k and GO-PEG-10k complexes, respectively, both of which are stable in physiological solutions. Cellular toxicity tests reveal that our GO-PEI-10k complex exhibits significantly reduced toxicity to the treated cells compared to the bare PEI

  4. Spin caloritronics in graphene

    SciTech Connect

    Ghosh, Angsula; Frota, H. O.

    2015-06-14

    Spin caloritronics, the combination of spintronics with thermoelectrics, exploiting both the intrinsic spin of the electron and its associated magnetic moment in addition to its fundamental electronic charge and temperature, is an emerging technology mainly in the development of low-power-consumption technology. In this work, we study the thermoelectric properties of a Rashba dot attached to two single layer/bilayer graphene sheets as leads. The temperature difference on the two graphene leads induces a spin current, which depends on the temperature and chemical potential. We demonstrate that the Rashba dot behaves as a spin filter for selected values of the chemical potential and is able to filter electrons by their spin orientation. The spin thermopower has also been studied where the effects of the chemical potential, temperature, and also the Rashba term have been observed.

  5. Brownian motion of graphene.

    PubMed

    Maragó, Onofrio M; Bonaccorso, Francesco; Saija, Rosalba; Privitera, Giulia; Gucciardi, Pietro G; Iatì, Maria Antonia; Calogero, Giuseppe; Jones, Philip H; Borghese, Ferdinando; Denti, Paolo; Nicolosi, Valeria; Ferrari, Andrea C

    2010-12-28

    Brownian motion is a manifestation of the fluctuation-dissipation theorem of statistical mechanics. It regulates systems in physics, biology, chemistry, and finance. We use graphene as prototype material to unravel the consequences of the fluctuation-dissipation theorem in two dimensions, by studying the Brownian motion of optically trapped graphene flakes. These orient orthogonal to the light polarization, due to the optical constants anisotropy. We explain the flake dynamics in the optical trap and measure force and torque constants from the correlation functions of the tracking signals, as well as comparing experiments with a full electromagnetic theory of optical trapping. The understanding of optical trapping of two-dimensional nanostructures gained through our Brownian motion analysis paves the way to light-controlled manipulation and all-optical sorting of biological membranes and anisotropic macromolecules.

  6. Nonlinear optomechanics with graphene

    NASA Astrophysics Data System (ADS)

    Shaffer, Airlia; Patil, Yogesh Sharad; Cheung, Hil F. H.; Wang, Ke; Vengalattore, Mukund

    2016-05-01

    To date, studies of cavity optomechanics have been limited to exploiting the linear interactions between the light and mechanics. However, investigations of quantum signal transduction, quantum enhanced metrology and manybody physics with optomechanics each require strong, nonlinear interactions. Graphene nanomembranes are an exciting prospect for realizing such studies due to their inherently nonlinear nature and low mass. We fabricate large graphene nanomembranes and study their mechanical and optical properties. By using dark ground imaging techniques, we correlate their eigenmode shapes with the measured dissipation. We study their hysteretic response present even at low driving amplitudes, and their nonlinear dissipation. Finally, we discuss ongoing efforts to use these resonators for studies of quantum optomechanics and force sensing. This work is supported by the DARPA QuASAR program through a Grant from the ARO.

  7. Semiconducting allotrope of graphene.

    PubMed

    Nisar, Jawad; Jiang, Xue; Pathak, Biswarup; Zhao, Jijun; Kang, Tae Won; Ahuja, Rajeev

    2012-09-28

    From first-principles calculations, we predict a planar stable graphene allotrope composed of a periodic array of tetragonal and octagonal (4, 8) carbon rings. The stability of this sheet is predicted from the room-temperature molecular dynamics study and the electronic structure is studied using state-of-the-art calculations such as the hybrid density functional and the GW approach. Moreover, the mechanical properties of (4, 8) carbon sheet are evaluated from the Young's modulus and intrinsic strength calculations. We find this is a stable planar semiconducting carbon sheet with a bandgap between 0.43 and 1.01 eV and whose mechanical properties are as good as graphene's.

  8. Doped graphene supercapacitors

    NASA Astrophysics Data System (ADS)

    Ashok Kumar, Nanjundan; Baek, Jong-Beom

    2015-12-01

    Heteroatom-doped graphitic frameworks have received great attention in energy research, since doping endows graphitic structures with a wide spectrum of properties, especially critical for electrochemical supercapacitors, which tend to complement or compete with the current lithium-ion battery technology/devices. This article reviews the latest developments in the chemical modification/doping strategies of graphene and highlights the versatility of such heteroatom-doped graphitic structures. Their role as supercapacitor electrodes is discussed in detail. This review is specifically focused on the concept of material synthesis, techniques for electrode fabrication and metrics of performance, predominantly covering the last four years. Challenges and insights into the future research and perspectives on the development of novel electrode architectures for electrochemical supercapacitors based on doped graphene are also discussed.

  9. Chiral Graphene Quantum Dots.

    PubMed

    Suzuki, Nozomu; Wang, Yichun; Elvati, Paolo; Qu, Zhi-Bei; Kim, Kyoungwon; Jiang, Shuang; Baumeister, Elizabeth; Lee, Jaewook; Yeom, Bongjun; Bahng, Joong Hwan; Lee, Jaebeom; Violi, Angela; Kotov, Nicholas A

    2016-02-23

    Chiral nanostructures from metals and semiconductors attract wide interest as components for polarization-enabled optoelectronic devices. Similarly to other fields of nanotechnology, graphene-based materials can greatly enrich physical and chemical phenomena associated with optical and electronic properties of chiral nanostructures and facilitate their applications in biology as well as other areas. Here, we report that covalent attachment of l/d-cysteine moieties to the edges of graphene quantum dots (GQDs) leads to their helical buckling due to chiral interactions at the "crowded" edges. Circular dichroism (CD) spectra of the GQDs revealed bands at ca. 210-220 and 250-265 nm that changed their signs for different chirality of the cysteine edge ligands. The high-energy chiroptical peaks at 210-220 nm correspond to the hybridized molecular orbitals involving the chiral center of amino acids and atoms of graphene edges. Diverse experimental and modeling data, including density functional theory calculations of CD spectra with probabilistic distribution of GQD isomers, indicate that the band at 250-265 nm originates from the three-dimensional twisting of the graphene sheet and can be attributed to the chiral excitonic transitions. The positive and negative low-energy CD bands correspond to the left and right helicity of GQDs, respectively. Exposure of liver HepG2 cells to L/D-GQDs reveals their general biocompatibility and a noticeable difference in the toxicity of the stereoisomers. Molecular dynamics simulations demonstrated that d-GQDs have a stronger tendency to accumulate within the cellular membrane than L-GQDs. Emergence of nanoscale chirality in GQDs decorated with biomolecules is expected to be a general stereochemical phenomenon for flexible sheets of nanomaterials.

  10. Graphene-based biosensors

    NASA Astrophysics Data System (ADS)

    Lebedev, A. A.; Davydov, V. Yu.; Novikov, S. N.; Litvin, D. P.; Makarov, Yu. N.; Klimovich, V. B.; Samoilovich, M. P.

    2016-07-01

    Results of developing and testing graphene-based sensors capable of detecting protein molecules are presented. The biosensor operation was checked using an immunochemical system comprising fluorescein dye and monoclonal antifluorescein antibodies. The sensor detects fluorescein concentration on a level of 1-10 ng/mL and bovine serum albumin-fluorescein conjugate on a level of 1-5 ng/mL. The proposed device has good prospects for use for early diagnostics of various diseases.

  11. Graphene Synthesis and Characterization

    DTIC Science & Technology

    2015-04-08

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

  12. All-carbon graphene bioelectronics.

    PubMed

    Nam, Sungwoo; Chun, Sunggyu; Choi, Jonghyun

    2013-01-01

    We report nano field-effect transistor (nanoFET) biosensors built from the monolithic integration of graphene and graphite. The monolithic integration enables nanoscopic field-effect detection of chemical and biological signals with mechanically flexible and robust interface with biological systems in several respects. Our nanoFET biosensors exhibit superior detection sensitivity, mechanical flexibility and nanoscopic detection resolution. First, we demonstrate that electrical detection can be achieved from nanoscale electric field modulation of the graphene channel while the signal integrity is not perturbed by mechanical deflection of graphene nanoFET sensors. Such capability is introduced by the advanced design of monolithic graphene-graphite without any need for metal-graphene heterointerfaces. Second, we explore the chemical detection capability of graphene nanoFET sensors, and show that our sensors are responsive to localized chemical environmental changes/perturbations. Our nanoFET sensors not only show clear response to nanoscopic charge perturbation but also demonstrate potential 3-D sensing capability due to the advanced monolithic graphene-graphite mechanical design. These unique capabilities of our monolithic graphene-graphite bioelectronics could be exploited in chemical and biological detection and conformal interface with biological systems in the future.

  13. Thermal conductivity of graphene laminate.

    PubMed

    Malekpour, H; Chang, K-H; Chen, J-C; Lu, C-Y; Nika, D L; Novoselov, K S; Balandin, A A

    2014-09-10

    We have investigated thermal conductivity of graphene laminate films deposited on polyethylene terephthalate substrates. Two types of graphene laminate were studied, as deposited and compressed, in order to determine the physical parameters affecting the heat conduction the most. The measurements were performed using the optothermal Raman technique and a set of suspended samples with the graphene laminate thickness from 9 to 44 μm. The thermal conductivity of graphene laminate was found to be in the range from 40 to 90 W/mK at room temperature. It was found unexpectedly that the average size and the alignment of graphene flakes are more important parameters defining the heat conduction than the mass density of the graphene laminate. The thermal conductivity scales up linearly with the average graphene flake size in both uncompressed and compressed laminates. The compressed laminates have higher thermal conductivity for the same average flake size owing to better flake alignment. Coating plastic materials with thin graphene laminate films that have up to 600× higher thermal conductivity than plastics may have important practical implications.

  14. Mechanical properties of graphene papers

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  15. Graphene in Photocatalysis: A Review.

    PubMed

    Li, Xin; Yu, Jiaguo; Wageh, S; Al-Ghamdi, Ahmed A; Xie, Jun

    2016-12-01

    In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets-supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis-related properties of graphene and its derivatives, and design rules and synthesis methods of graphene-based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi-junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H2 production, and CO2 reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene-based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.

  16. Superflexibility of graphene oxide

    PubMed Central

    Poulin, Philippe; Jalili, Rouhollah; Neri, Wilfrid; Nallet, Frédéric; Colin, Annie; Wallace, Gordon; Zakri, Cécile

    2016-01-01

    Graphene oxide (GO), the main precursor of graphene-based materials made by solution processing, is known to be very stiff. Indeed, it has a Young’s modulus comparable to steel, on the order of 300 GPa. Despite its very high stiffness, we show here that GO is superflexible. We quantitatively measure the GO bending rigidity by characterizing the flattening of thermal undulations in response to shear forces in solution. Characterizations are performed by the combination of synchrotron X-ray diffraction at small angles and in situ rheology (rheo-SAXS) experiments using the high X-ray flux of a synchrotron source. The bending modulus is found to be 1 kT, which is about two orders of magnitude lower than the bending rigidity of neat graphene. This superflexibility compares with the fluidity of self-assembled liquid bilayers. This behavior is discussed by considering the mechanisms at play in bending and stretching deformations of atomic monolayers. The superflexibility of GO is a unique feature to develop bendable electronics after reduction, films, coatings, and fibers. This unique combination of properties of GO allows for flexibility in processing and fabrication coupled with a robustness in the fabricated structure. PMID:27647890

  17. DNA adsorption on graphene

    NASA Astrophysics Data System (ADS)

    Alshehri, Mansoor H.; Cox, Barry J.; Hill, James M.

    2013-11-01

    Here we use classical applied mathematical modeling to determine surface binding energies between both single-strand and double-strand DNA molecules interacting with a graphene sheet. We adopt basic mechanical principles to exploit the 6-12 Lennard-Jones potential function and the continuum approximation, which assumes that intermolecular interactions can be approximated by average atomic line or surface densities. The minimum binding energy occurs when the single-strand DNA molecule is centred 20.2 Å from the surface of the graphene and the double-strand DNA molecule is centred 20.3 Å from the surface, noting that these close values apply for the case when the axis of the helix is perpendicular to the surface of graphene. For the case when the axis of the helix is parallel to the surface, the minimum binding energy occurs when the axis of the single-strand molecule is 8.3 Å from the surface, and the double-strand molecule has axis 13.3 Å from the surface. For arbitrary tilted axis, we determine the optimal angles Ω of the axis of the helix, which give the minimum values of the binding energies, and we observe that the optimal angles tend to occur in the intervals Ω ∈ ( π /4 ,π/2) and Ω ∈ ( π /7 ,π/5) for the single and double-strand DNA molecules, respectively.

  18. Graphene based GHz detectors

    NASA Astrophysics Data System (ADS)

    Boyd, Anthony K.; El Fatimy, Abdel; Barbara, Paola; Nath, Anindya; Campbell, Paul M.; Myers-Ward, Rachael; Daniels, Kevin; Gaskill, D. Kurt

    Graphene demonstrates great promise as a detector over a wide spectral range especially in the GHz range. This is because absorption is enhanced due to the Drude contribution. In the GHz range there are viable detection mechanisms for graphene devices. With this in mind, two types of GHz detectors are fabricated on epitaxial graphene using a lift off resist-based clean lithography process to produce low contact resistance. Both device types use asymmetry for detection, consistent with recent thoughts of the photothermoelectric effect (PTE) mechanism. The first is an antenna coupled device. It utilizes two dissimilar contact metals and the work function difference produces the asymmetry. The other device is a field effect transistor constructed with an asymmetric top gate that creates a PN junction and facilitates tuning the photovoltaic response. The response of both device types, tested from 100GHz to 170GHz, are reported. This work was sponsored by the U.S. Office of Naval Research (Award Number N000141310865).

  19. Electrical characterization of CVD graphene

    NASA Astrophysics Data System (ADS)

    Dávila, Yarely; Pinto, Nicholas; Luo, Zhengtang; Johnson, Alan, Jr.

    2012-02-01

    Graphene is a one atom thick carbon sheet that can be obtained via exfoliation of graphite or via chemical vapor deposition (CVD). By using a very simple shadow masking technique, gold contact pads were evaporated over the graphene thereby eliminating chemical etching that is required when using photolithography and often leads to sample contamination. CVD graphene was electrically characterized in a FET configuration under different experimental conditions that include UV exposure, gas sensing and temperature. Our measurements yielded a carrier mobility of up to 3000 cm^2/V-s for some devices. Exposure to UV dopes graphene in a controlled manner. The doping level could be maintained indefinitely in vacuum or could be completely reversed by slight heating in air without loss of device performance. The FET's were also tested at different temperatures with little change in the transconductance response. Exposure to ammonia gas n-doped graphene while exposure to NO2 p-doped it.

  20. Graphene electrochemistry: fabricating amperometric biosensors.

    PubMed

    Brownson, Dale A C; Banks, Craig E

    2011-05-21

    The electrochemical sensing of hydrogen peroxide is of substantial interest to the operation of oxidase-based amperometric biosensors. We explore the fabrication of a novel and highly sensitive electro-analytical biosensor using well characterised commercially available graphene and compare and contrast responses using Nafion -graphene and -graphite modified electrodes. Interestingly we observe that graphite exhibits a superior electrochemical response due to its enhanced percentage of edge plane sites when compared to graphene. However, when Nafion, routinely used in amperometric biosensors, is introduced onto graphene and graphite modified electrodes, re-orientation occurs in both cases which is beneficial in the former and detrimental in the latter; insights into this contrasting behaviour are consequently presented providing acuity into sensor design and development where graphene is utilised in biosensors.

  1. Molecular theory of graphene oxide.

    PubMed

    Sheka, Elena F; Popova, Nadezhda A

    2013-08-28

    Applied to graphene oxide, the molecular theory of graphene considers its oxide as a final product in the succession of polyderivatives related to a series of oxidation reactions involving different oxidants. The graphene oxide structure is created in the course of a stepwise computational synthesis of polyoxides of the (5,5) nanographene molecule governed by an algorithm that takes into account the molecule's natural radicalization due to the correlation of its odd electrons, the extremely strong influence of the structure on properties, and a sharp response of the molecule behavior on small actions of external factors. Taking these together, the theory has allowed for a clear, transparent and understandable explanation of the hot points of graphene oxide chemistry and suggesting reliable models of both chemically produced and chemically reduced graphene oxides.

  2. Bioapplications of graphene constructed functional nanomaterials.

    PubMed

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

    2017-01-25

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

  3. Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies.

    PubMed

    Campbell, Patrick G; Worsley, Marcus A; Hiszpanski, Anna M; Baumann, Theodore F; Biener, Juergen

    2015-11-05

    Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. Additionally, most reported graphene assemblies are held together through physical interactions (e.g., van der Waals forces) rather than chemical bonds, which limit their mechanical strength and conductivity. This video method details recently developed strategies to fabricate mass-producible, graphene-based bulk materials derived from either polymer foams or single layer graphene oxide. These materials consist primarily of individual graphene sheets connected through covalently bound carbon linkers. They maintain the favorable properties of graphene such as high surface area and high electrical and thermal conductivity, combined with tunable pore morphology and exceptional mechanical strength and elasticity. This flexible synthetic method can be extended to the fabrication of polymer/carbon nanotube (CNT) and polymer/graphene oxide (GO) composite materials. Furthermore, additional post-synthetic functionalization with anthraquinone is described, which enables a dramatic increase in charge storage performance in supercapacitor applications.

  4. Surface characterization of Zr/Ti/Nb tri-layered films deposited by magnetron sputtering on Si(111) and stainless steel substrates

    SciTech Connect

    Tallarico, Denise A.; Gobbi, Angelo L.; Filho, Pedro I. Paulin; Galtayries, Anouk; Nascente, Pedro A. P.

    2012-09-15

    Among metallic materials, commercially pure titanium and titanium alloys are very often used as biomaterials for implants. Among these alloys, titanium-aluminum-vanadium alloy Ti-6 A-4 V is one of the most commonly used due to its excellent biocompatibility and ability to allow bone-implant integration. A new class of Ti alloys employs Zr for solid-solution hardening and Nb as {beta}-phase stabilizer. Metals such as Ti, Nb, and Zr-known as valve metals-usually have their surfaces covered by a thin oxide film that forms spontaneously in air. This oxide film constitutes a barrier between the metal and the medium. The Ti-Nb-Zr alloys have mechanical and corrosion resistance characteristics which make them suitable for use as implants. Tri-layered films of Ti-Nb-Zr were deposited on both Si(111) and stainless steel (SS) substrates using dc magnetron sputtering equipment, under an argon atmosphere according to the following methodology: a 100 nm thick layer of Nb was deposited on the substrate, followed by a 200 nm thick layer of Ti, and finally a 50 nm thick layer of Zr, on top of the multilayer stack. The morphology and chemical composition of the films were analyzed by atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). AFM images showed that the Zr/Ti/Nb tri-layer films presented nanostructured grains and low roughness. The ToF-SIMS depth profiles confirmed the formation of a three-layered film on Si(111) with well-defined and sharp interfaces between the layers, while the deposition on the stainless steel substrate caused slight intermixing at the different alloy/Nb, Nb/Ti and Ti/Zr interfaces, reflecting the greater roughness of the raw substrate. The XPS results for the Zr/Ti/Nb layers deposited on Si(111) and SS confirmed that the outermost layer consisted of Zr only, with a predominance of ZrO{sub 2}, as the metal layer is passivated in air. An oxidation treatment of 1000 Degree

  5. Interplay of energy dissipation, ion-induced mixing, and crystal structure recovery, and surface effects in ion-irradiated magnetic Fe/Cr/Fe trilayers

    SciTech Connect

    Brodyanski, A.; Bock, W.; Kopnarski, M.; Reuscher, B.; Blomeier, S.; Hillebrands, B.; Gnaser, H.

    2011-12-01

    The influence of the ion irradiation by 30 keV Ga{sup +} ions on the crystal structure, chemical ordering, magnetic properties, and topography of epitaxial Fe/Cr/Fe trilayers was investigated by different analytical techniques. We present direct experimental evidence, supported by theoretical estimates, that two processes take place concurrently due to the Ga-ion implantation. (i) A complete atom mixing of the Cr atoms within the Fe multilayers is occurring due to the collision cascades during the ballistic regime, and (ii) an essentially complete recovery of the initial single-crystal quality of the Fe multilayers by healing the melted and damaged area through the thermal spike phase occurs. Based on the experimental range distributions and theoretical modeling, channeling of Ga{sup +} ions in the experiments is found to contribute weakly to ion penetration and stopping, and the relative fraction of the well-channeled ions is marginally small. On the other hand, this weak channeling is sufficient to reduce the sputter yield by a factor of more than 5 in comparison with the sputtering of polycrystalline samples, evidence for the fact that the magnitude of channeling is not of primary importance for the sputtering. We offer an explanation for the observation of dramatic and abrupt changes in the surface roughness with increasing fluences in terms of a transformation from a single-phase single-crystal implanted region (bcc-Fe) to a mixture of the polycrystalline {alpha}-Fe-like bcc and {alpha}-Fe{sub 3}Ga structures within the outer half of the original Fe/Cr/Fe trilayer at fluences above 6.25 x 10{sup 16} ion/cm{sup 2}. The wall-like elevations appearing at the boundary of the irradiated areas were analyzed experimentally by varying the irradiation conditions. We showed that the wall size is governed by the ion-current density applied. A physical explanation for the appearance of such topographic features is presented, which would be valid for any material

  6. Hydrophilic behavior of graphene and graphene-based materials

    NASA Astrophysics Data System (ADS)

    Accordino, Sebastián R.; Montes de Oca, Joan Manuel; Rodriguez Fris, J. Ariel; Appignanesi, Gustavo A.

    2015-10-01

    Graphene and the graphene-based materials like graphite, carbon nanotubes, and fullerenes are not only usually regarded as hydrophobic but also have been widely employed as paradigms for the investigation of the behavior of water under nonpolar confinement, a question of major concern for fields ranging from biology to materials design. However, some experimental and theoretical insights seem to contradict, at least partially, such a picture. In this work, we will provide firm evidence for a neat hydrophilic nature of graphene surfaces. Our molecular dynamics studies will demonstrate that parallel graphene sheets present a strong tendency to remain fully hydrated for moderately long times (even when the equilibrium state is indeed the collapse of the plates), and thus, they are less prone to self-assembly than model hydrophobic surfaces we shall employ as control which readily undergo a hydrophobic collapse. Potential of mean force calculations will indeed make evident that the solvent exerts a repulsive contribution on the self-assembly of graphene surfaces. Moreover, we shall also quantify graphene hydrophilicity by means of the calculation of water density at two pressures and water density fluctuations. This latter study has never been performed on graphene and represents a means both to confirm and to quantify its neat hydrophilic behavior. We shall also make evident the relevance of the mildly attractive water-carbon interactions, since their artificial weakening will be shown to revert from typically hydrophilic to typically hydrophobic behavior.

  7. New Approaches for Understanding of Hydrogen Interaction with Graphene, Graphene Hydroxide, and Lithiated Graphene

    NASA Astrophysics Data System (ADS)

    Adak, Sourav; Daemen, Luke; Hartl, Monika; Smith, Alice; Paradiso, Daniele; Strange, Nicholas; Thomas, George; Larese, J. Z.; Los Alamos National Laboratory Collaboration; University of Tennessee Team

    2014-03-01

    A combination of solid state NMR, neutron vibrational spectroscopy, and volumetric adsorption isotherms have been employed to characterize graphene, hydroxylated graphene, and lithium incorporated graphene and the interaction of molecular hydrogen with them. Recent synthetic activities have produced materials with unique properties and when coupled with our ssNMR measurements the results shed some new light on the surface chemical composition of these materials and the role they play in the hydrogen storage capacity. Graphene is found to have significantly higher hydrogen uptake than graphite and randomly oxidized graphite sheets (graphite oxide). Inelastic neutron scattering (INS) provides direct information concerning hydrogen dynamics. We have used INS to examine how the interaction of hydrogen changes when the graphene surface chemistry changes or when lithium is incorporated at the interface.

  8. Enhancement of the Stability of Fluorine Atoms on Defective Graphene and at Graphene/Fluorographene Interface.

    PubMed

    Ao, Zhimin; Jiang, Quanguo; Li, Shuang; Liu, Hao; Peeters, Francois M; Li, Sean; Wang, Guoxiu

    2015-09-09

    Fluorinated graphene is one of the most important derivatives of graphene and has been found to have great potential in optoelectronic and photonic nanodevices. However, the stability of F atoms on fluorinated graphene under different conditions, which is essential to maintain the desired properties of fluorinated graphene, is still unclear. In this work, we investigate the diffusion of F atoms on pristine graphene, graphene with defects, and at graphene/fluorographene interfaces by using density functional theory calculations. We find that an isolated F atom diffuses easily on graphene, but those F atoms can be localized by inducing vacancies or absorbates in graphene and by creating graphene/fluorographene interfaces, which would strengthen the binding energy of F atoms on graphene and increase the diffusion energy barrier of F atoms remarkably.

  9. Graphene growth from reduced graphene oxide by chemical vapour deposition: seeded growth accompanied by restoration

    NASA Astrophysics Data System (ADS)

    Chang, Sung-Jin; Hyun, Moon Seop; Myung, Sung; Kang, Min-A.; Yoo, Jung Ho; Lee, Kyoung G.; Choi, Bong Gill; Cho, Youngji; Lee, Gaehang; Park, Tae Jung

    2016-03-01

    Understanding the underlying mechanisms involved in graphene growth via chemical vapour deposition (CVD) is critical for precise control of the characteristics of graphene. Despite much effort, the actual processes behind graphene synthesis still remain to be elucidated in a large number of aspects. Herein, we report the evolution of graphene properties during in-plane growth of graphene from reduced graphene oxide (RGO) on copper (Cu) via methane CVD. While graphene is laterally grown from RGO flakes on Cu foils up to a few hundred nanometres during CVD process, it shows appreciable improvement in structural quality. The monotonous enhancement of the structural quality of the graphene with increasing length of the graphene growth from RGO suggests that seeded CVD growth of graphene from RGO on Cu surface is accompanied by the restoration of graphitic structure. The finding provides insight into graphene growth and defect reconstruction useful for the production of tailored carbon nanostructures with required properties.

  10. Recent advances in experimental basic research on graphene and graphene-based nanostructures

    NASA Astrophysics Data System (ADS)

    Hieu Nguyen, Van

    2016-06-01

    The present work is a review of the results achieved in the experimental basic research on following rapidly developing modern topics of nanoscience and nanotechnology related to graphene and graphene-based nanosystems: reduction of graphene oxide and investigation of physical properties of reduced graphene oxide; fabrication and investigation of graphene quantum dots; study of light emission from excited graphene; fabrication and investigation of graphene nanopores; preparation and investigation of graphene oxide-liquid crystals as well as aqueous graphene oxide dispersions. Besides presenting the scientific content of the above-mentioned five topics in detail, we briefly mention promising and interesting works, demonstrating that the area of basic research on graphene and graphene-based nanostructures is still being enlarged.

  11. Graphene Growth and Defects on Ni(111)

    NASA Astrophysics Data System (ADS)

    Batzill, Matthias; Lahiri, Jayeeta

    2011-03-01

    Using scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES) we have investigated the growth of graphene on Ni(111) surfaces by carbon segregation from the bulk. We reveal two distinct growth modes for graphene growth. Between 480 and 650 C graphene forms on clean Ni(111) and below 480 C graphene grows by an in-plane conversion of a surface carbide phase. This is the first time that graphene formation is observed by transformation of a surface carbide. STM indicates that a lattice-matched, one-dimensional in-plane domain boundary between graphene and the carbide forms and graphene grows by replacing Ni-atoms with carbon at this interface. In addition to the growth of graphene we will also briefly discuss atomic-scale defects that can be synthesized in Ni-supported graphene. In particular we emphasize the formation of an extended line-defect with metallic properties.

  12. Exploration of defect structures on graphene.

    PubMed

    Yu, Shansheng; Zheng, Weitao

    2013-02-01

    For graphene obtained by chemical vapor deposition, there are large amount of defects in the crystalline structures. The carbon atoms from the feedstock can attack the graphene surface in annealing process, which may be one of the reasons affecting the structure of graphene. In order to explore some defect structures on graphene, we investigate the adsorption of carbon adatoms and vacancies on graphene using first-principles calculations. It is demonstrated that the adatoms can form strong covalent bonds with the graphene and the C-C dimmer adsorption may be the most prolific defect model. The C adatom can even fill simple vacancy of graphene. Our numerical simulations also show that the defect structures can lead to the splitting of the mid-gap peak of perfect graphene in the electronic structures. It is suggested that its conductivity would be lower than that of the perfect graphene, which can explain the low mobility of the charge carriers in some experiments.

  13. Electrochemistry of Q-Graphene

    NASA Astrophysics Data System (ADS)

    Randviir, Edward P.; Brownson, Dale A. C.; Gómez-Mingot, Maria; Kampouris, Dimitrios K.; Iniesta, Jesús; Banks, Craig E.

    2012-09-01

    A newly synthesised type of graphene, Q-Graphene, has been physically and electrochemically characterised with Scanning and Transmission Electron Microscopy (SEM, TEM), X-ray Photoelectron Spectroscopy (XPS) and Cyclic Voltammetry (CV). Interpretation of SEM, TEM and XPS data reveal the material to consist of hollow carbon nanospheres of multi-layer graphene (viz. graphite), which exhibit a total oxygen content of ca. 36.0% (atomic weight via XPS). In addition to the carbon structures present, spherical magnesium oxide particles of <=50 nm in diameter are abundantly present in the sample (ca. 16.2%). Interestingly, although the TEM/SEM images show macroporous carbon structures, Raman spectroscopy shows peaks typically characteristic of graphene, which suggests the material is highly heterogeneous and consists of many types of carbon allotropes. Q-Graphene is electrochemically characterised using both inner-sphere and outer-sphere electrochemical redox probes, namely potassium ferrocyanide(ii), hexaammine-ruthenium(iii) chloride and hexachloroiridate(iii), in addition to the biologically relevant and electroactive analytes, norepinephrine, β-nicotinamide adenine dinucleotide (NADH) and l-ascorbic acid. The electrochemical response of Q-Graphene is benchmarked against edge plane- and basal plane-pyrolytic graphite (EPPG and BPPG respectively), pristine graphene and graphite alternatives. Q-Graphene is found to exhibit fast electron transfer kinetics, likely due to its high proportion of folded edges and surface defects, exhibiting a response similar to that of EPPG - which exhibits fast electron transfer rates due to the high proportion of edge plane sites it possesses. Furthermore, we demonstrate that the specific oxygen content plays a pivotal role in dictating the observed electrochemical response, which is analyte dependant. Consequently there is potential for this new member of the graphene family to be beneficially utilised in various electrochemical

  14. Casimir effect on graphene resonator

    NASA Astrophysics Data System (ADS)

    Inui, Norio

    2016-03-01

    We theoretically investigated the influence of the Casimir effect on mechanical properties of a graphene resonator, where a graphene sheet is located in parallel with a perfectly conducting plate. The Casimir force arising from this effect strongly attracts a graphene sheet to a perfectly conducting plate and increases the tension of a graphene sheet as the separation distance between them decreases. The maximum vertical displacement of a graphene sheet to the substrate increases obeying a power law of a separation distance with an exponent of 4/3 as the separation distance decreases. For small separation distances, the Casimir force is excessively strong for the graphene sheet to maintain a free-standing shape, consequently resulting in the adhesion of the sheet to the substrate below a critical separation distance. The resonant frequency increases over a wide range as the separation distance decreases for large separation distances. However, it then rapidly decreases for small separations and converges to zero at a critical separation. These various behaviors enable the control of a graphene resonator.

  15. Graphene transfer: key for applications

    NASA Astrophysics Data System (ADS)

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

    2012-08-01

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

  16. Electronic transport in polycrystalline graphene.

    PubMed

    Yazyev, Oleg V; Louie, Steven G

    2010-10-01

    Most materials in available macroscopic quantities are polycrystalline. Graphene, a recently discovered two-dimensional form of carbon with strong potential for replacing silicon in future electronics, is no exception. There is growing evidence of the polycrystalline nature of graphene samples obtained using various techniques. Grain boundaries, intrinsic topological defects of polycrystalline materials, are expected to markedly alter the electronic transport in graphene. Here, we develop a theory of charge carrier transmission through grain boundaries composed of a periodic array of dislocations in graphene based on the momentum conservation principle. Depending on the grain-boundary structure we find two distinct transport behaviours--either high transparency, or perfect reflection of charge carriers over remarkably large energy ranges. First-principles quantum transport calculations are used to verify and further investigate this striking behaviour. Our study sheds light on the transport properties of large-area graphene samples. Furthermore, purposeful engineering of periodic grain boundaries with tunable transport gaps would allow for controlling charge currents without the need to introduce bulk bandgaps in otherwise semimetallic graphene. The proposed approach can be regarded as a means towards building practical graphene electronics.

  17. Graphenal polymers for energy storage.

    PubMed

    Li, Xianglong; Song, Qi; Hao, Long; Zhi, Linjie

    2014-06-12

    A key to improve the electrochemical performance of energy storage systems (e.g., lithium ion batteries and supercapacitors) is to develop advanced electrode materials. In the last few years, although originating from the unique structure and property of graphene, interest has expanded beyond the originally literally defined graphene into versatile integration of numerous intermediate structures lying between graphene and organic polymer, particularly for the development of new electrode materials for energy storage devices. Notably, diverse designations have shaded common characteristics of the molecular configurations of these newly-emerging materials, severely impeding the design, synthesis, tailoring, functionalization, and control of functional electrode materials in a rational and systematical manner. This concept paper highlights all these intermediate materials, specifically comprising graphene subunits intrinsically interconnected by organic linkers or fractions, following a general concept of graphenal polymers. Combined with recent advances made by our group and others, two representative synthesis approaches (bottom-up and top-down) for graphenal polymers are outlined, as well as the structure-property relationships of these graphenal polymers as energy storage electrode materials are discussed.

  18. Toward clean suspended CVD graphene

    SciTech Connect

    Yulaev, Alexander; Cheng, Guangjun; Hight Walker, Angela R.; Vlassiouk, Ivan V.; Myers, Alline; Leite, Marina S.; Kolmakov, Andrei

    2016-08-26

    The application of suspended graphene as electron transparent supporting media in electron microscopy, vacuum electronics, and micromechanical devices requires the least destructive and maximally clean transfer from their original growth substrate to the target of interest. Here, we use thermally evaporated anthracene films as the sacrificial layer for graphene transfer onto an arbitrary substrate. We show that clean suspended graphene can be achieved via desorbing the anthracene layer at temperatures in the 100 °C to 150 °C range, followed by two sequential annealing steps for the final cleaning, using a Pt catalyst and activated carbon. The cleanliness of the suspended graphene membranes was analyzed employing the high surface sensitivity of low energy scanning electron microscopy and X-ray photoelectron spectroscopy. A quantitative comparison with two other commonly used transfer methods revealed the superiority of the anthracene approach to obtain a larger area of clean, suspended CVD graphene. Lastly, our graphene transfer method based on anthracene paves the way for integrating cleaner graphene in various types of complex devices, including the ones that are heat and humidity sensitive.

  19. Nonlinear graphene plasmonics (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Cox, Joel D.; Marini, Andrea; Garcia de Abajo, Javier F.

    2016-09-01

    The combination of graphene's intrinsically-high nonlinear optical response with its ability to support long-lived, electrically tunable plasmons that couple strongly with light has generated great expectations for application of the atomically-thin material to nanophotonic devices. These expectations are mainly reinforced by classical analyses performed using the response derived from extended graphene, neglecting finite-size and nonlocal effects that become important when the carbon layer is structured on the nanometer scale in actual device designs. Based on a quantum-mechanical description of graphene using tight-binding electronic states combined with the random-phase approximation, we show that finite-size effects produce large contributions that increase the nonlinear response associated with plasmons in nanostructured graphene to significantly higher levels than previously thought, particularly in the case of Kerr-type optical nonlinearities. Motivated by this finding, we discuss and compare saturable absorption in extended and nanostructured graphene, with or without plasmonic enhancement, within the context of passive mode-locking for ultrafast lasers. We also explore the possibility of high-harmonic generation in doped graphene nanoribbons and nanoislands, where illumination by an infrared pulse of moderate intensity, tuned to a plasmon resonance, is predicted to generate light at harmonics of order 13 or higher, extending over the visible and UV regimes. Our atomistic description of graphene's nonlinear optical response reveals its complex nature in both extended and nanostructured systems, while further supporting the exceptional potential of this material for nonlinear nanophotonic devices.

  20. Toward clean suspended CVD graphene

    DOE PAGES

    Yulaev, Alexander; Cheng, Guangjun; Hight Walker, Angela R.; ...

    2016-08-26

    The application of suspended graphene as electron transparent supporting media in electron microscopy, vacuum electronics, and micromechanical devices requires the least destructive and maximally clean transfer from their original growth substrate to the target of interest. Here, we use thermally evaporated anthracene films as the sacrificial layer for graphene transfer onto an arbitrary substrate. We show that clean suspended graphene can be achieved via desorbing the anthracene layer at temperatures in the 100 °C to 150 °C range, followed by two sequential annealing steps for the final cleaning, using a Pt catalyst and activated carbon. The cleanliness of the suspendedmore » graphene membranes was analyzed employing the high surface sensitivity of low energy scanning electron microscopy and X-ray photoelectron spectroscopy. A quantitative comparison with two other commonly used transfer methods revealed the superiority of the anthracene approach to obtain a larger area of clean, suspended CVD graphene. Lastly, our graphene transfer method based on anthracene paves the way for integrating cleaner graphene in various types of complex devices, including the ones that are heat and humidity sensitive.« less

  1. Toward Clean Suspended CVD Graphene.

    PubMed

    Yulaev, Alexander; Cheng, Guangjun; Walker, Angela R Hight; Vlassiouk, Ivan V; Myers, Alline; Leite, Marina S; Kolmakov, Andrei

    2016-01-01

    The application of suspended graphene as electron transparent supporting media in electron microscopy, vacuum electronics, and micromechanical devices requires the least destructive and maximally clean transfer from their original growth substrate to the target of interest. Here, we use thermally evaporated anthracene films as the sacrificial layer for graphene transfer onto an arbitrary substrate. We show that clean suspended graphene can be achieved via desorbing the anthracene layer at temperatures in the 100 °C to 150 °C range, followed by two sequential annealing steps for the final cleaning, using Pt catalyst and activated carbon. The cleanliness of the suspended graphene membranes was analyzed employing the high surface sensitivity of low energy scanning electron microscopy and x-ray photoelectron spectroscopy. A quantitative comparison with two other commonly used transfer methods revealed the superiority of the anthracene approach to obtain larger area of clean, suspended CVD graphene. Our graphene transfer method based on anthracene paves the way for integrating cleaner graphene in various types of complex devices, including the ones that are heat and humidity sensitive.

  2. Enhancement of Pure Spin Currents in Spin Pumping Y3Fe5O12/Cu/metal Trilayers Through Spin Impedance Matching

    NASA Astrophysics Data System (ADS)

    Hammel, P. Chris; Du, Chunhui; Wang, Hailong; Yang, Fengyuan

    2014-03-01

    Spin pumping, driven thermally as well as by Ferromagnetic Resonance (FMR), is being widely used to generate pure spin currents from ferromagnets (FM) into normal metals (NM). Typically, the NM is chosen to be a spin-sink-Pt, W or Ta, while lighter metals such as Cu are rarely used, except to decouple the FM and spin sink. The efficiency of spin pumping is largely determined by the spin mixing conductance of the FM/NM interface. Here, we report a comparative study of spin pumping in Y3Fe5O12 /Cu/Pt and Y3Fe5O12 /Cu/W trilayers with varying Cu thicknesses. Remarkably, we find that insertion of a Cu interlayer between YIG and W substantially improves (over a factor of 4) the spin current injection into W while similar insertion between YIG and Pt degrades the spin current. This is a consequence of a much improved YIG/Cu spin mixing conductance relative to that for YIG/W. This result shows that high quality multilayer FM/NM heterostructures can enable spin mixing conductances to be engineered to enable optimal spin pumping efficiency. We acknowledge the Center for Emergent Materials at OSU, a NSF MRSEC (DMR-0820414), the DOE through grant DE-FG02-03ER46054, LakeShore Cryotronics and NSL at OSU.

  3. Synergetic effects of II-VI sensitization upon TiO{sub 2} for photoelectrochemical water splitting; a tri-layered structured scheme

    SciTech Connect

    Mumtaz, Asad; Mohamed, Norani Muti

    2014-10-24

    World's energy demands are growing on a higher scale increasing the need of more reliable and long term renewable energy resources. Efficient photo-electrochemical (PEC) devices based on novel nano-structured designs for solar-hydrogen generation need to be developed. This study provides an insight of the tri-layered-TiO2 based nanostructures. Observing the mechanism of hydrogen production, the comparison of the structural order during the synthesis is pronounced. The sequence in the tri-layered structure affects the photogenerated electron (e{sup −}) and hole (h{sup +}) pair transfer and separation. It is also discussed that not only the semiconductors band gaps alignment is important with respect to the water redox potential but also the interfacial regions. Quasi-Fermi-level adjustment at the interfacial regions plays a key role in deciding the solar to hydrogen efficiency. More efficient multicomponent semiconductor nano-design (MCSN) could be developed with the approach given in this study.

  4. Magnetodielectric effect in trilayered Co65Fe35B20/PVDF/Co65Fe35B20 composite materials. Prediction and measurement for tunable microwave applications

    NASA Astrophysics Data System (ADS)

    Rasoanoavy, F.; Laur, V.; De Blasi, S.; Lezaca, J.; Quéffélec, P.; Garello, K.; Viala, B.

    2010-05-01

    The variation in the permeability of a multilayered polyvinylidene fluoride/CoFeB (piezoelectric/magnetostrictive) composite material under the action of a dc voltage is demonstrated. The driven-voltage permeability is first predicted using a finite element method-based multiphysics calculation. The simulation allows us to determine a magnetic anisotropy field of 45 Oe induced in the ferromagnetic layers by the mechanical coupling between magnetostrictive and piezoelectric layers due to the applied dc voltage. A variation of 30% for the permeability of the ferromagnetic layers is then measured using a radiofrequency permeameter and under the application of a dc voltage of 15 V applied on the ferromagnetic layers, which also act as electrodes for the bias of the polyvinylidene fluoride (PVDF). An additional measurement of the trilayered structure under the application of a dc magnetic field is finally performed to evaluate the magnetic field needed to get a 30% variation in the magnetic layers permeability in order to compare this value to the one predicted by multiphysics calculation. These experimental results are in good agreement with calculations and are very encouraging for the application of the CoFeB/PVDF/CoFeB composite material to ensure the tunability of microwave devices (filters, phase shifters, antennas, etc.)

  5. Enhancement of magneto-optical Faraday effects and extraordinary optical transmission in a tri-layer structure with rectangular annular arrays.

    PubMed

    Lei, Chengxin; Chen, Leyi; Tang, Zhixiong; Li, Daoyong; Cheng, Zhenzhi; Tang, Shaolong; Du, Youwei

    2016-02-15

    The properties of optics and magneto-optical Faraday effects in a metal-dielectric tri-layer structure with subwavelength rectangular annular arrays are investigated. It is noteworthy that we obtained the strongly enhanced Faraday rotation of the desired sign along with high transmittance by optimizing the parameters of the nanostructure in the visible spectral ranges. In this system, we obtained two extraordinary optical transmission (EOT) resonant peaks with enhanced Faraday rotations, whose signs are opposite, which may provide the possibility of designing multi-channel magneto-optical devices. Study results show that the maximum of the figure of merit (FOM) of the structure can be obtained between two EOT resonant peaks accompanied by an enhanced Faraday rotation. The positions of the maximum value of the FOM and resonant peaks of transmission along with a large Faraday rotation can be tailored by simply adjusting the geometric parameters of our models. These research findings are of great importance for future applications of magneto-optical devices.

  6. YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} trilayer junction with nm thick PrGaO{sub 3} barrier

    SciTech Connect

    Tsuchiya, R.; Kawasaki, M.; Kubota, H.; Nishino, J.; Sato, H.; Akoh, H.; Koinuma, H.

    1997-09-01

    We have established a deposition process of high quality a axis oriented YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (a-YBCO) and insulating epitaxial PrGaO{sub 3} (PGO) films to fabricate a-YBCO/PGO(2.0{endash}3.2 nm)/a-YBCO trilayer junction. The precipitate formation on the bottom a-YBCO was greatly suppressed by the atomic layer modification of the substrate surface with a wet etching and successive atomic layer epitaxy of SrO and BaO atomic layers prior to the YBCO deposition. Crack formation and residual stress in the film due to the thermal expansion mismatch along c axis of YBCO could be eliminated by inserting a buffer layer of a-YBCO deposited with changing the substrate temperature from 580 to 735{degree}C. The junctions showed a clear hysteresis with its current jump as large as 30{percent}, together with the Fraunhofer diffraction. {copyright} {ital 1997 American Institute of Physics.}

  7. Growth mode, magnetic and magneto-optical properties of pulsed-laser-deposited Au/Co/Au(1 1 1) trilayers

    NASA Astrophysics Data System (ADS)

    Clavero, C.; Cebollada, A.; Armelles, G.; Fruchart, O.

    2010-03-01

    The growth mode, magnetic and magneto-optical properties of epitaxial Au/Co/Au(1 1 1) ultrathin trilayers grown by pulsed-laser deposition (PLD) under ultra-high vacuum are presented. Sapphire wafers buffered with a single-crystalline Mo(1 1 0) buffer layer were used as substrates. Owing to PLD-induced interfacial intermixing at the lower Co/Au(1 1 1) interface, a close-to layer-by-layer growth mode is promoted. Surprisingly, despite this intermixing, ferromagnetic behavior is found at room temperature for coverings starting at 1 atomic layer (AL). The films display perpendicular magnetization with anisotropy constants reduced by 50% compared to TD-grown or electrodeposited films, and with a coercivity more than one order of magnitude lower (≲5 mT). The magneto-optical (MO) response in the low Co thickness range is dominated by Au/Co interface contributions. For thicknesses starting at 3 AL Co, the MO response has a linear dependence with the Co thickness, indicative of a continuous-film-like MO behavior.

  8. Smart antennas based on graphene

    SciTech Connect

    Aldrigo, Martino; Dragoman, Mircea; Dragoman, Daniela

    2014-09-21

    We report two configurations of smart graphene antennas, in which either the radiation pattern of the antenna or the backscattering of the periodic metallic arrays is controlled by DC biases that induce metal-insulator reversible transitions of graphene monolayers. Such a transition from a high surface resistance (no bias) to a low surface resistance state (finite bias voltage) causes the radiation pattern of metallic antennas backed with graphene to change dramatically, from omnidirectional to broadside. Moreover, reflectarrays enhance the backscattered field due to the same metal-dielectric transition.

  9. Graphene synthesis by ion implantation

    PubMed Central

    Garaj, Slaven; Hubbard, William; Golovchenko, J. A.

    2010-01-01

    We demonstrate an ion implantation method for large-scale synthesis of high quality graphene films with controllable thickness. Thermally annealing polycrystalline nickel substrates that have been ion implanted with carbon atoms results in the surface growth of graphene films whose average thickness is controlled by implantation dose. The graphene film quality, as probed with Raman and electrical measurements, is comparable to previously reported synthesis methods. The implantation synthesis method can be generalized to a variety of metallic substrates and growth temperatures, since it does not require a decomposition of chemical precursors or a solvation of carbon into the substrate. PMID:21124725

  10. Graphene Trans-Electrode Membranes

    NASA Astrophysics Data System (ADS)

    Kuan, Aaron; Bo, Lu; Rollings, Ryan; Dressen, Don; Branton, Daniel; Golovchenko, Jene

    2014-03-01

    We report an electrical study of suspended single-layer graphene membranes separating reservoirs of electrolyte solution. Because the opposing reservoirs are separated only by an atomically thin membrane, the trans-conductance (ionic current response to a voltage across the membrane) is extremely sensitive to nanoscale defects in the membrane. This sensitivity allows the precise examination and characterization of intrinsic defects in graphene membranes, as well as engineered defects for devices. We will discuss methods for creating single nanopores or distributed defects in our graphene membranes, with the applications of nanopore DNA sequencing and water desalination in mind.

  11. [Solidification of volatile oil with graphene oxide].

    PubMed

    Yan, Hong-Mei; Jia, Xiao-Bin; Zhang, Zhen-Hai; Sun, E; Xu, Yi-Hao

    2015-02-01

    To evaluate the properties of solidifying volatile oil with graphene oxide, clove oil and zedoary turmeric oil were solidified by graphene oxide. The amount of graphene oxide was optimized with the eugenol yield and curcumol yield as criteria. Curing powder was characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The effects of graphene oxide on dissolution in vitro and thermal stability of active components were studied. The optimum solidification ratio of graphene oxide to volatile oil was 1:1. Dissolution rate of active components had rare influence while their thermal stability improved after volatile oil was solidified. Solidifying herbal volatile oil with graphene oxide deserves further study.

  12. Graphene MEMS: AFM probe performance improvement.

    PubMed

    Martin-Olmos, Cristina; Rasool, Haider Imad; Weiller, Bruce H; Gimzewski, James K

    2013-05-28

    We explore the feasibility of growing a continuous layer of graphene in prepatterned substrates, like an engineered silicon wafer, and we apply this as a mold for the fabrication of AFM probes. This fabrication method proves the fabrication of SU-8 devices coated with graphene in a full-wafer parallel technology and with high yield. It also demonstrates that graphene coating enhances the functionality of SU-8 probes, turning them conductive and more resistant to wear. Furthermore, it opens new experimental possibilities such as studying graphene-graphene interaction at the nanoscale with the precision of an AFM or the exploration of properties in nonplanar graphene layers.

  13. Polyelectrolyte-graphene Nanocomposites for Biosensing Applications

    PubMed Central

    Priftis, Dimitrios

    2015-01-01

    Due to their unique structure, the optical and mechanical properties graphene and its derivatives (e.g. graphene oxide, reduced graphene oxide) have captured the attention of a constantly increasing number of scientists with regards to biomolecule sensing. This mini review focuses on one specific type of sensor, that consisting of graphene and polyelectrolytes. Polyelectrolyte-graphene nanocomposites exhibit outstanding detection capabilities by synergistically combining the characteristics of both components, outperforming traditional sensors in many cases. Characteristics and mechanistic details of the most important polyelectrolyte-graphene based sensors will be discussed in detail in addition to some current challenges and future perspectives. PMID:27713667

  14. Band gap opening in methane intercalated graphene.

    PubMed

    Hargrove, Jasmine; Shashikala, H B Mihiri; Guerrido, Lauren; Ravi, Natarajan; Wang, Xiao-Qian

    2012-08-07

    Recent experimental work has demonstrated production of quasi-free-standing graphene by methane intercalation. The intercalation weakens the coupling of adjacent graphene layers and yields Dirac fermion behaviour of monolayer graphene. We have investigated the electronic characteristics of a methane intercepted graphene bilayer under a perpendicularly applied electric field. Evolution of the band structure of intercalated graphene as a function of the bias is studied by means of density-functional theory including interlayer van der Waals interactions. The implications of controllable band gap opening in methane-intercalated graphene for future device applications are discussed.

  15. Highly oriented graphene growth and characterization

    NASA Astrophysics Data System (ADS)

    Saheed, Mohamed Salleh Mohamed; Mohamed, Norani Muti; Singh, Balbir Singh Mahinder; Saheed, Mohamed Shuaib Mohamed

    2016-11-01

    Combination of the highly ordered monolayers to form the multilayer interconnected graphene is essential to produce robust and free standing graphene unlike its counterpart 2D monolayers. Here, chemical vapor deposition (CVD) technique is employed to produce highly flexible and high mobility 3D graphene. In this study, the 3D graphene is grown via direct carbon deposition on sacrificial template. With the use of polymer coating such as poly methyl methacrylate (PMMA), it is observed that the graphene is bendable without any degradation. Great potential in term of electrical conductivity and flexibility can be exploited for future work for this CVD grown 3D graphene.

  16. Absorption of surface acoustic waves by graphene

    NASA Astrophysics Data System (ADS)

    Zhang, S. H.; Xu, W.

    2011-06-01

    We present a theoretical study on interactions of electrons in graphene with surface acoustic waves (SAWs). We find that owing to momentum and energy conservation laws, the electronic transition accompanied by the SAW absorption cannot be achieved via inter-band transition channels in graphene. For graphene, strong absorption of SAWs can be observed in a wide frequency range up to terahertz at room temperature. The intensity of SAW absorption by graphene depends strongly on temperature and can be adjusted by changing the carrier density. This study is relevant to the exploration of the acoustic properties of graphene and to the application of graphene as frequency-tunable SAW devices.

  17. Properties and applications of chemically functionalized graphene

    NASA Astrophysics Data System (ADS)

    Craciun, M. F.; Khrapach, I.; Barnes, M. D.; Russo, S.

    2013-10-01

    The vast and yet largely unexplored family of graphene materials has great potential for future electronic devices with novel functionalities. The ability to engineer the electrical and optical properties in graphene by chemically functionalizing it with a molecule or adatom is widening considerably the potential applications targeted by graphene. Indeed, functionalized graphene has been found to be the best known transparent conductor or a wide gap semiconductor. At the same time, understanding the mechanisms driving the functionalization of graphene with hydrogen is proving to be of fundamental interest for energy storage devices. Here we discuss recent advances on the properties and applications of chemically functionalized graphene.

  18. Nanostructured graphene for spintronics

    NASA Astrophysics Data System (ADS)

    Gregersen, Søren Schou; Power, Stephen R.; Jauho, Antti-Pekka

    2017-03-01

    Zigzag edges of the honeycomb structure of graphene exhibit magnetic polarization, making them attractive as building blocks for spintronic devices. Here, we show that devices with zigzag-edged triangular antidots perform essential spintronic functionalities, such as spatial spin splitting or spin filtering of unpolarized incoming currents. Near-perfect performance can be obtained with optimized structures. The device performance is robust against substantial disorder. The gate-voltage dependence of transverse resistance is qualitatively different for spin-polarized and spin-unpolarized devices, and can be used as a diagnostic tool. Importantly, the suggested devices are feasible within current technologies.

  19. Graphene nanoribbons with wings

    SciTech Connect

    Bischoff, D. Eich, M.; Ihn, T.; Ensslin, K.; Libisch, F.

    2015-11-16

    We have investigated electronic transport in graphene nanoribbon devices with additional bar-shaped extensions (“wings”) at each side of the device. We find that the Coulomb-blockade dominated transport found in conventional ribbons is strongly modified by the presence of the extensions. States localized far away from the central ribbon contribute significantly to transport. We discuss these findings within the picture of multiple coupled quantum dots. Finally, we compare the experimental results with tight-binding simulations which reproduce the experiment both qualitatively and quantitatively.

  20. Application of graphene/graphene oxide in biomedicine and biotechnology.

    PubMed

    Zhou, Xianfeng; Liang, Feng

    2014-03-01

    Graphene, a truly two-dimensional (2D) and fully π-conjugated honeycomb network, exhibits many unique physical and chemical properties that are interesting in a wide range of areas. Since its discovery in 2004, graphene has been extensively studied in many different fields including nano-electronics, composite materials, energy research, catalysis and so on. Based on the fascinating action of members in the carbon family, notably zero dimensional (0D) fullerenes and one dimensional (1D) carbon nanotubes (CNTs) in biomedical areas, increasing number of reports have explored the potential of graphene for different biomedical and biotechnical applications since 2008. This manuscript aims to provide a summary of current research progress of graphene-based carbon materials in biosensing, drug (gene) delivery and tissue engineering, and discusses the opportunities and challenges in this rapidly growing field.

  1. Graphene homojunction: closed-edge bilayer graphene by pseudospin interaction

    NASA Astrophysics Data System (ADS)

    Yan, Jiaxu; Li, Chao; Zhan, Da; Liu, Lei; Shen, Dezhen; Kuo, Jer-Lai; Chen, Shoushun; Shen, Zexiang

    2016-04-01

    Depending on the sublattices they are propagated in, low-energy electrons or holes are labeled with pseudospin. By engineering pseudospin interactions, we propose that two critical features of a junction, i.e., band gap opening and spatial charge separation, can be realized in graphene layers with proper stacking. We also demonstrate theoretically that such a graphene diode may play a role in future pseudospin electronics such as for harvesting solar energy.

  2. Thermoelectric Properties of Pristine and Doped Graphene Nanosheets and Graphene Nanoribbons: Part II

    NASA Astrophysics Data System (ADS)

    Muley, Sarang V.; Ravindra, N. M.

    2016-06-01

    In Part II of this study, approaches to improve the thermoelectric figure of merit ( ZT) of graphene nanosheets and nanoribbons is discussed. The presence of vacancies in graphene is found to increase the ZT of zigzag graphene nanoribbons significantly. Graphene can be a promising material with much better thermoelectric performance than conventional thermoelectrics.

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

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  4. Electrostatic transfer of epitaxial graphene to glass.

    SciTech Connect

    Ohta, Taisuke; Pan, Wei; Howell, Stephen Wayne; Biedermann, Laura Butler; Beechem Iii, Thomas Edwin; Ross, Anthony Joseph, III

    2010-12-01

    We report on a scalable electrostatic process to transfer epitaxial graphene to arbitrary glass substrates, including Pyrex and Zerodur. This transfer process could enable wafer-level integration of graphene with structured and electronically-active substrates such as MEMS and CMOS. We will describe the electrostatic transfer method and will compare the properties of the transferred graphene with nominally-equivalent 'as-grown' epitaxial graphene on SiC. The electronic properties of the graphene will be measured using magnetoresistive, four-probe, and graphene field effect transistor geometries [1]. To begin, high-quality epitaxial graphene (mobility 14,000 cm2/Vs and domains >100 {micro}m2) is grown on SiC in an argon-mediated environment [2,3]. The electrostatic transfer then takes place through the application of a large electric field between the donor graphene sample (anode) and the heated acceptor glass substrate (cathode). Using this electrostatic technique, both patterned few-layer graphene from SiC(000-1) and chip-scale monolayer graphene from SiC(0001) are transferred to Pyrex and Zerodur substrates. Subsequent examination of the transferred graphene by Raman spectroscopy confirms that the graphene can be transferred without inducing defects. Furthermore, the strain inherent in epitaxial graphene on SiC(0001) is found to be partially relaxed after the transfer to the glass substrates.

  5. Genotoxicity of Graphene in Escherichia coli

    NASA Astrophysics Data System (ADS)

    Sharma, Ananya

    Rapid advances in nanotechnology necessitate assessment of the safety of nanomaterials in the resulting products and applications. One key nanomaterial attracting much interest in many areas of science and technology is graphene. Graphene is a one atom thick carbon allotrope arranged in a two-dimensional honeycomb lattice. In addition to being extremely thin, graphene has several extraordinary physical properties such as its exceptional mechanical strength, thermal stability, and high electrical conductivity. Graphene itself is relatively chemically inert and therefore pristine graphene must undergo a process called functionalization, which is combination of chemical and physical treatments that change the properties of graphene, to make it chemically active. Functionalization of graphene is of crucial importance as the end application of graphene depends on proper functionalization. In the field of medicine, graphene is currently a nanomaterial of high interest for building biosensors, DNA transistors, and probes for cancer detection. Despite the promising applications of graphene in several areas of biomedicine, there have been only few studies in recent years that focus on evaluating cytotoxicity of graphene on cells, and almost no studies that investigate how graphene exposure affects cellular genetic material. Therefore, in this study we used a novel approach to evaluate the genotoxicity, i.e., the effects of graphene on DNA, using Escherichia coli as a prokaryotic model organism.

  6. Terahertz-wave generation using graphene: toward the creation of graphene injection lasers

    NASA Astrophysics Data System (ADS)

    Otsuji, T.; Satou, A.; Boubanga Tombet, S. A.; Ryzhii, M.; Ryzhii, V.

    2013-01-01

    This paper reviews recent advances in terahertz-wave generation in graphene toward the creation of new types of graphene terahertz lasers. Fundamental basis of the optoelectronic properties of graphene is first introduced. Second, nonequilibrium carrier relaxation/recombination dynamics and resultant negative terahertz conductivity in optically or electrically pumped graphene are described. Third, recent theoretical advances toward the creation of current-injection graphene terahertz lasers are described. Fourth, unique terahertz dynamics of the two-dimensional plasmons in graphene are discussed. Finally, the advantages of graphene materials and devices for terahertz-wave generation are summarized.

  7. Design of advanced porous graphene materials: from graphene nanomesh to 3D architectures.

    PubMed

    Jiang, Lili; Fan, Zhuangjun

    2014-02-21

    In order to make full utilization of the high intrinsic surface area of graphene, recently, porous graphene materials including graphene nanomesh, crumpled graphene and graphene foam, have attracted tremendous attention and research interest, owing to their exceptional porous structure (high surface area, and high pore volume) in combination with the inherent properties of graphene, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Interestingly, porous graphene materials and their derivatives have been explored in a wide range of applications in the fields of electronic and photonic devices, energy storage, gas separation/storage, oil absorption and sensors. This article reviews recent progress in the synthesis, characterization, properties, and applications of porous graphene materials. We aim to highlight the importance of designing different porous structures of graphene to meet future challenges, and the trend on future design of porous graphene materials is analyzed.

  8. Towards inducing superconductivity into graphene

    NASA Astrophysics Data System (ADS)

    Efetov, Dmitri K.

    Graphenes transport properties have been extensively studied in the 10 years since its discovery in 2004, with ground-breaking experimental observations such as Klein tunneling, fractional quantum Hall effect and Hofstadters butterfly. Though, so far, it turned out to be rather poor on complex correlated electronic ground states and phase transitions, despite various theoretical predictions. The purpose of this thesis is to help understanding the underlying theoretical and experimental reasons for the lack of strong electronic interactions in graphene, and, employing graphenes high tunability and versatility, to identify and alter experimental parameters that could help to induce stronger correlations. In particular graphene holds one last, not yet experimentally discovered prediction, namely exhibiting intrinsic superconductivity. With its vanishingly small Fermi surface at the Dirac point, graphene is a semi-metal with very weak electronic interactions. Though, if it is doped into the metallic regime, where the size of the Fermi surface becomes comparable to the size of the Brillouin zone, the density of states becomes sizeable and electronic interactions are predicted to be dramatically enhanced, resulting in competing correlated ground states such as superconductivity, magnetism and charge density wave formation. Following these predictions, this thesis first describes the creation of metallic graphene at high carrier doping via electrostatic doping techniques based on electrolytic gates. Due to graphenes surface only properties, we are able to induce carrier densities above n>1014 cm-2 (epsilonF>1eV) into the chemically inert graphene. While at these record high carrier densities we yet do not observe superconductivity, we do observe fundamentally altered transport properties as compared to semi-metallic graphene. Here, detailed measurements of the low temperature resistivity reveal that the electron-phonon interactions are governed by a reduced, density

  9. Grain boundary loops in graphene

    NASA Astrophysics Data System (ADS)

    Cockayne, Eric; Rutter, Gregory M.; Guisinger, Nathan P.; Crain, Jason N.; First, Phillip N.; Stroscio, Joseph A.

    2011-05-01

    Topological defects can affect the physical properties of graphene in unexpected ways. Harnessing their influence may lead to enhanced control of both material strength and electrical properties. Here we present a class of topological defects in graphene composed of a rotating sequence of dislocations that close on themselves, forming grain boundary loops that either conserve the number of atoms in the hexagonal lattice or accommodate vacancy or interstitial reconstruction, while leaving no unsatisfied bonds. One grain boundary loop is observed as a “flower” pattern in scanning tunneling microscopy studies of epitaxial graphene grown on SiC(0001). We show that the flower defect has the lowest energy per dislocation core of any known topological defect in graphene, providing a natural explanation for its growth via the coalescence of mobile dislocations.

  10. Hyperfine interaction in hydrogenated graphene

    NASA Astrophysics Data System (ADS)

    Garcia, Noel; Melle, Manuel; Fernandez-Rossier, Joaquin

    We study the hyperfine interaction of Hydrogen chemisorbed in graphene nanostructures with a gap in their spectrum, such as islands and ribbons. Chemisorption of Hydrogen on graphene results in a bound in-gap state that hosts a single electron localized around the adatom. Using both density functional theory and a four-orbital tight-binding model we study the hyperfine interaction between the hydrogen nuclear spin and the conduction electrons in graphene. We find that the strength of the hyperfine interaction decreases for larger nanostructures for which the energy gap is smaller. We then compare the results of the hyperfine interaction for large nanostructures with those of graphene 2D crystal with a periodic arrangement of chemisorbed Hydrogen atoms, obtaining very similar results. The magnitude of the hyperfine interaction is about 150 MHz, in line with that of Si:P. We acknowledge financial support by Marie-Curie-ITN 607904-SPINOGRAPH.

  11. The puzzle of graphene commercialization

    NASA Astrophysics Data System (ADS)

    Park, Seongjun

    2016-11-01

    The commercialization of graphene-based products is challenging, because many engineering and economical aspects have to be taken into consideration. A stronger collaboration between academia and industry would be beneficial for accelerating the process.

  12. Graphene-based Materials

    NASA Astrophysics Data System (ADS)

    Ruoff, Rodney

    2009-03-01

    Our top-down approaches [Lu et al.] inspired physicists to obtain graphene by micromechanical exfoliation. Another approach to individual layers involves converting graphite to graphite oxide (GO) to generate aqueous colloidal suspensions of `graphene oxide'(GO') sheets. (i) Reduced GO' (RGO') sheets were embedded in polymers such as polystyrene and their dispersion/morphology studied by SEM/TEM, and the conductivity/ percolation threshold of such composites was determined; (ii) individual GO' and RGO' sheets were studied to elucidate their chemical, optical, and electrical properties, (iii) GO' and RGO' sheets were embedded in thin glass films by a sol-gel route yielding conductive/transparent films, (iii) a `paper' material of stacked GO' sheets was made and characterized, (iv) powders composed of RGO' showed exceptional promise for use in ultracapacitors, and (v) C13-labeled GO was made and the detailed chemical structure of GO was determined with SS NMR. --Lu,Yu,Huang,Ruoff, ``Tailoring graphite with the goal of achieving single sheets'', Nanotechnology, 10, 269-272 (1999). See also http://bucky-central.me.utexas.edu/publications.htm 139, 146, 150, 155, 160, 164, 166, 168, 169, 174, 179-182, 184 where collaborators are shown as coauthors.

  13. Multilayer graphene rubber nanocomposites

    NASA Astrophysics Data System (ADS)

    Schartel, Bernhard; Frasca, Daniele; Schulze, Dietmar; Wachtendorf, Volker; Krafft, Bernd; Morys, Michael; Böhning, Martin; Rybak, Thomas

    2016-05-01

    Multilayer Graphene (MLG), a nanoparticle with a specific surface of BET = 250 m2/g and thus made of only approximately 10 graphene sheets, is proposed as a nanofiller for rubbers. When homogenously dispersed, it works at low loadings enabling the replacement of carbon black (CB), increase in efficiency, or reduction in filler concentration. Actually the appropriate preparation yielded nanocomposites in which just 3 phr are sufficient to significantly improve the rheological, curing and mechanical properties of different rubbers, as shown for Chlorine-Isobutylene-Isoprene Rubber (CIIR), Nitrile-Butadiene Rubber (NBR), Natural Rubber (NR), and Styrene-Butadiene Rubber (SBR). A mere 3 phr of MLG tripled the Young's modulus of CIIR, an effect equivalent to 20 phr of carbon black. Similar equivalents are observed for MLG/CB mixtures. MLG reduces gas permeability, increases thermal and electrical conductivities, and retards fire behavior. The later shown by the reduction in heat release rate in the cone calorimeter. The higher the nanofiller concentration is (3 phr, 5 phr, and 10 phr was investigated), the greater the improvement in the properties of the nanocomposites. Moreover, the MLG nanocomposites improve stability of mechanical properties against weathering. An increase in UV-absorption as well as a pronounced radical scavenging are proposed and were proved experimentally. To sum up, MLG is interesting as a multifunctional nanofiller and seems to be quite ready for rubber development.

  14. Discrete dislocations in graphene

    NASA Astrophysics Data System (ADS)

    Ariza, M. P.; Ortiz, M.

    2010-05-01

    In this work, we present an application of the theory of discrete dislocations of Ariza and Ortiz (2005) to the analysis of dislocations in graphene. Specifically, we discuss the specialization of the theory to graphene and its further specialization to the force-constant model of Aizawa et al. (1990). The ability of the discrete-dislocation theory to predict dislocation core structures and energies is critically assessed for periodic arrangements of dislocation dipoles and quadrupoles. We show that, with the aid of the discrete Fourier transform, those problems are amenable to exact solution within the discrete-dislocation theory, which confers the theory a distinct advantage over conventional atomistic models. The discrete dislocations exhibit 5-7 ring core structures that are consistent with observation and result in dislocation energies that fall within the range of prediction of other models. The asymptotic behavior of dilute distributions of dislocations is characterized analytically in terms of a discrete prelogarithmic energy tensor. Explicit expressions for this discrete prelogarithmic energy tensor are provided up to quadratures.

  15. Bilayer Graphene Electromechanical Systems

    NASA Astrophysics Data System (ADS)

    Champagne, Alexandre; Storms, Matthew; Yigen, Serap; Reulet, Bertrand

    Bilayer graphene is an outstanding electromechanical system, and its electronic and mechanical properties, as well as their coupling, are widely tunable. To the best of our knowledge, simultaneous charge transport and mechanical spectroscopy (via RF mixing) has not been realized in bilayer graphene. We present data showing clear electromechanical resonances in three suspended bilayer devices whose length range from 1 to 2 microns. We first describe the low-temperature current annealing of the devices which is crucial to achieve the transconductance, I -VG , necessary to implement a RF mixing detection method. We describe our RF mixing circuit and data. We measure clear mechanical resonances ranging in frequency from 50 to 140 MHz. We show that we can smoothly tune the resonance frequencies of our bilayer resonators with mechanical strain applied via a backgate voltage. We measure quality factors up to 4000. We briefly discuss the effects of the RF driving power on the dispersion of the mechanical resonance. We aim to use these high quality mechanical resonance as a mechanical sensor of the bilayer quantum Hall phase transitions. We show initial data of a bilayer mechanical resonance as a function of magnetic field and quantum Hall phase transitions.

  16. Atomic covalent functionalization of graphene.

    PubMed

    Johns, James E; Hersam, Mark C

    2013-01-15

    Although graphene's physical structure is a single atom thick, two-dimensional, hexagonal crystal of sp(2) bonded carbon, this simple description belies the myriad interesting and complex physical properties attributed to this fascinating material. Because of its unusual electronic structure and superlative properties, graphene serves as a leading candidate for many next generation technologies including high frequency electronics, broadband photodetectors, biological and gas sensors, and transparent conductive coatings. Despite this promise, researchers could apply graphene more routinely in real-world technologies if they could chemically adjust graphene's electronic properties. For example, the covalent modification of graphene to create a band gap comparable to silicon (∼1 eV) would enable its use in digital electronics, and larger band gaps would provide new opportunities for graphene-based photonics. Toward this end, researchers have focused considerable effort on the chemical functionalization of graphene. Due to its high thermodynamic stability and chemical inertness, new methods and techniques are required to create covalent bonds without promoting undesirable side reactions or irreversible damage to the underlying carbon lattice. In this Account, we review and discuss recent theoretical and experimental work studying covalent modifications to graphene using gas phase atomic radicals. Atomic radicals have sufficient energy to overcome the kinetic and thermodynamic barriers associated with covalent reactions on the basal plane of graphene but lack the energy required to break the C-C sigma bonds that would destroy the carbon lattice. Furthermore, because they are atomic species, radicals substantially reduce the likelihood of unwanted side reactions that confound other covalent chemistries. Overall, these methods based on atomic radicals show promise for the homogeneous functionalization of graphene and the production of new classes of two

  17. Applications of Graphene to Photonics

    DTIC Science & Technology

    2014-07-01

    graphene/ silicon carbide heterosystem,” Physical Review B - Condensed Matter and Materials Physics 82 (2010). [63] S. Das Sarma and E. H. Hwang...the damage threshold of silicon for similar optical pulse parameters [19]. However, silicon has a 10-µm absorp- tion depth (at these wavelengths...example, using linear absorption a 1000x higher carrier density is created in graphene vs. silicon . Other notable optical properties include nonlinear

  18. Scaling of graphene integrated circuits

    NASA Astrophysics Data System (ADS)

    Bianchi, Massimiliano; Guerriero, Erica; Fiocco, Marco; Alberti, Ruggero; Polloni, Laura; Behnam, Ashkan; Carrion, Enrique A.; Pop, Eric; Sordan, Roman

    2015-04-01

    The influence of transistor size reduction (scaling) on the speed of realistic multi-stage integrated circuits (ICs) represents the main performance metric of a given transistor technology. Despite extensive interest in graphene electronics, scaling efforts have so far focused on individual transistors rather than multi-stage ICs. Here we study the scaling of graphene ICs based on transistors from 3.3 to 0.5 μm gate lengths and with different channel widths, access lengths, and lead thicknesses. The shortest gate delay of 31 ps per stage was obtained in sub-micron graphene ROs oscillating at 4.3 GHz, which is the highest oscillation frequency obtained in any strictly low-dimensional material to date. We also derived the fundamental Johnson limit, showing that scaled graphene ICs could be used at high frequencies in applications with small voltage swing.The influence of transistor size reduction (scaling) on the speed of realistic multi-stage integrated circuits (ICs) represents the main performance metric of a given transistor technology. Despite extensive interest in graphene electronics, scaling efforts have so far focused on individual transistors rather than multi-stage ICs. Here we study the scaling of graphene ICs based on transistors from 3.3 to 0.5 μm gate lengths and with different channel widths, access lengths, and lead thicknesses. The shortest gate delay of 31 ps per stage was obtained in sub-micron graphene ROs oscillating at 4.3 GHz, which is the highest oscillation frequency obtained in any strictly low-dimensional material to date. We also derived the fundamental Johnson limit, showing that scaled graphene ICs could be used at high frequencies in applications with small voltage swing. Electronic supplementary information (ESI) available: Discussions on the cutoff frequency fT, the maximum frequency of oscillation fmax, and the intrinsic gate delay CV/I. See DOI: 10.1039/c5nr01126d

  19. Giant thermoelectric effect in graphene

    NASA Astrophysics Data System (ADS)

    Dragoman, D.; Dragoman, M.

    2007-11-01

    The paper predicts a giant thermoelectric coefficient in a nanostructure consisting of metallic electrodes periodically patterned over graphene, which is deposited on a silicon dioxide substrate. The Seebeck coefficient in this device attains 30mV/K, this value being among the largest reported ever. The calculations are based on a transfer matrix approach that takes a particular form for graphene-based devices. The results are important for future nanogenerators with applications in the area of sensors, energy harvesting, and scavenging.

  20. Discrete solitons in graphene metamaterials

    NASA Astrophysics Data System (ADS)

    Bludov, Yu. V.; Smirnova, D. A.; Kivshar, Yu. S.; Peres, N. M. R.; Vasilevskiy, M. I.

    2015-01-01

    We study nonlinear properties of multilayer metamaterials created by graphene sheets separated by dielectric layers. We demonstrate that such structures can support localized nonlinear modes described by the discrete nonlinear Schrödinger equation and that its solutions are associated with stable discrete plasmon solitons. We also analyze the nonlinear surface modes in truncated graphene metamaterials being a nonlinear analog of surface Tamm states.

  1. Encapsulation of graphene in Parylene

    NASA Astrophysics Data System (ADS)

    Skoblin, Grigory; Sun, Jie; Yurgens, August

    2017-01-01

    Graphene encapsulated between flakes of hexagonal boron nitride (hBN) demonstrates the highest known mobility of charge carriers. However, the technology is not scalable to allow for arrays of devices. We are testing a potentially scalable technology for encapsulating graphene where we replace hBN with Parylene while still being able to make low-ohmic edge contacts. The resulting encapsulated devices show low parasitic doping and a robust Quantum Hall effect in relatively low magnetic fields <5 T.

  2. Casimir interactions between graphene sheets and metamaterials

    SciTech Connect

    Drosdoff, D.; Woods, Lilia M.

    2011-12-15

    The Casimir force between graphene sheets and metamaterials is studied. Theoretical results based on the Lifshitz theory for layered, planar, two-dimensional systems in media are presented. We consider graphene-graphene, graphene-metamaterial, and metal-graphene-metamaterial configurations. We find that quantum effects of the temperature-dependent force are not apparent until the submicron range. In contrast to results with bulk dielectric and bulk metallic materials, no Casimir repulsion is found when graphene is placed on top of a magnetically active metamaterial substrate, regardless of the strength of the low-frequency magnetic response. In the case of the metal-graphene-metamaterial setting, repulsion between the metamaterial and the metal-graphene system is possible only when the dielectric response from the metal contributes significantly.

  3. Wettability of graphene-laminated micropillar structures

    NASA Astrophysics Data System (ADS)

    Bong, Jihye; Seo, Keumyoung; Park, Ji-Hoon; Ahn, Joung Real; Ju, Sanghyun

    2014-12-01

    The wetting control of graphene is of great interest for electronic, mechanical, architectural, and bionic applications. In this study, the wettability of graphene-laminated micropillar structures was manipulated by changing the height of graphene-laminated structures and employing the trichlorosilane (HDF-S)-based self-assembly monolayer. Graphene-laminated micropillar structures with HDF-S exhibited higher hydrophobicity (contact angle of 129.5°) than pristine graphene thin film (78.8°), pristine graphene-laminated micropillar structures (97.5°), and HDF-S self-assembled graphene thin film (98.5°). Wetting states of the graphene-laminated micropillar structure with HDF-S was also examined by using a urea solution, which flowed across the surface without leaving any residues.

  4. 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.

  5. Nature of Graphene Edges: A Review

    NASA Astrophysics Data System (ADS)

    Acik, Muge; Chabal, Yves J.

    2011-07-01

    Graphene edges determine the optical, magnetic, electrical, and electronic properties of graphene. In particular, termination, chemical functionalization and reconstruction of graphene edges leads to crucial changes in the properties of graphene, so control of the edges is critical to the development of applications in electronics, spintronics and optoelectronics. Up to date, significant advances in studying graphene edges have directed various smart ways of controlling the edge morphology. Though, it still remains as a major challenge since even minor deviations from the ideal shape of the edges significantly deteriorate the material properties. In this review, we discuss the fundamental edge configurations together with the role of various types of edge defects and their effects on graphene properties. Indeed, we highlight major demanding challenges to find the most suitable technique to characterize graphene edges for numerous device applications such as transistors, sensors, actuators, solar cells, light-emitting displays, and batteries in graphene technology.

  6. High-efficiency thermoelectrics with functionalized graphene.

    PubMed

    Kim, Jeong Yun; Grossman, Jeffrey C

    2015-05-13

    Graphene superlattices made with chemical functionalization offer the possibility of tuning both the thermal and electronic properties via nanopatterning of the graphene surface. Using classical and quantum mechanical calculations, we predict that suitable chemical functionalization of graphene can introduce peaks in the density of states at the band edge that result in a large enhancement in the Seebeck coefficient, leading to an increase in the room-temperature power factor of a factor of 2 compared to pristine graphene, despite the degraded electrical conductivity. Furthermore, the presence of patterns on graphene reduces the thermal conductivity, which when taken together leads to an increase in the figure of merit for functionalized graphene by up to 2 orders of magnitude over that of pristine graphene, reaching its maximum ZT ∼ 3 at room temperature according to our calculations. These results suggest that appropriate chemical functionalization could lead to efficient graphene-based thermoelectric materials.

  7. Wettability of graphene-laminated micropillar structures

    SciTech Connect

    Bong, Jihye; Seo, Keumyoung; Ju, Sanghyun E-mail: shju@kgu.ac.kr; Park, Ji-Hoon; Ahn, Joung Real E-mail: shju@kgu.ac.kr

    2014-12-21

    The wetting control of graphene is of great interest for electronic, mechanical, architectural, and bionic applications. In this study, the wettability of graphene-laminated micropillar structures was manipulated by changing the height of graphene-laminated structures and employing the trichlorosilane (HDF-S)-based self-assembly monolayer. Graphene-laminated micropillar structures with HDF-S exhibited higher hydrophobicity (contact angle of 129.5°) than pristine graphene thin film (78.8°), pristine graphene-laminated micropillar structures (97.5°), and HDF-S self-assembled graphene thin film (98.5°). Wetting states of the graphene-laminated micropillar structure with HDF-S was also examined by using a urea solution, which flowed across the surface without leaving any residues.

  8. Theory of graphene saturable absorption

    NASA Astrophysics Data System (ADS)

    Marini, A.; Cox, J. D.; García de Abajo, F. J.

    2017-03-01

    Saturable absorption is a nonperturbative nonlinear optical phenomenon that plays a pivotal role in the generation of ultrafast light pulses. Here we show that this effect emerges in graphene at unprecedentedly low light intensities, thus opening avenues to new nonlinear physics and applications in optical technology. Specifically, we theoretically investigate saturable absorption in extended graphene by developing a semianalytical nonperturbative single-particle approach, describing electron dynamics in the atomically-thin material using the two-dimensional Dirac equation for massless Dirac fermions, which is recast in the form of generalized Bloch equations. By solving the electron dynamics nonperturbatively, we account for both interband and intraband contributions to the intensity-dependent saturated conductivity and conclude that the former dominates regardless of the intrinsic doping state of the material. We obtain results in qualitative agreement with atomistic quantum-mechanical simulations of graphene nanoribbons including electron-electron interactions, finite-size, and higher-band effects. Remarkably, such effects are found to affect mainly the linear absorption, while the predicted saturation intensities are in good quantitative agreement in the limit of extended graphene. Additionally, we find that the modulation depth of saturable absorption in graphene can be electrically manipulated through an externally applied gate voltage. Our results are relevant for the development of graphene-based optoelectronic devices, as well as for applications in mode-locking and random lasers.

  9. Phonons in twisted bilayer graphene

    NASA Astrophysics Data System (ADS)

    Cocemasov, Alexandr I.; Nika, Denis L.; Balandin, Alexander A.

    2013-07-01

    We theoretically investigate phonon dispersion in AA-stacked, AB-stacked, and twisted bilayer graphene with various rotation angles. The calculations are performed using the Born-von Karman model for the intralayer atomic interactions and the Lennard-Jones potential for the interlayer interactions. It is found that the stacking order affects the out-of-plane acoustic phonon modes the most. The difference in the phonon densities of states in the twisted bilayer graphene and in AA- or AB-stacked bilayer graphene appears in the phonon frequency range 90-110 cm-1. Twisting bilayer graphene leads to the emergence of different phonon branches—termed hybrid folded phonons—which originate from the mixing of phonon modes from different high-symmetry directions in the Brillouin zone. The frequencies of the hybrid folded phonons depend strongly on the rotation angle and can be used for noncontact identification of the twist angles in graphene samples. The obtained results and the tabulated frequencies of phonons in twisted bilayer graphene are important for the interpretation of experimental Raman data and in determining the thermal conductivity of these material systems.

  10. Stability of suspended graphene under Casimir force

    NASA Astrophysics Data System (ADS)

    Chudnovsky, E. M.; Zarzuela, R.

    2016-08-01

    We consider a graphene sheet suspended above a conducting surface. Treating graphene as an elastic membrane subjected to Casimir force, we study its stability against sagging towards the conductor. There exists a critical elevation at the edges below which the central part of the suspended graphene nucleates a trunk that sinks under the action of the Casimir force. The dependence of the critical elevation on temperature, dimensions, and the elastic stress applied to the graphene sheet is computed.

  11. Graphene-supported metal oxide monolith

    DOEpatents

    Worsley, Marcus A.; Baumann, Theodore F.; Biener, Juergen; Biener, Monika A.; Wang, Yinmin; Ye, Jianchao; Tylski, Elijah

    2017-01-10

    A composition comprising at least one graphene-supported metal oxide monolith, said monolith comprising a three-dimensional structure of graphene sheets crosslinked by covalent carbon bonds, wherein the graphene sheets are coated by at least one metal oxide such as iron oxide or titanium oxide. Also provided is an electrode comprising the aforementioned graphene-supported metal oxide monolith, wherein the electrode can be substantially free of any carbon-black and substantially free of any binder.

  12. Disorder-free sputtering method on graphene

    SciTech Connect

    Qiu Xue Peng; Shin Young Jun; Niu Jing; Kulothungasagaran, Narayanapillai; Kalon, Gopinadhan; Yang, Hyunsoo; Qiu Caiyu; Yu Ting

    2012-09-15

    Deposition of various materials onto graphene without causing any disorder is highly desirable for graphene applications. Especially, sputtering is a versatile technique to deposit various metals and insulators for spintronics, and indium tin oxide to make transparent devices. However, the sputtering process causes damage to graphene because of high energy sputtered atoms. By flipping the substrate and using a high Ar pressure, we demonstrate that the level of damage to graphene can be reduced or eliminated in dc, rf, and reactive sputtering processes.

  13. Graphite-to-Graphene: Total Conversion.

    PubMed

    Buzaglo, Matat; Bar, Ilan Pri; Varenik, Maxim; Shunak, Liran; Pevzner, Svetlana; Regev, Oren

    2017-02-01

    The rush to develop graphene applications mandates mass production of graphene sheets. However, the currently available complex and expensive production technologies are limiting the graphene commercialization. The addition of a protective diluent to graphite during ball-milling is demonstrated to result in a game-changer yield (>90%) of defect-free graphene, whose size is controlled by the milling energy and the diluent type.

  14. Optimization of Immobilization of Nanodiamonds on Graphene

    NASA Astrophysics Data System (ADS)

    Pille, A.; Lange, S.; Utt, K.; Eltermann, M.

    2015-04-01

    We report using simple dip-coating method to cover the surface of graphene with nanodiamonds for future optical detection of defects on graphene. Most important part of the immobilization process is the pre-functionalization of both, nanodiamond and graphene surfaces to obtain the selectiveness of the method. This work focuses on an example of using electrostatic attraction to confine nanodiamonds to graphene. Raman spectroscopy, microluminescence imaging and scanning electron microscopy were applied to characterize obtained samples.

  15. Special issue on graphene nanophotonics

    NASA Astrophysics Data System (ADS)

    Nikitin, A. Yu; Maier, S. A.; Martin-Moreno, L.

    2013-11-01

    Graphene nanophotonics has recently appeared as a new research area, which combines the topics of nanophotonics (devoted to studying the behavior of electromagnetic fields on the deep subwavelength scale) and the several extraordinary material properties of graphene. Apart from being the thinnest existing material, graphene is very attractive for photonics due to its extreme flexibility, high mobility and the possibility of controlling its carrier concentration (and hence its electromagnetic response) via external gate voltages. From its very birth, graphene nanophotonics has the potential for innovative technological applications, aiming to complement (or in some cases even replace) the existing semiconductor/metallic photonic platforms. It has already shown exceptional capabilities in many directions, such as for instance in photodetection, photovoltaics, lasing, etc [1]. A special place in graphene photonics belongs to graphene plasmonics, which studies both intrinsic plasmons in graphene and the combination of graphene with plasmons supported by metallic structures [2]. Here, apart from the dynamic control via external voltages previously mentioned, the use of graphene brings with it the remarkable property that graphene plasmons have a wavelength λp that can be even one hundred times smaller than that in free space λ (for instance λp ~ 100 nm at λ ~ 10 μm). This provides both extreme confinement and extreme enhancement of the electromagnetic field at the graphene sheet which, together with its high sensitivity to the doping level, opens many interesting perspectives for new optical devices. The collection of papers presented in this special issue highlights different aspects of nanophotonics in graphene and related systems. The timely appearance of this publication was apparent during the monographic workshop 'Graphene Nanophotonics', sponsored by the European Science Foundation and held during 3-8 March 2013, in Benasque (Spain). This special issue

  16. Fabrication of Graphene on Kevlar Supercapacitor Electrodes

    DTIC Science & Technology

    2011-05-01

    Fabrication of Graphene on Kevlar Supercapacitor Electrodes by Jacquelyn M. Krintz and Matthew H. Ervin ARL-TR-5545 May 2011...Fabrication of Graphene on Kevlar Supercapacitor Electrodes Jacquelyn M. Krintz and Matthew H. Ervin Sensors and Electron Devices...to December 2010 4. TITLE AND SUBTITLE Fabrication of Graphene on Kevlar Supercapacitor Electrodes 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c

  17. Graphene for energy solutions and its industrialization

    NASA Astrophysics Data System (ADS)

    Wei, Di; Kivioja, Jani

    2013-10-01

    Graphene attracts intensive interest globally across academia and industry since the award of the Nobel Prize in Physics 2010. Within the last half decade, there has been an explosion in the number of scientific publications, patents and industry projects involved in this topic. On the other hand, energy is one of the biggest challenges of this century and related to the global sustainable economy. There are many reviews on graphene and its applications in various devices, however, few of the review articles connect the intrinsic properties of graphene with its energy. The IUPAC definition of graphene refers to a single carbon layer of graphite structure and its related superlative properties. A lot of scientific results on graphene published to date are actually dealing with multi-layer graphenes or reduced graphenes from insulating graphene oxides (GO) which contain defects and contaminants from the reactions and do not possess some of the intrinsic physical properties of pristine graphene. In this review, the focus is on the most recent advances in the study of pure graphene properties and novel energy solutions based on these properties. It also includes graphene metrology and analysis of both intellectual property and the value chain for the existing and forthcoming graphene industry that may cause a new `industry revolution' with the strong and determined support of governments and industries across the European Union, U. S., Asia and many other countries in the world.

  18. Phosphate functionalized graphene with tunable mechanical properties.

    PubMed

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

    2014-02-01

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

  19. Graphene-nickel interfaces: a review.

    PubMed

    Dahal, Arjun; Batzill, Matthias

    2014-03-07

    Graphene on nickel is a prototypical example of an interface between graphene and a strongly interacting metal, as well as a special case of a lattice matched system. The chemical interaction between graphene and nickel is due to hybridization of the metal d-electrons with the π-orbitals of graphene. This interaction causes a smaller separation between the nickel surface and graphene (0.21 nm) than the typical van der Waals gap-distance between graphitic layers (0.33 nm). Furthermore, the physical properties of graphene are significantly altered. Main differences are the opening of a band gap in the electronic structure and a shifting of the π-band by ∼2 eV below the Fermi-level. Experimental evidence suggests that the ferromagnetic nickel induces a magnetic moment in the carbon. Substrate induced geometric and electronic changes alter the phonon dispersion. As a consequence, monolayer graphene on nickel does not exhibit a Raman spectrum. In addition to reviewing these fundamental physical properties of graphene on Ni(111), we also discuss the formation and thermal stability of graphene and a surface-confined nickel-carbide. The fundamental growth mechanisms of graphene by chemical vapor deposition are also described. Different growth modes depending on the sample temperature have been identified in ultra high vacuum surface science studies. Finally, we give a brief summary for the synthesis of more complex graphene and graphitic structures using nickel as catalyst and point out some potential applications for graphene-nickel interfaces.

  20. Graphene for energy solutions and its industrialization.

    PubMed

    Wei, Di; Kivioja, Jani

    2013-11-07

    Graphene attracts intensive interest globally across academia and industry since the award of the Nobel Prize in Physics 2010. Within the last half decade, there has been an explosion in the number of scientific publications, patents and industry projects involved in this topic. On the other hand, energy is one of the biggest challenges of this century and related to the global sustainable economy. There are many reviews on graphene and its applications in various devices, however, few of the review articles connect the intrinsic properties of graphene with its energy. The IUPAC definition of graphene refers to a single carbon layer of graphite structure and its related superlative properties. A lot of scientific results on graphene published to date are actually dealing with multi-layer graphenes or reduced graphenes from insulating graphene oxides (GO) which contain defects and contaminants from the reactions and do not possess some of the intrinsic physical properties of pristine graphene. In this review, the focus is on the most recent advances in the study of pure graphene properties and novel energy solutions based on these properties. It also includes graphene metrology and analysis of both intellectual property and the value chain for the existing and forthcoming graphene industry that may cause a new 'industry revolution' with the strong and determined support of governments and industries across the European Union, U. S., Asia and many other countries in the world.

  1. Graphene field emission devices

    SciTech Connect

    Kumar, S. Raghavan, S.; Duesberg, G. S.; Pratap, R.

    2014-09-08

    Graphene field emission devices are fabricated using a scalable process. The field enhancement factors, determined from the Fowler-Nordheim plots, are within few hundreds and match the theoretical predictions. The devices show high emission current density of ∼10 nA μm{sup −1} at modest voltages of tens of volts. The emission is stable with time and repeatable over long term, whereas the noise in the emission current is comparable to that from individual carbon nanotubes emitting under similar conditions. We demonstrate a power law dependence of emission current on pressure which can be utilized for sensing. The excellent characteristics and relative ease of making the devices promise their great potential for sensing and electronic applications.

  2. Making Graphene Nanoribbons Photoluminescent.

    PubMed

    Senkovskiy, B V; Pfeiffer, M; Alavi, S K; Bliesener, A; Zhu, J; Michel, S; Fedorov, A V; German, R; Hertel, D; Haberer, D; Petaccia, L; Fischer, F R; Meerholz, K; van Loosdrecht, P H M; Lindfors, K; Grüneis, A

    2017-04-03

    We demonstrate the alignment-preserving transfer of parallel graphene nanoribbons (GNRs) onto insulating substrates. The photophysics of such samples is characterized by polarized Raman and photoluminescence (PL) spectroscopies. The Raman scattered light and the PL are polarized along the GNR axis. The Raman cross section as a function of excitation energy has distinct excitonic peaks associated with transitions between the one-dimensional parabolic subbands. We find that the PL of GNRs is intrinsically low but can be strongly enhanced by blue laser irradiation in ambient conditions or hydrogenation in ultrahigh vacuum. These functionalization routes cause the formation of sp(3) defects in GNRs. We demonstrate the laser writing of luminescent patterns in GNR films for maskless lithography by the controlled generation of defects. Our findings set the stage for further exploration of the optical properties of GNRs on insulating substrates and in device geometries.

  3. Tunable nanoscale graphene magnetometers.

    PubMed

    Pisana, Simone; Braganca, Patrick M; Marinero, Ernesto E; Gurney, Bruce A

    2010-01-01

    The detection of magnetic fields with nanoscale resolution is a fundamental challenge for scanning probe magnetometry, biosensing, and magnetic storage. Current technologies based on giant magnetoresistance and tunneling magnetoresistance are limited at small sizes by thermal magnetic noise and spin-torque instability. These limitations do not affect Hall sensors consisting of high mobility semiconductors or metal thin films, but the loss of magnetic flux throughout the sensor's thickness greatly limits spatial resolution and sensitivity. Here we demonstrate graphene extraordinary magnetoresistance devices that combine the Hall effect and enhanced geometric magnetoresistance, yielding sensitivities rivaling that of state of the art sensors but do so with subnanometer sense layer thickness at the sensor surface. Back-gating provides the ability to control sensor characteristics, which can mitigate both inherent variations in material properties and fabrication-induced device-to-device variability that is unavoidable at the nanoscale.

  4. Charging Graphene for Energy Storage

    SciTech Connect

    Liu, Jun

    2014-10-06

    Since 2004, graphene, including single atomic layer graphite sheet, and chemically derived graphene sheets, has captured the imagination of researchers for energy storage because of the extremely high surface area (2630 m2/g) compared to traditional activated carbon (typically below 1500 m2/g), excellent electrical conductivity, high mechanical strength, and potential for low cost manufacturing. These properties are very desirable for achieving high activity, high capacity and energy density, and fast charge and discharge. Chemically derived graphene sheets are prepared by oxidation and reduction of graphite1 and are more suitable for energy storage because they can be made in large quantities. They still contain multiply stacked graphene sheets, structural defects such as vacancies, and oxygen containing functional groups. In the literature they are also called reduced graphene oxide, or functionalized graphene sheets, but in this article they are all referred to as graphene for easy of discussion. Two important applications, batteries and electrochemical capacitors, have been widely investigated. In a battery material, the redox reaction occurs at a constant potential (voltage) and the energy is stored in the bulk. Therefore, the energy density is high (more than 100 Wh/kg), but it is difficult to rapidly charge or discharge (low power, less than 1 kW/kg)2. In an electrochemical capacitor (also called supercapacitors or ultracapacitor in the literature), the energy is stored as absorbed ionic species at the interface between the high surface area carbon and the electrolyte, and the potential is a continuous function of the state-of-charge. The charge and discharge can happen rapidly (high power, up to 10 kW/kg) but the energy density is low, less than 10 Wh/kg2. A device that can have both high energy and high power would be ideal.

  5. Flexible Graphene Composites for Human Space Flight Applications

    NASA Technical Reports Server (NTRS)

    Sosa, Edward D.

    2013-01-01

    Graphene oxide allows for better dispersion stability in aqueous and organic solvents. Stabilizers provide dispersion of pristine graphene. Roll coating provide the best coverage of polyurethane sheets. Graphene and GO coated polyurethane used to fabricate flexible laminate composite. Permeation testing indicates that pristine graphene acts as a better gas barrier material. Continuous graphene films are expected to provide even better gas barrier properties.

  6. Switching of Photonic Crystal Lasers by Graphene.

    PubMed

    Hwang, Min-Soo; Kim, Ha-Reem; Kim, Kyoung-Ho; Jeong, Kwang-Yong; Park, Jin-Sung; Choi, Jae-Hyuck; Kang, Ju-Hyung; Lee, Jung Min; Park, Won Il; Song, Jung-Hwan; Seo, Min-Kyo; Park, Hong-Gyu

    2017-03-08

    Unique features of graphene have motivated the development of graphene-integrated photonic devices. In particular, the electrical tunability of graphene loss enables high-speed modulation of light and tuning of cavity resonances in graphene-integrated waveguides and cavities. However, efficient control of light emission such as lasing, using graphene, remains a challenge. In this work, we demonstrate on/off switching of single- and double-cavity photonic crystal lasers by electrical gating of a monolayer graphene sheet on top of photonic crystal cavities. The optical loss of graphene was controlled by varying the gate voltage Vg, with the ion gel atop the graphene sheet. First, the fundamental properties of graphene were investigated through the transmittance measurement and numerical simulations. Next, optically pumped lasing was demonstrated for a graphene-integrated single photonic crystal cavity at Vg below -0.6 V, exhibiting a low lasing threshold of ∼480 μW, whereas lasing was not observed at Vg above -0.6 V owing to the intrinsic optical loss of graphene. Changing quality factor of the graphene-integrated photonic crystal cavity enables or disables the lasing operation. Moreover, in the double-cavity photonic crystal lasers with graphene, switching of individual cavities with separate graphene sheets was achieved, and these two lasing actions were controlled independently despite the close distance of ∼2.2 μm between adjacent cavities. We believe that our simple and practical approach for switching in graphene-integrated active photonic devices will pave the way toward designing high-contrast and ultracompact photonic integrated circuits.

  7. Noncovalent Functionalization of Graphene and Graphene Oxide for Energy Materials, Biosensing, Catalytic, and Biomedical Applications.

    PubMed

    Georgakilas, Vasilios; Tiwari, Jitendra N; Kemp, K Christian; Perman, Jason A; Bourlinos, Athanasios B; Kim, Kwang S; Zboril, Radek

    2016-05-11

    This Review focuses on noncovalent functionalization of graphene and graphene oxide with various species involving biomolecules, polymers, drugs, metals and metal oxide-based nanoparticles, quantum dots, magnetic nanostructures, other carbon allotropes (fullerenes, nanodiamonds, and carbon nanotubes), and graphene analogues (MoS2, WS2). A brief description of π-π interactions, van der Waals forces, ionic interactions, and hydrogen bonding allowing noncovalent modification of graphene and graphene oxide is first given. The main part of this Review is devoted to tailored functionalization for applications in drug delivery, energy materials, solar cells, water splitting, biosensing, bioimaging, environmental, catalytic, photocatalytic, and biomedical technologies. A significant part of this Review explores the possibilities of graphene/graphene oxide-based 3D superstructures and their use in lithium-ion batteries. This Review ends with a look at challenges and future prospects of noncovalently modified graphene and graphene oxide.

  8. Control of Superhydrophilic and Superhydrophobic Graphene Interface

    PubMed Central

    Dong, Jing; Yao, Zhaohui; Yang, Tianzhong; Jiang, Lili; Shen, Chengmin

    2013-01-01

    Superhydrophobic and superhydrophilic properties of chemically-modified graphene have been achieved in larger-area vertically aligned few-layer graphene nanosheets (FLGs), prepared on Si (111) substrate by microwave plasma chemical vapor deposition (MPCVD). Furthermore, in order to enhance wettability, silicon wafers with microstructures were fabricated, on which graphene nanosheets were grown and modified by a chemical method to form hydrophilic and hydrophobic structures. A superhydrophilic graphene surface (contact angle 0°) and a superhydrophobic graphene surface (contact angle 152.0°) were obtained. The results indicate that the microstructured silicon enhances the hydrophilic and hydrophobic wettabilities significantly.

  9. Single-mode cylindrical graphene plasmon waveguide

    NASA Astrophysics Data System (ADS)

    Yang, Jianfeng; Yang, Jingjing; Huang, Ming

    2016-08-01

    A cylindrical graphene plasmon waveguide (CGPW) which consists of two rolled graphene ribbons, a dielectric core and a dielectric interlayer is proposed. An analytical model for the single-mode condition and cutoff frequency of high-order graphene surface plasmon (GSP) modes is presented and verified by finite element method (FEM) simulations. Single-mode operation region of CGPW is identified in the frequency-radius space. By varying the separation between two graphene sheets and the Fermi level of graphene, a large tunability of the mode behavior is also demonstrated. The proposed structure may provide a new freedom to manipulate GSPs, and would lead to novel applications in optics.

  10. Surface acoustic wave propagation in graphene film

    SciTech Connect

    Roshchupkin, Dmitry Plotitcyna, Olga; Matveev, Viktor; Kononenko, Oleg; Emelin, Evgenii; Irzhak, Dmitry; Ortega, Luc; Zizak, Ivo; Erko, Alexei; Tynyshtykbayev, Kurbangali; Insepov, Zinetula

    2015-09-14

    Surface acoustic wave (SAW) propagation in a graphene film on the surface of piezoelectric crystals was studied at the BESSY II synchrotron radiation source. Talbot effect enabled the visualization of the SAW propagation on the crystal surface with the graphene film in a real time mode, and high-resolution x-ray diffraction permitted the determination of the SAW amplitude in the graphene/piezoelectric crystal system. The influence of the SAW on the electrical properties of the graphene film was examined. It was shown that the changing of the SAW amplitude enables controlling the magnitude and direction of current in graphene film on the surface of piezoelectric crystals.

  11. Surface acoustic wave propagation in graphene film

    NASA Astrophysics Data System (ADS)

    Roshchupkin, Dmitry; Ortega, Luc; Zizak, Ivo; Plotitcyna, Olga; Matveev, Viktor; Kononenko, Oleg; Emelin, Evgenii; Erko, Alexei; Tynyshtykbayev, Kurbangali; Irzhak, Dmitry; Insepov, Zinetula

    2015-09-01

    Surface acoustic wave (SAW) propagation in a graphene film on the surface of piezoelectric crystals was studied at the BESSY II synchrotron radiation source. Talbot effect enabled the visualization of the SAW propagation on the crystal surface with the graphene film in a real time mode, and high-resolution x-ray diffraction permitted the determination of the SAW amplitude in the graphene/piezoelectric crystal system. The influence of the SAW on the electrical properties of the graphene film was examined. It was shown that the changing of the SAW amplitude enables controlling the magnitude and direction of current in graphene film on the surface of piezoelectric crystals.

  12. Ion transport in graphene nanofluidic channels.

    PubMed

    Xie, Quan; Xin, Fang; Park, Hyung Gyu; Duan, Chuanhua

    2016-12-01

    Carbon nanofluidic structures made of carbon nanotubes or graphene/graphene oxide have shown great promise in energy and environment applications due to the newly discovered fast and selective mass transport. However, they have yet to be utilized in nanofluidic devices for lab-on-a-chip applications because of great challenges in their fabrication and integration. Herein we report the fabrication of two-dimensional planar graphene nanochannel devices and the study of ion transport inside a graphene nanochannel array. A MEMS fabrication process that includes controlled nanochannel etching, graphene wet transfer, and vacuum anodic bonding is developed to fabricate graphene nanochannels where graphene conformally coats the channel surfaces. We observe higher ionic conductance inside the graphene nanochannels compared with silica nanochannels with the same geometries at low electrolyte concentrations (10(-6) M-10(-2) M). Enhanced electroosmotic flow due to the boundary slip at graphene surfaces is attributed to the measured higher conductance in the graphene nanochannels. Our results also suggest that the surface charge on the graphene surface, originating from the dissociation of oxygen-containing functional groups, is crucial to the enhanced electroosmotic flow inside the nanochannels.

  13. Interlayer quality dependent graphene spin valve

    NASA Astrophysics Data System (ADS)

    Iqbal, Muhammad Zahir; Hussain, Ghulam; Siddique, Salma; Iqbal, Muhammad Waqas; Murtaza, Ghulam; Ramay, Shahid Mahmood

    2017-01-01

    It is possible to utilize the new class of materials for emerging two-dimensional (2D) spintronic applications. Here, the role of defects in the graphene interlayer and its influence on the spin valve signal is reported. The emergence of D peak in Raman spectrum reveals defects in the graphene layer. The linear I-V curve for defective and non-defective graphene samples indicate the ohmic nature of NiFe and graphene contact. A non-uniform magnetoresistive effect with a bump is persistently observed for defective graphene device at various temperatures, while a smooth and symmetric signal is detected for non-defective graphene spin valve. Parallel and antiparallel alignments of magnetization of magnetic materials shows low and high resistance states, respectively. The magnetoresistance (MR) ratio for defective graphene NiFe/graphene/NiFe spin valve is measured to be 0.16% at 300 K which progresses to 0.39% for non-defective graphene device at the same temperature. Similarly at 4.2 K the MR ratios are reported to be 0.41% and 0.78% for defective and non-defective graphene devices, respectively. Our investigation provides an evidence for relatively better response of the spin valve signal with high quality graphene interlayer.

  14. Electronic Transport in Novel Graphene Nanostructures

    NASA Astrophysics Data System (ADS)

    Gannett, William Joy

    Graphene, a single sheet of sp2-bonded carbon atoms, is a two-dimensional material with an array of unique electronic, chemical, and mechanical properties. Applications including high performance transistors, chemical sensors, and composite materials have already been demonstrated. The introduction of chemical vapor deposition growth of monolayer graphene was an important step towards scalability of such devices. In addition to scalability, the exploration and application of these properties require the fabrication of high quality devices with low carrier scattering. They also require the development of unique geometries and materials combinations to exploit the highly tunable nature of graphene. This dissertation presents the synthesis of materials, fabrication of devices, and measurement of those devices for three previously unexplored types of graphene devices. The first type of device is a field effect transistor made from chemical vapor deposited (CVD) graphene on hexagonal boron nitride (hBN) substrates. We demonstrate a significant improvement in carrier mobility from hBN substrates and are able to explore the sources of scattering in CVD graphene. The second type of device, fluorinated graphene transistors, allows us to examine doping and disorder effects from fluorination of the graphene crystal as well as electronic transport through unfluorinated folds in the graphene. With the third type of device we demonstrate a new route to graphene nanoribbon devices using both hBN flakes and BN nanotubes that may reduce disorder and allow precise measurements of quantum phenomena in graphene nanoribbons.

  15. Majorana Zero Modes in Graphene

    NASA Astrophysics Data System (ADS)

    San-Jose, P.; Lado, J. L.; Aguado, R.; Guinea, F.; Fernández-Rossier, J.

    2015-10-01

    A clear demonstration of topological superconductivity (TS) and Majorana zero modes remains one of the major pending goals in the field of topological materials. One common strategy to generate TS is through the coupling of an s -wave superconductor to a helical half-metallic system. Numerous proposals for the latter have been put forward in the literature, most of them based on semiconductors or topological insulators with strong spin-orbit coupling. Here, we demonstrate an alternative approach for the creation of TS in graphene-superconductor junctions without the need for spin-orbit coupling. Our prediction stems from the helicity of graphene's zero-Landau-level edge states in the presence of interactions and from the possibility, experimentally demonstrated, of tuning their magnetic properties with in-plane magnetic fields. We show how canted antiferromagnetic ordering in the graphene bulk close to neutrality induces TS along the junction and gives rise to isolated, topologically protected Majorana bound states at either end. We also discuss possible strategies to detect their presence in graphene Josephson junctions through Fraunhofer pattern anomalies and Andreev spectroscopy. The latter, in particular, exhibits strong unambiguous signatures of the presence of the Majorana states in the form of universal zero-bias anomalies. Remarkable progress has recently been reported in the fabrication of the proposed type of junctions, which offers a promising outlook for Majorana physics in graphene systems.

  16. 3D Printable Graphene Composite

    PubMed Central

    Wei, Xiaojun; Li, Dong; Jiang, Wei; Gu, Zheming; Wang, Xiaojuan; Zhang, Zengxing; Sun, Zhengzong

    2015-01-01

    In human being’s history, both the Iron Age and Silicon Age thrived after a matured massive processing technology was developed. Graphene is the most recent superior material which could potentially initialize another new material Age. However, while being exploited to its full extent, conventional processing methods fail to provide a link to today’s personalization tide. New technology should be ushered in. Three-dimensional (3D) printing fills the missing linkage between graphene materials and the digital mainstream. Their alliance could generate additional stream to push the graphene revolution into a new phase. Here we demonstrate for the first time, a graphene composite, with a graphene loading up to 5.6 wt%, can be 3D printable into computer-designed models. The composite’s linear thermal coefficient is below 75 ppm·°C−1 from room temperature to its glass transition temperature (Tg), which is crucial to build minute thermal stress during the printing process. PMID:26153673

  17. Graphene-based nanowire supercapacitors.

    PubMed

    Chen, Zhi; Yu, Dingshan; Xiong, Wei; Liu, Peipei; Liu, Yong; Dai, Liming

    2014-04-01

    We present a new type of electrochemical supercapacitors based on graphene nanowires. Graphene oxide (GO)/polypyrrole (PPy) nanowires are prepared via electrodepostion of GO/PPy composite into a micoroporous Al2O3 template, followed by the removal of template. PPy is electrochemically doped by oxygen-containing functional groups of the GO to enhance the charging/discharging rates of the supercapacitor. A high capacitance 960 F g(-1) of the GO/PPy nanowires is obtained due to the large surface area of the vertically aligned nanowires and the intimate contact between the nanowires and the substrate electrode. The capacitive performance remains stable after charging and discharging for 300 cycles. To improve the thermal stability and long-term charge storage, GO is further electrochemically reduced into graphene and PPy is subsequently thermally carbonized, leading to a high capacitance of 200 F g(-1) for the resultant pure reduced graphene oxide/carbon based nanowire supercapacitor. This value of capacitance (200 F g(-1)) is higher than that of conventional porous carbon materials while the reduced graphene oxide/carbon nanowires show a lower Faraday resistance and higher thermal stability than the GO/PPy nanowires.

  18. Work Function Engineering of Graphene

    PubMed Central

    Garg, Rajni; Dutta, Naba K.; Roy Choudhury, Namita

    2014-01-01

    Graphene is a two dimensional one atom thick allotrope of carbon that displays unusual crystal structure, electronic characteristics, charge transport behavior, optical clarity, physical & mechanical properties, thermal conductivity and much more that is yet to be discovered. Consequently, it has generated unprecedented excitement in the scientific community; and is of great interest to wide ranging industries including semiconductor, optoelectronics and printed electronics. Graphene is considered to be a next-generation conducting material with a remarkable band-gap structure, and has the potential to replace traditional electrode materials in optoelectronic devices. It has also been identified as one of the most promising materials for post-silicon electronics. For many such applications, modulation of the electrical and optical properties, together with tuning the band gap and the resulting work function of zero band gap graphene are critical in achieving the desired properties and outcome. In understanding the importance, a number of strategies including various functionalization, doping and hybridization have recently been identified and explored to successfully alter the work function of graphene. In this review we primarily highlight the different ways of surface modification, which have been used to specifically modify the band gap of graphene and its work function. This article focuses on the most recent perspectives, current trends and gives some indication of future challenges and possibilities. PMID:28344223

  19. Graphene-based nanomaterials for bioimaging.

    PubMed

    Lin, Jing; Chen, Xiaoyuan; Huang, Peng

    2016-10-01

    Graphene-based nanomaterials, due to their unique physicochemical properties, versatile surface functionalization, ultra-high surface area, and good biocompatibility, have attracted considerable interest in biomedical applications such as biosensors, drug delivery, bioimaging, theranostics, and so on. In this review, we will summarize the current advances in bioimaging of graphene-based nanomaterials, including graphene, graphene oxide (GO), reduced graphene oxide (rGO), graphene quantum dots (GQDs), and their derivatives. There are two methods to synthesize graphene-based nanomaterials: in situ synthesis and binding method. We will highlight the molecular imaging modalities including optical imaging (fluorescence (FL), two-photon FL, and Raman imaging), PET/SPECT (positron emission tomography/single photon emission computed tomography), MRI (magnetic resonance imaging), PAI (photoacoustic imaging), CT (computed tomography), and multimodal imaging. In the end, we will elaborate on the prospects and challenges of their future bioimaging applications.

  20. Tunable beam steering enabled by graphene metamaterials.

    PubMed

    Orazbayev, B; Beruete, M; Khromova, I

    2016-04-18

    We demonstrate tunable mid-infrared (MIR) beam steering devices based on multilayer graphene-dielectric metamaterials. The effective refractive index of such metamaterials can be manipulated by changing the chemical potential of each graphene layer. This can arbitrarily tailor the spatial distribution of the phase of the transmitted beam, providing mechanisms for active beam steering. Three different beam steerer (BS) designs are discussed: a graded-index (GRIN) graphene-based metamaterial block, an array of metallic waveguides filled with graphene-dielectric metamaterial and an array of planar waveguides created in a graphene-dielectric metamaterial block with a specific spatial profile of graphene sheets doping. The performances of the BSs are numerically analyzed, showing the tunability of the proposed designs for a wide range of output angles (up to approximately 70°). The proposed graphene-based tunable beam steering can be used in tunable transmitter/receiver modules for infrared imaging and sensing.

  1. Ultra-dark graphene stack metamaterials

    NASA Astrophysics Data System (ADS)

    Chugh, Sunny; Man, Mengren; Chen, Zhihong; Webb, Kevin J.

    2015-02-01

    We present a fabrication method to achieve a graphene stack metamaterial, a periodic array of unit cells composed of graphene and a thin insulating spacer, that allows accumulation of the strong absorption from individual graphene sheets and low reflectivity from the stack. The complex sheet conductivity of graphene from experimental data models the measured power transmitted as a function of wavelength and number of periods in the stack. Simulated results based on the extracted graphene complex sheet conductivity for thicker stacks suggest that the graphene stack reflectivity and the per-unit-length absorption can be controlled to exceed the performance of competing light absorbers. Furthermore, the electrical properties of graphene coupled with the stack absorption characteristics provide for applications in optoelectronic devices.

  2. Graphene based enzymatic bioelectrodes and biofuel cells.

    PubMed

    Karimi, Anahita; Othman, Ali; Uzunoglu, Aytekin; Stanciu, Lia; Andreescu, Silvana

    2015-04-28

    The excellent electrical conductivity and ease of functionalization make graphene a promising material for use in enzymatic bioelectrodes and biofuel cells. Enzyme based biofuel cells have attracted substantial interest due to their potential to harvest energy from organic materials. This review provides an overview of the functional properties and applications of graphene in the construction of biofuel cells as alternative power sources. The review covers the current state-of-the-art research in graphene based nanomaterials (physicochemical properties and surface functionalities), the role of these parameters in enhancing electron transfer, the stability and activity of immobilized enzymes, and how enhanced power density can be achieved. Specific examples of enzyme immobilization methods, enzyme loading, stability and function on graphene, functionalized graphene and graphene based nanocomposite materials are discussed along with their advantages and limitations. Finally, a critical evaluation of the performance of graphene based enzymatic biofuel cells, the current status, challenges and future research needs are provided.

  3. Graphene based enzymatic bioelectrodes and biofuel cells

    NASA Astrophysics Data System (ADS)

    Karimi, Anahita; Othman, Ali; Uzunoglu, Aytekin; Stanciu, Lia; Andreescu, Silvana

    2015-04-01

    The excellent electrical conductivity and ease of functionalization make graphene a promising material for use in enzymatic bioelectrodes and biofuel cells. Enzyme based biofuel cells have attracted substantial interest due to their potential to harvest energy from organic materials. This review provides an overview of the functional properties and applications of graphene in the construction of biofuel cells as alternative power sources. The review covers the current state-of-the-art research in graphene based nanomaterials (physicochemical properties and surface functionalities), the role of these parameters in enhancing electron transfer, the stability and activity of immobilized enzymes, and how enhanced power density can be achieved. Specific examples of enzyme immobilization methods, enzyme loading, stability and function on graphene, functionalized graphene and graphene based nanocomposite materials are discussed along with their advantages and limitations. Finally, a critical evaluation of the performance of graphene based enzymatic biofuel cells, the current status, challenges and future research needs are provided.

  4. Graphene and its electrochemistry - an update.

    PubMed

    Ambrosi, Adriano; Chua, Chun Kiang; Latiff, Naziah Mohamad; Loo, Adeline Huiling; Wong, Colin Hong An; Eng, Alex Yong Sheng; Bonanni, Alessandra; Pumera, Martin

    2016-05-07

    The electrochemistry of graphene and its derivatives has been extensively researched in recent years. In the aspect of graphene preparation methods, the efficiencies of the top-down electrochemical exfoliation of graphite, the electrochemical reduction of graphene oxide and the electrochemical delamination of CVD grown graphene, are currently on par with conventional procedures. Electrochemical analysis of graphene oxide has revealed an unexpected inherent redox activity with, in some cases, an astonishing chemical reversibility. Furthermore, graphene modified with p-block elements has shown impressive electrocatalytic performances in processes which have been historically dominated by metal-based catalysts. Further progress has also been achieved in the practical usage of graphene in sensing and biosensing applications. This review is an update of our previous article in Chem. Soc. Rev. 2010, 39, 4146-4157, with special focus on the developments over the past two years.

  5. Efficient adsorbate transport on graphene by electromigration

    NASA Astrophysics Data System (ADS)

    Velizhanin, Kirill; Solenov, Dmitry

    2012-02-01

    Chemical functionalization of the surface of graphene holds promise for various applications ranging from nanoelectronics to surface catalysis and nano-assembling. In many practical situations it would be beneficial to be able to propel adsorbates along the graphene sheet in a controlled manner. We propose to use electromigration as an efficient means to transport adsorbates along the graphene surface. Within the tight-binding approximation for graphene, parametrized by density functional theory calculations, we estimate the contributions of the direct force and the electron wind force to the drift velocity of electromigration and demonstrate that the electromigration can be rather efficient. In particular, we show that the drift velocity of atomic oxygen covalently bound to graphene can reach up to 4 cm/s for realistic graphene samples. Further, we discuss ways to dynamically, i.e., during experiment, control the efficiency of electromigration by charging and/or local heating of graphene.

  6. Emerging frontiers of graphene in biomedicine.

    PubMed

    Byun, Jonghoe

    2015-02-01

    Graphene is a next-generation biomaterial with increasing biomedical applicability. As a new class of one-atom-thick nanosheets, it is a true two-dimensional honeycomb network nanomaterial that attracts interest in various scientific fields and is rapidly becoming the most widely studied carbon-based material. Since its discovery in 2004, its unique optical, mechanical, electronic, thermal, and magnetic properties are the basis of exploration of the potential applicability of graphene. Graphene materials, such as graphene oxide and its reduced form, are studied extensively in the biotechnology arena owing to their multivalent functionalization and efficient surface loading with various biomolecules. This review provides a brief summary of the recent progress in graphene and graphene oxide biological research together with current findings to spark novel applications in biomedicine. Graphene-based applications are progressively developing; hence, the opportunities and challenges of this rapidly growing field are discussed together with the versatility of these multifaceted materials.

  7. Thermal conductivity of twisted bilayer graphene

    NASA Astrophysics Data System (ADS)

    Li, Hongyang; Ying, Hao; Chen, Xiangping; Nika, Denis L.; Cocemasov, Alexandr I.; Cai, Weiwei; Balandin, Alexander A.; Chen, Shanshan

    2014-10-01

    We have investigated experimentally the thermal conductivity of suspended twisted bilayer graphene. The measurements were performed using an optothermal Raman technique. It was found that the thermal conductivity of twisted bilayer graphene is lower than that of monolayer graphene and the reference, Bernal stacked bilayer graphene in the entire temperature range examined (~300-700 K). This finding indicates that the heat carriers - phonons - in twisted bilayer graphene do not behave in the same manner as that observed in individual graphene layers. The decrease in the thermal conductivity found in twisted bilayer graphene was explained by the modification of the Brillouin zone due to plane rotation and the emergence of numerous folded phonon branches that enhance the phonon Umklapp and normal scattering. The results obtained are important for understanding thermal transport in two-dimensional systems.

  8. Optical Third-Harmonic Microscopy of Graphene

    NASA Astrophysics Data System (ADS)

    Dadap, Jerry I.; Hong, Sung-Young; Petrone, Nicholas W.; Yeh, Po-Chun; Hone, James C.; Osgood, Richard M., Jr.

    2013-03-01

    We report strong third-harmonic (TH) generation in monolayer graphene mounted on an amorphous silica substrate using a photon energy that is three-photon resonant with the exciton-shifted van Hove singularity at the M-point of graphene. Our polarization-dependent and azimuthal rotation measurements confirm the expected isotropic symmetry properties for the TH nonlinear optical process in graphene. Since this monolayer graphene TH signal exceeds that of bulk glass by more than two orders of magnitude, the signal contrast permits background-free scanning of graphene and provides structural information that is difficult to obtain via linear optical microscopy. We also discuss the dependence of TH signals on the number of graphene layers and compare the graphene signal strength with that from crystalline Au(111) sample. We acknowledge support from AFOSR MURI Program #FA9550-09-1-0705.

  9. Graphene-based nanoprobes for molecular diagnostics.

    PubMed

    Chen, Shixing; Li, Fuwu; Fan, Chunhai; Song, Shiping

    2015-10-07

    In recent years, graphene has received widespread attention owing to its extraordinary electrical, chemical, optical, mechanical and structural properties. Lately, considerable interest has been focused on exploring the potential applications of graphene in life sciences, particularly in disease-related molecular diagnostics. In particular, the coupling of functional molecules with graphene as a nanoprobe offers an excellent platform to realize the detection of biomarkers, such as nucleic acids, proteins and other bioactive molecules, with high performance. This article reviews emerging graphene-based nanoprobes in electrical, optical and other assay methods and their application in various strategies of molecular diagnostics. In particular, this review focuses on the construction of graphene-based nanoprobes and their special advantages for the detection of various bioactive molecules. Properties of graphene-based materials and their functionalization are also comprehensively discussed in view of the development of nanoprobes. Finally, future challenges and perspectives of graphene-based nanoprobes are discussed.

  10. Graphene-Based Optical Biosensors and Imaging

    SciTech Connect

    Tang, Zhiwen; He, Shijiang; Pei, Hao; Du, Dan; Fan, Chunhai; Lin, Yuehe

    2014-01-13

    This chapter focuses on the design, fabrication and application of graphene based optical nanobiosensors. The emerging graphene based optical nanobiosensors demonstrated the promising bioassay and biomedical applications thanking to the unique optical features of graphene. According to the different applications, the graphene can be tailored to form either fluorescent emitter or efficient fluorescence quencher. The exceptional electronic feature of graphene makes it a powerful platform for fabricating the SPR and SERS biosensors. Today the graphene based optical biosensors have been constructed to detect various targets including ions, small biomolecules, DNA/RNA and proteins. This chapter reviews the recent progress in graphene-based optical biosensors and discusses the opportunities and challenges in this field.

  11. Electrical conductivity of PFPA functionalized graphene

    NASA Astrophysics Data System (ADS)

    Plachinda, P.; Evans, D.; Solanki, R.

    2013-01-01

    Chemical modification of graphene by covalently functionalizing its surface potentially allows a wider flexibility in engineering electronic structure, in particular the local density of states of the carbon atoms bound to the modifier that can result in opening of the band gap. Such binding can involve covalent hydrogenation of graphene to modify hybridization of carbon atoms from sp2 to sp3 geometry [1-3]. Methods have also been developed to functionalize graphene covalently with molecular species [4-8]. Among these, perfluorophenylazide (PFPA) functionalization of graphene is well-developed using a nitrene intermediate. Films of this molecule also act as adhesion layers that allow production of long ribbons of exfoliated graphene [7-9]. We have developed a theory to predict electrical properties of PFPA functionalized graphene and compared it to experimental results. Conductivity of these PFPA functionalized ribbons of exfoliated graphene show good agreement with our theory.

  12. Chemical vapor deposition of graphene single crystals.

    PubMed

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

    2014-04-15

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

  13. Chemistry at the dirac point of graphene

    NASA Astrophysics Data System (ADS)

    Sarkar, Santanu

    Graphene holds great potential as an electronic material because of its excellent transport properties, which derive from its unique Fermi surface and ballistic conductance. It exhibits extremely high mobility [~250,000 cm*2/(V*s)]. Despite its extraordinary properties, the absence of a band-gap in graphene makes it unsuitable for its use as an active element in conventional field effect transistors (FETs). Another problem with pristine graphene is its lack of solution processability, which inhibits it applications in numerous fields such as printed electronics, transparent conductors, nano-biodevices, and thin film technologies involving fuel cells, capacitors and solar cells. My thesis is focused on addressing theses issue by application of covalent chemistry on graphene. We have applied the Kolbe electro-oxidation strategy to achieve an efficient quasi-reversible electrochemical grafting of the naphthylmethyl radicals to graphene. The method facilitates reversible bandgap engineering in graphene and preparation of electrochemically erasable organic dielectric films. We have discovered that the zero-band-gap electronic structure of graphene enables it to function as either the diene or the dienophile in the Diels-Alder (DA) reaction, and this versatile synthetic method offers a powerful strategy for the reversible modification of the electronic properties of graphene under very mild conditions. We show that the application of the Diels-Alder (DA) chemistry to graphene, which is capable of simultaneous formation of a pair of sp3-carbon centers (balanced divacancies) in graphene, can selectively produce DA-modified graphene FET devices with mobility between 1,000-6,000 cm2V-1s-1 (with a variable range hopping transport mechanism). Most of the covalent chemistry applied on graphene leads to the change in hybridization of graphene sp2 carbon to sp3 (destructive hybridization) and the FET devices based on such covalently modified graphene shows a drastic reduction of

  14. Possible spin-triplet superconducting phase in the La0.7Sr0.3MnO3/YBa2Cu3O7/La0.7Sr0.3MnO3 trilayer

    NASA Astrophysics Data System (ADS)

    Dybko, K.; Werner-Malento, K.; Aleshkevych, P.; Wojcik, M.; Sawicki, M.; Przyslupski, P.

    2009-10-01

    We report on results of conductance spectroscopy measurements in the current-in-plane (CIP) and current-perpendicular-to-plane (CPP) geometries ([001] and [100] directions respectively) of La0.7Sr0.3MnO3/YBa2Cu3O7/La0.7Sr0.3MnO3 (LSMO/YBCO/LSMO) nonsymmetric trilayer structures in order to search for signature of the formation of spin-triplet phase. This trilayer shows an enhancement of the superconducting transition temperature in magnetic field parallel to the plane. We argue that this enhancement is a result of the formation of spin-triplet phase. The differential conductance (dI/dV) spectra show fully developed zero-bias conductance peaks (ZBCP). The ZBCP measured in CIP geometry demonstrates a sharp shape. This could be attributed to a spin-triplet state arising from the proximity effect at the interface of the half-metal with the d -wave superconductor, similar as was predicted theoretically for the p -wave superconductor and observed experimentally in p -wave Sr2RuO4 superconductor. The measurements of the dI/dV in CPP geometry reveal a V shape similar as was experimentally observed in YBCO superconductor and predicted theoretically for superconductor with a dx2-y2 pairing symmetry of the order parameter.

  15. Electronic Transport in Graphene Heterostructures

    NASA Astrophysics Data System (ADS)

    Young, Andrea F.; Kim, Philip

    2011-03-01

    The elementary excitations of monolayer graphene, which behave as massless Dirac particles, make it a fascinating venue in which to study relativistic quantum phenomena. One notable example is Klein tunneling, a phenomena in which electrons convert to holes to tunnel through a potential barrier. However, the omnipresence of charged impurities in substrate-supported samples keep the overall charge distribution nonuniform, obscuring much of this "Dirac" point physics in large samples. Using local gates, one can create tunable heterojunctions in graphene, isolating the contribution of small regions of the samples to transport. In this review, we give an overview of quantum transport theory and experiment on locally gated graphene heterostructures, with an emphasis on bipolar junctions.

  16. Quantum transport localization through graphene.

    PubMed

    Srivastava, Saurabh; Kino, Hiori; Nakaharai, Shu; Verveniotis, Elisseos; Okawa, Yuji; Ogawa, Shinichi; Joachim, Christian; Aono, Masakazu

    2017-01-20

    Localization of atomic defect-induced electronic transport through a single graphene layer is calculated using a full-valence electronic structure description as a function of the defect density and taking into account the atomic-scale deformations of the layer. The elementary electronic destructive interferences leading to Anderson localization are analyzed. The low-voltage current intensity decreases with increasing length and defect density, with a calculated localization length ζ = 3.5 nm for a defect density of 5%. The difference from the experimental defect density of 0.5% required for an oxide surface-supported graphene to obtain the same ζ is discussed, pointing out how interactions of the graphene supporting surface and surface chemical modifications also control electronic transport localization.

  17. Molecule-hugging graphene nanopores

    PubMed Central

    Garaj, Slaven; Liu, Song; Golovchenko, Jene A.; Branton, Daniel

    2013-01-01

    It has recently been recognized that solid-state nanopores in single-atomic-layer graphene membranes can be used to electronically detect and characterize single long charged polymer molecules. We have now fabricated nanopores in single-layer graphene that are closely matched to the diameter of a double-stranded DNA molecule. Ionic current signals during electrophoretically driven translocation of DNA through these nanopores were experimentally explored and theoretically modeled. Our experiments show that these nanopores have unusually high sensitivity (0.65 nA/Å) to extremely small changes in the translocating molecule’s outer diameter. Such atomically short graphene nanopores can also resolve nanoscale-spaced molecular structures along the length of a polymer, but do so with greatest sensitivity only when the pore and molecule diameters are closely matched. Modeling confirms that our most closely matched pores have an inherent resolution of ≤0.6 nm along the length of the molecule. PMID:23836648

  18. Graphene based multifunctional flame sensor.

    PubMed

    Ferry, Darim B; Pavan Kumar, R; Reddy, Siva K; Mukherjee, Anwesha; Misra, Abha

    2015-05-15

    Recently, graphene has attracted much attention due to its unique electrical and thermal properties along with its high surface area, and hence presents an ideal sensing material. We report a novel configuration of a graphene based flame sensor by exploiting the response of few layer graphene to a flame along two different directions, where flame detection results from a difference in heat transfer mechanisms. A complete sensor module was developed with a signal conditioning circuit that compensates for any drift in the baseline of the sensor, along with a flame detection algorithm implemented in a microcontroller to detect the flame. A pre-defined threshold for either of the sensors is tunable, which can be varied based on the nature of the flame, hence presenting a system that can be used for detection of any kind of flame. This finding also presents a scalable method that opens avenues to modify complicated sensing schemes.

  19. Quantum friction between graphene sheets

    NASA Astrophysics Data System (ADS)

    Farias, M. Belén; Fosco, César D.; Lombardo, Fernando C.; Mazzitelli, Francisco D.

    2017-03-01

    We study the Casimir friction phenomenon in a system consisting of two flat, infinite, and parallel graphene sheets, which are coupled to the vacuum electromagnetic (EM) field. Those couplings are implemented, in the description we use, by means of specific terms in the effective action for the EM field. They incorporate the distinctive properties of graphene, as well as the relative sliding motion of the sheets. Based on this description, we evaluate two observables due to the same physical effect: the probability of vacuum decay and the frictional force. The system exhibits a threshold for frictional effects; namely, they only exist if the speed of the sliding motion is larger than the Fermi velocity of the charge carriers in graphene.

  20. Transparent conductive graphene textile fibers

    PubMed Central

    Neves, A. I. S.; Bointon, T. H.; Melo, L. V.; Russo, S.; de Schrijver, I.; Craciun, M. F.; Alves, H.

    2015-01-01

    Transparent and flexible electrodes are widely used on a variety of substrates such as plastics and glass. Yet, to date, transparent electrodes on a textile substrate have not been explored. The exceptional electrical, mechanical and optical properties of monolayer graphene make it highly attractive as a transparent electrode for applications in wearable electronics. Here, we report the transfer of monolayer graphene, grown by chemical vapor deposition on copper foil, to fibers commonly used by the textile industry. The graphene-coated fibers have a sheet resistance as low as ~1 kΩ per square, an equivalent value to the one obtained by the same transfer process onto a Si substrate, with a reduction of only 2.3 per cent in optical transparency while keeping high stability under mechanical stress. With this approach, we successfully achieved the first example of a textile electrode, flexible and truly embedded in a yarn. PMID:25952133

  1. Graphene-based conformal devices.

    PubMed

    Park, Yong Ju; Lee, Seoung-Ki; Kim, Min-Seok; Kim, Hyunmin; Ahn, Jong-Hyun

    2014-08-26

    Despite recent progress in bendable and stretchable thin-film transistors using novel designs and materials, the development of conformal devices remains limited by the insufficient flexibility of devices. Here, we demonstrate the fabrication of graphene-based conformal and stretchable devices such as transistor and tactile sensor on a substrate with a convoluted surface by scaling down the device thickness. The 70 nm thick graphene-based conformal devices displayed a much lower bending stiffness than reported previously. The demonstrated devices provided excellent conformal coverage over an uneven animal hide surface without the need for an adhesive. In addition, the ultrathin graphene devices formed on the three-dimensionally curved animal hide exhibited stable electrical characteristics, even under repetitive bending and twisting. The advanced performance and flexibility demonstrated here show promise for the development and adoption of wearable electronics in a wide range of future applications.

  2. Antibacterial activity of graphene layers

    NASA Astrophysics Data System (ADS)

    Dybowska-Sarapuk, Ł.; Kotela, A.; Krzemiński, J.; Janczak, D.; Wróblewska, M.; Marchel, H.; Łegorz, P.; Jakubowska, M.

    2016-09-01

    The bacterial biofilm is a direct cause of complications in management of various medical conditions. There is an ongoing search for a feasible method to prevent its growth, as an alternative to antibiotics, which are ineffective. The aim of the study was to prepare and evaluate a detailed algorithm for production of graphene coatings, using economically efficient methods of printed electronics (such as ink-jet printing or spray coating), and assess their antibacterial properties. Based on the preliminary results of our work we suggest that graphene coating may inhibit the formation of microbial biofilms. Further research is needed to verify antibacterial properties of graphene coatings and its future applications in prevention of biofilm-related infections, e.g. by coating surgical instruments, catheters or tracheostomy tubes. In addition, we propose a series of hypotheses to be evaluated in further work.

  3. Ion selectivity of graphene nanopores

    DOE PAGES

    Rollings, Ryan C.; Kuan, Aaron T.; Golovchenko, Jene A.

    2016-04-22

    As population growth continues to outpace development of water infrastructure in many countries, desalination (the removal of salts from seawater) at high energy efficiency will likely become a vital source of fresh water. Due to its atomic thinness combined with its mechanical strength, porous graphene may be particularly well-suited for electrodialysis desalination, in which ions are removed under an electric field via ion-selective pores. Here, we show that single graphene nanopores preferentially permit the passage of K+ cations over Cl- anions with selectivity ratios of over 100 and conduct monovalent cations up to 5 times more rapidly than divalent cations.more » Furthermore, the observed K+/Cl- selectivity persists in pores even as large as about 20 nm in diameter, suggesting that high throughput, highly selective graphene electrodialysis membranes can be fabricated without the need for subnanometer control over pore size.« less

  4. Ion selectivity of graphene nanopores

    SciTech Connect

    Rollings, Ryan C.; Kuan, Aaron T.; Golovchenko, Jene A.

    2016-04-22

    As population growth continues to outpace development of water infrastructure in many countries, desalination (the removal of salts from seawater) at high energy efficiency will likely become a vital source of fresh water. Due to its atomic thinness combined with its mechanical strength, porous graphene may be particularly well-suited for electrodialysis desalination, in which ions are removed under an electric field via ion-selective pores. Here, we show that single graphene nanopores preferentially permit the passage of K+ cations over Cl- anions with selectivity ratios of over 100 and conduct monovalent cations up to 5 times more rapidly than divalent cations. Furthermore, the observed K+/Cl- selectivity persists in pores even as large as about 20 nm in diameter, suggesting that high throughput, highly selective graphene electrodialysis membranes can be fabricated without the need for subnanometer control over pore size.

  5. Ion selectivity of graphene nanopores.

    PubMed

    Rollings, Ryan C; Kuan, Aaron T; Golovchenko, Jene A

    2016-04-22

    As population growth continues to outpace development of water infrastructure in many countries, desalination (the removal of salts from seawater) at high energy efficiency will likely become a vital source of fresh water. Due to its atomic thinness combined with its mechanical strength, porous graphene may be particularly well-suited for electrodialysis desalination, in which ions are removed under an electric field via ion-selective pores. Here, we show that single graphene nanopores preferentially permit the passage of K(+) cations over Cl(-) anions with selectivity ratios of over 100 and conduct monovalent cations up to 5 times more rapidly than divalent cations. Surprisingly, the observed K(+)/Cl(-) selectivity persists in pores even as large as about 20 nm in diameter, suggesting that high throughput, highly selective graphene electrodialysis membranes can be fabricated without the need for subnanometer control over pore size.

  6. Quantum transport localization through graphene

    NASA Astrophysics Data System (ADS)

    Srivastava, Saurabh; Kino, Hiori; Nakaharai, Shu; Verveniotis, Elisseos; Okawa, Yuji; Ogawa, Shinichi; Joachim, Christian; Aono, Masakazu

    2017-01-01

    Localization of atomic defect-induced electronic transport through a single graphene layer is calculated using a full-valence electronic structure description as a function of the defect density and taking into account the atomic-scale deformations of the layer. The elementary electronic destructive interferences leading to Anderson localization are analyzed. The low-voltage current intensity decreases with increasing length and defect density, with a calculated localization length ζ = 3.5 nm for a defect density of 5%. The difference from the experimental defect density of 0.5% required for an oxide surface-supported graphene to obtain the same ζ is discussed, pointing out how interactions of the graphene supporting surface and surface chemical modifications also control electronic transport localization.

  7. Transparent conductive graphene textile fibers

    NASA Astrophysics Data System (ADS)

    Neves, A. I. S.; Bointon, T. H.; Melo, L. V.; Russo, S.; de Schrijver, I.; Craciun, M. F.; Alves, H.

    2015-05-01

    Transparent and flexible electrodes are widely used on a variety of substrates such as plastics and glass. Yet, to date, transparent electrodes on a textile substrate have not been explored. The exceptional electrical, mechanical and optical properties of monolayer graphene make it highly attractive as a transparent electrode for applications in wearable electronics. Here, we report the transfer of monolayer graphene, grown by chemical vapor deposition on copper foil, to fibers commonly used by the textile industry. The graphene-coated fibers have a sheet resistance as low as ~1 kΩ per square, an equivalent value to the one obtained by the same transfer process onto a Si substrate, with a reduction of only 2.3 per cent in optical transparency while keeping high stability under mechanical stress. With this approach, we successfully achieved the first example of a textile electrode, flexible and truly embedded in a yarn.

  8. Flexible transformation plasmonics using graphene.

    PubMed

    Lu, Wei Bing; Zhu, Wei; Xu, Hong Ju; Ni, Zhen Hua; Dong, Zheng Gao; Cui, Tie Jun

    2013-05-06

    The flexible control of surface plasmon polaritons (SPPs) is important and intriguing due to its wide application in novel plasmonic devices. Transformation optics (TO) offers the capability either to confine the SPP propagation on rigid curved/uneven surfaces, or to control the flow of SPPs on planar surfaces. However, TO has not permitted us to confine, manipulate, and control SPP waves on flexible curved surfaces. Here, we propose to confine and freely control flexible SPPs using TO and graphene. We show that SPP waves can be naturally confined and propagate on curved or uneven graphene surfaces with little bending and radiation losses, and the confined SPPs are further manipulated and controlled using TO. Flexible plasmonic devices are presented, including the bending waveguides, wave splitter, and Luneburg lens on curved surfaces. Together with the intrinsic flexibility, graphene can be served as a good platform for flexible transformation plasmonics.

  9. Toxicity of Graphene Shells, Graphene Oxide, and Graphene Oxide Paper Evaluated with Escherichia coli Biotests

    PubMed Central

    Efremova, Ludmila V.; Vasilchenko, Alexey S.; Rakov, Eduard G.; Deryabin, Dmitry G.

    2015-01-01

    The plate-like graphene shells (GS) produced by an original methane pyrolysis method and their derivatives graphene oxide (GO) and graphene oxide paper (GO-P) were evaluated with luminescent Escherichia coli biotests and additional bacterial-based assays which together revealed the graphene-family nanomaterials' toxicity and bioactivity mechanisms. Bioluminescence inhibition assay, fluorescent two-component staining to evaluate cell membrane permeability, and atomic force microscopy data showed GO expressed bioactivity in aqueous suspension, whereas GS suspensions and the GO-P surface were assessed as nontoxic materials. The mechanism of toxicity of GO was shown not to be associated with oxidative stress in the targeted soxS::lux and katG::lux reporter cells; also, GO did not lead to significant mechanical disruption of treated bacteria with the release of intracellular DNA contents into the environment. The well-coordinated time- and dose-dependent surface charge neutralization and transport and energetic disorders in the Escherichia coli cells suggest direct membrane interaction, internalization, and perturbation (i.e., “membrane stress”) as a clue to graphene oxide's mechanism of toxicity. PMID:26221608

  10. Graphene electrode modified with electrochemically reduced graphene oxide for label-free DNA detection.

    PubMed

    Li, Bing; Pan, Genhua; Avent, Neil D; Lowry, Roy B; Madgett, Tracey E; Waines, Paul L

    2015-10-15

    A novel printed graphene electrode modified with electrochemically reduced graphene oxide was developed for the detection of a specific oligonucleotide sequence. The graphene oxide was immobilized onto the surface of a graphene electrode via π-π bonds and electrochemical reduction of graphene oxide was achieved by cyclic voltammetry. A much higher redox current was observed from the reduced graphene oxide-graphene double-layer electrode, a 42% and 36.7% increase, respectively, in comparison with that of a bare printed graphene or reduced graphene oxide electrode. The good electron transfer activity is attributed to a combination of the large number of electroactive sites in reduced graphene oxide and the high conductivity nature of graphene. The probe ssDNA was further immobilized onto the surface of the reduced graphene oxide-graphene double-layer electrode via π-π bonds and then hybridized with its target cDNA. The change of peak current due to the hybridized dsDNA could be used for quantitative sensing of DNA concentration. It has been demonstrated that a linear range from 10(-7)M to 10(-12)M is achievable for the detection of human immunodeficiency virus 1 gene with a detection limit of 1.58 × 10(-13)M as determined by three times standard deviation of zero DNA concentration.

  11. Graphene Sandwiched Mesostructured Li-Ion Battery Electrodes.

    PubMed

    Liu, Jinyun; Zheng, Qiye; Goodman, Matthew D; Zhu, Haoyue; Kim, Jinwoo; Krueger, Neil A; Ning, Hailong; Huang, Xingjiu; Liu, Jinhuai; Terrones, Mauricio; Braun, Paul V

    2016-09-01

    A deterministic graphene-sandwiched Li-ion battery electrode consisting of an integrated 3D mesostructure of electrochemically active materials and graphene is presented. As demonstrations, electrodes with active nanomaterials that coat (V2 O5 @graphene@V2 O5 cathode) or are coated by (graphene@Si@graphene anode) graphene are fabricated. These electrodes exhibit high capacities and ultralong cycle lives (the cathode can be cycled over 2000 times with minimal capacity fade).

  12. Bending Rules in Graphene Kirigami

    NASA Astrophysics Data System (ADS)

    Grosso, Bastien F.; Mele, E. J.

    2015-11-01

    The three-dimensional shapes of graphene sheets produced by nanoscale cut-and-join kirigami are studied by combining large-scale atomistic simulations with continuum elastic modeling. Lattice segments are selectively removed from a graphene sheet, and the structure is allowed to close by relaxing in the third dimension. The surface relaxation is limited by a nonzero bending modulus which produces a smoothly modulated landscape instead of the ridge-and-plateau motif found in macroscopic lattice kirigami. The resulting surface shapes and their interactions are well described by a new set of microscopic kirigami rules that resolve the competition between bending and stretching energies.

  13. Bending Rules in Graphene Kirigami.

    PubMed

    Grosso, Bastien F; Mele, E J

    2015-11-06

    The three-dimensional shapes of graphene sheets produced by nanoscale cut-and-join kirigami are studied by combining large-scale atomistic simulations with continuum elastic modeling. Lattice segments are selectively removed from a graphene sheet, and the structure is allowed to close by relaxing in the third dimension. The surface relaxation is limited by a nonzero bending modulus which produces a smoothly modulated landscape instead of the ridge-and-plateau motif found in macroscopic lattice kirigami. The resulting surface shapes and their interactions are well described by a new set of microscopic kirigami rules that resolve the competition between bending and stretching energies.

  14. Versatile Flexible Graphene Multielectrode Arrays

    PubMed Central

    Kireev, Dmitry; Seyock, Silke; Ernst, Mathis; Maybeck, Vanessa; Wolfrum, Bernhard; Offenhäusser, Andreas

    2016-01-01

    Graphene is a promising material possessing features relevant to bioelectronics applications. Graphene microelectrodes (GMEAs), which are fabricated in a dense array on a flexible polyimide substrate, were investigated in this work for their performance via electrical impedance spectroscopy. Biocompatibility and suitability of the GMEAs for extracellular recordings were tested by measuring electrical activities from acute heart tissue and cardiac muscle cells. The recordings show encouraging signal-to-noise ratios of 65 ± 15 for heart tissue recordings and 20 ± 10 for HL-1 cells. Considering the low noise and excellent robustness of the devices, the sensor arrays are suitable for diverse and biologically relevant applications. PMID:28025564

  15. Versatile Flexible Graphene Multielectrode Arrays.

    PubMed

    Kireev, Dmitry; Seyock, Silke; Ernst, Mathis; Maybeck, Vanessa; Wolfrum, Bernhard; Offenhäusser, Andreas

    2016-12-23

    Graphene is a promising material possessing features relevant to bioelectronics applications. Graphene microelectrodes (GMEAs), which are fabricated in a dense array on a flexible polyimide substrate, were investigated in this work for their performance via electrical impedance spectroscopy. Biocompatibility and suitability of the GMEAs for extracellular recordings were tested by measuring electrical activities from acute heart tissue and cardiac muscle cells. The recordings show encouraging signal-to-noise ratios of 65 ± 15 for heart tissue recordings and 20 ± 10 for HL-1 cells. Considering the low noise and excellent robustness of the devices, the sensor arrays are suitable for diverse and biologically relevant applications.

  16. Ultrafast graphene oxide humidity sensors.

    PubMed

    Borini, Stefano; White, Richard; Wei, Di; Astley, Michael; Haque, Samiul; Spigone, Elisabetta; Harris, Nadine; Kivioja, Jani; Ryhänen, Tapani

    2013-12-23

    Sensors allow an electronic device to become a gateway between the digital and physical worlds, and sensor materials with unprecedented performance can create new applications and new avenues for user interaction. Graphene oxide can be exploited in humidity and temperature sensors with a number of convenient features such as flexibility, transparency and suitability for large-scale manufacturing. Here we show that the two-dimensional nature of graphene oxide and its superpermeability to water combine to enable humidity sensors with unprecedented response speed (∼30 ms response and recovery times). This opens the door to various applications, such as touchless user interfaces, which we demonstrate with a 'whistling' recognition analysis.

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

    PubMed

    Hatui, Goutam; Das, Chapal Kumar

    2012-10-01

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

  18. Synthesis and characterizations of graphene oxide and reduced graphene oxide nanosheets

    SciTech Connect

    Venkanna, M. Chakraborty, Amit K.

    2014-04-24

    Interest in graphene on its excellent mechanical, electrical, thermal and optical properties, it’s very high specific surface area, and our ability to influence these properties through chemical functionalization. Chemical reduction of graphene oxide is one of the main routes of preparation for large quantities of graphenes. Hydrazine hydrate used as reducing agent to prepare for the reduced graphene oxide (RGO). There are a number of methods for generating graphene and chemically modified graphene from natural graphite flakes, graphite derivative (such as graphite oxide) and graphite interaction compounds (i.e. expandable graphite). Here we review the use of colloidal suspensions of reduced graphene oxide (RGO) with large scalable, and is adaptable to a wide variety of applications. The graphene oxide (GO) and the reduced material (RGO) were characterized by XRD, UV-Vis spectroscopy, Thermo-gravimetric analysis (TGA), Raman spectroscopy and Field emission Scanning electron microscopy (FESEM) etc.

  19. Thermodynamics and kinetics of graphene chemistry: a graphene hydrogenation prototype study.

    PubMed

    Pham, Buu Q; Gordon, Mark S

    2016-12-07

    The thermodynamic and kinetic controls of graphene chemistry are studied computationally using a graphene hydrogenation reaction and polyaromatic hydrocarbons to represent the graphene surface. Hydrogen atoms are concertedly chemisorped onto the surface of graphene models of different shapes (i.e., all-zigzag, all-armchair, zigzag-armchair mixed edges) and sizes (i.e., from 16-42 carbon atoms). The second-order Z-averaged perturbation theory (ZAPT2) method combined with Pople double and triple zeta basis sets are used for all calculations. It is found that both the net enthalpy change and the barrier height of graphene hydrogenation at graphene edges are lower than at their interior surfaces. While the thermodynamic product distribution is mainly determined by the remaining π-islands of functionalized graphenes (Phys. Chem. Chem. Phys., 2013, 15, 3725-3735), the kinetics of the reaction is primarily correlated with the localization of the electrostatic potential of the graphene surface.

  20. Recent developments in superhydrophobic graphene and graphene-related materials: from preparation to potential applications.

    PubMed

    Wang, Jian-Nan; Zhang, Yong-Lai; Liu, Yan; Zheng, Wanhua; Lee, Luke P; Sun, Hong-Bo

    2015-04-28

    In the past decade, graphene has revealed a cornucopia of both fundamental science and potential applications due to its exceptional electrical, mechanical, thermal, and optical properties. Recently, increasing effort has been devoted to exploiting its new features, for example, wetting properties. Benefitting from its inherent material properties, graphene shows great potential for the fabrication of superhydrophobic surfaces, which could be potentially used for various anti-water applications. In this review, we summarize the recent developments in superhydrophobic graphene and graphene-related materials. Preparation strategies using pure graphene, graphene oxide, and graphene/polymer hybrids are presented and their potential applications are discussed. Finally, our own perspective of this dynamic field, including both current challenges and future demands, has been discussed. It is anticipated that the cooperation of the numerous merits of graphene and superhydrophobicity will lead to new opportunities for high-performance multifunctional devices.