Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session T17: Focus Session: Graphene Devices: Function, Fabrication, and Characterization: Graphene Nanostructures |
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Sponsoring Units: DMP Chair: Biddut Sarker, Purdue University Room: 102AB |
Thursday, March 5, 2015 11:15AM - 11:27AM |
T17.00001: In-plane electric polarization of bilayer graphene nanoribbon by interlayer bias voltage Ryo Okugawa, Junya Tanaka, Takashi Koretsune, Susumu Saito, Shuichi Murakami Bilayer graphene nanoribbons are known to show various energy bands depending on the shapes of the edges and the width of the nanoribbons. In particular, the energy bands of the graphene nanoribbons with armchair edges become gapless or gapped when the width changes. We theoretically study a polarization along the ribbon direction induced by an external interlayer bias voltage by using a tight-binding model, when the nanoribbon is insulating. We find that a polarization is induced for armchair-edges but not for zigzag-edges. The polarization shows different behavior depending on the width as well as the bias voltage. When the interlayer bias voltage is weak, the polarization has opposite signs depending on the width modulo three. This difference can be understood by an effective two-band model from the tight-binding model. Furthermore, our \textit{ab initio} calculations also agree with the results. On the other hand, under a strong bias voltage, we find that the polarization takes one-third or zero depending on the width modulo three. [Preview Abstract] |
Thursday, March 5, 2015 11:27AM - 11:39AM |
T17.00002: Characterization of graphene/metal interface and its modification by insertion of thin nano-carbon layer Akinobu Kanda, Kenta Katakura, Yu Ito, Youiti Ootuka Due to high mobility and atomic thickness, graphene is a promising candidate for the next-generation electronic material. While considerable effort has been devoted to achieve higher mobility in graphene films, relatively little attention has been paid to the effect of making contact between graphene and metals, which is indispensable to the electric devices. In general, at a graphene/metal interface, mainly due to the difference in work functions, carriers are injected from the metal to graphene. The resulting shift of Dirac point is not limited at the graphene/metal interface but extends by $\sim 1 \mu$m into the graphene channel, which affects more significantly the performance of graphene field effect devices with shorter channel. Here, we experimentally investigate the channel length dependence of graphene transport properties and extract the effect of metal contact (i.e., strength of carrier doping). Several metal species are investigated and results are compared with numerical models. Furthermore, we try to reduce the influence of metal contact by inserting a thin nano-carbon film at the interface. [Preview Abstract] |
Thursday, March 5, 2015 11:39AM - 11:51AM |
T17.00003: Ordered Self-assembled Alkane Monolayer on Graphite and Graphene Surface Yudan Su, Huiling Han, Feng Wang, Qun Cai, Chuanshan Tian, Y.R. Shen The 2D self-assembly of long chain alkane molecule on graphite and graphene had been studied with phase-sensitive sum-frequency vibrational spectroscopy (PS-SFVS) and scanning tunneling microscopy (STM). The spectrum of Im$\chi _{s}^{(2)} (\omega_{IR} )$ which directly characterizes the surface resonances, shows 10-cm$^{\mathrm{-1}}$ red-shift of the symmetric-stretch frequency of the CH$_{\mathrm{2}}$ groups pointing towards graphite (or graphene) surface indicating Van der Waals interaction in between. The Gibbs adsorption energy of polyethylene (PE, n $\sim$ 140) on graphite from chloroform solution was determined to be -42kJ/mol per molecule or -0.6 kJ/mol per CH$_{\mathrm{2}}$ unit. This large adsorption energy drives the long alkane chain to form an ordered self-assembled monolayer on graphite (or graphene). The sum frequency spectra suggest the orientation of carbon skeleton plane of alkane is predominately perpendicular to the graphite/graphene surface. Our STM result also provides clear evidence for the proposed molecular adsorption model. These results explain the large amount residual of long chain alkane on polystyrene (PS) or poly(methyl methacrylate) (PMMA) transferred graphene, and facilitate a better way to fabricate cleaner large-size graphene. [Preview Abstract] |
Thursday, March 5, 2015 11:51AM - 12:03PM |
T17.00004: Thin films of bottom-up synthesized graphene nanoribbons Mikhail Shekhirev, Alexey Lipatov, Timothy Vo, Mohammad Mehdi Pour, Alexander Sinitskii Bottom-up solution synthetic approaches for graphene nanoribbons (GNRs) receive a great deal of attention, because they yield large quantities of atomically precise GNRs with intriguing electronic and optical properties. However, poor solubility of these GNRs in conventional solvents remains a great challenge and limits their processability for applications in printable electronics, photovoltaics and composite materials. We studied the solubility of solution-synthesized GNRs in chlorosulfonic acid and developed a protocol for thin film fabrication that could be applied for different types of bottom-up synthesized GNRs. The developed procedure also provides control over the thickness of films that can be made as thin as one GNR thick. Reactivity of the GNRs with chlorosulfonic acid and electrical properties of fabricated films will also be discussed. [Preview Abstract] |
Thursday, March 5, 2015 12:03PM - 12:15PM |
T17.00005: Electropolymerization of low-k polymer on graphene for top-gated FETs Alexey Lipatov, Benjamin B. Wymore, Alexandra Fursina, Timothy H. Vo, Alexander Sinitskii, Jody G. Redepenning The most crucial step for field effect transistor (FET) fabrication is forming a thin and uniform layer of insulator on the surface of a body material to separate it from top-gate electrode. Due to hydrophobic and inert nature of graphene it has quickly become a challenge to deposit a uniform dielectric layer with atomic layer deposition (ALD). One promising method to overcome the problems associated with coating graphene is to incorporate a low dielectric constant (low-k) polymer buffer layer or an organic seed layer. This low-k dielectric layer on top of graphene provides the functional groups necessary for the ALD precursors to adhere. In our work we for the first time demonstrate electrodeposition of pinhole free thin (3-4 nm) layers of low-k polymer on monolayer graphene samples. Advantages of the technique include selectivity and scalability. It is possible to deposit the films selectively on a single graphene flake/device, and on a large number of devices simultaneously. The performance of top-gated FET devices demonstrates the utility of electrodeposited polymer films as a dielectric material between graphene and top-gate electrode. [Preview Abstract] |
Thursday, March 5, 2015 12:15PM - 12:27PM |
T17.00006: Processing of pristine graphene dispersions, gels, and composites Fahmida Irin, Sriya Das, Dorsa Parviz, Micah Green This work focuses on the central concept of producing graphene from graphite without covalently functionalizing the graphene basal plane; such graphene may be stabilized, dispersed, and processed for use in a range of high-performance materials. In particular, we show that various dispersants such as triphenylene derivatives, polymers (polyvinylpyrrolidone), pyrene derivatives etc. can naturally absorb to the graphene surface, create repulsive (steric and electrostatic) forces, and prevent aggregation. This allows for graphene dispersion in a wide range of organic solvents and composite precursors without compromising graphene structure. Such dispersions are stable against aggregation even when subjected to extreme temperature changes, pH changes, and freeze drying. The applications of these dispersions include the production of graphene/polymer nanocomposites, synthesis of self-healing hydrogels, and electrically conductive aerogels. We fabricate graphene loaded polyvinyl alcohol (PVA) films which show enhanced modulus, strength, and electrical conductivity. We also demonstrate novel results in the area of creating graphene loaded self-healing hydrogels. The hydrogels can be converted into electrically conductive aerogels that can be utilized as a template for doubly-percolated polymer composites. [Preview Abstract] |
Thursday, March 5, 2015 12:27PM - 12:39PM |
T17.00007: Facile preparation of reduced graphene oxide - ruthenium oxide nanocomposite electrodes for high-performance supercapacitors Fatima Amir, Viet Pham, James Dickerson Herein we report a facile approach of synthesis of graphene oxide (GO) sheets modified with ruthenium oxide (RuO$_{2}$) nanoparticles, followed by a reduction of graphene oxide in an alkaline medium. The as-prepared reduced graphene oxide (rGO)/ruthenium oxide (RuO$_{2}$) nanocomposite was used for the fabrication of a symmetric supercapacitor. The specific capacitance and charge-discharge periods of the supercapacitor were found to be dependent on both the structural and morphological properties, and the electrolytes used. Surface morphology analysis using scanning electron microscopy (SEM) shows the RuO$_{2}$ nanoparticles decorating rGO sheets, comprising a highly porous surface. Structural analysis obtained by x-ray diffraction (XRD) revealed an amorphous structure that is necessary to achieve a high cycling rate capability. The electrochemical properties of rGO/RuO$_{2}$ were measured in a two electrodes system, using two different electrolytes: H$_{2}$SO$_{4}$ and Na$_{2}$SO$_{4}$. The specific capacitance of rGO/RuO$_{2}$ in H$_{2}$SO$_{4}$ was found to be 318 F/g, and is much higher than that of Na$_{2}$SO$_{4}$ (184 F/g). [Preview Abstract] |
Thursday, March 5, 2015 12:39PM - 12:51PM |
T17.00008: Enhanced hydrogen storage from nanostructured graphene and nickel hybrids based on spillover mechanism Lin Wei, Yuanbing Mao As a fascinating 2-dimentional carbon material, graphene has been decorated with metal nanoparticles to enhance its hydrogen storage performance based on the spillover mechanism. In this work, Ni and Ni alloys have been used to decorate the surface of graphene. Graphene oxide was fabricated from graphite by improved Hummer method. To form Ni/graphene and Ni/Pd/graphene hybrids, the graphene oxide water dispersion was mixted with nickel chloride (and palladium chloride). Ni(OH)$_{\mathrm{2}}$/graphene and Ni(OH)$_{\mathrm{2}}$/Pd(OH)$_{\mathrm{2}}$/graphene hybrids were synthesized through hydrothermal treatment, using water as a solvent and HMT as a capping agent. After heat treatment and in situ reduction with hydrogen flow, the nanostructured Ni/graphene and Ni/Pd graphene hybrids were obtained. The nanostructured Ni/Pd/Ag/graphene hybrid was synthesized from graphene oxide in the ethylene glycol solution and metal nitrates using similar reactions. XRD, Raman, SEM, AFM were used to characterize these products. ASAP 2020 was used to test the hydrogen adsorption and desorption capacities. [Preview Abstract] |
Thursday, March 5, 2015 12:51PM - 1:03PM |
T17.00009: Tailored crumpling and unfolding of spray-dried pristine graphene and graphene oxide nanosheets Dorsa Parviz, Sriya Das, Fahmida Irin, Micah Green 3D Crumpled graphene was directly obtained from aqueous dispersions of pristine graphene using an industrially scalable spray drying technique. Capillary forces during the water evaporation induced the crumpling of nanosheets to multi-faced dimpled morphology. For the first time, the transition of 2D graphene nanosheets to a 3D crumpled morphology was directly observed inside the spray dryer. Graphene oxide (GO) was spray dried using the same procedure; however, their highly wrinkled final morphology was different than the crumpled pristine graphene nanosheets. The degree of crumpling of the nanosheets was controlled by changing the dimensionless ratio of evaporation rate to diffusion rate. Crumpled particles were redispersed into various solvents to evaluate their morphological changes as a response to rewetting. Crumpled GO nanosheets remained crumpled as a response to hydration, while the pristine graphene nanosheets unfolding behavior was solvent-dependent. This study holds significance for both fundamental understanding of the origins of nanosheets crumpling and also for the use of crumpled nanosheets for further material processing. [Preview Abstract] |
Thursday, March 5, 2015 1:03PM - 1:15PM |
T17.00010: Local field enhanced photoluminescence and Raman effect in Reduced Graphene Oxide Nanoclusters Sanjay Karna, Tae-Youl Choi, Rakesh Shah, Meg Mahat, Arup Neogi The increase in local field due to metal nanoparticles can influence the radiative emission and phonon interaction in semiconductors. Graphene oxide can be reduced to modify its bandgap and tune its emission energy from the red to the ultraviolet wavelength range. Reduced graphene oxide (rGO) with Ag nanoparticles has been synthesized to study the effect of resonant surface plasmon interaction on the light emission from rGO. Comparative study of sp$^{\mathrm{2}}$ cluster size, defect density and electrical conductivity has been performed. Preliminary result shows that the maximum decrease in the defects density in rGO structure as treated with Ag NPs and also in the same way the inter-defect distance increase as density of defects decrease and sp$^{\mathrm{2}}$ cluster size increase rapidly. The increase in size of sp$^{\mathrm{2}}$ cluster and decrease in defect density due to localized electric field due to Ag NPs is responsible~for the~increase in electrical conductivity and in PL emission. The localized electric field increases the electrical conductivity due to the decrease in sp$^{\mathrm{3}}$ clusters compared to an (defects oxides functional in GO)? increase in sp$^{\mathrm{2}}$ in the rGO clusters. The increase in electric field due to localized plasmon due to Ag NP resonant to the emission from rGO results in an increase in enhancement from emission from rGO. By controlling the localized surface plasmon density, the enhancement efficiency from rGO can be enhanced. [Preview Abstract] |
Thursday, March 5, 2015 1:15PM - 1:27PM |
T17.00011: Gas Barrier and Separation Behavior of Graphene Oxide Nanobrick Wall Thin Films Jaime Grunlan In many cases, electronics packaging requires electrical conductivity and barrier to oxygen, even under humid conditions. These two properties have simultaneously been realized through the use of surfactant-free aqueous layer-by-layer (LbL) processing, in the form of a polymer composite nanocoating. By layering graphene oxide (GO) with polyethyleneimine (PEI), a ``nano brick wall'' structure has been created, imparting gas barrier properties to the film. Reducing the graphene oxide with a thermal treatment further produces high oxygen barrier in humid conditions and imparts high electrical conductivity ($\sigma $ $\sim$ 1750 S/m). These thin films (\textless 400 nm) are flexible relative traditional conductive thin films (e.g. ITO), and processing occurs under ambient conditions with water as the only solvent. Additionally, these PEI/GO thin films exhibit H2/CO2 selectivity (\textgreater 300), making them interesting for gas purification membranes. The flexible nature of the aforementioned thin films, along with their excellent combination of transport properties, make them ideal candidates for use in a broad range of electronics and other packaging applications. [Preview Abstract] |
Thursday, March 5, 2015 1:27PM - 1:39PM |
T17.00012: Near-Field Radiation Between Graphene-Covered Carbon Nanotube Arrays Richard Zhang, Xianglei Liu, Zhuomin Zhang It has been shown that at nanometer gap distances, or the near-field, thermal radiation is enhanced over blackbody between hyperbolic metamaterials. It was shown that vertically aligned carbon nanotube (VACNT) arrays in the near-field demonstrate exceptional enhancement. In this study, graphene is covered on the surfaces of two semi-infinite VACNT arrays separated by a sub-micron vacuum gap. Doped graphene ($\mu \ge 0.3\mbox{\thinspace eV})$ is found to improve photon tunneling in a broad hyperbolic frequency range, due to the interaction with graphene-graphene surface plasmons. Increasing doping that shifts the peak spectral heat flux toward higher frequencies attests to the tunable bandgap of graphene. Although graphene covering of VACNT does not offer many magnitudes of near-field heat flux enhancement over uncovered VACNT, this study identifies conditions (i.e. gap distance and doping) that best augments heat transfer to that of VACNT arrays. In addition, this study demonstrates the near-field Poynting vector to determine the energy absorption due to graphene. It is found that graphene, in low frequencies and high chemical potentials, attenuates large penetration depths of hyperbolic modes, thereby increasing the contribution of graphene-graphene surface plasmons. This study has an impact toward designing carbon-based emitters and thermal junctions. [Preview Abstract] |
Thursday, March 5, 2015 1:39PM - 2:15PM |
T17.00013: Electronic and Optical Properties of Atomically Precise Graphene Nanoribbons and Heterojunctions Invited Speaker: Carlo Antonio Pignedoli Among graphene related materials, nanoribbons (GNRs) -- narrow stripes of graphene -- have emerged as promising building blocks for nanoelectronic devices. The lateral confinement in GNRs opens a bandgap that sensitively depends on the ribbon width, allowing in principle for the design of GNR-based structures with tunable properties. However, structuring with atomic precision is required to avoid detrimental effects induced by edge defects. Recently, we have introduced a versatile route for the bottom-up fabrication of GNRs [1], allowing for the atomically precise synthesis of ribbons with different shapes as well as heterojunctions be-tween doped and undoped ribbon segments [2,3]. Here, we report on detailed experimental and computational investigations of the structural, electronic and optical properties of selected GNRs and heterojunctions [1-3]. For the case of armchair GNRs of width N$=$7, the electronic band gap and band dispersion have been determined with high precision [4,5]. Optical characterization has revealed important excitonic effects [6], which are in good agreement with ab initio calculations including many-body effects. For the case of heterojunctions, consisting of seamlessly assembled segments of pristine (undoped) graphene nanoribbons and deterministically nitrogen-doped graphene nanoribbons, we find a behavior similar to traditional p--n junctions. With a band shift of 0.5 eV and an electric field of 2 $\times$ 108 V m--1 at the heterojunction, these materials bear a high potential for applications in photovoltaics and electronics. Finally, we will discuss the potential of the bottom-up approach with regard to the fabrication of GNRs exhibiting zigzag edges, which are predicted to exhibit spin-polarized edge states. \\[4pt] [1] J. Cai, et. al \textit{Nature} 466, 470 (2010).\\[0pt] [2] S. Blankenburg, et al. \textit{ACS Nano} \textbf{6}, 2020 (2012).\\[0pt] [3] J. Cai, et al\textit{. Nature Nanotech.} \textbf{9}, 896 (2014)\\[0pt] [4] P. Ruffieux, et al. \textit{ACS Nano} \textbf{6}, 6930 (2012).\\[0pt] [5] H. Soede, et al. \textit{Phys Rev. B}, submitted (2014)\\[0pt] [6] R. Denk, et al. \textit{Nat. Commun.} \textbf{5}, 4253 (2014) [Preview Abstract] |
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