Influence of synthesis conditions on properties of green-reduced graphene oxide

[EN] Green reduction of graphene oxide (GO) was performed using ascorbic acid (AA) in the presence of poly(sodium 4-styrenesulfonate), which resulted in reduced graphene oxide (PSS-rGO) with excellent solubility and stability in water. Large rGO sheets of 4 mu m(2) area and 1.1-nm thickness were obtained. The measurements showed that noncovalent functionalization with PSS molecules prevented rGO from aggregation. The parameters of graphite oxidation process and AA: GO w/w ratio were evaluated, and the obtained results showed that the properties of the reduced material (PSS-rGO) can be tailored by proper selection and adjustment of these parameters.The authors thank the European Commission for their financial support through the project no. NMP3-SL-2010-246073.Pruna, A.; Pullini, D.; Busquets, D. (2013). Influence of synthesis conditions on properties of green-reduced graphene oxide. Journal of Nanoparticle Research. 15(5):1-11. https://doi.org/10.1007/s11051-013-1605-6S111155Acik M, Lee G, Mattevi C et al (2011) The role of oxygen during thermal reduction of graphene oxide studied by infrared absorption spectroscopy. J Phys Chem C 115:1981–19761Akhavan O, Ghaderi E (2012) Escherichia coli bacteria reduce graphene oxide to bactericidal graphene in a self-limiting manner. Carbon 50:1853–1860Akhavan O, Ghaderi E, Esfandiar A (2011) Wrapping bacteria by graphene nanosheets for isolation from environment, reactivation by sonication, and inactivation by near-infrared irradiation. J Phys Chem B 115:6279–6288Akhavan O, Ghaderi E, Aghayee S, Fereydooni Y, Talebi A (2012) The use of a glucose-reduced graphene oxide suspension for photothermal cancer therapy. J Mater Chem 22:13773–13781Bae S, Kim H, Lee Y et al (2010) Roll to- roll production of 30-inch graphene films for transparent electrodes. Nat Nanotechnol 5:574–578Bai H, Xu Y, Zhao L, Li C, Shi G (2009) Non-covalent functionalization of graphene sheets by sulfonated polyaniline. Chem Commun 13:1667–1669Boehm HP (1994) Some aspects of the surface chemistry of carbon blacks and other carbons. Carbon 32:759–769Boukhvalov DW, Katsnelson MI (2008) Modeling of graphite oxide. J Am Chem Soc 130:10697–10701Buchsteiner A, Lerf A, Pieper J (2006) Water dynamics in graphite oxide investigated with neutron scattering. J Phys Chem B 110:22328Choi BG, Park H, Park TJ et al (2010) Solution chemistry of self-assembled graphene nanohybrids for high-performance flexible biosensors. ACS Nano 4:2910–2918Cote LJ, Silva RC, Huang J (2009) Flash reduction and patterning of graphite oxide and its polymer composite. J Am Chem Soc 131:11027–11032Dai B, Fu L, Liao L et al (2011) High-quality single-layer graphene via reparative reduction of graphene oxide. Nano Res 4:434–439Davies MB, Austin J, Partridge DA (1991) Vitamin C: its chemistry and biochemistry. Royal Society of Chemistry, CambridgeElias DC, Nair RR, Mohiuddin TMG, Morozov SV, Blake P, Halsall MP et al (2009) Control of graphene’s properties by reversible hydrogenation: evidence for graphene. Science 23:610–613Fan FRF, Park S, Zhu Y, Ruoff RS, Bard AJ (2009) Electrogenerated chemiluminescence of partially oxidized highly oriented pyrolytic graphite surfaces and of graphene oxide nanoparticles. J Am Chem Soc 131:937–939Fernandez-Merino MJ, Guardia L, Paredes JI, Villar-Rodil S et al (2010) Vitamin C is an ideal substitute for hydrazine in the reduction of graphene oxide suspensions. J Phys Chem C 114:6426–6432Ferrari AC, Meyer JC, Scardaci V, Casiraghi C, Lazzeri M, Mauri F, Piscanec S, Jiang D, Novoselov KS, Roth S, Geim AK (2006) Raman spectrum of graphene and graphene layers. Phys Rev Lett 97:187401–187405Ganguly A, Sharma S, Papakonstantinou P, Hamilton J (2011) Probing the thermal deoxygenation of graphene oxide using high-resolution in situ X-ray-based spectroscopies. J Phys Chem C 115:17009–17019Hancock RD, Viola R (2005) Biosynthesis and catabolism of l-ascorbic acid in plants. Crit Rev Plant Sci 24:167–188Hernandez Y, Nicolosi V, Lotya M et al (2008) High-yield production of graphene by liquid-phase exfoliation of graphite. Nat Nanotechnol 3:563–568Hontoria-Lucas C, Lopez-Peinado AJ, Loepz-Gonzalez JDD et al (1995) Study of oxygen-containing groups in a series of graphite oxides: physical and chemical characterization. Carbon 33:1585–1592Jeong HK, Lee YP, Lahaye RJWE et al (2008) Evidence of graphitic AB stacking order of graphite oxides. J Am Chem Soc 130:1362–1366Kim KS, Zhao Y, Jang H, Lee SY, Kim JM, Kim KS, Ahn JH, Kim P, Choi JY, Hong BH (2009) Large-scale pattern growth of graphene films for stretchable transparent electrodes. Nature 457:706–710Kuila T, Bose S, Mishra AK, Khanra P, Kim NH, Lee JH (2012) Chemical functionalization of graphene and its applications. Prog Mater Sci 57:1061–1105Kuilla T, Bhadra S, Yao D, Kim NH, Bose S, Lee JH (2010) Recent advances in graphene based polymer composites. Prog Polym Sci 35:1350–1375Kumar P, Subrahmanyam KS, Rao CNR (2011a) Graphene produced by radiation-induced reduction of graphene oxide. Intl J Nanosci 10:559–566Kumar P, Panchakarla LS, Rao CNR (2011b) Laser-induced unzipping of carbon nanotubes to yield graphene nanoribbons. Nanoscale 3:2127–2129Kumar P, Das B, Chitara B et al (2012) Novel radiation induced properties of graphene and related materials. Macromol Chem Phys 213:1146–1163Lee C, Wei X, Kysar JW, Hone J (2008) Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science 321:385–388Li D, Kaner RB (2008) Graphene-based materials. Science 320:1170–1171Li J, Liu CY (2010) Ag/Graphene heterostructures: synthesis, characterization and optical properties. Eur J Inorg Chem 8:1244–1248Li D, Muller MB, Gilje S, Kaner RB, Wallace GG (2008) Processable aqueous dispersions of graphene nanosheets. Nat Nanotechnol 3:101–105Li X, Cai W, An J et al (2009) Large-area synthesis of high-quality and uniform graphene films on copper foils. Science 324:1312–1314Maitra U, Matte HSRR, Kumar P, Rao CNR (2012) Strategies for the synthesis of graphene, graphene nanoribbons, nanoscrolls and related materials. Chimia 66:941–948Mei XG, Ouyang JY (2011) Ultrasonication-assisted ultrafast reduction of graphene oxide by zinc powder at room temperature. Carbon 49:5389–5397Mkhoyan K, Contryman A, Silcox J, Stewart D, Eda G, Mattevi C, Miller S, Chhowalla M (2009) Atomic and electronic structure of graphene-oxide. Nano Lett 9:1058–1063Nair RR, Blake P, Grigorenko AN et al (2008) Fine structure constant defines visual transparency of graphene. Science 320:1308Park S, Lee KS, Bozoklu G et al (2008) Graphene oxide papers modified by divalent ions enhancing mechanical properties via chemical cross-linking. ACS Nano 2:572–578Park S, An J, Jung I et al (2009) Colloidal suspensions of highly reduced graphene oxide in a wide variety of organic solvents. Nano Lett 9:1593–1597Park HJ, Meyer J, Roth S, Skákalová V (2010) Growth and properties of few-layer graphene prepared by chemical vapor deposition. Carbon 48:1088–1094Park S, An J, Potts JR, Velamakanni A, Murali S, Ruoff RS (2011) Hydrazine-reduction of graphite- and graphene oxide. Carbon 49:3019–3023Patil AJ, Vickery JL, Scott TB, Mann S (2009) Aqueous stabilization and self-assembly of graphene sheets into layered bio-nanocomposites using DNA. Adv Mater 21:3159–3164Stankovich S, Piner RD, Chen X, Wu N, Nguyen SBT, Ruoff RS (2006) Stable aqueous dispersions of graphitic nanoplatelets via the reduction of exfoliated graphite oxide in the presence of poly(sodium 4-styrenesulfonate). J Mater Chem 16:155–158Subrahmanyam KS, Panchakarla LS, Govindaraj A, Rao CNR (2009) Simple method of preparing graphene flakes by an arc-discharge method. J Phys Chem C 113:4257–4259Szabó T, Tombacz E, Illes E, Dékány I (2006) Enhanced acidity and pH-dependent surface charge characterization of successively oxidized graphite oxides. Carbon 44:537–545Wu JS, Pisula W, Mullen K (2007) Graphenes as potential material for electronics. Chem Rev 107:718–747Wu H, Zhao WF, Hu HW, Chen GH (2011) One-step in situ ball milling synthesis of polymer-functionalized graphene nanocomposites. J Mater Chem 21:8626–8632Xu Y, Bai H, Lu G, Li C, Shi G (2008) Flexible graphene films via the filtration of water-soluble noncovalent functionalized graphene sheets. J Am Chem Soc 130:5856–5857Yin Z, Wu S, Zhou X et al (2010) Electrochemical deposition of ZnO nanorods on transparent reduced graphene oxide electrodes for hybrid solar cells. Small 6:307–312Zhang L, Liang J, Huang Y, Ma Y, Wang Y, Chen YS (2009) Size-controlled synthesis of graphene oxide sheets on a large scale using chemical exfoliation. Carbon 47:3365–3380Zhang J, Yang H, Shen G, Cheng P, Zhang J, Guo S (2010) Reduction of graphene oxide via l-ascorbic acid. Chem Comm 46:1112–1114Zhou Y, Bao Q, Tang LAL, Zhong Y, Loh KP (2009) Hydrothermal dehydration for the ‘green’ reduction of exfoliated graphene oxide to graphene and demonstration of tunable optical limiting properties. Chem Mater 21:2950–295

Renormalization of Coulomb interactions in s-wave superconductor Nax_xCoO2_2

We study the renormalized Coulomb interactions due to retardation effect in Na$_x$CoO$_2$. Although the Morel-Anderson's pseudo potential for $a_{1g}$ orbital $\mu^*_{a1g}$ is relatively large because the direct Coulomb repulsion $U$ is large, that for interband transition between $a_{1g}$ and $e_g'$ orbitals $\mu^*_{a1g,eg'}$ is very small since the renormalization factor for pair hopping $J$ is square of that for $U$. Therefore, the s-wave superconductivity due to valence-band Suhl-Kondo mechanism will survive against strong Coulomb interactions. The interband hopping of Cooper pairs due to shear phonons is essential to understand the superconductivity in Na$_x$CoO$_2$.Comment: 2pages, 2figures, Proceedings of ICM in Kyoto, 200

Mr.Wolf: An Energy-Precision Scalable Parallel Ultra Low Power SoC for IoT Edge Processing

This paper presents Mr. Wolf, a parallel ultra-low power (PULP) system on chip (SoC) featuring a hierarchical architecture with a small (12 kgates) microcontroller (MCU) class RISC-V core augmented with an autonomous IO subsystem for efficient data transfer from a wide set of peripherals. The small core can offload compute-intensive kernels to an eight-core floating-point capable of processing engine available on demand. The proposed SoC, implemented in a 40-nm LP CMOS technology, features a 108-mu W fully retentive memory (512 kB). The IO subsystem is capable of transferring up to 1.6 Gbit/s from external devices to the memory in less than 2.5 mW. The eight-core compute cluster achieves a peak performance of 850 million of 32-bit integer multiply and accumulate per second (MMAC/s) and 500 million of 32-bit floating-point multiply and accumulate per second (MFMAC/s) -1 GFlop/s-with an energy efficiency up to 15 MMAC/s/mW and 9 MFMAC/s/mW. These building blocks are supported by aggressive on-chip power conversion and management, enabling energy-proportional heterogeneous computing for always-on IoT end nodes improving performance by several orders of magnitude with respect to traditional single-core MCUs within a power envelope of 153 mW. We demonstrated the capabilities of the proposed SoC on a wide set of near-sensor processing kernels showing that Mr. Wolf can deliver performance up to 16.4 GOp/s with energy efficiency up to 274 MOp/s/mW on real-life applications, paving the way for always-on data analytics on high-bandwidth sensors at the edge of the Internet of Things

Erratum: “Seed layer technique for high quality epitaxial manganite films” [AIP Advances 6, 085109 (2016)]

No abstract available

Surface nanostructures in manganite films

Ultrathin manganite films are widely used as active electrodes in organic spintronic devices. In this study, a scanning tunnelling microscopy (STM) investigation with atomic resolution revealed previously unknown surface features consisting of small non-stoichiometric islands. Based upon this evidence, a new mechanism for the growth of these complex materials is proposed. It is suggested that the non-stoichiometric islands result from nucleation centres that are below the critical threshold size required for stoichiometric crystalline growth. These islands represent a kinetic intermediate of single-layer growth regardless of the film thickness, and should be considered and possibly controlled in manganite thin-film applications

Pentacene thin films on ferromagnetic oxide: Growth mechanism and spintronic devices

[EN] Cation-exchange membranes made exclusively from ceramic materials have been synthesized by means of the impregnation of microporous ceramic supports with zirconium phosphate. Changes in the pore size distribution and total pore volume of the supports were provoked by the addition of starch as pore former in the fabrication procedure. This allowed the production of supports with increased effective electrical conductivities and with larger pores available for the zirconium phosphate deposition. An improved functionality for the exchange of cations was given to the ceramic membranes by means of their impregnation with the active particles of zirconium phosphate. The ion-exchange properties of the membranes were increased with further impregnation cycles and the resulting current–voltage curves showed a similar shape to that typical of commercial polymeric ion-exchange membranes. The production of ionexchange membranes with increased chemical and radiation stability will broaden their applicability for the treatment of specific industrial waste waters, which are very aggressive for the current commercial ion-exchange membranes.The authors acknowledge the technical help from Federico Bona at CNR-ISMN in Bologna and the extensive use of the scanning probe microscopes at "Centro Interfacolta Misure" of the University of Parma. Financial support from the FP7 Projects NMP-2010-SMALL-4-263104 (HINTS), NMP3-SL-2010-246073 (GRENADA), and NMP3-LA-2010-246102 (IFOX) is acknowledged.Graziosi, P.; Riminucci, A.; Prezioso, M.; Newby, C.; Brunel, D.; Bergenti, I.; Pullini, D.... (2014). Pentacene thin films on ferromagnetic oxide: Growth mechanism and spintronic devices. Applied Physics Letters. 105(2):1-5. https://doi.org/10.1063/1.4890328S15105

Vega: A Ten-Core SoC for IoT Endnodes with DNN Acceleration and Cognitive Wake-Up from MRAM-Based State-Retentive Sleep Mode

The Internet-of-Things (IoT) requires endnodes with ultra-low-power always-on capability for a long battery lifetime, as well as high performance, energy efficiency, and extreme flexibility to deal with complex and fast-evolving near-sensor analytics algorithms (NSAAs). We present Vega, an IoT endnode system on chip (SoC) capable of scaling from a 1.7- μW fully retentive cognitive sleep mode up to 32.2-GOPS (at 49.4 mW) peak performance on NSAAs, including mobile deep neural network (DNN) inference, exploiting 1.6 MB of state-retentive SRAM, and 4 MB of non-volatile magnetoresistive random access memory (MRAM). To meet the performance and flexibility requirements of NSAAs, the SoC features ten RISC-V cores: one core for SoC and IO management and a nine-core cluster supporting multi-precision single instruction multiple data (SIMD) integer and floating-point (FP) computation. Vega achieves the state-of-the-art (SoA)-leading efficiency of 615 GOPS/W on 8-bit INT computation (boosted to 1.3 TOPS/W for 8-bit DNN inference with hardware acceleration). On FP computation, it achieves the SoA-leading efficiency of 79 and 129 GFLOPS/W on 32- and 16-bit FP, respectively. Two programmable machine learning (ML) accelerators boost energy efficiency in cognitive sleep and active states

Fast route to obtain Al2O3-based nanocomposites employing graphene oxide: Synthesis and Sintering

A fast approach based on microwave technology was employed for the sintering of novel composites of alumina and using graphene oxide (GO) as susceptor. The thermal stability and structure of GO materials produced by chemical oxidation of graphite were characterized. The morphology, structure and mechanical properties of the composites sintered by microwave approach were reported to the counterparts sintered by conventional method. The results indicated the formation of an interconnecting graphene network promoted the electrical conductivity in the composite having only 2 wt.% GO. Hardness and elastic modulus decreased significantly in samples sintered by conventional method due to lower values of density while microwave technology allowed to achieve a positive effect on the densification and showed a smaller grain size when compared to the one achieved by conventional heating. (C) 2014 Elsevier Ltd. All rights reserved.Financial support from European Commission (project no. NMP3-SL-2010-246073), Universidad Politecnica de Valencia (project SP20120677) and Ministerio de Economia y Competitividad - MINECO (project TEC2012-37532-C02-01, co-funded by ERDF (European Regional Development Funds) is gratefully acknowledged. A.B. acknowledges the Spanish Ministry of Science and Innovation (contract JCI-2011-10498). A.P. acknowledges support from Romanian Authority for Scientific Research - UEFISCDI (project no. PN-II-RU-PD-2012-3-0124).Benavente Martínez, R.; Pruna, AI.; Borrell Tomás, MA.; Salvador Moya, MD.; Pullini, D.; Penaranda-Foix, FL.; Busquets Mataix, DJ. (2015). Fast route to obtain Al2O3-based nanocomposites employing graphene oxide: Synthesis and Sintering. Materials Research Bulletin. 64:245-251. https://doi.org/10.1016/j.materresbull.2014.12.075S2452516

Polaron framework to account for transport properties in metallic epitaxial manganite films

[EN] We propose a model for the consistent interpretation of the transport behavior of manganese perovskites in both the metallic and insulating regimes. The concept of polarons as charge carriers in the metallic ferromagnetic phase of manganites also solves the conflict between transport models, which usually neglects polaron effects in the metallic phase, and, on the other hand, optical conductivity, angle-resolved spectroscopy, and neutron scattering measurements, which identify polarons in the metallic phase of manganites down to 6 K. Transport characterizations of epitaxial La0.7Sr0.3MnO3 thin films in the thickness range of 5-40 nm and temperature interval of 25-410 K have been accurately collected. We show that taking into account polaron effects allows us to achieve an excellent fit of the transport curves in the whole temperature range. The current carriers density collapse picture accurately accounts for the properties variation across the metal-insulator transitions. The electron-phonon coupling parameter gamma estimations are in a good agreement with theoretical predictions. The results promote a clear and straightforward quantitative description of the manganite films involved in charge transport device applications and promises to describe other oxide systems involving a metal-insulator transition.The authors P.G., A.G., M.P., A.R., and I.B. thank F. Bona for technical help and A. Dediu and V. Kabanov for fruitful discussions. Financial support from the FP7 Projects No. NMP3-LA-2010-246102 (Interfacing oxides, IFOX), No. NMP-2010-SMALL-4-263104 (Next generation hybrid interfaces for spintronic applications, HINTS), No. NMP3-SL-2010-246073 (Graphene for nanoscaled applications, GRENADA), and the Italian government FIRB (Molecular nanomagnets on metallic and magnetic surfaces for applications in molecular spintronics) Project No. RBAP117RWN is acknowledged.Graziosi, P.; Gambardella, A.; Prezioso, M.; Riminucci, A.; Bergenti, I.; Homonnay, N.; Schmidt, G.... (2014). Polaron framework to account for transport properties in metallic epitaxial manganite films. Physical Review B. 89(21):1-7. https://doi.org/10.1103/PhysRevB.89.214411S17892