Critical parameters in exfoliating graphite into graphene

Buzaglo, Matat; Shtein, Michael; Kober, Sivan; Lovrinčić, Robert; Vilan, Ayelet; Regev, Oren

doi:10.1039/c3cp43205j

Cited by 71 publications

(73 citation statements)

References 39 publications

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“…[ 23 ] The topic of forming top contacts to molecular monolayers was covered recently in general [ 24 ] and Si-specifi c [ 25 ] reviews. For Si-molecular junctions, top-contacts are often formed by 'cold methods' [ 26 ] such as fl oatation, [ 27 ] lamination, [ 15 ] spin-coating of PEDOT:PSS, [ 28 ] or graphene suspensions, [ 29 ] and electroless plating of Au. [ 30 ] All these creative methods were developed to replace standard evaporation, which was shown to degrade molecular monolayers or cause metal diffusion through such monolayers.…”

Section: Fabrication Of Reproducible Integration-compatible Hybrid Mmentioning

confidence: 99%

Fabrication of Reproducible, Integration‐Compatible Hybrid Molecular/Si Electronics

Lovrinčić

Kraynis

et al. 2014

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Reproducible molecular junctions can be integrated within standard CMOS technology. Metal-molecule-semiconductor junctions are fabricated by direct Si-C binding of hexadecane or methyl-styrene onto oxide-free H-Si(111) surfaces, with the lateral size of the junctions defined by an etched SiO2 well and with evaporated Pb as the top contact. The current density, J, is highly reproducible with a standard deviation in log(J) of 0.2 over a junction diameter change from 3 to 100 μm. Reproducibility over such a large range indicates that transport is truly across the molecules and does not result from artifacts like edge effects or defects in the molecular monolayer. Device fabrication is tested for two n-Si doping levels. With highly doped Si, transport is dominated by tunneling and reveals sharp conductance onsets at room temperature. Using the temperature dependence of current across medium-doped n-Si, the molecular tunneling barrier can be separated from the Si-Schottky one, which is a 0.47 eV, in agreement with the molecular-modified surface dipole and quite different from the bare Si-H junction. This indicates that Pb evaporation does not cause significant chemical changes to the molecules. The ability to manufacture reliable devices constitutes important progress toward possible future hybrid Si-based molecular electronics.

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Section: Fabrication Of Reproducible Integration-compatible Hybrid Mmentioning

confidence: 99%

Fabrication of Reproducible, Integration‐Compatible Hybrid Molecular/Si Electronics

Lovrinčić

Kraynis

et al. 2014

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“…In liquid phase exfoliation, the main parameters are initial concentration of WS2 (Ci), processing/sonication time, t, power, P, and volume, V, as well as stabilizer concentration, CPVA, and centrifugation conditions. 27,59 As dispersed concentrations tend to scale monotonically with initial concentration and inputted energy density ( / P t V  ), 27,60 these parameters are important, but not very interesting. More interesting are the stabilizer concentration and centrifugation conditions as both these parameters tend to control not only the dispersed concentration but also the nanosheet size and so presumably the monolayer content.…”

Section: Optimization Of the Polymer Concentrationmentioning

confidence: 99%

Photoluminescence from Liquid‐Exfoliated WS₂ Monomers in Poly(Vinyl Alcohol) Polymer Composites

Vega‐Mayoral

Backes

Hanlon

et al. 2015

Adv Funct Materials

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While liquid phase exfoliation can be used to produce nanosheets stabilized in polymer solutions, very little is known about the resultant nanosheet size, thickness or monolayer content. Here we use semi-quantitative spectroscopic metrics based on extinction, Raman and photoluminescence (PL) spectroscopy to investigate these parameters for WS2 nanosheets exfoliated in aqueous polyvinylalcohol (PVA) solutions. By measuring Raman and PL simultaneously, we can track the monolayer content via the PL/Raman intensity ratio while varying processing conditions. We find the monolayer population to be maximized for a stabilizing polymer concentration of 2 g/L. In addition, the monolayer content can be controlled via the centrifugation conditions, exceeding 5% by mass in some cases. These techniques have allowed us to track the ratio of PL/Raman in a droplet of polymer-stabilized WS2 nanosheets as the water evaporates during composite formation. We find no evidence of nanosheet aggregation under these conditions although the PL becomes dominated by trion emission as drying proceeds and the balance of doping from PVA/water changes. Finally, we have produced bulk PVA/WS2 composites by freeze drying where >50% of the monolayers remain unaggregated, even at WS2 volume fractions as high as 10%.2

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“…Defect free graphene is generally produced by sonicating graphite powder either in certain solvents [9][10][11][12][13][14][15][16] or aqueous surfactant [17][18][19][20][21][22][23] solutions. The sonication tends to break up the graphite crystallites as well as exfoliating them to give large number of graphene nanosheets.…”

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confidence: 99%

“…The concentration, C, of sonication-exfoliated graphene tends to scale roughly linearly with the inputted energy density: C f (E/ V) ¼ Pt/V, where E, V, P and t are the total inputted energy, the liquid volume, the input power and the sonication time respectively. 23,26 This means the production rate (P R ¼ VC/t) is roughly independent of volume. This is a signicant problem as it means the simplest strategy for scaling up a process, increasing the production rate by increasing the volume, is unavailable.…”

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

et al. 2014

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To facilitate progression from the lab to commercial applications, it will be necessary to develop simple, scalable methods to produce high quality graphene. Here we demonstrate the production of large quantities of defect-free graphene using a kitchen blender and household detergent. We have characterised the scaling of both graphene concentration and production rate with the mixing parameters: mixing time, initial graphite concentration, rotor speed and liquid volume. We find the production rate to be invariant with mixing time and to increase strongly with mixing volume, results which are important for scale-up. Even in this simple system, concentrations of up to 1 mg ml À1 and graphene masses of >500 mg can be achieved after a few hours mixing. The maximum production rate was $0.15 g h À1 , much higher than for standard sonication-based exfoliation methods. We demonstrate that graphene production occurs because the mean turbulent shear rate in the blender exceeds the critical shear rate for exfoliation.Over the last decade, graphene has become one of the most studied of all nano-materials due to its 2-dimensional structure and its unique set of physical properties. 1,2 During this period, the focus of much of the research community has been on mapping out and understanding the fundamental physics and chemistry of graphene. However, in recent years, the emphasis has started to shi slightly towards the demonstration of applications. 3 Over the next few years, we expect the emphasis to shi further as both academic and industrial researchers concentrate on fullling the applications potential of graphene, eventually leading to a range of graphene-enabled products.However, before this can be achieved, it will be critically important to develop industrially scalable production methods for graphene. While graphene can be produced by a range of techniques, many applications will require solution-processed 4 graphene. In particular, a number of applications will require access to large volumes of graphene dispersions or inks. Using standard solution deposition techniques such as inkjet printing 5,6 or spray coating, 7,8 such inks can be used to prepare a range of lms, coatings or patterned structures. In particular, applications in areas such as printed electronics will require the production of conductive lms or traces. Here, defect free graphene performs particularly well, giving high conductivity structures without high temperature post treatments. 5 Thus, it is clear that large scale production techniques for defect-free graphene are urgently required.Defect free graphene is generally produced by sonicating graphite powder either in certain solvents 9-16 or aqueous surfactant 17-23 solutions. The sonication tends to break up the graphite crystallites as well as exfoliating them to give large number of graphene nanosheets. 11 Raman spectroscopy 15,24,25 shows this method to produce negligible quantities of basal plane defects while XPS shows the akes to be un-oxidised. 14 While the graphene produced by this m...

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Critical parameters in exfoliating graphite into graphene

Cited by 71 publications

References 39 publications

Fabrication of Reproducible, Integration‐Compatible Hybrid Molecular/Si Electronics

Fabrication of Reproducible, Integration‐Compatible Hybrid Molecular/Si Electronics

Photoluminescence from Liquid‐Exfoliated WS₂ Monomers in Poly(Vinyl Alcohol) Polymer Composites

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

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Critical parameters in exfoliating graphite into graphene

Cited by 71 publications

References 39 publications

Fabrication of Reproducible, Integration‐Compatible Hybrid Molecular/Si Electronics

Fabrication of Reproducible, Integration‐Compatible Hybrid Molecular/Si Electronics

Photoluminescence from Liquid‐Exfoliated WS2 Monomers in Poly(Vinyl Alcohol) Polymer Composites

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

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Photoluminescence from Liquid‐Exfoliated WS₂ Monomers in Poly(Vinyl Alcohol) Polymer Composites