We have demonstrated a method to disperse and exfoliate graphite to give graphene suspended in water-surfactant solutions. Optical characterisation of these suspensions allowed the partial optimisation of the dispersion process. Transmission electron microscopy showed the dispersed phase to consist of small graphitic flakes. More than 40% of these flakes had <5 layers with ~3% of flakes consisting of monolayers. These flakes are stabilised against reaggregation by Coulomb repulsion due to the adsorbed surfactant. However, the larger flakes tend to sediment out over ~6 weeks, leaving only small flakes dispersed. It is possible to form thin films by vacuum filtration of these dispersions. Raman and IR spectroscopic analysis of these films suggests the flakes to be largely free of defects and oxides. The deposited films are reasonably conductive and are semi-transparent. Further improvements may result in the development of cheap transparent conductors.
We investigated the effect of surfactants and their concentration (Csur) on the final graphene concentration (CG) via the liquid-phase exfoliation method. Six typical surfactants including ionic and non-ionic ones were explored and the optimized Csur for each surfactant was suggested. For ionic surfactants, CG increases with Csur before reaching its maximum and then maintains the high level. The different mechanisms of ionic and non-ionic surfactants in stabilizing graphene dispersions are explained by the theory for colloidal stability. The as-prepared graphene sheets are verified to be highl…
We use liquid phase exfoliation to produce dispersions of molybdenum disulphide (MoS2) nanoflakes in aqueous surfactant solutions. The chemical structures of the bile salt surfactants play a crucial role in the exfoliation and stabilization of MoS2. The resultant MoS2 dispersions are heavily enriched in single and few (<6) layer flakes with large edge to surface area ratio. We use the dispersions to fabricate free-standing polymer composite wide-band saturable absorbers to develop mode-locked and Q- switched fibre lasers, tunable from 1535-1565 and 1030-1070 nm, respectively. We attribute this…
Few layer graphene (FLG) was synthesized by $μ$-wave assisted exfoliation of expanded graphite in toluene with an overall yield from c.a. 7% to 20%. A significant difference in the absorption of $μ$-waves by the expanded graphite and toluene allowed a rapid heating of the medium. The number of FLG sheets varies from 3 to 12, while the lateral size of the sheets exceeds few $μ$ms. The obtained FLG exhibits very low resistance with average value of 1.6 k$Ω$ (500 $Ω$ minimum) which is comparable to that of high quality graphenes synthesized by CVD methods, and lower than numbers of exfoliated gra…
A method to produce suspensions of graphene sheets by combining solution-based bromine intercalation and mild sonochemical exfoliation is presented. Ultrasonic treatment of graphite in water leads to the formation of suspensions of graphite flakes. The delamination is dramatically improved by intercalation of bromine into the graphite before sonication. The bromine intercalation was verified by Raman spectroscopy as well as by x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations show an almost ten times lower interlayer binding energy after introducing Br2 i…
We have investigated the effect of ambient gas pressure (Argon) used during thermal exfoliation of graphite oxide on the number of graphene sheets in the resulting graphene. The ambience gas Ar pressures used are 80, 25, 1 atmosphere and 10-3 as well as 10-5 torr. We have found curious result that the number of graphene sheets in exfoliated graphene stack is dependent on the applied pressure for exfoliation of graphite oxide (GO). By lowering the exfoliation pressure, the numbers of sheets get reduced. The numbers of sheets in exfoliated graphene stack have been determined by Lorentzian fit of…
Owing to wide variety of applications of graphene, high-quality and economical way of synthesizing graphene is highly desirable. In this study, we report a cost effective and simple approach to production of high-quality graphene. Here the synthesis route is based on electrochemical exfoliation of graphite. Instead of using strong acids (which oxidise and damage the geometrical topology of graphene), we have used alkaline solution (KOH dissolved in water) as electrolyte. TEM analysis shows that as prepared graphene has 1-4 layers and large lateral size (up to ~18 micrometer). Raman analysis sh…
Liquid-phase exfoliation of two-dimensional materials is very attractive for large-scale applications. Although used extensively, isolating MoS2 layers (<10) with high efficiency is reported to be extremely difficult. Further, the importance of soaking has not yet been studied, and the surfactants' role in stabilizing MoS2 nanosheets is poorly understood1. Herein, we report a novel approach to exfoliating large quantities of MoS2 via high-pressure (HP) liquid-phase exfoliation (LPE) in deionized (DI) water. 4 to 7 layers of MoS2 nanosheets were obtained from 60 days-soaked samples and they wer…
Graphene is at the centre of nanotechnology research. In order to fully exploit its outstanding properties, a mass production method is necessary. Two main routes are possible: large-scale growth or large-scale exfoliation. Here, we demonstrate graphene dispersions with concentrations up to ~0.01 mg/ml by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone. This occurs because the energy required to exfoliate graphene is balanced by the solvent-graphene interaction for solvents whose surface energy matches that of graphene. We confirm the presence of individ…
Enrichment of rhombohedral stacking by mechanical exfoliation of graphite
Hungarian Research Network, Centre for Energy Research（匈牙利研究网络能源研究中心）；MTA - HUN-REN EK Lendület “Momentum” Topology in Nanomaterials Research Group（MTA-HUN-REN EK Lendulet“动量”纳米材料拓扑研究组）；Óbuda University（奥比乌斯大学）；Budapest University of Technology and Economics（布达佩斯技术与经济大学）；ELTE Eötvös Loránd University（罗兰大学）
We present a fabrication method producing large and flat graphene flakes that have a few layers down to a single layer based on substrate bonding of a thick sample of highly oriented pyrolytic graphite (HOPG), followed by its controlled exfoliation down to the few to single graphene atomic layers. As the graphite underlayer is intimately bonded to the substrate during the exfoliation process, the obtained graphene flakes are remarkably large and flat and present very few folds and pleats. The high occurrence of single layered graphene sheets having tens of micron wide in lateral dimensions is …
Defects induced by liquid-phase exfoliation of graphite using sonication were studied. It was shown that localized impact by cavitation shock waves can produce bulk ripplocations and various types of dislocations in graphite nanoplatelets. Formation of ripples is more pronounced in large aspect (length/width) ratio platelets or nanobelts. Quasi-periodical ripple systems were observed in many nanobelts after sonication. Mechanism of formation of ripples and dislocations during sonication was proposed. Surprisingly, fast high-temperature processing was found to anneal most of defects. This is co…
Surfactants are often used to stabilise two-dimensional (2D) materials in environmentally friendly solvents such as water. Aqueous-surfactant solutions prevent agglomeration of nanosheets through steric and electrostatic repulsion, facilitating the production of high concentration nanomaterial dispersions. Turbulent, shear-assisted liquid exfoliation of layered precursor materials produces defect-free nanosheets by promoting mixing and generating sufficiently high shear rates to overcome out-of-plane van der Waals bonds. In the presence of a liquid-gas interface, a consequence of using surfact…
Bulk quantities of graphene nanosheets and nanodots have been selectively fabricated by mechanical grinding exfoliation of natural graphite in a small quantity of ionic liquids. The resulting graphene sheets and dots are solvent free with low levels of naturally absorbed oxygen, inherited from the starting graphite. The sheets are only two to five layers thick. The graphene nanodots have diameters in the range of 9-29 nm and heights in the range of 1-16 nm, which can be controlled by changing the processing time.
We offer a brief overview of the solvent-based graphene production and summarize the current knowledge on the formation mechanism of graphite oxide that proceeds via graphite intercalation compounds. In addition, the results of our in situ X-ray diffraction investigation into this process are presented, discussed and contrasted to the findings by other authors, who employed the same oxidation protocol but examined the samples by ex situ X-ray diffraction. Our results suggest that, contrary to the numerous reports by other authors, no strong crystalline order, unique to graphite intercalation c…
In the present work, the use of a commercial ionic liquid as a convenient solvent medium for graphite exfoliation in mild and easy conditions without any chemical modification is presented. To confirm the presence of few layer graphene, its dispersion was charachterized by Raman spectroscopy, atomic force miscroscopy and field emission electron microscopy. From the UV-Vis characterization, a graphene concentration as high as 2.543 mg/ml was obtained, which is the highest value reported so far in any solvent.
We present a high scale method to produce few layer graphene (FLG) based on the mechanical exfoliation of graphite and compare the obtained FLG with the one reported earlier arising from pencil lead ablation. Several things are modified and improved in the new approach. The purification and the ablation set_up are simplified, and the morphology of the FLG is modified and improved in view of some applications. The morphology dependent properties of FLGs, lead FLG and graphite FLG, are investigated as conductive layers and in nanocomposites. Newly obtained FLG has higher aspect ratio (high later…
Bulk applications of graphene in fields such as advanced composites, conductive ink, and energy storage require cheap and scalable graphene. Fortunately, in the last decade, liquid-phase exfoliation of graphite to give pristine graphene has been thought as a promising way to massive production of graphene at high efficiency and low cost, in terms of the cheap and abundant graphite source and a variety of cost-effective exfoliation techniques. Though many exfoliation techniques are available so far, this article will highlight the recent progress of fluid dynamics route which emerges as a promi…
Herein, we report an easy, straight forward, and versatile approach to build 0D/2D hybrid nanoparticle/graphene architectures by means of non-covalent chemistry and a modified Layer-by-Layer assembly. Three water soluble perylene diimides were employed to efficiently exfoliate pristine graphite into positively charged few- and multilayer graphene flakes. Further combination of these cationic building blocks with anionic zinc oxide nanoparticles led to the formation of tailor-made hybrid films via electrostatic and van der Waals interactions. These supramolecular hybrid nano-structures were tho…
A novel WS2-graphite dual-ion battery (DIB) is developed by combining together a conventional graphite cathode and high-capacity few-layer WS2 flakes anode. The WS2 flakes are produced by exploiting wet-jet milling (WJM) exfoliation, which allows mass production of few-layer WS2 flakes in dispersion, with an exfoliation yield of 100%. The WS2-anodes enable DIBs, based on hexafluorophosphate (PF6-) and lithium (Li+) ions, to achieve charge specific capacities of 457, 438, 421, 403, 295 and 169 mAh g-1 at current rates of 0.1, 0.2, 0.3, 0.4, 0.8 and 1.0 A g-1, respectively, outperforming convent…
Ultrasound cavitation and exfoliation dynamics of 2D materials re-vealed in operando by X-ray free electron laser megahertz imaging
University of Hull（赫尔大学）；European XFEL（欧洲X射线自由电子激光装置）；Lund University（隆德大学）；University of Greenwich（格林威治大学）；Oxford Brookes University（牛津布鲁克斯大学）；Brunel University London（布鲁内尔伦敦大学）；University of Oxford（牛津大学）；La Trobe University（拉筹伯大学）；The Diamond Light Source Ltd（钻石光源有限公司）；Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器研究所）
Mechanical exfoliation is a widely used method to isolate high quality graphene layers from bulk graphite. In our recent experiments, some ordered microstructures, consisting of a periodic alternation of kinks and stripes, were observed in thin graphite flakes that were mechanically peeled from highly oriented pyrolytic graphite (HOPG). A theoretical model is presented in this paper to understand the formation of such ordered microstructures, based on elastic buckling of a graphite flake being subjected to a bending moment. The width of the stripes predicted from this model agrees reasonably w…
We combine high-level theoretical and \emph{ab initio} understanding of graphite to develop a simple, parametrised force-field model of interlayer binding in graphite, including the difficult non-pairwise-additive coupled-fluctuation dispersion interactions. The model is given as a simple additive correction to standard density functional theory (DFT) calculations, of form $ΔU(D)=f(D)[U^{vdW}(D)-U^{DFT}(D)]$ where $D$ is the interlayer distance. The functions are parametrised by matching contact properties, and long-range dispersion to known values, and the model is found to accurately match h…
We report the exfoliation of graphite in aqueous solutions under high shear rate [$\sim10^8s^{-1}$] turbulent flow conditions, with a 100\% exfoliation yield. The material is stabilized without centrifugation at concentrations up to 100 g/L using carboxymethylcellulose sodium salt to formulate conductive printable inks. The sheet resistance of blade coated films is below$\sim2Ω/\square$. This is a simple and scalable production route for graphene-based conductive inks for large area printing in flexible electronics.
We evaluate the effect of mechanical exfoliation of van der Waals materials on crystallographic orientations of the resulting flakes. Flakes originating from a single crystal of graphite, whose orientation is confirmed using STM, are studied using facet orientations and electron back-scatter diffraction (EBSD). While facets exhibit a wide distribution of angles after a single round of exfoliation ($ σ\approx 5^o $), EBSD shows that the true crystallographic orientations are more narrowly distributed ($ σ\approx 1.5^o $), and facets have an approximately error from the true orientation. Further…
A simple solvent exchange method is introduced to prepare high-concentration and surfactant-free graphene liquid dispersion. Natural graphite flakes are first exfoliated into graphene in dimethylformamide (DMF). DMF is then exchanged by terpineol through distillation, relying on their large difference in boiling points. Graphene can then be concentrated thanks to the volume difference between DMF and terpineol. The concentrated graphene dispersions are used to fabricate transparent conductive thin films, which possess comparable properties to those prepared by more complex methods.
Layered and nanotubular systems that are metallic or graphitic are known to exhibit unusual dispersive van der Waals (vdW) power laws under some circumstances. In this letter we investigate the vdW power laws of bulk and finite layered systems and their interactions with other layered systems and atoms in the electromagnetically non-retarded case. The investigation reveals substantial difference between `cleavage' and `exfoliation' of graphite and metals where cleavage obeys a $C_2 D^{-2}$ vdW power law while exfoliation obeys a $C_3 \log(D/D_0) D^{-3}$ law for graphitics and a $C_{5/2} D^{-5/…
Computational screening of battery electrolyte components is an extremely challenging task because very complex features like solidelectrolyte-interphase (SEI) formation and graphite exfoliation need to be taken into account at least at the final screening stage. We present estimators for both SEI formation and graphite exfoliation based on a combinatorial approach with quantum chemistry calculations on model system reactions, which can be applied automatically for a large number of compounds and thus allows for a systematic first assessment of the relevant properties within screening approach…
Understanding and exploiting the remarkable optical and electronic properties of phosphorene require mass production methods that avoid chemical degradation. While solution-based strategies have been developed for scalable exfoliation of black phosphorus, these techniques have thus far employed anhydrous organic solvents in an effort to minimize exposure to known oxidants, but at the cost of limited exfoliation yield and flake size distribution. Here, we present an alternative phosphorene production method based on surfactant-assisted exfoliation and post-processing of black phosphorus in deox…
In this work, linear polystyrene-poly(2-vinylpyridine) (PS-b-P2VP) and heteroarm star PS_22P2VP_22 ionizable block copolymers were used as dispersing agents for the liquid-phase exfoliation of pristine graphene. Various strategies such as direct exfoliation, film hydration and phase transfer have been employed and compared. The best strategy involved a two-step process, namely, pre-exfoliation of graphite in polymer/CHCl3 solutions followed by phase transfer to acidified water. High concentrations of stable aqueous suspensions of graphene flakes, highly enriched in monolayer structures, were t…
Based on density functional calculations, we demonstrate a significant difference in oxidation patterns between graphene and graphite and the formation of defects after oxidation. Step-by-step modeling demonstrates that oxidation of 80% of the graphite surface is favorable. Oxidation above half of the graphite surface significantly decreases the energy costs of vacancy formation with CO2 production. The presence of water is crucial in the transformation of epoxy groups to hydroxyl, the intercalation with further bundle and exfoliation. In water-rich conditions, water intercalates graphite at t…
Graphene has attracted much attention due to its interesting properties and potential applications. Chemical exfoliation methods have been developed to make graphene recently, aimed at large-scale assembly and applications such as composites and Li ion batteries. Although efficient, the chemical exfoliation methods involve oxidation of graphene and introduce defects in the as-made sheets. Hydrazine reduction at 100 has shown to partially restore the structure and conductance of graphite oxide. However, the reduced GO still shows strong defect peaks in Raman spectra with higher resistivity than…
The scalable and high-efficiency production of two-dimensional (2D) materials is a prerequisite to their commercial use. Currently, only graphene and graphene oxide can be produced on a ton scale, and the inability to produce other 2D materials on such a large scale hinders their technological applications. Here we report a grinding exfoliation method that uses micro-particles as force intermediates to resolve applied compressive forces into a multitude of small shear forces, inducing the highly-efficient exfoliation of layer materials. The method, referred to as intermediate-assisted grinding…
Graphene is an intriguing material with properties that are distinct from those of other graphitic systems. The first samples of pristine graphene were obtained by peeling off and epitaxial growth. Recently, the chemical reduction of graphite oxide was used to produce covalently functionalized single-layer graphene oxide. However, chemical approaches for the large-scale production of highly conducting graphene sheets remain elusive. Here, we report that the exfoliation-reintercalation-expansion of graphite can produce high-quality single-layer graphene sheets stably suspended in organic solven…
We have examined the interfacial thermal conductance σint of single and multi-layer graphene samples prepared on fused SiO2 substrates by mechanical exfoliation of graphite. By using an ultrafast optical pump pulse and monitoring the transient reflectivity on the picosecond time scale, we obtained an average σint of 5,000 W/cm2K for the graphene-SiO2 system. We observed significant variation in σint between individual samples, but found no systematic dependence on the thickness of the graphene layers.
We have studied magnetization of graphene nanocrystals obtained by sonic exfoliation of graphite. No ferromagnetism is detected at any temperature down to 2 K. Neither do we find strong paramagnetism expected due to the massive amount of edge defects. Rather, graphene is strongly diamagnetic, similar to graphite. Our nanocrystals exhibit only a weak paramagnetic contribution noticeable below 50K. The measurements yield a single species of defects responsible for the paramagnetism, with approximately one magnetic moment per typical graphene crystallite.
We observe optical third harmonic generation from graphene and few-layer graphite flakes produced by exfoliation. The emission scales with the cube of the intensity of the incident near-infrared femtosecond pulses and has a wavelength that is one-third of the incident wavelength, both consistent with third harmonic generation. We extract an effective third-order susceptibility for graphene that is on the order of 1e-16 square meter per square volt, which is comparable to that for materials that are resonantly excited, but larger than for materials that are transparent at the fundamental and th…
The surfactant assisted exfoliation and non-covalent functionalization of two-dimensional layered materials, like graphene, transition metal dichalcogenides, etc., has extraordinarily been propelled forward within the last 5 years. Numerous molecules have been designed and attached to the exfoliated layers, and based on their outstanding properties, perylene based dyes have become one of the most frequently used π-detergents. Therefore, the prospect of this micro review is to summarize the most prominent achievements in this rapidly progressing field of research.
Dispersing graphite in water to obtain true (single layer) graphene (SLG) in bulk quantity in a liquid has been an unreachable goal for materials scientists in the last decade. Likewise, a diagnostic tool for identifying solubilized SLG in situ has been long awaited. Homogeneous stable dispersions of SLG in water are obtained by mixing graphenide (negatively charged graphene) solutions in tetrahydrofuran (THF) with degassed water and evaporating the organic solvent. In situ Raman spectroscopy of these aqueous dispersions shows all the expected characteristics of single layer graphene, includin…
A simple one-stage solution-based method was developed to produce graphene nanoribbons by sonicating graphite powder in organic solutions with polymer surfactant. The graphene nanoribbons were deposited on silicon substrate, and characterized by Raman spectroscopy and atomic force microscopy. Single-layer and few-layer graphene nanoribbons with a width ranging from sub-10 nm to tens of nm and length ranging from hundreds of nm to 1 μm were routinely observed. Electrical transport properties of individual graphene nanoribbons were measured in both the back-gate and polymer-electrolyte top-gate …
Semiconductor InSb nanosheet/hexagonal boron nitride (hBN)/graphite trilayers are fabricated, and single- and double-gate devices made from the trilayers are realized and characterized. The InSb nanosheets employed in the trilayer devices are epitaxially grown, free-standing, zincblende crystals and are in micrometer lateral sizes. The hBN and graphite flakes are obtained by exfoliation. Each trilayer is made by successively stacking an InSb nanosheet on an hBN flake and on a graphite flake using a home-made alignment stacking/transfer setup. The fabricated single- and double-gate devices are …
We report on suspended single-layer graphene deposition by a transfer-printing approach based on polydimethylsiloxane stamps. The transfer printing method allows the exfoliation of graphite flakes from a bulk graphite sample and their residue-free deposition on a silicon dioxide substrate. This deposition system creates a blistered graphene surface due to strain induced by the transfer process itself. Single-layer-graphene deposition and its "blistering" on the substrate are demonstrated by a combination of Raman spectroscopy, scanning electron microscopy and atomic-force microscopy measuremen…
Liquid-phase exfoliation is one of the most promising routes for large scale production of multilayer graphene dispersions. These dispersions, which may be used in coatings, composites or paints, are believed to contain disorder-free graphene multilayers. Here we address the nature of defects in such samples obtained by liquid-phase exfoliation of graphite powder in N-methyl--2--pyrrolidone. Our Raman spectroscopy data challenges the assumption that these multilayers are free of bulk defects, revealing that defect localization strongly depends on the sonication time. For short ultrasound times…
The covalent functionalization of graphene represents a main topic in the growing field of nano materials. The reductive exfoliation of graphite with concomitant functionalization of the respective graphenide intermediates provides a promising approach towards functional graphene derivatives. In this article, we present new insights into the reductive arylation of graphene. Graphite intercalation compounds (GICs) with varying stoichiometries have been used as starting materials. Based on the spectroscopic data obtained by scanning Raman microscopy (SRM) and thermogravimetric analysis coupled t…
We demonstrate ink-jet printing as a viable method for large area fabrication of graphene devices. We produce a graphene-based ink by liquid phase exfoliation of graphite in N-Methylpyrrolidone. We use it to print thin-film transistors, with mobilities up to~95cm^2V^(-1)s(-1), as well as transparent and conductive patterns, with~80 % transmittance and~30kOhm/sq sheet resistance. This paves the way to all-printed, flexible and transparent graphene devices on arbitrary substrates
The adsorption of fluorine, chlorine, bromine, and iodine diatomic molecules on graphene has been investigated using density functional theory with taking into account nonlocal correlation effects by means of vdW-DF approach. It is shown that the van der Waals interaction plays a crucial role in the formation of chemical bonding between graphene and halogen molecules, and is therefore important for a proper description of adsorption in this system. In-plane orientation of the molecules has been found to be more stable than the orientation perpendicular to the graphene layer. In the cases of F$…
Liquid-phase chemical exfoliation is ideal to achieve industry scale production of two-dimensional (2D) materials for a wide range of application such as printable electronics, catalysis and energy storage. However, many impactful 2D materials with potentials in quantum technologies can only be studied in lab settings due to their air-sensitivity, and loss of physical performance after chemical processing. Here, we report a simple chemical exfoliation method to create a stable, aqueous, surfactant-free, superconducting ink containing phase-pure 1T'-WS$_2$ monolayers that are isotructural to th…
We have developed a method for depositing graphene monolayers and bilayers with minimum lateral dimensions of 2-10 nm by the mechanical exfoliation of graphite onto the Si(100)-2x1:H surface. Room temperature, ultra-high vacuum (UHV) tunnelling spectroscopy measurements of nanometer-sized single-layer graphene reveal a size dependent energy gap ranging from 0.1-1 eV. Furthermore, the number of graphene layers can be directly determined from scanning tunnelling microscopy (STM) topographic contours. This atomistic study provides an experimental basis for probing the electronic structure of nano…
Efficient and scalable production of two-dimensional (2D) materials is required to overcome technological hurdles towards the creation of a 2D-materials-based industry. Here, we present a novel approach developed for the exfoliation of layered crystals, i.e., graphite, hexagonal boron nitride and transition metal dichalcogenides. The process is based on high-pressure wet-jet-milling (WJM), resulting in 2 L/hr production of 10 g/L of single- and few-layer 2D crystal flakes in dispersion making the scaling-up more affordable. The WJM process enables the production of defect-free and high-quality…
We designed solution-processed, flexible hybrid graphene flake/2H-MoS2 quantum dot (QD) heterostructures, showing enhanced electrocatalytic activity for the hydrogen evolution reaction (HER) with respect to their native individual components. The 2H-MoS2 QDs are produced through a scalable, environmentally friendly, one-step solvothermal approach from two-dimensional (2D) 2H-MoS2 flakes obtained by liquid phase exfoliation (LPE) of their bulk counterpart in 2-Propanol. This QDs synthesis avoids the use of high boiling point and/or toxic solvents. Graphene flakes are produced by LPE of graphite…
Graphene oxide (GO) is one of chemically modified graphenes and has been extensively studied worldwide. A monolayer sheet of GO which is chemically produced in solution can be deposited on various substrates. We have proved that use of graphite powder with a large grain size enables preparation of a single layer GO film that is larger than 100 micrometers easily and reproducibly. If it is possible to reduce the GO film completely, one can obtain graphene without mechanical exfoliation. However, the reduction methods employed so far have been insufficient to remove oxygen or to restore the long…
We highlight the non-universality of the asymptotic behavior of dispersion forces, such that a sum of inverse sixth power contributions is often inadequate. We analytically evaluate the cross-correlation energy Ec between two pi-conjugated layers separated by a large distance D within the electromagnetically non-retarded Random Phase Approximation, via a tight-binding model. For two perfect semimetallic graphene sheets at T=0K we find Ec = C D^{-3}, in contrast to the "insulating" D^{-4} dependence predicted by currently accepted approximations. We also treat the case where one graphene layer …
Fabrication of graphene devices is often hindered by incompatibility between the silicon technology and the methods of graphene growth. Exfoliation from graphite yields excellent films but is good mainly for research. Graphene grown on metal has a technological potential but requires mechanical transfer. Growth by SiC decomposition requires a temperature budget exceeding the technological limits. These issues could be circumvented by growing graphene directly on insulator, implying Van der Waals growth. During growth, the insulator acts as a support defining the growth plane. In the device, it…
Few layer graphene/carbon (FLG/C) composites are prepared directly via the rapid and simple exfoliation of expanded graphite in the presence of carbon based natural precursors (i.e. protein, polysaccharide) in water, followed by carbonization process. Several parameters such as nature of C-precursor, FLG/C ratio and carbonization conditions (gas, temperature) are modified in order to optimize the morphology, composition and porosity of FLG/C and thereby investigate their impact on gravimetric and volumetric capacitance, their stability and contribution of pseudocapacitance (Ps) vs. double-laye…
We report the frictional response of few-layer graphene (FLG) flakes obtained by liquid phase exfoliation (LPE) of pristine graphite. To this end, we inkjet print FLG on bare and hexamethyldisilazane-terminated SiO2 substrates, producing micrometric patterns with nanoscopic roughness that are investigated by atomic force microscopy. Normal force spectroscopy and atomically resolved morphologies indicate reduced surface contamination by solvents after a vacuum annealing procedure. Notably, the printed FLG flakes show ultralow friction comparable with micromechanically exfoliated graphene flakes…
