Formation Of Multilayer Graphene Research Articles

Effect of graphene-based additives on mechanical strength and microstructure of gypsum plaster

In this study, graphene-based materials such as graphene oxide, reduced graphene oxide, and boron-doped reduced graphene oxide were synthesized, and their effects on the microstructure and mechanical properties of gypsum plaster were investigated. The graphene oxide (GO) sample was synthesized by modified Hummers’ method, and reduced graphene oxide (rGO) was obtained with the thermal reduction of GO. Boron doped reduced graphene oxide (B-rGO) was prepared via the impregnation method. The synthesized graphene-based materials were characterized using H 2 -TPR, TGA-DTA, XRD, FT-IR, SEM-EDS, TEM, Raman, and N 2 adsorption-desorption analysis. Analysis results confirmed that 450 o C was a sufficient temperature under an H 2 atmosphere to reduce GO and preserve rGO structure. XRD results revealed the presence of multilayer graphene structure in the rGO and B 2 O 3 crystals in the B-rGO sample. Multilayer graphene formation was also determined from the I 2D /I G ratio (0.1) of Raman analysis. Mechanical strength studies showed that while GO had a negative effect on both bending and compressive strength of gypsum plaster, rGO enhanced its bending and compressive strength. The addition of 0.1 wt% rGO added gypsum plaster increased the bending strength by 15.1% and compressive strength by 3.70%. SEM, He Pycnometry, and N 2 adsorption-desorption analyses revealed that rGO addition significantly changed the microstructure of gypsum plaster. The addition of B-rGO positively affected the compressive strength of the plaster and the highest increase was obtained as 8.6%; however, no significant change was observed in the microstructure of gypsum. • Electron microscopy images represented graphene nanosheets and graphene layers • X-ray diffraction results revealed the B 2 O 3 crystals in the boron-doped sample • Reduced graphene oxide increased the bending and compressive strength • Boron doped reduced graphene oxide enhanced the compressive strength • Reduced graphene oxide decreased the porosity of the gypsum

Ionic Liquids Based Cocktails as a Composite Redox Electrolyte for Natural Dye-Sensitized Solar Cells

Fatty-imidazolinium electrolytes, waste graphite dispersed composite electrolytes like cocktails (1,3-methyl octyl-1,2,3-benzotiazolium acetate–cis-oleyl-imidazolinium iodide), and graphite exfoliation using cis-oleyl-imidazolinium acetate have been studied to enhance the efficiency of a newly developing dye-sensitized solar cells (DSSCs). The DSSCs were fabricated in a sandwich structure and characterized using Solar Simulator. The graphite exfoliation was conducted by sonication and microwave energy, as well as the electrochemical method. Cis-oleyl-imidazolinium iodide efficiency (0.53%) was highest than stearyl-imidazolinium iodide and palmityl-imidazolinium iodide because cis-oleyl-imidazolinium iodide has a double bond and the longest alkyl chain which triggered a self-assembly structure formation and increased the rate of I-/I3- transport in cells. Then, the efficiency of DSSCs-based composite electrolytes was in the range of 0.020– 0.203%. Dispersion of 0.05% of the graphite results in efficiency enhancement of about 100%, but the greater fraction (0.10%) of the graphite causes a poor performance (lower efficiency), possibly due to interference of the internal electron transportation routes in the DSSC by insoluble graphite. After exfoliation, the conductivity of synthetic graphite (11.58 x 10-1 S/cm), new battery graphite (9.32 x 10-1 S/cm), and battery waste graphite (7.96 x 10-1 S/cm) were increased respectively 10 times, 2 times, and 4 times from the graphite before exfoliation due to changes in crystallinity, the distance between layers, crystal size, formation of multilayer graphene, and the occurrence of π to π* transition. This enhancement of solar conversion efficiency can give a new contribution to the development of DSSC.

Strong suppression of graphene growth by sulfur superstructure on a nickel substrate

The formation of multilayer graphene on a nickel substrate is usually unavoidable due to the precipitation of carbon upon cooling after the growth of the single layer of graphene. We found that the growth rate of graphene on a Ni(110) surface was markedly reduced when the surface was covered by sulfur atoms arranged in a c($2\ifmmode\times\else\texttimes\fi{}2$) periodicity. An atomistic survey by scanning tunneling microscopy revealed a compression of the sulfur superstructure as a result of the growth of graphene-covered regions. Photoelectron emission microscopy showed that the growth rate of graphene is linear with time, which indicates that carbon atoms are supplied only at the growth front of graphene islands. Density functional theory calculations rationalized these experimental results and suggested a mechanism for suppressing the growth of graphene. Sulfur atoms might extend the utility of nickel substrates for the production of single-layer graphene or nanographenes.

Laser-Induced Graphene Printed Wearable Flexible Antenna-Based Strain Sensor for Wireless Human Motion Monitoring

Leveraging laser-induced graphene (LIG) in various flexible polymer electronics applications is becoming tremendously popular. LIG is porous multilayer graphene generated by a single-step process using infrared CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser onto the carbon-based polymers. In this article, a direct LIG printed microstrip patch antenna operating at the 5.8-GHz unlicensed band is presented. Based on simulations, the proposed design exhibited the desired unidirectional radiation characteristics with a measured gain of 1.82 dBi at the resonant frequency. The LIG-based rectangular patch was printed using the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser by selective reduction of polyimide (PI) sheet. The chemical properties of LIG were examined using various structural and morphological characterization techniques, which confirmed the formation of multilayer graphene. The sensitivity of the patch antenna was analyzed for measuring strain and its effect on LIG. By harnessing LIG on flexible material such as PI sheet, the antenna exhibited a threshold increase in sensitivity. The proposed sensor shows a sensitivity of 14.08 and 11.34 for compressive and tensile strain, respectively. Inspired by the significant sensitivity, the fabricated device has been examined for human motion monitoring by attaching it to the human hand for practical usage in real-time applications. The proposed antenna-based sensor reduces the number of components by eliminating external wiring and onboard battery. Moreover, it serves as both the sensing and wireless data transmitting element. Overall, this work demonstrates designing a compact, easy-to-fabricate, sensitive, and flexible antenna-based Internet of Things (IoT) sensor for motion detection, structural health monitoring, and industrial strain sensing applications.

Features of Field Desorption of Sodium and Cesium from the Surface of a Carbonized Rhenium Field Emitter

We used field emission microscopy to study the field desorption of sodium and cesium atoms from a rhenium field emitter precarbonized in benzene vapor. The dependences of the ion currents of sodium and cesium on the voltage applied to the field emitter differ. The difference in the ion current dependences is explained by the formation of multilayer graphene on the crystalline surface of a rhenium field emitter in the regions of low-index faces and its intercalation by alkali metal atoms with different ionization potentials and different atomic and ionic radii.

Особенности полевой десорбции натрия и цезия с поверхности науглероженного рениевого полевого эмиттера

The field desorption of sodium and cesium atoms from a rhenium field emitter pre-carbonized in benzene vapor was studied using field emission microscopy. A difference was found in the dependence of the ion current Na and Cs on the voltage applied to the field emitter. The difference in the dependences of the ion current is explained by the formation of multilayer graphene on the crystal surface of the rhenium field emitter in the regions of low-index faces and its intercalation by alkali metal atoms with different ionization potentials and different atomic and ion radii.

Facile Preparation of Multilayered Graphene with CO2 as a Carbon Source

A facile and controllable route for fabricating multilayered graphene was provided using CO2 as a carbon source. A typical multilayered graphene structure was obtained with the reaction between CO2 and magnesium metal. The reaction was carried out under different CO2 gas flows, reaction temperatures, and reaction times with two types of metal Mg (Mg powder and Mg ribbon). Moreover, the effect of different concentrations of HCl solution for sample post-processing was discussed in this study. The results of transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), Raman spectroscopy and X-ray powder diffraction (XRD) confirm the formation of multilayered graphene. This work proposed a new method for a controllable way to produce multilayered graphene with gaseous CO2 as a carbon source.

Efficient Production of Multi-Layer Graphene from Graphite Flakes in Water by Lipase-Graphene Sheets Conjugation

Biographene was successfully produced in water from graphite flakes by a simple, rapid, and efficient methodology based on a bioexfoliation technology. The methodology consisted in the application of a lipase, with a unique mechanism of interaction with hydrophobic surfaces, combined with a previous mechanical sonication, to selectively generate lipase-graphene sheets conjugates in water at room temperature. The adsorption of the lipase on the graphene sheets permits to keep the sheets separated in comparison with other methods. It was possible to obtain more than 80% of graphene (in the form of multi-layer graphene) from low-cost graphite and with less damage compared to commercial graphene oxide (GO) or reduced GO. Experimental analysis demonstrated the formation of multi-layer graphene (MLG) mainly using lipase from Thermomyces Lanuginosus (TLL).

Effect of Cu surface treatment in graphene growth by chemical vapor deposition

Cu foils with various initial roughness were prepared and graphene was grown on each Cu foil. Graphene nuclei density was highly related to the initial surface roughness of Cu foil. Smoothing was done on Cu foil and initial roughness was relieved during 3 h annealing, but Cu surface with high surface roughness and impurity atoms provides larger nuclei density for the graphene growth. Heteronuclei effect of size variations of impurity atoms on multilayer graphene formation was calculated. Electropolishing was carried out to suppress the heteronuclei effect and the nuclei formation on Cu surface as well. For electropolished Cu substrate, nuclei density of graphene was extremely low even without extended pre-annealing step.

Improved capacitance of NiCo2O4/carbon composite resulted from carbon matrix with multilayered graphene

The optimized electric and ionic conductivity of metal oxides with pseudo-capacitive properties can greatly improve their electrochemical performances and can effectively amplify their applications in super-capacitors. Carbon spheres with multilayered graphene formed in their matrix are prepared by annealing them with sodium metal and they are combined with NiCo2O4 spheres by a simple hydro-thermal treatment. Structures and electrochemical performances of resulted samples are examined with X-ray diffraction, Raman scattering spectra, X-ray photoelectron spectroscopy, infrared spectroscopy, electron microscopy, gas physisorption, cyclic voltammetry and electrochemical impedance spectra, respectively. The largest specific capacitance of resulted composites is measured about 920 F g−1 at 1 A g−1, which is about 3.7 times larger than that of pure carbon spheres and 2.8 times larger than that of pure NiCo2O4 spheres. The formation of multilayered graphene in the matrix of carbon spheres not only increases the high specific capacitance based on electric double layers, but also makes metal oxides combined with them display greatly increased pseudo-capacitance. The electric and ionic conductivity of resulted composites with various weight ratios of NiCo2O4 and carbon spheres are respectively investigated and their effects on their electrochemical performances are also discussed.

Multilayer Graphene Growth Assisted by Sulfur Using the Arc Discharge Method at Ambient Conditions

Graphene, a 2-D hexagonal array of carbon atoms, has interesting physical properties, which make this material interesting in applications such as energy storage devices and supercapacitors. The approach here proposed is the use of sulfur as a promoter of sp2 bonds to form graphite domains and with the particularity of using air at atmospheric pressure to create an electric arc discharge. From diagnostic realized with Raman spectroscopy, it has been observed that the carbonaceous material obtained without the addition of sulfur has a defective graphitic structure, but when sulfur is added, the formation of multilayer graphene is enhanced. Scanning electronic microscopy corroborates the synthesis of graphene-like material. Optical emission spectroscopy studies were realized to the plasma; electronic and rotational temperatures obtained allow envisaging a local thermodynamic equilibrium; some spectra obtained show the existence of reactive sulfur species which possibly are nucleation centers of graphitic domains.

Synthesis of transfer-free graphene on cemented carbide surface

Direct growth of spherical graphene with large surface area is important for various applications in sensor technology. However, the preparation of transfer-free graphene on different substrates is still a challenge. This study presents a novel approach for the transfer-free graphene growth directly on cemented carbide. The used simple thermal annealing induces an in-situ transformation of magnetron-sputtered amorphous silicon carbide films into the graphene matrix. The study reveals the role of Co, a binding phase in cemented carbides, in Si sublimation process, and its interplay with the annealing temperature in development of the graphene matrix. A detailed physico-chemical characterisation was performed by structural (XRD analysis and Raman spectroscopy with mapping studies), morphological (SEM) and chemical (EDS) analyses. The optimal bilayer graphene matrix with hollow graphene spheres on top readily grows at 1000 °C. Higher annealing temperature critically decreases the amount of Si, which yields an increased number of the graphene layers and formation of multi-layer graphene (MLG). The proposed action mechanism involves silicidation of Co during thermal treatment, which influences the existing chemical form of Co, and thus, the graphene formation and variations in a number of the formed graphene layers.

Simultaneous etching and transfer — Free multilayer graphene sheets derived from C60 thin films

Despite the advantage of chemical vapor deposition (CVD) for realization of large area epitaxial growth of graphene on transition metal catalysts, both etching and transfer process of CVD-grown graphene sheets still remain a big challenge. Here we demonstrate the formation of multilayer graphene (MLG) sheets tailored from C60 thin films on the top of Si/Ni substrate without etching and transfer steps based on Ni films. This self-assembled process separates the MLG sheets from the conductive Ni catalyst, embarking a possibility for direct characterizations of MLG sheets. The fine-tuned C60 films (30nm) are transformed into approximately 17 MLG sheets, thus making it large-area MLG sheets for a variety of direct applications.

Growth of few- and multilayer graphene on different substrates using pulsed nanosecond Q-switched Nd:YAG laser

In this report, few- and multilayer graphene was fabricated on different substrates by pulsed laser ablation of a highly ordered pyrolytic graphite target under optimized growth conditions, using a pulsed nanosecond Q-switched Nd:YAG laser at 355 nm (3.5 eV). The nondestructive micro-Raman spectroscopic study on our samples has revealed few- and multilayer graphene formation. The number of graphene layers was found to be reduced with the increase in growth temperature. At substrate temperature of 750 °C, the ratio of intensities (I 2D/I G) was calculated from the Raman spectra of the graphene samples to be 0.15 which confirms the multilayer graphene formation, while for graphene film grown at 800 °C, I 2D/I G ratio was 0.27 indicating formation of less than five layers of graphene or few-layer graphene. The thickness of few- and multilayer graphene was also confirmed using atomic force microscopy, whereas the microstructure of few- and multilayer graphene was investigated using scanning electron microscopy. The electrical properties in function of growth temperature were evaluated with two-point probe measurements. This work presents a simple, fast, and controllable alternative effective laser technique to synthesize few- or multilayer graphene.

In situ TEM Observation of MultiLayer Graphene Formation from CO on Cobalt Nanoparticles at Atmospheric Pressure

<i>In situ</i> TEM Observation of MultiLayer Graphene Formation from CO on Cobalt Nanoparticles at Atmospheric Pressure

In situ TEM observation of the Boudouard reaction: multi-layered graphene formation from CO on cobalt nanoparticles at atmospheric pressure.

Using a MEMS nanoreactor in combination with a specially designed in situ Transmission Electron Microscope (TEM) holder and gas supply system, we imaged the formation of multiple layers of graphene encapsulating a cobalt nanoparticle, at 1 bar CO : N2 (1 : 1) and 500 °C. The cobalt nanoparticle was imaged live in a TEM during the Boudouard reaction. The in situ/operando TEM studies give insight into the behaviour of the catalyst at the nanometer-scale, under industrially relevant conditions. When switching from Fischer-Tropsch syngas conditions (CO : H2 : N2 1 : 2 : 3 at 1 bar) to CO-rich conditions (CO : N2 1 : 1 at 1 bar), we observed the formation of multi-layered graphene on Co nanoparticles at 500 °C. Due to the high temperature, the surface of the Co nanoparticles facilitated the Boudouard reaction, causing CO dissociation and the formation of layers of graphene. After the formation of the first patches of graphene at the surface of the nanoparticle, more and more layers grew over the course of about 40 minutes. In its final state, around 10 layers of carbon capped the nanoparticle. During this process, the carbon shell caused mechanical stress in the nanoparticle, inducing permanent deformation.

Preparation of low-dimensional carbon material-based metal nanocomposites using a polarizable organic/water interface

Abstract

Studies on p-TiO2/n-graphene heterojunction for hydrogen detection

Thermally oxidized p-type Si [resistivity (5–10)Ωcm and 〈100〉 orientation] with oxide thickness of 245nm was used as the substrate for the deposition of graphene by CVD. The formation of multilayer graphene (MLG) was confirmed by Raman spectroscopy. A heterojunction was fabricated by sol–gel coating of TiO2 on CVD grown graphene layer. The formation of titanium dioxide was verified by electron dispersion spectroscopy (EDS). The surfaces of TiO2, graphene as well as p-TiO2/n-graphene interface were characterized by scanning electron microscopy (SEM). Detail sensor study of the p-TiO2/n-graphene heterojunction was performed by taking two lateral catalytic metal (Pd) contacts deposited by e-beam evaporation. The response time of 16s and the corresponding recovery time of 61s were obtained for 0.5% H2 in air at 125°C. The p-TiO2/n-graphene junction showed selectivity for H2 compared to methane. The stability study was performed and it showed almost the steady results over a period of 3 days as tested by the discrete measurements. The sensing mechanism was formulated using a simplified energy band diagram.

Preparation of graphene on Cu foils by ion implantation with negative carbon clusters**Project supported by the National Natural Science Foundation of China (Grant Nos. 11105100, 11205116, and 11375135) and the State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, China (Grant No. AWJ-M13-03).

We report on few-layer graphene synthesized on Cu foils by ion implantation using negative carbon cluster ions, followed by annealing at 950 °C in vacuum. Raman spectroscopy reveals IG/I2D values varying from 1.55 to 2.38 depending on energy and dose of the cluster ions, indicating formation of multilayer graphene. The measurements show that the samples with more graphene layers have fewer defects. This is interpreted by graphene growth seeded by the first layers formed via outward diffusion of C from the Cu foil, though nonlinear damage and smoothing effects also play a role. Cluster ion implantation overcomes the solubility limit of carbon in Cu, providing a technique for multilayer graphene synthesis.

CVD-Grown Graphene Modified with Aryl Groups by Electroreduction of Corresponding Diazonium Salts

Graphene has been widely studied material because of its interesting properties (for example large surface area, high conductivity, good mechanical, electronic, optical, thermal and chemical properties). It is well-known that high-quality graphene can be prepared by mechanical exfoliation of highly oriented pyrolytic graphite, although this method is not suitable for large scale applications. According to the literature, chemical vapor deposition (CVD) is one of the most promising approach in producing high quality and large-scale graphene. Graphene has been widely grown by CVD on nickel or copper substrate. Also, it is well known that graphene synthesis by CVD yields a multi-layer graphene on the Ni surface.1 Based on the recent report,2 we can talk about multi-layer graphene if this material consist small number (between two and about 10) of graphene layers.Graphene is also a good model substrate to be modified because of its interesting properties. A very attractive method for the modification of electrode surfaces is the electrochemical reduction of aryldiazonium salts. This method is based on the formation of an aryl radical which reacts with the electrode surface giving a strong bond between substrate and organic layer.3 Numerous studies have been reported about spontaneous functionalization of various diazonium salts to modify graphene-based substrates (including CVD-grown graphene). However, according to our knowledge, the electrochemical grafting of CVD-grown graphene electrodes by diazonium reduction is relatively rare. Therefore, the aim of this study was to investigate the electrochemical grafting of graphene-based electrodes via electrochemical reduction of the corresponding diazonium salts. The synthesis of graphene was performed by CVD onto Ni foil and the functionalization of CVD-grown graphene with aryl groups was carried out in a specially designed three-electrode cell set-up using cyclic voltammetry (CV). Furthermore, the CVD-grown graphene on Ni foil electrografted with aryl groups was characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM) and CV.First of all, the quality of CVD-grown graphene on Ni foil was evaluated by using different surface analytical methods. The high-resolution scanning electron microscopy, Raman spectroscopy and AFM results revealed almost defect-free multilayer graphene formation on Ni foil.4 Next, the samples of CVD-grown graphene on Ni foil were electrografted either with azobenzene (AB), 9,10-anthraquinone (AQ), 2–methyl–4–([2–methylphenyl]azo)benzene (GBC), 2,5–dimethoxy–4–([4–nitrophenyl]azo)benzene (FBK), 4-nitrophenyl (NP) and 4-bromophenyl (PhBr) groups using pre–synthesized azobenzene diazonium salt, 9,10-anthraquinone-1-diazonium salt and commercially available Fast Garnet GBC sulfate salt, Fast Black K salt, 4-nitrobenzenediazonium and 4-bromobenzenediazonium salt, respectively (Scheme 1).The electrochemical grafting of the CVD-grown graphene electrodes by diazonium reduction was confirmed by a wide range of techniques. For example, the XPS results confirmed the presence of corresponding functional groups on CVD graphene electrodes. The AFM images of aryl-modified CVD graphene electrodes showed clearly that the surfaces of all electrodes were covered with granular layer. Furthermore, while NP and AQ groups are electrochemically active, the CV behavior of the NP- and AQ-modified CVD graphene electrodes was studied in Ar-saturated 0.1 M KOH and a quasi-reversible response was observed. These results are significant because the aryl-modified CVD graphene electrodes can be used for various applications, including electrocatalysis and electroanalysis.