Laser and ion beams graphene oxide reduction for microelectronic devices

Reduced graphene oxide (rGO) is a two-dimensional material, which is attracting increasing attention due to its special properties. It can be obtained by laser or ion beam irradiations of pristine graphene oxide (GO). It shows high mechanical resistance, considerable electric and thermal conductivity. All these rGO characteristics together with the high number of molecular species that can be embedded between its layers, make graphene oxide a potential material for electronic sensors or efficient support on which conductive strips, condensers, and micrometric electronic devices can be designed. In particular, as it is described in this paper, it is possible to carry out high spatial resolution lithography in GO by using a focused laser or micro ion beam in order to design macro, micro, and submicron geometrical structures. The use of the reduced graphene oxide for the laser and ion beam fabrication of electrical resistances and capacitances is presented.     

Self-assembly between graphene sheets and cationic poly(methyl methacrylate) (PMMA) particles: preparation and characterization of PMMA/graphene composites

In this study, we presented a simple approach to prepare poly(methyl methacrylate) (PMMA)/graphene composites based on the self-assembly between graphene oxide (GO) sheets and cationic PMMA emulsion particles. Briefly, cationic PMMA emulsion particles were first synthesized by a soap-free emulsion polymerization process, in which methacryloyloxyethyl trimethyl ammonium chloride was used as the emulsifier, and then blended with the aqueous solution of GO. Through electrostatic attraction, the exfoliated GO sheets were tightly adhered on the PMMA particles. The GO sheets could be reduced in situ into graphene sheets by a chemical method, without the aggregation. The structure of the prepared composites and the influences of GO and graphene sheets on the properties of PMMA were investigated. Both GO and graphene sheets can increase the glass transition temperature and storage modulus of PMMA. Moreover, graphene sheets provided a more significant reinforcement effect.     

Oxygenated Functional Group Density on Graphene Oxide: Its Effect on Cell Toxicity

The association of cellular toxicity with the physiochemical properties of graphene‐based materials is largely unexplored. A fundamental understanding of this relationship is essential to engineer graphene‐based nanomaterials for biomedical applications. Here, an in vitro toxicological assessment of graphene oxide (GO) and reduced graphene oxide (RGO) and in correlation with their physiochemical properties is reported. GO is found to be more toxic than RGO of same size. GO and RGO induce significant increases in both intercellular reactive oxygen species (ROS) levels and messenger RNA (mRNA) levels of heme oxygenase 1 (HO1) and thioredoxin reductase (TrxR). Moreover, a significant amount of DNA damage is observed in GO treated cells, but not in RGO treated cells. Such observations support the hypothesis that oxidative stress mediates the cellular toxicity of GO. Interestingly, oxidative stress induced cytotoxicity reduces with a decreasing extent of oxygen functional group density on the RGO surface. It is concluded that although size of the GO sheet plays a role, the functional group density on the GO sheet is one of the key components in mediating cellular cytotoxicity. By controlling the GO reduction and maintaining the solubility, it is possible to minimize the toxicity of GO and unravel its wide range of biomedical applications.     

Physical properties and device applications of graphene oxide

Graphene oxide (GO), the functionalized graphene with oxygenated groups (mainly epoxy and hydroxyl), has attracted resurgent interests in the past decade owing to its large surface area, superior physical and chemical properties, and easy composition with other materials via surface functional groups. Usually, GO is used as an important raw material for mass production of graphene via reduction. However, under different conditions, the coverage, types, and arrangements of oxygen-containing groups in GO can be varied, which give rise to excellent and controllable physical properties, such as tunable electronic and mechanical properties depending closely on oxidation degree, suppressed thermal conductivity, optical transparency and fluorescence, and nonlinear optical properties. Based on these outstanding properties, many electronic, optical, optoelectronic, and thermoelectric devices with high performance can be achieved on the basis of GO. Here we present a comprehensive review on recent progress of GO, focusing on the atomic structures, fundamental physical properties, and related device applications, including transparent and flexible conductors, field-effect transistors, electrical and optical sensors, fluorescence quenchers, optical limiters and absorbers, surface enhanced Raman scattering detectors, solar cells, light-emitting diodes, and thermal rectifiers.     

Enhanced Fluorescence of Graphene Oxide by Well-Controlled Au@SiO2 Core-Shell Nanoparticles

Graphene and graphene derivatives, including graphene oxide (GO) and reduced GO (rGO), have attracted remarkable attention in different fields due to their unique electronic, thermal, and mechanical properties, whereas the fluorescence property is rarely been studied. This paper reports on metal-enhanced fluorescence Au@SiO₂ composite nanoparticles adsorbed graphene oxide nanosheets, where the silica-shell is used to control the distance between gold-core and fluorophore GO, and a positively charged polyelectrolyte poly(allylamine hydrochloride) (PAH) is used to adsorb the negatively charged silica-shell and GO by layer-by-layer assembly (LbL) approach. The silica-shell around the 80 nm gold-core can be well-controlled by ending the reaction at different times. Various analytical techniques were applied to characterize the morphology and optical characters of the as-prepared particles. A more than three-fold increase of the fluorescence intensity of GO was obtained.     

Graphene resistive random memory — the promising memory device in next generation

Graphene-based resistive random access memory(GRRAM) has grasped researchers' attention due to its merits compared with ordinary RRAM. In this paper, we briefly review different types of GRRAMs. These GRRAMs can be divided into two categories: graphene RRAM and graphene oxide(GO)/reduced graphene oxide(r GO) RRAM. Using graphene as the electrode, GRRAM can own many good characteristics, such as low power consumption, higher density, transparency,SET voltage modulation, high uniformity, and so on. Graphene flakes sandwiched between two dielectric layers can lower the SET voltage and achieve multilevel switching. Moreover, the GRRAM with r GO and GO as the dielectric or electrode can be simply fabricated. Flexible and high performance RRAM and GO film can be modified by adding other materials layer or making a composite with polymer, nanoparticle, and 2D materials to further improve the performance. Above all,GRRAM shows huge potential to become the next generation memory.     

Electro‐optic switching with liquid crystal graphene

Graphene oxide (GO) particles in aqueous dispersions can form liquid crystal (LC) phases at extremely low concentrations due to the extremely high aspect ratio of the flakes and noticeably, they possess an extremely large Kerr coefficient attractive for low power consumption electro‐optic devices. Reduced graphene does not easily form LC phases in water due to its hydrophobic nature but here we show that stable dispersions of reduced graphene oxide can be realized with surfactants and that they exhibit birefringence upon shearing as well as under application of electric fields. The performance of the system is largely superior to GO LC possessing longer time stability and drastically improved electro‐optic properties with an induced birefringence twice as large at the same field strength thanks to the almost recovery of graphene properties upon reduction. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Synthesis and microwave absorption properties of graphene-oxide(GO)/polyaniline nanocomposite with gold nanoparticles

A composite of graphene/PANI/GAunano is synthesized using the co-blend method. The morphologies and microstructures of samples are examined by transition electron microscopy(TEM) and Fourier transform infrared spectroscopy(FTIR). Moreover, the microwave absorption properties of both graphene/PANI and GO/PANI/ GAunano composites are investigated in a microwave frequency band from 1 GHz to 18 GHz. The maximum reflection loss(RL) of GO/PANI/GAunano with a thickness of 2 mm is up to-24.61 d B at 15.45 GHz, and the bandwidth corresponding to RL at-10 d B can reach 4.08 GHz(from 13.92 GHz to 18.00 GHz) for a 2-mm-thick layer. The electromagnetic data demonstrate that GO/PANI/GAunano can be used as an attractive candidate for microwave absorbers.     

Quantification of the Particle Size and Stability of Graphene Oxide in a Variety of Solvents

The exceptional solution processing potential of graphene oxide (GO) is always one of its main advantages over graphene in terms of its industrial relevance in coatings, electronics, and energy storage. However, the presence of a variety of functional groups on the basal plane and edges of GO makes understanding suspension behavior in aqueous and organic solvents, a major challenge. Acoustic spectroscopy can also measure zeta potential to provide unique insight into flocculating, meta‐stable, and stable suspensions of GO in deionized water and a variety of organic solvents (including ethanol, ethylene glycol, and mineral oil). As expected, a match between solvent polarity and the polar functional groups on the GO surface favors stable colloidal suspensions accompanied by a smaller aggregate size tending toward disperse individual flakes of GO. This work is significant since it describes the characteristics of GO in solution and its ability to act as a precursor for graphene‐based materials.     

Frictional behavior of oxide graphene nanosheets as water-base lubricant additive

Oxide graphene (GO) nanosheets were prepared by modified Hummers and Offeman methods. The products were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FTIR), and thermogravimetric analysis (TGA). The tribological properties of GO nanosheets as water-base lubricant additive were investigated using a UMT-2 ball-plate tribotester. By the addition of GO nanosheets in pure water, the antiwear ability was improved and the friction coefficient was decreased. The water with GO nanosheets showed better tribological properties than the water with oxide multiwall carbon nanotubes (CNTs-COOH). It is concluded that the formation of a thin physical tribofilms on the substrate can explain the good friction and wear properties of GO nanosheets.     

1D graphene-like silicon systems: silicene nano-ribbons

Through this review we can follow the various phases that have led to the discovery of the new allotrope form of silicon: silicene. This is a one-atom thick silicon sheet arranged in a honeycomb lattice, similar to graphene. For silicon, which usually is sp3 hybridized, it represents an unusual and rare structure. First, silicene was theoretically hypothesized and subsequently its structure calculated as a possible candidate for nano-ribbons of Si grown on the anisotropic Ag(110) surface. It was only later, when the physical and chemical properties of this peculiar form of silicon, demonstrating the presence of π and π* bands giving the so-called Dirac cones at the K corners of the Brillouin zone, the sp2-like nature of the valence orbitals of the Si-Si bonds and its strong resistance towards oxygen were reported, that the real existence of silicene became recognized in the scientific community. This review is essentially focused on the experimental work performed on 1D isolated silicene nano-ribbons and their 1D dense array grown on Ag(110) surfaces.     

氧化石墨烯/壳聚糖复合薄膜材料的制备及其非线性光限幅效应的研究

石墨烯及其衍生物作为新型碳纳米结构,由于其优异的光限幅性能而受到广泛关注,但现有的工作多侧重于其在液相体系中光限幅效应及其起因研究.本文以壳聚糖为成膜基质,将氧化石墨烯(GO)与壳聚糖(CS)在液相中均匀共混后成膜,对比研究GO溶液和GO-CS复合膜的光限幅效应及其起因.结果表明在线性透过率相同的情况下,GO在固相基质中表现出比液相基质更强的光限幅效应和更弱的非线性散射.这说明不同于碳纳米管简单的非线性散射,在GO中可能存在多种非线性光学效应.     

Structural and optical properties of thermally reduced graphene oxide for energy devices

Natural intercalation of the graphite oxide, obtained as a product of Hummer's method, via ultra-sonication of water dispersed graphite oxide has been carried out to obtain graphene oxide(GO) and thermally reduced graphene oxide(RGO).Here we report the effect of metallic nitrate on the oxidation properties of graphite and then formation of metallic oxide(MO) composites with GO and RGO for the first time. We observed a change in the efficiency of the oxidation process as we replaced the conventionally used sodium nitrate with that of nickel nitrate Ni(NO_3)_2, cadmium nitrate Cd(NO_3)_2,and zinc nitrate Zn(NO_3)_2. The structural properties were investigated by x-ray diffraction and observed the successful formation of composite of MO–GO and MO–RGO(M = Zn, Cd, Ni). We sought to study the effect on the oxidation process through optical characterization via UV-Vis spectroscopy and Fourier Transform Infrared(FTIR) spectroscopy.Moreover, Thermo Gravimetric Analysis(TGA) was carried out to confirm 90% weight loss in each process thus proving the reliability of the oxidation cycles. We have found that the nature of the oxidation process of graphite powder and its optical and electrochemical characteristics can be tuned by replacing the sodium nitrate(NaNO_3) by other metallic nitrates as Cd(NO_3)_2, Ni(NO_3)_2, and Zn(NO_3)_2. On the basis of obtained results, the synthesized GO and RGO may be expected as a promising material in antibacterial activity and in electrodes fabrication for energy devices such as solar cell, fuel cell,and super capacitors.     

Tuning of electronic properties and dynamical stability of graphene oxide with different functional groups

The structural, electronic and vibrational properties of graphene oxide (GO) with varying proportion of epoxy and hydroxyl functional groups have been studied using density functional theory. The functional groups and oxygen density have an obvious influence on the electronic and vibrational properties. The dependence of band gap on associated functional groups and oxygen density shows a possibility of tuning the band gap of graphene by varying the functional groups as well as oxidation level. The absorption of high oxygen content in graphene leads to the gap opening and resulting in a transition from semimetal to semiconductor. Phonon dispersion curves show no imaginary frequency or no softening of any phonon mode throughout the Brillouin zone which confirms the dynamical stability of all considered GO models. Different groups and different oxygen density result into the varying characteristics of phonon modes. The computed results show good agreement with the experimental observations. Our results present interesting possibilities for engineering the electronic properties of graphene and GO and impact the fabrication of new electronics.     

First-principles insight into Li and Na ion storage in graphene oxide

The structural, electronic, and adsorption properties of Li/Na ions on graphene decorated by epoxy groups are investigated by first-principles calculations based on density functional theory.Our results show that the concentration of epoxy groups remarkably affects the structural and electronic properties of graphene.The bandgaps change monotonically from0.16 eV to 3.35 eV when the O coverage increases from 12.5% to 50%(O/C ratio).Furthermore, the highest lithiation potential of 2.714 V is obtained for the case of graphene oxide(GO) with 37.5 % O coverage, while the highest sodiation potential is 1.503 V for GO with 12.5% O coverage.This clearly demonstrates that the concentration of epoxy groups has different effects on Li and Na storage in GO.Our results provide a new insight into enhancing the Li and Na storage by tuning the concentration of epoxy groups on GO.     

Probing the role of hydrolytically stable, 3-aminopropyl triethoxysilane crosslinked chitosan/graphene oxide membrane towards Congo red dye adsorption

In this investigation, the practicability of utilizing 3-aminopropyl triethoxysilane (3-APTES) crosslinked chitosan (Ch)/graphene oxide (GO) membranes were explored for adsorptive removal of anionic dyes from aqueous medium. Membranes were successfully fabricated through solution casting technique. Strong interactions amongst matrix (chitosan), 3-APTES, polyvinylpyrrolidone (PVP) and GO were confirmed by Infrared spectroscopy. Thermal stability of the chitosan was improved by adding graphene oxide and results were verified via thermogravimetric (TGA) analysis. Swelling and hydrolytic results confirmed that 2 %-Ch/PVP was a stable membrane while increasing the amount of 3-APTES in the chitosan nanocomposites membrane decreased its stability in aqueous medium. The adsorption characteristics of the membranes were evaluated by the adsorption of Congo red (CR) dye from aqueous medium. The adsorbent can remove 80% of CR from aqueous medium and follows second order kinetics. This study outlines the possibility of exploring green membranes which can be easily fit in various flow systems.     

Investigation of Raman and photoluminescence studies of reduced graphene oxide sheets

In this paper, we are investigating the Raman and photoluminescence properties of reduced graphene oxide sheets (rGO). Moreover, graphene oxide (GO) sheets are synthesized using Hummer’s method and further reduced into graphene sheets using D-galactose. Both GO and rGO are characterized by UV-vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Thermogravimetric (TGA) analysis. Raman analysis of rGO shows the restoration of graphitic domains in GO after reduction. The photoluminescence of rGO showed emission in the UV region which is blue shifted along with luminescent quenching as compared to GO. This blue shift and quenching in photoluminescence arises due to the newly formed crystalline sp² clusters in rGO which created percolation pathways between the sp² clusters already present.     

Graphene oxide–gellan gum–sodium alginate nanocomposites: synthesis,characterization, and mechanical behavior

This paper reports the preparation and characterization of graphene oxide–gellan gum–sodium alginate nanocomposites (GO–GG–Alg). The nanocomposites were prepared by a simple solution mixing-evaporation method. Fourier transform infrared spectroscopy, X-ray diffractions, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, and mechanical testing were conducted to study the structure and properties of the nanocomposites. The obtained findings reveal that gellan gum, sodium alginate, and graphene oxide are able to form a homogeneous mixture. Small amount of GO loading on GO–GG–Alg drastically improves its tensile strength and Young’s modulus. Detailed material characteristics of the nanocomposites are addressed.     

Fe~(3+)对石墨烯氧化物荧光淬灭机理的研究

采用改进的Humer法合成了石墨烯氧化物,利用搭建的时间分辨光谱探测系统详细探究了Fe~(3+)(浓度为0.5、1、2 mmol/L)对石墨烯氧化物荧光淬灭物理机制。稳态荧光发射光谱中,随着Fe~(3+)浓度的增加,石墨烯氧化物的荧光强度急剧减弱。时间分辨荧光光谱和飞秒瞬态吸收光谱研究证实,加入不同浓度Fe~(3+)的GO其动力学衰减曲线基本没有任何变化。结果表明,Fe~(3+)对石墨烯氧化物的荧光淬灭主要是静态的荧光淬灭过程。     

pH‐dependent surface‐enhanced Raman scattering of aromatic molecules on graphene oxide

Graphene has become an ideal substrate for surface‐enhanced Raman scattering (SERS) to study the chemical enhancement mechanism. In comparison with mechanically exfoliated graphene, graphene oxide (GO) has been found to be a better substrate due to its highly negatively charged oxygen functional groups. In this work, the pH‐dependent SERS effect of aromatic molecules on GO are investigated. The results demonstrate that the Raman enhancement of dyes deposited on GO performs differently over a wide range of pH values (2 to 10). Adsorption experiments show that the pH‐dependent SERS effect is closely related to the adsorption of aromatic molecules on GO, which is dominated by the electrostatic interaction. Thus, the influence of pH in GO‐mediated SERS should be carefully considered, especially in its biomedical application. Copyright © 2012 John Wiley & Sons, Ltd.