Molecular beam growth of graphene nanocrystals on dielectric substrates

We demonstrate the growth of graphene nanocrystals by molecular beam methods that employ a solid carbon source, and that can be used on a diverse class of large area dielectric substrates. Characterization by Raman and near edge X-ray absorption fine structure spectroscopies reveal a sp² hybridized hexagonal carbon lattice in the nanocrystals. Lower growth rates (below 0.5 Å/min) favor the formation of layered, larger size multi-layer graphene crystallites (up to 22 nm) on all investigated substrates. The surface morphology is determined by the roughness of the underlying substrate (RMS ～8 Å) and graphitic monolayer steps are observed by ambient scanning tunneling microscopy.     

Electrodeposition of graphene oxide-hydroxyapatite composite coating on titanium substrate

In this work, graphene oxide (GO)/hydroxyapatite (HA) composite coatings were successfully prepared on titanium substrate by electrophoretic deposition technology. Subsequently, microstructure, phase composition, adhesion strength, hydrophilicity, corrosion resistance, bioactivity, antibacterial activity and biocompatibility of the coating were evaluated. The adhesion strength of coating increased by 76% from 6.46 MPa to 17.81 MPa with 0 wt% GO to 12 wt% GO and the corrosion rate of coating with 8 wt% GO was achieved at the minima of (1.493 × 10^-3mm/a). Biomineralization experiment indicated the excellent bioactivity of GO/HA composite coatings. The water contact angle of the composite coatings increased from 20.6°(0 wt% GO) to 38.1°(12 wt%GO). The antibacterial rates of coating with 5 wt% GO was 96.7%, while declined to 25% after thermal treatment. In-vitro L929 cell culture experiments indicated the composite coatings with 5 wt% GO exhibited good biocompatibility.     

Probing substrate influence on graphene by analyzing Raman lineshapes

We provide a new approach to identify the substrate influence on graphene surface. Distinguishing the substrate influences or the doping effects of charged impurities on graphene can be realized by optically probing the graphene surfaces, included the suspended and supported graphene. In this work, the line scan of Raman spectroscopy was performed across the graphene surface on the ordered square hole. Then, the bandwidths of G-band and 2D-band were fitted into the Voigt profile, a convolution of Gaussian and Lorentzian profiles. The bandwidths of Lorentzian parts were kept as constant whether it is the suspended and supported graphene. For the Gaussian part, the suspended graphene exhibits much greater Gaussian bandwidths than those of the supported graphene. It reveals that the doping effect on supported graphene is stronger than that of suspended graphene. Compared with the previous studies, we also used the peak positions of G bands, and I_2D/I_G ratios to confirm that our method really works. For the suspended graphene, the peak positions of G band are downshifted with respect to supported graphene, and the I_2D/I_G ratios of suspended graphene are larger than those of supported graphene. With data fitting into Voigt profile, one can find out the information behind the lineshapes.     

Microwave-assisted green synthesis of Ag/reduced graphene oxide nanocomposite as a surface-enhanced Raman scattering substrate with high uniformity

A nanocomposite of silver nanoparticles/reduced graphene oxide (Ag/rGO) has been fabricated as a surface-enhanced Raman scattering (SERS) substrate owing to the large surface area and two-dimensional nanosheet structure of rGO. A facile and rapid microwave-assisted green route has been used for the formation of Ag nanoparticles and the reduction of graphene oxide simultaneously with L-arginine as the reducing agent. By increasing the cycle number of microwave irradiation from 1 and 4 to 8, the mean diameters of Ag nanoparticles deposited on the surface of rGO increased from 10.3 ± 4.6 and 21.4 ± 10.5 to 41.1 ± 12.6 nm. The SERS performance of Ag/rGO nanocomposite was examined using the common Raman reporter molecule 4-aminothiophenol (4-ATP). It was found that the Raman intensity of 4-ATP could be significantly enhanced by increasing the size and content of silver nanoparticles deposited on rGO. Although the Raman intensities of D-band and G-band of rGO were also enhanced simultaneously by the deposited Ag nanoparticles which limited the further improvement of SERS detection sensitivity, the detectable concentration of 4-ATP with Ag/rGO nanocomposite as the SERS substrate still could be lowered to be 10⁻¹⁰ M and the enhancement factor could be increased to 1.27 × 10¹⁰. Furthermore, it was also achievable to lower the relative standard deviation (RSD) values of the Raman intensities to below 5%. This revealed that the Ag/rGO nanocomposite obtained in this work could be used as a SERS substrate with high sensitivity and homogeneity.     

Controlled synthesis of bilayer graphene on nickel

ABSTRACT: We report uniform and low-defect synthesis of bilayer graphene on evaporated polycrystalline nickel films. We use atmospheric pressure chemical vapor deposition with ultra-fast substrate cooling after exposure to methane at 1000C. The optimized process parameters i.e. growth-time, annealing profile and flow rates of various gases are reported. By using Raman spectroscopy mapping, the ratio of 2D to G peak intensities (I2D/IG) is in the 0.9-1.6 range over 96 percent of 200umx200um area. Moreover, the average ratio of D to G peak intensities (ID/IG) is about 0.1.     

石墨烯的制备及石墨烯/PVDF合材料介电性能的研究

通过Staudenmaier法制备了完全氧化的氧化石墨(GO),并通过高温热膨胀制备了单层石墨烯(graphene).用FT-IR、TG和XRD对GO的氧化程度、含氧官能团进行了表征;Graphene的XRD测试结果证明了单层石墨的存在.利用超声共混法制备了graphene/PV DF介电纳米复合材料.介电性能的测试表...     

Functionalised graphene sheets as effective high dielectric constant fillers

A new functionalised graphene sheet (FGS) filled poly(dimethyl)siloxane insulator nanocomposite has been developed with high dielectric constant, making it well suited for applications in flexible electronics. The dielectric permittivity increased tenfold at 10 Hz and 2 wt.% FGS, while preserving low dielectric losses and good mechanical properties. The presence of functional groups on the graphene sheet surface improved the compatibility nanofiller/polymer at the interface, reducing the polarisation process. This study demonstrates that functionalised graphene sheets are ideal nanofillers for the development of new polymer composites with high dielectric constant values.PACS: 78.20.Ci, 72.80.Tm, 62.23.Kn     

Two selective growth modes for graphene on a Cu substrate using thermal chemical vapor deposition

Here we provide evidence of two selective growth modes, namely the ‘surface adsorption (SA) mode’ and the ‘diffusion and precipitation (DP) mode’ for the synthesis of graphene on Cu foil by thermal chemical vapor deposition. Using acetylene feedstock, the number of graphene layers was controlled simply by adjusting the injection time, and the DP growth mode was clearly verified by the existence of a carbon-diffused Cu layer with expansion of the Cu lattice. With methane feedstock, either SA or DP growth modes could be selected for the growth of graphene at low or high partial pressure of carbon feedstocks, respectively. The critical pressure for switching the growth modes depends on reactivity of carbon feedstock to Cu substrate.     

Controlled synthesis of few-layered graphene sheets on a large scale using chemical exfoliation

The synthesis of few-layered graphene sheets with controlled number of layers (3-4) on a large scale was developed using chemical exfoliation by simply controlling the oxidation and exfoliation procedure. The obtained Few-layered Graphene Oxide (FGO) was characterized by atomic force microscopy, X-ray diffraction, thermal gravimetric analysis and Ultraviolet-visible spectroscopy. It is found that the FGO, which contains less functional groups than single-layered graphene oxide (GO), also has excellent water dispersion. Moreover, after reduction treatments under the same conditions as that used for GO, reduced FGO show a much better electrical conductivity of 108 S/cm, two-orders higher than reduced GO.     

One-step metal electroplating and patterning on a plastic substrate using an electrically-conductive layer of few-layer graphene

Few-layer graphene (FLG) was investigated as an electrically-conductive interleaf layer for one-step electroplating and patterning of metal on nonconductive polymer substrates without using multiple and toxic pretreatment processes in traditional electroplating. An individual FLG (5–10 nm of thickness with 6.4% of oxygen content) was obtained by expanding graphite with microwave followed by exfoliating the expanded graphite with sonication in N-methyl-pyrrolidone. Stacking FLG in the in-plane direction, a robust FLG film was obtained by the vacuum-assisted filtering and drying methods, and transferred to a polyethylene terephthalate (PET) substrate via an intermediate transfer to the water surface. The sheet resistance of the FLG film on the PET substrate was 0.9 kΩ/sq with a thickness of 80 nm and the root-mean-square roughness of 29 nm. In the electroplating of nickel on the FLG film, hemisphere-shape metal seeds appeared in the early stage of electroplating and they subsequently grew up to 200–480 nm, which became connected to form a continuous nickel layer. The thickness of the continuous nickel layer increased linearly with electroplating time. The developed electroplating method demonstrated its capability of selective patterning on nonconductive substrates using a simple masking technique.     

Size-controlled synthesis of graphene oxide sheets on a large scale using chemical exfoliation

The synthesis of graphene oxide (GO) sheets with controlled size on a large scale was developed using chemical exfoliation by simply controlling the oxidation and exfoliation procedure. The GO samples prepared under different conditions, which all have excellent water dispersion, are characterized by thermal gravimetric analysis, Ultraviolet-visible spectroscopy, X-ray diffraction and atomic force microscopy. It is found that as longer oxidation times and more oxidants are used, the mean size of the GO sheets, which has a Gaussian distribution, decreases from ∼59,000 to ∼550 nm².     

A nonvolatile memory device made of a graphene nanoribbon and a multiferroic BiFeO3 gate dielectric layer

We demonstrate a field-effect nonvolatile random access memory (NVRAM) device made of a graphene nanoribbon (GNR) and a multiferroic epitaxial BiFeO₃ thin film. The GNR and the source/drain electrodes were formed by position-controlled dip-pen nanolithography. The NVRAM device exhibited asymmetric hysteresis behavior originating from the combination of the p-type semiconducting behavior of the GNR and the ferroelectric hysteresis of the BiFeO₃ layer. The memory window of the NVRAM device was significantly improved by a NH₃ annealing process which changed the p-type GNR to n-type.     

Efficient synthesis of graphene sheets using pyrrole as a reducing agent

The efficient synthesis of graphene sheets using pyrrole as a reducing agent was explored. The obtained graphene sheets were dispersible in organic solvents such as ethanol, isopropanol, N,N-dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, tetrahydrofuran, and acetone. During this reduction reaction, pyrrole was oxidized, forming oxidation product of pyrrole and adsorbed on the graphene sheets surface by π–π interaction. The oxidation product of pyrrole acted as a capping agent for graphene sheets by preventing re-stacking and formed organically dispersible graphene. The formation of graphene and its crystalline nature was indicated by the transmission electron microscopy and the atomic force microscopy analysis. Raman, X-ray photoelectron spectroscopy and X-ray diffraction provided the evidence for graphene formation from graphene oxide precursor. Furthermore, the reduced oxygen content and N 1s peak observed by the X-ray photoelectron spectroscopy analysis of graphene sheets confirmed the reduction reaction and presence of adsorbed oxidation product on the surface of graphene sheets. The resulting graphene sheets were readily dispersible in solvents and easily to process.     

Reduction of graphene oxide at the interface between a Ni layer and a SiO2 substrate

Reduction of graphene oxide (GO) was carried out on SiO₂ using a thin Ni overlayer as a catalyst. A Ni/GO/SiO₂ structure was heated at 800 °C in high vacuum for 6 min. After removing the Ni overlayer, formation of graphene was confirmed by Raman spectroscopy. For the Ni overlayer thinner than 40 nm, GO was reduced to graphene on-site. For the thicker Ni overlayer, however, GO was completely decomposed and graphene was formed in a segregation and/or precipitation process. The use of GO with a thin Ni overlayer enabled on-site and transfer-free fabrication of graphene without use of such flammable gases as methane and hydrogen.     

聚合物功能化石墨烯的合成及应用研究进展(二)

着重评述了采用共价连接和非共价连接技术制备聚合物功能化石墨烯的方法,介绍了聚合物功能化石墨烯的应用概况。     

A review on synthesis and properties of polymer functionalized graphene

This review highlights the functionalization chemistry of graphene with polymers by both covalent and non-covalent approaches. Due to the strong cohesive interactions graphene platelets agglomerate, causing difficulty to attain its optimum properties. The covalent functionalization is illuminated both from ‘grafting to’ and ‘grafting from’ techniques discussing the merits and demerits of the processes. The controlled free radical polymerization techniques used for this purpose e.g. ATRP, SET–LRP and RAFT etc. are discussed along with the conventional free radical polymerization. We have also noted the various approaches used in non-covalent functionalization e.g. π–π, H-bonding and hydrophobic interactions. These functionalized graphenes show good and stable dispersion facilitating composite formation with commodity plastics enhancing it's mechanical, thermal and conductivity properties. The optoelectronic properties of these functionalized graphene are interesting to fabricate sensors, photovoltaics, supercapacitors etc. A short account of the properties of these modified graphenes is also embodied with an emphasis on different area where future developments are expected.     

聚合物功能化石墨烯的合成及应用研究进展(一)

着重评述了采用共价连接和非共价连接技术制备聚合物功能化石墨烯的方法,介绍了聚合物功能化石墨烯的应用概况。     

Controllable growth of single-layer graphene on a Pd(1 1 1) substrate

Using a surface segregation technique, single-layer graphene can be grown on a carbon-doped Pd(1 1 1) substrate. The growth was monitored and visualized using Auger electron spectroscopy, X-ray photoelectron spectroscopy, Raman microscopy, atomic force microscopy and scanning tunneling microscopy. Appropriate adjustment of annealing parameters enables controllable growth of single-layer graphene islands and homogeneous, wafer-scale, single-layer graphene. The chemical state of the C 1s peak from X-ray photoelectron spectroscopy indicates there is almost no charge transfer between graphene and the Pd(1 1 1) substrate, suggesting weak graphene–substrate interaction. These findings show surface segregation to be an effective method for synthesizing large-scale graphene for fundamental research as well as potential applications.     

石墨烯及化学改性石墨烯的胶状悬浮物合成研究进展

详细综述了石墨烯及化学改性石墨烯(CMG)的胶状悬浮物的合成工艺进展,从氧化石墨、氧化石墨烯及石墨其他衍生物的溶解性质和合成路径等方面展开论述。石墨烯的胶状悬浮物合成工艺既提供了大批量生产石墨烯的可能性,在化学改性修饰方面也有普遍的适用性。