Controlled Number Of Layers Research Articles

Preparation of Few Layer Three‐dimensional Graphene Networks by CVD for Energy Storage Applications

Three‐dimensional graphene networks (3DGNs) with a controllable number of layers (from monolayer to few layers) are fabricated by CVD on a Ni foam rod (NFR) template. The special morphology of the NFR and accompanying concentration gradients of CH4 gas provide the necessary conditions to deposit the 3DGNs with varied thicknesses on different areas of one substrate. The high conductivity, large Brunner‐Emmett‐Teller (BET) area, and three‐dimensional network of the 3DGNs make it a potential material for use in the electrochemical field. Supercapacitors with the 3DGNs‐based electrode show a high energy density ∼34.2 Wh kg−1 at a current density of 100 mA g−1, and a specific capacitance of 246 F g−1 is obtained in a 30 wt.‐% KOH aqueous electrolyte solution. Moreover, the resultant devices maintain high performances under high current density conditions, indicating the outstanding stability of the prepared 3DGNs.

Synthesis of graphene nanosheet powder with layer number control via a soluble salt-assisted route

The principle features in this study lay on the synthesis of graphene nanosheet powders with layer number control from pristine graphite powder via a soluble salt-assisted route and on the high thermal stability and good dispersibility of our products in ethanol.

Influence of Cu substrate topography on the growth morphology of chemical vapour deposited graphene

Raman spectroscopic maps were used to study the local properties of graphene films as grown on corrugated copper foils, by chemical vapour deposition, and after transfer onto SiO2(300nm)/Si substrates. Analysis of the Raman peaks show the films exhibit a striped periodic pattern of single- and bi-layer graphene. By performing simultaneous AFM–Raman line maps of the as grown film on Cu we find that the layer growth shows a strong correlation to substrate topography. As a result, compressively strained non-AB stacked bi-layer graphene forms preferentially along the ridges, whilst single-layer graphene grows inside the trenches, of the Cu foil topography. These experimental results suggest that surface mobility is not the dominating factor determining control of layer number in such growth regimes.

Universal Multilayer Assemblies of Graphene in Chemically Resistant Microtubes for Microextraction

Graphene is a new kind of two-dimensional carbon nanomaterial with excellent properties and is promising for solid-phase microextraction (SPME). Plastic microtubes such as poly(tetrafluoroethylene) (PTFE) and poly(ether ether ketone) are ideal substrates for in-tube SPME. However, immobilization of graphene layers onto these materials is still a problem due to their nature of chemical resistance. In order to solve the problem, we proposed a novel method based on universal mussel-inspired polydopamine (PD) and layer-by-layer assembly of graphene in this work. To make a graphene assembly layer inside PTFE, the strategy includes two major steps. First, a PD layer is made on the PTFE surface by noncovalent interaction. Second, multilayer graphene is assembled on the PD layer by covalent interaction. By repeating these two steps, a functional graphene oxide (FGO)-modified PTFE tube with a controllable number of layers can be obtained. Morphology of the multilayer structure of graphene has been confirmed by scanning electronic microscopy. Formation of the covalent layer has also been characterized by Foourier transform infrared and X-ray photoelectron spectroscopy. It is very interesting that (FGO-PD)3-PTFE shows exceptional efficiency for SPME. Enrichment from 1082- to 2331-fold was achieved for six polyaromatic hydrocarbons (PAHs). An online SPME-HPLC-fluorescent detection method has been developed on the basis of (FGO-PD)3-PTFE. For qualitative analysis of PAHs, the method has low limits of detection of 0.05-0.1 pg/mL, which is significantly lower (up to 1000 times) than that reported in literature. The method shows wide linear range (0.3-200 pg/mL), good linearity (R(2) ≥ 0.9968), and good reproducibility (relative standard deviation < 3.4%). The method has been applied to determine PAHs in environmental samples. Good recoveries were obtained, ranging from 85.1% to 96.7%.

Chemical vapour deposition growth of large single crystals of monolayer and bilayer graphene

The growth of large-domain single crystalline graphene with the controllable number of layers is of central importance for large-scale integration of graphene devices. Here we report a new pathway to greatly reduce the graphene nucleation density from ~10(6) to 4 nuclei cm(-2), enabling the growth of giant single crystals of monolayer graphene with a lateral size up to 5 mm and Bernal-stacked bilayer graphene with the lateral size up to 300 μm, both the largest reported to date. The formation of the giant graphene single crystals eliminates the grain boundary scattering to ensure excellent device-to-device uniformity and remarkable electronic properties with the expected quantum Hall effect and the highest carrier mobility up to 16,000 cm(2) V(-1) s(-1). The availability of the ultra large graphene single crystals can allow for high-yield fabrication of integrated graphene devices, paving a pathway to scalable electronic and photonic devices based on graphene materials.

Preparation and Photoelectric Conversion of Dipolar Hemicyanine Dye/Polyoxometalate Self-Assembled Films

A new inorganic-organic hybrid self-assembled film was prepared by alternative adsorption of polyoxometalate (K10P2W18Cd4(H2O)2O68) and dipolar hemicyanine dye (H 6 ) and studied by UV-Vis spec- troscopy and photoelectrochemistry. The film was uniformly deposited with controllable layer number, red-shifted visible absorption band, and stable and large photoelectric signal. The effects of bias voltages, electron donor and electron acceptor on the photocurrent generation were discussed.

Segregation Growth of Graphene on Cu–Ni Alloy for Precise Layer Control

A facile way to segregate wafer-size graphene with controllable layer number using Cu–Ni binary alloy under vacuum annealing condition is presented here. Increasing atomic percentage of Ni in Cu–Ni alloy was found to segregate thicker uniform graphene. To date, over 95% monolayer and 91% bilayer graphene films have been prepared by only changing atomic percentage of Ni in Cu–Ni alloy, respectively. The synergetic combination of the distinct carbon solubilities of Cu and Ni and the well-known segregation phenomenon is believed to be responsible for the formation of high-quality uniform few layer graphene. Together with the easy detachment from growth substrates, we believe this facile segregation technique will offer a great driving force for graphene research.

Fabrication of wafer-scale polystyrene photonic crystal multilayers via the layer-by-layer scooping transfer technique

This paper reports on a simple synthetic method for fabricating a wafer-scale colloidal crystal film of 2D crystals in a 1D stack based on a combination of two simple processes: the self-assembly of polystyrene (PS) nanospheres at the water–air interface and the layer-by-layer (LbL) scooping transfer technique. This method can routinely fabricate photonic crystal (PhC) multilayers over 4 inch diameter wafers with a controllable number of layers and vertically crack-free over wafer-scale area. We investigate the optical and morphological properties of the PhC multilayers fabricated using various mono-sized colloidal crystals (250, 300, 350, 420, 580, 720, and 850 nm), and mixed binary colloidal crystals (300/350 and 250/350 nm).

Halogen Based Surface Chemistries for Graphene Synthesis

AbstractHalogen based (CF4 and Cl2) inductively coupled reactive ion etching (ICP-RIE) has been used to selectively etch silicon from 6H-SiC to produce a controlled number of carbon layers. After annealing at temperatures in the range of 550 °C to 1100 °C to reconstruct the near surface layers, x-ray photoelectron spectroscopy has been used to characterize the composition of the films. For the Cl2 based ICP-RIE, two carbon species are observed. One is due to carbon bound as SiC in the substrate and a second which can be attributed to graphene. In the case of CF4 based etching the situation is similar except the second peak is most closely aligned with p-type graphene. This is most likely due to electron transfer from the graphene to the trace levels of fluorine remaining on the surface after annealing.

Localization and translocation of enzymes involved in the synthesis of leukotrienes

Microwave plasma chemical vapor deposition (MPCVD) is a promising method for the large-scale production of high-quality graphene. The aim of this work is to investigate the effect of in-situ hydrogen plasma post-treatment on the MPCVD-grown graphene films. By simply varying the duration time of in-situ hydrogen plasma, surface morphology, number of layers and defect density of as-grown graphene films can be manipulated. The role of hydrogen plasma can be proposed from our observations, promoting to further grow graphene films in the early stage and consequently acting as an etching agent to thin graphene films in the later stage. On the basis of above mechanism, monolayer graphene films with low defect density and smooth surface can be grown by adjusting the times of the growing step and the plasma post-treatment step. This additional in-situ hydrogen plasma post-treatment may be significant for growing well-defined graphene films with controllable defects and number of layers.

Formation of Ultrathin Multilayer and Hydrated Gel from Montmorillonite and Linear Polycations

Organized ceramic/polymer nanocomposites were designed from montmorillonite clay (Mont), cationic poly(ethylenimine) (PEI) or poly(dimethyldiallylammonium chloride) (PDDA) and proteins. Ordered multilayers with a controllable number of layers were prepared by alternate adsorption of delaminated montmorillonite (0.03 wt % dispersion) and polycations. Quartz crystal microbalance, X-ray diffraction, and scanning electron microscopy monitoring of the assembly have shown formation of ordered films with bilayer thickness of 3.3 nm for Mont/PEI and 3.6 nm for Mont /PDDA. Increased viscosity near the substrate was recognized at higher concentrations of Mont (1 wt %). At these and higher concentrations super hydrated (water content 99.4 wt %) solid gels of Mont and polycations were produced by mixing of their aqueous dispersions. Its open card-house structure was revealed with a scanning electron microscopy study.