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Graphene as a typical representative of carbon nanomaterials, which has attracted scientists' widespread concerns and is very interested in their extensive crystal form and electrical properties. On the one hand, the main preparation method and principle of graphene are introduced, on the other hand, the extensive application of graphene in many fields such as nano-electronic devices. Low-cost massively preparation of graphene materials to graphene research and application significance.
Carbon nanomaterials are a research hotspot that is widely concerned in the field of new materials in today's new materials, of which carbonnanotube (CNT), graphene, and fullerene are typical representatives of carbon nanomaterials. Since they have excellent and unique optical, electrical and mechanical properties, they have a wide range of application prospects. Among these three typical carbon nanomaterials, two-dimensional graphene is a basic unit constituting one-dimensional carbon nanotubes and zero-Vivolirene (Fig.
1), which has excellent crystalline form and electrical properties. Graphene has been widely concerned with scientists in the University of Manchester, England, and its strange performance has aroused scientists and is very interested in their strange performance. Single-layer graphene is present in a two-dimensional crystal structure, the thickness is only 0.
334 nm, which is a basic unit that constructs other dimensional carbonaceous materials, which can be wrapped up to form a zero-resolulent Fulrene, rolled up to form a one-dimensional carbon nanotube, Formation of three-dimensional graphite formation. Grainne is a semiconductor having no energy, has a carrier mobility (2 × 105 cm2 / v) having a high silicon, with a micrometer free run and a large coherence length at room temperature, so graphene is nanometers. Ideal material for circuit.
Graphie has good thermal conductivity [3000W / (m · k)], high strength (110GPa) and large specific surface area (2630 m2 / g). These excellent properties make graphene in the field of nano-electronic devices, gas sensors, energy storage, and composites. 1.
Preparation method of graphene At present, the preparation method of graphene is mainly mechanical, oxidized graphite reduction, thermal decomposition SiC method, chemical deposition growth method, epitaxial method, etc. 1.1, micromechanical stripping method 2004, GEIM first uses micromechanical stripping method, successfully peeled off from high-oriented thermal cracking graphite (high-oriented thermal cracking graphite) and observed single layer graphene.
The maximum width of single-layer graphene prepared by GEIM research group can reach 10 μm. The method is mainly based on oxygen plasma harness to etch the groove of width of 20 μm to 2 mm, deep 5 μm, and press it on the SiO2 / Si substrate attached to the photoresist. After the calcination, the excess graphite sheet was repeatedly peeled off with a transparent tape, and the remaining graphite sheet remaining on the Si wafer was soaked in acetone, and the large amount of water was easily cleaned in a large amount of water, and the substantially thick sheet was obtained.
The thickness of less than 10 nm, these thin layers mainly rely on Van Dehua's power or capillary force to closely bind to SiO2, and finally select a thickness of only a few single atomic layer thickness under the atomic force microscope. This method can be Get a graphene sheet having a width of micrometers, but it is not easy to obtain a separate single atomic layer thick graphene sheet, and the yield is also very low, so it is not suitable for large-scale production and application. Subsequently, Meyer et al.
Placed the Si wafer containing a single layer of graphene in the microcomputer stripping method on a etched metal frame, and the Si wafer was corroded with an acid, and the suspended single layer graphene supported by the metal bracket was successfully prepared. And use transmissive electron microscopy to observe their topography. They have studied that single-layer graphene is not a flat plane, but there is a level (5 ~ 10 nm) on the plane, and the degree of wrinkles of single layer graphene surfaces are significantly greater than bilateral graphene, and with graphene layers The increase in the number of wrinkles is getting smaller and smaller, which may be due to the single layer graphene to reduce its surface energy, converted from two-dimensional three-dimensional shape, and can speculate on the pleats of the graphene surface may be the necessary Condition, the impact of the pleats on the surface of the graphene is to be further explored.
The micromechanical stripping method can prepare high-quality graphene, but there is low yield and high cost, do not meet industrialization and scale production requirements, and can only be used as a laboratory small-scale preparation. 1.2, chemical vapor deposition method chemical vapor deposition method is a method of preparing semiconductor thin film materials in a large-scale industrialization.
The CVD method refers to the chemical reaction of the reaction substance under gaseous conditions, and generates the surface of the solid material deposited in the heated solid matrix, which in turn has a process of solid material. Its production process is very perfect, and it has also become a way for researchers preparation graphene. The chemical vapor deposition (CVD) method provides an effective method that controls graphene, which is different from the preparation of CNTs, preparing granular catalyst when preparing granular catalysts with CVD method, which is a flat substrate (such as a metal film, metal single crystal The et al.
In a high-temperature degradable precursor (e.g., methane, ethylene, etc.
) atmosphere, by high temperature annealing, depositing the carbon atom to form graphene, and finally obtain independent graphene by chemical corrosion. piece. By selecting a substrate type, a growth temperature, a precursor flow, such as growth rate, thickness, area, etc.
), this method has successfully prepared a single layer or multilayer graphene of the area of square centimeter. The greatest advantage is that graphene sheets with large area. 1.
3, the method of epitaxial growth method is generally by heating 6H-SiC single crystal surface, deretation of Si (0001 surface) atoms to prepare graphene. The 6H-SiC single crystal surface is first carried out, and the H2 etch pretreatment is pretreated, and the surface oxide is removed from 1000 ° C under ultra-high vacuum (1.33 × 10-8Pa), and the oxide is confirmed by the AugeRelectronspectroscopy.
After complete removal, the sample is heated to 1250 to 1450 ° C and the temperature is 10 to 20 minutes, and the thickness of the obtained graphene sheet is mainly determined by the temperature of this step, and this method can prepare 1 to 2 carbon atomic layers. Thick graphene, but since the surface structure of the SiC crystal is more complicated, it is difficult to obtain a large area, thickness is a graphene. BERGER et al.
Takes the method to prepare a single layer and multi-layered graphene and study its performance. Compared with the graphene obtained by mechanical stripping method, graphene prepared by epitaxial growth method exhibits a high carrier mobility, but observed that the quantum Hall effect is observed. 1.
4, electrochemical method LiU et al, graphene is prepared by electrochemically oxidation graphite rod. They insert two high-purity graphite bars into aqueous solution containing ionic liquids, and the control voltage was corroded at 10 to 20 V, 30 min, and the cationic cathode reduction in the ionic liquid formed free radicals, and the graphene sheet The π-electron is bonded to form a functionalized graphene sheet of ionic liquid, and finally the black precipitate in the electrolytic cell with anhydrous ethanol, and graphene can be obtained at 60 ° C for 2 h. This method can be prepared from the ionic liquid functionalized graphene, but the prepared graphene sheet is larger than the thickness of the monogen.
1.5, organic synthesis method Qian et al. Working with organic synthetic graphene nanocarbons with determining structures.
They were used as monomers using tetrabromide (Tetrabromo-Pelenebisimides), which can occur in a polymer coupling reaction under the activation of copper and L-proline, and obtained different sizes of parallel Immine, high-efficiency chemical synthesis of graphene nano-containing-containing-containing groups; they also separated two three-three-siphylimide isomers by high performance liquid phases, and combined with the theoretical calculation further elucidated Their structure. 2, graphene application graphene includes excellent electron transport, optical coupling, electromagnetic, thermodynamics, etc., so in nano-electronic devices, high-performance liquid crystal display materials, solar cells, field emission materials, gas sensors, energy Wide application in the fields of storage.
2.1, transparent electrode industrially commercialized transparent film materials are indium tin oxide (ITO), due to limited content on earth, prices are expensive, especially toxic, so that it is limited. As a new star of carbon-quality, graphene is considered to be an alternative material of indium tin oxide, and graphene is simple and low cost, which is the advantages of simple and low cost.
Flat road. The Mullen Study Group deposited the thermostat reduction by the impregnation coating method, the film resistance was 900Ω, the light transmittance was 70%, the film was made into a positive electrode of the dye solar cell, and the energy conversion efficiency of the solar cell was 0.26%.
In 2009, the study group made a repurrent gas and carbon source using acetylene, and graphene was prepared by high-temperature reduction method, providing a possibility that graphene as a replacement material of conductive glass. 2.2, sensor electrochemical sensor technology combines information technology and biotechnology, involving cross-disciplines such as chemical, biology, physics and electronics.
After graphene appeared, the researchers found that graphene provided a two-dimensional environment and rapid multiphase electron transfer on the edge portion, which made it an ideal material for electrochemical student sensors. The graphene prepared by CHEN is used as a sensor electrode material, and the low concentration NO2 can be detected at room temperature, the authors believe that if the quality of graphene is further increased, the sensitivity of the sensor to gas detection can be improved. Gostene demonstrates potential different from other materials in the sensor, so that more and more medical persons are concerned about it, and the current graphene is also used in medical detection of dopamine, glucose, etc.
2.3, Super Capacitor Super Capacitor is an efficient storage and transfer energy system, which has the advantages of large power density, large capacity, long service life, economic environmental protection, and is widely used in various power supply venues. Graphie has a high specific surface area and a high conductivity, unlike the distribution of the porous carbon material electrode to rely, which makes it the most potential electrode material.
CHEN et al, the supercapacitor power density prepared by graphene electrode material is 10 kW / kg, the energy density is 28.5WH / kg, the maximum specific capacitor is 205F / g, and 90% ratio is retained after 1200 cyclic charge and discharge test Capacitor, has a longer cycle life. The potential of graphene in supercapacitor should be concerned about more researchers.
2.4, composite graphene, physical, chemical and mechanical properties provide primary power for composite development, and it is desirable to open many new applications, such as new conductive polymer materials, multi-functional polymer composites and high-strength porous ceramics. Material, etc.
Fan et al, the high-specific surface area and high electron mobility of graphene are prepared, and the complex has a high ratio capacitor (1046F / g) far greater than pure poly. Beylamidine ratio capacitance 115f / g. The addition of graphene increases the multi-functionality of the composite, and the processing performance of the composite material, provides a broader application field for composite materials.
3, the conclusion, the conclusion, graphene is used as a new two-dimensional carbon material, with excellent electron transport, optical coupling, electromagnetic, thermodynamics and mechanics, etc., in nano-electronic devices, high-performance liquid crystal display materials, solar energy Battery, field launch material, gas sensor and energy storage are widely used in the fields, so becoming research hotspots at home and abroad. Low-cost massively preparation of graphene materials to graphene research and application significance.
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