Graphene is a honeycomb planar film formed by sp2 hybridization of carbon atoms. It is a quasi-two-dimensional material with only one atomic layer thickness, so it is also called monoatomic layer graphite.
It has a thickness of about 0.335 nm and has different undulations depending on the preparation method, usually about 1 nm in the vertical direction and about 10 nm to 25 nm in the horizontal direction. It is all carbon crystals other than diamond (zero-dimensional fullerene). The basic structural unit of one-dimensional carbon nanotubes, three-dimensional body-oriented graphite. It has long been predicted by physicists that the quasi-two-dimensional crystal itself is unstable in thermodynamic properties and will rapidly decompose or distort at room temperature, so it cannot exist alone. Until 2004, philosophers Andrew Gem and Konstantin Novoselov of the University of Manchester in the United Kingdom successfully separated graphene from graphite by micromechanical stripping, confirming that it can exist alone for graphene. The research began to be active, and the two also won the 2010 Nobel Prize in Physics. The most promising application of graphene is to become a substitute for silicon, making ultra-micro transistors for the production of future supercomputers. By replacing silicon with graphene, computer processors can run hundreds of times faster. In addition, graphene is almost completely transparent, absorbing only 2.3% of light. On the other hand, it is very dense, and even the smallest gas molecules (helium) cannot penetrate. These features make it ideal for use as a raw material for transparent electronic products such as transparent touch displays, luminescent panels and solar panels. As a new type of nanomaterial that is currently found to be the thinnest, strongest, and most conductive and thermally conductive, graphene is called "black gold" and is the "king of new materials." Scientists even predict that graphene will "completely change the 21st century." ". It is very possible to set off a revolutionary new technology and new industrial revolution that has swept the world.
Graphene quantum dots are quasi-zero-dimensional nanomaterials, and their internal electrons are restricted in all directions. Therefore, the quantum confinement effect is particularly remarkable and has many unique properties. This may bring revolutionary changes in the fields of electronics, optoelectronics and electromagnetism. Used in solar cells, electronic devices, optical dyes, biomarkers and composite particle systems. Graphene quantum dots have important potential applications in the fields of biology, medicine, materials, and new semiconductor devices. Single-molecule sensors can be implemented, or ultra-small transistors or on-chip communication using semiconductor lasers can be used to make chemical sensors, solar cells, medical imaging devices, or nanoscale circuits.
Quantum dot structures of different sizes, in which large quantum dots are also referred to as single-electron transistors (SET), are used as detectors to read the state of charge within small quantum dots. Single-electron transistor multi-gate controlled graphene series double quantum dot devices, through low temperature transport, the coupling strength of the two points can be adjusted from weak to strong. This causes a change in the coupling energy of the tunnel, indicating that this highly controllable system is very promising as a quantum information device for future nuclear-free spin. The scientists also measured the gate-regulated bilayer graphene parallel double quantum dots, which can be adjusted to different coupling intervals by the regulation of the back gate and the side gate electrodes. The high sensitivity of the parameters such as coupling capacitance and coupling energy is extracted from the two-point coupled honeycomb image, and the Coulomb blocking signal and the excited state energy spectrum in the quantum dot are clearly detected, even the weak coulomb which is not measured by the conventional transport. The charging signal can also be detected.
Graphene quantum dot (GQD)-based materials may result in lower production costs for OLED displays and solar cells. The new GQD does not use any toxic metals (eg cadmium, lead, etc.). Using GQD-based materials may make future OLED panels lighter, more flexible, and less costly.
In the field of biomedicine, graphene quantum dots have great application prospects.In terms of bioimaging, it has been confirmed theoretically and experimentally that the quantum confinement effect and the side effect can induce the fluorescence of graphene quantum dots. In the field of biomedical research, fluorescent markers are commonly used to calibrate subjects, but the failure of fluorescence due to excessive excitation time is called photo bleaching, which limits the application of general fluorescent agents in biomedicine. Graphene quantum dots have a stable fluorescent light source, and defects in the production of graphene quantum dots, when the nitrogen atoms occupy the position of the original carbon atoms in the production of graphene quantum dots, are separated, leaving a nitrogen vacancy at their position (NitrogenVacancy, NV), and the defect fluoresces after being excited by visible light. Different sizes of graphene quantum dots have different fluorescence spectra and can provide extremely stable phosphors for biomedical research. Compared with phosphors, graphene quantum dots have the advantage that the emitted fluorescence is more stable, and photobleaching does not occur, so that light attenuation is less likely to occur and its fluorescence is lost. This may be a very promising way to further explore bioimaging. Graphene quantum dots are also very good drug carriers. It has good biocompatibility and aqueous solution stability, and is beneficial to chemical functional modification to achieve the purpose of application in different fields. The chemical reactivity of oxygen-containing reactive groups can be covalently reacted with a variety of chemical and functional molecules with specific chemical and biological properties. The common covalent modification method is through acylation and esterification. The biomolecule or chemical group is modified on the graphene, and the surface functionalization of the graphene can also be performed by a non-covalent bond such as a π-π interaction, an ionic bond or a hydrogen bond. Graphene-based drug carriers are able to break through the blood-brain barrier and achieve direct brain administration due to their ultra-high drug loading, targeted delivery, and controlled release of drugs, and are expected to be clinically Realize the actual application.
Due to the edge states and quantum limitations, the shape and size of the graphene quantum dots will determine their electrical, optical, magnetic, and chemical properties. It is a problem to obtain a large number of graphene quantum dots of a specific edge shape and uniform size. At present, top-down graphene quantum dot synthesis methods are obtained by lithography, ultrasonic chemistry, fullerene entrainment, and carbon nanotube release chemical decomposition or electron beam etching.
Quantum confinement effect At least one dimension in the three-dimensional scale of a microstructured material is equivalent to the deBroglie wavelength, so the motion of electrons in this dimension is limited, and the electronic state is quantized, continuous. The energy band will be decomposed into discrete energy levels, ie, wave functions in the form of discrete energy levels and standing waves. When the energy level spacing is greater than some characteristic energy (such as thermal motion KB, Zeeman energy hω, superconducting energy gap Δ, etc.), the system will exhibit even unique properties different from bulk samples, such as in superlattices. Bandgap broadening due to energy level dispersion and blue shift of absorption edge.
Preparation, Characterization and Application of Graphene Quantum Dots Preparation of Graphite Oxide (GO)In this paper, the improved flake graphite was oxidized to prepare graphite oxide (GO) by the modified Hummers method. [20, 21] The details are as follows: 46 mL of 98% concentrated sulfuric acid was added to a dry three-necked flask and cooled to 0-4 ° C. . 2 g of natural flake graphite and 1 g of sodium nitrate were added with vigorous stirring, and the bath temperature was controlled to below 4 ° C for 1 hour. Then slowly add 6 g of potassium permanganate in several times, continue to stir the reaction for 1 h, the solution is dark green, then place the conical flask in a constant temperature water bath at 35 ° C, continue to stir the reaction for 2 h, stir at the end of the reaction. 100 mL of double distilled water, control the temperature to continue stirring at 90 ° C for 1 h, dilute the reaction solution with 150 mL of double distilled water, then add 10 mL of 30% hydrogen peroxide, stir until the solution is golden yellow. The mixture was filtered while hot, and the brownish yellow precipitate was thoroughly washed with 5% hydrochloric acid and deionized water to pH ≈7. The brownish yellow precipitate was placed in an oven at 60 ° C for 12 h to obtain a graphene oxide solid, which was stored for use.
Preparation of reduced grapheneThe chemically reduced graphene is obtained by reducing graphene oxide with hydrazine hydrate. Weigh out 50 mg of graphene oxide obtained in 4.2.2 in a 100 mL round bottom flask, add twice distilled water to 100 mL, and dissolve it completely for about 0.5 h. Take 50 mL of graphene oxide dispersion in a 250 mL beaker, then add 50 μL of 35% hydrazine hydrate solution and 350 μL of concentrated ammonia water, mix well, and stir vigorously for a few minutes. The reaction was carried out in a 95 ° C water bath for 1 h, and the solution slowly changed from tan to black. When the solution was cooled to room temperature, it was suction filtered with a 0.22 μm filter, and the filtered precipitate was dried at 60 ° C for 12 h to obtain a desired reduced graphene film.
Preparation of graphene quantum dots (GQDs)Electrochemical preparation of graphene quantum dots (GQDs) was carried out in 0.01 mol of L-1 phosphate buffered saline (PBS). Two drops of 4 mg/mL decylalanine solution were added as a dispersing agent to the buffer solution by a dropper, and a cyclic voltammetry (CV) scan was performed at a scan rate of 0.5 v s-1 within a voltage of ±0.3 volts. The graphene film (5 mm & TImes; 10 mm) prepared above was used as the working electrode, the Pt wire was used as the auxiliary electrode, and the calomel electrode was used as the reference electrode. During the process, graphene particles are peeled off the film into the solution, and the solution changes from colorless to yellow. The yellow solution was further dialyzed against a dialysis bag (dialysis bag molecular weight cutoff: 3000 Daltons, initial water volume outside the bag was 500 mL), water was changed twice a day, and dialyzed for three days to obtain a graphene quantum dot aqueous solution.
Relative to LC To SC UPC Duplex,Optical fiber jumpers (also known as optical fiber connectors), that is, optical fiber connectors that are connected to optical modules, are also available in many types, and they cannot be used mutually. The SFP module is connected to the LC fiber optic connector, and the GBIC is connected to the SC fiber optic connector. The following is a detailed description of several commonly used optical fiber connectors in network engineering:
â‘ FC-type fiber jumper: The external strengthening method is a metal sleeve, and the fastening method is a turnbuckle. Generally used on the ODF side (most used on the distribution frame)
â‘¡SC type optical fiber jumper: the connector that connects to the GBIC optical module, its shell is rectangular, and the fastening method is a plug-in latch type, without rotation. (Most used on router switches)
â‘¢ST type optical fiber jumper: commonly used in optical fiber distribution frame, the shell is round, and the fastening method is turnbuckle. (For 10Base-F connection, the connector is usually ST type. Commonly used in optical fiber distribution frame)
â‘£LC-type optical fiber jumper: the connector for connecting the SFP module, which is made by the easy-to-operate modular jack (RJ) latch mechanism. (Router commonly used)
Lc To Sc Upc Duplex,Lc To Sc Upc Simples,Lc Upc To Sc Apc Simplex,Lc Upc To Sc Apc Duplex
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