Note: There have been many articles in the past that have introduced graphene and its application fields, working principles, etc., and will not repeat them here. This article mainly focuses on the production of graphene.
There are several different methods for different materials and uses. Generally speaking, there are a vapor deposition method, a redox method, and an intercalation method .
The meteorological deposition method is mainly carbon-containing gas (methane, faint). Under certain temperature and pressure conditions, carbon atoms adhere to the growth base to form a single-layer carbon structure material and gradually grow.
Advantages : The obtained graphene structure is good and the size is not limited by the raw materials. Disadvantages : The preparation process is complicated and the production efficiency is low.
In the redox method, graphite is oxidized layer by layer using an oxidizing agent, and the oxidized layer is peeled off by ultrasonic or the like. Thereafter, the graphite oxide layer is reduced by a reducing agent to obtain graphene.
Advantages : low cost and high production efficiency.
Disadvantages : The size of the graphene produced is determined by the raw materials, and the oxidizing agent and reducing agent used may pollute the environment.
The intercalation method is to fill the intercalation material into the layer gap of the graphite, thereby overcoming the interlayer van der Waals force, so that the layers are dispersed, thereby obtaining graphene. This method is still in the research and development stage.
Micromechanical strippingGraphene is first produced by micromechanical stripping. The micro-mechanical stripping method is to press the highly oriented pyrolytic graphite sheet onto other surfaces with a transparent tape to perform multiple peeling, and finally obtain a single layer or several layers of graphene. In 2004, Geim, Novoselov, etc. obtained the first single layer of graphene in the world by this method, which proved that the two-dimensional crystal structure can exist at normal temperature.
The micro-mechanical stripping method is simple in operation and high in sample quality, and is currently the main method for preparing single-layer high-quality graphene. However, its controllability is poor, and the produced graphene is small in size and has great uncertainty, while being low in efficiency and high in cost, and is not suitable for mass production.
Epitaxial growth methodThe epitaxial growth method includes a silicon carbide epitaxial growth method and a metal catalytic epitaxial growth method. The silicon carbide epitaxial growth method refers to heating a SiC single crystal at a high temperature so that Si atoms on the surface of the SiC are evaporated to escape from the surface, and the remaining C atoms are reconstructed by an independent form to obtain graphene based on the SiC substrate.
The metal-catalyzed epitaxial growth method is to introduce a hydrocarbon into a catalytically active transition metal substrate such as Pt, Ir, Ru, Cu, etc. under ultra-high vacuum conditions, and catalytically dehydrogenate the adsorbed gas by heating to obtain graphene. . The gas can grow over the entire metal substrate during the adsorption process, and the growth process is a self-limiting process, that is, the substrate does not repeatedly absorb after adsorbing the gas. Therefore, the prepared graphene is mostly a single layer, and can be widely used. Uniform graphene was prepared.
Chemical vapor deposition CVD: the most promising large-scale production methodThe CVD method is considered to be the most promising preparation of high-quality, large-area graphene, and is the most promising method for industrial production of graphene films. The specific process of the chemical vapor deposition CVD method is: introducing hydrocarbon methane, ethanol, etc. into the surface of the high-temperature heated metal substrate Cu, Ni, and cooling after a certain period of time, and several layers are formed on the surface of the substrate during the cooling process or Single-layer graphene, in which carbon atoms are dissolved and diffused on the substrate. The method is similar to the metal catalytic epitaxial growth method, and has the advantages that it can be carried out at a lower temperature, thereby reducing the energy consumption in the preparation process, and the graphene and the substrate can be easily separated by the chemical corrosion metal method, which is advantageous for The graphene is processed later.
Existing methods cannot meet the requirements of graphene industrialization. Numerous preparation methods including micro mechanical peeling, epitaxial growth, chemical vapor deposition CVD and graphite oxide reduction are still unable to meet the requirements of industrialization. In particular, industrialization requires graphene preparation technology to produce graphene with large area and high purity at a stable and low cost. This technical problem has not yet been solved.
Other methods for preparing graphene include a carbon nanotube cutting method, a graphite intercalation method, an ion implantation method, a high temperature and high pressure HPHT growth method, an explosion method, and an organic synthesis method .
The preparation of large-area, high-quality graphene remains a major challenge. Although chemical vapor deposition and redox processes can produce graphene in large quantities, chemical vapor deposition is more complicated in the later stage of preparation, and the process of graphene transfer is more complicated, and the preparation cost is higher. defect. When using the redox method, since the single-layer graphene is very thin and easy to agglomerate, the conductive property and specific surface area of ​​the graphene are lowered, which further affects the application in the photovoltaic device, and in addition, the graphene is easily caused in the redox process. Crystal structure defects, such as the loss of carbon atoms on the carbon ring.
The system restricts the industrialization of graphene. The various top properties of graphene can only be manifested when the quality of graphene is very high. As the number of layers increases and the accumulation of internal defects, the superior performance of graphene will be reduced. In order to truly realize the industrialization of graphene applications and reflect the superior quality of graphene in replacing other materials, it is necessary to seek breakthroughs in the preparation methods. Only the method of graphene suitable for industrialization has emerged, and the industrialization of graphene can really come.
Camera Module is generally composed of the following parts: Lens, image sensor, base bar and line.
If it is a camera module with AF function (generally a mobile phone camera), most of them adopt VCM mode, which has one more coil than the above structure. By adding points to the coil, the lens can move vertically to achieve the function of focusing. In the case of a camera with a shake resistant feature, the lens is also able to move horizontally to achieve an optical shake resistant effect
Camera module selection
The sensor and lens in the camera module usually account for more than 90% of the cost, and the image quality is also determined by them.
First, choose the most appropriate sensor according to the price you can accept, the interface of the motherboard, and the resolution you need to take photos and video
The price of the sensor usually accounts for 40%-60% of the price of the module. In order to ensure that the resolution/frame rate can meet the requirements, sensors with better sensitivity and larger pixel area are selected at a certain cost.
Secondly, according to the purpose of the sensor you need, choose the lens with the appropriate size and field of view Angle. If a lens with a large field of view is needed, you can choose a fish-eye camera (also known as a wide-angle camera). However, for the image taken by the fisheye camera, there will be a distortion effect. In fact, the distortion effect can be corrected by itself.
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