Silicon Carbide (SiC) is synthesized through various methods, each with its own unique process and benefits.
1. Solid-State Reaction Method
In this method, silica and activated carbon are used as raw materials.
Silica is obtained from silica rice husk using an alkali extraction and a sol-gel method.
2. Sublimation Method
This method involves the controlled sublimation of SiC.
Epitaxial graphene is achieved by the thermal decomposition of a SiC substrate using either e-beam or resistive heating.
The process is conducted in an ultrahigh vacuum (UHV) to minimize contamination.
After Si desorption, excess carbon on the surface of the SiC wafer rearranges to form a hexagonal lattice.
However, this method has high cost and requires large amounts of Si for large-scale production.
3. Chemical Vapor Deposition (CVD) Method
CVD is used for the growth of SiC films.
The choice of source gas depends on the thermal stability of the substrate.
For example, silane (SiH4) deposits between 300 and 500 °C, dichlorosilane (SiCl2H2) at around 900 °C, and tetraethyl orthosilicate (Si(OC2H5)4) between 650 and 750 °C.
The process results in the formation of a layer of low-temperature oxide (LTO).
However, silane produces a lower-quality oxide compared to other methods.
CVD oxide generally has lower quality than thermal oxide.
4. CVD Graphene Growth on SiC
CVD preparation of graphene on SiC is a novel technique that offers more versatility and affects the quality of the graphene layer by considering various parameters.
The key factor in CVD preparation on SiC is the lower temperature, which prevents SiC atoms from diffusing into the bulk of the SiC crystals.
This leads to the formation of pinning points between the substrate and the graphene monolayer, resulting in the desired free-standing graphene.
This technique is suitable for large-scale fabrication of CVD graphene.
5. CVD Graphene on Polycrystalline Metals
SiC can also be used to grow graphene through CVD on polycrystalline metals.
This method utilizes the wear-resistant and high-temperature strength properties of SiC.
The reaction bonded SiC method involves infiltrating compacts made of mixtures of SiC and carbon with liquid silicon, which reacts with carbon to form silicon carbide.
The sintered SiC method is produced from pure SiC powder with non-oxide sintering aids and sintered in an inert atmosphere at high temperatures.
These are some of the synthesis methods used for SiC, each with its advantages and limitations.
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