What is a single crystal?
A single crystal is a solid substance composed of structural elements arranged periodically in three-dimensional space. Such as crystals, diamonds, gemstones, etc. Unidirectional ordered arrangement determines that it has the following characteristics: uniformity, anisotropy, self-limiting, symmetry, minimum internal energy and maximum stability. With the development of production and science and technology, natural single crystal can no longer meet people's needs. Various industries have put forward a large demand for single crystal materials, such as: the watch industry has put forward a large demand for rubies, and the mechanical processing industry has put forward a large demand for rubies. Demand for diamonds, etc. So the history of single crystal materials has entered the stage of artificial preparation.
Common preparation methods for single crystals
Commonly used preparation methods for single crystal growth are Czochralski method, volatilization method, crucible descending method, zone melting method, solution growth, directional solidification method, etc.
1. Czochralski (CZ method for short)
Principle: The Czochralski method, also known as the pulling method, is to heat and melt the raw materials constituting the crystal in a crucible, and then connect the seed crystal to the melt surface to pull the melt. Atoms or molecules are continuously rearranged on the interface, and a single crystal grows as the temperature gradually solidifies.
Method: First, heat and melt the raw material of the crystal to be grown in a high temperature resistant crucible, adjust the temperature field in the furnace, and make the upper part of the melt in a supercooled state; then place a seed crystal on the seed rod to let the seed crystal Contact the melt surface, after the seed crystal surface is slightly melted, pull and rotate the seed crystal rod, so that the melt is in a supercooled state and crystallizes on the seed crystal. During the continuous pulling and rotation process, a cylindrical crystal grows.
The pulling method is a common method for growing crystals from melts. With this method, a variety of crystals can be pulled out, such as single crystal silicon, scheelite, yttrium aluminum garnet and uniform and transparent ruby.
2. Volatilization method
Principle: Relying on the continuous volatilization of the solution, the solution is made from unsaturated to saturated and supersaturated state [2] .
Condition: The solid can be dissolved in a more volatile organic solvent. In theory, all solvents can be used, but generally choose 60～120℃ [2] .
Note: Different solvents may cultivate single crystal structures in different ways: dissolve the solid in the selected organic solvent, sometimes heating can be used to completely dissolve the solid, cool to room temperature or add solvent to make it unsaturated, filter, seal, Stationary cultivation.
3. Diffusion method
Principle: The use of two completely miscible organic solvents with a large difference in boiling point. Solids are easily soluble in high-boiling solvents, insoluble or insoluble in low-boiling solvents. In a sealed container, the low-boiling point solvent is volatilized into the high-boiling point solvent to reduce the solubility of the solid, thereby precipitating crystal nuclei and growing into a single crystal. liquid etc. Generally choose a non-volatile solvent, such as DMF, DMSO, glycerol or even ion [2] .
Condition: The solubility of solids in non-volatile solvents is relatively large or very large, and insoluble or insoluble in volatile solvents. Experience: The solubility of solids in less volatile solvents is better. During cultivation, the solid must be saturated or nearly supersaturated in a high-boiling solvent [2] .
Method: Dissolve the solid in a high boiling point solvent by heating, close to saturation, place it in a sealed container, put a volatile solvent in the sealed container, seal it well, and let it stand for culture [2] .
