A single crystal or monocrystalline solid is a material in which the crystal lattice of all samples is continuous and unbroken to the sample edge, with no grain boundaries. The absence of defects associated with grain boundaries may provide monocrystal, especially mechanical, optical and electrical properties, which can also be anisotropic, depending on the type of crystallographic structure. These properties, in addition to making them valuable in some gems, are industrially used in technological applications, especially in the field of optics and electronics.
Because the entropic effect supports the existence of some imperfections in the microstructure of solids, such as impurities, inhomogeneous strains and crystallographic defects such as dislocations, perfect single crystals of meaningless size are very rare in nature, and also difficult to produce in laboratories, although they can be made under condition under control. On the other hand, single imperfect crystals can reach very large sizes in nature: some mineral species such as beryl, gypsum and feldspars are known to have produced crystals of several meters.
The opposite of single crystals is an amorphous structure where atomic positions are limited only for short distances. Between the two extreme is polycrystalline , which consists of smaller crystals known as crystals , and paracrystalline phases.
Video Single crystal
Usage
Semiconductor industry
Single crystal silicon is used in the manufacture of semiconductors. On a microprocessor-operated quantum scale, the presence of grain boundaries will have a significant impact on the field effect transistor function by changing local electrical properties. Therefore, microprocessor assemblers have invested heavily in facilities to produce large single crystals of silicon.
Optics
- Monocrystals of sapphire and other materials are used for nonlinear lasers and optics.
- Fluorite monocrystals are sometimes used in the objective lens of apochromatic refracting telescopes.
Engineering materials
Another application of a single crystal solid is in material science in the production of high strength materials with low thermal creep, such as turbine blades. Here, the absence of grain boundaries actually gives a decrease in yield strength, but more importantly reduces the amount of creep that is essential for high temperatures, application tolerance parts close.
Conductor power supply
Single crystals provide a means to understand, and perhaps realize, the final performance of a metal conductor.
Of all the metal elements, silver and copper have the best conductivity at room temperature, so set blades for performance. Market size, and peculiarities in supply and cost, have provided strong incentives to find alternatives or find ways to use less by improving performance.
The conductivity of commercial conductors is often expressed relative to the International Annealing Copper Standards, which according to which the purest copper wire available in 1914 is about 100%. The purest modern copper wire is a better conductor, measuring more than 103% on this scale. The advantage comes from two sources. First, modern copper is purer. However, the road to this improvement seems to be over. Making copper purers still does not make a significant improvement. Second, the annealing and other processes have been improved. Annealing reduces dislocations and other crystal defects that are the source of resistance. But the resulting cable is still polycrystalline. Grain boundaries and residual crystal defects are responsible for some residual resistance. This can be measured and better understood by examining single crystals.
As anticipated, single crystal copper is shown to have better conductivity than polycrystalline copper.
But there are surprises in store (see table). Single crystal copper is not only a better conductor than high purity polycrystalline silver, but with specified heat and pressure treatment it can surpass even single-crystalline crystals. And although dirt is usually bad for conductivity, one-silver crystal with a small amount of copper substitution is a better conductor than all of them.
In 2009, no single crystal copper was manufactured on a large-scale industry basis, but the method produced a very large individual crystal size for copper conductors exploited for high performance electrical applications. It can be considered a single meta-crystal with only a few crystals per meter in length.
In research
Single crystals are very important in research especially condensed matter physics, materials science, surface science etc. Detailed studies of the crystalline structure of materials with techniques such as Bragg diffraction and helium atom scattering are much easier with monocrystals. Only in a single crystal is it possible to study the dependence of the direction of various properties. Furthermore, techniques such as scanning tunneling microscopy are possible only on the surface of a single crystal. In superconductivity there are cases of materials in which superconductivity is seen only on single crystal specimens. They can grow for this purpose, even when the material is only needed in polycrystalline form.
Maps Single crystal
Producing
In the case of silicon and single crystal fabrication, the techniques employed involve highly controllable crystallization and are therefore relatively slow.
Specific techniques for generating large single crystals (aka boules) include the Czochralski process and the Bridgman technique. Other less exotic crystallisation methods may be used, depending on the physical properties of the substance, including hydrothermal synthesis, sublimation, or solvent-based crystallization alone.
Different technologies for creating a single crystal material are called epitaxy. In 2009, this process was used to store very thin (micrometers to nanometer scale) layers of the same or different materials on the existing single crystal surface. This engineering application lies in the semiconductor production area, with potential usage in other fields of nanotechnology and catalysis.
See also
- Technical aspects of crystallization
- Crystallization of fractions (chemical)
- Heated Pedestal Growth Laser
- Drag-Pull Micro
- Recrystallization (metallurgy)
- Crystal seeds
References
Further reading
- "Crystallization of Small Molecules" (PDF) on the Illinois Institute of Technology website
Source of the article : Wikipedia
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