Single crystal

Although current methods are extremely sophisticated with modern technology, the origins of crystal growth can be traced back to salt purification by crystallization in 2500 BCE. A more advanced method using an aqueous solution was started in 1600 CE while the melt and vapor methods began around 1850 CE. Basic crystal growth methods can be separated into four categories based on what they are artificially grown from: melt, solid, vapor, and solution. Other methods of crystallization may be used, depending on the physical properties of the substance, including hydrothermal synthesis, sublimation, or simply solvent-based crystallization. For example, a modified Kyropoulos method can be used to grow high quality 300 kg sapphire single crystals. The Verneuil method, also called the flame-fusion method, was used in the early 1900s to make rubies before CZ. Epitaxy is used to deposit very thin (micrometer to nanometer scale) layers of the same or different materials on the surface of an existing single crystal. Applications of this technique lie in the areas of semiconductor production, with potential uses in other nanotechnological fields and catalysis. It is extremely difficult to grow single crystals of the polymers. It is mainly because that the polymer chains are of different length and due to the various entropy reasons. However, topochemical reactions are one of the easy methods to get single crystals of the polymer. == Applications ==

Semiconductor industry One of the most used single crystals is that of silicon in the semiconductor industry. The four main production methods for semiconductor single crystals are from metallic solutions: liquid phase epitaxy (LPE), liquid phase electroepitaxy (LPEE), the traveling heater method (THM), and liquid phase diffusion (LPD). However, there are many other single crystals besides inorganic single crystals capable semiconducting, including single-crystal organic semiconductors. single crystal, made by the floating zone process, some single crystalline fragments of tantalum, and a high-purity (99.99% = 4N) 1 cm3 tantalum cube for comparison. Monocrystalline silicon used in the fabrication of semiconductors and photovoltaics is the greatest use of single-crystal technology today. In photovoltaics, the most efficient crystal structure will yield the highest light-to-electricity conversion. On the quantum scale that microprocessors operate on, the presence of grain boundaries would have a significant impact on the functionality of field effect transistors by altering local electrical properties. Therefore, microprocessor fabricators have invested heavily in facilities to produce large single crystals of silicon. The Czochralski method and floating zone are popular methods for the growth of silicon crystals. Other inorganic semiconducting single crystals include GaAs, GaP, GaSb, Ge, InAs, InP, InSb, CdS, CdSe, CdTe, ZnS, ZnSe, and ZnTe. Most of these can also be tuned with various doping for desired properties. Single-crystal graphene is also highly desired for applications in electronics and optoelectronics with its large carrier mobility and high thermal conductivity, and remains a topic of fervent research. One of the main challenges has been growing uniform single crystals of bilayer or multilayer graphene over large areas; epitaxial growth and the new CVD (mentioned above) are among the new promising methods under investigation. Organic semiconducting single crystals are different from the inorganic crystals. The weak intermolecular bonds mean lower melting temperatures, and higher vapor pressures and greater solubility. For single crystals to grow, the purity of the material is crucial and the production of organic materials usually require many steps to reach the necessary purity. Extensive research is being done to look for materials that are thermally stable with high charge-carrier mobility. Past discoveries include naphthalene, tetracene, and 9,10-diphenylanthacene (DPA). Triphenylamine derivatives have shown promise, and recently in 2021, the single-crystal structure of α-phenyl-4′-(diphenylamino)stilbene (TPA) grown using the solution method exhibited even greater potential for semiconductor use with its anisotropic hole transport property. Optical application , potassium dihydrogen phosphate, crystal grown from a seed crystal in a supersaturated aqueous solution at LLNL which is to be cut into slices and used on the National Ignition Facility for frequency doubling and tripling.|182x182pxSingle crystals have unique physical properties due to being a single grain with molecules in a strict order and no grain boundaries. Indium phosphide: these single crystals are particularly appropriate for combining optoelectronics with high-speed electronics in the form of optical fiber with its large-diameter substrates. Other photonic devices include lasers, photodetectors, avalanche photo diodes, optical modulators and amplifiers, signal processing, and both optoelectronic and photonic integrated circuits. Germanium: this was the material in the first transistor invented by Bardeen, Brattain, and Shockley in 1947. It is used in some gamma-ray detectors and infrared optics. Now it has become the focus of ultrafast electronic devices for its intrinsic carrier mobility. By alloying CdTe and ZnTe together room-temperature X-ray and gamma-ray detectors can be made. Production of metallic single crystals have the highest quality requirements and are grown, or pulled, in the form of rods. Certain companies can produce specific geometries, grooves, holes, and reference faces along with varying diameters. The size of the market, and vagaries in supply and cost, have provided strong incentives to seek alternatives or find ways to use less of them by improving performance. The conductivity of commercial conductors is often expressed relative to the International Annealed Copper Standard, according to which the purest copper wire available in 1914 measured around 100%. The purest modern copper wire is a better conductor, measuring over 103% on this scale. The gains are from two sources. First, modern copper is more pure. However, this avenue for improvement seems at an end. Making the copper purer still makes no significant improvement. Second, annealing and other processes have been improved. Annealing reduces the dislocations and other crystal defects which are sources of resistance. But the resulting wires are still polycrystalline. The grain boundaries and remaining crystal defects are responsible for some residual resistance. This can be quantified and better understood by examining single crystals. Single-crystal copper did prove to have better conductivity than polycrystalline copper. However, the single-crystal copper not only became a better conductor than high purity polycrystalline silver, but with prescribed heat and pressure treatment could surpass even single-crystal silver. Although impurities are usually bad for conductivity, a silver single crystal with a small amount of copper substitutions proved to be the best. As of 2009, no single-crystal copper is manufactured on a large scale industrially, but methods of producing very large individual crystal sizes for copper conductors are exploited for high performance electrical applications. These can be considered meta-single crystals with only a few crystals per meter of length. Single-crystal turbine blades Whilst the absence of grain boundaries decreases yield strength, this is offset by a reduction in thermal creep, making single-crystal solids ideal for high temperature, close tolerance part applications, such as turbine blades. Researcher Barry Piearcey found that a right-angle bend at the casting mold would decrease the number of columnar crystals and later, scientist Giamei used this to start the blade's single-crystal structure. == In research ==

Single crystals are essential in research especially condensed-matter physics and all aspects of materials science such as surface science. Furthermore, macroscopically averaging techniques such as angle-resolved photoemission spectroscopy or low-energy electron diffraction are only possible or meaningful on surfaces of single crystals. Single crystals are further well-suited to investigate material-inherent properties using surface-sensitive techniques, as they are much less affected by preparation methods than thin films. In superconductivity there have been cases of materials where superconductivity is only seen in single-crystalline specimen. They may be grown for this purpose, even when the material is otherwise only needed in polycrystalline form. As such, numerous new materials are being studied in their single-crystal form. The young field of metal-organic-frameworks (MOFs) is one of many which qualify to have single crystals. In January 2021 Dr. Dong and Dr. Feng demonstrated how polycyclic aromatic ligands can be optimized to produce large 2D MOF single crystals of sizes up to 200 μm. This could mean scientists can fabricate single-crystal devices and determine intrinsic electrical conductivity and charge transport mechanism. The field of photodriven transformation can also be involved with single crystals with something called single-crystal-to-single-crystal (SCSC) transformations. These provide direct observation of molecular movement and understanding of mechanistic details. This photoswitching behavior has also been observed in cutting-edge research on intrinsically non-photo-responsive mononuclear lanthanide single-molecule-magnets (SMM). == Post-processing of single crystals ==

Single crystals used in semiconductors, optics, and ceramics must often be machined or sliced into wafers, prisms, or other precision components. Due to their hardness and brittleness, these materials require specialized cutting techniques that minimize subsurface damage and kerf loss. Inner diameter (ID) sawing is a conventional method, where a thin circular blade embedded with diamond abrasives slices through the crystal. It provides good dimensional accuracy but is limited by blade rigidity and maximum cutting depth. Multi-wire sawing, which uses long diamond wires moving reciprocally, became the mainstream process for silicon and sapphire wafers. It allows simultaneous slicing of multiple wafers from a single ingot, but the back-and-forth motion can cause vibration and wire wear, leading to surface marks and variable tension. Endless diamond wire sawing (loop-type) is a more recent approach. The wire forms a continuous closed loop, typically several meters in length, running in a single direction at high linear speeds (around 60–80 m/s). Because the wire tension and motion are steady, the process can achieve smoother surfaces, smaller kerf widths, and longer tool life. It has been applied to slicing hard and brittle single-crystal materials such as silicon, sapphire, and advanced ceramics. Other techniques, including laser slicing, ultrasonic machining, and ion-beam or chemical-mechanical polishing, are used for finishing or micro-fabrication stages, especially when optical-grade surface quality is required. == See also ==