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A single-crystal, or monocrystalline,
solid Solid is one of the four fundamental states of matter (the others being liquid, gas and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural ...

solid
is a material in which the
crystal lattice In geometry and crystallography, a Bravais lattice, named after , is an infinite array of discrete points generated by a set of Translation operator (quantum mechanics)#Discrete Translational Symmetry, discrete translation operations described in th ...
of the entire sample is continuous and unbroken to the edges of the sample, with no
grain boundaries of a polycrystalline A crystallite is a small or even microscopic crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, for ...
.RIWD. "Reade Advanced Materials - Single Crystals". ''www.reade.com''. Retrieved 2021-02-28. The absence of the defects associated with grain boundaries can give monocrystals unique properties, particularly mechanical, optical and electrical, which can also be
anisotropic Anisotropy () is the property of a material which allows it to change or assume different properties in different directions as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's physic ...
, depending on the type of
crystallographic Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek words ''crystallon'' "cold drop, frozen drop", with its mean ...
structure. These properties, in addition to making some gems precious, are industrially used in technological applications, especially in optics and electronics. Because effects favor the presence of some imperfections in the microstructure of solids, such as
impurities Impurities are chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
, inhomogeneous strain and crystallographic defects such as
dislocation In materials science The interdisciplinary field of materials science, also commonly termed materials science and engineering, covers the design and discovery of new materials, particularly solids. The intellectual origins of materials scienc ...
s, perfect single crystals of meaningful size are exceedingly rare in nature. The necessary laboratory conditions often add to the cost of production. On the other hand, imperfect single crystals can reach enormous sizes in nature: several
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (20 ...

mineral
species such as
beryl Beryl ( ) is a mineral composed of beryllium Beryllium is a chemical element with the Symbol (chemistry), symbol Be and atomic number 4. It is a Abundance of the chemical elements#Universe, relatively rare element in the universe, usually ...
,
gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard/ sidewalk chalk, and drywal ...

gypsum
and
feldspar Feldspars () are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight. Feldspars crystallize from magma as both Intrusive rock, intrusive and extrusive igneous rocks and are also pres ...
s are known to have produced crystals several meters across."Pure Element Single Crystals - Alfa Chemistry". ''www.alfa-chemistry.com''. Retrieved 2021-02-28. The opposite of a single crystal is an amorphous structure where the atomic position is limited to short range order only."4.1: Introduction". ''Engineering LibreTexts''. 2019-02-08. Retrieved 2021-02-28. In between the two extremes exist ''
polycrystalline A crystallite is a small or even microscopic crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice ...
'', which is made up of a number of smaller crystals known as ''
crystallite A crystallite is a small or even microscopic crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice ...
s'', and ''
paracrystalline Paracrystalline materials are defined as having short- and medium-range ordering in their lattice (similar to the liquid crystal phases) but lacking crystal A crystal or crystalline solid is a solid material whose constituents (such as atom ...
'' phases."DoITPoMS - TLP Library Atomic Scale Structure of Materials". ''www.doitpoms.ac.uk''. Retrieved 2021-02-28. Single crystals will usually have distinctive plane faces and some symmetry, where the angles between the faces will dictate its ideal shape. Gemstones are often single crystals artificially cut along crystallographic planes to take advantage of refractive and reflective properties.


Production Methods

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.(2007) Growing Single Crystals. In: Ceramic Materials. Springer, New York, NY. Basic crystal growth methods can be separated into four categories based on what they are artificially grown from: melt, solid, vapor, and solution. Specific techniques to produce large single crystals (aka
boules ''Boules'' () is a collective name for a wide range of games similar to bowls and bocce (In French: jeu or jeux, in Italian: gioco or giochi) in which the objective is to throw or roll heavy balls (called in France, and in Italy) as close as poss ...
) include the , Floating zone (or Zone Movement), and the
Bridgman techniqueBridgman is a surname, and may refer to: * David Bridgman, Australian architect * Elijah Coleman Bridgman (1801–1861), American missionary in China * Frederick Arthur Bridgman (1847-1928), American artist * George Bridgman (1865-1943), anatomis ...
. Dr. Teal and Dr. Little of Bell Telephone Laboratories were the first to use the Czochralski method to create Ge and Si single crystals. Other methods of crystallization may be used, depending on the physical properties of the substance, including
hydrothermal synthesis crystal grown by the hydrothermal method Hydrothermal synthesis includes the various techniques of crystallizing substances from high-temperature aqueous solution An aqueous solution is a solution Image:SaltInWaterSolutionLiquid.jpg, Making ...
, sublimation, or simply solvent-based crystallization. For example, a modified Kyropoulos method can be used to grow high quality 300 kg sapphire single crystals.Zalozhny, Eugene (Jul 13th, 2015). "Monocrystal enables high-volume LED and optical applications with 300-kg KY sapphire crystals". ''LED's Magazine''. Retrieved February 27, 2021. The Verneuil method, also called the flame-fusion method, was used in the early 1900s to make rubies before CZ. The diagram on the right illustrates most of the conventional methods. There have been new breakthroughs such as chemical vapor depositions (CVD) along with different variations and tweaks to the existing methods. These are not shown in the diagram. bar grown by the hydrothermal method In the case of metal single crystals, fabrication techniques also include
epitaxy Epitaxy refers to a type of crystal growth or material deposition in which new crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic ...
and abnormal grain growth in solids. 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.


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 silicon is used in the fabrication of semiconductors and
photovoltaics Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially u ...
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 In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "P ...
scale that
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circuitr ...

microprocessor
s operate on, the presence of grain boundaries would have a significant impact on the functionality of
field effect transistor The field-effect transistor (FET) is a type of transistor file:MOSFET Structure.png, upright=1.4, Metal-oxide-semiconductor field-effect transistor (MOSFET), showing Metal gate, gate (G), body (B), source (S) and drain (D) terminals. The gate ...
s 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 In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they under ...
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 Doping may refer to: * Doping, adding a dopant to something * Doping (semiconductor), intentionally introducing impurities into an extremely pure semiconductor to change its electrical properties * Aircraft dope, a lacquer that is applied to fabric ...
for desired properties. Single crystal
graphene Graphene () is an allotrope of carbon consisting of a single layer of atoms arranged in a 2D Materials, two-dimensional hexagonal lattice, honeycomb lattice. The name is a portmanteau of "graphite" and the suffix -ene, reflecting the fact that the ...

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 anistropic hole transport property.


Optical Application

A huge
KDP, potassium dihydrogen phosphate, crystal grown from a

_in_a_supersaturation.html" "title="seed crystal
KDP</a>, potassium dihydrogen phosphate, crystal grown from a seed crystal
in a supersaturation">supersaturated Supersaturation occurs with a chemical solution when the concentration of a solute exceeds the concentration specified by the value equilibrium solubility. Most commonly the term is applied to a solution of a solid in a liquid. A supersaturated sol ...
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. This includes optical properties, and single crystals of silicon is also used as optical windows because of its transparency at specific
infrared (IR) wavelengths
infrared (IR) wavelengths
, making it very useful for some instruments.
Sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived from the Latin "saphir ...

Sapphire
s: Better known as the alpha phase of aluminum oxide (Al2O3) by scientists, sapphire single crystals are widely used in hi-tech engineering. It can be grown from gaseous, solid, or solution phases. The diameter of the crystals resulting from the growth method are important when considering electronic uses after. They are used for
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term "laser" originated as an acronym for "light amplification by stimulated emission of radia ...

laser
s and
nonlinear optics Nonlinear optics (NLO) is the branch of optics Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that ...
. Some notable uses are as in the window of a biometric fingerprint reader, optical disks for long-term data storage, and X-ray interferometer.
Indium Phosphide Indium phosphide (InP) is a binary semiconductor A semiconductor material has an Electrical resistivity and conductivity, electrical conductivity value falling between that of a Electrical conductor, conductor, such as metallic copper, and an i ...

Indium Phosphide
: These single crystals are particularly appropriate for combining optoelectronics with high-speed electronics in the form of optical fiber wit 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 Germanium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...

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.
Arsenide In chemistry, an arsenide is a compound of arsenic Arsenic is a chemical element with the Symbol (chemistry), symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a ...
: Arsenide III can be combined with various elements such as B, Al, Ga, and In, with the GaAs compound being in high demand for wafers.
Cadmium Telluride Cadmium telluride (CdTe) is a stable crystalline Chemical compound, compound formed from cadmium and tellurium. It is mainly used as the semiconducting material in cadmium telluride photovoltaics and an infrared optical window. It is usually sand ...
: CdTe crystals have several applications as substrates for IR imaging, electrooptic devices, and
solar cells A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physics, physical and Chemical substance, chemical phenomenon.


Electrical Conductors

Metals can surprisingly be produced in single crystal form and provide a means to understand the ultimate performance of metallic conductors. It is vital for understanding the basic science such as catalytic chemistry, surface physics, electrons, and
monochromator A monochromator is an optical device that transmits a mechanically selectable narrow band of wavelength In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' ...

monochromator
s. 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. Of all the metallic elements, silver and copper have the best conductivity at room temperature, setting the bar for performance. 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 StandardThe International Annealed Copper Standard (IACS) is a standard Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requirement * Standard (metro ...
, 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. As anticipated, 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

Another application of single crystal solids is in materials science in the production of high strength materials with low thermal creep, such as turbine blades.Spittle, Peter
"Gas turbine technology"
''
Rolls-Royce plc Rolls-Royce Holdings plc is a British multinational aerospace and defence company incorporated in February 2011 that owns Rolls-Royce, a business established in 1904 which today designs, manufactures and distributes power systems for aviation ...
'', 2003. Retrieved: 21 July 2012.
Here, the absence of grain boundaries actually gives a decrease in yield strength, but more importantly decreases the amount of creep which is critical for high temperature, close tolerance part applications.Crown jewels - These crystals are the gems of turbine efficiency
Article on single crystal turbine blades ''memagazine.com''
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 single-crystal structure of the turbine blade.


In research

Single crystals are essential in research especially
condensed-matter physics Condensed matter physics is the field of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (p ...
and all aspects of
materials science The Interdisciplinarity, interdisciplinary field of materials science, also commonly termed materials science and engineering, covers the design and discovery of new materials, particularly solids. The intellectual origins of materials science ste ...
such as
surface science 250px, STM image of a self-assembled_supramolecular.html" ;"title="self-assembly.html" ;"title="adsorbate.html" ;"title="quinacridone adsorbate">quinacridone adsorbate. The self-assembly">self-assembled supramolecular">self-assembly.html" ;"tit ...

surface science
. The detailed study of the
crystal structure In crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek words ''crystallon'' "cold drop, frozen ...

crystal structure
of a material by techniques such as
Bragg diffractionBragg may refer to: Places * Bragg City, Missouri, United States * Bragg, Texas, a ghost town, United States * Bragg, West Virginia, an unincorporated community, United States *Electoral district of Bragg, a state electoral district in South Austral ...

Bragg diffraction
and
helium atom scatteringHelium atom scattering (HAS) is a surface analysis technique used in materials science. HAS provides information about the surface structure and lattice dynamics of a material by measuring the diffracted atoms from a monochromatic helium beam incide ...
is easier with single crystals because it is possible to study directional dependence of various properties and compare with theoretical predictions. Furthermore, macroscopically averaging techniques such as
angle-resolved photoemission spectroscopy Angle-resolved photoemission spectroscopy (ARPES) is a powerful technique used in condensed matter physics Condensed matter physics is the field of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), ...
or
low-energy electron diffraction Image:Si100Reconstructed.png, thumbnail, 280x280px, Figure 1: LEED pattern of a Si(100) reconstructed surface. The underlying lattice is a square lattice, while the surface reconstruction has a 2×1 periodicity. As discussed in the text, the pattern ...
are only possible or meaningful on surfaces of single crystals. In
superconductivity Superconductivity is a set of physical properties observed in certain materials where Electrical resistance and conductance, electrical resistance vanishes and magnetic field, magnetic flux fields are expelled from the material. Any material exh ...

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 A crystallite is a small or even microscopic crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice ...
form. As such, numerous new materials are being studied in their single crystal form. The young field of metal-organic-frameworks (MOF's) 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).


See also

* Engineering aspects of crystallisation * Fractional crystallization *
Laser-heated pedestal growth Laser-heated pedestal growth (LHPG) or laser floating zone (LFZ) is a crystal growth A crystal is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. ...
*
Micro-pulling-downThe micro-pulling-down (μ-PD) method is a crystal growth A crystal is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. Crystal growth is a major st ...
* Recrystallization *
Seed crystal A seed crystal is a small piece of single crystal or polycrystal material from which a large crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordere ...


References


Further reading


"Small Molecule Crystallization"
(
PDF Portable Document Format (PDF), standardized as ISO 32000, is a file format ogg-file: 154 kilobytes. A file format is a standard Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for pe ...
) at
Illinois Institute of Technology Illinois Institute of Technology (Illinois Tech) is a private research university A research university is a university A university ( la, universitas, 'a whole') is an educational institution, institution of higher education, higher (or T ...
website {{DEFAULTSORT:Single Crystal Crystals