1.
Ion
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An ion is an atom or a molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge. Ions can be created, by chemical or physical means. In chemical terms, if an atom loses one or more electrons. If an atom gains electrons, it has a net charge and is known as an anion. Ions consisting of only a single atom are atomic or monatomic ions, because of their electric charges, cations and anions attract each other and readily form ionic compounds, such as salts. In the case of ionization of a medium, such as a gas, which are known as ion pairs are created by ion impact, and each pair consists of a free electron. The word ion comes from the Greek word ἰόν, ion, going and this term was introduced by English physicist and chemist Michael Faraday in 1834 for the then-unknown species that goes from one electrode to the other through an aqueous medium. Faraday also introduced the words anion for a charged ion. In Faradays nomenclature, cations were named because they were attracted to the cathode in a galvanic device, arrhenius explanation was that in forming a solution, the salt dissociates into Faradays ions. Arrhenius proposed that ions formed even in the absence of an electric current, ions in their gas-like state are highly reactive, and do not occur in large amounts on Earth, except in flames, lightning, electrical sparks, and other plasmas. These gas-like ions rapidly interact with ions of charge to give neutral molecules or ionic salts. These stabilized species are commonly found in the environment at low temperatures. A common example is the present in seawater, which are derived from the dissolved salts. Electrons, due to their mass and thus larger space-filling properties as matter waves, determine the size of atoms. Thus, anions are larger than the parent molecule or atom, as the excess electron repel each other, as such, in general, cations are smaller than the corresponding parent atom or molecule due to the smaller size of its electron cloud. One particular cation contains no electrons, and thus consists of a single proton - very much smaller than the parent hydrogen atom. Since the electric charge on a proton is equal in magnitude to the charge on an electron, an anion, from the Greek word ἄνω, meaning up, is an ion with more electrons than protons, giving it a net negative charge. A cation, from the Greek word κατά, meaning down, is an ion with fewer electrons than protons, there are additional names used for ions with multiple charges
2.
Fabrication (semiconductor)
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Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a sequence of photo lithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon is almost always used, but various compound semiconductors are used for specialized applications, the entire manufacturing process, from start to packaged chips ready for shipment, takes six to eight weeks and is performed in highly specialized facilities referred to as fabs. When feature widths were far greater than about 10 micrometres, purity was not the issue that it is today in device manufacturing, as devices became more integrated, cleanrooms became even cleaner. Today, the fabs are pressurized with filtered air to remove even the smallest particles, the workers in a semiconductor fabrication facility are required to wear cleanroom suits to protect the devices from human contamination. Semiconductor device manufacturing has spread from Texas and California in the 1960s to the rest of the world, including Europe, the Middle East and it is a global business today. The leading semiconductor manufacturers typically have facilities all over the world, intel, the worlds largest manufacturer, has facilities in Europe and Asia as well as the U. S. A typical wafer is made out of pure silicon that is grown into mono-crystalline cylindrical ingots up to 300 mm in diameter using the Czochralski process. These ingots are sliced into wafers about 0.75 mm thick and polished to obtain a very regular. In semiconductor device fabrication, the processing steps fall into four general categories, deposition, removal, patterning. Deposition is any process that grows, coats, or otherwise transfers a material onto the wafer, available technologies include physical vapor deposition, chemical vapor deposition, electrochemical deposition, molecular beam epitaxy and more recently, atomic layer deposition among others. Removal is any process that removes material from the wafer, examples include etch processes, patterning is the shaping or altering of deposited materials, and is generally referred to as lithography. After etching or other processing, the remaining photoresist is removed by plasma ashing, modification of electrical properties has historically entailed doping transistor sources and drains. These doping processes are followed by annealing or, in advanced devices. Modification of electrical properties now also extends to the reduction of a dielectric constant in low-k insulators via exposure to ultraviolet light in UV processing. Modern chips have up to eleven metal levels produced in over 300 sequenced processing steps, FEOL processing refers to the formation of the transistors directly in the silicon. The raw wafer is engineered by the growth of an ultrapure, in the most advanced logic devices, prior to the silicon epitaxy step, tricks are performed to improve the performance of the transistors to be built. One method involves introducing a straining step wherein a silicon variant such as silicon-germanium is deposited, once the epitaxial silicon is deposited, the crystal lattice becomes stretched somewhat, resulting in improved electronic mobility
3.
Materials science
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The interdisciplinary field of materials science, also commonly termed materials science and engineering, involves the discovery and design of new materials, with an emphasis on solids. Materials science still incorporates elements of physics, chemistry, and engineering, as such, the field was long considered by academic institutions as a sub-field of these related fields. Materials science is a syncretic discipline hybridizing metallurgy, ceramics, solid-state physics and it is the first example of a new academic discipline emerging by fusion rather than fission. Many of the most pressing scientific problems humans currently face are due to the limits of the materials that are available, thus, breakthroughs in materials science are likely to affect the future of technology significantly. Materials scientists emphasize understanding how the history of a material influences its structure, the understanding of processing-structure-properties relationships is called the § materials paradigm. This paradigm is used to advance understanding in a variety of areas, including nanotechnology, biomaterials. Such investigations are key to understanding, for example, the causes of various accidents and incidents. The material of choice of a given era is often a defining point, phrases such as Stone Age, Bronze Age, Iron Age, and Steel Age are great examples. Originally deriving from the manufacture of ceramics and its putative derivative metallurgy, materials science is one of the oldest forms of engineering, modern materials science evolved directly from metallurgy, which itself evolved from mining and ceramics and the use of fire. Materials science has driven, and been driven by, the development of technologies such as rubbers, plastics, semiconductors. Before the 1960s, many materials science departments were named metallurgy departments, reflecting the 19th, a material is defined as a substance that is intended to be used for certain applications. There are a myriad of materials around us—they can be found in anything from buildings to spacecraft, Materials can generally be divided into two classes, crystalline and non-crystalline. The traditional examples of materials are metals, semiconductors, ceramics, New and advanced materials that are being developed include nanomaterials and biomaterials, etc. The basis of science involves studying the structure of materials. Once a materials scientist knows about this structure-property correlation, they can go on to study the relative performance of a material in a given application. The major determinants of the structure of a material and thus of its properties are its constituent chemical elements and these characteristics, taken together and related through the laws of thermodynamics and kinetics, govern a materials microstructure, and thus its properties. As mentioned above, structure is one of the most important components of the field of materials science, Materials science examines the structure of materials from the atomic scale, all the way up to the macro scale. Characterization is the way materials scientists examine the structure of a material, structure is studied at various levels, as detailed below
4.
Crystal structure
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In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter. The smallest group of particles in the material that constitutes the pattern is the unit cell of the structure. The unit cell completely defines the symmetry and structure of the crystal lattice. The repeating patterns are said to be located at the points of the Bravais lattice, the lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called lattice parameters. The symmetry properties of the crystal are described by the concept of space groups, all possible symmetric arrangements of particles in three-dimensional space may be described by the 230 space groups. The crystal structure and symmetry play a role in determining many physical properties, such as cleavage, electronic band structure. The crystal structure of a material can be described in terms of its unit cell, the unit cell is a box containing one or more atoms arranged in three dimensions. The unit cells stacked in three-dimensional space describe the arrangement of atoms of the crystal. Commonly, atomic positions are represented in terms of fractional coordinates, the atom positions within the unit cell can be calculated through application of symmetry operations to the asymmetric unit. The asymmetric unit refers to the smallest possible occupation of space within the unit cell and this does not, however imply that the entirety of the asymmetric unit must lie within the boundaries of the unit cell. Symmetric transformations of atom positions are calculated from the group of the crystal structure. Vectors and planes in a lattice are described by the three-value Miller index notation. It uses the indices ℓ, m, and n as directional parameters, which are separated by 90°, by definition, the syntax denotes a plane that intercepts the three points a1/ℓ, a2/m, and a3/n, or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane with the unit cell, if one or more of the indices is zero, it means that the planes do not intersect that axis. A plane containing a coordinate axis is translated so that it no longer contains that axis before its Miller indices are determined, the Miller indices for a plane are integers with no common factors. Negative indices are indicated with horizontal bars, as in, in an orthogonal coordinate system for a cubic cell, the Miller indices of a plane are the Cartesian components of a vector normal to the plane. Likewise, the planes are geometric planes linking nodes
5.
Collision cascade
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A collision cascade is a set of nearby adjacent energetic collisions of atoms induced by an energetic particle in a solid or liquid. The initial energetic atom can be, e. g, the nature of collision cascades can vary strongly depending on the energy and mass of the recoil/incoming ion and density of the material. This kind of a cascade can be well treated using the binary collision approximation simulation approach. For instance, H and He ions with energies below 10 keV can be expected to lead to purely linear cascades in all materials. The most commonly used BCA code SRIM can be used to simulate linear collision cascades in disordered materials for all ion in all materials up to ion energies of 1 GeV. Note, however, that SRIM does not treat such as damage due to electronic energy deposition or damage produced by excited electrons. The nuclear and electronic stopping powers used are averaging fits to experiments, when the ion is heavy and energetic enough, and the material is dense, the collisions between the ions may occur so near to each other that they can not be considered independent of each other. Computer simulation-based animations of collision cascades in the heat spike regime are available on YouTube, typically, a heat spike is characterized by the formation of a transient underdense region in the center of the cascade, and an overdense region around it. After the cascade, the region becomes interstitial defects. If the kinetic energy of the atoms in the region of collisions is recalculated into temperature. Because of this, the region can be considered to be very hot, the heat spike cools down to the ambient temperature in 1–100 ps, so the temperature here does not correspond to thermodynamic equilibrium temperature. In many cases, the same condition is a combination of linear cascades. For example,10 MeV Cu ions bombarding Cu would initially move in the lattice in a linear cascade regime, but once the Cu ion would slow down enough, the nuclear stopping power would increase and a heat spike would be produced. Moreover, many of the primary and secondary recoils of the ions would likely have energies in the keV range. For instance, for copper irradiation of copper, recoil energies of around 5–20 keV are almost guaranteed to produce heat spikes, at lower energies, the cascade energy is too low to produce a liquid-like zone. At much higher energies, the Cu ions would most likely lead initially to a linear cascade, the concept subcascade breakdown threshold energy signifies the energy above which a recoil in a material is likely to produce several isolated heat spikes rather than a single dense one. Swift heavy ions, i. e. However, at least the stage of the damage might be better understood in terms of a Coulomb explosion mechanism. Regardless of what the mechanism is, it is well established that swift heavy ions in insulators typically produce ion tracks forming long cylindrical damage zones of reduced density
6.
Ion source
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An ion source is a device that creates atomic and molecular ions. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters, Electron ionization is widely used in mass spectrometry, particularly for organic molecules. The electrons may be created by an arc discharge between a cathode and an anode, an electron beam ion source is used in atomic physics to produce highly charged ions by bombarding atoms with a powerful electron beam. Its principle of operation is shared by the electron beam ion trap, Electron capture ionization is the ionization of a gas phase atom or molecule by attachment of an electron to create an ion of the form A−•. The reaction is A + e − → M A − where the M over the arrow denotes that to conserve energy, Electron capture can be used in conjunction with chemical ionization. An electron capture detector is used in gas chromatography systems. Chemical ionization is a lower energy process than electron ionization because it involves ion/molecule reactions rather than electron removal, the lower energy yields less fragmentation, and usually a simpler spectrum. A typical CI spectrum has an easily identifiable molecular ion, in a CI experiment, ions are produced through the collision of the analyte with ions of a reagent gas in the ion source. Some common reagent gases include, methane, ammonia, and isobutane, inside the ion source, the reagent gas is present in large excess compared to the analyte. Electrons entering the source will preferentially ionize the reagent gas, the resultant collisions with other reagent gas molecules will create an ionization plasma. Positive and negative ions of the analyte are formed by reactions with this plasma. For example, protonation occurs by CH4 + e − ⟶ CH4 + +2 e −, charge-exchange ionization is a gas phase reaction between an ion and an atom or molecule in which the charge of the ion is transferred to the neutral species. A + + B ⟶ A + B + Chemi-ionization is the formation of an ion through the reaction of a gas atom or molecule with an atom or molecule in an excited state. Associative ionization is a gas phase reaction in which two atoms or molecules interact to form a single product ion, one or both of the interacting species may have excess internal energy. For example, A ∗ + B ⟶ AB + ∙ + e − where species A with excess internal energy interacts with B to form the ion AB+, Penning ionization is a form of chemi-ionization involving reactions between neutral atoms or molecules. The process is named after the Dutch physicist Frans Michel Penning who first reported it in 1927, Penning ionization involves a reaction between a gas-phase excited-state atom or molecule G* and a target molecule M resulting in the formation of a radical molecular cation M+. In a radioactive ion source, a piece of radioactive material. This is used in smoke detectors and ion mobility spectrometers
7.
Particle accelerator
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A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to nearly light speed and to contain them in well-defined beams. Large accelerators are used in physics as colliders, or as synchrotron light sources for the study of condensed matter physics. There are currently more than 30,000 accelerators in operation around the world, there are two basic classes of accelerators, electrostatic and electrodynamic accelerators. Electrostatic accelerators use electric fields to accelerate particles. The most common types are the Cockcroft–Walton generator and the Van de Graaff generator, a small-scale example of this class is the cathode ray tube in an ordinary old television set. The achievable kinetic energy for particles in these devices is determined by the accelerating voltage, electrodynamic or electromagnetic accelerators, on the other hand, use changing electromagnetic fields to accelerate particles. Since in these types the particles can pass through the accelerating field multiple times. This class, which was first developed in the 1920s, is the basis for most modern large-scale accelerators, because colliders can give evidence of the structure of the subatomic world, accelerators were commonly referred to as atom smashers in the 20th century. Despite the fact that most accelerators actually propel subatomic particles, the term persists in popular usage when referring to particle accelerators in general. Beams of high-energy particles are useful for both fundamental and applied research in the sciences, and also in many technical and industrial fields unrelated to fundamental research and it has been estimated that there are approximately 30,000 accelerators worldwide. The bar graph shows the breakdown of the number of industrial accelerators according to their applications, for the most basic inquiries into the dynamics and structure of matter, space, and time, physicists seek the simplest kinds of interactions at the highest possible energies. These typically entail particle energies of many GeV, and the interactions of the simplest kinds of particles, leptons and quarks for the matter, the largest and highest energy particle accelerator used for elementary particle physics is the Large Hadron Collider at CERN, operating since 2009. These investigations often involve collisions of heavy nuclei – of atoms like iron or gold – at energies of several GeV per nucleon, the largest such particle accelerator is the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. An example of type of machine is LANSCE at Los Alamos. A large number of light sources exist worldwide. The ESRF in Grenoble, France has been used to extract detailed 3-dimensional images of trapped in amber. Thus there is a demand for electron accelerators of moderate energy. Everyday examples of particle accelerators are cathode ray tubes found in television sets and these low-energy accelerators use a single pair of electrodes with a DC voltage of a few thousand volts between them
8.
Particle radiation
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Particle radiation is the radiation of energy by means of fast-moving subatomic particles. Particle radiation is referred to as a particle beam if the particles are all moving in the same direction, due to the wave–particle duality, all moving particles also have wave character. Higher energy particles more easily exhibit particle characteristics, while lower energy particles more easily exhibit wave characteristics, particles can be electrically charged or uncharged, Particle radiation can be emitted by an unstable atomic nucleus, or it can be the product from some other kind of nuclear reaction. Ion irradiation is used in the semiconductor industry to introduce dopants into materials. Particle accelerators can also produce neutrino beams, neutron beams are mostly produced by nuclear reactors. For the production of electromagnetic radiation, there are many methods, in radiation protection, radiation is often separated into two categories, ionizing and non-ionizing, to denote the level of danger posed to humans. Ionization is the process of removing electrons from atoms, leaving two electrically charged particles behind, the negatively charged electrons and positively charged ions created by ionizing radiation may cause damage in living tissue. Basically, a particle is ionizing if its energy is higher than the energy of a typical substance, i. e. a few eV. The charged particles mentioned above all belong to the ionizing radiations, when passing through matter, they ionize and thus lose energy in many small steps. The distance to the point where the particle has lost all its energy is called the range of the particle. The range depends upon the type of particle, its energy. Similarly, the loss per unit path length, the stopping power, depends on the type and energy of the charged particle. The stopping power and hence, the density of ionization, usually increases toward the end of range and reaches a maximum, the Bragg Peak, shortly before the energy drops to zero
9.
Electronvolt
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In physics, the electronvolt is a unit of energy equal to approximately 1. 6×10−19 joules. By definition, it is the amount of energy gained by the charge of an electron moving across an electric potential difference of one volt. Thus it is 1 volt multiplied by the elementary charge, therefore, one electronvolt is equal to 6981160217662079999♠1. 6021766208×10−19 J. The electronvolt is not a SI unit, and its definition is empirical, like the elementary charge on which it is based, it is not an independent quantity but is equal to 1 J/C √2hα / μ0c0. It is a unit of energy within physics, widely used in solid state, atomic, nuclear. It is commonly used with the metric prefixes milli-, kilo-, in some older documents, and in the name Bevatron, the symbol BeV is used, which stands for billion electronvolts, it is equivalent to the GeV. By mass–energy equivalence, the electronvolt is also a unit of mass and it is common in particle physics, where units of mass and energy are often interchanged, to express mass in units of eV/c2, where c is the speed of light in vacuum. It is common to express mass in terms of eV as a unit of mass. The mass equivalent of 1 eV/c2 is 1 eV / c 2 = ⋅1 V2 =1.783 ×10 −36 kg. For example, an electron and a positron, each with a mass of 0.511 MeV/c2, the proton has a mass of 0.938 GeV/c2. In general, the masses of all hadrons are of the order of 1 GeV/c2, the unified atomic mass unit,1 gram divided by Avogadros number, is almost the mass of a hydrogen atom, which is mostly the mass of the proton. To convert to megaelectronvolts, use the formula,1 u =931.4941 MeV/c2 =0.9314941 GeV/c2, in high-energy physics, the electronvolt is often used as a unit of momentum. A potential difference of 1 volt causes an electron to gain an amount of energy and this gives rise to usage of eV as units of momentum, for the energy supplied results in acceleration of the particle. The dimensions of units are LMT−1. The dimensions of units are L2MT−2. Then, dividing the units of energy by a constant that has units of velocity. In the field of particle physics, the fundamental velocity unit is the speed of light in vacuum c. Thus, dividing energy in eV by the speed of light, the fundamental velocity constant c is often dropped from the units of momentum by way of defining units of length such that the value of c is unity
10.
Ion beam deposition
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Ion Beam Deposition is a process of applying materials to a target through the application of an ion beam. An ion beam deposition apparatus typically consists of an ion source, ion optics, optionally a mass analyzer can be incorporated. In the ion source source materials in the form of a gas, for atomic ion IBD, electron ionization, field ionization or cathodic arc sources are employed. Cathodic arc sources are used particularly for carbon ion deposition, molecular ion beam deposition employs electrospray ionization or MALDI sources. The ions are accelerated, focused or deflected using high voltages or magnetic fields. Optional deceleration at the substrate can be employed to define the deposition energy and this energy usually ranges from a few eV up to a few keV. Ion optics can be mass selective, in IBD they are used to select a single, or a range of ion species for deposition in order to avoid contamination. For organic materials in particular, this process is monitored by a mass spectrometer. The ion beam current, which is quantitative measure for the amount of material. Switching of the mass range can be used to define a stoichiometry. Cathodic Arc Deposition Sputter deposition Ion beam assisted deposition Ion beam induced deposition Electrospray ionization MALDI
11.
Bragg peak
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The Bragg peak is a pronounced peak on the Bragg curve which plots the energy loss of ionizing radiation during its travel through matter. For protons, α-rays, and other ion rays, the peak occurs immediately before the particles come to rest and this is called Bragg peak, after William Henry Bragg who discovered it in 1903. When a fast charged particle moves through matter, it ionizes atoms of the material, a peak occurs because the interaction cross section increases as the charged particles energy decreases. Energy lost by charged particles is proportional to the square of their velocity. In the upper figure, it is the peak for alpha particles of 5.49 MeV moving through air, in the lower figure, it is the narrow peak of the native proton beam curve which is produced by a particle accelerator of 250 MeV. The figure also shows the absorption of a beam of photons which is entirely different in nature. The phenomenon is exploited in particle therapy of cancer, to concentrate the effect of ion beams on the tumor being treated while minimizing the effect on the surrounding healthy tissue. The blue curve in the figure shows how the originally monoenergetic proton beam with the peak is widened by increasing the range of energies. This can be achieved by using variable thickness attenuators like spinning wedges, stopping power Bremsstrahlung Linear Energy Transfer Wagenaar, Douglas. Archived from the original on 1 March 2016
12.
Stopping power (particle radiation)
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Its application is important in areas such as radiation protection and nuclear medicine. Both charged and uncharged particles lose energy while passing through matter, positive ions are considered in most cases below. The stopping power depends on the type and energy of the radiation and on the properties of the material it passes, since the production of an ion pair requires a fixed amount of energy, the density of ionization is proportional to the stopping power. The stopping power of the material is numerically equal to the loss of energy E per unit path length, the force usually increases toward the end of range and reaches a maximum, the Bragg peak, shortly before the energy drops to zero. The curve that describes the force as function of the depth is called the Bragg curve. This is of practical importance for radiation therapy. The equation above defines the linear stopping power which in the system is expressed in N but is usually indicated in other units like MeV/mm or similar. If a substance is compared in gaseous and solid form, then the linear stopping powers of the two states are very different just because of the different density, the mass stopping power then depends only very little on the density of the material. The picture shows how the power of 5.49 MeV alpha particles increases while the particle traverses air. This particular energy corresponds to that of the alpha radiation from naturally radioactive gas radon which is present in the air in minute amounts. The deposited energy can be obtained by integrating the stopping power over the path length of the ion while it moves in the material. Electronic stopping refers to the slowing down of a projectile ion due to the collisions between bound electrons in the medium and the ion moving through it. The term inelastic is used to signify that energy is lost during the process, linear electronic stopping power is identical to unrestricted linear energy transfer. Instead of energy transfer, some consider the electronic stopping power as momentum transfer between electron gas and energetic ion. This is consistent with the result of Bethe in the energy range. Instead, the stopping power is often given as a simple function of energy F e which is an average taken over all energy loss processes for different charge states. It can be determined to an accuracy of a few % in the energy range above several hundred keV per nucleon from theoretical treatments. At energies lower than about 100 keV per nucleon, it more difficult to determine the electronic stopping theoretically
13.
Binary collision approximation
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In the method, the ion is approximated to travel through a material by experiencing a sequence of independent binary collisions with sample atoms. Between the collisions, the ion is assumed to travel in a path, experiencing electronic stopping power. Solution of the integral gives the angle of the ion as well as its energy loss to the sample atoms. The scattering integral is defined in the coordinate system and relates the angle of scatter with the interatomic potential. It is also possible to solve the time integral of the collision to know what time has elapsed during the collision and this is necessary at least when BCA is used in the full cascade mode, see below. The energy loss to electrons, i. e, the selection method for the impact parameter divided BCA codes into two main varieties, Monte Carlo BCA and crystal-BCA codes. This approach essentially simulates ion passage in an amorphous material. SRIM and SDTrimSP are Monte-Carlo BCA codes, in this approach BCA can be used to simulate also atom motion during channelling. Codes such as MARLOWE operate with this approach, the binary collision approximation can also be extended to simulate dynamic composition changes of a material due to prolonged ion irradiation, i. e. due to ion implantation and sputtering. At low ion energies, the approximation of independent collisions between atoms starts to break down and this issue can be to some extent augmented by solving the collision integral for multiple simultaneous collisions. The MD simulations can either follow only the incoming ion or simulate all atoms involved in a collision cascade, the BCA simulations can be further subdivided by type depending on whether they only follow the incoming ion, or also follow the recoils produced by the ion. If the code does not account for secondary collisions, the number of defects is then calculated using the Robinson extension of the Kinchin-Pease model and this kind of a cascade can be theoretically well treated using BCA. The BCA simulations give naturally the ion penetration depth, lateral spread and nuclear, however, this approach should be used with great caution for several reasons. BCA codes can, however, be extended with damage clustering, finally, the average threshold displacement energy is not very accurately known in most materials. SRIM offers a user interface and is likely the most used BCA code now. It can be used to simulate linear collision cascades in amorphous materials for all ion in all materials up to ion energies of 1 GeV. Note, however, that SRIM does not treat such as channelling. The calculated sputter yields may be accurate than that from other codes
14.
Annealing (metallurgy)
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It involves heating a material to above its recrystallization temperature, maintaining a suitable temperature, and then cooling. In annealing, atoms migrate in the lattice and the number of dislocations decreases, leading to the change in ductility. In the cases of copper, steel, silver, and brass, copper, silver and brass can be cooled slowly in air, or quickly by quenching in water, unlike ferrous metals, such as steel, which must be cooled slowly to anneal. In this fashion, the metal is softened and prepared for further work—such as shaping, stamping, annealing occurs by the diffusion of atoms within a solid material, so that the material progresses towards its equilibrium state. Heat increases the rate of diffusion by providing the energy needed to break bonds, the movement of atoms has the effect of redistributing and eradicating the dislocations in metals and in ceramics. This alteration to existing dislocations allows an object to deform more easily. The amount of process-initiating Gibbs free energy in a metal is also reduced by the annealing process. In practice and industry, this reduction of Gibbs free energy is termed stress relief, the relief of internal stresses is a thermodynamically spontaneous process, however, at room temperatures, it is a very slow process. The high temperatures at which annealing occurs serve to accelerate this process, the creation of lattice vacancies is governed by the Arrhenius equation, and the migration/diffusion of lattice vacancies are governed by Fick’s laws of diffusion. The three stages of the process that proceed as the temperature of the material is increased are, recovery, recrystallization. The first stage is recovery, and it results in softening of the metal through removal of primarily linear defects called dislocations, recovery occurs at the lower temperature stage of all annealing processes and before the appearance of new strain-free grains. The grain size and shape do not change, the second stage is recrystallization, where new strain-free grains nucleate and grow to replace those deformed by internal stresses. If annealing is allowed to continue once recrystallization has completed, then grain growth occurs, in grain growth, the microstructure starts to coarsen and may cause the metal to lose a substantial part of its original strength. This can however be regained with hardening, the high temperature of annealing may result in oxidation of the metal’s surface, resulting in scale. If scale must be avoided, annealing is carried out in a special atmosphere, annealing is also done in forming gas, a mixture of hydrogen and nitrogen. The magnetic properties of mu-metal are introduced by annealing the alloy in a hydrogen atmosphere, typically, large ovens are used for the annealing process. The inside of the oven is large enough to place the workpiece in a position to receive exposure to the circulating heated air. For high volume process annealing, gas fired conveyor furnaces are often used, for large workpieces or high quantity parts, car-bottom furnaces are used so workers can easily move the parts in and out
15.
Electron hole
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In physics, chemistry, and electronic engineering, an electron hole is the lack of an electron at a position where one could exist in an atom or atomic lattice. Holes in a crystal lattice can move through the lattice as electrons can. They play an important role in the operation of devices such as transistors, diodes. However they are not actually particles, but rather quasiparticles, they are different from the positron, if an electron is excited into a higher state it leaves a hole in its old state. This meaning is used in Auger electron spectroscopy, in computational chemistry, in crystals, electronic band structure calculations lead to an effective mass for the electrons, which typically is negative at the top of a band. The negative mass is a concept, and in these situations a more familiar picture is found by considering a positive charge with a positive mass. In solid-state physics, a hole is the absence of an electron from a full valence band. A hole is essentially a way to conceptualize the interactions of the electrons within a full system. In some ways, the behavior of a hole within a crystal lattice is comparable to that of the bubble in a full bottle of water. Hole conduction in a band can be explained by the following analogy. Imagine a row of people seated in an auditorium, where there are no spare chairs, someone in the middle of the row wants to leave, so he jumps over the back of the seat into an empty row, and walks out. The empty row is analogous to the band, and the person walking out is analogous to a free electron. Now imagine someone else comes along and wants to sit down, the empty row has a poor view, so he does not want to sit there. Instead, a person in the crowded row moves into the empty seat the first person left behind, the empty seat moves one spot closer to the edge and the person waiting to sit down. The next person follows, and the next, et cetera, one could say that the empty seat moves towards the edge of the row. Once the empty seat reaches the edge, the new person can sit down, in the process everyone in the row has moved along. If those people were charged, this movement would constitute conduction. If the seats themselves were positively charged, then only the vacant seat would be positive and this is a very simple model of how hole conduction works
16.
Extrinsic semiconductor
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An extrinsic semiconductor is one that has been doped, that is, into which a doping agent has been introduced, giving it different electrical properties than the intrinsic semiconductor. Dominant carrier concentrations in an extrinsic semiconductor classify it as either an n-type or p-type semiconductor, the electrical properties of extrinsic semiconductors make them essential components of many electronic devices. Semiconductor doping is the process changes a intrinsic semiconductor to an extrinsic semiconductor. During doping, impurity atoms are introduced to an intrinsic semiconductor, impurity atoms are atoms of a different element than the atoms of the intrinsic semiconductor. Impurity atoms act as donors or acceptors to the intrinsic semiconductor, changing the electron. Impurity atoms are classified as donor or acceptor atoms based on the effect they have on the intrinsic semiconductor, donor impurity atoms have more valence electrons than the atoms they replace in the intrinsic semiconductor lattice. Donor impurities donate their extra valence electrons to a conduction band. Excess electrons increase the electron concentration of the semiconductor, making it n-type. Acceptor impurity atoms have fewer electrons than the atoms they replace in the intrinsic semiconductor lattice. They accept electrons from the valence band. This provides excess holes to the intrinsic semiconductor, excess holes increase the hole carrier concentration of the semiconductor, creating a p-type semiconductor. Semiconductors and dopant atoms are defined by the column of the table in which they fall. The column definition of the semiconductor determines how many valence electrons its atoms have, group IV semiconductors use group V atoms as donors and group III atoms as acceptors. Group III-V semiconductors, the semiconductors, use group VI atoms as donors. Group III-V semiconductors can also use group IV atoms as donors or acceptors. When a group IV atom replaces the group III element in the semiconductor lattice, conversely, when a group IV atom replaces the group V element, the group IV atom acts as an acceptor. Group IV atoms can act as donors and acceptors, therefore, they are known as amphoteric impurities. N-type semiconductors have a larger electron concentration than hole concentration, the term n-type comes from the negative charge of the electron
17.
MOSFET
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The metal–oxide–semiconductor field-effect transistor is a type of field-effect transistor. It has a gate, whose voltage determines the conductivity of the device. This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals, although FET is sometimes used when referring to MOSFET devices, other types of field-effect transistors also exist. Because these two terminals are connected to each other internally, only three terminals appear in electrical diagrams. The basic principle of the transistor was first patented by Julius Edgar Lilienfeld in 1925. The main advantage of a MOSFET over a regular transistor is that it very little current to turn on. In enhancement mode MOSFETs, a voltage drop across the oxide induces a conducting channel between the source and drain contacts via the field effect. The term enhancement mode refers to the increase of conductivity with increase in oxide field that adds carriers to the channel, also referred to as the inversion layer. The channel can contain electrons, or holes, opposite in type to the substrate, so nMOS is made with a p-type substrate, the metal in the name MOSFET is now often a misnomer because the previously metal gate material is now often a layer of polysilicon. Aluminium had been the material until the mid-1970s, when polysilicon became dominant. Metallic gates are regaining popularity, since it is difficult to increase the speed of operation of transistors without metal gates, likewise, the oxide in the name can be a misnomer, as different dielectric materials are used with the aim of obtaining strong channels with smaller applied voltages. An insulated-gate field-effect transistor or IGFET is a term almost synonymous with MOSFET. The term may be inclusive, since many MOSFETs use a gate that is not metal. Another synonym is MISFET for metal–insulator–semiconductor FET, the MOSFET is by far the most common transistor in both digital and analog circuits, though the bipolar junction transistor was at one time much more common. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925. Twenty five years later, when Bell Telephone attempted to patent the junction transistor, they found Lilienfeld already holding a patent, Bell Labs was able to work out an agreement with Lilienfeld, who was still alive at that time. It was at time the Bell Labs version was given the name bipolar junction transistor, or simply junction transistor. In 1959, Dawon Kahng and Martin M. Atalla at Bell Labs invented the metal–oxide–semiconductor field-effect transistor as an offshoot to the patented FET design and it used crystalline silicon for the semiconductor and a thermally oxidized layer of silicon dioxide for the insulator
18.
Silicon
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Silicon is a chemical element with symbol Si and atomic number 14. A hard and brittle crystalline solid with a metallic luster. It is a member of group 14 in the table, along with carbon above it and germanium, tin, lead. It is not very reactive, although more reactive than germanium, Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earths crust. It is most widely distributed in dusts, sands, planetoids, over 90% of the Earths crust is composed of silicate minerals, making silicon the second most abundant element in the Earths crust after oxygen. Most silicon is used commercially without being separated, and often with little processing of the natural minerals, such use includes industrial construction with clays, silica sand, and stone. Silicate is used in Portland cement for mortar and stucco, and mixed with sand and gravel to make concrete for walkways, foundations. Silicates are used in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass, Silicon compounds such as silicon carbide are used as abrasives and components of high-strength ceramics. Elemental silicon also has an impact on the modern world economy. Most free silicon is used in the refining, aluminium-casting. Silicon is the basis of the widely used synthetic polymers called silicones, Silicon is an essential element in biology, although only tiny traces are required by animals. However, various sea sponges and microorganisms, such as diatoms and radiolaria, silica is deposited in many plant tissues, such as in the bark and wood of Chrysobalanaceae and the silica cells and silicified trichomes of Cannabis sativa, horsetails and many grasses. Silicon is a solid at room temperature, with a point of 1,414 °C. Like water, it has a density in a liquid state than in a solid state and it expands when it freezes. With a relatively high conductivity of 149 W·m−1·K−1, silicon conducts heat well. In its crystalline form, pure silicon has a gray color, like germanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a cubic crystal structure with a lattice spacing of 0.5430710 nm. The outer electron orbital of silicon, like that of carbon, has four valence electrons, the 1s, 2s, 2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six
19.
Epitaxy
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Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate. The overlayer is called a film or epitaxial layer. The term epitaxy comes from the Greek roots epi, meaning above and it can be translated as arranging upon. For most technological applications, it is desired that the material form a crystalline overlayer that has one well-defined orientation with respect to the substrate crystal structure. Epitaxial films may be grown from gaseous or liquid precursors, because the substrate acts as a seed crystal, the deposited film may lock into one or more crystallographic orientations with respect to the substrate crystal. If the overlayer either forms a random orientation with respect to the substrate or does not form an ordered overlayer, if an epitaxial film is deposited on a substrate of the same composition, the process is called homoepitaxy, otherwise it is called heteroepitaxy. Homoepitaxy is a kind of epitaxy performed with only one material and this technology is used to grow a film which is more pure than the substrate and to fabricate layers having different doping levels. In academic literature, homoepitaxy is often abbreviated to homoepi, heteroepitaxy is a kind of epitaxy performed with materials that are different from each other. In heteroepitaxy, a crystalline film grows on a substrate or film of a different material. This technology is used to grow crystalline films of materials for which crystals cannot otherwise be obtained. Examples include silicon on sapphire, gallium nitride on sapphire, aluminium gallium indium phosphide on gallium arsenide or diamond or iridium. Heterotopotaxy is a similar to heteroepitaxy except that thin film growth is not limited to two-dimensional growth. Pendeo-epitaxy is a process in which the film is growing vertically and laterally at the same time. Epitaxy is used in nanotechnology and in semiconductor fabrication, indeed, epitaxy is the only affordable method of high quality crystal growth for many semiconductor materials. In surface science, epitaxy is used to create and study monolayer and multilayer films of adsorbed organic molecules on single crystalline surfaces, adsorbed molecules form ordered structures on atomically flat terraces of single crystalline surfaces and can directly be observed via scanning tunnelling microscopy. Molecular-beam and liquid-phase epitaxy are also used, mainly for compound semiconductors, solid-phase epitaxy is used primarily for crystal-damage healing. Growth rates above 2 micrometres per minute produce polycrystalline silicon, an additional etching reaction competes with the deposition reaction, SiCl4 + Si ↔ 2SiCl2 Silicon VPE may also use silane, dichlorosilane, and trichlorosilane source gases. VPE is sometimes classified by the chemistry of the gases, such as hydride VPE
20.
Nanoparticle
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Nanoparticles are particles between 1 and 100 nanometers in size. In nanotechnology, a particle is defined as an object that behaves as a whole unit with respect to its transport. Particles are further classified according to diameter, scientific research on nanoparticles is intense as they have many potential applications in medicine, physics, optics, and electronics. The U. S. National Nanotechnology Initiative offers government funding focused on nanoparticle research, the term nanoparticle is not usually applied to individual molecules, it usually refers to inorganic materials. However, during the 1990s before the National Nanotechnology Initiative was launched in the USA, nanoparticles can exhibit size-related properties significantly different from those of either fine particles or bulk materials. Nanoclusters have at least one dimension between 1 and 10 nanometers and a size distribution. Nanopowders are agglomerates of ultrafine particles, nanoparticles, or nanoclusters, nanometer-sized single crystals, or single-domain ultrafine particles, are often referred to as nanocrystals. Although nanoparticles are associated with science, they have a long history. In modern times, pottery from the Middle Ages and Renaissance often retains a distinct gold- or copper-colored metallic glitter and this luster is caused by a metallic film that was applied to the transparent surface of a glazing. The luster can still be visible if the film has resisted atmospheric oxidation, the luster originates within the film itself, which contains silver and copper nanoparticles dispersed homogeneously in the glassy matrix of the ceramic glaze. These nanoparticles are created by the artisans by adding copper and silver salts and oxides together with vinegar, ochre, the object is then placed into a kiln and heated to about 600 °C in a reducing atmosphere. In the heat the glaze softens, causing the copper and silver ions to migrate into the layers of the glaze. There the reducing atmosphere reduced the ions back to metals, which came together forming the nanoparticles that give the color. Luster technique showed that ancient craftsmen had an empirical knowledge of materials. The technique originated in the Muslim world, as Muslims were not allowed to use gold in artistic representations, they sought a way to create a similar effect without using real gold. The solution they found was using luster, michael Faraday provided the first description, in scientific terms, of the optical properties of nanometer-scale metals in his classic 1857 paper. The result is white light is now freely transmitted, reflection is correspondingly diminished. Uncontrolled agglomeration of powders due to van der Waals forces can also give rise to microstructural heterogeneity
21.
Sapphire
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Sapphire is a gemstone, a variety of the mineral corundum, an aluminium oxide. It is typically blue in color, but natural fancy sapphires also occur in yellow, purple, orange, the only color which sapphire cannot be is red - as red colored corundum is called ruby, another corundum variety. This variety in color is due to amounts of elements such as iron, titanium, chromium, copper. Commonly, natural sapphires are cut and polished into gemstones and worn in jewelry and they also may be created synthetically in laboratories for industrial or decorative purposes in large crystal boules. Sapphire is the birthstone for September and the gem of the 45th anniversary, a sapphire jubilee occurs after 65 years. Sapphire is one of the two gem-varieties of corundum, the other being ruby, although blue is the best-known sapphire color, they occur in other colors, including gray and black, and they can be colorless. A a pinkish orange variety of sapphire is called padparadscha, significant sapphire deposits are found in Eastern Australia, Thailand, Sri Lanka, China, Madagascar, East Africa, and in North America in a few locations, mostly in Montana. Sapphire and rubies are often found in the geological setting. Every sapphire mine produces a range of quality - and origin is not a guarantee of quality. For sapphire, Kashmir receives the highest premium although Burma, Sri Lanka, the cost of natural sapphires varies depending on their color, clarity, size, cut, and overall quality. For gems of exceptional quality, an independent determination from a respected laboratory such as the GIA, gemstone color can be described in terms of hue, saturation, and tone. Hue is commonly understood as the color of the gemstone, saturation refers to the vividness or brightness of the hue, and tone is the lightness to darkness of the hue. Blue sapphire exists in various mixtures of its primary and secondary hues, various tonal levels, blue sapphires are evaluated based upon the purity of their primary hue. Purple, violet, and green are the most common secondary hues found in blue sapphires, violet and purple can contribute to the overall beauty of the color, while green is considered to be distinctly negative. Blue sapphires with up to 15% violet or purple are generally said to be of fine quality, gray is the normal saturation modifier or mask found in blue sapphires. Gray reduces the saturation or brightness of the hue, and therefore has a negative effect. The 423-carat Logan sapphire in the National Museum of Natural History, in Washington, sapphires in colors other than blue are called fancy or parti colored sapphires. Fancy sapphires are found in yellow, orange, green sapphires, brown, purple
22.
Nonlinear optics
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The nonlinearity is typically observed only at very high light intensities such as those provided by lasers. Above the Schwinger limit, the vacuum itself is expected to become nonlinear, in nonlinear optics, the superposition principle no longer holds. However, some effects were discovered before the development of the laser. The theoretical basis for many nonlinear processes were first described in Bloembergens monograph Nonlinear Optics, Nonlinear optics explains nonlinear response of properties such as frequency, polarization, phase or path of incident light. Third-harmonic generation, generation of light with a frequency, three photons are destroyed, creating a single photon at three times the frequency. High-harmonic generation, generation of light with much greater than the original. Sum-frequency generation, generation of light with a frequency that is the sum of two other frequencies, difference-frequency generation, generation of light with a frequency that is the difference between two other frequencies. Optical parametric amplification, amplification of an input in the presence of a higher-frequency pump wave. Optical parametric oscillation, generation of a signal and idler wave using an amplifier in a resonator. Optical parametric generation, like parametric oscillation but without a resonator, spontaneous parametric down-conversion, the amplification of the vacuum fluctuations in the low-gain regime. Optical rectification, generation of electric fields. Nonlinear light-matter interaction with electrons and plasmas. Optical Kerr effect, intensity-dependent refractive index, self-focusing, an effect due to the optical Kerr effect caused by the spatial variation in the intensity creating a spatial variation in the refractive index. Kerr-lens modelocking, the use of self-focusing as a mechanism to mode-lock laser, self-phase modulation, an effect due to the optical Kerr effect caused by the temporal variation in the intensity creating a temporal variation in the refractive index. Optical solitons, a solution for either an optical pulse or spatial mode that does not change during propagation due to a balance between dispersion and the Kerr effect. Cross-phase modulation, where one wavelength of light can affect the phase of another wavelength of light through the optical Kerr effect, four-wave mixing, can also arise from other nonlinearities. Cross-polarized wave generation, a χ effect in which a wave with polarization vector perpendicular to the one is generated. Stimulated Brillouin scattering, interaction of photons with acoustic phonons Multi-photon absorption, multiple photoionisation, near-simultaneous removal of many bound electrons by one photon
23.
Crystallographic defect
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Crystalline solids exhibit a periodic crystal structure. The positions of atoms or molecules occur on repeating fixed distances, however, the arrangement of atoms or molecules in most crystalline materials is not perfect. The regular patterns are interrupted by crystallographic defects, point defects are defects that occur only at or around a single lattice point. They are not extended in space in any dimension, strict limits for how small a point defect is are generally not defined explicitly. However, these defects typically involve at most a few extra or missing atoms, larger defects in an ordered structure are usually considered dislocation loops. For historical reasons, many point defects, especially in ionic crystals, are called centers, for example a vacancy in many ionic solids is called a luminescence center and these dislocations permit ionic transport through crystals leading to electrochemical reactions. These are frequently specified using Kröger–Vink Notation, vacancy defects are lattice sites which would be occupied in a perfect crystal, but are vacant. If a neighboring atom moves to occupy the vacant site, the moves in the opposite direction to the site which used to be occupied by the moving atom. The stability of the crystal structure guarantees that the neighboring atoms will not simply collapse around the vacancy. In some materials, neighboring atoms actually move away from a vacancy, a vacancy is sometimes called a Schottky defect. Interstitial defects are atoms that occupy a site in the structure at which there is usually not an atom. They are generally high energy configurations, small atoms in some crystals can occupy interstices without high energy, such as hydrogen in palladium. A nearby pair of a vacancy and an interstitial is often called a Frenkel defect or Frenkel pair and this is caused when an ion moves into an interstitial site and creates a vacancy. Due to fundamental limitations of material purification methods, materials are never 100% pure, in the case of an impurity, the atom is often incorporated at a regular atomic site in the crystal structure. This is neither a vacant site nor is the atom on an interstitial site, the atom is not supposed to be anywhere in the crystal, and is thus an impurity. In some cases where the radius of the atom is substantially smaller than that of the atom it is replacing. These types of defects are often referred to as off-center ions. There are two different types of defects, Isovalent substitution and aliovalent substitution
24.
Dislocation
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In materials science, a dislocation is a crystallographic defect or irregularity within a crystal structure. The presence of dislocations strongly influences many of the properties of materials, some types of dislocations can be visualized as being caused by the termination of a plane of atoms in the middle of a crystal. In such a case, the planes are not straight. The two primary types of dislocations are edge dislocations and screw dislocations, mixed dislocations are intermediate between these. Mathematically, dislocations are a type of defect, sometimes called a soliton. Dislocations behave as stable particles, they can move around, two dislocations of opposite orientation can cancel when brought together, but a single dislocation typically cannot disappear on its own. Two main types of dislocations exist, edge and screw, dislocations found in real materials are typically mixed, meaning that they have characteristics of both. A crystalline material consists of an array of atoms, arranged into lattice planes. One approach is to begin by considering a 3D representation of a crystal lattice. The viewer may then start to simplify the representation by visualising planes of atoms instead of the atoms themselves, an edge dislocation is a defect where an extra half-plane of atoms is introduced mid way through the crystal, distorting nearby planes of atoms. When enough force is applied from one side of the crystal structure, a simple schematic diagram of such atomic planes can be used to illustrate lattice defects such as dislocations. In an edge dislocation, the Burgers vector is perpendicular to the line direction, the stresses caused by an edge dislocation are complex due to its inherent asymmetry. A screw dislocation is much harder to visualize, imagine cutting a crystal along a plane and slipping one half across the other by a lattice vector, the halves fitting back together without leaving a defect. This is similar to the Riemann surface of the complex logarithm, if the cut only goes part way through the crystal, and then slipped, the boundary of the cut is a screw dislocation. It comprises a structure in which a path is traced around the linear defect by the atomic planes in the crystal lattice. Perhaps the closest analogy is a spiral-sliced ham, in pure screw dislocations, the Burgers vector is parallel to the line direction. Despite the difficulty in visualization, the caused by a screw dislocation are less complex than those of an edge dislocation. This equation suggests a long cylinder of stress radiating outward from the cylinder, please note, this simple model results in an infinite value for the core of the dislocation at r=0 and so it is only valid for stresses outside of the core of the dislocation
25.
Amorphous solid
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In condensed matter physics and materials science, an amorphous or non-crystalline solid is a solid that lacks the long-range order that is characteristic of a crystal. In some older books, the term has been used synonymously with glass, nowadays, glassy solid or amorphous solid is considered to be the overarching concept, and glass the more special case, A glass is an amorphous solid that exhibits a glass transition. Other types of solids include gels, thin films. Amorphous materials have a structure made of interconnected structural blocks. Even amorphous materials have some shortrange order at the length scale due to the nature of chemical bonding. Furthermore, in small crystals a large fraction of the atoms are the crystal, relaxation of the surface and interfacial effects distort the atomic positions. Amorphous phases are important constituents of thin films, which are layers of a few nm to some tens of µm thickness deposited upon a substrate. For higher values, the diffusion of deposited atomic species would allow for the formation of crystallites with long range atomic order. Regarding their applications, amorphous metallic layers played an important role in the discussion of a suspected superconductivity in amorphous metals, today, optical coatings made from TiO2, SiO2, Ta2O5 etc. and combinations of them in most cases consist of amorphous phases of these compounds. Much research is carried out into thin films as a gas separating membrane layer. Also, hydrogenated amorphous silicon, a-Si, H in short, is of significance for thin film solar cells. In case of a-Si, H the missing long-range order between silicon atoms is partly induced by the presence by hydrogen in the percent range, the occurrence of amorphous phases turned out as a phenomenon of particular interest for studying thin film growth. Remarkably, the growth of polycrystalline films is used and preceded by an initial amorphous layer. The most investigated example is represented by thin multicrystalline silicon films, an initial amorphous layer was observed in many studies. The phenomenon has been interpreted in the framework of Ostwalds rule of stages that predicts the formation of phases to proceed with increasing condensation time towards increasing stability. Experimental studies of the phenomenon require a clearly defined state of the substrate surface, the Physics of Structurally Disordered Matter, An Introduction. Amorphous Solids and the Liquid State
26.
Glass
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Glass is a non-crystalline amorphous solid that is often transparent and has widespread practical, technological, and decorative usage in, for example, window panes, tableware, and optoelectronics. The most familiar, and historically the oldest, types of glass are silicate glasses based on the chemical compound silica, the primary constituent of sand. The term glass, in usage, is often used to refer only to this type of material. Many applications of silicate glasses derive from their optical transparency, giving rise to their use as window panes. Glass can be coloured by adding metallic salts, and can also be painted and printed with vitreous enamels and these qualities have led to the extensive use of glass in the manufacture of art objects and in particular, stained glass windows. Although brittle, silicate glass is extremely durable, and many examples of glass fragments exist from early glass-making cultures, because glass can be formed or moulded into any shape, it has been traditionally used for vessels, bowls, vases, bottles, jars and drinking glasses. In its most solid forms it has also used for paperweights, marbles. Some objects historically were so commonly made of glass that they are simply called by the name of the material, such as drinking glasses. Porcelains and many polymer thermoplastics familiar from everyday use are glasses and these sorts of glasses can be made of quite different kinds of materials than silica, metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers. For many applications, like glass bottles or eyewear, polymer glasses are a lighter alternative than traditional glass, silica is a common fundamental constituent of glass. In nature, vitrification of quartz occurs when lightning strikes sand, forming hollow, fused quartz is a glass made from chemically-pure SiO2. It has excellent resistance to shock, being able to survive immersion in water while red hot. However, its high melting-temperature and viscosity make it difficult to work with, normally, other substances are added to simplify processing. One is sodium carbonate, which lowers the transition temperature. The soda makes the glass water-soluble, which is undesirable, so lime, some magnesium oxide. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass, soda-lime glasses account for about 90% of manufactured glass. Most common glass contains other ingredients to change its properties, lead glass or flint glass is more brilliant because the increased refractive index causes noticeably more specular reflection and increased optical dispersion. Adding barium also increases the refractive index, iron can be incorporated into glass to absorb infrared energy, for example in heat absorbing filters for movie projectors, while cerium oxide can be used for glass that absorbs UV wavelengths
27.
Sputtering
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Sputtering is a process whereby particles are ejected from a solid target material due to bombardment of the target by energetic particles, particularly, in the laboratory, gas ions. It only happens when the energy of the incoming particles is much higher than conventional thermal energies. This process can lead, during prolonged ion or plasma bombardment of a material, to significant erosion of materials, on the other hand, it is commonly used for thin-film deposition, etching and analytical techniques. Sputtering is done either using DC Voltage or using AC Voltage, in DC Sputtering, voltage is set from 3-5 kV and in RF Sputtering, power supply is set at 14 MHz. Due to application of alternating current, the ions inside the plasma will oscillate and as a result, physical sputtering is driven by momentum exchange between the ions and atoms in the target materials, due to collisions. The incident ions set off collision cascades in the target, when such cascades recoil and reach the target surface with an energy greater than the surface binding energy, an atom would be ejected, and this process is known as sputtering. If the target is thin on a scale, the collision cascade can reach the back side of the target. For a crystalline target the orientation of the axes with respect to the target surface is relevant. The primary particles for the process can be supplied in a number of ways, for example by a plasma, an ion source. A model for describing sputtering in the regime for amorphous flat targets is Thompsons analytical model. An algorithm that simulates sputtering based on a mechanical treatment including electrons stripping at high energy is implemented in the program TRIM. A different mechanism of physical sputtering is heat spike sputtering and this may occur when the solid is dense enough, and then the incoming ion heavy enough, that the collisions occur very close to each other. Then the binary collision approximation is no longer valid, but rather the process should be understood as a many-body process. The dense collisions induce a heat spike, which melts the crystal locally. If the molten zone is close enough to a surface, large numbers of atoms may sputter due to flow of liquid to the surface and/or microexplosions. Heat spike sputtering is most important for heavy ions with energies in the keV–MeV range bombarding dense, the heat spike sputtering often increases nonlinearly with energy, and can for small cluster ions lead to dramatic sputtering yields per cluster of the order of 10,000. For animations of such a process see Re, Displacement Cascade 1 in the links section. This threshold typically is somewhere in the range 10–100 eV, preferential sputtering can occur at the start when a multicomponent solid target is bombarded and there is no solid state diffusion
28.
Crystallography
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Crystallography is the experimental science of determining the arrangement of atoms in the crystalline solids. The word crystallography derives from the Greek words crystallon cold drop, frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein to write. In July 2012, the United Nations recognised the importance of the science of crystallography by proclaiming that 2014 would be the International Year of Crystallography, X-ray crystallography is used to determine the structure of large biomolecules such as proteins. Before the development of X-ray diffraction crystallography, the study of crystals was based on measurements of their geometry. This involved measuring the angles of crystal faces relative to other and to theoretical reference axes. This physical measurement is carried out using a goniometer, the position in 3D space of each crystal face is plotted on a stereographic net such as a Wulff net or Lambert net. The pole to face is plotted on the net. Each point is labelled with its Miller index, the final plot allows the symmetry of the crystal to be established. Crystallographic methods now depend on analysis of the patterns of a sample targeted by a beam of some type. X-rays are most commonly used, other beams used include electrons or neutrons and this is facilitated by the wave properties of the particles. Crystallographers often explicitly state the type of beam used, as in the terms X-ray crystallography and these three types of radiation interact with the specimen in different ways. X-rays interact with the distribution of electrons in the sample. Electrons are charged particles and therefore interact with the charge distribution of both the atomic nuclei and the electrons of the sample. Neutrons are scattered by the atomic nuclei through the nuclear forces, but in addition. They are therefore also scattered by magnetic fields, when neutrons are scattered from hydrogen-containing materials, they produce diffraction patterns with high noise levels. However, the material can sometimes be treated to substitute deuterium for hydrogen, because of these different forms of interaction, the three types of radiation are suitable for different crystallographic studies. An image of an object is made using a lens to focus the beam. However, the wavelength of light is three orders of magnitude longer than the length of typical atomic bonds and atoms themselves
29.
Diamond cubic
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The diamond cubic crystal structure is a repeating pattern of 8 atoms that certain materials may adopt as they solidify. Diamond cubic is in the Fd3m space group, which follows the face-centered cubic Bravais lattice, the diamond lattice can be viewed as a pair of intersecting face-centered cubic lattices, with each separated by 1/4 of the width of the unit cell in each dimension. Many compound semiconductors such as gallium arsenide, β-silicon carbide, and indium antimonide adopt the analogous zincblende structure, zincblendes space group is F43m, but many of its structural properties are quite similar to the diamond structure. The atomic packing factor of the cubic structure is π√3/16 ≈0.34. Zincblende structures have higher packing factors than 0.34 depending on the sizes of their two component atoms. The first-, second-, third-, fourth- and fifth-nearest-neighbor distances in units of the lattice constant are √3/4, √2/2, √11/4,1 and √19/4. Mathematically, the points of the cubic structure can be given coordinates as a subset of a three-dimensional integer lattice by using a cubic unit cell four units across. With these coordinates, the points of the structure have coordinates satisfying the equations x = y = z, and x + y + z =0 or 1. There are eight points that satisfy these conditions, All of the points in the structure may be obtained by adding multiples of four to the x, y. Adjacent points in this structure are at distance √3 apart in the integer lattice and this structure may be scaled to a cubical unit cell that is some number a of units across by multiplying all coordinates by a/4. Alternatively, each point of the cubic structure may be given by four-dimensional integer coordinates whose sum is either zero or one. Two points are adjacent in the structure if and only if their four-dimensional coordinates differ by one in a single coordinate. The total difference in values between any two points gives the number of edges in the shortest path between them in the diamond structure. These four-dimensional coordinates may be transformed into three-dimensional coordinates by the formula →, because the diamond structure forms a distance-preserving subset of the four-dimensional integer lattice, it is a partial cube. Yet another coordinatization of the diamond cubic involves the removal of some of the edges from a grid graph. The diamond cubic is sometimes called the lattice but it is not, mathematically. However, it is still a highly symmetric structure, any incident pair of a vertex, moreover the diamond crystal as a network in space has a strong isotropic property. Another crystal with this property is the Laves graph, the compressive strength and hardness of diamond and various other materials, such as boron nitride, is attributed to the diamond cubic structure
30.
Channelling (physics)
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All of these processes have cross sections which depend on the impact parameters involved in collisions with individual target atoms. Or in other words, the power of the particle is much lower in certain directions than others. This effect is called the channelling effect. It is related to other orientation-dependent effects, such as particle diffraction and these relationships will be discussed in detail later. The simulated prediction was confirmed experimentally the following year by measurements of ion penetration depths in single-crystalline tungsten. If it is not in a major crystal direction or plane, it is more likely to undergo large-angle scattering. If the direction of the momentum is close to the crystalline plane, but it is not close to major crystalline axes. Channelling usually leads to deeper penetration of the ions in the material and this is called the dechannelling process. So positively charged particles tend to follow the direction between two neighboring crystalline planes, but at the largest possible distance from each of them, therefore, the positively charged particles have a smaller probability of interacting with the nuclei and electrons of the planes and travel longer distances. The same phenomena occur when the direction of momentum of the charged particles lies close to a major crystalline and this phenomenon is called axial channelling. At low energies the channelling effects in crystals are not present because small-angle scattering at low energies requires large impact parameters, the particles diffraction is dominating here. At high energies the quantum effects and diffraction are less effective, there are several particularly interesting applications of the channelling effects. Channelling effects can be used as tools to investigate the properties of the crystal lattice and this is an important variation of the Rutherford backscattering ion beam analysis technique, commonly called Rutherford backscattering/channeling. J. W. Mayer and E. Rimini, Ion Beam Handbook for Material Analysis, Academic Press, New York L. C. Feldman, J. W. Mayer and S. T. Picraux, Material Analysis by Ion Channelling, Academic Press, New York R. Hovden, H. L. Xin, D. A. Muller, Phys. B86,195415 arXiv,1212.1154 G. R. Anstis, cai, and D. J. H. Cockayne, Ultramicroscopy 94,309. D. Van Dyck and J. H. Chen, Solid State Communications 109,501, S. Hillyard and J. Silcox, Ultramicroscopy 58,6. S. J. Pennycook and D. E. Jesson, M. V. Berry and Ozoriode. Am, Journal of Physics a-Mathematical and General 6,1451
31.
Rutherford backscattering spectrometry
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Rutherford backscattering spectrometry is an analytical technique used in materials science. Rutherford backscattering spectrometry is named after Lord Ernest Rutherford, a physicist sometimes referred to as the father of nuclear physics, Rutherford supervised a series of experiments carried out by Hans Geiger and Ernest Marsden between 1909 and 1914 studying the scattering of alpha particles through metal foils. At most small deflections should occur as the alpha particles passed almost unhindered through the foil, instead, when Marsden positioned the detector on the same side of the foil as the alpha particle source, he immediately detected a noticeable backscattered signal. According to Rutherford, It was quite the most incredible event that has happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of paper and it came back. Rutherford interpreted the result of the Geiger–Marsden experiment as an indication of a Coulomb collision with a massive positive particle. This led him to the conclusion that the positive charge could not be diffuse but instead must be concentrated in a single massive core. Calculations indicated that the necessary to accomplish this deflection was approximately 100 times the charge of the electron. This model was superseded by the Bohr atom, incorporating some early results from quantum mechanics. If the energy of the incident particle is increased sufficiently, the Coulomb barrier is exceeded and this may result in nuclear reactions in certain cases, but frequently the interaction remains elastic, although the scattering cross-sections may fluctuate wildly as a function of energy. This case is known as Elastic Backscattering Spectrometry, there has recently been great progress in determining EBS scattering cross-sections, by solving Schrödingers equation for each interaction. We describe Rutherford backscattering as an elastic, hard-sphere collision between a kinetic energy particle from the incident beam and a stationary particle located in the sample. Elastic in this means that no energy is transferred between the incident particle and the stationary particle during the collision, and the state of the stationary particle is not changed. Note that nuclear interactions are not elastic, since a collision may result in a nuclear reaction. Nuclear reaction analysis is useful for detecting light elements, however, this is not Rutherford scattering. The plus sign is taken when the mass of the projectile is less than that of the target, while this equation correctly determines the energy of the scattered projectile for any particular scattering angle, it does not describe the probability of observing such an event. For that we need the differential cross-section of the event, d ω d Ω =214. This equation is written in the centre of mass frame of reference and is not a function of the mass of either the projectile or the target nucleus
32.
Wafer (electronics)
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Finally the individual microcircuits are separated and packaged. By 1960, silicon wafers were being manufactured in the U. S. by companies such as MEMC/SunEdison. In 1965, American engineers Eric O. Ernst, Donald J. Hurd, Wafers are formed of highly pure, nearly defect-free single crystalline material. One process for forming crystalline wafers is known as Czochralski growth invented by the Polish chemist Jan Czochralski. In this process, an ingot of high purity mono crystalline semiconductor, such as silicon or germanium. The boule is then sliced with a saw and polished to form wafers. The size of wafers for photovoltaics is 100–200 mm square and the thickness is 200–300 μm, in the future,160 μm will be the standard. Electronics use wafer sizes from 100–450 mm diameter, Wafers are cleaned with weak acids to remove unwanted particles, or repair damage caused during the sawing process. When used for cells, the wafers are textured to create a rough surface to increase their efficiency. The generated PSG is removed from the edge of the wafer in the etching, silicon wafers are available in a variety of diameters from 25.4 mm to 300 mm. Semiconductor fabrication plants are defined by the diameter of wafers that they are tooled to produce, Wafers grown using materials other than silicon will have different thicknesses than a silicon wafer of the same diameter. Wafer thickness is determined by the strength of the material used. This was the cost basis for increasing wafer size, conversion to 300 mm wafers from 200 mm wafers began in earnest in 2000, and reduced the price per die about 30-40%. However, this was not without significant problems for the industry, there is considerable resistance to the 450 mm transition despite the possible productivity improvement, because of concern about insufficient return on investment. Higher cost semiconductor fabrication equipment for larger wafers increases the cost of 450 mm fabs, converting to larger 450 mm wafers would reduce price per die only for process operations such as etch where cost is related to wafer count, not wafer area. Cost for processes such as lithography is proportional to wafer area, nikon plans to deliver 450-mm lithography equipment in 2015, with volume production in 2017. In November 2013 ASML paused development of 450-mm lithography equipment, citing uncertain timing of chipmaker demand, the time-line for 450 mm has not been fixed. Mark Durcan, CEO of Micron Technology, said in February 2014 that he expects 450 mm adoption to be delayed indefinitely or discontinued, “I am not convinced that 450mm will ever happen but, to the extent that it does, it’s a long way out in the future
33.
Toxic
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Toxicity is the degree to which a substance can damage an organism. Toxicity can refer to the effect on an organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism. By extension, the word may be used to describe toxic effects on larger and more complex groups. Sometimes the word is more or less synonymous with poisoning in everyday usage, toxicity is species-specific, making cross-species analysis problematic. Newer paradigms and metrics are evolving to bypass animal testing, while maintaining the concept of toxicity endpoints, disease-causing microorganisms and parasites are toxic in a broad sense, but are generally called pathogens rather than toxicants. The biological toxicity of pathogens can be difficult to measure because the dose may be a single organism. Theoretically one virus, bacterium or worm can reproduce to cause a serious infection, in some cases, e. g. cholera, the disease is chiefly caused by a nonliving substance secreted by the organism, rather than the organism itself. Such nonliving biological toxicants are generally called toxins if produced by a microorganism, plant, or fungus, Physical toxicants are substances that, due to their physical nature, interfere with biological processes. Examples include coal dust, asbestos fibers or finely divided silicon dioxide, corrosive chemicals possess physical toxicity because they destroy tissues, but theyre not directly poisonous unless they interfere directly with biological activity. Water can act as a physical toxicant if taken in high doses because the concentration of vital ions decreases dramatically if theres too much water in the body. Asphyxiant gases can be considered physical toxicants because they act by displacing oxygen in the environment but they are inert, as already mentioned, radiation can have a toxic effect on organisms. Toxicity can be measured by its effects on the target, one such measure is the LD50. When such data does not exist, estimates are made by comparison to known similar toxic things, then, safety factors are added to account for uncertainties in data and evaluation processes. Similarly, an extra protection factor may be used for individuals believed to be susceptible to toxic effects such as in pregnancy or with certain diseases. Obviously, this approach is approximate, but such protection factors are deliberately very conservative. In addition, it is possible that a single cell transformed into a cell is all it takes to develop the full effect. Common mixtures include gasoline, cigarette smoke, and industrial waste, even more complex are situations with more than one type of toxic entity, such as the discharge from a malfunctioning sewage treatment plant, with both chemical and biological agents. The preclinical toxicity testing on various biological systems reveals the species-, organ-, the toxicity of substances can be observed by studying the accidental exposures to a substance in vitro studies using cells/ cell lines in vivo exposure on experimental animals
34.
Arsine
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Arsine is an inorganic compound with the formula AsH3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic, despite its lethality, it finds some applications in the semiconductor industry and for the synthesis of organoarsenic compounds. The term arsine is commonly used to describe a class of compounds of the formula AsH3−xRx. For example, As3, called triphenylarsine, is referred to as an arsine, at its standard state, arsine is a colorless, denser-than-air gas that is slightly soluble in water and in many organic solvents as well. Whereas arsine itself is odorless, owing to its oxidation by air it is possible to smell a slight garlic or fish-like scent when the compound is present above 0.5 ppm and this compound is generally regarded as stable, since at room temperature it decomposes only slowly. At temperatures of ca.230 °C decomposition to arsenic and hydrogen is rapid, several factors, such as humidity, presence of light and certain catalysts facilitate the rate of decomposition. AsH3 is a molecule with H–As–H angles of 91. 8°. AsH3 is generally prepared by the reaction of As3+ sources with H− equivalents,4 AsCl3 +3 NaBH4 →4 AsH3 +3 NaCl +3 BCl3 As reported in 1775, Carl Scheele reduced arsenic oxide with zinc in the presence of acid. This reaction is a prelude to the Marsh test, described below, typical for a heavy hydride, AsH3 is unstable with respect to its elements. In other words, AsH3 is stable kinetically but not thermodynamically,2 AsH3 →3 H2 +2 As This decomposition reaction is the basis of the Marsh Test described below, which detects the metallic As. AsH3 is used as a precursor to metal complexes of naked As, illustrative is the dimanganese species 2AsH, wherein the Mn2AsH core is planar. A characteristic test for arsenic involves the reaction of AsH3 with Ag+, although this test has become obsolete in analytical chemistry, the underlying reactions further illustrate the affinity of AsH3 for soft metal cations. In the Gutzeit test, AsH3 is generated by reduction of arsenic compounds, typically arsenites. The evolved gaseous AsH3 is then exposed to AgNO3 either as powder or as a solution, with solid AgNO3, AsH3 reacts to produce yellow Ag4AsNO3, whereas AsH3 reacts with a solution of AgNO3 to give black Ag3As. The acidic properties of the As–H bond are often exploited, thus, AsH3 can be deprotonated, AsH3 + NaNH2 → NaAsH2 + NH3 Upon reaction with the aluminium trialkyls, AsH3 gives the trimeric 3, where R = 3C. This reaction is relevant to the mechanism by which GaAs forms from AsH3, AsH3 is generally considered non-basic, but it can be protonated by superacids to give isolable salts of the tetrahedral species +. Reactions of arsine with the halogens or some of their compounds, such as nitrogen trichloride, are extremely dangerous, in contrast to the behavior of PH3, AsH3 does not form stable chains, although H2As–AsH2 and even H2As–As–AsH2 have been detected. The diarsine is unstable above −100 °C, AsH3 is used in the synthesis of semiconducting materials related to microelectronics and solid-state lasers
35.
Phosphine
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Phosphine is the compound with the chemical formula PH3. It is a colorless, flammable, toxic gas and pnictogen hydride, pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like garlic or rotting fish, due to the presence of substituted phosphine and diphosphane. With traces of P2H4 present, PH3 is spontaneously flammable in air, phosphines are also a group of organophosphorus compounds with the formula R3P. Organophosphines are important in catalysts where they complex to various ions, complexes derived from a chiral phosphine can catalyze reactions to give chiral. Philippe Gengembre, a student of Lavoisier, first obtained phosphine in 1783 by heating phosphorus in a solution of potash. He considered diphosphine’s formula to be PH2, and thus an intermediate between elemental phosphorus, the polymers, and phosphine. Calcium phosphide produces more P2H4 than other phosphides because of the preponderance of P-P bonds in the starting material, the name phosphine first appeared in combined form in 1857. The gas PH3 was named phosphine by 1865, PH3 is a trigonal pyramidal molecule with C3v molecular symmetry. The length of the P-H bond is 1.42 Å, the H-P-H bond angles are 93. 5°. The dipole moment is 0.58 D, which increases with substitution of methyl groups in the series, CH3PH2,1.10 D, 2PH,1.23 D, 3P,1.19 D. In contrast, the moments of amines decrease with substitution, starting with ammonia. For this reason, the pair on phosphorus may be regarded as predominantly formed by the 3s orbital of phosphorus. The upfield chemical shift of the atom in the 31P NMR spectrum accords with the conclusion that the lone pair electrons occupy the 3s orbital. This electronic structure leads to a lack of nucleophilicity and an ability to form only weak hydrogen bonds, the aqueous solubility of PH3 is slight,0.22 mL of gas dissolve in 1 mL of water. Phosphine dissolves more readily in non-polar solvents than in water because of the non-polar P-H bonds and it is technically amphoteric in water, but acid and base activity is poor. Proton exchange proceeds via a phosphonium ion in solutions and via PH2− at high pH, with equilibrium constants Kb =4 × 10−28. Phosphine burns producing a white cloud of phosphorus pentoxide,2 PH3 +4 O2 → P2O5 +3 H2O Phosphine may be prepared in a variety of ways. Industrially it can be made by the reaction of phosphorus with sodium or potassium hydroxide
36.
Carcinogen
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A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes, several radioactive substances are considered carcinogens, but their carcinogenic activity is attributed to the radiation, for example gamma rays and alpha particles, which they emit. Common examples of non-radioactive carcinogens are inhaled asbestos, certain dioxins, although the public generally associates carcinogenicity with synthetic chemicals, it is equally likely to arise in both natural and synthetic substances. Carcinogens are not necessarily immediately toxic, thus their effect can be insidious, Cancer is any disease in which normal cells are damaged and do not undergo programmed cell death as fast as they divide via mitosis. Usually, severe DNA damage leads to apoptosis, but if the cell death pathway is damaged. Aflatoxin B1, which is produced by the fungus Aspergillus flavus growing on stored grains, nuts and peanut butter, is an example of a potent, certain viruses such as hepatitis B and human papilloma virus have been found to cause cancer in humans. The first one shown to cause cancer in animals is Rous sarcoma virus, other infectious organisms which cause cancer in humans include some bacteria and helminths. Dioxins and dioxin-like compounds, benzene, kepone, EDB, vinyl chloride, from which PVC is manufactured, is a carcinogen and thus a hazard in PVC production. Co-carcinogens are chemicals that do not necessarily cause cancer on their own, after the carcinogen enters the body, the body makes an attempt to eliminate it through a process called biotransformation. The purpose of these reactions is to make the carcinogen more water-soluble so that it can be removed from the body, however, in some cases, these reactions can also convert a less toxic carcinogen into a more toxic carcinogen. DNA is nucleophilic, therefore soluble carbon electrophiles are carcinogenic, because DNA attacks them, for example, some alkenes are toxicated by human enzymes to produce an electrophilic epoxide. DNA attacks the epoxide, and is bound permanently to it and this is the mechanism behind the carcinogenicity of benzopyrene in tobacco smoke, other aromatics, aflatoxin and mustard gas. Carcinogenicity of radiation depends on the type of radiation, type of exposure, for example, alpha radiation has low penetration and is not a hazard outside the body, but emitters are carcinogenic when inhaled or ingested. Low-level ionizing radiation may induce irreparable DNA damage leading to pre-mature aging, not all types of electromagnetic radiation are carcinogenic. Higher-energy radiation, including radiation, x-rays, and gamma radiation, generally is carcinogenic. For most people, ultraviolet radiations from sunlight is the most common cause of skin cancer, in Australia, where people with pale skin are often exposed to strong sunlight, melanoma is the most common cancer diagnosed in people aged 15–44 years. Substances or foods irradiated with electrons or electromagnetic radiation are not carcinogenic, in contrast, non-electromagnetic neutron radiation produced inside nuclear reactors can produce secondary radiation through nuclear transmutation. Chemicals used in processed and cured such as some brands of bacon, sausages
37.
Corrosion
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Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the dedicated to controlling and stopping corrosion. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfur, rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide or salt of the original metal, corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids, many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the surface, such as passivation and chromate conversion. However, some corrosion mechanisms are less visible and less predictable, in a galvanic couple, the more active metal corrodes at an accelerated rate and the more noble metal corrodes at a slower rate. When immersed separately, each metal corrodes at its own rate, what type of metal to use is readily determined by following the galvanic series. For example, zinc is used as a sacrificial anode for steel structures. Galvanic corrosion is of major interest to the industry and also anywhere water contacts pipes or metal structures. Factors such as size of anode, types of metal. The surface area ratio of the anode and cathode directly affects the corrosion rates of the materials, galvanic corrosion is often prevented by the use of sacrificial anodes. In any given environment, one metal will be more noble or more active than others. Two metals in electrical contact share the same electrons, so that the tug-of-war at each surface is analogous to competition for free electrons between the two materials. Using the electrolyte as a host for the flow of ions in the same direction, the resulting mass flow or electric current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a series and is useful in predicting and understanding corrosion
38.
Combustibility and flammability
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Combustibility is a measure of how easily a substance will set on fire, through fire or combustion. This is an important property to consider when a substance is used for construction or is being stored and it is also important in processes that produce combustible substances as a by-product. Special precautions are required for substances that are easily combustible. These measures may include installation of fire sprinklers or storage remote from possible sources of ignition, substances with low combustibility may be selected for construction where the fire risk needs to be reduced, such as apartment buildings, houses, or offices. If combustible resources are used there is chance of fire accidents. Fire resistant substances are preferred for building materials and furnishings, for an Authority Having Jurisdiction, combustibility is defined by the local code. BS 476-4,1970 defines a test for combusibility in which 3 specimens of a material are heated in a furnace, otherwise, the material shall be deemed combustible. Various countries have tests for determining noncombustibility of materials, most involve the heating of a specified quantity of the test specimen for a set duration. Usually, the material cannot support combustion and must not undergo a loss of mass. In Canada, for instance, firewalls must be made of concrete, in building construction, buildings are typically divided into combustible and noncombustible ones. Combustible structures have more stringent limits on building height and area. A number of industrial processes produce combustible dust as a by-product, the most common being wood dust. In addition to wood, combustible dusts include metals, especially magnesium, titanium and aluminum, there are at least a 140 known substances that produce combustible dust. While the particles in a combustible dusts may be of any size, as of 2012, the United States Occupational Safety and Health Administration has yet to adopt a comprehensive set of rules on combustible dust. When suspended in air, the particles of combustible dust present a potential for explosions. Accumulated dust, even when not suspended in air, remains a fire hazard, collectors designed to reduce airborne dust account for more than 40 percent of all dust explosions. Other important processes are grinding and pulverizing, transporting powders, filing silos and containers, investigation of 200 dust explosions and fires, between 1980 to 2005, indicated approximately 100 fatalities and 600 injuries. In January 2003, a powder explosion and fire at the West Pharmaceutical Services plant in Kinston, North Carolina resulted in the deaths of six workers
39.
Toxicity
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Toxicity is the degree to which a substance can damage an organism. Toxicity can refer to the effect on an organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism. By extension, the word may be used to describe toxic effects on larger and more complex groups. Sometimes the word is more or less synonymous with poisoning in everyday usage, toxicity is species-specific, making cross-species analysis problematic. Newer paradigms and metrics are evolving to bypass animal testing, while maintaining the concept of toxicity endpoints, disease-causing microorganisms and parasites are toxic in a broad sense, but are generally called pathogens rather than toxicants. The biological toxicity of pathogens can be difficult to measure because the dose may be a single organism. Theoretically one virus, bacterium or worm can reproduce to cause a serious infection, in some cases, e. g. cholera, the disease is chiefly caused by a nonliving substance secreted by the organism, rather than the organism itself. Such nonliving biological toxicants are generally called toxins if produced by a microorganism, plant, or fungus, Physical toxicants are substances that, due to their physical nature, interfere with biological processes. Examples include coal dust, asbestos fibers or finely divided silicon dioxide, corrosive chemicals possess physical toxicity because they destroy tissues, but theyre not directly poisonous unless they interfere directly with biological activity. Water can act as a physical toxicant if taken in high doses because the concentration of vital ions decreases dramatically if theres too much water in the body. Asphyxiant gases can be considered physical toxicants because they act by displacing oxygen in the environment but they are inert, as already mentioned, radiation can have a toxic effect on organisms. Toxicity can be measured by its effects on the target, one such measure is the LD50. When such data does not exist, estimates are made by comparison to known similar toxic things, then, safety factors are added to account for uncertainties in data and evaluation processes. Similarly, an extra protection factor may be used for individuals believed to be susceptible to toxic effects such as in pregnancy or with certain diseases. Obviously, this approach is approximate, but such protection factors are deliberately very conservative. In addition, it is possible that a single cell transformed into a cell is all it takes to develop the full effect. Common mixtures include gasoline, cigarette smoke, and industrial waste, even more complex are situations with more than one type of toxic entity, such as the discharge from a malfunctioning sewage treatment plant, with both chemical and biological agents. The preclinical toxicity testing on various biological systems reveals the species-, organ-, the toxicity of substances can be observed by studying the accidental exposures to a substance in vitro studies using cells/ cell lines in vivo exposure on experimental animals
40.
Antimony
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Antimony is a chemical element with symbol Sb and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite, Antimony compounds have been known since ancient times and were powdered for use as medicine and cosmetics, often known by the Arabic name, kohl. Metallic antimony was known, but it was erroneously identified as lead upon its discovery. In the West, it was first isolated by Vannoccio Biringuccio, for some time, China has been the largest producer of antimony and its compounds, with most production coming from the Xikuangshan Mine in Hunan. The industrial methods for refining antimony are roasting and reduction with carbon or direct reduction of stibnite with iron, the largest applications for metallic antimony is an alloy with lead and tin and the lead antimony plates in lead–acid batteries. Alloys of lead and tin with antimony have improved properties for solders, bullets, Antimony compounds are prominent additives for chlorine and bromine-containing fire retardants found in many commercial and domestic products. An emerging application is the use of antimony in microelectronics, Antimony is in a pnictogen and has an electronegativity of 2.05. In accordance with periodic trends, it is more electronegative than tin or bismuth, Antimony is stable in air at room temperature, but reacts with oxygen if heated to produce antimony trioxide, Sb2O3. Antimony is resistant to attack by acids, four allotropes of antimony are known, a stable metallic form and three metastable forms. Elemental antimony is a brittle, silver-white shiny metalloid, when slowly cooled, molten antimony crystallizes in a trigonal cell, isomorphic with the gray allotrope of arsenic. A rare explosive form of antimony can be formed from the electrolysis of antimony trichloride, when scratched with a sharp implement, an exothermic reaction occurs and white fumes are given off as metallic antimony forms, when rubbed with a pestle in a mortar, a strong detonation occurs. Black antimony is formed upon cooling of antimony vapor. It has the crystal structure as red phosphorus and black arsenic, it oxidizes in air. At 100 °C, it transforms into the stable form. The yellow allotrope of antimony is the most unstable and it has only been generated by oxidation of stibine at −90 °C. Above this temperature and in ambient light, this metastable allotrope transforms into the more stable black allotrope, elemental antimony adopts a layered structure in which layers consist of fused, ruffled, six-membered rings. The nearest and next-nearest neighbors form an octahedral complex, with the three atoms in each double layer slightly closer than the three atoms in the next. This relatively close packing leads to a density of 6.697 g/cm3
41.
Arsenic
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Arsenic is a chemical element with symbol As and atomic number 33. Arsenic occurs in minerals, usually in combination with sulfur and metals. It has various allotropes, but only the form is important to industry. The primary use of arsenic is in alloys of lead. Arsenic is a common dopant in semiconductor electronic devices. Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, a few species of bacteria are able to use arsenic compounds as respiratory metabolites. Trace quantities of arsenic are a dietary element in rats, hamsters, goats, chickens. However, arsenic poisoning occurs in multicellular life if quantities are larger than needed, Arsenic contamination of groundwater is a problem that affects millions of people across the world. The three most common allotropes are metallic gray, yellow, and black arsenic, with gray being the most common. Gray arsenic adopts a structure consisting of many interlocked, ruffled, six-membered rings. Because of weak bonding between the layers, gray arsenic is brittle and has a relatively low Mohs hardness of 3.5. Nearest and next-nearest neighbors form an octahedral complex, with the three atoms in the same double-layer being slightly closer than the three atoms in the next. This relatively close packing leads to a density of 5.73 g/cm3. Gray arsenic is a semimetal, but becomes a semiconductor with a bandgap of 1. 2–1.4 eV if amorphized, gray arsenic is also the most stable form. Yellow arsenic is soft and waxy, and somewhat similar to tetraphosphorus, both have four atoms arranged in a tetrahedral structure in which each atom is bound to each of the other three atoms by a single bond. This unstable allotrope, being molecular, is the most volatile, least dense, solid yellow arsenic is produced by rapid cooling of arsenic vapor, As 4. It is rapidly transformed into gray arsenic by light, the yellow form has a density of 1.97 g/cm3. Black arsenic is similar in structure to red phosphorus, black arsenic can also be formed by cooling vapor at around 100–220 °C
42.
Phosphorus
–
Phosphorus is a chemical element with symbol P and atomic number 15. As an element, phosphorus exists in two major forms—white phosphorus and red phosphorus—but because it is reactive, phosphorus is never found as a free element on Earth. At 0. 099%, phosphorus is the most abundant pnictogen in the Earths crust, with few exceptions, minerals containing phosphorus are in the maximally oxidised state as inorganic phosphate rocks. The glow of phosphorus itself originates from oxidation of the white phosphorus — a process now termed chemiluminescence, together with nitrogen, arsenic, antimony, and bismuth, phosphorus is classified as a pnictogen. Phosphates are a component of DNA, RNA, ATP, and the phospholipids, demonstrating the link between phosphorus and life, elemental phosphorus was first isolated from human urine, and bone ash was an important early phosphate source. Phosphate mines contain fossils, especially marine fossils, because phosphate is present in the deposits of animal remains. Low phosphate levels are an important limit to growth in aquatic systems. The vast majority of compounds produced are consumed as fertilisers. Phosphate is needed to replace the phosphorus that plants remove from the soil, other applications include the role of organophosphorus compounds in detergents, pesticides, and nerve agents. Phosphorus exists as several forms that exhibit different properties. The two most common allotropes are white phosphorus and red phosphorus, from the perspective of applications and chemical literature, the most important form of elemental phosphorus is white phosphorus, often abbreviated as WP. It is a soft and waxy solid consists of tetrahedral P4 molecules. This P4 tetrahedron is also present in liquid and gaseous phosphorus up to the temperature of 800 °C when it starts decomposing to P2 molecules, White phosphorus exists in two crystalline forms, α and β. At room temperature, the α-form is stable, which is common and it has cubic crystal structure and at 195.2 K, it transforms into β-form. These forms differ in terms of the orientations of the constituent P4 tetrahedra. White phosphorus is the least stable, the most reactive, the most volatile, the least dense, White phosphorus gradually changes to red phosphorus. This transformation is accelerated by light and heat, and samples of white phosphorus almost always some red phosphorus. For this reason, white phosphorus that is aged or otherwise impure is also called yellow phosphorus, when exposed to oxygen, white phosphorus glows in the dark with a very faint tinge of green and blue
43.
Boron
–
Boron is a chemical element with symbol B and atomic number 5. Produced entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, it is an element in the Solar system. Boron is concentrated on Earth by the water-solubility of its more common naturally occurring compounds and these are mined industrially as evaporites, such as borax and kernite. The largest known deposits are in Turkey, the largest producer of boron minerals. Elemental boron is a metalloid that is found in small amounts in meteoroids, industrially, very pure boron is produced with difficulty because of refractory contamination by carbon or other elements. Several allotropes of boron exist, amorphous boron is a powder, crystalline boron is silvery to black, extremely hard. The primary use of boron is as boron filaments with applications similar to carbon fibers in some high-strength materials. Boron is primarily used in chemical compounds, about half of all consumption globally, boron is used as an additive in glass fibers of boron-containing fiberglass for insulation and structural materials. The next leading use is in polymers and ceramics in high-strength, lightweight structural, borosilicate glass is desired for its greater strength and thermal shock resistance than ordinary soda lime glass. Boron compounds are used as fertilizers in agriculture and in sodium perborate bleaches, a small amount of boron is used as a dopant in semiconductors, and reagent intermediates in the synthesis of organic fine chemicals. A few boron-containing organic pharmaceuticals are used or are in study, natural boron is composed of two stable isotopes, one of which has a number of uses as a neutron-capturing agent. In biology, borates have low toxicity in mammals, but are toxic to arthropods and are used as insecticides. Boric acid is mildly antimicrobial, and several natural boron-containing organic antibiotics are known, small amounts of boron compounds play a strengthening role in the cell walls of all plants, making boron a necessary plant nutrient. Boron is involved in the metabolism of calcium in both plants and animals and it is considered an essential nutrient for humans, and boron deficiency is implicated in osteoporosis. The word boron was coined from borax, the mineral from which it was isolated, by analogy with carbon, marco Polo brought some glazes back to Italy in the 13th century. Agricola, around 1600, reports the use of borax as a flux in metallurgy, in 1777, boric acid was recognized in the hot springs near Florence, Italy, and became known as sal sedativum, with primarily medical uses. The rare mineral is called sassolite, which is found at Sasso, Sasso was the main source of European borax from 1827 to 1872, when American sources replaced it. Boron compounds were relatively rarely used until the late 1800s when Francis Marion Smiths Pacific Coast Borax Company first popularized and produced them in volume at low cost
44.
Semiconductor device fabrication
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Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a sequence of photo lithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon is almost always used, but various compound semiconductors are used for specialized applications, the entire manufacturing process, from start to packaged chips ready for shipment, takes six to eight weeks and is performed in highly specialized facilities referred to as fabs. When feature widths were far greater than about 10 micrometres, purity was not the issue that it is today in device manufacturing, as devices became more integrated, cleanrooms became even cleaner. Today, the fabs are pressurized with filtered air to remove even the smallest particles, the workers in a semiconductor fabrication facility are required to wear cleanroom suits to protect the devices from human contamination. Semiconductor device manufacturing has spread from Texas and California in the 1960s to the rest of the world, including Europe, the Middle East and it is a global business today. The leading semiconductor manufacturers typically have facilities all over the world, intel, the worlds largest manufacturer, has facilities in Europe and Asia as well as the U. S. A typical wafer is made out of pure silicon that is grown into mono-crystalline cylindrical ingots up to 300 mm in diameter using the Czochralski process. These ingots are sliced into wafers about 0.75 mm thick and polished to obtain a very regular. In semiconductor device fabrication, the processing steps fall into four general categories, deposition, removal, patterning. Deposition is any process that grows, coats, or otherwise transfers a material onto the wafer, available technologies include physical vapor deposition, chemical vapor deposition, electrochemical deposition, molecular beam epitaxy and more recently, atomic layer deposition among others. Removal is any process that removes material from the wafer, examples include etch processes, patterning is the shaping or altering of deposited materials, and is generally referred to as lithography. After etching or other processing, the remaining photoresist is removed by plasma ashing, modification of electrical properties has historically entailed doping transistor sources and drains. These doping processes are followed by annealing or, in advanced devices. Modification of electrical properties now also extends to the reduction of a dielectric constant in low-k insulators via exposure to ultraviolet light in UV processing. Modern chips have up to eleven metal levels produced in over 300 sequenced processing steps, FEOL processing refers to the formation of the transistors directly in the silicon. The raw wafer is engineered by the growth of an ultrapure, in the most advanced logic devices, prior to the silicon epitaxy step, tricks are performed to improve the performance of the transistors to be built. One method involves introducing a straining step wherein a silicon variant such as silicon-germanium is deposited, once the epitaxial silicon is deposited, the crystal lattice becomes stretched somewhat, resulting in improved electronic mobility
