Misplaced Pages

#483516

135-435: A hole is an opening in or through a particular medium, usually a solid body . Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of engineering . Depending on the material and the placement, a hole may be an indentation in a surface (such as a hole in the ground), or may pass completely through that surface (such as

270-439: A cut-off frequency of one cycle per second, too low for any practical applications, but an effective application of the available theory. At Bell Labs , William Shockley and A. Holden started investigating solid-state amplifiers in 1938. The first p–n junction in silicon was observed by Russell Ohl about 1941 when a specimen was found to be light-sensitive, with a sharp boundary between p-type impurity at one end and n-type at

405-426: A dimer , it can embed itself in cellular bilayer membranes and form a hole through which water molecules can pass. In engineering , machining , and tooling , a hole may be a blind hole or a through hole (also called a thru-hole or clearance hole ). A blind hole is a hole that is reamed , drilled , or milled to a specified depth without breaking through to the other side of the workpiece. A through hole

540-511: A rock sample is a random aggregate of minerals and/or mineraloids , and has no specific chemical composition. The vast majority of the rocks of the Earth's crust consist of quartz (crystalline SiO 2 ), feldspar, mica, chlorite , kaolin , calcite, epidote , olivine , augite , hornblende , magnetite , hematite , limonite and a few other minerals. Some minerals, like quartz , mica or feldspar are common, while others have been found in only

675-572: A biological revulsion that associates trypophobic shapes with danger or disease, and may therefore have an evolutionary basis. An example of the use of holes in popular culture can be found in the Beatles lyric from the song, " A Day in the Life ", from their 1967 album Sgt. Pepper's Lonely Hearts Club Band : I read the news today, oh boy: Four thousand holes in Blackburn Lancashire. And though

810-513: A common semi-insulator is gallium arsenide . Some materials, such as titanium dioxide , can even be used as insulating materials for some applications, while being treated as wide-gap semiconductors for other applications. The partial filling of the states at the bottom of the conduction band can be understood as adding electrons to that band. The electrons do not stay indefinitely (due to the natural thermal recombination ) but they can move around for some time. The actual concentration of electrons

945-423: A completely full valence band is inert, not conducting any current. If an electron is taken out of the valence band, then the trajectory that the electron would normally have taken is now missing its charge. For the purposes of electric current, this combination of the full valence band, minus the electron, can be converted into a picture of a completely empty band containing a positively charged particle that moves in

1080-541: A composite made up of a thermoplastic matrix such as acrylonitrile butadiene styrene (ABS) in which calcium carbonate chalk, talc , glass fibers or carbon fibers have been added for strength, bulk, or electro-static dispersion. These additions may be referred to as reinforcing fibers, or dispersants, depending on their purpose. Thus, the matrix material surrounds and supports the reinforcement materials by maintaining their relative positions. The reinforcements impart their special mechanical and physical properties to enhance

1215-1043: A few locations worldwide. The largest group of minerals by far is the silicates (most rocks are ≥95% silicates), which are composed largely of silicon and oxygen , with the addition of ions of aluminium, magnesium , iron, calcium and other metals. Ceramic solids are composed of inorganic compounds, usually oxides of chemical elements. They are chemically inert, and often are capable of withstanding chemical erosion that occurs in an acidic or caustic environment. Ceramics generally can withstand high temperatures ranging from 1,000 to 1,600 °C (1,830 to 2,910 °F). Exceptions include non-oxide inorganic materials, such as nitrides , borides and carbides . Traditional ceramic raw materials include clay minerals such as kaolinite , more recent materials include aluminium oxide ( alumina ). The modern ceramic materials, which are classified as advanced ceramics, include silicon carbide and tungsten carbide . Both are valued for their abrasion resistance, and hence find use in such applications as

1350-410: A guide to the construction of more capable and reliable devices. Alexander Graham Bell used the light-sensitive property of selenium to transmit sound over a beam of light in 1880. A working solar cell, of low efficiency, was constructed by Charles Fritts in 1883, using a metal plate coated with selenium and a thin layer of gold; the device became commercially useful in photographic light meters in

1485-425: A hole created by a hole puncher in a piece of paper). Holes can occur for a number of reasons, including natural processes and intentional actions by humans or animals. Holes in the ground that are made intentionally, such as holes made while searching for food, for replanting trees, or postholes made for securing an object, are usually made through the process of digging . Unintentional holes in an object are often

SECTION 10

#1732848375484

1620-464: A hole is a supermassive black hole , an astronomical object which can be billions of times more massive than Earth's sun . The deepest hole on Earth is the man-made Kola Superdeep Borehole , with a true vertical drill-depth of more than 7.5 miles (12 kilometers), which is only a fraction of the nearly 4,000 mile (6,400 kilometer) distance to the center of the Earth. In mathematics , holes are examined in

1755-445: A low-pressure chamber to create plasma . A common etch gas is chlorofluorocarbon , or more commonly known Freon . A high radio-frequency voltage between the cathode and anode is what creates the plasma in the chamber. The silicon wafer is located on the cathode, which causes it to be hit by the positively charged ions that are released from the plasma. The result is silicon that is etched anisotropically . The last process

1890-580: A material can absorb before mechanical failure, while fracture toughness (denoted K Ic ) describes the ability of a material with inherent microstructural flaws to resist fracture via crack growth and propagation. If a material has a large value of fracture toughness , the basic principles of fracture mechanics suggest that it will most likely undergo ductile fracture. Brittle fracture is very characteristic of most ceramic and glass-ceramic materials that typically exhibit low (and inconsistent) values of K Ic . For an example of applications of ceramics,

2025-558: A material that indicates its ability to conduct heat . Solids also have a specific heat capacity , which is the capacity of a material to store energy in the form of heat (or thermal lattice vibrations). Electrical properties include both electrical resistivity and conductivity , dielectric strength , electromagnetic permeability , and permittivity . Electrical conductors such as metals and alloys are contrasted with electrical insulators such as glasses and ceramics. Semiconductors behave somewhere in between. Whereas conductivity in metals

2160-440: A meltdown of the metallic parts. Work is also being done in developing ceramic parts for gas turbine engines . Turbine engines made with ceramics could operate more efficiently, giving aircraft greater range and payload for a set amount of fuel. Such engines are not in production, however, because the manufacturing of ceramic parts in the sufficient precision and durability is difficult and costly. Processing methods often result in

2295-578: A metallic conductor, current is carried by the flow of electrons, but in semiconductors, current can be carried either by electrons or by the positively charged " holes " in the electronic band structure of the material. Common semiconductor materials include silicon, germanium and gallium arsenide . Many traditional solids exhibit different properties when they shrink to nanometer sizes. For example, nanoparticles of usually yellow gold and gray silicon are red in color; gold nanoparticles melt at much lower temperatures (~300 °C for 2.5 nm size) than

2430-422: A non-crystalline intergranular phase. Glass-ceramics are used to make cookware (originally known by the brand name CorningWare ) and stovetops that have high resistance to thermal shock and extremely low permeability to liquids. The negative coefficient of thermal expansion of the crystalline ceramic phase can be balanced with the positive coefficient of the glassy phase. At a certain point (~70% crystalline)

2565-430: A number of ways. One of these is in homology , which is a general way of associating certain algebraic objects to other mathematical objects such as topological spaces . Homology groups were originally defined in algebraic topology , and homology was originally a rigorous mathematical method for defining and categorizing holes in a mathematical object called a manifold . The initial motivation for defining homology groups

2700-519: A pair is completed. Such carrier traps are sometimes purposely added to reduce the time needed to reach the steady-state. The conductivity of semiconductors may easily be modified by introducing impurities into their crystal lattice . The process of adding controlled impurities to a semiconductor is known as doping . The amount of impurity, or dopant, added to an intrinsic (pure) semiconductor varies its level of conductivity. Doped semiconductors are referred to as extrinsic . By adding impurity to

2835-529: A periodic lattice. Mathematically, the potential of the ion cores can be treated by various models, the simplest being the nearly free electron model . Minerals are naturally occurring solids formed through various geological processes under high pressures. To be classified as a true mineral, a substance must have a crystal structure with uniform physical properties throughout. Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms. In contrast,

SECTION 20

#1732848375484

2970-443: A person who provides an account of an event that lacks important details can be said to have "holes in their story", and a fictional work with unexplained narrative elements can be said to have plot holes . A person who has suffered loss is often referred to as having a "hole in their heart". The concept of a "God-shaped hole" occurs in religious discourse: [H]umans are commonly said to have “a God-shaped hole” in our souls. If you are

3105-501: A physical object is taken to its logical extreme in the fictional concept of a portable hole , exemplified in role-playing games and characterized as a "hole" that a person can carry with them, keep things in, and enter themselves as needed. In art holes are sometimes referred to as negative space , as in the case of the Japanese concept of Ma . Holes can also be referenced metaphorically as existing in non-tangible things. For example,

3240-582: A piezoelectric response several times larger than the traditional piezoelectric material quartz (crystalline SiO 2 ). The deformation (~0.1%) lends itself to useful technical applications such as high-voltage sources, loudspeakers, lasers, as well as chemical, biological, and acousto-optic sensors and/or transducers. Semi-conductor A semiconductor is a material that is between the conductor and insulator in ability to conduct electrical current. In many cases their conducting properties may be altered in useful ways by introducing impurities (" doping ") into

3375-623: A religious person, you can explain the hole by saying that God put it there in order to make it easier for us to receive Him. If you are a naturalist or an atheist, you believe the God-shaped hole is in our minds, not our souls. You then look for reasons that the concept of God might have evolved in our species. The Unicode symbol for HOLE, U+1F573, was approved in 2014 as part of the Miscellaneous Symbols and Pictographs chart in Unicode 7.0, and

3510-499: A resin during processing, which is then shaped into a final form. Polymers that have been around, and that are in current widespread use, include carbon-based polyethylene , polypropylene , polyvinyl chloride , polystyrene , nylons, polyesters , acrylics , polyurethane , and polycarbonates , and silicon-based silicones . Plastics are generally classified as "commodity", "specialty" and "engineering" plastics. Composite materials contain two or more macroscopic phases, one of which

3645-431: A semiconducting material would cause it to leave thermal equilibrium and create a non-equilibrium situation. This introduces electrons and holes to the system, which interact via a process called ambipolar diffusion . Whenever thermal equilibrium is disturbed in a semiconducting material, the number of holes and electrons changes. Such disruptions can occur as a result of a temperature difference or photons , which can enter

3780-426: A semiconductor is doped by Group III elements, they will behave like acceptors creating free holes, known as " p-type " doping. The semiconductor materials used in electronic devices are doped under precise conditions to control the concentration and regions of p- and n-type dopants. A single semiconductor device crystal can have many p- and n-type regions; the p–n junctions between these regions are responsible for

3915-426: A sign of damage . Potholes and sinkholes can damage human settlements. Holes can occur in a wide variety of materials, and at a wide range of scales. The smallest holes observable by humans include pinholes and perforations , but the smallest phenomenon described as a hole is an electron hole , which is a position in an atom or atomic lattice where an electron is missing. The largest phenomenon described as

4050-442: A significant portion of the fields of solid-state chemistry, physics, materials science and engineering. Metallic solids are held together by a high density of shared, delocalized electrons, known as " metallic bonding ". In a metal, atoms readily lose their outermost ("valence") electrons , forming positive ions . The free electrons are spread over the entire solid, which is held together firmly by electrostatic interactions between

4185-501: A silicon atom in the crystal, a vacant state (an electron "hole") is created, which can move around the lattice and function as a charge carrier. Group V elements have five valence electrons, which allows them to act as a donor; substitution of these atoms for silicon creates an extra free electron. Therefore, a silicon crystal doped with boron creates a p-type semiconductor whereas one doped with phosphorus results in an n-type material. During manufacture , dopants can be diffused into

Hole - Misplaced Pages Continue

4320-420: A single hole serves all of these purposes. The formation of holes is a significant event in the development of an animal: All animals start out in development with one hole, the blastopore . If there are two holes, the second hole forms later. The blastopore can arise at the top or the bottom of the embryo. Gramicidin A , a polypeptide with a helical shape, has been described as a portable hole. When it forms

4455-773: A theory of solid-state physics , which developed greatly in the first half of the 20th century. In 1878 Edwin Herbert Hall demonstrated the deflection of flowing charge carriers by an applied magnetic field, the Hall effect . The discovery of the electron by J.J. Thomson in 1897 prompted theories of electron-based conduction in solids. Karl Baedeker , by observing a Hall effect with the reverse sign to that in metals, theorized that copper iodide had positive charge carriers. Johan Koenigsberger  [ de ] classified solid materials like metals, insulators, and "variable conductors" in 1914 although his student Josef Weiss already introduced

4590-472: A vacuum, though with a different effective mass . Because the electrons behave like an ideal gas, one may also think about conduction in very simplistic terms such as the Drude model , and introduce concepts such as electron mobility . For partial filling at the top of the valence band, it is helpful to introduce the concept of an electron hole . Although the electrons in the valence band are always moving around,

4725-567: A variety of proportions. These compounds share with better-known semiconductors the properties of intermediate conductivity and a rapid variation of conductivity with temperature, as well as occasional negative resistance . Such disordered materials lack the rigid crystalline structure of conventional semiconductors such as silicon. They are generally used in thin film structures, which do not require material of higher electronic quality, being relatively insensitive to impurities and radiation damage. Almost all of today's electronic technology involves

4860-692: A way that the strain is directly proportional to the stress ( Hooke's law ). The coefficient of the proportion is called the modulus of elasticity or Young's modulus . This region of deformation is known as the linearly elastic region. Three models can describe how a solid responds to an applied stress: Many materials become weaker at high temperatures. Materials that retain their strength at high temperatures, called refractory materials , are useful for many purposes. For example, glass-ceramics have become extremely useful for countertop cooking, as they exhibit excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000 °C. In

4995-471: A wide distribution of microscopic flaws that frequently play a detrimental role in the sintering process, resulting in the proliferation of cracks, and ultimate mechanical failure. Glass-ceramic materials share many properties with both non-crystalline glasses and crystalline ceramics . They are formed as a glass, and then partially crystallized by heat treatment, producing both amorphous and crystalline phases so that crystalline grains are embedded within

5130-414: A wide variety of polymers and plastics . Wood is a natural organic material consisting primarily of cellulose fibers embedded in a matrix of lignin . Regarding mechanical properties, the fibers are strong in tension, and the lignin matrix resists compression. Thus wood has been an important construction material since humans began building shelters and using boats. Wood to be used for construction work

5265-415: Is a combination of processes that are used to prepare semiconducting materials for ICs. One process is called thermal oxidation , which forms silicon dioxide on the surface of the silicon . This is used as a gate insulator and field oxide . Other processes are called photomasks and photolithography . This process is what creates the patterns on the circuit in the integrated circuit. Ultraviolet light

5400-467: Is a function of the temperature, as the probability of getting enough thermal energy to produce a pair increases with temperature, being approximately exp(− E G / kT ) , where k is the Boltzmann constant , T is the absolute temperature and E G is bandgap. The probability of meeting is increased by carrier traps – impurities or dislocations which can trap an electron or hole and hold it until

5535-415: Is a hole that is made to go completely through the material of an object. In other words, a through hole is a hole that goes all the way through something. Taps used for through holes are generally tapered since it will tap faster and the chips will be released when the tap exits the hole. The etymology of the blind hole is that it is not possible to see through it. It may also refer to any feature that

Hole - Misplaced Pages Continue

5670-474: Is a natural organic material consisting primarily of cellulose fibers embedded in a matrix of organic lignin . In materials science, composites of more than one constituent material can be designed to have desired properties. The forces between the atoms in a solid can take a variety of forms. For example, a crystal of sodium chloride (common salt) is made up of ionic sodium and chlorine , which are held together by ionic bonds . In diamond or silicon,

5805-686: Is also a fundamental feature of many biological materials and the manner by which the structures are assembled from the molecular level up. Thus, self-assembly is emerging as a new strategy in the chemical synthesis of high performance biomaterials. Physical properties of elements and compounds that provide conclusive evidence of chemical composition include odor, color, volume, density (mass per unit volume), melting point, boiling point, heat capacity, physical form and shape at room temperature (solid, liquid or gas; cubic, trigonal crystals, etc.), hardness, porosity, index of refraction and many others. This section discusses some physical properties of materials in

5940-404: Is called diffusion . This is the process that gives the semiconducting material its desired semiconducting properties. It is also known as doping . The process introduces an impure atom to the system, which creates the p–n junction . To get the impure atoms embedded in the silicon wafer, the wafer is first put in a 1,100 degree Celsius chamber. The atoms are injected in and eventually diffuse with

6075-469: Is caused by electrons, both electrons and holes contribute to current in semiconductors. Alternatively, ions support electric current in ionic conductors . Many materials also exhibit superconductivity at low temperatures; they include metallic elements such as tin and aluminium, various metallic alloys, some heavily doped semiconductors, and certain ceramics. The electrical resistivity of most electrical (metallic) conductors generally decreases gradually as

6210-416: Is commonly known as lumber or timber . In construction, wood is not only a structural material, but is also used to form the mould for concrete. Wood-based materials are also extensively used for packaging (e.g. cardboard) and paper, which are both created from the refined pulp. The chemical pulping processes use a combination of high temperature and alkaline (kraft) or acidic (sulfite) chemicals to break

6345-410: Is increased by adding a small amount (of the order of 1 in 10 ) of pentavalent ( antimony , phosphorus , or arsenic ) or trivalent ( boron , gallium , indium ) atoms. This process is known as doping, and the resulting semiconductors are known as doped or extrinsic semiconductors . Apart from doping, the conductivity of a semiconductor can be improved by increasing its temperature. This is contrary to

6480-776: Is inert, blocking the passage of other electrons via that state. The energies of these quantum states are critical since a state is partially filled only if its energy is near the Fermi level (see Fermi–Dirac statistics ). High conductivity in material comes from it having many partially filled states and much state delocalization. Metals are good electrical conductors and have many partially filled states with energies near their Fermi level. Insulators , by contrast, have few partially filled states, their Fermi levels sit within band gaps with few energy states to occupy. Importantly, an insulator can be made to conduct by increasing its temperature: heating provides energy to promote some electrons across

6615-841: Is neither a very good insulator nor a very good conductor. However, one important feature of semiconductors (and some insulators, known as semi-insulators ) is that their conductivity can be increased and controlled by doping with impurities and gating with electric fields. Doping and gating move either the conduction or valence band much closer to the Fermi level and greatly increase the number of partially filled states. Some wider-bandgap semiconductor materials are sometimes referred to as semi-insulators . When undoped, these have electrical conductivity nearer to that of electrical insulators, however they can be doped (making them as useful as semiconductors). Semi-insulators find niche applications in micro-electronics, such as substrates for HEMT . An example of

6750-411: Is no long-range order in the position of the atoms. These solids are known as amorphous solids ; examples include polystyrene and glass. Whether a solid is crystalline or amorphous depends on the material involved, and the conditions in which it was formed. Solids that are formed by slow cooling will tend to be crystalline, while solids that are frozen rapidly are more likely to be amorphous. Likewise,

6885-460: Is often ceramic. For example, a continuous matrix, and a dispersed phase of ceramic particles or fibers. Applications of composite materials range from structural elements such as steel-reinforced concrete, to the thermally insulative tiles that play a key and integral role in NASA's Space Shuttle thermal protection system , which is used to protect the surface of the shuttle from the heat of re-entry into

SECTION 50

#1732848375484

7020-499: Is taken to a specific depth, more specifically referring to internally threaded hole (tapped holes). Not considering the drill point, the depth of the blind hole, conventionally, may be slightly deeper than that of the threaded depth. There are three accepted methods of threading blind holes: At least two U.S. tool manufacturers have manufactured tools for thread milling in blind holes: Ingersoll Cutting Tools of Rockford, Illinois, and Tooling Systems of Houston, Texas, who introduced

7155-409: Is the ability of crystals to generate a voltage in response to an applied mechanical stress. The piezoelectric effect is reversible in that piezoelectric crystals, when subjected to an externally applied voltage, can change shape by a small amount. Polymer materials like rubber, wool, hair, wood fiber, and silk often behave as electrets . For example, the polymer polyvinylidene fluoride (PVDF) exhibits

7290-421: Is the notion of homotopy group : these are invariants of a topological space that, when non-trivial (one also says in this case that the space is not k-connected ), detect the presence of "holes" in the sense that the space contains a sphere that cannot be contracted to a point. The term of hole is often used informally when discussing these objects. For surfaces a notion closer to the intuitive meaning exists:

7425-400: Is the study of the behavior of solid matter under external actions such as external forces and temperature changes. A solid does not exhibit macroscopic flow, as fluids do. Any degree of departure from its original shape is called deformation . The proportion of deformation to original size is called strain. If the applied stress is sufficiently low, almost all solid materials behave in such

7560-500: Is typically very dilute, and so (unlike in metals) it is possible to think of the electrons in the conduction band of a semiconductor as a sort of classical ideal gas , where the electrons fly around freely without being subject to the Pauli exclusion principle . In most semiconductors, the conduction bands have a parabolic dispersion relation , and so these electrons respond to forces (electric field, magnetic field, etc.) much as they would in

7695-402: Is used along with a photoresist layer to create a chemical change that generates the patterns for the circuit. The etching is the next process that is required. The part of the silicon that was not covered by the photoresist layer from the previous step can now be etched. The main process typically used today is called plasma etching . Plasma etching usually involves an etch gas pumped in

7830-479: Is used in pinhole cameras to form an image without the use of a lens . Pinholes on produce packaging have been used to control the atmosphere and relative humidity within the packaging. In many fields, pinholes are a harmful side effect of manufacturing processes. For example, in the assembly of microcircuits , pinholes in the dielectric insulator layer coating the circuit can cause the circuit to fail. Therefore, "[t]o avoid pinholes that might protrude through

7965-483: Is used in capacitors. A capacitor is an electrical device that can store energy in the electric field between a pair of closely spaced conductors (called 'plates'). When voltage is applied to the capacitor, electric charges of equal magnitude, but opposite polarity, build up on each plate. Capacitors are used in electrical circuits as energy-storage devices, as well as in electronic filters to differentiate between high-frequency and low-frequency signals. Piezoelectricity

8100-527: The Annalen der Physik und Chemie in 1835; Rosenschöld's findings were ignored. Simon Sze stated that Braun's research was the earliest systematic study of semiconductor devices. Also in 1874, Arthur Schuster found that a copper oxide layer on wires had rectification properties that ceased when the wires are cleaned. William Grylls Adams and Richard Evans Day observed the photovoltaic effect in selenium in 1876. A unified explanation of these phenomena required

8235-429: The Pauli exclusion principle ). These states are associated with the electronic band structure of the material. Electrical conductivity arises due to the presence of electrons in states that are delocalized (extending through the material), however in order to transport electrons a state must be partially filled , containing an electron only part of the time. If the state is always occupied with an electron, then it

SECTION 60

#1732848375484

8370-450: The Siege of Leningrad after successful completion. In 1926, Julius Edgar Lilienfeld patented a device resembling a field-effect transistor , but it was not practical. R. Hilsch  [ de ] and R. W. Pohl  [ de ] in 1938 demonstrated a solid-state amplifier using a structure resembling the control grid of a vacuum tube; although the device displayed power gain, it had

8505-445: The band gap , be accompanied by the emission of thermal energy (in the form of phonons ) or radiation (in the form of photons ). In some states, the generation and recombination of electron–hole pairs are in equipoise. The number of electron-hole pairs in the steady state at a given temperature is determined by quantum statistical mechanics . The precise quantum mechanical mechanisms of generation and recombination are governed by

8640-470: The conservation of energy and conservation of momentum . As the probability that electrons and holes meet together is proportional to the product of their numbers, the product is in the steady-state nearly constant at a given temperature, providing that there is no significant electric field (which might "flush" carriers of both types, or move them from neighbor regions containing more of them to meet together) or externally driven pair generation. The product

8775-406: The crystal structure . When two differently doped regions exist in the same crystal, a semiconductor junction is created. The behavior of charge carriers , which include electrons , ions , and electron holes , at these junctions is the basis of diodes , transistors , and most modern electronics . Some examples of semiconductors are silicon , germanium , gallium arsenide , and elements near

8910-462: The genus of a connected, orientable surface is an integer representing the maximum number of cuttings along non-intersecting closed simple curves without rendering the resultant manifold disconnected. In layman's terms, it is exactly the number of "holes" the surface has, when represented as a submanifold in 3-space. In physics, antimatter is pervasively described as a hole, a location that, when brought together with ordinary matter to fill

9045-513: The periodic table moving diagonally downward right from boron . They separate the electrical conductors (or metals, to the left) from the insulators (to the right). Devices made from semiconductor materials are the foundation of modern electronics, including radio, computers, telephones, etc. Semiconductor devices include the transistor , solar cells , diodes and integrated circuits . Solar photovoltaic panels are large semiconductor devices that directly convert light into electrical energy. In

9180-428: The physical and chemical properties of solids. Solid-state chemistry is especially concerned with the synthesis of novel materials, as well as the science of identification and chemical composition . The atoms, molecules or ions that make up solids may be arranged in an orderly repeating pattern, or irregularly. Materials whose constituents are arranged in a regular pattern are known as crystals . In some cases,

9315-461: The 1930s. Point-contact microwave detector rectifiers made of lead sulfide were used by Jagadish Chandra Bose in 1904; the cat's-whisker detector using natural galena or other materials became a common device in the development of radio . However, it was somewhat unpredictable in operation and required manual adjustment for best performance. In 1906, H.J. Round observed light emission when electric current passed through silicon carbide crystals,

9450-405: The Earth's atmosphere. One example is Reinforced Carbon-Carbon (RCC), the light gray material that withstands reentry temperatures up to 1,510 °C (2,750 °F) and protects the nose cap and leading edges of Space Shuttle's wings. RCC is a laminated composite material made from graphite rayon cloth and impregnated with a phenolic resin . After curing at high temperature in an autoclave,

9585-543: The Thread Mill in 1977, a device that milled large internal threads in the blind holes of oil well blowout preventers . Today many CNC milling machines can run such a thread milling cycle (see a video of such a cut in the "External links" section). One use of through holes in electronics is with through-hole technology , a mounting scheme involving the use of leads on the components that are inserted into holes drilled in printed circuit boards (PCB) and soldered to pads on

9720-427: The aerospace industry, high performance materials used in the design of aircraft and/or spacecraft exteriors must have a high resistance to thermal shock. Thus, synthetic fibers spun out of organic polymers and polymer/ceramic/metal composite materials and fiber-reinforced polymers are now being designed with this purpose in mind. Because solids have thermal energy , their atoms vibrate about fixed mean positions within

9855-493: The atoms share electrons and form covalent bonds . In metals, electrons are shared in metallic bonding . Some solids, particularly most organic compounds, are held together with van der Waals forces resulting from the polarization of the electronic charge cloud on each molecule. The dissimilarities between the types of solid result from the differences between their bonding. Metals typically are strong, dense, and good conductors of both electricity and heat . The bulk of

9990-416: The band gap, inducing partially filled states in both the band of states beneath the band gap ( valence band ) and the band of states above the band gap ( conduction band ). An (intrinsic) semiconductor has a band gap that is smaller than that of an insulator and at room temperature, significant numbers of electrons can be excited to cross the band gap. A pure semiconductor, however, is not very useful, as it

10125-467: The behavior of a metal, in which conductivity decreases with an increase in temperature. The modern understanding of the properties of a semiconductor relies on quantum physics to explain the movement of charge carriers in a crystal lattice . Doping greatly increases the number of charge carriers within the crystal. When a semiconductor is doped by Group V elements, they will behave like donors creating free electrons , known as " n-type " doping. When

10260-553: The brief stated: "There are 4,000 holes in the road in Blackburn, Lancashire, or one twenty-sixth of a hole per person, according to a council survey. If Blackburn is typical, there are two million holes in Britain's roads and 300,000 in London". Holes have also been described as ontological parasites because they can only exist as aspects of another object. The psychological concept of a hole as

10395-663: The chemical bonds of the lignin before burning it out. One important property of carbon in organic chemistry is that it can form certain compounds, the individual molecules of which are capable of attaching themselves to one another, thereby forming a chain or a network. The process is called polymerization and the chains or networks polymers, while the source compound is a monomer. Two main groups of polymers exist: those artificially manufactured are referred to as industrial polymers or synthetic polymers (plastics) and those naturally occurring as biopolymers. Monomers can have various chemical substituents, or functional groups, which can affect

10530-467: The chemical properties of organic compounds, such as solubility and chemical reactivity, as well as the physical properties, such as hardness, density, mechanical or tensile strength, abrasion resistance, heat resistance, transparency, color, etc.. In proteins, these differences give the polymer the ability to adopt a biologically active conformation in preference to others (see self-assembly ). People have been using natural organic polymers for centuries in

10665-489: The concept of band gaps had been developed. Walter H. Schottky and Nevill Francis Mott developed models of the potential barrier and of the characteristics of a metal–semiconductor junction . By 1938, Boris Davydov had developed a theory of the copper-oxide rectifier, identifying the effect of the p–n junction and the importance of minority carriers and surface states. Agreement between theoretical predictions (based on developing quantum mechanics) and experimental results

10800-855: The construction of light-emitting diodes and fluorescent quantum dots . Semiconductors with high thermal conductivity can be used for heat dissipation and improving thermal management of electronics. They play a crucial role in electric vehicles , high-brightness LEDs and power modules , among other applications. Semiconductors have large thermoelectric power factors making them useful in thermoelectric generators , as well as high thermoelectric figures of merit making them useful in thermoelectric coolers . A large number of elements and compounds have semiconducting properties, including: The most common semiconducting materials are crystalline solids, but amorphous and liquid semiconductors are also known. These include hydrogenated amorphous silicon and mixtures of arsenic , selenium , and tellurium in

10935-411: The early 1980s, Toyota researched production of an adiabatic ceramic engine with an operating temperature of over 6,000 °F (3,320 °C). Ceramic engines do not require a cooling system and hence allow a major weight reduction and therefore greater fuel efficiency. In a conventional metallic engine, much of the energy released from the fuel must be dissipated as waste heat in order to prevent

11070-453: The electrical properties of materials. The properties of the time-temperature coefficient of resistance, rectification, and light-sensitivity were observed starting in the early 19th century. Thomas Johann Seebeck was the first to notice that semiconductors exhibit special feature such that experiment concerning an Seebeck effect emerged with much stronger result when applying semiconductors, in 1821. In 1833, Michael Faraday reported that

11205-530: The electrons in the conduction band). When ionizing radiation strikes a semiconductor, it may excite an electron out of its energy level and consequently leave a hole. This process is known as electron-hole pair generation . Electron-hole pairs are constantly generated from thermal energy as well, in the absence of any external energy source. Electron-hole pairs are also apt to recombine. Conservation of energy demands that these recombination events, in which an electron loses an amount of energy larger than

11340-543: The elements in the periodic table , those to the left of a diagonal line drawn from boron to polonium , are metals. Mixtures of two or more elements in which the major component is a metal are known as alloys . People have been using metals for a variety of purposes since prehistoric times. The strength and reliability of metals has led to their widespread use in construction of buildings and other structures, as well as in most vehicles, many appliances and tools, pipes, road signs and railroad tracks. Iron and aluminium are

11475-435: The entire thickness of the dielectric layer, it is a common practice to screen several layers of dielectric with drying and firing after each screening", thereby preventing the pinholes from becoming continuous. It has been noted that holes occupy an unusual ontological position in philosophy, as people tend to refer to them as tangible and countable objects, when in fact they are the absence of something in another object. In

11610-474: The excess or shortage of electrons, respectively. A balanced number of electrons would cause a current to flow throughout the material. Homojunctions occur when two differently doped semiconducting materials are joined. For example, a configuration could consist of p-doped and n-doped germanium . This results in an exchange of electrons and holes between the differently doped semiconducting materials. The n-doped germanium would have an excess of electrons, and

11745-578: The extreme hardness of zirconia is utilized in the manufacture of knife blades, as well as other industrial cutting tools. Ceramics such as alumina , boron carbide and silicon carbide have been used in bulletproof vests to repel large-caliber rifle fire. Silicon nitride parts are used in ceramic ball bearings, where their high hardness makes them wear resistant. In general, ceramics are also chemically resistant and can be used in wet environments where steel bearings would be susceptible to oxidation (or rust). As another example of ceramic applications, in

11880-514: The fast response of crystal detectors. Considerable research and development of silicon materials occurred during the war to develop detectors of consistent quality. Detector and power rectifiers could not amplify a signal. Many efforts were made to develop a solid-state amplifier and were successful in developing a device called the point contact transistor which could amplify 20 dB or more. In 1922, Oleg Losev developed two-terminal, negative resistance amplifiers for radio, but he died in

12015-433: The form of waxes and shellac , which is classified as a thermoplastic polymer. A plant polymer named cellulose provided the tensile strength for natural fibers and ropes, and by the early 19th century natural rubber was in widespread use. Polymers are the raw materials (the resins) used to make what are commonly called plastics. Plastics are the final product, created after one or more polymers or additives have been added to

12150-535: The glass-ceramic has a net coefficient of thermal expansion close to zero. This type of glass-ceramic exhibits excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000 °C. Glass ceramics may also occur naturally when lightning strikes the crystalline (e.g. quartz) grains found in most beach sand . In this case, the extreme and immediate heat of the lightning (~2500 °C) creates hollow, branching rootlike structures called fulgurite via fusion . Organic chemistry studies

12285-673: The gold slabs (1064 °C); and metallic nanowires are much stronger than the corresponding bulk metals. The high surface area of nanoparticles makes them extremely attractive for certain applications in the field of energy. For example, platinum metals may provide improvements as automotive fuel catalysts , as well as proton exchange membrane (PEM) fuel cells. Also, ceramic oxides (or cermets) of lanthanum , cerium , manganese and nickel are now being developed as solid oxide fuel cells (SOFC). Lithium, lithium-titanate and tantalum nanoparticles are being applied in lithium-ion batteries. Silicon nanoparticles have been shown to dramatically expand

12420-483: The hole, results in both the hole and the matter cancelling each-other out. This is analogous to patching a pothole with asphalt, or filling a bubble below the surface of water with an equal amount of water to cancel it out. The most direct example is the electron hole ; a fairly general theoretical description is provided by the Dirac sea , which treats positrons (or anti-particles in general) as holes. Holes provide one of

12555-505: The holes were rather small, They had to count them all, Now they know how many holes it takes to fill the Albert Hall. The reference to 4,000 holes was written by John Lennon , and inspired by a Far & Near news brief from the same 17 January edition of the Daily Mail , which had also provided inspiration for previous verses of the song. Under the headline "The holes in our roads",

12690-556: The incoming light prior to capture. Here again, surface area of the nanoparticles (and thin films) plays a critical role in maximizing the amount of absorbed radiation. Many natural (or biological) materials are complex composites with remarkable mechanical properties. These complex structures, which have risen from hundreds of million years of evolution, are inspiring materials scientists in the design of novel materials. Their defining characteristics include structural hierarchy, multifunctionality and self-healing capability. Self-organization

12825-495: The invention of the transistor in 1947 and the integrated circuit in 1958. Semiconductors in their natural state are poor conductors because a current requires the flow of electrons, and semiconductors have their valence bands filled, preventing the entire flow of new electrons. Several developed techniques allow semiconducting materials to behave like conducting materials, such as doping or gating . These modifications have two outcomes: n-type and p-type . These refer to

12960-448: The ions and the electron cloud. The large number of free electrons gives metals their high values of electrical and thermal conductivity. The free electrons also prevent transmission of visible light, making metals opaque, shiny and lustrous . More advanced models of metal properties consider the effect of the positive ions cores on the delocalised electrons. As most metals have crystalline structure, those ions are usually arranged into

13095-496: The laminate is pyrolized to convert the resin to carbon, impregnated with furfural alcohol in a vacuum chamber, and cured/pyrolized to convert the furfural alcohol to carbon. In order to provide oxidation resistance for reuse capability, the outer layers of the RCC are converted to silicon carbide. Domestic examples of composites can be seen in the "plastic" casings of television sets, cell-phones and so on. These plastic casings are usually

13230-543: The material's majority carrier . The opposite carrier is called the minority carrier , which exists due to thermal excitation at a much lower concentration compared to the majority carrier. For example, the pure semiconductor silicon has four valence electrons that bond each silicon atom to its neighbors. In silicon, the most common dopants are group III and group V elements. Group III elements all contain three valence electrons, causing them to function as acceptors when used to dope silicon. When an acceptor atom replaces

13365-418: The matrix properties. A synergism produces material properties unavailable from the individual constituent materials, while the wide variety of matrix and strengthening materials provides the designer with the choice of an optimum combination. Semiconductors are materials that have an electrical resistivity (and conductivity) between that of metallic conductors and non-metallic insulators. They can be found in

13500-518: The opposite side either by manual assembly (hand placement) or by the use of automated insertion mount machines. A pinhole is a small hole, usually made by pressing a thin, pointed object such as a pin through an easily penetrated material such as a fabric or a very thin layer of metal . Similar holes made by other means are also often called pinholes. Pinholes may be intentionally made for various reasons. For example, in optics pinholes are used as apertures to select certain rays of light. This

13635-409: The ordered (or disordered) lattice. The spectrum of lattice vibrations in a crystalline or glassy network provides the foundation for the kinetic theory of solids . This motion occurs at the atomic level, and thus cannot be observed or detected without highly specialized equipment, such as that used in spectroscopy . Thermal properties of solids include thermal conductivity , which is the property of

13770-588: The other, showing variable resistance, and having sensitivity to light or heat. Because the electrical properties of a semiconductor material can be modified by doping and by the application of electrical fields or light, devices made from semiconductors can be used for amplification, switching, and energy conversion . The term semiconductor is also used to describe materials used in high capacity, medium- to high-voltage cables as part of their insulation, and these materials are often plastic XLPE ( Cross-linked polyethylene ) with carbon black. The conductivity of silicon

13905-449: The other. A slice cut from the specimen at the p–n boundary developed a voltage when exposed to light. The first working transistor was a point-contact transistor invented by John Bardeen , Walter Houser Brattain , and William Shockley at Bell Labs in 1947. Shockley had earlier theorized a field-effect amplifier made from germanium and silicon, but he failed to build such a working device, before eventually using germanium to invent

14040-417: The p-doped germanium would have an excess of holes. The transfer occurs until an equilibrium is reached by a process called recombination , which causes the migrating electrons from the n-type to come in contact with the migrating holes from the p-type. The result of this process is a narrow strip of immobile ions , which causes an electric field across the junction. A difference in electric potential on

14175-409: The perception of a figure rather than a hole. There is a debate on whether holes are special and whether they are perceived as having their own shape. They may be special in some cases, but not in the ownership of the contours. Some people have an aversion to the sight of irregular patterns or clusters of small holes, a condition called trypophobia . Researchers hypothesize that this is the result of

14310-508: The point-contact transistor. In France, during the war, Herbert Mataré had observed amplification between adjacent point contacts on a germanium base. After the war, Mataré's group announced their " Transistron " amplifier only shortly after Bell Labs announced the " transistor ". In 1954, physical chemist Morris Tanenbaum fabricated the first silicon junction transistor at Bell Labs . However, early junction transistors were relatively bulky devices that were difficult to manufacture on

14445-524: The principle behind the light-emitting diode . Oleg Losev observed similar light emission in 1922, but at the time the effect had no practical use. Power rectifiers, using copper oxide and selenium, were developed in the 1920s and became commercially important as an alternative to vacuum tube rectifiers. The first semiconductor devices used galena , including German physicist Ferdinand Braun's crystal detector in 1874 and Indian physicist Jagadish Chandra Bose's radio crystal detector in 1901. In

14580-499: The production of polycrystalline transparent ceramics such as transparent alumina and alumina compounds for such applications as high-power lasers. Advanced ceramics are also used in the medicine, electrical and electronics industries. Ceramic engineering is the science and technology of creating solid-state ceramic materials, parts and devices. This is done either by the action of heat, or, at lower temperatures, using precipitation reactions from chemical solutions. The term includes

14715-574: The pure semiconductors, the electrical conductivity may be varied by factors of thousands or millions. A 1 cm specimen of a metal or semiconductor has the order of 10 atoms. In a metal, every atom donates at least one free electron for conduction, thus 1 cm of metal contains on the order of 10 free electrons, whereas a 1 cm sample of pure germanium at 20   °C contains about 4.2 × 10 atoms, but only 2.5 × 10 free electrons and 2.5 × 10 holes. The addition of 0.001% of arsenic (an impurity) donates an extra 10 free electrons in

14850-439: The purification of raw materials, the study and production of the chemical compounds concerned, their formation into components, and the study of their structure, composition and properties. Mechanically speaking, ceramic materials are brittle, hard, strong in compression and weak in shearing and tension. Brittle materials may exhibit significant tensile strength by supporting a static load. Toughness indicates how much energy

14985-507: The regular ordering can continue unbroken over a large scale, for example diamonds, where each diamond is a single crystal . Solid objects that are large enough to see and handle are rarely composed of a single crystal, but instead are made of a large number of single crystals, known as crystallites , whose size can vary from a few nanometers to several meters. Such materials are called polycrystalline . Almost all common metals, and many ceramics , are polycrystalline. In other materials, there

15120-629: The resistance of specimens of silver sulfide decreases when they are heated. This is contrary to the behavior of metallic substances such as copper. In 1839, Alexandre Edmond Becquerel reported observation of a voltage between a solid and a liquid electrolyte, when struck by light, the photovoltaic effect . In 1873, Willoughby Smith observed that selenium resistors exhibit decreasing resistance when light falls on them. In 1874, Karl Ferdinand Braun observed conduction and rectification in metallic sulfides , although this effect had been discovered earlier by Peter Munck af Rosenschöld ( sv ) writing for

15255-534: The same volume and the electrical conductivity is increased by a factor of 10,000. The materials chosen as suitable dopants depend on the atomic properties of both the dopant and the material to be doped. In general, dopants that produce the desired controlled changes are classified as either electron acceptors or donors . Semiconductors doped with donor impurities are called n-type , while those doped with acceptor impurities are known as p-type . The n and p type designations indicate which charge carrier acts as

15390-472: The same way as the electron. Combined with the negative effective mass of the electrons at the top of the valence band, we arrive at a picture of a positively charged particle that responds to electric and magnetic fields just as a normal positively charged particle would do in a vacuum, again with some positive effective mass. This particle is called a hole, and the collection of holes in the valence band can again be understood in simple classical terms (as with

15525-591: The scale at which the materials are used. A high degree of crystalline perfection is also required, since faults in the crystal structure (such as dislocations , twins , and stacking faults ) interfere with the semiconducting properties of the material. Crystalline faults are a major cause of defective semiconductor devices. The larger the crystal, the more difficult it is to achieve the necessary perfection. Current mass production processes use crystal ingots between 100 and 300 mm (3.9 and 11.8 in) in diameter, grown as cylinders and sliced into wafers . There

15660-425: The semiconductor body by contact with gaseous compounds of the desired element, or ion implantation can be used to accurately position the doped regions. Some materials, when rapidly cooled to a glassy amorphous state, have semiconducting properties. These include B, Si , Ge, Se, and Te, and there are multiple theories to explain them. The history of the understanding of semiconductors begins with experiments on

15795-458: The silicon. After the process is completed and the silicon has reached room temperature, the doping process is done and the semiconducting wafer is almost prepared. Semiconductors are defined by their unique electric conductive behavior, somewhere between that of a conductor and an insulator. The differences between these materials can be understood in terms of the quantum states for electrons, each of which may contain zero or one electron (by

15930-445: The so-called " metalloid staircase " on the periodic table . After silicon, gallium arsenide is the second-most common semiconductor and is used in laser diodes , solar cells , microwave-frequency integrated circuits , and others. Silicon is a critical element for fabricating most electronic circuits . Semiconductor devices can display a range of different useful properties, such as passing current more easily in one direction than

16065-527: The solid state. The mechanical properties of materials describe characteristics such as their strength and resistance to deformation. For example, steel beams are used in construction because of their high strength, meaning that they neither break nor bend significantly under the applied load. Mechanical properties include elasticity , plasticity , tensile strength , compressive strength , shear strength , fracture toughness , ductility (low in brittle materials) and indentation hardness . Solid mechanics

16200-447: The specific crystal structure adopted by a crystalline solid depends on the material involved and on how it was formed. While many common objects, such as an ice cube or a coin, are chemically identical throughout, many other common materials comprise a number of different substances packed together. For example, a typical rock is an aggregate of several different minerals and mineraloids , with no specific chemical composition. Wood

16335-479: The storage capacity of lithium-ion batteries during the expansion/contraction cycle. Silicon nanowires cycle without significant degradation and present the potential for use in batteries with greatly expanded storage times. Silicon nanoparticles are also being used in new forms of solar energy cells. Thin film deposition of silicon quantum dots on the polycrystalline silicon substrate of a photovoltaic (solar) cell increases voltage output as much as 60% by fluorescing

16470-442: The structure, properties, composition, reactions, and preparation by synthesis (or other means) of chemical compounds of carbon and hydrogen , which may contain any number of other elements such as nitrogen , oxygen and the halogens: fluorine , chlorine , bromine and iodine . Some organic compounds may also contain the elements phosphorus or sulfur . Examples of organic solids include wood, paraffin wax , naphthalene and

16605-416: The study of visual perception, a hole is a special case of figure-ground , because the ground region is entirely surrounded by the figure. For a region to be perceived as a visual hole three factors are important: depth factors indicating that the enclosed region lies behind; grouping between the enclosed region and the surround; and figural factors (for example symmetry, convexity, or familiarity) that lead to

16740-427: The system and create electrons and holes. The processes that create or annihilate electrons and holes are called generation and recombination, respectively. In certain semiconductors, excited electrons can relax by emitting light instead of producing heat. Controlling the semiconductor composition and electrical current allows for the manipulation of the emitted light's properties. These semiconductors are used in

16875-508: The temperature is lowered, but remains finite. In a superconductor, however, the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source. A dielectric , or electrical insulator, is a substance that is highly resistant to the flow of electric current. A dielectric, such as plastic, tends to concentrate an applied electric field within itself, which property

17010-407: The term Halbleiter (a semiconductor in modern meaning) in his Ph.D. thesis in 1910. Felix Bloch published a theory of the movement of electrons through atomic lattices in 1928. In 1930, B. Gudden  [ de ] stated that conductivity in semiconductors was due to minor concentrations of impurities. By 1931, the band theory of conduction had been established by Alan Herries Wilson and

17145-794: The two most commonly used structural metals. They are also the most abundant metals in the Earth's crust . Iron is most commonly used in the form of an alloy, steel, which contains up to 2.1% carbon , making it much harder than pure iron. Because metals are good conductors of electricity, they are valuable in electrical appliances and for carrying an electric current over long distances with little energy loss or dissipation. Thus, electrical power grids rely on metal cables to distribute electricity. Home electrical systems, for example, are wired with copper for its good conducting properties and easy machinability. The high thermal conductivity of most metals also makes them useful for stovetop cooking utensils. The study of metallic elements and their alloys makes up

17280-483: The two primary forms of conduction in a semi-conductor , that is, the material from which transistors are made; without holes, current could not flow, and transistors turn on and off by enabling or disabling the creation of holes. Animal bodies tend to contain specialized holes which serve various biological functions, such as the intake of oxygen or food, the excretion of waste, and the intake or expulsion of other fluids for reproductive purposes. In some simple animals,

17415-406: The use of semiconductors, with the most important aspect being the integrated circuit (IC), which are found in desktops , laptops , scanners, cell-phones , and other electronic devices. Semiconductors for ICs are mass-produced. To create an ideal semiconducting material, chemical purity is paramount. Any small imperfection can have a drastic effect on how the semiconducting material behaves due to

17550-498: The useful electronic behavior. Using a hot-point probe , one can determine quickly whether a semiconductor sample is p- or n-type. A few of the properties of semiconductor materials were observed throughout the mid-19th and first decades of the 20th century. The first practical application of semiconductors in electronics was the 1904 development of the cat's-whisker detector , a primitive semiconductor diode used in early radio receivers. Developments in quantum physics led in turn to

17685-464: The wear plates of crushing equipment in mining operations. Most ceramic materials, such as alumina and its compounds, are formed from fine powders, yielding a fine grained polycrystalline microstructure that is filled with light-scattering centers comparable to the wavelength of visible light . Thus, they are generally opaque materials, as opposed to transparent materials . Recent nanoscale (e.g. sol-gel ) technology has, however, made possible

17820-467: The years preceding World War II, infrared detection and communications devices prompted research into lead-sulfide and lead-selenide materials. These devices were used for detecting ships and aircraft, for infrared rangefinders, and for voice communication systems. The point-contact crystal detector became vital for microwave radio systems since available vacuum tube devices could not serve as detectors above about 4000 MHz; advanced radar systems relied on

17955-411: Was part of Emoji 1.0, published in 2015. As pictorial representations for emoji are platform-dependent, Emojipedia shows images of the hole symbol as depicted on various platforms. Solid The branch of physics that deals with solids is called solid-state physics , and is the main branch of condensed matter physics (which also includes liquids). Materials science is primarily concerned with

18090-637: Was sometimes poor. This was later explained by John Bardeen as due to the extreme "structure sensitive" behavior of semiconductors, whose properties change dramatically based on tiny amounts of impurities. Commercially pure materials of the 1920s containing varying proportions of trace contaminants produced differing experimental results. This spurred the development of improved material refining techniques, culminating in modern semiconductor refineries producing materials with parts-per-trillion purity. Devices using semiconductors were at first constructed based on empirical knowledge before semiconductor theory provided

18225-445: Was the observation that two shapes can be distinguished by examining their holes. For instance, a circle is not a disk because the circle has a hole through it while the disk is solid, and the ordinary sphere is not a circle because the sphere encloses a two-dimensional hole while the circle encloses a one-dimensional hole. Because a hole is immaterial, it is not immediately obvious how to define one or distinguish it from others. Another

#483516