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Secondary Ion Mass Spectrometry
SECONDARY-ION MASS SPECTROMETRY (SIMS) is a technique used to analyze the composition of solid surfaces and thin films by sputtering the surface of the specimen with a focused primary ion beam and collecting and analyzing ejected secondary ions. The mass/charge ratios of these secondary ions are measured with a mass spectrometer to determine the elemental, isotopic, or molecular composition of the surface to a depth of 1 to 2 nm. Due to the large variation in ionization probabilities among different materials, SIMS is generally considered to be a qualitative technique, although quantitation is possible with the use of standards. SIMS is the most sensitive surface analysis technique, with elemental detection limits ranging from parts per million to parts per billion
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Electron Ionization
ELECTRON IONIZATION (EI, formerly known as ELECTRON IMPACT IONIZATION and ELECTRON BOMBARDMENT IONIZATION ) is an ionization method in which energetic electrons interact with solid or gas phase atoms or molecules to produce ions . EI was one of the first ionization techniques developed for mass spectrometry . However, this method is still a popular ionization technique. This technique is considered a hard (high fragmentation) ionization method, since it uses high energetic electrons to produce ions. This leads to extensive fragmentation, which can be helpful for structure determination of unknown compounds. EI is the most useful for organic compounds which have a molecular weight below 600. Also, several other thermally stable and volatile compounds in solid, liquid and gas states can be detected with the use of this technique when coupled with various separation methods
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Duoplasmatron
The DUOPLASMATRON is an ion source in which a cathode filament emits electrons into a vacuum chamber . A gas such as argon is introduced in very small quantities into the chamber, where it becomes charged or ionized through interactions with the free electrons from the cathode, forming a plasma . The plasma is then accelerated through a series of at least two highly charged grids, and becomes an ion beam, moving at fairly high speed from the aperture of the device. CONTENTS * 1 History * 2 References * 3 Further reading * 4 External links HISTORYThe duoplasmatron was invented by Manfred von Ardenne
Manfred von Ardenne
. Later development by Harold R. Kaufman resulted in the Kaufman Duoplasmatron which has been used for applications as diverse as semiconductor manufacture, and spacecraft propulsion . REFERENCES * ^ Bernhard Wolf (31 August 1995). Handbook of Ion Sources. CRC Press . pp. 47–. ISBN 978-0-8493-2502-1 . * ^ J. M
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Noble Gas
The NOBLE GASES (historically also the INERT GASES) make up a group of chemical elements with similar properties; under standard conditions , they are all odorless, colorless, monatomic gases with very low chemical reactivity . The six noble gases that occur naturally are helium (He) , neon (Ne) , argon (Ar) , krypton (Kr) , xenon (Xe) , and the radioactive radon (Rn) . Oganesson
Oganesson
(Og) is predicted to be a noble gas as well, but its chemistry has not yet been investigated. For the first six periods of the periodic table, the noble gases are exactly the members of GROUP 18 of the periodic table . Noble gases are typically highly unreactive except when under particular extreme conditions. The inertness of noble gases makes them very suitable in applications where reactions are not wanted
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Argon
ARGON is a chemical element with symbol AR and atomic number 18. It is in group 18 of the periodic table and is a noble gas . Argon
Argon
is the third-most abundant gas in the Earth\'s atmosphere , at 0.934% (9340 ppmv ). It is more than twice as abundant as water vapor (which averages about 4000 ppmv, but varies greatly), 23 times as abundant as carbon dioxide (400 ppmv), and more than 500 times as abundant as neon (18 ppmv). Argon
Argon
is the most abundant noble gas in Earth's crust, comprising 0.00015% of the crust. Nearly all of the argon in Earth's atmosphere is radiogenic argon-40 , derived from the decay of potassium-40 in the Earth's crust. In the universe, argon-36 is by far the most common argon isotope , being the preferred argon isotope produced by stellar nucleosynthesis in supernovas
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Xenon
XENON is a chemical element with symbol XE and atomic number 54. It is a colorless, dense, odorless noble gas found in the Earth\'s atmosphere in trace amounts. Although generally unreactive, xenon can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate , the first noble gas compound to be synthesized. Xenon is used in flash lamps and arc lamps , and as a general anesthetic . The first excimer laser design used a xenon dimer molecule (Xe2) as the lasing medium , and the earliest laser designs used xenon flash lamps as pumps . Xenon is used to search for hypothetical weakly interacting massive particles and as the propellant for ion thrusters in spacecraft. Naturally occurring xenon consists of eight stable isotopes . More than 40 unstable xenon isotopes undergo radioactive decay , and the isotope ratios of xenon are an important tool for studying the early history of the Solar System
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Adsorption
ADSORPTION is the adhesion of atoms , ions , or molecules from a gas, liquid, or dissolved solid to a surface . This process creates a film of the adsorbate on the surface of the adsorbent. This process differs from absorption , in which a fluid (the absorbate) is dissolved by or permeates a liquid or solid (the absorbent), respectively. Adsorption is a surface-based process while absorption involves the whole volume of the material. The term sorption encompasses both processes, while desorption is the reverse of it. Adsorption
Adsorption
is a surface phenomenon . IUPAC Definition Increase in the concentration of a substance at the interface of a condensed and a liquid or gaseous layer owing to the operation of surface forces. Note 1: Adsorption
Adsorption
of proteins is of great importance when a material is in contact with blood or body fluids
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Mean Free Path
In physics , the MEAN FREE PATH is the average distance traveled by a moving particle (such as an atom , a molecule , a photon ) between successive impacts (collisions), which modify its direction or energy or other particle properties. The following table lists some typical values for air at different pressures at room temperature
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Vacuum
VACUUM is space void of matter . The word stems from the Latin adjective _vacuus_ for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure . Physicists often discuss ideal test results that would occur in a _perfect_ vacuum, which they sometimes simply call "vacuum" or FREE SPACE, and use the term PARTIAL VACUUM to refer to an actual imperfect vacuum as one might have in a laboratory or in space . In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is lower than atmospheric pressure. The Latin term _IN VACUO_ is used to describe an object that is surrounded by a vacuum. The _quality_ of a partial vacuum refers to how closely it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum. For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%
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Pascal (unit)
The PASCAL (symbol: Pa) is the SI derived unit
SI derived unit
of pressure used to quantify internal pressure , stress , Young\'s modulus and ultimate tensile strength . It is defined as one newton per square metre . It is named after the French polymath Blaise Pascal
Blaise Pascal
. Common multiple units of the pascal are the hectopascal (1 hPa = 100 Pa) which is equal to one millibar , and the kilopascal (1 kPa = 1000 Pa) which is equal to one centibar. The unit of measurement called standard atmosphere (atm) is defined as 101325 Pa and approximates to the average pressure at sea-level at the latitude 45° N. Meteorological reports typically state atmospheric pressure in hectopascals
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Bar (unit)
The BAR is a metric unit of pressure , but is not approved as part of the International System of Units
International System of Units
(SI). It is defined as exactly equal to 100,000 Pa , which is slightly less than the current average atmospheric pressure on Earth at sea level . The bar and the millibar were introduced by the Norwegian meteorologist Vilhelm Bjerknes
Vilhelm Bjerknes
, who was a founder of the modern practice of weather forecasting . Use of the bar is deprecated by professional bodies in some fields. The International Bureau of Weights and Measures
International Bureau of Weights and Measures
(BIPM) lists the bar as one of the "non- SI units
SI units
should have the freedom to use", but declines to include it among the "Non- SI units
SI units
accepted for use with the SI"
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Torr
The TORR (symbol: Torr) is a unit of pressure based on an absolute scale , now defined as exactly 1/760 of a standard atmosphere . Thus one torr is exactly 7005101325000000000♠101325/760 pascals (~133.3 Pa). Historically, one torr was intended to be the same as one "millimetre of mercury ". However, subsequent redefinitions of the two units made them slightly different (by less than 6993150000000000000♠0.000015%). The torr is not part of the International System of Units
International System of Units
(SI), but it is often combined with the metric prefix milli to name one MILLITORR (mTorr) or 0.001 Torr. The unit was named after Evangelista Torricelli
Evangelista Torricelli
, an Italian physicist and mathematician who discovered the principle of the barometer in 1644
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Oxygen
OXYGEN is a chemical element with symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table and is a highly reactive nonmetal and oxidizing agent that readily forms oxides with most elements as well as other compounds . By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium . At standard temperature and pressure , two atoms of the element bind to form dioxygen , a colorless and odorless diatomic gas with the formula O 2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20.8% of the Earth\'s atmosphere . Additionally, as oxides the element makes up almost half of the Earth\'s crust
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Sulfur Hexafluoride
Esaflon Sulfur(VI) fluoride Sulfuric fluoride IDENTIFIERS CAS Number * 2551-62-4 Y 3D model ( JSmol
JSmol
) * Interactive image ChEBI
ChEBI
* CHEBI:30496 Y ChemSpider
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Faraday Cup
A FARADAY CUP is a metal (conductive) cup designed to catch charged particles in vacuum . The resulting current can be measured and used to determine the number of ions or electrons hitting the cup. The Faraday cup
Faraday cup
is named after Michael Faraday who first theorized ions around 1830. CONTENTS * 1 Principle of operation * 2 Faraday cup
Faraday cup
in plasma diagnostics * 3 Error sources * 4 See also * 5 References * 6 External links PRINCIPLE OF OPERATIONWhen a beam or packet of ions hits the metal it gains a small net charge while the ions are neutralized. The metal can then be discharged to measure a small current equivalent to the number of impinging ions. Essentially the Faraday cup
Faraday cup
is part of a circuit where ions are the charge carriers in vacuum and the faraday cup is the interface to the solid metal where electrons act as the charge carriers (as in most circuits)
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Melting Point
The MELTING POINT (or, rarely, LIQUEFACTION POINT) of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard pressure . When considered as the temperature of the reverse change from liquid to solid, it is referred to as the FREEZING POINT or CRYSTALLIZATION POINT. Because of the ability of some substances to supercool , the freezing point is not considered as a characteristic property of a substance. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is almost always "the principle of observing the disappearance rather than the formation of ice", that is, the melting point
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