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Field-emission Microscope
Field-emission microscopy (FEM) is an analytical technique used in materials science to investigate molecular surface structures and their electronic properties. Invented by Erwin Wilhelm Müller in 1936, the FEM was one of the first surface-analysis instruments that approached near-atomic resolution. Introduction Microscopy techniques are used to produce real-space magnified images of a surface showing what it looks like. In general, microscopy information concerns surface crystallography (i.e. how the atoms are arranged at the surface), surface morphology (i.e. the shape and size of topographic features making the surface), and surface composition (the elements and compounds the surface is composed of). Field-emission microscopy (FEM) was invented by Erwin Müller in 1936. In FEM, the phenomenon of field electron emission was used to obtain an image on the detector on the basis of the difference in work function of the various crystallographic planes on the surface. Design A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 was named after Michael Faraday who first theorized ions around 1830. Examples of devices which use Faraday cups include space probes (Voyager 1, & 2, Parker Solar Probe, etc.) and mass spectrometers. Principle of operation When a beam or packet of ions hits the metallic body of the cup, the apparatus gains a small net charge while the ions are neutralized as the charge is transferred to the metal walls. The metal part can then be discharged to measure a small current proportional to the number of impinging ions. The Faraday cup is essentially part of a circuit where ions are the charge carriers in vacuum and it is the interface to the solid metal where electrons act as the charge carriers (as in most circuits). By measuring the electric current (the number of electr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Microscopy Techniques
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron's mass is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value, expressed in units of the reduced Planck constant, . Being fermions, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: They can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Surface Analysis Methods
This is a list of analysis methods used in materials science. Analysis methods are listed by their acronym, if one exists. Symbols * μSR – see muon spin spectroscopy * χ – see magnetic susceptibility A * AAS – Atomic absorption spectroscopy * AED – Auger electron diffraction * AES – Auger electron spectroscopy * AFM – Atomic force microscopy * AFS – Atomic fluorescence spectroscopy * Analytical ultracentrifugation * APFIM – Atom probe field ion microscopy * APS – Appearance potential spectroscopy * ARPES – Angle resolved photoemission spectroscopy * ARUPS – Angle resolved ultraviolet photoemission spectroscopy * ATR – Attenuated total reflectance B * BET – BET surface area measurement (BET from Brunauer, Emmett, Teller) * BiFC – Bimolecular fluorescence complementation * BKD – Backscatter Kikuchi diffraction, see EBSD * BRET – Bioluminescence resonance energy transfer * BSED – Back scattered electron diffraction, see EBSD C * CA ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Field Ion Microscope
The Field ion microscope (FIM) was invented by Müller in 1951. It is a type of microscope that can be used to image the arrangement of atoms at the surface of a sharp metal tip. On October 11, 1955, Erwin Müller and his Ph.D. student, Kanwar Bahadur (Pennsylvania State University) observed individual tungsten atoms on the surface of a sharply pointed tungsten tip by cooling it to 21 K and employing helium as the imaging gas. Müller & Bahadur were the first persons to observe individual atoms directly. Introduction In FIM, a sharp (<50 nm tip radius) metal tip is produced and placed in an chamber, which is backfilled with an imaging gas such as or |
Electron Microscope
An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a higher resolving power than light microscopes and can reveal the structure of smaller objects. A scanning transmission electron microscope has achieved better than 50 pm resolution in annular dark-field imaging mode and magnifications of up to about 10,000,000× whereas most light microscopes are limited by diffraction to about 200 nm resolution and useful magnifications below 2000×. Electron microscopes use shaped magnetic fields to form electron optical lens systems that are analogous to the glass lenses of an optical light microscope. Electron microscopes are used to investigate the ultrastructure of a wide range of biological and inorganic specimens including microorganisms, cells, large molecules, biopsy samples, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atom Probe
The atom probe was introduced at th14th Field Emission Symposium in 1967by Erwin Wilhelm Müller and J. A. Panitz. It combined a field ion microscope with a mass spectrometer having a single particle detection capability and, for the first time, an instrument could “... determine the nature of one single atom seen on a metal surface and selected from neighboring atoms at the discretion of the observer”. Atom probes are unlike conventional optical or electron microscopes, in that the magnification effect comes from the magnification provided by a highly curved electric field, rather than by the manipulation of radiation paths. The method is destructive in nature removing ions from a sample surface in order to image and identify them, generating magnifications sufficient to observe individual atoms as they are removed from the sample surface. Through coupling of this magnification method with time of flight mass spectrometry, ions evaporated by application of electric pulses c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Refractory Metals
Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definition of which elements belong to this group differs. The most common definition includes five elements: two of the fifth period (niobium and molybdenum) and three of the sixth period (tantalum, tungsten, and rhenium). They all share some properties, including a melting point above 2000 °C and high hardness at room temperature. They are chemically inert and have a relatively high density. Their high melting points make powder metallurgy the method of choice for fabricating components from these metals. Some of their applications include tools to work metals at high temperatures, wire filaments, casting molds, and chemical reaction vessels in corrosive environments. Partly due to the high melting point, refractory metals are stable against creep deformation to very high temperatu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ultra-high Vacuum
Ultra-high vacuum (UHV) is the vacuum regime characterised by pressures lower than about . UHV conditions are created by pumping the gas out of a UHV chamber. At these low pressures the mean free path of a gas molecule is greater than approximately 40 km, so the gas is in free molecular flow, and gas molecules will collide with the chamber walls many times before colliding with each other. Almost all molecular interactions therefore take place on various surfaces in the chamber. UHV conditions are integral to scientific research. Surface science experiments often require a chemically clean sample surface with the absence of any unwanted adsorbates. Surface analysis tools such as X-ray photoelectron spectroscopy and low energy ion scattering require UHV conditions for the transmission of electron or ion beams. For the same reason, beam pipes in particle accelerators such as the Large Hadron Collider are kept at UHV. Overview Maintaining UHV conditions requires the use of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surface Diffusion
Surface diffusion is a general process involving the motion of adatoms, molecules, and atomic clusters ( adparticles) at solid material surfaces.Oura, Lifshits, Saranin, Zotov, and Katayama 2003, p. 325 The process can generally be thought of in terms of particles jumping between adjacent adsorption sites on a surface, as in figure 1. Just as in bulk diffusion, this motion is typically a thermally promoted process with rates increasing with increasing temperature. Many systems display diffusion behavior that deviates from the conventional model of nearest-neighbor jumps. Tunneling diffusion is a particularly interesting example of an unconventional mechanism wherein hydrogen has been shown to diffuse on clean metal surfaces via the quantum tunneling effect. Various analytical tools may be used to elucidate surface diffusion mechanisms and rates, the most important of which are field ion microscopy and scanning tunneling microscopy.Oura, Lifshits, Saranin, Zotov, and Katayama 2003, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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''). Adsorption is a '' surface phenomenon'', while absorption involves the whole volume of the material, although adsorption does often precede absorption. The term ''sorption'' encompasses both processes, while ''desorption'' is the reverse of it. Like surface tension, adsorption is a consequence of surface energy. In a bulk material, all the bonding requirements (be they ionic, covalent or metallic) of the constituent atoms of the material are fulfilled by other atoms in the material. However, atoms on the surface of the adsorbent are not wholly surrounded by other adsorbent atoms and therefore can attract adsorbates. The exact nature of the bon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fermi Velocity
The Fermi energy is a concept in quantum mechanics usually referring to the energy difference between the highest and lowest occupied single-particle states in a quantum system of non-interacting fermions at absolute zero temperature. In a Fermi gas, the lowest occupied state is taken to have zero kinetic energy, whereas in a metal, the lowest occupied state is typically taken to mean the bottom of the conduction band. The term "Fermi energy" is often used to refer to a different yet closely related concept, the Fermi level, Fermi ''level'' (also called electrochemical potential).The use of the term "Fermi energy" as synonymous with Fermi level (a.k.a. electrochemical potential) is widespread in semiconductor physics. For example:''Electronics (fundamentals And Applications)''by D. Chattopadhyay''Semiconductor Physics and Applications''by Balkanski and Wallis. There are a few key differences between the Fermi level and Fermi energy, at least as they are used in this article: * The F ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
