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Thermal Properties Of Nanostructures
The transport of heat in solids involves both electrons and vibrations of the atoms (phonons). When the solid is perfectly ordered over hundreds of thousands of atoms, this transport obeys established physics. However, when the size of the ordered regions decreases new physics can arise, thermal transport in nanostructures. In some cases heat transport is more effective, in others it is not. The effect of the limited length of structure In general two carrier types can contribute to thermal conductivity - electrons and phonons. In nanostructures phonons usually dominate and the phonon properties of the structure become of a particular importance for thermal conductivity. These phonon properties include: phonon group velocity, phonon scattering mechanisms, heat capacity, Grüneisen parameter. Unlike bulk materials, nanoscale devices have thermal properties which are complicated by boundary effects due to small size. It has been shown that in some cases phonon-boundary scattering ef ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phonons
A phonon is a collective excitation in a periodic, Elasticity (physics), elastic arrangement of atoms or molecules in condensed matter physics, condensed matter, specifically in solids and some liquids. In the context of optically trapped objects, the quantized vibration mode can be defined as phonons as long as the modal wavelength of the oscillation is smaller than the size of the object. A type of quasiparticle in physics, a phonon is an excited state in the quantum mechanical Quantization (physics), quantization of the mode of vibration, modes of vibrations for elastic structures of interacting particles. Phonons can be thought of as quantized sound waves, similar to photons as quantized light waves. The study of phonons is an important part of condensed matter physics. They play a major role in many of the physical properties of condensed matter systems, such as thermal conductivity and electrical conductivity, as well as in models of neutron scattering and related effects. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wiedemann–Franz Law
In physics, the Wiedemann–Franz law states that the ratio of the electronic contribution of the thermal conductivity (''κ'') to the electrical conductivity (''σ'') of a metal is proportional to the temperature (''T''). : \frac \kappa \sigma = LT Theoretically, the proportionality constant ''L'', known as the Lorenz number, is equal to : L = \frac \kappa = \frac 3 \left(\frac e \right)^2 = 2.44\times 10^\;\mathrm^, where ''k''B is the Boltzmann constant and ''e'' is the elementary charge. This empirical law is named after Gustav Wiedemann and Rudolph Franz, who in 1853 reported that ''κ''/''σ'' has approximately the same value for different metals at the same temperature. The proportionality of ''κ''/''σ'' with temperature was discovered by Ludvig Lorenz in 1872. Derivation Qualitatively, this relationship is based upon the fact that the heat and electrical transport both involve the free electrons in the metal. The mathematical expre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Suspensions
In chemistry, a suspension is a heterogeneous mixture of a fluid that contains solid particles sufficiently large for sedimentation. The particles may be visible to the naked eye, usually must be larger than one micrometer, and will eventually settle, although the mixture is only classified as a suspension when and while the particles have not settled out. Properties A suspension is a heterogeneous mixture in which the solid particles do not dissolve, but get suspended throughout the bulk of the solvent, left floating around freely in the medium. The internal phase (solid) is dispersed throughout the external phase (fluid) through mechanical agitation, with the use of certain excipients or suspending agents. An example of a suspension would be sand in water. The suspended particles are visible under a microscope and will settle over time if left undisturbed. This distinguishes a suspension from a colloid, in which the colloid particles are smaller and do not settle. Colloids ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aluminium
Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has a great affinity towards oxygen, passivation (chemistry), forming a protective layer of aluminium oxide, oxide on the surface when exposed to air. It visually resembles silver, both in its color and in its great ability to reflect light. It is soft, magnetism, nonmagnetic, and ductility, ductile. It has one stable isotope, 27Al, which is highly abundant, making aluminium the abundance of the chemical elements, 12th-most abundant element in the universe. The radioactive decay, radioactivity of aluminium-26, 26Al leads to it being used in radiometric dating. Chemically, aluminium is a post-transition metal in the boron group; as is common for the group, aluminium forms compounds primarily in the +3 oxidation state. The aluminium cation Al3+ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silicon
Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a member of group 14 in the periodic table: carbon is above it; and germanium, tin, lead, and flerovium are below it. It is relatively unreactive. Silicon is a significant element that is essential for several physiological and metabolic processes in plants. Silicon is widely regarded as the predominant semiconductor material due to its versatile applications in various electrical devices such as transistors, solar cells, integrated circuits, and others. These may be due to its significant band gap, expansive optical transmission range, extensive absorption spectrum, surface roughening, and effective anti-reflection coating. Because of its high chemical affinity for oxygen, it was not until 1823 that Jöns Jakob Berzelius was first able to p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Field-effect Transistor
The field-effect transistor (FET) is a type of transistor that uses an electric field to control the current through a semiconductor. It comes in two types: junction FET (JFET) and metal-oxide-semiconductor FET (MOSFET). FETs have three terminals: ''source'', ''gate'', and ''drain''. FETs control the current by the application of a voltage to the gate, which in turn alters the conductivity between the drain and source. FETs are also known as unipolar transistors since they involve single-carrier-type operation. That is, FETs use either electrons (n-channel) or holes (p-channel) as charge carriers in their operation, but not both. Many different types of field effect transistors exist. Field effect transistors generally display very high input impedance at low frequencies. The most widely used field-effect transistor is the MOSFET (metal–oxide–semiconductor field-effect transistor). History The concept of a field-effect transistor (FET) was first patented by the Austr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thin Films
A thin film is a layer of materials ranging from fractions of a nanometer ( monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many applications. A familiar example is the household mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors, while more recently the metal layer is deposited using techniques such as sputtering. Advances in thin film deposition techniques during the 20th century have enabled a wide range of technological breakthroughs in areas such as magnetic recording media, electronic semiconductor devices, integrated passive devices, light-emitting diodes, optical coatings (such as antireflective coatings), hard coatings on cutting tools, and for both energy generation (e.g. thin-film solar cells) and storage ( thin-film ba ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Van Hove Singularity
In condensed matter physics, a Van Hove singularity is a singularity (non-smooth point) in the density of states (DOS) of a crystalline solid. The wavevectors at which Van Hove singularities occur are often referred to as critical points of the Brillouin zone. For three-dimensional crystals, they take the form of kinks (where the density of states is not differentiable). The most common application of the Van Hove singularity concept comes in the analysis of optical absorption spectra. The occurrence of such singularities was first analyzed by the Belgian physicist Léon Van Hove in 1953 for the case of phonon densities of states. Theory Consider a one-dimensional lattice of ''N'' particle sites, with each particle site separated by distance ''a'', for a total length of ''L'' = ''Na''. Instead of assuming that the waves in this one-dimensional box are standing waves, it is more convenient to adopt periodic boundary conditions: :k=\frac=n\frac where \lambda is wavelength, and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotopically Pure Diamond
An isotopical pure diamond is a type of diamond that is composed entirely of one isotope of carbon. Isotopically pure diamonds have been manufactured from either the more common carbon isotope with mass number 12 (abbreviated as 12C) or the less common 13C isotope. Compared to natural diamonds that are composed of a mixture of 12C and 13C isotopes, isotopically pure diamonds possess improved characteristics such as increased thermal conductivity. Thermal conductivity of diamonds is at a minimum when 12C and 13C are in a ratio of 1:1 and reaches a maximum when the composition is 100% 12C or 100% 13C. Manufacture The isotopes of carbon can be separated in the form of carbon dioxide gas by cascaded chemical exchange reactions with amine carbamate. Such CO2 can be converted to methane and from there to isotopically pure synthetic diamonds. Isotopically enriched diamonds have been synthesized by application of chemical vapor deposition followed by high pressure. Types Carbon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Museum Of Modern Art
The Museum of Modern Art (MoMA) is an art museum located in Midtown Manhattan, New York City, on 53rd Street (Manhattan), 53rd Street between Fifth Avenue, Fifth and Sixth Avenues. MoMA's collection spans the late 19th century to the present, and includes over 200,000 works of architecture and design, drawing, painting, sculpture, photography, screen printing, prints, book illustration, illustrated and artist's books, film, as well as electronic media. The institution was conceived in 1929 by Abby Aldrich Rockefeller, Lillie P. Bliss, and Mary Quinn Sullivan. Initially located in the Crown Building (Manhattan), Heckscher Building on Fifth Avenue, it opened just days after the Wall Street Crash of 1929, Wall Street Crash. The museum was led by Anson Goodyear, A. Conger Goodyear as president and Abby Rockefeller as treasurer, with Alfred H. Barr Jr., Alfred H. Barr Jr. as its first director. Under Barr's leadership, the museum's collection rapidly expanded, beginning with an inaug ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Michael Roukes
Michael Lee Roukes is an American experimental physicist, nanoscientist, and the Frank J. Roshek Professor of Physics, Applied Physics, and Bioengineering at the California Institute of Technology (Caltech). Education Roukes earned Bachelor of Arts, B.A. degrees in physics and chemistry (double majors) in 1978 at University of California, Santa Cruz, with highest honors in both majors, he received his Doctor of Philosophy, Ph.D. in physics from Cornell University in 1985. His graduate advisor at Cornell was Nobel Laureate, Robert Coleman Richardson. Roukes' thesis research at Cornell elucidated the electron–phonon bottleneck at ultra low temperatures; the hot electron effect that is now recapitulated in texts on solid state transport physics. Stated in simplest terms, when electrons carry current in normal conductors, they heat up. At low temperatures and, now, in nanoscale devices at ordinary temperatures, their ability to dissipate this heat can be significantly impaired. T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Keith Schwab
Keith Schwab (born May 18, 1968) is an American physicist and a professor of applied physics at the California Institute of Technology (Caltech). His contributions are in the areas of nanoscience, ultra-low temperature physics, and quantum effects. Biography After attending St. Louis University High, Schwab received a Bachelor of Arts in physics from the University of Chicago in 1990 and a Ph.D. in physics from University of California, Berkeley in 1996. He wrote a dissertation "Experiments with Superfluid Oscillators" under advisor Richard Packard, where he demonstrated an ultra-sensitive gyroscope based on the quantum properties of superfluid helium. He joined Caltech in 1996 as a Sherman Fairchild Distinguished Postdoctoral Scholar In the group of Professor Michael Roukes. There he made the first observation of the quantum of thermal conductance which is the quantum mechanical limit for energy flow through single quantum channels An electron micrograph of the nanodevic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
