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Thermal Properties Of Nanostructures
As the devices continue to shrink further into the sub-100 nm range following the trend predicted by Moore’s law, the topic of thermal properties and transport in such nanoscale devices becomes increasingly important. Display of great potential by nanostructures for thermoelectric applications also motivates the studies of thermal transport in such devices. These fields, however, generate two contradictory demands: high thermal conductivity to deal with heating issues in sub-100 nm devices and low thermal conductivity for thermoelectric applications. These issues can be addressed with phonon engineering, once nanoscale thermal behaviors have been studied and understood. 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 prope ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Moore’s Law
Moore's law is the observation that the number of transistors in a dense integrated circuit (IC) doubles about every two years. Moore's law is an observation and projection of a historical trend. Rather than a law of physics, it is an empirical relationship linked to gains from experience in production. The observation is named after Gordon Moore, the co-founder of Fairchild Semiconductor and Intel (and former CEO of the latter), who in 1965 posited a doubling every year in the number of components per integrated circuit, and projected this rate of growth would continue for at least another decade. In 1975, looking forward to the next decade, he revised the forecast to doubling every two years, a compound annual growth rate (CAGR) of 41%. While Moore did not use empirical evidence in forecasting that the historical trend would continue, his prediction held since 1975 and has since become known as a "law". Moore's prediction has been used in the semiconductor industry to gu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interatomic Potential
Interatomic potentials are mathematical functions to calculate the potential energy of a system of atoms with given positions in space.M. P. Allen and D. J. Tildesley. Computer Simulation of Liquids. Oxford University Press, Oxford, England, 1989.R. Lesar. Introduction to Computational Materials Science. Cambridge University Press, 2013. Interatomic potentials are widely used as the physical basis of molecular mechanics and molecular dynamics simulations in computational chemistry, computational physics and computational materials science to explain and predict materials properties. Examples of quantitative properties and qualitative phenomena that are explored with interatomic potentials include lattice parameters, surface energies, interfacial energies, adsorption, cohesion, thermal expansion, and elastic and plastic material behavior, as well as chemical reactions.N. W. Ashcroft and N. D. Mermin. Solid State Physics.Saunders College, Philadelphia, 1976.Charles Kittel. Introduct ... [...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 flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs control the flow of 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 Austro-Hungarian physicist Julius Edgar Lilienfeld in 192 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thin Films
A thin film is a layer of material 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, LEDs, 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 batteries). It is also being ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Van Hove Singularity
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 ''n'' is an integer. (Positive ... [...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 between Fifth and Sixth Avenues. It plays a major role in developing and collecting modern art, and is often identified as one of the largest and most influential museums of modern art in the world. MoMA's collection offers an overview of modern and contemporary art, including works of architecture and design, drawing, painting, sculpture, photography, prints, illustrated and artist's books, film, and electronic media. The MoMA Library includes about 300,000 books and exhibition catalogs, more than 1,000 periodical titles, and more than 40,000 files of ephemera about individual artists and groups. The archives hold primary source material related to the history of modern and contemporary art. It attracted 1,160,686 visitors in 2021, an increase of 64% from 2020. It ranked 15th on the list of most visited art museums in the world in 2021.'' The Art Newspaper'' an ... [...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 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 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. This has generic implications for the o ... [...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 nanodevice ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Of Thermal Conductance
In physics, the thermal conductance quantum g_0 describes the rate at which heat is transported through a single ballistic phonon channel with temperature T. It is given by :g_ = \frac \approx (9.464\times10^ ^)\;T. The thermal conductance of any electrically insulating structure that exhibits ballistic phonon transport is a positive integer multiple of g_0. The thermal conductance quantum was first measured in 2000. These measurements employed suspended silicon nitride () nanostructures that exhibited a constant thermal conductance of 16 g_0 at temperatures below approximately 0.6 kelvin. Relation to the quantum of electrical conductance For ballistic electrical conductors, the electron contribution to the thermal conductance is also quantized as a result of the electrical conductance quantum and the 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 co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basal Plane
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter. The smallest group of particles in the material that constitutes this repeating pattern is the unit cell of the structure. The unit cell completely reflects the symmetry and structure of the entire crystal, which is built up by repetitive translation of the unit cell along its principal axes. The translation vectors define the nodes of the Bravais lattice. The lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called ''lattice parameters'' or ''cell parameters''. The symmetry properties of the crystal are described by the concept of space groups. All possible symmetric arrangements of particles ... [...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^2\mathrm^, where ''k''B is Boltzmann's 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 e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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