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Disambiguation: This page refers to the sub-discipline of condensed matter physics, not the branch of meterology concerned with the study of weather systems smaller than synoptic scale systems. Mesoscopic physics is a sub-discipline of condensed matter physics which deals with materials of an intermediate length scale. The scale of such materials can be described as being between the size of a quantity of atoms (such as a molecule) and of materials measuring micrometres. The lower limit can also be defined as being the size of individual atoms. At the micrometre level are bulk materials. Both mesoscopic and macroscopic objects contain a large number of atoms. Whereas average properties derived from its constituent materials describe macroscopic objects, as they usually obey the laws of classical mechanics, a mesoscopic object, by contrast, is affected by fluctuations around the average, and is subject to quantum mechanics.〔Sci-Tech Dictionary. McGraw-Hill Dictionary of Scientific and Technical Terms. 2003. McGraw-Hill Companies, Inc〕〔 In other words, a macroscopic device, when scaled down to a meso-size, starts revealing quantum mechanical properties. For example, at the macroscopic level the conductance of a wire increases continuously with its diameter. However, at the mesoscopic level, the wire's conductance is quantized - the increases occur in discrete, or individual, whole steps. During research, mesoscopic devices are constructed, measured, and observed experimentally and theoretically in order to advance understanding of the physics of insulators, semiconductors, metals, and superconductors. The applied science of mesoscopic physics deals with the potential of building nano-devices. ''Mesoscopic physics'' also addresses fundamental practical problems which occur when a macroscopic object is miniaturized, as with the miniaturization of transistors in semiconductor electronics. The physical properties of materials change as their size approaches the nanoscale, where the percentage of atoms at the surface of the material becomes significant. For bulk materials larger than one micrometre, the percentage of atoms at the surface is insignificant in relation to the number of atoms in the entire material. This sub-discipline has dealt primarily with artificial structures of metal or semiconducting material which have been fabricated by the techniques employed for producing microelectronic circuits.〔〔 There is no rigid definition for ''mesoscopic physics'', but the systems studied are normally in the range of 100 nm (the size of a typical virus) to 1 000 nm (the size of a typical bacterium). 100 nanometers is the approximate upper limit for a nanoparticle. Thus mesoscopic physics has a close connection to the fields of nanofabrication and nanotechnology. Devices used in nanotechnology are examples of mesoscopic systems. Three categories of new phenomena in such systems are interference effects, quantum confinement effects, and charging effects.〔〔"Mesoscopic physics." McGraw-Hill Encyclopedia of Science and Technology. The McGraw-Hill Companies, Inc., 2005. Answers.com 25 Jan 2010. http://www.answers.com/topic/mesoscopic-physics-1〕 ==Quantum confinement effects== Quantum confinement effects describe electrons in terms of energy levels, potential well, valence bands, conduction band, and electron energy band gaps. Electrons in bulk dielectric material (larger than 10 nm) can be described by energy bands or electron energy levels. Electrons exist at different energy levels or bands. In bulk materials these energy levels are described as continuous because the difference in energy is negligible. As electrons stabilise at various energy levels, most vibrate in valence bands below a forbidden energy level, named the band gap. This region is an energy range in where no electron states exist. A smaller amount have energy levels above the forbidden gap, and this is the conduction band. The quantum confinement effect can be observed once the diameter of the particle is of the same magnitude as the wavelength of the electron's wave function.〔(“Quantum Confinement IV” ) ISBN 1-56677-352-0〕 When materials are this small, their electronic and optical properties deviate substantially from those of bulk materials.〔(“Quantum Theory of the Optical and Electronic Properties of Semiconductor” ) ISBN 981-02-2002-2〕 As the material is miniaturized towards nano-scale the confining dimension naturally decreases. But the characteristics are no longer averaged by bulk, and hence continuous, but are at the level of quanta and thus discrete. In other words, the energy spectrum becomes discrete, measured as quanta, rather than continuous as in bulk materials. As a result, the bandgap asserts itself: there is a small and finite separation between energy levels. This situation of discrete energy levels is called ''quantum confinement''. In addition, quantum confinement effects consist of isolated islands of electrons that may be formed at the patterned interface between two different semiconducting materials. The electrons typically are confined to disk-shaped regions termed quantum dots. The confinement of the electrons in these systems changes their interaction with electromagnetic radiation significantly, as noted above.〔 Because the electron energy levels of quantum dots are discrete rather than continuous, the addition or subtraction of just a few atoms to the quantum dot has the effect of altering the boundaries of the bandgap. Changing the geometry of the surface of the quantum dot also changes the bandgap energy, owing again to the small size of the dot, and the effects of quantum confinement.〔(Quantum dots ). 2008 Evident Technologies, Inc.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mesoscopic physics」の詳細全文を読む スポンサード リンク
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