amorphous
American Heritage Dictionary:
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a·mor·phous
(ə-môr'fəs) 
adj.
amorphousness a·mor'phous·ness n.
adj.
- Lacking definite form; shapeless. See synonyms at shapeless.
- Of no particular type; anomalous.
- Lacking organization; formless.
- Lacking distinct crystalline structure.
[From Greek amorphos : a-, without; see a-1 + morphē, shape.]
amorphously a·mor'phous·ly adv.amorphousness a·mor'phous·ness n.
McGraw-Hill Science & Technology Encyclopedia:
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Amorphous solid
A rigid material whose structure lacks crystalline periodicity; that is, the pattern of its constituent atoms or molecules does not repeat periodically in three dimensions. In the present terminology amorphous and noncrystalline are synonymous. A solid is distinguished from its other amorphous counterparts (liquids and gases) by its viscosity: a material is considered solid (rigid) if its shear viscosity exceeds 1014.6 poise (1013.6 Pa · s). See also Crystal; Viscosity.
Oxide glasses, generally the silicates, are the most familiar amorphous solids. However, as a state of matter, amorphous solids are much more widespread than just the oxide glasses. There are both organic (for example, polyethylene and some hard candies) and inorganic (for example, the silicates) amorphous solids. Glasses can be prepared which span a broad range of physical properties. Dielectrics (for example, SiO2) have very low electrical conductivity and are optically transparent, hard, and brittle. Semiconductors (for example, As2SeTe2) have intermediate electrical conductivities and are optically opaque and brittle. Metallic glasses have high electrical and thermal conductivities, have metallic luster, and are ductile and strong. See also Metallic glasses.
The obvious uses for amorphous solids are as window glass, container glass, and the glassy polymers (plastics). Less widely recognized but nevertheless established technological uses include the dielectrics and protective coatings used in integrated circuits, and the active element in photocopying by xerography, which depends for its action upon photoconduction in an amorphous semiconductor. In optical communications a highly transparent dielectric glass in the form of a fiber is used as the transmission medium.
It is the changes in short-range order (on the scale of a localized electron), rather than the loss of long-range order alone, that have a profound effect on the properties of amorphous semiconductors. For example, the difference in resistivity between the crystalline and amorphous states for dielectrics and metals is always less than an order of magnitude and is generally less than a factor of 3. For semiconductors, however, resistivity changes of 10 orders of magnitude between the crystalline and amorphous states are not uncommon, and accompanying changes in optical properties can also be large.
One class of amorphous semiconductors is the glassy chalcogenides, which contain one (or more) of the chalcogens sulfur, selenium, or tellurium as major constituents. These materials have application in switching and memory devices. Another group is the tetrahedrally bonded amorphous solids, such as amorphous silicon and germanium. These materials cannot be formed by quenching from the melt (that is, as glasses) but must be prepared by one of the deposition techniques mentioned above.
When amorphous silicon (or germanium) is prepared by evaporation, not all bonding requirements are satisfied, so a large number of dangling bonds are introduced into the material. These dangling bonds create states deep in the gap which limit the transport properties. The number of dangling bonds can be reduced by a thermal anneal below the crystallization temperature, but the number cannot be reduced sufficiently to permit doping. See also Semiconductor.
Roget's Thesaurus:
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amorphous
Antonyms by Answers.com:
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amorphous
adj
Definition: without definite shape, character
Antonyms: definite, distinct, distinctive, shaped, shapely
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Said of rock having no crystal structure.
Oxford Dictionary of Biochemistry:
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amorphous
- lacking definite shape or form.
- noncrystalline; devoid of real or apparent crystalline form.
| amorph, amoeboid, amoebapore | |
| amount of substance, amp, ampakine |
Mosby's Dental Dictionary:
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amorphous
(āmôr′fus, əmôr′fus)
adj
adj
A substance having no specific space lattice, the molecules being distributed at random.
Random House Word Menu:
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categories related to 'amorphous'
- Physical Properties and Changes - amorphous: (adj) describing a solid without crystalline structure
See crossword solutions for the clue Wikipedia on Answers.com:
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Amorphous solid
"Amorphous" redirects here. For amorphousness in computational systems, see amorphous computing. For amorphousness in science fiction, see amorphous creature. For amorphousness in set theory, see amorphous set.
| What is the nature of the glass transition between a fluid or regular solid and a glassy phase? What are the physical processes giving rise to the general properties of glasses? |  |
In condensed matter physics, an amorphous (from the Greek a, without, morphé, shape, form) or non-crystalline solid is a solid that lacks the long-range order characteristic of a crystal.
In part of the older literature, the term has been used synonymously with glass. Nowadays, "amorphous solid" is considered to be the overarching concept, and "glass" the more special case: A glass is an amorphous solid that transforms into a liquid upon heating through the glass transition.[1]
Other types of amorphous solids include gels, thin films, and nanostructured materials.
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Nanostructured materials
Even amorphous materials have some short-range order at the atomic length scale due to the nature of chemical bonding. Furthermore, in very small crystals a large fraction of the atoms are located at or near the surface of the crystal; relaxation of the surface and interfacial effects distort the atomic positions, decreasing the structural order. Amorphous form have higher dissolution rate compare to any other form.Even the most advanced structural characterization techniques, such as x-ray diffraction and transmission electron microscopy, have difficulty in distinguishing between amorphous and crystalline structures on these length scales.[citation needed]
Amorphous thin films
Amorphous phases are important constituents of thin films, which are solid layers of a few nm to some tens of µm thickness deposited upon an underlying substrate. So-called structure zone models were developed to describe the micro structure and ceramics of thin films as a function of the homologous temperature Th that is the ratio of deposition temperature over melting temperature.[2][3] According to these models, a necessary (but not sufficient) condition for the occurrence of amorphous phases is that Th has to be smaller than 0.3, that is the deposition temperature must be below 30% of the melting temperature. For higher values, the surface diffusion of deposited atomic species would allow for the formation of crystallites with long range atomic order.
Regarding their applications, amorphous metallic layers played an important role in the discussion of a suspected superconductivity in amorphous metals.[4] Today, optical coatings made from TiO2, SiO2, Ta2O5 etc. and combinations of them in most cases consist of amorphous phases of these compounds. Much research is carried out into thin amorphous films as a gas separating membrane layer.[5] The technologically most important thin amorphous film is probably represented by few nm thin SiO2 layers serving as isolator above the conducting channel of a metal-oxide semiconductor field-effect transistor (MOSFET). Also, hydrogenated amorphous silicon, a-Si:H in short, is of technical significance for thin film solar cells. In case of a-Si:H the missing long-range order between silicon atoms is partly induced by the presence by hydrogen in the percent range.
The occurrence of amorphous phases turned out as a phenomenon of particular interest for studying thin film growth. Remarkably, the growth of polycrystalline films is often used and preceded by an initial amorphous layer, the thickness of which may amount to only a few nm. The most investigated example is represented by thin multicrystalline silicon films, where such as the unoriented molecule.An initial amorphous layer was observed in many studies.[6] Wedge-shaped polycrystals were identified by transmission electron microscopy to grow out of the amorphous phase only after the latter has exceeded a certain thickness, the precise value of which depends on deposition temperature, background pressure and various other process parameters. The phenomenon has been interpreted in the framework of Ostwald's rule of stages[7] that predicts the formation of phases to proceed with increasing condensation time towards increasing stability.[4][6] Experimental studies of the phenomenon require a clearly defined state of the substrate surface and its contaminant density etc., upon which the thin film is deposited.
References
- ^ J. Zarzycki: Les verres et l'état vitreux. Paris: Masson 1982. English translation available.
- ^ B. A. Movchan and A. V. Demchishin (1969). "Study of the structure and properties of thick vacuum condensates of nickel, titanium, tungsten, aluminium oxide and zirconium dioxide". Phys. Met. Metallogr. 28: 83–90.
- ^ J.A. Thornton (1974). "Influence of apparatus geometry and deposition conditions on the structure and topography of thick sputtered coatings". J. Vac. Sci. Tech. 11 (4): 666–670. Bibcode 1974JVST...11..666T. doi:10.1116/1.1312732.
- ^ a b Buckel, W. (1961). "The influence of crystal bonds on film growth". Elektrische en Magnetische Eigenschappen van dunne Metallaagies. Leuven, Belgium.
- ^ R.M. de Vos, H. Verweij (1998). "High-Selectivity, High-Flux Silica Membranes for Gas Separation". Science 279 (5357): 1710–1. Bibcode 1998Sci...279.1710D. doi:10.1126/science.279.5357.1710. PMID 9497287.
- ^ a b M. Birkholz, B. Selle, W. Fuhs, S. Christiansen, H. P. Strunk, and R. Reich (2001). "Amorphous-crystalline phase transition during the growth of thin films: the case of microcrystalline silicon". Phys. Rev. B 64 (8): 085402. Bibcode 2001PhRvB..64h5402B. doi:10.1103/PhysRevB.64.085402. http://www.mariobirkholz.de/PRB2001.pdf.
- ^ W. Ostwald (1897). "Studien über die Umwandlung fester Körper". Z. Phys. Chem. 22: 289–330.
Further reading
- R. Zallen (1998). The Physics of Amorphous Solids. Wiley Interscience.
- S.R. Elliot (1990). The Physics of Amorphous Materials (2nd ed.). Longman.
- N. Cusack (1987). The Physics of Structurally Disordered Matter: An Introduction. IOP Publishing.
- N.H. March, R.A. Street, M.P. Tosi, Eds., (1985). Amorphous Solids and the Liquid State. Springer.
- D.A. Adler, B.B. Schwartz, M.C. Steele, Eds. (1985). Physical Properties of Amorphous Materials. Springer.
- A. Inoue, K. Hasimoto, Eds. (1985). Amorphous and Nanocrystalline Materials. Springer.
External links
- Journal of non-crystalline solids (Elsevier)
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Translations:
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Amorphous
Dansk (Danish)
adj. - amorf, uden bestemt form
Français (French)
adj. - amorphe, informe, sans forme
Deutsch (German)
adj. - amorph, formlos
Ελληνική (Greek)
adj. - άμορφος, στερούμενος μορφής, ασχημάτιστος, (χημ.) ακρυστάλλωτος, στερούμενος κρυσταλλικής δομής
Português (Portuguese)
adj. - amorfo
Русский (Russian)
аморфный, хаотичный
Español (Spanish)
adj. - amorfo
Svenska (Swedish)
adj. - amorf
中文（简体）(Chinese (Simplified))
无定形的, 无组织的, 非结晶形的, 乱七八糟的
中文（繁體）(Chinese (Traditional))
adj. - 無定形的, 無組織的, 非結晶形的, 亂七八糟的
日本語 (Japanese)
adj. - 無定形の, 組織のない, 非結晶の
العربيه (Arabic)
(صفه) غير متبلور, لا متبلور, لا شكل له, غير منظم
עברית (Hebrew)
adj. - נטול צורה, אמורפי
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