| 释义 |
impurity|ɪmˈpjʊərɪtɪ|
[a. OF. impurité (15th c. in Littré) = mod.F. impureté, ad. L. impūritās, f. impūrus: see impure a. and -ty.]
1. The quality or condition of being impure or of containing something foul or unclean; concr. foul or offensive matter, dirt.
1597A. M. tr. Guillemeau's Fr. Chirurg. 11 b/1 The matter, and all impuritye might therout have free passage. 1660F. Brooke tr. Le Blanc's Trav. 14 By reason of the impurity of the ayr, there is scarce any more then these two townes in the whole country. 1797T. Bewick Brit. Birds (1847) I. 156 Its entrails are shaken out, leaving only the body thus cleansed from all its impurities. 1806Med. Jrnl. XV. 547 Wipe out the little subjacent drop of pus, in order to guard against impurity. 1860Ruskin Mod. Paint. viii. i. §7 (1897) V. 175 Exclusive of animal decay, we can hardly arrive at a more absolute type of impurity than the mud or slime of a damp, over-trodden path, in the outskirts of a manufacturing town.
2. a. The state or condition of being morally impure; uncleanness, unchastity; defilement by sin.
1548Udall, etc. Erasm. Par. John xiii. 74 Excepte..the affeccions of his mynde be often purged from all impuritie of this worlde. a1610Healey Theophrastus (1636) 44 Impurity or beastlinesse is not hard to be defined. a1711Ken Div. Love Wks. (1838) 292 Let thy love, who art purity itself, create in me a perfect abhorrence of all impurity. 1874Sayce Compar. Philol. viii. 305 Sin and moral impurity are words which he would not understand.
b. With an and pl. That which is or makes impure morally; moral uncleanness or corruption.
c1450tr. De Imitatione iii. liii. 126 Come, heuenly swetnes, & make fle fro þi visage all maner impurite. 1593Shakes. Lucr. 854 But no perfection is so absolute, That some impuritie doth not pollute. 1639Du Verger tr. Camus' Admir. Events To Rdr. a ij b, Novels..full of impurities, impieties. 1790Beattie Moral Sc. i. ii. §6. 347 Let no visible or audible impurity..enter the apartment of a child.
3. a. The quality of containing some extraneous or foreign admixture, esp. of an inferior or baser kind; concr. foreign matter which detracts from the purity of any substance.
1605Timme Quersit. i. ix. 37 Saltes haue their corporall impurities. 1704Norris Ideal World ii. iii. 182 The metaphysical..impurity of thought is the..materiality of its object. 1750tr. Leonardus' Mirr. Stones 25 These virtues are varied..by reason of..the purity or impurity of the matter. 1799G. Smith Laboratory I. 142 Neal the copper..to prevent ashes or other impurities getting to it. 1842Parnell Chem. Anal. (1845) 19 The hydrochloric acid of commerce is always contaminated with impurities which render it quite unfit for general use as a reagent.
b. An impurity atom; esp. an atom of dopant present at a normal lattice site in an impurity semiconductor.
1931A. H. Wilson in Proc. R. Soc. A. CXXXIV. 279 Electrons on a foreign atom [in a semiconductor] do not take part directly in conduction. They must first be transferred by the effect of the lattice vibrations to an atom of the pure substance. In this case the main function of the impurities is to provide electrons for the upper unoccupied energy bands of the crystal, while acting as scatterers is only a secondary function. 1950W. Shockley Electrons & Holes in Semiconductors i. 12 The conductivity [of the silicon] arises from the presence of arsenic atoms which are termed ‘impurities’, even though added deliberately in the otherwise pure silicon. Ibid. 14 Impurities with a valence of five are called ‘donor impurities’ because they donate an excess electron to the crystal; those with a valence of three are called ‘acceptor impurities’, since they accept an electron from somewhere else in the crystal.., thus leaving a hole to conduct. 1952J. S. Koehler in W. Shockley et al. Imperfections in nearly Perfect Crystals vii. 206 The maximum value..of this force occurs when the impurity is two or three atomic distances from the dislocation. 1959R. A. Smith Semiconductors iii. 45 We must distinguish two types of impurity, substitutional impurities, which replace atoms of the host crystal on their lattice sites, and interstitial impurities which occupy positions in between the lattice sites. 1972F. J. Bailey Introd. Semiconductor Devices i. 21 By the addition of donor impurities to the silicon, large numbers of free electrons become available as current carriers.
4. Special Comb.: impurity atom, an atom that differs from the bulk of those present in a substance in being of a different element; impurity level, an energy level in a semiconductor that is due to an impurity atom and generally lies either just above the highest filled (valence) energy band (in the case of an acceptor) or just below the lowest empty (conduction) band (in the case of a donor); impurity scattering, scattering of current carriers by impurity atoms in a crystalline solid; impurity semiconductor, a semiconductor in which most of the carriers of electric current are electrons and holes from impurity atoms.
1939A. H. Wilson Semi-Conductors & Metals i. 3 The [electrical] resistance in a metal is caused by the scattering of the electrons by irregularities in the crystal; these irregularities may be due to the presence of impurity atoms and strains or to the temperature motion of the atoms. 1949Physical Rev. LXXV. 866/1 A substitutional impurity atom from the fifth group has one more valence electron than is required to fill the four valence bonds with neighboring silicon atoms. 1970W. Bollmann Crystal Defects iv. 37 The elementary point defects are vacancies and interstitial atoms, and also impurity atoms. 1972F. J. Bailey Introd. Semiconductor Devices i. 21 The doping level refers to the ratio of impurity atoms to silicon atoms. For a transistor this may typically be 1:108, i.e. one impurity atom for every hundred million silicon atoms. 1973Sci. Amer. Feb. 93/2 If other atoms, which can be referred to as impurity atoms if their concentration is relatively small, are introduced into a helium discharge, the random collisions in the discharge will mix the impurity atoms with the helium atoms.
1933R. H. Fowler in Proc. R. Soc. A. CXL. 507 Semi-conductors with impurity levels full of electrons at low temperatures owe their conductivity to the excitation of electrons to band 1 both from the impurity levels and from band 2, the former predominating at ordinary temperatures. 1964J. M. Ziman Princ. Theory Solids vi. 169 In a semiconductor there may also be scattering from a neutral impurity—where, for example, an electron has settled in a donor impurity level, or a hole is resident on an acceptor level.
1946Physical Rev. LXIX. 258/2 (heading) Theory of impurity scattering in semiconductors. 1965Lindmayer & Wrigley Fund. Semiconductor Devices vii. 259 In crystals used for devices, thermal scattering and impurity scattering dominate the collision processes.
1946Trans. Amer. Inst. Electr. Engin. Nov. 713/3 At low temperatures the conductivity of different samples varies by large factors. In this region silicon is said to be an impurity semiconductor. 1950W. Shockley Electrons & Holes in Semiconductors i. 12 (heading) Impurity semiconductors; donors and acceptors. |