Electrons in glasses

Refs. [i] Mott NF, Gurney RW (1948) Electronic processes in ionic crystals. Clarendon Press, Oxford [ii] Mott NF (1949) Proc Phys Soc London A62 416 [iii] Mott NF (reprinted 1992) Electrons in glass. In Lundqvist S (ed) Nobel lectures, physics 1971-1980. World Scientific Publishing Co., Singapore [iv] Mott NF, Davis EA (1979) Electronic processes in noncrystalline materials. Clarendon Press, Oxford... 

Low temperatures that allowed one to trap long-lived species and electrons in glasses could be studied using spin resonance techniques. ... 

There exist no free or Fermi electrons in glass, which is considered to be a semiconductor with a very low specific conductivity (10 to 10 ohm cm. i). The question then arises Where do the secondary electrons originate in ozonizer tubes when the discharge enters the self-maintained region ... 

Initially, DADC polymers were used in military aircraft for windows of fuel and deicer-fluid gauges and in glass-fiber laminates for wing reinforcements of B-17 bombers. Usage in impact-resistant, lightweight eyewear lenses has grown rapidly and is now the principal appHcation. Other uses include safety shields, filters for photographic and electronic equipment, transparent enclosures, equipment for office, laboratory, and hospital use, and for detection of nuclear radiation. 

Small amounts of TAIC together with DAP have been used to cure unsaturated polyesters in glass-reinforced thermo sets (131). It has been used with polyfunctional methacrylate esters in anaerobic adhesives (132). TAIC and vinyl acetate are copolymerized in aqueous suspension, and vinyl alcohol copolymer gels are made from the products (133). Electron cure of poly(ethylene terephthalate) moldings containing TAIC improves heat resistance and transparency (134). 

The 215-nm band may be intrinsic to sihca. This band can be produced in Coming Code 7940 glass by long-term x-ray irradiation (210). This band is attributed to an E center, which may also be observed in irradiated a-quart2. Stmcturahy, the E center is assumed to be a pyramidal SiO unit having an unpaired electron in the dangling orbital of Si (207). 

Semiconductivity in oxide glasses involves polarons. An electron in a localized state distorts its surroundings to some extent, and this combination of the electron plus its distortion is called a polaron. As the electron moves, the distortion moves with it through the lattice. In oxide glasses the polarons are very localized, because of substantial electrostatic interactions between the electrons and the lattice. Conduction is assisted by electron-phonon coupling, ie, the lattice vibrations help transfer the charge carriers from one site to another. The polarons are said to "hop" between sites. 

The dielectric constant is a measure of the ease with which charged species in a material can be displaced to form dipoles. There are four primary mechanisms of polarization in glasses (13) electronic, atomic, orientational, and interfacial polarization. Electronic polarization arises from the displacement of electron clouds and is important at optical (ultraviolet) frequencies. At optical frequencies, the dielectric constant of a glass is related to the refractive index k =. Atomic polarization occurs at infrared frequencies and involves the displacement of positive and negative ions. 

These excitations are widely used to characterize electronic states and excitations, to test theories about electronic phenomena, and to delineate the nature of local sites in glasses, disordered soHds, intercalates, etc. However, this aspect of changing color with pressure is so general as to be hardly satisfactory for defining piezochromism. 

The colors obtained depend primarily on the oxidation state and coordination number of the coloring ion (3). Table 1 Hsts the solution colors of several ions in glass. AH of these ions are transition metals some rare-earth ions show similar effects. The electronic transitions within the partially filled d andy shells of these ions are of such frequency that they fall in that narrow band of frequencies from 400 to 700 nm, which constitutes the visible spectmm (4). Hence, they are suitable for producing color (qv). 

After adequate analitical prepai ation according to standai d EPA method 608 samples were analysed gas chromatographic on a gas chromatograph 8500 Perkin Elmer, in glass and capilar columns using a capture electron detector and mass spectrometry, temperature program. 

Suppose a long thin metal wire is connected by a pair of thick wires between the terminals of a battery. This is a basic electric circuit as shown in Figure 3a. In all metals, each atom permits roughly one of the outer electrons to move quite freely in the material these are called the free electrons. In contrast, all electrons of the atoms of good electrical insulators, such as glass, rubber, and air, are tightly bound to the atoms and are not free to move through the body of... 

Table 6.4 gives the radiation yields of stabilized electrons in some selected glasses at 77 K with about 15% uncertainty. A detailed discussion of these yields has been given by Kevan (1974). Hase et al. (1972a) observed et spectrum in ethanol at 4 K with a peak at 1500 nm on quick warming to 77 K, the spectrum relaxed with the same peak in the visible as that of es in liquid ethanol. Hase et al. (1972b) also observed et spectrum at 4 K in 3MP with no clear maximum. On quick warming to 77 K, the spectrum relaxed with a clear maximum at -1700 nm. 

TABLE 6.4 Radiation Yields (G Values) of Stabilized Electrons in Organic Glasses Under /-Irradiation at 77 K... 

Related ion-radicals have been prepared photochemically in rigid media by Lewis.146 When tetramethylbenzidine is exposed to ultraviolet light in a rigid medium, an electron is ejected as in the production of color centers in glass. 

Photolysis of vinyldiazomethane in an organic glass at 6 K leads to vinylcarbene in its triplet ground state,14,56,57 which — as is indicated by the ESR spectra — forms a pair of the s-cis and s-trans isomer. The delocalization of one unpaired electron in the rr-system is similar to that of the allyl radical, while the other unpaired electron is localized in a sp2-orbital at the carbenic C atom (see formula T-33 ).58... 

Measuring body temperature is important for the detection of disease and assessment of the response to treatments. The first thermometer was developed by Galileo in 1603. Thermometers for measuring body temperature have been in use since about 1870. The first measurements taken were axillary, and later oral and rectal measuring methods were introduced. The working principle of those thermometers, the expansion of matter by temperature increase, is still used for body temperature measurement in mercury-in-glass thermometers. Electronic thermo-... 

The infrared ear thermometer is a major step in the development of thermometers for body temperature measurements. Compared to traditional mercury-in-glass or electronic contact thermometers it is more convenient, safer and faster. During its 10 years in the consumer market it has been gradually replacing conventional thermometers, especially for temperature measuring in children. 

Domestic consumption of selenium in 1981 exceeded 453,000 kg. About 50% was used in electronic and copier components, 22% in glass manufacturing, 20% in chemicals and pigments, and 8% miscellaneous (Cleveland et al. 1993). In 1987, world production of selenium was about 1.4 million kg (USPHS 1996). In 1986, 46% of the global selenium produced was used in the semiconductor and photoelectric industries 27% in the glass industry to counter coloration impurities from iron 14% in pigments and 13% in medicine, in antidandruff shampoos, as catalysts in... 

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