Germanium and Silicon

This information comes from a quite remarkable book. Crystal Fire The Birth of the Information Age (Riordan and Hoddeson 1997), which maps out systematically but very accessibly the events that led to the discovery of the transistor and the aftermath of that episode. I know of no better aceount of the interloeking sequence of events that led to eventual success, and of the personal characteristics of the principal participants that played such a great part in the story. 

Two Bell Labs employees, Russell Ohl and George Southworth, were trying in the late 1930s to detect ultrahigh-frequency radio waves with vacuum tubes, and like Skinner on the other side of the Atlantic, had no success. So, Southworth, a radio ham since childhood, remembered his early silicon-and-cat s-whisker deviees and managed to retrieve some old ones from a seeondhand radio store. Just as they did 

Ohl demonstrated his results to Kelly early in 1940 Kelly felt that his instincts had been proved justified. Thereupon, Bell Labs had to focus single-mindedly on radar and on silicon rectifiers for this purpose. It was not till 1945 that basic research restarted. This was the year that the theorist John Bardeen was recruited, and he in due course became inseparable from Walter Brattain, an older man and a fine experimenter who had been with Bell since the late 1920s. William Shockley formed the third member of the triumvirate, though from an early stage he and Bardeen found themselves so mutually antagonistic that Bardeen was sometimes close to resignation. But tension can be productive as well as depressing. 

Some Bell employees had been trying to focus attention on germanium, the sister element to silicon, but had been discouraged, just as Wilson had been discouraged across the Atlantic a decade earlier. It was Bardeen who eventually focused on the merits of germanium and the research which led to the transistor in 1947 was centred on this element the fact that on germanium, surface oxide could be washed off with water played a major role. 

John Bardeen was a truly remarkable scientist, and also a very private, taciturn man. Pippard (1995) in his obituary of Bardeen, recounts how John returned home from the Bell Labs and walked into the kitchen to say We discovered something today to (his wife) Jane s regret, all she could find in reply to what proved a momentous statement was That s interesting, but I have to get dinner on the table .  

Intramolecular electron transfer occurs on irradiation of the stilbene derivative (319) in methylene chloride. Irradiation populates a charge transfer state that undergoes ,Z-isomerism and when methanol is added to the system not only is isomerism, observed but also the trisilanyl group in (319) is converted into the silane (320). The photochemical reactivity of the vinyldisi-lanes (321) has been examined and direct irradiation of (321a) in cyclohexane is reported to yield two products identified as the (2+2)-dimers (322) and (323). Irradiation of (321c) in cyclohexane with added methanol afforded the methoxy addition product (324). Both these results are in agreement with the intermediacy of silenes such as (325) and (326) in these experiments and 

SET induced cyclisations have been carried out on a series of non-conjugated dienes one component of which is a silyl ether. Irradiation in acetonitrile of dienes such as (330, R = H) using DCA as the electron accepting sensitiser results in the formation of the radical-cation of the diene which on cyclisation affords the cyclic ketone (331) in 25% yield. The reaction is solvent sensitive and in a mixture of acetonitrile/propan-2-ol yields three products which are identified as (331, 30%) and two minor products (332, 11%) and (333, 9%). The reaction is suggested to have some considerable synthetic potential and the effect of chain length and substituents on the reaction has been evaluated. Thus (334) is converted into (335, 11%) while (330, R = Me) affords an isomeric mixture of products (336). Other studies with silyl ether derivatives have examined the electron transfer-induced ring opening processes encountered with the cyclopropane derivatives (337).  

Poly(phenylsiloxanes) are formed on irradiation (CO2 laser) of liquid 1,3-diphenyldisiloxanes. The polymerisation is the result of extrusion of PhHSiO and its insertion into the disiloxane. Dimethoxydisilanes are formed on irradiation of the bicyclodienes (338) under electron-transfer conditions.  

The photophysical properties of a series on metalloles (339) have been 

The majority of the above systems involve a bimolecular substitution mechanism. Evidence for the transient existence of RaSi as an intermediate, and hence for a dissociative mechanism of substitution at silicon, has been sought but not obtained. Another variant on simple 8 2 substitution at 

Beronius, U. Isacsson, and A.-M. Nilsson, Acta Chem. Scand., 1970. 24, 189. 

Reactions of tetra-alkyltin compounds with mercury(n) iodide in 96% methanol, as with mercury(n) chloride, - are bimolecular. The variation of rate constant with alkyl group suggests an open S 2 transition state (5). Further evidence for this mechanism is provided by the variation of rate constant with solvent Y values for the particular case of the tetraethyltin compound reacting with mercury(n) chloride in a range of aqueous methanol mixtures. Solvent effects in this last series of reactions have been separated into initial state and transition state contributions by the determination of heats of solution and of transfer of the reactants. The effect of added lithium perchlorate on reaction rates for tetra-alkyltin compounds with mercury(ii) iodide again indicates bimolecular electrophilic 

Photochemical or radical reactions of tetra-alkyltin and analogous compounds have also been studied. Examples include the foregoing reaction of tetra-alkyltins with iodine monobromide under photochemical conditions and photolysis of the thermally stable compound 1,1-diphenyl-l-stannacyclohepta-2,6-diene (7). Reactions of tetra-alkyltin compounds 

Turning from the commonly studied tetrahedral compounds of tin to octahedral complexes, the kinetics of substitution at SnCl4py2 in nitrobenzene have been investigated. The activation parameters are reported to an astonishing precision the mechanism for solvolysis, as for chloride exchange, is said to be dissociative despite the very different rates reported for the two reactions. 

Several primary photoprocesses have been identified for MeSiHj excited by 147 nm radiation in the gas phase. Of these the processes represented in equations (3)-(5) have quantum yields greater than 0.2.  

For polysilanes in 2,3-dimethylbutane solution, photolysis induces a net disproportionation e.g. Si3Hg and Si7Hj from Si5Hi2)- If acetone is present then isopropoxysilanes [e.g. Me2CHOSiH(SiH3)2 from S13H8] are formed.The insertion of CCl into the Si-H bond of silanes has been studied.  

Upon photoexcitation, either in the gas phase or as liquid, SiMe4 undergoes mainly two primary photoprocesses (6) and (7) ( I) = 0.55 and 0.22, respectively). The Me2SiCH2, so formed, may react further by dimerization to give the l,l,3,3-tetramethyl-l,3-disilacyclobutane (4a). However in the gas phase the 

F Fischer, and D, Skrodzki, Z. Anorg. Allg. Cherts., 1980, 466, 29. 

may be conveniently generated by photolysis of o c/o-Si6Me,2, and this method has been used in the study of its insertion into Si—H bonds (e.g. in Me3SiH), Si—O bonds e.g. MejSiOEt)/ and into HCl. In low-temperature matrices it has been shown that SiMej may be converted by visible light (A = 450nm) into MeHSi = CH2. Annealing the photolysed matrix yields (4b). 

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Cheshnovsky O, Yang S H, Pettiette C L, Craycraft M J, Liu Y and Smalley R E 1987 Ultraviolet photoelectron spectroscopy of semiconductor clusters silicon and germanium Chem. Phys. Lett. 138 119... 

Seitz F 1995 Research on silicon and germanium in World War II Phys. Today January, p 22... 

Silicon and germanium readily react with even very dilute solutions of caustic alkali. Silicon is so sensitive to attack that it will dissolve when boiled with water which has been in contact with glass ... 

Areen silicon and germanium are ascribed to the d electron states silicon does not have 3 d electrons, whereas germanium does. Certain transitions (e.g. carbon /3 hn) do depend upon the d character of the electronic configuration in contrast to subsequent isitions. 

Silicon (3), which resembles metals in its chemical behavior, generally has a valence of +4. In a few compounds it exhibits a +2 valence, and in silicides it exists as a negative ion and largely violates the normal valency rules. Silicon, carbon, germanium, tin, and lead comprise the Group 14 (IVA) elements. Silicon and carbon form the carbide, SiC (see Carbides). Silicon and germanium are isomorphous and thus mutually soluble in all proportions. Neither tin nor lead reacts with silicon. Molten silicon is immiscible in both molten tin and molten lead. 

The technology of silicon and germanium production has developed rapidly, and knowledge of die self-diffusion properties of diese elements, and of impurity atoms has become reasonably accurate despite die experimental difficulties associated widi die measurements. These arise from die chemical affinity of diese elements for oxygen, and from die low values of die diffusion coefficients. 

It will be noted that because of the low self-diffusion coefficients the numerical values for representations of self-diffusion in silicon and germanium by Anhenius expressions are subject to considerable uncertainty. It does appear, however, that if this representation is used to average most of the experimental data the equations are for silicon... 

Covalent bonding appears in its pure form in diamond, silicon and germanium - all materials with large moduli (that of diamond is the highest known). It is the dominant... 

The semiconductor industry would have been impossible had not the process of zone refining been invented first. It is the standard way of producing ultrapure materials, both for research and for making silicon and germanium-based devices. 

Chain reactions of heterocycles with participation of silicon and germanium hydrides 98AG(E)3072. 

Materials in which there is a substantial difference in energy between occupied and vacant MOs are poor electron conductors. Diamond, where the gap between the filled valence band and the empty conduction band is 500 kj/mol, is an insulator. Silicon and germanium, where the gaps are 100 kj/mol and 60 kj/mol respectively, are semiconductors. 

Carbon is central to life and natural intelligence. Silicon and germanium are central to electronic technology and artificial intelligence (Fig. 14.28). The unique properties of Group 14/IV elements make both types of intelligence possible. The half-filled valence shell of these elements gives them special properties that straddle... 

This chapter is a review of the CVD of non-metallic elements and covers boron, silicon, and germanium. Silicon and germanium are borderline elements with metalloid characteristics. Both are important semiconductor materials, particularly silicon, which forms the backbone of the largest business in the world the electronic industry. All three materials are deposited by CVD on an industrial scale and a wide variety of CVD reactions are available. 

A bis(chelate) structure was found for the closely related germylene [MeC(NPr )2]2Ge, which was also made from GeCl2(dioxane) and 2 equivalents of the lithium amidinate (colorless crystals, 81%). The same synthetic approach was used to make bis(amidinato) metal dichlorides of silicon and germanium in high yields (83-95%). Rapid oxidative addition of chalcogen atom sources (styrene sulfide and elemental Se) to the germylene derivatives resulted in a series... 

Matrix Infrared Spectroscopy of Intermediates with Low Coordinated Carbon, Silicon and Germanium Atoms... 

Unstable compounds with double-bonded silicon and germanium atoms... 

The preference for formation of dihalocarbenes (but not the trihalomethyl radicals) upon thermolysis of trihalomethyl mercury, silicon and germanium derivatives seems to be a result of intermolecular coordination, of type [1], and of a thermodynamic preference for the carbene-forming pathway. The... 

Unstable compounds with double-bonded silicon and germanium atoms (silenes, silanones, germanones, germathiones)... 

Compounds containing double-bonded silicon and germanium atoms are the nearest analogues of olefins, ketones and thioketones. However, most of them are very unstable and highly reactive species. 

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