Ether-like Si-Ge hydrides for applications in synthesis of nanostructured semiconductors and dielectrics.
Hydrolysis reactions of silyl-germyl triflates are used to produce ether-like Si-Ge hydride compounds including H(3)SiOSiH(3) and the previously unknown O(SiH(2)GeH(3))(2). The structural, energetic and vibrational properties of the latter were investigated by experimental and quantum chemical simulation methods. A combined Raman, infrared and theoretical analysis indicated that the compound consists of an equal mixture of linear and gauche isomers in analogy to the butane-like H(3)GeSiH(2)SiH(2)GeH(3) with an exceedingly small torsional barrier of approximately 0.2 kcal mol(-1). This is also corroborated by thermochemistry simulations which indicate that the energy difference between the isomers is less than 1 kcal mol(-1). Proof-of-principle depositions of O(SiH(2)GeH(3))(2) at 500 degrees C on Si(100) yielded nearly stoichiometric Si(2)Ge(2)O materials, closely reflecting the composition of the molecular core. A complete characterization of the film by RBS, XTEM, Raman and IR ellipsometry revealed the presence of Si(0.30)Ge(0.70) quantum dots embedded within an amorphous matrix of Si-Ge-O suboxide, as required for the fabrication of high performance nonvolatile memory devices. The use of readily available starting materials coupled with facile purification and high yields also makes the above molecular approach an attractive synthesis route to H(3)SiOSiH(3) with industrial applications in the formation of Si-O-N high-k gate materials in high-mobility SiGe based transistors.
Synthetic pathways to disilylmethane, H3SiCH2SiH3, and methyldisilane, CH3SiH2SiH3
Disilylmethane is available in a four-step synthesis starting with phenylsilane. This is converted into chlorophenylsilane by HCl/AlCl3. The reaction of PhSiH2Cl and dibromomethane with magnesium in tetrahydrofuran affords bis(phenylsilyl)-methane, which yields bis(bromosilyl)methane by treatment with anhydrous hydrogen bromide. (BrH2Si)2CH2 is converted into disilylmethane by reduction with LiAlH4 in a two-phase system using a phase-transfer catalyst. - Methyldisilane is available by alkylation of a monohalodisilane, XSi2H5 (X Cl, Br), with methyllithium in a high-boiling ether or by silylation of bromomethylsilane with silylpotassium. Due to secondary silylation reactions the overall yields of methyldisilane are low in all cases.
The Poet, The Critic, and the Moralist: Horace, Epistles 1.19
I begin by quoting from two valuable recent works on Horace. Professor Brink in his Horace on Poetry (1964) writes: ‘The centre of the short piece lies in lines 21—34. Readers, among them critics and poets, had denied one aspect of the Odes which was surely above criticism—the striking originality of these poems. Horace's defence turns on the question of originality’ (p. 180) and ‘Epistle 19 is unique in that it alone among the literary satires and letters reiterates Horace's claim to be the Latin fidicen’ (p. 182). And Dr. McGann in his Studies in Horace's First Book of Epistles (Collection Latomus 100: 1969): ‘In Ep. 19... as in the literary satires, Horace is a practising poet or at least a very recently practising one, engaged in defending himself against hostile criticism’ (p. 40) and ‘As the only epistle concerned exclusively with literary matters, the nineteenth stands apart’ (p. 82).