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The surface morphology of vicinal (100) single-crystal diamond surfaces homoepitaxially grown in a microwave plasma-assisted chemical vapor deposition (MPACVD) reactor is studied. High-pressure and high-temperature (HPHT) single-crystal diamond substrates produced by different vendors are used as substrates. Prior to the CVD growth, substrates were mechanically polished and etched in a separate inductively coupled plasma/reactive ion etching (ICP/RIE) tool using an Ar/Cl 2 gas mixture. The impact of (a) ICP etching regime of the HPHT substrate, (b) substrate polishing, and (c) the HPHT substrate misorientation (off-axis) vicinal angle on the surface morphology is examined. It was found that the ICP etching removes polishing-induced defects in the bulk and also removes diamond particles which are left on the surface of single-crystalline diamond after polishing. The morphology of the surface of the homoepitaxial CVD diamond grown on a substrate, which is free of polishing defects, depends not only on the parameters of the growth process (substrate temperature, composition of the gas mixture, pressure, etc.), but also on the value and direction of the off-axis angle.

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The reactions of bis(borohydride) complexes [(RN=)Mo(BH4)2(PMe3)2] (4: R = 2,6-Me2C6H3; 5: R = 2,6-iPr2C6H3) with hydrosilanes afford new silyl hydride derivatives [(RN=)Mo(H)(SiR'3)(PMe3)3] (3: R = Ar, R'3 = H2Ph; 8: R = Ar', R'3 = H2Ph; 9: R = Ar, R'3 = (OEt)3; 10: R = Ar, R'3 = HMePh). These compounds can also be conveniently prepared by reacting [(RN=)Mo(H)(Cl)(PMe3)3] with one equivalent of LiBH4 in the presence of a silane. Complex 3 undergoes intramolecular and intermolecular phosphine exchange, as well as exchange between the silyl ligand and the free silane. Kinetic and DFT studies show that the intermolecular phosphine exchange occurs through the predissociation of a PMe3 group, which, surprisingly, is facilitated by the silane. The intramolecular exchange proceeds through a new non-Bailar-twist pathway. The silyl/silane exchange proceeds through an unusual Mo(VI) intermediate, [(ArN=)Mo(H)2(SiH2Ph)2(PMe3)2] (19). Complex 3 was found to be the catalyst of a variety of hydrosilylation reactions of carbonyl compounds (aldehydes and ketones) and nitriles, as well as of silane alcoholysis. Stoichiometric mechanistic studies of the hydrosilylation of acetone, supported by DFT calculations, suggest the operation of an unexpected mechanism, in that the silyl ligand of compound 3 plays an unusual role as a spectator ligand. The addition of acetone to compound 3 leads to the formation of [trans-(ArN)Mo(OiPr)(SiH2Ph)(PMe3)2] (18). This latter species does not undergo the elimination of a Si-O group (which corresponds to the conventional Ojima's mechanism of hydrosilylation). Rather, complex 18 undergoes unusual reversible β-CH activation of the isopropoxy ligand. In the hydrosilylation of benzaldehyde, the reaction proceeds through the formation of a new intermediate bis(benzaldehyde) adduct, [(ArN=)Mo(η(2)-PhC(O)H)2(PMe3)], which reacts further with hydrosilane through a η(1)-silane complex, as studied by DFT calculations.