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Thin films of superhard nanocrystalline nc-W2N/amorphous a-Si3N4 composite have been prepared by plasma chemical vapor deposition at temperatures in the range, 500–550 °C. Maximum hardness of 5200 kg/mm2 (about 51 GPa) and elastic modulus of ≥500 GPa is reached at a silicon content of 7–8 at. %. During the indentation experiment the material shows a large elastic recovery of 80%, which compares favorably with those of hard a-C:H (hardness only about 2000 kg/mm2). The results are similar to those recently obtained with nc-TiN/a-Si3N4 and thus support our concept for the design of novel superhard composite materials with a variety of transition metal nitrides. The question of the upper limit of the strength of these materials is addressed and discussed.

The spontaneous and photolytically induced reactions of AlF and AlCl in the presence of HCl and HBr in solid argon matrices were followed and the products identified and characterized by means of IR spectroscopy. Quantum mechanical calculations allow for a further evaluation of the properties of the reaction products. These are the adducts AlF.HCl, AlF.HBr, and AlCl.HBr, representing the products of spontaneous reactions, and the trivalent Al(III) hydrides HAlFCl, HAlFBr, and HAlClBr, which were formed upon photoactivation of these complexes. All three hydrides are planar molecules (C(s)() symmetry) with bond angles in agreement with the predictions of the VSEPR theory. In addition, the mixed halides AlFCl(2), AlFBr(2), and AlClBr(2) were formed upon photolysis. The bisadducts AlF.(HCl)(2) and AlF.(HBr)(2) are likely to be the precursors to these species.

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