Hard BCN films were deposited by chemical vapour deposition (CVD) on Si(100) substrates. TCVD (thermal activated) and PECVD (GD or RF microwave plasma-activated, respectively) were used. The films were analysed with respect to chemical state, composition, morphology and microstructure, oxidation behaviour and hardness. Wavelength dispersive X-ray spectroscopy (EPMA), infrared spectroscopy (IR), transmission electron microscopy (TEM), differential thermal analysis (DTA) and hardness evaluation were employed for film characterization. A correlation between deposition parameters and film composition, structure and hardness could be proved in every CVD process. Parallels between TCVD and PECVD films emerged in the case of chemical composition and the correlation between carbon content and hardness values. Considerable differences exist with regard to the microstructure, especially the texture of the films. Moreover in TCVD films the carbon is preferentially incorporated between the BN basal planes, whereas in PECVD films it is incorporated preferentially in as well as between the BN basal planes.

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Two competitive regio‐ and stereoselective epimerization reactions were investigated in four cyclitols characterized by four contiguous OH groups with a cis‐trans‐trans sequence and by varied substituents (OMe, OBz, F, H) adjacent to this tetrol unit. The starting materials were synthesized from L‐quebrachitol (compounds 5−7) and myo‐inositol (compound 8). Their acetalization with the chloral/DCC reagent system gave cyclic acetals with one epimerized chiral ring atom and also with two epimerized chiral centres. The single epimerization takes place exclusively at the middle C‐atom of the cis‐trans triol unit in the tetrol sequence (products 15, 17, 19/20 and 24−27), whereas the double epimerization occurs at both of the "centrally located" C‐atoms in the cis‐trans‐trans tetrol unit (products 16, 18, 21 and 28). The product ratios of singly to doubly inverted compounds change as follows: the lower the electron‐withdrawing effect of the substituents adjacent to the tetrol unit, the higher the percentage of the corresponding doubly inverted product. However, the singly inverted products remain the major products in all cases. X‐ray analyses are given for the starting material 1‐fluoro‐2‐O‐(methyl)cyclohexane‐2,3,4,5,6‐pentol (5) and for the products 1‐O‐cyclohexylcarbamoyl‐2,3‐O‐(2,2,2‐trichloroethylidene)5‐O‐(methyl)cyclohexane‐1,2,3,4,5‐pentol (17), 3‐O‐acetyl‐1‐O‐benzoyl‐6‐O‐cyclohexylcarbamoyl‐2‐O‐methyl‐4,5‐O‐(2,2,2‐trichloroethylidene)‐muco‐inositol (22) and 2,3‐di‐O‐ethylidene)‐(+/‐)‐chiro‐inositol (24). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)