HREM and nanoindentation studies of BN:C films deposited by reactive sputtering from a B4C target

Boron nitride:carbon (BN: C) compounds containing up to similar to 20 at% of C were reactively sputtered from B4C targets in a mixed Ar/N-2 discharge onto Si(001) substrates held at 150 degrees C. As-deposited films were characterized by EPMA, FTIR, TEM, and nanoindentation experiments, respectively. The results show that the structure and correspondingly the mechanical response of BN:C films can be controlled by the applied ion-bombardment during growth. Films grown at a fixed ion energy Ei of 110 eV and increasing ion-to-neutral flux ratios J(i)/J(n) of similar to 3, similar to 12, and similar to 24 resulted in distorted hexagonal-like h-BN: C, textured h-BN:C, and textured cubic-phase c-BN:C structures, respectively. Moreover, the film C content decreased from similar to 20 at% at J(i)/J(n) similar to 3 to similar to 6 at% in c-BN:C. Textured h-BN:C exhibits a fullerene-like microstructure with curved and buckled basal planes, possibly arranged in a cross-linked three-dimensional network. This structure was also observed for a thin intermediate layer in c-BN:C films prior to the onset of the cubic-phase growth. The mechanical response of thin c-BN:C films indicates very hard although extremely elastic layers with up to 90% elastic recoveries. Also, large elasticity (similar to 82%) was measured for fullerene-like h-BN:C. (C) 1999 Elsevier Science Ltd. All rights reserved.